Surface Gravity Waves: Resonance in a Fish Tank

ERIC Educational Resources Information Center

Sinick, Scott J.; Lynch, John J.

2010-01-01

In this work, an inexpensive 10-gallon glass aquarium was used to study wave motion in water. The waves travel at speeds comparable to a person walking ([approximately]1 m/s). The scale of the motion allows for distances to be measured with a meterstick and for times to be measured with a stopwatch. For a wide range of water depths, standing waves…

Application of a simplified calculation for full-wave microtremor H/ V spectral ratio based on the diffuse field approximation to identify underground velocity structures

NASA Astrophysics Data System (ADS)

Wu, Hao; Masaki, Kazuaki; Irikura, Kojiro; Sánchez-Sesma, Francisco José

2017-12-01

Under the diffuse field approximation, the full-wave (FW) microtremor H/ V spectral ratio ( H/ V) is modeled as the square root of the ratio of the sum of imaginary parts of the Green's function of the horizontal components to that of the vertical one. For a given layered medium, the FW H/ V can be well approximated with only surface waves (SW) H/ V of the "cap-layered" medium which consists of the given layered medium and a new larger velocity half-space (cap layer) at large depth. Because the contribution of surface waves can be simply obtained by the residue theorem, the computation of SW H/ V of cap-layered medium is faster than that of FW H/ V evaluated by discrete wavenumber method and contour integration method. The simplified computation of SW H/ V was then applied to identify the underground velocity structures at six KiK-net strong-motion stations. The inverted underground velocity structures were used to evaluate FW H/ Vs which were consistent with the SW H/ Vs of corresponding cap-layered media. The previous study on surface waves H/ Vs proposed with the distributed surface sources assumption and a fixed Rayleigh-to-Love waves amplitude ratio for horizontal motions showed a good agreement with the SW H/ Vs of our study. The consistency between observed and theoretical spectral ratios, such as the earthquake motions of H/ V spectral ratio and spectral ratio of horizontal motions between surface and bottom of borehole, indicated that the underground velocity structures identified from SW H/ V of cap-layered medium were well resolved by the new method.[Figure not available: see fulltext.

Prototype of web-based database of surface wave investigation results for site classification

NASA Astrophysics Data System (ADS)

Hayashi, K.; Cakir, R.; Martin, A. J.; Craig, M. S.; Lorenzo, J. M.

2016-12-01

As active and passive surface wave methods are getting popular for evaluating site response of earthquake ground motion, demand on the development of database for investigation results is also increasing. Seismic ground motion not only depends on 1D velocity structure but also on 2D and 3D structures so that spatial information of S-wave velocity must be considered in ground motion prediction. The database can support to construct 2D and 3D underground models. Inversion of surface wave processing is essentially non-unique so that other information must be combined into the processing. The database of existed geophysical, geological and geotechnical investigation results can provide indispensable information to improve the accuracy and reliability of investigations. Most investigations, however, are carried out by individual organizations and investigation results are rarely stored in the unified and organized database. To study and discuss appropriate database and digital standard format for the surface wave investigations, we developed a prototype of web-based database to store observed data and processing results of surface wave investigations that we have performed at more than 400 sites in U.S. and Japan. The database was constructed on a web server using MySQL and PHP so that users can access to the database through the internet from anywhere with any device. All data is registered in the database with location and users can search geophysical data through Google Map. The database stores dispersion curves, horizontal to vertical spectral ratio and S-wave velocity profiles at each site that was saved in XML files as digital data so that user can review and reuse them. The database also stores a published 3D deep basin and crustal structure and user can refer it during the processing of surface wave data.

Free-surface turbulent wake of a surface-piercing slender body at various Froude numbers

NASA Astrophysics Data System (ADS)

Seo, Jeonghwa; Samad, Abdus; Rhee, Shin Hyung

2016-11-01

Free-surface effects on the near-wake around a surface-piercing slender body were investigated through flow field and wave elevation measurements. The near-wake flow field was measured by a towed underwater stereoscopic particle image velocimetry (SPIV) system. The measured flow field was analyzed to obtain coherent turbulence structures by using the Reynolds and proper orthogonal decomposition methods. Three different Froude numbers (Fr) - 0.126, 0.282, and 0.400 - were selected to represent mild, intermediate, and violent free-surface motions. At Fr = 0.126, the wave was hardly visible, although the turbulence strength and isotropy increased near the free-surface. At Fr = 0.282, though it was steady and smooth, wave-induced separation was clearly observed near the juncture of the free-surface and model trailing edge. At Fr = 0.400, wave breaking and the resulting bubbly free-surface were developed with an expanded wave-induced separation region. The wave-induced separation stimulated momentum transfer and turbulence dissipation, resulting in a significant change in the frequency of dominant free-surface motion in the downstream. This research was supported by the IT R&D program of MOTIE/KEIT (Grant No. 100660329) and the National Research Foundation of Korea, Grant funded by the Korean government (Grant No. 2013R1A1A2012597).

Unsteady motion of laser ablation plume by vortex induced by the expansion of curved shock wave

NASA Astrophysics Data System (ADS)

Tran, D. T.; Mori, K.

2017-02-01

There are a number of industrial applications of laser ablation in a gas atmosphere. When an intense pulsed laser beam is irradiated on a solid surface in the gas atmosphere, the surface material is ablated and expands into the atmosphere. At the same time, a spherical shock wave is launched by the ablation jet to induce the unsteady flow around the target surface. The ablated materials, luminously working as tracer, exhibit strange unsteady motions depending on the experimental conditions. By using a high-speed video camera (HPV-X2), unsteady motion ablated materials are visualized at the frame rate more than 106 fps, and qualitatively characterized.

Far-Field Noise Induced by Bubble near Free Surface

NASA Astrophysics Data System (ADS)

Ye, Xi; Li, Jiang-tao; Liu, Jian-hua; Chen, Hai-long

2018-03-01

The motion of a bubble near the free surface is solved by the boundary element method based on the linear wave equation, and the influence of fluid compressibility on bubble dynamics is analyzed. Based on the solution of the bubble motion, the far-field radiation noise induced by the bubble is calculated using Kirchhoff moving boundary integral equation, and the influence of free surface on far-field noise is researched. As the results, the oscillation amplitude of the bubble is weakened in compressible fluid compared with that in incompressible fluid, and the free surface amplifies the effect of fluid compressibility. When the distance between the bubble and an observer is much larger than that between the bubble and free surface, the sharp wave trough of the sound pressure at the observer occurs. With the increment of the distance between the bubble and free surface, the time of the wave trough appearing is delayed and the value of the wave trough increase. When the distance between the observer and the bubble is reduced, the sharp wave trough at the observer disappears.

Dérive à la surface de l'océan sous l'effet des vagues

NASA Astrophysics Data System (ADS)

Ardhuin, Fabrice; Martin-Lauzer, François-Régis; Chapron, Bertrand; Craneguy, Philippe; Girard-Ardhuin, Fanny; Elfouhaily, Tanos

2004-09-01

We model the drift velocity near the ocean surface separating the motion induced by the local current, itself influenced by winds and waves, and the motion induced by the waves, which are generated by local and remote winds. Application to the drift of 'tar balls', following the sinking of the oil tanker Prestige-Nassau in November 2002, shows that waves contribute at least one third of the drift for pollutants floating 1 m below the surface, with a mean direction about 30° to the right of the wind-sea direction. Although not new, this result was previously obtained with specific models, whereas the formalism used here combines classical wave and circulation forecasting models. To cite this article: F. Ardhuin et al., C. R. Geoscience 336 (2004).

Thunder-induced ground motions: 1. Observations

NASA Astrophysics Data System (ADS)

Lin, Ting-L.; Langston, Charles A.

2009-04-01

Acoustic pressure from thunder and its induced ground motions were investigated using a small array consisting of five three-component short-period surface seismometers, a three-component borehole seismometer, and five infrasound microphones. We used the array to constrain wave parameters of the incident acoustic and seismic waves. The incident slowness differences between acoustic pressure and ground motions suggest that ground reverberations were first initiated somewhat away from the array. Using slowness inferred from ground motions is preferable to obtain the seismic source parameters. We propose a source equalization procedure for acoustic/seismic deconvolution to generate the time domain transfer function, a procedure similar to that of obtaining teleseismic earthquake receiver functions. The time domain transfer function removes the incident pressure time history from the seismogram. An additional vertical-to-radial ground motion transfer function was used to identify the Rayleigh wave propagation mode of induced seismic waves complementing that found using the particle motions and amplitude variations in the borehole. The initial motions obtained by the time domain transfer functions suggest a low Poisson's ratio for the near-surface layer. The acoustic-to-seismic transfer functions show a consistent reverberation series at frequencies near 5 Hz. This gives an empirical measure of site resonance that depends on the ratio of the layer velocity to layer thickness for earthquake P and S waves. The time domain transfer function approach by transferring a spectral division into the time domain provides an alternative method for studying acoustic-to-seismic coupling.

Recordings from the deepest borehole in the New Madrid Seismic Zone

USGS Publications Warehouse

Wang, Z.; Woolery, E.W.

2006-01-01

The recordings at the deepest vertical strong-motion array (VSAS) from three small events, the 21 October 2004 Tiptonville, Tennessee, earthquake; the 10 February 2005 Arkansas earthquake; and the 2 June 2005 Ridgely, Tennessee, earthquake show some interesting wave-propagation phenomena through the soils: the S-wave is attenuated from 260 m to 30 m depth and amplified from 30 m to the surface. The S-wave arrival times from the three events yielded different shear-wave velocity estimates for the soils. These different estimates may be the result of different incident angles of the S-waves due to different epicentral distances. The epicentral distances are about 22 km, 110 km, and 47 km for the Tiptonville, Arkansas, and Ridgely earthquakes, respectively. These recordings show the usefulness of the borehole strong-motion array. The vertical strong-motion arrays operated by the University of Kentucky have started to accumulate recordings that will provide a database for scientists and engineers to study the effects of the near-surface soils on the strong ground motion in the New Madrid Seismic Zone. More information about the Kentucky Seismic and Strong-Motion Network can be found at www.uky.edu/KGS/geologichazards. The digital recordings are available at ftp://kgsweb.uky.edu.

P-wave fault-plane solutions and the generation of surface waves by earthquakes in the western United States

NASA Astrophysics Data System (ADS)

Patton, Howard J.

1985-08-01

Surface waves recorded at regional distances are used to study the source mechanisms of seven earthquakes in the western United States with magnitudes between 4.3 and 5.5. The source mechanisms of events in or on the margins of the Basin and Range show T-axis with an azimuth of N85°W +/- 16° and a plunge of 12° +/- 16°. Of the seven events, four have P-wave solutions that are inconsistent with surface-wave observations. Azimuths of the T-axis obtained from the surface-wave mechanisms and from the P-wave solutions differ by up to 45°. These events have dip-slip or oblique-slip mechanisms, and the source depths for three of the events are 5 km or less. Their source mechanisms and small magnitudes make identification of the P-wave first motion difficult due to poor signal-to-noise ratio of the initial P-wave and close arrivals of pP or sP with significant amplitude. We suggest that mis-identification of the P-wave first motion and distortion of the body-wave ray paths due to non-planar structure were sources of error in determining the nodal planes for these events.

Shear Wave Generation and Modeling Ground Motion From a Source Physics Experiment (SPE) Underground Explosion

NASA Astrophysics Data System (ADS)

Pitarka, Arben; Mellors, Robert; Rodgers, Arthur; Vorobiev, Oleg; Ezzedine, Souheil; Matzel, Eric; Ford, Sean; Walter, Bill; Antoun, Tarabay; Wagoner, Jeffery; Pasyanos, Mike; Petersson, Anders; Sjogreen, Bjorn

2014-05-01

We investigate the excitation and propagation of far-field (epicentral distance larger than 20 m) seismic waves by analyzing and modeling ground motion from an underground chemical explosion recorded during the Source Physics Experiment (SPE), Nevada. The far-field recorded ground motion is characterized by complex features, such as large azimuthal variations in P- and S-wave amplitudes, as well as substantial energy on the tangential component of motion. Shear wave energy is also observed on the tangential component of the near-field motion (epicentral distance smaller than 20 m) suggesting that shear waves were generated at or very near the source. These features become more pronounced as the waves propagate away from the source. We address the shear wave generation during the explosion by modeling ground motion waveforms recorded in the frequency range 0.01-20 Hz, at distances of up to 1 km. We used a physics based approach that combines hydrodynamic modeling of the source with anelastic modeling of wave propagation in order to separate the contributions from the source and near-source wave scattering on shear motion generation. We found that wave propagation scattering caused by the near-source geological environment, including surface topography, contributes to enhancement of shear waves generated from the explosion source. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-06NA25946/ NST11-NCNS-TM-EXP-PD15.

Dual differential interferometer for measurements of broadband surface acoustic waves

NASA Technical Reports Server (NTRS)

Turner, T. M.; Claus, R. O.

1981-01-01

A simple duel interferometer which uses two pairs of orthogonally polarized optical beams to measure both the amplitude and direction of propagation of broadband ultrasonic surface waves is described. Each pair of focused laser probe beams is used in a separate wideband differential interferometer to independently detect the component of surface wave motion along one direction on the surface. By combining the two output signals corresponding to both components, the two dimensional surface profile and its variation as a function of time is determined.

New Hybridized Surface Wave Approach for Geotechnical Modeling of Shear Wave Velocity at Strong Motion Recording Stations

NASA Astrophysics Data System (ADS)

Kayen, R.; Carkin, B.; Minasian, D.

2006-12-01

Strong motion recording (SMR) networks often have little or no shear wave velocity measurements at stations where characterization of site amplification and site period effects is needed. Using the active Spectral Analysis of Surface Waves (SASW) method, and passive H/V microtremor method we have investigated nearly two hundred SMR sites in California, Alaska, Japan, Australia, China and Taiwan. We are conducting these studies, in part, to develop a new hybridized method of site characterization that utilizes a parallel array of harmonic-wave sources for active-source SASW, and a single long period seismometer for passive-source microtremor measurement. Surface wave methods excel in their ability to non-invasively and rapidly characterize the variation of ground stiffness properties with depth below the surface. These methods are lightweight, inexpensive to deploy, and time-efficient. They have been shown to produce accurate and deep soil stiffness profiles. By placing and wiring shakers in a large parallel circuit, either side-by-side on the ground or in a trailer-mounted array, a strong in-phase harmonic wave can be produced. The effect of arraying many sources in parallel is to increase the amplitude of waves received at far-away spaced seismometers at low frequencies so as to extend the longest wavelengths of the captured dispersion curve. The USGS system for profiling uses this concept by arraying between two and eight electro-mechanical harmonic-wave shakers. With large parallel arrays of vibrators, a dynamic force in excess of 1000 lb can be produced to vibrate the ground and produce surface waves. We adjust the harmonic wave through a swept-sine procedure to profile surface wave dispersion down to a frequency of 1 Hz and out to surface wave-wavelengths of 200-1000 meters, depending on the site stiffness. The parallel-array SASW procedure is augmented using H/V microtremor data collected with the active source turned off. Passive array microtremor data reveal the natural and resonance characteristics of the ground by capturing persistent natural vibrations. These microtremors are the result of the interaction of surface waves arriving from distant sources and the stiffness structure of the site under investigation. As such, these resonance effects are effective in constraining the layer thicknesses of the SASW shear wave velocity structure and aid in determining the depth of the deepest layer. Together, the hybridized SASW and H/V procedure provides a complete data set for modeling the geotechnical aspects of ground amplification of earthquake motions. Data from these investigations are available at http://walrus.wr.usgs.gov/geotech.

Surface and downhole shear wave seismic methods for thick soil site investigations

USGS Publications Warehouse

Hunter, J.A.; Benjumea, B.; Harris, J.B.; Miller, R.D.; Pullan, S.E.; Burns, R.A.; Good, R.L.

2002-01-01

Shear wave velocity-depth information is required for predicting the ground motion response to earthquakes in areas where significant soil cover exists over firm bedrock. Rather than estimating this critical parameter, it can be reliably measured using a suite of surface (non-invasive) and downhole (invasive) seismic methods. Shear wave velocities from surface measurements can be obtained using SH refraction techniques. Array lengths as large as 1000 m and depth of penetration to 250 m have been achieved in some areas. High resolution shear wave reflection techniques utilizing the common midpoint method can delineate the overburden-bedrock surface as well as reflecting boundaries within the overburden. Reflection data can also be used to obtain direct estimates of fundamental site periods from shear wave reflections without the requirement of measuring average shear wave velocity and total thickness of unconsolidated overburden above the bedrock surface. Accurate measurements of vertical shear wave velocities can be obtained using a seismic cone penetrometer in soft sediments, or with a well-locked geophone array in a borehole. Examples from thick soil sites in Canada demonstrate the type of shear wave velocity information that can be obtained with these geophysical techniques, and show how these data can be used to provide a first look at predicted ground motion response for thick soil sites. ?? 2002 Published by Elsevier Science Ltd.

Seismic velocity site characterization of 10 Arizona strong-motion recording stations by spectral analysis of surface wave dispersion

USGS Publications Warehouse

Kayen, Robert E.; Carkin, Brad A.; Corbett, Skye C.

2017-10-19

Vertical one-dimensional shear wave velocity (VS) profiles are presented for strong-motion sites in Arizona for a suite of stations surrounding the Palo Verde Nuclear Generating Station. The purpose of the study is to determine the detailed site velocity profile, the average velocity in the upper 30 meters of the profile (VS30), the average velocity for the entire profile (VSZ), and the National Earthquake Hazards Reduction Program (NEHRP) site classification. The VS profiles are estimated using a non-invasive continuous-sine-wave method for gathering the dispersion characteristics of surface waves. Shear wave velocity profiles were inverted from the averaged dispersion curves using three independent methods for comparison, and the root-mean-square combined coefficient of variation (COV) of the dispersion and inversion calculations are estimated for each site.

Numerical study of acoustophoretic motion of particles in a PDMS microchannel driven by surface acoustic waves.

PubMed

Nama, Nitesh; Barnkob, Rune; Mao, Zhangming; Kähler, Christian J; Costanzo, Francesco; Huang, Tony Jun

2015-06-21

We present a numerical study of the acoustophoretic motion of particles suspended in a liquid-filled PDMS microchannel on a lithium niobate substrate acoustically driven by surface acoustic waves. We employ a perturbation approach where the flow variables are divided into first- and second-order fields. We use impedance boundary conditions to model the PDMS microchannel walls and we model the acoustic actuation by a displacement function from the literature based on a numerical study of piezoelectric actuation. Consistent with the type of actuation, the obtained first-order field is a horizontal standing wave that travels vertically from the actuated wall towards the upper PDMS wall. This is in contrast to what is observed in bulk acoustic wave devices. The first-order fields drive the acoustic streaming, as well as the time-averaged acoustic radiation force acting on suspended particles. We analyze the motion of suspended particles driven by the acoustic streaming drag and the radiation force. We examine a range of particle diameters to demonstrate the transition from streaming-drag-dominated acoustophoresis to radiation-force-dominated acoustophoresis. Finally, as an application of our numerical model, we demonstrate the capability to tune the position of the vertical pressure node along the channel width by tuning the phase difference between two incoming surface acoustic waves.

Estimating material viscoelastic properties based on surface wave measurements: A comparison of techniques and modeling assumptions

PubMed Central

Royston, Thomas J.; Dai, Zoujun; Chaunsali, Rajesh; Liu, Yifei; Peng, Ying; Magin, Richard L.

2011-01-01

Previous studies of the first author and others have focused on low audible frequency (<1 kHz) shear and surface wave motion in and on a viscoelastic material comprised of or representative of soft biological tissue. A specific case considered has been surface (Rayleigh) wave motion caused by a circular disk located on the surface and oscillating normal to it. Different approaches to identifying the type and coefficients of a viscoelastic model of the material based on these measurements have been proposed. One approach has been to optimize coefficients in an assumed viscoelastic model type to match measurements of the frequency-dependent Rayleigh wave speed. Another approach has been to optimize coefficients in an assumed viscoelastic model type to match the complex-valued frequency response function (FRF) between the excitation location and points at known radial distances from it. In the present article, the relative merits of these approaches are explored theoretically, computationally, and experimentally. It is concluded that matching the complex-valued FRF may provide a better estimate of the viscoelastic model type and parameter values; though, as the studies herein show, there are inherent limitations to identifying viscoelastic properties based on surface wave measurements. PMID:22225067

Diffraction of waves past two vertical thin plates on the free surface: A comparison of theory and experiment

NASA Astrophysics Data System (ADS)

Shin, Dong Min; Cho, Yeunwoo

2017-11-01

Diffraction of waves past two vertical thin plates on the free surface is studied theoretically and experimentally. A particular attention is paid to the wave motions depending on the relationship between the wavelength (λ) and the width (b) between the two plates for a given draft (d) and water depth (h). For d/h =0.19, at resonance modes when b/ λ = 0.245 (first), 0.695 (second), 1.11 (third), 1.55 (fourth), etc., the overall transmission features the maximum with no reflection. In the first mode, the water column between the plates moves up and down with no wave motions. In the second mode, it shows the fundamental standing wave motion. In the remaining modes, it shows another standing wave motions with relatively higher frequencies. As d/h increases (0.1-0.4), the resonance points move to values b/ λ = 0, 0.5, 1, 1.5, etc., and, at those resonance points, the peaks of reflection and transmission coefficients become more sharp and narrow. The loss of energy of incoming waves is also observed at every transmission in the two plate system, and, in particular, more energy loss near a resonant frequency. In addition, it is found that energy is lost mainly due to the transmission process not the reflection process. This work was supported by the National Research Foundation of Korea (NRF). (NRF-2017R1D1A1B03028299).

Preliminary Analysis of a Submerged Wave Energy Device

NASA Astrophysics Data System (ADS)

Wagner, J. R.; Wagner, J. J.; Hayatdavoodi, M.; Ertekin, R. C.

2016-02-01

Preliminary analysis of a submerged wave energy harvesting device is presented. The device is composed of a thin, horizontally submerged plate that is restricted to heave oscillations under the influence of surface waves. The submerged plate is oscillating, and it can be attached to a fixed rotor, or a piston, to harvest the wave energy. A fully submerged wave energy converter is preferred over a surface energy convertor due to its durability and less visual and physical distractions it presents. In this study, the device is subject to nonlinear shallow-water waves. Wave loads on the submerged oscillating plate are obtained via the Level I Green-Naghdi equations. The unsteady motion of the plate is obtained by solving the nonlinear equations of motion. The results are obtained for a range of waves with varying heights and periods. The amplitude and period of plate oscillations are analyzed as functions of the wave parameters and plate width. Particular attention is given to the selection of the site of desired wave field. Initial estimation on the amount of energy extraction from the device, located near shore at a given site, is provided.

Magnetic skyrmion bubble motion driven by surface acoustic waves

DOE PAGES

Nepal, Rabindra; Güngördü, Utkan; Kovalev, Alexey A.

2018-03-12

Here, we study the dynamical control of a magnetic skyrmion bubble by using counter-propagating surface acoustic waves (SAWs) in a ferromagnet. First, we determine the bubble mass and derive the force due to SAWs acting on a magnetic bubble using Thiele’s method. The force that pushes the bubble is proportional to the strain gradient for the major strain component. We then study the dynamical pinning and motion of magnetic bubbles by SAWs in a nanowire. In a disk geometry, we propose a SAWs-driven skyrmion bubble oscillator with two resonant frequencies.

Magnetic skyrmion bubble motion driven by surface acoustic waves

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nepal, Rabindra; Güngördü, Utkan; Kovalev, Alexey A.

Here, we study the dynamical control of a magnetic skyrmion bubble by using counter-propagating surface acoustic waves (SAWs) in a ferromagnet. First, we determine the bubble mass and derive the force due to SAWs acting on a magnetic bubble using Thiele’s method. The force that pushes the bubble is proportional to the strain gradient for the major strain component. We then study the dynamical pinning and motion of magnetic bubbles by SAWs in a nanowire. In a disk geometry, we propose a SAWs-driven skyrmion bubble oscillator with two resonant frequencies.

Surfing surface gravity waves

NASA Astrophysics Data System (ADS)

Pizzo, Nick

2017-11-01

A simple criterion for water particles to surf an underlying surface gravity wave is presented. It is found that particles travelling near the phase speed of the wave, in a geometrically confined region on the forward face of the crest, increase in speed. The criterion is derived using the equation of John (Commun. Pure Appl. Maths, vol. 6, 1953, pp. 497-503) for the motion of a zero-stress free surface under the action of gravity. As an example, a breaking water wave is theoretically and numerically examined. Implications for upper-ocean processes, for both shallow- and deep-water waves, are discussed.

Numerical Simulation of Floating Bodies in Extreme Free Surface Waves

NASA Astrophysics Data System (ADS)

Hu, Zheng Zheng; Causon, Derek; Mingham, Clive; Qiang, Ling

2010-05-01

A task of the EPSRC funded research project 'Extreme Wave loading on Offshore Wave Energy Devices: a Hierarchical Team Approach' is to investigate the survivability of two wave energy converter (WEC) devices Pelamis and the Manchester Bobber using different CFD approaches. Both devices float on the water surface, generating the electricity from the motion of the waves. In this paper, we describe developments of the AMAZON-SC 3D numerical wave tank (NWT) to study extreme wave loading of a fixed or floating (in Heave motion) structure. The extreme wave formulation as an inlet condition is due to Dalzell (1999) and Ning et. al. (2009) in which a first or second-order Stokes focused wave can be prescribed. The AMAZON-SC 3D code (see e.g. Hu et al. (2009)) uses a cell centred finite volume method of the Godunov-type for the space discretization of the Euler and Navier Stokes equations. The computational domain includes both air and water regions with the air/water boundary captured as a discontinuity in the density field thereby admitting the break up and recombination of the free surface. Temporal discretisation uses the artificial compressibility method and a dual time stepping strategy to maintain a divergence free velocity field. Cartesian cut cells are used to provide a fully boundary-fitted gridding capability on an regular background Cartesian grid. Solid objects are cut out of the background mesh leaving a set of irregularly shaped cells fitted to the boundary. The advantages of the cut cell approach have been outlined previously by Causon et al. (2000, 2001) including its flexibility for dealing with complex geometries whether stationary or in relative motion. The field grid does not need to be recomputed globally or even locally for moving body cases; all that is necessary is to update the local cut cell data at the body contour for as long as the motion continues. The handing of numerical wave paddles and device motion in a NWT is therefore straightforward and efficient. Firstly, extreme design wave conditions are generated in an empty NWT and compared with physical experiments as a precursor to calculations to investigate the survivability of the Bobber device operating in a challenging wave climate. Secondly, we consider a bench-mark test case involving in a first order regular wave maker acting on a fixed cylinder and Pelamis. Finally, a floating Bobber has been simulated under extreme wave conditions. These results will be reported at the meeting. Causon D.M., Ingram D.M., Mingham C.G., Yang G. Pearson R.V. (2000). Calculation of shallow water flows using a Cartesian cut cell approach. Advances in Water resources, 23: 545-562. Causon D.M., Ingram D.M., Mingham C.G. (2000). A Cartesian cut cell method for shallow water flows with moving boundaries. Advances in Water resources, 24: 899-911. Dalzell J.F. 1999 A note on finite depth second-order wave-wave interactions. Appl. Ocean Res. 21, 105-111. Ning D.Z., Zang J., Liu S.X. Eatock Taylor R. Teng B. & Taylor P.H. 2009 Free surface and wave kinematics for nonlinear focused wave groups. J. Ocean Engineering. Accepted. Hu Z.Z., Causon D.M., Mingham C.M. and Qian L.(2009). Numerical wave tank study of a wave energy converter in heave. Proceedlings 19th ISOPE conference, Osaka, Japan Qian L., Causon D.M. & Mingham C.G., Ingram D.M. 2006 A free-surface capturing method for two fluid flows with moving bodies. Proc. Roy. Soc. London, Vol. A 462 21-42.

Comparison of shear-wave slowness profiles at 10 strong-motion sites from noninvasive SASW measurements and measurements made in boreholes

USGS Publications Warehouse

Brown, L.T.; Boore, D.M.; Stokoe, K.H.

2002-01-01

The spectral-analysis-of-surface-waves (SASW) method is a relatively new in situ method for determining shear-wave slownesses. All measurements are made on the ground surface, making it much less costly than methods that require boreholes. The SASW method uses a number of active sources (ranging from a commercial Vibroseis truck to a small handheld hammer for the study conducted here) and different receiver spacings to map a curve of apparent phase velocity versus frequency. With the simplifying assumption that the phase velocities correspond to fundamental mode surface waves, forward modeling yields an estimate of the sub-surface shear-wave slownesses. To establish the reliability of this indirect technique, we conducted a blind evaluation of the SASW method. SASW testing was performed at 10 strong-motion stations at which borehole seismic measurements were previously or subsequently made; if previously made, the borehole results were not used for the interpretation of the SASW data, and vice-versa. Comparisons of the shear-wave slownesses from the SASW and borehole measurements are generally very good. The differences in predicted ground-motion amplifications are less than about 15% for most frequencies. In addition, both methods gave the same NEHRP site classification for seven of the sites. For the other three sites the average velocities from the downhole measurements were only 5-13 m/sec larger than the velocity defining the class C/D boundary. This study demonstrates that in many situations the SASW method can provide subsurface information suitable for site response predictions.

Megaquakes, prograde surface waves and urban evolution

NASA Astrophysics Data System (ADS)

Lomnitz, C.; Castaños, H.

2013-05-01

Cities grow according to evolutionary principles. They move away from soft-ground conditions and avoid vulnerable types of structures. A megaquake generates prograde surface waves that produce unexpected damage in modern buildings. The examples (Figs. 1 and 2) were taken from the 1985 Mexico City and the 2010 Concepción, Chile megaquakes. About 400 structures built under supervision according to modern building codes were destroyed in the Mexican earthquake. All were sited on soft ground. A Rayleigh wave will cause surface particles to move as ellipses in a vertical plane. Building codes assume that this motion will be retrograde as on a homogeneous elastic halfspace, but soft soils are intermediate materials between a solid and a liquid. When Poisson's ratio tends to ν→0.5 the particle motion turns prograde as it would on a homogeneous fluid halfspace. Building codes assume that the tilt of the ground is not in phase with the acceleration but we show that structures on soft ground tilt into the direction of the horizontal ground acceleration. The combined effect of gravity and acceleration may destabilize a structure when it is in resonance with its eigenfrequency. Castaños, H. and C. Lomnitz, 2013. Charles Darwin and the 1835 Chile earthquake. Seismol. Res. Lett., 84, 19-23. Lomnitz, C., 1990. Mexico 1985: the case for gravity waves. Geophys. J. Int., 102, 569-572. Malischewsky, P.G. et al., 2008. The domain of existence of prograde Rayleigh-wave particle motion. Wave Motion 45, 556-564.; Figure 1 1985 Mexico megaquake--overturned 15-story apartment building in Mexico City ; Figure 2 2010 Chile megaquake Overturned 15-story R-C apartment building in Concepción

Source and path effects in the wave fields of tremor and explosions at Stromboli Volcano, Italy

USGS Publications Warehouse

Chouet, B.; Saccorotti, G.; Martini, M.; Dawson, P.; De Luca, G.; Milana, G.; Scarpa, R.

1997-01-01

The wave fields generated by Strombolian activity are investigated using data from small-aperture seismic arrays deployed on the north flank of Stromboli and data from seismic and pressure transducers set up near the summit crater. Measurements of slowness and azimuth as a function of time clearly indicate that the sources of tremor and explosions are located beneath the summit crater at depths shallower than 200 m with occasional bursts of energy originating from sources extending to a depth of 3 km. Slowness, azimuth, and particle motion measurements reveal a complex composition of body and surface waves associated with topography, structure, and source properties. Body waves originating at depths shallower than 200 m dominate the wave field at frequencies of 0.5-2.5 Hz, and surface waves generated by the surficial part of the source and by scattering sources distributed around the island dominate at frequencies above 2.5 Hz. The records of tremor and explosions are both dominated by SH motion. Far-field records from explosions start with radial motion, and near-field records from those events show dominantly horizontal motion and often start with a low-frequency (1-2 Hz) precursor characterized by elliptical particle motion, followed within a few seconds by a high-frequency radial phase (1-10 Hz) accompanying the eruption of pyroclastics. The dominant component of the near- and far-field particle motions from explosions, and the timing of air and body wave phases observed in the near field, are consistent with a gaspiston mechanism operating on a shallow (<200 m deep), vertical crack-like conduit. Models of a degassing fluid column suggest that noise emissions originating in the collective oscillations of bubbles ascending in the magma conduit may provide an adequate self-excitation mechanism for sustained tremor generation at Stromboli. Copyright 1997 by the American Geophysical Union.

Inbound waves in the solar corona: A direct indicator of Alfvén surface location

DOE Office of Scientific and Technical Information (OSTI.GOV)

DeForest, C. E.; Howard, T. A.; McComas, D. J., E-mail: deforest@boulder.swri.edu

The tenuous supersonic solar wind that streams from the top of the corona passes through a natural boundary—the Alfvén surface—that marks the causal disconnection of individual packets of plasma and magnetic flux from the Sun itself. The Alfvén surface is the locus where the radial motion of the accelerating solar wind passes the radial Alfvén speed, and therefore any displacement of material cannot carry information back down into the corona. It is thus the natural outer boundary of the solar corona and the inner boundary of interplanetary space. Using a new and unique motion analysis to separate inbound and outboundmore » motions in synoptic visible-light image sequences from the COR2 coronagraph on board the STEREO-A spacecraft, we have identified inbound wave motion in the outer corona beyond 6 solar radii for the first time and used it to determine that the Alfvén surface is at least 12 solar radii from the Sun over the polar coronal holes and 15 solar radii in the streamer belt, well beyond the distance planned for NASA's upcoming Solar Probe Plus mission. To our knowledge, this is the first measurement of inbound waves in the outer solar corona and the first direct measurement of lower bounds for the Alfvén surface.« less

Comment on "Propagation of a TE surface mode in a relativistic electron beam-quantum plasma system" [Phys. Lett. A 376 (2012) 169

NASA Astrophysics Data System (ADS)

Moradi, Afshin

2016-07-01

In a recent paper Abdel Aziz [Phys. Lett. A 376 (2012) 169] obtained the dispersion properties of TE surface modes propagating at the interface between a magnetized quantum plasma and vacuum in the Faraday configuration, where these TE surface waves are excited during the interaction of relativistic electron beam with magnetized quantum plasma. The present Comment points out that in the Faraday configuration the surface waves acquire both TM and TE components due to the cyclotron motion of electrons. Therefore, the TE surface waves cannot propagate on surface of the present system and the general dispersion relations for surface waves, derived by Abdel Aziz are incorrect.

Shear-wave velocity compilation for Northridge strong-motion recording sites

USGS Publications Warehouse

Borcherdt, Roger D.; Fumal, Thomas E.

2002-01-01

Borehole and other geotechnical information collected at the strong-motion recording sites of the Northridge earthquake of January 17, 1994 provide an important new basis for the characterization of local site conditions. These geotechnical data, when combined with analysis of strong-motion recordings, provide an empirical basis to evaluate site coefficients used in current versions of US building codes. Shear-wave-velocity estimates to a depth of 30 meters are derived for 176 strong-motion recording sites. The estimates are based on borehole shear-velocity logs, physical property logs, correlations with physical properties and digital geologic maps. Surface-wave velocity measurements and standard penetration data are compiled as additional constraints. These data as compiled from a variety of databases are presented via GIS maps and corresponding tables to facilitate use by other investigators.

A new point contact surface acoustic wave transducer for measurement of acoustoelastic effect of polymethylmethacrylate.

PubMed

Lee, Yung-Chun; Kuo, Shi Hoa

2004-01-01

A new acoustic transducer and measurement method have been developed for precise measurement of surface wave velocity. This measurement method is used to investigate the acoustoelastic effects for waves propagating on the surface of a polymethylmethacrylate (PMMA) sample. The transducer uses two miniature conical PZT elements for acoustic wave transmitter and receiver on the sample surface; hence, it can be viewed as a point-source/point-receiver transducer. Acoustic waves are excited and detected with the PZT elements, and the wave velocity can be accurately determined with a cross-correlation waveform comparison method. The transducer and its measurement method are particularly sensitive and accurate in determining small changes in wave velocity; therefore, they are applied to the measurement of acoustoelastic effects in PMMA materials. Both the surface skimming longitudinal wave and Rayleigh surface wave can be simultaneously excited and measured. With a uniaxial-loaded PMMA sample, both acoustoelastic effects for surface skimming longitudinal wave and Rayleigh waves of PMMA are measured. The acoustoelastic coefficients for both types of surface wave motions are simultaneously determined. The transducer and its measurement method provide a practical way for measuring surface stresses nondestructively.

Hydroelectromechanical modelling of a piezoelectric wave energy converter

NASA Astrophysics Data System (ADS)

Renzi, E.

2016-11-01

We investigate the hydroelectromechanical-coupled dynamics of a piezoelectric wave energy converter. The converter is made of a flexible bimorph plate, clamped at its ends and forced to motion by incident ocean surface waves. The piezoceramic layers are connected in series and transform the elastic motion of the plate into useful electricity by means of the piezoelectric effect. By using a distributed-parameter analytical approach, we couple the linear piezoelectric constitutive equations for the plate with the potential-flow equations for the surface water waves. The resulting system of governing partial differential equations yields a new hydroelectromechanical dispersion relation, whose complex roots are determined with a numerical approach. The effect of the piezoelectric coupling in the hydroelastic domain generates a system of short- and long-crested weakly damped progressive waves travelling along the plate. We show that the short-crested flexural wave component gives a dominant contribution to the generated power. We determine the hydroelectromechanical resonant periods of the device, at which the power output is significant.

Calibration and Validation of Inertial Measurement Unit for Wave Resolving Drifters

DTIC Science & Technology

2013-12-01

wave field just described experiences accelerations due to both the wave induced pressure variations and the force of gravity. The gravitational ...with the vertical component also containing the gravitational acceleration constant (i.e., 9.81m/s2). B. SURFACE WAVE ORBITAL MOTION SIMULATOR...18 C. ACCELERATION TO DISPLACEMENT .................................................19 IV

Effects of UGTs on the ionosphere

NASA Astrophysics Data System (ADS)

Argo, P. E.; Fitzgerald, T. J.

The processes that propagate local effects of underground nuclear tests from the ground into the upper atmosphere, and produce a detectable signal in the ionosphere are described. Initially, the blast wave from a underground test (UGT) radially expands, until it reaches the surface of the earth. The wave is both reflected and transmitted at this sharp discontinuity in propagation media. Tne reflected wave combines with the incident wave to form an 'Airy surface,' at which very strong ripping forces tear the earth apart. This broken region is called the 'spat zone,' and is launched into ballistic motion. The resultant ground motion launches an acoustical wave into the atmosphere. This acoustic wave, with overpressures of a few tenths of one percent, propagates upwards at the speed of sound. Assuming purely linear propagation, the path of the acoustic energy can be tracked using raytracing models. Most of the wave energy, which is radiated nearly vertically, tends to propagate into the upper atmosphere, while wave energy radiated at angles greater than about 30 degrees to the vertical will be reflected back to earth and is probably what is seen by most infrasonde measurements.

Internal Waves and Wave Attractors in Enceladus' Subsurface Ocean

NASA Astrophysics Data System (ADS)

van Oers, A. M.; Maas, L. R.; Vermeersen, B. L. A.

2016-12-01

One of the most peculiar features on Saturn moon Enceladus is its so-called tiger stripe pattern at the geologically active South Polar Terrain (SPT), as first observed in detail by the Cassini spacecraft early 2005. It is generally assumed that the four almost parallel surface lines that constitute this pattern are faults in the icy surface overlying a confined salty water reservoir. In 2013, we formulated the original idea [Vermeersen et al., AGU Fall Meeting 2013, abstract #P53B-1848] that the tiger stripe pattern is formed and maintained by induced, tidally and rotationally driven, wave-attractor motions in the ocean underneath the icy surface of the tiger-stripe region. Such wave-attractor motions are observed in water tank experiments in laboratories on Earth and in numerical experiments [Maas et al., Nature, 338, 557-561, 1997; Drijfhout and Maas, J. Phys. Oceanogr., 37, 2740-2763, 2007; Hazewinkel et al., Phys. Fluids, 22, 107102, 2010]. Numerical simulations show the persistence of wave attractors for a range of ocean shapes and stratifications. The intensification of the wave field near the location of the surface reflections of wave attractors has been numerically and experimentally confirmed. We measured the forces a wave attractor exerts on a solid surface, near a reflection point. These reflection points would correspond to the location of the tiger stripes. Combining experiments and numerical simulations we conclude that (1) wave attractors can exist in Enceladus' subsurface sea, (2) their shape can be matched to the tiger stripes, (3) the wave attractors cause a localized force at the water-ice boundaries, (4) this force could have been large enough to contribute to fracturing the ice and (5) the wave attractors localize energy (and particles) and cause dissipation along its path, helping explain Enceladus' enigmatic heat output at the tiger stripes.

Low frequency events on Montserrat

NASA Astrophysics Data System (ADS)

Visser, K.; Neuberg, J.

2003-04-01

Earthquake swarms observed on volcanoes consist generally of low frequency events. The low frequency content of these events indicates the presence of interface waves at the boundary of the magma filled conduit and the surrounding country rock. The observed seismic signal at the surface shows therefore a complicated interference pattern of waves originating at various parts of the magma filled conduit, interacting with the free surface and interfaces in the volcanic edifice. This research investigates the applicability of conventional seismic tools on these low frequency events, focusing on hypocenter location analysis using arrival times and particle motion analysis for the Soufrière Hills Volcano on Montserrat. Both single low frequency events and swarms are observed on this volcano. Synthetic low frequency events are used for comparison. Results show that reliable hypocenter locations and particle motions can only be obtained if the low frequency events are single events with an identifiable P wave onset, for example the single events preceding swarms on Montserrat or the first low frequency event of a swarm. Consecutive events of the same swarm are dominated by interface waves which are converted at the top of the conduit into weak secondary P waves and surface waves. Conventional seismic tools fail to correctly analyse these events.

Seismic Hazard Assessment for the Baku City and Absheron Peninsula, Azerbaijan

DOE Office of Scientific and Technical Information (OSTI.GOV)

Babayev, Gulam R.

2006-03-23

This paper deals with the seismic hazard assessment for Baku and the Absheron peninsula. The assessment is based on the information on the features of earthquake ground motion excitation, seismic wave propagation (attenuation), and site effect. I analyze active faults, seismicity, soil and rock properties, geological cross-sections, the borehole data of measured shear-wave velocity, lithology, amplification factor of each geological unit, geomorphology, topography, and basic rock and surface ground motions. To estimate peak ground acceleration (PGA) at the surface, PGA at the basic rock is multiplied by the amplification parameter of each surface layers. Quaternary soft deposits, representing a highmore » risk due to increasing PGA values at surface, are studied in detail. For a near-zone target earthquake PGA values are compared to intensity at MSK-64 scale for the Absheron peninsula. The amplification factor for the Baku city is assessed and provides estimations for a level of a seismic motion and seismic intensity of the studied area.« less

Surface response of a fractional order viscoelastic halfspace to surface and subsurface sources

PubMed Central

Meral, F. Can; Royston, Thomas J.; Magin, Richard L.

2009-01-01

Previous studies by the second author published in this journal focused on low audible frequency (40–400 Hz) shear and surface wave motion in and on a viscoelastic material representative of biological tissue. Specific cases considered were that of surface wave motion on a halfspace caused by a finite rigid circular disk located on the surface and oscillating normal to it [Royston et al., J. Acoust. Soc. Am. 106, 3678–3686 (1999)] and compression, shear, and surface wave motion in a halfspace generated by a subsurface finite dipole [Royston et al., J. Acoust. Soc. Am. 113, 1109–1121 (2003)]. In both studies, a Voigt model of viscoelasticity was assumed in the theoretical treatment, which resulted in agreement between theoretical predictions and experimental measurements over a limited frequency range. In the present article, the linear viscoelastic assumption in these two prior works is revisited to consider a (still linear) fractional order Voigt model, where the rate-dependent damping component that is dependent on the first derivative of time is replaced with a component that is dependent on a fractional derivative of time. It is shown that in both excitation source configurations, the fractional order Voigt model assumption improves the match of theory to experiment over a wider frequency range (in some cases up to the measured range of 700 Hz). PMID:20000941

Numerical modeling of surface wave development under the action of wind

NASA Astrophysics Data System (ADS)

Chalikov, Dmitry

2018-06-01

The numerical modeling of two-dimensional surface wave development under the action of wind is performed. The model is based on three-dimensional equations of potential motion with a free surface written in a surface-following nonorthogonal curvilinear coordinate system in which depth is counted from a moving surface. A three-dimensional Poisson equation for the velocity potential is solved iteratively. A Fourier transform method, a second-order accuracy approximation of vertical derivatives on a stretched vertical grid and fourth-order Runge-Kutta time stepping are used. Both the input energy to waves and dissipation of wave energy are calculated on the basis of earlier developed and validated algorithms. A one-processor version of the model for PC allows us to simulate an evolution of the wave field with thousands of degrees of freedom over thousands of wave periods. A long-time evolution of a two-dimensional wave structure is illustrated by the spectra of wave surface and the input and output of energy.

Long-period ground motions at near-regional distances caused by the PL wave from, inland earthquakes: Observation and numerical simulation of the 2004 Mid-Niigata, Japan, Mw6.6 earthquake

NASA Astrophysics Data System (ADS)

Furumura, T.; Kennett, B. L. N.

2017-12-01

We examine the development of large, long-period ground motions at near-regional distances (D=50-200 km) generated by the PL wave from large, shallow inland earthquakes, based on the analysis of strong motion records and finite-difference method (FDM) simulations of seismic wave propagation. PL wave can be represented as leaking modes of the crustal waveguide and are commonly observed at regional distances between 300 to 1000 km as a dispersed, long-period signal with a dominant period of about 20 s. However, observations of recent earthquakes at the dense K-NET and KiK-net strong motion networks in Japan demonstrate the dominance of the PL wave at near-regional (D=50-200 km) distances as, e.g., for the 2004 Mid Niigata, Japan, earthquake (Mw6.6; h=13 km). The observed PL wave signal between P and S wave shows a large, dispersed wave packet with dominant period of about T=4-10 s with amplitude almost comparable to or larger than the later arrival of the S and surface waves. Thus, the early arrivals of the long-period PL wave immediately after P wave can enhance resonance with large-scale constructions such as high-rise buildings and large oil-storage tanks etc. with potential for disaster. Such strong effects often occurred during the 2004 Mid Niigata earthquakes and other large earthquakes which occurred nearby the Kanto (Tokyo) basin. FDM simulation of seismic wave propagation employing realistic 3-D sedimentary structure models demonstrates the process by which the PL wave develops at near-regional distances from shallow, crustal earthquakes by constructive interference of the P wave in the long-period band. The amplitude of the PL wave is very sensitive to low-velocity structure in the near-surface. Lowered velocities help to develop large SV-to-P conversion and weaken the P-to-SV conversion at the free surface. Both effects enhance the multiple P reflections in the crustal waveguide and prevent the leakage of seismic energy into the mantle. However, a very thick (>3 km) cover of sediment above the source disrupts the coherent reflections to form the PL wave. This explains the weak close-range PL wave from the 2007 Off Niigata earthquake (Mw=6.6; h=16 km), which occurred near-by the 2004 event but located beneath the deep Echigo basin.

Water waves generated by impulsively moving obstacle

NASA Astrophysics Data System (ADS)

Makarenko, Nikolay; Kostikov, Vasily

2017-04-01

There are several mechanisms of tsunami-type wave formation such as piston displacement of the ocean floor due to a submarine earthquake, landslides, etc. We consider simplified mathematical formulation which involves non-stationary Euler equations of infinitely deep ideal fluid with submerged compact wave-maker. We apply semi-analytical method [1] based on the reduction of fully nonlinear water wave problem to the integral-differential system for the wave elevation together with normal and tangential fluid velocities at the free surface. Recently, small-time asymptotic solutions were constructed by this method for submerged piston modeled by thin elliptic cylinder which starts with constant acceleration from rest [2,3]. By that, the leading-order solution terms describe several regimes of non-stationary free surface flow such as formation of inertial fluid layer, splash jets and diverging waves over the obstacle. Now we construct asymptotic solution taking into account higher-order nonlinear terms in the case of submerged circular cylinder. The role of non-linearity in the formation mechanism of surface waves is clarified in comparison with linear approximations. This work was supported by RFBR (grant No 15-01-03942). References [1] Makarenko N.I. Nonlinear interaction of submerged cylinder with free surface, JOMAE Trans. ASME, 2003, 125(1), 75-78. [2] Makarenko N.I., Kostikov V.K. Unsteady motion of an elliptic cylinder under a free surface, J. Appl. Mech. Techn. Phys., 2013, 54(3), 367-376. [3] Makarenko N.I., Kostikov V.K. Non-linear water waves generated by impulsive motion of submerged obstacle, NHESS, 2014, 14(4), 751-756.

The vertical propagation of disturbances triggered by seismic waves of the 11 March 2011 M9.0 Tohoku earthquake over Taiwan

NASA Astrophysics Data System (ADS)

Liu, J. Y.; Chen, C. H.; Sun, Y. Y.; Chen, C. H.; Tsai, H. F.; Yen, H. Y.; Chum, J.; Lastovicka, J.; Yang, Q. S.; Chen, W. S.; Wen, S.

2016-02-01

In this paper, concurrent/colocated measurements of seismometers, infrasonic systems, magnetometers, HF-CW (high frequency-continuous wave) Doppler sounding systems, and GPS receivers are employed to detect disturbances triggered by seismic waves of the 11 March 2011 M9.0 Tohoku earthquake. No time delay between colocated infrasonic (i.e., super long acoustic) waves and seismic waves indicates that the triggered acoustic and/or gravity waves in the atmosphere (or seismo-traveling atmospheric disturbances, STADs) near the Earth's surface can be immediately activated by vertical ground motions. The circle method is used to find the origin and compute the observed horizontal traveling speed of the triggered infrasonic waves. The speed of about 3.3 km/s computed from the arrival time versus the epicentral distance suggests that the infrasonic waves (i.e., STADs) are mainly induced by the Rayleigh waves. The agreements in the travel time at various heights between the observation and theoretical calculation suggest that the STADs triggered by the vertical motion of ground surface caused by the Tohoku earthquake traveled vertically from the ground to the ionosphere with speed of the sound in the atmosphere over Taiwan.

The physical basis for estimating wave energy spectra from SAR imagery

NASA Technical Reports Server (NTRS)

Lyzenga, David R.

1987-01-01

Ocean surface waves are imaged by synthetic aperture radar (SAR) through a combination of the effects of changes in the surface slope, surface roughness, and surface motion. Over a limited range of conditions, each of these effects can be described in terms of a linear modulation-transfer function. In such cases, the wave-height spectrum can be estimated in a straightforward manner from the SAR image-intensity spectrum. The range of conditions over which this assumption of linearity is valid is investigated using a numerical simulation model, and the implications of various departures from linearity are discussed.

Effective surface Debye temperature for NiMnSb(100) epitaxial films

NASA Astrophysics Data System (ADS)

Borca, C. N.; Komesu, Takashi; Jeong, Hae-kyung; Dowben, P. A.; Ristoiu, D.; Hordequin, Ch.; Pierre, J.; Nozières, J. P.

2000-07-01

The surface Debye temperature of the NiMnSb (100) epitaxial films has been obtained using low energy electron diffraction, inverse photoemission, and core-level photoemission. The normal dynamic motion of the (100) surface results in a value for the effective surface Debye temperature of 145±13 K. This is far smaller than the bulk Debye temperature of 312±5 K obtained from wave vector dependent inelastic neutron scattering. The large difference between these measures of surface and bulk dynamic motion indicates a soft and compositionally different (100) surface.

Nonlinear water waves generated by impulsive motion of submerged obstacle

NASA Astrophysics Data System (ADS)

Makarenko, N.; Kostikov, V.

2012-04-01

The fully nonlinear problem on generation of unsteady water waves by impulsively moving obstacle is studied analytically. The method involves the reduction of basic Euler equations to the integral-differential system for the wave elevation together with normal and tangential fluid velocities at the free surface. Exact model equations are derived in explicit form when the isolated obstacle is presented by totally submerged circular- or elliptic cylinder. Small-time asymptotic solution is constructed for the cylinder which starts moving with constant acceleration from rest. It is demonstrated that the leading-order solution terms describe several wave regimes such as the formation of non-stationary splash jets by vertical rising or vertical submersion of the obstacle, as well as the generation of diverging waves by horizontal- and combined motion of the obstacle under free surface. This work was supported by RFBR (grant No 10-01-00447) and by Research Program of the Russian Government (grant No 11.G34.31.0035).

Complex Rayleigh Waves Produced by Shallow Sedimentary Basins and their Potential Effects on Mid-Rise Buildings

NASA Astrophysics Data System (ADS)

Kohler, M. D.; Castillo, J.; Massari, A.; Clayton, R. W.

2017-12-01

Earthquake-induced motions recorded by spatially dense seismic arrays in buildings located in the northern Los Angeles basin suggest the presence of complex, amplified surface wave effects on the seismic demand of mid-rise buildings. Several moderate earthquakes produced large-amplitude, seismic energy with slow shear-wave velocities that cannot be explained or accurately modeled by any published 3D seismic velocity models or by Vs30 values. Numerical experiments are conducted to determine if sedimentary basin features are responsible for these rarely modeled and poorly documented contributions to seismic demand computations. This is accomplished through a physics-based wave propagation examination of the effects of different sedimentary basin geometries on the nonlinear response of a mid-rise structural model based on an existing, instrumented building. Using two-dimensional finite-difference predictive modeling, we show that when an earthquake focal depth is near the vertical edge of an elongated and relatively shallow sedimentary basin, dramatically amplified and complex surface waves are generated as a result of the waveguide effect introduced by this velocity structure. In addition, for certain source-receiver distances and basin geometries, body waves convert to secondary Rayleigh waves that propagate both at the free-surface interface and along the depth interface of the basin that show up as multiple large-amplitude arrivals. This study is motivated by observations from the spatially dense, high-sample-rate acceleration data recorded by the Community Seismic Network, a community-hosted strong-motion network, currently consisting of hundreds of sensors located in the southern California area. The results provide quantitative insight into the causative relationship between a sedimentary basin shape and the generation of Rayleigh waves at depth, surface waves at the free surface, scattered seismic energy, and the sensitivity of building responses to each of these.

ARRA-funded VS30 measurements using multi-technique approach at strong-motion stations in California and central-eastern United States

USGS Publications Warehouse

Yong, Alan; Martin, Antony; Stokoe, Kenneth; Diehl, John

2013-01-01

Funded by the 2009 American Recovery and Reinvestment Act (ARRA), we conducted geophysical site characterizations at 191 strong-motion stations: 187 in California and 4 in the Central-Eastern United States (CEUS). The geophysical methods used at each site included passive and active surface-wave and body-wave techniques. Multiple techniques were used at most sites, with the goal of robustly determining VS (shear-wave velocity) profiles and VS30 (the time-averaged shear-wave velocity in the upper 30 meters depth). These techniques included: horizontal-to-vertical spectral ratio (HVSR), two-dimensional (2-D) array microtremor (AM), refraction microtremor (ReMi™), spectral analysis of surface wave (SASW), multi-channel analysis of surface waves (Rayleigh wave: MASRW; and Love wave: MASLW), and compressional- and shear-wave refraction. Of the selected sites, 47 percent have crystalline, volcanic, or sedimentary rock at the surface or at relatively shallow depth, and 53 percent are of Quaternary sediments located in either rural or urban environments. Calculated values of VS30 span almost the full range of the National Earthquake Hazards Reduction Program (NEHRP) Site Classes, from D (stiff soils) to B (rock). The NEHRP Site Classes based on VS30 range from being consistent with the Class expected from analysis of surficial geology, to being one or two Site Classes below expected. In a few cases where differences between the observed and expected Site Class occurred, it was the consequence of inaccurate or coarse geologic mapping, as well as considerable degradation of the near-surface rock. Additionally, several sites mapped as rock have Site Class D (stiff soil) velocities, which is due to the extensive weathering of the surficial rock.

Analysis of Ground Motion from An Underground Chemical Explosion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pitarka, Arben; Mellors, Robert J.; Walter, William R.

Here in this paper we investigate the excitation and propagation of far-field seismic waves from the 905 kg trinitrotoluene equivalent underground chemical explosion SPE-3 recorded during the Source Physics Experiment (SPE) at the Nevada National Security Site. The recorded far-field ground motion at short and long distances is characterized by substantial shear-wave energy, and large azimuthal variations in P-and S-wave amplitudes. The shear waves observed on the transverse component of sensors at epicentral distances <50 m suggests they were generated at or very near the source. The relative amplitude of the shear waves grows as the waves propagate away frommore » the source. We analyze and model the shear-wave excitation during the explosion in the 0.01–10 Hz frequency range, at epicentral distances of up to 1 km. We used two simulation techniques. One is based on the empirical isotropic Mueller–Murphy (MM) (Mueller and Murphy, 1971) nuclear explosion source model, and 3D anelastic wave propagation modeling. The second uses a physics-based approach that couples hydrodynamic modeling of the chemical explosion source with anelastic wave propagation modeling. Comparisons with recorded data show the MM source model overestimates the SPE-3 far-field ground motion by an average factor of 4. The observations show that shear waves with substantial high-frequency energy were generated at the source. However, to match the observations additional shear waves from scattering, including surface topography, and heterogeneous shallow structure contributed to the amplification of far-field shear motion. Comparisons between empirically based isotropic and physics-based anisotropic source models suggest that both wave-scattering effects and near-field nonlinear effects are needed to explain the amplitude and irregular radiation pattern of shear motion observed during the SPE-3 explosion.« less

Analysis of Ground Motion from An Underground Chemical Explosion

DOE PAGES

Pitarka, Arben; Mellors, Robert J.; Walter, William R.; ...

2015-09-08

Here in this paper we investigate the excitation and propagation of far-field seismic waves from the 905 kg trinitrotoluene equivalent underground chemical explosion SPE-3 recorded during the Source Physics Experiment (SPE) at the Nevada National Security Site. The recorded far-field ground motion at short and long distances is characterized by substantial shear-wave energy, and large azimuthal variations in P-and S-wave amplitudes. The shear waves observed on the transverse component of sensors at epicentral distances <50 m suggests they were generated at or very near the source. The relative amplitude of the shear waves grows as the waves propagate away frommore » the source. We analyze and model the shear-wave excitation during the explosion in the 0.01–10 Hz frequency range, at epicentral distances of up to 1 km. We used two simulation techniques. One is based on the empirical isotropic Mueller–Murphy (MM) (Mueller and Murphy, 1971) nuclear explosion source model, and 3D anelastic wave propagation modeling. The second uses a physics-based approach that couples hydrodynamic modeling of the chemical explosion source with anelastic wave propagation modeling. Comparisons with recorded data show the MM source model overestimates the SPE-3 far-field ground motion by an average factor of 4. The observations show that shear waves with substantial high-frequency energy were generated at the source. However, to match the observations additional shear waves from scattering, including surface topography, and heterogeneous shallow structure contributed to the amplification of far-field shear motion. Comparisons between empirically based isotropic and physics-based anisotropic source models suggest that both wave-scattering effects and near-field nonlinear effects are needed to explain the amplitude and irregular radiation pattern of shear motion observed during the SPE-3 explosion.« less

A novel control algorithm for interaction between surface waves and a permeable floating structure

NASA Astrophysics Data System (ADS)

Tsai, Pei-Wei; Alsaedi, A.; Hayat, T.; Chen, Cheng-Wu

2016-04-01

An analytical solution is undertaken to describe the wave-induced flow field and the surge motion of a permeable platform structure with fuzzy controllers in an oceanic environment. In the design procedure of the controller, a parallel distributed compensation (PDC) scheme is utilized to construct a global fuzzy logic controller by blending all local state feedback controllers. A stability analysis is carried out for a real structure system by using Lyapunov method. The corresponding boundary value problems are then incorporated into scattering and radiation problems. They are analytically solved, based on separation of variables, to obtain series solutions in terms of the harmonic incident wave motion and surge motion. The dependence of the wave-induced flow field and its resonant frequency on wave characteristics and structure properties including platform width, thickness and mass has been thus drawn with a parametric approach. From which mathematical models are applied for the wave-induced displacement of the surge motion. A nonlinearly inverted pendulum system is employed to demonstrate that the controller tuned by swarm intelligence method can not only stabilize the nonlinear system, but has the robustness against external disturbance.

Comment on “Propagation of surface waves on a semi-bounded quantum magnetized collisional plasma” [Phys. Plasmas 20, 122106 (2013)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moradi, Afshin, E-mail: a.moradi@kut.ac.ir

2016-04-15

In a recent article [Niknam et al., Phys. Plasmas 20, 122106 (2013)], Niknam et al. investigated the propagation of TM surface waves on a semi-bounded quantum magnetized collisional plasma in the Faraday configuration (in this case, the magnetic field is parallel to the both of the plasma surface and direction of propagation). Here, we present a fresh look at the problem and show that TM surface waves cannot propagate on surface of the present system. We find in the Faraday configuration the surface waves acquire both TM and TE components due to the cyclotron motion of electrons. Therefore, the mainmore » result of the work by Niknam et al. is incorrect.« less

Observation of `third sound' in superfluid 3He

NASA Astrophysics Data System (ADS)

Schechter, A. M. R.; Simmonds, R. W.; Packard, R. E.; Davis, J. C.

1998-12-01

Waves on the surface of a fluid provide a powerful tool for studying the fluid itself and the surrounding physical environment. For example, the wave speed is determined by the force per unit mass at the surface, and by the depth of the fluid: the decreasing speed of ocean waves as they approach the shore reveals the changing depth of the sea and the strength of gravity. Other examples include propagating waves in neutron-star oceans and on the surface of levitating liquid drops. Although gravity is a common restoring force, others exist, including the electrostatic force which causes a thin liquid film to adhere to a solid. Usually surface waves cannot occur on such thin films because viscosity inhibits their motion. However, in the special case of thin films of superfluid 4He, surface waves do exist and are called `third sound'. Here we report the detection of similar surface waves in thin films of superfluid 3He. We describe studies of the speed of these waves, the properties of the surface force, and the film's superfluid density.

Remote pipeline assessment and condition monitoring using low-frequency axisymmetric waves: a theoretical study of torsional wave motion

NASA Astrophysics Data System (ADS)

Muggleton, J. M.; Rustighi, E.; Gao, Y.

2016-09-01

Waves that propagate at low frequencies in buried pipes are of considerable interest in a variety of practical scenarios, for example leak detection, remote pipe detection, and pipeline condition assessment and monitoring. Particularly useful are the n = 0, or axisymmetric, modes in which there is no displacement (or pressure) variation over the pipe cross section. Previous work has focused on two of the three axisymmetric wavetypes that can propagate: the s = 1, fluid- dominated wave; and the s = 2, shell-dominated wave. In this paper, the third axisymmetric wavetype, the s = 0 torsional wave, is studied. Whilst there is a large body of research devoted to the study of torsional waves and their use for defect detection in pipes at ultrasonic frequencies, little is known about their behaviour and possible exploitation at lower frequencies. Here, a low- frequency analytical dispersion relationship is derived for the torsional wavenumber for a buried pipe from which both the wavespeed and wave attenuation can be obtained. How the torsional waves subsequently radiate to the ground surface is then investigated, with analytical expressions being presented for the ground surface displacement above the pipe resulting from torsional wave motion within the pipe wall. Example results are presented and, finally, how such waves might be exploited in practice is discussed.

Derivation of Nonlinear Wave Equation for Flexural Motions of AN Elastic Beam Travelling in AN Air-Filled Tube

NASA Astrophysics Data System (ADS)

Sugimoto, N.; Kugo, K.; Watanabe, Y.

2002-07-01

Asymptotic analysis is carried out to derive a nonlinear wave equation for flexural motions of an elastic beam of circular cross-section travelling along the centre-axis of an air-filled, circular tube placed coaxially. Both the beam and tube are assumed to be long enough for end-effects to be ignored and the aerodynamic loading on the lateral surface of the beam is considered. Assuming a compressible inviscid fluid, the velocity potential of the air is sought systematically in the form of power series in terms of the ratios of the tube radius to a wavelength and of a typical deflection to the radius. Evaluating the pressure force acting on the lateral surface of the beam, the aerodynamic loading including the effects of finite deflection as well as of air's compressibility and axial curvature of the beam are obtained. Although the nonlinearity arises from the kinematical condition on the beam surface, it may be attributed to the presence of the tube wall. With the aerodynamic loading thus obtained, a nonlinear wave equation is derived, whereas linear theory is assumed for the flexural motions of the beam. Some discussions are given on the results.

Liquefaction, ground oscillation, and soil deformation at the Wildlife Array, California

USGS Publications Warehouse

Holzer, T.L.; Youd, T.L.

2007-01-01

Excess pore-water pressure and liquefaction at the Wildlife Liquefaction Array in 1987 were caused by deformation associated with both high-frequency strong ground motion and 5.5-second-period Love waves. The Love waves produced large (???1.5%) cyclic shear strains well after the stronger high-frequency ground motion abated. These cyclic strains generated approximately from 13 to 35% of the excess pore-water pressure in the liquefied layer and caused excess pore-water pressures ultimately to reach effective overburden stress. The deformation associated with the Love waves explains the "postearthquake" increase of pore-water pressure that was recorded at the array. This explanation suggests that conventional methods for predicting liquefaction based on peak ground acceleration are incomplete and may need to consider cyclic strains associated with long-period surface waves. A post-earthquake survey of an inclinometer casing indicated permanent shear strain associated with lateral spreading primarily occurred in the upper part of the liquefied layer. Comparison of cone penetration test soundings conducted after the earthquake with pre-earthquake soundings suggests sleeve friction increased. Natural lateral variability of the liquefied layer obscured changes in tip resistance despite a ???1% reduction in volume. The large oscillatory motion associated with surface waves explains ground oscillation that has been reported at some liquefaction sites during earthquakes.

Tsunami generation and associated waves in the water column and seabed due to an asymmetric earthquake motion within an anisotropic substratum

NASA Astrophysics Data System (ADS)

Bagheri, Amirhossein; Greenhalgh, Stewart; Khojasteh, Ali; Rahimian, Mohammad; Attarnejad, Reza

2016-10-01

In this paper, closed-form integral expressions are derived to describe how surface gravity waves (tsunamis) are generated when general asymmetric ground displacement (due to earthquake rupturing), involving both horizontal and vertical components of motion, occurs at arbitrary depth within the interior of an anisotropic subsea solid beneath the ocean. In addition, we compute the resultant hydrodynamic pressure within the seawater and the elastic wavefield within the seabed at any position. The method of potential functions and an integral transform approach, accompanied by a special contour integration scheme, are adopted to handle the equations of motion and produce the numerical results. The formulation accounts for any number of possible acoustic-gravity modes and is valid for both shallow and deep water situations as well as for any focal depth of the earthquake source. Phase and group velocity dispersion curves are developed for surface gravity (tsunami mode), acoustic-gravity, Rayleigh, and Scholte waves. Several asymptotic cases which arise from the general analysis are discussed and compared to existing solutions. The role of effective parameters such as hypocenter location and frequency of excitation is examined and illustrated through several figures which show the propagation pattern in the vertical and horizontal directions. Attention is directed to the unexpected contribution from the horizontal ground motion. The results have important application in several fields such as tsunami hazard prediction, marine seismology, and offshore and coastal engineering. In a companion paper, we examine the effect of ocean stratification on the appearance and character of internal and surface gravity waves.

6-C polarization analysis using point measurements of translational and rotational ground-motion: theory and applications

NASA Astrophysics Data System (ADS)

Sollberger, David; Greenhalgh, Stewart A.; Schmelzbach, Cedric; Van Renterghem, Cédéric; Robertsson, Johan O. A.

2018-04-01

We provide a six-component (6-C) polarization model for P-, SV-, SH-, Rayleigh-, and Love-waves both inside an elastic medium as well as at the free surface. It is shown that single-station 6-C data comprised of three components of rotational motion and three components of translational motion provide the opportunity to unambiguously identify the wave type, propagation direction, and local P- and S-wave velocities at the receiver location by use of polarization analysis. To extract such information by conventional processing of three-component (3-C) translational data would require large and dense receiver arrays. The additional rotational components allow the extension of the rank of the coherency matrix used for polarization analysis. This enables us to accurately determine the wave type and wave parameters (propagation direction and velocity) of seismic phases, even if more than one wave is present in the analysis time window. This is not possible with standard, pure-translational 3-C recordings. In order to identify modes of vibration and to extract the accompanying wave parameters, we adapt the multiple signal classification algorithm (MUSIC). Due to the strong nonlinearity of the MUSIC estimator function, it can be used to detect the presence of specific wave types within the analysis time window at very high resolution. We show how the extracted wavefield properties can be used, in a fully automated way, to separate the wavefield into its different wave modes using only a single 6-C recording station. As an example, we apply the method to remove surface wave energy while preserving the underlying reflection signal and to suppress energy originating from undesired directions, such as side-scattered waves.

Surface waves generated by shallow underwater explosions

NASA Technical Reports Server (NTRS)

Falade, A.; Holt, M.

1978-01-01

Surface water waves generated by surface and near surface point explosions are calculated. Taking the impulse distribution imparted at the water surface by the explosion as the overriding mechanism for transferring energy of the explosive to surface wave motion, the linearized theory of Kranzer and Keller is used to obtain the wave displacement in the far field. The impulse distribution is obtained by integrating the pressure wave over an appropriate time interval on a horizontal surface just beneath the undisturbed water surface. For surface explosions, a modified form of the similarity method first used by Collins and Holt is used to obtain the flow field. In the case of submerged explosions, the flow field is estimated by making necessary modifications to Sedov's similarity solution to account for the venting that accompanies the interaction of the leading (blast) wave with the ocean surface. Surface waves generated by a charge at six depths of placement (0.15 m, 0.30 m, 0.61 m, 0.91 m, 1.37 m, 3.05 m) are considered in addition to surface explosions. The results seem to support the existence of an upper critical depth phenomenon (of the type already established for chemical explosions) for point (nuclear) explosions.

Numerical study on wave loads and motions of two ships advancing in waves by using three-dimensional translating-pulsating source

NASA Astrophysics Data System (ADS)

Xu, Yong; Dong, Wen-Cai

2013-08-01

A frequency domain analysis method based on the three-dimensional translating-pulsating (3DTP) source Green function is developed to investigate wave loads and free motions of two ships advancing on parallel course in waves. Two experiments are carried out respectively to measure the wave loads and the freemotions for a pair of side-byside arranged ship models advancing with an identical speed in head regular waves. For comparison, each model is also tested alone. Predictions obtained by the present solution are found in favorable agreement with the model tests and are more accurate than the traditional method based on the three dimensional pulsating (3DP) source Green function. Numerical resonances and peak shift can be found in the 3DP predictions, which result from the wave energy trapped in the gap between two ships and the extremely inhomogeneous wave load distribution on each hull. However, they can be eliminated by 3DTP, in which the speed affects the free surface and most of the wave energy can be escaped from the gap. Both the experiment and the present prediction show that hydrodynamic interaction effects on wave loads and free motions are significant. The present solver may serve as a validated tool to predict wave loads and motions of two vessels under replenishment at sea, and may help to evaluate the hydrodynamic interaction effects on the ships safety in replenishment operation.

Induced dynamic nonlinear ground response at Gamer Valley, California

USGS Publications Warehouse

Lawrence, Z.; Bodin, P.; Langston, C.A.; Pearce, F.; Gomberg, J.; Johnson, P.A.; Menq, F.-Y.; Brackman, T.

2008-01-01

We present results from a prototype experiment in which we actively induce, observe, and quantify in situ nonlinear sediment response in the near surface. This experiment was part of a suite of experiments conducted during August 2004 in Garner Valley, California, using a large mobile shaker truck from the Network for Earthquake Engineering Simulation (NEES) facility. We deployed a dense accelerometer array within meters of the mobile shaker truck to replicate a controlled, laboratory-style soil dynamics experiment in order to observe wave-amplitude-dependent sediment properties. Ground motion exceeding 1g acceleration was produced near the shaker truck. The wave field was dominated by Rayleigh surface waves and ground motions were strong enough to produce observable nonlinear changes in wave velocity. We found that as the force load of the shaker increased, the Rayleigh-wave phase velocity decreased by as much as ???30% at the highest frequencies used (up to 30 Hz). Phase velocity dispersion curves were inverted for S-wave velocity as a function of depth using a simple isotropic elastic model to estimate the depth dependence of changes to the velocity structure. The greatest change in velocity occurred nearest the surface, within the upper 4 m. These estimated S-wave velocity values were used with estimates of surface strain to compare with laboratory-based shear modulus reduction measurements from the same site. Our results suggest that it may be possible to characterize nonlinear soil properties in situ using a noninvasive field technique.

Surface acoustic wave micromotor with arbitrary axis rotational capability

NASA Astrophysics Data System (ADS)

Tjeung, Ricky T.; Hughes, Mark S.; Yeo, Leslie Y.; Friend, James R.

2011-11-01

A surface acoustic wave (SAW) actuated rotary motor is reported here, consisting of a millimeter-sized spherical metal rotor placed on the surface of a lead zirconate titanate piezoelectric substrate upon which the SAW is made to propagate. At the design frequency of 3.2 MHz and with a fixed preload of 41.1 μN, the maximum rotational speed and torque achieved were approximately 1900 rpm and 5.37 μN-mm, respectively, producing a maximum output power of 1.19 μW. The surface vibrations were visualized using laser Doppler vibrometry and indicate that the rotational motion arises due to retrograde elliptical motions of the piezoelectric surface elements. Rotation about orthogonal axes in the plane of the substrate has been obtained by using orthogonally placed interdigital electrodes on the substrate to generate SAW impinging on the rotor, offering a means to generate rotation about an arbitrary axis in the plane of the substrate.

Motion measurement of acoustically levitated object

NASA Technical Reports Server (NTRS)

Watkins, John L. (Inventor); Barmatz, Martin B. (Inventor)

1993-01-01

A system is described for determining motion of an object that is acoustically positioned in a standing wave field in a chamber. Sonic energy in the chamber is sensed, and variation in the amplitude of the sonic energy is detected, which is caused by linear motion, rotational motion, or drop shape oscillation of the object. Apparatus for detecting object motion can include a microphone coupled to the chamber and a low pass filter connected to the output of the microphone, which passes only frequencies below the frequency of sound produced by a transducer that maintains the acoustic standing wave field. Knowledge about object motion can be useful by itself, can be useful to determine surface tension, viscosity, and other information about the object, and can be useful to determine the pressure and other characteristics of the acoustic field.

Experimental investigation of the sloshing motion of the water free surface in the draft tube of a Francis turbine operating in synchronous condenser mode

NASA Astrophysics Data System (ADS)

Vagnoni, Elena; Favrel, Arthur; Andolfatto, Loïc; Avellan, François

2018-06-01

Hydropower units may be required to operate in condenser mode to supply reactive power. In this operating mode, the water level in the turbine or pump-turbine is decreased below the runner by closing the guide vanes and injecting pressurized air. While operating in condenser mode the machine experiences power losses due to several air-water interaction phenomena which cause air losses. One of such phenomena is the sloshing motion of the water free surface below the runner in the draft tube cone of a Francis turbine. The objective of the present work is to experimentally investigate the sloshing motion of the water free surface in the draft tube cone of a reduced scale physical model of a Francis turbine operating in condenser mode. Images acquisition and simultaneous pressure fluctuation measurements are performed and an image processing method is developed to investigate amplitude and frequency of the sloshing motion of the free surface. It is found that this motion is excited at the natural frequency of the water volume and corresponds to the azimuthal wavenumber m = 1 of a rotating gravity wave. The amplitude of the motion is perturbed by wave breaking and it decreases by increasing the densimetric Froude number. The sloshing frequency slightly increases with respect to the natural frequency of the water volume by increasing the densimetric Froude number. Moreover, it results that this resonant phenomenon is not related to the torque perturbation.

Surface motion of a fluid planet induced by impacts

NASA Astrophysics Data System (ADS)

Ni, Sidao; Ahrens, Thomas J.

2006-10-01

In order to approximate the free-surface motion of an Earth-sized planet subjected to a giant impact, we have described the excitation of body and surface waves in a spherical compressible fluid planet without gravity or intrinsic material attenuation for a buried explosion source. Using the mode summation method, we obtained an analytical solution for the surface motion of the fluid planet in terms of an infinite series involving the products of spherical Bessel functions and Legendre polynomials. We established a closed form expression for the mode summation excitation coefficient for a spherical buried explosion source, and then calculated the surface motion for different spherical explosion source radii a (for cases of a/R = 0.001 to 0.035, R is the radius of the Earth) We also studied the effect of placing the explosion source at different radii r0 (for cases of r0/R = 0.90 to 0.96) from the centre of the planet. The amplitude of the quasi-surface waves depends substantially on a/R, and slightly on r0/R. For example, in our base-line case, a/R = 0.03, r0/R = 0.96, the free-surface velocity above the source is 0.26c, whereas antipodal to the source, the peak free surface velocity is 0.19c. Here c is the acoustic velocity of the fluid planet. These results can then be applied to studies of atmosphere erosion via blow-off caused by asteroid impacts.

The interaction of sound with a poroelastic ground

NASA Astrophysics Data System (ADS)

Hickey, C. J.

2012-12-01

An airborne acoustic wave impinging on the surface of the ground provides a good mechanical source for investigating the near surface. Since the ground is porous, the impinging sound wave induces motion of the fluid within the pores as well as vibrating the solid framework. The most complete understanding of the interaction of airborne sound with the ground is to treat the ground as a poroelastic or poroviscoelastic medium. This treatment predicts that three types of waves can propagate in a ground with a deformable framework: two compressional waves, the fast or Type I and slow or Type II wave and one shear wave. Model calculations of the energy partition and an air-soil interface predict that most of the energy is partitioned into the Type II compressional wave, less into the Type I compressional wave, and little energy is partitioned into the shear wave. However, when measuring the solid motion of the soil one must consider how much of that wave energy is in terms of solid velocity. The deformation associated with Type II compressional wave has only a small contribution from the solid component whereas the bulk deformation of the Type I compressional wave has a solid to fluid deformation ratio of approximately one. This modeling suggests that the soil solid velocity induced by an acoustic source is associated with the Type I compressional wave. In other words, the airborne source is simply an inefficient seismic source.

Seismic loading due to mining: Wave amplification and vibration of structures

NASA Astrophysics Data System (ADS)

Lokmane, N.; Semblat, J.-F.; Bonnet, G.; Driad, L.; Duval, A.-M.

2003-04-01

A vibration induced by the ground motion, whatever its source is, can in certain cases damage surface structures. The scientific works allowing the analysis of this phenomenon are numerous and well established. However, they generally concern dynamic motion from real earthquakes. The goal of this work is to analyse the impact of shaking induced by mining on the structures located on the surface. The methods allowing to assess the consequences of earthquakes of strong amplitude are well established, when the methodology to estimate the consequences of moderate but frequent dynamic loadings is not well defined. The mining such as the "Houillères de Bassin du Centre et du Midi" (HBCM) involves vibrations which are regularly felt on the surface. An extracting work of coal generates shaking similar to those caused by earthquakes (standard waves and laws of propagation) but of rather low magnitude. On the other hand, their recurrent feature makes the vibrations more harmful. A three-dimensional modeling of standard structure of the site was carried out. The first results show that the fundamental frequencies of this structure are compatible with the amplification measurements carried out on site. The motion amplification in the surface soil layers is then analyzed. The modeling works are performed on the surface soil layers of Gardanne (Provence), where measurements of microtremors were performed. The analysis of H/V spectral ratio (horizontal on vertical component) indeed makes it possible to characterize the fundamental frequencies of the surface soil layers. This experiment also allows to characterize local evolution of amplification induced by the topmost soil layers. The numerical methods we consider to model seismic wave propagation and amplification in the site, is the Boundary Element Methode (BEM) The main advantage of the boundary element method is to get rid of artificial truncations of the mesh (as in Finite Element Method) in the case of infinite medium. For dynamic problems, these truncations lead to spurious wave reflections giving a numerical error in the solution. The experimental and numerical (BEM) results on surface motion amplification are then compared in terms of both amplitude and frequency range.

Near-Inertial Surface Currents and their influence on Surface Dispersion in the Northeastern Gulf of Mexico near the Deepwater Horizon Oil Spill

NASA Astrophysics Data System (ADS)

Gough, M.; Reniers, A.; MacMahan, J. H.; Howden, S. D.

2014-12-01

The continental shelf along the northeastern Gulf of Mexico is transected by the critical latitude (30°N) for inertial motions. At this latitude the inertial period is 24 hours and diurnal surface current oscillations can amplify due to resonance with diurnal wind and tidal forcing. Tidal amplitudes are relatively small in this region although K1 tidal currents can be strong over the shelf west of the DeSoto Canyon where the K1 tide propagates onshore as a Sverdrup wave. Other sources of diurnal motions include internal tidal currents, Poincaré waves, and basin resonance. It is therefore very difficult to separate inertial wind-driven motions from other diurnal motions. Spatiotemporal surface currents were measured using hourly 6 km resolution HF radar data collected in June 2010 during the Deepwater Horizon oil spill and July 2012 during the Grand Lagrangian Deployment (GLAD). Surface currents were also measured using GLAD GPS-tracked drifters. NDBC buoy wind data were used to determine wind-forcing, and OSU Tidal Inversion Software (OTIS) were used to predict tidal currents. The relative spatiotemporal influence of diurnal wind and tidal forcing on diurnal surface current oscillations is determined through a series of comparative analyses: phase and amplitude of bandpassed timeseries, wavelet analyses, wind-driven inertial oscillation calculations, and tidal current predictions. The wind-driven inertial ocean response is calculated by applying a simple "slab" model where wind-forcing is allowed to excite a layer of low-density water riding over high density water. The spatial variance of diurnal motions are found to be correlated with satellite turbidity imagery indicating that stratification influences the sea surface inertial response to wind-forcing. Surface dispersion is found to be minimized in regions of high diurnal variance suggesting that mean surface transport is restricted in regions of inertial motions associated with stratification.

Analysis of Site Effect in the Izmit Basin of Turkey by Wave Propagation Simulation Using the Spectral Element Method: Preliminary Results

NASA Astrophysics Data System (ADS)

Firtana Elcomert, K.; Kocaoglu, A. H.

2013-12-01

Sedimentary basins generally cause significant ground motion amplification during an earthquake. Along with the resonance controlled by the impedance contrast between the sedimentary cover and bedrock, surface waves generated within the basin make the waveforms more complex and longer in duration. When a dense network of weak and/or strong motion sensors is available, site effect or more specifically sedimentary basin amplification can be directly estimated experimentally provided that significant earthquakes occur during the period of study. Alternatively, site effect can be investigated through simulation of ground motion. The objective of this study is to investigate the 2-D and/or 3-D site effect in the Izmit Basin located in the eastern Marmara region of Turkey, using the currently available bedrock topography and shear-wave velocity data. The Izmit Basin was formed in Plio-Quaternary period and is known to be controlled by the northern branch of the North Anatolian Fault Zone. A thorough analysis of seismic hazard is important since the city of Izmit and its metropolitan area is located in this region. This work presents some of the preliminary results obtained from 2-D and 3-D seismic wave propagation simulations using the spectral element method, which is based on high order polynomial approximation of the weak formulation of the wave equation. In this study, the numerical simulations were carried out with SPECFEM2D/3D program. Comparison of seismograms recorded on the top of sedimentary layer with those recorded on the bedrock show more complex waveforms with higher amplitudes on seismograms recorded at the free surface. Furthermore, modeling clearly reveals that observed seismograms include surface waves whose excitation is clearly related with the basin geometry.

Propagation and damping of Alfvén waves in low solar atmosphere

NASA Astrophysics Data System (ADS)

Ryu, Chang-Mo; Huynh, Cong Tuan

2017-10-01

Propagation and damping of Alfvén waves in the inner solar corona are studied using a 2D magnetohydrodynamics (MHD) simulation code with realistic density and temperature profiles in a uniform background magnetic field. A linear wave is launched by ascribing a sinusoidal fluid motion at about 1000 km from the surface of the Sun, which is shown to generate Alfvénic wave motions along the height. The 2D MHD simulation shows that for B0 ≈ 3 G, Alfvén waves of about 10-2 Hz with an infinite horizontal length-scale can penetrate into the corona, transferring about 90 per cent their energies. This raises the possibility that the wave can be dissipated by various physical processes. The results show that the propagating wave can effectively damp via viscosity in the lower region of the corona, if a horizontal scale of granular size is incorporated.

Regarding tracer transport in Mars' winter atmosphere in the presence of nearly stationary, forced planetary waves

NASA Technical Reports Server (NTRS)

Hollingsworth, Jeffrey L.; Haberle, R. M.; Houben, Howard C.

1993-01-01

Large-scale transport of volatiles and condensates on Mars, as well as atmospheric dust, is ultimately driven by the planet's global-scale atmospheric circulation. This circulation arises in part from the so-called mean meridional (Hadley) circulation that is associated with rising/poleward motion in low latitudes and sinking/equatorward motion in middle and high latitudes. Intimately connected to the mean circulation is an eddy-driven component due to large-scale wave activity in the planet's atmosphere. During winter this wave activity arises both from traveling weather systems (i.e., barotropic and baroclinic disturbances) and from 'forced' disturbances (e.g., the thermal tides and surface-forced planetary waves). Possible contributions to the effective (net) transport circulation from forced planetary waves are investigated.

Wave energy trapping and localization in a plate with a delamination

NASA Astrophysics Data System (ADS)

Glushkov, Evgeny; Glushkova, Natalia; Golub, Mikhail V.; Moll, Jochen; Fritzen, Claus-Peter

2012-12-01

The research aims at an experimental approval of the trapping mode effect theoretically predicted for an elastic plate-like structure with a horizontal crack. The effect is featured by a sharp capture of incident wave energy at certain resonance frequencies with its localization between the crack and plate surfaces in the form of energy vortices yielding long-enduring standing waves. The trapping modes are eigensolutions of the related diffraction problem associated with nearly real complex points of its discrete frequency spectrum. To detect such resonance motion, a laser vibrometer based system has been employed for the acquisition and appropriate visualization of piezoelectrically actuated out-of-plane surface motion of a two-layer aluminum plate with an artificial strip-like delamination. The measurements at resonance and off-resonance frequencies have revealed a time-harmonic oscillation of good quality above the delamination in the resonance case. It lasts for a long time after the scattered waves have left that area. The measured frequency of the trapped standing-wave oscillation is in a good agreement with that predicted using the integral equation based mathematical model.

Excitation of high-frequency surface waves with long duration in the Valley of Mexico

NASA Astrophysics Data System (ADS)

Iida, Masahiro

1999-04-01

During the 1985 Michoacan earthquake (Ms = 8.1), large-amplitude seismograms with extremely long duration were recorded in the lake bed zone of Mexico City. We interpret high-frequency seismic wave fields in the three geotechnical zones (the hill, the transition, and the lake bed zones) in the Valley of Mexico on the basis of a systematic analysis for borehole strong motion recordings. We make identification of wave types for real seismograms. First, amplitude ratios between surface and underground seismograms indicate that predominant periods of the surface seismograms are largely controlled by the wave field incident into surficial layers in the Valley of Mexico. We interpret recorded surface waves as fundamental-mode Love waves excited in the Mexican Volcanic Belt by calculating theoretical amplification for different-scale structures. Second, according to a cross-correlation analysis, the hill and transition seismograms are mostly surface waves. In the lake bed zone, while early portions are noisy body waves, late portions are mostly surface waves. Third, using two kinds of surface arrays with different station intervals, we investigate high-frequency surface-wave propagation in the lake bed zone. The wave propagation is very complicated, depending upon the time section and the frequency band. Finally, on the basis of a statistical time series model with an information criterion, we separate S- and surface-wave portions from lake bed seismograms. Surface waves are dominant and are recognized even in the early time section. Thus high-frequency surface waves with long duration in the Valley of Mexico are excited by the Mexican Volcanic Belt.

Acoustically levitated dancing drops: Self-excited oscillation to chaotic shedding.

PubMed

Lin, Po-Cheng; I, Lin

2016-02-01

We experimentally demonstrate self-excited oscillation and shedding of millimeter-sized water drops, acoustically levitated in a single-node standing waves cavity, by decreasing the steady acoustic wave intensity below a threshold. The perturbation of the acoustic field by drop motion is a possible source for providing an effective negative damping for sustaining the growing amplitude of the self-excited motion. Its further interplay with surface tension, drop inertia, gravity and acoustic intensities, select various self-excited modes for different size of drops and acoustic intensity. The large drop exhibits quasiperiodic motion from a vertical mode and a zonal mode with growing coupling, as oscillation amplitudes grow, until falling on the floor. For small drops, chaotic oscillations constituted by several broadened sectorial modes and corresponding zonal modes are self-excited. The growing oscillation amplitude leads to droplet shedding from the edges of highly stretched lobes, where surface tension no longer holds the rapid expanding flow.

Acoustically levitated dancing drops: Self-excited oscillation to chaotic shedding

NASA Astrophysics Data System (ADS)

Lin, Po-Cheng; I, Lin

2016-02-01

We experimentally demonstrate self-excited oscillation and shedding of millimeter-sized water drops, acoustically levitated in a single-node standing waves cavity, by decreasing the steady acoustic wave intensity below a threshold. The perturbation of the acoustic field by drop motion is a possible source for providing an effective negative damping for sustaining the growing amplitude of the self-excited motion. Its further interplay with surface tension, drop inertia, gravity and acoustic intensities, select various self-excited modes for different size of drops and acoustic intensity. The large drop exhibits quasiperiodic motion from a vertical mode and a zonal mode with growing coupling, as oscillation amplitudes grow, until falling on the floor. For small drops, chaotic oscillations constituted by several broadened sectorial modes and corresponding zonal modes are self-excited. The growing oscillation amplitude leads to droplet shedding from the edges of highly stretched lobes, where surface tension no longer holds the rapid expanding flow.

Tropical Convection's Roles in Tropical Tropopause Cirrus

NASA Technical Reports Server (NTRS)

Boehm, Matthew T.; Starr, David OC.; Verlinde, Johannes; Lee, Sukyoung

2002-01-01

The results presented here show that tropical convection plays a role in each of the three primary processes involved in the in situ formation of tropopause cirrus. First, tropical convection transports moisture from the surface into the upper troposphere. Second, tropical convection excites Rossby waves that transport zonal momentum toward the ITCZ, thereby generating rising motion near the equator. This rising motion helps transport moisture from where it is detrained from convection to the cold-point tropopause. Finally, tropical convection excites vertically propagating tropical waves (e.g. Kelvin waves) that provide one source of large-scale cooling near the cold-point tropopause, leading to tropopause cirrus formation.

The case for 6-component ground motion observations in planetary seismology

NASA Astrophysics Data System (ADS)

Joshi, Rakshit; van Driel, Martin; Donner, Stefanie; Nunn, Ceri; Wassermann, Joachim; Igel, Heiner

2017-04-01

The imminent INSIGHT mission will place a single seismic station on Mars to learn more about the structure of the Martian interior. Due to cost and difficulty, only single stations are currently feasible for planetary missions. We show that future single station missions should also measure rotational ground motions, in addition to the classic 3 components of translational motion. The joint, collocated, 6 component (6C) observations offer access to additional information that can otherwise only be obtained through seismic array measurements or are associated with large uncertainties. An example is the access to local phase velocity information from measurements of amplitude ratios of translations and rotations. When surface waves are available, this implies (in principle) that 1D velocity models can be estimated from Love wave dispersion curves. In addition, rotational ground motion observations can distinguish between Love and Rayleigh waves as well as S and P type motions. Wave propagation directions can be estimated by maximizing (or minimizing) coherence between translational and rotational motions. In combination with velocity-depth estimates, locations of seismic sources can be determined from a single station with little or no prior knowledge of the velocity structure. We demonstrate these points with both theoretical and real data examples using the vertical component of motion from ring laser recordings at Wettzell and all components of motion from the ROMY ring near Munich. Finally, we present the current state of technology concerning portable rotation sensors and discuss the relevance to planetary seismology.

On the potential of seismic rotational motion measurements for extraterrestrial seismology

NASA Astrophysics Data System (ADS)

Schmelzbach, Cedric; Sollberger, David; Khan, Amir; Greenhalgh, Stewart; Van Renterghem, Cederic; Robertsson, Johan

2017-04-01

Classically, seismological recordings consist of measurements of translational ground motion only. However, in addition to three vector components of translation there are three components of rotation to consider, leading to six degrees of freedom. Of particular interest is thereby the fact that measuring rotational motion means isolating shear (S) waves. Recording the rotational motion requires dedicated rotational sensors. Alternatively, since the rotational motion is given by the curl of the vectorial displacements, the rotational motion around the two horizontal axes can be computed from the horizontal spatial gradients of vertical translational recordings if standard translational seismometers are placed in an areal array at the free surface. This follows from the zero stress free surface condition. Combining rotational and translational motion measurements opens up new ways of analyzing seismic data, such as facilitating much improved arrival identification and wavefield separation (e.g., P-/S-wave separation), and local slowness (arrival direction and velocity) determination. Such combined measurements maximize the seismic information content that a single six-component station or a small station array can provide, and are of particular interest for sparse or single-station measurements such as in extraterrestrial seismology. We demonstrate the value of the analysis of combined translational and rotational recordings by re-evaluating data from the Apollo 17 lunar seismic profiling experiment (LSPE). The LSPE setup consisted of four vertical-component geophones arranged in a star-like geometry. This areal receiver layout enables computing the horizontal spatial gradients by spatial finite differencing of the vertical-component data for two perpendicular directions and, hence, the estimation of rotational motion around two horizontal axes. Specifically, the recorded seismic waveform data originated from eight explosive packages as well as from continuously listening to the natural lunar seismic activity of moonquakes. As an example, the combined analysis of translational and rotational motion from the active-source LSPE data provides, for the first time, the possibility to extract S-wave information from the enigmatic and reverbatory lunar seismic waveform data, which hithertofore had masked later arriving S-waves. The identification of S-waves enables to characterize the shallow lunar crust in a full elastic sense. The resultant Poisson's ratio profile allows discriminating shallow basalt layers of different degree of fracturing. Our successful analysis of the Apollo 17 data highlights the anticipated significant value of rotational measurements for future extraterrestrial seismology missions.

Comparison of internal wave properties calculated by Boussinesq equations with/without rigid-lid assumption

NASA Astrophysics Data System (ADS)

Liu, C. M.

2017-12-01

Wave properties predicted by the rigid-lid and the free-surface Boussinesq equations for a two-fluid system are theoretically calculated and compared in this study. Boussinesq model is generally applied to numerically simulate surface waves in coastal regions to provide credible information for disaster prevention and breaker design. As for internal waves, Liu et al. (2008) and Liu (2016) respectively derived a free-surface model and a rigid-lid Boussinesq models for a two-fluid system. The former and the latter models respectively contain four and three key variables which may result in different results and efficiency while simulating. Therefore, present study shows the results theoretically measured by these two models to provide more detailed observation and useful information for motions of internal waves.

European Science Notes Information Bulletin. Report on Current European and Middle Eastern Science

DTIC Science & Technology

1992-10-01

oceanographers. This has occurred at a time of current radar systems . The independent develop- rapidly increasing government interest in and fund...over each area in which surface current is ment of the waves (some motions caused by wave determined (for HF systems , averaging time spans action and...Ocean Observing System ; high-resolution model capabilities; ocean- atmosphere interface; Surface Density Depression Pool; forecasting INTRODUCTION tion

Investigation on earthquake ground motions observed along a north-south survey line in the Kumamoto Plain, during the aftershocks of 2016 Kumamoto earthquake

NASA Astrophysics Data System (ADS)

Tsuno, S.; Korenaga, M.; Okamoto, K.; Chimoto, K.; Yamanaka, H.; Yamada, N.; Matsushima, T.

2017-12-01

To evaluate local site effects in the Kumamoto Plain, we installed 15 temporary seismic stations along the north-south survey line, after the 2016 Kumamoto earthquake foreshock (Mj 6.4). In this report, to investigate earthquake ground motions observed along the north-south survey line, we estimated site amplification factors from weak ground motion data and estimated S-wave velocity structures by array microtremor observations at temporary seismic stations. We installed 15 temporary seismic stations at an interval of 300m to 2.5km along the north-south survey line. We estimated site amplification factors, with a station at Mt. Kinbo as a reference. Site amplification factors at the middle part and the southern part along the survey line, located in the alluvial lowland, were dominated in the frequency of 1-2Hz. On the other hand, site amplification factors at the northern part along the survey line were dominated in the frequency of 2-5Hz. It suggests that the ground profiles near the surface are complicate along this north-south survey line in the Kumamoto Plain. Therefore, we performed array microtremor observations at the temporary seismic stations, to estimate S-wave velocity structures along the north-south survey line. We obtained phase velocities of Rayleigh waves by the SPAC method and estimated S-wave velocity structures by applying the Genetic Algorism to those phase velocity. The low velocity layer with a thickness of around 15m was deposited on the surface at sites located in the alluvial lowland. Finally, we compared the distribution of PGAs observed along the north-south survey line to AVs30 estimated by S-wave velocity structures. As a result, PGAs along the survey line were strongly concerned by AVs30. We concluded that earthquake ground motions in the frequency of more than 1Hz observed in this north-south survey line were excited by the low velocity layer near the surface.

Wave induced coastal cliff top ground motions and infragravity wave dissipation under high energy wave conditions.

NASA Astrophysics Data System (ADS)

Earlie, C. S.; le Dantec, N.; Young, A.

2016-12-01

Coastal cliff erosion is a widespread problem that threatens property and infrastructure globally. The prediction of this risk calls for robust understanding of the processes and mechanisms involved in causing coastal cliff failure. Over the last decade, a number of geomorphological studies have highlighted the importance of the relationship between the offshore wave climate and cliff-toe water levels, and the resultant coastal response in terms of cliff-top ground motion and erosion. Field-based studies of instantaneous cliff response to direct wave impact have shown that wave-induced loading of the foreshore leads to cliff-top ground motions that may have the potential to weaken the integrity of the rocks and prepare them for failure. In order to understand wave-cliff interaction and how beach morphodynamics influences cliff-top ground motion and cliff erosion, two field experiments were carried out simultaneously at two locations in Northern Brittany (France). This three-month long winter field campaign (Jan-Mar 2016) included, for the first time, a comparison of cliff-top ground motion and cliff erosion at sites fronted by different beach morphologies (reflective/dissipative), along with monitoring of hydrodynamic forcing and beach topography. The magnitude of cliff-top displacements at both sites were dependent on tidal stage and free water surface elevation at the cliff toe, with the greatest contributions of cliff-top ground motions found at infragravity frequencies (0.05-0.005 Hz). Vertical displacements at infragravity and incident sea-swell (0.1-0.5 Hz) frequencies were greater at the dissipative site, apart from during spring high tide and energetic wave conditions, where displacements were two times that at the reflective site. Combining these wave-cliff interaction data with beach morphology and nearshore bathymetry will be key to understanding the spatial variability in cliff erosion under a variety of environmental settings and forcing conditions.

Formation of a wave on an ice-sheet above the dipole, moving in a fluid

NASA Astrophysics Data System (ADS)

Il'ichev, A. T.; Savin, A. A.; Savin, A. S.

2012-05-01

Theory of wave motions of a fluid with an ice-sheet was developed due to the necessity of solving of a number of problems of marine and land physics. The main attention in these investigations was focused on propagation and interaction of free waves, and also on appearance of waves under action of different loadings on the ice-sheet. From the other side, the problems dealing with waves on the fluid surface, free from the ice due to motion in the mass of the fluid of rigid bodies, has the known solutions. In this connection, it seems natural to disserminate the formulation and methods of such problems to the case of the fluid with the ice-sheet. In the present note we describe the character of formation of waves from the singularity, localized in the fluid of infinite depth beneath the ice-sheet. We use the example of the dipole, which models a cylinder in the infinite mass of the fluid. The character of the formation does not depend on the type of singularity. The ice-sheet is considered as a thin elastic plate of a constant width, floating on the water surface.

Shear Wave Velocity and Site Amplification Factors for 25 Strong-Motion Instrument Stations Affected by the M5.8 Mineral, Virginia, Earthquake of August 23, 2011

USGS Publications Warehouse

Kayen, Robert E.; Carkin, Brad A.; Corbett, Skye C.; Zangwill, Aliza; Estevez, Ivan; Lai, Lena

2015-01-01

Vertical one-dimensional shear wave velocity (Vs) profiles are presented for 25 strong-motion instrument sites along the Mid-Atlantic eastern seaboard, Piedmont region, and Appalachian region, which surround the epicenter of the M5.8 Mineral, Virginia, Earthquake of August 23, 2011. Testing was performed at sites in Pennsylvania, Maryland, West Virginia, Virginia, the District of Columbia, North Carolina, and Tennessee. The purpose of the study is to determine the detailed site velocity profile, the average velocity in the upper 30 meters of the profile (VS,30), the average velocity for the entire profile (VS,Z), and the National Earthquake Hazards Reduction Program (NEHRP) site classification. The Vs profiles are estimated using a non-invasive continuous-sine-wave method for gathering the dispersion characteristics of surface waves. A large trailer-mounted active source was used to shake the ground during the testing and produce the surface waves. Shear wave velocity profiles were inverted from the averaged dispersion curves using three independent methods for comparison, and the root-mean square combined coefficient of variation (COV) of the dispersion and inversion calculations are estimated for each site.

Seismic Wave Amplification in Las Vegas: Site Characterization Measurements and Response Models

NASA Astrophysics Data System (ADS)

Louie, J. N.; Anderson, J. G.; Luke, B.; Snelson, C.; Taylor, W.; Rodgers, A.; McCallen, D.; Tkalcic, H.; Wagoner, J.

2004-12-01

As part of a multidisciplinary effort to understand seismic wave amplification in Las Vegas Valley, we conducted geotechnical and seismic refraction field studies, geologic and lithologic interpretation, and geophysical model building. Frequency-dependent amplifications (site response) and peak ground motions strongly correlate with site conditions as characterized by the models. The models include basin depths and velocities, which also correlate against ground motions. Preliminary geologic models were constructed from detailed geologic and fault mapping, logs of over 500 wells penetrating greater than 200 m depth, gravity-inversion results from the USGS, and USDA soil maps. Valley-wide refraction studies we conducted in 2002 and 2003 were inverted for constraints on basin geometry, and deep basin and basement P velocities with some 3-d control to depths of 5 km. Surface-wave studies during 2002-2004 characterized more than 75 sites within the Valley for shear velocity to depths exceeding 100 m, including all the legacy sites where nuclear-blast ground motions were recorded. The SASW and refraction-microtremor surface-surveying techniques proved to provide complementary, and coordinating Rayleigh dispersion-curve data at a dozen sites. Borehole geotechnical studies at a half-dozen sites confirmed the shear-velocity profiles that we derived from surface-wave studies. We then correlated all the geotechnical data against a detailed stratigraphic model, derived from drilling logs, to create a Valley-wide model for shallow site conditions. This well-log-based model predicts site measurements better than do models based solely on geologic or soil mapping.

The cause of larger local magnitude (Mj) in western Japan

NASA Astrophysics Data System (ADS)

Kawamoto, H.; Furumura, T.

2017-12-01

The local magnitude of the Japan Meteorological Agency (JMA) scale (Mj) in Japan sometimes show a significant discrepancy between Mw. The Mj is calculated using the amplitude of the horizontal component of ground displacement recorded by seismometers with the natural period of T0=5 s using Katsumata et al. (2004). A typical example of such a discrepancy in estimating Mj was an overestimation of the 2000 Western Tottori earthquake (Mj=7.3, Mw=6.7; hereafter referred to as event T). In this study, we examined the discrepancy between Mj and Mw for recent large earthquakes occurring in Japan.We found that the most earthquakes with larger Mj (>Mw) occur in western Japan while the earthquakes in northern Japan show reasonable Mj (=Mw). To understand the cause of such larger Mj for western Japan earthquakes we examined the strong motion record from the K-NET and KiK-net network for the event T and other earthquakes for reference. The observed ground displacement record from the event T shows a distinctive Love wave packet in tangential motion with a dominant period of about T=5 s which propagates long distances without showing strong dispersions. On the other hand, the ground motions from the earthquakes in northeastern Japan do not have such surface wave packet, and attenuation of ground motion is significant. Therefore, the overestimation of the Mj for earthquakes in western Japan may be attributed to efficient generation and propagation properties of Love wave probably relating to the crustal structure of western Japan. To explain this, we then conducted a numerical simulation of seismic wave propagation using 3D sedimentary layer model (JIVSM; Koketsu et al., 2012) and the source model of the event T. The result demonstrated the efficient generation of Love wave from the shallow strike-slip source which propagates long distances in western Japan without significant dispersions. On the other hand, the generation of surface wave was not so efficient when using a sedimentary layer model of northeastern Japan. In this case, the attenuation of surface wave is very significant due to the dispersion and scattering as propagating through sedimentary basins. Therefore, overestimation of the Mj for earthquakes in western Japan strongly relates to the structure of western Japan to generate distinctive Love wave packet for long distances.

Interfacial waves generated by contact line motion through electrowetting

NASA Astrophysics Data System (ADS)

Ha, Jonghyun; Park, Jaebum; Kim, Yunhee; Bae, Jungmok; Kim, Ho-Young

2013-11-01

The contact angle of a liquid-fluid interface can be effectively modulated by EWOD (electrowetting on dielectric). Rapid movement of the contact line, which can be achieved by swift change of voltages at the electrodes, can give rise to interfacial waves under the strong influence of surface tension. Many optofluidic devices employing EWOD actuation, such as lenses, three-dimensional displays and laser radar, use two different liquids in a single cell, implying that the motions of the two liquids should be considered simultaneously to solve the dynamics of interfacial waves. Furthermore, the capillary waves excited by moving contact lines, which inherently involve slipping flows at solid boundaries, pose an interesting problem that has not been treated so far. We perform a perturbation analysis for this novel wave system to find the dispersion relation that relates the wavenumber, and the decay length over which the wave is dissipated by viscous effects. We experimentally corroborate our theory.

GPS-Acoustic Seafloor Geodesy using a Wave Glider

NASA Astrophysics Data System (ADS)

Chadwell, C. D.

2013-12-01

The conventional approach to implement the GPS-Acoustic technique uses a ship or buoy for the interface between GPS and Acoustics. The high cost and limited availability of ships restricts occupations to infrequent campaign-style measurements. A new approach to address this problem uses a remote controlled, wave-powered sea surface vehicle, the Wave Glider. The Wave Glider uses sea-surface wave action for forward propulsion with both upward and downward motions producing forward thrust. It uses solar energy for power with solar panels charging the onboard 660 W-h battery for near continuous operation. It uses Iridium for communication providing command and control from shore plus status and user data via the satellite link. Given both the sea-surface wave action and solar energy are renewable, the vehicle can operate for extended periods (months) remotely. The vehicle can be launched from a small boat and can travel at ~ 1 kt to locations offshore. We have adapted a Wave Glider for seafloor geodesy by adding a dual frequency GPS receiver embedded in an Inertial Navigation Unit, a second GPS antenna/receiver to align the INU, and a high precision acoustic ranging system. We will report results of initial testing of the system conducted at SIO. In 2014, the new approach will be used for seafloor geodetic measurements of plate motion in the Cascadia Subduction Zone. The project is for a three-year effort to measure plate motion at three sites along an East-West profile at latitude 44.6 N, offshore Newport Oregon. One site will be located on the incoming plate to measure the present day convergence between the Juan de Fuca and North American plates and two additional sites will be located on the continental slope of NA to measure the elastic deformation due to stick-slip behavior on the mega-thrust fault. These new seafloor data will constrain existing models of slip behavior that presently are poorly constrained by land geodetic data 100 km from the deformation front.

Bottom boundary layer forced by finite amplitude long and short surface waves motions

NASA Astrophysics Data System (ADS)

Elsafty, H.; Lynett, P.

2018-04-01

A multiple-scale perturbation approach is implemented to solve the Navier-Stokes equations while including bottom boundary layer effects under a single wave and under two interacting waves. In this approach, fluid velocities and the pressure field are decomposed into two components: a potential component and a rotational component. In this study, the two components are exist throughout the entire water column and each is scaled with appropriate length and time scales. A one-way coupling between the two components is implemented. The potential component is assumed to be known analytically or numerically a prior, and the rotational component is forced by the potential component. Through order of magnitude analysis, it is found that the leading-order coupling between the two components occurs through the vertical convective acceleration. It is shown that this coupling plays an important role in the bottom boundary layer behavior. Its effect on the results is discussed for different wave-forcing conditions: purely harmonic forcing and impurely harmonic forcing. The approach is then applied to derive the governing equations for the bottom boundary layer developed under two interacting wave motions. Both motions-the shorter and the longer wave-are decomposed into two components, potential and rotational, as it is done in the single wave. Test cases are presented wherein two different wave forcings are simulated: (1) two periodic oscillatory motions and (2) short waves interacting with a solitary wave. The analysis of the two periodic motions indicates that nonlinear effects in the rotational solution may be significant even though nonlinear effects are negligible in the potential forcing. The local differences in the rotational velocity due to the nonlinear vertical convection coupling term are found to be on the order of 30% of the maximum boundary layer velocity for the cases simulated in this paper. This difference is expected to increase with the increase in wave nonlinearity.

Basin-edge generated Rayleigh waves in the Almaty basin and corresponding consequences for ground motion amplification

NASA Astrophysics Data System (ADS)

Pilz, Marco; Parolai, Stefano; Petrovic, Bojana; Silacheva, Natalya; Abakanov, Tanatkan; Orunbaev, Sagynbek; Moldobekov, Bolot

2018-04-01

During the past two centuries, several large earthquakes have caused extensive damages in the city of Almaty in Kazakhstan. Increasing the preparedness for future events, the definition of the optimal engineering designs for civil structures and the corresponding mitigation of earthquake risks involves the accomplishment of site response studies. To this regard, a temporary seismological network of 15 stations was installed in the city aiming at the accurate identification of local variations of site response at different locations. As the city is settled on a deep sediment-filled plain with laterally strongly varying thicknesses, bound to the south by the Tien-Shan mountain range, the city might face important site effects: large amplification and significant increase of shaking duration. In addition, surface waves in the low-frequency range around and slightly higher than the fundamental resonance frequency, which could be generated at the boundaries of the basin, can carry a large amount of energy. In turn, this will influence both the spatial distribution of the level of amplification and the temporal lengthening of ground motion significantly. For quantifying these effects, we apply complex trace analysis, which uses the instantaneous polarization characteristics of the seismic signal for separating waves arriving at a single site from different directions. In this way, secondary surface waves originating at various sites along the edge of the Almaty basin can be identified as well as their generation regions. After having assessed 1-D amplification effects with well-established techniques like the standard spectral ratio and the horizontal-to-vertical spectral ratio techniques, the results further indicate that thick layers of soft clay deposits and the 3-D structure of the basin give rise to lengthening of ground motion and high amplification values at low frequencies around 0.2 Hz. The steep structure of the sediment-bedrock interface at the southern edge of the Almaty basin can generate surface waves with distinct azimuths, meaning that the spatial variability of ground motion is not only related to a simple 1-D response but it can be strongly modified by secondary waves generated at the margin of the basin.

Estimation of viscoelastic surface wave parameters using a low cost optical deflection method

NASA Astrophysics Data System (ADS)

Brum, J.; Balay, G.; Arzúa, A.; Núñez, I.; Negreira, C.

2010-01-01

In this work an optical deflection method was used to study surface vibrations created by a low frequency source placed on the sample's surface. The optical method consists in placing a laser beam perpendicularly the sample's surface (gelatine based phantom). A beam-splitter is placed between the laser and the sample to project the reflected beam into a screen. As the surface moves due to the action of the low frequency source the laser beam on the screen also moves. Recording this movement with a digital camera allow us to reconstruct de surface motion using the light reflection law. If the scattering of the surface is very strong (such the one in biological tissue) a lens is placed between the surface and the beam-splitter to collect the scattered light. As validation method the surface movement was measured using a 10 MHz ultrasonic transducer placed normal to the surface in pulse-eco mode. The optical measurements were in complete agreement with the acoustical measurements. The optical measurement has the following advantages over the acoustic: 2-dimensional motion could be recorded and it is low cost. Since the acquisition was synchronized and the source-laser beam distance is known, measuring the time of flight an estimation of the surface wave velocity is obtained in order to measure the elasticity of the sample. The authors conclude that a reliable optical, low cost method for obtaining surface wave parameters of biological tissue was developed and successfully validate.

Calculation of broadband time histories of ground motion: Comparison of methods and validation using strong-ground motion from the 1994 Northridge earthquake

USGS Publications Warehouse

Hartzell, S.; Harmsen, S.; Frankel, A.; Larsen, S.

1999-01-01

This article compares techniques for calculating broadband time histories of ground motion in the near field of a finite fault by comparing synthetics with the strong-motion data set for the 1994 Northridge earthquake. Based on this comparison, a preferred methodology is presented. Ground-motion-simulation techniques are divided into two general methods: kinematic- and composite-fault models. Green's functions of three types are evaluated: stochastic, empirical, and theoretical. A hybrid scheme is found to give the best fit to the Northridge data. Low frequencies ( 1 Hz) are calculated using a composite-fault model with a fractal subevent size distribution and stochastic, bandlimited, white-noise Green's functions. At frequencies below 1 Hz, theoretical elastic-wave-propagation synthetics introduce proper seismic-phase arrivals of body waves and surface waves. The 3D velocity structure more accurately reproduces record durations for the deep sedimentary basin structures found in the Los Angeles region. At frequencies above 1 Hz, scattering effects become important and wave propagation is more accurately represented by stochastic Green's functions. A fractal subevent size distribution for the composite fault model ensures an ??-2 spectral shape over the entire frequency band considered (0.1-20 Hz).

On possible plume-guided seismic waves

USGS Publications Warehouse

Julian, B.R.; Evans, J.R.

2010-01-01

Hypothetical thermal plumes in the Earth's mantle are expected to have low seismic-wave speeds and thus would support the propagation of guided elastic waves analogous to fault-zone guided seismic waves, fiber-optic waves, and acoustic waves in the oceanic SOund Fixing And Ranging channel. Plume-guided waves would be insensitive to geometric complexities in the wave guide, and their dispersion would make them distinctive on seismograms and would provide information about wave-guide structure that would complement seismic tomography. Detecting such waves would constitute strong evidence of a new kind for the existence of plumes. A cylindrical channel embedded in an infinite medium supports two classes of axially symmetric elastic-wave modes, torsional and longitudinal-radial. Torsional modes have rectilinear particle motion tangent to the cylinder surface. Longitudinal-radial modes have elliptical particle motion in planes that include the cylinder axis, with retrograde motion near the axis. The direction of elliptical particle motion reverses with distance from the axis: once for the fundamental mode, twice for the first overtone, and so on. Each mode exists only above its cut-off frequency, where the phase and group speeds equal the shear-wave speed in the infinite medium. At high frequencies, both speeds approach the shear-wave speed in the channel. All modes have minima in their group speeds, which produce Airy phases on seismograms. For shear wave-speed contrasts of a few percent, thought to be realistic for thermal plumes in the Earth, the largest signals are inversely dispersed and have dominant frequencies of about 0.1-1 Hz and durations of 15-30 sec. There are at least two possible sources of observable plume waves: (1) the intersection of mantle plumes with high-amplitude core-phase caustics in the deep mantle; and (2) ScS-like reflection at the core-mantle boundary of downward-propagating guided waves. The widespread recent deployment of broadband seismometers makes searching for these waves possible.

Particle motions beneath irrotational water waves

NASA Astrophysics Data System (ADS)

Bakhoday-Paskyabi, Mostafa

2015-08-01

Neutral and buoyant particle motions in an irrotational flow are investigated under the passage of linear, nonlinear gravity, and weakly nonlinear solitary waves at a constant water depth. The developed numerical models for the particle trajectories in a non-turbulent flow incorporate particle momentum, size, and mass (i.e., inertial particles) under the influence of various surface waves such as Korteweg-de Vries waves which admit a three parameter family of periodic cnoidal wave solutions. We then formulate expressions of mass-transport velocities for the neutral and buoyant particles. A series of test cases suggests that the inertial particles possess a combined horizontal and vertical drifts from the locations of their release, with a fall velocity as a function of particle material properties, ambient flow, and wave parameters. The estimated solutions exhibit good agreement with previously explained particle behavior beneath progressive surface gravity waves. We further investigate the response of a neutrally buoyant water parcel trajectories in a rotating fluid when subjected to a series of wind and wave events. The results confirm the importance of the wave-induced Coriolis-Stokes force effect in both amplifying (destroying) the pre-existing inertial oscillations and in modulating the direction of the flow particles. Although this work has mainly focused on wave-current-particle interaction in the absence of turbulence stochastic forcing effects, the exercise of the suggested numerical models provides additional insights into the mechanisms of wave effects on the passive trajectories for both living and nonliving particles such as swimming trajectories of plankton in non-turbulent flows.

Measuring ionospheric movements using totally reflected radio waves

NASA Astrophysics Data System (ADS)

Sadler, Elaine M.; Whitehead, J. D.; From, W. R.

1988-02-01

It is shown that for radio waves of a particular frequency reflected totally from the ionosphere the effect of refraction as well as reflection can be simulated by an effective reflecting surface. This mirror-like surface will give the correct angle of arrival and Doppler shift for all radars operating at this frequency. It is theoretically possible for the effective reflecting surface to be folded back on itself, but this is unlikely except for F-region echoes refracted by sporadic E-clouds. If the surface is not folded and exists everywhere, it is always possible to describe its motion and change in terms of wave undulations. Experimental data for F-region echoes show that these wave undulations are very dispersive. However, the matching between the best fitting model and the experimental data is worse than expected for reasons we do not understand.

Measuring ionospheric movements using totally reflected radio waves

NASA Astrophysics Data System (ADS)

From, W. R.; Sadler, Elaine M.; Whitehead, J. D.

1988-02-01

It is shown that for radio waves of a particular frequency reflected totally from the ionosphere the effect of refraction as well as reflection can be simulated by an effective reflecting surface. This mirrorlike surface will give the correct angle of arrival and Doppler shift for all radars operating at this frequency. It is theoretically possible for the effective reflecting surface to be folded back on itself, but this is unlikely except for F-region echoes refracted by sporadic E-clouds. If the surface is not folded and exists everywhere, it is always possible to describe its motion and change in terms of wave undulations. Experimental data for F-region echoes show that these wave undulations are very dispersive. However, the matching between the best fitting model and the experimental data is worse than expected for reasons we do not understand.

Relationship between strong-motion array parameters and the accuracy of source inversion and physical waves

USGS Publications Warehouse

Iida, M.; Miyatake, T.; Shimazaki, K.

1990-01-01

We develop general rules for a strong-motion array layout on the basis of our method of applying a prediction analysis to a source inversion scheme. A systematic analysis is done to obtain a relationship between fault-array parameters and the accuracy of a source inversion. Our study of the effects of various physical waves indicates that surface waves at distant stations contribute significantly to the inversion accuracy for the inclined fault plane, whereas only far-field body waves at both small and large distances contribute to the inversion accuracy for the vertical fault, which produces more phase interference. These observations imply the adequacy of the half-space approximation used throughout our present study and suggest rules for actual array designs. -from Authors

Local amplification of seismic waves from the Denali earthquake and damaging seiches in Lake Union, Seattle, Washington

USGS Publications Warehouse

Barberopoulou, A.; Qamar, A.; Pratt, T.L.; Creager, K.C.; Steele, W.P.

2004-01-01

The Mw7.9 Denali, Alaska earthquake of 3 November, 2002, caused minor damage to at least 20 houseboats in Seattle, Washington by initiating water waves in Lake Union. These water waves were likely initiated during the large amplitude seismic surface waves from this earthquake. Maps of spectral amplification recorded during the Denali earthquake on the Pacific Northwest Seismic Network (PNSN) strong-motion instruments show substantially increased shear and surface wave amplitudes coincident with the Seattle sedimentary basin. Because Lake Union is situated on the Seattle basin, the size of the water waves may have been increased by local amplification of the seismic waves by the basin. Complete hazard assessments require understanding the causes of these water waves during future earthquakes. Copyright 2004 by the American Geophysical Union.

Nonlocal Sediment Transport on Steep Lateral Moraines, Eastern Sierra Nevada, California, USA

NASA Astrophysics Data System (ADS)

Doane, Tyler H.; Furbish, David Jon; Roering, Joshua J.; Schumer, Rina; Morgan, Daniel J.

2018-01-01

Recent work has highlighted the significance of long-distance particle motions in hillslope sediment transport. Such motions imply that the flux at a given hillslope position is appropriately described as a weighted function of surrounding conditions that influence motions reaching the given position. Although the idea of nonlocal sediment transport is well grounded in theory, limited field evidence has been provided. We test local and nonlocal formulations of the flux and compare their ability to reproduce land surface profiles of steep moraines in California. We show that nonlocal and nonlinear models better reproduce evolved land surface profiles, notably the amount of lowering and concavity near the moraine crest and the lengthening and straightening of the depositional apron. The analysis provides the first estimates of key parameters that set sediment entrainment rates and travel distances in nonlocal formulations and highlights the importance of correctly specifying the entrainment rate when modeling land surface evolution. Moraine evolution associated with nonlocal and nonlinear transport formulations, when described in terms of the evolution of the Fourier transform of the moraine surface, displays a distinct behavior involving growth of certain wave numbers, in contrast to the decay of all wave numbers associated with linear transport. Nonlinear and nonlocal formulations share key mathematical elements yielding a nonlinear relation between the flux and the land surface slope.

Time-domain hybrid method for simulating large amplitude motions of ships advancing in waves

NASA Astrophysics Data System (ADS)

Liu, Shukui; Papanikolaou, Apostolos D.

2011-03-01

Typical results obtained by a newly developed, nonlinear time domain hybrid method for simulating large amplitude motions of ships advancing with constant forward speed in waves are presented. The method is hybrid in the way of combining a time-domain transient Green function method and a Rankine source method. The present approach employs a simple double integration algorithm with respect to time to simulate the free-surface boundary condition. During the simulation, the diffraction and radiation forces are computed by pressure integration over the mean wetted surface, whereas the incident wave and hydrostatic restoring forces/moments are calculated on the instantaneously wetted surface of the hull. Typical numerical results of application of the method to the seakeeping performance of a standard containership, namely the ITTC S175, are herein presented. Comparisons have been made between the results from the present method, the frequency domain 3D panel method (NEWDRIFT) of NTUA-SDL and available experimental data and good agreement has been observed for all studied cases between the results of the present method and comparable other data.

Spectra of Baroclinic Inertia-Gravity Wave Turbulence

NASA Technical Reports Server (NTRS)

Glazman, Roman E.

1996-01-01

Baroclinic inertia-gravity (IG) waves form a persistent background of thermocline depth and sea surface height oscillations. They also contribute to the kinetic energy of horizontal motions in the subsurface layer. Measured by the ratio of water particle velocity to wave phase speed, the wave nonlinearity may be rather high. Given a continuous supply of energy from external sources, nonlinear wave-wave interactions among IG waves would result in inertial cascades of energy, momentum, and wave action. Based on a recently developed theory of wave turbulence in scale-dependent systems, these cascades are investigated and IG wave spectra are derived for an arbitrary degree of wave nonlinearity. Comparisons with satellite-altimetry-based spectra of surface height variations and with energy spectra of horizontal velocity fluctuations show good agreement. The well-known spectral peak at the inertial frequency is thus explained as a result of the inverse cascade. Finally, we discuss a possibility of inferring the internal Rossby radius of deformation and other dynamical properties of the upper thermocline from the spectra of SSH (sea surface height) variations based on altimeter measurements.

A surface wave reflector in Southwestern Japan

NASA Astrophysics Data System (ADS)

Mak, S.; Koketsu, K.; Miyake, H.; Obara, K.; Sekine, S.

2009-12-01

Surface waves at short periods (<35s) are affected severely by heterogeneities in the crust and the uppermost mantle. When the scale of heterogeneity is sufficiently large, its effect can be studied in a deterministic way using conventional concepts of reflection and refraction. A well-known example is surface wave refraction at continental margin. We present a case study to investigate the composition of surface wave coda in a deterministic approach. A long duration of surface wave coda with a predominant period of 20s is observed during various strong earthquakes around Japan. The coda shows an unambiguous propagation direction, implying a deterministic nature. Beamforming and particle motion analysis suggest that the surface wave later arrivals could be explained by Love wave reflections by a point reflector located at offshore southeast to Kyushu. The reflection demonstrates a seemingly incidence-independent favorable azimuth in emitting strength. In additional to beamforming, we use a new regional crustal velocity model to perform a grid-search ray-tracing with the assumption of point reflector to further constrain to location of coda generation. Because strong velocity anomalies exist near the zone of interest, we decide to use a network shortest-path ray-tracing method, instead of analytical methods like shooting and bending, to avoid the problems like convergence, shadow zone, and smooth model assumption. Two geological features are found to be related to the formation of the coda. The primary one is the intersection between the Kyushu-Palau Ridge and the Nankai Trough at offshore southeast to Kyushu (hereafter referred as "KPR-NT"), which may act as a point reflector. There is a strong Love wave phase velocity anomaly at KPR-NT but not other parts of the ridge, implying that topography is irrelevant. Rayleigh wave phase velocity does not experience a strong anomaly there, which is consistent to the absence of Rayleigh wave reflections implied by the observed particle motions. The secondary one is a low phase velocity (<2km/s for T=20s) at the accretionary wedge of the Nankai Trough due to the thick sediment. Such a long and narrow low velocity zone, with its southwest tip at KPR-NT, is a potential wave-guide to channel waves towards KPR-NT. The longer duration of deterministic later arrivals than the direct arrival is partially explained by multi-pathing due to the wave-guide. The surface wave coda is observable for earthquakes whose propagation path does not include the accretionary wedge, implying that the wedge is an enhancer but not indispensable of the formation of the observed coda.

Nonlinear coseismic infrasound waves in the upper atmosphere and ionosphere

NASA Astrophysics Data System (ADS)

Chum, J.; Liu, J. Y.; Cabrera, M. A.

2017-12-01

Vertical motion of the ground surface caused by seismic waves generates acoustic waves that propagate nearly vertically upward because of supersonic speed of seismic waves. As the air density decreases with height, the amplitude of acoustic waves increases to conserve the energy flux. If the initial perturbation is large enough (larger than 10 mm/s) and the period of waves is long (>10 s), then the amplitude reaches significant values in the upper atmosphere (e.g. oscillation velocities of the air particles become comparable with sound speed) and the nonlinear phenomena start to play an important role before the wave is dissipated. The nonlinear phenomena lead to changes of spectral content of the wave packet. The energy is transferred to lower frequencies, which can cause the formation of roughly bipolar N-shaped pulse in the vicinity of the epicenters (up to distance about 1000-1500 km) of strong, M>7, earthquakes. The nonlinear propagation is studied on the basis of numerical solution of continuity, momentum and heat equations in 1D (along vertical axis) for viscous compressible atmosphere. Boundary conditions on the ground are determined by real measurements of the vertical motion of the ground surface. The results of numerical simulations are in a good agreement with atmospheric fluctuations observed by continuous Doppler sounding at heights of about 200 km and epicenter distance around 800 km. In addition, the expected fluctuations of GSP-TEC are calculated.

Generation of Magnetohydrodynamic Waves in Low Solar Atmospheric Flux Tubes by Photospheric Motions

NASA Astrophysics Data System (ADS)

Mumford, S. J.; Fedun, V.; Erdélyi, R.

2015-01-01

Recent ground- and space-based observations reveal the presence of small-scale motions between convection cells in the solar photosphere. In these regions, small-scale magnetic flux tubes are generated via the interaction of granulation motion and the background magnetic field. This paper studies the effects of these motions on magnetohydrodynamic (MHD) wave excitation from broadband photospheric drivers. Numerical experiments of linear MHD wave propagation in a magnetic flux tube embedded in a realistic gravitationally stratified solar atmosphere between the photosphere and the low choromosphere (above β = 1) are performed. Horizontal and vertical velocity field drivers mimic granular buffeting and solar global oscillations. A uniform torsional driver as well as Archimedean and logarithmic spiral drivers mimic observed torsional motions in the solar photosphere. The results are analyzed using a novel method for extracting the parallel, perpendicular, and azimuthal components of the perturbations, which caters to both the linear and non-linear cases. Employing this method yields the identification of the wave modes excited in the numerical simulations and enables a comparison of excited modes via velocity perturbations and wave energy flux. The wave energy flux distribution is calculated to enable the quantification of the relative strengths of excited modes. The torsional drivers primarily excite Alfvén modes (≈60% of the total flux) with small contributions from the slow kink mode, and, for the logarithmic spiral driver, small amounts of slow sausage mode. The horizontal and vertical drivers primarily excite slow kink or fast sausage modes, respectively, with small variations dependent upon flux surface radius.

Swimming droplets driven by a surface wave

PubMed Central

Ebata, Hiroyuki; Sano, Masaki

2015-01-01

Self-propelling motion is ubiquitous for soft active objects such as crawling cells, active filaments, and liquid droplets moving on surfaces. Deformation and energy dissipation are required for self-propulsion of both living and non-living matter. From the perspective of physics, searching for universal laws of self-propelled motions in a dissipative environment is worthwhile, regardless of the objects' details. In this article, we propose a simple experimental system that demonstrates spontaneous migration of a droplet under uniform mechanical agitation. As we vary control parameters, spontaneous symmetry breaking occurs sequentially, and cascades of bifurcations of the motion arise. Equations describing deformable particles and hydrodynamic simulations successfully describe all of the observed motions. This system should enable us to improve our understanding of spontaneous motions of self-propelled objects. PMID:25708871

Swimming droplets driven by a surface wave

NASA Astrophysics Data System (ADS)

Ebata, Hiroyuki; Sano, Masaki

2015-02-01

Self-propelling motion is ubiquitous for soft active objects such as crawling cells, active filaments, and liquid droplets moving on surfaces. Deformation and energy dissipation are required for self-propulsion of both living and non-living matter. From the perspective of physics, searching for universal laws of self-propelled motions in a dissipative environment is worthwhile, regardless of the objects' details. In this article, we propose a simple experimental system that demonstrates spontaneous migration of a droplet under uniform mechanical agitation. As we vary control parameters, spontaneous symmetry breaking occurs sequentially, and cascades of bifurcations of the motion arise. Equations describing deformable particles and hydrodynamic simulations successfully describe all of the observed motions. This system should enable us to improve our understanding of spontaneous motions of self-propelled objects.

Difference of Horizontal-to-Vertical (H/V) Spectral Ratios of Microtremors and Earthquake Motions: Theory and Observation

NASA Astrophysics Data System (ADS)

Kawase, H.; Nagashima, F.; Matsushima, S.; Sanchez-Sesma, F. J.

2013-05-01

Horizontal-to-vertical spectral ratios (HVRs) of microtremors have been traditionally interpreted theoretically as representing the Rayleigh wave ellipticity or just utilized a convenient tool to extract predominant periods of ground. However, based on the diffuse field theory (Sánchez-Sesma et al., 2011) the microtremor H/V spectral ratios (MHVRs) correspond to the square root of the ratio of the imaginary part of horizontal displacement for a horizontally applied unit harmonic load and the imaginary part of vertical displacement for a vertically applied unit load. The same diffuse field concept leads us to derive a simple formula for earthquake HVRs (EHVRs), that is, the ratio of the horizontal motion on the surface for a vertical incidence of S wave divided by the vertical motion on the surface for a vertical incidence of P wave with a fixed coefficient (Kawase et al., 2011). The difference for EHVRs comes from the fact that primary contribution of earthquake motions would be of plane body waves. Traditionally EHVRs are interpreted as the responses of inclined SV wave incidence only for their S wave portions. Without these compact theoretical solutions, EHVRs and MHVRs are either considered to be very similar/equivalent, or totally different in the previous studies. With these theoretical solutions we need to re-focus our attention on the difference of HVRs. Thus we have compared here HVRs at several dozens of strong motion stations in Japan. When we compared observed HVRs we found that EHVRs tend to be higher in general than the MHVRs, especially around their peaks. As previously reported, their general shapes share the common features. Especially their fundamental peak and trough frequencies show quite a good match to each other. However, peaks in EHVRs in the higher frequency range would not show up in MHVRs. When we calculated theoretical HVRs separately at these target sites, their basic characteristics correspond to these observed differences. At this stage of research we found that the underground structures that are optimized for EHVRs would not explain perfectly MHVRs. This strongly suggests that we need to optimize underground structures to explain both EHVRs and MHVRs at the same time.

Comparison of phase velocities from array measurements of Rayleigh waves associated with microtremor and results calculated from borehole shear-wave velocity profiles

USGS Publications Warehouse

Liu, Hsi-Ping; Boore, David M.; Joyner, William B.; Oppenheimer, David H.; Warrick, Richard E.; Zhang, Wenbo; Hamilton, John C.; Brown, Leo T.

2000-01-01

Shear-wave velocities (VS) are widely used for earthquake ground-motion site characterization. VS data are now largely obtained using borehole methods. Drilling holes, however, is expensive. Nonintrusive surface methods are inexpensive for obtaining VS information, but not many comparisons with direct borehole measurements have been published. Because different assumptions are used in data interpretation of each surface method and public safety is involved in site characterization for engineering structures, it is important to validate the surface methods by additional comparisons with borehole measurements. We compare results obtained from a particular surface method (array measurement of surface waves associated with microtremor) with results obtained from borehole methods. Using a 10-element nested-triangular array of 100-m aperture, we measured surface-wave phase velocities at two California sites, Garner Valley near Hemet and Hollister Municipal Airport. The Garner Valley site is located at an ancient lake bed where water-saturated sediment overlies decomposed granite on top of granite bedrock. Our array was deployed at a location where seismic velocities had been determined to a depth of 500 m by borehole methods. At Hollister, where the near-surface sediment consists of clay, sand, and gravel, we determined phase velocities using an array located close to a 60-m deep borehole where downhole velocity logs already exist. Because we want to assess the measurements uncomplicated by uncertainties introduced by the inversion process, we compare our phase-velocity results with the borehole VS depth profile by calculating fundamental-mode Rayleigh-wave phase velocities from an earth model constructed from the borehole data. For wavelengths less than ~2 times of the array aperture at Garner Valley, phase-velocity results from array measurements agree with the calculated Rayleigh-wave velocities to better than 11%. Measurement errors become larger for wavelengths 2 times greater than the array aperture. At Hollister, the measured phase velocity at 3.9 Hz (near the upper edge of the microtremor frequency band) is within 20% of the calculated Rayleigh-wave velocity. Because shear-wave velocity is the predominant factor controlling Rayleigh-wave phase velocities, the comparisons suggest that this nonintrusive method can provide VS information adequate for ground-motion estimation.

Complex-valued derivative propagation method with approximate Bohmian trajectories: Application to electronic nonadiabatic dynamics

NASA Astrophysics Data System (ADS)

Wang, Yu; Chou, Chia-Chun

2018-05-01

The coupled complex quantum Hamilton-Jacobi equations for electronic nonadiabatic transitions are approximately solved by propagating individual quantum trajectories in real space. Equations of motion are derived through use of the derivative propagation method for the complex actions and their spatial derivatives for wave packets moving on each of the coupled electronic potential surfaces. These equations for two surfaces are converted into the moving frame with the same grid point velocities. Excellent wave functions can be obtained by making use of the superposition principle even when nodes develop in wave packet scattering.

The Shock and Vibration Digest. Volume 16, Number 11

DTIC Science & Technology

1984-11-01

wave [19], a secular equation for Rayleigh waves on ing, seismic risk, and related problems are discussed. the surface of an anisotropic half-space...waves in an !so- tive equation of an elastic-plastic rack medium was....... tropic linear elastic half-space with plane material used; the coefficient...pair of semi-linear hyperbolic partial differential -- " Conditions under which the equations of motion equations governing slow variations in amplitude

Skyrmion motion induced by plane stress waves

NASA Astrophysics Data System (ADS)

Gungordu, Utkan; Kovalev, Alexey A.

Skyrmions are typically driven by currents and magnetic fields. We propose an alternative method of driving skyrmions using plane stress waves in a chiral ferromagnetic nanotrack. We find that the effective force due to surface acoustic waves couples both to the helicity and the topological charge of the skyrmion. This coupling can be used to probe the helicity of the skyrmion as well as the nature of the Dzyaloshinskii-Moriya interaction. This is particularly important when a ferromagnet lacks both surface- and bulk-inversion symmetry. Plane stress waves can be generated using a pair of interdigital transducers (IDTs). As the nanowire is subject to half-open space boundary conditions, the skyrmion is driven by normal stress in this setup. We find that skyrmions get pinned at the antinodes of the stress wave, much similar to domain walls, which enables skyrmion motion by detuned IDTs. We also consider a nanotrack sandwiched between a piezoelectric layer and a substrate, with electrical contacts placed on top, which results in shear stress in addition to normal stress in nanotrack. We find that unlike domain walls, skyrmions can be driven using shear component of a standing stress wave. This work was supported primarily by the DOE Early Career Award DE-SC0014189, and in part by the NSF under Grants Nos. Phy-1415600, and DMR-1420645 (UG).

Site Effect Analysis in the Izmit Basin of Turkey: Preliminary Results from the Wave Propagation Simulation using the Spectral Element Method

NASA Astrophysics Data System (ADS)

Firtana Elcomert, Karolin; Kocaoglu, Argun

2014-05-01

Sedimentary basins affect the propagation characteristics of the seismic waves and cause significant ground motion amplification during an earthquake. While the impedance contrast between the sedimentary layer and bedrock predominantly controls the resonance frequencies and their amplitudes (seismic amplification), surface waves generated within the basin, make the waveforms more complex and longer in duration. When a dense network of weak and/or strong motion sensors is available, site effect or more specifically sedimentary basin amplification can be directly estimated experimentally provided that significant earthquakes occur during the period of study. Alternatively, site effect can be investigated through simulation of ground motion. The objective of this study is to investigate the 2-D site effect in the Izmit Basin located in the eastern Marmara region of Turkey, using the currently available bedrock topography and shear-wave velocity data. The Izmit Basin was formed in Plio-Quaternary period and is known to be a pull-apart basin controlled by the northern branch of the North Anatolian Fault Zone (Şengör et al. 2005). A thorough analysis of seismic hazard is important since the city of Izmit and its metropolitan area is located in this region. Using a spectral element code, SPECFEM2D (Komatitsch et al. 1998), this work presents some of the preliminary results of the 2-D seismic wave propagation simulations for the Izmit basin. The spectral-element method allows accurate and efficient simulation of seismic wave propagation due to its advantages over the other numerical modeling techniques by means of representation of the wavefield and the computational mesh. The preliminary results of this study suggest that seismic wave propagation simulations give some insight into the site amplification phenomena in the Izmit basin. Comparison of seismograms recorded on the top of sedimentary layer with those recorded on the bedrock show more complex waveforms with higher amplitudes on seismograms recorded at the free surface. Furthermore, modeling reveals that observed seismograms include surface waves whose excitation is clearly related to the basin geometry.

Ground-motion site effects from multimethod shear-wave velocity characterization at 16 seismograph stations deployed for aftershocks of the August 2011 Mineral, Virginia earthquake

USGS Publications Warehouse

Stephenson, William J.; Odum, Jackson K.; McNamara, Daniel E.; Williams, Robert A.; Angster, Stephen J

2014-01-01

We characterize shear-wave velocity versus depth (Vs profile) at 16 portable seismograph sites through the epicentral region of the 2011 Mw 5.8 Mineral (Virginia, USA) earthquake to investigate ground-motion site effects in the area. We used a multimethod acquisition and analysis approach, where active-source horizontal shear (SH) wave reflection and refraction as well as active-source multichannel analysis of surface waves (MASW) and passive-source refraction microtremor (ReMi) Rayleigh wave dispersion were interpreted separately. The time-averaged shear-wave velocity to a depth of 30 m (Vs30), interpreted bedrock depth, and site resonant frequency were estimated from the best-fit Vs profile of each method at each location for analysis. Using the median Vs30 value (270–715 m/s) as representative of a given site, we estimate that all 16 sites are National Earthquake Hazards Reduction Program (NEHRP) site class C or D. Based on a comparison of simplified mapped surface geology to median Vs30 at our sites, we do not see clear evidence for using surface geologic units as a proxy for Vs30 in the epicentral region, although this may primarily be because the units are similar in age (Paleozoic) and may have similar bulk seismic properties. We compare resonant frequencies calculated from ambient noise horizontal:vertical spectral ratios (HVSR) at available sites to predicted site frequencies (generally between 1.9 and 7.6 Hz) derived from the median bedrock depth and average Vs to bedrock. Robust linear regression of HVSR to both site frequency and Vs30 demonstrate moderate correlation to each, and thus both appear to be generally representative of site response in this region. Based on Kendall tau rank correlation testing, we find that Vs30 and the site frequency calculated from average Vs to median interpreted bedrock depth can both be considered reliable predictors of weak-motion site effects in the epicentral region.

On singular and highly oscillatory properties of the Green function for ship motions

NASA Astrophysics Data System (ADS)

Chen, Xiao-Bo; Xiong Wu, Guo

2001-10-01

The Green function used for analysing ship motions in waves is the velocity potential due to a point source pulsating and advancing at a uniform forward speed. The behaviour of this function is investigated, in particular for the case when the source is located at or close to the free surface. In the far field, the Green function is represented by a single integral along one closed dispersion curve and two open dispersion curves. The single integral along the open dispersion curves is analysed based on the asymptotic expansion of a complex error function. The singular and highly oscillatory behaviour of the Green function is captured, which shows that the Green function oscillates with indefinitely increasing amplitude and indefinitely decreasing wavelength, when a field point approaches the track of the source point at the free surface. This sheds some light on the nature of the difficulties in the numerical methods used for predicting the motion of a ship advancing in waves.

Domain decomposition and matching for time-domain analysis of motions of ships advancing in head sea

NASA Astrophysics Data System (ADS)

Tang, Kai; Zhu, Ren-chuan; Miao, Guo-ping; Fan, Ju

2014-08-01

A domain decomposition and matching method in the time-domain is outlined for simulating the motions of ships advancing in waves. The flow field is decomposed into inner and outer domains by an imaginary control surface, and the Rankine source method is applied to the inner domain while the transient Green function method is used in the outer domain. Two initial boundary value problems are matched on the control surface. The corresponding numerical codes are developed, and the added masses, wave exciting forces and ship motions advancing in head sea for Series 60 ship and S175 containership, are presented and verified. A good agreement has been obtained when the numerical results are compared with the experimental data and other references. It shows that the present method is more efficient because of the panel discretization only in the inner domain during the numerical calculation, and good numerical stability is proved to avoid divergence problem regarding ships with flare.

Radio Frequencies Emitted by Mobile Granular Materials: A Basis for Remote Sensing of Sand and Dust Activity on Mars and Earth

NASA Technical Reports Server (NTRS)

Marshall, J.; Farrell, W.; Houser, G.; Bratton, C.

1999-01-01

In recent laboratory experiments, measurements were made of microsecond radio-wave (RF) bursts emitted by grains of sand as they energetically circulated in a closed, electrically ungrounded chamber. The bursts appeared to result from nanoscale electrical discharging from grain surfaces. Both the magnitude and wave form of the RF pulses varied with the type of material undergoing motion. The release of RF from electrical discharging is a well-known phenomenon, but it is generally measured on much larger energy scales (e.g., in association with lightning or electrical motors). This phenomenon might be used to detect, on planetary surfaces, the motion and composition of sand moving over dunes, the turbulent motion of fine particles in dust storms, highly-energetic grain and rock collisions in volcanic eruptions, and frictional grinding of granular materials in dry debris flows, landslides, and avalanches. The occurrence of these discharges has been predicted from theoretical considerations Additional information is contained in the original.

Wave propagation in fluid-conveying viscoelastic carbon nanotubes under longitudinal magnetic field with thermal and surface effect via nonlocal strain gradient theory

NASA Astrophysics Data System (ADS)

Zhen, Yaxin; Zhou, Lin

2017-03-01

Based on nonlocal strain gradient theory, wave propagation in fluid-conveying viscoelastic single-walled carbon nanotubes (SWCNTs) is studied in this paper. With consideration of thermal effect and surface effect, wave equation is derived for fluid-conveying viscoelastic SWCNTs under longitudinal magnetic field utilizing Euler-Bernoulli beam theory. The closed-form expressions are derived for the frequency and phase velocity of the wave motion. The influences of fluid flow velocity, structural damping coefficient, temperature change, magnetic flux and surface effect are discussed in detail. SWCNTs’ viscoelasticity reduces the wave frequency of the system and the influence gets remarkable with the increase of wave number. The fluid in SWCNTs decreases the frequency of wave propagation to a certain extent. The frequency (phase velocity) gets larger due to the existence of surface effect, especially when the diameters of SWCNTs and the wave number decrease. The wave frequency increases with the increase of the longitudinal magnetic field, while decreases with the increase of the temperature change. The results may be helpful for better understanding the potential applications of SWCNTs in nanotechnology.

Motion of the surface of the human tympanic membrane measured with stroboscopic holography

PubMed Central

Cheng, Jeffrey Tao; Aarnisalo, Antti A.; Harrington, Ellery; Hernandez-Montes, Maria del Socorro; Furlong, Cosme; Merchant, Saumil N.; Rosowski, John J.

2010-01-01

Sound-induced motion of the surface of the human tympanic membrane (TM) was studied by stroboscopic holographic interferometery, which measures the amplitude and phase of the displacement at each of about 40000 points on the surface of the TM. Measurements were made with tonal stimuli of 0.5, 1, 4 and 8 kHz. The magnitude and phase of the sinusoidal displacement of the TM at each driven frequency were derived from the fundamental Fourier component of the raw displacement data computed from stroboscopic holograms of the TM recorded at eight stimulus phases. The correlation between the Fourier estimates and measured motion data was generally above 0.9 over the entire TM surface. We used three data presentations: (i) Plots of the phasic displacements along a single chord across the surface of the TM, (ii) Phasic surface maps of the displacement of the entire TM surface, and (iii) Plots of the Fourier derived amplitude and phase-angle of the surface displacement along four diameter lines that define and bisect each of the four quadrants of the TM. These displays led to some common conclusions: At 0.5 and 1 kHz, the entire TM moved roughly in-phase with some small phase delay apparent between local areas of maximal displacement in the posterior half of the TM. At 4 and 8 kHz, the motion of the TM became more complicated with multiple local displacement maxima arranged in rings around the manubrium. The displacements at most of these maxima were roughly in-phase, while some moved out-of-phase. Superposed on this in- and out-of-phase behavior were significant cyclic variations in phase with location of less than 0.2 cycles or occasionally rapid half-cycle step-like changes in phase. The high frequency displacement amplitude and phase maps discovered in this study can not be explained by any single wave motion, but are consistent with a combination of low and higher order modal motions plus some small traveling-wave-like components. The observations of the dynamics of TM surface motion from this study will help us better understand the sound-receiving function of the TM and how it couples sound to the ossicular chain and inner ear. PMID:20034549

On the propagation of elasto-thermodiffusive surface waves in heat-conducting materials

NASA Astrophysics Data System (ADS)

Sharma, J. N.; Sharma, Y. D.; Sharma, P. K.

2008-09-01

The present paper deals with the study of the propagation of Rayleigh surface waves in homogeneous isotropic, thermodiffusive elastic half-space. After developing the formal solution of the model, the secular equations for stress free, thermally insulated or isothermal, and isoconcentrated boundary conditions of the half-space have been obtained. The secular equations have been solved by using irreducible Cardano's method with the help of DeMoivre's theorem in order to obtain phase velocity and attenuation coefficient of waves under consideration. The motion of the surface particles during the Rayleigh surface wave propagation is also discussed and found to be elliptical in general. The inclinations of wave normal with the major axis of the elliptical path of a typical particle have also been computed. Finally, the numerically simulated results regarding phase velocity, attenuation coefficient, specific loss and thermo-mechanical coupling factors of thermoelastic diffusive waves have been obtained and presented graphically. Some very interesting and useful characteristics of surface acoustic waves have been obtained, which may help in improving the fabrication quality of optical and electronic devices in addition to construction and design of materials such as semiconductors and composite structures. Therefore, this work finds applications in the geophysics and electronics industry.

Effects of elastic bed on hydrodynamic forces for a submerged sphere in an ocean of finite depth

NASA Astrophysics Data System (ADS)

Mohapatra, Smrutiranjan

2017-08-01

In this paper, we consider a hydroelastic model to examine the radiation of waves by a submerged sphere for both heave and sway motions in a single-layer fluid flowing over an infinitely extended elastic bottom surface in an ocean of finite depth. The elastic bottom is modeled as a thin elastic plate and is based on the Euler-Bernoulli beam equation. The effect of the presence of surface tension at the free-surface is neglected. In such situation, there exist two modes of time-harmonic waves: the one with a lower wavenumber (surface mode) propagates along the free-surface and the other with higher wavenumber (flexural mode) propagates along the elastic bottom surface. Based on the small amplitude wave theory and by using the multipole expansion method, we find the particular solution for the problem of wave radiation by a submerged sphere of finite depth. Furthermore, this method eliminates the need to use large and cumbersome numerical packages for the solution of such problem and leads to an infinite system of linear algebraic equations which are easily solved numerically by any standard technique. The added-mass and damping coefficients for both heave and sway motions are derived and plotted for different submersion depths of the sphere and flexural rigidity of the elastic bottom surface. It is observed that, whenever the sphere nearer to the elastic bed, the added-mass move toward to a constant value of 1, which is approximately twice of the value of added-mass of a moving sphere in a single-layer fluid flowing over a rigid and flat bottom surface.

Inverting Coseismic TEC Disturbances for Neutral Atmosphere Pressure Wave

NASA Astrophysics Data System (ADS)

Lee, R. F.; Mikesell, D.; Rolland, L.

2017-12-01

Research from the past 20 years has shown that we can detect coseismic disturbances in the total electron content (TEC) using global navigation space systems (GNSS). In the near field, TEC disturbances are created by the direct wave from rupture on the surface. This pressure wave travels through the neutral atmosphere to the ionosphere within about 10 minutes. This provides the opportunity to almost immediately characterize the source of the acoustic disturbance on the surface using methods from seismology. In populated areas, this could provide valuable information to first responders. To retrieve the surface motion amplitude information we must account for changes in the waveform caused by the geomagnetic field, motion of the satellites and the geometry of the satellites and receivers. One method is to use a transfer function to invert for the neutral atmosphere pressure wave. Gómez et al (2015) first employed an analytical model to invert for acoustic waves produced by Rayleigh waves propagating along the Earth's surface. Here, we examine the same model in the near field using the TEC disturbances from the direct wave produced by rupture at the surface. We compare results from the forward model against a numerical model that has been shown to be in good agreement with observations from the 2011 Van (Turkey) earthquake. We show the forward model predictions using both methods for the Van earthquake. We then analyze results for hypothetical events at different latitudes and discuss the reliability of the analytical model in each scenario. Gómez, D., R. Jr. Smalley, C. A. Langston, T. J. Wilson, M. Bevis, I. W. D. Dalziel, E. C. Kendrick, S. A. Konfal, M. J. Willis, D. A. Piñón, et al. (2015), Virtual array beamforming of GPS TEC observations of coseismic ionospheric disturbances near the Geomagnetic South Pole triggered by teleseismic megathrusts, J. Geophys. Res. Space Physics, 120, 9087-9101, doi:10.1002/2015JA021725.

Shear-wave velocity profile and seismic input derived from ambient vibration array measurements: the case study of downtown L'Aquila

NASA Astrophysics Data System (ADS)

Di Giulio, Giuseppe; Gaudiosi, Iolanda; Cara, Fabrizio; Milana, Giuliano; Tallini, Marco

2014-08-01

Downtown L'Aquila suffered severe damage (VIII-IX EMS98 intensity) during the 2009 April 6 Mw 6.3 earthquake. The city is settled on a top flat hill, with a shear-wave velocity profile characterized by a reversal of velocity at a depth of the order of 50-100 m, corresponding to the contact between calcareous breccia and lacustrine deposits. In the southern sector of downtown, a thin unit of superficial red soils causes a further shallow impedance contrast that may have influenced the damage distribution during the 2009 earthquake. In this paper, the main features of ambient seismic vibrations have been studied in the entire city centre by using array measurements. We deployed six 2-D arrays of seismic stations and 1-D array of vertical geophones. The 2-D arrays recorded ambient noise, whereas the 1-D array recorded signals produced by active sources. Surface-wave dispersion curves have been measured by array methods and have been inverted through a neighbourhood algorithm, jointly with the H/V ambient noise spectral ratios related to Rayleigh waves ellipticity. We obtained shear-wave velocity (Vs) profiles representative of the southern and northern sectors of downtown L'Aquila. The theoretical 1-D transfer functions for the estimated Vs profiles have been compared to the available empirical transfer functions computed from aftershock data analysis, revealing a general good agreement. Then, the Vs profiles have been used as input for a deconvolution analysis aimed at deriving the ground motion at bedrock level. The deconvolution has been performed by means of EERA and STRATA codes, two tools commonly employed in the geotechnical engineering community to perform equivalent-linear site response studies. The waveform at the bedrock level has been obtained deconvolving the 2009 main shock recorded at a strong motion station installed in downtown. Finally, this deconvolved waveform has been used as seismic input for evaluating synthetic time-histories in a strong-motion target site located in the middle Aterno river valley. As a target site, we selected the strong-motion station of AQV 5 km away from downtown L'Aquila. For this site, the record of the 2009 L'Aquila main shock is available and its surface stratigraphy is adequately known making possible to propagate the deconvolved bedrock motion back to the surface, and to compare recorded and synthetic waveforms.

Investigating the generation of Love waves in secondary microseisms using 3D numerical simulations

NASA Astrophysics Data System (ADS)

Wenk, Stefan; Hadziioannou, Celine; Pelties, Christian; Igel, Heiner

2014-05-01

Longuet-Higgins (1950) proposed that secondary microseismic noise can be attributed to oceanic disturbances by surface gravity wave interference causing non-linear, second-order pressure perturbations at the ocean bottom. As a first approximation, this source mechanism can be considered as a force acting normal to the ocean bottom. In an isotropic, layered, elastic Earth model with plain interfaces, vertical forces generate P-SV motions in the vertical plane of source and receiver. In turn, only Rayleigh waves are excited at the free surface. However, several authors report on significant Love wave contributions in the secondary microseismic frequency band of real data measurements. The reason is still insufficiently analysed and several hypothesis are under debate: - The source mechanism has strongest influence on the excitation of shear motions, whereas the source direction dominates the effect of Love wave generation in case of point force sources. Darbyshire and Okeke (1969) proposed the topographic coupling effect of pressure loads acting on a sloping sea-floor to generate the shear tractions required for Love wave excitation. - Rayleigh waves can be converted into Love waves by scattering. Therefore, geometric scattering at topographic features or internal scattering by heterogeneous material distributions can cause Love wave generation. - Oceanic disturbances act on large regions of the ocean bottom, and extended sources have to be considered. In combination with topographic coupling and internal scattering, the extent of the source region and the timing of an extended source should effect Love wave excitation. We try to elaborate the contribution of different source mechanisms and scattering effects on Love to Rayleigh wave energy ratios by 3D numerical simulations. In particular, we estimate the amount of Love wave energy generated by point and extended sources acting on the free surface. Simulated point forces are modified in their incident angle, whereas extended sources are adapted in their spatial extent, magnitude and timing. Further, the effect of variations in the correlation length and perturbation magnitude of a random free surface topography as well as an internal random material distribution are studied.

Skylab

NASA Image and Video Library

1973-01-01

W. Brian Dunlap of Youngstown, Ohio, proposed Skylab student experiment ED-78, Liquid Motion in Zero-G, a study of wave motion in a liquid. He was particularly interested in comparing surface waves over a liquid in zero-gravity with those occurring on Earth. In space, with the absence of gravity, a liquid does not necessarily take the shape of its container as it does on Earth. Adhesion forces may hold the liquid in contact with its container, but the liquid can also assume a free-floating condition. It was in this latter state that Dunlap wished to examine the behavior of surface waves. Data were recorded on videotape and subsequently converted to 16-mm film. Dunlap analyzed these data to determine periods of oscillation of free-floating globules and found agreement with the theory to be much better than expected. In March 1972, NASA and the National Science Teachers Association selected 25 experiment proposals for flight on Skylab. Science advisors from the Marshall Space Flight Center aided and assisted the students in developing the proposals for flight on Skylab.

Full-wave and half-wave rectification in second-order motion perception

NASA Technical Reports Server (NTRS)

Solomon, J. A.; Sperling, G.

1994-01-01

Microbalanced stimuli are dynamic displays which do not stimulate motion mechanisms that apply standard (Fourier-energy or autocorrelational) motion analysis directly to the visual signal. In order to extract motion information from microbalanced stimuli, Chubb and Sperling [(1988) Journal of the Optical Society of America, 5, 1986-2006] proposed that the human visual system performs a rectifying transformation on the visual signal prior to standard motion analysis. The current research employs two novel types of microbalanced stimuli: half-wave stimuli preserve motion information following half-wave rectification (with a threshold) but lose motion information following full-wave rectification; full-wave stimuli preserve motion information following full-wave rectification but lose motion information following half-wave rectification. Additionally, Fourier stimuli, ordinary square-wave gratings, were used to stimulate standard motion mechanisms. Psychometric functions (direction discrimination vs stimulus contrast) were obtained for each type of stimulus when presented alone, and when masked by each of the other stimuli (presented as moving masks and also as nonmoving, counterphase-flickering masks). RESULTS: given sufficient contrast, all three types of stimulus convey motion. However, only one-third of the population can perceive the motion of the half-wave stimulus. Observers are able to process the motion information contained in the Fourier stimulus slightly more efficiently than the information in the full-wave stimulus but are much less efficient in processing half-wave motion information. Moving masks are more effective than counterphase masks at hampering direction discrimination, indicating that some of the masking effect is interference between motion mechanisms, and some occurs at earlier stages. When either full-wave and Fourier or half-wave and Fourier gratings are presented simultaneously, there is a wide range of relative contrasts within which the motion directions of both gratings are easily determinable. Conversely, when half-wave and full-wave gratings are combined, the direction of only one of these gratings can be determined with high accuracy. CONCLUSIONS: the results indicate that three motion computations are carried out, any two in parallel: one standard ("first order") and two non-Fourier ("second-order") computations that employ full-wave and half-wave rectification.

Numerical and Analytical Study of Nonlinear Effects of Transonic Flow Past a Wing Airfoil in Oscillation of its Surface Element

NASA Astrophysics Data System (ADS)

Aul'chenko, S. M.; Zamuraev, V. P.; Kalinina, A. P.

2014-05-01

The present work is devoted to a criterial analysis and mathematical modeling of the influence of forced oscillations of surface elements of a wing airfoil on the shock-wave structure of transonic flow past it. Parameters that govern the regimes of interaction of the oscillatory motion of airfoil sections with the breakdown compression shock have been established. The qualitative and quantitative influence of these parameters on the wave resistance of the airfoil has been investigated.

Wave-induced response of a floating two-dimensional body with a moonpool

PubMed Central

Fredriksen, Arnt G.; Kristiansen, Trygve; Faltinsen, Odd M.

2015-01-01

Regular wave-induced behaviour of a floating stationary two-dimensional body with a moonpool is studied. The focus is on resonant piston-mode motion in the moonpool and rigid-body motions. Dedicated two-dimensional experiments have been performed. Two numerical hybrid methods, which have previously been applied to related problems, are further developed. Both numerical methods couple potential and viscous flow. The semi-nonlinear hybrid method uses linear free-surface and body-boundary conditions. The other one uses fully nonlinear free-surface and body-boundary conditions. The harmonic polynomial cell method solves the Laplace equation in the potential flow domain, while the finite volume method solves the Navier–Stokes equations in the viscous flow domain near the body. Results from the two codes are compared with the experimental data. The nonlinear hybrid method compares well with the data, while certain discrepancies are observed for the semi-nonlinear method. In particular, the roll motion is over-predicted by the semi-nonlinear hybrid method. Error sources in the semi-nonlinear hybrid method are discussed. The moonpool strongly affects heave motions in a frequency range around the piston-mode resonance frequency of the moonpool. No resonant water motions occur in the moonpool at the piston-mode resonance frequency. Instead large moonpool motions occur at a heave natural frequency associated with small damping near the piston-mode resonance frequency. PMID:25512594

High Frequency Near-Field Ground Motion Excited by Strike-Slip Step Overs

NASA Astrophysics Data System (ADS)

Hu, Feng; Wen, Jian; Chen, Xiaofei

2018-03-01

We performed dynamic rupture simulations on step overs with 1-2 km step widths and present their corresponding horizontal peak ground velocity distributions in the near field within different frequency ranges. The rupture speeds on fault segments are determinant in controlling the near-field ground motion. A Mach wave impact area at the free surface, which can be inferred from the distribution of the ratio of the maximum fault-strike particle velocity to the maximum fault-normal particle velocity, is generated in the near field with sustained supershear ruptures on fault segments, and the Mach wave impact area cannot be detected with unsustained supershear ruptures alone. Sub-Rayleigh ruptures produce stronger ground motions beyond the end of fault segments. The existence of a low-velocity layer close to the free surface generates large amounts of high-frequency seismic radiation at step over discontinuities. For near-vertical step overs, normal stress perturbations on the primary fault caused by dipping structures affect the rupture speed transition, which further determines the distribution of the near-field ground motion. The presence of an extensional linking fault enhances the near-field ground motion in the extensional regime. This work helps us understand the characteristics of high-frequency seismic radiation in the vicinities of step overs and provides useful insights for interpreting the rupture speed distributions derived from the characteristics of near-field ground motion.

3-D numerical simulations of earthquake ground motion in sedimentary basins: testing accuracy through stringent models

NASA Astrophysics Data System (ADS)

Chaljub, Emmanuel; Maufroy, Emeline; Moczo, Peter; Kristek, Jozef; Hollender, Fabrice; Bard, Pierre-Yves; Priolo, Enrico; Klin, Peter; de Martin, Florent; Zhang, Zhenguo; Zhang, Wei; Chen, Xiaofei

2015-04-01

Differences between 3-D numerical predictions of earthquake ground motion in the Mygdonian basin near Thessaloniki, Greece, led us to define four canonical stringent models derived from the complex realistic 3-D model of the Mygdonian basin. Sediments atop an elastic bedrock are modelled in the 1D-sharp and 1D-smooth models using three homogeneous layers and smooth velocity distribution, respectively. The 2D-sharp and 2D-smooth models are extensions of the 1-D models to an asymmetric sedimentary valley. In all cases, 3-D wavefields include strongly dispersive surface waves in the sediments. We compared simulations by the Fourier pseudo-spectral method (FPSM), the Legendre spectral-element method (SEM) and two formulations of the finite-difference method (FDM-S and FDM-C) up to 4 Hz. The accuracy of individual solutions and level of agreement between solutions vary with type of seismic waves and depend on the smoothness of the velocity model. The level of accuracy is high for the body waves in all solutions. However, it strongly depends on the discrete representation of the material interfaces (at which material parameters change discontinuously) for the surface waves in the sharp models. An improper discrete representation of the interfaces can cause inaccurate numerical modelling of surface waves. For all the numerical methods considered, except SEM with mesh of elements following the interfaces, a proper implementation of interfaces requires definition of an effective medium consistent with the interface boundary conditions. An orthorhombic effective medium is shown to significantly improve accuracy and preserve the computational efficiency of modelling. The conclusions drawn from the analysis of the results of the canonical cases greatly help to explain differences between numerical predictions of ground motion in realistic models of the Mygdonian basin. We recommend that any numerical method and code that is intended for numerical prediction of earthquake ground motion should be verified through stringent models that would make it possible to test the most important aspects of accuracy.

Numerical analysis of two and three dimensional buoyancy driven water-exit of a circular cylinder

NASA Astrophysics Data System (ADS)

Moshari, Shahab; Nikseresht, Amir Hossein; Mehryar, Reza

2014-06-01

With the development of the technology of underwater moving bodies, the need for developing the knowledge of surface effect interaction of free surface and underwater moving bodies is increased. Hence, the two-phase flow is a subject which is interesting for many researchers all around the world. In this paper, the non-linear free surface deformations which occur during the water-exit of a circular cylinder due to its buoyancy are solved using finite volume discretization based code, and using Volume of Fluid (VOF) scheme for solving two phase flow. Dynamic mesh model is used to simulate dynamic motion of the cylinder. In addition, the effect of cylinder mass in presence of an external force is studied. Moreover, the oblique exit and entry of a circular cylinder with two exit angles is simulated. At last, water-exit of a circular cylinder in six degrees of freedom is simulated in 3D using parallel processing. The simulation errors of present work (using VOF method) for maximum velocity and height of a circular cylinder are less than the corresponding errors of level set method reported by previous researchers. Oblique exit shows interesting results; formation of waves caused by exit of the cylinder, wave motion in horizontal direction and the air trapped between the waves are observable. In 3D simulation the visualization of water motion on the top surface of the cylinder and the free surface breaking on the front and back faces of the 3D cylinder at the exit phase are observed which cannot be seen in 2D simulation. Comparing the results, 3D simulation shows better agreement with experimental data, specially in the maximum height position of the cylinder.

Excited-State Vibrational Coherence in Perylene Bisimide Probed by Femtosecond Broadband Pump-Probe Spectroscopy.

PubMed

Son, Minjung; Park, Kyu Hyung; Yoon, Min-Chul; Kim, Pyosang; Kim, Dongho

2015-06-18

Broadband laser pulses with ultrashort duration are capable of triggering impulsive excitation of the superposition of vibrational eigenstates, giving rise to quantum beating signals originating from coherent wave packet motions along the potential energy surface. In this work, coherent vibrational wave packet dynamics of an N,N'-bis(2,6-dimethylphenyl)perylene bisimide (DMP-PBI) were investigated by femtosecond broadband pump-probe spectroscopy which features fast and balanced data acquisition with a wide spectral coverage of >200 nm. Clear modulations were observed in the envelope of the stimulated emission decay profiles of DMP-PBI with the oscillation frequencies of 140 and 275 cm(-1). Fast Fourier transform analysis of each oscillatory mode revealed characteristic phase jumps near the maxima of the steady-state fluorescence, indicating that the observed vibrational coherence originates from an excited-state wave packet motion. Quantum calculations of the normal modes at the low-frequency region suggest that low-frequency C-C (C═C) stretching motions accompanied by deformation of the dimethylphenyl substituents are responsible for the manifestation of such coherent wave packet dynamics.

Time and space analysis of turbulence of gravity surface waves

NASA Astrophysics Data System (ADS)

Mordant, Nicolas; Aubourg, Quentin; Viboud, Samuel; Sommeria, Joel

2016-11-01

Wave turbulence is a statistical state made of a very large number of nonlinearly interacting waves. The Weak Turbulence Theory was developed to describe such a situation in the weakly nonlinear regime. Although, oceanic data tend to be compatible with the theory, laboratory data fail to fulfill the theoretical predictions. A space-time resolved measurement of the waves have proven to be especially fruitful to identify the mechanism at play in turbulence of gravity-capillary waves. We developed an image processing algorithm to measure the motion of the surface of water with both space and time resolution. We first seed the surface with slightly buoyant polystyrene particles and use 3 cameras to reconstruct the surface. Our stereoscopic algorithm is coupled to PIV so that to obtain both the surface deformation and the velocity of the water surface. Such a coupling is shown to improve the sensitivity of the measurement by one order of magnitude. We use this technique to probe the existence of weakly nonlinear turbulence excited by two small wedge wavemakers in a 13-m diameter wave flume. We observe a truly weakly nonlinear regime of isotropic wave turbulence. This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (Grant Agreement No 647018-WATU).

The Utility of SAR to Monitor Ocean Processes.

DTIC Science & Technology

1981-11-01

echo received from ocean waves include the motion of the a horizontally polarized wave will have its E vector parallel to scattering surfaces, the so...radiation is defined by the direction of the electric field intensity, E, vector . For example, a horizontally polarized wave will have its E vector ...Oil Spill Off the East Coast of the United States ................ .... 55 19. L-band Parallel and Cross Polarized SAR Imagery of Ice in the Beaufort

Numerical simulation of solitary waves on deep water with constant vorticity

NASA Astrophysics Data System (ADS)

Dosaev, A. S.; Shishina, M. I.; Troitskaya, Yu I.

2018-01-01

Characteristics of solitary deep water waves on a flow with constant vorticity are investigated by numerical simulation within the framework of fully nonlinear equations of motion (Euler equations) using the method of surface-tracking conformal coordinates. To ensure that solutions observed are stable, soliton formation as a result of disintegration of an initial pulse-like disturbance is modeled. Evidence is obtained that solitary waves with height above a certain threshold are unstable.

Actuating mechanism and design of a cylindrical traveling wave ultrasonic motor using cantilever type composite transducer.

PubMed

Liu, Yingxiang; Chen, Weishan; Liu, Junkao; Shi, Shengjun

2010-04-02

Ultrasonic motors (USM) are based on the concept of driving the rotor by a mechanical vibration excited on the stator via piezoelectric effect. USM exhibit merits such as simple structure, quick response, quiet operation, self-locking when power off, nonelectromagnetic radiation and higher position accuracy. A cylindrical type traveling wave ultrasonic motor using cantilever type composite transducer was proposed in this paper. There are two cantilevers on the outside surface of cylinder, four longitudinal PZT ceramics are set between the cantilevers, and four bending PZT ceramics are set on each outside surface of cantilevers. Two degenerate flexural vibration modes spatially and temporally orthogonal to each other in the cylinder are excited by the composite transducer. In this new design, a single transducer can excite a flexural traveling wave in the cylinder. Thus, elliptical motions are achieved on the teeth. The actuating mechanism of proposed motor was analyzed. The stator was designed with FEM. The two vibration modes of stator were degenerated. Transient analysis was developed to gain the vibration characteristic of stator, and results indicate the motion trajectories of nodes on the teeth are nearly ellipses. The study results verify the feasibility of the proposed design. The wave excited in the cylinder isn't an ideal traveling wave, and the vibration amplitudes are inconsistent. The distortion of traveling wave is generated by the deformation of bending vibration mode of cylinder, which is caused by the coupling effect between the cylinder and transducer. Analysis results also prove that the objective motions of nodes on the teeth are three-dimensional vibrations. But, the vibration in axial direction is minute compared with the vibrations in circumferential and radial direction. The results of this paper can guide the development of this new type of motor.

Streaming and particle motion in acoustically-actuated leaky systems

NASA Astrophysics Data System (ADS)

Nama, Nitesh; Barnkob, Rune; Jun Huang, Tony; Kahler, Christian; Costanzo, Francesco

2017-11-01

The integration of acoustics with microfluidics has shown great promise for applications within biology, chemistry, and medicine. A commonly employed system to achieve this integration consists of a fluid-filled, polymer-walled microchannel that is acoustically actuated via standing surface acoustic waves. However, despite significant experimental advancements, the precise physical understanding of such systems remains a work in progress. In this work, we investigate the nature of acoustic fields that are setup inside the microchannel as well as the fundamental driving mechanism governing the fluid and particle motion in these systems. We provide an experimental benchmark using state-of-art 3D measurements of fluid and particle motion and present a Lagrangian velocity based temporal multiscale numerical framework to explain the experimental observations. Following verification and validation, we employ our numerical model to reveal the presence of a pseudo-standing acoustic wave that drives the acoustic streaming and particle motion in these systems.

Ground-motion prediction equations for the average horizontal component of PGA, PGV, and 5%-damped PSA at spectral periods between 0.01 s and 10.0 s

USGS Publications Warehouse

Boore, D.M.; Atkinson, G.M.

2008-01-01

This paper contains ground-motion prediction equations (GMPEs) for average horizontal-component ground motions as a function of earthquake magnitude, distance from source to site, local average shear-wave velocity, and fault type. Our equations are for peak ground acceleration (PGA), peak ground velocity (PGV), and 5%-damped pseudo-absolute-acceleration spectra (PSA) at periods between 0.01 s and 10 s. They were derived by empirical regression of an extensive strong-motion database compiled by the 'PEER NGA' (Pacific Earthquake Engineering Research Center's Next Generation Attenuation) project. For periods less than 1 s, the analysis used 1,574 records from 58 mainshocks in the distance range from 0 km to 400 km (the number of available data decreased as period increased). The primary predictor variables are moment magnitude (M), closest horizontal distance to the surface projection of the fault plane (RJB), and the time-averaged shear-wave velocity from the surface to 30 m (VS30). The equations are applicable for M=5-8, RJB<200 km, and VS30= 180-1300 m/s. ?? 2008, Earthquake Engineering Research Institute.

Stress wave riveting. [of aircraft metal skin

NASA Technical Reports Server (NTRS)

Leftheris, B. P.

1972-01-01

The stress wave riveter deforms the rivet material by a high amplitude stress wave. Thus, the entire rivet is set in motion radially. The rivet expands rapidly and impacts the hole surface before the rivet tail begins to form. Unlike the oversqueezed rivets, therefore, it sets up uniform interference without distortion in the skins. Furthermore, the radial velocity is so high (over 200 in./sec) that upon impact with the hole surface it deforms the surface plastically. This is especially effective in aluminum skins. Thus the SWR combines the advantages of plastically deforming the hole and the economic advantage of a relatively nonprecision hole and inexpensive rivets like those used in oversqueezing. The additional advantage SWR offers is that it is a portable tool.

Ultrasensitive, passive and wearable sensors for monitoring human muscle motion and physiological signals.

PubMed

Cai, Feng; Yi, Changrui; Liu, Shichang; Wang, Yan; Liu, Lacheng; Liu, Xiaoqing; Xu, Xuming; Wang, Li

2016-03-15

Flexible sensors have attracted more and more attention as a fundamental part of anthropomorphic robot research, medical diagnosis and physical health monitoring. Here, we constructed an ultrasensitive and passive flexible sensor with the advantages of low cost, lightness and wearability, electric safety and reliability. The fundamental mechanism of the sensor is based on triboelectric effect inducing electrostatic charges on the surfaces between two different materials. Just like a plate capacitor, current will be generated while the distance or size of the parallel capacitors changes caused by the small mechanical disturbance upon it and therefore the output current/voltage will be produced. Typically, the passive sensor unambiguously monitors muscle motions including hand motion from stretch-clench-stretch, mouth motion from open-bite-open, blink and respiration. Moreover, this sensor records the details of the consecutive phases in a cardiac cycle of the apex cardiogram, and identify the peaks including percussion wave, tidal wave and diastolic wave of the radial pulse wave. To record subtle human physiological signals including radial pulsilogram and apex cardiogram with excellent signal/noise ratio, stability and reproducibility, the sensor shows great potential in the applications of medical diagnosis and daily health monitoring. Copyright © 2015 Elsevier B.V. All rights reserved.

Impedance of strip-traveling waves on an elastic half space - Asymptotic solution

NASA Technical Reports Server (NTRS)

Crandall, S. H.; Nigam, A. K.

1973-01-01

The dynamic normal-load distribution across a strip that is required to maintain a plane progressive wave along its length is studied for the case where the strip is of infinite length and lies on the surface of a homogeneous isotropic elastic half space. This configuration is proposed as a preliminary idealized model for analyzing the dynamic interaction between soils and flexible foundations. The surface load distribution across the strip and the motion of the strip are related by a pair of dual integral equations. An asymptotic solution is obtained for the limiting case of small wavelength. The nature of this solution depends importantly on the propagation velocity of the strip-traveling wave in comparison with the Rayleigh wave speed, the shear wave speed and the dilatational wave speed. When the strip-traveling wave propagates faster than the Rayleigh wave speed, a pattern of trailing Rayleigh waves is shed from the strip. The limiting amplitude of the trailing waves is provided by the asymptotic solution.

Plasma Modes

NASA Astrophysics Data System (ADS)

Dubin, D. H. E.

This chapter explores several aspects of the linear electrostatic normal modes of oscillation for a single-species non-neutral plasma in a Penning trap. Linearized fluid equations of motion are developed, assuming the plasma is cold but collisionless, which allow derivation of the cold plasma dielectric tensor and the electrostatic wave equation. Upper hybrid and magnetized plasma waves in an infinite uniform plasma are described. The effect of the plasma surface in a bounded plasma system is considered, and the properties of surface plasma waves are characterized. The normal modes of a cylindrical plasma column are discussed, and finally, modes of spheroidal plasmas, and finite temperature effects on the modes, are briefly described.

High Attenuation Rate for Shallow, Small Earthquakes in Japan

NASA Astrophysics Data System (ADS)

Si, Hongjun; Koketsu, Kazuki; Miyake, Hiroe

2017-09-01

We compared the attenuation characteristics of peak ground accelerations (PGAs) and velocities (PGVs) of strong motion from shallow, small earthquakes that occurred in Japan with those predicted by the equations of Si and Midorikawa (J Struct Constr Eng 523:63-70, 1999). The observed PGAs and PGVs at stations far from the seismic source decayed more rapidly than the predicted ones. The same tendencies have been reported for deep, moderate, and large earthquakes, but not for shallow, moderate, and large earthquakes. This indicates that the peak values of ground motion from shallow, small earthquakes attenuate more steeply than those from shallow, moderate or large earthquakes. To investigate the reason for this difference, we numerically simulated strong ground motion for point sources of M w 4 and 6 earthquakes using a 2D finite difference method. The analyses of the synthetic waveforms suggested that the above differences are caused by surface waves, which are predominant at stations far from the seismic source for shallow, moderate earthquakes but not for shallow, small earthquakes. Thus, although loss due to reflection at the boundaries of the discontinuous Earth structure occurs in all shallow earthquakes, the apparent attenuation rate for a moderate or large earthquake is essentially the same as that of body waves propagating in a homogeneous medium due to the dominance of surface waves.

An Integrated Approach for the Large-Scale Simulation of Sedimentary Basins to Study Seismic Wave Amplification

NASA Astrophysics Data System (ADS)

Poursartip, B.

2015-12-01

Seismic hazard assessment to predict the behavior of infrastructures subjected to earthquake relies on ground motion numerical simulation because the analytical solution of seismic waves is limited to only a few simple geometries. Recent advances in numerical methods and computer architectures make it ever more practical to reliably and quickly obtain the near-surface response to seismic events. The key motivation stems from the need to access the performance of sensitive components of the civil infrastructure (nuclear power plants, bridges, lifelines, etc), when subjected to realistic scenarios of seismic events. We discuss an integrated approach that deploys best-practice tools for simulating seismic events in arbitrarily heterogeneous formations, while also accounting for topography. Specifically, we describe an explicit forward wave solver based on a hybrid formulation that couples a single-field formulation for the computational domain with an unsplit mixed-field formulation for Perfectly-Matched-Layers (PMLs and/or M-PMLs) used to limit the computational domain. Due to the material heterogeneity and the contrasting discretization needs it imposes, an adaptive time solver is adopted. We use a Runge-Kutta-Fehlberg time-marching scheme that adjusts optimally the time step such that the local truncation error rests below a predefined tolerance. We use spectral elements for spatial discretization, and the Domain Reduction Method in accordance with double couple method to allow for the efficient prescription of the input seismic motion. Of particular interest to this development is the study of the effects idealized topographic features have on the surface motion when compared against motion results that are based on a flat-surface assumption. We discuss the components of the integrated approach we followed, and report the results of parametric studies in two and three dimensions, for various idealized topographic features, which show motion amplification that depends, as expected, on the relation between the topographic feature's characteristics and the dominant wavelength. Lastly, we report results involving three-dimensional simulations.

Observation of the seismic anisotropy effects on free oscillations below 4 mHz

NASA Astrophysics Data System (ADS)

Hu, X.; Liu, L.

2009-12-01

We present observations of significant fundamental spheroidal-toroidal mode coupling at frequencies below 4 mHz in the early part of vertical component records from seismic stations on near-equatorial source-receiver propagation paths and in Antarctica after the 26 December 2004 and 28 March 2005 great Sumatra earthquakes. When seismic surface waves propagate along the equator, the particle motion of Love waves runs parallels to the Earth’s rotation axis, and the particle motion of Rayleigh waves runs perpendicular to it, thus the Coriolis force has no vertical deflection effect on Love waves and no transverse deflection effect on the Rayleigh waves. Coriolis coupling can be naturally minimized at a station on a nearequatorial source-receiver propagation path. In Antarctica, especially near the South Pole, the vertical deflection of toroidial motion is very weak but there are lateral gradients in the anisotropic properties of upper mantle. Therefore, we can find a chance to directly observe seismic anisotropy coupling below 4 mHz without the disturbance of Coriolis coupling at Antarctic station, and at the seismic station locate close to the Earth’s equator when the epicenter also locates close to the equator. Our observations of strong anomalous toroidal-spheroidal coupling at these stations provide direct evidence to confirm the theory that the azimuthal anisotropy has pronounced effects on the quasi-toroidal mode excitations at the frequencies below 4 mHz, which can convince the skeptics that anisotropy really is visible in the low-frequency normal mode data. Strong anisotropic coupling is usually observed at stations having the geometric nodes for the spheroidal fundamentals, giving the association of quasi-toroidal excitation with the geometric effect. The presence of significant anisotropy coupling below 4 mHz depends not only on anisotropic depth, anisotropic identities and orientations but also on radiation nodes for Rayleigh waves and geometry nodes for spheroidal fundamentals. The quasi-toroidal modes below 4 mHz have significant sensitivity throughout most of the mantle, extending into the lower mantle, and therefore, it is likely that the resolution of locating the depth of origin of azimuthal anisotropy in the mantle will be improved by joint inversions that take advantage of the partly complementary depth resolution of anisotropy coupling measurements, quasi-Love surface-wave measurements, body wave splitting measurements and surface-wave dispersion measurements.

The Alabama, U.S.A., seismic event and strata collapse of May 7, 1986

USGS Publications Warehouse

Long, L.T.; Copeland, C.W.

1989-01-01

On May 7, 1986, the residents of Tuscaloosa, Alabama, felt a seismic event of local magnitude 3.6 that occurred at the same time as a rock burst and roof collapse in an active longwall coal mine. Visual inspection of the seismograms reveals a deficiency in energy at frequencies above 20 Hz compared to tectonic earthquakes or surface blasts. The predominance of energy below 5 Hz may explain reports of body wave magnitudes (mb) greater than 4.2. Also, 1.0 Hz surface waves were more strongly excited than body waves and may explain local felt effects more typically associated with greater epicentral distances. All recorded first motions were dilatational. The concentration of stations in the northern hemisphere allows reverse motion on an east-trending near-vertical plane or strike-slip motion on northwest or southeast trending planes. The reverse focal mechanism is preferred, because the area of roof collapse and the area of active longwall mining are located between two east-striking loose vertical fracture zones. The characteristics of the seismic event suggest that it might have been sudden shear failure resulting from accumulated strain energy in overlying strata behind an active longwall. Although an alternate interpretation of the focal mechanism as an implosion or shear failure in the strata above previously mined out areas is also allowed by the first motion data, this alternate intepretation is not supported by geological data. ?? 1989 Birkha??user Verlag.

Characterization of rotary-percussion drilling as a seismic-while-drilling source

NASA Astrophysics Data System (ADS)

Xiao, Yingjian; Hurich, Charles; Butt, Stephen D.

2018-04-01

This paper focuses on an evaluation of rotary-percussion drilling (RPD) as a seismic source. Two field experiments were conducted to characterize seismic sources from different rocks with different strengths, i.e. weak shale and hard arkose. Characterization of RPD sources consist of spectral analysis and mean power measurements, along with field measurements of the source radiation patterns. Spectral analysis shows that increase of rock strength increases peak frequency and widens bandwidth, which makes harder rock more viable for seismic-while-drilling purposes. Mean power analysis infers higher magnitude of body waves in RPD than in conventional drillings. Within the horizontal plane, the observed P-wave energy radiation pattern partially confirms the theoretical radiation pattern under a single vertical bit vibration. However a horizontal lobe of energy is observed close to orthogonal to the axial bit vibration. From analysis, this lobe is attributed to lateral bit vibration, which is not documented elsewhere during RPD. Within the horizontal plane, the observed radiation pattern of P-waves is generally consistent with a spherically-symmetric distribution of energy. In addition, polarization analysis is conducted on P-waves recorded at surface geophones for understanding the particle motions. P-wave particle motions are predominantly in the vertical direction showing the interference of the free-surface.

Estimates of Lagrangian particle transport by wave groups: forward transport by Stokes drift and backward transport by the return flow

NASA Astrophysics Data System (ADS)

van den Bremer, Ton S.; Taylor, Paul H.

2014-11-01

Although the literature has examined Stokes drift, the net Lagrangian transport by particles due to of surface gravity waves, in great detail, the motion of fluid particles transported by surface gravity wave groups has received considerably less attention. In practice nevertheless, the wave field on the open sea often has a group-like structure. The motion of particles is different, as particles at sufficient depth are transported backwards by the Eulerian return current that was first described by Longuet-Higgins & Stewart (1962) and forms an inseparable counterpart of Stokes drift for wave groups ensuring the (irrotational) mass balance holds. We use WKB theory to study the variation of the Lagrangian transport by the return current with depth distinguishing two-dimensional seas, three-dimensional seas, infinite depth and finite depth. We then provide dimensional estimates of the net horizontal Lagrangian transport by the Stokes drift on the one hand and the return flow on the other hand for realistic sea states in all four cases. Finally we propose a simple scaling relationship for the transition depth: the depth above which Lagrangian particles are transported forwards by the Stokes drift and below which such particles are transported backwards by the return current.

Seismic moulin tremor

NASA Astrophysics Data System (ADS)

Roeoesli, Claudia; Walter, Fabian; Ampuero, Jean-Paul; Kissling, Edi

2016-08-01

Through glacial moulins, meltwater is routed from the glacier surface to its base. Moulins are a main feature feeding subglacial drainage systems and thus influencing basal motion and ice dynamics, but their geometry remains poorly known. Here we show that analysis of the seismic wavefield generated by water falling into a moulin can help constrain its geometry. We present modeling results of hour-long seimic tremors emitted from a vertical moulin shaft, observed with a seismometer array installed at the surface of the Greenland Ice Sheet. The tremor was triggered when the moulin water level exceeded a certain height, which we associate with the threshold for the waterfall to hit directly the surface of the moulin water column. The amplitude of the tremor signal changed over each tremor episode, in close relation to the amount of inflowing water. The tremor spectrum features multiple prominent peaks, whose characteristic frequencies are distributed like the resonant modes of a semiopen organ pipe and were found to depend on the moulin water level, consistent with a source composed of resonant tube waves (water pressure waves coupled to elastic deformation of the moulin walls) along the water-filled moulin pipe. Analysis of surface particle motions lends further support to this interpretation. The seismic wavefield was modeled as a superposition of sustained wave radiation by pressure sources on the side walls and at the bottom of the moulin. The former was found to dominate the wave field at close distance and the latter at large distance to the moulin.

SITE AMPLIFICATION OF EARTHQUAKE GROUND MOTION.

USGS Publications Warehouse

Hays, Walter W.

1986-01-01

When analyzing the patterns of damage in an earthquake, physical parameters of the total earthquake-site-structure system are correlated with the damage. Soil-structure interaction, the cause of damage in many earthquakes, involves the frequency-dependent response of both the soil-rock column and the structure. The response of the soil-rock column (called site amplification) is controversial because soil has strain-dependent properties that affect the way the soil column filters the input body and surface seismic waves, modifying the amplitude and phase spectra and the duration of the surface ground motion.

New technique for excitation of bulk and surface spin waves in ferromagnets

NASA Astrophysics Data System (ADS)

Bogacz, S. A.; Ketterson, J. B.

1985-09-01

A meander-line magnetic transducer is discussed in the context of bulk and surface spin-wave generation in ferromagnets. The magnetic field created by the transducer was calculated in closed analytic form for this model. The linear response of the ferromagnet to the inhomogenous surface disturbance of arbitrary ω and k was obtained as a self-consistent solution to the Bloch equation of motion and the Maxwell equations, subject to appropriate boundary condition. In particular, the energy flux through the boundary displays a sharp resonantlike absorption maximum concentrated at the frequency of the magnetostatic Damon-Eshbach (DE) surface mode; furthermore, the energy transfer spectrum is cut off abruptly below the threshold frequency of the bulk spin waves. The application of the meander line to the spin diffusion problem in NMR is also discussed.

The Tympanic Membrane Motion in Forward and Reverse Middle-Ear Sound Transmission

NASA Astrophysics Data System (ADS)

Cheng, Jeffrey Tao; Harrington, Ellery; Horwitz, Rachelle; Furlong, Cosme; Rosowski, John J.

2011-11-01

Sound-induced displacement of the tympanic membrane (TM) is the first stage in the forward transformation of environmental sound to sound within the inner ear, while displacement of the TM induced by mechanical motions of the ossicular chain is the last stage in the reverse transformation of sound generated within the inner ear to clinically valuable otoacoustic emissions (OAEs). In this study, we use stroboscopic holographic interferometry to study motions of the human cadaveric TM evoked by both forward and reverse stimuli. During forward acoustic stimulation, pure tones from 500 to 10000 Hz are used to stimulate the TM, while reverse stimulation is produced by direct mechanical stimulation of the ossicular chain. The TM surface motions in response to both forward and reverse stimuli show differences and similarities, including the modal motion patterns at specific frequencies as well as the presence and directions of traveling waves on the TM surface.

Adapting Surface Ground Motion Relations to Underground conditions: A case study for the Sudbury Neutrino Observatory in Sudbury, Ontario, Canada

NASA Astrophysics Data System (ADS)

Babaie Mahani, A.; Eaton, D. W.

2013-12-01

Ground Motion Prediction Equations (GMPEs) are widely used in Probabilistic Seismic Hazard Assessment (PSHA) to estimate ground-motion amplitudes at Earth's surface as a function of magnitude and distance. Certain applications, such as hazard assessment for caprock integrity in the case of underground storage of CO2, waste disposal sites, and underground pipelines, require subsurface estimates of ground motion; at present, such estimates depend upon theoretical modeling and simulations. The objective of this study is to derive correction factors for GMPEs to enable estimation of amplitudes in the subsurface. We use a semi-analytic approach along with finite-difference simulations of ground-motion amplitudes for surface and underground motions. Spectral ratios of underground to surface motions are used to calculate the correction factors. Two predictive methods are used. The first is a semi-analytic approach based on a quarter-wavelength method that is widely used for earthquake site-response investigations; the second is a numerical approach based on elastic finite-difference simulations of wave propagation. Both methods are evaluated using recordings of regional earthquakes by broadband seismometers installed at the surface and at depths of 1400 m and 2100 m in the Sudbury Neutrino Observatory, Canada. Overall, both methods provide a reasonable fit to the peaks and troughs observed in the ratios of real data. The finite-difference method, however, has the capability to simulate ground motion ratios more accurately than the semi-analytic approach.

The Effect of Sedimentary Basins on Through-Passing Short-Period Surface Waves

NASA Astrophysics Data System (ADS)

Feng, L.; Ritzwoller, M. H.

2017-12-01

Surface waves propagating through sedimentary basins undergo elastic wave field complications that include multiple scattering, amplification, the formation of secondary wave fronts, and subsequent wave front healing. Unless these effects are accounted for accurately, they may introduce systematic bias to estimates of source characteristics, the inference of the anelastic structure of the Earth, and ground motion predictions for hazard assessment. Most studies of the effects of basins on surface waves have centered on waves inside the basins. In contrast, we investigate wave field effects downstream from sedimentary basins, with particular emphasis on continental basins and propagation paths, elastic structural heterogeneity, and Rayleigh waves at 10 s period. Based on wave field simulations through a recent 3D crustal and upper mantle model of East Asia, we demonstrate significant Rayleigh wave amplification downstream from sedimentary basins in eastern China such that Ms measurements obtained on the simulated wave field vary by more than a magnitude unit. We show that surface wave amplification caused by basins results predominantly from elastic focusing and that amplification effects produced through 3D basin models are reproduced using 2D membrane wave simulations through an appropriately defined phase velocity map. The principal characteristics of elastic focusing in both 2D and 3D simulations include (1) retardation of the wave front inside the basins; (2) deflection of the wave propagation direction; (3) formation of a high amplitude lineation directly downstream from the basin bracketed by two low amplitude zones; and (4) formation of a secondary wave front. Finally, by comparing the impact of elastic focusing with anelastic attenuation, we argue that on-continent sedimentary basins are expected to affect surface wave amplitudes more strongly through elastic focusing than through the anelastic attenuation.

Simulations of Magnetohydrodynamic Waves Driven by Photospheric Motions

NASA Astrophysics Data System (ADS)

Mumford, Stuart

2016-04-01

This thesis investigates the properties of various modelled photospheric motions as generation mechanisms for magnetohydrodynamic (MHD) waves in the low solar atmosphere. The solar atmosphere is heated to million-degree temperatures, yet there is no fully understood heating mechanism which can provide the ≈ 300 W/m^2) required to keep the quiet corona at its observed temperatures. MHD waves are one mechanism by which this energy could be provided to the upper solar atmosphere, however, these waves need to be excited. The excitation of these waves, in or below the photosphere is a complex interaction between the plasma and the magnetic field embedded within it. This thesis studies a model of a small-scale magnetic flux tube based upon a magnetic bright point (MBP). These features are very common in the photosphere and have been observed to be affected by the plasma motions. The modelled flux tube has a foot point magnetic field strength of 120 mT and a FWHM of 90 km, and is embedded in a realistic, stratified solar atmosphere based upon the VALIIIc model. To better understand the excitation of MHD waves in this type of magnetic structures, a selection of velocity profiles are implemented to excite waves. Initially a study of five different driving profiles was performed. A uniform torsional driver as well as Archimedean and logarithmic spiral drivers which mimic observed torsional motions in the solar photosphere, along with vertical and horizontal drivers to mimic different motions caused by convection in the photosphere. The results are then analysed using a novel method for extracting the parallel, perpendicular and azimuthal components of the perturbations, which caters to both the linear and non-linear cases. Employing this method yields the identification of the wave modes excited in the numerical simulations and enables a comparison of excited modes via velocity perturbations and wave energy flux. The wave energy flux distribution is calculated, to enable the quantification of the relative strengths of excited modes. The torsional drivers primarily excite Alfvén modes (≈ 60 %) of the total flux) with contributions from the slow mode. The horizontal and vertical drivers primarily excite slow and fast modes respectively, with small variations dependent upon flux surface radius. This analysis is then applied to more in depth studies of the logarithmic spiral driver. Firstly, five different values for the (B_L) spiral expansion factor are chosen which control how rapidly the spiral expands. Larger values of (B_L) make the driving profile more radial. The results of this analysis show that the Alfvén wave is the dominant wave for lower values of the expansion factor, whereas, for the higher values the parallel component is dominant. This transition occurs within the range of the observational constraints, demonstrating that under realistic conditions spiral drivers may not excite most of their wave flux in the Alfvén mode. Finally, the logarithmic spiral is further studied, but with a variety of different periods. Ten periods from 30 to 300 seconds are chosen, and the simulations are again analysed using the flux surface method employed previously. The results of this study are minimal variation in the percentage wave flux in each mode, with no more than 20 % variation in any mode for any flux surface studied. Within this small variation, some non-linear changes in the wave flux were observed, especially around the more important small periods. Due to the short life time of the MBPs it is thought the short period waves would have more effect and therefore this non-linear variation in wave flux could have some impact on the modes present in the solar atmosphere.

Numerical comparisons of ground motion predictions with kinematic rupture modeling

NASA Astrophysics Data System (ADS)

Yuan, Y. O.; Zurek, B.; Liu, F.; deMartin, B.; Lacasse, M. D.

2017-12-01

Recent advances in large-scale wave simulators allow for the computation of seismograms at unprecedented levels of detail and for areas sufficiently large to be relevant to small regional studies. In some instances, detailed information of the mechanical properties of the subsurface has been obtained from seismic exploration surveys, well data, and core analysis. Using kinematic rupture modeling, this information can be used with a wave propagation simulator to predict the ground motion that would result from an assumed fault rupture. The purpose of this work is to explore the limits of wave propagation simulators for modeling ground motion in different settings, and in particular, to explore the numerical accuracy of different methods in the presence of features that are challenging to simulate such as topography, low-velocity surface layers, and shallow sources. In the main part of this work, we use a variety of synthetic three-dimensional models and compare the relative costs and benefits of different numerical discretization methods in computing the seismograms of realistic-size models. The finite-difference method, the discontinuous-Galerkin method, and the spectral-element method are compared for a range of synthetic models having different levels of complexity such as topography, large subsurface features, low-velocity surface layers, and the location and characteristics of fault ruptures represented as an array of seismic sources. While some previous studies have already demonstrated that unstructured-mesh methods can sometimes tackle complex problems (Moczo et al.), we investigate the trade-off between unstructured-mesh methods and regular-grid methods for a broad range of models and source configurations. Finally, for comparison, our direct simulation results are briefly contrasted with those predicted by a few phenomenological ground-motion prediction equations, and a workflow for accurately predicting ground motion is proposed.

Vertically reciprocating auger

NASA Technical Reports Server (NTRS)

Etheridge, Mark; Morgan, Scott; Fain, Robert; Pearson, Jonathan; Weldi, Kevin; Woodrough, Stephen B., Jr.

1988-01-01

The mathematical model and test results developed for the Vertically Reciprocating Auger (VRA) are summarized. The VRA is a device capable of transporting cuttings that result from below surface drilling. It was developed chiefly for the lunar surface, where conventional fluid flushing while drilling would not be practical. The VRA uses only reciprocating motion and transports material through reflections with the surface above. Particles are reflected forward and land ahead of radially placed fences, which prevent the particles from rolling back down the auger. Three input wave forms are considered to drive the auger. A modified sawtooth wave form was chosen for testing, over a modified square wave or sine wave, due to its simplicity and effectiveness. The three-dimensional mathematical model predicted a sand throughput rate of 0.2667 pounds/stroke, while the actual test setup transported 0.075 pounds/stroke. Based on this result, a correction factor of 0.281 is suggested for a modified sawtooth input.

Unsteady viscous effects in the flow over an oscillating surface. [mathematical model

NASA Technical Reports Server (NTRS)

Lerner, J. I.

1972-01-01

A theoretical model for the interaction of a turbulent boundary layer with an oscillating wavy surface over which a fluid is flowing is developed, with an application to wind-driven water waves and to panel flutter in low supersonic flow. A systematic methodology is developed to obtain the surface pressure distribution by considering separately the effects on the perturbed flow of a mean shear velocity profile, viscous stresses, the turbulent Reynolds stresses, compressibility, and three-dimensionality. The inviscid theory is applied to the wind-water wave problem by specializing to traveling-wave disturbances, and the pressure magnitude and phase shift as a function of the wave phase speed are computed for a logarithmic mean velocity profile and compared with inviscid theory and experiment. The results agree with experimental evidence for the stabilization of the panel motion due to the influence of the unsteady boundary layer.

Depth-variant azimuthal anisotropy in Tibet revealed by surface wave tomography

NASA Astrophysics Data System (ADS)

Pandey, Shantanu; Yuan, Xiaohui; Debayle, Eric; Tilmann, Frederik; Priestley, Keith; Li, Xueqing

2015-06-01

Azimuthal anisotropy derived from multimode Rayleigh wave tomography in China exhibits depth-dependent variations in Tibet, which can be explained as induced by the Cenozoic India-Eurasian collision. In west Tibet, the E-W fast polarization direction at depths <100 km is consistent with the accumulated shear strain in the Tibetan lithosphere, whereas the N-S fast direction at greater depths is aligned with Indian Plate motion. In northeast Tibet, depth-consistent NW-SE directions imply coupled deformation throughout the whole lithosphere, possibly also involving the underlying asthenosphere. Significant anisotropy at depths of 225 km in southeast Tibet reflects sublithospheric deformation induced by northward and eastward lithospheric subduction beneath the Himalaya and Burma, respectively. The multilayer anisotropic surface wave model can explain some features of SKS splitting measurements in Tibet, with differences probably attributable to the limited back azimuthal coverage of most SKS studies in Tibet and the limited horizontal resolution of the surface wave results.

Three-dimensional site response at KiK-net downhole arrays

USGS Publications Warehouse

Thompson, Eric M.; Tanaka, Yasuo; Baise, Laurie G.; Kayen, Robert E.

2010-01-01

Ground motions at two Kiban-Kyoshin Network (KiK-net) strong motion downhole array sites in Hokkaido, Japan (TKCH08 in Taiki and TKCH05 in Honbetsu) illustrate the importance of three-dimensional (3D) site effects. These sites recorded the M8.0 2003 Tokachi-Oki earthquake, with recorded accelerations above 0.4 g at both sites as well as numerous ground motions from smaller events. Weak ground motions indicate that site TKCH08 is well modeled with the assumption of plane SH waves traveling through a 1D medium (SH1D), while TKCH05 is characteristic of a poor fit to the SH1D theoretical response. We hypothesized that the misfit at TKCH05results from the heterogeneity of the subsurface. To test this hypothesis, we measured four S-wave velocity profiles in the vicinity (< 300 m) of each site with the spectral analysis of surface waves (SASW) method. This KiK-net site pair is ideal for assessing the relative importance of 3D site effects and nonlinear site effects. The linear ground motions at TKCH05 isolate the 3D site effects, as we hypothesized from the linear ground motions and confirmed with our subsequent SASW surveys. The Tokachi-Oki time history at TKCH08 isolates the effects of nonlinearity from spatial heterogeneity because the 3D effects are negligible. The Tokachi-Oki time history at TKCH05 includes both nonlinear and 3D site effects. Comparisons of the accuracy of the SH1D model predictions of these surface time histories from the downhole time histories indicates that the 3D site effects are at least as important as nonlinear effects in this case. The errors associated with the assumption of a 1D medium and 1D wave propagation will be carried into a nonlinear analysis that relies on these same assumptions. Thus, the presence of 3D effects should be ruled out prior to a 1D nonlinear analysis. The SH1D residuals show that 3D effects can be mistaken for nonlinear effects.

Modelling strong seismic ground motion: three-dimensional loading path versus wavefield polarization

NASA Astrophysics Data System (ADS)

Santisi d'Avila, Maria Paola; Lenti, Luca; Semblat, Jean-François

2012-09-01

Seismic waves due to strong earthquakes propagating in surficial soil layers may both reduce soil stiffness and increase the energy dissipation into the soil. To investigate seismic wave amplification in such cases, past studies have been devoted to one-directional shear wave propagation in a soil column (1D-propagation) considering one motion component only (1C-polarization). Three independent purely 1C computations may be performed ('1D-1C' approach) and directly superimposed in the case of weak motions (linear behaviour). This research aims at studying local site effects by considering seismic wave propagation in a 1-D soil profile accounting for the influence of the 3-D loading path and non-linear hysteretic behaviour of the soil. In the proposed '1D-3C' approach, the three components (3C-polarization) of the incident wave are simultaneously propagated into a horizontal multilayered soil. A 3-D non-linear constitutive relation for the soil is implemented in the framework of the Finite Element Method in the time domain. The complex rheology of soils is modelled by mean of a multisurface cyclic plasticity model of the Masing-Prandtl-Ishlinskii-Iwan type. The great advantage of this choice is that the only data needed to describe the model is the modulus reduction curve. A parametric study is carried out to characterize the changes in the seismic motion of the surficial layers due to both incident wavefield properties and soil non-linearities. The numerical simulations show a seismic response depending on several parameters such as polarization of seismic waves, material elastic and dynamic properties, as well as on the impedance contrast between layers and frequency content and oscillatory character of the input motion. The 3-D loading path due to the 3C-polarization leads to multi-axial stress interaction that reduces soil strength and increases non-linear effects. The non-linear behaviour of the soil may have beneficial or detrimental effects on the seismic response at the free surface, depending on the energy dissipation rate. Free surface time histories, stress-strain hysteresis loops and in-depth profiles of octahedral stress and strain are estimated for each soil column. The combination of three separate 1D-1C non-linear analyses is compared to the proposed 1D-3C approach, evidencing the influence of the 3C-polarization and the 3-D loading path on strong seismic motions.

Seagrass blade motion under waves and its impact on wave decay

NASA Astrophysics Data System (ADS)

Luhar, M.; Infantes, E.; Nepf, H.

2017-05-01

The hydrodynamic drag generated by seagrass meadows can dissipate wave-energy, causing wave decay. It is well known that this drag depends on the relative motion between the water and the seagrass blades, yet the impact of blade motion on drag and wave-energy dissipation remains to be fully characterized. In this experimental study, we examined the impact of blade motion on wave decay by concurrently recording blade posture during a wave cycle and measuring wave decay over a model seagrass meadow. We also identified a scaling law that predicts wave decay over the model meadow for a range of seagrass blade density, wave period, wave height, and water depth scaled from typical field conditions. Blade flexibility led to significantly lower drag and wave decay relative to theoretical predictions for rigid, upright blades. To quantify the impact of blade motion on wave decay, we employed an effective blade length, le, defined as the rigid blade length that leads to equivalent wave-energy dissipation. We estimated le directly from images of blade motion. Consistent with previous studies, these estimates showed that the effective blade length depends on the dimensionless Cauchy number, which describes the relative magnitude of the wave hydrodynamic drag and the restoring force due to blade rigidity. As the hydrodynamic forcing increases, the blades exhibit greater motion. Greater blade motion leads to smaller relative velocities, reducing drag, and wave-energy dissipation (i.e., smaller le).

Topographic enhancement of tidal motion in the western Barents Sea

NASA Technical Reports Server (NTRS)

Kowalik, Z.; Proshutinsky, A. YU.

1995-01-01

A high-resolution numerical lattice is used to study a topographically trapped motion around islands and shallow banks of the western Barents Sea caused both by the semidiurnal and diurnal tidal waves. Observations and model computations in the vicinity of Bear Island show well-developed trapped motion with distinctive tidal oscillatory motion. Numerical investigations demonstrate that one source of the trapped motion is tidal current rectification over shallow topgraphy. Tidal motion supports residual currents of the order of 8 cm/s around Bear Island and shallow Spitsbergenbanken. The structures of enhanced tidal currents for the semidiurnal components are generated in the shallow areas due to topographic amplification. In the diurnal band of oscillations the maximum current is associated with the shelf wave occurrence. Residual currents due to diurnal tides occur at both the shallow areas and the shelf slope in regions of maximum topographic gradients. Surface manifestation of the diurnal current enhancement is the local maximum of tidal amplitude at the shelf break of the order of 5 to 10 cm. Tidal current enhancement and tidally generated residual currents in the Bear Island and Spitsbergenabanken regions cause an increased generation of ice leads, ridges and, trapped motion of the ice floes.

Wave-induced response of a floating two-dimensional body with a moonpool.

PubMed

Fredriksen, Arnt G; Kristiansen, Trygve; Faltinsen, Odd M

2015-01-28

Regular wave-induced behaviour of a floating stationary two-dimensional body with a moonpool is studied. The focus is on resonant piston-mode motion in the moonpool and rigid-body motions. Dedicated two-dimensional experiments have been performed. Two numerical hybrid methods, which have previously been applied to related problems, are further developed. Both numerical methods couple potential and viscous flow. The semi-nonlinear hybrid method uses linear free-surface and body-boundary conditions. The other one uses fully nonlinear free-surface and body-boundary conditions. The harmonic polynomial cell method solves the Laplace equation in the potential flow domain, while the finite volume method solves the Navier-Stokes equations in the viscous flow domain near the body. Results from the two codes are compared with the experimental data. The nonlinear hybrid method compares well with the data, while certain discrepancies are observed for the semi-nonlinear method. In particular, the roll motion is over-predicted by the semi-nonlinear hybrid method. Error sources in the semi-nonlinear hybrid method are discussed. The moonpool strongly affects heave motions in a frequency range around the piston-mode resonance frequency of the moonpool. No resonant water motions occur in the moonpool at the piston-mode resonance frequency. Instead large moonpool motions occur at a heave natural frequency associated with small damping near the piston-mode resonance frequency. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

System for determining the angle of impact of an object on a structure

NASA Technical Reports Server (NTRS)

Prosser, William H. (Inventor); Gorman, Michael R. (Inventor)

1993-01-01

A method for determining the angle of impact of an object on a thin-walled structure which determines the angle of impact through analysis of the acoustic waves which result when an object impacts a structure is presented. Transducers are placed on and in the surface of the structure which sense the wave caused in the structure by impact. The waves are recorded and saved for analysis. For source motion normal to the surface, the antisymmetric mode has a large amplitude while that of the symmetric mode is very small. As the source angle increases with respect to the surface normal, the symmetric mode amplitude increases while the antisymmetric mode amplitude decreases. Thus, the angle of impact is determined by measuring the relative amplitudes of these two lowest order modes.

Amplification of seismic waves by the Seattle basin, Washington State

USGS Publications Warehouse

Pratt, T.L.; Brocher, T.M.; Weaver, C.S.; Creager, K.C.; Snelson, C.M.; Crosson, R.S.; Miller, K.C.; Trehu, A.M.

2003-01-01

Recordings of the 1999 Mw 7.6 Chi-Chi (Taiwan) earthquake, two local earthquakes, and five blasts show seismic-wave amplification over a large sedimentary basin in the U.S. Pacific Northwest. For weak ground motions from the Chi-Chi earthquake, the Seattle basin amplified 0.2- to 0.8-Hz waves by factors of 8 to 16 relative to bedrock sites west of the basin. The amplification and peak frequency change during the Chi-Chi coda: the initial S-wave arrivals (0-30 sec) had maximum amplifications of 12 at 0.5-0.8 Hz, whereas later arrivals (35-65 sec) reached amplifications of 16 at 0.3-0.5 Hz. Analysis of local events in the 1.0- to 10.0-Hz frequency range show fourfold amplifications for 1.0-Hz weak ground motion over the Seattle basin. Amplifications decrease as frequencies increase above 1.0 Hz, with frequencies above 7 Hz showing lower amplitudes over the basin than at bedrock sites. Modeling shows that resonance in low-impedance deposits forming the upper 550 m of the basin beneath our profile could cause most of the observed amplification, and the larger amplification at later arrival times suggests surface waves also play a substantial role. These results emphasize the importance of shallow deposits in determining ground motions over large basins.

INWARD MOTIONS IN THE OUTER SOLAR CORONA BETWEEN 7 AND 12 R {sub ⊙}: EVIDENCE FOR WAVES OR MAGNETIC RECONNECTION JETS?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tenerani, Anna; Velli, Marco; DeForest, Craig, E-mail: annatenerani@epss.ucla.edu

DeForest et al. used synoptic visible-light image sequences from the COR2 coronagraph on board the STEREO-A spacecraft to identify inbound wave motions in the outer corona beyond 7 solar radii and inferred, from the observation, that the Alfvén surface separating the magnetically dominated corona from the flow dominated wind must be located beyond at least 12 solar radii from the Sun over polar coronal holes and beyond 15 solar radii in the streamer belt. Here, we attempt identification of the observed inward signal by theoretically reconstructing height-speed diagrams and comparing them to the observed profiles. Interpretation in terms of Alfvénmore » waves or Alfvénic turbulence appears to be ruled out by the fact that the observed signal shows a deceleration of inward motion when approaching the Sun. Fast magnetoacoustic waves are not directly ruled out in this way, as it is possible for inward waves observed in quadrature, but not propagating exactly radially, to suffer total reflection as the Alfvén speed rises close to the Sun. However, the reconstructed signal in the height-speed diagram has the wrong concavity. A final possibility is decelerating reconnection jets, most probably from component reconnection, in the accelerating wind: the profile in this case appears to match the observations very well. This interpretation does not alter the conclusion that the Alfvén surface must be at least 12 solar radii from the photosphere. Further observations should help constrain this process, never identified previously in this way, in the distance range from 7 to 12 solar radii.« less

Conductivity dependence of seismoelectric wave phenomena in fluid-saturated sediments

NASA Astrophysics Data System (ADS)

Block, Gareth I.; Harris, John G.

2006-01-01

Seismoelectric phenomena in sediments arise from acoustic wave-induced fluid motion in the pore space, which perturbs the electrostatic equilibrium of the electric double layer on the grain surfaces. Experimental techniques and the apparatus built to study the conductivity dependence of the electrokinetic (EK) effect are described, and outcomes for studies in loose glass microspheres and medium-grain sand are presented. By varying the NaCl concentration in the pore fluid, we measured the conductivity dependence of two kinds of EK behavior: (1) the electric fields generated within the samples by the passage of transmitted acoustic waves and (2) the electromagnetic waves produced at the fluid-sediment interface by the incident acoustic wave. Both phenomena are caused by relative fluid motion in the sediment pores; this feature is characteristic of poroelastic (Biot) media but is not predicted by either viscoelastic fluid or solid models. A model of plane wave reflection from a fluid-sediment interface using EK-Biot theory leads to theoretical predictions that compare well to the experimental data for both loose glass microspheres and medium-grain sand.

Interfacial instabilities in vibrated fluids

NASA Astrophysics Data System (ADS)

Porter, Jeff; Laverón-Simavilla, Ana; Tinao Perez-Miravete, Ignacio; Fernandez Fraile, Jose Javier

2016-07-01

Vibrations induce a range of different interfacial phenomena in fluid systems depending on the frequency and orientation of the forcing. With gravity, (large) interfaces are approximately flat and there is a qualitative difference between vertical and horizontal forcing. Sufficient vertical forcing produces subharmonic standing waves (Faraday waves) that extend over the whole interface. Horizontal forcing can excite both localized and extended interfacial phenomena. The vibrating solid boundaries act as wavemakers to excite traveling waves (or sloshing modes at low frequencies) but they also drive evanescent bulk modes whose oscillatory pressure gradient can parametrically excite subharmonic surface waves like cross-waves. Depending on the magnitude of the damping and the aspect ratio of the container, these locally generated surfaces waves may interact in the interior resulting in temporal modulation and other complex dynamics. In the case where the interface separates two fluids of different density in, for example, a rectangular container, the mass transfer due to vertical motion near the endwalls requires a counterflow in the interior region that can lead to a Kelvin-Helmholtz type instability and a ``frozen wave" pattern. In microgravity, the dominance of surface forces favors non-flat equilibrium configurations and the distinction between vertical and horizontal applied forcing can be lost. Hysteresis and multiplicity of solutions are more common, especially in non-wetting systems where disconnected (partial) volumes of fluid can be established. Furthermore, the vibrational field contributes a dynamic pressure term that competes with surface tension to select the (time averaged) shape of the surface. These new (quasi-static) surface configurations, known as vibroequilibria, can differ substantially from the hydrostatic state. There is a tendency for the interface to orient perpendicular to the vibrational axis and, in some cases, a bulge or cavity is induced that leads to splitting (fluid separation). We investigate the interaction of these prominent interfacial instabilities in the absence of gravity, concentrating on harmonically vibrated rectangular containers of fluid. We compare vibroequilibria theory with direct numerical simulations and consider the effect of surfaces waves, which can excite sloshing motion of the vibroequilibria. We systematically investigate the saddle-node bifurcation experienced by a symmetric singly connected vibroequilibria solution, for sufficiently deep containers, as forcing is increased. Beyond this instability, the fluid rapidly separates into (at least) two distinct masses. Pronounced hysteresis is associated with this transition, even in the presence of gravity. The interaction of vibroequilibria and frozen waves is investigated in two-fluid systems. Preparations for a parabolic flight experiment on fluids vibrated at high frequencies are discussed.

Numerical evaluation of longitudinal motions of Wigley hulls advancing in waves by using Bessho form translating-pulsating source Green'S function

NASA Astrophysics Data System (ADS)

Xiao, Wenbin; Dong, Wencai

2016-06-01

In the framework of 3D potential flow theory, Bessho form translating-pulsating source Green's function in frequency domain is chosen as the integral kernel in this study and hybrid source-and-dipole distribution model of the boundary element method is applied to directly solve the velocity potential for advancing ship in regular waves. Numerical characteristics of the Green function show that the contribution of local-flow components to velocity potential is concentrated at the nearby source point area and the wave component dominates the magnitude of velocity potential in the far field. Two kinds of mathematical models, with or without local-flow components taken into account, are adopted to numerically calculate the longitudinal motions of Wigley hulls, which demonstrates the applicability of translating-pulsating source Green's function method for various ship forms. In addition, the mesh analysis of discrete surface is carried out from the perspective of ship-form characteristics. The study shows that the longitudinal motion results by the simplified model are somewhat greater than the experimental data in the resonant zone, and the model can be used as an effective tool to predict ship seakeeping properties. However, translating-pulsating source Green function method is only appropriate for the qualitative analysis of motion response in waves if the ship geometrical shape fails to satisfy the slender-body assumption.

Wave excited motion of a body floating on water confined between two semi-infinite ice sheets

NASA Astrophysics Data System (ADS)

Ren, K.; Wu, G. X.; Thomas, G. A.

2016-12-01

The wave excited motion of a body floating on water confined between two semi-infinite ice sheets is investigated. The ice sheet is treated as an elastic thin plate and water is treated as an ideal and incompressible fluid. The linearized velocity potential theory is adopted in the frequency domain and problems are solved by the method of matched eigenfunctions expansion. The fluid domain is divided into sub-regions and in each sub-region the velocity potential is expanded into a series of eigenfunctions satisfying the governing equation and the boundary conditions on horizontal planes including the free surface and ice sheets. Matching is conducted at the interfaces of two neighbouring regions to ensure the continuity of the pressure and velocity, and the unknown coefficients in the expressions are obtained as a result. The behaviour of the added mass and damping coefficients of the floating body with the effect of the ice sheets and the excitation force are analysed. They are found to vary oscillatorily with the wave number, which is different from that for a floating body in the open sea. The motion of the body confined between ice sheets is investigated, in particular its resonant behaviour with extremely large motion found to be possible under certain conditions. Standing waves within the polynya are also observed.

One-dimensional modelling of upper ocean mixing by turbulence due to wave orbital motion

NASA Astrophysics Data System (ADS)

Ghantous, M.; Babanin, A. V.

2014-02-01

Mixing of the upper ocean affects the sea surface temperature by bringing deeper, colder water to the surface. Because even small changes in the surface temperature can have a large impact on weather and climate, accurately determining the rate of mixing is of central importance for forecasting. Although there are several mixing mechanisms, one that has until recently been overlooked is the effect of turbulence generated by non-breaking, wind-generated surface waves. Lately there has been a lot of interest in introducing this mechanism into ocean mixing models, and real gains have been made in terms of increased fidelity to observational data. However, our knowledge of the mechanism is still incomplete. We indicate areas where we believe the existing parameterisations need refinement and propose an alternative one. We use two of the parameterisations to demonstrate the effect on the mixed layer of wave-induced turbulence by applying them to a one-dimensional mixing model and a stable temperature profile. Our modelling experiment suggests a strong effect on sea surface temperature due to non-breaking wave-induced turbulent mixing.

Near-surface energy transfers from internal tide beams to smaller vertical scale motions

NASA Astrophysics Data System (ADS)

Chou, S.; Staquet, C.; Carter, G. S.; Luther, D. S.

2016-02-01

Mechanical energy capable of causing diapycnal mixing in the ocean is transferred to the internal wave field when barotropic tides pass over underwater topography and generate internal tides. The resulting internal tide energy is confined in vertically limited structures, or beams. As internal tide beams (ITBs) propagate through regions of non-uniform stratification in the upper ocean, wave energy can be scattered through multiple reflections and refractions, be vertically trapped, or transferred to non-tidal frequencies through different nonlinear processes. Various observations have shown that ITBs are no longer detectable in horizontal kinetic energy beyond the first surface reflection. Importantly, this implies that some of the internal tide energy no longer propagates in to the abyssal ocean and consequently will not be available to maintain the density stratification. Using the NHM, a nonlinear and nonhydrostatic model based on the MITgcm, simulations of an ITB propagating up to the sea surface are examined in order to quantify the transformation of ITB energy to other motions. We compare and contrast the transformations enabled by idealized, smoothly-varying stratification with transformations enabled by realistic stratification containing a broad-band vertical wavenumber spectrum of variations. Preliminary two-dimensional results show that scattering due to small-scale structure in realistic stratification profiles from Hawaii can lead to energy being vertically trapped near the surface. Idealized simulations of "locally" generated internal solitary waves are analyzed in terms of energy flux transfers from the ITB to solitary waves, higher harmonics, and mean flow. The amount of internal tide energy which propagates back down after near-surface reflection of the ITB in different environments is quantified.

Water Surface Currents, Short Gravity-Capillary Waves and Radar Backscatter

NASA Technical Reports Server (NTRS)

Atakturk, Serhad S.; Katsaros, Kristina B.

1993-01-01

Despite their importance for air-sea interaction and microwave remote sensing of the ocean surface, intrinsic properties of short gravity-capillary waves are not well established. This is largely due to water surface currents and their effects on the direct measurements of wave parameters conducted at a fixed point. Frequencies of small scale waves propagating on a surface which itself is in motion, are subject to Doppler shifts. Hence, the high frequency tail of the wave spectra obtained from such temporal observations is smeared. Conversion of this smeared measured-frequency spectra to intrinsic-frequency (or wavenumber) spectra requires corrections for the Doppler shifts. Such attempts in the past have not been very successful in particular when field data were used. This becomes evident if the amplitude modulation of short waves by underlying long waves is considered. Microwave radar studies show that the amplitude of a short wave component attains its maximum value near the crests and its minimum in the troughs of the long waves. Doppler-shifted wave data yield similar results but much larger in modulation magnitude, as expected. In general, Doppler shift corrections reduce the modulation magnitude. Overcorrection may result in a negligible modulation or even in a strong modulation with the maximum amplitude in the wave troughs. The latter situation is clearly contradictory to our visual observations as well as the radar results and imply that the advection by currents is overestimated. In this study, a differential-advection approach is used in which small scale waves are advected by the currents evaluated not at the free surface, but at a depth proportional to their wavelengths. Applicability of this approach is verified by the excellent agreement in phase and magnitude of short-wave modulation between results based on radar and on wave-gauge measurements conducted on a lake.

Effects of Second-Order Sum- and Difference-Frequency Wave Forces on the Motion Response of a Tension-Leg Platform Considering the Set-down Motion

NASA Astrophysics Data System (ADS)

Wang, Bin; Tang, Yougang; Li, Yan; Cai, Runbo

2018-04-01

This paper presents a study on the motion response of a tension-leg platform (TLP) under first- and second-order wave forces, including the mean-drift force, difference and sum-frequency forces. The second-order wave force is calculated using the full-field quadratic transfer function (QTF). The coupled effect of the horizontal motions, such as surge, sway and yaw motions, and the set-down motion are taken into consideration by the nonlinear restoring matrix. The time-domain analysis with 50-yr random sea state is performed. A comparison of the results of different case studies is made to assess the influence of second-order wave force on the motions of the platform. The analysis shows that the second-order wave force has a major impact on motions of the TLP. The second-order difference-frequency wave force has an obvious influence on the low-frequency motions of surge and sway, and also will induce a large set-down motion which is an important part of heave motion. Besides, the second-order sum-frequency force will induce a set of high-frequency motions of roll and pitch. However, little influence of second-order wave force is found on the yaw motion.

A theoretical study of the fundamental torsional wave in buried pipes for pipeline condition assessment and monitoring

NASA Astrophysics Data System (ADS)

Muggleton, J. M.; Kalkowski, M.; Gao, Y.; Rustighi, E.

2016-07-01

Waves that propagate at low frequencies in buried pipes are of considerable interest in a variety of practical scenarios, for example leak detection, remote pipe detection, and pipeline condition assessment and monitoring. Whilst there has been considerable research and commercial attention on the accurate location of pipe leakage for many years, the various causes of pipe failures and their identification, have not been well documented; moreover, there are still a number of gaps in the existing knowledge. Previous work has focused on two of the three axisymmetric wavetypes that can propagate: the s=1, fluid-dominated wave; and the s=2, shell-dominated wave. In this paper, the third axisymmetric wavetype, the s=0 torsional wave, is investigated. The effects of the surrounding soil on the characteristics of wave propagation and attenuation are analysed for a compact pipe/soil interface for which there is no relative motion between the pipe wall and the surrounding soil. An analytical dispersion relationship is derived for the torsional wavenumber from which both the wavespeed and wave attenuation can be obtained. How torsional waves can subsequently radiate to the ground surface is then investigated. Analytical expressions are derived for the ground surface displacement above the pipe resulting from torsional wave motion within the pipe wall. A numerical model is also included, primarily in order to validate some of the assumptions made whilst developing the analytical solutions, but also so that some comparison in the results may be made. Example results are presented for both a cast iron pipe and an MDPE pipe buried in two typical soil types.

Infrasound from thunder: A natural seismic source

NASA Astrophysics Data System (ADS)

Lin, Ting-L.; Langston, Charles A.

2007-07-01

A small array consisting of five three-component short-period surface seismometers, a three-component borehole seismometer, and five infrasound microphones was built to investigate thunder-induced ground motions. Data from two thunder events with similar N-wave waveforms but different horizontal slownesses are chosen as examples of data collected by the array. These impulsive acoustic waves excited P and S reverberations in the near surface that depend on both the incident wave horizontal slowness and the velocity structure in the upper 30 meters at the site. Although the depth of the borehole is relatively shallow compared to a seismic wave wavelength, velocity amplitude in the radial component decays as much as 63 percent with depth but vertical component amplitudes are unaffected consistent with air-coupled Rayleigh wave excitation. Naturally occurring thunder appears to be a useful seismic source to empirically determine site resonance characteristics for hazards assessments.

Turbulence generation by waves

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaftori, D.; Nan, X.S.; Banerjee, S.

The interaction between two-dimensional mechanically generated waves, and a turbulent stream was investigated experimentally in a horizontal channel, using a 3-D LDA synchronized with a surface position measuring device and a micro-bubble tracers flow visualization with high speed video. Results show that although the wave induced orbital motion reached all the way to the wall, the characteristics of the turbulence wall structures and the turbulence intensity close to the wall were not altered. Nor was the streaky nature of the wall layer. On the other hand, the mean velocity profile became more uniform and the mean friction velocity was increased.more » Close to the free surface, the turbulence intensity was substantially increased as well. Even in predominantly laminar flows, the introduction of 2-D waves causes three dimensional turbulence. The turbulence enhancement is found to be proportional to the wave strength.« less

Imaging Strong Lateral Heterogeneities with USArray using Body-to-Surface Wave Scattering

NASA Astrophysics Data System (ADS)

Yu, C.; Zhan, Z.; Hauksson, E.; Cochran, E. S.

2017-12-01

Seismic scattering is commonly observed and results from wave propagation in heterogeneous medium. Yet, deterministic characterization of scatterers remains challenging. In this study, we analyze broadband waveforms recorded by the USArray across the entire conterminous US. With array analysis, we observe strong scattered surface waves following the arrival of teleseismic body waves over several hundreds of kilometers. We use back-projection to locate the body-to-surface scattering sources, and detect strong scatterers both around and within the conterminous US. For the former, strong scattering is associated with pronounced bathymetric relief, such as the Patton Escarpment in the Southern California Continental Borderland. For the latter, scatterers are consistent with sharp lateral heterogeneities, such as near the Yellowstone hotspot and Southern California fault zones. We further model the body-to-surface wave scattering using finite-difference simulations. As an example, in the Southern California Continental Borderland a simplified 2-D bathymetric and crustal model are able to predict the arrival times and amplitudes of major scatterers. The modeling also suggests a relatively low shear wave velocity in the Continental Borderland. These observation of strong body-to-surface wave scattering and waveform modeling not only helps us image sharp heterogeneities but also are useful for assessing seismic hazard, including the calibration and refinement of seismic velocity models used to locate earthquakes and simulate strong ground motions.

Rough surface wavelength measurement through self mixing of Doppler microwave backscatter. [from ocean waves

NASA Technical Reports Server (NTRS)

Weissman, D. E.; Johnson, J. W.

1979-01-01

A microwave backscatter technique is presented that has the ability to sense the dominant surface wavelength of a random rough surface. The purpose of this technique is to perform this measurement from an aircraft or spacecraft, wherein the horizontal velocity of the radar is an important parameter of the measurement system. Attention will be directed at water surface conditions for which a dominant wavelength can be defined, then the spatial variations of reflectivity will have a two dimensional spectrum that is sufficiently close to that of waves to be useful. The measurement concept is based on the relative motion between the water waves and a nadir looking radar, and the fact that while the instantaneous Doppler frequency at the receiver returned by any elementary group of scatterers on a water wave is monotonically changing, the difference in the Doppler frequency between any two scattering 'patches' stays approximately constant as these waves travel parallel to the major axis of an elliptical antenna footprint. The results of a theoretical analysis and a laboratory experiment with a continuous wave (CW) radar that encompasses several of the largest waves in the illuminated area show how the structure in the Doppler spectrum of the backscattered signal is related to the surface spectrum and its parameters in an especially direct and simple way when an incoherent envelope detector is the receiver.

Nonlinear dynamics of steep surface waves as derived from a Lagrangian

NASA Astrophysics Data System (ADS)

Longuet-Higgins, Michael

1999-11-01

A simple and natural method for calculating the deformation of surface gravity waves on deep water was recently formulated by A.M. Balk (1996). The equations of motion are derived from a Lagrangian (T-V) where T and V are the kinetic and potential energies, expressed in terms of the Fourier coefficients a_n(t) of the motion in an auxiliary half-space. The method has certain advantages over the more usual Hamiltonian equations: (1) The expressions for T and V are of finite order N <= 4 in the Fourier coefficients a_n(t) and their rates of change dota(t); (2) the constants in these expressions are low integers, mainly ± 1 or 0; (3) breaking or overturning waves are described by single-valued functions of a parameter. The analysis leads to dynamical equations for än of the form sumj P_ij äj = Qi (a, ; dota) (P_ij and Qi being polynomials of low degree in the coefficients a_n) which can in general be solved to allow time-stepping to proceed. Conveniently, the determinant Δ of P_ij is found to factorise. Some examples will be discussed, particularly the case of standing waves, when the coefficients a_n(t) are all real. The phenomena of ``flip through'' and jet formation are of special interest.

Actuating Mechanism and Design of a Cylindrical Traveling Wave Ultrasonic Motor Using Cantilever Type Composite Transducer

PubMed Central

Liu, Yingxiang; Chen, Weishan; Liu, Junkao; Shi, Shengjun

2010-01-01

Background Ultrasonic motors (USM) are based on the concept of driving the rotor by a mechanical vibration excited on the stator via piezoelectric effect. USM exhibit merits such as simple structure, quick response, quiet operation, self-locking when power off, nonelectromagnetic radiation and higher position accuracy. Principal Findings A cylindrical type traveling wave ultrasonic motor using cantilever type composite transducer was proposed in this paper. There are two cantilevers on the outside surface of cylinder, four longitudinal PZT ceramics are set between the cantilevers, and four bending PZT ceramics are set on each outside surface of cantilevers. Two degenerate flexural vibration modes spatially and temporally orthogonal to each other in the cylinder are excited by the composite transducer. In this new design, a single transducer can excite a flexural traveling wave in the cylinder. Thus, elliptical motions are achieved on the teeth. The actuating mechanism of proposed motor was analyzed. The stator was designed with FEM. The two vibration modes of stator were degenerated. Transient analysis was developed to gain the vibration characteristic of stator, and results indicate the motion trajectories of nodes on the teeth are nearly ellipses. Conclusions The study results verify the feasibility of the proposed design. The wave excited in the cylinder isn't an ideal traveling wave, and the vibration amplitudes are inconsistent. The distortion of traveling wave is generated by the deformation of bending vibration mode of cylinder, which is caused by the coupling effect between the cylinder and transducer. Analysis results also prove that the objective motions of nodes on the teeth are three-dimensional vibrations. But, the vibration in axial direction is minute compared with the vibrations in circumferential and radial direction. The results of this paper can guide the development of this new type of motor. PMID:20368809

A Study of Fundamental Shock Noise Mechanisms

NASA Technical Reports Server (NTRS)

Meadows, Kristine R.

1997-01-01

This paper investigates two mechanisms fundamental to sound generation in shocked flows: shock motion and shock deformation. Shock motion is modeled numerically by examining the interaction of a sound wave with a shock. This numerical approach is validated by comparison with results obtained by linear theory for a small-disturbance case. Analysis of the perturbation energy with Myers' energy corollary demonstrates that acoustic energy is generated by the interaction of acoustic disturbances with shocks. This analysis suggests that shock motion generates acoustic and entropy disturbance energy. Shock deformation is modeled numerically by examining the interaction of a vortex ring with a shock. These numerical simulations demonstrate the generation of both an acoustic wave and contact surfaces. The acoustic wave spreads cylindrically. The sound intensity is highly directional and the sound pressure increases with increasing shock strength. The numerically determined relationship between the sound pressure and the Mach number is found to be consistent with experimental observations of shock noise. This consistency implies that a dominant physical process in the generation of shock noise is modeled in this study.

Full-field drift Hamiltonian particle orbits in 3D geometry

NASA Astrophysics Data System (ADS)

Cooper, W. A.; Graves, J. P.; Brunner, S.; Isaev, M. Yu

2011-02-01

A Hamiltonian/Lagrangian theory to describe guiding centre orbit drift motion which is canonical in the Boozer coordinate frame has been extended to include full electromagnetic perturbed fields in anisotropic pressure 3D equilibria with nested magnetic flux surfaces. A redefinition of the guiding centre velocity to eliminate the motion due to finite equilibrium radial magnetic fields and the choice of a gauge condition that sets the radial component of the electromagnetic vector potential to zero are invoked to guarantee that the Boozer angular coordinates retain the canonical structure. The canonical momenta are identified and the guiding centre particle radial drift motion and parallel gyroradius evolution are derived. The particle coordinate position is linearly modified by wave-particle interactions. All the nonlinear wave-wave interactions appear explicitly only in the evolution of the parallel gyroradius. The radial variation of the electrostatic potential is related to the binormal component of the displacement vector for MHD-type perturbations. The electromagnetic vector potential projections can then be determined from the electrostatic potential and the radial component of the MHD displacement vector.

Analytical and numerical solution for wave reflection from a porous wave absorber

NASA Astrophysics Data System (ADS)

Magdalena, Ikha; Roque, Marian P.

2018-03-01

In this paper, wave reflection from a porous wave absorber is investigated theoretically and numerically. The equations that we used are based on shallow water type model. Modification of motion inside the absorber is by including linearized friction term in momentum equation and introducing a filtered velocity. Here, an analytical solution for wave reflection coefficient from a porous wave absorber over a flat bottom is derived. Numerically, we solve the equations using the finite volume method on a staggered grid. To validate our numerical model, comparison of the numerical reflection coefficient is made against the analytical solution. Further, we implement our numerical scheme to study the evolution of surface waves pass through a porous absorber over varied bottom topography.

Langasite, langanite, and langatate bulk-wave Y-cut resonators.

PubMed

Smythe, R C; Helmbold, R C; Hague, G E; Snow, K A

2000-01-01

Materials in the langasite family are of current interest for both bulk wave and surface wave devices. Piano-convex Y-cut bulk wave resonators have been built and tested on overtones 1 through 9 using LGS (langasite; La(3)Ga(5)SiO(14)), LGN (langanite; La(3)Ga(5.5)Nb(0.5)O(14)), and LGT (langatate; La(3)Ga(5.5)Ta(5.5)O(14)). Frequencies and motional inductances are compared with calculated values, with good agreement except for the motional inductance of LGT. For all three materials, frequency variation is an essentially parabolic function of temperature. For LGN and LGT, reported values of the Q-frequency product are significantly above the classical limit for AT-cut quartz. A maximum 4 f value of 25.6x10(6), where frequency is in megahertz;, was observed for an LGT resonator; for an unplated resonator, 29.2x10(6) was measured. Still higher values are believed possible.

Unmanned Sea Surface Vehicle (USSV) Motion Data and Refueling Equipment Design

DTIC Science & Technology

2010-01-01

knowledge of on-coming waves and craft controls system elements. The same information could be used to optimize structural design of USSV hull or host...Carderock Division, Detachment Norfolk Code 232- Systems Design &Integration Little Creek Amphibious Base 2600 Tarawa Court, Norfolk, VA. 23521-3239...and USSV speed. The resulting extensive set of motion and positional data will be useful for future system designers for years to come. This work

Stably Stratified Atmospheric Boundary Layers

NASA Astrophysics Data System (ADS)

Mahrt, L.

2014-01-01

Atmospheric boundary layers with weak stratification are relatively well described by similarity theory and numerical models for stationary horizontally homogeneous conditions. With common strong stratification, similarity theory becomes unreliable. The turbulence structure and interactions with the mean flow and small-scale nonturbulent motions assume a variety of scenarios. The turbulence is intermittent and may no longer fully satisfy the usual conditions for the definition of turbulence. Nonturbulent motions include wave-like motions and solitary modes, two-dimensional vortical modes, microfronts, intermittent drainage flows, and a host of more complex structures. The main source of turbulence may not be at the surface, but rather may result from shear above the surface inversion. The turbulence is typically not in equilibrium with the nonturbulent motions, sometimes preventing the formation of an inertial subrange. New observational and analysis techniques are expected to advance our understanding of the very stable boundary layer.

Near Surface Seismic Hazard Characterization in the Presence of High Velocity Contrasts

NASA Astrophysics Data System (ADS)

Gribler, G.; Mikesell, D.; Liberty, L. M.

2017-12-01

We present new multicomponent surface wave processing techniques that provide accurate characterization of near-surface conditions in the presence of large lateral or vertical shear wave velocity boundaries. A common problem with vertical component Rayleigh wave analysis in the presence of high contrast subsurface conditions is Rayleigh wave propagation mode misidentification due to an overlap of frequency-phase velocity domain dispersion, leading to an overestimate of shear wave velocities. By using the vertical and horizontal inline component signals, we isolate retrograde and prograde particle motions to separate fundamental and higher mode signals, leading to more accurate and confident dispersion curve picks and shear wave velocity estimates. Shallow, high impedance scenarios, such as the case with shallow bedrock, are poorly constrained when using surface wave dispersion information alone. By using a joint inversion of dispersion and horizontal-to-vertical (H/V) curves within active source frequency ranges (down to 3 Hz), we can accurately estimate the depth to high impedance boundaries, a significant improvement compared to the estimates based on dispersion information alone. We compare our approach to body wave results that show comparable estimates of bedrock topography. For lateral velocity contrasts, we observe horizontal polarization of Rayleigh waves identified by an increase in amplitude and broadening of the horizontal spectra with little variation in the vertical component spectra. The horizontal spectra offer a means to identify and map near surface faults where there is no topographic or clear body wave expression. With these new multicomponent active source seismic data processing and inversion techniques, we better constrain a variety of near surface conditions critical to the estimation of local site response and seismic hazards.

Free Motion Scanning System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sword, Charles K.

The present invention relates to an ultrasonic scanner and method for the imaging of a part surface, the scanner comprising: a probe assembly spaced apart from the surface including at least two tracking signals for emitting electromagnetic radiation and a transmitter for emitting ultrasonic waves onto a surface in order to induce at least a portion of said waves to be reflected from the surface, at least one detector for receiving the electromagnetic radiation wherein the detector is positioned to receive said radiation from the tracking signals, an analyzing means for recognizing a three-dimensional location of the tracking signals basedmore » on said emitted electromagnetic radiation, a differential conversion means for generating an output signal representative of the waveform of the reflected waves, and a means for relating said tracking signal location with the output signal and projecting an image of the resulting data. The scanner and method are particularly useful to acquire ultrasonic inspection data by scanning the probe-over a complex part surface in an arbitrary scanning pattern.« less

Direct ambient noise tomography for 3-D near surface shear velocity structure: methodology and applications

NASA Astrophysics Data System (ADS)

Yao, H.; Fang, H.; Li, C.; Liu, Y.; Zhang, H.; van der Hilst, R. D.; Huang, Y. C.

2014-12-01

Ambient noise tomography has provided essential constraints on crustal and uppermost mantle shear velocity structure in global seismology. Recent studies demonstrate that high frequency (e.g., ~ 1 Hz) surface waves between receivers at short distances can be successfully retrieved from ambient noise cross-correlation and then be used for imaging near surface or shallow crustal shear velocity structures. This approach provides important information for strong ground motion prediction in seismically active area and overburden structure characterization in oil and gas fields. Here we propose a new tomographic method to invert all surface wave dispersion data for 3-D variations of shear wavespeed without the intermediate step of phase or group velocity maps.The method uses frequency-dependent propagation paths and a wavelet-based sparsity-constrained tomographic inversion. A fast marching method is used to compute, at each period, surface wave traveltimes and ray paths between sources and receivers. This avoids the assumption of great-circle propagation that is used in most surface wave tomographic studies, but which is not appropriate in complex media. The wavelet coefficients of the velocity model are estimated with an iteratively reweighted least squares (IRLS) algorithm, and upon iterations the surface wave ray paths and the data sensitivity matrix are updated from the newly obtained velocity model. We apply this new method to determine the 3-D near surface wavespeed variations in the Taipei basin of Taiwan, Hefei urban area and a shale and gas production field in China using the high-frequency interstation Rayleigh wave dispersion data extracted from ambient noisecross-correlation. The results reveal strong effects of off-great-circle propagation of high-frequency surface waves in these regions with above 30% shear wavespeed variations. The proposed approach is more efficient and robust than the traditional two-step surface wave tomography for imaging complex structures. In the future, approximate 3-D sensitivity kernels for dispersion data will be incorporated to account for finite-frequency effect of surface wave propagation. In addition, our approach provides a consistent framework for joint inversion of surface wave dispersion and body wave traveltime data for 3-D Vp and Vs structures.

Quantum trajectories in elastic atom-surface scattering: threshold and selective adsorption resonances.

PubMed

Sanz, A S; Miret-Artés, S

2005-01-01

The elastic resonant scattering of He atoms off the Cu(117) surface is fully described with the formalism of quantum trajectories provided by Bohmian mechanics. Within this theory of quantum motion, the concept of trapping is widely studied and discussed. Classically, atoms undergo impulsive collisions with the surface, and then the trapped motion takes place covering at least two consecutive unit cells. However, from a Bohmian viewpoint, atom trajectories can smoothly adjust to the equipotential energy surface profile in a sort of sliding motion; thus the trapping process could eventually occur within one single unit cell. In particular, both threshold and selective adsorption resonances are explained by means of this quantum trapping considering different space and time scales. Furthermore, a mapping between each region of the (initial) incoming plane wave and the different parts of the diffraction and resonance patterns can be easily established, an important issue only provided by a quantum trajectory formalism. (c) 2005 American Institute of Physics.

The wave numbers of supercritical surface tension driven Benard convection

NASA Technical Reports Server (NTRS)

Koschmieder, E. L.; Switzer, D. W.

1991-01-01

The cell size or the wave numbers of supercritical hexagonal convection cells in primarily surface tension driven convection on a uniformly heated plate was studied experimentally in thermal equilibrium in thin layers of silicone oil of large aspect ratio. It was found that the cell size decreases with increased temperature difference in the slightly supercritical range, and that the cell size is unique within the experimental error. It was also observed that the cell size reaches a minimum and begins to increase at larger temperature differences. This reversal of the rate of change of the wave number with temperature difference is attributed to influences of buoyancy on the fluid motion. The consequences of buoyancy were tested with three fluid layers of different depth.

Towards an exact factorization of the molecular wave function

NASA Astrophysics Data System (ADS)

Parashar, Shubham; Sajeev, Y.; Ghosh, Swapan K.

2015-10-01

An exact single-product factorisation of the molecular wave function for the timedependent Schrödinger equation is investigated by using an ansatz involving a phase factor. By using the Frenkel variational method, we obtain the Schrödinger equations for the electronic and nuclear wave functions. The concept of a potential energy surface (PES) is retained by introducing a modified Hamiltonian as suggested earlier by Cederbaum. The parameter ω in the phase factor is chosen such that the equations of motion retain the physically appealing Born- Oppenheimer-like form, and is therefore unique.

Nonlinear Wave propagation at sediment layers

NASA Astrophysics Data System (ADS)

Tsuda, K.; Archuleta, R. J.; O'Connell, D. R.; Bonilla, F. L.

2002-12-01

Data from some large earthquakes, such as the 2000 Tottoriken-Seibu earthquake, the 1995 Kobe earthquake, and 1994 Northridge earthquake have reinforced the importance of the effect of surface soil on seismic waves. This is especially true of the Tottoriken-Seibu earthquake where the damage from the liquefaction of surface soil was very severe. The mechanism of the liquefaction of soil is understood as the result of the nonlinear soil behavior-the pore water pressure build up-during the strong shaking. The model to explain the mechanics of pore water pressure build up has been proposed by many studies. In this study, we tried to predict the pore water pressure based on the constitutive model proposed by Iai et al. (1992). This model has been already applied to predict nonlinear soil behavior by Bonilla (2000) whose simulated results showed good agreement with the laboratory data in the VELACS program. We have applied this method to simulate ground motions at Jackson Lake Dam, Wyoming. We constructed a 140 m one-dimensional shear-wave velocity/depth profile for the sediment layers. The water table is at 2 m depth. The elastic material properties are based on in situ measurements. However, the parameters needed for the nonlinear response are taken from generic data for similar materials. To check for consistency we have constructed liquefaction resistance curves using a range of parameters that will be assumed for the soil column. These curves are compared with measured point values of the liquefaction resistance. To estimate the response at Jackson Lake Dam we have used strong motion records-JMA records from the 1995 Kobe earthquake and the Pleasant Valley Pumping Plant records from the 1983 Coalinga earthquake-as input motions at 140 m depth. We have also used synthetic ground motions computed from scenario earthquakes that might occur on the Teton Fault, very close to the dam. In the case of the synthetic input motions, the calculated shear strain approaches 20% in the sand layer. The material between 0 and 10 m shows maximum strain of about 1%, which still produces an increase in the fundamental period of the layer as well as a deamplification of the amplitude of the seismic waves.

3D Ground-Motion Simulations for Magnitude 9 Earthquakes on the Cascadia Megathrust: Sedimentary Basin Amplification, Rupture Directivity, and Ground-Motion Variability

NASA Astrophysics Data System (ADS)

Frankel, A. D.; Wirth, E. A.; Marafi, N.; Vidale, J. E.; Stephenson, W. J.

2017-12-01

We have produced broadband (0-10 Hz) synthetic seismograms for Mw 9 earthquakes on the Cascadia subduction zone by combining synthetics from 3D finite-difference simulations at low frequencies (≤ 1 Hz) and stochastic synthetics at high frequencies (≥ 1 Hz). These synthetic ground motions are being used to evaluate building response, liquefaction, and landslides, as part of the M9 Project of the University of Washington, in collaboration with the U.S. Geological Survey. The kinematic rupture model is composed of high stress drop sub-events with Mw 8, similar to those observed in the Mw 9.0 Tohoku, Japan and Mw 8.8 Maule, Chile earthquakes, superimposed on large background slip with lower slip velocities. The 3D velocity model is based on active and passive-source seismic tomography studies, seismic refraction and reflection surveys, and geologic constraints. The Seattle basin portion of the model has been validated by simulating ground motions from local earthquakes. We have completed 50 3D simulations of Mw 9 earthquakes using a variety of hypocenters, slip distributions, sub-event locations, down-dip limits of rupture, and other parameters. For sites not in deep sedimentary basins, the response spectra of the synthetics for 0.1-6.0 s are similar, on average, to the values from the BC Hydro ground motion prediction equations (GMPE). For periods of 7-10 s, the synthetic response spectra exceed these GMPE, partially due to the shallow dip of the plate interface. We find large amplification factors of 2-5 for response spectra at periods of 1-10 s for locations in the Seattle and Tacoma basins, relative to sites outside the basins. This amplification depends on the direction of incoming waves and rupture directivity. The basin amplification is caused by surface waves generated at basin edges from incoming S-waves, as well as amplification and focusing of S-waves and surface waves by the 3D basin structure. The inter-event standard deviation of response spectral amplitudes from the synthetics is larger for sites nearer the coast, because of their higher sensitivity to the sub-event locations and rupture directivity. The total standard deviations of spectral accelerations from 30 simulations for periods greater than 2 s are similar to those determined in the BC Hydro GMPE from strong-motion recordings in subduction zones.

Study of Rayleigh-Love coupling from Spatial Gradient Observation

NASA Astrophysics Data System (ADS)

Lin, C. J.; Hosseini, K.; Donner, S.; Vernon, F.; Wassermann, J. M.; Igel, H.

2017-12-01

We present a new method to study Rayleigh-Love coupling. Instead of using seismograms solely, where ground motion is recorded as function of time, we incorporate with rotation and strain, also called spatial gradient where ground is represented as function of distance. Seismic rotation and strain are intrinsic different observable wavefield so are helpful to indentify wave type and wave propagation. A Mw 7.5 earthquake on 29 March 2015 occurred in Kokopo, Papua New Guinea recorded by a dense seismic array at PFO, California are used to obtaint seismic spatial gradient. We firstly estimate time series of azimuthal direction and phase velocity of SH wave and Rayleigh wave by analyzing collocated seismograms and rotations. This result also compares with frequency wavenumber methods using a nearby ANZA seismic array. We find the direction of Rayleigh wave fits well with great-circle back azimuth during wave propagation, while the direction of Love wave deviates from that, especially when main energy of Rayleigh wave arrives. From the analysis of cross-correlation between areal strain and vertical rotation, it reveals that high coherence, either positive or negative, happens at the same time when Love wave deparate from great-circle path. We also find the observed azimuth of Love wave and polarized particle motion of Rayleigh wave fits well with the fast direction of Rayleigh wave, for the period of 50 secs. We conclude the cause of deviated azimuth of Love wave is due to Rayleigh-Love coupling, as surface wave propagates through the area with anisotropic structure.

Propagation and attenuation of Rayleigh waves in generalized thermoelastic media

NASA Astrophysics Data System (ADS)

Sharma, M. D.

2014-01-01

This study considers the propagation of Rayleigh waves in a generalized thermoelastic half-space with stress-free plane boundary. The boundary has the option of being either isothermal or thermally insulated. In either case, the dispersion equation is obtained in the form of a complex irrational expression due to the presence of radicals. This dispersion equation is rationalized into a polynomial equation, which is solvable, numerically, for exact complex roots. The roots of the dispersion equation are obtained after removing the extraneous zeros of this polynomial equation. Then, these roots are filtered out for the inhomogeneous propagation of waves decaying with depth. Numerical examples are solved to analyze the effects of thermal properties of elastic materials on the dispersion of existing surface waves. For these thermoelastic Rayleigh waves, the behavior of elliptical particle motion is studied inside and at the surface of the medium. Insulation of boundary does play a significant role in changing the speed, amplitude, and polarization of Rayleigh waves in thermoelastic media.

Three-dimensional manipulation of single cells using surface acoustic waves.

PubMed

Guo, Feng; Mao, Zhangming; Chen, Yuchao; Xie, Zhiwei; Lata, James P; Li, Peng; Ren, Liqiang; Liu, Jiayang; Yang, Jian; Dao, Ming; Suresh, Subra; Huang, Tony Jun

2016-02-09

The ability of surface acoustic waves to trap and manipulate micrometer-scale particles and biological cells has led to many applications involving "acoustic tweezers" in biology, chemistry, engineering, and medicine. Here, we present 3D acoustic tweezers, which use surface acoustic waves to create 3D trapping nodes for the capture and manipulation of microparticles and cells along three mutually orthogonal axes. In this method, we use standing-wave phase shifts to move particles or cells in-plane, whereas the amplitude of acoustic vibrations is used to control particle motion along an orthogonal plane. We demonstrate, through controlled experiments guided by simulations, how acoustic vibrations result in micromanipulations in a microfluidic chamber by invoking physical principles that underlie the formation and regulation of complex, volumetric trapping nodes of particles and biological cells. We further show how 3D acoustic tweezers can be used to pick up, translate, and print single cells and cell assemblies to create 2D and 3D structures in a precise, noninvasive, label-free, and contact-free manner.

Wave friction factor rediscovered

NASA Astrophysics Data System (ADS)

Le Roux, J. P.

2012-02-01

The wave friction factor is commonly expressed as a function of the horizontal water particle semi-excursion ( A wb) at the top of the boundary layer. A wb, in turn, is normally derived from linear wave theory by {{U_{{wb}}/T_{{w}}}}{{2π }} , where U wb is the maximum water particle velocity measured at the top of the boundary layer and T w is the wave period. However, it is shown here that A wb determined in this way deviates drastically from its real value under both linear and non-linear waves. Three equations for smooth, transitional and rough boundary conditions, respectively, are proposed to solve this problem, all three being a function of U wb, T w, and δ, the thickness of the boundary layer. Because these variables can be determined theoretically for any bottom slope and water depth using the deepwater wave conditions, there is no need to physically measure them. Although differing substantially from many modern attempts to define the wave friction factor, the results coincide with equations proposed in the 1960s for either smooth or rough boundary conditions. The findings also confirm that the long-held notion of circular water particle motion down to the bottom in deepwater conditions is erroneous, the motion in fact being circular at the surface and elliptical at depth in both deep and shallow water conditions, with only horizontal motion at the top of the boundary layer. The new equations are incorporated in an updated version (WAVECALC II) of the Excel program published earlier in this journal by Le Roux et al. Geo-Mar Lett 30(5): 549-560, (2010).

Sound transmission in porcine thorax through airway insonification.

PubMed

Peng, Ying; Dai, Zoujun; Mansy, Hansen A; Henry, Brian M; Sandler, Richard H; Balk, Robert A; Royston, Thomas J

2016-04-01

Many pulmonary injuries and pathologies may lead to structural and functional changes in the lungs resulting in measurable sound transmission changes on the chest surface. Additionally, noninvasive imaging of externally driven mechanical wave motion in the chest (e.g., using magnetic resonance elastography) can provide information about lung structural property changes and, hence, may be of diagnostic value. In the present study, a comprehensive computational simulation (in silico) model was developed to simulate sound wave propagation in the airways, lung, and chest wall under normal and pneumothorax conditions. Experiments were carried out to validate the model. Here, sound waves with frequency content from 50 to 700 Hz were introduced into airways of five porcine subjects via an endotracheal tube, and transmitted waves were measured by scanning laser Doppler vibrometry at the chest wall surface. The computational model predictions of decreased sound transmission with pneumothorax were consistent with experimental measurements. The in silico model can also be used to visualize wave propagation inside and on the chest wall surface for other pulmonary pathologies, which may help in developing and interpreting diagnostic procedures that utilize sound and vibration.

Sound transmission in porcine thorax through airway insonification

PubMed Central

Dai, Zoujun; Mansy, Hansen A.; Henry, Brian M.; Sandler, Richard H.; Balk, Robert A.; Royston, Thomas J.

2015-01-01

Many pulmonary injuries and pathologies may lead to structural and functional changes in the lungs resulting in measurable sound transmission changes on the chest surface. Additionally, noninvasive imaging of externally driven mechanical wave motion in the chest (e.g., using magnetic resonance elastography) can provide information about lung structural property changes and, hence, may be of diagnostic value. In the present study, a comprehensive computational simulation (in silico) model was developed to simulate sound wave propagation in the airways, lung, and chest wall under normal and pneumothorax conditions. Experiments were carried out to validate the model. Here, sound waves with frequency content from 50 to 700 Hz were introduced into airways of five porcine subjects via an endotracheal tube, and transmitted waves were measured by scanning laser Doppler vibrometry at the chest wall surface. The computational model predictions of decreased sound transmission with pneumothorax were consistent with experimental measurements. The in silico model can also be used to visualize wave propagation inside and on the chest wall surface for other pulmonary pathologies, which may help in developing and interpreting diagnostic procedures that utilize sound and vibration. PMID:26280512

Seismic interferometry of railroad induced ground motions: body and surface wave imaging

NASA Astrophysics Data System (ADS)

Quiros, Diego A.; Brown, Larry D.; Kim, Doyeon

2016-04-01

Seismic interferometry applied to 120 hr of railroad traffic recorded by an array of vertical component seismographs along a railway within the Rio Grande rift has recovered surface and body waves characteristic of the geology beneath the railway. Linear and hyperbolic arrivals are retrieved that agree with surface (Rayleigh), direct and reflected P waves observed by nearby conventional seismic surveys. Train-generated Rayleigh waves span a range of frequencies significantly higher than those recovered from typical ambient noise interferometry studies. Direct P-wave arrivals have apparent velocities appropriate for the shallow geology of the survey area. Significant reflected P-wave energy is also present at relatively large offsets. A common midpoint stack produces a reflection image consistent with nearby conventional reflection data. We suggest that for sources at the free surface (e.g. trains) increasing the aperture of the array to record wide angle reflections, in addition to longer recording intervals, might allow the recovery of deeper geological structure from railroad traffic. Frequency-wavenumber analyses of these recordings indicate that the train source is symmetrical (i.e. approaching and receding) and that deeper refracted energy is present although not evident in the time-offset domain. These results confirm that train-generated vibrations represent a practical source of high-resolution subsurface information, with particular relevance to geotechnical and environmental applications.

Seismic-hazard maps and time histories for the commonwealth of Kentucky.

DOT National Transportation Integrated Search

2008-06-01

The ground-motion hazard maps and time histories for three earthquake scenarios, expected earthquakes, probable earthquakes, and maximum credible earthquakes on the free surface in hard rock (shear-wave velocity >1,500 m/s), were derived using the de...

A Vs30-derived Near-surface Seismic Velocity Model

NASA Astrophysics Data System (ADS)

Ely, G. P.; Jordan, T. H.; Small, P.; Maechling, P. J.

2010-12-01

Shallow material properties, S-wave velocity in particular, strongly influence ground motions, so must be accurately characterized for ground-motion simulations. Available near-surface velocity information generally exceeds that which is accommodated by crustal velocity models, such as current versions of the SCEC Community Velocity Model (CVM-S4) or the Harvard model (CVM-H6). The elevation-referenced CVM-H voxel model introduces rasterization artifacts in the near-surface due to course sample spacing, and sample depth dependence on local topographic elevation. To address these issues, we propose a method to supplement crustal velocity models, in the upper few hundred meters, with a model derived from available maps of Vs30 (the average S-wave velocity down to 30 meters). The method is universally applicable to regions without direct measures of Vs30 by using Vs30 estimates from topographic slope (Wald, et al. 2007). In our current implementation for Southern California, the geology-based Vs30 map of Wills and Clahan (2006) is used within California, and topography-estimated Vs30 is used outside of California. Various formulations for S-wave velocity depth dependence, such as linear spline and polynomial interpolation, are evaluated against the following priorities: (a) capability to represent a wide range of soil and rock velocity profile types; (b) smooth transition to the crustal velocity model; (c) ability to reasonably handle poor spatial correlation of Vs30 and crustal velocity data; (d) simplicity and minimal parameterization; and (e) computational efficiency. The favored model includes cubic and square-root depth dependence, with the model extending to a depth of 350 meters. Model parameters are fit to Boore and Joyner's (1997) generic rock profile as well as CVM-4 soil profiles for the NEHRP soil classification types. P-wave velocity and density are derived from S-wave velocity by the scaling laws of Brocher (2005). Preliminary assessment of the new model is preformed with ground motion simulations for a selection of likely M > 7 scenario events for Southern California (as define by the SCEC Big Ten project).

Fractional Whirl Motion in Wave Journal Bearings

NASA Technical Reports Server (NTRS)

Dimofte, Florin; Hendricks, Robert C.

1996-01-01

Unloaded gas, plain journal bearings experience sub-synchronous whirl motion due to fluid film instabilities and wall contact usually occurs immediately after the onset of the whirl motion. An alternative is the wave journal bearing which significantly improves bearing stability. The predicted threshold where the sub-synchronous whirl motion starts was well confirmed by the experimental observation. In addition, both a two-wave and a three-wave journal bearing can operate free of sub-synchronous whirl motion over a large range in speeds. When the sub-synchronous whirl motion occurs, both the two-wave and three-wave bearing can run in a whirl orbit well within the bearing clearance. At large clearances and wave amplitudes a two-wave bearing, unliKe other bearings, can exhibit a sub-synchronous whirl movement at both low and high speeds, but can run extremely stable and without whirl at intermediate speeds. Moreover, in these cases, the whirl frequencies are close to a quarter of the synchronous speed. The three-wave bearing can exhibit sub-synchronous whirl motion only after a specific threshold when the speed increases and the whirl frequencies are close to half of the synchronous speed.

Electrogastrograms during motion sickness in fasted and fed subjects

NASA Technical Reports Server (NTRS)

Stewart, John J.; Wood, Mary J.; Wood, Charles D.

1989-01-01

Seven human volunteers were subjected to stressful Coriolis stimulation (rotating chair) either during the fasted state or following the ingestion of yogurt (6 oz). Subjects tested after yogurt reached a malaise-III (M-III) endpoint of motion sickness after significantly (p smaller than 0.01) fewer head movements than subjects tested in the fasted state. Surface electrogastrogram (EGG) recordings at M-III were similar for both dietary stats and consisted of a brief period of tachygastria, followed by a period of low-amplitude EGG waves. Ingestion of yogurt enhanced susceptibility to motion sickness but did not affect the associated pattern of EGG.

Seismological investigation of earthquakes in the New Madrid seismic zone and the northeastern extent of the New Madrid seismic zone: Final report, September 1981-December 1986

DOE Office of Scientific and Technical Information (OSTI.GOV)

Herrmann, R.B.; Taylor, K.; Nguyen, B.

1988-07-01

Earthquake activity in the Central Mississippi Valley has been monitored by an eight station seismograph network in the Wabash River Valley of southeastern Illinois and by a six station seismograph network in the New Madrid seismic zone. This network is a major component of a larger network in the region, jointly sponsored by the NRC, USGS, universities and states. During the time period of the contract, October 1981 through December 1986, 1206 earthquakes were located in the Central Mississippi Valley, of which 808 were in the New Madrid, Missouri area. Significant earthquakes studied in detail occurred in northeastern Ohio onmore » January 31, 1986 and in southeastern Illinois on June 10, 1987. Focal mechanisms have been calculated for the 10 June 1987 southern Illinois earthquake using both P-wave first motions and long-period surface-wave spectral amplitude data. The long-period surface-wave and strong ground motion accelerogram recordings of the January 3, 1986, northeastern Ohio earthquake were used to estimate the focal mechanism and source time function of the source.reverse arrow« less

Blind shear-wave velocity comparison of ReMi and MASW results with boreholes to 200 m in Santa Clara Valley: Implications for earthquake ground-motion assessment

USGS Publications Warehouse

Stephenson, W.J.; Louie, J.N.; Pullammanappallil, S.; Williams, R.A.; Odum, J.K.

2005-01-01

Multichannel analysis of surface waves (MASW) and refraction microtremor (ReMi) are two of the most recently developed surface acquisition techniques for determining shallow shear-wave velocity. We conducted a blind comparison of MASW and ReMi results with four boreholes logged to at least 260 m for shear velocity in Santa Clara Valley, California, to determine how closely these surface methods match the downhole measurements. Average shear-wave velocity estimates to depths of 30, 50, and 100 m demonstrate that the surface methods as implemented in this study can generally match borehole results to within 15% to these depths. At two of the boreholes, the average to 100 m depth was within 3%. Spectral amplifications predicted from the respective borehole velocity profiles similarly compare to within 15 % or better from 1 to 10 Hz with both the MASW and ReMi surface-method velocity profiles. Overall, neither surface method was consistently better at matching the borehole velocity profiles or amplifications. Our results suggest MASW and ReMi surface acquisition methods can both be appropriate choices for estimating shearwave velocity and can be complementary to each other in urban settings for hazards assessment.

Acousto-optical interaction of surface acoustic and optical waves in a two-dimensional phoxonic crystal hetero-structure cavity.

PubMed

Ma, Tian-Xue; Zou, Kui; Wang, Yue-Sheng; Zhang, Chuanzeng; Su, Xiao-Xing

2014-11-17

Phoxonic crystal is a promising material for manipulating sound and light simultaneously. In this paper, we theoretically demonstrate the propagation of acoustic and optical waves along the truncated surface of a two-dimensional square-latticed phoxonic crystal. Further, a phoxonic crystal hetero-structure cavity is proposed, which can simultaneously confine surface acoustic and optical waves. The interface motion and photoelastic effects are taken into account in the acousto-optical coupling. The results show obvious shifts in eigenfrequencies of the photonic cavity modes induced by different phononic cavity modes. The symmetry of the phononic cavity modes plays a more important role in the single-phonon exchange process than in the case of the multi-phonon exchange. Under the same deformation, the frequency shift of the photonic transverse electric mode is larger than that of the transverse magnetic mode.

Detection of ground motions using high-rate GPS time-series

NASA Astrophysics Data System (ADS)

Psimoulis, Panos A.; Houlié, Nicolas; Habboub, Mohammed; Michel, Clotaire; Rothacher, Markus

2018-05-01

Monitoring surface deformation in real-time help at planning and protecting infrastructures and populations, manage sensitive production (i.e. SEVESO-type) and mitigate long-term consequences of modifications implemented. We present RT-SHAKE, an algorithm developed to detect ground motions associated with landslides, sub-surface collapses, subsidences, earthquakes or rock falls. RT-SHAKE detects first transient changes in individual GPS time series before investigating for spatial correlation(s) of observations made at neighbouring GPS sites and eventually issue a motion warning. In order to assess our algorithm on fast (seconds to minute), large (from 1 cm to meters) and spatially consistent surface motions, we use the 1 Hz GEONET GNSS network data of the Tohoku-Oki MW9.0 2011 as a test scenario. We show the delay of detection of seismic wave arrival by GPS records is of ˜10 seconds with respect to an identical analysis based on strong-motion data and this time delay depends on the level of the time-variable noise. Nevertheless, based on the analysis of the GPS network noise level and ground motion stochastic model, we show that RT-SHAKE can narrow the range of earthquake magnitude, by setting a lower threshold of detected earthquakes to MW6.5-7, if associated with a real-time automatic earthquake location system.

Analysis of X-band radar images for the detection of the reflected and diffracted waves in coastal zones

NASA Astrophysics Data System (ADS)

Ludeno, Giovanni; Natale, Antonio; Soldovieri, Francesco; Vicinanza, Diego; Serafino, Francesco

2014-05-01

The observation of nearshore waves and the knowledge of the sea state parameters can play a crucial role for the safety of harbors and ocean engineering. In the last two decades, different algorithms for the estimation of sea state parameters, surface currents and bathymetry from X-band radar data have been developed and validated [1, 2]. The retrieval of ocean wave parameters such as significant height, period, direction and wavelength of the dominant wave is based on the spectral analysis of data sequences collected by nautical X-band radars [3]. In particular, the reconstruction of the wave motion is carried out through the inversion procedure explained in [1-3], which exploits the dispersion relationship to define a band pass filter used to separate the energy associated with the ocean waves from the background noise. It is worth to note that the shape of such a band pass filter depends upon the value of both the surface currents and bathymetry; in our reconstruction algorithm these parameters are estimated through the (Normalized Scalar Product) procedure [1], which outperforms other existing methods (e.g., the Least Squares) [4]. From the reconstructed wave elevation sequences we can get the directional spectrum that provides useful information (i.e., wavelength, period, direction and amplitude) relevant to the main waves contributing to the wave motion. Of course, in coastal zones a number of diffraction and reflection phenomena can be observed, due to sea-waves impinging obstacles as jetties, breakwaters and boats. In the present paper we want to show the capability to detect reflected and diffracted sea-waves offered by the processing of X-band radar data. Further details relevant to the obtained results will be provided in the full paper and at the conference time. References [1] F. Serafino, C. Lugni, F. Soldovieri, "A novel strategy for the surface current determination from marine X-Band radar data", IEEE Geosci. and Remote Sensing Letters, vol. 7, no.2, pp. 231-235, April 2010. [2] Senet, C. M., Seemann, J., Flampouris, S., and Ziemer, F. (2008). Determination of bathymetric and current maps by the method DiSC based on the analysis of nautical X-Band radar image sequences of the sea surface (November 2007). IEEE Trans. on Geoscience and Remote Sensing, 46(8), 2267-2279. [3] F. Ziemer, and W. Rosenthal, "Directional spectra from shipboard navigation radar during LEWEX". Directional Ocean Wave Spectra: Measuring, Modeling, Predicting, and Applying, 1991 R. C. Beal, Ed., The Johns Hopkins University Press, pp. 125-127. [4] Weimin Huang ; Gill, E.," Surface Current Measurement Under Low Sea State Using Dual Polarized X-Band Nautical Radar", Selected Topics in Applied Earth Observations and Remote Sensing, IEEE Journal of, vol. 5, no.6, page 186-1873, 2012.

Water entry and exit of horizontal circular cylinders

NASA Astrophysics Data System (ADS)

Greenhow, M.; Moyo, S.

This paper describes fully nonlinear two-dimensional numerical calculations of the free-surface deformations of initially calm water caused by the forced motion of totally or partially submerged horizontal circular cylinders. The paper considers the following. (i) Totally submerged cylinders moving with constant velocity in vertical, horizontal or combined motions. Results are compared with the small-time asymptotic solution obtained by Tyvand and Milohin 1995. Their results, which are taken to third-order (which is when gravity terms first appear in the expansions), are in excellent agreement with the numerical calculations for small times; beyond this only the numerical method gives accurate results until the free surface breaks or the cylinder emerges from the free surface. Breaking can occur during exit due to strongly negative pressures arising on the cylinder surface, or during the downwards motion causing a free-surface depression which closes up rapidly, forming splashes. Downwards motion is also shown to give rise to high-frequency waves in some cases. (ii) The free-surface deformations, pressures and forces acting on a cylinder in vertical or oblique forced motion during engulfment when it submerges from being initially half-submerged. The initial stages, when the cylinder still pierces the free surface, specify the initial conditions for a separate program for a completely submerged body, thereby allowing complete engulfment to be studied. The free surface closes up violently over the top of the cylinder resulting in jet flow, which, while difficult to handle numerically, has been shown to be insignificant for the bulk flow and the cylinder pressures and forces.

Physical limits on ground motion at Yucca Mountain

USGS Publications Warehouse

Andrews, D.J.; Hanks, T.C.; Whitney, J.W.

2007-01-01

Physical limits on possible maximum ground motion at Yucca Mountain, Nevada, the designated site of a high-level radioactive waste repository, are set by the shear stress available in the seismogenic depth of the crust and by limits on stress change that can propagate through the medium. We find in dynamic deterministic 2D calculations that maximum possible horizontal peak ground velocity (PGV) at the underground repository site is 3.6 m/sec, which is smaller than the mean PGV predicted by the probabilistic seismic hazard analysis (PSHA) at annual exceedance probabilities less than 10-6 per year. The physical limit on vertical PGV, 5.7 m/sec, arises from supershear rupture and is larger than that from the PSHA down to 10-8 per year. In addition to these physical limits, we also calculate the maximum ground motion subject to the constraint of known fault slip at the surface, as inferred from paleoseismic studies. Using a published probabilistic fault displacement hazard curve, these calculations provide a probabilistic hazard curve for horizontal PGV that is lower than that from the PSHA. In all cases the maximum ground motion at the repository site is found by maximizing constructive interference of signals from the rupture front, for physically realizable rupture velocity, from all parts of the fault. Vertical PGV is maximized for ruptures propagating near the P-wave speed, and horizontal PGV is maximized for ruptures propagating near the Rayleigh-wave speed. Yielding in shear with a Mohr-Coulomb yield condition reduces ground motion only a modest amount in events with supershear rupture velocity, because ground motion consists primarily of P waves in that case. The possibility of compaction of the porous unsaturated tuffs at the higher ground-motion levels is another attenuating mechanism that needs to be investigated.

Characterizing directional variations in long-period ground motion amplifications in the Kanto Basin, Japan

NASA Astrophysics Data System (ADS)

Mukai, Y.; Furumura, T.; Maeda, T.

2017-12-01

In the Kanto Basin (including Tokyo in Japan), the long-period (T=3-10 s) ground motions are strongly developed when large earthquakes occur nearby. The amplitude of the long-period ground motion in the basin varies strongly among earthquakes; it is tremendous from the earthquakes in Niigata (northwest of Kanto), but is several times weaker from the earthquakes in Tohoku (north of Kanto). In this study, we examined the cause of such azimuthal-dependent amplitude variation for the 2004 Niigata Chuetsu (M6.8) and the 2011 Fukushima Hamadori (M7.0) earthquake based on numerical simulations of seismic wave propagation by the finite-difference method. We first examined the non-isotropic source-radiation effect of these events. By performing numerical simulations for different strike angles of these source faults, significant variation in amplitude of the long-period ground motions were observed in Tokyo for both the events. Among tested strike angles, the source of the 2004 event (strike = 212 deg.) produced the largest long-period ground motion due to strong radiation of surface wave towards the Kanto Basin, while the 2011 event (strike = 132 deg.) produced the least. The minimum-to-maximum ratio of their amplitudes with respect to strike angle is about 2 and 1.3, respectively. These investigations suggest the source radiation effect considerably contributes to the variations of the long-period ground motions. We then examined the effect of the 3D structure of the Kanto Basin on the generation of the long-period ground motion. For the 2004 event, we found that the long-period signal first arrives at the central Tokyo from the western edge of the Kanto Basin. Then, later signals containing both the Rayleigh and Love waves were amplified dramatically due to the localized low-velocity structure to the northwestern part of the basin. On the other hand, in the case of the 2011 event, the seismic waves propagating towards the basin were dissipated significantly as it travels over the ridge structure of the basement in the northern part of the basin, where the seismic wave speed is faster than the surroundings. Therefore, the large variation of the long-period ground motion among earthquakes occurs due to the combined effects of source radiation and propagation properties in the 3D heterogeneous structure of the Kanto Basin.

Wave impedance selection for passivity-based bilateral teleoperation

NASA Astrophysics Data System (ADS)

D'Amore, Nicholas John

When a task must be executed in a remote or dangerous environment, teleoperation systems may be employed to extend the influence of the human operator. In the case of manipulation tasks, haptic feedback of the forces experienced by the remote (slave) system is often highly useful in improving an operator's ability to perform effectively. In many of these cases (especially teleoperation over the internet and ground-to-space teleoperation), substantial communication latency exists in the control loop and has the strong tendency to cause instability of the system. The first viable solution to this problem in the literature was based on a scattering/wave transformation from transmission line theory. This wave transformation requires the designer to select a wave impedance parameter appropriate to the teleoperation system. It is widely recognized that a small value of wave impedance is well suited to free motion and a large value is preferable for contact tasks. Beyond this basic observation, however, very little guidance exists in the literature regarding the selection of an appropriate value. Moreover, prior research on impedance selection generally fails to account for the fact that in any realistic contact task there will simultaneously exist contact considerations (perpendicular to the surface of contact) and quasi-free-motion considerations (parallel to the surface of contact). The primary contribution of the present work is to introduce an approximate linearized optimum for the choice of wave impedance and to apply this quasi-optimal choice to the Cartesian reality of such a contact task, in which it cannot be expected that a given joint will be either perfectly normal to or perfectly parallel to the motion constraint. The proposed scheme selects a wave impedance matrix that is appropriate to the conditions encountered by the manipulator. This choice may be implemented as a static wave impedance value or as a time-varying choice updated according to the instantaneous conditions encountered. A Lyapunov-like analysis is presented demonstrating that time variation in wave impedance will not violate the passivity of the system. Experimental trials, both in simulation and on a haptic feedback device, are presented validating the technique. Consideration is also given to the case of an uncertain environment, in which an a priori impedance choice may not be possible.

Ultrafast Imaging of Chiral Surface Plasmon by Photoemission Electron Microscopy

NASA Astrophysics Data System (ADS)

Dai, Yanan; Dabrowski, Maciej; Petek, Hrvoje

We employ Time-Resolved Photoemission Electron Microscopy (TR-PEEM) to study surface plasmon polariton (SPP) wave packet dynamics launched by tunable (VIS-UV) femtosecond pulses of various linear and circular polarizations. The plasmonic structures are micron size single-crystalline Ag islands grown in situ on Si surfaces and characterized by Low Energy Electron Microscopy (LEEM). The local fields of plasmonic modes enhance two and three photon photoemission (2PP and 3PP) at the regions of strong field enhancement. Imaging of the photoemission signal with PEEM electron optics thus images the plasmonic fields excited in the samples. The observed PEEM images with left and right circularly polarized light show chiral images, which is a consequence of the transverse spin momentum of surface plasmon. By changing incident light polarization, the plasmon interference pattern shifts with light ellipticity indicating a polarization dependent excitation phase of SPP. In addition, interferometric-time resolved measurements record the asymmetric SPP wave packet motion in order to characterize the dynamical properties of chiral SPP wave packets.

Fluid film force control in lubricated journal bearings by means of a travelling wave generated with a piezoelectric actuators' system

NASA Astrophysics Data System (ADS)

Iula, Antonio; Lamberti, Nicola; Savoia, Alessandro; Caliano, Giosue

2012-05-01

In this work an experimental evaluation of the possiblity to influence and control the fluid film forces in the gap of a lubricated journal bearing by means of a rotating travelling wave is carried out. The travellig wave is generated by two power actuators opportunely positioned on the outer surface of the bearing and electrically driven with a phase shift of 90°. Each transducer is designed to work at the natural frequency of the radial nonaxisymmetrical mode 0-5 (23.6 kHz). Experimental results show that the travelling wave is capable to control the motion of an oil drop on the inner surface of the bearing and that it is capable to put in rotation a rotor layed on the drop oil via the viscous forces in the oil drop itself.

Seismic Velocity Measurements at Expanded Seismic Network Sites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Woolery, Edward W; Wang, Zhenming

2005-01-01

Structures at the Paducah Gaseous Diffusion Plant (PGDP), as well as at other locations in the northern Jackson Purchase of western Kentucky may be subjected to large far-field earthquake ground motions from the New Madrid seismic zone, as well as those from small and moderate-sized local events. The resultant ground motion a particular structure is exposed from such event will be a consequence of the earthquake magnitude, the structures' proximity to the event, and the dynamic and geometrical characteristics of the thick soils upon which they are, of necessity, constructed. This investigation evaluated the latter. Downhole and surface (i.e., refractionmore » and reflection) seismic velocity data were collected at the Kentucky Seismic and Strong-Motion Network expansion sites in the vicinity of the Paducah Gaseous Diffusion Plant (PGDP) to define the dynamic properties of the deep sediment overburden that can produce modifying effects on earthquake waves. These effects are manifested as modifications of the earthquake waves' amplitude, frequency, and duration. Each of these three ground motion manifestations is also fundamental to the assessment of secondary earthquake engineering hazards such as liquefaction.« less

Improved Shear Wave Motion Detection Using Pulse-Inversion Harmonic Imaging with a Phased Array Transducer

PubMed Central

Song, Pengfei; Zhao, Heng; Urban, Matthew W.; Manduca, Armando; Pislaru, Sorin V.; Kinnick, Randall R.; Pislaru, Cristina; Greenleaf, James F.; Chen, Shigao

2013-01-01

Ultrasound tissue harmonic imaging is widely used to improve ultrasound B-mode imaging quality thanks to its effectiveness in suppressing imaging artifacts associated with ultrasound reverberation, phase aberration, and clutter noise. In ultrasound shear wave elastography (SWE), because the shear wave motion signal is extracted from the ultrasound signal, these noise sources can significantly deteriorate the shear wave motion tracking process and consequently result in noisy and biased shear wave motion detection. This situation is exacerbated in in vivo SWE applications such as heart, liver, and kidney. This paper, therefore, investigated the possibility of implementing harmonic imaging, specifically pulse-inversion harmonic imaging, in shear wave tracking, with the hypothesis that harmonic imaging can improve shear wave motion detection based on the same principles that apply to general harmonic B-mode imaging. We first designed an experiment with a gelatin phantom covered by an excised piece of pork belly and show that harmonic imaging can significantly improve shear wave motion detection by producing less underestimated shear wave motion and more consistent shear wave speed measurements than fundamental imaging. Then, a transthoracic heart experiment on a freshly sacrificed pig showed that harmonic imaging could robustly track the shear wave motion and give consistent shear wave speed measurements while fundamental imaging could not. Finally, an in vivo transthoracic study of seven healthy volunteers showed that the proposed harmonic imaging tracking sequence could provide consistent estimates of the left ventricular myocardium stiffness in end-diastole with a general success rate of 80% and a success rate of 93.3% when excluding the subject with Body Mass Index (BMI) higher than 25. These promising results indicate that pulse-inversion harmonic imaging can significantly improve shear wave motion tracking and thus potentially facilitate more robust assessment of tissue elasticity by SWE. PMID:24021638

Robust laser-based detection of Lamb waves using photo-EMF sensors

NASA Astrophysics Data System (ADS)

Klein, Marvin B.; Bacher, Gerald D.

1998-03-01

Lamb waves are easily generated and detected using laser techniques. It has been shown that both symmetric and antisymmetric modes can be produced, using single-spot and phased array generation. Detection has been demonstrated with Michelson interferometers, but these instruments can not function effectively on rough surfaces. By contrast, the confocal Fabry-Perot interferometer can interrogate rough surfaces, but generally is not practical for operation below 300 kHz. In this paper we will present Lamb wave data on a number of parts using a robust, adaptive receiver based on photo-emf detection. This receiver has useful sensitivity down to at least 100 kHz, can process speckled beams and can be easily configured to measure both out-of-plane and in- plane motion with a single probe beam.

Energy Harvesting from Surface River/Ocean Waves

NASA Astrophysics Data System (ADS)

Cai, Wenzheng

The renewable energy is an important subject especially today as the world is facing the results of the pollution and depletion of the conventional energy resources. Around 70% of the Earth's surface is covered by water where the energy of the waves/tides could be used as alternative source of energy that is sustainable and environmental friendly. Most of the research efforts are focused on the development of the large-scale technologies that can operate in the open Ocean. The potential of the low-frequency and small-amplitude wave condition in shallow rivers and lakes where most of the world wave energy exists has not been explored yet. The objective of the current study is to design and develop new concepts for wave energy extraction, which depend on oscillatory wave motion and have the ability to convert the small and medium waves. The proposed devices are self-generating without any external sources, which makes them lightweight and naturally floating on the surface of the water. Feasibility studies of both designs were performed using numerical modeling and field experiments. The final prototypes achieved power output of 5.0+/-0.6mW and 0.25+/-0.01mW, respectively. Array systems implementing both concepts were also introduced to improve the performance of the devices.

Nonlinear dynamics of a two-dimensional Wigner solid on superfluid helium

NASA Astrophysics Data System (ADS)

Monarkha, Yu. P.

2018-04-01

Nonlinear dynamics and transport properties of a 2D Wigner solid (WS) on the free surface of superfluid helium are theoretically studied. The analysis is nonperturbative in the amplitude of the WS velocity. An anomalous nonlinear response of the liquid helium surface to the oscillating motion of the WS is shown to appear when the driving frequency is close to subharmonics of the frequency of a capillary wave (ripplon) whose wave vector coincides with a reciprocal-lattice vector. As a result, the effective mass of surface dimples formed under electrons and the kinetic friction acquire sharp anomalies in the low-frequency range, which affects the mobility and magnetoconductivity of the WS. The results obtained here explain a variety of experimental observations reported previously.

Precise measurement of surface plasmon forces at a metal-dielectric interface using a calibrated evanescent wave

NASA Astrophysics Data System (ADS)

Liu, Lulu; Woolf, Alex

2015-03-01

By observing the motion of an optically trapped microscopic colloid, sub-piconewton static and dynamical forces have been measured using a technique called photonic force microscopy. This technique, though potentially powerful, has in the past struggled to make precise measurements in the vicinity of a reflective or metallic interface, due to distortions of the optical field. We introduce a new in-situ, contact-free calibration method for particle tracking using an evanescent wave, and demonstrate its expanded capability by the precise measurement of forces of interaction between a single colloid and the optical field generated by a propagating surface plasmon polariton on gold.

A deformable surface model for real-time water drop animation.

PubMed

Zhang, Yizhong; Wang, Huamin; Wang, Shuai; Tong, Yiying; Zhou, Kun

2012-08-01

A water drop behaves differently from a large water body because of its strong viscosity and surface tension under the small scale. Surface tension causes the motion of a water drop to be largely determined by its boundary surface. Meanwhile, viscosity makes the interior of a water drop less relevant to its motion, as the smooth velocity field can be well approximated by an interpolation of the velocity on the boundary. Consequently, we propose a fast deformable surface model to realistically animate water drops and their flowing behaviors on solid surfaces. Our system efficiently simulates water drop motions in a Lagrangian fashion, by reducing 3D fluid dynamics over the whole liquid volume to a deformable surface model. In each time step, the model uses an implicit mean curvature flow operator to produce surface tension effects, a contact angle operator to change droplet shapes on solid surfaces, and a set of mesh connectivity updates to handle topological changes and improve mesh quality over time. Our numerical experiments demonstrate a variety of physically plausible water drop phenomena at a real-time rate, including capillary waves when water drops collide, pinch-off of water jets, and droplets flowing over solid materials. The whole system performs orders-of-magnitude faster than existing simulation approaches that generate comparable water drop effects.

Evaluation of site effects on ground motions based on equivalent linear site response analysis and liquefaction potential in Chennai, south India

NASA Astrophysics Data System (ADS)

Nampally, Subhadra; Padhy, Simanchal; Trupti, S.; Prabhakar Prasad, P.; Seshunarayana, T.

2018-05-01

We study local site effects with detailed geotechnical and geophysical site characterization to evaluate the site-specific seismic hazard for the seismic microzonation of the Chennai city in South India. A Maximum Credible Earthquake (MCE) of magnitude 6.0 is considered based on the available seismotectonic and geological information of the study area. We synthesized strong ground motion records for this target event using stochastic finite-fault technique, based on a dynamic corner frequency approach, at different sites in the city, with the model parameters for the source, site, and path (attenuation) most appropriately selected for this region. We tested the influence of several model parameters on the characteristics of ground motion through simulations and found that stress drop largely influences both the amplitude and frequency of ground motion. To minimize its influence, we estimated stress drop after finite bandwidth correction, as expected from an M6 earthquake in Indian peninsula shield for accurately predicting the level of ground motion. Estimates of shear wave velocity averaged over the top 30 m of soil (V S30) are obtained from multichannel analysis of surface wave (MASW) at 210 sites at depths of 30 to 60 m below the ground surface. Using these V S30 values, along with the available geotechnical information and synthetic ground motion database obtained, equivalent linear one-dimensional site response analysis that approximates the nonlinear soil behavior within the linear analysis framework was performed using the computer program SHAKE2000. Fundamental natural frequency, Peak Ground Acceleration (PGA) at surface and rock levels, response spectrum at surface level for different damping coefficients, and amplification factors are presented at different sites of the city. Liquefaction study was done based on the V S30 and PGA values obtained. The major findings suggest show that the northeast part of the city is characterized by (i) low V S30 values (< 200 m/s) associated with alluvial deposits, (ii) relatively high PGA value, at the surface, of about 0.24 g, and (iii) factor of safety and liquefaction below unity at three sites (no. 12, no. 37, and no. 70). Thus, this part of the city is expected to experience damage for the expected M6 target event.

Slippery Liquid-Infused Porous Surfaces and Droplet Transportation by Surface Acoustic Waves

NASA Astrophysics Data System (ADS)

Luo, J. T.; Geraldi, N. R.; Guan, J. H.; McHale, G.; Wells, G. G.; Fu, Y. Q.

2017-01-01

On a solid surface, a droplet of liquid will stick due to the capillary adhesion, and this causes low droplet mobility. To reduce contact line pinning, surface chemistry can be coupled to micro- and/or nanostructures to create superhydrophobic surfaces on which a droplet balls up into an almost spherical shape, thus, minimizing the contact area. Recent progress in soft matter has now led to alternative lubricant-impregnated surfaces capable of almost zero contact line pinning and high droplet mobility without causing droplets to ball up and minimize the contact area. Here we report an approach to surface-acoustic-wave- (SAW) actuated droplet transportation enabled using such a surface. These surfaces maintain the contact area required for efficient energy and momentum transfer of the wave energy into the droplet while achieving high droplet mobility and a large footprint, therefore, reducing the threshold power required to induce droplet motion. In our approach, we use a slippery layer of lubricating oil infused into a self-assembled porous hydrophobic layer, which is significantly thinner than the SAW wavelength, and avoid damping of the wave. We find a significant reduction (up to 85%) in the threshold power for droplet transportation compared to that using a conventional surface-treatment method. Moreover, unlike droplets on superhydrophobic surfaces, where interaction with the SAW induces a transition from a Cassie-Baxter state to a Wenzel state, the droplets on our liquid-impregnated surfaces remain in a mobile state after interaction with the SAW.

Experimental Modeling of Dynamic Shallow Dip-Slip Faulting

NASA Astrophysics Data System (ADS)

Uenishi, K.

2010-12-01

In our earlier study (AGU 2005, SSJ 2005, JPGU 2006), using a finite difference technique, we have conducted some numerical simulations related to the source dynamics of shallow dip-slip earthquakes, and suggested the possibility of the existence of corner waves, i.e., shear waves that carry concentrated kinematic energy and generate extremely strong particle motions on the hanging wall of a nonvertical fault. In the numerical models, a dip-slip fault is located in a two-dimensional, monolithic linear elastic half space, and the fault plane dips either vertically or 45 degrees. We have investigated the seismic wave field radiated by crack-like rupture of this straight fault. If the fault rupture, initiated at depth, arrests just below or reaches the free surface, four Rayleigh-type pulses are generated: two propagating along the free surface into the opposite directions to the far field, the other two moving back along the ruptured fault surface (interface) downwards into depth. These downward interface pulses may largely control the stopping phase of the dynamic rupture, and in the case the fault plane is inclined, on the hanging wall the interface pulse and the outward-moving Rayleigh surface pulse interact with each other and the corner wave is induced. On the footwall, the ground motion is dominated simply by the weaker Rayleigh pulse propagating along the free surface because of much smaller interaction between this Rayleigh and the interface pulse. The generation of the downward interface pulses and corner wave may play a crucial role in understanding the effects of the geometrical asymmetry on the strong motion induced by shallow dip-slip faulting, but it has not been well recognized so far, partly because those waves are not expected for a fault that is located and ruptures only at depth. However, the seismological recordings of the 1999 Chi-Chi, Taiwan, the 2004 Niigata-ken Chuetsu, Japan, earthquakes as well as a more recent one in Iwate-Miyagi Inland, Japan in 2008, for example, seem to support the need for careful mechanical consideration. In this contribution, utilizing two-dimensional dynamic photoelasticity in conjunction with high speed digital cinematography, we try to perform "fully controlled" laboratory experiments of dip-slip faulting and observe the propagation of interface pulses and corner waves mentioned above. A birefringent material containing a (model) dip-slip fault plane is prepared, and rupture is initiated in that material using an Nd:YAG laser system, and the evolution of time-dependent isochromatic fringe patterns (contours of maximum in-plane shear stress) associated with the dynamic process of shallow dip-slip faulting is recorded. Use of Nd:YAG laser pulses, instead of ignition of explosives, for rupture initiation may enhance the safety of laboratory fracture experiments and enable us to evaluate the energy entering the material (and hence the energy balance in the system) more precisely, possibly in a more controlled way.

Cluster observations of Shear-mode surface waves diverging from Geomagnetic Tail reconnection

NASA Astrophysics Data System (ADS)

Dai, L.; Wygant, J. R.; Dombeck, J. P.; Cattell, C. A.; Thaller, S. A.; Mouikis, C.; Balogh, A.; Reme, H.

2010-12-01

We present the first Cluster spacecraft study of the intense (δB/B~0.5, δE/VAB~0.5) equatorial plane surface waves diverging from magnetic reconnection in the geomagnetic tail at ~17 Re. Using phase lag analysis with multi-spacecraft measurements, we quantitatively determine the wavelength and phase velocity of the waves with spacecraft frame frequencies from 0.03 Hz to 1 Hz and wavelengths from much larger (4Re) than to comparable to the H+ gyroradius (~300km). The phase velocities track the strong variations in the equatorial plane projection of the reconnection outflow velocity perpendicular to the magnetic field. The propagation direction and wavelength of the observed surface waves resemble those of flapping waves of the magnetotail current sheet, suggesting a same origin shared by both of these waves. The observed waves appear ubiquitous in the outflows near magnetotail reconnection. Evidence is found that the observed waves are associated with velocity shear in reconnection outflows. Analysis shows that observed waves are associated with strong field-aligned Alfvenic Poynting flux directed away from the reconnection region toward Earth. These observations present a scenario in which the observed surface waves are driven and convected through a velocity-shear type instability by high-speed (~1000km) reconnection outflows tending to slow down due to power dissipation through Poynting flux. The mapped Poynting flux (100ergs/cm2s) and longitudinal scales (10-100 km) to 100km altitude suggest that the observed waves and their motions are an important boundary condition for night-side aurora. Figure: a) The BX-GSM in the geomagnetic tail current sheet. b) The phase difference wavelet spectrum between Bz_GSM from SC2 and SC3, used to determine the wave phase velocity, is correlated with the reconnection outflow velocity (represented by H+ VX-GSM) c) The spacecraft trajectory through magnetotail reconnection. d) The observed equatorial plane surface wave propagating outward from reconnection region.

The generation and propagation of internal gravity waves in a rotating fluid

NASA Technical Reports Server (NTRS)

Maxworthy, T.; Chabert Dhieres, G.; Didelle, H.

1984-01-01

The present investigation is concerned with an extension of a study conducted bu Maxworthy (1979) on internal wave generation by barotropic tidal flow over bottom topography. A short series of experiments was carried out during a limited time period on a large (14-m diameter) rotating table. It was attempted to obtain, in particular, information regarding the plan form of the waves, the exact character of the flow over the obstacle, and the evolution of the waves. The main basin was a dammed section of a long free surface water tunnel. The obstacle was towed back and forth by a wire harness connected to an electronically controlled hydraulic piston, the stroke and period of which could be independently varied. Attention is given to the evolution of the wave crests, the formation of solitary wave groups the evolution of the three-dimensional wave field wave shapes, the wave amplitudes, and particle motion.

Implosion of Cylindrical Cavities via Short Duration Impulsive Loading

NASA Astrophysics Data System (ADS)

Huneault, Justin; Higgins, Andrew

2014-11-01

An apparatus has been developed to study the collapse of a cylindrical cavity in gelatin subjected to a symmetric impact-driven impulsive loading. A gas-driven annular projectile is accelerated to approximately 50 m/s, at which point it impacts a gelatin casting confined by curved steel surfaces that allow a transition from an annular geometry to a cylindrically imploding motion. The implosion is visualized by a high-speed camera through a window which forms the top confining wall of the implosion cavity. The initial size of the cavity is such that the gelatin wall is two to five times thicker than the impacting projectile. Thus, during impact the compression wave which travels towards the cavity is closely followed by a rarefaction resulting from the free surface reflection of the compression wave in the projectile. As the compression wave in the gelatin reaches the inner surface, it will also reflect as a rarefaction wave. The interaction between the rarefaction waves from the gelatin and projectile free surfaces leads to large tensile stresses resulting in the spallation of a relatively thin shell. The study focuses on the effect of impact parameters on the thickness and uniformity of the imploding shell formed by the cavitation in the imploding gelatin cylinder.

Predictive Sea State Estimation for Automated Ride Control and Handling - PSSEARCH

NASA Technical Reports Server (NTRS)

Huntsberger, Terrance L.; Howard, Andrew B.; Aghazarian, Hrand; Rankin, Arturo L.

2012-01-01

PSSEARCH provides predictive sea state estimation, coupled with closed-loop feedback control for automated ride control. It enables a manned or unmanned watercraft to determine the 3D map and sea state conditions in its vicinity in real time. Adaptive path-planning/ replanning software and a control surface management system will then use this information to choose the best settings and heading relative to the seas for the watercraft. PSSEARCH looks ahead and anticipates potential impact of waves on the boat and is used in a tight control loop to adjust trim tabs, course, and throttle settings. The software uses sensory inputs including IMU (Inertial Measurement Unit), stereo, radar, etc. to determine the sea state and wave conditions (wave height, frequency, wave direction) in the vicinity of a rapidly moving boat. This information can then be used to plot a safe path through the oncoming waves. The main issues in determining a safe path for sea surface navigation are: (1) deriving a 3D map of the surrounding environment, (2) extracting hazards and sea state surface state from the imaging sensors/map, and (3) planning a path and control surface settings that avoid the hazards, accomplish the mission navigation goals, and mitigate crew injuries from excessive heave, pitch, and roll accelerations while taking into account the dynamics of the sea surface state. The first part is solved using a wide baseline stereo system, where 3D structure is determined from two calibrated pairs of visual imagers. Once the 3D map is derived, anything above the sea surface is classified as a potential hazard and a surface analysis gives a static snapshot of the waves. Dynamics of the wave features are obtained from a frequency analysis of motion vectors derived from the orientation of the waves during a sequence of inputs. Fusion of the dynamic wave patterns with the 3D maps and the IMU outputs is used for efficient safe path planning.

Design of Visco-Elastic Dampers for RC Frame for Site-Specific Earthquake

NASA Astrophysics Data System (ADS)

Kamatchi, P.; Rama Raju, K.; Ravisankar, K.; Iyer, Nagesh R.

2016-12-01

Number of Reinforced Concrete (RC) framed buildings have got damaged at Ahmedabad city, India located at about 240 km away from epicenter during January 2001, 7.6 moment magnitude (Mw) Bhuj earthquake. In the present study, two dimensional nonlinear time history dynamic analyses of a typical 13 storey frame assumed to be located at Ahmedabad is carried out with the rock level and surface level site-specific ground motion for scenario earthquake of Mw 7.6 from Bhuj. Artificial ground motions are generated using extended finite source stochastic model with seismological parameters reported in literature for 2001 Bhuj earthquake. Surface level ground motions are obtained for a typical soil profile of 100 m depth reported in literature through one dimensional equivalent linear wave propagation analyses. From the analyses, failure of frame is observed for surface level ground motions which indicates that, in addition to the in-adequacy of the cross sections and reinforcement of the RC members of the frame chosen, the rich energy content of the surface level ground motion near the fundamental time period of the frame has also contributed for the failure of frame. As a part of retrofitting measure, five Visco-elastic Dampers (VED) in chevron bracing are added to frame. For the frame considered in the present study, provision of VED is found to be effective to mitigate damage for the soil site considered.

An IBEM solution to the scattering of plane SH-waves by a lined tunnel in elastic wedge space

NASA Astrophysics Data System (ADS)

Liu, Zhongxian; Liu, Lei

2015-02-01

The indirect boundary element method (IBEM) is developed to solve the scattering of plane SH-waves by a lined tunnel in elastic wedge space. According to the theory of single-layer potential, the scattered-wave field can be constructed by applying virtual uniform loads on the surface of lined tunnel and the nearby wedge surface. The densities of virtual loads can be solved by establishing equations through the continuity conditions on the interface and zero-traction conditions on free surfaces. The total wave field is obtained by the superposition of free field and scattered-wave field in elastic wedge space. Numerical results indicate that the IBEM can solve the diffraction of elastic wave in elastic wedge space accurately and efficiently. The wave motion feature strongly depends on the wedge angle, the angle of incidence, incident frequency, the location of lined tunnel, and material parameters. The waves interference and amplification effect around the tunnel in wedge space is more significant, causing the dynamic stress concentration factor on rigid tunnel and the displacement amplitude of flexible tunnel up to 50.0 and 17.0, respectively, more than double that of the case of half-space. Hence, considerable attention should be paid to seismic resistant or anti-explosion design of the tunnel built on a slope or hillside.

Spatial correlation of shear-wave velocity in the San Francisco Bay Area sediments

USGS Publications Warehouse

Thompson, E.M.; Baise, L.G.; Kayen, R.E.

2007-01-01

Ground motions recorded within sedimentary basins are variable over short distances. One important cause of the variability is that local soil properties are variable at all scales. Regional hazard maps developed for predicting site effects are generally derived from maps of surficial geology; however, recent studies have shown that mapped geologic units do not correlate well with the average shear-wave velocity of the upper 30 m, Vs(30). We model the horizontal variability of near-surface soil shear-wave velocity in the San Francisco Bay Area to estimate values in unsampled locations in order to account for site effects in a continuous manner. Previous geostatistical studies of soil properties have shown horizontal correlations at the scale of meters to tens of meters while the vertical correlations are on the order of centimeters. In this paper we analyze shear-wave velocity data over regional distances and find that surface shear-wave velocity is correlated at horizontal distances up to 4 km based on data from seismic cone penetration tests and the spectral analysis of surface waves. We propose a method to map site effects by using geostatistical methods based on the shear-wave velocity correlation structure within a sedimentary basin. If used in conjunction with densely spaced shear-wave velocity profiles in regions of high seismic risk, geostatistical methods can produce reliable continuous maps of site effects. ?? 2006 Elsevier Ltd. All rights reserved.

Structure of the airflow above surface waves

NASA Astrophysics Data System (ADS)

Buckley, Marc; Veron, Fabrice

2016-04-01

Weather, climate and upper ocean patterns are controlled by the exchanges of momentum, heat, mass, and energy across the ocean surface. These fluxes are, in turn, influenced by the small-scale physics at the wavy air-sea interface. We present laboratory measurements of the fine-scale airflow structure above waves, achieved in over 15 different wind-wave conditions, with wave ages Cp/u* ranging from 1.4 to 66.7 (where Cp is the peak phase speed of the waves, and u* the air friction velocity). The experiments were performed in the large (42-m long) wind-wave-current tank at University of Delaware's Air-Sea Interaction laboratory (USA). A combined Particle Image Velocimetry and Laser Induced Fluorescence system was specifically developed for this study, and provided two-dimensional airflow velocity measurement as low as 100 um above the air-water interface. Starting at very low wind speeds (U10~2m/s), we directly observe coherent turbulent structures within the buffer and logarithmic layers of the airflow above the air-water interface, whereby low horizontal velocity air is ejected away from the surface, and higher velocity fluid is swept downward. Wave phase coherent quadrant analysis shows that such turbulent momentum flux events are wave-phase dependent. Airflow separation events are directly observed over young wind waves (Cp/u*<3.7) and counted using measured vorticity and surface viscous stress criteria. Detached high spanwise vorticity layers cause intense wave-coherent turbulence downwind of wave crests, as shown by wave-phase averaging of turbulent momentum fluxes. Mean wave-coherent airflow motions and fluxes also show strong phase-locked patterns, including a sheltering effect, upwind of wave crests over old mechanically generated swells (Cp/u*=31.7), and downwind of crests over young wind waves (Cp/u*=3.7). Over slightly older wind waves (Cp/u* = 6.5), the measured wave-induced airflow perturbations are qualitatively consistent with linear critical layer theory.

Extension of Kirchhoff's formula to radiation from moving surfaces

NASA Technical Reports Server (NTRS)

Farassat, F.; Myers, M. K.

1988-01-01

Kirchhoff's formula for radiation from a closed surface has been used recently for prediction of the noise of high speed rotors and propellers. Because the closed surface on which the boundary data are prescribed in these cases is in motion, an extension of Kirchhoff's formula to this condition is required. In this paper such a formula, obtained originally by Morgans for the interior problem, is derived for regions exterior to surfaces moving at speeds below the wave propagation speed by making use of some results of generalized function theory. It is shown that the usual Kirchhoff formula is a special case of the main result of the paper. The general result applies to a deformable surface. However, the special form it assumes for a rigid surface in motion is also noted. In addition, Morgans' result is further extended by showing that edge line integrals appear in the formula when applied to a surface that is piecewise smooth. Some possible areas of application of the formula to problems of current interest in aeroacoustics are discussed.

Extension of Kirchhoff's formula to radiation from moving surfaces

NASA Technical Reports Server (NTRS)

Farassat, F.; Myers, M. K.

1987-01-01

Kirchhoff's formula for radiation from a closed surface has been used recently for prediction of the noise of high speed rotors and propellers. Because the closed surface on which the boundary data are prescribed in these cases is in motion, an extension of Kirchhoff's formula to this condition is required. In this paper such a formula, obtained originally by Morgans for the interior problem, is derived for regions exterior to surfaces moving at speeds below the wave propagation speed by making use of some results of generalized function theory. It is shown that the usual Kirchhoff formula is a special case of the main result of the paper. The general result applies to a deformable surface. However, the special form it assumes for a rigid surface in motion is also noted. In addition, Morgans' result is further extended by showing that edge line integrals appear in the formula when applied to a surface that is piecewise smooth. Some possible areas of application of the formula to problems of current interest in aeroacoustics are discussed.

Characteristics of ground motion at permafrost sites along the Qinghai-Tibet railway

USGS Publications Warehouse

Wang, L.; Wu, Z.; Sun, Jielun; Liu, Xiuying; Wang, Z.

2009-01-01

Based on 14 typical drilling holes distributed in the permafrost areas along the Qinghai-Tibet railway, the distribution of wave velocities of soils in the permafrost regions were determined. Using results of dynamic triaxial tests, the results of dynamic triaxiality test and time histories of ground motion acceleration in this area, characteristics of ground motion response were analyzed for these permafrost sites for time histories of ground accelerations with three exceedance probabilities (63%, 10% and 2%). The influence of ground temperature on the seismic displacement, velocity, acceleration and response spectrum on the surface of permafrost were also studied. ?? 2008 Elsevier Ltd. All rights reserved.

Fluid dynamics of liquids on Titans surface

NASA Astrophysics Data System (ADS)

Ori, Gian Gabriele; Marinangeli, Lucia; Baliva, Antonio; Bressan, Mario; Strom, Robert G.

1998-10-01

On the surface of Titan liquids can be present in three types of environments : (i) oceans, (ii) seas and lakes, and (iii) fluvial channels. The liquid in these environments will be affected by several types of motion: progressive (tidal) waves, wind-generated waves and unidirectional currents. The physical parameters of the liquid on Titans surface can be reconstructed using the Peng-Robinson equation of state. The total energy of the waves, both tidal and wind, depends on the gravity and liquid density ; both values are lower on Titan than on Earth. Thus, the same total energy will produce larger waves on Titan. This is also valid also for the progressive waves, as it is confirmed by the physical relationship between horizontal velocity, wave amplitude, and depth of the liquid. Wind-driven waves also will tend to be larger, because the viscosity of the liquid (which is lower on Titan) controls the deformation of the liquid under shear stress. Wind-generated waves would be rather large, but the dimension of the liquid basin limits the size of the waves ; in small lakes or seas the wave power cannot reach large values. Unidirectional currents are also affected by the liquid properties. Both the relations from driving and resting forces and the Reynolds number suggests that the flows exhibit a large erosional capacity and that, theoretically, a true fluvial network could be formed. However, caution should be exercised, because the cohesion of the sedimentary interface can armour bottom and induce laterally extensive, unchanelled sheet flows with small erosional capacity.

An exact solution for effects of topography on free Rayleigh waves

USGS Publications Warehouse

Savage, W.Z.

2004-01-01

An exact solution for the effects of topography on Rayleigh wave amplification is presented. The solution is obtained by incorporating conformal mapping into complex-variable stress functions developed for free Rayleigh wave propagation in an elastic half-space with a flat upper surface. Results are presented for free Rayleigh wave propagation across isolated symmetric ridges and valleys. It is found for wavelengths that are comparable to ridge widths that horizontal Rayleigh wave amplitudes are amplified at ridge crests and that vertical amplitudes are strongly reduced near ridge crests relative to horizontal and vertical amplitudes of free Rayleigh waves in the flat case. Horizontal amplitudes are strongly deamplified at valley bottoms relative to those for the flat case for Rayleigh wavelengths comparable to valley widths. Wave amplitudes in the symmetric ridges and valleys asymptotically approach those for the flat case with increased wavelengths, increased ridge and valley widths, and with horizontal distance from and depth below the isolated ridges and valleys. Also, prograde particle motion is predicted near crests of narrow ridges and near the bottoms of narrow valleys. Finally, application of the theory at two sites known for topographic wave amplification gives a predicted surface wave amplification ratio of 3.80 at the ridge center for a frequency of 1.0 Hz at Robinwood Ridge in northern California and a predicted surface wave amplification ratio of 1.67 at the ridge center for the same frequency at the Cedar Hill Nursery site at Tarzana in southern California.

Comparison of CFD simulations with experimental data for a tanker model advancing in waves

NASA Astrophysics Data System (ADS)

Orihara, Hideo

2011-03-01

In this paper, CFD simulation results for a tanker model are compared with experimental data over a range of wave conditions to verify a capability to predict the sea-keeping performance of practical hull forms. CFD simulations are conducted using WISDAM-X code which is capable of unsteady RANS calculations in arbitrary wave conditions. Comparisons are made of unsteady surface pressures, added resistance and ship motions in regular waves for cases of fully-loaded and ballast conditions of a large tanker model. It is shown that the simulation results agree fairly well with the experimental data, and that WISDAM-X code can predict sea-keeping performance of practical hull forms.

Effect of a gas on the ejection of particles from the free surface of a sample subjected to a shock wave with various intensities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ogorodnikov, V. A., E-mail: root@gdd.vniief.ru; Mikhailov, A. L.; Sasik, V. S.

2016-08-15

In view of the possible effect of contamination of a plasma by metal particles on the operation of a number of facilities or on the detection of the motion of liners by Doppler methods, a particular attention has been recently focused on the problem of the ejection of particles from the shock-loaded free surface of a sample or on the “dusting” problem. Most information concerns the dusting source associated with the roughness of the surface, manufacturing technology, and the defectiveness and aging of a material. Factors affecting this process such as the profile and amplitude of the pressure on themore » front of the shock wave arriving at the free surface of the sample, the presence of the gas in front of the free surface, and the pressure in this gas are less studied.« less

Spin-wave-driven high-speed domain-wall motions in soft magnetic nanotubes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Jaehak; Yoo, Myoung-Woo; Kim, Sang-Koog, E-mail: sangkoog@snu.ac.kr

We report on a micromagnetic simulation study of interactions between propagating spin waves and a head-to-head domain wall in geometrically confined magnetic nanotubes. We found that incident spin waves of specific frequencies can lead to sufficiently high-speed (on the order of a few hundreds of m/s or higher) domain-wall motions in the same direction as that of the incident spin-waves. The domain-wall motions and their speed vary remarkably with the frequency and the amplitude of the incident spin-waves. High-speed domain-wall motions originate from the transfer torque of spin waves' linear momentum to the domain wall, through the partial or completemore » reflection of the incident spin waves from the domain wall. This work provides a fundamental understanding of the interaction of the spin waves with a domain wall in the magnetic nanotubes as well as a route to all-magnetic control of domain-wall motions in the magnetic nanoelements.« less

Ground Motion Prediction for M7+ scenarios on the San Andreas Fault using the Virtual Earthquake Approach

NASA Astrophysics Data System (ADS)

Denolle, M.; Dunham, E. M.; Prieto, G.; Beroza, G. C.

2013-05-01

There is no clearer example of the increase in hazard due to prolonged and amplified shaking in sedimentary, than the case of Mexico City in the 1985 Michoacan earthquake. It is critically important to identify what other cities might be susceptible to similar basin amplification effects. Physics-based simulations in 3D crustal structure can be used to model and anticipate those effects, but they rely on our knowledge of the complexity of the medium. We propose a parallel approach to validate ground motion simulations using the ambient seismic field. We compute the Earth's impulse response combining the ambient seismic field and coda-wave enforcing causality and symmetry constraints. We correct the surface impulse responses to account for the source depth, mechanism and duration using a 1D approximation of the local surface-wave excitation. We call the new responses virtual earthquakes. We validate the ground motion predicted from the virtual earthquakes against moderate earthquakes in southern California. We then combine temporary seismic stations on the southern San Andreas Fault and extend the point source approximation of the Virtual Earthquake Approach to model finite kinematic ruptures. We confirm the coupling between source directivity and amplification in downtown Los Angeles seen in simulations.

Single actuator wave-like robot (SAW): design, modeling, and experiments.

PubMed

Zarrouk, David; Mann, Moshe; Degani, Nir; Yehuda, Tal; Jarbi, Nissan; Hess, Amotz

2016-07-01

In this paper, we present a single actuator wave-like robot, a novel bioinspired robot which can move forward or backward by producing a continuously advancing wave. The robot has a unique minimalistic mechanical design and produces an advancing sine wave, with a large amplitude, using only a single motor but with no internal straight spine. Over horizontal surfaces, the robot does not slide relative to the surface and its direction of locomotion is determined by the direction of rotation of the motor. We developed a kinematic model of the robot that accounts for the two-dimensional mechanics of motion and yields the speed of the links relative to the motor. Based on the optimization of the kinematic model, and accounting for the mechanical constraints, we have designed and built multiple versions of the robot with different sizes and experimentally tested them (see movie). The experimental results were within a few percentages of the expectations. The larger version attained a top speed of 57 cm s(-1) over a horizontal surface and is capable of climbing vertically when placed between two walls. By optimizing the parameters, we succeeded in making the robot travel by 13% faster than its own wave speed.

Seismic site characterization of an urban dedimentary basin, Livermore Valley, California: Site tesponse, basin-edge-induced surface waves, and 3D simulations

USGS Publications Warehouse

Hartzell, Stephen; Leeds, Alena L.; Ramirez-Guzman, Leonardo; Allen, James P.; Schmitt, Robert G.

2016-01-01

Thirty‐two accelerometers were deployed in the Livermore Valley, California, for approximately one year to study sedimentary basin effects. Many local and near‐regional earthquakes were recorded, including the 24 August 2014 Mw 6.0 Napa, California, earthquake. The resulting ground‐motion data set is used to quantify the seismic response of the Livermore basin, a major structural depression in the California Coast Range Province bounded by active faults. Site response is calculated by two methods: the reference‐site spectral ratio method and a source‐site spectral inversion method. Longer‐period (≥1  s) amplification factors follow the same general pattern as Bouguer gravity anomaly contours. Site response spectra are inverted for shallow shear‐wave velocity profiles, which are consistent with independent information. Frequency–wavenumber analysis is used to analyze plane‐wave propagation across the Livermore Valley and to identify basin‐edge‐induced surface waves with back azimuths different from the source back azimuth. Finite‐element simulations in a 3D velocity model of the region illustrate the generation of basin‐edge‐induced surface waves and point out strips of elevated ground velocities along the margins of the basin.

Establishment of Antakya Basin Strong Ground Motion Monitoring System

NASA Astrophysics Data System (ADS)

Durukal, E.; Özel, O.; Bikce, M.; Geneş, M. C.; Kacın, S.; Erdik, M.; Safak, E.; Över, S.

2009-04-01

Turkey is located in one of the most active earthquake zones of the world. The cities located along the North Anatolian Fault (NAF) and the East Anatolian Fault (EAF) are exposed to significant earthquake hazard. The Hatay province near the southern terminus of the EAF has always experienced a significant seismic activity, since it is on the intersection of the northernmost segment of Dead Sea Fault Zone coming from the south, with the Cyprean Arc approaching from south-west. Historical records extending over the last 2000 years indicate that Antakya, founded in the 3rd century B.C., is effected by intensity IX-X earthquakes every 150 years. In the region, the last destructive earthquake occurred in 1872. Destructive earthquakes should be expected in the region in the near future similar to the ones that occurred in the past. The strong response of sedimentary basins to seismic waves was largely responsible for the damage produced by the devastating earthquakes of 1985 Michoacan Earthquake which severely damaged parts of Mexico City, and the 1988 Spitak Earthquake which destroyed most of Leninakan, Armenia. Much of this devastating response was explained by the conversion of seismic body waves to surface waves at the sediment/rock contacts of sedimentary basins. "Antakya Basin Strong Ground Motion Monitoring System" is set up with the aim of monitoring the earthquake response of the Antakya Basin, contributing to our understanding of basin response, contributing to earthquake risk assessment of Antakya, monitoring of regional earthquakes and determining the effects of local and regional earthquakes on the urban environment of Antakya. The soil properties beneath the strong motion stations (S-Wave velocity structure and dominant soil frequency) are determined by array measurements that involve broad-band seismometers. The strong motion monitoring system consists of six instruments installed in small buildings. The stations form a straight line along the short axis of Antakya basin passing through the city center. They are equipped with acceleration sensors, GPS and communication units and operate in continuous recording mode. For on-line data transmission the EDGE mode of available GSM systems are employed. In the array measurements for the determination of soil properties beneath the stations two 4-seismometer sets have been utilized. The system is the first monitoring installment in Turkey dedicated to understanding basin effects. The records obtained will allow for the visualization of the propagation of long-period ground motion in the basin and show the refraction of surface waves at the basin edge. The records will also serve to enhance our capacity to realistically synthesize the strong ground motion in basin-type environments.

Extremely Fast Numerical Integration of Ocean Surface Wave Dynamics

DTIC Science & Technology

2007-09-30

sub-processor must be added as shown in the blue box of Fig. 1. We first consider the Kadomtsev - Petviashvili (KP) equation ηt + coηx +αηηx + βη ...analytic integration of the so-called “soliton equations ,” I have discovered how the GFT can be used to solved higher order equations for which study...analytical study and extremely fast numerical integration of the extended nonlinear Schroedinger equation for fully three dimensional wave motion

Three-dimensional manipulation of single cells using surface acoustic waves

PubMed Central

Guo, Feng; Mao, Zhangming; Chen, Yuchao; Xie, Zhiwei; Lata, James P.; Li, Peng; Ren, Liqiang; Liu, Jiayang; Yang, Jian; Dao, Ming; Suresh, Subra; Huang, Tony Jun

2016-01-01

The ability of surface acoustic waves to trap and manipulate micrometer-scale particles and biological cells has led to many applications involving “acoustic tweezers” in biology, chemistry, engineering, and medicine. Here, we present 3D acoustic tweezers, which use surface acoustic waves to create 3D trapping nodes for the capture and manipulation of microparticles and cells along three mutually orthogonal axes. In this method, we use standing-wave phase shifts to move particles or cells in-plane, whereas the amplitude of acoustic vibrations is used to control particle motion along an orthogonal plane. We demonstrate, through controlled experiments guided by simulations, how acoustic vibrations result in micromanipulations in a microfluidic chamber by invoking physical principles that underlie the formation and regulation of complex, volumetric trapping nodes of particles and biological cells. We further show how 3D acoustic tweezers can be used to pick up, translate, and print single cells and cell assemblies to create 2D and 3D structures in a precise, noninvasive, label-free, and contact-free manner. PMID:26811444

Infrasound signal detection and characterization using ground-coupled airwaves on a single seismo-acoustic sensor pair

NASA Astrophysics Data System (ADS)

McKee, K. F.; Fee, D.; Haney, M. M.; Lyons, J. J.; Matoza, R. S.

2016-12-01

A ground-coupled airwave (GCA) occurs when an incident atmospheric pressure wave encounters the Earth's surface and part of the energy of the wave is transferred to the ground (i.e. coupled to the ground) as a seismic wave. This seismic wave propagates as a surface Rayleigh wave evidenced by the retrograde particle motion detected on a three-component seismometer. Acoustic waves recorded on a collocated microphone and seismometer can be coherent and have a 90-degree phase difference, predicted by theory and in agreement with observations. If the sensors are separated relative to the frequencies of interest, usually 10s to 100s of meters, then recorded wind noise becomes incoherent and an additional phase shift is present due to the separation distance. These characteristics of GCAs have been used to distinguish wind noise from other sources as well as to determine the acoustic contribution to seismic recordings. Here we aim to develop a minimalist infrasound signal detection and characterization technique requiring just one microphone and one three-component seismometer. Based on GCA theory, determining a source azimuth should be possible using a single seismo-acoustic sensor pair by utilizing the phase difference and exploiting the characteristic particle motion. We will use synthetic seismo-acoustic data generated by a coupled Earth-atmosphere 3D finite difference code to test and tune the detection and characterization method. The method will then be further tested using various well-constrained sources (e.g. Chelyabinsk meteor, Pagan Volcano, Cleveland Volcano). Such a technique would be advantageous in situations where resources are limited and large sensor networks are not feasible.

Shear-wave velocity characterization of the USGS Hawaiian strong-motion network on the Island of Hawaii and development of an NEHRP site-class map

USGS Publications Warehouse

Wong, Ivan G.; Stokoe, Kenneth; Cox, Brady R.; Yuan, Jiabei; Knudsen, Keith L.; Terra, Fabia; Okubo, Paul G.; Lin, Yin-Cheng

2011-01-01

To assess the level and nature of ground shaking in Hawaii for the purposes of earthquake hazard mitigation and seismic design, empirical ground-motion prediction models are desired. To develop such empirical relationships, knowledge of the subsurface site conditions beneath strong-motion stations is critical. Thus, as a first step to develop ground-motion prediction models for Hawaii, spectral-analysis-of-surface-waves (SASW) profiling was performed at the 22 free-field U.S. Geological Survey (USGS) strong-motion sites on the Big Island to obtain shear-wave velocity (VS) data. Nineteen of these stations recorded the 2006 Kiholo Bay moment magnitude (M) 6.7 earthquake, and 17 stations recorded the triggered M 6.0 Mahukona earthquake. VS profiling was performed to reach depths of more than 100 ft. Most of the USGS stations are situated on sites underlain by basalt, based on surficial geologic maps. However, the sites have varying degrees of weathering and soil development. The remaining strong-motion stations are located on alluvium or volcanic ash. VS30 (average VS in the top 30 m) values for the stations on basalt ranged from 906 to 1908 ft/s [National Earthquake Hazards Reduction Program (NEHRP) site classes C and D], because most sites were covered with soil of variable thickness. Based on these data, an NEHRP site-class map was developed for the Big Island. These new VS data will be a significant input into an update of the USGS statewide hazard maps and to the operation of ShakeMap on the island of Hawaii.

3-D velocity structure model for long-period ground motion simulation of the hypothetical Nankai Earthquake

NASA Astrophysics Data System (ADS)

Kagawa, T.; Petukhin, A.; Koketsu, K.; Miyake, H.; Murotani, S.; Tsurugi, M.

2010-12-01

Three dimensional velocity structure model of southwest Japan is provided to simulate long-period ground motions due to the hypothetical subduction earthquakes. The model is constructed from numerous physical explorations conducted in land and offshore areas and observational study of natural earthquakes. Any available information is involved to explain crustal structure and sedimentary structure. Figure 1 shows an example of cross section with P wave velocities. The model has been revised through numbers of simulations of small to middle earthquakes as to have good agreement with observed arrival times, amplitudes, and also waveforms including surface waves. Figure 2 shows a comparison between Observed (dash line) and simulated (solid line) waveforms. Low velocity layers have added on seismological basement to reproduce observed records. The thickness of the layer has been adjusted through iterative analysis. The final result is found to have good agreement with the results from other physical explorations; e.g. gravity anomaly. We are planning to make long-period (about 2 to 10 sec or longer) simulations of ground motion due to the hypothetical Nankai Earthquake with the 3-D velocity structure model. As the first step, we will simulate the observed ground motions of the latest event occurred in 1946 to check the source model and newly developed velocity structure model. This project is partly supported by Integrated Research Project for Long-Period Ground Motion Hazard Maps by Ministry of Education, Culture, Sports, Science and Technology (MEXT). The ground motion data used in this study were provided by National Research Institute for Earth Science and Disaster Prevention Disaster (NIED). Figure 1 An example of cross section with P wave velocities Figure 2 Observed (dash line) and simulated (solid line) waveforms due to a small earthquake

The role of local soil-induced amplification in the 27 July 1980 northeastern Kentucky earthquake

USGS Publications Warehouse

Woolery, E.W.; Lin, T.-L.; Wang, Z.; Shi, B.

2008-01-01

Amplification of earthquake ground motions by near-surface soil deposits was believed to have occurred in Maysville, Kentucky, U.S.A. during the northeast Kentucky (Sharpsburg) earthquake (mb,Lg 5.3) of July 27, 1980. The city of Maysville, founded on approximately 30 m of Late Quaternary Ohio River flood plain alluvium, was 52 km from the epicenter, but experienced equivalent or higher Modified Mercalli Intensity (MMI) VII, compared with the epicentral area of the earthquake (i.e., MMI VI-VII). In this study, dynamic soil properties were obtained at 10 sites in Maysville using seismic P-wave and S-wave (SH-mode) refraction and reflection methods. Synthetically generated composite time histories and limited geotechnical information, along with the measured dynamic properties, were used to perform one-dimensional linear-equivalent amplification analyses. The results indicated the soils generated ground-motion amplification factors between 3.0 and 6.0 and at a frequency range between 2.0 and 5.0 Hz (0.2 to 0.5 s). The building damage in Maysville from the Sharpsburg earthquake was predominantly found in one- to three-story masonry structures. The estimated fundamental period for one- to three-story masonry buildings is approximately 0.11 to 0.26 s (3.8 to 9 Hz). These correlations suggest the elevated ground motion intensity in Maysville can be accounted for by near-surface soil-amplification effects and resonance of the ground motion by the buildings (i.e., double resonance).

Displaced rocks, strong motion, and the mechanics of shallow faulting associated with the 1999 Hector Mine, California, earthquake

USGS Publications Warehouse

Michael, Andrew J.; Ross, Stephanie L.; Stenner, Heidi D.

2002-01-01

The paucity of strong-motion stations near the 1999 Hector Mine earthquake makes it impossible to make instrumental studies of key questions about near-fault strong-motion patterns associated with this event. However, observations of displaced rocks allow a qualitative investigation of these problems. By observing the slope of the desert surface and the frictional coefficient between these rocks and the desert surface, we estimate the minimum horizontal acceleration needed to displace the rocks. Combining this information with observations of how many rocks were displaced in different areas near the fault, we infer the level of shaking. Given current empirical shaking attenuation relationships, the number of rocks that moved is slightly lower than expected; this implies that slightly lower than expected shaking occurred during the Hector Mine earthquake. Perhaps more importantly, stretches of the fault with 4 m of total displacement at the surface displaced few nearby rocks on 15?? slopes, suggesting that the horizontal accelerations were below 0.2g within meters of the fault scarp. This low level of shaking suggests that the shallow parts of this rupture did not produce strong accelerations. Finally, we did not observe an increased incidence of displaced rocks along the fault zone itself. This suggests that, despite observations of fault-zone-trapped waves generated by aftershocks of the Hector Mine earthquake, such waves were not an important factor in controlling peak ground acceleration during the mainshock.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rutqvist, Jonny; Cappa, Frédéric; Rinaldi, Antonio P.

In this paper, we present model simulations of ground motions caused by CO 2 -injection-induced fault reactivation and analyze the results in terms of the potential for damage to ground surface structures and nuisance to the local human population. It is an integrated analysis from cause to consequence, including the whole chain of processes starting from earthquake inception in the subsurface, wave propagation toward the ground surface, and assessment of the consequences of ground vibration. For a small magnitude (M w =3) event at a hypocenter depth of about 1000m, we first used the simulated ground-motion wave train in anmore » inverse analysis to estimate source parameters (moment magnitude, rupture dimensions and stress drop), achieving good agreement and thereby verifying the modeling of the chain of processes from earthquake inception to ground vibration. We then analyzed the ground vibration results in terms of peak ground acceleration (PGA), peak ground velocity (PGV) and frequency content, with comparison to U.S. Geological Survey's instrumental intensity scales for earthquakes and the U.S. Bureau of Mines' vibration criteria for cosmetic damage to buildings, as well as human-perception vibration limits. Our results confirm the appropriateness of using PGV (rather than PGA) and frequency for the evaluation of potential ground-vibration effects on structures and humans from shallow injection-induced seismic events. For the considered synthetic M w =3 event, our analysis showed that the short duration, high frequency ground motion may not cause any significant damage to surface structures, but would certainly be felt by the local population.« less

Joint inversion of surface wave dispersion and receiver functions for crustal structure in Oklahoma

NASA Astrophysics Data System (ADS)

Guo, Hao

The surge in seismicity in Oklahoma starting in 2008 raises questions about the actual locations of the earthquakes in the upper crust. The key to answering this is an improved crustal model that explains as many observations as possible. Love and Rayleigh wave dispersion, teleseismic P-wave receiver functions and some unique transverse motions observed at distances less than 100 km that are characteristics of rays reverberating in a basin provide data to derive the crustal model. The surface wave dispersion data set consists of over 300,000 Love/Rayleigh phase/group values obtained from ambient noise cross-correlation of BH channels of the 133 Transportable Array (TA) stations of Earthscope to periods as short as 2 seconds. Station coverage is dense enough to perform the tomography on a 25*25 km grid that should be able to image shallow geological structures. In addition, receiver functions were obtained using teleseismic data recorded from 3 US Geological Survey Networks (GS) stations and 6 Oklahoma Seismic Network (OK) stations from 2011 to 2014. The 1-D S-wave velocity models derived by the joint inversion of surface wave dispersion and receiver functions with geological constraints are tested by fitting the independent transverse seismograms. This test also provides constraints on the earthquake depths in relation to the geological structure.

Near Source Structural Effects on Seismic Waves: Implication for Shear Motion Generation During SPE-4Prime

NASA Astrophysics Data System (ADS)

Pitarka, A.

2015-12-01

Arben Pitarka, Souheil M. Ezzedine, Oleg Y. Vorobiev, Tarabay H. Antoun, Lew A. Glenn, William R. Walter, Robert J. Mellors, and Evan Hirakawa. We have analyzed effects of wave scattering due to near-source structural complexity and sliding joint motion on generation of shear waves from SPE-4Pprime, a shallow chemical explosion conducted at the Nevada National Security Site. In addition to analyzing far-field ground motion recorded on three-component geophones, we performed high-frequency simulations of the explosion using a finite difference method and heterogeneous media with stochastic variability. The stochastic variations of seismic velocity were modeled using Gaussian correlation functions. Using simulations and recorded waveforms we demonstrate the implication of wave scattering on generation of shear motion, and show the gradual increase of shear motion energy as the waves propagate through media with variable scattering. The amplitude and duration of shear waves resulting from wave scattering are found to be dependent on the model complexity and to a lesser extent to source distance. Analysis of shear-motion generation due to joint motion were conducted using numerical simulations performed with GEODYN-L, a parallelized Lagrangian hydrocode, while a stochastic approach was used in depicting the properties of joints. Separated effects of source and wave scattering on shear motion generation will be shown through simulated motion. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 Release Number: LLNL-ABS-675570

Sensitivity of ground motion parameters to local site effects for areas characterised by a thick buried low-velocity layer.

NASA Astrophysics Data System (ADS)

Farrugia, Daniela; Galea, Pauline; D'Amico, Sebastiano; Paolucci, Enrico

2016-04-01

It is well known that earthquake damage at a particular site depends on the source, the path that the waves travel through and the local geology. The latter is capable of amplifying and changing the frequency content of the incoming seismic waves. In regions of sparse or no strong ground motion records, like Malta (Central Mediterranean), ground motion simulations are used to obtain parameters for purposes of seismic design and analysis. As an input to ground motion simulations, amplification functions related to the shallow subsurface are required. Shear-wave velocity profiles of several sites on the Maltese islands were obtained using the Horizontal-to-Vertical Spectral Ratio (H/V), the Extended Spatial Auto-Correlation (ESAC) technique and the Genetic Algorithm. The sites chosen were all characterised by a layer of Blue Clay, which can be up to 75 m thick, underlying the Upper Coralline Limestone, a fossiliferous coarse grained limestone. This situation gives rise to a velocity inversion. Available borehole data generally extends down till the top of the Blue Clay layer therefore the only way to check the validity of the modelled shear-wave velocity profile is through the thickness of the topmost layer. Surface wave methods are characterised by uncertainties related to the measurements and the model used for interpretation. Moreover the inversion procedure is also highly non-unique. Such uncertainties are not commonly included in site response analysis. Yet, the propagation of uncertainties from the extracted dispersion curves to inversion solutions can lead to significant differences in the simulations (Boaga et al., 2011). In this study, a series of sensitivity analyses will be presented with the aim of better identifying those stratigraphic properties which can perturb the ground motion simulation results. The stochastic one-dimensional site response analysis algorithm, Extended Source Simulation (EXSIM; Motazedian and Atkinson, 2005), was used to perform these analyses. The amplification functions were extracted using the programme SITE_AMP (Boore, 2003), which computes amplifications based on the square root of the effective seismic impedance. Sensitivity indices were obtained by changing two parameters (thickness and shear-wave velocity) of the different layers while keeping the others constant. Additional analyses were carried out by producing various profiles within specified boundaries which are able to fit the experimental data. The analyses also show the important role that the shear-wave velocity profiles play in ground motion simulations. The results obtained highlight the importance of the correct knowledge of both the properties of the Upper Coralline Limestone and the Blue Clay, especially the Blue Clay thickness.

Urban seismology - Northridge aftershocks recorded by multi-scale arrays of portable digital seismographs

USGS Publications Warehouse

Meremonte, M.; Frankel, A.; Cranswick, E.; Carver, D.; Worley, D.

1996-01-01

We deployed portable digital seismographs in the San Fernando Valley (SFV), the Los Angeles basin (LAB), and surrounding hills to record aftershocks of the 17 January 1994 Northridge California earthquake. The purpose of the deployment was to investigate factors relevant to seismic zonation in urban areas, such as site amplification, sedimentary basin effects, and the variability of ground motion over short baselines. We placed seismographs at 47 sites (not all concurrently) and recorded about 290 earthquakes with magnitudes up to 5.1 at five stations or more. We deployed widely spaced stations for profiles across the San Fernando Valley, as well as five dense arrays (apertures of 200 to 500 m) in areas of high damage, such as the collapsed Interstate 10 overpass, Sherman Oaks, and the collapsed parking garage at CalState Northridge. Aftershock data analysis indicates a correlation of site amplification with mainshock damage. We found several cases where the site amplification depended on the azimuth of the aftershock, possibly indicating focusing from basin structures. For the parking garage array, we found large ground-motion variabilities (a factor of 2) over 200-m distances for sites on the same mapped soil unit. Array analysis of the aftershock seismograms demonstrates that sizable arrivals after the direct 5 waves consist of surface waves traveling from the same azimuth as that of the epicenter. These surface waves increase the duration of motions and can have frequencies as high as about 4 Hz. For the events studied here, we do not observe large arrivals reflected from the southern edge of the San Fernando Valley.

Nonlinear surge motions of a ship in bi-chromatic following waves

NASA Astrophysics Data System (ADS)

Spyrou, Kostas J.; Themelis, Nikos; Kontolefas, Ioannis

2018-03-01

Unintended motions of a ship operating in steep and long following waves are investigated. A well-known such case is ;surf-riding; where a ship is carried forward by a single wave, an event invoking sometimes lateral instability and even capsize. The dynamics underlying this behavior has been clarified earlier for monochromatic waves. However, the unsteadiness of the phase space associated with ship behavior in a multichromatic sea, combined with the intrinsically strong system nonlinearity, pose new challenges. Here, current theory is extended to cover surging and surf-riding behavior in unidirectional bi-chromatic waves encountering a ship from the stern. Excitation is provided by two unidirectional harmonic wave components having their lengths comparable to the ship length and their frequencies in rational ratio. The techniques applied include (a) continuation analysis; (b) tracking of Lagrangian coherent structures in phase space, approximated through a finite-time Lyapunov exponents' calculation; and (c) large scale simulation. A profound feature of surf-riding in bi-chromatic waves is that it is turned oscillatory. Initially it appears as a frequency-locked motion, ruled by the harmonic wave component dominating the excitation. Transformations of oscillatory surf-riding are realized as the waves become steeper. In particular, heteroclinic tanglings are identified, governing abrupt transitions between qualitatively different motions. Chaotic transients, as well as long-term chaotic motions, exist near to these events. Some extraordinary patterns of ship motion are discovered. These include a counterintuitive low speed motion at very high wave excitation level; and a hybrid motion characterized by a wildly fluctuating velocity. Due to the quite generic nature of the core mathematical model of our investigation, the current results are believed to offer clues about the behavior of a class of nonlinear dynamical systems having in their modeling some analogy with a perturbed pendulum with bias.

Wave processes in dusty plasma near the Moon’s surface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morozova, T. I.; Kopnin, S. I.; Popel, S. I., E-mail: popel@iki.rssi.ru

2015-10-15

A plasma—dust system in the near-surface layer on the illuminated side of the Moon is described. The system involves photoelectrons, solar-wind electrons and ions, neutrals, and charged dust grains. Linear and nonlinear waves in the plasma near the Moon’s surface are discussed. It is noticed that the velocity distribution of photoelectrons can be represented as a superposition of two distribution functions characterized by different electron temperatures: lower energy electrons are knocked out of lunar regolith by photons with energies close to the work function of regolith, whereas higher energy electrons are knocked out by photons corresponding to the peak atmore » 10.2 eV in the solar radiation spectrum. The anisotropy of the electron velocity distribution function is distorted due to the solar wind motion with respect to photoelectrons and dust grains, which leads to the development of instability and excitation of high-frequency oscillations with frequencies in the range of Langmuir and electromagnetic waves. In addition, dust acoustic waves can be excited, e.g., near the lunar terminator. Solutions in the form of dust acoustic solitons corresponding to the parameters of the dust—plasma system in the near-surface layer of the illuminated Moon’s surface are found. Ranges of possible Mach numbers and soliton amplitudes are determined.« less

Transport of inertial anisotropic particles under surface gravity waves

NASA Astrophysics Data System (ADS)

Dibenedetto, Michelle; Koseff, Jeffrey; Ouellette, Nicholas

2016-11-01

The motion of neutrally and almost-neutrally buoyant particles under surface gravity waves is relevant to the transport of microplastic debris and other small particulates in the ocean. Consequently, a number of studies have looked at the transport of spherical particles or mobile plankton in these conditions. However, the effects of particle-shape anisotropy on the trajectories and behavior of irregularly shaped particles in this type of oscillatory flow are still relatively unknown. To better understand these issues, we created an idealized numerical model which simulates the three-dimensional behavior of anisotropic spheroids in flow described by Airy wave theory. The particle's response is calculated using a simplified Maxey-Riley equation coupled with Jeffery's equation for particle rotation. We show that the particle dynamics are strongly dependent on their initial conditions and shape, with some some additional dependence on Stokes number.

A comparative study of surface waves inversion techniques at strong motion recording sites in Greece

USGS Publications Warehouse

Panagiotis C. Pelekis,; Savvaidis, Alexandros; Kayen, Robert E.; Vlachakis, Vasileios S.; Athanasopoulos, George A.

2015-01-01

Surface wave method was used for the estimation of Vs vs depth profile at 10 strong motion stations in Greece. The dispersion data were obtained by SASW method, utilizing a pair of electromechanical harmonic-wave source (shakers) or a random source (drop weight). In this study, three inversion techniques were used a) a recently proposed Simplified Inversion Method (SIM), b) an inversion technique based on a neighborhood algorithm (NA) which allows the incorporation of a priori information regarding the subsurface structure parameters, and c) Occam's inversion algorithm. For each site constant value of Poisson's ratio was assumed (ν=0.4) since the objective of the current study is the comparison of the three inversion schemes regardless the uncertainties resulting due to the lack of geotechnical data. A penalty function was introduced to quantify the deviations of the derived Vs profiles. The Vs models are compared as of Vs(z), Vs30 and EC8 soil category, in order to show the insignificance of the existing variations. The comparison results showed that the average variation of SIM profiles is 9% and 4.9% comparing with NA and Occam's profiles respectively whilst the average difference of Vs30 values obtained from SIM is 7.4% and 5.0% compared with NA and Occam's.

Analysis of sediment particle velocity in wave motion based on wave flume experiments

NASA Astrophysics Data System (ADS)

Krupiński, Adam

2012-10-01

The experiment described was one of the elements of research into sediment transport conducted by the Division of Geotechnics of West-Pomeranian University of Technology. The experimental analyses were performed within the framework of the project "Building a knowledge transfer network on the directions and perspectives of developing wave laboratory and in situ research using innovative research equipment" launched by the Institute of Hydroengineering of the Polish Academy of Sciences in Gdańsk. The objective of the experiment was to determine relations between sediment transport and wave motion parameters and then use the obtained results to modify formulas defining sediment transport in rivers, like Ackers-White formula, by introducing basic parameters of wave motion as the force generating bed material transport. The article presents selected results of the experiment concerning sediment velocity field analysis conducted for different parameters of wave motion. The velocity vectors of particles suspended in water were measured with a Particle Image Velocimetry (PIV) apparatus registering suspended particles in a measurement flume by producing a series of laser pulses and analysing their displacement with a high-sensitivity camera connected to a computer. The article presents velocity fields of suspended bed material particles measured in the longitudinal section of the wave flume and their comparison with water velocity profiles calculated for the definite wave parameters. The results presented will be used in further research for relating parameters essential for the description of monochromatic wave motion to basic sediment transport parameters and "transforming" mean velocity and dynamic velocity in steady motion to mean wave front velocity and dynamic velocity in wave motion for a single wave.

Coherent Wave Measurement Buoy Arrays to Support Wave Energy Extraction

NASA Astrophysics Data System (ADS)

Spada, F.; Chang, G.; Jones, C.; Janssen, T. T.; Barney, P.; Roberts, J.

2016-02-01

Wave energy is the most abundant form of hydrokinetic energy in the United States and wave energy converters (WECs) are being developed to extract the maximum possible power from the prevailing wave climate. However, maximum wave energy capture is currently limited by the narrow banded frequency response of WECs as well as extended protective shutdown requirements during periods of large waves. These limitations must be overcome in order to maximize energy extraction, thus significantly decreasing the cost of wave energy and making it a viable energy source. Techno-economic studies of several WEC devices have shown significant potential to improve wave energy capture efficiency through operational control strategies that incorporate real-time information about local surface wave motions. Integral Consulting Inc., with ARPA-E support, is partnering with Sandia National Laboratories and Spoondrift LLC to develop a coherent array of wave-measuring devices to relay and enable the prediction of wave-resolved surface dynamics at a WEC location ahead of real time. This capability will provide necessary information to optimize power production of WECs through control strategies, thereby allowing for a single WEC design to perform more effectively across a wide range of wave environments. The information, data, or work presented herein was funded in part by the Advanced Research Projects Agency-Energy (ARPA-E), U.S. Department of Energy, under Award Number DE-AR0000514.

Expressions to Rayleigh circumferential phase velocity and dispersion relation for a cylindrical surface under mechanical pressure

NASA Astrophysics Data System (ADS)

Sebold, Jean Eduardo; de Lacerda, Luiz Alkimin

2018-04-01

This paper describes a substantiated mathematical theory for Rayleigh waves propagated on some types of metal cylinders. More specifically, it presents not only a new way to express the dispersion relation of Rayleigh waves propagated on the cylindrical surface, but also how it can be used to construct a mathematical equation showing that the applied static mechanical pressure affects the shear modulus of the metal cylinder. All steps, required to conclude the process, consider the equation of motion as a function of radial and circumferential coordinates only, while the axial component can be overlooked without causing any problems. Some numerical experiments are done to illustrate the changes in the Rayleigh circumferential phase velocity in a metal cylindrical section due to static mechanical pressure around its external surface.

Nanomachining by rubbing at ultrasonic frequency under controlled shear force.

PubMed

Muraoka, Mikio

2011-03-01

This study proposes a new method of proximal-probe machining that uses a rubbing process by introducing concentrated-mass (CM) cantilevers. At the second resonance of the CM cantilever vibration, the tip site of the cantilever becomes a node of the standing deflection wave because of the sufficient inertia of the attached concentrated mass. The tip makes a cyclic motion that is tangential to the sample surface, not vertical to it, as in a tapping motion. This lateral tip motion that is selectively excited by CM cantilevers was effective for the material modification of a sample due to the friction between the tip and the sample. Imaging and nanomachining under controlled shear force were demonstrated by means of the modified cantilever and a normal atomic force microscope. We were able to write a micron-sized letter "Z" having a line width of 30-100 nm on a resin surface.

Oceanic-wave-measurement system

NASA Technical Reports Server (NTRS)

Holmes, J. F.; Miles, R. T.

1980-01-01

Barometer mounted on bouy senses wave heights. As wave motion raises and lowers barometer, pressure differential is proportional to wave height. Monitoring circuit samples barometer output every half cycle of wave motion and adds magnitudes of adjacent positive and negative peaks. Resulting output signals, proportional to wave height, are transmitted to central monitoring station.

Observed and simulated ground motions in the San Bernardino basin region for the Hector Mine, California, earthquake

USGS Publications Warehouse

Graves, R.W.; Wald, D.J.

2004-01-01

During the MW 7.1 Hector Mine earthquake, peak ground velocities recorded at sites in the central San Bernardino basin region were up to 2 times larger and had significantly longer durations of strong shaking than sites just outside the basin. To better understand the effects of 3D structure on the long-period ground-motion response in this region, we have performed finite-difference simulations for this earthquake. The simulations are numerically accurate for periods of 2 sec and longer and incorporate the detailed spatial and temporal heterogeneity of source rupture, as well as complex 3D basin structure. Here, we analyze three models of the San Bernardino basin: model A (with structural constraints from gravity and seismic reflection data), model F (water well and seismic refraction data), and the Southern California Earthquake Center version 3 model (hydrologic and seismic refraction data). Models A and F are characterized by a gradual increase in sediment thickness toward the south with an abrupt step-up in the basement surface across the San Jacinto fault. The basin structure in the SCEC version 3 model has a nearly uniform sediment thickness of 1 km with little basement topography along the San Jacinto fault. In models A and F, we impose a layered velocity structure within the sediments based on the seismic refraction data and an assumed depth-dependent Vp/Vs ratio. Sediment velocities within the SCEC version 3 model are given by a smoothly varying rule-based function that is calibrated to the seismic refraction measurements. Due to computational limitations, the minimum shear-wave velocity is fixed at 600 m/sec in all of the models. Ground-motion simulations for both models A and F provide a reasonably good match to the amplitude and waveform characteristics of the recorded motions. In these models, surface waves are generated as energy enters the basin through the gradually sloping northern margin. Due to the basement step along the San Jacinto fault, the surface wave energy is confined to the region north of this structure, consistent with the observations. The SCEC version 3 model, lacking the basin geometry complexity present in the other two models, fails to provide a satisfactory match to the characteristics of the observed motions. Our study demonstrates the importance of using detailed and accurate basin geometry for predicting ground motions and also highlights the utility of integrating geological, geophysical, and seismological observations in the development and validation of 3D velocity models.

Spectral element modelling of seismic wave propagation in visco-elastoplastic media including excess-pore pressure development

NASA Astrophysics Data System (ADS)

Oral, Elif; Gélis, Céline; Bonilla, Luis Fabián; Delavaud, Elise

2017-12-01

Numerical modelling of seismic wave propagation, considering soil nonlinearity, has become a major topic in seismic hazard studies when strong shaking is involved under particular soil conditions. Indeed, when strong ground motion propagates in saturated soils, pore pressure is another important parameter to take into account when successive phases of contractive and dilatant soil behaviour are expected. Here, we model 1-D seismic wave propagation in linear and nonlinear media using the spectral element numerical method. The study uses a three-component (3C) nonlinear rheology and includes pore-pressure excess. The 1-D-3C model is used to study the 1987 Superstition Hills earthquake (ML 6.6), which was recorded at the Wildlife Refuge Liquefaction Array, USA. The data of this event present strong soil nonlinearity involving pore-pressure effects. The ground motion is numerically modelled for different assumptions on soil rheology and input motion (1C versus 3C), using the recorded borehole signals as input motion. The computed acceleration-time histories show low-frequency amplification and strong high-frequency damping due to the development of pore pressure in one of the soil layers. Furthermore, the soil is found to be more nonlinear and more dilatant under triaxial loading compared to the classical 1C analysis, and significant differences in surface displacements are observed between the 1C and 3C approaches. This study contributes to identify and understand the dominant phenomena occurring in superficial layers, depending on local soil properties and input motions, conditions relevant for site-specific studies.

Finite-fault inversion of the Mw 5.9 2012 Emilia-Romagna earthquake (Northern Italy) using aftershocks as near-field Green's function approximations

NASA Astrophysics Data System (ADS)

Causse, Mathieu; Cultrera, Giovanna; Herrero, André; Courboulex, Françoise; Schiappapietra, Erika; Moreau, Ludovic

2017-04-01

On May 29, 2012 occurred a Mw 5.9 earthquake in the Emilia-Romagna region (Po Plain) on a thrust fault system. This shock, as well as hundreds of aftershocks, were recorded by 10 strong motion stations located less than 10 km away from the rupture plane, with 4 stations located within the surface rupture projection. The Po Plain is a very large EW trending syntectonic alluvial basin, delimited by the Alps and Apennines chains to the North and South. The Plio-Quaternary sedimentary sequence filling the Po Plain is characterized by an uneven thickness, ranging from several thousands of meters to a few tens of meters. This particular context results especially in a resonance basin below 1 Hz and strong surface waves, which makes it particularly difficult to model wave propagation and hence to obtain robust images of the rupture propagation. This study proposes to take advantage of the large set of recorded aftershocks, considered as point sources, to model wave propagation. Due to the heterogeneous distribution of the aftershocks on the fault plane, an interpolation technique is proposed to compute an approximation of the Green's function between each fault point and each strong motion station in the frequency range [0.2-1Hz]. We then use a Bayesian inversion technique (Monte Carlo Markov Chain algorithm) to obtain images of the rupture propagation from the strong motion data. We propose to retrieve the slip distribution by inverting the final slip value at some control points, which are allowed to move on the fault plane, and by interpolating the slip value between these points. We show that the use of 5 control points to describe the slip, coupled with the hypothesis of spatially constant rupture velocity and rise-time (that is 18 free source parameters), results in a good level of fit with the data. This indicates that despite their complexity, the strong motion data can be properly modeled up to 1 Hz using a relatively simple rupture. The inversion results also reveal that the rupture propagated slowly, at a speed of about 45% of the shear wave velocity.

Wave drift damping acting on multiple circular cylinders (model tests)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kinoshita, Takeshi; Sunahara, Shunji; Bao, W.

1995-12-31

The wave drift damping for the slow drift motion of a four-column platform is experimentally investigated. The estimation of damping force of the slow drift motion of moored floating structures in ocean waves, is one of the most important topics. Bao et al. calculated an interaction of multiple circular cylinders based on the potential flow theory, and showed that the wave drift damping is significantly influenced by the interaction between cylinders. This calculation method assumes that the slow drift motion is approximately replaced by steady current, that is, structures on slow drift motion are supposed to be equivalent to onesmore » in both regular waves and slow current. To validate semi-analytical solutions of Bao et al., experiments were carried out. At first, added resistance due to waves acting on a structure composed of multiple (four) vertical circular cylinders fixed to a slowly moving carriage, was measured in regular waves. Next, the added resistance of the structure moored by linear spring to the slowly moving carriage were measured in regular waves. Furthermore, to validate the assumption that the slow drift motion is replaced by steady current, free decay tests in still water and in regular waves were compared with the simulation of the slow drift motion using the wave drift damping coefficient obtained by the added resistance tests.« less

An Autonomous, Low Cost Platform for Seafloor Geodetic Observations

NASA Astrophysics Data System (ADS)

Ericksen, T.; Foster, J. H.; Bingham, B. S.

2013-12-01

The high cost of acquiring geodetic data from the sea floor has limited the observations available to help us understand and model the behavior of seafloor geodetic processes. To address this problem, the Pacific GPS Facility at the University of Hawaii is developing a cost effective approach for accurately measuring short-term vertical motions of the seafloor and maintaining a continuous long-term record of seafloor pressure without the requirement for costly ship time. There is a recognized need to vastly increase our underwater geodetic observing capacity. Most of the largest recorded earthquakes and most devastating tsunamis are generated at subduction zones underwater. Similarly, many volcanoes are partly (e.g. Santorini) or completely (e.g. Loihi) submerged, and are not well observed and understood. Furthermore, landslide features ring many ocean basins, and huge debris deposits surround many volcanic oceanic islands. Our approach will lower the cost of collecting sea-floor geodetic data, reducing the barriers preventing us from acquiring the information we need to observe and understand these types of structures and provide a direct societal benefit in improving hazard assessment. The capability is being developed by equipping one of the University of Hawaii Wave Gliders with an integrated acoustic telemetry package, a dual frequency geodetic-grade Global Positioning System (GPS) receiver, processing unit, and cellular communications. The Wave Glider will interrogate high accuracy pressure sensors on the sea floor to maintain a near-continuous stream of pressure and temperature data, but seafloor pressure data includes contribution from a variety of sources and on its own may not provide the accuracy required for geodetic investigations. Independent measurements of sea surface pressure and sea surface height can be used to remove these contributions from the observed sea floor pressure timeseries. We will integrate our seafloor pressure measurements with air pressure data, and precise vertical measurements of the sea surface from kinematic positioning of the Wave Glider over the bottom sensor, to determine cm-scale vertical seafloor motions. The seafloor package will consist of a simple tripod frame that seats the pressure sensor unit, and includes an attachment onto which an ROV can install a mobile pressure recorder (MPR) should ship and ROV time be available. Two visits with an MPR would allow calibration of the linear drift of the continuous sensor, further enhancing the value of the timeseries. The pressure sensor is recoverable and serviceable and using the MPR calibration will enable the seafloor monument to be re-occupied to extend the pressure record beyond a single 5+ year deployment. We are currently focused on retrieving high accuracy vertical sea floor motions, but, importantly, we have chosen a development approach that provides a simple upgrade path for incorporating the Wave Glider GPS-Acoustic (GPS/A) measurement system under development at SIO. With this upgrade, Wave Gliders could also acquire accurate horizontal motions of the sea floor sensors, and provide a cost-effective way of performing full, 3-dimensional, surveys of sea-floor motions.

Correlated electron-nuclear dynamics with conditional wave functions.

PubMed

Albareda, Guillermo; Appel, Heiko; Franco, Ignacio; Abedi, Ali; Rubio, Angel

2014-08-22

The molecular Schrödinger equation is rewritten in terms of nonunitary equations of motion for the nuclei (or electrons) that depend parametrically on the configuration of an ensemble of generally defined electronic (or nuclear) trajectories. This scheme is exact and does not rely on the tracing out of degrees of freedom. Hence, the use of trajectory-based statistical techniques can be exploited to circumvent the calculation of the computationally demanding Born-Oppenheimer potential-energy surfaces and nonadiabatic coupling elements. The concept of the potential-energy surface is restored by establishing a formal connection with the exact factorization of the full wave function. This connection is used to gain insight from a simplified form of the exact propagation scheme.

Long Duration of Ground Motion in the Paradigmatic Valley of Mexico

NASA Astrophysics Data System (ADS)

Cruz-Atienza, V. M.; Tago, J.; Sanabria-Gómez, J. D.; Chaljub, E.; Etienne, V.; Virieux, J.; Quintanar, L.

2016-12-01

Built-up on top of ancient lake deposits, Mexico City experiences some of the largest seismic site effects worldwide. Besides the extreme amplification of seismic waves, duration of intense ground motion from large subduction earthquakes exceeds three minutes in the lake-bed zone of the basin, where hundreds of buildings collapsed or were seriously damaged during the magnitude 8.0 Michoacán earthquake in 1985. Different mechanisms contribute to the long lasting motions, such as the regional dispersion and multiple-scattering of the incoming wavefield from the coast, more than 300 km away the city. By means of high performance computational modeling we show that, despite the highly dissipative basin deposits, seismic energy can propagate long distances in the deep structure of the valley, promoting also a large elongation of motion. Our simulations reveal that the seismic response of the basin is dominated by surface-waves overtones, and that this mechanism increases the duration of ground motion by more than 170% and 290% of the incoming wavefield duration at 0.5 and 0.3 Hz, respectively, which are two frequencies with the largest observed amplification. This conclusion contradicts what has been previously stated from observational and modeling investigations, where the basin itself has been discarded as a preponderant factor promoting long and devastating shaking in Mexico City.

Long Duration of Ground Motion in the Paradigmatic Valley of Mexico.

PubMed

Cruz-Atienza, V M; Tago, J; Sanabria-Gómez, J D; Chaljub, E; Etienne, V; Virieux, J; Quintanar, L

2016-12-09

Built-up on top of ancient lake deposits, Mexico City experiences some of the largest seismic site effects worldwide. Besides the extreme amplification of seismic waves, duration of intense ground motion from large subduction earthquakes exceeds three minutes in the lake-bed zone of the basin, where hundreds of buildings collapsed or were seriously damaged during the magnitude 8.0 Michoacán earthquake in 1985. Different mechanisms contribute to the long lasting motions, such as the regional dispersion and multiple-scattering of the incoming wavefield from the coast, more than 300 km away the city. By means of high performance computational modeling we show that, despite the highly dissipative basin deposits, seismic energy can propagate long distances in the deep structure of the valley, promoting also a large elongation of motion. Our simulations reveal that the seismic response of the basin is dominated by surface-waves overtones, and that this mechanism increases the duration of ground motion by more than 170% and 290% of the incoming wavefield duration at 0.5 and 0.3 Hz, respectively, which are two frequencies with the largest observed amplification. This conclusion contradicts what has been previously stated from observational and modeling investigations, where the basin itself has been discarded as a preponderant factor promoting long and devastating shaking in Mexico City.

Propagation of nonlinear shock waves for the generalised Oskolkov equation and its dynamic motions in the presence of an external periodic perturbation

NASA Astrophysics Data System (ADS)

Ak, Turgut; Aydemir, Tugba; Saha, Asit; Kara, Abdul Hamid

2018-06-01

Propagation of nonlinear shock waves for the generalised Oskolkov equation and dynamic motions of the perturbed Oskolkov equation are investigated. Employing the unified method, a collection of exact shock wave solutions for the generalised Oskolkov equations is presented. Collocation finite element method is applied to the generalised Oskolkov equation for checking the accuracy of the proposed method by two test problems including the motion of shock wave and evolution of waves with Gaussian and undular bore initial conditions. Considering an external periodic perturbation, the dynamic motions of the perturbed generalised Oskolkov equation are studied depending on the system parameters with the help of phase portrait and time series plot. The perturbed generalised Oskolkov equation exhibits period-3, quasiperiodic and chaotic motions for some special values of the system parameters, whereas the generalised Oskolkov equation presents shock waves in the absence of external periodic perturbation.

New Tsunami Forecast Tools for the French Polynesia Tsunami Warning System

NASA Astrophysics Data System (ADS)

Clément, Joël; Reymond, Dominique

2015-03-01

This paper presents the tsunami warning tools, which are used for the estimation of the seismic source parameters. These tools are grouped under a method called Preliminary Determination of Focal Mechanism_2 ( PDFM2), that has been developed at the French Polynesia Warning Center, in the framework of the system, as a plug-in concept. The first tool determines the seismic moment and the focal geometry (strike, dip, and slip), and the second tool identifies the "tsunami earthquakes" (earthquakes that cause much bigger tsunamis than their magnitude would imply). In a tsunami warning operation, initial assessment of the tsunami potential is based on location and magnitude. The usual quick magnitude methods which use waves, work fine for smaller earthquakes. For major earthquakes these methods drastically underestimate the magnitude and its tsunami potential because the radiated energy shifts to the longer period waves. Since French Polynesia is located far away from the subduction zones of the Pacific rim, the tsunami threat is not imminent, and this luxury of time allows to use the long period surface wave data to determine the true size of a major earthquake. The source inversion method presented in this paper uses a combination of surface waves amplitude spectra and P wave first motions. The advantage of using long period surface data is that there is a much more accurate determination of earthquake size, and the advantage of using P wave first motion is to have a better constrain of the focal geometry than using the surface waves alone. The method routinely gives stable results at minutes, with being the origin time of an earthquake. Our results are then compared to the Global Centroid Moment Tensor catalog for validating both the seismic moment and the source geometry. The second tool discussed in this paper is the slowness parameter and is the energy-to-moment ratio. It has been used to identify tsunami earthquakes, which are characterized by having unusual slow rupture velocity and release seismic energy that has been shifted to longer periods and, therefore, have low values. The slow rupture velocity would indicate weaker material and bigger uplift and, thus, bigger tsunami potential. The use of the slowness parameter is an efficient tool for monitoring the near real-time identification of tsunami earthquakes.

Retrieving both phase and amplitude information of Green's functions by ambient seismic wave field cross-correlation: A case study with a limestone mine induced seismic event

NASA Astrophysics Data System (ADS)

Kwak, S.; Song, S. G.; Kim, G.; Shin, J. S.

2015-12-01

Recently many seismologists have paid attention to ambient seismic field, which is no more referred as noise and called as Earth's hum, but as useful signal to understand subsurface seismic velocity structure. It has also been demonstrated that empirical Green's functions can be constructed by retrieving both phase and amplitude information from ambient seismic field (Prieto and Beroza 2008). The constructed empirical Green's functions can be used to predict strong ground motions after focal depth and double-couple mechanism corrections (Denolle et al. 2013). They do not require detailed subsurface velocity model and intensive computation for ground motion simulation. In this study, we investigate the capability of predicting long period surface waves by the ambient seismic wave field with a seismic event of Mw 4.0, which occurred with a limestone mine collapse in South Korea on January 31, 2015. This limestone-mine event provides an excellent opportunity to test the efficiency of the ambient seismic wave field in retrieving both phase and amplitude information of Green's functions due to the single force mechanism of the collapse event. In other words, both focal depth and double-couple mechanism corrections are not required for this event. A broadband seismic station, which is about 5.4 km away from the mine event, is selected as a source station. Then surface waves retrieved from the ambient seismic wave field cross-correlation are compared with those generated by the event. Our preliminary results show some potential of the ambient seismic wave field in retrieving both phase and amplitude of Green's functions from a single force impulse source at the Earth's surface. More comprehensive analysis by increasing the time length of stacking may improve the results in further studies. We also aim to investigate the efficiency of retrieving the full empirical Green's functions with the 2007 Mw 4.6 Odaesan earthquake, which is one of the strongest earthquakes occurred in South Korea in the last decade.

SIR-B ocean-wave enhancement with fast Fourier transform techniques

NASA Technical Reports Server (NTRS)

Tilley, David G.

1987-01-01

Shuttle Imaging Radar (SIR-B) imagery is Fourier filtered to remove the estimated system-transfer function, reduce speckle noise, and produce ocean scenes with a gray scale that is proportional to wave height. The SIR-B system response to speckled scenes of uniform surfaces yields an estimate of the stationary wavenumber response of the imaging radar, modeled by the 15 even terms of an eighth-order two-dimensional polynomial. Speckle can also be used to estimate the dynamic wavenumber response of the system due to surface motion during the aperture synthesis period, modeled with a single adaptive parameter describing an exponential correlation along track. A Fourier filter can then be devised to correct for the wavenumber response of the remote sensor and scene correlation, with subsequent subtraction of an estimate of the speckle noise component. A linearized velocity bunching model, combined with a surface tilt and hydrodynamic model, is incorporated in the Fourier filter to derive estimates of wave height from the radar intensities corresponding to individual picture elements.

Free motion scanning system

DOEpatents

Sword, Charles K.

2000-01-01

The present invention relates to an ultrasonic scanner system and method for the imaging of a part system, the scanner comprising: a probe assembly spaced apart from the surface of the part including at least two tracking signals for emitting radiation and a transmitter for emitting ultrasonic waves onto a surface in order to induce at least a portion of the waves to be reflected from the part, at least one detector for receiving the radiation wherein the detector is positioned to receive the radiation from the tracking signals, an analyzer for recognizing a three-dimensional location of the tracking signals based on the emitted radiation, a differential converter for generating an output signal representative of the waveform of the reflected waves, and a device such as a computer for relating said tracking signal location with the output signal and projecting an image of the resulting data. The scanner and method are particularly useful to acquire ultrasonic inspection data by scanning the probe over a complex part surface in an arbitrary scanning pattern.

Mechanical energy transport. [during stellar turbulences

NASA Technical Reports Server (NTRS)

Stein, R. F.; Leibacher, J. W.

1980-01-01

The properties, generation, and dissipation mechanisms of acoustic, gravity and Alfven waves are described, whose restoring forces are pressure, buoyancy, and magnetic tension, respectively. For acoustic waves, generation by turbulent convective motions and by the Eddington Valve thermal overstability is discussed, considering the 'five-minute' oscillation; dissipation is possible either by radiation or shocks. Generation of gravity waves by penetrative convective motions and by shear arising from supergranule motions is reviewed, and dissipation due to wave breaking, interaction with the mean horizontal fluid flow, and very severe radiative damping is considered. Attention is given to Alfven wave generation by convective motions and thermal overstability, and to dissipation by mode coupling, wave decay, current dissipation, and particle collisions producing Joule or viscous heating.

Wave Dissipation over Nearshore Beach Morphology: Insights from High-Resolution LIDAR Observations and the SWASH Wave Model

NASA Astrophysics Data System (ADS)

Mulligan, R. P.; Gomes, E.; McNinch, J.; Brodie, K. L.

2016-02-01

Numerical modelling of the nearshore zone can be computationally intensive due to the complexity of wave breaking, and the need for high temporal and spatial resolution. In this study we apply the SWASH non-hydrostatic wave-flow model that phase-resolves the free surface and fluid motions in the water column at high resolution. The model is forced using observed directional energy spectra, and results are compared to wave observations during moderate storm events. Observations are collected outside the surf zone using acoustic wave and currents sensors, and inside the surf zone over a 100 m transect using high-resolution LIDAR measurements of the sea surface from a sensor mounted on a tower on the beach dune at the Field Research Facility in Duck, NC. The model is applied to four cases with different wave conditions and bathymetry, and used to predict the spatial variability in wave breaking, and correlation between energy dissipation and morphologic features. Model results compare well with observations of spectral evolution outside the surf zone, and with the remotely sensed observations of wave transformation inside the surf zone. The results indicate the importance of nearshore bars, rip-channels, and larger features (major scour depression under the pier following large waves from Hurricane Irene) on the location of wave breaking and alongshore variability in wave energy dissipation.

Dynamics of a fluid-driven crack in three dimensions by the finite difference method

NASA Astrophysics Data System (ADS)

Chouet, Bernard

1986-12-01

The finite difference method is applied to the study of the dynamics of a three-dimensional fluid-filled crack excited into resonance by the sudden failure of a small barrier of area ΔS on the crack surface. The impulse response of the crack is examined for various ratios of crack width to crack length and for several values of the crack stiffness C = (b/μ)(L/d), where b is the bulk modulus of the fluid, μ is the rigidity of the solid, and L and d are the crack length and crack thickness, respectively. The motion of the crack is characterized by distinct time scales representing the duration of brittle failure and the periods of acoustic resonance in the lateral and longitudinal dimensions of the source. The rupture has a duration proportional to the area of crack expansion and is the trigger responsible for the excitation of the crack into resonance; the resonant periods are proportional to the crack stiffness and to the width and length of the crack. The crack wave sustaining the resonance is analogous to the tube wave propagating in a fluid-filled borehole. It is dispersive, showing a phase velocity that decreases with increasing wavelength. Its wave speed is always lower than the acoustic velocity of the fluid and shows a strong dependence on the crack stiffness, decreasing as the stiffness increases. The initial motion of the crack surface is an opening, and the radiated far-field compressional wave starts with a strong but brief compression which has a duration proportional to the crack stiffness and size of the rupture area; the amplitude of this pulse increases with the area of rupture but decreases with increasing stiffness. Flow into the newly created cavity triggers a pressure drop in the fluid, which produces a partial collapse of the wall propagated over the crack surface at the speed of the crack wave. The collapse of the crack surface generates a weak long-period component of dilatation following the compressional first motion in the far-field P wave train; the dilatational component is clearer in the signal from stiffer cracks when seen in the direction of the rupture. The energy loss by radiation is stronger for high frequencies, resulting in a progressive enrichment of the crack response in lower frequencies over the duration of resonance. These source characteristics translate into a far-field signature that is marked by a high-frequency content near its onset and dominated by a longer-period component in its coda. The source duration shows a strong dependence on the fluid viscosity and associated viscous damping at the crack wall.

Surface Instability of Liquid Propellant under Vertical Oscillatory Forcing

NASA Technical Reports Server (NTRS)

Yang, H. Q.; Peugeot, John

2011-01-01

Fluid motion in a fuel tank produced during thrust oscillations can circulate sub-cooled hydrogen near the liquid-vapor interface resulting in increased condensation and ullage pressure collapse. The first objective of this study is to validate the capabilities of a Computational Fluid Dynamics (CFD) tool, CFD-ACE+, in modeling the fundamental interface transition physics occurring at the propellant surface. The second objective is to use the tool to assess the effects of thrust oscillations on surface dynamics. Our technical approach is to first verify the CFD code against known theoretical solutions, and then validate against existing experiments for small scale tanks and a range of transition regimes. A 2D axisymmetric, multi-phase model of gases, liquids, and solids is used to verify that CFD-ACE+ is capable of modeling fluid-structure interaction and system resonance in a typical thrust oscillation environment. Then, the 3D mode is studied with an assumed oscillatory body force to simulate the thrust oscillating effect. The study showed that CFD modeling can capture all of the transition physics from solid body motion to standing surface wave and to droplet ejection from liquid-gas interface. Unlike the analytical solutions established during the 1960 s, CFD modeling is not limited to the small amplitude regime. It can extend solutions to the nonlinear regime to determine the amplitude of surface waves after the onset of instability. The present simulation also demonstrated consistent trends from numerical experiments through variation of physical properties from low viscous fluid to high viscous fluids, and through variation of geometry and input forcing functions. A comparison of surface wave patterns under various forcing frequencies and amplitudes showed good agreement with experimental observations. It is concluded that thrust oscillations can cause droplet formation at the interface, which results in increased surface area and enhanced heat transfer between the liquid and gas phases as the ejected droplets travel well into the warmer gas region.

Joint Inversion of 1-Hz GPS Data and Strong Motion Records for the Rupture Process of the 2008 Iwate-Miyagi Nairiku Earthquake: Objectively Determining Relative Weighting

NASA Astrophysics Data System (ADS)

Wang, Z.; Kato, T.; Wang, Y.

2015-12-01

The spatiotemporal fault slip history of the 2008 Iwate-Miyagi Nairiku earthquake, Japan, is obtained by the joint inversion of 1-Hz GPS waveforms and near-field strong motion records. 1-Hz GPS data from GEONET is processed by GAMIT/GLOBK and then a low-pass filter of 0.05 Hz is applied. The ground surface strong motion records from stations of K-NET and Kik-Net are band-pass filtered for the range of 0.05 ~ 0.3 Hz and integrated once to obtain velocity. The joint inversion exploits a broader frequency band for near-field ground motions, which provides excellent constraints for both the detailed slip history and slip distribution. A fully Bayesian inversion method is performed to simultaneously and objectively determine the rupture model, the unknown relative weighting of multiple data sets and the unknown smoothing hyperparameters. The preferred rupture model is stable for different choices of velocity structure model and station distribution, with maximum slip of ~ 8.0 m and seismic moment of 2.9 × 1019 Nm (Mw 6.9). By comparison with the single inversion of strong motion records, the cumulative slip distribution of joint inversion shows sparser slip distribution with two slip asperities. One common slip asperity extends from the hypocenter southeastward to the ground surface of breakage; another slip asperity, which is unique for joint inversion contributed by 1-Hz GPS waveforms, appears in the deep part of fault where very few aftershocks are occurring. The differential moment rate function of joint and single inversions obviously indicates that rich high frequency waves are radiated in the first three seconds but few low frequency waves.

Experimental Physics

NASA Astrophysics Data System (ADS)

Wilson, Harold A.

2014-05-01

Preface; Introduction; Part I. Mechanics and Properties of Matter: 1. Space and time; 2. Motion; 3. The laws of motion and matter; 4. Force and motion; 5. Work and study; 6. Mechanics of rigid bodies; 7. Gravitation; 8. Elasticity; 9. The properties of liquids; Part II. Heat: 1. Temperature; 2. The expansion of solid bones with rise of temperature; 3. The expansion of liquids with rise of temperature; 4. The properties of gases; 5. Quantity of heat. Specific heat; 6. Change of state. Solid-liquid; 7. Change of state. Liquid-vapour; 8. Convection and conduction; 9. Heat a form of energy; 10. The conversion of heat into work; 11. The kinetic theory of gases; Part III. Sound: 1. Production and velocity of sound; 2. Wave motion; 3. Wave trains; 4. Musical notes; 5. Reflection, refraction, interference of sound and composition of perpendicular vibrations; 6. Resonance; 7. Vibration of strings; 8. Vibration of air in open and closed spaces; Part IV. Light: 1. Sources of light. Photometry; 2. Reflection and refraction at plane surfaces; 3. Spherical mirrors; 4. Lenses; 5. Dispersion; 6. Colour; 7. Optical instruments; 8. The velocity of light; 9. Interference and diffraction; 10. Polarization and double refraction; 11. Energy of light. Invisible radiations; Index.

Tropospheric Waves, Jet Streams, and United States Weather Patterns. Resource Paper No. 11.

ERIC Educational Resources Information Center

Harman, Jay R.

Intended as a supplement to undergraduate college geography courses, this resource paper reviews the mechanism by which surface weather features are linked with the mid-atmospheric circulation within the westerly wind belt. Specifically, vertical atmospheric motions associated with certain aspects of the upper tropospheric flow, including jet…

Rainfall, ground-water flow, and seasonal movement at Minor Creek landslide, northwestern California: physical interpretation of empirical relations

USGS Publications Warehouse

Iverson, R.M.; Major, J.J.

1987-01-01

We present data on rainfall, ground-water flow, and repetitive seasonal motion that occurred from 1982 to 1985 at Minor Creek landslide in northwestern Californa, and we interpret these data in the context of physically based theories. We find that landslide motion is closely regulated by the direction and magnitude of near-surface hydraulic gradients and by waves of pore pressure caused by intermittent rainfall. Hummocky topography that results from slope instability may cause ground-water flow that perpetuates instability. -from Authors

Geotechnical Site Investigation Using S-waves with Implications for Ground Motion Analysis

NASA Astrophysics Data System (ADS)

Hassan, Bilal; Butt, Stephen D.; Hurich, Charles A.

2017-12-01

Evaluation results of shear wave attenuation-based ground motion restricted by fracture orientation and rheology, from among those of an extended experimental study, are presented herein. The issues of competence of fractured bedrock dynamically disturbed multilaterally are assessed. Disturbance is primarily modelled by Sh and Sv stimulation, given fracture orientation, while subjected to direct fracture stress regime conditions varying in time. Hence, directionalities of polarisation and stress are taken into consideration simultaneously following simple site-specific non-erodetic approach. Comparison of spectral curves and spectral ratio curves of attenuation with respect to variations of direction and stress emphasise the amplification of the `seismic response' in one direction compared to the other, i.e. vertical vs. horizontal, in terms of weighing possibilities of or predicting structural integrity against failure. The composite analyses of multiple spectral curves not only enable determination of the orientation of the fracture set/s in space but also allow inferring the nature of more amplified response perpendicular to the crack surface compared to that of a response parallel to the crack surface.

Aerodynamic sound of a body in arbitrary, deformable motion, with application to phonation

NASA Astrophysics Data System (ADS)

Howe, M. S.; McGowan, R. S.

2013-08-01

The method of tailored Green's functions advocated by Doak [Acoustic radiation from a turbulent fluid containing foreign bodies, Proceedings of the Royal Society A 254 (1960) 129-145] for the solution of aeroacoustic problems is used to analyse the contribution of the mucosal wave to self-sustained modulation of air flow through the glottis during the production of voiced speech. The amplitude and phase of the aerodynamic surface force that maintains vocal fold vibration are governed by flow separation from the region of minimum cross-sectional area of the glottis, which moves back and forth along its effective length accompanying the mucosal wave peak. The correct phasing is achieved by asymmetric motion of this peak during the opening and closing phases of the glottis. Limit cycle calculations using experimental data of Berry et al. [High-speed digital imaging of the medial surface of the vocal folds, Journal of the Acoustical Society of America110 (2001) 2539-2547] obtained using an excised canine hemilarynx indicate that the mechanism is robust enough to sustain oscillations over a wide range of voicing conditions.

The observation of ocean surface phenomena using imagery from the SEASAT synthetic aperture radar: An assessment

NASA Astrophysics Data System (ADS)

Vesecky, John F.; Stewart, Robert H.

1982-04-01

Over the period July 4 to October 10, 1978, the SEASAT synthetic aperture radar (SAR) gathered 23 cm wavelength radar images of some 108 km2 of the earth's surface, mainly of ocean areas, at 25-40 m resolution. Our assessment is in terms of oceanographic and ocean monitoring objectives and is directed toward discovering the proper role of SAR imagery in these areas of interest. In general, SAR appears to have two major and somewhat overlapping roles: first, quantitative measurement of ocean phenomena, like long gravity waves and wind fields, as well as measurement of ships; second, exploratory observations of large-scale ocean phenomena, such as the Gulf Stream and its eddies, internal waves, and ocean fronts. These roles are greatly enhanced by the ability of 23 cm SAR to operate day or night and through clouds. To begin we review some basics of synthetic aperture radar and its implementation on the SEASAT spacecraft. SEASAT SAR imagery of the ocean is fundamentally a map of the radar scattering characteristics of ˜30 cm wavelength ocean waves, distorted in some cases by ocean surface motion. We discuss how wind stress, surface currents, long gravity waves, and surface films modulate the scattering properties of these resonant waves with particular emphasis on the mechanisms that could produce images of long gravity waves. Doppler effects by ocean motion are also briefly described. Measurements of long (wavelength ≳100 m) gravity waves, using SEASAT SAR imagery, are compared with surface measurements during several experiments. Combining these results we find that dominant wavelength and direction are measured by SEASAT SAR within ±12% and ±15°, respectively. However, we note that ocean waves are not always visible in SAR images and discuss detection criteria in terms of wave height, length, and direction. SAR estimates of omnidirectional wave height spectra made by assuming that SAR image intensity is proportional to surface height fluctuations are more similar to corresponding surface measurements of wave height spectra than to wave slope spectra. Because SEASAT SAR images show the radar cross section σ° of ˜30 cm waves (neglecting doppler effects), and because these waves are raised by wind stress on the ocean surface, wind measurements are possible. Comparison between wind speeds estimated from SEASAT SAR imagery and from the SEASAT satellite scatterometer (SASS) agreed to within ±0.7 m s- over a 350-km comparison track and for wind speeds from 2 to 15 m s-. The great potential of SAR wind measurements lies in studying the spatial structure of the wind field over a range of spatial scales of from ≲1 km to ≳100 km. At present, the spatial and temporal structure of ocean wind fields is largely unknown. Because SAR responds to short waves whose energy density is a function of wind stress at the surface rather than wind speed at some distance above the surface, variations in image intensity may also reflect changes in air-sea temperature difference (thus complicating wind measurements by SAR). Because SAR images show the effects of surface current shear, air-sea temperature difference, and surface films through their modulation of the ˜30 cm waves, SEASAT images can be used to locate and study the Gulf Stream and related warm water rings, tidal flows at inlets, internal waves, and slicks resulting from surface films. In many of these applications, SAR provides a remote sensing capability that is complementary to infrared imagery because the two techniques sense largely different properties, namely, surface roughness and temperature. Both stationary ships and moving ships with their attendant wakes are often seen in SAR images. Ship images can be used to estimate ship size, heading, and speed. However, ships known to be in areas imaged by SAR are not always detectable. Clearly, a variety of factors, such as image resolution, ship size, sea state, and winds could affect ship detection. Overall, the role of SAR imagery in oceanography is definitely evolving at this time, but its ultimate role is unclear. We have assessed the ability of SEASAT SAR to measure a variety of ocean phenomena and have commented briefly on applications. In the end, oceanographers and others will have to judge from these capabilities the proper place for SAR in oceanography and remote sensing of the ocean.

Dependence of Arctic climate on the latitudinal position of stationary waves and to high-latitudes surface warming

NASA Astrophysics Data System (ADS)

Shin, Yechul; Kang, Sarah M.; Watanabe, Masahiro

2017-12-01

Previous studies suggest large uncertainties in the stationary wave response under global warming. Here, we investigate how the Arctic climate responds to changes in the latitudinal position of stationary waves, and to high-latitudes surface warming that mimics the effect of Arctic sea ice loss under global warming. To generate stationary waves in an atmospheric model coupled to slab ocean, a series of experiments is performed where the thermal forcing with a zonal wavenumber-2 (with zero zonal-mean) is prescribed at the surface at different latitude bands in the Northern Hemisphere. When the stationary waves are generated in the subtropics, the cooling response dominates over the warming response in the lower troposphere due to cloud radiative effects. Then, the low-level baroclinicity is reduced in the subtropics, which gives rise to a poleward shift of the eddy driven jet, thereby inducing substantial cooling in the northern high latitudes. As the stationary waves are progressively generated at higher latitudes, the zonal-mean climate state gradually becomes more similar to the integration with no stationary waves. These differences in the mean climate affect the Arctic climate response to high-latitudes surface warming. Additional surface heating over the Arctic is imposed to the reference climates in which the stationary waves are located at different latitude bands. When the stationary waves are positioned at lower latitudes, the eddy driven jet is located at higher latitude, closer to the prescribed Arctic heating. As baroclinicity is more effectively perturbed, the jet shifts more equatorward that accompanies a larger reduction in the poleward eddy transport of heat and momentum. A stronger eddy-induced descending motion creates greater warming over the Arctic. Our study calls for a more accurate simulation of the present-day stationary wave pattern to enhance the predictability of the Arctic warming response in a changing climate.

Control of wave-driven turbulence and surface heating on the mixing of microplastic marine debris

NASA Astrophysics Data System (ADS)

Kukulka, T.; Lavender Law, K. L.; Proskurowski, G. K.

2016-02-01

Buoyant microplastic marine debris (MPMD) is a pollutant in the ocean surface boundary layer (OSBL) that is submerged by turbulent transport processes. Langmuir circulation (LC) is a turbulent process driven by wind and surface waves that enhances mixing in the OSBL. Sea surface cooling also contributes to OSBL turbulence by driving convection. On the other hand, sea surface heating stratifies and stabilizes the water column to reduce turbulent motion. We analyze observed MPMD surface concentrations in the Atlantic and Pacific Oceans to reveal a significant increase in MPMD concentrations during surface heating and a decrease during surface cooling. Turbulence resolving large eddy simulations of the OSBL for an idealized diurnal heating cycle suggest that turbulent downward fluxes of buoyant tracers are enhanced at night, facilitating deep submergence of plastics, and suppressed in heating conditions, resulting in surface trapped MPMD. Simulations agree with observations if enhanced mixing due to LC is included. Our results demonstrate the controlling influence of surface heat fluxes and LC on turbulent transport in the OSBL and on vertical distributions of buoyant marine particles.

Modeling of induced seismicity and ground vibrations associated with geologic CO 2 storage, and assessing their effects on surface structures and human perception

DOE PAGES

Rutqvist, Jonny; Cappa, Frédéric; Rinaldi, Antonio P.; ...

2014-05-01

In this paper, we present model simulations of ground motions caused by CO 2 -injection-induced fault reactivation and analyze the results in terms of the potential for damage to ground surface structures and nuisance to the local human population. It is an integrated analysis from cause to consequence, including the whole chain of processes starting from earthquake inception in the subsurface, wave propagation toward the ground surface, and assessment of the consequences of ground vibration. For a small magnitude (M w =3) event at a hypocenter depth of about 1000m, we first used the simulated ground-motion wave train in anmore » inverse analysis to estimate source parameters (moment magnitude, rupture dimensions and stress drop), achieving good agreement and thereby verifying the modeling of the chain of processes from earthquake inception to ground vibration. We then analyzed the ground vibration results in terms of peak ground acceleration (PGA), peak ground velocity (PGV) and frequency content, with comparison to U.S. Geological Survey's instrumental intensity scales for earthquakes and the U.S. Bureau of Mines' vibration criteria for cosmetic damage to buildings, as well as human-perception vibration limits. Our results confirm the appropriateness of using PGV (rather than PGA) and frequency for the evaluation of potential ground-vibration effects on structures and humans from shallow injection-induced seismic events. For the considered synthetic M w =3 event, our analysis showed that the short duration, high frequency ground motion may not cause any significant damage to surface structures, but would certainly be felt by the local population.« less

The amplitude effects of sedimentary basins on through-passing surface waves

NASA Astrophysics Data System (ADS)

Feng, L.; Ritzwoller, M. H.; Pasyanos, M.

2016-12-01

Understanding the effect of sedimentary basins on through-passing surface waves is essential in many aspects of seismology, including the estimation of the magnitude of natural and anthropogenic events, the study of the attenuation properties of Earth's interior, and the analysis of ground motion as part of seismic hazard assessment. In particular, knowledge of the physical causes of amplitude variations is important in the application of the Ms:mb discriminant of nuclear monitoring. Our work addresses two principal questions, both in the period range between 10 s and 20 s. The first question is: In what respects can surface wave propagation through 3D structures be simulated as 2D membrane waves? This question is motivated by our belief that surface wave amplitude effects down-stream from sedimentary basins result predominantly from elastic focusing and defocusing, which we understand as analogous to the effect of a lens. To the extent that this understanding is correct, 2D membrane waves will approximately capture the amplitude effects of focusing and defocusing. We address this question by applying the 3D simulation code SW4 (a node-based finite-difference code for 3D seismic wave simulation) and the 2D code SPECFEM2D (a spectral element code for 2D seismic wave simulation). Our results show that for surface waves propagating downstream from 3D sedimentary basins, amplitude effects are mostly caused by elastic focusing and defocusing which is modeled accurately as a 2D effect. However, if the epicentral distance is small, higher modes may contaminate the fundamental mode, which may result in large errors in the 2D membrane wave approximation. The second question is: Are observations of amplitude variations across East Asia following North Korean nuclear tests consistent with simulations of amplitude variations caused by elastic focusing/defocusing through a crustal reference model of China (Shen et al., A seismic reference model for the crust and uppermost mantle beneath China from surface wave dispersion, Geophys. J. Int., 206(2), 2015)? We simulate surface wave propagation across Eastern Asia with SES3D (a spectral element code for 3D seismic wave simulation) and observe significant amplitude variations caused by focusing and defocusing with a magnitude that is consistent with the observations.

Stokes drift

NASA Astrophysics Data System (ADS)

van den Bremer, T. S.; Breivik, Ø.

2017-12-01

During its periodic motion, a particle floating at the free surface of a water wave experiences a net drift velocity in the direction of wave propagation, known as the Stokes drift (Stokes 1847 Trans. Camb. Philos. Soc. 8, 441-455). More generally, the Stokes drift velocity is the difference between the average Lagrangian flow velocity of a fluid parcel and the average Eulerian flow velocity of the fluid. This paper reviews progress in fundamental and applied research on the induced mean flow associated with surface gravity waves since the first description of the Stokes drift, now 170 years ago. After briefly reviewing the fundamental physical processes, most of which have been established for decades, the review addresses progress in laboratory and field observations of the Stokes drift. Despite more than a century of experimental studies, laboratory studies of the mean circulation set up by waves in a laboratory flume remain somewhat contentious. In the field, rapid advances are expected due to increasingly small and cheap sensors and transmitters, making widespread use of small surface-following drifters possible. We also discuss remote sensing of the Stokes drift from high-frequency radar. Finally, the paper discusses the three main areas of application of the Stokes drift: in the coastal zone, in Eulerian models of the upper ocean layer and in the modelling of tracer transport, such as oil and plastic pollution. Future climate models will probably involve full coupling of ocean and atmosphere systems, in which the wave model provides consistent forcing on the ocean surface boundary layer. Together with the advent of new space-borne instruments that can measure surface Stokes drift, such models hold the promise of quantifying the impact of wave effects on the global atmosphere-ocean system and hopefully contribute to improved climate projections. This article is part of the theme issue 'Nonlinear water waves'.

Scale-dependent Ocean Wave Turbulence

NASA Technical Reports Server (NTRS)

Glazman, R. E.

1995-01-01

Wave turbulence is a common feature of nonlinear wave motions observed when external forcing acts during a long period of time, resulting in developed spectral cascades of energy, momentum, and other conserved integrals. In the ocean, wave turbulence occurs on various scales from capillary ripples, and those of baroclinic inertia-gravity, to Rossby waves. Oceanic wave motions are discussed.

Low-velocity zone and topography as a source of site amplification effect on Tarzana hill, California

USGS Publications Warehouse

Graizer, V.

2009-01-01

Tarzana station is located in the foothills of the Santa Monica Mountains in California near the crest of a low (<20 m) natural hill with gentle slopes. The hill is about 500 m in length by 130 m in width and is formed of extremely weathered shale at the surface to fresh at depth. Average S-wave is about 250 m/s in the top 17-18 m, and S- and P-wave velocities significantly increase below this depth. According to the NEHRP classification based on VS30???300 m/s it is a site class D. Strong-motion instrumentation at Tarzana consisted of an accelerograph at the top of the hill, a downhole instrument at 60 m depth, and an accelerograph at the base of the hill. More than 20 earthquakes were recorded by at least three instruments at Tarzana from 1998 till 2003. Comparisons of recordings and Fourier spectra indicate strong directional resonance in a direction perpendicular to the strike of the hill. The dominant peaks in ground motion amplification on the top of the hill relative to the base are at frequencies ???3.6 and 8-9 Hz for the horizontal components. Our hypothesis is that the hill acts like a wave trap. This results in an amplification at predominant frequencies f=V/4 h (h is layer's thickness) at f???3.6 Hz for S-waves (using average VS17=246 m/s and h=17 m) and f???7.9 Hz for P-waves (using average VP17=535 m/s and h=17 m). As was shown by Bouchon and Barker [Seismic response of a hill: the example of Tarzana, California. Bull Seism Soc Am 1996;86(1A):66-72], topography of this hill amplifies and polarizes ground motion in the frequency range of 3-5 Hz. Hill acts as a magnifying polarizing glass: It polarizes ground motion in the direction perpendicular to the strike of the hill and also amplifies ground motions that had been also amplified by a low-velocity layer.

Bedforms induced by solitary waves: laboratory studies on generation and migration rate

NASA Astrophysics Data System (ADS)

la Forgia, Giovanni; Adduce, Claudia; Falcini, Federico; Paola, Chris

2017-04-01

This study presents experiments on the formation of sandy bedforms, produced by surface solitary waves (SSWs) in shallow water conditions. The experiments were carried out in a 12.0 m long, 0.15 m wide and 0.5 m high flume, at Saint Anthony Falls Laboratory in Minneapolis. The tank is filled by fresh water and a removable gate, placed at the left hand-side of the tank, divides the flume in two regions: the lock region and the ambient fluid region. The standard lock-release method generates SSWs by producing a displacement between the free surfaces that are divided by the gate. Wave amplitude, wavelength, and celerity depend on the lock length and on the water level difference between the two regions. Natural sand particles (D50=0.64) are arranged on the bottom in order to form a horizontal flat layer with a thickness of 2 cm. A digital pressure gauge and a high-resolution acoustic velocimeter allowed us to measure, locally, both pressure and 3D water velocity induced on the bottom by each wave. Image analysis technique is then used to obtain the main wave features: amplitude, wavelength, and celerity. Dye is finally used as vertical tracer to mark the horizontal speed induced by the wave. For each experiment we generated 400 waves, having the same features and we analyzed their action on sand particles placed on the bottom. The stroke, induced by each wave, entails a shear stress on the sand particles, causing sediment transport in the direction of wave propagation. Immediately after the wave passage, a back flow occurs near the bottom. The horizontal pressure gradient and the velocity field induced by the wave cause the boundary layer separation and the consequent reverse flow. Depending on the wave features and on the water depth, the boundary shear stress induced by the reverse flow can exceed the critical value inducing the back motion of the sand particles. The experiments show that the particle back motion is localized at particular cross sections along the tank, where the wave steepening occur. For this reason, the pressure and velocity measures were collected in several cross sections along the tank. The propagation of consecutive waves with the same features induces the generation of erosion and accumulation zones, which slowly evolve in isometric bedforms.

Nonlinear ionospheric responses to large-amplitude infrasonic-acoustic waves generated by undersea earthquakes

NASA Astrophysics Data System (ADS)

Zettergren, M. D.; Snively, J. B.; Komjathy, A.; Verkhoglyadova, O. P.

2017-02-01

Numerical models of ionospheric coupling with the neutral atmosphere are used to investigate perturbations of plasma density, vertically integrated total electron content (TEC), neutral velocity, and neutral temperature associated with large-amplitude acoustic waves generated by the initial ocean surface displacements from strong undersea earthquakes. A simplified source model for the 2011 Tohoku earthquake is constructed from estimates of initial ocean surface responses to approximate the vertical motions over realistic spatial and temporal scales. Resulting TEC perturbations from modeling case studies appear consistent with observational data, reproducing pronounced TEC depletions which are shown to be a consequence of the impacts of nonlinear, dissipating acoustic waves. Thermospheric acoustic compressional velocities are ˜±250-300 m/s, superposed with downward flows of similar amplitudes, and temperature perturbations are ˜300 K, while the dominant wave periodicity in the thermosphere is ˜3-4 min. Results capture acoustic wave processes including reflection, onset of resonance, and nonlinear steepening and dissipation—ultimately leading to the formation of ionospheric TEC depletions "holes"—that are consistent with reported observations. Three additional simulations illustrate the dependence of atmospheric acoustic wave and subsequent ionospheric responses on the surface displacement amplitude, which is varied from the Tohoku case study by factors of 1/100, 1/10, and 2. Collectively, results suggest that TEC depletions may only accompany very-large amplitude thermospheric acoustic waves necessary to induce a nonlinear response, here with saturated compressional velocities ˜200-250 m/s generated by sea surface displacements exceeding ˜1 m occurring over a 3 min time period.

Angular-momentum couplings in ultra-long-range giant dipole molecules

NASA Astrophysics Data System (ADS)

Stielow, Thomas; Scheel, Stefan; Kurz, Markus

2018-02-01

In this article we extend the theory of ultra-long-range giant dipole molecules, formed by an atom in a giant dipole state and a ground-state alkali-metal atom, by angular-momentum couplings known from recent works on Rydberg molecules. In addition to s -wave scattering, the next higher order of p -wave scattering in the Fermi pseudopotential describing the binding mechanism is considered. Furthermore, the singlet and triplet channels of the scattering interaction as well as angular-momentum couplings such as hyperfine interaction and Zeeman interactions are included. Within the framework of Born-Oppenheimer theory, potential energy surfaces are calculated in both first-order perturbation theory and exact diagonalization. Besides the known pure triplet states, mixed-spin character states are obtained, opening up a whole new landscape of molecular potentials. We determine exact binding energies and wave functions of the nuclear rotational and vibrational motion numerically from the various potential energy surfaces.

3-D Voxel FEM Simulation of Seismic Wave Propagation in a Land-Sea Structure with Topography

NASA Astrophysics Data System (ADS)

Ikegami, Y.; Koketsu, K.

2003-12-01

We have already developed the voxel FEM (finite element method) code to simulate seismic wave propagation in a land structure with surface topography (Koketsu, Fujiwara and Ikegami, 2003). Although the conventional FEM often requires much larger memory, longer computation time and farther complicated mesh generation than the Finite Difference Method (FDM), this code consumes a similar amount of memory to FDM and spends only 1.4 times longer computation time thanks to the simplicity of voxels (hexahedron elements). The voxel FEM was successfully applied to inland earthquakes, but most earthquakes in a subduction zone occur beneath a sea, so that a simulation in a land-sea structure should be essential for waveform modeling and strong motion prediction there. We now introduce a domain of fluid elements into the model and formulate displacements in the elements using the Lagrange method. Sea-bottom motions are simulated for the simple land-sea models of Okamoto and Takenaka (1999). The simulation results agree well with their reflectivity and FDM seismograms. In order to enhance numerical stability, not only a variable mesh but also an adaptive time step is introduced. We can now choose the optimal time steps everywhere in the model based the Courant condition. This doubly variable formulation may result in inefficient parallel computing. The wave velocity in a shallow part is lower than that in a deeper part. Therefore, if the model is divided into horizontal slices and they are assigned to CPUs, a shallow slice will consist of only small elements. This can cause unbalanced loads on the CPUs. Accordingly, the model is divided into vertical slices in this study. They also reduce inter-processor communication, because a vertical cross section is usually smaller than a horizontal one. In addition, we will consider higher-order FEM formulation compatible to the fourth-order FDM. We will also present numerical examples to demonstrate the effects of a sea and surface topography on seismic waves and ground motions.

Azimuthal resolution degradation due to ocean surface motion in focused arrays and SARS

NASA Astrophysics Data System (ADS)

1990-06-01

During the meeting at WHOI (5-18-90), a discussion arose of the ability of the focused array to simulate the R/v ratios typical of airborne and/or spaceborne SARs. In particular, the ability was questioned of the focused array to yield the same azimuthal resolution, rho, as the SAR. Although the focused array can be sampled to yield the same azimuthal resolution as the SAR, it is likely that the images generated by the focused array will not be identical to those produced by a SAR with the same azimuth resolution. For a true SAR, biases in the Doppler history of azimuthally traveling waves due to their along-track motion will cause shifts in their apparent position. This will cause waves which are physically at one location to shift over several pixel widths in the image. The limited swath width of the focused array will prevent if from observing scattered power from waves falling outside the swath, thus such waves will not affect the image formed within the swath, as would happen in the SAR. Thus, it is likely that the focused array will not yield the same image as a SAR having the same resolution.

Formation of Hydro-acoustic Waves in Dissipative Coupled Weakly Compressible Fluids

NASA Astrophysics Data System (ADS)

Abdolali, A.; Kirby, J. T., Jr.; Bellotti, G.

2014-12-01

Recent advances in deep sea measurement technology provide an increasing opportunity to detect and interpret hydro-acoustic waves as a component in improved Tsunami Early Warning Systems (TEWS). For the idealized case of a homogeneous water column above a moving but otherwise rigid bottom (in terms of assessing acoustic wave interaction), the description of the infinite family of acoustic modes is characterized by local water depth at source area; i.e. the period of the first acoustic mode is given by four times the required time for sound to travel from the seabed to the surface. Spreading off from earthquake zone, the dominant spectrum is filtered and enriched by seamounts and barriers. This study focuses on the characteristics of hydro-acoustic waves generated by sudden sea bottom motion in a weakly compressible fluid coupled with an underlying sedimentary layer, where the added complexity of the sediment layer rheology leads to both the lowering of dominant spectral peaks and wave attenuation across the full spectrum. To overcome the computational difficulties of three-dimensional models, we derive a depth integrated equation valid for varying water depth and sediment thickness. Damping behavior of the two layered system is initially taken into account by introducing the viscosity of fluid-like sedimentary layer. We show that low frequency pressure waves which are precursor components of tsunamis contain information of seafloor motion.

Airborne ultrasound surface motion camera: Application to seismocardiography

NASA Astrophysics Data System (ADS)

Shirkovskiy, P.; Laurin, A.; Jeger-Madiot, N.; Chapelle, D.; Fink, M.; Ing, R. K.

2018-05-01

The recent achievements in the accelerometer-based seismocardiography field indicate a strong potential for this technique to address a wide variety of clinical needs. Recordings from different locations on the chest can give a more comprehensive observation and interpretation of wave propagation phenomena than a single-point recording, can validate existing modeling assumptions (such as the representation of the sternum as a single solid body), and provide better identifiability for models using richer recordings. Ultimately, the goal is to advance our physiological understanding of the processes to provide useful data to promote cardiovascular health. Accelerometer-based multichannel system is a contact method and laborious for use in practice, and also even ultralight accelerometers can cause non-negligible loading effects. We propose a contactless ultrasound imaging method to measure thoracic and abdominal surface motions, demonstrating that it is adequate for typical seismocardiogram (SCG) use. The developed method extends non-contact surface-vibrometry to fast 2D mapping by originally combining multi-element airborne ultrasound arrays, a synthetic aperture implementation, and pulsed-waves. Experimental results show the ability of the developed method to obtain 2D seismocardiographic maps of the body surface 30 × 40 cm2 in dimension, with a temporal sampling rate of several hundred Hz, using ultrasound waves with the central frequency of 40 kHz. Our implementation was validated in-vivo on eight healthy human participants. The shape and position of the zone of maximal absolute acceleration and velocity during the cardiac cycle were also observed. This technology could potentially be used to obtain more complete cardio-vascular information than single-source SCG in and out of clinical environments, due to enhanced identifiability provided by the distributed measurements, and observation of propagation phenomena.

Containerless Ripple Turbulence

NASA Astrophysics Data System (ADS)

Putterman, Seth; Wright, William; Duval, Walter; Panzarella, Charles

2002-11-01

One of the longest standing unsolved problems in physics relates to the behavior of fluids that are driven far from equilibrium such as occurs when they become turbulent due to fast flow through a grid or tidal motions. In turbulent flows the distribution of vortex energy as a function of the inverse length scale [or wavenumber 'k'] of motion is proportional to 1/k5/3 which is the celebrated law of Kolmogorov. Although this law gives a good description of the average motion, fluctuations around the average are huge. This stands in contrast with thermally activated motion where large fluctuations around thermal equilibrium are highly unfavorable. The problem of turbulence is the problem of understanding why large fluctuations are so prevalent which is also called the problem of 'intermittency'. Turbulence is a remarkable problem in that its solution sits simultaneously at the forefront of physics, mathematics, engineering and computer science. A recent conference [March 2002] on 'Statistical Hydrodynamics' organized by the Los Alamos Laboratory Center for Nonlinear Studies brought together researchers in all of these fields. Although turbulence is generally thought to be described by the Navier-Stokes Equations of fluid mechanics the solution as well as its existence has eluded researchers for over 100 years. In fact proof of the existence of such a solution qualifies for a 1 M millennium prize. As part of our NASA funded research we have proposed building a bridge between vortex turbulence and wave turbulence. The latter occurs when high amplitude waves of various wavelengths are allowed to mutually interact in a fluid. In particular we have proposed measuring the interaction of ripples [capillary waves] that run around on the surface of a fluid sphere suspended in a microgravity environment. The problem of ripple turbulence poses similar mathematical challenges to the problem of vortex turbulence. The waves can have a high amplitude and a strong nonlinear interaction. Furthermore, the steady state distribution of energy again follows a Kolmogorov scaling law; in this case the ripple energy is distributed according to 1/k 7/4. Again, in parallel with vortex turbulence ripple turbulence exhibits intermittency. The problem of ripple turbulence presents an experimental opportunity to generate data in a controlled, benchmarked system. In particular the surface of a sphere is an ideal environment to study ripple turbulence. Waves run around the sphere and interact with each other, and the effect of walls is eliminated. In microgravity this state can be realized for over 2 decades of frequency. Wave turbulence is a physically relevant problem in its own right. It has been studied on the surface of liquid hydrogen and its application to Alfven waves in space is a source of debate. Of course, application of wave turbulence perspectives to ocean waves has been a major success. The experiment which we plan to run in microgravity is conceptually straightforward. Ripples are excited on the surface of a spherical drop of fluid and then their amplitude is recorded with appropriate photography. A key challenge is posed by the need to stably position a 10cm diameter sphere of water in microgravity. Two methods are being developed. Orbitec is using controlled puffs of air from at least 6 independent directions to provided the positioning force. This approach has actually succeeded to position and stabilize a 4cm sphere during a KC 135 segment. Guigne International is using the radiation pressure of high frequency sound. These transducers have been organized into a device in the shape of a dodecahedron. This apparatus 'SPACE DRUMS' has already been approved for use for combustion synthesis experiments on the International Space Station. A key opportunity presented by the ripple turbulence data is its use in driving the development of codes to simulate its properties.

Containerless Ripple Turbulence

NASA Technical Reports Server (NTRS)

Putterman, Seth; Wright, William; Duval, Walter; Panzarella, Charles

2002-01-01

One of the longest standing unsolved problems in physics relates to the behavior of fluids that are driven far from equilibrium such as occurs when they become turbulent due to fast flow through a grid or tidal motions. In turbulent flows the distribution of vortex energy as a function of the inverse length scale [or wavenumber 'k'] of motion is proportional to 1/k(sup 5/3) which is the celebrated law of Kolmogorov. Although this law gives a good description of the average motion, fluctuations around the average are huge. This stands in contrast with thermally activated motion where large fluctuations around thermal equilibrium are highly unfavorable. The problem of turbulence is the problem of understanding why large fluctuations are so prevalent which is also called the problem of 'intermittency'. Turbulence is a remarkable problem in that its solution sits simultaneously at the forefront of physics, mathematics, engineering and computer science. A recent conference [March 2002] on 'Statistical Hydrodynamics' organized by the Los Alamos Laboratory Center for Nonlinear Studies brought together researchers in all of these fields. Although turbulence is generally thought to be described by the Navier-Stokes Equations of fluid mechanics the solution as well as its existence has eluded researchers for over 100 years. In fact proof of the existence of such a solution qualifies for a 1 M$ millennium prize. As part of our NASA funded research we have proposed building a bridge between vortex turbulence and wave turbulence. The latter occurs when high amplitude waves of various wavelengths are allowed to mutually interact in a fluid. In particular we have proposed measuring the interaction of ripples [capillary waves] that run around on the surface of a fluid sphere suspended in a microgravity environment. The problem of ripple turbulence poses similar mathematical challenges to the problem of vortex turbulence. The waves can have a high amplitude and a strong nonlinear interaction. Furthermore, the steady state distribution of energy again follows a Kolmogorov scaling law; in this case the ripple energy is distributed according to 1/k (sup 7/4). Again, in parallel with vortex turbulence ripple turbulence exhibits intermittency. The problem of ripple turbulence presents an experimental opportunity to generate data in a controlled, benchmarked system. In particular the surface of a sphere is an ideal environment to study ripple turbulence. Waves run around the sphere and interact with each other, and the effect of walls is eliminated. In microgravity this state can be realized for over 2 decades of frequency. Wave turbulence is a physically relevant problem in its own right. It has been studied on the surface of liquid hydrogen and its application to Alfven waves in space is a source of debate. Of course, application of wave turbulence perspectives to ocean waves has been a major success. The experiment which we plan to run in microgravity is conceptually straightforward. Ripples are excited on the surface of a spherical drop of fluid and then their amplitude is recorded with appropriate photography. A key challenge is posed by the need to stably position a 10cm diameter sphere of water in microgravity. Two methods are being developed. Orbitec is using controlled puffs of air from at least 6 independent directions to provided the positioning force. This approach has actually succeeded to position and stabilize a 4cm sphere during a KC 135 segment. Guigne International is using the radiation pressure of high frequency sound. These transducers have been organized into a device in the shape of a dodecahedron. This apparatus 'SPACE DRUMS' has already been approved for use for combustion synthesis experiments on the International Space Station. A key opportunity presented by the ripple turbulence data is its use in driving the development of codes to simulate its properties.

Interactions between gravity waves and cold air outflows in a stably stratified uniform flow

NASA Technical Reports Server (NTRS)

Lin, Yuh-Lang; Wang, Ting-An; Weglarz, Ronald P.

1993-01-01

Interactions between gravity waves and cold air outflows in a stably stratified uniform flow forced by various combinations of prescribed heat sinks and sources are studied using a hydrostatic two-dimensional nonlinear numerical model. The formation time for the development of a stagnation point or reversed flow at the surface is not always directly proportional to the Froude number when wave reflections exist from upper levels. A density current is able to form by the wave-otuflow interaction, even though the Froude number is greater than a critical value. This is the result of the wave-outflow interaction shifting the flow response to a different location in the characteristic parameter space. A density current is able to form or be destroyed due to the wave-outflow interaction between a traveling gravity wave and cold air outflow. This is proved by performing experiments with a steady-state heat sink and an additional transient heat source. In a quiescent fluid, a region of cold air, convergence, and upward motion is formed after the collision between two outflows produced by two prescribed heat sinks. After the collision, the individual cold air outflows lose their own identity and merge into a single, stationary, cold air outflow region. Gravity waves tend to suppress this new stationary cold air outflow after the collision. The region of upward motion associated with the collision is confined to a very shallow layer. In a moving airstream, a density current produced by a heat sink may be suppressed or enhanced nonlinearly by an adjacent heat sink due to the wave-outflow interaction.

6C polarization analysis - seismic direction finding in coherent noise, automated event identification, and wavefield separation

NASA Astrophysics Data System (ADS)

Schmelzbach, C.; Sollberger, D.; Greenhalgh, S.; Van Renterghem, C.; Robertsson, J. O. A.

2017-12-01

Polarization analysis of standard three-component (3C) seismic data is an established tool to determine the propagation directions of seismic waves recorded by a single station. A major limitation of seismic direction finding methods using 3C recordings, however, is that a correct propagation-direction determination is only possible if the wave mode is known. Furthermore, 3C polarization analysis techniques break down in the presence of coherent noise (i.e., when more than one event is present in the analysis time window). Recent advances in sensor technology (e.g., fibre-optical, magnetohydrodynamic angular rate sensors, and ring laser gyroscopes) have made it possible to accurately measure all three components of rotational ground motion exhibited by seismic waves, in addition to the conventionally recorded three components of translational motion. Here, we present an extension of the theory of single station 3C polarization analysis to six-component (6C) recordings of collocated translational and rotational ground motions. We demonstrate that the information contained in rotation measurements can help to overcome some of the main limitations of standard 3C seismic direction finding, such as handling multiple arrivals simultaneously. We show that the 6C polarisation of elastic waves measured at the Earth's free surface does not only depend on the seismic wave type and propagation direction, but also on the local P- and S-wave velocities just beneath the recording station. Using an adaptation of the multiple signal classification algorithm (MUSIC), we demonstrate how seismic events can univocally be identified and characterized in terms of their wave type. Furthermore, we show how the local velocities can be inferred from single-station 6C data, in addition to the direction angles (inclination and azimuth) of seismic arrivals. A major benefit of our proposed 6C method is that it also allows the accurate recovery of the wave type, propagation directions, and phase velocities of multiple, interfering arrivals in one time window. We demonstrate how this property can be exploited to separate the wavefield into its elastic wave-modes and to isolate or suppress waves arriving from specific directions (directional filtering), both in a fully automated fashion.

Upper ocean moored current and density profiler applied to winter conditions near Bermuda

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eriksen, C.C.; Dahlen, J.M.; Shillingford, J.T. Jr.

1982-09-20

A new moored instrument which makes repeated high vertical resolution profiles of current, temperature, and salinity in the upper ocean over extended periods was used to observe midwinter conditions near Bermuda. The operation and performance of the instrument, called the profiling current meter (PCM), in the surface wave environment of winter storms is reported here. The PCM profiles along the upper portion of a slightly subsurface mooring by adjusting its buoyancy under computer control. This design decouples the instrument from vertical motions of the mooring induced by surface waves, so that its electromagnetic current sensor operates in a favorable mean-to-fluctuatingmore » flow regime. Current, temperature, and electrical conductivity are (vector) averaged into contiguous preselected bins several meters wide over the possible profile range of 20- to 250-m depth. The PCM is capable of collecting 1000--4000 profiles in a 6- to 12-month period, depending on depth range and ambient currents. A variety of baroclinic motions are evident in the Bermuda observations. Upper ocean manifestations of both Kelvin and superinertial island-trapped waves dominate longshore currents. Vertical coherence of onshore current and temperature suggest that internal wave vertical wave number energy distribution is independent of frequency but modified by island bathymetry. Kinetic energy in shear integrated over a 115.6-m-thick layer in the upper ocean is limited to values less than or equal to the potential energy required to mix the existing stratification. Mixing events occur when kinetic energy associated with shear drives the bulk Richardson number (defined by the ratio of energy integrals over the range profiles) to unity, where it remains while shear and stratification disappear together.« less

A Novel Approach to Constrain Near-Surface Seismic Wave Speed Based on Polarization Analysis

NASA Astrophysics Data System (ADS)

Park, S.; Ishii, M.

2016-12-01

Understanding the seismic responses of cities around the world is essential for the risk assessment of earthquake hazards. One of the important parameters is the elastic structure of the sites, in particular, near-surface seismic wave speed, that influences the level of ground shaking. Many methods have been developed to constrain the elastic structure of the populated sites or urban basins, and here, we introduce a new technique based on analyzing the polarization content or the three-dimensional particle motion of seismic phases arriving at the sites. Polarization analysis of three-component seismic data was widely used up to about two decades ago, to detect signals and identify different types of seismic arrivals. Today, we have good understanding of the expected polarization direction and ray parameter for seismic wave arrivals that are calculated based on a reference seismic model. The polarization of a given phase is also strongly sensitive to the elastic wave speed immediately beneath the station. This allows us to compare the observed and predicted polarization directions of incoming body waves and infer the near-surface wave speed. This approach is applied to High-Sensitivity Seismograph Network in Japan, where we benchmark the results against the well-log data that are available at most stations. There is a good agreement between our estimates of seismic wave speeds and those from well logs, confirming the efficacy of the new method. In most urban environments, where well logging is not a practical option for measuring the seismic wave speeds, this method can provide a reliable, non-invasive, and computationally inexpensive estimate of near-surface elastic properties.

Newtonian noise and ambient ground motion for gravitational wave detectors

NASA Astrophysics Data System (ADS)

Beker, M. G.; van den Brand, J. F. J.; Hennes, E.; Rabeling, D. S.

2012-06-01

Fluctuations of the local gravitational field as a result of seismic and atmospheric displacements will limit the sensitivity of ground based gravitational wave detectors at frequencies below 10 Hz. We discuss the implications of Newtonian noise for future third generation gravitational wave detectors. The relevant seismic wave fields are predominately of human origin and are dependent on local infrastructure and population density. Seismic studies presented here show that considerable seismic noise reduction is possible compared to current detector locations. A realistic seismic amplitude spectral density of a suitably quiet site should not exceed 0.5 nm/(Hz/f)2 above 1 Hz. Newtonian noise models have been developed both analytically and by finite element analysis. These show that the contribution to Newtonian noise from surface waves due to distance sources significantly reduces with depth. Seismic displacements from local sources and body waves then become the dominant contributors to the Newtonian fluctuations.

Interaction of two walkers: wave-mediated energy and force.

PubMed

Borghesi, Christian; Moukhtar, Julien; Labousse, Matthieu; Eddi, Antonin; Fort, Emmanuel; Couder, Yves

2014-12-01

A bouncing droplet, self-propelled by its interaction with the waves it generates, forms a classical wave-particle association called a "walker." Previous works have demonstrated that the dynamics of a single walker is driven by its global surface wave field that retains information on its past trajectory. Here we investigate the energy stored in this wave field for two coupled walkers and how it conveys an interaction between them. For this purpose, we characterize experimentally the "promenade modes" where two walkers are bound and propagate together. Their possible binding distances take discrete values, and the velocity of the pair depends on their mutual binding. The mean parallel motion can be either rectilinear or oscillating. The experimental results are recovered analytically with a simple theoretical framework. A relation between the kinetic energy of the droplets and the total energy of the standing waves is established.

Dynamic modeling of injection-induced fault reactivation and ground motion and impact on surface structures and human perception

DOE PAGES

Rutqvist, Jonny; Cappa, Frederic; Rinaldi, Antonio P.; ...

2014-12-31

We summarize recent modeling studies of injection-induced fault reactivation, seismicity, and its potential impact on surface structures and nuisance to the local human population. We used coupled multiphase fluid flow and geomechanical numerical modeling, dynamic wave propagation modeling, seismology theories, and empirical vibration criteria from mining and construction industries. We first simulated injection-induced fault reactivation, including dynamic fault slip, seismic source, wave propagation, and ground vibrations. From co-seismic average shear displacement and rupture area, we determined the moment magnitude to about M w = 3 for an injection-induced fault reactivation at a depth of about 1000 m. We then analyzedmore » the ground vibration results in terms of peak ground acceleration (PGA), peak ground velocity (PGV), and frequency content, with comparison to the U.S. Bureau of Mines’ vibration criteria for cosmetic damage to buildings, as well as human-perception vibration limits. For the considered synthetic M w = 3 event, our analysis showed that the short duration, high frequency ground motion may not cause any significant damage to surface structures, and would not cause, in this particular case, upward CO 2 leakage, but would certainly be felt by the local population.« less

A novel sandwich-type traveling wave piezoelectric tracked mobile system.

PubMed

Wang, Liang; Shu, Chengyou; Zhang, Quan; Jin, Jiamei

2017-03-01

In this paper, a novel sandwich-type traveling wave piezoelectric tracked mobile system was proposed, designed, fabricated and experimentally investigated. The proposed system exhibits the advantages of simple structure, high mechanical integration, lack of electromagnetic interference, and lack of lubrication requirement, and hence shows potential application to robotic rovers for planetary exploration. The tracked mobile system is comprised of a sandwich actuating mechanism and a metal track. The actuating mechanism includes a sandwich piezoelectric transducer and two annular parts symmetrically placed at either end of the transducer, while the metal track is tensioned along the outer surfaces of the annular parts. Traveling waves with the same rotational direction are generated in the two annular parts, producing the microscopic elliptical motions of the surface particles on the annular parts. In this situation, if the pre-load is applied properly, the metal track can be driven by friction force to achieve bidirectional movement. At first, the finite element method was adopted to conduct the modal analysis and harmonic response analysis of the actuating mechanism, and the vibration characteristics were measured to confirm the operating principle. Then the optimal driving frequency of the system prototype, namely 35.1kHz, was measured by frequency sensitivity experiments. At last, the mechanical motion characteristics of the prototype were investigated experimentally. The results show that the average motion speeds of the prototype in dual directions were as 72mm/s and 61.5mm/s under the excitation voltage of 500V RMS , respectively. The optimal loading weights of the prototype in bi-directions were 0.32kg and 0.24kg with a maximum speed of 59.5mm/s and 61.67mm/s at the driving voltage of 300V RMS , respectively. Copyright © 2016 Elsevier B.V. All rights reserved.

Motion and dynamic responses of a semisubmersible in freak waves

NASA Astrophysics Data System (ADS)

Li, Xin; Deng, Yan-fei; Li, Lei; Tian, Xin-liang; Li, Jun

2017-12-01

The present research aims at clarifying the effects of freak wave on the motion and dynamic responses of a semisubmersible. To reveal the effects of mooring stiffness, two mooring systems were employed in the model tests and time-domain simulations. The 6-DOF motion responses and mooring tensions have been measured and the 3-DOF motions of fairleads were calculated as well. From the time series, trajectories and statistics information, the interactions between the freak wave and the semisubmersible have been demonstrated and the effects of mooring stiffness have been identified. The shortage of numerical simulations based on 3D potential flow theory is presented. Results show that the freak wave is likely to cause large horizontal motions for soft mooring system and to result in extremely large mooring tensions for tight mooring system. Therefore, the freak wave is a real threat for the marine structure, which needs to be carefully considered at design stage.

Chaotic ion motion in magnetosonic plasma waves

NASA Technical Reports Server (NTRS)

Varvoglis, H.

1984-01-01

The motion of test ions in a magnetosonic plasma wave is considered, and the 'stochasticity threshold' of the wave's amplitude for the onset of chaotic motion is estimated. It is shown that for wave amplitudes above the stochasticity threshold, the evolution of an ion distribution can be described by a diffusion equation with a diffusion coefficient D approximately equal to 1/v. Possible applications of this process to ion acceleration in flares and ion beam thermalization are discussed.

Incompressible SPH Model for Simulating Violent Free-Surface Fluid Flows

NASA Astrophysics Data System (ADS)

Staroszczyk, Ryszard

2014-06-01

In this paper the problem of transient gravitational wave propagation in a viscous incompressible fluid is considered, with a focus on flows with fast-moving free surfaces. The governing equations of the problem are solved by the smoothed particle hydrodynamics method (SPH). In order to impose the incompressibility constraint on the fluid motion, the so-called projection method is applied in which the discrete SPH equations are integrated in time by using a fractional-step technique. Numerical performance of the proposed model has been assessed by comparing its results with experimental data and with results obtained by a standard (weakly compressible) version of the SPH approach. For this purpose, a plane dam-break flow problem is simulated, in order to investigate the formation and propagation of a wave generated by a sudden collapse of a water column initially contained in a rectangular tank, as well as the impact of such a wave on a rigid vertical wall. The results of simulations show the evolution of the free surface of water, the variation of velocity and pressure fields in the fluid, and the time history of pressures exerted by an impacting wave on a wall.

Reflection and refraction of hydromagnetic waves at the magnetopause

NASA Technical Reports Server (NTRS)

Verzariu, P.

1973-01-01

Reflection and transmission coefficients of MHD waves are obtained at a stable, plane interface which separates two compressible, perfectly conducting media in relative motion to each other. The coefficients are evaluated for representative conditions of the quiet-time, near-earth magnetopause. The transmission coefficient averaged over a hemispherical distribution of incident waves is found to be 1-2%. Yet the magnitude of the energy flux deposited into the magnetosphere in a day averaged over a hemispherical distribution of waves having amplitudes of say 2-3 gamma, is estimated to be of the order 10 to the 22-nd power erg. Therefore the energy input of MHD waves must contribute significantly to the energy budget of the magnetosphere. The assumption that the boundary surface is a tangential discontinuity with no curvature limits the present theory to hydromagnetic frequencies higher than about .1 Hz.

Surface waves on the tailward flanks of the Earth's magnetopause

NASA Technical Reports Server (NTRS)

Seon, J.; Frank, L. A.; Lazarus, A. J.; Lepping, R. P.

1995-01-01

Forty-three examples of ISEE 1 tailward flank side magnetopause crossings are examined and directly compared with upstream solar wind parameters. The crossings are classified into two groups. In the first group, a few sudden magnetopause crossings are observed, whereas repeated magnetopause crossings and oscillatory motions, often with boundary layer signatures, are observed in the second group. These distinctive characteristics of the two groups are interpreted in terms of the surface waves due to the Kelvin-Helmholtz instability. It is found that low solar wind speed tends to favor characteristics of the first group, whereas high solar wind speed yields those of the second group. However, no evident correlations between the groups and the interplanetary magnetic field directions are found.

Langmuir Turbulence

DTIC Science & Technology

2015-09-30

1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Langmuir Turbulence Eric A. D’Asaro, Ramsey Harcourt...definitive experimental tests of the hypothesis that Langmuir Turbulence , specifically the equations of motion with the addition of the Craik-Leibovich...vortex force and advection by the surface wave Stokes drift, can accurately describe turbulence in the upper ocean boundary layer under conditions of

Validation and Performance Comparison of Numerical Codes for Tsunami Inundation

NASA Astrophysics Data System (ADS)

Velioglu, D.; Kian, R.; Yalciner, A. C.; Zaytsev, A.

2015-12-01

In inundation zones, tsunami motion turns from wave motion to flow of water. Modelling of this phenomenon is a complex problem since there are many parameters affecting the tsunami flow. In this respect, the performance of numerical codes that analyze tsunami inundation patterns becomes important. The computation of water surface elevation is not sufficient for proper analysis of tsunami behaviour in shallow water zones and on land and hence for the development of mitigation strategies. Velocity and velocity patterns are also crucial parameters and have to be computed at the highest accuracy. There are numerous numerical codes to be used for simulating tsunami inundation. In this study, FLOW 3D and NAMI DANCE codes are selected for validation and performance comparison. Flow 3D simulates linear and nonlinear propagating surface waves as well as long waves by solving three-dimensional Navier-Stokes (3D-NS) equations. FLOW 3D is used specificaly for flood problems. NAMI DANCE uses finite difference computational method to solve linear and nonlinear forms of shallow water equations (NSWE) in long wave problems, specifically tsunamis. In this study, these codes are validated and their performances are compared using two benchmark problems which are discussed in 2015 National Tsunami Hazard Mitigation Program (NTHMP) Annual meeting in Portland, USA. One of the problems is an experiment of a single long-period wave propagating up a piecewise linear slope and onto a small-scale model of the town of Seaside, Oregon. Other benchmark problem is an experiment of a single solitary wave propagating up a triangular shaped shelf with an island feature located at the offshore point of the shelf. The computed water surface elevation and velocity data are compared with the measured data. The comparisons showed that both codes are in fairly good agreement with each other and benchmark data. All results are presented with discussions and comparisons. The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement No 603839 (Project ASTARTE - Assessment, Strategy and Risk Reduction for Tsunamis in Europe)

The geometry and fluid dynamics of two- and three-dimensional maneuvers of burrowing and swimming C. elegans

NASA Astrophysics Data System (ADS)

Blawzdziewicz, Jerzy; Bilbao, Alejandro; Patel, Amar; Rahman, Mizanur; Vanapalli, Siva A.

2016-11-01

In its natural environment, which is decomposing organic matter and water, C. elegans swims and burrows in 3D complex media. Yet quantitative investigations of C. elegans locomotion have been limited to 2D motion. Recently we have provided a quantitative analysis of turning maneuvers of crawling and swimming nematodes on flat surfaces and in 2D fluid layers. Here, we follow with the first full 3D description of how C. elegans moves in complex 3D environments. We show that the nematode can explore 3D space by combining 2D turns with roll maneuvers that result in rotation of the undulation plane around the direction of motion. Roll motion is achieved by superposing a 2D curvature wave with nonzero body torsion; 2D turns (within the current undulation plane) are attained by variation of undulation wave parameters. Our results indicate that while hydrodynamic interactions reduce angles of 2D turns, the roll efficiency is significantly enhanced. This hydrodynamic effect explains the rapid nematode reorientation observed in 3D swimming.

Earthquake early warning using P-waves that appear after initial S-waves

NASA Astrophysics Data System (ADS)

Kodera, Y.

2017-12-01

As measures for underprediction for large earthquakes with finite faults and overprediction for multiple simultaneous earthquakes, Hoshiba (2013), Hoshiba and Aoki (2015), and Kodera et al. (2016) proposed earthquake early warning (EEW) methods that directly predict ground motion by computing the wave propagation of observed ground motion. These methods are expected to predict ground motion with a high accuracy even for complicated scenarios because these methods do not need source parameter estimation. On the other hand, there is room for improvement in their rapidity because they predict strong motion prediction mainly based on the observation of S-waves and do not explicitly use P-wave information available before the S-waves. In this research, we propose a real-time P-wave detector to incorporate P-wave information into these wavefield-estimation approaches. P-waves within a few seconds from the P-onsets are commonly used in many existing EEW methods. In addition, we focus on P-waves that may appear in the later part of seismic waves. Kurahashi and Irikura (2013) mentioned that P-waves radiated from strong motion generation areas (SMGAs) were recognizable after S-waves of the initial rupture point in the 2011 off the Pacific coast of Tohoku earthquake (Mw 9.0) (the Tohoku-oki earthquake). Detecting these P-waves would enhance the rapidity of prediction for the peak ground motion generated by SMGAs. We constructed a real-time P-wave detector that uses a polarity analysis. Using acceleration records in boreholes of KiK-net (band-pass filtered around 0.5-10 Hz with site amplification correction), the P-wave detector performed the principal component analysis with a sliding window of 4 s and calculated P-filter values (e.g. Ross and Ben-Zion, 2014). The application to the Tohoku-oki earthquake (Mw 9.0) showed that (1) peaks of P-filter that corresponded to SMGAs appeared in several stations located near SMGAs and (2) real-time seismic intensities (Kunugi et al., 2013) reached the local maximum several seconds after the P-filter peaks appeared. These findings indicate that the proposed P-wave detector allows wavefield-estimation approaches to predict the peak ground motion of SMGAs with a certain lead time.

Dynamic Behavior of Spicules Inferred from Perpendicular Velocity Components

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sharma, Rahul; Verth, Gary; Erdélyi, Robertus

2017-05-10

Understanding the dynamic behavior of spicules, e.g., in terms of magnetohydrodynamic (MHD) wave mode(s), is key to unveiling their role in energy and mass transfer from the photosphere to corona. The transverse, torsional, and field-aligned motions of spicules have previously been observed in imaging spectroscopy and analyzed separately for embedded wave-mode identification. Similarities in the Doppler signatures of spicular structures for both kink and torsional Alfvén wave modes have led to the misinterpretation of the dominant wave mode in these structures and is a subject of debate. Here, we aim to combine line- of-sight (LOS) and plane-of-sky (POS) velocity componentsmore » using the high spatial/temporal resolution H α imaging-spectroscopy data from the CRisp Imaging SpectroPolarimeter based at the Swedish Solar Telescope to achieve better insight into the underlying nature of these motions as a whole. The resultant three-dimensional velocity vectors and the other derived quantities (e.g., magnetic pressure perturbations) are used to identify the MHD wave mode(s) responsible for the observed spicule motion. We find a number of independent examples where the bulk transverse motion of the spicule is dominant either in the POS or along the LOS. It is shown that the counterstreaming action of the displaced external plasma due to spicular bulk transverse motion has a similar Doppler profile to that of the m = 0 torsional Alfvén wave when this motion is predominantly perpendicular to the LOS. Furthermore, the inferred magnetic pressure perturbations support the kink wave interpretation of observed spicular bulk transverse motion rather than any purely incompressible MHD wave mode, e.g., the m = 0 torsional Alfvén wave.« less

Observations and modeling of the effects of waves and rotors on submeso and turbulence variability within the stable boundary layer over central Pennsylvania

NASA Astrophysics Data System (ADS)

Suarez Mullins, Astrid

Terrain-induced gravity waves and rotor circulations have been hypothesized to enhance the generation of submeso motions (i.e., nonstationary shear events with spatial and temporal scales greater than the turbulence scale and smaller than the meso-gamma scale) and to modulate low-level intermittency in the stable boundary layer (SBL). Intermittent turbulence, generated by submeso motions and/or the waves, can affect the atmospheric transport and dispersion of pollutants and hazardous materials. Thus, the study of these motions and the mechanisms through which they impact the weakly to very stable SBL is crucial for improving air quality modeling and hazard predictions. In this thesis, the effects of waves and rotor circulations on submeso and turbulence variability within the SBL is investigated over the moderate terrain of central Pennsylvania using special observations from a network deployed at Rock Springs, PA and high-resolution Weather Research and Forecasting (WRF) model forecasts. The investigation of waves and rotors over central PA is important because 1) the moderate topography of this region is common to most of the eastern US and thus the knowledge acquired from this study can be of significance to a large population, 2) there have been little evidence of complex wave structures and rotors reported for this region, and 3) little is known about the waves and rotors generated by smaller and more moderate topographies. Six case studies exhibiting an array of wave and rotor structures are analyzed. Observational evidence of the presence of complex wave structures, resembling nonstationary trapped gravity waves and downslope windstorms, and complex rotor circulations, resembling trapped and jump-type rotors, is presented. These motions and the mechanisms through which they modulate the SBL are further investigated using high-resolution WRF forecasts. First, the efficacy of the 0.444-km horizontal grid spacing WRF model to reproduce submeso and meso-gamma motions, generated by waves and rotors and hypothesized to impact the SBL, is investigated using a new wavelet-based verification methodology for assessing non-deterministic model skill in the submeso and meso-gamma range to complement standard deterministic measures. This technique allows the verification and/or intercomparison of any two nonstationary stochastic systems without many of the limitations of typical wavelet-based verification approaches (e.g., selection of noise models, testing for significance, etc.). Through this analysis, it is shown that the WRF model largely underestimates the number of small amplitude fluctuations in the small submeso range, as expected; and it overestimates the number of small amplitude fluctuations in the meso-gamma range, generally resulting in forecasts that are too smooth. Investigation of the variability for different initialization strategies shows that deterministic wind speed predictions are less sensitive to the choice of initialization strategy than temperature forecasts. Similarly, investigation of the variability for various planetary boundary layer (PBL) parameterizations reveals that turbulent kinetic energy (TKE)-based schemes have an advantage over the non-local schemes for non-deterministic motions. The larger spread in the verification scores for various PBL parameterizations than initialization strategies indicates that PBL parameterization may play a larger role modulating the variability of non-deterministic motions in the SBL for these cases. These results confirm previous findings that have shown WRF to have limited skill forecasting submeso variability for periods greater than ~20 min. The limited skill of the WRF at these scales in these cases is related to the systematic underestimation of the amplitude of observed fluctuations. These results are implemented in the model design and configuration for the investigation of nonstationary waves and rotor structures modulating submeso and mesogamma motions and the SBL. Observations and WRF forecasts of two wave cases characterized by nonstationary waves and rotors are investigated to show the WRF model to have reasonable accuracy forecasting low-level temperature and wind speed in the SBL and to qualitatively produce rotors, similar to those observed, as well as some of the mechanisms modulating their development and evolution. Finally, observations and high-resolution WRF forecasts under different environmental conditions using various initialization strategies are used to investigate the impact of nonlinear gravity waves and rotor structures on the generation of intermittent turbulence and valley transport in the SBL. Evidence of the presence of elevated regions of TKE generated by the complex waves and rotors is presented and investigated using an additional four case studies, exhibiting two synoptic flow regimes and different wave and rotor structures. Throughout this thesis, terrain-induced gravity waves and rotors in the SBL are shown to synergistically interact with the surface cold pool and to enhance low-level turbulence intermittency through the development of submeso and meso-gamma motions. These motions are shown to be an important source of uncertainty for the atmospheric transport and dispersion of pollutants and hazardous materials under very stable conditions. (Abstract shortened by ProQuest.).

On the measurement of guided wavefields via air-coupled ultrasonic transducers

NASA Astrophysics Data System (ADS)

Michaels, Jennifer E.; Michaels, Thomas E.

2015-03-01

Guided wavefields are now routinely measured with scanning laser vibrometers for both characterization of guided wave propagation and damage assessment. However, these measurements are usually time-consuming, particularly for imaging of large areas, primarily because of the degree of signal averaging required to reduce incoherent noise. A scanned air-coupled transducer is an alternative wavefield acquisition method that is based upon recording the very small amplitude pressure waves that leak into air from the out-of-plane motion of the guided wavefield. Air-coupled methods are attractive because they are not sensitive to small variations in surface optical reflectivity and special surface preparations are thus not necessary. In addition, not as much averaging is needed, making the acquisition process much faster. Unlike laser vibrometry, the recorded signals are not a direct measure of the wave motion, but experiments have shown that the acquired wavefields resemble those obtained from laser-based systems. For the work presented here, wavefield data were recorded with both methods for the same aluminum plate and composite panel specimens. Data are qualitatively compared in several domains to assess differences in temporal characteristics and modal content. Although signals are not identical, it is shown that the air-coupled transducer data exhibits similar modal content to that of the laser vibrometry data and may provide a reasonable alternative for some applications.

Long Duration of Ground Motion in the Paradigmatic Valley of Mexico

PubMed Central

Cruz-Atienza, V. M.; Tago, J.; Sanabria-Gómez, J. D.; Chaljub, E.; Etienne, V.; Virieux, J.; Quintanar, L.

2016-01-01

Built-up on top of ancient lake deposits, Mexico City experiences some of the largest seismic site effects worldwide. Besides the extreme amplification of seismic waves, duration of intense ground motion from large subduction earthquakes exceeds three minutes in the lake-bed zone of the basin, where hundreds of buildings collapsed or were seriously damaged during the magnitude 8.0 Michoacán earthquake in 1985. Different mechanisms contribute to the long lasting motions, such as the regional dispersion and multiple-scattering of the incoming wavefield from the coast, more than 300 km away the city. By means of high performance computational modeling we show that, despite the highly dissipative basin deposits, seismic energy can propagate long distances in the deep structure of the valley, promoting also a large elongation of motion. Our simulations reveal that the seismic response of the basin is dominated by surface-waves overtones, and that this mechanism increases the duration of ground motion by more than 170% and 290% of the incoming wavefield duration at 0.5 and 0.3 Hz, respectively, which are two frequencies with the largest observed amplification. This conclusion contradicts what has been previously stated from observational and modeling investigations, where the basin itself has been discarded as a preponderant factor promoting long and devastating shaking in Mexico City. PMID:27934934

Transformation of Elastic Wave Energy to the Energy of Motion of Bodies

NASA Astrophysics Data System (ADS)

Vesnitskiĭ, A. I.; Lisenkova, E. E.

2002-01-01

The motion of a body along an elastic guide under the effect of an incident wave is considered. An equation describing the longitudinal motion of a body along an arbitrary guide is derived from the laws governing the energy and momentum variations for the case when the incident wave generates a single reflected wave. The equations that describe the motion of a body along a string and along a beam corresponding to the Bernoulli-Euler model are considered as examples. The process of the body acceleration along a beam of the aforementioned type is investigated. For the subcritical velocities, the law governing the motion of the body and the ratio of the kinetic energy variation to the energy supplied to the body are determined.

Measurement of Near-Surface Salinity, Temperature and Directional Wave Spectra using a Novel Wave-Following, Lagrangian Surface Contact Buoy

NASA Astrophysics Data System (ADS)

Boyle, J. P.

2016-02-01

Results from a surface contact drifter buoy which measures near-surface conductivity ( 10 cm depth), sea state characteristics and near-surface water temperature ( 2 cm depth) are described. This light (< 750 gram), wave-following discus buoy platform has a hull diameter of 25 cm and a thickness of approximately 3 cm. The buoy is designed to allow for capsize events, but remains top up because it is ballasted for self-righting. It has a small above-surface profile and low windage, resulting in near-Lagrangian drift characteristics. It is autonomous, with low power requirements and solar panel battery recharging. Onboard sensors include an inductive toroidal conductivity probe for salinity measurement, a nine-degrees-of-freedom motion package for derivation of directional wave spectra and a thermocouple for water temperature measurement. Data retrieval for expendable, ocean-going operation uses an onboard Argos transmitter. Scientific results as well as data processing algorithms are presented from laboratory and field experiments which support qualification of buoy platform measurements. These include sensor calibration experiments, longer-term dock-side biofouling experiments during 2013-2014 and a series of short-duration ocean deployments in the Gulf Stream in 2014. In addition, a treatment method will be described which appears to minimize the effects of biofouling on the inductive conductivity probe when in coastal surface waters. Due to its low cost and ease of deployment, scores, perhaps hundreds of these novel instruments could be deployed from ships or aircraft during process studies or to provide surface validation for satellite-based measurements, particularly in high precipitation regions.

The interaction of extreme waves with hull elements

NASA Astrophysics Data System (ADS)

Galiev, Shamil; Flay, Richard

2010-05-01

The problem of the impact of a rogue wave onto a deformable marine structure is formulated in a few publications (see, for example, a short review in http://researchspace.auckland.ac.nz/handle/2292/4474). In this paper the results from numerical and experimental investigations of the effect of cavitation on the deformation of a hull element, loaded by a wall of water, generated by an extreme ocean surface wave are considered. The hull element is modelled as a circular metal plate with the edge of the plate rigidly clamped. The plate surface is much smaller than the surface of the wave front, so that at the initial moment of the interaction, the pressure is constant on the plate surface. At the next instant, because of the plate deformation, axisymmetric loading of the plate occurs. The influences of membrane forces and plastic deformations are ignored, and therefore, the equation of plate motion has the following classical form Eh3(wrrrr+2r -1wrrrr- r-2wrr+r-3wr) = - 121- ν2)[ρhwtt+ δ(r,t)(p+ ρ0a0wt)]. Here w is the plate displacement, subscripts t and rindicate derivatives with respect to time and the radial coordinate, PIC is the plate material density, his the plate thickness, Eis Young's modulus, PIC is Poisson's ratio and p is the pressure of the incident surface wave measured on the wall, PIC is the water density, PIC is the speed of sound in water, and PIC is the normal velocity of the plate. The term PIC takes into account the effect of the deformability of the plate. Obviously, the hull of a vessel is not rigid like a solid wall, but starts to deform and to move. This motion produces a reflected pressure wave, which travels from the hull into the water wave with a magnitude equal to PIC . The normal velocity is positive so the reflected pressure PIC is negative (tensile wave). If the fluid pressure drops below some critical value pk, the wet plate surface separates from the water, and cavitation may be generated. The function δ(r,t) takes into account the effect of the hull cavitation. The function PIC or 0, and is determined during the numerical calculations. Case PIC is valid for the case with no cavitation, and the case δ(r,t) = 0 corresponds to the case with hull cavitation. The results from these calculations allow us to draw the following conclusions. 1) The pressures generated depend greatly on the irregularity of waves. In particular, the shock pressures are affected by this irregularity, making the prediction of their magnitude almost impossible. 2) In the majority of cases, the elastic deformation of thin hull elements by a short duration water wave pressure pulse is accompanied by hull cavitation. The effect of cavitation may be important, provided that the time of loading by the water wall pressure is less than the period of the fundamental frequency of the hull element oscillations. 3) The cavitation zones can enclose practically the whole wet surface and thus completely change the water loading onto the hull element, compared to the pressures that would be developed in the absence of cavitation. 4) The hull element deformation generates surface pressure and cavitation waves. 5) Cavitation interaction of extreme water waves with structures, and hull response, are complex topics, which are not well understood and are expected to be important in the design of advanced ships in the future. 6) The existence of rogue waves makes it important to re-examine some of the ideas developed earlier which are fundamental to merchant ship design.

Chaos and ion heating in a slow shock

NASA Technical Reports Server (NTRS)

Lin, Y.; Lee, L. C.

1991-01-01

An ion heating mechanism is proposed of slow shocks, which is associated with the chaotic motion of particles in the downstream wave field. For a coherent electromagnetic wave propagating along the downstream magnetic field, corresponding to switch-off shocks, the particle motions are not chaotic. For an oblique wave, the interaction between the particles and the wave field may lead to chaotic particle motions. Such particles may be greatly thermalized within one wavelength after they are incident into the downstream wave field. The results can be used to explain the existence of the critical intermediate Mach number observed in the hybrid simulations.

Surface current balance and thermoelectric whistler wings at airless astrophysical bodies: Cassini at Rhea.

PubMed

Teolis, B D; Sillanpää, I; Waite, J H; Khurana, K K

2014-11-01

Sharp magnetic perturbations found by the Cassini spacecraft at the edge of the Rhea flux tube are consistent with field-aligned flux tube currents. The current system results from the difference of ion and electron gyroradii and the requirement to balance currents on the sharp Rhea surface. Differential-type hybrid codes that solve for ion velocity and magnetic field have an intrinsic difficulty modeling the plasma absorber's sharp surface. We overcome this problem by instead using integral equations to solve for ion and electron currents and obtain agreement with the magnetic perturbations at Rhea's flux tube edge. An analysis of the plasma dispersion relations and Cassini data reveals that field-guided whistler waves initiated by (1) the electron velocity anisotropy in the flux tube and (2) interaction with surface sheath electrostatic waves on topographic scales may facilitate propagation of the current system to large distances from Rhea. Current systems like those at Rhea should occur generally, for plasma absorbers of any size such as spacecraft or planetary bodies, in a wide range of space plasma environments. Motion through the plasma is not essential since the current system is thermodynamic in origin, excited by heat flow into the object. The requirements are a difference of ion and electron gyroradii and a sharp surface, i.e., without a significant thick atmosphere. Surface current balance condition yields a current system at astronomical bodiesCurrent system possible for sharp (airless) objects of any sizeCurrent system is thermoelectric and motion through the plasma nonessential.

Surface current balance and thermoelectric whistler wings at airless astrophysical bodies: Cassini at Rhea

PubMed Central

Teolis, B D; Sillanpää, I; Waite, J H; Khurana, K K

2014-01-01

Sharp magnetic perturbations found by the Cassini spacecraft at the edge of the Rhea flux tube are consistent with field-aligned flux tube currents. The current system results from the difference of ion and electron gyroradii and the requirement to balance currents on the sharp Rhea surface. Differential-type hybrid codes that solve for ion velocity and magnetic field have an intrinsic difficulty modeling the plasma absorber's sharp surface. We overcome this problem by instead using integral equations to solve for ion and electron currents and obtain agreement with the magnetic perturbations at Rhea's flux tube edge. An analysis of the plasma dispersion relations and Cassini data reveals that field-guided whistler waves initiated by (1) the electron velocity anisotropy in the flux tube and (2) interaction with surface sheath electrostatic waves on topographic scales may facilitate propagation of the current system to large distances from Rhea. Current systems like those at Rhea should occur generally, for plasma absorbers of any size such as spacecraft or planetary bodies, in a wide range of space plasma environments. Motion through the plasma is not essential since the current system is thermodynamic in origin, excited by heat flow into the object. The requirements are a difference of ion and electron gyroradii and a sharp surface, i.e., without a significant thick atmosphere. Key Points Surface current balance condition yields a current system at astronomical bodies Current system possible for sharp (airless) objects of any size Current system is thermoelectric and motion through the plasma nonessential PMID:26167436

Mesh-free distributed point source method for modeling viscous fluid motion between disks vibrating at ultrasonic frequency.

PubMed

Wada, Yuji; Kundu, Tribikram; Nakamura, Kentaro

2014-08-01

The distributed point source method (DPSM) is extended to model wave propagation in viscous fluids. Appropriate estimation on attenuation and boundary layer formation due to fluid viscosity is necessary for the ultrasonic devices used for acoustic streaming or ultrasonic levitation. The equations for DPSM modeling in viscous fluids are derived in this paper by decomposing the linearized viscous fluid equations into two components-dilatational and rotational components. By considering complex P- and S-wave numbers, the acoustic fields in viscous fluids can be calculated following similar calculation steps that are used for wave propagation modeling in solids. From the calculations reported the precision of DPSM is found comparable to that of the finite element method (FEM) for a fundamental ultrasonic field problem. The particle velocity parallel to the two bounding surfaces of the viscous fluid layer between two rigid plates (one in motion and one stationary) is calculated. The finite element results agree well with the DPSM results that were generated faster than the transient FEM results.

Time-lapse changes in velocity and anisotropy in Japan's near surface after the 2011 Tohoku earthquake

NASA Astrophysics Data System (ADS)

Snieder, R.; Nakata, N.

2012-12-01

A strong-motion recording network, KiK-net, helps us to monitor temporal changes in the near surface in Japan. Each KiK-net station has two seismometers at the free surface and in a borehole a few hundred meters deep, and we can retrieve a traveling wave from the borehole receiver to the surface receiver by applying deconvolution based seismic interferometry. KiK-net recorded the 2011 Tohoku earthquake, which is one of the largest earthquakes in recent history, and seismicity around the time of the main shock. Using records of these seismicity and computing mean values of near-surface shear-wave velocities in the periods of January 1--March 10 and March 12--May 26 in 2011, we detect about a 5% reduction in the velocity after the Tohoku earthquake. The area of the velocity reduction is about 1,200 km wide, which is much wider than earlier studies reporting velocity reductions after larger earthquakes. The reduction partly recovers with time. We can also estimate the azimuthal anisotropy by detecting shear-wave splitting after applying seismic interferometry. Estimating mean values over the same periods as the velocity, we find the strength of anisotropy increased in most parts of northeastern Japan, but fast shear-wave polarization directions in the near surface did not significantly change. The changes in anisotropy and velocity are generally correlated, especially in the northeastern Honshu (the main island in Japan).

Suggested Courseware for the Non-Calculus Physics Student: Simple Harmonic Motion, Wave Motion, and Sound.

ERIC Educational Resources Information Center

Grable-Wallace, Lisa; And Others

1989-01-01

Evaluates 5 courseware packages covering the topics of simple harmonic motion, 7 packages for wave motion, and 10 packages for sound. Discusses the price range, sub-topics, program type, interaction, time, calculus required, graphics, and comments of each courseware. Selects several packages based on the criteria. (YP)

Coupling of an acoustic wave to shear motion due to viscous heating

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Bin; Goree, J.

2016-07-15

Viscous heating due to shear motion in a plasma can result in the excitation of a longitudinal acoustic wave, if the shear motion is modulated in time. The coupling mechanism is a thermal effect: time-dependent shear motion causes viscous heating, which leads to a rarefaction that can couple into a longitudinal wave, such as an acoustic wave. This coupling mechanism is demonstrated in an electrostatic three-dimensional (3D) simulation of a dusty plasma, in which a localized shear flow is initiated as a pulse, resulting in a delayed outward propagation of a longitudinal acoustic wave. This coupling effect can be profoundmore » in plasmas that exhibit localized viscous heating, such as the dusty plasma we simulated using parameters typical of the PK-4 experiment. We expect that a similar phenomenon can occur with other kinds of plasma waves.« less

Autocalibrating motion-corrected wave-encoding for highly accelerated free-breathing abdominal MRI.

PubMed

Chen, Feiyu; Zhang, Tao; Cheng, Joseph Y; Shi, Xinwei; Pauly, John M; Vasanawala, Shreyas S

2017-11-01

To develop a motion-robust wave-encoding technique for highly accelerated free-breathing abdominal MRI. A comprehensive 3D wave-encoding-based method was developed to enable fast free-breathing abdominal imaging: (a) auto-calibration for wave-encoding was designed to avoid extra scan for coil sensitivity measurement; (b) intrinsic butterfly navigators were used to track respiratory motion; (c) variable-density sampling was included to enable compressed sensing; (d) golden-angle radial-Cartesian hybrid view-ordering was incorporated to improve motion robustness; and (e) localized rigid motion correction was combined with parallel imaging compressed sensing reconstruction to reconstruct the highly accelerated wave-encoded datasets. The proposed method was tested on six subjects and image quality was compared with standard accelerated Cartesian acquisition both with and without respiratory triggering. Inverse gradient entropy and normalized gradient squared metrics were calculated, testing whether image quality was improved using paired t-tests. For respiratory-triggered scans, wave-encoding significantly reduced residual aliasing and blurring compared with standard Cartesian acquisition (metrics suggesting P < 0.05). For non-respiratory-triggered scans, the proposed method yielded significantly better motion correction compared with standard motion-corrected Cartesian acquisition (metrics suggesting P < 0.01). The proposed methods can reduce motion artifacts and improve overall image quality of highly accelerated free-breathing abdominal MRI. Magn Reson Med 78:1757-1766, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

Rupture Dynamics along Thrust Dipping Fault: Inertia Effects due to Free Surface Wave Interactions

NASA Astrophysics Data System (ADS)

Vilotte, J. P.; Scala, A.; Festa, G.

2017-12-01

We numerically investigate the dynamic interaction between free surface and up-dip, in-plane rupture propagation along thrust faults, under linear slip-weakening friction. With reference to shallow along-dip rupture propagation during large subduction earthquakes, we consider here low dip-angle fault configurations with fixed strength excess and depth-increasing initial stress. In this configuration, the rupture undergoes a break of symmetry with slip-induced normal stress perturbations triggered by the interaction with reflected waves from the free surface. We found that both body-waves - behind the crack front - and surface waves - at the crack front - can trigger inertial effects. When waves interact with the rupture before this latter reaches its asymptotic speed, the rupture can accelerate toward the asymptotic speed faster than in the unbounded symmetric case, as a result of these inertial effects. Moreover, wave interaction at the crack front also affects the slip rate generating large ground motion on the hanging wall. Imposing the same initial normal stress, frictional strength and stress drop while varying the static friction coefficient we found that the break of symmetry makes the rupture dynamics dependent on the absolute value of friction. The higher the friction the stronger the inertial effect both in terms of rupture acceleration and slip amount. When the contact condition allows the fault interface to open close to the free surface, the length of the opening zone is shown to depend on the propagation length, the initial normal stress and the static friction coefficient. These new results are shown to agree with analytical results of rupture propagation in bounded media, and open new perspectives for understanding the shallow rupture of large subduction earthquakes and tsunami sources.

Plasmonic rack-and-pinion gear with chiral metasurface

NASA Astrophysics Data System (ADS)

Gorodetski, Yuri; Karabchevsky, Alina

2016-04-01

The effect of circularly polarized beaming excited by traveling surface plasmons, via chiral metasurface is experimentally studied. Here we show that the propagation direction of the plasmonic wave, evanescently excited on the thin gold film affects the handedness of the scattered beam polarization. Nanostructured metasurface leads to excitation of localized plasmonic modes whose relative spatial orientation induces overall spin-orbit interaction. This effect is analogical to the rack-and-pinion gear: the rotational motion into the linear motion converter. From the practical point of view, the observed effect can be utilized in integrated optical circuits for communication systems, cyber security and sensing.

New Astrometric Limits on the Stochastic Gravitational Wave Background

NASA Astrophysics Data System (ADS)

Darling, Jeremiah K.; Truebenbach, Alexandra; Paine, Jennie

2018-06-01

We present new limits on the low frequency (f < 10-8 Hz) stochastic gravitational wave background using correlated extragalactic proper motions. The familiar methods for gravitational wave detection are ground- and space-based laser interferometry, pulsar timing, and polarization of the cosmic microwave background. Astrometry offers an additional path to gravitational wave detection because gravitational waves deflect the light rays of extragalactic objects, creating apparent proper motions in a quadrupolar (and higher order modes) pattern. Astrometry is sensitive to gravitational waves with frequencies between roughly 10-18 Hz and 10-8 Hz (between H0 and 1/3 yr-1), which overlaps and bridges the pulsar timing and CMB polarization regimes. We present the methods and results of two complementary approaches to astrometric gravitational wave detection: (1) a small ~500-object radio interferometric sample with low per-source proper motion uncertainty but large intrinsic proper motions caused by radio jets, and (2) a thousand-fold larger sample with large per-source uncertainties that has small intrinsic proper motions (Gaia active galactic nuclei). Both approaches produce limits on ΩGW, the energy density of gravitational waves as a fraction of the cosmological critical energy density.The authors acknowledge support from the NSF grant AST-1411605 and the NASA grant 14-ATP14-0086.

Teleseismic body waves from dynamically rupturing shallow thrust faults: Are they opaque for surface-reflected phases?

USGS Publications Warehouse

Smith, D.E.; Aagaard, Brad T.; Heaton, T.H.

2005-01-01

We investigate whether a shallow-dipping thrust fault is prone to waveslip interactions via surface-reflected waves affecting the dynamic slip. If so, can these interactions create faults that are opaque to radiated energy? Furthermore, in this case of a shallow-dipping thrust fault, can incorrectly assuming a transparent fault while using dislocation theory lead to underestimates of seismic moment? Slip time histories are generated in three-dimensional dynamic rupture simulations while allowing for varying degrees of wave-slip interaction controlled by fault-friction models. Based on the slip time histories, P and SH seismograms are calculated for stations at teleseismic distances. The overburdening pressure caused by gravity eliminates mode I opening except at the tip of the fault near the surface; hence, mode I opening has no effect on the teleseismic signal. Normalizing by a Haskell-like traditional kinematic rupture, we find teleseismic peak-to-peak displacement amplitudes are approximately 1.0 for both P and SH waves, except for the unrealistic case of zero sliding friction. Zero sliding friction has peak-to-peak amplitudes of 1.6 for P and 2.0 for SH waves; the fault slip oscillates about its equilibrium value, resulting in a large nonzero (0.08 Hz) spectral peak not seen in other ruptures. These results indicate wave-slip interactions associated with surface-reflected phases in real earthquakes should have little to no effect on teleseismic motions. Thus, Haskell-like kinematic dislocation theory (transparent fault conditions) can be safety used to simulate teleseismic waveforms in the Earth.

Gravity waves

NASA Technical Reports Server (NTRS)

Fritts, David

1987-01-01

Gravity waves contributed to the establishment of the thermal structure, small scale (80 to 100 km) fluctuations in velocity (50 to 80 m/sec) and density (20 to 30%, 0 to peak). Dominant gravity wave spectrum in the middle atmosphere: x-scale, less than 100 km; z-scale, greater than 10 km; t-scale, less than 2 hr. Theorists are beginning to understand middle atmosphere motions. There are two classes: Planetary waves and equatorial motions, gravity waves and tidal motions. The former give rise to variability at large scales, which may alter apparent mean structure. Effects include density and velocity fluctuations, induced mean motions, and stratospheric warmings which lead to the breakup of the polar vortex and cooling of the mesosphere. On this scale are also equatorial quasi-biennial and semi-annual oscillations. Gravity wave and tidal motions produce large rms fluctuations in density and velocity. The magnitude of the density fluctuations compared to the mean density is of the order of the vertical wavelength, which grows with height. Relative density fluctuations are less than, or of the order of 30% below the mesopause. Such motions may cause significant and variable convection, and wind shear. There is a strong seasonal variation in gravity wave amplitude. Additional observations are needed to address and quantify mean and fluctuation statistics of both density and mean velocity, variability of the mean and fluctuations, and to identify dominant gravity wave scales and sources as well as causes of variability, both temporal and geographic.

A formulation of directivity for earthquake sources using isochrone theory

USGS Publications Warehouse

Spudich, Paul; Chiou, Brian S.J.; Graves, Robert; Collins, Nancy; Somerville, Paul

2004-01-01

A functional form for directivity effects can be derived from isochrone theory, in which the measure of the directivity-induced amplification of an S body wave is c, the isochrone velocity. Ground displacement of the near-, intermediate-, and far-field terms of P and S waves is linear in isochrone velocity for a finite source in a whole space. We have developed an approximation c-tilde-prime of isochrone velocity that can easily be implemented as a predictor of directivity effects in empirical ground motion prediction relations. Typically, for a given fault surface, hypocenter, and site geometry, c-tilde-prime is a simple function of the hypocentral distance, the rupture distance, the crustal shear wave speed in the seismogenic zone, and the rupture velocity. c-tilde-prime typically ranges in the interval 0.44, for rupture away from the station, to about 4, for rupture toward the station. In this version of the theory directivity is independent of period. Additionally, we have created another functional form which is c-tilde-prime modified to include the approximate radiation pattern of a finite fault having a given rake. This functional form can be used to model the spatial variations of fault-parallel and fault-normal horizontal ground motions. The strengths of this formulation are 1) the proposed functional form is based on theory, 2) the predictor is unambiguously defined for all possible site locations and source rakes, and 3) it can easily be implemented for well-studied important previous earthquakes. We compare predictions of our functional form with synthetic ground motions calculated for finite strike-slip and dip-slip faults in the magnitude range 6.5 - 7.5. In general our functional form correlates best with computed fault-normal and fault-parallel motions in the synthetic motions calculated for events with M6.5. Correlation degrades but is still useful for larger events and for the geometric average horizontal motions. We have had limited success applying it to geometrically complicated faults.

Crustal Structure of Iraq from Receiver Functions and Surface Wave Dispersion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gok, R; Mahdi, H; Al-Shukri, H

2006-08-31

We report the crustal structure of Iraq, located in the northeastern Arabian plate, estimated by joint inversion of P-wave receiver functions and surface wave group velocity dispersion. Receiver functions were computed from teleseismic recordings at two temporary broadband seismic stations in Mosul (MSL) and Baghdad (BHD), separated by approximately 360 km. Group velocity dispersion curves at the sites were derived from continental-scale tomography of Pasyanos (2006). The inversion results show that the crustal thicknesses are 39 km at MSL and 43 km at BHD. Both sites reveal low velocity surface layers consistent with sedimentary thickness of about 3 km atmore » station MSL and 7 km at BHD, agreeing well with the existing models. Ignoring the sediments, the crustal velocities and thicknesses are remarkably similar between the two stations, suggesting that the crustal structure of the proto-Arabian Platform in northern Iraq was uniform before subsidence and deposition of the sediments in the Cenozoic. Deeper low velocity sediments at BHD are expected to result in higher ground motions for earthquakes.« less

Controlled rotation and translation of spherical particles or living cells by surface acoustic waves.

PubMed

Bernard, Ianis; Doinikov, Alexander A; Marmottant, Philippe; Rabaud, David; Poulain, Cédric; Thibault, Pierre

2017-07-11

We show experimental evidence of the acoustically-assisted micromanipulation of small objects like solid particles or blood cells, combining rotation and translation, using high frequency surface acoustic waves. This was obtained from the leakage in a microfluidic channel of two standing waves arranged perpendicularly in a LiNbO 3 piezoelectric substrate working at 36.3 MHz. By controlling the phase lag between the emitters, we could, in addition to translation, generate a swirling motion of the emitting surface which, in turn, led to the rapid rotation of spherical polystyrene Janus beads suspended in the channel and of human red and white blood cells up to several rounds per second. We show that these revolution velocities are compatible with a torque caused by the acoustic streaming that develops at the particles surface, like that first described by [F. Busse et al., J. Acoust. Soc. Am., 1981, 69(6), 1634-1638]. This device, based on standard interdigitated transducers (IDTs) adjusted to emit at equal frequencies, opens a way to a large range of applications since it allows the simultaneous control of the translation and rotation of hard objects, as well as the investigation of the response of cells to shear stress.

Inferring Upper Ocean Dynamics from Horizontal Wavenumber Spectra in the Southern California Current System

NASA Astrophysics Data System (ADS)

Chereskin, T. K.; Gille, S. T.; Rocha, C. B.; Menemenlis, D.

2016-02-01

At the largest horizontal scales (> 100 km), the surface kinetic energy of the ocean appears dominated by a regime of balanced geostrophic motions. At the smallest scales, it transitions to a regime where unbalanced motions (such as internal waves, mixed-layer instabilities, etc.) dominate the surface kinetic energy. The length scale at which the transition occurs depends on the relative energies of balanced and unbalanced motions, which in turn display significant geographic variability. Wavenumber spectra in the upper ocean have been hypothesized to have slopes consistent with either quasi-geostrophic (QG) or surface quasi-geostrophic (SQG) theory. In previous analyses of repeat-track shipboard acoustic Doppler Current profiler (ADCP) velocity observations in the Gulf Stream and the Antarctic Circumpolar Current, spectral slopes were more consistent with QG than SQG theory for length scales between 40 km and 200 km. For scales less than 40 km, the spectra deviated from both QG and SQG theory, and this was attributed in part to internal wave effects. A spectral Helmholtz decomposition was used to split the kinetic energy spectra into rotational and divergent components, identified with balanced and ageostrophic motions, respectively. The California Current System (CCS) provides a contrasting environment characterized by a weak mean flow and an energetic meso- and submeso- scale. It is a nonlinear regime where the amplitude of eddies can be as large as the total steric height increase across the California Current, and hence southward flow in the CCS can, and often is, disrupted by its eddies. This study uses 10 years of shipboard ADCP observations collected on the quarterly cruises of the California Cooperative Oceanic Fisheries Investigations. Horizontal wavenumber spectra from 36 cruises along 6 repeated tracks in the southern CCS that extend from the coast to the subtropical gyre are used to diagnose the dominant governing dynamics at meso- to submeso- scales (10-200 km), with particular attention to the partition into balanced and ageostrophic flows.

Stochastic strong motion generation using slip model of 21 and 22 May 1960 mega-thrust earthquakes in the main cities of Central-South Chile

NASA Astrophysics Data System (ADS)

Ruiz, S.; Ojeda, J.; DelCampo, F., Sr.; Pasten, C., Sr.; Otarola, C., Sr.; Silva, R., Sr.

2017-12-01

In May 1960 took place the most unusual seismic sequence registered instrumentally. The Mw 8.1, Concepción earthquake occurred May, 21, 1960. The aftershocks of this event apparently migrated to the south-east, and the Mw 9.5, Valdivia mega-earthquake occurred after 33 hours. The structural damage produced by both events is not larger than other earthquakes in Chile and lower than crustal earthquakes of smaller magnitude. The damage was located in the sites with shallow soil layers of low shear wave velocity (Vs). However, no seismological station recorded this sequence. For that reason, we generate synthetic acceleration times histories for strong motion in the main cities affected by these events. We use 155 points of vertical surface displacements recopiled by Plafker and Savage in 1968, and considering the observations of this authors and local residents we separated the uplift and subsidence information associated to the first earthquake Mw 8.1 and the second mega-earthquake Mw 9.5. We consider the elastic deformation propagation, assume realist lithosphere geometry, and compute a Bayesian method that maximizes the probability density a posteriori to obtain the slip distribution. Subsequently, we use a stochastic method of generation of strong motion considering the finite fault model obtained for both earthquakes. We considered the incidence angle of ray to the surface, free surface effect and energy partition for P, SV and SH waves, dynamic corner frequency and the influence of site effect. The results show that the earthquake Mw 8.1 occurred down-dip the slab, the strong motion records are similar to other Chilean earthquake like Tocopilla Mw 7.7 (2007). For the Mw 9.5 earthquake we obtain synthetic acceleration time histories with PGA values around 0.8 g in cities near to the maximum asperity or that have low velocity soil layers. This allows us to conclude that strong motion records have important influence of the shallow soil deposits. These records correlate well with our structural damage observations.

Evaluating the role of higher order nonlinearity in water of finite and shallow depth with a direct numerical simulation method of Euler equations

NASA Astrophysics Data System (ADS)

Fernandez, L.; Toffoli, A.; Monbaliu, J.

2012-04-01

In deep water, the dynamics of surface gravity waves is dominated by the instability of wave packets to side band perturbations. This mechanism, which is a nonlinear third order in wave steepness effect, can lead to a particularly strong focusing of wave energy, which in turn results in the formation of waves of very large amplitude also known as freak or rogue waves [1]. In finite water depth, however, the interaction between waves and the ocean floor induces a mean current. This subtracts energy from wave instability and causes it to cease for relative water depth , where k is the wavenumber and h the water depth [2]. Yet, this contradicts field observations of extreme waves such as the infamous 26-m "New Year" wave that have mainly been recorded in regions of relatively shallow water . In this respect, recent studies [3] seem to suggest that higher order nonlinearity in water of finite depth may sustain instability. In order to assess the role of higher order nonlinearity in water of finite and shallow depth, here we use a Higher Order Spectral Method [4] to simulate the evolution of surface gravity waves according to the Euler equations of motion. This method is based on an expansion of the vertical velocity about the surface elevation under the assumption of weak nonlinearity and has a great advantage of allowing the activation or deactivation of different orders of nonlinearity. The model is constructed to deal with an arbitrary order of nonlinearity and water depths so that finite and shallow water regimes can be analyzed. Several wave configurations are considered with oblique and collinear with the primary waves disturbances and different water depths. The analysis confirms that nonlinearity higher than third order play a substantial role in the destabilization of a primary wave train and subsequent growth of side band perturbations.

Bottom boundary layer spectral dissipation estimates in the presence of wave motions

NASA Astrophysics Data System (ADS)

Gross, T. F.; Williams, A. J.; Terray, E. A.

1994-08-01

Turbulence measurements are an essential element of the Sediment TRansport Events on Shelves and Slopes experiment (STRESS). Sediment transport under waves is initiated within the wave boundary layer at the seabed, at most a few tens of centimeters deep. The suspended load is carried by turbulent diffusion above the wave boundary layer. Quantification of the turbulent diffusion active above the wave boundary layer requires estimates of shear stress or energy dissipation in the presence of oscillating flows. Measurements by Benthic Acoustic Stress Sensors of velocity fluctuations were used to derive the dissipation rate from the energy level of the spectral inertial range (the -5/3 spectrum). When the wave orbital velocity is of similar magnitude to the mean flow, kinematic effects on the estimation techniques of stress and dissipation must be included. Throughout the STRESS experiment there was always significant wave energy affecting the turbulent bottom boundary layer. LUMLEY and TERRAY [(1983) Journal of Physical Oceanography, 13, 2000-2007] presented a theory describing the effect of orbital motions on kinetic energy spectra. Their model is used here with observations of spectra taken within a turbulent boundary layer which is affected by wave motion. While their method was an explicit solution for circular wave orbits aligned with mean current we extrapolated it to the case of near bed horizontal motions, not aligned with the current. The necessity of accounting for wave orbital motion is demonstrated, but variability within the field setting limited our certainty of the improvement in accuracy the corrections afforded.

Single-station 6C beamforming

NASA Astrophysics Data System (ADS)

Nakata, N.; Hadziioannou, C.; Igel, H.

2017-12-01

Six-component measurements of seismic ground motion provide a unique opportunity to identify and decompose seismic wavefields into different wave types and incoming azimuths, as well as estimate structural information (e.g., phase velocity). By using the relationship between the transverse component and vertical rotational motion for Love waves, we can find the incident azimuth of the wave and the phase velocity. Therefore, when we scan the entire range of azimuth and slownesses, we can process the seismic waves in a similar way to conventional beamforming processing, without using a station array. To further improve the beam resolution, we use the distribution of amplitude ratio between translational and rotational motions at each time sample. With this beamforming, we decompose multiple incoming waves by azimuth and phase velocity using only one station. We demonstrate this technique using the data observed at Wettzell (vertical rotational motion and 3C translational motions). The beamforming results are encouraging to extract phase velocity at the location of the station, apply to oceanic microseism, and to identify complicated SH wave arrivals. We also discuss single-station beamforming using other components (vertical translational and horizontal rotational components). For future work, we need to understand the resolution limit of this technique, suitable length of time windows, and sensitivity to weak motion.

Eulerian-Lagrangian analysis for particle velocities and trajectories in a pure wave motion using particle image velocimetry.

PubMed

Umeyama, Motohiko

2012-04-13

This paper investigates the velocity and the trajectory of water particles under surface waves, which propagate at a constant water depth, using particle image velocimetry (PIV). The vector fields and vertical distributions of velocities are presented at several phases in one wave cycle. The third-order Stokes wave theory was employed to express the physical quantities. The PIV technique's ability to measure both temporal and spatial variations of the velocity was proved after a series of attempts. This technique was applied to the prediction of particle trajectory in an Eulerian scheme. Furthermore, the measured particle path was compared with the positions found theoretically by integrating the Eulerian velocity to the higher order of a Taylor series expansion. The profile of average travelling distance is also presented with a solution of zero net mass flux in a closed wave flume.

Evidence for infragravity wave-tide resonance in deep oceans.

PubMed

Sugioka, Hiroko; Fukao, Yoshio; Kanazawa, Toshihiko

2010-10-05

Ocean tides are the oscillatory motions of seawater forced by the gravitational attraction of the Moon and Sun with periods of a half to a day and wavelengths of the semi-Pacific to Pacific scale. Ocean infragravity (IG) waves are sea-surface gravity waves with periods of several minutes and wavelengths of several dozen kilometres. Here we report the first evidence of the resonance between these two ubiquitous phenomena, mutually very different in period and wavelength, in deep oceans. The evidence comes from long-term, large-scale observations with arrays of broadband ocean-bottom seismometers located at depths of more than 4,000 m in the Pacific Ocean. This observational evidence is substantiated by a theoretical argument that IG waves and the tide can resonantly couple and that such coupling occurs over unexpectedly wide areas of the Pacific Ocean. Through this resonant coupling, some of ocean tidal energy is transferred in deep oceans to IG wave energy.

A numerical study of fundamental shock noise mechanisms. Ph.D. Thesis - Cornell Univ.

NASA Technical Reports Server (NTRS)

Meadows, Kristine R.

1995-01-01

The results of this thesis demonstrate that direct numerical simulation can predict sound generation in unsteady aerodynamic flows containing shock waves. Shock waves can be significant sources of sound in high speed jet flows, on helicopter blades, and in supersonic combustion inlets. Direct computation of sound permits the prediction of noise levels in the preliminary design stage and can be used as a tool to focus experimental studies, thereby reducing cost and increasing the probability of a successfully quiet product in less time. This thesis reveals and investigates two mechanisms fundamental to sound generation by shocked flows: shock motion and shock deformation. Shock motion is modeled by the interaction of a sound wave with a shock. During the interaction, the shock wave begins to move and the sound pressure is amplified as the wave passes through the shock. The numerical approach presented in this thesis is validated by the comparison of results obtained in a quasi-one dimensional simulation with linear theory. Analysis of the perturbation energy demonstrated for the first time that acoustic energy is generated by the interaction. Shock deformation is investigated by the numerical simulation of a ring vortex interacting with a shock. This interaction models the passage of turbulent structures through the shock wave. The simulation demonstrates that both acoustic waves and contact surfaces are generated downstream during the interaction. Analysis demonstrates that the acoustic wave spreads cylindrically, that the sound intensity is highly directional, and that the sound pressure level increases significantly with increasing shock strength. The effect of shock strength on sound pressure level is consistent with experimental observations of shock noise, indicating that the interaction of a ring vortex with a shock wave correctly models a dominant mechanism of shock noise generation.

Kinesthetic Transverse Wave Demonstration

NASA Astrophysics Data System (ADS)

Pantidos, Panagiotis; Patapis, Stamatis

2005-09-01

This is a variation on the String and Sticky Tape demonstration "The Wave Game," suggested by Ron Edge. A group of students stand side by side, each one holding a card chest high with both hands. The teacher cues the first student to begin raising and lowering his card. When he starts lowering his card, the next student begins to raise his. As succeeding students move their cards up and down, a wave such as that shown in the figure is produced. To facilitate the process, students' motions were synchronized with the ticks of a metronome (without such synchronization it was nearly impossible to generate a satisfactory wave). Our waves typically had a frequency of about 1 Hz and a wavelength of around 3 m. We videotaped the activity so that the students could analyze the motions. The (17-year-old) students had not received any prior instruction regarding wave motion and did not know beforehand the nature of the exercise they were about to carry out. During the activity they were asked what a transverse wave is. Most of them quickly realized, without teacher input, that while the wave propagated horizontally, the only motion of the transmitting medium (them) was vertical. They located the equilibrium points of the oscillations, the crests and troughs of the waves, and identified the wavelength. The teacher defined for them the period of the oscillations of the motion of a card to be the total time for one cycle. The students measured this time and then several asserted that it was the same as the wave period. Knowing the length of the waves and the number of waves per second, the next step can easily be to find the wave speed.

Flutter and forced response of mistuned rotors using standing wave analysis

NASA Technical Reports Server (NTRS)

Dugundji, J.; Bundas, D. J.

1983-01-01

A standing wave approach is applied to the analysis of the flutter and forced response of tuned and mistuned rotors. The traditional traveling wave cascade airforces are recast into standing wave arbitrary motion form using Pade approximants, and the resulting equations of motion are written in the matrix form. Applications for vibration modes, flutter, and forced response are discussed. It is noted that the standing wave methods may prove to be more versatile for dealing with certain applications, such as coupling flutter with forced response and dynamic shaft problems, transient impulses on the rotor, low-order engine excitation, bearing motions, and mistuning effects in rotors.

Flutter and forced response of mistuned rotors using standing wave analysis

NASA Technical Reports Server (NTRS)

Bundas, D. J.; Dungundji, J.

1983-01-01

A standing wave approach is applied to the analysis of the flutter and forced response of tuned and mistuned rotors. The traditional traveling wave cascade airforces are recast into standing wave arbitrary motion form using Pade approximants, and the resulting equations of motion are written in the matrix form. Applications for vibration modes, flutter, and forced response are discussed. It is noted that the standing wave methods may prove to be more versatile for dealing with certain applications, such as coupling flutter with forced response and dynamic shaft problems, transient impulses on the rotor, low-order engine excitation, bearing motion, and mistuning effects in rotors.

Three-dimensional simulations of ground motions in the San Bernardino Valley, California, for hypothetical earthquakes on the San Andreas Fault

USGS Publications Warehouse

Frankel, A.

1993-01-01

Three-dimensional finite difference simulations of elastic waves in the San Bernardino Valley were performed for two hypothetical earthquakes on the San Andreas fault: a point source with moment magnitude M5 and an extended rupture with M6.5. A method is presented for incorporating a source with arbitrary focal mechanism in the grid. Synthetics from the 3-D simulations are compared with those derived from 2-D (vertical cross section) and 1-D (flat-layered) models. The synthetic seismograms from the 3-D and 2-D simulations exhibit large surface waves produced by conversion of incident S waves at the edge of the basin. Seismograms from the flat-layered model do not contain these converted surface waves and underestimate the duration of shaking. Maps of maximum ground velocities occur in localized portions of the basin. The location of the largest velocities changes with the rupture propagation direction. Contours of maximum shaking are also dependent on asperity positions and radiation pattern. -from Author

Trajectory Control of Small Rotating Projectiles by Laser Sparks

NASA Astrophysics Data System (ADS)

Starikovskiy, Andrey; Limbach, Christopher; Miles, Richard

2015-09-01

The possibility of controlling the trajectory of the supersonic motion of a rotating axisymmetric projectile using a remotely generated laser spark was investigated. The dynamic images of the interaction of thermal inhomogeneity created by the laser spark with the bow shock in front of the projectile were obtained. The criterion for a strong shock wave interaction with the thermal inhomogeneity at different angles of a shock wave was derived. Significant changes in the configuration of the bow shock wave and changes in the pressure distribution over the surface of the rotating projectile can appear for laser spark temperature of T' = 2500-3000 K. The experiment showed that strong interaction takes place for both plane and oblique shock waves. The measurement of the velocity of the precession of the rotating projectile axis from the initial position in time showed that the angle of attack of the projectile deviates with a typical time of perturbation propagation along the projectile's surface. Thus the laser spark can change the trajectory of the rotating projectile, moving at supersonic speed, through the creation of thermal heterogeneity in front of it.

A Fully Nonlinear, Dynamically Consistent Numerical Model for Solid-Body Ship Motion. I. Ship Motion with Fixed Heading

NASA Technical Reports Server (NTRS)

Lin, Ray-Quing; Kuang, Weijia

2011-01-01

In this paper, we describe the details of our numerical model for simulating ship solidbody motion in a given environment. In this model, the fully nonlinear dynamical equations governing the time-varying solid-body ship motion under the forces arising from ship wave interactions are solved with given initial conditions. The net force and moment (torque) on the ship body are directly calculated via integration of the hydrodynamic pressure over the wetted surface and the buoyancy effect from the underwater volume of the actual ship hull with a hybrid finite-difference/finite-element method. Neither empirical nor free parametrization is introduced in this model, i.e. no a priori experimental data are needed for modelling. This model is benchmarked with many experiments of various ship hulls for heave, roll and pitch motion. In addition to the benchmark cases, numerical experiments are also carried out for strongly nonlinear ship motion with a fixed heading. These new cases demonstrate clearly the importance of nonlinearities in ship motion modelling.

Frontal Generation of Waves: A Geostrophic Adjustment Interpretation of The Observations

NASA Astrophysics Data System (ADS)

Blumen, W.; Lundquist, J. K.

Data were collected during the stable boundary layer observational field program, the Cooperative Atmosphere-Surface Exchange Study 1999 (CASES-99), carried out in southeastern Kansas USA during the month of October 1999 These data reveal that on at least two different occasions, 16 and 22 October, the passage of surface cold fronts were associated with the initiation of gravity-inertia waves. The periods of these waves ranged from about 4 minutes for gravity waves, relatively unaffected by the Earth's rotation, to about 20 hours for inertial oscillations, characterized by the Coriolis frequency f. Boundary layer radar wind profilers at locations surrounding the main observational site provided wind data through the boundary layer and above. A 60 m tower at the main site contained high frequency temperature, wind, humidity and pressure sensors distributed at various levels along the vertical. These data were used to identify the frontal passages and the wave characteristics. The wind profiler data were used to identify the inertial oscillations. These data indicate that as time progresses, following the frontal passages, the postfrontal energy levels return to pre- frontal levels, and inertial oscillations represent the dominant frequency observed. A linear model is developed and solved to provide evidence that a geostrophic adjust- ment process occurs during the postfrontal period of each frontal passage. the solution obtained shows that the higher frequency waves disperse their energy rapidly leaving the lower frequency inertial oscillation, which is characterized by a zero group ve- locity, at the site of its initiation. The observations reveal that the adjustment to this state occurs within a time span of about 8 hours for each frontal event. This time span is consistent with the model solution using parameter values that are based on ob- servational data. The present model also provides a means to estimate how much of the initial energy is distributed to wave motions and how much is associated with a geostrophically balanced state. It is not possible to separate waves from other types of motion from the observed energy spectrum, but there is evidence of a spectral peak in the range of 7 to 23 minutes in the 16 October energy spectrum. This peak is assumed to be associated with wave excitation by the frontal passage, although other types of motion may also be a contributors. A model calculation reveals that the energy con- tained in this spectral peak represents about 10 to 15 percent of the energy contained in the initial state (time t = 0). This result, although based on crude estimates of the 1 observed wave energy is, nevertheless, in general agreement with the prediction of geostrophic theory:a relatively small amount of energy is expected to be associated with relatively high-frequency, small-scale gravity waves. Additional details regard- ing the geostrophic adjustment interpretation of the observations will be presented in the talk. 2

Measuring sea surface height with a GNSS-Wave Glider

NASA Astrophysics Data System (ADS)

Morales Maqueda, Miguel Angel; Penna, Nigel T.; Foden, Peter R.; Martin, Ian; Cipollini, Paolo; Williams, Simon D.; Pugh, Jeff P.

2017-04-01

A GNSS-Wave Glider is a novel technique to measure sea surface height autonomously using the Global Navigation Satellite System (GNSS). It consists of an unmanned surface vehicle manufactured by Liquid Robotics, a Wave Glider, and a geodetic-grade GNSS antenna-receiver system, with the antenna installed on a mast on the vehicle's deck. The Wave Glider uses the differential wave motion through the water column for propulsion, thus guaranteeing an, in principle, indefinite autonomy. Solar energy is collected to power all on-board instrumentation, including the GNSS system. The GNSS-Wave Glider was first tested in Loch Ness in 2013, demonstrating that the technology is capable of mapping geoid heights within the loch with an accuracy of a few centimetres. The trial in Loch Ness did not conclusively confirm the reliability of the technique because, during the tests, the state of the water surface was much more benign than would normally be expect in the open ocean. We now report on a first deployment of a GNSS-Wave Glider in the North Sea. The deployment took place in August 2016 and lasted thirteen days, during which the vehicle covered a distance of about 350 nautical miles in the north western North Sea off Great Britain. During the experiment, the GNSS-Wave Glider experienced sea states between 1 (0-0.1 m wave heights) and 5 (2.5-4 m wave heights). The GNSS-Wave Glider data, recorded at 5 Hz frequency, were analysed using a post-processed kinematic GPS-GLONASS precise point positioning (PPP) approach, which were quality controlled using double difference GPS kinematic processing with respect to onshore reference stations. Filtered with a 900 s moving-average window, the PPP heights reveal geoid patterns in the survey area that are very similar to the EGM2008 geoid model, thus demonstrating the potential use of a GNSS-Wave Glider for marine geoid determination. The residual of subtracting the modelled or measured marine geoid from the PPP signal combines information about dynamic topography and sea state. GNSS-Wave Glider data will next be validated against concurrent and co-located satellite altimetry data from the Jason-1, Jason-2, CryoSat-2 and AltiKa missions.

The Three-Dimensionality of Spiral Shocks: Did Chondrules Catch a Breaking Wave?

NASA Astrophysics Data System (ADS)

Boley, A. C.; Durisen, R. H.; Pickett, M. K.

2005-12-01

Spiral shocks in vertically stratified disks lead to hydraulic/shock-jumps (hs-jumps) that stimulate large scale (tenths of an AU or more) radial and vertical motions, breaking surface waves, high-altitude shocks, and vortical flows. These effects are demonstrated by three-dimensional hydrodynamics simulations in Solar Nebula models. Trajectories of fluid elements, along with their thermal histories, suggest that hs-jumps mix the nebular gas and provide diverse pre-shock conditions, some of which are conducive to chondrule formation. In addition, hs-jumps may provide an energy source for driving nebular turbulence to size-sort chondrules.

Doppler-shifted self-reflected wave from a semiconductor

NASA Astrophysics Data System (ADS)

Schuelzgen, Alex; Hughes, S.; Peyghambarian, Nasser

1997-06-01

We report the first experimental observation of a self- reflected wave inside a very dense saturable absorber. An intense femtosecond pulse saturates the absorption and causes a density front moving into the semiconductor sample. Due to the motion of the boundary between saturated and unsaturated areas of the sample the light reflected at this boundary is red-shifted by the Doppler effect. The spectrally shifted reflection makes it possible to distinguish between surface reflection and self-reflection and is used to proof the concept of the dynamic nonlinear skin effect experimentally. Quite well agreement with model calculations is found.

Enhancing power generation of floating wave power generators by utilization of nonlinear roll-pitch coupling

NASA Astrophysics Data System (ADS)

Yerrapragada, Karthik; Ansari, M. H.; Karami, M. Amin

2017-09-01

We propose utilization of the nonlinear coupling between the roll and pitch motions of wave energy harvesting vessels to increase their power generation by orders of magnitude. Unlike linear vessels that exhibit unidirectional motion, our vessel undergoes both pitch and roll motions in response to frontal waves. This significantly magnifies the motion of the vessel and thus improves the power production by several orders of magnitude. The ocean waves result in roll and pitch motions of the vessel, which in turn causes rotation of an onboard pendulum. The pendulum is connected to an electric generator to produce power. The coupled electro-mechanical system is modeled using energy methods. This paper investigates the power generation of the vessel when the ratio between pitch and roll natural frequencies is about 2 to 1. In that case, a nonlinear energy transfer occurs between the roll and pitch motions, causing the vessel to perform coupled pitch and roll motion even though it is only excited in the pitch direction. It is shown that co-existence of pitch and roll motions significantly enhances the pendulum rotation and power generation. A method for tuning the natural frequencies of the vessel is proposed to make the energy generator robust to variations of the frequency of the incident waves. It is shown that the proposed method enhances the power output of the floating wave power generators by multiple orders of magnitude. A small-scale prototype is developed for the proof of concept. The nonlinear energy transfer and the full rotation of the pendulum in the prototype are observed in the experimental tests.

Visualizing the Vibration of Laryngeal Tissue during Phonation Using Ultrafast Plane Wave Ultrasonography.

PubMed

Jing, Bowen; Tang, Shanshan; Wu, Liang; Wang, Supin; Wan, Mingxi

2016-12-01

Ultrafast plane wave ultrasonography is employed in this study to visualize the vibration of the larynx and quantify the vibration phase as well as the vibration amplitude of the laryngeal tissue. Ultrasonic images were obtained at 5000 to 10,000 frames/s in the coronal plane at the level of the glottis. Although the image quality degraded when the imaging mode was switched from conventional ultrasonography to ultrafast plane wave ultrasonography, certain anatomic structures such as the vocal folds, as well as the sub- and supraglottic structures, including the false vocal folds, can be identified in the ultrafast plane wave ultrasonic image. The periodic vibration of the vocal fold edge could be visualized in the recorded image sequence during phonation. Furthermore, a motion estimation method was used to quantify the displacement of laryngeal tissue from hundreds of frames of ultrasonic data acquired. Vibratory displacement waveforms of the sub- and supraglottic structures were successfully obtained at a high level of ultrasonic signal correlation. Moreover, statistically significant differences in vibration pattern between the sub- and supraglottic structures were found. Variation of vibration amplitude along the subglottic mucosal surface is significantly smaller than that along the supraglottic mucosal surface. Phase delay of vibration along the subglottic mucosal surface is significantly smaller than that along the supraglottic mucosal surface. Copyright © 2016 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

Energy in a String Wave

ERIC Educational Resources Information Center

Ng, Chiu-king

2010-01-01

When one end of a taut horizontal elastic string is shaken repeatedly up and down, a transverse wave (assume sine waveform) will be produced and travel along it. College students know this type of wave motion well. They know when the wave passes by, each element of the string will perform an oscillating up-down motion, which in mechanics is termed…

Sea Surface Slope Statistics for Intermediate and Shore Scale Ocean Waves Measured Using a Low-Altitude Aircraft

NASA Technical Reports Server (NTRS)

Vandemack, Douglas; Crawford, Tim; Dobosy, Ron; Elfouhaily, Tanos; Busalacchi, Antonio J. (Technical Monitor)

1999-01-01

Ocean surface remote sensing techniques often rely on scattering or emission linked to shorter- scale gravity-capillary ocean wavelets. However, it is increasingly apparent that slightly longer wavelengths of O(10 to 500 cm) are vital components in the robust sea surface description needed to link varied global remote sensing data sets. This paper describes a sensor suite developed to examine sea surface slope variations in the field using an aircraft flying at very low altitude (below 30 m) and will also provide preliminary measurements detailing changes in slope characteristics versus sea state and friction velocity. Two-dimensional surface slope is measured using simultaneous range measurements from three compact short-range laser altimeters mounted in an equilateral triangle arrangement with spacing of about 1 m. In addition, all three lasers provide independent wave elevation profiles after GPS-aided correction for aircraft altitude. Laser range precision is 1 cm rms while vertical motion correction is 15 cm rms. The measurements are made along-track at approximately 1 m intervals setting the spatial scale of the measurement to cover waves of intermediate to long scale. Products available for this array then include surface elevation, two-dimensional slope distribution, and the cross- and along-track 1-D slope distributions. To complement the laser, a down-looking mm-wave radar scatterometer is centered within the laser array to measure radar backscatter simultaneously with the laser slope. The radar's footprint is nominally 1 m in diameter. Near-vertical radar backscatter is inversely proportional to the small-scale surface slope variance and to the tilt of the underlying (laser-measured) surface facet. Together the laser and radar data provide information on wave roughness from the longest scales down to about 1 cm. These measurements are complemented by aircraft turbulence probe data that provides robust surface flux information.

Intensification of heat transfer across falling liquid films

NASA Astrophysics Data System (ADS)

Ruyer-Quil, Christian; Cellier, Nicolas; Stutz, Benoit; Caney, Nadia; Bandelier, Philippe; Locie Team; Legi Team

2017-11-01

The wavy motion of a liquid film is well known to intensify heat or mass transfers. Yet, if film thinning and wave merging are generally invoked, the physical mechanisms which enable this intensification are still unclear. We propose a systematic investigation of the impact of wavy motions on the heat transfer across 2D falling films on hot plates as a function of the inlet frequency and flow parameters. Computations over extended domains and for sufficient durations to achieve statistically established flows have been made possible by low-dimensional modeling and the development of a fast temporal solver based on graph optimizations. Heat transfer has been modeled using the weighted residual technique as a set of two evolution equations for the free-surface temperature and the wall heat flux. This new model solves the shortcomings of previous attempts, namely their inability to capture the onset of thermal boundary layers in large-amplitude waves and their limitation to low Prandtl numbers. Our study reveals that heat transfer is enhanced at the crests of the waves and that heat transfer intensification is maximum at the maximum of density of wave crests, which does not correspond to the natural wavy regime (no inlet forcing). Supports from Institut Universitaire de France and Région Auvergne-Rhones-Alpes are warmly acknowledged.

Waves in Radial Gravity Using Magnetic Fluid

NASA Technical Reports Server (NTRS)

Ohlsen, D. R.; Hart, J. E.; Weidman, P. D.

1999-01-01

Terrestrial laboratory experiments studying various fluid dynamical processes are constrained, by being in an Earth laboratory, to have a gravitational body force which is uniform and unidirectional. Therefore fluid free-surfaces are horizontal and flat. Such free surfaces must have a vertical solid boundary to keep the fluid from spreading horizontally along a gravitational potential surface. In atmospheric, oceanic, or stellar fluid flows that have a horizontal scale of about one-tenth the body radius or larger, sphericity is important in the dynamics. Further, fluids in spherical geometry can cover an entire domain without any sidewall effects, i.e. have truly periodic boundary conditions. We describe spherical body-force laboratory experiments using ferrofluid. Ferrofluids are dilute suspensions of magnetic dipoles, for example magnetite particles of order 10 nm diameter, suspended in a carrier fluid. Ferrofluids are subject to an additional body force in the presence of an applied magnetic field gradient. We use this body force to conduct laboratory experiments in spherical geometry. The present study is a laboratory technique improvement. The apparatus is cylindrically axisymmetric. A cylindrical ceramic magnet is embedded in a smooth, solid, spherical PVC ball. The geopotential field and its gradient, the body force, were made nearly spherical by careful choice of magnet height-to-diameter ratio and magnet size relative to the PVC ball size. Terrestrial gravity is eliminated from the dynamics by immersing the "planet" and its ferrofluid "ocean" in an immiscible silicone oil/freon mixture of the same density. Thus the earth gravity is removed from the dynamics of the ferrofluid/oil interface and the only dynamically active force there is the radial magnetic gravity. The entire apparatus can rotate, and waves are forced on the ferrofluid surface by exterior magnets. The biggest improvement in technique is in the wave visualization. Fluorescing dye is added to the oil/freon mixture and an argon ion laser generates a horizontal light that can be scanned vertically. Viewed from above, the experiment is a black circle with wave deformations surrounded by a light background. A contour of the image intensity at any light sheet position gives the surface of the ferrofluid "ocean" at that "latitude". Radial displacements of the waves as a function of longitude are obtained by subtracting the contour line positions from a no-motion contour at that laser sheet latitude. The experiments are run by traversing the forcing magnet with the laser sheet height fixed and images are frame grabbed to obtain a time-series at one latitude. The experiment is then re-run with another laser-sheet height to generate a full picture of the three-dimensional wave structure in the upper hemisphere of the ball as a function of time. We concentrate here on results of laboratory studies of waves that are important in Earth's atmosphere and especially the ocean. To get oceanic scaling in the laboratory, the experiment must rotate rapidly (4-second rotation period) so that the wave speed is slow compared to the planetary rotation speed as in the ocean. In the Pacific Ocean, eastward propagating Kelvin waves eventually run into the South American coast. Theory predicts that some of the wave energy should scatter into coastal-trapped Kelvin waves that propagate north and south along the coast. Some of this coastal wave energy might then scatter into mid-latitude Rossby waves that propagate back westward. Satellite observations of the Pacific Ocean sea-surface temperature and height seem to show signatures of westward propagating mid-latitude Rossby waves, 5 to 10 years after the 1982-83 El Nino. The observational data is difficult to interpret unambiguously owing to the large range of motions that fill the ocean at shorter timescales. This series of reflections giving eastward, north- ward, and then westward traveling waves is observed cleanly in the laboratory experiments, confirming the theoretical expectations.

Characterization of microchannel anechoic corners formed by surface acoustic waves

NASA Astrophysics Data System (ADS)

Destgeer, Ghulam; Alam, Ashar; Ahmed, Husnain; Park, Jinsoo; Jung, Jin Ho; Park, Kwangseok; Sung, Hyung Jin

2018-02-01

Surface acoustic waves (SAWs) generated in a piezoelectric substrate couple with a liquid according to Snell's law such that a compressional acoustic wave propagates obliquely at a Rayleigh angle ( θ t) inside the microchannel to form a region devoid of a direct acoustic field, which is termed a microchannel anechoic corner (MAC). In the present study, we used microchannels with various heights and widths to characterize the width of the MAC region formed by a single travelling SAW. The attenuation of high-frequency SAWs produced a strong acoustic streaming flow that moved the particles in and out of the MAC region, whereas reflections of the acoustic waves within the microchannel resulted in standing acoustic waves that trapped particles at acoustic pressure nodes located within or outside of the MAC region. A range of actuation frequencies and particle diameters were used to investigate the effects of the acoustic streaming flow and the direct acoustic radiation forces by the travelling as well as standing waves on the particle motion with respect to the MAC region. The width of the MAC ( w c), measured experimentally by tracing the particles, increased with the height of the microchannel ( h m) according to a simple trigonometric equation w c = h m × tan ( θ t ).

Dynamics of the Trans-Neptune Region: Apsidal Waves in the Kuiper Belt

NASA Technical Reports Server (NTRS)

Ward, William R.; Hahn, Joseph M.

1998-01-01

The role of apsidal density waves propagating in a primordial trans-Neptune disk (i.e., Kuiper belt) is investigated. It is shown that Neptune launches apsidal waves at its secular resonance near 40 AU that propagate radially outward, deeper into the particle disk. The wavelength of apsidal waves is considerably longer than waves that might be launched at Lindblad resonances, because the pattern speed, g(sub s), resulting from the apsis precession of Neptune is much slower than its mean motion, Omega(sub s). If the early Kuiper belt had a sufficient surface density, sigma, the disk's wave response to Neptune's secular perturbation would have spread the disturbing torque radially over a collective scale lambda(sub *) approx. = r(2(mu)(sub d)Omega/ absolute value of r dg/dr)(sup 1/2), where mu(sub d)equivalent pi(sigma)r(exp 2)/(1 solar mass) and Omega(r) and g(r) are respectively the mean motion and precession frequency of the disk particles. This results in considerably smaller eccentricities at resonance than had the disk particles been treated as noninteracting test particles. Consequently, particles are less apt to be excited into planet-crossing orbits, implying that the erosion timescales reported by earlier test-particle simulations of the Kuiper belt may be underestimated. It is also shown that the torque the disk exerts upon the planet (due to its gravitational attraction for the disk's spiral wave pattern) damps the planet's eccentricity and further inhibits the planet's ability to erode the disk. Key words: celestial mechanics, stellar dynamics - comets: general minor planets, asteroids

Rupture dynamics along dipping thrust faults: free surface interaction and the case of Tohoku earthquake

NASA Astrophysics Data System (ADS)

Festa, Gaetano; Scala, Antonio; Vilotte, Jean-Pierre

2017-04-01

To address the influence of the free surface interaction on rupture propagating along subduction zones, we numerically investigate dynamic interactions, involving coupling between normal and shear tractions, between in-plane rupture propagating along dipping thrust faults and a free surface for different structural and geometrical conditions. When the rupture occurs along reverse fault with a dip angle different from 90° the symmetry is broken as an effect of slip-induced normal stress perturbations and a larger ground motion is evidenced on the hanging wall. The ground motion is amplified by multiple reflections of waves trapped between the fault and the free surface. This effect is shown to occur when the rupture tip lies on the vertical below the intersection between the S-wave front and the surface that is when waves along the surface start to interact with the rupture front. This interaction is associated with a finite region where the rupture advances in a massive regime preventing the shrinking of the process zone and the emission of high-frequency radiation. The smaller the dip angle the larger co-seismic slip in the shallow part as an effect of the significant break of symmetry. Radiation from shallow part is still depleted in high frequencies due to the massive propagating regime and the interaction length dominating the rupture dynamics. Instantaneous shear response to normal traction perturbations may lead to unstable solutions as in the case of bimaterial rupture. A parametric study has been performed to analyse the effects of a regularised shear traction response to normal traction variations. Finally the case of Tohoku earthquake is considered and we present 2D along-dip numerical results. At first order the larger slip close to the trench can be ascribed to the break of symmetry and the interaction with free surface. When shear/normal coupling is properly regularised the signal from the trench is depleted in high frequencies whereas during deep propagation high-frequency radiations emerge associated to geometrical and structural complexities or to frictional strength asperities.

Experimental and numerical investigation of the roll motion behavior of a floating liquefied natural gas system

NASA Astrophysics Data System (ADS)

Zhao, WenHua; Yang, JianMin; Hu, ZhiQiang; Xiao, LongFei; Peng, Tao

2013-03-01

The present paper does an experimental and numerical investigation of the hydrodynamic interaction and the response of a single point turret-moored Floating Liquefied Natural Gas (FLNG) system, which is a new type of floating LNG (Liquid Natural Gas) platform that consists of a ship-type FPSO hull equipped with LNG storage tanks and liquefaction plants. In particular, this study focuses on the investigation of the roll response of FLNG hull in free-decay motions, white noise waves and also in irregular waves. Model tests of the FLNG system in 60%H filling condition excited by both white noise waves and irregular waves combined with steady wind and current have been carried out. Response Amplitude Operators (RAOs) and time histories of the responses are obtained for sway, roll and yaw motions. Obvious Low Frequency (LF) components of the roll motions are observed, which may be out of expectation. To facilitate the physical understanding of this phenomenon, we filter the roll motions at the period of 30 s into two parts: the Wave Frequency (WF) motions and the Low Frequency (LF) motions respectively. The results indicate that the LF motions are closely related to the sway and yaw motions. Possible reasons for the presence of the LF motions of roll have been discussed in detail, through the comparison with the sway and yaw motions. As for the numerical part, the simulation of the modeled case is conducted with the help of the software SESAM®. A good agreement between experiments and calculations is reported within the scope of trends. However, the numerical simulations should be further improved for the prediction of the FLNG system in the heading sea.

Modeling Tsunami Wave Generation Using a Two-layer Granular Landslide Model

NASA Astrophysics Data System (ADS)

Ma, G.; Kirby, J. T., Jr.; Shi, F.; Grilli, S. T.; Hsu, T. J.

2016-12-01

Tsunamis can be generated by subaerial or submarine landslides in reservoirs, lakes, fjords, bays and oceans. Compared to seismogenic tsunamis, landslide or submarine mass failure (SMF) tsunamis are normally characterized by relatively shorter wave lengths and stronger wave dispersion, and potentially may generate large wave amplitudes locally and high run-up along adjacent coastlines. Due to a complex interplay between the landslide and tsunami waves, accurate simulation of landslide motion as well as tsunami generation is a challenging task. We develop and test a new two-layer model for granular landslide motion and tsunami wave generation. The landslide is described as a saturated granular flow, accounting for intergranular stresses governed by Coulomb friction. Tsunami wave generation is simulated by the three-dimensional non-hydrostatic wave model NHWAVE, which is capable of capturing wave dispersion efficiently using a small number of discretized vertical levels. Depth-averaged governing equations for the granular landslide are derived in a slope-oriented coordinate system, taking into account the dynamic interaction between the lower-layer granular landslide and upper-layer water motion. The model is tested against laboratory experiments on impulsive wave generation by subaerial granular landslides. Model results illustrate a complex interplay between the granular landslide and tsunami waves, and they reasonably predict not only the tsunami wave generation but also the granular landslide motion from initiation to deposition.

Frequency of Inverted Electrocardiographic T Waves (Cerebral T Waves) in Patients With Acute Strokes and Their Relation to Left Ventricular Wall Motion Abnormalities.

PubMed

Stone, Jeremy; Mor-Avi, Victor; Ardelt, Agnieszka; Lang, Roberto M

2018-01-01

Transient, symmetric, and deep inverted electrocardiogram (ECG) T waves in the setting of stroke, commonly referred to as cerebral T waves, are rare, and the underlying mechanism is unclear. Our study aimed to test the hypothesis that cerebral T waves are associated with transient cardiac dysfunction. This retrospective study included 800 patients admitted with the primary diagnosis of hemorrhagic or ischemic stroke. ECGs were examined for cerebral T waves, defined as T-wave inversion of ≥5 mm depth in ≥4 contiguous precordial leads. Echocardiograms of those meeting these criteria were examined for the presence of left ventricular (LV) wall motion abnormalities. Follow-up evaluation included both ECG and echocardiogram. Of the 800 patients, 17 had cerebral T waves on ECG (2.1%). All 17 patients had ischemic strokes, of which 11 were in the middle cerebral artery distribution (65%), and 2 were cerebellar (12%), whereas the remaining 4 involved other locations. Follow-up ECG showed resolution of the T-wave changes in all 17 patients. Of these patients, 14 (82%) had normal wall motion, and 3 had transient wall motion abnormalities (18%). Two of these patients had Takotsubo-like cardiomyopathy with apical ballooning, and the third had globally reduced LV function. Coronary angiography showed no significant disease to explain the LV dysfunction. In summary, in our cohort of patients with acute stroke, cerebral T waves were rare and occurred only in ischemic stroke. Eighteen percent of patients with cerebral T waves had significant transient wall motion abnormalities. Patients with stroke with cerebral T waves, especially in those with ischemic strokes, should be assessed for cardiac dysfunction. Copyright © 2017 Elsevier Inc. All rights reserved.

Theoretical prediction of a rotating magnon wave packet in ferromagnets.

PubMed

Matsumoto, Ryo; Murakami, Shuichi

2011-05-13

We theoretically show that the magnon wave packet has a rotational motion in two ways: a self-rotation and a motion along the boundary of the sample (edge current). They are similar to the cyclotron motion of electrons, but unlike electrons the magnons have no charge and the rotation is not due to the Lorentz force. These rotational motions are caused by the Berry phase in momentum space from the magnon band structure. Furthermore, the rotational motion of the magnon gives an additional correction term to the magnon Hall effect. We also discuss the Berry curvature effect in the classical limit of long-wavelength magnetostatic spin waves having macroscopic coherence length.

Image velocimetry for clouds with relaxation labeling based on deformation consistency

NASA Astrophysics Data System (ADS)

Horinouchi, Takeshi; Murakami, Shin-ya; Kouyama, Toru; Ogohara, Kazunori; Yamazaki, Atsushi; Yamada, Manabu; Watanabe, Shigeto

2017-08-01

Correlation-based cloud tracking has been extensively used to measure atmospheric winds, but still difficulty remains. In this study, aiming at developing a cloud tracking system for Akatsuki, an artificial satellite orbiting Venus, a formulation is developed for improving the relaxation labeling technique to select appropriate peaks of cross-correlation surfaces which tend to have multiple peaks. The formulation makes an explicit use of consistency inherent in the type of cross-correlation method where template sub-images are slid without deformation; if the resultant motion vectors indicate a too-large deformation, it is contradictory to the assumption of the method. The deformation consistency is exploited further to develop two post processes; one clusters the motion vectors into groups within each of which the consistency is perfect, and the other extends the groups using the original candidate lists. These processes are useful to eliminate erroneous vectors, distinguish motion vectors at different altitudes, and detect phase velocities of waves in fluids such as atmospheric gravity waves. As a basis of the relaxation labeling and the post processes as well as uncertainty estimation, the necessity to find isolated (well-separated) peaks of cross-correlation surfaces is argued, and an algorithm to realize it is presented. All the methods are implemented, and their effectiveness is demonstrated with initial images obtained by the ultraviolet imager onboard Akatsuki. Since the deformation consistency regards the logical consistency inherent in template matching methods, it should have broad application beyond cloud tracking.

Breaking Waves on the Ocean Surface

NASA Astrophysics Data System (ADS)

Schwendeman, Michael S.

In the open ocean, breaking waves are a critical mechanism for the transfer of energy, momentum, and mass between the atmosphere and the ocean. Despite much study, fundamental questions about wave breaking, such as what determines whether a wave will break, remain unresolved. Measurements of oceanic breakers, or "whitecaps," are often used to validate the hypotheses derived in simplified theoretical, numerical, or experimental studies. Real-world measurements are also used to improve the parameterizations of wave-breaking in large global models, such as those forecasting climate change. Here, measurements of whitecaps are presented using ship-based cameras, from two experiments in the North Pacific Ocean. First, a method for georectifying the camera imagery is described using the distant horizon, without additional instrumentation. Over the course of the experiment, this algorithm correctly identifies the horizon in 92% of images in which it is visible. In such cases, the calculation of camera pitch and roll is accurate to within 1 degree. The main sources of error in the final georectification are from mislabeled horizons due to clouds, rain, or poor lighting, and from vertical "heave" motions of the camera, which cannot be calculated with the horizon method. This method is used for correcting the imagery from the first experiment, and synchronizing the imagery from the second experiment to an onboard inertial motion package. Next, measurements of the whitecap coverage, W, are shown from both experiments. Although W is often used in models to represent whitecapping, large uncertainty remains in the existing parameterizations. The data show good agreement with recent measurements using the wind speed. Although wave steepness and dissipation are hypothesized to be more robust predictors of W, this is shown to not always be the case. Wave steepness shows comparable success to the wind parameterizations only when using a mean-square slope variable calculated over the equilibrium range waves and normalizing by the wave directional spread. Meanwhile, correlation of W with turbulent dissipation measurements is significantly worse, which may be due to uncertainty in the measurements or bias related to micro-breaking waves. Finally, phase-resolved, three-dimensional, measurements of the whitecaps were made from a new ship-based stereo video system. Comparison with concurrent buoy measurements indicate that the stereo data accurately reproduces the wave statistics, including the frequency spectra. The whitecaps are characterized by transient and spatially localized regions of extreme surface gradients, rather than large crest-to-trough steepnesses. It was found that whitecaps were around 10 times more likely to have extreme slopes, and 50% of the observed extreme surface slopes were in the vicinity of the breaking waves. The maximum whitecap slopes show good agreement with the Stokes 120 degree limiting crest geometry, and the whitecap crest loses much of its maximum steepness shortly after the onset of breaking. The whitecap phase speeds are consistently less than the linear or weakly nonlinear predicted phase speed, which indicate the effect of narrow-band wave groups, despite the broad-band wave spectra.

SU-D-17A-07: Development and Evaluation of a Prototype Ultrasonography Respiratory Monitoring System for 4DCT Reconstruction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yan, P; Cheng, S; Chao, C

Purpose: Respiratory motion artifacts are commonly seen in the abdominal and thoracic CT images. A Real-time Position Management (RPM) system is integrated with CT simulator using abdominal surface as a surrogate for tracking the patient respiratory motion. The respiratory-correlated four-dimensional computed tomography (4DCT) is then reconstructed by GE advantage software. However, there are still artifacts due to inaccurate respiratory motion detecting and sorting methods. We developed an Ultrasonography Respiration Monitoring (URM) system which can directly monitor diaphragm motion to detect respiratory cycles. We also developed a new 4DCT sorting and motion estimation method to reduce the respiratory motion artifacts. Themore » new 4DCT system was compared with RPM and the GE 4DCT system. Methods: Imaging from a GE CT scanner was simultaneously correlated with both the RPM and URM to detect respiratory motion. A radiation detector, Blackcat GM-10, recorded the X-ray on/off and synchronized with URM. The diaphragm images were acquired with Ultrasonix RP system. The respiratory wave was derived from diaphragm images and synchronized with CT scanner. A more precise peaks and valleys detection tool was developed and compared with RPM. The motion is estimated for the slices which are not in the predefined respiratory phases by using block matching and optical flow method. The CT slices were then sorted into different phases and reconstructed, compared with the images reconstructed from GE Advantage software using respiratory wave produced from RPM system. Results: The 4DCT images were reconstructed for eight patients. The discontinuity at the diaphragm level due to an inaccurate identification of phases by the RPM was significantly improved by URM system. Conclusion: Our URM 4DCT system was evaluated and compared with RPM and GE 4DCT system. The new system is user friendly and able to reduce motion artifacts. It also has the potential to monitor organ motion during therapy.« less

The Vajont disaster: a 3D numerical simulation for the slide and the waves

NASA Astrophysics Data System (ADS)

Rubino, Angelo; Androsov, Alexey; Vacondio, Renato; Zanchettin, Davide; Voltzinger, Naum

2016-04-01

A very high resolution O(5 m), 3D hydrostatic nonlinear numerical model was used to simulate the dynamics of both the slide and the surface waves produced during the Vajont disaster (north Italy, 1963), one of the major landslide-induced tsunamis ever documented. Different simulated wave phenomena like, e.g., maximum run-up on the opposite shore, maximum height, and water velocity were analyzed and compared with data available in literature, including the results of a fully 3D simulation obtained with a Smoothed Particle Hydrodynamic code. The difference between measured and simulated after-slide bathymetries was calculated and used in an attempt to quantify the relative magnitude and extension of rigid and fluid motion components during the event.

Interfacial waves generated by electrowetting-driven contact line motion

NASA Astrophysics Data System (ADS)

Ha, Jonghyun; Park, Jaebum; Kim, Yunhee; Shin, Bongsu; Bae, Jungmok; Kim, Ho-Young

2016-10-01

The contact angle of a liquid-fluid interface can be effectively modulated by the electrowetting-on-dielectric (EWOD) technology. Rapid movement of the contact line can be achieved by swift changes of voltage at the electrodes, which can give rise to interfacial waves under the strong influence of surface tension. Here we experimentally demonstrate EWOD-driven interfacial waves of overlapping liquids and compare their wavelength and decay length with the theoretical results obtained by a perturbation analysis. Our theory also allows us to predict the temporal evolution of the interfacial profiles in either rectangular or cylindrical containers, as driven by slipping contact lines. This work builds a theoretical framework to understand and predict the dynamics of capillary waves of a liquid-liquid interface driven by EWOD, which has practical implications on optofluidic devices used to guide light.

Improved shear wave group velocity estimation method based on spatiotemporal peak and thresholding motion search

PubMed Central

Amador, Carolina; Chen, Shigao; Manduca, Armando; Greenleaf, James F.; Urban, Matthew W.

2017-01-01

Quantitative ultrasound elastography is increasingly being used in the assessment of chronic liver disease. Many studies have reported ranges of liver shear wave velocities values for healthy individuals and patients with different stages of liver fibrosis. Nonetheless, ongoing efforts exist to stabilize quantitative ultrasound elastography measurements by assessing factors that influence tissue shear wave velocity values, such as food intake, body mass index (BMI), ultrasound scanners, scanning protocols, ultrasound image quality, etc. Time-to-peak (TTP) methods have been routinely used to measure the shear wave velocity. However, there is still a need for methods that can provide robust shear wave velocity estimation in the presence of noisy motion data. The conventional TTP algorithm is limited to searching for the maximum motion in time profiles at different spatial locations. In this study, two modified shear wave speed estimation algorithms are proposed. The first method searches for the maximum motion in both space and time (spatiotemporal peak, STP); the second method applies an amplitude filter (spatiotemporal thresholding, STTH) to select points with motion amplitude higher than a threshold for shear wave group velocity estimation. The two proposed methods (STP and STTH) showed higher precision in shear wave velocity estimates compared to TTP in phantom. Moreover, in a cohort of 14 healthy subjects STP and STTH methods improved both the shear wave velocity measurement precision and the success rate of the measurement compared to conventional TTP. PMID:28092532

Improved Shear Wave Group Velocity Estimation Method Based on Spatiotemporal Peak and Thresholding Motion Search.

PubMed

Amador Carrascal, Carolina; Chen, Shigao; Manduca, Armando; Greenleaf, James F; Urban, Matthew W

2017-04-01

Quantitative ultrasound elastography is increasingly being used in the assessment of chronic liver disease. Many studies have reported ranges of liver shear wave velocity values for healthy individuals and patients with different stages of liver fibrosis. Nonetheless, ongoing efforts exist to stabilize quantitative ultrasound elastography measurements by assessing factors that influence tissue shear wave velocity values, such as food intake, body mass index, ultrasound scanners, scanning protocols, and ultrasound image quality. Time-to-peak (TTP) methods have been routinely used to measure the shear wave velocity. However, there is still a need for methods that can provide robust shear wave velocity estimation in the presence of noisy motion data. The conventional TTP algorithm is limited to searching for the maximum motion in time profiles at different spatial locations. In this paper, two modified shear wave speed estimation algorithms are proposed. The first method searches for the maximum motion in both space and time [spatiotemporal peak (STP)]; the second method applies an amplitude filter [spatiotemporal thresholding (STTH)] to select points with motion amplitude higher than a threshold for shear wave group velocity estimation. The two proposed methods (STP and STTH) showed higher precision in shear wave velocity estimates compared with TTP in phantom. Moreover, in a cohort of 14 healthy subjects, STP and STTH methods improved both the shear wave velocity measurement precision and the success rate of the measurement compared with conventional TTP.

Upper Ocean Meso-Submesoscale Eddy Variability in the Northwestern Pacific from Repeat ADCP Measurements and 1/48-deg MITgcm Simulation

NASA Astrophysics Data System (ADS)

Qiu, B.; Nakano, T.; Chen, S.; Wang, J.; Fu, L. L.; Klein, P.

2016-12-01

With the use of Ka-band radar interferometry, the Surface Water and Ocean Topography (SWOT) satellite will improve the measured sea surface height (SSH) resolution down to the spectral wavelength of 15km, allowing us to investigate for the first time the upper oceancirculation variability at the submesoscale range on the global scale. By analyzing repeat shipboardAcoustic Doppler Current Profiler (ADCP) measurements along 137°E, as well as the 1/48-deg MITgcm simulation output, in the northwest Pacific, we demonstrate that the observed/modeled upper ocean velocities are comprised of balanced geostrophic motions and unbalanced ageostrophic wave motions. The length scale, Lc, that separates the dominance between these two types of motions is found to depend sensitively on the energy level of local mesoscale eddy variability. In the eddy-abundant western boundary current region of Kuroshio, Lc can be shorter than 15km, whereas Lc exceeds 200km along the path of relatively stable North Equatorial Current. Judicious separation between the balanced and unbalanced surface ocean signals will both be a challenge and opportunity for the SWOT mission.

Spectral decomposition of internal gravity wave sea surface height in global models

NASA Astrophysics Data System (ADS)

Savage, Anna C.; Arbic, Brian K.; Alford, Matthew H.; Ansong, Joseph K.; Farrar, J. Thomas; Menemenlis, Dimitris; O'Rourke, Amanda K.; Richman, James G.; Shriver, Jay F.; Voet, Gunnar; Wallcraft, Alan J.; Zamudio, Luis

2017-10-01

Two global ocean models ranging in horizontal resolution from 1/12° to 1/48° are used to study the space and time scales of sea surface height (SSH) signals associated with internal gravity waves (IGWs). Frequency-horizontal wavenumber SSH spectral densities are computed over seven regions of the world ocean from two simulations of the HYbrid Coordinate Ocean Model (HYCOM) and three simulations of the Massachusetts Institute of Technology general circulation model (MITgcm). High wavenumber, high-frequency SSH variance follows the predicted IGW linear dispersion curves. The realism of high-frequency motions (>0.87 cpd) in the models is tested through comparison of the frequency spectral density of dynamic height variance computed from the highest-resolution runs of each model (1/25° HYCOM and 1/48° MITgcm) with dynamic height variance frequency spectral density computed from nine in situ profiling instruments. These high-frequency motions are of particular interest because of their contributions to the small-scale SSH variability that will be observed on a global scale in the upcoming Surface Water and Ocean Topography (SWOT) satellite altimetry mission. The variance at supertidal frequencies can be comparable to the tidal and low-frequency variance for high wavenumbers (length scales smaller than ˜50 km), especially in the higher-resolution simulations. In the highest-resolution simulations, the high-frequency variance can be greater than the low-frequency variance at these scales.

Stokes drift.

PubMed

van den Bremer, T S; Breivik, Ø

2018-01-28

During its periodic motion, a particle floating at the free surface of a water wave experiences a net drift velocity in the direction of wave propagation, known as the Stokes drift (Stokes 1847 Trans. Camb. Philos. Soc. 8 , 441-455). More generally, the Stokes drift velocity is the difference between the average Lagrangian flow velocity of a fluid parcel and the average Eulerian flow velocity of the fluid. This paper reviews progress in fundamental and applied research on the induced mean flow associated with surface gravity waves since the first description of the Stokes drift, now 170 years ago. After briefly reviewing the fundamental physical processes, most of which have been established for decades, the review addresses progress in laboratory and field observations of the Stokes drift. Despite more than a century of experimental studies, laboratory studies of the mean circulation set up by waves in a laboratory flume remain somewhat contentious. In the field, rapid advances are expected due to increasingly small and cheap sensors and transmitters, making widespread use of small surface-following drifters possible. We also discuss remote sensing of the Stokes drift from high-frequency radar. Finally, the paper discusses the three main areas of application of the Stokes drift: in the coastal zone, in Eulerian models of the upper ocean layer and in the modelling of tracer transport, such as oil and plastic pollution. Future climate models will probably involve full coupling of ocean and atmosphere systems, in which the wave model provides consistent forcing on the ocean surface boundary layer. Together with the advent of new space-borne instruments that can measure surface Stokes drift, such models hold the promise of quantifying the impact of wave effects on the global atmosphere-ocean system and hopefully contribute to improved climate projections.This article is part of the theme issue 'Nonlinear water waves'. © 2017 The Author(s).

Analytical treatment of particle motion in circularly polarized slab-mode wave fields

NASA Astrophysics Data System (ADS)

Schreiner, Cedric; Vainio, Rami; Spanier, Felix

2018-02-01

Wave-particle interaction is a key process in particle diffusion in collisionless plasmas. We look into the interaction of single plasma waves with individual particles and discuss under which circumstances this is a chaotic process, leading to diffusion. We derive the equations of motion for a particle in the fields of a magnetostatic, circularly polarized, monochromatic wave and show that no chaotic particle motion can arise under such circumstances. A novel and exact analytic solution for the equations is presented. Additional plasma waves lead to a breakdown of the analytic solution and chaotic particle trajectories become possible. We demonstrate this effect by considering a linearly polarized, monochromatic wave, which can be seen as the superposition of two circularly polarized waves. Test particle simulations are provided to illustrate and expand our analytical considerations.

Near-field non-radial motion generation from underground chemical explosions in jointed granite

NASA Astrophysics Data System (ADS)

Vorobiev, Oleg; Ezzedine, Souheil; Hurley, Ryan

2018-01-01

This paper describes analysis of non-radial ground motion generated by chemical explosions in a jointed rock formation during the Source Physics Experiment (SPE). Such motion makes it difficult to discriminate between various subsurface events such as explosions, implosions (i.e. mine collapse) and earthquakes. We apply 3-D numerical simulations to understand experimental data collected during the SPEs. The joints are modelled explicitly as compliant thin inclusions embedded into the rock mass. Mechanical properties of the rock and the joints as well as the joint spacing and orientation are inferred from experimental test data, and geophysical and geological characterization of the SPE site which is dominantly Climax Stock granitic outcrop. The role of various factors characterizing the joints such as joint spacing, frictional properties, orientation and persistence in generation of non-radial motion is addressed. The joints in granite at the SPE site are oriented in nearly orthogonal directions with two vertical sets dipping at 70-80 degrees with the same strike angle, one vertical set almost orthogonal to the first two and one shallow angle joint set dipping 15 degrees. In this study we establish the relationship between the joint orientation and azimuthal variations in the polarity of the observed shear motion. The majority of the shear motion is generated due to the effects of non-elastic sliding on the joints near the source, where the wave can create significant shear stress to overcome the cohesive forces at the joints. Near the surface the joints are less confined and are subject to sliding when the pressure waves are reflected. In the far field, where the cohesive forces on the joints cannot be overcome, additional shear motion can be generated due to elastic anisotropy of the rock mass given by preferred spatial orientations of compliant joints.

An Autonomous, Low Cost Platform for Seafloor Geodetic Observations

NASA Astrophysics Data System (ADS)

Ericksen, T.; Foster, J. H.; Bingham, B. S.; Oshiro, J.

2014-12-01

The Pacific GPS Facility and the Field Robotics Laboratory at the University of Hawaii have developed an approach to significantly reduce costs below ship based methods of accurately measuring short-term vertical motions of the seafloor and maintaining a continuous long-term record of seafloor pressure. Our goal has been to reduce the primary barrier preventing us from acquiring the observations we need to understand geodetic processes, and the hazards they present, at subduction zones, submarine volcanoes, and subsea landslides. To this end, we have designed a payload package for one of the University of Hawaii Wave Gliders which incorporates an acoustic telemetry package, a dual frequency geodetic-grade Global Positioning System (GPS) receiver, meteorological sensors, processing computer, and cellular communications. The Wave Glider will interrogate high accuracy pressure sensors on the seafloor to maintain a near-continuous stream of pressure and temperature data. The seafloor geodetic monument seats a sensor capable of recording pressure, temperature, and sound velocity for a deployment duration of over 5 years with an acoustic modem for communications, and an integral acoustic release for recovery and replacement of batteries. The design of the geodetic monument allows for precise repositioning of the sensor to extend the pressure record beyond a single 5+ year deployment, and includes the capability to install a mobile pressure recorder for calibration of the linear drift of the continuous pressure sensor. We will present the design of the Wave Glider payload and seafloor geodetic monument, as well as a discussion of nearshore and offshore field tests and operational procedures. An assessment of our ability to determine cm-scale vertical seafloor motions will be made by integrating the seafloor pressure measurements recovered during field testing with independent measurements of sea surface pressure and sea surface height made by the sea surface payload.

Observations of basin ground motions from a dense seismic array in San Jose, California

USGS Publications Warehouse

Frankel, A.; Carver, D.; Cranswick, E.; Bice, T.; Sell, R.; Hanson, S.

2001-01-01

We installed a dense array of 41 digital seismographs in San Jose, California, to evaluate in detail the effects of a deep sedimentary basin and shallow sedimentary deposits on earthquake ground motions. This urban array is located near the eastern edge of the Santa Clara Valley and spans the Evergreen sedimentary basin identified by gravity data. Average station spacing is 1 km, with three stations initially spaced 110 m apart. Despite the high-noise urban environment, the stations of the array successfully triggered on and recorded small local earthquakes (M 2.5-2.8 at 10-25 km distance) and larger regional events such as the M 5.0 Bolinas earthquake (90 km distance), M 4.6-5.6 earthquakes near Mammoth Lakes (270 km distance), M 4.9-5.6 events in western Nevada (420 km distance) and the M 7.1 Hector Mine earthquake (590 km distance). Maps of spectral ratios across the array show that the highest amplitudes in all frequency bands studied (0.125-8 Hz) are generally observed at stations farther from the eastern edge of the Santa Clara Valley. Larger spectral amplitudes are often observed above the western edge of the Evergreen Basin. Snapshots of the recorded wavefield crossing the array for regional events to the east reveal that large, low-frequency (0.125-0.5 Hz) arrivals after the S-wave travel from south to north across the array. A moving-window, cross-correlation analysis finds that these later arrivals are surface waves traveling from the south. The timing and propagation direction of these arrivals indicates that they were likely produced by scattering of incident S waves at the border of the Santa Clara Valley to the south of the array. It is remarkable that the largest low-frequency phases at many of the valley sites for regional events to the east are basin surface waves coming from a direction about 70 degrees different from that of the epicenters. Basin surface waves emanating from the eastern edge of the valley are also identified by the cross-correlation analysis.

LDR structural technology activities at JPL

NASA Technical Reports Server (NTRS)

Wada, Ben

1988-01-01

The status of the Large Deployable Reflector (LDR) technology requirements and the availability of that technology in the next few years are summarized. The research efforts at JPL related to these technology needs are also discussed. LDR requires that a large and relatively stiff truss-type backup structure have a surface accurate to 100 microns in space (initial position with thermal distortions) and the dynamic characteristics predictable and/or measurable by on-orbit system identification for micron level motion. This motion may result from the excitation of the lower modes or from wave-type motions. It is also assumed that the LDR structure can be ground tested to validate its ability to meet mission requirements. No program manager will commit a structural design based solely on analysis, unless the analysis is backed by a validation test program.

Simple Harmonic Motion in Harmonic Plane Waves.

ERIC Educational Resources Information Center

Benumof, Reuben

1980-01-01

Discusses the distribution of kinetic and potential energy in transverse and longitudinal waves and examines the transmission of power and momentum. This discussion is intended to aid in understanding the simple harmonic motion of a particle involved in the propagation of a harmonic mechanical plane wave. (HM)

Development of a Single Station 6C-Approach for Array Analysis and Microzonation: Using Vertical Rotation Rate to Estimate Love-Wave Disperion Curves and Direction Finding

NASA Astrophysics Data System (ADS)

Wassermann, J. M.; Wietek, A.; Hadziioannou, C.; Igel, H.

2014-12-01

Microzonation, i.e. the estimation of (shear) wave velocity profiles of the upper few 100m in dense 2D surface grids is one of the key methods to understand the variation in seismic hazard caused by ground shaking events. In this presentation we introduce a novel method for estimating the Love-wave phase velocity dispersion by using ambient noise recordings. We use the vertical component of rotational motions inherently present in ambient noise and the well established relation to simultaneous recordings of transverse acceleration. In this relation the frequency dependent phase velocity of a plane SH (or Love)-type wave acts as a proportionality factor between the anti-correlated amplitudes of both measures. In a first step we used synthetic data sets with increasing complexity to evaluate the proposed technique and the developed algorithm to extract the direction and amplitude of the incoming ambient noise wavefield measured at a single site. Since reliable weak rotational motion sensors are not yet readily available, we apply array derived rotation measurements in order to test our method. We next use the technique to analyze different real data sets of ambient noise measurements as well as seismic recordings at active volcanoes and compare these results with findings of the Spatial AutoCorrelation technique which was applied to the same data set. We demonstrate that the newly developed technique shows comparable results to more classical, strictly array based methods. Furthermore, we show that as soon as portable weak motion rotational motion sensors are available, a single 6C-station approach will be feasible, not only for microzonation but also for general array applications, with performance comparable to more classical techniques. An important advantage, especially in urban environments, is that with this approach, the number of seismic stations needed is drastically reduced.

Three-dimensional long-period groundmotion simulations in the upper Mississippi embayment

USGS Publications Warehouse

Macpherson, K.A.; Woolery, E.W.; Wang, Z.; Liu, P.

2010-01-01

We employed a 3D velocity model and 3D wave propagation code to simulate long-period ground motions in the upper Mississippi embayment. This region is at risk from large earthquakes in the New Madrid seismic zone (NMSZ) and observational data are sparse, making simulation a valuable tool for predicting the effects of large events. We undertook these simulations to estimate the magnitude of shaking likely to occur and to investigate the influence of the 3D embayment structure and finite-fault mechanics on ground motions. There exist three primary fault zones in the NMSZ, each of which was likely associated with one of the main shocks of the 1811-12 earthquake triplet. For this study, three simulations have been conducted on each major segment, exploring the impact of different epicentral locations and rupture directions on ground motions. The full wave field up to a frequency of 0.5 Hz is computed on a 200 ?? 200 ?? 50-km 3 volume using a staggered-grid finite-difference code. Peak horizontal velocity and bracketed durations were calculated at the free surface. The NMSZ simulations indicate that for the considered bandwidth, finite-fault mechanics such as fault proximity, directivity effect, and slip distribution exert the most control on ground motions. The 3D geologic structure of the upper Mississippi embayment also influences ground motion with indications that amplification is induced by the sharp velocity contrast at the basin edge.

Simultaneous observations of ice motion, calving and seismicity on the Yahtse Glacier, Alaska. (Invited)

NASA Astrophysics Data System (ADS)

Larsen, C. F.; Bartholomaus, T. C.; O'Neel, S.; West, M. E.

2010-12-01

We observe ice motion, calving and seismicity simultaneously and with high-resolution on an advancing tidewater glacier in Icy Bay, Alaska. Icy Bay’s tidewater glaciers dominate regional glacier-generated seismicity in Alaska. Yahtse emanates from the St. Elias Range near the Bering-Bagley-Seward-Malaspina Icefield system, the most extensive glacier cover outside the polar regions. Rapid rates of change and fast flow (>16 m/d near the terminus) at Yahtse Glacier provide a direct analog to the disintegrating outlet systems in Greenland. Our field experiment co-locates GPS and seismometers on the surface of the glacier, with a greater network of bedrock seismometers surrounding the glacier. Time-lapse photogrammetry, fjord wave height sensors, and optical survey methods monitor iceberg calving and ice velocity near the terminus. This suite of geophysical instrumentation enables us to characterize glacier motion and geometry changes while concurrently listening for seismic energy release. We are performing a close examination of calving as a seismic source, and the associated mechanisms of energy transfer to seismic waves. Detailed observations of ice motion (GPS and optical surveying), glacier geometry and iceberg calving (direct observations and timelapse photogrammetry) have been made in concert with a passive seismic network. Combined, the observations form the basis of a rigorous analysis exploring the relationship between glacier-generated seismic events and motion, glacier-fiord interactions, calving and hydraulics. Our work is designed to demonstrate the applicability and utility of seismology to study the impact of climate forcing on calving glaciers.

Inertial wave beams and inertial wave modes in a rotating cylinder with time-modulated rotation rate

NASA Astrophysics Data System (ADS)

Borcia, Ion D.; Ghasemi V., Abouzar; Harlander, Uwe

2014-05-01

Inertial gravity waves play an crucial role in atmospheres, oceans, and the fluid inside of planets and moons. In the atmosphere, the effect of rotation is neglected for small wavelength and the waves bear the character of internal gravity waves. For long waves, the hydrostatic assumption is made which in turn makes the atmosphere inelastic with respect to inertial motion. In contrast, in the Earth's interior, pure inertial waves are considered as an important fundamental part of the motion. Moreover, as the deep ocean is nearly homogeneous, there the inertial gravity waves bear the character of inertial waves. Excited at the oceans surface mainly due to weather systems the waves can propagate downward and influence the deep oceans motion. In the light of the aforesaid it is important to understand better fundamental inertial wave dynamics. We investigate inertial wave modes by experimental and numerical methods. Inertial modes are excited in a fluid filled rotating annulus by modulating the rotation rate of the outer cylinder and the upper and lower lids. This forcing leads to inertial wave beams emitted from the corner regions of the annulus due to periodic motions in the boundary layers (Klein et al., 2013). When the forcing frequency matches with the eigenfrequency of the rotating annulus the beam pattern amplitude is increasing, the beams broaden and mode structures can be observed (Borcia et al., 2013a). The eigenmodes are compared with analytical solutions of the corresponding inviscid problem (Borcia et al, 2013b). In particular for the pressure field a good agreement can be found. However, shear layers related to the excited wave beams are present for all frequencies. This becomes obvious in particular in the experimental visualizations that are done by using Kalliroscope particles, highlighting relative motion in the fluid. Comparing the eigenfrequencies we find that relative to the analytical frequencies, the experimental and numerical ones show a small shift towards higher frequencies. This frequency shift is due to the reduction of the effective resonance volume that results from the existence of a Stokes boundary layer at the outer librating wall. Due to the symmetry of the forcing not all possible modes can be excited. It is shown that only symmetric modes with respect to the rotation axis exist. From a fundamental perspective, the study might help to understand better inertial mode excitation in librating planets and moons where inertial waves are emitted from critical points on the inner or outer spherical boundary. Recently, Zhang et al. (2013) pointed out the resonance should not occur in symmetric librating bodies without precession. We will discuss how this assumption depends on the boundary conditions. It might turn out that even when the projection of the Euler (or Poincare) force on the modes is zero, the projection of the excited wave beams on the modes is non-zero. K. Zhang, K. H. Chan, X. Liao, and J. M. Aurnou. The non-resonant response of fluid in a rapidly rotating sphere undergoing longitudinal libration, J. Fluid Mech.,720, 212-235, 2013. I. D. Borcia and U. Harlander. Inertial waves in a rotating annulus with inclined inner cylinder, Theoret. Comp. Fluid Dynamics, 27, 397-413, 2013. I. D. Borcia, A. Ghasemi V., and U. Harlander. Inertial wave mode excitation inside a rotating cylindrical container with librating walls, submitted to Fluid Dyn. Res.,2013. M. Klein, T. Seelig, M. V. Kurgansky, A. Ghasemi V., I. D. Borcia, A. Will, E. Schaller, C. Egbers, and Uwe Harlander. Inertial wave excitation and focusing in a liquid bounded by a frustum and a cylinder, submitted to J. Fluid Mech., 2013.

Silicone-Based Triboelectric Nanogenerator for Water Wave Energy Harvesting.

PubMed

Xiao, Tian Xiao; Jiang, Tao; Zhu, Jian Xiong; Liang, Xi; Xu, Liang; Shao, Jia Jia; Zhang, Chun Lei; Wang, Jie; Wang, Zhong Lin

2018-01-31

Triboelectric nanogenerator (TENG) has been proven to be efficient for harvesting water wave energy, which is one of the most promising renewable energy sources. In this work, a TENG with a silicone rubber/carbon black composite electrode was designed for converting the water wave energy into electricity. The silicone-based electrode with a soft texture provides a better contact with the dielectric film. Furthermore, a spring structure is introduced to transform low-frequency water wave motions into high-frequency vibrations. They together improve the output performance and efficiency of TENG. The output performances of TENGs are further enhanced by optimizing the triboelectric material pair and tribo-surface area. A spring-assisted TENG device with the segmented silicone rubber-based electrode structure was sealed into a waterproof box, which delivers a maximum power density of 2.40 W m -3 , as triggered by the water waves. The present work provides a new strategy for fabricating high-performance TENG devices by coupling flexible electrodes and spring structure for harvesting water wave energy.

Featured Image: Mixing Chemicals in Stars

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-10-01

How do stars mix chemicals in their interiors, leading to the abundances we measure at their surfaces? Two scientists from the Planetary Science Institute in Arizona, Tamara Rogers (Newcastle University, UK) and Jim McElwaine (Durham University, UK), have investigated the role that internal gravity waves have in chemical mixing in stellar interiors. Internal gravity waves not to be confused with the currently topical gravitational waves are waves that oscillate within a fluid that has a density gradient. Rogers and McElwaine used simulations to explore how these waves can cause particles in a stars interior to move around, gradually mixing the different chemical elements. Snapshots from four different times in their simulation can be seen below, with the white dots marking tracer particles and the colors indicating vorticity. You can see how the particles move in response to wave motion after the first panel. For more information, check out the paper below!CitationT. M. Rogers and J. N. McElwaine 2017 ApJL 848 L1. doi:10.3847/2041-8213/aa8d13

Models and observations of foam coverage and bubble content in the surf zone

NASA Astrophysics Data System (ADS)

Kirby, J. T.; Shi, F.; Holman, R. A.

2010-12-01

Optical and acoustical observations and communications are hampered in the nearshore by the presence of bubbles and foam generated by breaking waves. Bubble clouds in the water column provide a highly variable (both spatially and temporally) obstacle to direct acoustic and optical paths. Persistent foam riding on the water surface creates a primary occlusion of optical penetration into the water column. In an effort to better understand and predict the level of bubble and foam content in the surfzone, we have been pursuing the development of a detailed phase resolved model of fluid and gaseous components of the water column, using a Navier-Stokes/VOF formulation extended to include a multiphase description of polydisperse bubble populations. This sort of modeling provides a detailed description of large scale turbulent structures and associated bubble transport mechanisms under breaking wave crests. The modeling technique is too computationally intensive, however, to provide a wider-scale description of large surfzone regions. In order to approach the larger scale problem, we are developing a model for spatial and temporal distribution of foam and bubbles within the framework of a Boussinesq model. The basic numerical framework for the code is described by Shi et al (2010, this conference). Bubble effects are incorporated both in the mass and momentum balances for weakly dispersive, fully nonlinear waves, with spatial and temporal bubble distributions parameterized based on the VOF modeling and measurements and tied to the computed rate of dissipation of energy during breaking. A model of a foam layer on the water surface is specified using a shallow water formulation. Foam mass conservation includes source and sink terms representing outgassing of the water column, direct foam generation due to surface agitation, and erosion due to bubble bursting. The foam layer motion in the plane of the water surface arises due to a balance of drag forces due to wind and water column motion. Preliminary steps to calibrate and verify the resulting models will be taken based on results to be collected during the Surf Zone Optics experiment at Duck, NC in September 2010. Initial efforts will focus on an examination of breaking wave patterns and persistent foam distributions, using ARGUS imagery.

An exact solution to the relativistic equation of motion of a charged particle driven by a linearly polarized electromagnetic wave

NASA Technical Reports Server (NTRS)

Shebalin, John V.

1988-01-01

An exact analytic solution is found for a basic electromagnetic wave-charged particle interaction by solving the nonlinear equations of motion. The particle position, velocity, and corresponding time are found to be explicit functions of the total phase of the wave. Particle position and velocity are thus implicit functions of time. Applications include describing the motion of a free electron driven by an intense laser beam..

Rupture Dynamics and Ground Motion from Earthquakes in Heterogeneous Media

NASA Astrophysics Data System (ADS)

Bydlon, S.; Dunham, E. M.; Kozdon, J. E.

2012-12-01

Heterogeneities in the material properties of Earth's crust scatter propagating seismic waves. The effects of scattered waves are reflected in the seismic coda and depend on the relative strength of the heterogeneities, spatial arrangement, and distance from source to receiver. In the vicinity of the fault, scattered waves influence the rupture process by introducing fluctuations in the stresses driving propagating ruptures. Further variability in the rupture process is introduced by naturally occurring geometric complexity of fault surfaces, and the stress changes that accompany slip on rough surfaces. We have begun a modeling effort to better understand the origin of complexity in the earthquake source process, and to quantify the relative importance of source complexity and scattering along the propagation path in causing incoherence of high frequency ground motion. To do this we extended our two-dimensional high order finite difference rupture dynamics code to accommodate material heterogeneities. We generate synthetic heterogeneous media using Von Karman correlation functions and their associated power spectral density functions. We then nucleate ruptures on either flat or rough faults, which obey strongly rate-weakening friction laws. Preliminary results for flat faults with uniform frictional properties and initial stresses indicate that off-fault material heterogeneity alone can lead to a complex rupture process. Our simulations reveal the excitation of high frequency bursts of waves, which radiate energy away from the propagating rupture. The average rupture velocity is thus reduced relative to its value in simulations employing homogeneous material properties. In the coming months, we aim to more fully explore parameter space by varying the correlation length, Hurst exponent, and amplitude of medium heterogeneities, as well as the statistical properties characterizing fault roughness.

Influence of magnetic field configuration on magnetohydrodynamic waves in Earth's core

NASA Astrophysics Data System (ADS)

Knezek, Nicholas; Buffett, Bruce

2018-04-01

We develop a numerical model to study magnetohydrodynamic waves in a thin layer of stratified fluid near the surface of Earth's core. Past studies have been limited to using simple background magnetic field configurations. However, the choice of field distribution can dramatically affect the structure and frequency of the waves. To permit a more general treatment of background magnetic field and layer stratification, we combine finite volume and Fourier methods to describe the wave motions. We validate our model by comparisons to previous studies and examine the influence of background magnetic field configuration on two types of magnetohydrodynamic waves. We show that the structure of zonal Magnetic-Archimedes-Coriolis (MAC) waves for a dipole background field is unstable to small perturbations of the field strength in the equatorial region. Modifications to the wave structures are computed for a range of field configurations. In addition, we show that non-zonal MAC waves are trapped near the equator for realistic magnetic field distributions, and that their latitudinal extent depends upon the distribution of magnetic field strength at the CMB.

Single spontaneous photon as a coherent beamsplitter for an atomic matter-wave

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tomkovič, Jiří; Welte, Joachim; Oberthaler, Markus K.

2014-12-04

In free space the spontaneous emission of a single photon destroys motional coherence. Close to a mirror surface the reflection erases the which-path information and the single emitted photon can be regarded as a coherent beam splitter for an atomic matter-wavewhich can be verified by atom interferometry. Our experiment is a realization of the recoiling slit Gedanken experiment by Einstein.

Hydrodynamic Drag Reduction

DTIC Science & Technology

2015-04-01

Computational Engineering unstructured RANS/LES/DES solver , Tenasi, was used to predict drag and simulate the free surface flow around the ACV over a...using a second-order accurate Roe approximate Riemann scheme, while viscous fluxes are evaluated using a second-order directional derivative approach...Predictions of rigid body ship motions for the SI75 container ship in incident waves and methodology for a one-way coupling of the Tenasi flow solver

The role of conductivity discontinuities in design of cardiac defibrillation

NASA Astrophysics Data System (ADS)

Lim, Hyunkyung; Cun, Wenjing; Wang, Yue; Gray, Richard A.; Glimm, James

2018-01-01

Fibrillation is an erratic electrical state of the heart, of rapid twitching rather than organized contractions. Ventricular fibrillation is fatal if not treated promptly. The standard treatment, defibrillation, is a strong electrical shock to reinitialize the electrical dynamics and allow a normal heart beat. Both the normal and the fibrillatory electrical dynamics of the heart are organized into moving wave fronts of changing electrical signals, especially in the transmembrane voltage, which is the potential difference between the cardiac cellular interior and the intracellular region of the heart. In a normal heart beat, the wave front motion is from bottom to top and is accompanied by the release of Ca ions to induce contractions and pump the blood. In a fibrillatory state, these wave fronts are organized into rotating scroll waves, with a centerline known as a filament. Treatment requires altering the electrical state of the heart through an externally applied electrical shock, in a manner that precludes the existence of the filaments and scroll waves. Detailed mechanisms for the success of this treatment are partially understood, and involve local shock-induced changes in the transmembrane potential, known as virtual electrode alterations. These transmembrane alterations are located at boundaries of the cardiac tissue, including blood vessels and the heart chamber wall, where discontinuities in electrical conductivity occur. The primary focus of this paper is the defibrillation shock and the subsequent electrical phenomena it induces. Six partially overlapping causal factors for defibrillation success are identified from the literature. We present evidence in favor of five of these and against one of them. A major conclusion is that a dynamically growing wave front starting at the heart surface appears to play a primary role during defibrillation by critically reducing the volume available to sustain the dynamic motion of scroll waves; in contrast, virtual electrodes occurring at the boundaries of small, isolated blood vessels only cause minor effects. As a consequence, we suggest that the size of the heart (specifically, the surface to volume ratio) is an important defibrillation variable.

A Laboratory Study of a Water Surface in Response to Rainfall

NASA Astrophysics Data System (ADS)

Liu, Ren; Liu, Xinan; Duncan, James

2016-11-01

The shape of a water surface in response to the impact of raindrops is studied experimentally in a 1.22-m-by-1.22-m water pool with a water depth of 0.3 m. Simulated raindrops are generated by an array of 22-gauge hypodermic needles that are attached to the bottom of an open-surface water tank. The tank is connected to a 2D translation stage to provide a small-radius horizontal circular or oval motion to the needles, thus avoiding repeated drop impacts at the same location under each needle. The drop diameter is about 2.6 mm and the height of the water tank above the water surface of the pool is varied from 1 m to 4.8 m to provide different impact velocities. The water surface features including stalks, crowns and ring waves are measured with a cinematic laser-induced- fluorescence (LIF) technique. It is found that the average stalk height is strongly correlated to the impact velocities of raindrops and the phase speeds of ring waves inside the rain field are different from that measured outside the rain field.

Integrated Verification Experiment data collected as part of the Los Alamos National Laboratory's Source Region Program

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fitzgerald, T.J.; Carlos, R.C.; Argo, P.E.

As part of the integrated verification experiment (IVE), we deployed a network of hf ionospheric sounders to detect the effects of acoustic waves generated by surface ground motion following underground nuclear tests at the Nevada Test Site. The network sampled up to four geographic locations in the ionosphere from almost directly overhead of the surface ground zero out to a horizontal range of 60 km. We present sample results for four of the IVEs: Misty Echo, Texarkana, Mineral Quarry, and Bexar.

Site response, shallow shear-wave velocity, and wave propagation at the San Jose, California, dense seismic array

USGS Publications Warehouse

Hartzell, S.; Carver, D.; Williams, R.A.; Harmsen, S.; Zerva, A.

2003-01-01

Ground-motion records from a 52-element dense seismic array near San Jose, California, are analyzed to obtain site response, shallow shear-wave velocity, and plane-wave propagation characteristics. The array, located on the eastern side of the Santa Clara Valley south of the San Francisco Bay, is sited over the Evergreen basin, a 7-km-deep depression with Miocene and younger deposits. Site response values below 4 Hz are up to a factor of 2 greater when larger, regional records are included in the analysis, due to strong surface-wave development within the Santa Clara Valley. The pattern of site amplification is the same, however, with local or regional events. Site amplification increases away from the eastern edge of the Santa Clara Valley, reaching a maximum over the western edge of the Evergreen basin, where the pre-Cenozoic basement shallows rapidly. Amplification then decreases further to the west. This pattern may be caused by lower shallow shear-wave velocities and thicker Quaternary deposits further from the edge of the Santa Clara Valley and generation/trapping of surface waves above the shallowing basement of the western Evergreen basin. Shear-wave velocities from the inversion of site response spectra based on smaller, local earthquakes compare well with those obtained independently from our seismic reflection/refraction measurements. Velocities from the inversion of site spectra that include larger, regional records do not compare well with these measurements. A mix of local and regional events, however, is appropriate for determination of site response to be used in seismic hazard evaluation, since large damaging events would excite both body and surface waves with a wide range in ray parameters. Frequency-wavenumber, plane-wave analysis is used to determine the backazimuth and apparent velocity of coherent phases at the array. Conventional, high-resolution, and multiple signal characterization f-k power spectra and stacked slowness power spectra are compared. These spectra show surface waves generated/ scattered at the edges of the Santa Clara Valley and possibly within the valley at the western edge of the Evergreen basin.

Wave propagation modelling of induced earthquakes at the Groningen gas production site

NASA Astrophysics Data System (ADS)

Paap, Bob; Kraaijpoel, Dirk; Bakker, Marcel; Gharti, Hom Nath

2018-06-01

Gas extraction from the Groningen natural gas field, situated in the Netherlands, frequently induces earthquakes in the reservoir that cause damage to buildings and pose a safety hazard and a nuisance to the local population. Due to the dependence of the national heating infrastructure on Groningen gas, the short-term mitigation measures are mostly limited to a combination of spatiotemporal redistribution of gas production and strengthening measures for buildings. All options become more effective with a better understanding of both source processes and seismic wave propagation. Detailed wave propagation simulations improve both the inference of source processes from observed ground motions and the forecast of ground motions as input for hazard studies and seismic network design. The velocity structure at the Groningen site is relatively complex, including both deep high-velocity and shallow low-velocity deposits showing significant thickness variations over relatively small spatial extents. We performed a detailed three-dimensional wave propagation modelling study for an induced earthquake in the Groningen natural gas field using the spectral-element method. We considered an earthquake that nucleated along a normal fault with local magnitude of {{{M}}_{{L}}} = 3. We created a dense mesh with element size varying from 12 to 96 m, and used a source frequency of 7 Hz, such that frequencies generated during the simulation were accurately sampled up to 10 Hz. The velocity/density model is constructed using a three-dimensional geological model of the area, including both deep high-velocity salt deposits overlying the source region and shallow low-velocity sediments present in a deep but narrow tunnel valley. The results show that the three-dimensional density/velocity model in the Groningen area clearly play a large role in the wave propagation and resulting surface ground motions. The 3d structure results in significant lateral variations in site response. The high-velocity salt deposits have a dispersive effect on the radiated wavefield, reducing the seismic energy reaching the surface near the epicentre. In turn, the presence of low-velocity tunnel valley deposits can locally cause a significant increase in peak ground acceleration. Here we study induced seismicity on a local scale and use SPECFEM3D to conduct full waveform simulations and show how local velocity variations can affect seismic records.

Micro-seismic measurements of cliff motion under wave impact and implications for the development of near-horizontal shore platforms

NASA Astrophysics Data System (ADS)

Dickson, Mark E.; Pentney, Rachael

2012-05-01

Few high-resolution measurements of process-form interactions have been taken on rock coasts, but recent studies in California have shown that portable seismometers enable useful proxy measurements of wave-energy delivery to cliffs. Here we describe measurements over 20 days of high frequency ground motion of cliffs formed in sedimentary (flysch) rocks at Okakari Point, north of Auckland, New Zealand. Three sensors were located in a shore-normal array inland from the cliff top and a fourth sensor was bolted to a ledge 2 m above the cliff toe. The nearshore wave field in front of the cliff and shore platform was monitored using a shore-normal array of 5 wave gauges. The instrumentation provided measurements of wave-energy delivery and consequent ground motion, including the first observations of motion at the top and bottom of cliffs. Results showed that horizontal ground motion is dominant at the cliff top, whereas vertical motion is dominant at the cliff toe. Power spectra show that several high frequency peaks occur in data from the cliff toe, whereas a single, broader peak frequency occurs at the cliff top resulting from signal modification as seismic waves pass through tens of metres of cliff rock. A 100 m wide shore platform at the cliff toe fundamentally controls the patterns of observed energy delivery. The shore platform is nearly horizontal, elevated close to high water level, and abruptly plunges into water > 10 m deep at its seaward edge. As expected, the magnitude of ground motion at all sensors is greatest during larger waves. Measurements further show that ground motion, both at the bottom and top of the cliff, is strongest at low tide and weakest at high tide. This observation is opposite to that noted at Santa Cruz, where ground motion was greatest at high tide. At Okakari Point the most significant high frequency ground motions occur at low tide when waves are forced to break (sometimes violently) against the seaward edge of the shore platform. Four distinctive frequency peaks between 1 and 50 Hz increase in magnitude as tidal stage drops, implying that wave breaking against the outside edge of the shore platform represents an important source of vibration. A detailed understanding of the energy source (e.g. short duration shock pressures) and rock resonance is not provided by this study. However, quantifying the spatial and temporal patterns of energy delivery places strong emphasis on the important role of shore platform geometry in filtering wave-energy delivery to the cliff. During the 20-day experiment most wave energy was delivered to the outside edge of the shore platform, not the cliff toe. The geomorphic role of high-frequency shaking from wave impacts remains to be clearly demonstrated, but if wave impacts are capable of eroding rock then the data from this study imply that under present conditions the outside edge of the shore platform may be subject to higher erosion rates than the cliff toe. It is possible that the shore platform is currently being destroyed rather than created, but a longer programme of measurements is required to test this notion.

Using SW4 for 3D Simulations of Earthquake Strong Ground Motions: Application to Near-Field Strong Motion, Building Response, Basin Edge Generated Waves and Earthquakes in the San Francisco Bay Are

NASA Astrophysics Data System (ADS)

Rodgers, A. J.; Pitarka, A.; Petersson, N. A.; Sjogreen, B.; McCallen, D.; Miah, M.

2016-12-01

Simulation of earthquake ground motions is becoming more widely used due to improvements of numerical methods, development of ever more efficient computer programs (codes), and growth in and access to High-Performance Computing (HPC). We report on how SW4 can be used for accurate and efficient simulations of earthquake strong motions. SW4 is an anelastic finite difference code based on a fourth order summation-by-parts displacement formulation. It is parallelized and can run on one or many processors. SW4 has many desirable features for seismic strong motion simulation: incorporation of surface topography; automatic mesh generation; mesh refinement; attenuation and supergrid boundary conditions. It also has several ways to introduce 3D models and sources (including Standard Rupture Format for extended sources). We are using SW4 to simulate strong ground motions for several applications. We are performing parametric studies of near-fault motions from moderate earthquakes to investigate basin edge generated waves and large earthquakes to provide motions to engineers study building response. We show that 3D propagation near basin edges can generate significant amplifications relative to 1D analysis. SW4 is also being used to model earthquakes in the San Francisco Bay Area. This includes modeling moderate (M3.5-5) events to evaluate the United States Geologic Survey's 3D model of regional structure as well as strong motions from the 2014 South Napa earthquake and possible large scenario events. Recently SW4 was built on a Commodity Technology Systems-1 (CTS-1) at LLNL, new systems for capacity computing at the DOE National Labs. We find SW4 scales well and runs faster on these systems compared to the previous generation of LINUX clusters.

On the Integration of Medium Wave Infrared Cameras for Vision-Based Navigation

DTIC Science & Technology

2015-03-01

SWIR Short Wave Infrared VisualSFM Visual Structure from Motion WPAFB Wright Patterson Air Force Base xi ON THE INTEGRATION OF MEDIUM WAVE INFRARED...Structure from Motion Visual Structure from Motion ( VisualSFM ) is an application that performs incremental SfM using images fed into it of a scene [20...too drastically in between frames. When this happens, VisualSFM will begin creating a new model with images that do not fit to the old one. These new

Influence of a thin compressible insoluble liquid film on the eddy currents generated by interacting surface waves

NASA Astrophysics Data System (ADS)

Parfenyev, Vladimir M.; Vergeles, Sergey S.

2018-06-01

Recently the generation of eddy currents by interacting surface waves was observed experimentally. The phenomenon provides the possibility for manipulation of particles which are immersed in the fluid. The analysis shows that the amplitude of the established eddy currents produced by stationary surface waves does not depend on the fluid viscosity in the free surface case. The currents become parametrically larger, being inversely proportional to the square root of the fluid viscosity in the case when the fluid surface is covered by an almost incompressible thin liquid (i.e., shear elasticity is zero) film formed by an insoluble agent with negligible internal viscous losses as compared to the dissipation in the fluid bulk. Here we extend the theory for a thin insoluble film with zero shear elasticity and small shear and dilational viscosities on the case of an arbitrary elastic compression modulus. We find both contributions into the Lagrangian motion of passive tracers, which are the advection by the Eulerian vertical vorticity and the Stokes drift. Whereas the Stokes drift contribution preserves its value for the free surface case outside a thin viscous sublayer, the Eulerian vertical vorticity strongly depends on the fluid viscosity at high values of the film compression modulus. The Stokes drift acquires a strong dependence on the fluid viscosity inside the viscous sublayer; however, the change is compensated by an opposite change in the Eulerian vertical vorticity. As a result, the vertical dependence of the intensity of eddy currents is given by a sum of two decaying exponents with both decrements being of the order of the wave number. The decrements are numerically different, so the Eulerian contribution becomes dominant at some depth for the surface film with any compression modulus.

Determination of the thermal stress wave propagation in orthotropic hollow cylinder based on classical theory of thermoelasticity

NASA Astrophysics Data System (ADS)

Shahani, Amir Reza; Sharifi Torki, Hamid

2018-01-01

The thermoelasticity problem in a thick-walled orthotropic hollow cylinder is solved analytically using finite Hankel transform and Laplace transform. Time-dependent thermal and mechanical boundary conditions are applied on the inner and the outer surfaces of the cylinder. For solving the energy equation, the temperature itself is considered as boundary condition to be applied on both the inner and the outer surfaces of the orthotropic cylinder. Two different cases are assumed for solving the equation of motion: traction-traction problem (tractions are prescribed on both the inner and the outer surfaces) and traction-displacement (traction is prescribed on the inner surface and displacement is prescribed on the outer surface of the hollow orthotropic cylinder). Due to considering uncoupled theory, after obtaining temperature distribution, the dynamical structural problem is solved and closed-form relations are derived for radial displacement, radial and hoop stress. As a case study, exponentially decaying temperature with respect to time is prescribed on the inner surface of the cylinder and the temperature of the outer surface is considered to be zero. Owing to solving dynamical problem, the stress wave propagation and its reflections were observed after plotting the results in both cases.

Chaotic Motion of Relativistic Electrons Driven by Whistler Waves

NASA Technical Reports Server (NTRS)

Khazanov, G. V.; Telnikhin, A. A.; Kronberg, Tatiana K.

2007-01-01

Canonical equations governing an electron motion in electromagnetic field of the whistler mode waves propagating along the direction of an ambient magnetic field are derived. The physical processes on which the equations of motion are based .are identified. It is shown that relativistic electrons interacting with these fields demonstrate chaotic motion, which is accompanied by the particle stochastic heating and significant pitch angle diffusion. Evolution of distribution functions is described by the Fokker-Planck-Kolmogorov equations. It is shown that the whistler mode waves could provide a viable mechanism for stochastic energization of electrons with energies up to 50 MeV in the Jovian magnetosphere.

The wave-equivalent of the Black-Scholes option price: an interpretation

NASA Astrophysics Data System (ADS)

Haven, Emmanuel

2004-12-01

We propose an interpretation of the wave-equivalent of the Black-Scholes option price. We consider Nelson's version of the Brownian motion (Dynamical Theories of Brownian Motion, Princeton University Press, Princeton, NJ, 1967) and we use this specific motion as an input to produce a Black-Scholes PDE with a risk premium.

Real-time detection and characterization of nuclear explosion using broadband analyses of regional seismic stations

NASA Astrophysics Data System (ADS)

Prastowo, T.; Madlazim

2018-01-01

This preliminary study aims to propose a new method of real-time detection and characterization of nuclear explosions by analyzing broadband seismic waveforms acquired from a network of regional seismic stations. Signal identification generated by a nuclear test was differentiated from natural sources of either earthquakes or other natural seismo-tectonic events by verifying crucial parameters, namely source depth, type of first motion, and P-wave domination of the broadband seismic wavesunder consideration. We examined and analyzed a recently hypothetical nuclear test performed by the North Koreangovernment that occurred on September 3, 2017 as a vital point to study. From spectral analyses, we found that the source of corresponding signals associated with detonations of the latest underground nuclear test was at a much shallower depth below the surface relatively compared with that of natural earthquakes, the suspected nuclear explosions produced compressional waves with radially directed outward from the source for their first motions, and the waves were only dominated by P-components. The results are then discussed in the context of potential uses of the proposed methodology for human-induced disaster early warning system and/or the need of rapid response purposes for minimizing the disaster risks.

Sloshing dynamics modulated fluid angular momentum and moment fluctuations driven by orbital gravity gradient and jitter accelerations in microgravity

NASA Technical Reports Server (NTRS)

Hung, R. J.; Pan, H. L.

1995-01-01

The dynamical behavior of spacecraft propellant affected by the asymmetric combined gravity gradient and jitter accelerations, in particular the effect of surface tension on partially-filled rotating fluids applicable to a full-scale Gravity Probe-B Spacecraft dewar tank has been investigated. Three different cases of orbital accelerations: (1) gravity gradient-dominated, (2) equally weighted between gravity gradient and jitter, and (3) gravity jitter-dominated accelerations are studied. The results of slosh wave excitation along the liquid-vapor interface induced by gravity gradient-dominated accelerations provide a torsional moment with tidal motion of bubble oscillations in the rotating dewar. The results are clearly seen from the twisting shape of the bubble oscillations driven by gravity gradient-dominated acceleration. The results of slosh wave excitation along the liquid-vapor interface induced by gravity jitter-dominated acceleration indicate the results of bubble motion in a manner of down-and-up and leftward-and-rightward movement of oscillation when the bubble is rotating with respect to rotating dewar axis. Fluctuations of angular momentum, fluid moment and bubble mass center caused by slosh wave excitations driven by gravity gradient acceleration or gravity jitter acceleration are also investigated.

FDM simulation of earthquakes off western Kyushu, Japan, using a land-ocean unified 3D structure model

NASA Astrophysics Data System (ADS)

Okamoto, Taro; Takenaka, Hiroshi; Nakamura, Takeshi; Hara, Tatsuhiko

2017-07-01

Seismic activity occurred off western Kyushu, Japan, at the northern end of the Okinawa Trough on May 6, 2016 (14:11 JST), 22 days after the onset of the 2016 Kumamoto earthquake sequence. The area is adjacent to the Beppu-Shimabara graben where the 2016 Kumamoto earthquake sequence occurred. In the area off western Kyushu, a M7.1 earthquake also occurred on November 14, 2015 (5:51 JST), and a tsunami with a height of 0.3 m was observed. In order to better understand these seismic activity and tsunamis, it is necessary to study the sources of, and strong motions due to, earthquakes in the area off western Kyushu. For such studies, validation of synthetic waveforms is important because of the presence of the oceanic water layer and thick sediments in the source area. We show the validation results for synthetic waveforms through nonlinear inversion analyses of small earthquakes ( M5). We use a land-ocean unified 3D structure model, 3D HOT finite-difference method ("HOT" stands for Heterogeneity, Ocean layer and Topography) and a multi-graphic processing unit (GPU) acceleration to simulate the wave propagations. We estimate the first-motion augmented moment tensor (FAMT) solution based on both the long-period surface waves and short-period body waves. The FAMT solutions systematically shift landward by about 13 km, on average, from the epicenters determined by the Japan Meteorological Agency. The synthetics provide good reproductions of the observed full waveforms with periods of 10 s or longer. On the other hand, for waveforms with shorter periods (down to 4 s), the later surface waves are not reproduced well, while the first parts of the waveforms (comprising P- and S-waves) are reproduced to some extent. These results indicate that the current 3D structure model around Kyushu is effective for generating full waveforms, including surface waves with periods of about 10 s or longer. Based on these findings, we analyze the 2015 M7.1 event using the cross-correlations between the observed and synthetic waveforms. The result suggests a rupture propagation toward the NNE, with a major radiation about 25 km north of the onset point.[Figure not available: see fulltext.

Surface-seismic imaging for nehrp soil profile classifications and earthquake hazards in urban areas

USGS Publications Warehouse

Williams, R.A.; Stephenson, W.J.; Odum, J.K.

1998-01-01

We acquired high-resolution seismic-refraction data on the ground surface in selected areas of the San Fernando Valley (SFV) to help explain the earthquake damage patterns and the variation in ground motion caused by the 17 January 1994 magnitude 6.7 Northridge earthquake. We used these data to determine the compressional- and shear-wave velocities (Vp and Vs) at 20 aftershock recording sites to 30-m depth ( V??s30, and V??p30). Two other sites, located next to boreholes with downhole Vp and Vs data, show that we imaged very similar seismic-vefocity structures in the upper 40 m. Overall, high site response appears to be associated with tow Vs in the near surface, but there can be a wide rangepf site amplifications for a given NEHRP soil type. The data suggest that for the SFV, if the V??s30 is known, we can determine whether the earthquake ground motion will be amplified above a factor of 2 relative to a local rock site.

Anomalous hydrodynamics and normal fluids in rapidly rotating Bose-Einstein condensates.

PubMed

Bourne, A; Wilkin, N K; Gunn, J M F

2006-06-23

In rapidly rotating condensed Bose systems we show that there is a regime of anomalous hydrodynamics which coincides with the mean field quantum Hall regime. A consequence is the absence of a normal fluid in any conventional sense. However, even the superfluid hydrodynamics is not described by conventional Bernoulli and continuity equations. We show that there are constraints which connect spatial variations of density and phase and that the vortex positions are not the simplest description of the dynamics. We demonstrate, inter alia, a simple relation between vortices and surface waves. We show that the surface waves can emulate a "normal fluid," allowing dissipation by energy and angular momentum absorbtion from vortex motion in the trap. The time scale is sensitive to the initial configuration, which can lead to long-lived vortex patches--perhaps related to those observed at JILA.

The Effect of Surface Topography on the Nonlinear Dynamics of Rossby Waves

NASA Technical Reports Server (NTRS)

Abarzhi, S. I.; Desjardins, O.; Pitsch, H.

2003-01-01

Boussinesq convection in rotating systems attracts a sustained attention of the fluid dynamics community, because it has intricate non-linear dynamics (Cross & Hohenberg 1993) and plays an important role in geophysical and astrophysical applications, such as the motion of the liquid outer core of Earth, the Red Spot in Jupiter, the giant cells in the Sun etc. (Alridge et al. 1990). A fundamental distinction between the real geo- and astrophysical problems and the idealized laboratory studies is that natural systems are inhomogeneous (Alridge et al. 1990). Heterogeneities modulate the flow and influence significantly the dynamics of convective patterns (Alridge et al. 1990; Hide 1971). The effect of modulations on pattern formation and transition to turbulence in Boussinesq convection is far from being completely understood (Cross & Hohenberg 1993; Aranson & Kramer 2002). It is generally accepted that in the liquid outer core of the Earth the transport of the angular momentum and internal heat occurs via thermal Rossby waves (Zhang et al. 2001; Kuang & Bloxham 1999). These waves been visualized in laboratory experiments in rotating liquid-filled spheres and concentric spherical shells (Zhang et al. 2001; Kuang & Bloxham 1999). The basic dynamical features of Rossby waves have been reproduced in a cylindrical annulus, a system much simpler than the spherical ones (Busse & Or 1986; Or & Busse 1987). For convection in a cylindrical annulus, the fluid motion is two-dimensional, and gravity is replaced by a centrifugal force, (Busse & Or 1986; Or & Busse 1987). Hide (1971) has suggested that the momentum and heat transport in the core might be influenced significantly by so-called bumps, which are heterogeneities on the mantle-core boundary. To model the effect of surface topography on the transport of momentum and energy in the liquid outer core of the Earth, Bell & Soward (1996), Herrmann & Busse (1998) and Westerburg & Busse (2001) have studied the nonlinear dynamics of thermal Rossby waves in a cylindrical annulus with azimuthally modulated height.

Remotely triggered nonvolcanic tremor in Sumbawa, Indonesia

NASA Astrophysics Data System (ADS)

Fuchs, Florian; Lupi, Matteo; Miller, Stephen

2015-04-01

Nonvolcanic (or tectonic) tremor is a seismic phenomenom which can provide important information about dynamics of plate boundaries but the underlying mechanisms are not well understood. Tectonic tremor is often associated with slow-slip (termed episodic tremor and slip) and understanding the mechanisms driving tremor presents an important challenge because it is likely a dominant aspect of the evolutionary processes leading to tsunamigenic, megathrust subduction zone earthquakes. Tectonic tremor is observed worldwide, mainly along major subduction zones and plate boundaries such as in Alaska/Aleutians, Cascadia, the San Andreas Fault, Japan or Taiwan. We present, for the first time, evidence for triggered tremor beneath the island of Sumbawa, Indonesia. The island of Sumbawa, Indonesia, is part of the Lesser Sunda Group about 250 km north of the Australian/Eurasian plate collision at the Java Trench with a convergence rate of approximately 70 mm/yr. We show surface wave triggered tremor beneath Sumbawa in response to three teleseismic earthquakes: the Mw9.0 2011 Tohoku earthquake and two oceanic strike-slip earthquakes (Mw 8.6 and Mw8.2) offshore of Sumatra in 2012. Tremor amplitudes scale with ground motion and peak at 180 nm/s ground velocity on the horizontal components. A comparison of ground motion of the three triggering events and a similar (nontriggering) Mw7.6 2012 Philippines event constrains an apparent triggering threshold of approximately 1 mm/s ground velocity or 8 kPa dynamic stress. Surface wave periods of 45-65 s appear optimal for triggering tremor at Sumbawa which predominantly correlates with Rayleigh waves, even though the 2012 oceanic events have stronger Love wave amplitudes and triggering potential. Rayleigh wave triggering, low-triggering amplitudes, and the tectonic setting all favor a model of tremor generated by localized fluid transport. We could not locate the tremor because of minimal station coverage, but data indicate several potential source volumes including the Flores Thrust, the Java subduction zone, or Tambora volcano.

CONTRIBUTION OF VELOCITY VORTICES AND FAST SHOCK REFLECTION AND REFRACTION TO THE FORMATION OF EUV WAVES IN SOLAR ERUPTIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Hongjuan; Liu, Siqing; Gong, Jiancun

2015-06-01

We numerically study the detailed evolutionary features of the wave-like disturbance and its propagation in the eruption. This work is a follow-up to Wang et al., using significantly upgraded new simulations. We focus on the contribution of the velocity vortices and the fast shock reflection and refraction in the solar corona to the formation of the EUV waves. Following the loss of equilibrium in the coronal magnetic structure, the flux rope exhibits rapid motions and invokes the fast-mode shock at the front of the rope, which then produces a type II radio burst. The expansion of the fast shock, whichmore » is associated with outward motion, takes place in various directions, and the downward expansion shows the reflection and the refraction as a result of the non-uniform background plasma. The reflected component of the fast shock propagates upward and the refracted component propagates downward. As the refracted component reaches the boundary surface, a weak echo is excited. The Moreton wave is invoked as the fast shock touches the bottom boundary, so the Moreton wave lags the type II burst. A secondary echo occurs in the area where reflection of the fast shock encounters the slow-mode shock, and the nearby magnetic field lines are further distorted because of the interaction between the secondary echo and the velocity vortices. Our results indicate that the EUV wave may arise from various processes that are revealed in the new simulations.« less

Negative stiffness honeycombs as tunable elastic metamaterials

NASA Astrophysics Data System (ADS)

Goldsberry, Benjamin M.; Haberman, Michael R.

2018-03-01

Acoustic and elastic metamaterials are media with a subwavelength structure that behave as effective materials displaying atypical effective dynamic properties. These material systems are of interest because the design of their sub-wavelength structure allows for direct control of macroscopic wave dispersion. One major design limitation of most metamaterial structures is that the dynamic response cannot be altered once the microstructure is manufactured. However, the ability to modify wave propagation in the metamaterial with an external stimulus is highly desirable for numerous applications and therefore remains a significant challenge in elastic metamaterials research. In this work, a honeycomb structure composed of a doubly periodic array of curved beams, known as a negative stiffness honeycomb (NSH), is analyzed as a tunable elastic metamaterial. The nonlinear static elastic response that results from large deformations of the NSH unit cell leads to a large variation in linear elastic wave dispersion associated with infinitesimal motion superposed on the externally imposed pre-strain. A finite element model is utilized to model the static deformation and subsequent linear wave motion at the pre-strained state. Analysis of the slowness surface and group velocity demonstrates that the NSH exhibits significant tunability and a high degree of anisotropy which can be used to guide wave energy depending on static pre-strain levels. In addition, it is shown that partial band gaps exist where only longitudinal waves propagate. The NSH therefore behaves as a meta-fluid, or pentamode metamaterial, which may be of use for applications of transformation elastodynamics such as cloaking and gradient index lens devices.

One-dimensional wave propagation in particulate suspensions

NASA Technical Reports Server (NTRS)

Rochelle, S. G.; Peddieson, J., Jr.

1976-01-01

One-dimensional small-amplitude wave motion in a two-phase system consisting of an inviscid gas and a cloud of suspended particles is analyzed using a continuum theory of suspensions. Laplace transform methods are used to obtain several approximate solutions. Properties of acoustic wave motion in particulate suspensions are inferred from these solutions.

AERODYNAMIC SOUND OF A BODY IN ARBITRARY, DEFORMABLE MOTION, WITH APPLICATION TO PHONATION

PubMed Central

Howe, M. S.; McGowan, R. S.

2012-01-01

The method of tailored Green’s functions advocated by Doak (Proceedings of the Royal Society A254 (1960) 129 – 145.) for the solution of aeroacoustic problems is used to analyse the contribution of the mucosal wave to self-sustained modulation of air flow through the glottis during the production of voiced speech. The amplitude and phase of the aerodynamic surface force that maintains vocal fold vibration are governed by flow separation from the region of minimum cross-sectional area of the glottis, which moves back and forth along its effective length accompanying the mucosal wave peak. The correct phasing is achieved by asymmetric motion of this peak during the opening and closing phases of the glottis. Limit cycle calculations using experimental data of Berry et al. (Journal of the Acoustical Society of America 110 (2001) 2539 – 2547.) obtained using an excised canine hemilarynx indicate that the mechanism is robust enough to sustain oscillations over a wide range of voicing conditions. PMID:24031098

Nonlinear equations of motion for Landau resonance interactions with a whistler mode wave

NASA Technical Reports Server (NTRS)

Inan, U. S.; Tkalcevic, S.

1982-01-01

A simple set of equations is presented for the description of the cyclotron averaged motion of Landau resonant particles in a whistler mode wave propagating at an angle to the static magnetic field. A comparison is conducted of the wave magnetic field and electric field effects for the parameters of the magnetosphere, and the parameter ranges for which the wave magnetic field effects would be negligible are determined. It is shown that the effect of the wave magnetic field can be neglected for low pitch angles, high normal wave angles, and/or high normalized wave frequencies.

Nearshore wave-induced cyclical flexing of sea cliffs

USGS Publications Warehouse

Adams, P.N.; Storlazzi, C.D.; Anderson, R. Scott

2005-01-01

[1] Evolution of a tectonically active coast is driven by geomorphically destructive energy supplied by ocean waves. Wave energy is episodic and concentrated; sea cliffs are battered by the geomorphic wrecking ball every 4-25 s. We measure the response of sea cliffs to wave assault by sensing the ground motion using near-coastal seismometers. Sea cliffs respond to waves in two distinct styles. High-frequency motion (20 Hz) reflects the natural frequency of the sea cliff as it rings in response to direct wave impact. Low-frequency motion in the 0.1-0.05 Hz (10-20 s) band consistently agrees with the dominant nearshore wave period. Integrating microseismic velocities suggests 50 ??m and 10 ??m displacements in horizontal and vertical directions, respectively. Displacement ellipsoids exhibit simultaneous downward and seaward sea cliff motion with each wave. Video footage corroborates the downward sea cliff flex in response to the imposed water load on the wave cut platform. Gradients in displacement amplitudes documented using multiple seismometers suggest longitudinal and shear strain of the flexing sea cliff on the order of 0.5-4 ?? strains during each wave loading cycle. As this sea cliff flexure occurs approximately 3 million times annually, it has the potential to fatigue the rock through cyclical loading. Local sea cliff retreat rates of 10 cm/yr imply that a given parcel of rock is flexed through roughly 109 cycles of increasing amplitude before exposure to direct wave attack at the cliff face. Copyright 2005 by the American Geophysical Union.

Approximating SIR-B response characteristics and estimating wave height and wavelength for ocean imagery

NASA Technical Reports Server (NTRS)

Tilley, David G.

1987-01-01

NASA Space Shuttle Challenger SIR-B ocean scenes are used to derive directional wave spectra for which speckle noise is modeled as a function of Rayleigh random phase coherence downrange and Poisson random amplitude errors inherent in the Doppler measurement of along-track position. A Fourier filter that preserves SIR-B image phase relations is used to correct the stationary and dynamic response characteristics of the remote sensor and scene correlator, as well as to subtract an estimate of the speckle noise component. A two-dimensional map of sea surface elevation is obtained after the filtered image is corrected for both random and deterministic motions.

Real-time observation of intramolecular proton transfer in the electronic ground state of chloromalonaldehyde: an ab initio study of time-resolved photoelectron spectra.

PubMed

do N Varella, Márcio T; Arasaki, Yasuki; Ushiyama, Hiroshi; Takatsuka, Kazuo; Wang, Kwanghsi; McKoy, Vincent

2007-02-07

The authors report on studies of time-resolved photoelectron spectra of intramolecular proton transfer in the ground state of chloromalonaldehyde, employing ab initio photoionization matrix elements and effective potential surfaces of reduced dimensionality, wherein the couplings of proton motion to the other molecular vibrational modes are embedded by averaging over classical trajectories. In the simulations, population is transferred from the vibrational ground state to vibrationally hot wave packets by pumping to an excited electronic state and dumping with a time-delayed pulse. These pump-dump-probe simulations demonstrate that the time-resolved photoelectron spectra track proton transfer in the electronic ground state well and, furthermore, that the geometry dependence of the matrix elements enhances the tracking compared with signals obtained with the Condon approximation. Photoelectron kinetic energy distributions arising from wave packets localized in different basins are also distinguishable and could be understood, as expected, on the basis of the strength of the optical couplings in different regions of the ground state potential surface and the Franck-Condon overlaps of the ground state wave packets with the vibrational eigenstates of the ion potential surface.

Analysis of seismic waves crossing the Santa Clara Valley using the three-component MUSIQUE array algorithm

NASA Astrophysics Data System (ADS)

Hobiger, Manuel; Cornou, Cécile; Bard, Pierre-Yves; Le Bihan, Nicolas; Imperatori, Walter

2016-10-01

We introduce the MUSIQUE algorithm and apply it to seismic wavefield recordings in California. The algorithm is designed to analyse seismic signals recorded by arrays of three-component seismic sensors. It is based on the MUSIC and the quaternion-MUSIC algorithms. In a first step, the MUSIC algorithm is applied in order to estimate the backazimuth and velocity of incident seismic waves and to discriminate between Love and possible Rayleigh waves. In a second step, the polarization parameters of possible Rayleigh waves are analysed using quaternion-MUSIC, distinguishing retrograde and prograde Rayleigh waves and determining their ellipticity. In this study, we apply the MUSIQUE algorithm to seismic wavefield recordings of the San Jose Dense Seismic Array. This array has been installed in 1999 in the Evergreen Basin, a sedimentary basin in the Eastern Santa Clara Valley. The analysis includes 22 regional earthquakes with epicentres between 40 and 600 km distant from the array and covering different backazimuths with respect to the array. The azimuthal distribution and the energy partition of the different surface wave types are analysed. Love waves dominate the wavefield for the vast majority of the events. For close events in the north, the wavefield is dominated by the first harmonic mode of Love waves, for farther events, the fundamental mode dominates. The energy distribution is different for earthquakes occurring northwest and southeast of the array. In both cases, the waves crossing the array are mostly arriving from the respective hemicycle. However, scattered Love waves arriving from the south can be seen for all earthquakes. Combining the information of all events, it is possible to retrieve the Love wave dispersion curves of the fundamental and the first harmonic mode. The particle motion of the fundamental mode of Rayleigh waves is retrograde and for the first harmonic mode, it is prograde. For both modes, we can also retrieve dispersion and ellipticity curves. Wave motion simulations for two earthquakes are in good agreement with the real data results and confirm the identification of the wave scattering formations to the south of the array, which generate the scattered Love waves visible for all earthquakes.

Sedimentary basin effects in Seattle, Washington: Ground-motion observations and 3D simulations

USGS Publications Warehouse

Frankel, Arthur; Stephenson, William; Carver, David

2009-01-01

Seismograms of local earthquakes recorded in Seattle exhibit surface waves in the Seattle basin and basin-edge focusing of S waves. Spectral ratios of Swaves and later arrivals at 1 Hz for stiff-soil sites in the Seattle basin show a dependence on the direction to the earthquake, with earthquakes to the south and southwest producing higher average amplification. Earthquakes to the southwest typically produce larger basin surface waves relative to S waves than earthquakes to the north and northwest, probably because of the velocity contrast across the Seattle fault along the southern margin of the Seattle basin. S to P conversions are observed for some events and are likely converted at the bottom of the Seattle basin. We model five earthquakes, including the M 6.8 Nisqually earthquake, using 3D finite-difference simulations accurate up to 1 Hz. The simulations reproduce the observed dependence of amplification on the direction to the earthquake. The simulations generally match the timing and character of basin surface waves observed for many events. The 3D simulation for the Nisqually earth-quake produces focusing of S waves along the southern margin of the Seattle basin near the area in west Seattle that experienced increased chimney damage from the earthquake, similar to the results of the higher-frequency 2D simulation reported by Stephenson et al. (2006). Waveforms from the 3D simulations show reasonable agreement with the data at low frequencies (0.2-0.4 Hz) for the Nisqually earthquake and an M 4.8 deep earthquake west of Seattle.

Mathematical investigation of tsunami-like long waves interaction with submerge dike of different thickness

NASA Astrophysics Data System (ADS)

Zhiltsov, Konstantin; Kostyushin, Kirill; Kagenov, Anuar; Tyryshkin, Ilya

2017-11-01

This paper presents a mathematical investigation of the interaction of a long tsunami-type wave with a submerge dike. The calculations were performed by using the freeware package OpenFOAM. Unsteady two-dimensional Navier-Stokes equations were used for mathematical modeling of incompressible two-phase medium. The Volume of Fluid (VOF) method is used to capture the free surface of a liquid. The effects caused by long wave of defined amplitude motion through a submerged dike of varying thickness were discussed in detail. Numerical results show that after wave passing through the barrier, multiple vortex structures were formed behind. Intensity of vortex depended on the size of the barrier. The effectiveness of the submerge barrier was estimated by evaluating the wave reflection and transmission coefficients using the energy integral method. Then, the curves of the dependences of the reflection and transmission coefficients were obtained for the interaction of waves with the dike. Finally, it was confirmed that the energy of the wave could be reduced by more than 50% when it passed through the barrier.

Real-time 3-D space numerical shake prediction for earthquake early warning

NASA Astrophysics Data System (ADS)

Wang, Tianyun; Jin, Xing; Huang, Yandan; Wei, Yongxiang

2017-12-01

In earthquake early warning systems, real-time shake prediction through wave propagation simulation is a promising approach. Compared with traditional methods, it does not suffer from the inaccurate estimation of source parameters. For computation efficiency, wave direction is assumed to propagate on the 2-D surface of the earth in these methods. In fact, since the seismic wave propagates in the 3-D sphere of the earth, the 2-D space modeling of wave direction results in inaccurate wave estimation. In this paper, we propose a 3-D space numerical shake prediction method, which simulates the wave propagation in 3-D space using radiative transfer theory, and incorporate data assimilation technique to estimate the distribution of wave energy. 2011 Tohoku earthquake is studied as an example to show the validity of the proposed model. 2-D space model and 3-D space model are compared in this article, and the prediction results show that numerical shake prediction based on 3-D space model can estimate the real-time ground motion precisely, and overprediction is alleviated when using 3-D space model.

Focusing of Shear Shock Waves

NASA Astrophysics Data System (ADS)

Giammarinaro, Bruno; Espíndola, David; Coulouvrat, François; Pinton, Gianmarco

2018-01-01

Focusing is a ubiquitous way to transform waves. Recently, a new type of shock wave has been observed experimentally with high-frame-rate ultrasound: shear shock waves in soft solids. These strongly nonlinear waves are characterized by a high Mach number, because the shear wave velocity is much slower, by 3 orders of magnitude, than the longitudinal wave velocity. Furthermore, these waves have a unique cubic nonlinearity which generates only odd harmonics. Unlike longitudinal waves for which only compressional shocks are possible, shear waves exhibit cubic nonlinearities which can generate positive and negative shocks. Here we present the experimental observation of shear shock wave focusing, generated by the vertical motion of a solid cylinder section embedded in a soft gelatin-graphite phantom to induce linearly vertically polarized motion. Raw ultrasound data from high-frame-rate (7692 images per second) acquisitions in combination with algorithms that are tuned to detect small displacements (approximately 1 μ m ) are used to generate quantitative movies of gel motion. The features of shear shock wave focusing are analyzed by comparing experimental observations with numerical simulations of a retarded-time elastodynamic equation with cubic nonlinearities and empirical attenuation laws for soft solids.

Development of a nearshore oscillating surge wave energy converter with variable geometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tom, N. M.; Lawson, M. J.; Yu, Y. H.

This paper presents an analysis of a novel wave energy converter concept that combines an oscillating surge wave energy converter (OSWEC) with control surfaces. The control surfaces allow for a variable device geometry that enables the hydrodynamic properties to be adapted with respect to structural loading, absorption range and power-take-off capability. The device geometry is adjusted on a sea state-to-sea state time scale and combined with wave-to-wave manipulation of the power take-off (PTO) to provide greater control over the capture efficiency, capacity factor, and design loads. This work begins with a sensitivity study of the hydrodynamic coefficients with respect tomore » device width, support structure thickness, and geometry. A linear frequency domain analysis is used to evaluate device performance in terms of absorbed power, foundation loads, and PTO torque. Previous OSWEC studies included nonlinear hydrodynamics, in response a nonlinear model that includes a quadratic viscous damping torque that was linearized via the Lorentz linearization. Inclusion of the quadratic viscous torque led to construction of an optimization problem that incorporated motion and PTO constraints. Results from this study found that, when transitioning from moderate-to-large sea states the novel OSWEC was capable of reducing structural loads while providing a near constant power output.« less

Time-lapse changes of P- and S-wave velocities and shear wave splitting in the first year after the 2011 Tohoku earthquake, Japan: shallow subsurface

NASA Astrophysics Data System (ADS)

Sawazaki, Kaoru; Snieder, Roel

2013-04-01

We detect time-lapse changes in P- and S-wave velocities (hereafter, VP and VS, respectively) and shear wave splitting parameters associated with the 2011 Tohoku earthquake, Japan, at depths between 0 and 504 m. We estimate not only medium parameters but also the 95 per cent confidence interval of the estimated velocity change by applying a new least squares inversion scheme to the deconvolution analysis of KiK-net vertical array records. Up to 6 per cent VS reduction is observed at more than half of the analysed KiK-net stations in northeastern Japan with over 95 per cent confidence in the first month after the main shock. There is a considerable correlation between the S-wave traveltime delay and the maximum horizontal dynamic strain (MDS) by the main shock motion when the strain exceeds 5 × 10- 4 on the ground surface. This correlation is not clearly observed for MDS at the borehole bottom. On the contrary, VP and shear wave splitting parameters do not show systematic changes after the Tohoku earthquake. These results indicate that the time-lapse change is concentrated near the ground surface, especially in loosely packed soil layers. We conclude that the behaviour of VP, VS and shear wave splitting parameters are explained by the generation of omnidirectional cracks near the ground surface and by the diffusion of water in the porous subsurface. Recovery of VS should be related to healing of the crack which is proportional to the logarithm of the lapse time after the main shock and/or to decompaction after shaking.

Extension of the spatial autocorrelation (SPAC) method to mixed-component correlations of surface waves

USGS Publications Warehouse

Haney, Matthew M.; Mikesell, T. Dylan; van Wijk, Kasper; Nakahara, Hisashi

2012-01-01

Using ambient seismic noise for imaging subsurface structure dates back to the development of the spatial autocorrelation (SPAC) method in the 1950s. We present a theoretical analysis of the SPAC method for multicomponent recordings of surface waves to determine the complete 3 × 3 matrix of correlations between all pairs of three-component motions, called the correlation matrix. In the case of isotropic incidence, when either Rayleigh or Love waves arrive from all directions with equal power, the only non-zero off-diagonal terms in the matrix are the vertical–radial (ZR) and radial–vertical (RZ) correlations in the presence of Rayleigh waves. Such combinations were not considered in the development of the SPAC method. The method originally addressed the vertical–vertical (ZZ), RR and TT correlations, hence the name spatial autocorrelation. The theoretical expressions we derive for the ZR and RZ correlations offer additional ways to measure Rayleigh wave dispersion within the SPAC framework. Expanding on the results for isotropic incidence, we derive the complete correlation matrix in the case of generally anisotropic incidence. We show that the ZR and RZ correlations have advantageous properties in the presence of an out-of-plane directional wavefield compared to ZZ and RR correlations. We apply the results for mixed-component correlations to a data set from Akutan Volcano, Alaska and find consistent estimates of Rayleigh wave phase velocity from ZR compared to ZZ correlations. This work together with the recently discovered connections between the SPAC method and time-domain correlations of ambient noise provide further insights into the retrieval of surface wave Green’s functions from seismic noise.

A novel sensor for two-degree-of-freedom motion measurement of linear nanopositioning stage using knife edge displacement sensing technique

NASA Astrophysics Data System (ADS)

Zolfaghari, Abolfazl; Jeon, Seongkyul; Stepanick, Christopher K.; Lee, ChaBum

2017-06-01

This paper presents a novel method for measuring two-degree-of-freedom (DOF) motion of flexure-based nanopositioning systems based on optical knife-edge sensing (OKES) technology, which utilizes the interference of two superimposed waves: a geometrical wave from the primary source of light and a boundary diffraction wave from the secondary source. This technique allows for two-DOF motion measurement of the linear and pitch motions of nanopositioning systems. Two capacitive sensors (CSs) are used for a baseline comparison with the proposed sensor by simultaneously measuring the motions of the nanopositioning system. The experimental results show that the proposed sensor closely agrees with the fundamental linear motion of the CS. However, the two-DOF OKES technology was shown to be approximately three times more sensitive to the pitch motion than the CS. The discrepancy in the two sensor outputs is discussed in terms of measuring principle, linearity, bandwidth, control effectiveness, and resolution.

Effects of volcano topography on seismic broad-band waveforms

NASA Astrophysics Data System (ADS)

Neuberg, Jürgen; Pointer, Tim

2000-10-01

Volcano seismology often deals with rather shallow seismic sources and seismic stations deployed in their near field. The complex stratigraphy on volcanoes and near-field source effects have a strong impact on the seismic wavefield, complicating the interpretation techniques that are usually employed in earthquake seismology. In addition, as most volcanoes have a pronounced topography, the interference of the seismic wavefield with the stress-free surface results in severe waveform perturbations that affect seismic interpretation methods. In this study we deal predominantly with the surface effects, but take into account the impact of a typical volcano stratigraphy as well as near-field source effects. We derive a correction term for plane seismic waves and a plane-free surface such that for smooth topographies the effect of the free surface can be totally removed. Seismo-volcanic sources radiate energy in a broad frequency range with a correspondingly wide range of different Fresnel zones. A 2-D boundary element method is employed to study how the size of the Fresnel zone is dependent on source depth, dominant wavelength and topography in order to estimate the limits of the plane wave approximation. This approximation remains valid if the dominant wavelength does not exceed twice the source depth. Further aspects of this study concern particle motion analysis to locate point sources and the influence of the stratigraphy on particle motions. Furthermore, the deployment strategy of seismic instruments on volcanoes, as well as the direct interpretation of the broad-band waveforms in terms of pressure fluctuations in the volcanic plumbing system, are discussed.

Improvement of the free-surface tension model in shallow water basin by using in-situ bottom-friction measurements

NASA Astrophysics Data System (ADS)

Alekseenko, Elena; Kuznetsov, Konstantin; Roux, Bernard

2016-04-01

Wind stress on the free surface is the main driving force behind the circulation of the upper part of the ocean, which in hydrodynamic models are usually defined in terms of the coefficient of surface tension (Zhang et al., 2009, Davies et al., 2003). Moreover, wave motion impacts local currents and changes sea level, impacts the transport and the stratification of the entire water column. Influence of surface waves at the bottom currents is particularly pronounced in the shallow coastal systems. However, existing methods of parameterization of the surface tension have significant limits, especially in strong wind waves (Young et al., 2001, Jones et al., 2004) due to the difficulties of measuring the characteristics of surface waves in stormy conditions. Thus, the formula for calculating the coefficient of surface tension in our day is the actual problem in modeling fluid dynamics, particularly in the context of strong surface waves. In the hydrodynamic models usually a coefficient of surface tension is calculated once at the beginning of computation as a constant that depends on the averaged wind waves characteristic. Usually cases of strongly nonlinear wind waves are not taken into account, what significantly reduces the accuracy of the calculation of the flow structures and further calculation of the other processes in water basins, such as the spread of suspended matter and pollutants. Thus, wave motion influencing the pressure on the free surface and at the bottom must be considered in hydrodynamic models particularly in shallow coastal systems. A method of reconstruction of a free-surface drag coefficient based on the measured in-situ bottom pressure fluctuations is developed and applied in a three-dimensional hydrodynamic model MARS3D, developed by the French laboratory of IFREMER (IFREMER - French Research Institute for Marine Dynamics). MARS3D solves the Navier-Stokes equations for incompressible fluid in the Boussinesq approximation and with the hydrostatic assumption (Lazure and Dumas, 2008, Blumberg et al., 1986). Precisely, we introduce a formulation of the surface drag coefficient as a logarithmic function of the sea surface roughness (Zhang et al., 2009), which in turn can be predicted from the height and steepness of the waves (Taylor and Yelland, 2000), measured by the bottom pressure sensors. Using numerous field data, Taylor and Yelland (2000) showed that the surface drag coefficient values in lakes and sheltered waters are typically significantly higher than is observed in the open ocean. In particular, the effect of limited water depth is very significant in the case of the strong wind forcing. Wind waves propagating into shoaling water begin to be limited by bottom friction and become "younger". This kind of approach is used to predict a more relevant surface drag coefficient for the coastal areas of the Mediterranean Berre lagoon (France) for which experimental data of pressure measurements under storm conditions are available (Paquier, 2014). This is important to better understand the development problematics of the nearshore submerged aquatic vegetation (Alekseenko et al., 2013). *This work is supported by grant of Russian Foundation for Basic Research (RFBR) n°16-35-00526 and by the French Water Agency (Agence de l'Eau-RMC - convention n°2010-0042). References 1. E. Alekseenko E., Roux B., Sukhinov A., Kotarba R., Fougere D.: Near shoreline hydrodynamics in a Mediterranean lagoon. Nonlinear Processes in Geophysics, 20, 189-198, 2013. 2. Blumberg A.F. and Mellor G.L.: A description of a Tree-Dimensional Coastal Ocean Circulation Model, Geophysical Fluid Dynamics Program, Princeton Univ., Princeton, New Jersey, 1-16, 1986. 3. Davies A., Xing M., Jiuxing I.: Processes influencing wind-induced current profiles in near coastal stratified regions. Continental Shelf Research 23 (14-15): 1379-1400, 2003. 4. Jones, I.S.F. and Toba Y. (Eds.): Wind Stress over the Ocean. Cambridge Univ. Press, 307pp, 2001. 5. Lazure P. and Dumas F.: An external-internal mode coupling for a 3D hydrodynamical model for applications at regional scale (MARS). Adv. Wat. Res. 31: 233-250, 2008. 6. Paquier A-E.: - Interactions de la dynamique hydro-sédimentaire avec les herbiers de phanérogames, Étang de Berre ; PhD thesis Aix-Marseille University; 27 Nov. 2014. 7. Taylor P. and Yelland M.: The Dependence of Sea Surface Roughness on the Height and Steepness of the Waves, Physical Oceanography, 2000. 8. Young I.R., Banner M.L., Donelan M.A., Babanin A.V., Melville W.K., Veron F., and McCormic C.: An Integrated Study of the Wind Wave Source Term Balance in Finite Depth Water, J. Atmos. Oceanic Technol. 22: 814-831, 2004. 9. Zhang H, Sannasiraj S.A., and Chan E.S.: Wind Wave Effects on Hydrodynamic Modeling of Ocean Circulation in the South China Sea, The Open Civil Engineering Journal, 3, 48-61, 2009.

Investigations and Tests in the Towing Basin at Guidonia

NASA Technical Reports Server (NTRS)

Cremona, C

1939-01-01

The experimental methods at the Guidonia towing basin are discussed including specifications. Some of the components examined are the bridge towing carriage, side towing carriage, catapult installation, and dynamometer systems. Tests were performed on hulls and floats, as well as motor boats and torpedo shaped bodies. Theoretical investigations were also performed to determine pressure distributions on geometrically simple bodies, propagation of small wave motions, and planing and submerged surfaces.

Improved Multiple-DOF SAW Piezoelectric Motors

NASA Technical Reports Server (NTRS)

Bar-Cohen, Yoseph; Bao, Xiaoqi; Hull, Anthony; Wright, John

2003-01-01

Surface-acoustic-wave (SAW) piezoelectric motors of a proposed type would be capable of operating in multiple degrees of freedom (DOFs) simultaneously and would be amenable to integration into diverse structures and mechanisms. These motors would be compact and structurally simple and would not contain bearings or lead screws. One example of a particularly useful motor of this type would be a two-dimensional- translation stage. Another such example would be a self-actuated spherical joint that could be made to undergo controlled, simultaneous rotations about two orthogonal axes: Such a motor could serve as a mechanism for aiming an "eyeball" camera or as a compact transducer in, and an integral part of, a joint in a robot arm. The multiple-DOF SAW piezoelectric motors as now proposed would be successors to the ones reported in "Multiple-DOF Surface-Acoustic-Wave Piezoelectric Motors" (NPO-20735), NASA Tech Briefs, Vol. 24, No. 12 (December 2000), page 5b. The basic principle of operation of a multiple-DOF SAW piezoelectric motor is a straightforward extension of that of single-DOF SAW piezoelectric motors, which have been reported in several previous NASA Tech Briefs articles: For example, in the case of a linear SAW piezoelectric motor, piezoelectric transducers at opposite ends of a stator excite surface acoustic waves that travel along the surface of the stator. An object (denoted the slider) is pressed against the stator with sufficient pressure (in practice .300 MPa) that it remains in frictional contact with the stator at all times. The slider rides the crests of the waves and is thereby made to move along the surface of the stator. The direction of motion (forward or backward) is controlled by selecting the relative phase of waves generated by the two piezoelectric transducers. The speed increases with the amplitude of the waves and thus with the magnitude of the voltage applied to the transducers.

Radio crickets: chirping jets from black hole binaries entering their gravitational wave inspiral

NASA Astrophysics Data System (ADS)

Kulkarni, Girish; Loeb, Abraham

2016-03-01

We study a novel electromagnetic signature of supermassive black hole (BH) binaries whose inspiral starts being dominated by gravitational wave (GW) emission. Recent simulations suggest that the binary's member BHs can continue to accrete gas from the circumbinary accretion disc in this phase of the binary's evolution, all the way until coalescence. If one of the binary members produces a radio jet as a result of accretion, the jet precesses along a biconical surface due to the binary's orbital motion. When the binary enters the GW phase of its evolution, the opening angle widens, the jet exhibits milliarcsecond-scale wiggles, and the conical surface of jet precession is twisted due to apparent superluminal motion. The rapidly increasing orbital velocity of the binary gives the jet an appearance of a `chirp'. This helical chirping morphology of the jet can be used to infer the binary parameters. For binaries with mass 107-1010 M⊙ at redshifts z < 0.5, monitoring these features in current and archival data will place a lower limit on sources that could be detected by Evolved Laser Interferometer Space Antenna and Pulsar Timing Arrays. In the future, microarcsecond interferometry with the Square Kilometre Array will increase the potential usefulness of this technique.

Application of τc*Pd for identifying damaging earthquakes for earthquake early warning

NASA Astrophysics Data System (ADS)

Huang, P. L.; Lin, T. L.; Wu, Y. M.

2014-12-01

Earthquake Early Warning System (EEWS) is an effective approach to mitigate earthquake damage. In this study, we used the seismic record by the Kiban Kyoshin network (KiK-net), because it has dense station coverage and co-located borehole strong-motion seismometers along with the free-surface strong-motion seismometers. We used inland earthquakes with moment magnitude (Mw) from 5.0 to 7.3 between 1998 and 2012. We choose 135 events and 10950 strong ground accelerograms recorded by the 696 strong ground accelerographs. Both the free-surface and the borehole data are used to calculate τc and Pd, respectively. The results show that τc*Pd has a good correlation with PGV and is a robust parameter for assessing the potential of damaging earthquake. We propose the value of τc*Pd determined from seconds after the arrival of P wave could be a threshold for the on-site type of EEW.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Agostini, Federica; Abedi, Ali; Suzuki, Yasumitsu

The decomposition of electronic and nuclear motion presented in Abedi et al. [Phys. Rev. Lett. 105, 123002 (2010)] yields a time-dependent potential that drives the nuclear motion and fully accounts for the coupling to the electronic subsystem. Here, we show that propagation of an ensemble of independent classical nuclear trajectories on this exact potential yields dynamics that are essentially indistinguishable from the exact quantum dynamics for a model non-adiabatic charge transfer problem. We point out the importance of step and bump features in the exact potential that are critical in obtaining the correct splitting of the quasiclassical nuclear wave packetmore » in space after it passes through an avoided crossing between two Born-Oppenheimer surfaces and analyze their structure. Finally, an analysis of the exact potentials in the context of trajectory surface hopping is presented, including preliminary investigations of velocity-adjustment and the force-induced decoherence effect.« less

Generation of realistic tsunami waves using a bottom-tilting wave maker

NASA Astrophysics Data System (ADS)

Park, Yong Sung; Hwang, Jin Hwan

2016-11-01

Tsunamis have caused more than 260,000 human losses and 250 billion in damage worldwide in the last ten years. Observations made during 2011 Japan Tohoku Tsunami revealed that the commonly used waves (solitary waves) to model tsunamis are at least an order-of-magnitude shorter than the real tsunamis, which calls for re-evaluation of the current understanding of tsunamis. To prompt the required paradigm shift, a new wave generator, namely the bottom-tilting wave generator, has been developed at the University of Dundee. The wave tank is fitted with an adjustable slope and a bottom flap hinged at the beginning of the slope. By moving the bottom flap up and down, we can generate very long waves. Here we will report characteristics of waves generated by simple bottom motions, either moving it upward or downward from an initial displacement ending it being horizontal. Two parameters, namely the initial displacement of the bottom and the speed of the motion, determine characteristics of the generated waves. Wave amplitudes scale well with the volume flux of the displaced water. On the other hand, due to combined effects of nonlinearity and dispersion, wavelengths show more complicated relationship with the two bottom motion parameters. We will also demonstrate that by combining simple up and down motions, it is possible to generate waves resembling the one measured during 2011 tsunami. YSP acknowledges financial support from the Royal Society of Edinburgh through the Royal Society of Edinburgh and Scottish Government Personal Research Fellowship Co-Funded by the Marie-Curie Actions.

General analytic results for nonlinear waves and solitons in molecular clouds

NASA Technical Reports Server (NTRS)

Adams, Fred C.; Fatuzzo, Marco; Watkins, Richard

1994-01-01

We study nonlinear wave phenomena in self-gravitating fluid systems, with a particular emphasis on applications to molecular clouds. This paper presents analytical results for one spatial dimension. We show that a large class of physical systems can be described by theories with a 'charge density' q(rho); this quantity replaces the density on the right-hand side of the Poisson equation for the gravitational potential. We use this formulation to prove general results about nonlinear wave motions in self-gravitating systems. We show that in order for stationary waves to exist, the total charge (the integral of the charge density over the wave profile) must vanish. This 'no-charge' property for solitary waves is related to the capability of a system to be stable to gravitational perturbations for arbitrarily long wavelengths. We find necessary and sufficient conditions on the charge density for the existence of solitary waves and stationary waves. We study nonlinear wave motions for Jeans-type theories (where q(rho) = rho-rho(sub 0)) and find that nonlinear waves of large amplitude are confined to a rather narrow range of wavelengths. We also study wave motions for molecular clouds threaded by magnetic fields and show how the allowed range of wavelengths is affected by the field strength. Since the gravitational force in one spatial dimension does not fall off with distance, we consider two classes of models with more realistic gravity: Yukawa potentials and a pseudo two-dimensional treatment. We study the allowed types of wave behavior for these models. Finally, we discuss the implications of this work for molecular cloud structure. We argue that molecular clouds can support a wide variety of wave motions and suggest that stationary waves (such as those considered in this paper) may have already been observed.

Long-period effects of the Denali earthquake on water bodies in the Puget Lowland: Observations and modeling

USGS Publications Warehouse

Barberopoulou, A.; Qamar, A.; Pratt, T.L.; Steele, W.P.

2006-01-01

Analysis of strong-motion instrument recordings in Seattle, Washington, resulting from the 2002 Mw 7.9 Denali, Alaska, earthquake reveals that amplification in the 0.2-to 1.0-Hz frequency band is largely governed by the shallow sediments both inside and outside the sedimentary basins beneath the Puget Lowland. Sites above the deep sedimentary strata show additional seismic-wave amplification in the 0.04- to 0.2-Hz frequency range. Surface waves generated by the Mw 7.9 Denali, Alaska, earthquake of 3 November 2002 produced pronounced water waves across Washington state. The largest water waves coincided with the area of largest seismic-wave amplification underlain by the Seattle basin. In the current work, we present reports that show Lakes Union and Washington, both located on the Seattle basin, are susceptible to large water waves generated by large local earthquakes and teleseisms. A simple model of a water body is adopted to explain the generation of waves in water basins. This model provides reasonable estimates for the water-wave amplitudes in swimming pools during the Denali earthquake but appears to underestimate the waves observed in Lake Union.

The choice of speed and clearance for RAS on 3D method

NASA Astrophysics Data System (ADS)

Wang, Jian-Fang; Li, Ji-De; Cai, Xin-Gong

2003-12-01

In this paper, a 3D source distribution technique is used to calculate the coupled motions between two ships which advance in the wave with the same speed. The numerical results of coupled motions for a frigate and a supply ship have a good agreement with the experimental results. Based on the 3D coupled motions of two ships, a spectral analysis is employed to clearly observe the effect of speed, clearance and wave heading on the significant relative motion amplitude (SRMA) of two ships. The method presented in this paper will be helpful to select suitable clearance, speed and wave heading for underway replenishment at sea(RAS).

The motions of hinged-barge systems in regular seas

NASA Astrophysics Data System (ADS)

Kraemer, David Robert Burke

Harnessing the oceans' vast, clean, and renewable energy to do useful work is a tempting prospect. For over a century, wave-energy conversion devices have been proposed, but none has emerged as a clearly practical and economical solution. One promising system is the McCabe Wave Pump (MWP), an articulated-barge system consisting of three barges hinged together with a large horizontal plate attached below the central barge. Water pumps are driven by the relative pitching motions of the barges excited by ocean waves. This high-pressure water can be used to produce potable water or electricity. A simulation of the motions of a generic hinged-barge system is developed. The equations of motion are developed so that the nonlinear interactions between the barges are included. The simulation is general so that it can be used to study other hinged-barge systems, such as causeway ferry systems or floating airports. The simulation is used to predict the motions of a scale model that was studied in wave-tank experiments. In the experimental study, it was observed that the plate attached to the central barge acted as a pendulum. It was also observed that the phases of the pitching motions of the barges was such that the motions were enhanced by the pendulum effect at all of the wave periods studied. Hence, the increased angular displacements produced greater relative pitching motions which would lead to higher volume rates of pumped water in the operational system. The numerical simulations are found to predict the pendulum effect. In addition, the theory predicted that the after barge motions were significantly less than those of the forward barge, as was observed in the experimental study. The good agreement between the two data sets gives confidence in the ability of the theory to predict the performance of the MWP prototype. The motions of the MWP prototype in regular ocean waves are predicted by the simulation, and its performance is calculated. By modifying the length of the system to be compatible with the wavelength for maximum pitching excitation, the power output of the system is shown to increase by more than 150%.

Nonlinear ship waves and computational fluid dynamics

PubMed Central

MIYATA, Hideaki; ORIHARA, Hideo; SATO, Yohei

2014-01-01

Research works undertaken in the first author’s laboratory at the University of Tokyo over the past 30 years are highlighted. Finding of the occurrence of nonlinear waves (named Free-Surface Shock Waves) in the vicinity of a ship advancing at constant speed provided the start-line for the progress of innovative technologies in the ship hull-form design. Based on these findings, a multitude of the Computational Fluid Dynamic (CFD) techniques have been developed over this period, and are highlighted in this paper. The TUMMAC code has been developed for wave problems, based on a rectangular grid system, while the WISDAM code treats both wave and viscous flow problems in the framework of a boundary-fitted grid system. These two techniques are able to cope with almost all fluid dynamical problems relating to ships, including the resistance, ship’s motion and ride-comfort issues. Consequently, the two codes have contributed significantly to the progress in the technology of ship design, and now form an integral part of the ship-designing process. PMID:25311139

Remote sensing of the correlation between breakpoint oscillations and infragravity waves in the surf and swash zone

NASA Astrophysics Data System (ADS)

Moura, T.; Baldock, T. E.

2017-04-01

A novel remote sensing methodology to determine the dominant infragravity mechanism in the inner surf and swash zone in the field is presented. Video observations of the breakpoint motion are correlated with the shoreline motion and inner surf zone water levels to determine the relationship between the time-varying breakpoint oscillations and the shoreline motion. The results of 13 field data sets collected from three different beaches indicate that, inside the surf zone, the dominance of bound wave or breakpoint forcing is strongly dependent on the surf zone width and the type of short wave breaking. Infragravity generation by bound wave release was stronger for conditions with relatively narrow surf zones and plunging waves; breakpoint forcing was dominant for wider surf zones and spilling breaker conditions.

Numerical solution of equations governing longitudinal suspension line wave motion during the parachute unfurling process. Ph.D. Thesis - George Washington Univ., Washington, D. C.

NASA Technical Reports Server (NTRS)

Poole, L. R.

1973-01-01

Equations are presented which govern the dynamics of the lines-first parachute unfurling process, including wave motion in the parachute suspension lines. Techniques are developed for obtaining numerical solutions to the governing equations. Histories of tension at test data, and generally good agreement is observed. Errors in computed results are attributed to several areas of uncertainty, the most significant being a poorly defined boundary condition on the wave motion at the vehicle-suspension line boundary.

Air motions accompanying the development of a planetary wave critical layer

NASA Technical Reports Server (NTRS)

Salby, Murry L.; O'Sullivan, Donal; Callaghan, Patrick; Garcia, Rolando R.

1990-01-01

The horizontal air motions accompanying the development of a planetary wave critical layer are presently investigated on the sphere, in terms of wave amplitude, the characteristics of the zonal flow, and dissipation. While attention is given to adiabatic motions, which should furnish an upper bound on the redistribution of conserved quantities by eddy stirring, nonconservative processes may be important in determining how large a role eddy stirring actually plays in the redistribution of atmospheric constituents. Nonconservative processes may also influence tracer distributions by directly affecting dynamics.

An unified numerical simulation of seismic ground motion, ocean acoustics, coseismic deformations and tsunamis of 2011 Tohoku earthquake

NASA Astrophysics Data System (ADS)

Maeda, T.; Furumura, T.; Noguchi, S.; Takemura, S.; Iwai, K.; Lee, S.; Sakai, S.; Shinohara, M.

2011-12-01

The fault rupture of the 2011 Tohoku (Mw9.0) earthquake spread approximately 550 km by 260 km with a long source rupture duration of ~200 s. For such large earthquake with a complicated source rupture process the radiation of seismic wave from the source rupture and initiation of tsunami due to the coseismic deformation is considered to be very complicated. In order to understand such a complicated process of seismic wave, coseismic deformation and tsunami, we proposed a unified approach for total modeling of earthquake induced phenomena in a single numerical scheme based on a finite-difference method simulation (Maeda and Furumura, 2011). This simulation model solves the equation of motion of based on the linear elastic theory with equilibrium between quasi-static pressure and gravity in the water column. The height of tsunami is obtained from this simulation as a vertical displacement of ocean surface. In order to simulate seismic waves, ocean acoustics, coseismic deformations, and tsunami from the 2011 Tohoku earthquake, we assembled a high-resolution 3D heterogeneous subsurface structural model of northern Japan. The area of simulation is 1200 km x 800 km and 120 km in depth, which have been discretized with grid interval of 1 km in horizontal directions and 0.25 km in vertical direction, respectively. We adopt a source-rupture model proposed by Lee et al. (2011) which is obtained by the joint inversion of teleseismic, near-field strong motion, and coseismic deformation. For conducting such a large-scale simulation, we fully parallelized our simulation code based on a domain-partitioning procedure which achieved a good speed-up by parallel computing up to 8192 core processors with parallel efficiency of 99.839%. The simulation result demonstrates clearly the process in which the seismic wave radiates from the complicated source rupture over the fault plane and propagating in heterogeneous structure of northern Japan. Then, generation of tsunami from coseismic ground deformation at sea floor due to the earthquake and propagation is also well demonstrated . The simulation also demonstrates that a very large slip up to 40 m at shallow plate boundary near the trench pushes up sea floor with source rupture propagation, and the highly elevated sea surface gradually start propagation as tsunamis due to the gravity. The result of simulation of vertical-component displacement waveform matches the ocean-bottom pressure gauge record which is installed just above the source fault area (Maeda et al., 2011) very consistently. Strong reverberation of the ocean-acoustic waves between sea surface and sea bottom particularly near the Japan Trench for long time after the source rupture ends is confirmed in the present simulation. Accordingly, long wavetrains of high-frequency ocean acoustic waves is developed and overlap to later tsunami waveforms as we found in the observations.

Exploration of S-wave velocity profiles at strong motion stations in Eskisehir, Turkey, using microtremor phase velocity and S-wave amplification

NASA Astrophysics Data System (ADS)

Yamanaka, Hiroaki; Özmen, Ögur Tuna; Chimoto, Kosuke; Alkan, Mehmet Akif; Tün, Muammer; Pekkan, Emrah; Özel, Oguz; Polat, Derya; Nurlu, Murat

2018-05-01

We have explored 1D S-wave velocity profiles of shallow and deep soil layers over a basement at strong motion stations in Eskisehir Province, Turkey. Microtremor array explorations were conducted at eight strong motion stations in the area to know shallow 1D S-wave velocity models. Rayleigh wave phase velocity at a frequency range from 3 to 30 Hz was estimated with the spatial autocorrelation analysis of array records of vertical microtremors at each station. Individual phase velocity was inverted to a shallow S-wave velocity profile. Low-velocity layers were identified at the stations in the basin. Site amplification factors from S-wave parts of earthquake records that had been estimated at the strong motion stations by Yamanaka et al. (2017) were inverted to the S-wave velocities and Q-values of the sedimentary layers. The depths to the basement with an S-wave velocity of 2.2 km/s are about 1 km in the central part of the basin, while the basement becomes shallow as 0.3 km in the marginal part of the basin. We finally discussed the effects of the shallow and deep sedimentary layers on the 1D S-wave amplification characteristics using the revealed profiles. It is found that the shallow soil layers have no significant effects in the amplification at a frequency range lower than 3 Hz in the area.

Chasing the reflected wave back into the heart: a new hypothesis while the jury is still out

PubMed Central

Codreanu, Ion; Robson, Matthew D; Rider, Oliver J; Pegg, Tammy J; Jung, Bernd A; Dasanu, Constantin A; Clarke, Kieran; Holloway, Cameron J

2011-01-01

Background: Arterial stiffness directly influences cardiac function and is independently associated with cardiovascular risk. However, the influence of the aortic reflected pulse pressure wave on left ventricular function has not been well characterized. The aim of this study was to obtain detailed information on regional ventricular wall motion patterns corresponding to the propagation of the reflected aortic wave on ventricular segments. Methods: Left ventricular wall motion was investigated in a group of healthy volunteers (n = 14, age 23 ± 3 years), using cardiac magnetic resonance navigator-gated tissue phase mapping. The left ventricle was divided into 16 segments and regional wall motion was studied in high temporal detail. Results: Corresponding to the expected timing of the reflected aortic wave reaching the left ventricle, a characteristic “notch” of regional myocardial motion was seen in all radial, circumferential, and longitudinal velocity graphs. This notch was particularly prominent in septal segments adjacent to the left ventricular outflow tract on radial velocity graphs and in anterior and posterior left ventricular segments on circumferential velocity graphs. Similarly, longitudinal velocity graphs demonstrated a brief deceleration in the upward recoil motion of the entire ventricle at the beginning of diastole. Conclusion: These results provide new insights into the possible influence of the reflected aortic waves on ventricular segments. Although the association with the reflected wave appears to us to be unambiguous, it represents a novel research concept, and further studies enabling the actual recording of the pulse wave are required. PMID:21731888

Analysis of the seismic wavefield in the Moesian Platform (Bucharest area)

NASA Astrophysics Data System (ADS)

-Florinela Manea, Elena; Hobiger, Manuel-Thomas; Michel, Clotaire; Fäh, Donat; -Ortanza Cioflan, Carmen

2016-04-01

Bucharest is located in the center of the Moesian platform, in a large and deep sedimentary basin (450 km long, 300 km wide and in some places up to 20 km depth). During large earthquakes generated by the Vrancea seismic zone, located approximately 140 km to the North, the ground motion recorded in Bucharest area is characterized by predominant long periods and large amplification. This phenomenon has been explained by the influence of both source mechanism (azimuth and type of incident waves) and mechanical properties of the local structure (geological layering and geometry). The main goal of our study is to better characterize and understand the seismic wave field produced by earthquakes in the area of Bucharest. We want to identify the contribution of different seismic surface waves, such as the ones produced at the edges of the large sedimentary basin or multipath interference waves (Airy phases of Love and Rayleigh waves) to the ground motion. The data from a 35 km diameter array (URS experiment) installed by the National Institute for Earth Physics during 10 months in 2003 and 2004 in the urban area of Bucharest and adjacent zones was used. In order to perform the wave field characterization of the URS array, the MUSIQUE technique was used. This technique consists in a combination of the classical MUSIC and the quaternion-MUSIC algorithms and analyzes the three-component signals of all sensors of a seismic array together in order to analyze the Love and Rayleigh wave dispersion curves as well as the Rayleigh wave ellipticity curve. The analysis includes 20 regional earthquakes with Mw >3 and 5 teleseismic events with Mw> 7 that have enough energy at low frequency (0.1 - 1 Hz), i.e. in the resolution range of the array. For all events, the greatest energy is coming from the backazimuth of the source and the wave field is dominated by Love waves. The results of the array analyses clearly indicate a significant scattering corresponding to 2D or 3D effects in the Moesian Platform. The backazimuth distribution of energy shows that the scattering comes primarily from the southern and northern edges of the basin. The Airy phases of Love waves were identified in the direction of the backazimuth and its reflection around the fundamental frequency (0.15 - 0.25 Hz). Love and Rayleigh wave dispersion curves are successfully retrieved after combining the records of all events, and show a good match with the ones obtained in previous studies using ambient vibration measurements. Additionally, the first higher mode of Rayleigh waves was retrieved using earthquakes records. We could also identify the Rayleigh wave ellipticity curves, distinguishing between prograde and retrograde particle motion.

The Atmospheric Dynamics of Venus

NASA Astrophysics Data System (ADS)

Sánchez-Lavega, Agustín; Lebonnois, Sebastien; Imamura, Takeshi; Read, Peter; Luz, David

2017-11-01

We review our current knowledge of the atmospheric dynamics of Venus prior to the Akatsuki mission, in the altitude range from the surface to approximately the cloud tops located at about 100 km altitude. The three-dimensional structure of the wind field in this region has been determined with a variety of techniques over a broad range of spatial and temporal scales (from the mesoscale to planetary, from days to years, in daytime and nighttime), spanning a period of about 50 years (from the 1960s to the present). The global panorama is that the mean atmospheric motions are essentially zonal, dominated by the so-called super-rotation (an atmospheric rotation that is 60 to 80 times faster than that of the planetary body). The zonal winds blow westward (in the same direction as the planet rotation) with a nearly constant speed of ˜ 100 m s^{-1} at the cloud tops (65-70 km altitude) from latitude 50°N to 50°S, then decreasing their speeds monotonically from these latitudes toward the poles. Vertically, the zonal winds decrease with decreasing altitude towards velocities ˜ 1-3 m s^{-1} in a layer of thickness ˜ 10 km close to the surface. Meridional motions with peak speeds of ˜ 15 m s^{-1} occur within the upper cloud at 65 km altitude and are related to a Hadley cell circulation and to the solar thermal tide. Vertical motions with speeds ˜1-3 m s^{-1} occur in the statically unstable layer between altitudes of ˜ 50 - 55 km. All these motions are permanent with speed variations of the order of ˜10%. Various types of wave, from mesoscale gravity waves to Rossby-Kelvin planetary scale waves, have been detected at and above cloud heights, and are considered to be candidates as agents for carrying momentum that drives the super-rotation, although numerical models do not fully reproduce all the observed features. Momentum transport by atmospheric waves and the solar tide is thought to be an indispensable component of the general circulation of the Venus atmosphere. Another conspicuous feature of the atmospheric circulation is the presence of polar vortices. These are present in both hemispheres and are regions of warmer and lower clouds, seen prominently at infrared wavelengths, showing a highly variable morphology and motions. The vortices spin with a period of 2-3 days. The South polar vortex rotates around a geographical point which is itself displaced from the true pole of rotation by ˜ 3 degrees. The polar vortex is surrounded and constrained by the cold collar, an infrared-dark region of lower temperatures. We still lack detailed models of the mechanisms underlying the dynamics of these features and how they couple (or not) to the super-rotation. The nature of the super-rotation relates to the angular momentum stored in the atmosphere and how it is transported between the tropics and higher latitudes, and between the deep atmosphere and upper levels. The role of eddy processes is crucial, but likely involves the complex interaction of a variety of different types of eddy, either forced directly by radiative heating and mechanical interactions with the surface or through various forms of instability. Numerical models have achieved some significant recent success in capturing some aspects of the observed super-rotation, consistent with the scenario discussed by Gierasch (J. Atmos. Sci. 32:1038-1044, 1975) and Rossow and Williams (J. Atmos. Sci. 36:377-389, 1979), but many uncertainties remain, especially in the deep atmosphere. The theoretical framework developed to explain the circulation in Venus's atmosphere is reviewed, as well as the numerical models that have been built to elucidate the super-rotation mechanism. These tools are used to analyze the respective roles of the different waves in the processes driving the observed motions. Their limitations and suggested directions for improvements are discussed.

Wave Impact on a Wall: Comparison of Experiments with Similarity Solutions

NASA Astrophysics Data System (ADS)

Wang, A.; Duncan, J. H.; Lathrop, D. P.

2014-11-01

The impact of a steep water wave on a fixed partially submerged cube is studied with experiments and theory. The temporal evolution of the water surface profile upstream of the front face of the cube in its center plane is measured with a cinematic laser-induced fluorescence technique using frame rates up to 4,500 Hz. For a small range of cube positions, the surface profiles are found to form a nearly circular arc with upward curvature between the front face of the cube and a point just downstream of the wave crest. As the crest approaches the cube, the effective radius of this portion of the profile decreases rapidly. At the same time, the portion of the profile that is upstream of the crest approaches a straight line with a downward slope of about 15°. As the wave impact continues, the circular arc shrinks to zero radius with very high acceleration and a sudden transition to a high-speed vertical jet occurs. This flow singularity is modeled with a power-law scaling in time, which is used to create a time-independent system of equations of motion. The scaled governing equations are solved numerically and the similarly scaled measured free surface shapes, are favorably compared with the solutions. The support of the Office of Naval Research is gratefully acknowledged.

A dynamic model of the piezoelectric traveling wave rotary ultrasonic motor stator with the finite volume method.

PubMed

Renteria Marquez, I A; Bolborici, V

2017-05-01

This manuscript presents a method to model in detail the piezoelectric traveling wave rotary ultrasonic motor (PTRUSM) stator response under the action of DC and AC voltages. The stator is modeled with a discrete two dimensional system of equations using the finite volume method (FVM). In order to obtain accurate results, a model of the stator bridge is included into the stator model. The model of the stator under the action of DC voltage is presented first, and the results of the model are compared versus a similar model using the commercial finite element software COMSOL Multiphysics. One can observe that there is a difference of less than 5% between the displacements of the stator using the proposed model and the one with COMSOL Multiphysics. After that, the model of the stator under the action of AC voltages is presented. The time domain analysis shows the generation of the traveling wave in the stator surface. One can use this model to accurately calculate the stator surface velocities, elliptical motion of the stator surface and the amplitude and shape of the stator traveling wave. A system of equations discretized with the finite volume method can easily be transformed into electrical circuits, because of that, FVM may be a better choice to develop a model-based control strategy for the PTRUSM. Copyright © 2017 Elsevier B.V. All rights reserved.

Surface seismic measurements of near-surface P-and S-wave seismic velocities at earthquake recording stations, Seattle, Washington

USGS Publications Warehouse

Williams, R.A.; Stephenson, W.J.; Frankel, A.D.; Odum, J.K.

1999-01-01

We measured P-and S-wave seismic velocities to about 40-m depth using seismic-refraction/reflection data on the ground surface at 13 sites in the Seattle, Washington, urban area, where portable digital seismographs recently recorded earthquakes. Sites with the lowest measured Vs correlate with highest ground motion amplification. These sites, such as at Harbor Island and in the Duwamish River industrial area (DRIA) south of the Kingdome, have an average Vs in the upper 30 m (V??s30) of 150 to 170 m/s. These values of V??s30 place these sites in soil profile type E (V??s30 < 180 m/s). A "rock" site, located at Seward Park on Tertiary sedimentary deposits, has a V??S30 of 433 m/s, which is soil type C (V??s30: 360 to 760 m/s). The Seward Park site V??s30 is about equal to, or up to 200 m/s slower than sites that were located on till or glacial outwash. High-amplitude P-and S-wave seismic reflections at several locations appear to correspond to strong resonances observed in earthquake spectra. An S-wave reflector at the Kingdome at about 17 to 22 m depth probably causes strong 2-Hz resonance that is observed in the earthquake data near the Kingdome.

Modeling and validation of a 3D velocity structure for the Santa Clara Valley, California, for seismic-wave simulations

USGS Publications Warehouse

Hartzell, S.; Harmsen, S.; Williams, R.A.; Carver, D.; Frankel, A.; Choy, G.; Liu, P.-C.; Jachens, R.C.; Brocher, T.M.; Wentworth, C.M.

2006-01-01

A 3D seismic velocity and attenuation model is developed for Santa Clara Valley, California, and its surrounding uplands to predict ground motions from scenario earthquakes. The model is developed using a variety of geologic and geophysical data. Our starting point is a 3D geologic model developed primarily from geologic mapping and gravity and magnetic surveys. An initial velocity model is constructed by using seismic velocities from boreholes, reflection/refraction lines, and spatial autocorrelation microtremor surveys. This model is further refined and the seismic attenuation is estimated through waveform modeling of weak motions from small local events and strong-ground motion from the 1989 Loma Prieta earthquake. Waveforms are calculated to an upper frequency of 1 Hz using a parallelized finite-difference code that utilizes two regions with a factor of 3 difference in grid spacing to reduce memory requirements. Cenozoic basins trap and strongly amplify ground motions. This effect is particularly strong in the Evergreen Basin on the northeastern side of the Santa Clara Valley, where the steeply dipping Silver Creek fault forms the southwestern boundary of the basin. In comparison, the Cupertino Basin on the southwestern side of the valley has a more moderate response, which is attributed to a greater age and velocity of the Cenozoic fill. Surface waves play a major role in the ground motion of sedimentary basins, and they are seen to strongly develop along the western margins of the Santa Clara Valley for our simulation of the Loma Prieta earthquake.

Development of a Shipboard Remote Control and Telemetry Experimental System for Large-Scale Model’s Motions and Loads Measurement in Realistic Sea Waves

PubMed Central

Jiao, Jialong; Ren, Huilong; Adenya, Christiaan Adika; Chen, Chaohe

2017-01-01

Wave-induced motion and load responses are important criteria for ship performance evaluation. Physical experiments have long been an indispensable tool in the predictions of ship’s navigation state, speed, motions, accelerations, sectional loads and wave impact pressure. Currently, majority of the experiments are conducted in laboratory tank environment, where the wave environments are different from the realistic sea waves. In this paper, a laboratory tank testing system for ship motions and loads measurement is reviewed and reported first. Then, a novel large-scale model measurement technique is developed based on the laboratory testing foundations to obtain accurate motion and load responses of ships in realistic sea conditions. For this purpose, a suite of advanced remote control and telemetry experimental system was developed in-house to allow for the implementation of large-scale model seakeeping measurement at sea. The experimental system includes a series of technique sensors, e.g., the Global Position System/Inertial Navigation System (GPS/INS) module, course top, optical fiber sensors, strain gauges, pressure sensors and accelerometers. The developed measurement system was tested by field experiments in coastal seas, which indicates that the proposed large-scale model testing scheme is capable and feasible. Meaningful data including ocean environment parameters, ship navigation state, motions and loads were obtained through the sea trial campaign. PMID:29109379

Dynamics of the Venus atmosphere

NASA Technical Reports Server (NTRS)

Ingersoll, A. P.

1992-01-01

The superrotation of the Venus atmosphere is a major unanswered problem in planetary science. At cloud-top levels (65-70 km altitude) the atmosphere rotates with a five-day period, corresponding to an equatorial wind speed of 90 m/s. Angular velocity is roughly constant on spherical shells, and decreases linearly with altitude to zero at the surface. The direction of rotation is the same as that of the solid planet, which is retrograde--opposite to the direction of orbital motion, but the 5-day period is short compared to the 243-day spin period of the solid planet or to the mean solar day, which is 117 Earth-days at the surface. The problem with the superrotation is that shearing stresses tend to transfer angular momentum downward, and would slow the atmosphere until it is spinning with the solid planet. Some organized circulation pattern is counteracting the tendency, but the pattern has not been identified. A simple Hadley-type circulation cannot do it because such a circulation is zonally symmetric and Hide's Theorem states that in an axisymmetric circulation an extremum in angular momentum per unit mass M can exist only at the surface. Venus violates the last condition, having a maximum of retrograde M on the equator at 70-80 km altitude. This leaves waves and eddies to maintain the superrotation but the length scales and forcing mechanisms for these motions need to be specified. Possible forcing mechanisms associated with waves, eddies and tides are discussed.

Path planning and parameter optimization of uniform removal in active feed polishing

NASA Astrophysics Data System (ADS)

Liu, Jian; Wang, Shaozhi; Zhang, Chunlei; Zhang, Linghua; Chen, Huanan

2015-06-01

A high-quality ultrasmooth surface is demanded in short-wave optical systems. However, the existing polishing methods have difficulties meeting the requirement on spherical or aspheric surfaces. As a new kind of small tool polishing method, active feed polishing (AFP) could attain a surface roughness of less than 0.3 nm (RMS) on spherical elements, although AFP may magnify the residual figure error or mid-frequency error. The purpose of this work is to propose an effective algorithm to realize uniform removal of the surface in the processing. At first, the principle of the AFP and the mechanism of the polishing machine are introduced. In order to maintain the processed figure error, a variable pitch spiral path planning algorithm and the dwell time-solving model are proposed. For suppressing the possible mid-frequency error, the uniformity of the synthesis tool path, which is generated by an arbitrary point at the polishing tool bottom, is analyzed and evaluated, and the angular velocity ratio of the tool spinning motion to the revolution motion is optimized. Finally, an experiment is conducted on a convex spherical surface and an ultrasmooth surface is finally acquired. In conclusion, a high-quality ultrasmooth surface can be successfully obtained with little degradation of the figure and mid-frequency errors by the algorithm.

Harvesting water wave energy by asymmetric screening of electrostatic charges on a nanostructured hydrophobic thin-film surface.

PubMed

Zhu, Guang; Su, Yuanjie; Bai, Peng; Chen, Jun; Jing, Qingshen; Yang, Weiqing; Wang, Zhong Lin

2014-06-24

Energy harvesting from ambient water motions is a desirable but underexplored solution to on-site energy demand for self-powered electronics. Here we report a liquid-solid electrification-enabled generator based on a fluorinated ethylene propylene thin film, below which an array of electrodes are fabricated. The surface of the thin film is charged first due to the water-solid contact electrification. Aligned nanowires created on the thin film make it hydrophobic and also increase the surface area. Then the asymmetric screening to the surface charges by the waving water during emerging and submerging processes causes the free electrons on the electrodes to flow through an external load, resulting in power generation. The generator produces sufficient output power for driving an array of small electronics during direct interaction with water bodies, including surface waves and falling drops. Polymer-nanowire-based surface modification increases the contact area at the liquid-solid interface, leading to enhanced surface charging density and thus electric output at an efficiency of 7.7%. Our planar-structured generator features an all-in-one design without separate and movable components for capturing and transmitting mechanical energy. It has extremely lightweight and small volume, making it a portable, flexible, and convenient power solution that can be applied on the ocean/river surface, at coastal/offshore areas, and even in rainy places. Considering the demonstrated scalability, it can also be possibly used in large-scale energy generation if layers of planar sheets are connected into a network.

Broadband ground-motion simulation using a hybrid approach

USGS Publications Warehouse

Graves, R.W.; Pitarka, A.

2010-01-01

This paper describes refinements to the hybrid broadband ground-motion simulation methodology of Graves and Pitarka (2004), which combines a deterministic approach at low frequencies (f 1 Hz). In our approach, fault rupture is represented kinematically and incorporates spatial heterogeneity in slip, rupture speed, and rise time. The prescribed slip distribution is constrained to follow an inverse wavenumber-squared fall-off and the average rupture speed is set at 80% of the local shear-wave velocity, which is then adjusted such that the rupture propagates faster in regions of high slip and slower in regions of low slip. We use a Kostrov-like slip-rate function having a rise time proportional to the square root of slip, with the average rise time across the entire fault constrained empirically. Recent observations from large surface rupturing earthquakes indicate a reduction of rupture propagation speed and lengthening of rise time in the near surface, which we model by applying a 70% reduction of the rupture speed and increasing the rise time by a factor of 2 in a zone extending from the surface to a depth of 5 km. We demonstrate the fidelity of the technique by modeling the strong-motion recordings from the Imperial Valley, Loma Prieta, Landers, and Northridge earthquakes.

Observations and a model of gravity-wave variability in the middle atmosphere

NASA Technical Reports Server (NTRS)

Fritts, D. C.; Vincent, R. A.

1986-01-01

A major goal was to determine what portion of the gravity-wave frequency spectrum accounted for the majority of the momentum flux and divergence, as this has important implications for the middle atmosphere response. It was found that approx. 70% of the total flux and divergence was due to wave motions with observed periods less than 1 hour, consistent with expectations based on the shape of the observed gravity-wave spectrum (FrItts, 1984). This dominance of the momentum flux and divergence by high-frequency motions implies a potential for the modulation of those quantities by large-amplitude motions at lower frequencies. A second, striking aspect of the velocity and momentum flux data is its dramatic diurnal variability, particularly at certain levels. This variability is illustrated with the momentum flux, computed in 8-hr blocks. The dominant contributions here are due to waves with periods less than 1 hr. The variability with height and size of the mean square velocity in the west beam and the momentum flux, energed over the 3-day period. A detailed analysis of the various tidal motions present during this data interval was performed, and it was determined that variations in the zontal wind profile imposed by the diurnal tidal motion are probably responsible for the modulation of the gravity-wave amplitudes and momentum fluxes.

Characterisation of ground motion recording stations in the Groningen gas field

NASA Astrophysics Data System (ADS)

Noorlandt, Rik; Kruiver, Pauline P.; de Kleine, Marco P. E.; Karaoulis, Marios; de Lange, Ger; Di Matteo, Antonio; von Ketelhodt, Julius; Ruigrok, Elmer; Edwards, Benjamin; Rodriguez-Marek, Adrian; Bommer, Julian J.; van Elk, Jan; Doornhof, Dirk

2018-05-01

The seismic hazard and risk analysis for the onshore Groningen gas field requires information about local soil properties, in particular shear-wave velocity ( V S). A fieldwork campaign was conducted at 18 surface accelerograph stations of the monitoring network. The subsurface in the region consists of unconsolidated sediments and is heterogeneous in composition and properties. A range of different methods was applied to acquire in situ V S values to a target depth of at least 30 m. The techniques include seismic cone penetration tests (SCPT) with varying source offsets, multichannel analysis of surface waves (MASW) on Rayleigh waves with different processing approaches, microtremor array, cross-hole tomography and suspension P-S logging. The offset SCPT, cross-hole tomography and common midpoint cross-correlation (CMPcc) processing of MASW data all revealed lateral variations on length scales of several to tens of metres in this geological setting. SCPTs resulted in very detailed V S profiles with depth, but represent point measurements in a heterogeneous environment. The MASW results represent V S information on a larger spatial scale and smooth some of the heterogeneity encountered at the sites. The combination of MASW and SCPT proved to be a powerful and cost-effective approach in determining representative V S profiles at the accelerograph station sites. The measured V S profiles correspond well with the modelled profiles and they significantly enhance the ground motion model derivation. The similarity between the theoretical transfer function from the V S profile and the observed amplification from vertical array stations is also excellent.

Characterisation of ground motion recording stations in the Groningen gas field

NASA Astrophysics Data System (ADS)

Noorlandt, Rik; Kruiver, Pauline P.; de Kleine, Marco P. E.; Karaoulis, Marios; de Lange, Ger; Di Matteo, Antonio; von Ketelhodt, Julius; Ruigrok, Elmer; Edwards, Benjamin; Rodriguez-Marek, Adrian; Bommer, Julian J.; van Elk, Jan; Doornhof, Dirk

2018-01-01

The seismic hazard and risk analysis for the onshore Groningen gas field requires information about local soil properties, in particular shear-wave velocity (V S). A fieldwork campaign was conducted at 18 surface accelerograph stations of the monitoring network. The subsurface in the region consists of unconsolidated sediments and is heterogeneous in composition and properties. A range of different methods was applied to acquire in situ V S values to a target depth of at least 30 m. The techniques include seismic cone penetration tests (SCPT) with varying source offsets, multichannel analysis of surface waves (MASW) on Rayleigh waves with different processing approaches, microtremor array, cross-hole tomography and suspension P-S logging. The offset SCPT, cross-hole tomography and common midpoint cross-correlation (CMPcc) processing of MASW data all revealed lateral variations on length scales of several to tens of metres in this geological setting. SCPTs resulted in very detailed V S profiles with depth, but represent point measurements in a heterogeneous environment. The MASW results represent V S information on a larger spatial scale and smooth some of the heterogeneity encountered at the sites. The combination of MASW and SCPT proved to be a powerful and cost-effective approach in determining representative V S profiles at the accelerograph station sites. The measured V S profiles correspond well with the modelled profiles and they significantly enhance the ground motion model derivation. The similarity between the theoretical transfer function from the V S profile and the observed amplification from vertical array stations is also excellent.

Spectral evolution and extreme value analysis of non-linear numerical simulations of narrow band random surface gravity waves.

NASA Astrophysics Data System (ADS)

Socquet-Juglard, H.; Dysthe, K. B.; Trulsen, K.; Liu, J.; Krogstad, H. E.

2003-04-01

Numerical simulations of a narrow band gaussian spectrum of random surface gravity waves have been carried out in two and three spatial dimensions [7]. Different types of non-linear Schr&{uml;o}dinger equations, [1] and [4], have been used in these simulations. Simulations have now been carried with a JONSWAP spectrum associated with a spreading function of the type cosine-squared [5]. The evolution of the spectrum, skewness, kurtosis, ... will be presented. In addition, some results about stochastic properties of the surface will be shown. Based on the approach found in [2], [3] and [6], the results are presented in terms of deviations from linear Gaussian theory and the standard second order small slope perturbation theory. begin{thebibliography}{9} bibitem{kk96} Trulsen, K. &Dysthe, K. B. (1996). A modified nonlinear Schr&{uml;o}dinger equation for broader bandwidth gravity waves on deep water. Wave Motion, 24, pp. 281-289. bibitem{BK2000} Krogstad, H.E. and S.F. Barstow (2000). A uniform approach to extreme value analysis of ocean waves, Proc. ISOPE'2000, Seattle, USA, 3, pp. 103-108. bibitem{PRK} Prevosto, M., H. E. Krogstad and A. Robin (2000). Probability distributions for maximum wave and crest heights, Coast. Eng., 40, 329-360. bibitem{ketal} Trulsen, K., Kliakhandler, I., Dysthe, K. B. &Velarde, M. G. (2000) On weakly nonlinear modulation of waves on deep water, Phys. Fluids, 12, pp. L25-L28. bibitem{onorato} Onorato, M., Osborne, A.R. and Serio, M. (2002) Extreme wave events in directional, random oceanic sea states, Phys. Fluids, 14, pp. 2432-2437. bibitem{BK2002} Krogstad, H.E. and S.F. Barstow (2002). Analysis and Applications of Second Order Models for the Maximum Crest height, % Proc. 21nd Int. Conf. Offshore Mechanics and Arctic Engineering, Oslo. Paper no. OMAE2002-28479. bibitem{JFMP} Dysthe, K. B., Trulsen, K., Krogstad, H. E. and Socquet-Juglard, H. (2002, in press) Evolution of a narrow band spectrum of random surface gravity waves, J. Fluid Mech.

Modeling Seismoacoustic Propagation from the Nonlinear to Linear Regimes

NASA Astrophysics Data System (ADS)

Chael, E. P.; Preston, L. A.

2015-12-01

Explosions at shallow depth-of-burial can cause nonlinear material response, such as fracturing and spalling, up to the ground surface above the shot point. These motions at the surface affect the generation of acoustic waves into the atmosphere, as well as the surface-reflected compressional and shear waves. Standard source scaling models for explosions do not account for such nonlinear interactions above the shot, while some recent studies introduce a non-isotropic addition to the moment tensor to represent them (e.g., Patton and Taylor, 2011). We are using Sandia's CTH shock physics code to model the material response in the vicinity of underground explosions, up to the overlying ground surface. Across a boundary where the motions have decayed to nearly linear behavior, we couple the signals from CTH into a linear finite-difference (FD) seismoacoustic code to efficiently propagate the wavefields to greater distances. If we assume only one-way transmission of energy through the boundary, then the particle velocities there suffice as inputs for the FD code, simplifying the specification of the boundary condition. The FD algorithm we use applies the wave equations for velocity in an elastic medium and pressure in an acoustic one, and matches the normal traction and displacement across the interface. Initially we are developing and testing a 2D, axisymmetric seismoacoustic routine; CTH can use this geometry in the source region as well. The Source Physics Experiment (SPE) in Nevada has collected seismic and acoustic data on numerous explosions at different scaled depths, providing an excellent testbed for investigating explosion phenomena (Snelson et al., 2013). We present simulations for shots SPE-4' and SPE-5, illustrating the importance of nonlinear behavior up to the ground surface. Our goal is to develop the capability for accurately predicting the relative signal strengths in the air and ground for a given combination of source yield and depth. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

VS Characterization of Hard-Rock DAM Sites in British Columbia

NASA Astrophysics Data System (ADS)

Addo, K. O.; Catchings, R.; Yong, A.; Goldman, M.; Chan, J. H.; Martin, A. J.

2017-12-01

We present results consisting of shear-wave velocity (VS) profiles and the time-averaged VS in the uppermost 30 m (VS30) measured with multiple noninvasive seismic methods and acquired at five hydro dam locations in British Columbia, Canada. VS30 is typically the main parameter used to account for site amplification in ground motion models (GMMs), including models for western (WNA) and central/eastern North America (CENA). As VS30 quantifies soil shear stiffness, which affects frequency content and damping within shallow sediments, it correlates with the shallow-crustal damping parameter, kappa (k), and particularly the site component of kappa (k0). The upper limit on k0-VS30-scaling is in the range of 1100 to 1500 m/s (or less) and the lack of data from stiffer sites reflects the scarcity of direct VS measurements for such site conditions in North America. Hard-rock sites (VS30 > 1500 m/s) are of great engineering interest, but the lack of such measurements increases epistemic uncertainties in the GMMs. Moreover, it is currently not possible to correlate site-to-site variations in k0 with VS30 for such conditions because most hard-rock sites are assigned a generic VS30 of 2000 m/s, due to the lack of measured VS30 values. For the British Columbia sites, our preliminary analysis of field records indicates near-surface shear-wave velocities in excess of 2500 m/s in the upper few meters. Additional analysis of body- and surface-waves will include: refraction tomography, multi-channel analysis of surface waves (MASW), reflection, extended-spatial-autocorrelation, horizontal-to-vertical spectral ratio, and multi-spectral analysis of surface waves

First seismic shear wave velocity profile of the lunar crust as extracted from the Apollo 17 active seismic data by wavefield gradient analysis

NASA Astrophysics Data System (ADS)

Sollberger, David; Schmelzbach, Cedric; Robertsson, Johan O. A.; Greenhalgh, Stewart A.; Nakamura, Yosio; Khan, Amir

2016-04-01

We present a new seismic velocity model of the shallow lunar crust, including, for the first time, shear wave velocity information. So far, the shear wave velocity structure of the lunar near-surface was effectively unconstrained due to the complexity of lunar seismograms. Intense scattering and low attenuation in the lunar crust lead to characteristic long-duration reverberations on the seismograms. The reverberations obscure later arriving shear waves and mode conversions, rendering them impossible to identify and analyze. Additionally, only vertical component data were recorded during the Apollo active seismic experiments, which further compromises the identification of shear waves. We applied a novel processing and analysis technique to the data of the Apollo 17 lunar seismic profiling experiment (LSPE), which involved recording seismic energy generated by several explosive packages on a small areal array of four vertical component geophones. Our approach is based on the analysis of the spatial gradients of the seismic wavefield and yields key parameters such as apparent phase velocity and rotational ground motion as a function of time (depth), which cannot be obtained through conventional seismic data analysis. These new observables significantly enhance the data for interpretation of the recorded seismic wavefield and allow, for example, for the identification of S wave arrivals based on their lower apparent phase velocities and distinct higher amount of generated rotational motion relative to compressional (P-) waves. Using our methodology, we successfully identified pure-mode and mode-converted refracted shear wave arrivals in the complex LSPE data and derived a P- and S-wave velocity model of the shallow lunar crust at the Apollo 17 landing site. The extracted elastic-parameter model supports the current understanding of the lunar near-surface structure, suggesting a thin layer of low-velocity lunar regolith overlying a heavily fractured crust of basaltic material showing high (>0.4 down to 60 m) Poisson's ratios. Our new model can be used in future studies to better constrain the deep interior of the Moon. Given the rich information derived from the minimalistic recording configuration, our results demonstrate that wavefield gradient analysis should be critically considered for future space missions that aim to explore the interior structure of extraterrestrial objects by seismic methods. Additionally, we anticipate that the proposed shear wave identification methodology can also be applied to the routinely recorded vertical component data from land seismic exploration on Earth.

A Coupled Model of Langmuir Circulations and Ramp-like Structures in the Upper Ocean Turbulent Boundary Layer

NASA Astrophysics Data System (ADS)

Soloviev, A.; Dean, C.; Lukas, R.; Donelan, M. A.; Terray, E. A.

2016-12-01

Surface-wave breaking is a powerful mechanism producing significant energy flux to small scale turbulence. Most of the turbulent energy produced by breaking waves dissipates within one significant wave height, while the turbulent diffusion layer extends to approximately ten significant wave heights. Notably, the near-surface shear may practically vanish within the wave-stirred layer due to small-scale turbulent mixing. The surface ocean temperature-salinity structure, circulation, and mass exchanges (including greenhouse gases and pollutants) substantially depend on turbulent mixing and non-local transport in the near-surface layer of the ocean. Spatially coherent organized motions have been recognized as an important part of non-local transport. Langmuir circulation (LC) and ramp-like structures are believed to vertically transfer an appreciable portion of the momentum, heat, gases, pollutants (e.g., oil), and other substances in the upper layer of the ocean. Free surface significantly complicates the analysis of turbulent exchanges at the air-sea interface and the coherent structures are not yet completely understood. In particular, there is growing observational evidence that in the case of developing seas when the wind direction may not coincide with the direction of the energy containing waves, the Langmuir lines are oriented in the wind rather than the wave direction. In addition, the vortex force due to Stokes drift in traditional models is altered in the breaking-wave-stirred layer. Another complication is that the ramp-like structures in the upper ocean turbulent boundary layer have axes perpendicular to the axes of LC. The ramp-like structures are not considered in the traditional model. We have developed a new model, which treats the LC and ramp-like structures in the near-surface layer of the ocean as a coupled system. Using computational fluid dynamics tools (LES), we have been able to reproduce both LC and ramp-like structures coexisting in space though intermittent in time. In the model, helicity isosurfaces appear to be tilted and, in general, coordinated with the tilted velocity isosurfaces produced by ramp-like structures. This is an indication of coupling between the LC and ramp-like structures. Remarkably, the new model is able to explain observations of LC under developing seas.

Nano-optomechanical system based on microwave frequency surface acoustic waves

NASA Astrophysics Data System (ADS)

Tadesse, Semere Ayalew

Cavity optomechnics studies the interaction of cavity confined photons with mechanical motion. The emergence of sophisticated nanofabrication technology has led to experimental demonstrations of a wide range of novel optomechanical systems that exhibit strong optomechanical coupling and allow exploration of interesting physical phenomena. Many of the studies reported so far are focused on interaction of photons with localized mechanical modes. For my doctoral research, I did experimental investigations to extend this study to propagating phonons. I used surface travelling acoustic waves as the mechanical element of my optomechanical system. The optical cavities constitute an optical racetrack resonator and photonic crystal nanocavity. This dissertation discusses implementation of this surface acoustic wave based optomechanical system and experimental demonstrations of important consequences of the optomechanical coupling. The discussion focuses on three important achievements of the research. First, microwave frequency surface acoustic wave transducers were co-integrated with an optical racetrack resonator on a piezoelectric aluminum nitride film deposited on an oxidized silicon substrate. Acousto-optic modulation of the resonance modes at above 10 GHz with the acoustic wavelength significantly below the optical wavelength was achieved. The phase and modal matching conditions in this paradigm were investigated for efficient optmechanical coupling. Second, the optomechanical coupling was pushed further into the sideband resolved regime by integrating the high frequency surface acoustic wave transducers with a photonic crystal nanocavity. This device was used to demonstrate optomecahnically induced transparency and absorption, one of the interesting consequences of cavity optomechanics. Phase coherent interaction of the acoustic wave with multiple nanocavities was also explored. In a related experiment, the photonic crystal nanoscavity was placed inside an acoustic echo-chamber, and interaction of a phonon pulse with the photonic nanocavity was investigated. Third, an effort was made to address a major limitation of the surface acoustic wave based optomechanical system - loss of acoustic energy into the oxidized silicon substrate. To circumvent this problem, the optomechanical system was implemented in a suspended aluminum nitride membrane. The system confined the optical and acoustic wave within the thickness of the membrane and led to a stronger optomechanical coupling. At the end a summary is given that highlights important features of the optmechanical system and its prospects in future fundamental research and application.