Science.gov

Sample records for floating attenuator wave

  1. WindWaveFloat

    SciTech Connect

    Weinstein, Alla

    2011-11-01

    Presentation from the 2011 Water Peer Review includes in which principal investigator Alla Weinstein discusses project progress in development of a floating offshore wind structure - the WindFloat - and incorporation therin of a Spherical Wave Energy Device.

  2. Wave drag on floating bodies

    PubMed Central

    Le Merrer, Marie; Clanet, Christophe; Quéré, David; Raphaël, Élie; Chevy, Frédéric

    2011-01-01

    We measure the deceleration of liquid nitrogen drops floating at the surface of a liquid bath. On water, the friction force is found to be about 10 to 100 times larger than on a solid substrate, which is shown to arise from wave resistance. We investigate the influence of the bath viscosity and show that the dissipation decreases as the viscosity is increased, owing to wave damping. The measured resistance is well predicted by a model imposing a vertical force (i.e., the drop weight) on a finite area, as long as the wake can be considered stationary. PMID:21876186

  3. WindWaveFloat (WWF): Final Scientific Report

    SciTech Connect

    Alla Weinstein; Roddier, Dominique; Banister, Kevin

    2012-03-30

    Principle Power Inc. and National Renewable Energy Lab (NREL) have completed a contract to assess the technical and economic feasibility of integrating wave energy converters into the WindFloat, resulting in a new concept called the WindWaveFloat (WWF). The concentration of several devices on one platform could offer a potential for both economic and operational advantages. Wind and wave energy converters can share the electrical cable and power transfer equipment to transport the electricity to shore. Access to multiple generation devices could be simplified, resulting in cost saving at the operational level. Overall capital costs may also be reduced, provided that the design of the foundation can be adapted to multiple devices with minimum modifications. Finally, the WindWaveFloat confers the ability to increase energy production from individual floating support structures, potentially leading to a reduction in levelized energy costs, an increase in the overall capacity factor, and greater stability of the electrical power delivered to the grid. The research conducted under this grant investigated the integration of several wave energy device types into the WindFloat platform. Several of the resulting system designs demonstrated technical feasibility, but the size and design constraints of the wave energy converters (technical and economic) make the WindWaveFloat concept economically unfeasible at this time. Not enough additional generation could be produced to make the additional expense associated with wave energy conversion integration into the WindFloat worthwhile.

  4. Hydrodynamic analysis of elastic floating collars in random waves

    NASA Astrophysics Data System (ADS)

    Bai, Xiao-dong; Zhao, Yun-peng; Dong, Guo-hai; Li, Yu-cheng

    2015-06-01

    As the main load-bearing component of fish cages, the floating collar supports the whole cage and undergoes large deformations. In this paper, a mathematical method is developed to study the motions and elastic deformations of elastic floating collars in random waves. The irregular wave is simulated by the random phase method and the statistical approach and Fourier transfer are applied to analyze the elastic response in both time and frequency domains. The governing equations of motions are established by Newton's second law, and the governing equations of deformations are obtained based on curved beam theory and modal superposition method. In order to validate the numerical model of the floating collar attacked by random waves, a series of physical model tests are conducted. Good relationship between numerical simulation and experimental observations is obtained. The numerical results indicate that the transfer function of out-of-plane and in-plane deformations increase with the increasing of wave frequency. In the frequency range between 0.6 Hz and 1.1 Hz, a linear relationship exists between the wave elevations and the deformations. The average phase difference between the wave elevation and out-of-plane deformation is 60° with waves leading and the phase between the wave elevation and in-plane deformation is 10° with waves lagging. In addition, the effect of fish net on the elastic response is analyzed. The results suggest that the deformation of the floating collar with fish net is a little larger than that without net.

  5. Lg wave attenuation in Britain

    NASA Astrophysics Data System (ADS)

    Sargeant, Susanne; Ottemöller, Lars

    2009-12-01

    The Lg wave quality factor (QLg) in Britain has been modelled using data from the UK Seismic Network, operated by the British Geological Survey. The data set consists of 631 vertical, mostly short-period recordings of Lg waves from 64 earthquakes (2.7-4.7 ML) and 93 stations. We have inverted for both regional average QLg and tomographic images of QLg, and simultaneously a source term for each event and a site term for each station for 22 frequencies in the band 0.9-10.0 Hz. The regional average model is 266f0.53 between 1.0 and 10.0 Hz and indicates that attenuation in Britain is slightly higher than in France, and significantly higher than in eastern North America and Scandinavia. Tomographic inversions at each frequency indicate that QLg varies spatially. Broadly speaking, southeastern England, the Lake District and parts of the East Irish Sea Basin, and a small region between the Highland Boundary Fault and the Southern Uplands Fault are characterized by higher than average attenuation. Southwestern England, eastern central England and northwestern Scotland are regions of relatively low attenuation. To some extent, these regions correlate with what is known about the tectonics and structure of the crust in the UK.

  6. Surface waves on floating liquids induced by ultrasound field

    NASA Astrophysics Data System (ADS)

    Geng, D. L.; Xie, W. J.; Yan, N.; Wei, B.

    2013-01-01

    We demonstrate a kind of wave pattern on the surface of floating liquids in a modulated ultrasound field. The waves are related to the liquid/solid phase transformation process. The nucleation sites of the eutectics locate at the center of these waves, and the eutectic growth direction is parallel to the propagation direction of the waves. It is revealed that such wave phenomenon can be ascribed to the interaction between ultrasound and eutectic growth at the liquid/solid interface. This result may provide a potential method for fabricating wave patterned surfaces on eutectic alloys.

  7. Development of Floating Wave Barriers for Cost Effective Protection of Irrigation and Catfish Pond Levees

    NASA Astrophysics Data System (ADS)

    Ozeren, Y.; Wren, D. G.; Alonso, C. V.

    2007-12-01

    Earth levees for catfish ponds and irrigation water storage experience significant embankment erosion due to wind generated waves. Large seasonal fluctuations in water level make vegetative bank protection impractical, and other stabilization methods such as the use of old tires or riprap are not acceptable due to ecological and economic concerns. The goal of the present work is to define configurations and construction techniques for inexpensive floating breakwaters made of polyethylene irrigation tubing. Based on wave characteristics measured in an irrigation pond near Lonoke, Arkansas, a laboratory scale wave generating flume was designed, constructed, and used to test multiple wave barrier configurations for regular waves in deep and transitional water depths. Wave transmission characteristics were investigated for the following breakwater arrangements: (1) fully restrained, (2) vertically restrained with a single mooring line, (3) horizontally restrained with a rigid arm hinged at one end, and (4) horizontally restrained with piles at both sides of the breakwater. The test results show that cylindrical pipes can be used effectively as floating breakwaters and that wave transmission characteristics strongly depend on the draft of the breakwater and the mooring configuration. The use of multiple small cylinders instead of a single large one can reduce cost while maintaining the same level of wave attenuation. The wave characteristics measured in the field and the results of laboratory testing resulted in a final design that is to be tested at the prototype scale in an irrigation pond.

  8. Incorporating floating surface objects into a fully dispersive surface wave model

    NASA Astrophysics Data System (ADS)

    Orzech, Mark D.; Shi, Fengyan; Veeramony, Jayaram; Bateman, Samuel; Calantoni, Joseph; Kirby, James T.

    2016-06-01

    The shock-capturing, non-hydrostatic, three-dimensional (3D) finite-volume model NHWAVE was originally developed to simulate wave propagation and landslide-generated tsunamis in finite water depth (Ma, G., Shi, F., Kirby, J. T., 2012. Ocean Model. 43-44, 22-35). The model is based on the incompressible Navier-Stokes equations, in which the z-axis is transformed to a σ-coordinate that tracks the bed and surface. As part of an ongoing effort to simulate waves in polar marginal ice zones (MIZs), the model has now been adapted to allow objects of arbitrary shape and roughness to float on or near its water surface. The shape of the underside of each floating object is mapped onto an upper σ-level slightly below the surface. In areas without floating objects, this σ-level continues to track the surface and bed as before. Along the sides of each floating object, an immersed boundary method is used to interpolate the effects of the object onto the neighboring fluid volume. Provided with the object's shape, location, and velocity over time, NHWAVE determines the fluid fluxes and pressure variations from the corresponding accelerations at neighboring cell boundaries. The system was validated by comparison with analytical solutions and a VOF model for a 2D floating box and with laboratory measurements of wave generation by a vertically oscillating sphere. A steep wave simulation illustrated the high efficiency of NHWAVE relative to a VOF model. In a more realistic MIZ simulation, the adapted model produced qualitatively reasonable results for wave attenuation, diffraction, and scattering.

  9. Vibrations of a floating beam on marine waves

    SciTech Connect

    Sabaneev, Valentin S.; Tovstik, Petr E.; Tovstik, Tatiana M.; Shekhovtsov, Alexei S.

    2015-03-10

    Vertical vibrations of a floating pipe-concrete beam caused by a harmonic waves excitation are studied. The apparent additional mass of water, resisting force and the velocity of towing are considered. The vibration amplitude and the maximum deformations of concrete, caused by these fluctuations, are calculated.

  10. Numerical simulation of floating bodies in extreme free surface waves

    NASA Astrophysics Data System (ADS)

    Hu, Z. Z.; Causon, D. M.; Mingham, C. G.; Qian, L.

    2011-02-01

    In this paper, we use the in-house Computational Fluid Dynamics (CFD) flow code AMAZON-SC as a numerical wave tank (NWT) to study wave loading on a wave energy converter (WEC) device in heave motion. This is a surface-capturing method for two fluid flows that treats the free surface as contact surface in the density field that is captured automatically without special provision. A time-accurate artificial compressibility method and high resolution Godunov-type scheme are employed in both fluid regions (air/water). The Cartesian cut cell method can provide a boundary-fitted mesh for a complex geometry with no requirement to re-mesh globally or even locally for moving geometry, requiring only changes to cut cell data at the body contour. Extreme wave boundary conditions are prescribed in an empty NWT and compared with physical experiments prior to calculations of extreme waves acting on a floating Bobber-type device. The validation work also includes the wave force on a fixed cylinder compared with theoretical and experimental data under regular waves. Results include free surface elevations, vertical displacement of the float, induced vertical velocity and heave force for a typical Bobber geometry with a hemispherical base under extreme wave conditions.

  11. Imaging Rayleigh wave attenuation with USArray

    NASA Astrophysics Data System (ADS)

    Bao, Xueyang; Dalton, Colleen A.; Jin, Ge; Gaherty, James B.; Shen, Yang

    2016-07-01

    The EarthScope USArray provides an opportunity to obtain detailed images of the continental upper mantle at an unprecedented scale. The majority of mantle models derived from USArray data to date contain spatial variations in seismic-wave speed; however, in many cases these data sets do not by themselves allow a non-unique interpretation. Joint interpretation of seismic attenuation and velocity models can improve upon the interpretations based only on velocity and provide important constraints on the temperature, composition, melt content, and volatile content of the mantle. The surface wave amplitudes that constrain upper-mantle attenuation are sensitive to factors in addition to attenuation, including the earthquake source excitation, focusing and defocusing by elastic structure, and local site amplification. Because of the difficulty of isolating attenuation from these other factors, little is known about the attenuation structure of the North American upper mantle. In this study, Rayleigh wave traveltime and amplitude in the period range 25-100 s are measured using an interstation cross-correlation technique, which takes advantage of waveform similarity at nearby stations. Several estimates of Rayleigh wave attenuation and site amplification are generated at each period, using different approaches to separate the effects of attenuation and local site amplification on amplitude. It is assumed that focusing and defocusing effects can be described by the Laplacian of the traveltime field. All approaches identify the same large-scale patterns in attenuation, including areas where the attenuation values are likely contaminated by unmodelled focusing and defocusing effects. Regionally averaged attenuation maps are constructed after removal of the contaminated attenuation values, and the variations in intrinsic shear attenuation that are suggested by these Rayleigh wave attenuation maps are explored.

  12. Applicability of WaveWatch-III wave model to fatigue assessment of offshore floating structures

    NASA Astrophysics Data System (ADS)

    Zou, Tao; Kaminski, Miroslaw Lech

    2016-09-01

    In design and operation of floating offshore structures, one has to avoid fatigue failures caused by action of ocean waves. The aim of this paper is to investigate the applicability of WaveWatch-III wave model to fatigue assessment of offshore floating structures. The applicability was investigated for Bluewaters' FPSO (Floating Production, Storage and Offloading) which had been turret moored at Sable field for half a decade. The waves were predicted as sea-state time series consisting of one wind sea and one swell. The predicted waves were compared with wave data obtained from ERA-interim and buoy measurements. Furthermore, the fatigue calculations were also carried out for main deck and side shell locations. It has been concluded that predicted fatigue damages of main deck using WaveWatch-III are in a very good agreement regardless of differences in predicted wind waves and swells caused by differences in wave system partitioning. When compared to buoy measurements, the model underestimates fatigue damages of side shell by approximately 30 %. The reason for that has been found in wider directional spreading of actual waves. The WaveWatch-III wave model has been found suitable for the fatigue assessment. However, more attention should be paid on relative wave directionality, wave system partitioning and uncertainty analysis in further development.

  13. Compressional head waves in attenuative formations

    SciTech Connect

    Liu, Q.H.; Chang, C.

    1994-12-31

    The attenuation of compressional head waves in a fluid-filled borehole is studied with the branch-cut integration method. The borehole fluid and solid formation are both assumed lossy with quality factors Q{sub f}({omega}) for the fluid, and Q{sub c}({omega}) and Q{sub s}({omega}) for the compressional and shear waves in the solid, respectively. The branch-cut integration method used in this work is an extension of that for a lossless medium. With this branch-cut integration method, the authors can isolate the groups of individual arrivals such as the compressional head waves and shear head waves, and study the attenuation of those particular wavefields in lossy media. This study, coupled with experimental work to be performed, may result in an effective way of measuring compressional head wave attenuation in the field.

  14. 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

  15. UHF Radio Wave Attenuation Factor Database

    NASA Astrophysics Data System (ADS)

    Khomenko, S. I.; Kostina, V. L.; Mytsenko, I. M.; Roenko, A. N.

    2007-07-01

    As is known each sea-going vessel is equipped with navigation, communication and other radio engineering facilities that serve to secure the safety of navigation and are chiefly operated at UHF-wave band. In developing these systems and calculating the energy potential for a necessary coverage range one should be well aware of the radio signal attenuation processes on a propagation path. The key parameter of this path is the (radio) wave attenuation factor V and its distance dependence V(R). A diversity of factors influencing the radio signal attenuation over the oceanic expanses, especially well pronounced and quite stable tropospheric ducts, and the lack of experimental data were the compelling reasons why the researchers of the Institute for Radiophysics and Electronics, NASU, had spent many years on comprehensive radiophysical investigations carried out in different regions of the Atlantic, Indian, Arctic and Pacific Oceans. The experimental data obtained allow creating the database of radio wave attenuation factor V.

  16. Attenuation of a shock wave in organoplastic

    SciTech Connect

    Bordzilovskii, S.A.; Karakhanov, S.M.; Merzhievskii, L.A.; Resnyanskii, A.D.

    1995-09-01

    The attenuation of a plane shock wave in organoplastic was experimentally and numerically investigated during its interaction with an overtaking rarefaction wave. Measurements were carried out with manganin gauges. An earlier formulation model of the dynamic deformation of composites was used in calculations. A comparison of calculated and experimental data has shown their good agreement.

  17. Hydroelastic response of a floating runway to cnoidal waves

    SciTech Connect

    Ertekin, R. C.; Xia, Dingwu

    2014-02-15

    The hydroelastic response of mat-type Very Large Floating Structures (VLFSs) to severe sea conditions, such as tsunamis and hurricanes, must be assessed for safety and survivability. An efficient and robust nonlinear hydroelastic model is required to predict accurately the motion of and the dynamic loads on a VLFS due to such large waves. We develop a nonlinear theory to predict the hydroelastic response of a VLFS in the presence of cnoidal waves and compare the predictions with the linear theory that is also developed here. This hydroelastic problem is formulated by directly coupling the structure with the fluid, by use of the Level I Green-Naghdi theory for the fluid motion and the Kirchhoff thin plate theory for the runway. The coupled fluid structure system, together with the appropriate jump conditions are solved in two-dimensions by the finite-difference method. The numerical model is used to study the nonlinear response of a VLFS to storm waves which are modeled by use of the cnoidal-wave theory. Parametric studies show that the nonlinearity of the waves is very important in accurately predicting the dynamic bending moment and wave run-up on a VLFS in high seas.

  18. Wave energy absorption by a floating air bag

    NASA Astrophysics Data System (ADS)

    Kurniawan, A.; Chaplin, J. R.; Greaves, D. M.; Hann, M.

    2017-02-01

    A floating air bag, ballasted in water, expands and contracts as it heaves under wave action. Connecting the bag to a secondary volume via a turbine transforms the bag into a device capable of generating useful energy from the waves. Small-scale measurements of the device reveal some interesting properties, which are successfully predicted numerically. Owing to its compressibility, the device can have a heave resonance period longer than that of a rigid device of the same shape and size, without any phase control. Furthermore, varying the amount of air in the bag is found to change its shape and hence its dynamic response, while varying the turbine damping or the air volume ratio changes the dynamic response without changing the shape.

  19. Evaluation on Micro Cracks in Ceramic Bearing Balls by Using the Floating Resonance of Surface Acoustic Waves

    NASA Astrophysics Data System (ADS)

    Cho, Hideo; Komatsu, Kouichi; Ishikawa, Satoru; Tanimoto, Kiyoshi; Takii, Hirokazu; Yamanaka, Kazushi

    2003-05-01

    Although resonant ultrasound spectroscopy is useful for testing the surface and the inside of objects, the acoustic properties (resonance frequency, mode amplitude ratio, attenuation, etc.) are disturbed by the contact made with supports and transducers. To eliminate this disturbance, we developed the floating resonance (FR) method in which the acoustic properties of bulk and surface acoustic waves (SAWs) are evaluated using laser ultrasound after floating the objects, thus avoiding the contact with the supports and transducers. In this work we applied the FR method to detect artificial flaws on the surface of ceramic bearing balls and a slit as shallow as 50 μm was successfully detected from the attenuation of SAWs after multiple round trips with as many as 20 turns.

  20. Attenuation of sound waves in drill strings

    SciTech Connect

    Drumheller, D.S. )

    1993-10-01

    During drilling of deep wells, digital data are often transmitted from sensors located near the drill bit to the surface. Development of a new communication system with increased data capacity is of paramount importance to the drilling industry. Since steel drill strings are used, transmission of these data by elastic carrier waves traveling within the drill pipe is possible, but the potential communication range is uncertain. The problem is complicated by the presence of heavy-threaded tool joints every 10 m, which form a periodic structure and produce classical patterns of passbands and stop bands in the wave spectra. In this article, field measurements of the attenuation characteristics of a drill string in the Long Valley Scientific Well in Mammoth Lakes, California are presented. Wave propagation distances approach 2 km. A theoretical model is discussed which predicts the location, width, and attenuation of the passbands. Mode conversion between extensional and bending waves, and spurious reflections due to deviations in the periodic spacings of the tool joints are believed to be the sources of this attenuation. It is estimated that attenuation levels can be dramatically reduced by rearranging the individual pipes in the drill string according to length. 7 refs., 20 figs., 4 tabs.

  1. Bubbles attenuate elastic waves at seismic frequencies

    NASA Astrophysics Data System (ADS)

    Tisato, Nicola; Quintal, Beatriz; Chapman, Samuel; Podladchikov, Yury; Burg, Jean-Pierre

    2016-04-01

    The vertical migration of multiphase fluids in the crust can cause hazardous events such as eruptions, explosions, pollution and earthquakes. Although seismic tomography could potentially provide a detailed image of such fluid-saturated regions, the interpretation of the tomographic signals is often controversial and fails in providing a conclusive map of the subsurface saturation. Seismic tomography should be improved considering seismic wave attenuation (1/Q) and the dispersive elastic moduli which allow accounting for the energy lost by the propagating elastic wave. In particular, in saturated media a significant portion of the energy carried by the propagating wave is dissipated by the wave-induced-fluid-flow and the wave-induced-gas-exsolution-dissolution (WIGED) mechanisms. The WIGED mechanism describes how a propagating wave modifies the thermodynamic equillibrium between different fluid phases causing the exsolution and the dissolution of the gas in the liquid, which in turn causes a significant frequency dependent 1/Q and moduli dispersion. The WIGED theory was initially postulated for bubbly magmas but only recently was extended to bubbly water and experimentally demonstrated. Here we report these theory and laboratory experiments. Specifically, we present i) attenuation measurements performed by means of the Broad Band Attenuation Vessel on porous media saturated with water and different gases, and ii) numerical experiments validating the laboratory observations. Finally, we will extend the theory to fluids and to pressure-temperature conditions which are typical of phreatomagmatic and hydrocarbon domains and we will compare the propagation of seismic waves in bubble-free and bubble-bearing subsurface domains. With the present contribution we extend the knowledge about attenuation in rocks which are saturated with multiphase fluid demonstrating that the WIGED mechanism could be extremely important to image subsurface gas plumes.

  2. Physical measurements of breaking wave impact on a floating wave energy converter

    NASA Astrophysics Data System (ADS)

    Hann, Martyn R.; Greaves, Deborah M.; Raby, Alison

    2013-04-01

    Marine energy converter must both efficiently extract energy in small to moderate seas and also successfully survive storms and potential collisions. Extreme loads on devices are therefore an important consideration in their design process. X-MED is a SuperGen UKCMER project and is a collaboration between the Universities of Manchester, Edinburgh and Plymouth and the Scottish Association for Marine Sciences. Its objective is to extend the knowledge of extreme loads due to waves, currents, flotsam and mammal impacts. Plymouth Universities contribution to the X-MED project involves measuring the loading and response of a taut moored floating body due to steep and breaking wave impacts, in both long crested and directional sea states. These measurements are then to be reproduced in STAR-CCM+, a commercial volume of fluid CFD solver, so as to develop techniques to predict the wave loading on wave energy converters. The measurements presented here were conducted in Plymouth Universities newly opened COAST laboratories 35m long, 15.5m wide and 3m deep ocean basin. A 0.5m diameter taut moored hemispherical buoy was used to represent a floating wave energy device or support structure. The changes in the buoys 6 degree of freedom motion and mooring loads are presented due to focused breaking wave impacts, with the breaking point of the wave changed relative to the buoy.

  3. Effects of Wave Nonlinearity on Wave Attenuation by Vegetation

    NASA Astrophysics Data System (ADS)

    Wu, W. C.; Cox, D. T.

    2014-12-01

    The need to explore sustainable approaches to maintain coastal ecological systems has been widely recognized for decades and is increasingly important due to global climate change and patterns in coastal population growth. Submerged aquatic vegetation and emergent vegetation in estuaries and shorelines can provide ecosystem services, including wave-energy reduction and erosion control. Idealized models of wave-vegetation interaction often assume rigid, vertically uniform vegetation under the action of waves described by linear wave theory. A physical model experiment was conducted to investigate the effects of wave nonlinearity on the attenuation of random waves propagating through a stand of uniform, emergent vegetation in constant water depth. The experimental conditions spanned a relative water depth from near shallow to near deep water waves (0.45 < kh <1.49) and wave steepness from linear to nonlinear conditions (0.03 < ak < 0.18). The wave height to water depth ratios were in the range 0.12 < Hs/h < 0.34, and the Ursell parameter was in the range 2 < Ur < 68. Frictional losses from the side wall and friction were measured and removed from the wave attenuation in the vegetated cases to isolate the impact of vegetation. The normalized wave height attenuation decay for each case was fit to the decay equation of Dalrymple et al. (1984) to determine the damping factor, which was then used to calculate the bulk drag coefficients CD. This paper shows that the damping factor is dependent on the wave steepness ak across the range of relative water depths from shallow to deep water and that the damping factor can increase by a factor of two when the value of ak approximately doubles. In turn, this causes the drag coefficient CD to decrease on average by 23%. The drag coefficient can be modeled using the Keulegan-Carpenter number using the horizontal orbital wave velocity estimate from linear wave theory as the characteristic velocity scale. Alternatively, the Ursell

  4. Performance analysis of floating double-acting wave-energy pump

    SciTech Connect

    Ueki, H.; Kawaguty, K.; Kira, T.

    1994-12-31

    A double-acting wave-energy pump with floating caisson has been reported experimentally by the authors in a previous paper. This mobile device operates independently both tidal amplitude and incidence for wave propagation. A discharge pipe connects a pressure piston to the float which is the wave energy absorber. The cylinder and piston are set under the sea level in the middle of the caisson. Four hollow columns act as the float of the caisson. In order to investigate analytically the performance of the floating wave-energy pump, motions of both caisson and float-piston were analyzed by solving the equation of vertical motion in regular water waves. In-cylinder pressure was concerned with the external force acting to both float-piston and caisson, and was calculated by the equation for conservation of mass and the Bernoulli`s equation for an unsteady flow by a personal computer. The calculated performance of the flow rate to pump head, and the displacement of both caisson and float-piston were compared well with experimental results.

  5. RANS Simulation of the Heave Response of a Two-Body Floating Point Wave Absorber: Preprint

    SciTech Connect

    Yu, Y.; Li, Y.

    2011-03-01

    A preliminary study on a two-body floating wave absorbers is presented in this paper. A Reynolds-Averaged Navier-Stokes computational method is applied for analyzing the hydrodynamic heave response of the absorber in operational wave conditions. The two-body floating wave absorber contains a float section and a submerged reaction section. For validation purposes, our model is first assumed to be locked. The two sections are forced to move together with each other. The locked single body model is used in a heave decay test, where the RANS result is validated with the experimental measurement. For the two-body floating point absorber simulation, the two sections are connected through a mass-spring-damper system, which is applied to simulate the power take-off mechanism under design wave conditions. Overall, the details of the flow around the absorber and its nonlinear interaction with waves are investigated, and the power absorption efficiency of the two-body floating wave absorber in waves with a constant value spring-damper system is examined.

  6. Extended Onshore Control of a Floating Wind Turbine with Wave Disturbance Reduction

    NASA Astrophysics Data System (ADS)

    Christiansen, S.; Knudsen, T.; Bak, T.

    2014-12-01

    Reaching for higher wind resources beyond the water depth limitations of monopile wind turbines, there has arisen the alternative of using floating wind turbines. But the response of wave induced loads significantly increases for floating wind turbines. Applying conventional onshore control strategies to floating wind turbines has been shown to impose negative damped oscillations in fore-aft due to the low natural frequency of the floating structure. Thus, we suggest a control loop extension of the onshore controller which stabilizes the system and reduces the wave disturbance. The results shows that when adding the suggested control loop with disturbance reduction to the system, improved performance is observed in power fluctuations, blade pitch activity, and platform oscillations.

  7. Smart structures for shock wave attenuation using ER inserts

    NASA Astrophysics Data System (ADS)

    Kim, Jaehwan; Kim, Jung-Yup; Choi, Seung-Bok; Kim, Kyung-Su

    2001-08-01

    This Paper demonstrates the possibility of shock wave attenuation propagating through a smart structure that incorporates ER insert. The wave transmission of ER inserted beam is theoretically derived using Mead & Markus model and the theoretical results are compared with the finite element analysis results. To experimentally verify the shock wave attenuation, ER insert in an aluminum plate is made and two piezoceramic disks are used as transmitter and receiver of the wave. The transmitter sends a sine pulse signal such that a component of shock wave travels through the plate structure and the receiver gets the transmitted wave signal. Wave propagation of the ER insert can be adjusted by changing the applied electric field on the ER insert. Details of the experiment are addressed and the possibility of shock wave attenuation is experimentally verified. This kind of smart structure can be used for warship and submarine hull structures to protect fragile and important equipment.

  8. Wind/Wave Misalignment in the Loads Analysis of a Floating Offshore Wind Turbine: Preprint

    SciTech Connect

    Barj, L.; Stewart, S.; Stewart, G.; Lackner, M.; Jonkman, J.; Robertson, A.

    2014-02-01

    Wind resources far from the shore and in deeper seas have encouraged the offshore wind industry to look into floating platforms. The International Electrotechnical Commission (IEC) is developing a new technical specification for the design of floating offshore wind turbines that extends existing design standards for land-based and fixed-bottom offshore wind turbines. The work summarized in this paper supports the development of best practices and simulation requirements in the loads analysis of floating offshore wind turbines by examining the impact of wind/wave misalignment on the system loads under normal operation. Simulations of the OC3-Hywind floating offshore wind turbine system under a wide range of wind speeds, significant wave heights, peak-spectral periods and wind/wave misalignments have been carried out with the aero-servo-hydro-elastic tool FAST [4]. The extreme and fatigue loads have been calculated for all the simulations. The extreme and fatigue loading as a function of wind/wave misalignment have been represented as load roses and a directional binning sensitivity study has been carried out. This study focused on identifying the number and type of wind/wave misalignment simulations needed to accurately capture the extreme and fatigue loads of the system in all possible metocean conditions considered, and for a down-selected set identified as the generic US East Coast site. For this axisymmetric platform, perpendicular wind and waves play an important role in the support structure and including these cases in the design loads analysis can improve the estimation of extreme and fatigue loads. However, most structural locations see their highest extreme and fatigue loads with aligned wind and waves. These results are specific to the spar type platform, but it is expected that the results presented here will be similar to other floating platforms.

  9. Concentration of frequencies of trapped waves in problems on freely floating bodies

    SciTech Connect

    Nazarov, Sergei A

    2012-09-30

    It is shown that by choosing the shape of two identical bodies floating freely in a channel with symmetric cross-section it is possible to form any pre-assigned number of linearly independent trapped waves (localized solutions). Bibliography: 27 titles.

  10. Signature of seismic wave attenuation during fracture network formation

    NASA Astrophysics Data System (ADS)

    Barnhoorn, Auke; Zhubayev, Alimzhan; Houben, Maartje; Hardebol, Nico; Smeulders, David

    2015-04-01

    Seismic waves are significantly affected by the presence of fractures and faults. Fractures alter the arrival time of a seismic wave and the amplitude of the seismic wave. Attenuation of a seismic wave is the reduction of wave amplitude due to the presence of e.g. fractures. Attenuation of acoustic compressional P- and shear S-waves have been measured in laboratory studies on different rock types. These studies generally show a decrease in attenuation with an increase in stress. This decrease in attenuation is attributed to progressive crack closure of pre-existing cracks. The stress-dependent decrease in attenuation reported in these studies all occur within the elastic deformation field, i.e. below yield stress levels and thus no additional cracks/micro-fractures have yet been formed. At stress levels just above the yield strength the first fractures start to form. With increasing stress, fractures nucleate, grow and coalesce until a connected network of fractures has developed at which failure of the rock sample occurs. The change in attenuation during the fracturing process however has seldom been investigated. In analogy to fracture closure, where attenuation generally decreases, fracture formation should cause again an increase in attenuation. Here we report an experimental study on shales from Whitby (UK), where s-wave attenuation was measured in the laboratory during an increase in stress towards fracture formation until complete failure of the shale samples. Before yield stress conditions, as expected an increase in stress caused a gradual decrease in attenuation. At the transition from elastic to inelastic deformation behaviour, the first microfractures start to form and attenuation starts to increase again. This reversal in attenuation behaviour could potentially be used as an indicator that failure of a rock mass under stress is imminent (imminence of seismicity). The measured seismic velocities do not depict the transition from elastic to inelastic

  11. Effects of wave induced motion on power generation of offshore floating wind farms

    NASA Astrophysics Data System (ADS)

    Shoele, Kourosh

    2014-11-01

    Wind power has been the world's fastest growing energy source for more than a decade. There is a continuous effort to study the potentials of offshore floating wind farms in producing electricity. One of the major technical challenges in studying the performance of offshore floating wind farms is the hydrodynamic and aerodynamic interactions between individual turbines. In this study, a novel approach is presented to study the hydrodynamic interaction between group of floating wind turbines and determine how wave induced motion of the platforms modifies the power generation of the farm. In particular, exact analytical models are presented to solve the hydrodynamic diffraction and radiation problem of a group of floating wind turbine platforms, to model the aerodynamic interaction between turbines, and to quantify the nonlinear dynamic of the mooring lines used to stabilize the floating platforms through connecting them to the seabed. The overall performance of the farm with different configuration and at different wind and wave conditions are investigated and the effects of the sea state condition as well as the distance between the turbines in the farm on the low frequency temporal variation of the power output are discussed.

  12. Incorporating Floating Surface Objects into a Fully Dispersive Surface Wave Model

    DTIC Science & Technology

    2016-04-19

    axis is transformed to a σ -coordinate that tracks the bed and surface. As part of an ongoing effort to simulate waves in polar marginal ice zones...to track the surface and bed as before. Along the sides of each floating object, an immersed boundary method is used to interpolate the effects of...open water continue to grow in the Arctic during spring and summer months, more powerful waves are playing an increasingly impor- tant role in the

  13. On Long Baroclinic Rossby Waves in the Tropical North Atlantic Observed From Profiling Floats

    DTIC Science & Technology

    2007-05-16

    coastline. Unstable standing Rossby waves with annual and semiannual periods are shown in both the subbasins. All unstable waves, decaying , radiate shorter...42] The bin average produced a new sampling repre- senting a set of smoothed velocities related to centers of float clusters embedded into...computations (Figures 4b–4d) demonstrate frequent changes in the structure of the perturbations associated with their merger, decay , and dissipation and that the

  14. Oceanic Rossby waves acting as a "hay rake" for ecosystem floating by-products.

    PubMed

    Dandonneau, Yves; Vega, Andres; Loisel, Hubert; du Penhoat, Yves; Menkes, Christophe

    2003-11-28

    Recent satellite observations of Rossby waves and chlorophyll anomalies propagating in subtropical gyres have suggested that wave-induced upwelling could stimulate photosynthesis. Instead, we show that chlorophyll maxima are located in abnormally warm water, in Rossby wave-induced convergences. This excludes inputs of nutrients from deeper water. We argue that the sea color anomalies are not caused by chlorophyll but by floating particles evolved from the ecosystem and accumulated by Rossby waves, acting as "marine hay rakes," in convergence zones. Such processes may be determinant for the distribution of living organisms in oligotrophic areas.

  15. Identification of wave energy potential with floating oscillating water column technology in Pulau Baai Beach, Bengkulu

    NASA Astrophysics Data System (ADS)

    Alifdini, I.; Sugianto, D. N.; Andrawina, Y. O.; Widodo, A. B.

    2017-02-01

    Pulau Baai is a beach which is located in Bengkulu, Indonesia. This location has swell waves which is beneficial for wave energy, because it directly faces the Indian Ocean. Floating Oscillating Water Column (OWC) is a prototype used to generate electricity from wave energy. The objective of this research is to identify how much electricity can be generated from floating OWC. This research used a quantitative method by processing wind data (speed and direction) from ogimet.com in 2000-2016. The wind speed rate for wave energy potential of this location is above 5.14 m/s. Wind data is converted to significant wave height and periods data by Sverdrup, Munk, and Bretschneider (SMB) method. Significant wave height rate of this location is 0.06 – 5.33 meters. Assuming that this power plant uses 3 chambers of floating OWC, the power output of OWC is 1.9 GW/year. Thus, suppose each residents’ house uses 1300 watt, this power plant can be used for 1,461,538 residents per year.

  16. Wave attenuation over porous seabeds: A numerical study

    NASA Astrophysics Data System (ADS)

    Torres-Freyermuth, Alec; Brocchini, Maurizio; Corvaro, Sara; Pintado-Patiño, Jose Carlos

    2017-09-01

    We investigate wave attenuation over porous seabeds by means of a phase- and depth- resolving numerical model that solves the Volume-Averaged Reynolds-Averaged Navier-Stokes (VARANS) equations. The numerical model is calibrated with laboratory data from Corvaro et al. (2010). The numerical model predicts the wave attenuation and the velocity field near the porous bed for different regular wave conditions. Subsequently, a parametric analysis on the physical characteristics of the porous media is made to investigate their relative role on wave attenuation. The results of the analysis indicate nonlinear dependencies of wave attenuation on both, total porosity and mean grain diameter. The widely used parabolic model in terms of the dispersiveness parameter predicts both types of dependencies, effectively. Hence, new parametric formulations are derived for the determination of the coefficients involved in the parabolic model for each type of dependence. On the other hand, the role of the spectral shape on the wave spectrum bulk dissipation is investigated. Numerical results for irregular waves show a clear dependence of the dissipation rate with the Ursell (Ur) parameter. The dissipation rate becomes sensitive to frequency spreading for Ur < 20. Moreover, forcing the model assuming an f - 5 tail in the incident wave spectrum underpredicts seabed attenuation with respect to an f - 4 formulation. Finally, bispectral analysis of irregular wave propagation allow us to investigate the mechanism of wave attenuation. The numerical results suggest that energy is directly dissipated at the peak frequency, whereas nonlinear energy transfer plays an important role in energy attenuation at higher harmonics.

  17. Performance characteristics of a wave attenuation for pulsed chemical lasers

    NASA Astrophysics Data System (ADS)

    Buonadonna, V.; Weisbach, M. F.; Tong, K.-O.; McClure, J. D.

    1981-06-01

    Parametric performance measurements are reported for a pulsed chemical laser wave attenuator. The attenuator utilizes the combined effects of flow channel area expansion, caustic water spray, and flow-through damping screens to suppress and control the pressure disturbances produced by the chemical heat release of the F2 + D2 chain reaction. Experimental results that illustrate the effects of different area expansion geometries, water spray configurations, and damping screen arrangements are presented. Capability to tune the attenuator system to provide short pressure wave clearing times is emphasized. An attenuator configuration is reported which gives a wave clearing time of 2 msec with a corresponding entropy-wave density nonuniformity of 0.001 for a 18.5/6/76.5 F2/O2/diluent gas mixture at a pulse repetition frequency of 100 Hz.

  18. Wave energy absorption by a submerged air bag connected to a rigid float.

    PubMed

    Kurniawan, A; Chaplin, J R; Hann, M R; Greaves, D M; Farley, F J M

    2017-04-01

    A new wave energy device features a submerged ballasted air bag connected at the top to a rigid float. Under wave action, the bag expands and contracts, creating a reciprocating air flow through a turbine between the bag and another volume housed within the float. Laboratory measurements are generally in good agreement with numerical predictions. Both show that the trajectory of possible combinations of pressure and elevation at which the device is in static equilibrium takes the shape of an S. This means that statically the device can have three different draughts, and correspondingly three different bag shapes, for the same pressure. The behaviour in waves depends on where the mean pressure-elevation condition is on the static trajectory. The captured power is highest for a mean condition on the middle section.

  19. Multi-Scale Modeling of Wave Attenuation by Vegetation

    NASA Astrophysics Data System (ADS)

    Chen, Q. J.; Zhu, L.; Chakrabarti, A.

    2016-02-01

    In the past decade, interest in wave attenuation by vegetation has increased considerably as coastal scientists and engineers search for sustainable solutions to mitigate the impacts of climate change and natural hazards. It is well known that vegetation in wetlands can effectively reduce the flow speed, modify turbulence structure, attenuate wave energy, and affect sediment dynamics. Restoring coastal wetlands and reducing flood risks require improved understanding and better predictive capability of wave and surge attenuation over inundated coastal landscapes with vegetation. The interactions of surface weaves and natural vegetation span over a large range of scales, from turbulence and eddies at the vegetation stem scale to wave generation in vast inundated wetlands of hundreds of square miles under hurricane conditions. The study is focused on a phase-averaged energy-based model and phase-resolving Euler and Navier-Stokes (N-S) solvers with different representations of submerged vegetation. We will present recent advances in multi-scale modeling of wave attenuation by wetland vegetation. Numerical modeling results ranging from vegetation-resolved large eddy simulation under idealized conditions to incorporating vegetation-induced drag forces into conservation laws of momentum and energy for engineering applications will be shown. Effects of vegetation flexibility, turbulence closure, and various wave theories on the prediction of wave attenuation and the choice of vegetation drag coefficients will be discussed.

  20. Bubbles cause seismic wave attenuation: Laboratory measurements and numerical simulations

    NASA Astrophysics Data System (ADS)

    Tisato, Nicola; Quintal, Beatriz; Chapman, Samuel; Podladchikov, Yury; Grasselli, Giovanni; Burg, Jean-Pierre

    2015-04-01

    Seismic wave attenuation (1/Q) is a key to uncover the saturation and, in general, to improve the monitoring and surveying of subsurface domains. Nevertheless, how fluids that saturate rocks absorb elastic energy (i.e. cause 1/Q) is still poorly understood, studied and incorporated in geophysical methods. One of the invoked mechanisms, wave induced fluid flow (WIFF), is reputed to cause significant attenuation. This mechanism is governed by the flow of viscous fluids into a porous rock, and causes attenuation as a function of the fluid diffusivity [m2/s] and the pressure gradient [Pa/m], which is generated by the propagation of the elastic wave. However, some published, and newly acquired laboratory data-sets reporting 1/Q in almost fully saturated sandstones are difficult to explain with WIFF theories as they are frequency-dependent and have maximum of attenuation at frequencies

  1. Wave attenuation in thick graphite/epoxy composites

    NASA Technical Reports Server (NTRS)

    Mal, A. K.; Bar-Cohen, Y.

    1992-01-01

    The mechanics of wave attenuation in thick graphite/epoxy composites is examined in order to facilitate interpretation of the wave amplitudes recorded in ultrasonic experiments. The values of a small number of parameters are determined through comparison between calculated and measured waveforms for four specimens. The agreement between the measured and calculated waveforms are shown to be excellent in all four cases.

  2. Development of performance specifications for hybrid modeling of floating wind turbines in wave basin tests

    DOE PAGES

    Hall, Matthew; Goupee, Andrew; Jonkman, Jason

    2017-08-24

    Hybrid modeling—combining physical testing and numerical simulation in real time$-$opens new opportunities in floating wind turbine research. Wave basin testing is an important validation step for floating support structure design, but the conventional approaches that use physical wind above the basin are limited by scaling problems in the aerodynamics. Applying wind turbine loads with an actuation system that is controlled by a simulation responding to the basin test in real time offers a way to avoid scaling problems and reduce cost barriers for floating wind turbine design validation in realistic coupled wind and wave conditions. This paper demonstrates the developmentmore » of performance specifications for a system that couples a wave basin experiment with a wind turbine simulation. Two different points for the hybrid coupling are considered: the tower-base interface and the aero-rotor interface (the boundary between aerodynamics and the rotor structure). Analyzing simulations of three floating wind turbine designs across seven load cases reveals the motion and force requirements of the coupling system. By simulating errors in the hybrid coupling system, the sensitivity of the floating wind turbine response to coupling quality can be quantified. The sensitivity results can then be used to determine tolerances for motion tracking errors, force actuation errors, bandwidth limitations, and latency in the hybrid coupling system. These tolerances can guide the design of hybrid coupling systems to achieve desired levels of accuracy. An example demonstrates how the developed methods can be used to generate performance specifications for a system at 1:50 scale. Results show that sensitivities vary significantly between support structure designs and that coupling at the aero-rotor interface has less stringent requirements than those for coupling at the tower base. As a result, the methods and results presented here can inform design of future hybrid coupling

  3. Mathematical modelling of wave impact on floating breakwater

    NASA Astrophysics Data System (ADS)

    Ghani, Fadhlyya Arawaney Abdul; Shahridwan Ramli, Mohd; Noar, Nor Aida Zuraimi Md; Kasim, Abdul Rahman Mohd; Greenhow, Martin

    2017-09-01

    The impact of breaking wave on shoreline can be lessen or prevented by placing some kind of protection before the wave to reduce the speed of the wave before attacking the shoreline. Such protection can be in the form of a breakwater which is a structure designed to help reducing the wave intensity in whether in inshore waters or relatively shallow water. Thus, a mathematical model of Pressure Impulse, P is used to model the effect of waves exerted on a wall of a breakwater. A two-dimensional field of equations is derived for P which are applicable in three regions of breakwater problems by expressing this in terms of eigenfunctions that satisfy the boundary conditions apart from that the impact region and the matching of the three regions (before the breakwater, under the breakwater and after the breakwater). As in Cooker, we found that the equations of P in region 1 and region 3 are same as Cooker only that equation in region 3 has to include a secular term.

  4. Interaction of wave with a body floating on a wide polynya

    NASA Astrophysics Data System (ADS)

    Li, Z. F.; Shi, Y. Y.; Wu, G. X.

    2017-09-01

    A method based on wide spacing approximation is proposed for the interaction of water wave with a body floating on a polynya. The ice sheet is modelled as an elastic plate and fluid flow is described by the velocity potential theory. The solution procedure is constructed based on the assumption that when the distance between two disturbances to the free surface is sufficiently large, the interactions between them involve only the travelling waves caused by the disturbances and the effect of the evanescent waves is ignored. The solution for the problem can then be obtained from those for a floating body without an ice sheet and for an ice sheet/free surface without a floating body. Both latter solutions have already been found previously and therefore there will be no additional effort in solution once the wide spacing approximation formulation is derived. Extensive numerical results are provided to show that the method is very accurate compared with the exact solution. The obtained formulations are then used to provide some insightful explanations for the physics of flow behaviour, as well as the mechanism for the highly oscillatory features of the hydrodynamic force and body motion. Some explicit equations are derived to show zero reflection by the polynya and peaks and troughs of the force and excited body motion. It is revealed that some of the peaks of the body motion are due to resonance while others are due to the wave characters in the polynya.

  5. Experimental Investigation of the Power Generation Performance of Floating-Point Absorber Wave Energy Systems: Preprint

    SciTech Connect

    Li, Y.; Yu, Y.; Epler, J.; Previsic, M.

    2012-04-01

    The extraction of energy from ocean waves has gained interest in recent years. The floating-point absorber (FPA) is one of the most promising devices among a wide variety of wave energy conversion technologies. Early theoretical studies mainly focused on understanding the hydrodynamics of the system and on predicting the maximum power that could be extracted by a heaving body. These studies evolve from the investigation of floating-body interactions in offshore engineering and naval architecture disciplines. To our best knowledge, no systematic study has been reported about the investigation of the power generation performance of an FPA with a close-to-commercial design. A series of experimental tests was conducted to investigate the power extraction performance of an FPA system.

  6. Computation of Wave Loads under Multidirectional Sea States for Floating Offshore Wind Turbines: Preprint

    SciTech Connect

    Duarte, T.; Gueydon, S.; Jonkman, J.; Sarmento, A.

    2014-03-01

    This paper focuses on the analysis of a floating wind turbine under multidirectional wave loading. Special attention is given to the different methods used to synthesize the multidirectional sea state. This analysis includes the double-sum and single-sum methods, as well as an equal-energy discretization of the directional spectrum. These three methods are compared in detail, including the ergodicity of the solution obtained. From the analysis, the equal-energy method proved to be the most computationally efficient while still retaining the ergodicity of the solution. This method was chosen to be implemented in the numerical code FAST. Preliminary results on the influence of these wave loads on a floating wind turbine showed significant additional roll and sway motion of the platform.

  7. Wave attenuation by a model of vegetation in a flume

    NASA Astrophysics Data System (ADS)

    Chastel, Thibault; Durand, Nathalie

    2017-04-01

    The quantification of wave attenuation by vegetation is important for understanding shore protection and modeling coastal hydrodynamics. We investigate experimentally how different devices can modify the dynamics of irregular waves propagated in a flume. In particular we focus on a model of vegetation represented by flexible propylene stems with a modulus of elasticity E = 1200 MPa, a height l = 0.28 m and a diameter 2a = 0.025 m. The vegetation-like surface density is N = 720 stems/m2. The flume is 80 m long, 1.5 m wide and 1.2 m deep with 20 capacitance-type wave probes distributed over 20 meters. A flap type paddle generated waves using the JONSWAP spectrum. Experiments are for 500 wave cycles for water depth wd varying between 0.30 and 0.83 m and several significant wave heights Hs and wave periods Tp. We measure the wave height attenuation compared to flat-bed experiments and we apply a spectral analysis for post-processing. The loss of energy due to the stems is quantified and depends strongly on wave characteristics and geometrical parameters, in particular on the ratio l/wd. From these experiments we can estimate a drag coefficient CD by using a model of wave energy dissipation developed by Méndez and Losada (2004) which takes into account both wave and vegetation parameters.

  8. Scattering of flexural gravity waves at the boundaries between three floating sheets with applications

    NASA Astrophysics Data System (ADS)

    Williams, T. D.; Squire, V. A.

    2006-12-01

    A theoretical model is reported that describes wave propagation between three floating Euler Bernoulli thin elastic sheets extending, respectively, from -infty to 0, from 0 to l, and from l to infty, with properties, e.g. thickness, that can be specified independently. The sheets are assumed either to be welded together or to have free edges separating them. Two methods of solution are employed the Wiener Hopf technique and residue calculus, which allows the theoretical development to be verified at various points along the way. The model generalizes the considerable body of published work concerned with wave propagation into and out of floating ice sheets, and across features contained therein such as cracks, open or refrozen leads and embedded icebergs. It can also be applied to breakwaters, very large floating structures and vessels in a seaway. After validation, results are presented showing (a) the details of how the reflection coefficient depends on the geometry of the configuration being modelled; and (b) how a wave energy spectrum evolves as it propagates in a marginal ice zone composed of a large number of identical (coherent) or randomly specified (incoherent) sea-ice plates, as commonly observed in the polar or subpolar oceans.

  9. Attenuation of propagating spin wave induced by layered nanostructures

    NASA Astrophysics Data System (ADS)

    Sekiguchi, K.; Vader, T. N.; Yamada, K.; Fukami, S.; Ishiwata, N.; Seo, S. M.; Lee, S. W.; Lee, K. J.; Ono, T.

    2012-03-01

    Spin wave attenuation in the layered [FeNi/Pt]6/FeNi thin films was investigated by the time-domain electrical measurement. The spin-wave waveform was detected with an asymmetric coplanar strip transmission line, as an induced voltage flowing into a fast oscilloscope. We report that the amplitude of a spin-wave packet was systematically changed by controlling the thickness of a platinum layer, up to a maximum change of 50%. The virtues of spin wave, ultrafast propagation velocity and non-reciprocal emission, are preserved in this manner. This means that the Pt layer can manipulate an arbitral power-level of spin-wave input signal (reliable attenuator).

  10. Attenuation of Seismic Waves at Regional Distances

    DTIC Science & Technology

    1984-11-27

    States (SALMON, GASBUOG, RULISON and RIO BLANCA) and in the French Sahara ( SAPHIR and RUBIS). The hard-rook ITS calibration curve, when applied to these...so that two of the explosions, SAPHIR and RUBIS, had measure- able Lg-wave amplitudes. Figure 4 gives an example of Lg waves of SAPHIR recorded at...for RUBIS and SAPHIR . Station HLW is in Egypt, and SDB in Angola. Both shots were in granite. For the Nevada explosions SHOAL and PILEDRIVER, also in

  11. Guided wave attenuation in pipes buried in sand

    NASA Astrophysics Data System (ADS)

    Leinov, Eli; Cawley, Peter; Lowe, Michael JS

    2015-03-01

    Long-range ultrasonic guided wave testing of pipelines is used routinely for detection of corrosion defects in a variety of industries, e.g. petrochemical and energy. When the method is applied to pipelines that are buried in soil, test ranges tend to be significantly compromised compared to those achieved for pipelines above ground because of the attenuation of the guided wave, due to energy leaking into the embedding soil. The attenuation characteristics of guided wave propagation in a pipe buried in sand are investigated using a full scale experimental rig. The apparatus consists of an 8"-diameter, 6-meters long steel pipe embedded over 3 meters in a rectangular container filled with sand and fitted with an air-bladder for the application of overburden pressure. Measurements of the attenuation of the T(0,1) and L(0,2) guided wave modes over a range of sand conditions, including loose, compacted, water saturated and drained, are presented. Attenuation values are found to be in the range of 1-5.5 dB/m. The application of overburden pressure modifies the compaction of the sand and increases the attenuation. The attenuation decreases in the fully water-saturated sand, while it increases in drained sand to values comparable with those obtained for the compacted sand. The attenuation behavior of the torsional guided wave mode is found not to be captured by a uniform soil model; comparison with predictions obtained with the Disperse software suggest that this is likely to be due to a layer of sand adhering to the surface of the pipe.

  12. The anatomy of floating shock fitting. [shock waves computation for flow field

    NASA Technical Reports Server (NTRS)

    Salas, M. D.

    1975-01-01

    The floating shock fitting technique is examined. Second-order difference formulas are developed for the computation of discontinuities. A procedure is developed to compute mesh points that are crossed by discontinuities. The technique is applied to the calculation of internal two-dimensional flows with arbitrary number of shock waves and contact surfaces. A new procedure, based on the coalescence of characteristics, is developed to detect the formation of shock waves. Results are presented to validate and demonstrate the versatility of the technique.

  13. The anatomy of floating shock fitting. [shock waves computation for flow field

    NASA Technical Reports Server (NTRS)

    Salas, M. D.

    1975-01-01

    The floating shock fitting technique is examined. Second-order difference formulas are developed for the computation of discontinuities. A procedure is developed to compute mesh points that are crossed by discontinuities. The technique is applied to the calculation of internal two-dimensional flows with arbitrary number of shock waves and contact surfaces. A new procedure, based on the coalescence of characteristics, is developed to detect the formation of shock waves. Results are presented to validate and demonstrate the versatility of the technique.

  14. Model of attenuation of long waves under continuous ice layer

    NASA Astrophysics Data System (ADS)

    Kochanov, M. B.; Petrov, B. A.

    2017-01-01

    In this work new mathematical model of long wave propagation on water surface with ice cover is proposed. The model of thin elastic plate is used to describe ice layer movement. Equation for ice cover contain additional term to takes into account dissipation effects in the ice cover to explain wave attenuation. Proposed model was reduced to one nonlinear evolution equation for water level perturbation. The expression for wave energy was obtained under assumption of long waves. Proposed model is numerically studied, energy of system is computed. Obtained results are compared with results of suggested before model that takes into account the flow law of Glen.

  15. Attenuation measurements of ultrasonic P-wave and S-wave in partially frozen unconsolidated sands

    NASA Astrophysics Data System (ADS)

    Matsushima, J.; Suzuki, M.; Kato, Y.; Rokugawa, S.; Kato, A.

    2012-12-01

    Seismic attenuation which controls both the amplitude decay of seismic waves and the accompanying frequency change is a signature of the wave-rock interaction. Seismic attenuation in rocks is a highly variable parameter, which depends on the confining pressure, porosity, degree of fluid saturation, and fluid type. Although seismic attenuation has been widely used to estimate physical conditions and rock properties in various fields, the loss mechanisms responsible for seismic attenuation often are unclear and controversial. To elucidate a plausible mechanism for seismic attenuation, the joint use of both P- and S-waves will provide more helpful information because these two types of waves respond differently to fluid and solid combinations. We have conducted ultrasonic P- and S-wave transmission measurements to examine the influence of ice-brine coexisting system grown in the pore space of unconsolidated sands on ultrasonic P- and S-waves. We observed the variations of a transmitted wave with a frequency content of 100-1000 kHz , changing its temperature from 20°C to -15°C. We use not only impulse-type signals but also sweep-type signals to prevent from the spectral leakage effect caused by the effect of windowing. We concern with attenuation at ultrasonic frequencies of 500-1000 kHz for P-waves and 100-400 kHz for S-waves. Our observation of the variation of the Poisson's ratio and the ratio of P- to S-wave attenuation with changing temperature indicates the possibilities of the joint use of both P- and S-waves to elucidate a plausible mechanism for seismic attenuation.

  16. Analysis and Forecasting of Winds and Waves at Floating Type Wind Turbine Demonstration Site

    NASA Astrophysics Data System (ADS)

    Mase, Hajime; Yasuda, Tomohiro; Mori, Nobuhito; Tom, Tracey; Ikemoto, Ai; Utsunomiya, Tomoaki

    2013-04-01

    1. Introduction The floating type wind turbine demonstration project is being performed in Japan, and a 1:2 scale model was installed off the Kabashima Island in Nagasaki Prefecture on June 11th, 2012. As for the design, external forces such as wind and wave on the floating type wind turbine demonstration site were evaluated using various kinds of re-analysis and prediction data including NCEP wind data, JMA meteorological GPV data and NEDO data. Considerations for the design were given for wave characteristics of maximum and mean wave height, crest height, 2D height-period distribution, and wave energy spectrum. Tides, currents and winds were also evaluated. In addition the extreme wind speed was estimated including typhoon effects considering grid resolution dependence gust factor. A wind and wave prediction system was developed and its validity was examined by statistically comparing predicted values with measured data at the demonstration site. The present information system gives information for various user selected areas and lead times with both visual animations and time series graphs. 2. Design wave and wind The site is located off the Kabashima Island in Nagasaki Prefecture, Japan. Design forces were determined from extreme wind and wave statistics and an empirical method. The results are: 50 years return period wave and wind: Hs = 7.73 m, Ts = 14.0 s, U = 53.1 m/s 100 years return period wave and wind: Hs = 8.20 m, Ts = 14.3 m, U = 57.0 m/s Other characteristics were also determined, such as the maximum wave height, crest height, 2D height-period distribution and wave energy spectrum, tide, current and maximum wind. 3. Wind and wave prediction system The system composed of NCEP GFS (Global Forecasting System) meteorological data, down-scaling wind field by WRF (Weather Research Forecasting), JMA HAGPV (Hourly Analyzed Grid Point Value) 10m wind data, and wind-wave forecast data by SWAN (Simulating Waves Nearshore). The flowchart shown in Fig. 1 displays

  17. Parametric study of two-body floating-point wave absorber

    NASA Astrophysics Data System (ADS)

    Amiri, Atena; Panahi, Roozbeh; Radfar, Soheil

    2016-03-01

    In this paper, we present a comprehensive numerical simulation of a point wave absorber in deep water. Analyses are performed in both the frequency and time domains. The converter is a two-body floating-point absorber (FPA) with one degree of freedom in the heave direction. Its two parts are connected by a linear mass-spring-damper system. The commercial ANSYS-AQWA software used in this study performs well in considering validations. The velocity potential is obtained by assuming incompressible and irrotational flow. As such, we investigated the effects of wave characteristics on energy conversion and device efficiency, including wave height and wave period, as well as the device diameter, draft, geometry, and damping coefficient. To validate the model, we compared our numerical results with those from similar experiments. Our study results can clearly help to maximize the converter's efficiency when considering specific conditions.

  18. Wave speed propagation measurements on highly attenuative heated materials

    SciTech Connect

    Moore, David G.; Ober, Curtis C.; Rodacy, Phil J.; Nelson, Ciji L.

    2015-09-19

    Ultrasonic wave propagation decreases as a material is heated. Two factors that can characterize material properties are changes in wave speed and energy loss from interactions within the media. Relatively small variations in velocity and attenuation can detect significant differences in microstructures. This paper discusses an overview of experimental techniques that document the changes within a highly attenuative material as it is either being heated or cooled from 25°C to 90°C. The experimental set-up utilizes ultrasonic probes in a through-transmission configuration. The waveforms are recorded and analyzed during thermal experiments. To complement the ultrasonic data, a Discontinuous-Galerkin Model (DGM) was also created which uses unstructured meshes and documents how waves travel in these anisotropic media. This numerical method solves particle motion travel using partial differential equations and outputs a wave trace per unit time. As a result, both experimental and analytical data are compared and presented.

  19. Attenuation of coda waves in northern Greece

    NASA Astrophysics Data System (ADS)

    Hatzidimitriou, P. M.

    1993-03-01

    The single scattering model has been applied for the estimation of coda Q values for local earthquakes that occurred in northern Greece during the period 1983 1989 and recorded by the telemetered network of the Geophysical Laboratory of the University of Thessaloniki. Coda Q estimations were made for four frequency bands centered at 1.5 Hz, 3.0 Hz, 6.0 Hz and 12.0 Hz and for the lapse time windows 10 20 sec, 15 30 sec, 20 45 sec, 30 60 sec and 50 100 sec. The coda Q values obtained show a clear frequency dependence of the form Q c =Q 0 f n , while Q 0 and n depend on the lapse time window. Q 0 was found equal to 33 and n equal to 1.01 for the time window of 10 to 20 sec, while for the other windows Q 0 increased from 60 to 129, with n being stable, close to 0.75. This lapse time dependence is interpreted as due to a depth dependent attenuation. The high attenuation and the strong frequency dependence found are characteristic of an area with high seismicity, in agreement with studies in other seismic regions.

  20. Fault-zone attenuation of high-frequency seismic waves

    NASA Astrophysics Data System (ADS)

    Blakeslee, Sam; Malin, Peter; Alvarez, Marcos

    1989-11-01

    We have developed a technique to measure seismic attenuation within an active fault-zone at seismogenic depths. Utilizing a pair of stations and pairs of earthquakes, spectral ratios are performed to isolate attenuation produced by wave-propagation within the fault-zone. This empirical approach eliminates common source, propagation, instrument and near-surface site effects. The technique was applied to a cluster of 19 earthquakes recorded by a pair of downhole instruments located within the San Andreas fault-zone, at Parkfield California. Over the 1-40 Hz bandwidth used in this analysis, amplitudes are found to decrease exponentially with frequency. Furthermore, the fault-zone propagation distance correlates with the severity of attenuation. Assuming a constant Q attenuation operator, the S-wave quality factor within the fault-zone at a depth of 5-6 kilometers is 31 (+7,-5). If fault-zones are low-Q environments, then near-source attenuation of high-frequency seismic waves may help to explain phenomenon such as fmax. Fault-zone Q may prove to be a valuable indicator of the mechanical behavior and rheology of fault-zones. Specific asperities can be monitored for precursory changes associated with the evolving stress-field within the fault-zone. The spatial and temporal resolution of the technique is fundamentally limited by the uncertainty in earthquake location and the interval time between earthquakes.

  1. Stress wave attenuation in shock-damaged rock

    NASA Astrophysics Data System (ADS)

    Liu, Cangli; Ahrens, Thomas J.

    1997-03-01

    The velocity and attenuation of ultrasonic stress waves in gabbroic rock samples (San Marcos, California) subjected to shock loading in the 2 GPa range were studied. Prom P wave velocity measurements we determined the damage parameter Dp and crack density ɛ of the samples and related these to the attenuation coefficient (quality factor) under dynamic strains of 2×10-7 and at a frequency of 2 MHz using the ultrasonic pulse-echo method. A fit to the data yields the P wave spatial attenuation coefficient at a frequency of 2 MHz, αp(Dp) = 1.1 + 28.2DP (decibels per centimeter). From the relation between the attenuation coefficient and quality factor, the quality factor Q is given by Q-1 = 0.011(1 + 25.6Dp)(1 - Dp)½. Using O'Connell-Budiansky theory relating crack density to velocity, the parameter in Walsh's theory was determined based on experimental data. An approximate method is also proposed to estimate the average half-length of cracks based on the attenuation measurements.

  2. Shear Wave Attenuation in Unconsolidated Laboratory Sediments.

    DTIC Science & Technology

    1983-06-01

    pressure) exponent of one-fourth for prediction of shear wave velocities in sands. This recommendation is based upon both in situ and laboratory...measurements. However, as we have seen from the data presented, there is consider- able scatter in the pressure exponent with values varying from...standard deviation of 0.98. Hamilton 5 4 takes % . -. ... .... . ...... .. ............ ...... 21 exception to this frequency exponent , pointing out

  3. Radiation and attenuation of waves in a random medium

    NASA Technical Reports Server (NTRS)

    Wenzel, A. R.

    1982-01-01

    The physical mechanisms of excess attenuation are analyzed on the basis of a one-dimensional time-independent model of propagation in a random medium. Attenuation is regarded as the rate of decrease in the mean intensity and the mean energy flux within a propagation range. A source function is assumed to be determinate, appropriate statistical properties are chosen for the sound speed, and specified statistical properties are found for the wave functions, i.e., the mean intensity and the mean energy flux. The medium is considered to be weakly homogeneous, and expansions are developed for the intensity and mean energy flux, along with an attenuation coefficient in two parts, the second of which defines the excess attenuation. The mean radiated power is defined, and backscattering by the random inhomogeneities in the medium is modeled as redistributing the mean intensity and energy flux, with a resultant decay which occurs more quickly than with randomness.

  4. Bubbles attenuate elastic waves at seismic frequencies: First experimental evidence

    NASA Astrophysics Data System (ADS)

    Tisato, Nicola; Quintal, Beatriz; Chapman, Samuel; Podladchikov, Yury; Burg, Jean-Pierre

    2015-05-01

    The migration of gases from deep to shallow reservoirs can cause damageable events. For instance, some gases can pollute the biosphere or trigger explosions and eruptions. Seismic tomography may be employed to map the accumulation of subsurface bubble-bearing fluids to help mitigating such hazards. Nevertheless, how gas bubbles modify seismic waves is still unclear. We show that saturated rocks strongly attenuate seismic waves when gas bubbles occupy part of the pore space. Laboratory measurements of elastic wave attenuation at frequencies <100 Hz are modeled with a dynamic gas dissolution theory demonstrating that the observed frequency-dependent attenuation is caused by wave-induced-gas-exsolution-dissolution (WIGED). This result is incorporated into a numerical model simulating the propagation of seismic waves in a subsurface domain containing CO2-gas bubbles. This simulation shows that WIGED can significantly modify the wavefield and illustrates how accounting for this physical mechanism can potentially improve the monitoring and surveying of gas bubble-bearing fluids in the subsurface.

  5. Attenuation of 7 GHz surface acoustic waves on silicon

    NASA Astrophysics Data System (ADS)

    Li, Dongyao; Cahill, David G.

    2016-09-01

    We measured the attenuation of GHz frequency surface acoustic waves (SAWs) on the Si (001) surface using an optical pump-probe technique at temperatures between 300 and 600 K. SAWs are generated and detected by a 700 nm Al grating fabricated by nanoimprint lithography. The grating for SAW generation is separated from the grating for SAW detection by ≈150 μ m . The amplitude of SAWs is attenuated by coupling to bulk waves created by the Al grating, diffraction due to the finite size of the source, and the intrinsic relaxational Akhiezer damping of elastic waves in Si. Thermal phonon relaxation time and Grüneisen parameters are fitted using temperature-dependent measurement. The f Q product of a hypothetical micromechanical oscillator limited by Akhiezer damping at this frequency is ˜3 ×1013 Hz.

  6. Body Wave Crustal Attenuation Characteristics in the Garhwal Himalaya, India

    NASA Astrophysics Data System (ADS)

    Negi, Sanjay S.; Paul, Ajay; Joshi, Anand; Kamal

    2015-06-01

    We estimate frequency-dependent attenuation of P and S waves in Garhwal Himalaya using the extended coda normalization method for the central frequencies 1.5, 2, 3, 4, 6, 8, 10, 12, and 16 Hz, with earthquake hypocentral distance ranging from 27 to 200 km. Forty well-located local earthquake waveforms were used to study the seismic attenuation characteristics of the Garhwal Himalaya, India, as recorded by eight stations operated by Wadia Institute of Himalayan Geology, Dehradun, India, from 2007 to 2012. We find frequency-dependent P and S wave quality factors as defined by the relations Q P = 56 ± 8 f 0.91±0.002 and Q S = 151 ± 8 f 0.84±0.002 by fitting a power-law frequency dependence model for the estimated values over the whole region. Both the Q P and Q S values indicate strong attenuation in the crust of Garhwal Himalaya. The ratio of Q S/ Q P > 1 obtained for the entire analyzed frequency range suggests that the scattering loss is due to a random and high degree of heterogeneities in the earth medium, playing an important role in seismic wave attenuation in the Himalayan crust.

  7. Attenuation of seismic waves obtained by coda waves analysis in the West Bohemia earthquake swarm region

    NASA Astrophysics Data System (ADS)

    Bachura, Martin; Fischer, Tomas

    2014-05-01

    Seismic waves are attenuated by number of factors, including geometrical spreading, scattering on heterogeneities and intrinsic loss due the anelasticity of medium. Contribution of the latter two processes can be derived from the tail part of the seismogram - coda (strictly speaking S-wave coda), as these factors influence the shape and amplitudes of coda. Numerous methods have been developed for estimation of attenuation properties from the decay rate of coda amplitudes. Most of them work with the S-wave coda, some are designed for the P-wave coda (only on teleseismic distances) or for the whole waveforms. We used methods to estimate the 1/Qc - attenuation of coda waves, methods to separate scattering and intrinsic loss - 1/Qsc, Qi and methods to estimate attenuation of direct P and S wave - 1/Qp, 1/Qs. In this study, we analyzed the S-wave coda of local earthquake data recorded in the West Bohemia/Vogtland area. This region is well known thanks to the repeated occurrence of earthquake swarms. We worked with data from the 2011 earthquake swarm, which started late August and lasted with decreasing intensity for another 4 months. During the first week of swarm thousands of events were detected with maximum magnitudes ML = 3.6. Amount of high quality data (including continuous datasets and catalogues with an abundance of well-located events) is available due to installation of WEBNET seismic network (13 permanent and 9 temporary stations) monitoring seismic activity in the area. Results of the single-scattering model show seismic attenuations decreasing with frequency, what is in agreement with observations worldwide. We also found decrease of attenuation with increasing hypocentral distance and increasing lapse time, which was interpreted as a decrease of attenuation with depth (coda waves on later lapse times are generated in bigger depths - in our case in upper lithosphere, where attenuations are small). We also noticed a decrease of frequency dependence of 1/Qc

  8. Elimination of cavitation-related attenuation in shock wave lithotripsy

    NASA Astrophysics Data System (ADS)

    Sankin, G. N.; Lautz, J. M.; Simmons, W. N.; Zhong, P.; Frank, S. T.; Szeri, A. J.

    2017-03-01

    In shock wave lithotripsy (SWL), acoustic pulses with a leading compression wave followed by a tensile wave are delivered into the patient's body using a water-filled coupling cushion. Cavitation-related acoustic energy loss in the coupling unit depends critically on water conditions, e.g. dissolved gas concentration and exchange flow rate. We have systematically investigated the attenuation mechanism in the coupling water via pressure measurements and cavitation characterization. In non-degassed water the bubble cluster became progressively dense (i.e., proliferated because of gas diffusion into bubbles and splitting of bubbles into many daughter bubbles) in shock waves delivered at 1 Hz leading to reduction in the tensile wave duration from a nominal value of 4.6 to 1.8 µs. To reduce cavitation in the coupling water along the beam path, we have used a continuous jet flow to remove residual daughter bubbles between consecutive shocks. As a result, stone fragmentation efficiency was increased from 16±4% to 30±5% (p = 0.002) after 250 shocks. Such a hydrodynamic approach for tensile wave attenuation in the coupling water may be used to provide a flexible means for a novel treatment strategy with tissue protection.

  9. Wave attenuation in the shallows of San Francisco Bay

    USGS Publications Warehouse

    Lacy, Jessica R.; MacVean, Lissa J.

    2016-01-01

    Waves propagating over broad, gently-sloped shallows decrease in height due to frictional dissipation at the bed. We quantified wave-height evolution across 7 km of mudflat in San Pablo Bay (northern San Francisco Bay), an environment where tidal mixing prevents the formation of fluid mud. Wave height was measured along a cross shore transect (elevation range−2mto+0.45mMLLW) in winter 2011 and summer 2012. Wave height decreased more than 50% across the transect. The exponential decay coefficient λ was inversely related to depth squared (λ=6×10−4h−2). The physical roughness length scale kb, estimated from near-bed turbulence measurements, was 3.5×10−3 m in winter and 1.1×10−2 m in summer. Estimated wave friction factor fw determined from wave-height data suggests that bottom friction dominates dissipation at high Rew but not at low Rew. Predictions of near-shore wave height based on offshore wave height and a rough formulation for fw were quite accurate, with errors about half as great as those based on the smooth formulation for fw. Researchers often assume that the wave boundary layer is smooth for settings with fine-grained sediments. At this site, use of a smooth fw results in an underestimate of wave shear stress by a factor of 2 for typical waves and as much as 5 for more energetic waves. It also inadequately captures the effectiveness of the mudflats in protecting the shoreline through wave attenuation.

  10. A disorder-based strategy for tunable, broadband wave attenuation

    NASA Astrophysics Data System (ADS)

    Zhang, Weiting; Celli, Paolo; Cardella, Davide; Gonella, Stefano

    2017-04-01

    One of the most daunting limitations of phononic crystals and acoustic/elastic metamaterials is their passivity: a given configuration is bound to display its phononic properties only around its design point, i.e., working at some pre-determined operating conditions. In the past decade, this shortcoming has inspired the design of phononic media with tunable wave characteristics; noteworthy results have been obtained through a family of methodologies involving shunted piezoelectric elements. Shunting a piezoelectric element means connecting it to a passive electric circuit; tunability stems from the ability to modify the effective mechanical properties of the piezoelectric medium by modifying the circuit characteristics. One of the most popular shunting circuits is the resistor-inductor, which allows the patch-and-shunt system to behave as an electromechanical resonator. A common motif among the works employing shunted piezos for phononic control is periodicity: the patches are typically periodically placed in the domain and the circuits are identically tuned. The objective of this work is to demonstrate that the wave attenuation performance of structures with shunted piezoelectric patches can be improved by leveraging notions of organized disorder. Based on the idea of rainbow trapping broadband wave attenuation obtained by tuning an array of resonators at distinct neighboring frequencies we design and test an electromechanical waveguide structure capable of attenuating waves over broad frequency ranges. In order to emphasize the fact that periodicity is not a binding requirement when working with RL shunts (which induce locally resonant bandgaps), we report on the performance of random arrangements of patches. In an attempt to demonstrate the tunability attribute of our strategy, we take advantage of the reconfigurability of the circuits to show how a single waveguide can attenuate both waves and vibrations over different frequency ranges.

  11. On the concept of sloped motion for free-floating wave energy converters

    PubMed Central

    Payne, Grégory S.; Pascal, Rémy; Vaillant, Guillaume

    2015-01-01

    A free-floating wave energy converter (WEC) concept whose power take-off (PTO) system reacts against water inertia is investigated herein. The main focus is the impact of inclining the PTO direction on the system performance. The study is based on a numerical model whose formulation is first derived in detail. Hydrodynamics coefficients are obtained using the linear boundary element method package WAMIT. Verification of the model is provided prior to its use for a PTO parametric study and a multi-objective optimization based on a multi-linear regression method. It is found that inclining the direction of the PTO at around 50° to the vertical is highly beneficial for the WEC performance in that it provides a high capture width ratio over a broad region of the wave period range. PMID:26543397

  12. On the concept of sloped motion for free-floating wave energy converters.

    PubMed

    Payne, Grégory S; Pascal, Rémy; Vaillant, Guillaume

    2015-10-08

    A free-floating wave energy converter (WEC) concept whose power take-off (PTO) system reacts against water inertia is investigated herein. The main focus is the impact of inclining the PTO direction on the system performance. The study is based on a numerical model whose formulation is first derived in detail. Hydrodynamics coefficients are obtained using the linear boundary element method package WAMIT. Verification of the model is provided prior to its use for a PTO parametric study and a multi-objective optimization based on a multi-linear regression method. It is found that inclining the direction of the PTO at around 50° to the vertical is highly beneficial for the WEC performance in that it provides a high capture width ratio over a broad region of the wave period range.

  13. Attenuation of the detonation wave in hydrogen-air mixture

    NASA Astrophysics Data System (ADS)

    Bivol, G. Yu; Golovastov, S. V.; Golub, V. V.

    2016-11-01

    The deceleration and attenuation of a detonation wave in hydrogen-air mixture was experimentally studied in a cylindrical channel. Inner walls of the wide section of the channel were covered with an acoustically absorbing layer. Experiments were carried out in hydrogen-air mixture at atmospheric pressure. Initially detonation was formed as a result of a deflagration to detonation transition. The dependence of velocity and pressure at the front of the detonation or shock wave on the thickness of the acoustically absorbing material and mixture composition (equivalence ratio) was presented. The results demonstrate that increasing the thickness of the porous material on the walls lead to further attenuation of the detonation wave to the point where it is not re-initiated at the distance of 15 calibers from the porous section. It was found that the recovery of the detonation wave after the passage of the acoustically absorbing section can happen if the shock wave velocity does not drop below Chapman-Jouguet acoustic velocity.

  14. Surface Wave Attenuation in the Tibetan Plateau from Ambient Noise

    DTIC Science & Technology

    2015-08-31

    is unlimited. 16 DISTRIBUTION LIST DTIC/OCP 8725 John J. Kingman Rd, Suite 0944 Ft Belvoir, VA 22060-6218 1 cy AFRL /RVIL Kirtland AFB, NM... AFRL -RV-PS- TR-2015-0150 AFRL -RV-PS- TR-2015-0150 SURFACE WAVE ATTENUATION IN THE TIBETAN PLATEAU FROM AMBIENT NOISE University of Illinois at...DISTRIBUTION IS UNLIMITED. AIR FORCE RESEARCH LABORATORY Space Vehicles Directorate 3550 Aberdeen Ave SE AIR FORCE MATERIEL COMMAND KIRTLAND AIR

  15. Theory of the synchronous motion of an array of floating flap gates oscillating wave surge converter

    NASA Astrophysics Data System (ADS)

    Michele, Simone; Sammarco, Paolo; d'Errico, Michele

    2016-08-01

    We consider a finite array of floating flap gates oscillating wave surge converter (OWSC) in water of constant depth. The diffraction and radiation potentials are solved in terms of elliptical coordinates and Mathieu functions. Generated power and capture width ratio of a single gate excited by incoming waves are given in terms of the radiated wave amplitude in the far field. Similar to the case of axially symmetric absorbers, the maximum power extracted is shown to be directly proportional to the incident wave characteristics: energy flux, angle of incidence and wavelength. Accordingly, the capture width ratio is directly proportional to the wavelength, thus giving a design estimate of the maximum efficiency of the system. We then compare the array and the single gate in terms of energy production. For regular waves, we show that excitation of the out-of-phase natural modes of the array increases the power output, while in the case of random seas we show that the array and the single gate achieve the same efficiency.

  16. Attenuation of shock waves in copper and stainless steel

    SciTech Connect

    Harvey, W.B.

    1986-06-01

    By using shock pins, data were gathered on the trajectories of shock waves in stainless steel (SS-304L) and oxygen-free-high-conductivity copper (OFHC-Cu). Shock pressures were generated in these materials by impacting the appropriate target with thin (approx.1.5 mm) flying plates. The flying plates in these experiments were accelerated to high velocities (approx.4 km/s) by high explosives. Six experiments were conducted, three using SS-304L as the target material and three experiments using OFHC-Cu as the target material. Peak shock pressures generated in the steel experiments were approximately 109, 130, and 147 GPa and in the copper experiments, the peak shock pressures were approximately 111, 132, and 143 GPa. In each experiment, an attenuation of the shock wave by a following release wave was clearly observed. An extensive effort using two characteristic codes (described in this work) to theoretically calculate the attenuation of the shock waves was made. The efficacy of several different constitutive equations to successfully model the experiments was studied by comparing the calculated shock trajectories to the experimental data. Based on such comparisons, the conclusion can be drawn that OFHC-Cu enters a melt phase at about 130 GPa on the principal Hugoniot. There was no sign of phase changes in the stainless-steel experiments. In order to match the observed attenuation of the shock waves in the SS-304L experiments, it was necessary to include strength effects in the calculations. It was found that the values for the parameters in the strength equations were dependent on the equation of state used in the modeling of the experiments. 66 refs., 194 figs., 77 tabs.

  17. Guided wave attenuation in coated pipes buried in sand

    NASA Astrophysics Data System (ADS)

    Leinov, Eli; Cawley, Peter; Lowe, Michael J. S.

    2016-02-01

    Long-range guided wave testing (GWT) is routinely used for the monitoring and detection of corrosion defects in above ground pipelines in various industries. The GWT test range in buried, coated pipelines is greatly reduced compared to aboveground pipelines due to energy leakage into the embedding soil. In this study, we aim to increase test ranges for buried pipelines. The effect of pipe coatings on the T(0,1) and L(0,2) guided wave attenuation is investigated using a full-scale experimental apparatus and model predictions. Tests are performed on a fusion-bonded epoxy (FBE)-coated 8" pipe, buried in loose and compacted sand over a frequency range of 10-35 kHz. The application of a low impedance coating is shown to effectively decouple the influence of the sand on the ultrasound leakage from the buried pipe. We demonstrate ultrasonic isolation of a buried pipe by coating the pipe with a Polyethylene (PE)-foam layer that has a smaller impedance than both pipe and sand and the ability to withstand the overburden load from the sand. The measured attenuation in the buried PE-foam-FBE-coated pipe is substantially reduced, in the range of 0.3-1.2 dBm-1 for loose and compacted sand conditions, compared to buried FBE-coated pipe without the PE-foam, where the measured attenuation is in the range of 1.7-4.7 dBm-1. The acoustic properties of the PE-foam are measured independently using ultrasonic interferometry technique and used in model predictions of guided wave propagation in a buried coated pipe. Good agreement is found between the attenuation measurements and model predictions. The attenuation exhibits periodic peaks in the frequency domain corresponding to the through-thickness resonance frequencies of the coating layer. The large reduction in guided wave attenuation for PE-coated pipes would lead to greatly increased GWT test ranges, so such coatings would be attractive for new pipeline installations.

  18. Lg-wave attenuation in the Australian crust

    NASA Astrophysics Data System (ADS)

    Wei, Zhi; Kennett, Brian L. N.; Zhao, Lian-Feng

    2017-10-01

    We estimate the Lg-wave quality factor (Q) across the Australian continent from vertical-component Lg waveforms. A tomographic inversion is performed to construct an Lg attenuation model for 58 frequencies between 0.05 and 10.0 Hz. The available spatial resolution is approximately 1.5° × 1.5° for the 0.5-2.0 Hz band. At 1.0 Hz, the Lg-wave Q over the whole island continent varies from 50 to 1250 with an average value of 850. Significant regional variations in the Lg-wave Q images tie well with many geological features and boundaries in Australia. The cratons in western, northern and southern parts of Australia usually have higher Q values (700-1250), while the volcanic regions, sedimentary basins and orogenic areas in eastern Australia are characterized by increased attenuation (lower Q values, 50-650). We determine the frequency-dependent Q of Lg waves for different blocks across Australia, and find the frequency dependence of Q is much more complex than the traditional single power law representation. When combined with the assumed geometrical spreading relation, the Lg Q maps provide a new way of assessing potential ground motion across the continent for any event location.

  19. Observation and parametrization of wave attenuation through the MIZ

    NASA Astrophysics Data System (ADS)

    Ardhuin, F.; Stopa, J.; Dumont, D.; Sévigny, C.; Collard, F.; Boutin, G.

    2016-02-01

    Swell evolution from the open ocean into sea ice is poorly understood, in particular the amplitude attenuation expected from scattering and dissipation. New synthetic aperture radar (SAR) data from Sentinel-1 wave mode reveal intriguing patterns of bright oscillating lines shaped like instant noodles. We investigate cases in which the oscillations are in the azimuth direction, around a straight line in the range direction. This observation is interpreted as the distortion by the SAR processing of crests from a first swell, due to the presence of a second swell. Since deviations from a straight line should be proportional to the orbital velocity towards the satellite, swell height can be estimated. The intensity of the backscatter modulation with a single swell can also be used to retrieve swell height as it is found that the constructive velocity bunching is very sensitive to wave height. Using a novel algorithm to invert the wave directional spectrum, we investigate several cases of attenuation in the Arctic and southern ocean. On this basis we have adjusted an empirical wave-ice dissipation source term in the WAVEWATCH III model.

  20. Wave speed propagation measurements on highly attenuative heated materials

    DOE PAGES

    Moore, David G.; Ober, Curtis C.; Rodacy, Phil J.; ...

    2015-09-19

    Ultrasonic wave propagation decreases as a material is heated. Two factors that can characterize material properties are changes in wave speed and energy loss from interactions within the media. Relatively small variations in velocity and attenuation can detect significant differences in microstructures. This paper discusses an overview of experimental techniques that document the changes within a highly attenuative material as it is either being heated or cooled from 25°C to 90°C. The experimental set-up utilizes ultrasonic probes in a through-transmission configuration. The waveforms are recorded and analyzed during thermal experiments. To complement the ultrasonic data, a Discontinuous-Galerkin Model (DGM) wasmore » also created which uses unstructured meshes and documents how waves travel in these anisotropic media. This numerical method solves particle motion travel using partial differential equations and outputs a wave trace per unit time. As a result, both experimental and analytical data are compared and presented.« less

  1. A heterogeneous nonlinear attenuating full-wave model of ultrasound.

    PubMed

    Pinton, Gianmarco F; Dahl, Jeremy; Rosenzweig, Stephen; Trahey, Gregg E

    2009-03-01

    A full-wave equation that describes nonlinear propagation in a heterogeneous attenuating medium is solved numerically with finite differences in the time domain (FDTD). Three-dimensional solutions of the equation are verified with water tank measurements of a commercial diagnostic ultrasound transducer and are shown to be in excellent agreement in terms of the fundamental and harmonic acoustic fields and the power spectrum at the focus. The linear and nonlinear components of the algorithm are also verified independently. In the linear nonattenuating regime solutions match results from Field II, a well established software package used in transducer modeling, to within 0.3 dB. Nonlinear plane wave propagation is shown to closely match results from the Galerkin method up to 4 times the fundamental frequency. In addition to thermoviscous attenuation we present a numerical solution of the relaxation attenuation laws that allows modeling of arbitrary frequency dependent attenuation, such as that observed in tissue. A perfectly matched layer (PML) is implemented at the boundaries with a numerical implementation that allows the PML to be used with high-order discretizations. A -78 dB reduction in the reflected amplitude is demonstrated. The numerical algorithm is used to simulate a diagnostic ultrasound pulse propagating through a histologically measured representation of human abdominal wall with spatial variation in the speed of sound, attenuation, nonlinearity, and density. An ultrasound image is created in silico using the same physical and algorithmic process used in an ultrasound scanner: a series of pulses are transmitted through heterogeneous scattering tissue and the received echoes are used in a delay-and-sum beam-forming algorithm to generate a images. The resulting harmonic image exhibits characteristic improvement in lesion boundary definition and contrast when compared with the fundamental image. We demonstrate a mechanism of harmonic image quality

  2. A Heterogeneous Nonlinear Attenuating Full-Wave Model of Ultrasound

    PubMed Central

    Pinton, Gianmarco F.; Dahl, Jeremy; Rosenzweig, Stephen; Trahey, Gregg E.

    2015-01-01

    A full-wave equation that describes nonlinear propagation in a heterogeneous attenuating medium is solved numerically with finite differences in the time domain (FDTD). Three-dimensional solutions of the equation are verified with water tank measurements of a commercial diagnostic ultrasound transducer and are shown to be in excellent agreement in terms of the fundamental and harmonic acoustic fields and the power spectrum at the focus. The linear and nonlinear components of the algorithm are also verified independently. In the linear nonattenuating regime solutions match results from Field II, a well established software package used in transducer modeling, to within 0.3 dB. Nonlinear plane wave propagation is shown to closely match results from the Galerkin method up to 4 times the fundamental frequency. In addition to thermoviscous attenuation we present a numerical solution of the relaxation attenuation laws that allows modeling of arbitrary frequency dependent attenuation, such as that observed in tissue. A perfectly matched layer (PML) is implemented at the boundaries with a numerical implementation that allows the PML to be used with high-order discretizations. A −78 dB reduction in the reflected amplitude is demonstrated. The numerical algorithm is used to simulate a diagnostic ultrasound pulse propagating through a histologically measured representation of human abdominal wall with spatial variation in the speed of sound, attenuation, nonlinearity, and density. An ultrasound image is created in silico using the same physical and algorithmic process used in an ultrasound scanner: a series of pulses are transmitted through heterogeneous scattering tissue and the received echoes are used in a delay-and-sum beam-forming algorithm to generate a images. The resulting harmonic image exhibits characteristic improvement in lesion boundary definition and contrast when compared with the fundamental image. We demonstrate a mechanism of harmonic image quality

  3. Attenuation characteristics of nonlinear pressure waves propagating in pipes

    NASA Technical Reports Server (NTRS)

    Shih, C. C.

    1974-01-01

    A series of experiments was conducted to investigate temporal and spatial velocity distributions of fluid flow in 3-in. open-end pipes of various lengths up to 210 ft, produced by the propagation of nonlinear pressure waves of various intensities. Velocity profiles across each of five sections along the pipes were measured as a function of time with the use of hot-film and hot-wire anemometers for two pressure waves produced by a piston. Peculiar configurations of the velocity profiles across the pipe section were noted, which are uncommon for steady pipe flow. Theoretical consideration was given to this phenomenon of higher velocity near the pipe wall for qualitative confirmation. Experimentally time-dependent velocity distributions along the pipe axis were compared with one-dimensional theoretical results obtained by the method of characteristics with or without diffusion term for the purpose of determining the attenuation characteristics of the nonlinear wave propagation in the pipes.

  4. Quantifying Wave Attenuation due to Salt Marshes with a Phase-Averaged Wave Model

    NASA Astrophysics Data System (ADS)

    Marsooli, R.; Orton, P. M.; Blumberg, A. F.; Georgas, N.

    2016-12-01

    This study uses a mixture of laboratory validation, real-world site/scenario modeling, and data on seasonal variation in salt marsh characteristics to quantify their capacity to mitigate storm waves. We assess the accuracy of four existing empirical formulas to determine the vegetation drag coefficient and, in turn, vegetation-induced wave attenuation. We adopt these formulas in the phase-averaged wave model of Mellor et al. (2008), MDO hereafter, which is improved in the present study to simulate wave energy dissipation due to vegetation drag force. One attribute of MDO is speed, due to parameterized energy in frequency space, and as a result the model may be preferable for hazard assessments and ensemble forecasting. We evaluate the performance of the improved MDO wave model and the empirical drag formulas using existing laboratory data. Comparisons between the model results and measurements show that the model based on the drag formula of Kobayashi et al. (1993) performs better than other models. We further apply MDO based on this formula to Jamaica Bay, the largest natural open space left in New York City, to quantify the influence of estuarine-scale salt marshes on storm waves. The model results show that the vegetation in summer season, when Spartina alterniflora is at its maximum height, is more effective to reduce wave height than in fall season. Moreover, the influence of the Spartina on wave height is more pronounced during a severe storm than a moderate storm. This is because the smaller water depth during a moderate storm causes intense depth-induced wave breaking over shallow marsh islands and thus the contribution of vegetation drag to wave attenuation becomes negligible. On the other hand, during a severe storm with high water elevation, the depth-induced breaking is small and vegetation-induced drag becomes the primary source of wave attenuation.

  5. Propagation characteristics of dust-acoustic waves in presence of a floating cylindrical object in the DC discharge plasma

    NASA Astrophysics Data System (ADS)

    Choudhary, Mangilal; Mukherjee, S.; Bandyopadhyay, P.

    2016-08-01

    The experimental observation of the self-excited dust acoustic waves (DAWs) and its propagation characteristics in the absence and presence of a floating cylindrical object is investigated. The experiments are carried out in a direct current (DC) glow discharge dusty plasma in a background of argon gas. Dust particles are found levitated at the interface of plasma and cathode sheath region. The DAWs are spontaneously excited in the dust medium and found to propagate in the direction of ion drift (along the gravity) above a threshold discharge current at low pressure. Excitation of such a low frequency wave is a result of the ion-dust streaming instability in the dust cloud. Characteristics of the propagating dust acoustic wave get modified in the presence of a floating cylindrical object of radius larger than that of the dust Debye length. Instead of propagation in the vertical direction, the DAWs are found to propagate obliquely in the presence of the floating object (kept either vertically or horizontally). In addition, a horizontally aligned floating object forms a wave structure in the cone shaped dust cloud in the sheath region. Such changes in the propagation characteristics of DAWs are explained on the basis of modified potential (or electric field) distribution, which is a consequence of coupling of sheaths formed around the cylindrical object and the cathode.

  6. Propagation characteristics of dust–acoustic waves in presence of a floating cylindrical object in the DC discharge plasma

    SciTech Connect

    Choudhary, Mangilal; Mukherjee, S.; Bandyopadhyay, P.

    2016-08-15

    The experimental observation of the self–excited dust acoustic waves (DAWs) and its propagation characteristics in the absence and presence of a floating cylindrical object is investigated. The experiments are carried out in a direct current (DC) glow discharge dusty plasma in a background of argon gas. Dust particles are found levitated at the interface of plasma and cathode sheath region. The DAWs are spontaneously excited in the dust medium and found to propagate in the direction of ion drift (along the gravity) above a threshold discharge current at low pressure. Excitation of such a low frequency wave is a result of the ion–dust streaming instability in the dust cloud. Characteristics of the propagating dust acoustic wave get modified in the presence of a floating cylindrical object of radius larger than that of the dust Debye length. Instead of propagation in the vertical direction, the DAWs are found to propagate obliquely in the presence of the floating object (kept either vertically or horizontally). In addition, a horizontally aligned floating object forms a wave structure in the cone shaped dust cloud in the sheath region. Such changes in the propagation characteristics of DAWs are explained on the basis of modified potential (or electric field) distribution, which is a consequence of coupling of sheaths formed around the cylindrical object and the cathode.

  7. Temporal Change in Coda Wave Attenuation Observed at Colima Volcano

    NASA Astrophysics Data System (ADS)

    DOMINGUEZ, T.; FLORES, F.; REYES, G.

    2001-12-01

    The last eruptive processes of Colima volcano (November 1998- January 1999) was characterized by the occurrence of several seismic swarms. During the year previous to the eruption, the seismic activity developed in such a form that we could identified several stages in the evolution of the activity. By measuring the amplitude decay of coda waves we estimated coda attenuation Qc in the frequency range 2-10 Hz. We used Sato's (1977) single scattering model for coda windows of 10 to 15 seconds beginning at twice the S-wave travel time. We found a change in Q0 of approximately a 20-30% lower toward the end of the period. We also found that Qc was frequency dependent within this range. This dependence was progressively lower until the last month of activity just before the eruption. Studies of the same type that have been carried out in other volcanoes (Fehler, et al., 1998, Londoño, 1996) showed changes in the attenuation of the seismic waves related to volcanic eruptions. Changes of coda Q can be attributed to the change of density of the open microcracks in the rocks because of the pressure generated by the pushing of magma toward the surface which is also responsible for the inflation of the volcanic edifice.

  8. An inequality for longitudinal and transverse wave attenuation coefficients.

    PubMed

    Norris, Andrew N

    2017-01-01

    Total absorption, defined as the net flux of energy out of a bounded region averaged over one cycle for time harmonic motion, must be non-negative when there are no sources of energy within the region. This passivity condition places constraints on the non-dimensional absorption coefficients of longitudinal and transverse waves, γL and γT, in isotropic linearly viscoelastic materials. Typically, γL, γT are small, in which case the constraints imply that coefficients of attenuation per unit length, αL, αT, must satisfy the inequality αL/αT≥4cT(3)/3cL(3) where cL, cT are the wave speeds. This inequality, which as far as the author is aware, has not been presented before, provides a relative bound on wave speed in terms of attenuation, or vice versa. It also serves as a check on the consistency of ultrasonic measurements from the literature, with most but not all of the data considered passing the positive absorption test.

  9. Impact of attenuator models on computed traveling wave tube performances

    SciTech Connect

    Duan Zhaoyun; Gong Yubin; Wei Yanyu; Wang Wenxiang

    2007-09-15

    Radio frequency characteristics of helix traveling wave tubes are analyzed with a one-dimensional numerical model that includes a new, more rigorous, self-consistent attenuator model. The nonlinear properties of the beam-wave interaction, including gain, phase distortion, and intermodulation distortion, are analyzed and compared with simulations using a conventional one-dimensional model of the attenuator. The comparative results show that the small signal gain is about 2-5 dB smaller with the new model than with the conventional and wave phase has a difference of 2 deg. - 6 deg. between the new and conventional models in the intermediate and large signal regions. The amplitude modulation/phase modulation (AM/PM) conversion from the new model shows a slower reach to maximum than that from the conventional, and when the large input signal is applied, the conventional model's AM/PM conversion oscillates more quickly compared to the new. Under two-frequency excitation, the fundamental tones are about 5-7 dB smaller with the new model than the conventional, while the intermodulation products are approximately 10 dB smaller relative to the conventional model.

  10. Wave dispersion and attenuation on human femur tissue.

    PubMed

    Strantza, Maria; Louis, Olivia; Polyzos, Demosthenes; Boulpaep, Frans; van Hemelrijck, Danny; Aggelis, Dimitrios G

    2014-08-15

    Cortical bone is a highly heterogeneous material at the microscale and has one of the most complex structures among materials. Application of elastic wave techniques to this material is thus very challenging. In such media the initial excitation energy goes into the formation of elastic waves of different modes. Due to "dispersion", these modes tend to separate according to the velocities of the frequency components. This work demonstrates elastic wave measurements on human femur specimens. The aim of the study is to measure parameters like wave velocity, dispersion and attenuation by using broadband acoustic emission sensors. First, four sensors were placed at small intervals on the surface of the bone to record the response after pencil lead break excitations. Next, the results were compared to measurements on a bulk steel block which does not exhibit heterogeneity at the same wave lengths. It can be concluded that the microstructure of the tissue imposes a dispersive behavior for frequencies below 1 MHz and care should be taken for interpretation of the signals. Of particular interest are waveform parameters like the duration, rise time and average frequency, since in the next stage of research the bone specimens will be fractured with concurrent monitoring of acoustic emission.

  11. Experimental study on load characteristics in a floating type pendulum wave energy converter

    NASA Astrophysics Data System (ADS)

    Murakami, Tengen; Imai, Yasutaka; Nagata, Shuichi

    2014-10-01

    A floating type pendulum wave energy converter (FPWEC) with a rotary vane pump as the power take-off system was proposed by Watabe et al. in 1998. They showed that this device had high energy conversion efficiency. In the previous research, the authors conducted 2D wave tank tests in regular waves to evaluate the generating efficiency of FPWEC with a power take-off system composed of pulleys, belts and a generator. As a result, the influence of the electrical load on the generating efficiency was shown. Continuously, the load characteristics of FPWEC are pursued experimentally by using the servo motors to change the damping coefficient in this paper. In a later part of this paper, the motions of the model with the servo motors are compared with that of the case with the same power take-off system as the previous research. From the above experiment, it may be concluded that the maximum primary conversion efficiency is achieved as high as 98% at the optimal load.

  12. Simulation based study of the effect of ocean waves on floating wind farm

    NASA Astrophysics Data System (ADS)

    Yang, Di; Meneveau, Charles; Shen, Lian

    2012-11-01

    A hybrid numerical capability is developed for the simulation of floating wind farm offshore, in which large-eddy simulation is performed for wind turbulence, and a potential flow based method is used for the simulation of ocean wavefield. The wind and wave simulations are coupled through a two-way feedback scheme. The effect of wind turbines on the wind field is represented by an actuator disk model. A variety of fully-developed and fetch-limited wind-sea conditions are considered in the study. The simulation results indicate that the offshore wind farm obtains a higher wind power extraction rate under the fully-developed wind-sea condition compared with the fetch-limited condition. This higher extraction rate is caused by the faster propagating waves and the lower sea-surface resistance on the wind when the wind-seas are fully developed. Such wave effect becomes more prominent when the turbine density of the wind farm increases. DY and LS acknowledge the support of NSF-CBET-1133700. CM acknowledges the support of NSF-CBET-1133800 and NSF-AGS-1045189.

  13. Aerodynamic Thrust Modelling in Wave Tank Tests of Offshore Floating Wind Turbines Using a Ducted Fan

    NASA Astrophysics Data System (ADS)

    Azcona, José; Bouchotrouch, Faisal; González, Marta; Garciandía, Joseba; Munduate, Xabier; Kelberlau, Felix; Nygaard, Tor A.

    2014-06-01

    Wave tank testing of scaled models is standard practice during the development of floating wind turbine platforms for the validation of the dynamics of conceptual designs. Reliable recreation of the dynamics of a full scale floating wind turbine by a scaled model in a basin requires the precise scaling of the masses and inertias and also the relevant forces and its frequencies acting on the system. The scaling of floating wind turbines based on the Froude number is customary for basin experiments. This method preserves the hydrodynamic similitude, but the resulting Reynolds number is much lower than in full scale. The aerodynamic loads on the rotor are therefore out of scale. Several approaches have been taken to deal with this issue, like using a tuned drag disk or redesigning the scaled rotor. This paper describes the implementation of an alternative method based on the use of a ducted fan located at the model tower top in the place of the rotor. The fan can introduce a variable force that represents the total wind thrust by the rotor. A system controls this force by varying the rpm, and a computer simulation of the full scale rotor provides the desired thrust to be introduced by the fan. This simulation considers the wind turbine control, gusts, turbulent wind, etc. The simulation is performed in synchronicity with the test and it is fed in real time by the displacements and velocities of the platform captured by the acquisition system. Thus, the simulation considers the displacements of the rotor within the wind field and the calculated thrust models the effect of the aerodynamic damping. The system is not able currently to match the effect of gyroscopic momentum. The method has been applied during a test campaign of a semisubmersible platform with full catenary mooring lines for a 6MW wind turbine in scale 1/40 at Ecole Centrale de Nantes. Several tests including pitch free decay under constant wind and combined wave and wind cases have been performed. Data

  14. Seismic Wave Attenuation and Yield Determination at Regional Distances

    DTIC Science & Technology

    1989-05-25

    Rayleigh and 1-Hz Lg data for eastern North America, eastern South America, and the Indian Shield, respectively. If Q is assumed to be independent of...system, the Atlas Mountains, and the Cape Fold Belt, regions which have undergone Mesozoic or younger deformation. A seismically active region in an...seismic zone 56 VI. Attenuative body wave dispersion at La Cerdanya ( Eastern Pyrenees) 88 AeoesstI- For NTIS (;FA3& DTIC T’ ju t ,nic-,t Ion_ A;z1LbJ:Y

  15. 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.

  16. Experimental and Numerical Investigations of Floating Breakwater Performance.

    USDA-ARS?s Scientific Manuscript database

    Floating breakwaters are commonly used to protect small marinas and for shoreline erosion control in coastal areas. They are efficient wave attenuation structures for relatively short waves and shallow water depths. The main objective of the current study is to investigate the hydrodynamic interacti...

  17. Wave velocity dispersion and attenuation in media exhibiting internal oscillations

    NASA Astrophysics Data System (ADS)

    Frehner, Marcel; Steeb, Holger; Schmalholz, Stefan M.

    2010-05-01

    Understanding the dynamical and acoustical behavior of porous and heterogeneous rocks is of great importance in geophysics, e.g. earthquakes, and for various seismic engineering applications, e.g. hydrocarbon exploration. Within a heterogeneous medium oscillations with a characteristic resonance frequency, depending on the mass and internal length of the heterogeneity, can occur. When excited, heterogeneities can self-oscillate with their natural frequency. Another example of internal oscillations is the dynamical behavior of non-wetting fluid blobs or fluid patches in residually saturated pore spaces. Surface tension forces or capillary forces act as the restoring force that drives the oscillation. Whatever mechanism is involved, an oscillatory phenomena within a heterogeneous medium will have an effect on acoustic or seismic waves propagating through such a medium, i.e. wave velocity dispersion and frequency-dependent attenuation. We present two models for media exhibiting internal oscillations and discuss the frequency-dependent wave propagation mechanism. Both models give similar results: (1) The low-frequency (i.e. quasi-static) limit for the phase velocity is identical with the Gassmann-Wood limit and the high-frequency limit is larger than this value and (2) Around the resonance frequency a very strong phase velocity change and the largest attenuation occurs. (1) Model for a homogeneous medium exhibiting internal oscillations We present a continuum model for an acoustic medium exhibiting internal damped oscillations. The obvious application of this model is water containing oscillating gas bubbles, providing the material and model parameters for this study. Two physically based momentum interaction terms between the two inherent constituents are used: (1) A purely elastic term of oscillatory nature that scales with the volume of the bubbles and (2) A viscous term that scales with the specific surface of the bubble. The model is capable of taking into account

  18. Seismic attenuation due to wave-induced flow

    SciTech Connect

    Pride, S.R.; Berryman, J.G.; Harris, J.M.

    2003-10-09

    Analytical expressions for three P-wave attenuation mechanisms in sedimentary rocks are given a unified theoretical framework. Two of the models concern wave-induced flow due to heterogeneity in the elastic moduli at mesoscopic scales (scales greater than grain sizes but smaller than wavelengths). In the first model, the heterogeneity is due to lithological variations (e.g., mixtures of sands and clays) with a single fluid saturating all the pores. In the second model, a single uniform lithology is saturated in mesoscopic ''patches'' by two immiscible fluids (e.g., air and water). In the third model, the heterogeneity is at ''microscopic'' grain scales (broken grain contacts and/or micro-cracks in the grains) and the associated fluid response corresponds to ''squirt flow''. The model of squirt flow derived here reduces to proper limits as any of the fluid bulk modulus, crack porosity, and/or frequency is reduced to zero. It is shown that squirt flow is incapable of explaining the measured level of loss (10{sup -2} < Q{sup -1} < 10{sup -1}) within the seismic band of frequencies (1 to 10{sup 4} Hz); however, either of the two mesoscopic scale models easily produce enough attenuation to explain the field data.

  19. Nonlinear attenuation of S-waves and Love waves within ambient rock

    NASA Astrophysics Data System (ADS)

    Sleep, Norman H.; Erickson, Brittany A.

    2014-04-01

    obtain scaling relationships for nonlinear attenuation of S-waves and Love waves within sedimentary basins to assist numerical modeling. These relationships constrain the past peak ground velocity (PGV) of strong 3-4 s Love waves from San Andreas events within Greater Los Angeles, as well as the maximum PGV of future waves that can propagate without strong nonlinear attenuation. During each event, the shaking episode cracks the stiff, shallow rock. Over multiple events, this repeated damage in the upper few hundred meters leads to self-organization of the shear modulus. Dynamic strain is PGV divided by phase velocity, and dynamic stress is strain times the shear modulus. The frictional yield stress is proportional to depth times the effective coefficient of friction. At the eventual quasi-steady self-organized state, the shear modulus increases linearly with depth allowing inference of past typical PGV where rock over the damaged depth range barely reaches frictional failure. Still greater future PGV would cause frictional failure throughout the damaged zone, nonlinearly attenuating the wave. Assuming self-organization has taken place, estimated maximum past PGV within Greater Los Angeles Basins is 0.4-2.6 m s-1. The upper part of this range includes regions of accumulating sediments with low S-wave velocity that may have not yet compacted, rather than having been damaged by strong shaking. Published numerical models indicate that strong Love waves from the San Andreas Fault pass through Whittier Narrows. Within this corridor, deep drawdown of the water table from its currently shallow and preindustrial levels would nearly double PGV of Love waves reaching Downtown Los Angeles.

  20. Attenuation of the LG wave across the contiguous United States

    NASA Astrophysics Data System (ADS)

    Gallegos, Andrea Christina

    Lg waveforms recorded by EarthScope's Transportable Array (TA) are used to estimate Lg Q in the contiguous United States. Shear-wave crustal attenuation is calculated based on Lg spectral amplitudes filtered at several narrow bandwidths with central frequencies of 0.5, 1, 2, and 3 Hz. The two-station and reverse two-station techniques were used to calculate these Q values. 349 crustal earthquakes occurring from 2004 to 2015 and ranging from magnitude 3 to magnitude 6 were used in this study. The results show that the western U.S., an area ranging from 25°N to 50°N and from 125°W to 105°W is a primarily low Q (high attenuation) area, with isolated high Q (low attenuation) regions corresponding to the Colorado Plateau, the Rocky Mountains, the Columbia Plateau, and the Sierra Nevada Mountains. The central and eastern U.S., an area ranging from 105°W to 60°W, is found to be high Q overall, with isolated low Q areas along ft... Coastal Plain, the Reelfoot Rift, and the Wisconsin-Minnesota border region. A positive correlation between high heat flow, the presence of thick sediments, recent tectonic activity, and low Q is observed. Areas with low heat flow, thin sediment cover, and no recent tectonic activity were observed to have consistently high Q. Lg Q was found to have a power law type frequency dependence throughout the U.S., with an increase in central frequency resulting in an increase in Q. At higher frequencies, crustal attenuation is dominated by scattering. These new Lg tomography models are based on an unprecedented amount and coverage of data, providing improved accuracy and detail. This increase in detail can improve high frequency ground motion predictions of future large earthquakes for more accurate hazard assessment and improve overall understanding of the structure and assemblage of the contiguous United States.

  1. Attenuation Characteristics of High Frequency Seismic Waves in Southern India

    NASA Astrophysics Data System (ADS)

    Sivaram, K.; Utpal, Saikia; Kanna, Nagaraju; Kumar, Dinesh

    2017-07-01

    We present a systematic study of seismic attenuation and its related Q structure derived from the spectral analysis of P-, S-waves in the southern India. The study region is separated into parts of EDC (Eastern Dharwar Craton), Western Dharwar Craton (WDC) and Southern Granulite Terrain (SGT). The study is carried out in the frequency range 1-20 Hz, using a single-station spectral ratio technique. We make use of about 45 earthquakes, recorded in a network of about 32 broadband 3-component seismograph-stations, having magnitudes ( M L) varying from 1.6 to 4.5, to estimate the average seismic body wave attenuation quality factors; Q P and Q S. Their estimated average values are observed to be fitting to the power law form of Q = Q 0 f n . The averaged power law relations for Southern Indian region (as a whole) are obtained as Q P = (95 ± 1.12) f (1.32±0.01); Q S = (128 ± 1.84) f (1.49±0.01). Based on the stations and recorded local earthquakes, for parts of EDC, WDC and SGT, the average power law estimates are obtained as: Q P = (97 ± 5) f (1.40±0.03), Q S = (116 ± 1.5) f (1.48±0.01) for EDC region; Q P = (130 ± 7) f (1.20±0.03), Q S = (103 ± 3) f (1.49±0.02) for WDC region; Q P = (68 ± 2) f (1.4±0.02), Q S = (152 ± 6) f (1.48±0.02) for SGT region. These estimates are weighed against coda Q ( Q C) estimates, using the coda decay technique, which is based on a weak backscattering of S-waves. A major observation in the study of body wave analysis is the low body wave Q ( Q 0 < 200), moderately high value of the frequency-exponent, ` n' (>0.5) and Q S/ Q P ≫ 1, suggesting lateral stretches of dominant scattering mode of seismic wave propagation. This primarily could be attributed to possible thermal anomalies and spread of partially fluid-saturated rock-masses in the crust and upper mantle of the southern Indian region, which, however, needs further laboratory studies. Such physical conditions might partly be correlated to the active seismicity and

  2. Fluid-structure interaction simulation of floating wind turbines interacting with complex, large-scale ocean waves

    NASA Astrophysics Data System (ADS)

    Calderer, Antoni; Guo, Xin; Shen, Lian; Sotiropoulos, Fotis

    2013-11-01

    We develop a numerical method for simulating coupled interactions of complex floating structures with large-scale ocean waves and atmospheric turbulence. The Fluid-Structure Interaction (FSI) solver integrates the curvilinear immersed boundary method of Borazjani et al. (JCP 2008) with the level-set method of Kang et al. (Adv. in Water Res. 2012) and is capable of simulating the coupled dynamic interaction of arbitrarily complex bodies with airflow and waves. The large-scale wave model is based on the two-fluid coupled approach of Yang et al. (JCP 2011), which employs a high-order spectral method for simulating the water motion and a viscous solver with undulatory boundaries for the air motion. The large-scale wave field solver is coupled with the near-field FSI solver by feeding into the latter large-scale waves via the pressure-forcing method of Guo et al. (JCP 2009), appropriately adapted herein for the level set method. We validate the model under both simple wave trains and three-dimensional directional waves and compare the results with experimental and theoretical solutions. Finally, we demonstrate the capabilities of the new solver by carrying out large eddy simulation of a floating offshore wind turbine platform interacting with realistic ocean waves. This work is supported by the US Department of Energy (DE-EE0005482), the National Science Foundation (CBET-1341062), the University of Minnesota Initiative for Renewable Energy and the Environment, and the Minnesota Supercomputing Institute.

  3. Crustal Lg-wave attenuation in and around Tibetan plateau

    NASA Astrophysics Data System (ADS)

    Zhao, L.; Xie, X.; Yao, Z.

    2011-12-01

    Based on regional Lg-wave data, we develop a broadband high-resolution attenuation model for Tibetan Plateau and its surrounding regions. We collect vertical component seismograms recorded at 146 stations form 232 crustal earthquakes to calculate the Lg-wave amplitude spectra. The spectra are sampled at 58 discrete frequencies distributed log evenly between 0.05 and 10.0 Hz. Both dual-station and single-station datasets are constructed for jointly inverting the Lg Q distribution and Lg wave excitation function. The maximum spatial resolution is approximately 0.8°×0.8° in well-covered areas and for frequencies between 0.5 and 2.0 Hz. The Lg Q image reveals the relations between attenuations and geological structures. The average Lg Q0 (1 Hz Q) is 280 for Tibetan Plateau (regions with elevations above 4,000 m ). The Q0 values change from the south to north by first decrease (the Himalaya: 386, Lhasa : 284, Qiangtang: 238, and Songpan-Ganze blocks: 217), and then increase ( East Kunlun: 289, West Kunlun: 330, and Qilianshan blocks: 315). The QLg distributions are consistent with the lower crust material flow around the Eastern Himalayan syntaxis and the rigid Sichuan basin. The regions surrounding the Tibetan plateau are characterized by high Q0 values (Tarim basin: 433, Altyn mountain: 517, Qaidam basin: 385, Alashan uplift: 452, Inner Mongolian platform: 444, Ordos: 395, and Sichuan basins: 456), except for Yungui Plateau which has a relatively low Q0 of 247. A statistical method is used to investigate the regional variations of the Lg Q frequency dependence. The Lg Q generally increases with the increase of frequencies but show complex frequency dependency, indicating the commonly used power-law Q model may not be appropriate within a broad frequency band. The Lg Q frequency dependence also shows regional variations.

  4. Tide Effects on Wave Attenuation and Wave Set-up on a Caribbean Coral Reef

    NASA Astrophysics Data System (ADS)

    Lugo-Fernández, A.; Roberts, H. H.; Wiseman, W. J., Jr.

    1998-10-01

    The effects of tides on wave attenuation and wave set-up were investigated at Great Pond Bay, a Caribbean reef located in St Croix, U.S. Virgin Islands. Measurements of wave pressure fluctuations were made at three stations across the reef profile. Total wave set-up was measured between the forereef and the reef crest or backreef lagoon. Wave spectra indicate significant filtering of energy at the peak frequencies as waves traveled across the reef. The energy dissipation calculations imply an average energy reduction of 62% between the forereef and reef crest. Mean energy reduction between the forereef and lagoon was 90%. Energy dissipation between the forereef and reef crest increased 15% between high and low tide and 6% between forereef and lagoon. Tidal reduction of water depth at the reef crest intensified wave breaking and this condition increased energy dissipation. Measurements of wave set-up ranged from 0·8 to 1·5 cm. Calculations of wave set-up using Tait's 1972 model showed good agreement with observations.

  5. Phase Aberration and Attenuation Effects on Acoustic Radiation Force-Based Shear Wave Generation.

    PubMed

    Carrascal, Carolina Amador; Aristizabal, Sara; Greenleaf, James F; Urban, Matthew W

    2016-02-01

    Elasticity is measured by shear wave elasticity imaging (SWEI) methods using acoustic radiation force to create the shear waves. Phase aberration and tissue attenuation can hamper the generation of shear waves for in vivo applications. In this study, the effects of phase aberration and attenuation in ultrasound focusing for creating shear waves were explored. This includes the effects of phase shifts and amplitude attenuation on shear wave characteristics such as shear wave amplitude, shear wave speed, shear wave center frequency, and bandwidth. Two samples of swine belly tissue were used to create phase aberration and attenuation experimentally. To explore the phase aberration and attenuation effects individually, tissue experiments were complemented with ultrasound beam simulations using fast object-oriented C++ ultrasound simulator (FOCUS) and shear wave simulations using finite-element-model (FEM) analysis. The ultrasound frequency used to generate shear waves was varied from 3.0 to 4.5 MHz. Results: The measured acoustic pressure and resulting shear wave amplitude decreased approximately 40%-90% with the introduction of the tissue samples. Acoustic intensity and shear wave displacement were correlated for both tissue samples, and the resulting Pearson's correlation coefficients were 0.99 and 0.97. Analysis of shear wave generation with tissue samples (phase aberration and attenuation case), measured phase screen, (only phase aberration case), and FOCUS/FEM model (only attenuation case) showed that tissue attenuation affected the shear wave generation more than tissue aberration. Decreasing the ultrasound frequency helped maintain a focused beam for creation of shear waves in the presence of both phase aberration and attenuation.

  6. Phase Aberration and Attenuation Effects on Acoustic Radiation Force-Based Shear Wave Generation

    PubMed Central

    Amador, Carolina; Aristizabal, Sara; Greenleaf, James F.; Urban, Matthew W.

    2016-01-01

    Tissue elasticity is measured by shear wave elasticity imaging methods using acoustic radiation force to create the shear waves. Phase aberration and tissue attenuation can hamper the generation of shear waves for in vivo applications. In this study effects of phase aberration and attenuation in ultrasound focusing for creating shear waves were explored. This includes the effects of phase shifts and amplitude attenuation on shear wave characteristics such as shear wave amplitude, shear wave speed, shear wave center frequency and bandwidth. Two samples of swine belly tissue were used to create phase aberration and attenuation experimentally. To explore the phase aberration and attenuation effects individually, tissue experiments were complemented with ultrasound beam simulations using FOCUS and shear wave simulations using Finite Element Model (FEM) analysis. The ultrasound frequency used to generate shear waves was varied from 3.0 to 4.5 MHz. Results The measured acoustic pressure and resulting shear wave amplitude decreased approximately 40% to 90% with the introduction of the tissue samples. Acoustic intensity and shear wave displacement were correlated for both tissue samples, the resulting Pearson’s correlation coefficients were 0.99 and 0.97. Analysis of shear wave generation with tissue samples (Phase Aberration and Attenuation case), measured phase screen (Only Phase Aberration case) and FOCUS/FEM model (Only Attenuation case) showed that tissue attenuation affected the shear wave generation more than tissue aberration. Decreasing the ultrasound frequency helped maintain a focused beam for creation of shear waves in the presence of both phase aberration and attenuation. PMID:26742131

  7. Statistics and Physics of Stratospheric Gravity Wave Attenuation over New Zealand

    NASA Astrophysics Data System (ADS)

    Kruse, C. G.; Smith, R. B.

    2015-12-01

    The DEEPWAVE field project took place over the New Zealand region during June and July of 2014 and was focused on observing orographic and non-orographic gravity waves from their source regions in the troposphere to attenuation regions in the stratosphere, mesosphere, and thermosphere. An important preliminary finding of this project is that many mountain wave events are attenuated in a 15-20km "valve layer" in the lower stratosphere, characterized by weak winds and non-linearity. This valve layer strongly attenuates about half of New Zealand mountain wave events, reducing wave momentum fluxes by as much as 90% and producing a maximum in momentum flux divergence. This work further characterizes this lower-stratospheric mountain wave attenuation and seeks to understand the physics of actual wave attenuation events "reproduced" within 6- and 2-km resolution realistic WRF simulations. Local attenuation diagnostics, such as Richardson Number, stratification, and the non-linearity ratio, are used to characterize the size and 3-D distribution of attenuation regions and to diagnose dissipation mechanisms. Potential vorticity (PV) is also used as a diagnostic to identify attenuation regions and also to trace the influences of these regions downstream. Preliminary work has revealed that mountain wave attenuation over New Zealand is spatially inhomogeneous, generates PV in dipoles, and that lateral shear instabilities cause lateral mixing 1000s of kilometers downstream of the attenuation regions.

  8. Experimental Wave Tank Test for Reference Model 3 Floating-Point Absorber Wave Energy Converter Project

    SciTech Connect

    Yu, Y. H.; Lawson, M.; Li, Y.; Previsic, M.; Epler, J.; Lou, J.

    2015-01-01

    The U.S. Department of Energy established a reference model project to benchmark a set of marine and hydrokinetic technologies including current (tidal, open-ocean, and river) turbines and wave energy converters. The objectives of the project were to first evaluate the status of these technologies and their readiness for commercial applications. Second, to evaluate the potential cost of energy and identify cost-reduction pathways and areas where additional research could be best applied to accelerate technology development to market readiness.

  9. Attenuation of High-Frequency Seismic Waves in Eastern Iran

    NASA Astrophysics Data System (ADS)

    Mahood, M.

    2014-09-01

    We investigated the frequency-dependent attenuation of the crust in Eastern Iran by analysis data from 132 local earthquakes having focal depths in the range of 5-25 km. We estimated the quality factor of coda waves ( Q c) and body waves ( Q p and Q s) in the frequency band of 1.5-24 Hz by applying the single backscattering theory of S-coda envelopes and the extended coda-normalization method, respectively. Considering records from recent earthquakes (Rigan M w 6.5, 2010/12/20, Goharan M w 6.2, 2013/5/11 and Sirch M w 5.5, 2013/1/21), the estimated values of Q c, Q p and Q s vary from 151 ± 49, 63 ± 6, and 93 ± 14 at 1.5 Hz to 1,994 ± 124, 945 ± 84 and 1,520 ± 123 at 24 Hz, respectively. The average frequency-dependent relationships ( Q = Q o f n ) estimated for the region are Q c = (108 ± 10) f (0.96±0.01), Q p = (50 ± 5) f (1.01±0.04), and Q s = (75 ± 6) f (1.03±0.06). These results evidenced a frequency dependence of the quality factors Q c, Q p, and Q s, as commonly observed in tectonically active zones characterized by a high degree of heterogeneity, and the low value of Q indicated an attenuative crust beneath the entire region.

  10. 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

  11. 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.

  12. Stratospheric mountain wave attenuation in positive and negative ambient wind shear

    NASA Astrophysics Data System (ADS)

    Kruse, C. G.; Smith, R. B.

    2016-12-01

    Recently, much has been learned about the vertical propagation and attenuation of mountain waves launched by the Southern Alps of New Zealand (NZ) from the Deep Propagating Gravity Wave Experiment (DEEPWAVE) field campaign. Over NZ, approximately half of mountain wave events are strongly attenuated in a lower-stratospheric "valve layer," defined as a layer of reduced wind with no critical levels. Within a valve layer, negative wind shear causes mountain waves steepen and attenuate, with the amount of transmitted momentum flux controlled by the minimum wind speed within the layer. The other half of wave events are deep (propagating to 35+ km), usually with positive wind shear. Within these deep events, increasing amplitude with decreasing density causes mountain waves to attenuate gradually (after spatial/temporal averaging). Global reanalyses indicate that this valve layer is a climatological feature in the wintertime mid-latitudes above the subtropical jet, while deep events and gradual attenuation occur over higher latitudes below the polar stratospheric jet. The local physics of mountain wave attenuation in positive and negative ambient wind shear are investigated using realistic winter-long (JJA) 6-km resolution Weather Research and Forecasting (WRF) model simulations over the Andes. Attention is given to the spatiotemporal variability of wave attenuation and the various factors driving this variability (e.g. variability in wave generation, ambient conditions at attenuation level, inherent wave-induced instabilities). Mesoscale potential vorticity generation is used as an indicator of wave attenuation. Additionally, regionally integrated wave momentum flux and gravity wave drag (GWD) within WRF are quantified and compared with parameterized quantities in the MERRA1 and 2 reanalyses.

  13. Blast wave attenuation by lightly destructable granular materials

    NASA Astrophysics Data System (ADS)

    Golub, V. V.; Lu, F. K.; Medin, S. A.; Mirova, O. A.; Parshikov, A. N.; Petukhov, V. A.; Volodin, V. V.

    Terrorist bombings are a dismal reality nowadays. One of the most effective ways for protection against blast overpressure is the use of lightly compacted materials such as sand [1] and aqueous foam [2] as a protective envelope or barrier. According to [1], shock wave attenuation in a mine tunnel (one-dimensional case) behind a destroyed object is given by q_e ≈ q {1}/{1 + 4(S/q)^{1/6} bρ _{mat} /L^{1/3} }where qe — effective charge, S — exposed area of the obstacle, q — TNT equivalent (grams), L — distance between charge and obstacle, b — obstacle thickness and ρ mat — material density. This empirical equation is applicable only in a one-dimensional case but not for a less confined environment. Another way of protecting a structure against blast is to coat the surface with a sacrificial layer. In [3] full-scale experiments were carried out to investigate the behaviour of a covering of aluminum foam under the effect of a blast wave.

  14. Coda wave attenuation at Jalisco Block, Western Mexico

    NASA Astrophysics Data System (ADS)

    Garcia Millan, N.; Escudero, C. R.; Escalona, F.; Gutierrez, Q. J.; Nuñez-Cornu, F. J.

    2015-12-01

    Coda waves are very important to study the properties of the continental crust. We analyze the coda wave attenuation at Jalisco Block through Simple isotropic scattering model proposed by Sato (1977). We measure coda Q using around 1700 seismograms recorded at the Mapping the Rivera Subduction Zone (MARS) seismic experiment and 1500seismograms at the Red Sismológica y Acelerométrica Telemétrica de Jalisco (RESAJ).The study provides new information on the statistical properties and spatial variation of coda Q, where present values of 23 ± 13 for 1-5 Hz, 60 ± 27 for 5-10 Hz, 94 ± 37 for 10-15 Hz, and 120 ± 40 for 15-20 Hz frequency band. The frequency-dependent quality factor is modeled in the form Q(f)=Q0f α. We made Coda Q cartography in comparison with the region's geology and seismicity. We observed a clear correlation of the coda Q anomalies with major tectonic features within the studied area. Large coda Q values correlate with the Colima Volcano Complex, the Colima Graben, and the Trans Mexican Volcanic Belt.

  15. Coupled fluid-structure interaction simulation of floating offshore wind turbines and waves: a large eddy simulation approach

    NASA Astrophysics Data System (ADS)

    Calderer, Antoni; Guo, Xin; Shen, Lian; Sotiropoulos, Fotis

    2014-06-01

    We develop a computational framework for simulating the coupled interaction of complex floating structures with large-scale ocean waves and atmospheric turbulent winds. The near-field approach features a partitioned fluid-structure interaction model (FSI) combining the curvilinear immersed boundary (CURVIB) method of Borazjani and Sotiropoulos (J. Comput. Phys. 2008) and the two-phase flow level set formulation of Kang and Sotiropoulos (Adv. in Water Res. 2012) and is capable of solving complex free-surface flows interacting non-linearly with complex real life floating structures. The near-field solver is coupled with a large-scale wave and wind model based on the two-fluid approach of Yang and Shen (J. Comput. Phys. 2011) which integrates a viscous Navier-Stokes solver with undulatory boundaries for the motion of the air and an efficient potential-flow based wave solver. The large-scale turbulent wind is incorporated from the far-field solver to the near-field solver by feeding into the latter inlet boundary conditions. The wave field is incorporated to the near-field solver by using the pressure-forcing method of Guo and Shen (J. Comput. Phys. 2009) which has been appropriately adapted to the level set method. The algorithm for coupling the two codes has been validated for a variety of wave cases including a broadband spectrum showing excellent agreement when compared to theoretical results. Finally, the capabilities of the numerical framework are demonstrated by carrying out large eddy simulation (LES) of a floating wind turbine interacting with realistic ocean wind and wave conditions.

  16. Numerical Study of Shock Wave Attenuation Using Logarithmic Spiral Liquid Sheet

    NASA Astrophysics Data System (ADS)

    Wan, Qian; Deiterding, Ralf; Eliasson, Veronica

    2016-11-01

    Research of shock wave attenuation has drawn much attention due to its military and civilian applications. One method to attenuate shock waves is to use water to block the shock wave propagation path and allow the shock wave to lose energy by breaking up the water sheet. We propose a way by holding a water sheet in logarithmic spiral shape, which has the ability of focusing the incident shock wave to its focal region. In addition, the shock wave will break up the bulk water and thus lose energy. The process of shock wave reflecting off and transmitting through the water sheet is numerically modeled using Euler equations and stiffened gas equation of state. In this study, the shock focusing ability of a logarithmic spiral water sheet is compared for various logarithmic spiral sheets. Further, the attenuation effect is quantified by the measurement of pressure impulse and peak pressure behind the transmitted and reflected shock waves.

  17. Attenuation of acoustic waves in glacial ice and salt domes

    NASA Astrophysics Data System (ADS)

    Price, P. B.

    2006-02-01

    Two classes of natural solid media, glacial ice and salt domes, are under consideration as media in which to deploy instruments for detection of neutrinos with energy ≥1018 eV. Though insensitive to 1011 to 1016 eV neutrinos for which observatories (e.g., AMANDA and IceCube) that utilize optical Cherenkov radiation detectors are designed, radio and acoustic methods are suited for searches for the very low fluxes of neutrinos with energies >1017 eV. This is because owing to the very long attenuation lengths of radio and acoustic waves produced by interactions of such neutrinos in ice and salt, detection modules can be spaced at horizontal distances ˜1 km, in contrast to the 0.12 km distances between strings of IceCube modules. In this paper, I calculate the absorption and scattering coefficients as a function of frequency and grain size for acoustic waves in glacial ice and salt domes and show that experimental measurements on laboratory samples and in glacial ice and salt domes are consistent with theory. For South Pole ice with grain size ˜0.2 cm at depths ≤600 m, scattering lengths are calculated to be 2000 and 25 km at frequencies 10 and 30 kHz, respectively; for grain size ˜0.4 cm at 1500 m (the maximum depth to be instrumented acoustically), scattering lengths are calculated to be 250 and 3 km. These are within the range of frequencies where most of the energy of the acoustic wave is concentrated. The absorption length is calculated to be 9 ± 3 km at all frequencies above ˜100 Hz. For NaCl (rock salt) with grain size 0.75 cm, scattering lengths are calculated to be 120 and 1.4 km at 10 and 30 kHz, and absorption lengths are calculated to be 3 × 104 and 3300 km at 10 and 30 kHz. Existing measurements are consistent with theory. For ice, absorption is the limiting factor; for salt, scattering is the limiting factor. Both media would be suitable for detection of acoustic waves from ultrahigh-energy neutrino interactions.

  18. Frequency-dependent Lg-wave attenuation in northern Morocco

    NASA Astrophysics Data System (ADS)

    Noriega, Raquel; Ugalde, Arantza; Villaseñor, Antonio; Harnafi, Mimoun

    2015-11-01

    Frequency-dependent attenuation (Q- 1) in the crust of northern Morocco is estimated from Lg-wave spectral amplitude measurements every quarter octave in the frequency band 0.8 to 8 Hz. This study takes advantage of the improved broadband data coverage in the region provided by the deployment of the IberArray seismic network. Earthquake data consist of 71 crustal events with magnitudes 4 ≤ mb ≤ 5.5 recorded on 110 permanent and temporary seismic stations between January 2008 and December 2013 with hypocentral distances between 100 and 900 km. 1274 high-quality Lg waveforms provide dense path coverage of northern Morocco, crossing a region with a complex structure and heterogeneous tectonic setting as a result of continuous interactions between the African and Eurasian plates. We use two different methods: the coda normalization (CN) analysis, that allows removal of the source and site effects from the Lg spectra, and the spectral amplitude decay (SAD) method, that simultaneously inverts for source, site, and path attenuation terms. The CN and SAD methods return similar results, indicating that the Lg Q models are robust to differences in the methodologies. Larger errors and no significant frequency dependence are observed for frequencies lower than 1.5 Hz. For distances up to 400 km and the frequency band 1.5 ≤ ƒ (Hz) ≤ 4.5, the model functions Q(f) = (529- 22+ 23)(f/1.5)0.23 ± 0.06 and Q(f) = (457- 7+ 7)(f/1.5)0.44 ± 0.02 are obtained using the CN and SAD methods, respectively. A change in the frequency dependence is observed above 4.5 Hz for both methods which may be related to the influence of the Sn energy on the Lg window. The frequency-dependent Q- 1 estimates represent an average attenuation beneath a broad region including the Rif and Tell mountains, the Moroccan and Algerian mesetas, the Atlas Mountains and the Sahara Platform structural domains, and correlate well with areas of moderate seismicity where intermediate Q values have been obtained.

  19. 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.

  20. Attenuation of intense sinusoidal waves in air-saturated, bulk porous materials

    NASA Technical Reports Server (NTRS)

    Kuntz, Herbert L.; Blackstock, David T.

    1987-01-01

    As intense, initially sinusoidal waves propagate in fluids, shocks form and excess attenuation of the wave occurs. Data are presented indicating that shock formation is not necessary for the occurrence of excess attenuation in nonlinear, lossy media, i.e., air-saturated, porous materials. An empirical equation is used to describe the excess attenuation of intense sinusoids in porous materials. The acoustic nonlinearity of and the excess attenuation in porous materials may be predicted directly from dc flow resistivity data. An empirical relationship is used to relate an acoustic nonlinearity parameter to the fundamental frequency and relative dc nonlinearity of two structurally different materials.

  1. Laboratory and field investigations of wave attenuation by live marsh vegetation

    USDA-ARS?s Scientific Manuscript database

    Wave attenuation by live marsh vegetation was investigated experimentally in this study. Laboratory experiments were conducted in a 20.6 m long, 0.69 m wide and 1.22 m deep wave flume under regular and random waves. The vegetation species used are Spartina alterniflora and Juncus roemerianus, which ...

  2. Measurement of the dispersion and attenuation of cylindrical ultrasonic guided waves in long bone.

    PubMed

    Ta, Dean; Wang, Weiqi; Wang, YuanYuan; Le, Lawrence H; Zhou, Yuqing

    2009-04-01

    Osteoporotic bones are likely to have less cortical bone than healthy bones. The velocities of guided waves propagating in a long cylindrical bone are very sensitive to bone properties and cortical thickness (CTh). This work studies the dispersion and attenuation of ultrasonic guided waves propagating in long cylindrical bone. A hollow cylinder filled with a viscous liquid was used to model the long bone and then to calculate the theoretical phase and group velocities, as well as the attenuation of the waves. The generation and selection of guided wave modes were based on theoretical dispersive curves. The phase velocity and attenuation of cylindrical guided wave modes, such as L(0,1), L(0,2) and L(0,3), were measured in bovine tibia using angled beam transducers at various propagation distances ranging from 75 to 160 mm. The results showed that the phase velocity of the L(0,2) guided wave mode decreased with an increase in CTh. The attenuation of the low cylindrical guided wave modes was a nonlinear function that increased with propagation distance and mode order. The L(0,2) mode had a different attenuation for each CTh. The experimental results were in good agreement with the predicted values. Cylindrical guided waves of low-frequency and low-order have been shown to demonstrate more dispersion and less attenuation and should, therefore, be used to evaluate long bone.

  3. A New Approach for Quantitative Evaluation of Ultrasonic Wave Attenuation in Composites

    NASA Astrophysics Data System (ADS)

    Ni, Qing-Qing; Li, Ran; Xia, Hong

    2017-02-01

    When ultrasonic waves propagate in composite materials, the propagation behaviors result from the combination effects of various factors, such as material anisotropy and viscoelastic property, internal microstructure and defects, incident wave characteristics and interface condition between composite components. It is essential to make it clear how these factors affect the ultrasonic wave propagation and attenuation characteristics, and how they mutually interact on each other. In the present paper, based on a newly developed time-domain finite element analysis code, PZflex, a unique approach for clarifying the detailed influence mechanism of aforementioned factors is proposed, in which each attenuation component can be extracted from the overall attenuation and analyzed respectively. By taking into consideration the interrelation between each individual attenuation component, the variation behaviors of each component and internal dynamic stress distribution against material anisotropy and matrix viscosity are separately and quantitatively evaluated. From the detailed analysis results of each attenuation component, the energy dissipation at interface is a major component in ultrasonic wave attenuation characteristics, which can provide a maximum contribution rate of 68.2 % to the overall attenuation, and each attenuation component is closely related to the material anisotropy and viscoelasticity. The results clarify the correlation between ultrasonic wave propagation characteristics and material viscoelastic properties, which will be useful in the further development of ultrasonic technology in defect detection.

  4. Studies on Shock Attenuation in Plastic Materials and Applications in Detonation Wave Shaping

    NASA Astrophysics Data System (ADS)

    Khurana, Ritu; Gautam, P. C.; Rai, Rajwant; Kumar, Anil; Sharma, A. C.; Singh, Manjit, Dr

    2012-07-01

    Pressure in plastic materials attenuates due to change of impedance, phase change in the medium and plastic deformation. A lot of theoretical and experimental efforts have been devoted to the attenuation of shock wave produced by the impact of explosive driven flyer plate. However comparatively less work has been done on the attenuation of shock waves due to contact explosive detonation. Present studies deal with the attenuation of explosive driven shock waves in various plastic materials and its applications in design of Hybrid Detonation Wave Generator In present work shock attenuating properties of different polymers such as Perspex, Teflon, nylon, polypropylene and viton has been studied experimentally using rotating mirror streak camera and electrical position pins. High explosive RDX/TNT and OCTOL of diameter 75-100mm and thickness 20 to 50mm were detonated to induce shock wave in the test specimens. From experimental determined shock velocity at different locations the attenuation in shock pressure was calculated. The attenuation of shock velocity with thickness in the material indicates exponential decay according to relation US = UOexp(-ax). In few of the experiments manganin gauge of resistance 50 ohms was used to record stress time profile across shock wave. The shock attenuation data of Viton has successfully been used in the design of hybrid detonation wave generator using Octol as high explosive. While selecting a material it was ensured that the attenuated shock remains strong enough to initiate an acceptor explosive. Theoretical calculation were supported by Autodyne 2D hydro-code simulation which were validated with the experiments conducted using high speed streak photography and electrical shock arrival pins. Shock attenuation data of Perspex was used to establishing card gap test and wedge test in which test items is subjected to known pressure pulse by selecting the thickness of the plastic material.

  5. Scaling and kinematics of a floating wind turbine under ocean waves and variable thrust: an experimental study

    NASA Astrophysics Data System (ADS)

    Feist, Chris; Ruehl, Kelley; Guala, Michele

    2013-11-01

    Scale model wave channel experiments were performed to study the motion of an offshore floating wind turbine in operational sea states. The model tests were conducted on a 1:100 Froude scaled Sandia National Labs 13.2 MW prototype offshore wind turbine with a barge style floating platform. The platform is modeled after the MIT/NREL Shallow Drafted Barge designed for the 5MW Offshore Baseline wind turbine. The wave environment used in the model tests is representative of the deep-water sea states off the coast of Maine as well as the Pacific Northwest. The purpose of the tests is to validate a computational model of the turbine-wave interaction where the effects of airflow are not considered. To simplify the tests and validation, the platform motion is restricted to two degrees of freedom, pitch and heave, by attaching two roller support types at the center of gravity along the pitch axis. The major aerodynamic force acting on the turbine, i.e. the rotor thrust, is provided by spinning a scaled rotor at a controlled rotational speed. A subset of experiments were performed to study the effect of a mean or fluctuating rotor thrust on the platform dynamics, exploring strategies to control the thrust as a function of platform pitch angle and minimize platform oscillations.

  6. Dynamics of dual pontoon floating structure for cage aquaculture in a two-dimensional numerical wave tank

    NASA Astrophysics Data System (ADS)

    Tang, Hung-Jie; Huang, Chai-Cheng; Chen, Wei-Ming

    2011-10-01

    The trend of using floating structures with cage aquaculture is becoming more popular in the open sea. The purpose of this paper is to investigate the dynamic properties of a dual pontoon floating structure (DPFS) when attached to a fish net by using physical and numerical models. A two-dimensional (2-D) fully nonlinear numerical wave tank (NWT), based on the boundary element method (BEM), is developed to calculate the wave forces on the DPFS. The wave forces on a fish net system are then evaluated using a modified Morison equation. The comparisons of dynamic behaviors between numerical simulations and experimental measurements on the DPFS show good agreement. Results also display that a fish net system causes the resonant response of body motions and mooring forces to be slightly lower due to the net's damping effect. Finally, for designing the rearing space of cage aquaculture, the influences which net depth and net width have on the DPFS dynamic responses are also presented in this paper.

  7. Lamb wave attenuation in a rough plate. I. Analytical and experimental results in an anisotropic plate

    NASA Astrophysics Data System (ADS)

    Potel, Catherine; Leduc, Damien; Morvan, Bruno; Depollier, Claude; Hladky-Hennion, Anne-Christine; Izbicki, Jean-Louis; Pareige, Pascal; Bruneau, Michel

    2008-10-01

    The characterization of bounded roughened surfaces before applying adhesive joint, in order to detect poor cohesive and adhesive properties, remains difficult. Earlier studies based on analysis of surface wave (Rayleigh waves or Scholte waves) are not really adapted to the characterization of such surfaces. Guided acoustic waves, i.e., Lamb waves, turn out to be the best adapted kind of waves to characterize this roughness when plates are bounded together. It is the aim of this paper to provide analytical and experimental approaches to analyze the behavior of Lamb waves propagating inside plates with a rough surface (small perturbations). First, experimental results of the attenuation effects are given on roughened glass plates. Second, the attenuation factor of the Lamb wave in an anisotropic rough solid plate is calculated through a complex analytical model of the dispersion equation which accounts for the effect of the power spectrum density of the rough profile (including the effect of the statistical roughness parameters).

  8. Seismic-wave attenuation associated with crustal faults in the new madrid seismic zone.

    PubMed

    Hamilton, R M; Mooney, W D

    1990-04-20

    The attenuation of upper crustal seismic waves that are refracted with a velocity of about 6 kilometers per second varies greatly among profiles in the area of the New Madrid seismic zone in the central Mississippi Valley. The waves that have the strongest attenuation pass through the seismic trend along the axis of the Reelfoot rift in the area of the Blytheville arch. Defocusing of the waves in a low-velocity zone and/or seismic scattering and absorption could cause the attenuation; these effects are most likely associated with the highly deformed rocks along the arch. Consequently, strong seismic-wave attenuation may be a useful criterion for identifying seismogenic fault zones.

  9. Propagation and attenuation characteristics of azimuthal symmetric surface waves in un-magnetized plasma column

    NASA Astrophysics Data System (ADS)

    Li, Wenqiu; Wang, Gang; Xiang, Dong; Su, Xiaobao

    2016-11-01

    Phase and attenuation properties of azimuthal symmetric surface waves are investigated analytically in an un-magnetized cylindrical plasma column based on the transcendental dispersion relation. A novel method of calculating the wave power deposition in terms of complex electric conductivity is proposed. Electron density distribution is obtained theoretically through charged particle balance theory. It is shown that the effect of the electron temperature on the dispersion curve can be neglected when kzα < 1. Both the phase/attenuation characteristics and wave energy deposition properties of the azimuthal symmetric surface wave have an evident dependence on the electron density and the electron collision frequency.

  10. Bio-Argo float data suggest that disaggregation is a major driver of flux attenuation during large phytoplankton blooms in the North Atlantic

    NASA Astrophysics Data System (ADS)

    Briggs, N.; Claustre, H.; Dall'Olmo, G.; Bittig, H. C.

    2016-02-01

    Approximately 5-12 Pg of organic carbon is exported from the ocean's euphotic zone each year. The rate at which this organic carbon flux decreases with depth has critical consequences for both the functioning of deep ocean ecosystems and the timescale of biological CO2 sequestration. However, it has been difficult to constrain the mechanisms behind this attenuation of organic carbon flux and the variability of these mechanisms in time and space. In situ measurements of one or more individual processes that attenuate flux, therefore, are highly desirable, especially when accompanied by estimates of total flux attenuation at the same temporal and spatial scales. Substantial effort has been made to connect vertical flux attenuation with bacterial and/or zooplankton metabolism. However, the disaggregation of fast-sinking aggregates, another potential mechanism of flux attenuation, has not, to our knowledge, been quantified in the ocean. Here we simultaneously estimate both the loss of sinking phytoplankton aggregates with depth and the production of small particles at depth (possibly a signature disaggregation) using three years of chlorophyll a fluorescence data from 21 autonomous "bio-Argo" profiling floats in the sub-polar North Atlantic. Fluorescence data were divided into "spikes" caused by phytoplankton aggregates and a "baseline" due to smaller particles. During several large spring blooms, we found a clear matchup in depth and time between the attenuation of phytoplankton aggregate flux, calculated from fluorescence spikes, and a rapid increase in small phytoplankton particles well below the productive layer. This pattern is best explained by disaggregation, which appears to cause at least 30-50% of phytoplankton aggregate flux attenuation at the peak of these blooms. These results reveal the importance of disaggregation to oceanic carbon cycling and highlight the potential of bio-Argo to advance understanding of disaggregation globally.

  11. Determining attenuation properties of interfering fast and slow ultrasonic waves in cancellous bone

    PubMed Central

    Nelson, Amber M.; Hoffman, Joseph J.; Anderson, Christian C.; Holland, Mark R.; Nagatani, Yoshiki; Mizuno, Katsunori; Matsukawa, Mami; Miller, James G.

    2011-01-01

    Previous studies have shown that interference between fast waves and slow waves can lead to observed negative dispersion in cancellous bone. In this study, the effects of overlapping fast and slow waves on measurements of the apparent attenuation as a function of propagation distance are investigated along with methods of analysis used to determine the attenuation properties. Two methods are applied to simulated data that were generated based on experimentally acquired signals taken from a bovine specimen. The first method uses a time-domain approach that was dictated by constraints imposed by the partial overlap of fast and slow waves. The second method uses a frequency-domain log-spectral subtraction technique on the separated fast and slow waves. Applying the time-domain analysis to the broadband data yields apparent attenuation behavior that is larger in the early stages of propagation and decreases as the wave travels deeper. In contrast, performing frequency-domain analysis on the separated fast waves and slow waves results in attenuation coefficients that are independent of propagation distance. Results suggest that features arising from the analysis of overlapping two-mode data may represent an alternate explanation for the previously reported apparent dependence on propagation distance of the attenuation coefficient of cancellous bone. PMID:21973378

  12. Determining attenuation properties of interfering fast and slow ultrasonic waves in cancellous bone.

    PubMed

    Nelson, Amber M; Hoffman, Joseph J; Anderson, Christian C; Holland, Mark R; Nagatani, Yoshiki; Mizuno, Katsunori; Matsukawa, Mami; Miller, James G

    2011-10-01

    Previous studies have shown that interference between fast waves and slow waves can lead to observed negative dispersion in cancellous bone. In this study, the effects of overlapping fast and slow waves on measurements of the apparent attenuation as a function of propagation distance are investigated along with methods of analysis used to determine the attenuation properties. Two methods are applied to simulated data that were generated based on experimentally acquired signals taken from a bovine specimen. The first method uses a time-domain approach that was dictated by constraints imposed by the partial overlap of fast and slow waves. The second method uses a frequency-domain log-spectral subtraction technique on the separated fast and slow waves. Applying the time-domain analysis to the broadband data yields apparent attenuation behavior that is larger in the early stages of propagation and decreases as the wave travels deeper. In contrast, performing frequency-domain analysis on the separated fast waves and slow waves results in attenuation coefficients that are independent of propagation distance. Results suggest that features arising from the analysis of overlapping two-mode data may represent an alternate explanation for the previously reported apparent dependence on propagation distance of the attenuation coefficient of cancellous bone.

  13. Effects of elastic focusing on global models of Rayleigh wave attenuation

    NASA Astrophysics Data System (ADS)

    Bao, Xueyang; Dalton, Colleen A.; Ritsema, Jeroen

    2016-11-01

    Rayleigh wave amplitudes are the primary data set used for imaging shear attenuation in the upper mantle on a global scale. In addition to attenuation, surface-wave amplitudes are influenced by excitation at the earthquake source, focusing and scattering by elastic heterogeneity, and local structure at the receiver and the instrument response. The challenge of isolating the signal of attenuation from these other effects limits both the resolution of global attenuation models and the level of consistency between different global attenuation studies. While the source and receiver terms can be estimated using relatively simple approaches, focusing effects on amplitude are a large component of the amplitude signal and are sensitive to multiscale velocity anomalies. In this study we investigate how different theoretical treatments for focusing effects on Rayleigh wave amplitude influence the retrieved attenuation models. A new data set of fundamental-mode Rayleigh wave phase and amplitude at periods of 50 and 100 sis analysed. The amplitudes due to focusing effects are predicted using the great-circle ray approximation (GCRA), exact ray theory (ERT), and finite-frequency theory (FFT). Phase-velocity maps expanded to spherical-harmonic degree 20 and degree 40 are used for the predictions. After correction for focusing effects, the amplitude data are inverted for global attenuation maps and frequency-dependent source and receiver correction factors. The degree-12 attenuation maps, based on different corrections for focusing effects, all contain the same large-scale features, though the magnitude of the attenuation variations depends on the focusing correction. The variance reduction of the amplitudes strongly depends on the predicted focusing amplitudes, with the highest variance reduction for the ray-based approaches at 50 s and for FFT at 100 s. Although failure to account for focusing effects introduces artefacts into the attenuation models at higher spherical

  14. The thermal structure of cratonic lithosphere from global Rayleigh wave attenuation

    NASA Astrophysics Data System (ADS)

    Dalton, C. A.; Bao, X.; Ma, Z.

    2016-12-01

    Knowledge of the anelastic properties of the upper mantle complements the information provided by the elastic properties and can allow more robust inferences to be drawn about temperature, partial melt, and volatiles. Complexities associated with extracting attenuation from seismic-wave amplitudes have historically served as an impediment to attenuation imaging and limited both the resolution of and level of agreement between different models. For Rayleigh waves, removing the amplitude signal from focusing and defocusing effects is the greatest challenge. We analyze three independent data sets of Rayleigh wave amplitude to investigate how three factors contribute to discrepancies between the attenuation models: uncertainties in the amplitude measurements, variable path coverage, and the treatment of focusing effects. Regionalized pure-path and fully two-dimensional attenuation models are derived and compared. The approach for determining attenuation models from real data is guided by an analysis of amplitudes measured from synthetic spectral-element waveforms. The results show that differences in the amplitude measurements introduce minor differences in the attenuation models; path coverage and focusing effects are more important. The pure-path attenuation values exhibit a clear dependence on tectonic region at shorter periods that disappears at long periods. The 2-D attenuation maps are highly correlated with each other to spherical-harmonic degree 16 and can resolve smaller features than the previous generation of global attenuation models. Anomalously low attenuation is nearly perfectly associated with continental cratons. Variations in lithospheric thickness are determined by forward modeling the global attenuation variations as a thermal boundary layer of variable thickness. Temperature profiles that satisfy the attenuation values systematically overpredict and underpredict Rayleigh wave phase velocity in cratons at short and long periods, respectively

  15. Anomalous shear wave attenuation in the shallow crust beneath the Coso volcanic region, California

    SciTech Connect

    Sanders, C.; Ho-Liu, P.; Rinn, D.; Kanamori, H.

    1988-04-10

    We use seismograms of local earthquakes to image relative shear wave attenuation structure in the shallow crust beneath the region containing the Coso volcanic-geothermal area of eastern California. SV and P wave amplitudes were measured from vertical component seismograms of earthquakes that occurred in the Coso-southern Sierra Nevada region from July 1983 to 1985. Seismograms of 16 small earthquakes show SV amplitudes which are greatly diminished at some azimuths and takeoff angles, indicating strong lateral variations in S wave attenuation in the area. Three-dimensional images of the relative S wave attenuation structure are obtained from forward modeling and a back projection inversion of the amplitude data. The results indicate regions within a 20 by 30 by 10 km volume of the shallow crust (one shallower than 5 km) that severely attenuate SV waves passing through them. These anomalies lie beneath the Indian Wells Valley 30 km south of the Coso volcanic field, and are coincident with the epicentral locations of recent earthquake swarms. No anomalous attenuation is seen beneath the Coso volcanic field above about 5 km depth. Geologic relations and the coincidence of anomalous slow P wave velocities suggest that the attenuation anomalies may be related to magmatism along the eastern Sierra front. copyright American Geophysical Union 1988

  16. P-wave attenuation anisotropy in TI media and its application in fracture parameters inversion

    NASA Astrophysics Data System (ADS)

    He, Yi-Yuan; Hu, Tian-Yue; He, Chuan; Tan, Yu-Yang

    2016-12-01

    The existence of aligned fractures in fluid-saturated rocks leads to obvious attenuation anisotropy and velocity anisotropy. Attenuation anisotropy analysis can be applied to estimate fracture density and scale, which provide important information for reservoir identification. This paper derives P-wave attenuation anisotropy in the ATI media where the symmetry axis is in the arbitrary direction theoretically and modifies the spectral ratio method to measure attenuation anisotropy in the ATI media, thus avoiding a large measurement error when applied to wide azimuth or full azimuth data. Fracture dip and azimuth can be estimated through attenuation anisotropy analysis. For small-scale fractures, fracture scale and fracture density can be determined with enhanced convergence if velocity and attenuation information are both used. We also apply the modified spectralratio method to microseismic field data from an oilfield in East China and extract the fracture dip through attenuation anisotropy analysis. The result agrees with the microseismic monitoring.

  17. Investigation of guided wave propagation and attenuation in pipe buried in sand

    NASA Astrophysics Data System (ADS)

    Leinov, Eli; Lowe, Michael J. S.; Cawley, Peter

    2015-07-01

    Long-range guided wave testing is a well-established method for detection of corrosion defects in pipelines. The method is currently used routinely for above ground pipelines in a variety of industries, e.g. petrochemical and energy. When the method is applied to pipes buried in soil, test ranges tend to be significantly compromised and unpredictable due to attenuation of the guided wave resulting from energy leakage into the embedding soil. The attenuation characteristics of guided wave propagation in an 8 in. pipe buried in sand are investigated using a laboratory full-scale experimental rig and model predictions. We report measurements of attenuation of the T(0,1) and L(0,2) guided wave modes over a range of sand conditions, including loose, compacted, mechanically compacted, water saturated and drained. Attenuation values are found to be in the range of 1.65-5.5 dB/m and 0.98-3.2 dB/m for the torsional and longitudinal modes, respectively, over the frequency of 11-34 kHz. The application of overburden pressure modifies the compaction of the sand and increases the attenuation. Mechanical compaction of the sand yields similar attenuation values to those obtained with applied overburden pressure. The attenuation decreases in the fully water-saturated sand, and increases in drained sand to values comparable with those obtained for compacted sand. Attenuation measurements are compared with Disperse software model predictions and confirm that the attenuation phenomenon in buried pipes is essentially governed by the bulk shear velocity in the sand. The attenuation behaviour of the torsional guided wave mode is found not to be captured by a uniform soil model; comparison with predictions obtained with the Disperse software suggest that this is likely to be due to a layer of sand adhering to the surface of the pipe.

  18. A Frequency-Shift Method to Measure Shear-Wave Attenuation in Soft Tissues.

    PubMed

    Bernard, Simon; Kazemirad, Siavash; Cloutier, Guy

    2017-03-01

    In vivo quantification of shear-wave attenuation in soft tissues may help to better understand human tissue rheology and lead to new diagnostic strategies. Attenuation is difficult to measure in acoustic radiation force elastography because the shear-wave amplitude decreases due to a combination of diffraction and viscous attenuation. Diffraction correction requires assuming a cylindrical wavefront and an isotropic propagation medium, which may not be the case in some applications. In this paper, the frequency-shift method, used in ultrasound imaging and seismology, was adapted for shear-wave attenuation measurement in elastography. This method is not sensitive to diffraction effects. For a linear frequency dependence of the attenuation, a closed-form relation was obtained between the decrease in the peak frequency of the gamma-distributed wave amplitude spectrum and the attenuation coefficient of the propagation medium. The proposed method was tested against a plane-wave reference method in homogeneous agar-gelatin phantoms with 0%, 10%, and 20% oil concentrations, and hence different attenuations of 0.117, 0.202, and 0.292 [Formula: see text]/Hz, respectively. Applicability to biological tissues was demonstrated with two ex vivo porcine liver samples (0.79 and 1.35 [Formula: see text]/Hz) and an in vivo human muscle, measured along (0.43 [Formula: see text]/Hz) and across (1.77 [Formula: see text]/Hz) the tissue fibers. In all cases, the data supported the assumptions of a gamma-distributed spectrum for the source and linear frequency attenuation for the tissue. This method provides tissue attenuation, which is relevant diagnostic information to model viscosity, in addition to shear-wave velocity used to assess elasticity. Data processing is simple and could be performed automatically in real time for clinical applications.

  19. Dynamic response signatures of a scaled model platform for floating wind turbines in an ocean wave basin.

    PubMed

    Jaksic, V; O'Shea, R; Cahill, P; Murphy, J; Mandic, D P; Pakrashi, V

    2015-02-28

    Understanding of dynamic behaviour of offshore wind floating substructures is extremely important in relation to design, operation, maintenance and management of floating wind farms. This paper presents assessment of nonlinear signatures of dynamic responses of a scaled tension-leg platform (TLP) in a wave tank exposed to different regular wave conditions and sea states characterized by the Bretschneider, the Pierson-Moskowitz and the JONSWAP spectra. Dynamic responses of the TLP were monitored at different locations using load cells, a camera-based motion recognition system and a laser Doppler vibrometer. The analysis of variability of the TLP responses and statistical quantification of their linearity or nonlinearity, as non-destructive means of structural monitoring from the output-only condition, remains a challenging problem. In this study, the delay vector variance (DVV) method is used to statistically study the degree of nonlinearity of measured response signals from a TLP. DVV is observed to create a marker estimating the degree to which a change in signal nonlinearity reflects real-time behaviour of the structure and also to establish the sensitivity of the instruments employed to these changes. The findings can be helpful in establishing monitoring strategies and control strategies for undesirable levels or types of dynamic response and can help to better estimate changes in system characteristics over the life cycle of the structure.

  20. Dynamic response signatures of a scaled model platform for floating wind turbines in an ocean wave basin

    PubMed Central

    Jaksic, V.; O'Shea, R.; Cahill, P.; Murphy, J.; Mandic, D. P.; Pakrashi, V.

    2015-01-01

    Understanding of dynamic behaviour of offshore wind floating substructures is extremely important in relation to design, operation, maintenance and management of floating wind farms. This paper presents assessment of nonlinear signatures of dynamic responses of a scaled tension-leg platform (TLP) in a wave tank exposed to different regular wave conditions and sea states characterized by the Bretschneider, the Pierson–Moskowitz and the JONSWAP spectra. Dynamic responses of the TLP were monitored at different locations using load cells, a camera-based motion recognition system and a laser Doppler vibrometer. The analysis of variability of the TLP responses and statistical quantification of their linearity or nonlinearity, as non-destructive means of structural monitoring from the output-only condition, remains a challenging problem. In this study, the delay vector variance (DVV) method is used to statistically study the degree of nonlinearity of measured response signals from a TLP. DVV is observed to create a marker estimating the degree to which a change in signal nonlinearity reflects real-time behaviour of the structure and also to establish the sensitivity of the instruments employed to these changes. The findings can be helpful in establishing monitoring strategies and control strategies for undesirable levels or types of dynamic response and can help to better estimate changes in system characteristics over the life cycle of the structure. PMID:25583866

  1. Rain attenuation statistics over millimeter wave bands in South Korea

    NASA Astrophysics Data System (ADS)

    Shrestha, Sujan; Choi, Dong-You

    2017-01-01

    Rain induced degradations are significant for terrestrial microwave links operating at frequencies higher than 10 GHz. Paper presents analyses done on rain attenuation and rainfall data for three years between 2013 till 2015, in 3.2 km experimental link of 38 GHz and 0.1 km link at 75 GHz. The less link distance is maintained for 75 GHz operating frequency in order to have better recording of propagation effect as such attenuation induced by rain. OTT Parsivel is used for collection of rain rate database which show rain rate of about 50 mm/h and attenuation values of 20.89 and 28.55 dB are obtained at 0.01% of the time for vertical polarization under 38 and 75 GHz respectively. Prediction models, namely, ITU-R P. 530-16, Da Silva Mello, Moupfouma, Abdulrahman, Lin and differential equation approach are analyzed. This studies help to identify most suitable rain attenuation model for higher microwave bands. While applying ITU-R P. 530-16, the relative error margin of about 3%, 38% and 42% along with 80, 70, 61% were obtained in 0.1%, 0.01% and 0.001% of the time for vertical polarization under 38 and 75 GHz respectively. Interestingly, ITU-R P. 530-16 shows relatively closer estimation to measured rain attenuation at 75 GHz with relatively less error probabilities and additionally, Abdulrahman and ITU-R P. 530-16 results in better estimation to the measured rain attenuation at 38 GHz link. The performance of prominent rain attenuation models are judged with different error matrices as recommended by ITU-R P. 311-15. Furthermore, the efficacy of frequency scaling technique of rain attenuation between links distribution are also discussed. This study shall be useful for making good considerations in rain attenuation predictions for terrestrial link operating at higher frequencies.

  2. Stabilized floating platforms

    DOEpatents

    Thomas, David G.

    1976-01-01

    The subject invention is directed to a floating platform for supporting nuclear reactors and the like at selected offshore sites. The platform is provided with a stabilizer mechanism which significantly reduces the effects of wave action upon the platform and which comprises a pair of relatively small floats attached by rigid booms to the platform at locations spaced therefrom for reducing wave pitch, acceleration, and the resonance period of the wave.

  3. Attenuation of Lamb waves in the vicinity of a forbidden band in a phononic crystal.

    PubMed

    Bavencoffe, Maxime; Hladky-Hennion, Anne-Christine; Morvan, Bruno; Izbicki, Jean-Louis

    2009-09-01

    When a Lamb wave propagates on a plate engraved by a periodic grating, it may exhibit attenuation. This attenuation is related to a coupling of this incident mode with other propagating modes. As the propagation takes place in a periodic medium, the dispersion curves of the modes are of interest because they exhibit passbands and stopbands related to the geometry of the waveguide. The goal of this work is to quantitatively establish the relation between the value of the attenuation of the propagating waves and the width of the forbidden bands appearing inside the Brillouin zone. This study is performed by using a finite element method (ATILA code).

  4. Laboratory measurements of wave attenuation through model and live vegetation

    USDA-ARS?s Scientific Manuscript database

    Surge and waves generated by hurricanes and tropical storms often cause severe damage and loss of life in coastal areas. It is widely recognized that wetlands along coastal fringes reduce storm surge and waves. Yet, the potential role and primary mechanisms of wave mitigation by wetland vegetation a...

  5. Attenuation of high-frequency body waves in the crust of the Central External Dinarides

    NASA Astrophysics Data System (ADS)

    Dasović, Iva; Ruščić, Marija; Herak, Davorka; Herak, Marijan

    2015-10-01

    The Central External Dinarides are known as a tectonically complex region of moderate seismicity where several strong earthquakes occurred in the last century. In order to gain insight into the attenuation of seismic waves in the area, the extended coda normalization method was applied to band-pass-filtered seismograms of local earthquakes recorded at seven seismological broadband stations. Obtained results indicate strong attenuation of direct body waves: Q 0,P = Q P(1 Hz) is found between 21 and 120 and Q 0,S = Q S(1 Hz) is between 46 and 113, whereas the exponent n in the power law of frequency dependence of the quality factor is found in the range of 0.63-1.52 and 0.65-0.97 for n P and n S, respectively. P-waves are, on the average, attenuated more than S-waves. The three island stations (Dugi Otok (DUGI), Žirje (ZIRJ), Hvar (HVAR)) are distinguished by the strong low-frequency P-wave attenuation and more pronounced frequency dependence of the Q P factor ( Q 0,S/ Q 0,P > 1.7, Q 0,P < 60, n P > n S). The remaining four inland stations (Udbina (UDBI), Morići (MORI), Kijevo (KIJV), Čačvina (CACV)) all exhibit similar qualitative attenuation properties for P- and S-waves ( n P ≈ n S ≈ 1 and Q 0,S ≈ Q 0,P), although individual values of the Q-factors vary notably within this group. Low-frequency attenuation of direct S-waves in the crust is stronger than mean attenuation of scattered coda waves in the lithosphere, especially for long coda lapse times. The results are also qualitatively in agreement with the thermal regime in the area.

  6. Anisotropy of attenuation of high-frequency body waves in the External Dinarides

    NASA Astrophysics Data System (ADS)

    Dasović, Iva; Herak, Davorka; Herak, Marijan

    2017-04-01

    The Dinarides are a part of the complex Alpine-Carpathian-Dinaric orogenic system. They formed as a result of the push of the African plate and a collision of the Adriatic microplate with the European plate. The External Dinarides represent western part of the Dinarides derived from the Adriatic microplate, i.e. the Adriatic carbonate platform. They are characterised by NW trend and SW vergence of compressional and imbricated structures. Recent seismicity in the area varies from moderate to high with rare occurrence of strong earthquakes. Prevailing compressional stresses result in mainly reverse faulting, with or without a dextral strike-slip component. This area represents one of the geologically and tectonically most complicated and puzzling regions in Europe. We used local earthquakes recorded at broadband seismic stations of the Croatian seismological network to analyse attenuation of high-frequency body waves. To estimate attenuation of P- and S-waves, i.e. the quality factors QP and QS, we applied the extended coda normalization method. These quality factors reflect the total attenuation of the direct body waves in the crust. The results indicate strong attenuation of P- and S- waves. Moreover, further analysis of the Q-factors indicates existence of anisotropy in seismic attenuation, with higher attenuation in the direction perpendicular to the strike of the Dinarides and lower attenuation parallel to it.

  7. Teleseismic Body-Wave Attenuation beneath the Western and Central United States

    NASA Astrophysics Data System (ADS)

    Yang, B.; Reed, C. A.; Liu, K. H.; Gao, S. S.

    2014-12-01

    Attenuation of seismic waves is the consequence of anelasticity of the Earth's layers along the path of propagation. Joint analyses of seismic velocity with attenuation anomalies can significantly reduce the non-uniqueness in the interpretation of velocity images and result in a better understanding of the Earth's interior structure, composition, and dynamics. Employing a Bayesian approach with a common spectrum simultaneous inversion for attenuation factors (Gao, 1997), we have processed over 14,000 teleseismic body-wave seismograms recorded by all publicly available broadband seismic stations in the western and central United States. Preliminary results show extensive low-attenuation areas beneath the central United States probably related to fragments of the ancient Farallon slab, while less pronounced regions of likely cold material underlie the Colorado Plateau. High-attenuation anomalies are discovered in association with the Snake River Plain and the Rio Grande Rift. We apply station-averaged parameters and P-S attenuation ratios and compare our findings with published shear-wave splitting results to examine the presence of partial melt and asthenospheric upwelling. Additionally, we examine the azimuthal variation of attenuation measurements to constrain the possible existence of attenuation anisotropy and attempt to constrain the source depth of anisotropy through tomographic methods.

  8. [Attenuation of photosynthetically available radiation (PAR) in Meiliang Bay under different winds and waves].

    PubMed

    Zhang, Yunlin; Qin, Boqiang; Chen, Weimin; Hu, Weiping; Gao, Guang; Zhu, Guangwei; Luo, Liancong

    2005-06-01

    Based on the successive underwater irradiance measurement in situ from Jul. 12 to 17 in 2003, the attenuation of photosynthetically available radiation (PAR) and euphotic depth in Meiliang Bay were analyzed under different winds and waves. The results showed that the downward PAR attenuation coefficients ranged from 2.63 to 4.7 m(-1), with an average of 3.63 +/- 0.47 x m(-1), and the corresponding euphotic depth ranged from 0.98 to 1.75 m, with an average of 1.29 +/- 0.18 m, which demonstrated that phytoplankton and macrophyte could not grow below 1.5 m due to the lack of adequate solar radiation. The total suspended solids resulted from wind and wave increased the attenuation of light, with the downward attenuation coefficients of PAR being 2.63, 3.72 and 4.37 x m(-1) under small, medium and large wind and wave, respectively. Significant linear correlations were found between transparence, PAR attenuation coefficient, euphotic depth and total suspended solid, especially inorganic suspended solid, while chlorophyll a was the most nonsignificant light attenuator. Multiple stepwise linear regressions showed that inorganic suspended solid was the most important light attenuator dominating the light attenuation in wind-exposed Meiliang Bay.

  9. Attenuation characteristics of electromagnetic waves in a weak collisional and fully ionized dusty plasma

    NASA Astrophysics Data System (ADS)

    Dan, Li; Guo, Li-Xin; Li, Jiang-Ting; Chen, Wei; Yan, Xu; Huang, Qing-Qing

    2017-09-01

    The expression of complex dielectric permittivity for non-magnetized fully ionized dusty plasma is obtained based on the kinetic equation in the Fokker-Planck-Landau collision model and the charging equation of the statistical theory. The influences of density, average size of dust grains, and balanced charging of the charge number of dust particles on the attenuation properties of electromagnetic waves in fully ionized dusty plasma are investigated by calculating the attenuation constant. In addition, the attenuation characteristics of weakly ionized and fully ionized dusty plasmas are compared. Results enriched the physical mechanisms of microwave attenuation for fully ionized dusty plasma and provide a theoretical basis for future studies.

  10. Wave attenuation and mode dispersion in a waveguide coated with lossy dielectric material

    NASA Technical Reports Server (NTRS)

    Lee, C. S.; Chuang, S. L.; Lee, S. W.; Lo, Y. T.

    1984-01-01

    The modal attenuation constants in a cylindrical waveguide coated with a lossy dielectric material are studied as functions of frequency, dielectric constant, and thickness of the dielectric layer. A dielectric material best suited for a large attenuation is suggested. Using Kirchhoff's approximation, the field attenuation in a coated waveguide which is illuminated by a normally incident plane wave is also studied. For a circular guide which has a diameter of two wavelengths and is coated with a thin lossy dielectric layer (omega sub r = 9.1 - j2.3, thickness = 3% of the radius), a 3 dB attenuation is achieved within 16 diameters.

  11. Anomalous shear wave attenuation in the shallow crust beneath the Coso volcanic regionn, California ( USA).

    USGS Publications Warehouse

    Sanders, C.; Ho-Liu, P.; Rinn, D.; Hiroo, Kanamori

    1988-01-01

    We use seismograms of local earthquakes to image relative shear wave attenuation structure in the shallow crust beneath the region containing the Coso volcanic-geothermal area of E California. Seismograms of 16 small earthquakes show SV amplitudes which are greatly diminished at some azimuths and takeoff angles, indicating strong lateral variations in S wave attenuation in the area. 3-D images of the relative S wave attenuation structure are obtained from forward modeling and a back projection inversion of the amplitude data. The results indicate regions within a 20 by 30 by 10 km volume of the shallow crust (one shallower than 5 km) that severely attenuate SV waves passing through them. These anomalies lie beneath the Indian Wells Valley, 30 km S of the Coso volcanic field, and are coincident with the epicentral locations of recent earthquake swarms. No anomalous attenuation is seen beneath the Coso volcanic field above about 5 km depth. Geologic relations and the coincidence of anomalously slow P wave velocities suggest that the attenuation anomalies may be related to magmatism along the E Sierra front.-from Authors

  12. Transionospheric attenuation of 100 kHz radio waves inferred from satellite and ground based observations

    NASA Astrophysics Data System (ADS)

    Fullekrug, Martin; Parrot, Michel; Ash, Matthew; Astin, Ivan; Williams, Paul; Talhi, R.

    2009-03-01

    Around fifty LORAN (LOng RAnge Navigation) transmitters in the northern hemisphere currently launch continuously pulsed 100 kHz radio waves into the Earth's atmosphere for marine navigation. It is discovered that the 100 kHz radio waves from the LORAN transmissions can be detected by the DEMETER satellite at an altitude of ~660 km above the transmitters. These novel electric field measurements in space enable the determination of the nocturnal transionospheric attenuation by comparison with ground based electric field measurements. The electric field measurements on the satellite indicate that the nocturnal transionospheric attenuation of 100 kHz radio waves from LORAN transmissions is equivalent to a nocturnal subionospheric attenuation of the 100 kHz radio waves at a distance of ~7-9 Mm. The radio waves exhibit an average subionospheric attenuation of ~5 dB/Mm and it is concluded that the nocturnal transionospheric attenuation of 100 kHz radio waves is ~35-45 dB. This result enables future space missions to quantify the intensity of lightning discharges associated with transient luminous events and terrestrial γ-ray flashes.

  13. Anisotropic changes in P-wave velocity and attenuation during deformation and fluid infiltration of granite

    USGS Publications Warehouse

    Stanchits, S.A.; Lockner, D.A.; Ponomarev, A.V.

    2003-01-01

    Fluid infiltration and pore fluid pressure changes are known to have a significant effect on the occurrence of earthquakes. Yet, for most damaging earthquakes, with nucleation zones below a few kilometers depth, direct measurements of fluid pressure variations are not available. Instead, pore fluid pressures are inferred primarily from seismic-wave propagation characteristics such as Vp/Vs ratio, attenuation, and reflectivity contacts. We present laboratory measurements of changes in P-wave velocity and attenuation during the injection of water into a granite sample as it was loaded to failure. A cylindrical sample of Westerly granite was deformed at constant confining and pore pressures of 50 and 1 MPa, respectively. Axial load was increased in discrete steps by controlling axial displacement. Anisotropic P-wave velocity and attenuation fields were determined during the experiment using an array of 13 piezoelectric transducers. At the final loading steps (86% and 95% of peak stress), both spatial and temporal changes in P-wave velocity and peak-to-peak amplitudes of P and S waves were observed. P-wave velocity anisotropy reached a maximum of 26%. Transient increases in attenuation of up to 483 dB/m were also observed and were associated with diffusion of water into the sample. We show that velocity and attenuation of P waves are sensitive to the process of opening of microcracks and the subsequent resaturation of these cracks as water diffuses in from the surrounding region. Symmetry of the orientation of newly formed microcracks results in anisotropic velocity and attenuation fields that systematically evolve in response to changes in stress and influx of water. With proper scaling, these measurements provide constraints on the magnitude and duration of velocity and attenuation transients that can be expected to accompany the nucleation of earthquakes in the Earth's crust.

  14. Estimation of near-surface quality factors by constrained inversion of Rayleigh-wave attenuation coefficients

    NASA Astrophysics Data System (ADS)

    Xia, Jianghai; Xu, Yixian; Miller, Richard D.; Ivanov, Julian

    2012-07-01

    Quality factors (Q) of near-surface materials are as important as velocities of the materials in many applications. Only phase information of surface-wave data is utilized when high-frequency (≥ 2 Hz) surface-wave data are routinely inverted to determine near-surface shear (S)-wave velocities. Amplitude information of high-frequency surface-wave data can be used to determine quality factors of near-surface materials. Given S-wave velocity, compressional (P)-wave velocity, and Rayleigh-wave phase velocities, it is feasible to solve for S-wave quality factor QS and P-wave quality factor QP (for some specific velocity models) down to 30 m below the ground surface in many settings by inverting high-frequency Rayleigh-wave attenuation coefficients in a layered earth model. Amplitude of seismic data is an exponential function of attenuation coefficients. When calculating attenuation coefficients from changes in amplitude, this nonlinear nature would result in that small variations in amplitude cause huge changes in attenuation coefficients. This result suggests data (attenuation coefficients) that normally possess large errors could eventually transfer to a model (quality factors); therefore, constraints (or a priori information) on models are necessary. Because an inversion system to solve this problem is unstable, a regularization parameter must be introduced into an inversion algorithm to stabilize the inversion. These characteristics of the inversion problem allow us to solve the problem as a constrained and regularized linear system. Usually, a set of models that meet the defined constraints can be obtained by solving the system. Based on the linear nature of the inversion system, a smooth model can be selected from the set of models as a solution of the inversion using the L-curve method. This approach is a trade-off solution between data misfit and model length. Several real-world examples demonstrate the importance of constraints in finding acceptable realistic

  15. Frequency-Dependent Attenuation of Blasting Vibration Waves

    NASA Astrophysics Data System (ADS)

    Zhou, Junru; Lu, Wenbo; Yan, Peng; Chen, Ming; Wang, Gaohui

    2016-10-01

    The dominant frequency, in addition to the peak particle velocity, is a critical factor for assessing adverse effects of the blasting vibration on surrounding structures; however, it has not been fully considered in blasting design. Therefore, the dominant frequency-dependent attenuation mechanism of blast-induced vibration is investigated in the present research. Starting with blasting vibration induced by a spherical charge propagating in an infinite viscoelastic medium, a modified expression of the vibration amplitude spectrum was derived to reveal the frequency dependency of attenuation. Then, ground vibration induced by more complex and more commonly used cylindrical charge that propagates in a semi-infinite viscoelastic medium was analyzed by numerical simulation. Results demonstrate that the absorptive property of the medium results in the frequency attenuation versus distance, whereas a rapid drop or fluctuation occurs during the attenuation of ground vibration. Fluctuation usually appears at moderate to far field, and the dominant frequency generally decreases to half the original value when rapid drop occurs. The decay rate discrepancy between different frequency components and the multimodal structure of vibration spectrum lead to the unsmooth frequency-dependent attenuation. The above research is verified by two field experiments. Furthermore, according to frequency-based vibration standards, frequency drop and fluctuation should be considered when evaluating blast safety. An optimized piecewise assessment is proposed for more accurate evaluation: With the frequency drop point as the breakpoint, the assessment is divided into two independent sections along the propagating path.

  16. Rigid polyurethane foam as an efficient material for shock wave attenuation

    NASA Astrophysics Data System (ADS)

    Komissarov, P. V.; Borisov, A. A.; Sokolov, G. N.; Lavrov, V. V.

    2016-09-01

    A new method for reducing parameters of blast waves generated by explosions of HE charges on ground is presented. Most of the traditional techniques reduce the wave parameters at a certain distance from the charge, i.e. as a matter of fact the damping device interacts with a completely formed shock wave. The proposed approach is to use rigid polyurethane foam coating immediately the explosive charge. A distributed structure of such a foam block that provides most efficient shock wave attenuation is suggested. Results of experimental shock wave investigations recorded in tests in which HE charges have been exploded with damping devices and without it are compared.

  17. Propagation and attenuation of inhomogeneous waves in double-porosity dual-permeability materials

    NASA Astrophysics Data System (ADS)

    Sharma, M. D.

    2017-02-01

    This study considers the propagation of harmonic plane waves in a double-porosity dual-permeability solid saturated with single viscous fluid. Christoffel system is obtained to explain the existence of three longitudinal waves and a transverse wave in the medium considered. Each wave is identified with a complex velocity, which is resolved for inhomogeneous propagation to calculate the phase velocity and attenuation of the wave. Pore-fluid pressures are expressed in terms of velocities of solid particles corresponding to the propagation of three longitudinal waves. Then, transfer rate of pore-fluid between two porosities induced by each longitudinal wave is calculated as a function of its complex velocity. Numerical example is solved to study the dispersion in phase velocity and attenuation for each of the four waves. Effects of pore-fluid viscosity, wave-inhomogeneity and composition of double porosity on inhomogeneous propagation are analysed graphically. Transfer rate of pore-fluid, induced by each of the three longitudinal waves, is calculated as a periodic waveform. Variations in the fluid-flow profile are exhibited for different values of pore-fluid viscosity, skeleton permeability, wave-frequency and wave-inhomogeneity.

  18. Propagation and attenuation of inhomogeneous waves in double-porosity dual-permeability materials

    NASA Astrophysics Data System (ADS)

    Sharma, M. D.

    2016-11-01

    This study considers the propagation of harmonic plane waves in a double-porosity dual-permeability solid saturated with single viscous fluid. Christoffel system is obtained to explain the existence of three longitudinal waves and a transverse wave in the medium considered. Each wave is identified with a complex velocity, which is resolved for inhomogeneous propagation to calculate the phase velocity and attenuation of the wave. Pore-fluid pressures are expressed in terms of velocities of solid particles corresponding to the propagation of three longitudinal waves. Then, transfer rate of pore-fluid between two porosities induced by each longitudinal wave is calculated as a function of its complex velocity. Numerical example is solved to study the dispersion in phase velocity and attenuation for each of the four waves. Effects of pore-fluid viscosity, wave-inhomogeneity and composition of double porosity on inhomogeneous propagation are analysed graphically. Transfer rate of pore-fluid, induced by each of the three longitudinal waves, is calculated as a periodic waveform. Variations in the fluid-flow profile are exhibited for different values of pore-fluid viscosity, skeleton permeability, wave-frequency and wave-inhomogeneity.

  19. Shear wave anisotropy from aligned inclusions: ultrasonic frequency dependence of velocity and attenuation

    NASA Astrophysics Data System (ADS)

    de Figueiredo, J. J. S.; Schleicher, J.; Stewart, R. R.; Dayur, N.; Omoboya, B.; Wiley, R.; William, A.

    2013-04-01

    To understand their influence on elastic wave propagation, anisotropic cracked media have been widely investigated in many theoretical and experimental studies. In this work, we report on laboratory ultrasound measurements carried out to investigate the effect of source frequency on the elastic parameters (wave velocities and the Thomsen parameter γ) and shear wave attenuation) of fractured anisotropic media. Under controlled conditions, we prepared anisotropic model samples containing penny-shaped rubber inclusions in a solid epoxy resin matrix with crack densities ranging from 0 to 6.2 per cent. Two of the three cracked samples have 10 layers and one has 17 layers. The number of uniform rubber inclusions per layer ranges from 0 to 100. S-wave splitting measurements have shown that scattering effects are more prominent in samples where the seismic wavelength to crack aperture ratio ranges from 1.6 to 1.64 than in others where the ratio varied from 2.72 to 2.85. The sample with the largest cracks showed a magnitude of scattering attenuation three times higher compared with another sample that had small inclusions. Our S-wave ultrasound results demonstrate that elastic scattering, scattering and anelastic attenuation, velocity dispersion and crack size interfere directly in shear wave splitting in a source-frequency dependent manner, resulting in an increase of scattering attenuation and a reduction of shear wave anisotropy with increasing frequency.

  20. Experimental investigation of wave attenuation through model and live vegetation

    USDA-ARS?s Scientific Manuscript database

    Hurricanes and tropical storms often cause severe damage and loss of life in coastal areas. It is widely recognized that wetlands along coastal fringes reduce storm surge and waves. Yet, the potential role and primary mechanisms of wave mitigation by wetland vegetation are not fully understood. K...

  1. Wave attenuation as a measure of muscle quality as measured by magnetic resonance elastography: initial results.

    PubMed

    Domire, Zachary J; McCullough, Matthew B; Chen, Qingshan; An, Kai-Nan

    2009-03-11

    Advances in imaging technologies such as magnetic resonance elastography (MRE) have allowed researchers to gain insights into muscle function in vivo. MRE has been used to examine healthy and diseased muscle by calculating shear modulus. However, additional information can be measured from visualizing a mechanical wave as it passes through a tissue. One such measurable quantity is wave attenuation. The purpose of this study was to determine if a simple measure of wave attenuation could be used to distinguish between healthy and diseased muscle. Twenty seven subjects (14 healthy controls, 7 hyperthyroid myopathy patients, 6 myositis patients) participated in this study. Wave amplitude was determined along a linear profile through the center of the muscle, and an exponential decay curve was fit to the data. This measure was able to find significant differences in attenuation between healthy and diseased muscle. Furthermore, four hyperthyroid myopathy subjects who were tested following treatment all showed improvement by this measure. A likely reason for patients with hyperthyroid myopathy and myositis behaving similarly is that this measurement may reflect similar changes in the muscle extracellular matrix. In addition to modulus, attenuation seems to be an important parameter to measure in skeletal muscle. Further research is needed to investigate other potential measures of attenuation as well as examining other potential measures that can be found from visualizing wave propagation. Future studies should also include muscle biopsies to confirm that the changes seen are as a result of changes in extracellular matrix structure.

  2. Separating Internal Waves and Vortical Motions: Analysis of LatMix -EM-APEX Float Measurements

    DTIC Science & Technology

    2015-09-30

    1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Separating Internal Waves and Vortical Motions: Analysis...identify mechanisms of small-scale processes––i.e., internal tides, inertial waves , nonlinear internal waves , vortical modes, and turbulence mixing...focus as the complex interplay of internal waves from a variety of sources and turbulence makes this a current locus of uncertainty. Our focus is on

  3. Comparison of fractional wave equations for power law attenuation in ultrasound and elastography.

    PubMed

    Holm, Sverre; Näsholm, Sven Peter

    2014-04-01

    A set of wave equations with fractional loss operators in time and space are analyzed. The fractional Szabo equation, the power law wave equation and the causal fractional Laplacian wave equation are all found to be low-frequency approximations of the fractional Kelvin-Voigt wave equation and the more general fractional Zener wave equation. The latter two equations are based on fractional constitutive equations, whereas the former wave equations have been derived from the desire to model power law attenuation in applications like medical ultrasound. This has consequences for use in modeling and simulation, especially for applications that do not satisfy the low-frequency approximation, such as shear wave elastography. In such applications, the wave equations based on constitutive equations are the viable ones. Copyright © 2014 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

  4. Seismic wave attenuation and velocity dispersion in UAE carbonates

    NASA Astrophysics Data System (ADS)

    Ogunsami, Abdulwaheed Remi

    Interpreting the seismic property of fluids in hydrocarbon reservoirs at low frequency scale has been a cherished goal of petroleum geophysics research for decades. Lately, there has been tremendous interest in understanding attenuation as a result of fluid flow in porous media. Although interesting, the emerging experimental and theoretical information still remain ambiguous and are practically not utilized for reasons not too obscure. Attenuation is frequency dependent and hard to measure in the laboratory at low frequency. This thesis describes and reports the results of an experimental study of low frequency attenuation and velocity dispersion on a selected carbonate reservoir samples in the United Arab Emirates (UAE). For the low frequency measurements, stress-strain method was used to measure the moduli from which the velocity is derived. Attenuation was measured as the phase difference between the applied stress and the strain. For the ultrasonic component, the pulse propagation method was employed. To study the fluid effect especially at reservoir in situ conditions, the measurements were made dry and saturated with liquid butane and brine at differential pressures of up to 5000 psi with pore pressure held constant at 500 psi. Similarly to what has been documented in the literatures for sandstone, attenuation of the bulk compressibility mode dominates the losses in these dry and somewhat partially saturated carbonate samples with butane and brine. Overall, the observed attenuation cannot be simply said to be frequency dependent within this low seismic band. While attenuation seems to be practically constant in the low frequency band for sample 3H, such conclusion cannot be made for sample 7H. For the velocities, significant dispersion is observed and Gassmann generally fails to match the measured velocities. Only the squirt model fairly fits the velocities, but not at all pressures. Although the observed dispersion is larger than Biot's prediction, the fact

  5. The thermal structure of cratonic lithosphere from global Rayleigh wave attenuation

    NASA Astrophysics Data System (ADS)

    Dalton, Colleen A.; Bao, Xueyang; Ma, Zhitu

    2017-01-01

    The resolution of and level of agreement between different attenuation models have historically been limited by complexities associated with extracting attenuation from seismic-wave amplitudes, which are also affected by the source, the receiver, and propagation through velocity heterogeneities. For intermediate- and long-period Rayleigh waves, removing the amplitude signal due to focusing and defocusing effects is the greatest challenge. In this paper, three independent data sets of fundamental-mode Rayleigh wave amplitude are analyzed to investigate how three factors contribute to discrepancies between the attenuation models: uncertainties in the amplitude measurements themselves, variable path coverage, and the treatment of focusing effects. Regionalized pure-path and fully two-dimensional attenuation models are derived and compared. The approach for determining attenuation models from real data is guided by an analysis of amplitudes measured from synthetic spectral-element waveforms, for which the input Earth model is perfectly known. The results show that differences in the amplitude measurements introduce only very minor differences between the attenuation models; path coverage and the removal of focusing effects are more important. The pure-path attenuation values exhibit a clear dependence on tectonic region at shorter periods that disappears at long periods, in agreement with pure-path phase-velocity results obtained by inverting Rayleigh wave phase delays. The 2-D attenuation maps are highly correlated with each other to spherical-harmonic degree 16 and can resolve smaller features than the previous generation of global attenuation models. Anomalously low attenuation is nearly perfectly associated with continental cratons. Variations in lithospheric thickness are determined by forward modeling the global attenuation variations as a thermal boundary layer of variable thickness. Temperature profiles that satisfy the attenuation values systematically

  6. Linking multiple relaxation, power-law attenuation, and fractional wave equations.

    PubMed

    Näsholm, Sven Peter; Holm, Sverre

    2011-11-01

    The acoustic wave attenuation is described by an experimentally established frequency power law in a variety of complex media, e.g., biological tissue, polymers, rocks, and rubber. Recent papers present a variety of acoustical fractional derivative wave equations that have the ability to model power-law attenuation. On the other hand, a multiple relaxation model is widely recognized as a physically based description of the acoustic loss mechanisms as developed by Nachman et al. [J. Acoust. Soc. Am. 88, 1584-1595 (1990)]. Through assumption of a continuum of relaxation mechanisms, each with an effective compressibility described by a distribution related to the Mittag-Leffler function, this paper shows that the wave equation corresponding to the multiple relaxation approach is identical to a given fractional derivative wave equation. This work therefore provides a physically based motivation for use of fractional wave equations in acoustic modeling.

  7. Experimental study of the stress effect on attenuation of normally incident P-wave through coal

    NASA Astrophysics Data System (ADS)

    Feng, Junjun; Wang, Enyuan; Chen, Liang; Li, Xuelong; Xu, Zhaoyong; Li, Guoai

    2016-09-01

    The purpose of this study is to experimentally investigate the stress effect on normally incident P-wave attenuation through coal specimens. Laboratory tests were carried out using a Split Hopkinson pressure bar (SHPB) system, and a modified method was proposed to determine the quality factor (Q) of P-waves through coal specimens. Larger quality factor denotes less energy attenuated during P-wave propagating through coal. Experimental results indicate that the quality factor and stress (σ) within coal specimens are positively correlated. The P-wave propagation through coal specimens causes crack closure at the beginning of the coal fracture process in SHPB tests, an innovative model was thus proposed to describe the relationship between the crack closure length and the dynamic stress induced by P-wave. Finally, the stress effect on P-wave attenuation through coal was quantitatively represented by a power function Q = a(c-bσ)- 6, and the material constants a, b, and c were determined as 1.227, 1.314, and 0.005, respectively. The results obtained in this study would be helpful for engineers to estimate seismic energy attenuation and coal mass instability in coal mines.

  8. Resonant attenuation of surface acoustic waves by a disordered monolayer of microspheres

    NASA Astrophysics Data System (ADS)

    Eliason, J. K.; Vega-Flick, A.; Hiraiwa, M.; Khanolkar, A.; Gan, T.; Boechler, N.; Fang, N.; Nelson, K. A.; Maznev, A. A.

    2016-02-01

    Attenuation of surface acoustic waves (SAWs) by a disordered monolayer of polystyrene microspheres is investigated. Surface acoustic wave packets are generated by a pair of crossed laser pulses in a glass substrate coated with a thin aluminum film and detected via the diffraction of a probe laser beam. When a 170 μm-wide strip of micron-sized spheres is placed on the substrate between the excitation and detection spots, strong resonant attenuation of SAWs near 240 MHz is observed. The attenuation is caused by the interaction of SAWs with a contact resonance of the microspheres, as confirmed by acoustic dispersion measurements on the microsphere-coated area. Frequency-selective attenuation of SAWs by such a locally resonant metamaterial may lead to reconfigurable SAW devices and sensors, which can be easily manufactured via self-assembly techniques.

  9. Importance of Second-Order Difference-Frequency Wave-Diffraction Forces in the Validation of a Fast Semi-Submersible Floating Wind Turbine Model: Preprint

    SciTech Connect

    Couling, A. J.; Goupee, A. J.; Robertson, A. N.; Jonkman, J. M.

    2013-06-01

    To better access the abundant offshore wind resource, efforts across the world are being undertaken to develop and improve floating offshore wind turbine technologies. A critical aspect of creating reliable, mature floating wind turbine technology is the development, verification, and validation of efficient computer-aided-engineering (CAE) tools that can be relied upon in the design process. The National Renewable Energy Laboratory (NREL) has created a comprehensive, coupled analysis CAE tool for floating wind turbines, FAST, which has been verified and utilized in numerous floating wind turbine studies. Several efforts are currently underway that leverage the extensive 1/50th-scale DeepCwind wind/wave basin model test dataset, obtained at the Maritime Research Institute Netherlands (MARIN) in 2011, to validate the floating platform functionality of FAST to complement its already validated aerodynamic and structural simulation capabilities. In this paper, further work is undertaken to continue this validation. In particular, the ability of FAST to replicate global response behaviors associated with dynamic wind forces, second-order difference-frequency wave-diffraction forces and their interaction with one another are investigated.

  10. Detailed Study of Seismic Wave Attenuation in Carbonate Rocks: Application on Abu Dhabi Oil Fields

    NASA Astrophysics Data System (ADS)

    Bouchaala, F.; Ali, M. Y.; Matsushima, J.

    2015-12-01

    Seismic wave attenuation is a promising attribute for the petroleum exploration, thanks to its high sensitivity to physical properties of subsurface. It can be used to enhance the seismic imaging and improve the geophysical interpretation which is crucial for reservoir characterization. However getting an accurate attenuation profile is not an easy task, this is due to complex mechanism of this parameter, although that many studies were carried out to understand it. The degree of difficulty increases for the media composed of carbonate rocks, known to be highly heterogeneous and with complex lithology. That is why few attenuation studies were done successfully in carbonate rocks. The main objectives of this study are, Getting an accurate and high resolution attenuation profiles from several oil fields. The resolution is very important target for us, because many reservoirs in Abu Dhabi oil fields are tight.Separation between different modes of wave attenuation (scattering and intrinsic attenuations).Correlation between the attenuation profiles and other logs (Porosity, resistivity, oil saturation…), in order to establish a relationship which can be used to detect the reservoir properties from the attenuation profiles.Comparison of attenuation estimated from VSP and sonic waveforms. Provide spatial distribution of attenuation in Abu Dhabi oil fields.To reach these objectives we implemented a robust processing flow and new methodology to estimate the attenuation from the downgoing waves of the compressional VSP data and waveforms acquired from several wells drilled in Abu Dhabi. The subsurface geology of this area is primarily composed of carbonate rocks and it is known to be highly fractured which complicates more the situation, then we separated successfully the intrinsic attenuation from the scattering. The results show that the scattering is significant and cannot be ignored. We found also a very interesting correlation between the attenuation profiles and the

  11. Measurement of alkali-silica reaction progression by ultrasonic waves attenuation

    SciTech Connect

    Saint-Pierre, Francois; Rivard, Patrice . E-mail: Patrice.Rivard@Usherbrooke.ca; Ballivy, Gerard

    2007-06-15

    Development of non-destructive methods, developed specifically for assessing the damage induced by alkali-silica reaction (ASR) in concrete structures, is needed in order to carry out a systematic evaluation of the concrete condition. The aim of this study is to monitor the evolution of the ASR-damage in laboratory with concrete samples with ultrasonic pulse velocity and attenuation of ultrasonic waves methods. For this study, results of both methods were compared with expansion and mass variation. One reactive concrete mixture was made with reactive aggregate, and one other mixture, incorporating non-reactive aggregate, was made as a control. Specimens were kept at 38 deg. C in a 1 mol l{sup -1} NaOH solution to accelerate the reaction. Attenuation of transmitted ultrasonic waves appeared to be more appropriate for the evaluation of ASR-damage compared with pulse velocity. The attenuation of accelerated reactive concrete cylinders increased by 90% after 1 year while it increased by 40% for the non-reactive concrete used as a control. Major part of the attenuation increase in the non-reactive concrete is due to liquid absorption. This work suggests that in-situ non-destructive techniques based on ultrasonic wave attenuation, like ultrasonic attenuation tomography, should be developed in order to evaluate the development of ASR in concrete structures. Petrographic examination confirmed that damage to concrete is associated with ASR.

  12. Dynamic aspects of apparent attenuation and wave localization in layered media

    USGS Publications Warehouse

    Haney, M.M.; Van Wijk, K.

    2008-01-01

    We present a theory for multiply-scattered waves in layered media which takes into account wave interference. The inclusion of interference in the theory leads to a new description of the phenomenon of wave localization and its impact on the apparent attenuation of seismic waves. We use the theory to estimate the localization length at a CO2 sequestration site in New Mexico at sonic frequencies (2 kHz) by performing numerical simulations with a model taken from well logs. Near this frequency, we find a localization length of roughly 180 m, leading to a localization-induced quality factor Q of 360.

  13. Attenuation in the Upper Mantle Beneath the Juan de Fuca Plate Using Rayleigh Wave Tomography

    NASA Astrophysics Data System (ADS)

    Forsyth, D. W.; Ruan, Y.; Bell, S. W.

    2016-12-01

    We have measured shear attenuation beneath the Juan de Fuca plate using Rayleigh waves from teleseismic earthquakes propagating across the Cascadia Initiative ocean-bottom seismometer (OBS) arrays. We employ the two-plane-wave technique to account for multi-path interference arising from velocity heterogeneities outside the array, the Born approximation to account for focusing and defocusing within the study area, and station corrections to account for site response and errors in instrument corrections. We solve simultaneously for phase velocity variations within the plate and average Rayleigh wave attenuation coefficients across the entire plate. Rayleigh wave attenuation coefficients extend from periods of 20 s to 143 s. The age of the seafloor ranges from 0 to about 10 Ma. The Juan de Fuca area is slightly more attenuating than seafloor of similar age near the East Pacific Rise in the GLIMPSE and MELT experiments, and the broader period range gives better depth resolution in the asthenosphere than in those studies. The minimum shear quality factor Q is found centered at about 80 km, just below the expected dry solidus and coinciding roughly with the minimum in shear velocity. Q averaged over the well-resolved depth range of 70 to 110 km is 45-50. We compare these observations to predictions of thermal models and various attenuation models. Lateral variations in velocity reveal asymmetry across the ridge axis associated with seamount asymmetry and a minimum in velocity in the vicinity of Axial Seamount.

  14. The effect of frequency on Young`s modulus and seismic wave attenuation

    SciTech Connect

    Price, R.H.; Martin, R.J. III; Haupt, R.W.

    1994-07-01

    Laboratory experiments were performed to measure the effect of frequency, water-saturation, and strain amplitude on Young`s modulus and seismic wave attenuation on rock cores recovered on or near the site of a potential nuclear waste repository at Yucca Mountain, Nevada. The purpose of this investigation is to perform the measurements using four techniques: cyclic loading, waveform inversion, resonant bar, and ultrasonic velocity. The measurements ranged in frequency between 10{sup {minus}2} and 10{sup 6} Hz. For the dry specimens Young`s modulus and attenuation were independent of frequency; that is, all four techniques yielded nearly the same values for modulus and attenuation. For saturated specimens, a frequency dependence for both Young`s modulus and attenuation was observed. In general, saturation reduced Young`s modulus and increased seismic wave attenuation. The effect of strain amplitude on Young`s modulus and attenuation was measured using the cyclic loading technique at a frequency of 10{sup {minus}1} Hz. The effect of strain amplitude in all cases was small. For some rocks, such as the potential repository horizon of the Topopah Spring Member tuff (TSw2), the effect of strain amplitude on both attenuation and modulus was minimal.

  15. Effect of small floating disks on the propagation of gravity waves

    NASA Astrophysics Data System (ADS)

    De Santi, F.; Olla, P.

    2017-04-01

    A dispersion relation for gravity waves in water covered by disk-like impurities embedded in a viscous matrix is derived. The macroscopic equations are obtained by ensemble-averaging the fluid equations at the disk scale in the asymptotic limit of long waves and low disk surface fraction. Various regimes are identified depending on the disk radii and the thickness and viscosity of the top layer. Semi-quantitative analysis in the close-packing regime suggests dramatic modification of the dynamics, with orders of magnitude increase in wave damping and wave dispersion. A simplified model working in this regime is proposed. Possible applications to wave propagation in an ice-covered ocean are discussed and comparison with field data is provided.

  16. Numerical modeling of floating oil boom motions in wave-current coupling conditions

    NASA Astrophysics Data System (ADS)

    Shi, Yang; Li, Shaowu; Zhang, Huaqin; Peng, Shitao; Chen, Hanbao; Zhou, Ran; Mao, Tianyu

    2017-08-01

    Containment booms are commonly used in collecting and containing spilled oil on the sea surface and in protecting specific sea areas against oil slick spreading. In the present study, a numerical model is proposed based on the N-S equations in a mesh frame. The proposed model tracks the outline of the floating boom in motion by using the fractional area/volume obstacle representation technique. The boom motion is then simulated by the technique of general moving object. The simulated results of the rigid oil boom motions are validated against the experimental results. Then, the failure mechanism of the boom is investigated through numerical experiments. Based on the numerical results, the effects of boom parameters and dynamic factors on the oil containment performance are also assessed.

  17. Multiple attenuation to reflection seismic data using Radon filter and Wave Equation Multiple Rejection (WEMR) method

    SciTech Connect

    Erlangga, Mokhammad Puput

    2015-04-16

    Separation between signal and noise, incoherent or coherent, is important in seismic data processing. Although we have processed the seismic data, the coherent noise is still mixing with the primary signal. Multiple reflections are a kind of coherent noise. In this research, we processed seismic data to attenuate multiple reflections in the both synthetic and real seismic data of Mentawai. There are several methods to attenuate multiple reflection, one of them is Radon filter method that discriminates between primary reflection and multiple reflection in the τ-p domain based on move out difference between primary reflection and multiple reflection. However, in case where the move out difference is too small, the Radon filter method is not enough to attenuate the multiple reflections. The Radon filter also produces the artifacts on the gathers data. Except the Radon filter method, we also use the Wave Equation Multiple Elimination (WEMR) method to attenuate the long period multiple reflection. The WEMR method can attenuate the long period multiple reflection based on wave equation inversion. Refer to the inversion of wave equation and the magnitude of the seismic wave amplitude that observed on the free surface, we get the water bottom reflectivity which is used to eliminate the multiple reflections. The WEMR method does not depend on the move out difference to attenuate the long period multiple reflection. Therefore, the WEMR method can be applied to the seismic data which has small move out difference as the Mentawai seismic data. The small move out difference on the Mentawai seismic data is caused by the restrictiveness of far offset, which is only 705 meter. We compared the real free multiple stacking data after processing with Radon filter and WEMR process. The conclusion is the WEMR method can more attenuate the long period multiple reflection than the Radon filter method on the real (Mentawai) seismic data.

  18. Laboratory Studies of Wave Attenuation through Artificial and Real Vegetation

    DTIC Science & Technology

    2013-09-01

    33  Figure 35. Securing S. alterniflora in coir mats (left...alterniflora sections in the flume (left) with completed bed (right). ............. 39  Figure 42. Wave spectral transformation through coir control...44  Figure 45. Decay coefficient for S. alterniflora (N = 162 stems/m2) versus unplanted coir

  19. Relative velocity of seagrass blades: Implications for wave attenuation in low-energy environments

    NASA Astrophysics Data System (ADS)

    Bradley, Kevin; Houser, Chris

    2009-03-01

    While the ability of subaquatic vegetation to attenuate wave energy is well recognized in general, there is a paucity of data from the field to describe the rate and mechanisms of wave decay, particularly with respect to the relative motion of the vegetation. The purpose of this study was to quantify the attenuation of incident wave height through a seagrass meadow and characterize the blade movement under oscillatory flow under the low-energy conditions characteristic of fetch-limited and sheltered environments. The horizontal motion of the seagrass blades and the velocity just above the seagrass canopy were measured using a digital video camera and an acoustic Doppler velicometer (ADV) respectively in order to refine the estimates of the drag coefficient based on the relative velocity. Significant wave heights (Hs) were observed to increase by ˜0.02 m (˜20%) through the first 5 m of the seagrass bed but subsequently decrease exponentially over the remainder of the bed. The exponential decay coefficient varied in response to the Reynolds number calculated using blade width (as the length scale) and the oscillatory velocity measured immediately above the canopy. The ability of the seagrass to attenuate wave energy decreases as incident wave heights increase and conditions become more turbulent. Estimates of the time-averaged canopy height and the calculated hydraulic roughness suggest that, as the oscillatory velocity increases, the seagrass becomes fully extended and leans in the direction of flow for a longer part of the wave cycle. The relationship between the drag coefficient and the Reynolds number further suggests that the vegetation is swaying (going with the flow) at low-energy conditions but becomes increasingly rigid as oscillatory velocities increase over the limited range of the conditions observed (200 < Re < 800). In addition to the changing behavior of the seagrass motion, the attenuation was not uniform with wave frequency, and waves at a

  20. Wave Height Attenuation in Heterogeneous Vegetation using Laboratory Observation and Numerical Simulations

    NASA Astrophysics Data System (ADS)

    Blackmar, P.; Wu, W.; Cox, D. T.

    2012-12-01

    Coastal vegetation is commonly accepted as a means of wave damping, but existing methodologies for predicting the wave height attenuation focus on homogeneous vegetation, primarily in periodic waves. In this project, quarter scale experiments were performed in conjunction with numerical modeling in FUNWAVE to evaluate random wave attenuation through two types of synthetic vegetation. The experiment was performed with two peak periods, three water depths, and two stem densities. For each combination of parameters, free surface time series were collected at 7 locations throughout the vegetation field and 1 location seaward of the vegetation. Each combination of wave conditions was evaluated for four different cases: Case 1 with no vegetation, Case 2 and 3 with short and long specimens, respectively, and Case 4 with mixed vegetation. The decay of the spectral wave heights were fit with the Dalrymple et al. (1984) and Kobayashi et al. (1993) equations. The decay equations provided reasonable predictions, with an average mean square error of 1.3%. We found that adding the coefficients obtained for the cases of the individual plants provided a reasonable prediction of the coefficient for the cases of the combined, heterogeneous vegetation. Use of a reduction factor on the sum of the two coefficients improved the predictions, giving an average mean square error of 2.1% between the predictions and the measured values. A phase resolved numerical model (FUNWAVE) was used to model wave attenuation for these tests using a bottom drag coefficient calibrated for each run. The numerical attenuation followed the same trends as the measured data, with an average mean square error of 1.7% when considering all of the observation locations throughout the vegetation field. Similar to the physical model study, we found that adding the calibrated model drag coefficients for the cases of the individual plants reasonably predicted the wave height attenuation for the cases of the combined

  1. Fully nonlinear time-domain simulation of a backward bent duct buoy floating wave energy converter using an acceleration potential method

    NASA Astrophysics Data System (ADS)

    Lee, Kyoung-Rok; Koo, Weoncheol; Kim, Moo-Hyun

    2013-12-01

    A floating Oscillating Water Column (OWC) wave energy converter, a Backward Bent Duct Buoy (BBDB), was simulated using a state-of-the-art, two-dimensional, fully-nonlinear Numerical Wave Tank (NWT) technique. The hydrodynamic performance of the floating OWC device was evaluated in the time domain. The acceleration potential method, with a full-updated kernel matrix calculation associated with a mode decomposition scheme, was implemented to obtain accurate estimates of the hydrodynamic force and displacement of a freely floating BBDB. The developed NWT was based on the potential theory and the boundary element method with constant panels on the boundaries. The mixed Eulerian-Lagrangian (MEL) approach was employed to capture the nonlinear free surfaces inside the chamber that interacted with a pneumatic pressure, induced by the time-varying airflow velocity at the air duct. A special viscous damping was applied to the chamber free surface to represent the viscous energy loss due to the BBDB's shape and motions. The viscous damping coefficient was properly selected using a comparison of the experimental data. The calculated surface elevation, inside and outside the chamber, with a tuned viscous damping correlated reasonably well with the experimental data for various incident wave conditions. The conservation of the total wave energy in the computational domain was confirmed over the entire range of wave frequencies.

  2. Measurement of attenuation coefficients of the fundamental and second harmonic waves in water

    NASA Astrophysics Data System (ADS)

    Zhang, Shuzeng; Jeong, Hyunjo; Cho, Sungjong; Li, Xiongbing

    2016-02-01

    Attenuation corrections in nonlinear acoustics play an important role in the study of nonlinear fluids, biomedical imaging, or solid material characterization. The measurement of attenuation coefficients in a nonlinear regime is not easy because they depend on the source pressure and requires accurate diffraction corrections. In this work, the attenuation coefficients of the fundamental and second harmonic waves which come from the absorption of water are measured in nonlinear ultrasonic experiments. Based on the quasilinear theory of the KZK equation, the nonlinear sound field equations are derived and the diffraction correction terms are extracted. The measured sound pressure amplitudes are adjusted first for diffraction corrections in order to reduce the impact on the measurement of attenuation coefficients from diffractions. The attenuation coefficients of the fundamental and second harmonics are calculated precisely from a nonlinear least squares curve-fitting process of the experiment data. The results show that attenuation coefficients in a nonlinear condition depend on both frequency and source pressure, which are much different from a linear regime. In a relatively lower drive pressure, the attenuation coefficients increase linearly with frequency. However, they present the characteristic of nonlinear growth in a high drive pressure. As the diffraction corrections are obtained based on the quasilinear theory, it is important to use an appropriate source pressure for accurate attenuation measurements.

  3. Waveform inversion of seismic velocities and attenuation from low-frequency waves in cylindrical bars

    SciTech Connect

    Tang, Xiao Ming )

    1993-10-01

    A new technique for laboratory measurement of seismic wave velocities and attenuation in the frequency range of 10--150 kHz consists of measuring extensional waveforms using two cylindrical bars of the same material but unequal length. Based on the dispersion equation of the bar and rough estimates of compressional and shear velocities of the bar material, the waveform measured within the shorter bar is theoretically continued to the length of the longer bar to match with the waveform measured there. An inversion is then performed to minimize the phase difference between the two waveforms. The velocities are obtained when the phase difference reaches a minimum, at which the two waveforms attain the optimum phase match. After the phase match, a further inversion is performed to minimize the amplitude difference between the two waveforms to derive the extensional wave attenuation within the bar. By this inversion procedure, wave velocities and attenuation can be jointly determined at frequencies much lower than those of the ultrasonic measurements. By using the technique, compressional and shear velocities and extensional attenuation values in a lucite material and in dry Sierra White granite were measured. The results from the present technique are consistent with the results from other techniques (resonant bar and ultrasonic), if the effect of intrinsic attenuation is accounted for.

  4. A contrast source method for nonlinear acoustic wave fields in media with spatially inhomogeneous attenuation.

    PubMed

    Demi, L; van Dongen, K W A; Verweij, M D

    2011-03-01

    Experimental data reveals that attenuation is an important phenomenon in medical ultrasound. Attenuation is particularly important for medical applications based on nonlinear acoustics, since higher harmonics experience higher attenuation than the fundamental. Here, a method is presented to accurately solve the wave equation for nonlinear acoustic media with spatially inhomogeneous attenuation. Losses are modeled by a spatially dependent compliance relaxation function, which is included in the Westervelt equation. Introduction of absorption in the form of a causal relaxation function automatically results in the appearance of dispersion. The appearance of inhomogeneities implies the presence of a spatially inhomogeneous contrast source in the presented full-wave method leading to inclusion of forward and backward scattering. The contrast source problem is solved iteratively using a Neumann scheme, similar to the iterative nonlinear contrast source (INCS) method. The presented method is directionally independent and capable of dealing with weakly to moderately nonlinear, large scale, three-dimensional wave fields occurring in diagnostic ultrasound. Convergence of the method has been investigated and results for homogeneous, lossy, linear media show full agreement with the exact results. Moreover, the performance of the method is demonstrated through simulations involving steered and unsteered beams in nonlinear media with spatially homogeneous and inhomogeneous attenuation. © 2011 Acoustical Society of America

  5. Flexural wave attenuation in a sandwich beam with viscoelastic periodic cores

    NASA Astrophysics Data System (ADS)

    Guo, Zhiwei; Sheng, Meiping; Pan, Jie

    2017-07-01

    The flexural-wave attenuation performance of traditional constraint-layer damping in a sandwich beam is improved by using periodic constrained-layer damping (PCLD), where the monolithic viscoelastic core is replaced with two periodically alternating viscoelastic cores. Closed-form solutions of the wave propagation constants of the infinite periodic sandwich beam and the forced response of the corresponding finite sandwich structure are theoretically derived, providing computational support on the analysis of attenuation characteristics. In a sandwich beam with PCLD, the flexural waves can be attenuated by both Bragg scattering effect and damping effect, where the attenuation level is mainly dominated by Bragg scattering in the band-gaps and by damping in the pass-bands. Affected by these two effects, when the parameters of periodic cores are properly selected, a sandwich beam with PCLD can effectively reduce vibrations of much lower frequencies than that with traditional constrained-layer damping. The effects of the parameters of viscoelastic periodic cores on band-gap properties are also discussed, showing that the average attenuation in the desired frequency band can be maximized by tuning the length ratio and core thickness to proper values. The research in this paper could possibly provide useful information for the researches and engineers to design damping structures.

  6. Inversion of Surface Waves for Path Structure and Attenuation

    DTIC Science & Technology

    1981-11-01

    Dispersion curves from inversion model #2 . . . . . 26 12. Inverted Q-model and actual Q-model . . . . . . . 30 13. Surface waves from SAPHIRE , February... SAPHIRE seismograms: (a) SHI, (b) AAE .. . . . . . . . . 33 is Inverted Qg(z) structures from SAPHIRE seismograms: (a) SHI, (5) AAE ..... .. . . . . .35...from the Hoggar explosion SAPHIRE , recorded at AAE and SHI. We were able to retrieve stable dispersion curve estimates in the range 10-50 seconds from

  7. Study of transmission line attenuation in broad band millimeter wave frequency range

    SciTech Connect

    Pandya, Hitesh Kumar B.; Austin, M. E.; Ellis, R. F.

    2013-10-15

    Broad band millimeter wave transmission lines are used in fusion plasma diagnostics such as electron cyclotron emission (ECE), electron cyclotron absorption, reflectometry and interferometry systems. In particular, the ECE diagnostic for ITER will require efficient transmission over an ultra wide band, 100 to 1000 GHz. A circular corrugated waveguide transmission line is a prospective candidate to transmit such wide band with low attenuation. To evaluate this system, experiments of transmission line attenuation were performed and compared with theoretical loss calculations. A millimeter wave Michelson interferometer and a liquid nitrogen black body source are used to perform all the experiments. Atmospheric water vapor lines and continuum absorption within this band are reported. Ohmic attenuation in corrugated waveguide is very low; however, there is Bragg scattering and higher order mode conversion that can cause significant attenuation in this transmission line. The attenuation due to miter bends, gaps, joints, and curvature are estimated. The measured attenuation of 15 m length with seven miter bends and eighteen joints is 1 dB at low frequency (300 GHz) and 10 dB at high frequency (900 GHz), respectively.

  8. Natural attenuation of contaminated marine sediments from an old floating dock - Part I: Spatial and temporal changes of organic and inorganic pollutants.

    PubMed

    Wang, Ya-Fen; Tam, Nora Fung-Yee

    2012-03-15

    Temporal and spatial changes of mixed pollutants, including eight heavy metals, 16 US EPA priority polycyclic aromatic hydrocarbons (PAHs) and tributyltin (TBT) in surface marine sediments were examined for a one-year period after the removal of an old floating dock in Hong Kong SAR, South China. The sediments from the impacted stations close to the dock were highly polluted with zinc (Zn) and copper (Cu), and were moderately polluted with TBT and total PAHs, based on their effects range-low (ERL) guideline values, while those collected in the reference stations away from the dock were lower than the ERL. Strong, positive correlations were found between the organic pollutants and heavy metals only in the impacted stations, suggesting that the old floating dock was a significant source of mixed pollutants. There was no significant decline in the levels of total PAHs, TBT and heavy metals and "hot spots" of contamination were still detected a year after the removal of the dock. However, the profiles of 16 PAHs in the impacted stations changed 6 months after the removal of the dock, with decreases of certain low-molecular-weight PAHs, especially fluorene, as a sign of biodegradation in situ. Further, principal component analysis (PCA) based on an integrated dataset of the pollutants together with general sediment properties showed that the temporal changes of the biodegradable low-molecular-weight PAHs were highly associated with the pH value and total Kjeldahl nitrogen, while heavy metals were independent of time and other sediment properties during natural attenuation in the dock area. Copyright © 2012 Elsevier B.V. All rights reserved.

  9. Seismic Wave Attenuation Estimated from Tectonic Tremor and Radiated Energy in Tremor for Various Subduction Zones

    NASA Astrophysics Data System (ADS)

    Yabe, S.; Baltay, A.; Ide, S.; Beroza, G. C.

    2013-12-01

    Ground motion prediction is an essential component of earthquake hazard assessment. Seismic wave attenuation with distance is an important, yet difficult to constrain, factor for such estimation. Using the empirical method of ground motion prediction equations (GMPEs), seismic wave attenuation with distance, which includes both the effect of anelastic attenuation and scattering, can be estimated from the distance decay of peak ground velocity (PGV) or peak ground acceleration (PGA) of ordinary earthquakes; however, in some regions where plate-boundary earthquakes are infrequent, such as Cascadia and Nankai, there are fewer data with which to constrain the empirical parameters. In both of those subduction zones, tectonic tremor occurs often. In this study, we use tectonic tremor to estimate the seismic wave attenuation with distance, and in turn use the attenuation results to estimate the radiated seismic energy of tremor. Our primary interest is in the variations among subduction zones. Ground motion attenuation and the distribution of released seismic energy from tremors are two important subduction zone characteristics. Therefore, it is very interesting to see whether there are variations of these parameters in different subduction zones, or regionally within the same subduction zone. It is also useful to estimate how much energy is released by tectonic tremor from accumulated energy to help understand subduction dynamics and the difference between ordinary earthquakes and tremor. We use the tectonic tremor catalog of Ide (2012) in Nankai, Cascadia, Mexico and southern Chile. We measured PGV and PGA of individual tremor bursts at each station. We assume a simple GMPE relationship and estimate seismic attenuation and relative site amplification factors from the data. In the Nankai subduction zone, there are almost no earthquakes on the plate interface, but intra-slab earthquakes occur frequently. Both the seismic wave attenuation with distance and the site

  10. Magnesium oxide doping reduces acoustic wave attenuation in lithium metatantalate and lithium metaniobate crystals

    NASA Technical Reports Server (NTRS)

    Croft, W.; Damon, R.; Kedzie, R.; Kestigian, M.; Smith, A.; Worley, J.

    1970-01-01

    Single crystals of lithium metatantalate and lithium metaniobate, grown from melts having different stoichiometries and different amounts of magnesium oxide, show that doping lowers temperature-independent portion of attenuation of acoustic waves. Doped crystals possess optical properties well suited for electro-optical and photoelastic applications.

  11. Developing a Short-Period, Fundamental-Mode Rayleigh-Wave Attenuation Model for Asia

    NASA Astrophysics Data System (ADS)

    Yang, X.; Levshin, A. L.; Barmin, M. P.; Ritzwoller, M. H.

    2008-12-01

    We are developing a 2D, short-period (12 - 22 s), fundamental-mode Rayleigh-wave attenuation model for Asia. This model can be used to invert for a 3D attenuation model of the Earth's crust and upper mantle as well as to implement more accurate path corrections in regional surface-wave magnitude calculations. The prerequisite for developing a reliable Rayleigh-wave attenuation model is the availability of accurate fundamental-mode Rayleigh-wave amplitude measurements. Fundamental-mode Rayleigh-wave amplitudes could be contaminated by a variety of sources such as multipathing, focusing and defocusing, body wave, higher-mode surface wave, and other noise sources. These contaminations must be reduced to the largest extent possible. To achieve this, we designed a procedure by taking advantage of certain Rayleigh-wave characteristics, such as dispersion and elliptical particle motion, for accurate amplitude measurements. We first analyze the dispersion of the surface-wave data using a spectrogram. Based on the characteristics of the data dispersion, we design a phase-matched filter by using either a manually picked dispersion curve, or a group-velocity-model predicted dispersion curve, or the dispersion of the data, and apply the filter to the seismogram. Intelligent filtering of the seismogram and windowing of the resulting cross-correlation based on the spectrogram analysis and the comparison between the phase-match filtered data spectrum, the raw-data spectrum and the theoretical source spectrum effectively reduces amplitude contaminations and results in reliable amplitude measurements in many cases. We implemented these measuring techniques in a graphic-user-interface tool called Surface Wave Amplitude Measurement Tool (SWAMTOOL). Using the tool, we collected and processed waveform data for 200 earthquakes occurring throughout 2003-2006 inside and around Eurasia. The records from 135 broadband stations were used. After obtaining the Rayleigh-wave amplitude

  12. Water saturation effects on elastic wave attenuation in porous rocks with aligned fractures

    NASA Astrophysics Data System (ADS)

    Amalokwu, Kelvin; Best, Angus I.; Sothcott, Jeremy; Chapman, Mark; Minshull, Tim; Li, Xiang-Yang

    2014-05-01

    Elastic wave attenuation anisotropy in porous rocks with aligned fractures is of interest to seismic remote sensing of the Earth's structure and to hydrocarbon reservoir characterization in particular. We investigated the effect of partial water saturation on attenuation in fractured rocks in the laboratory by conducting ultrasonic pulse-echo measurements on synthetic, silica-cemented, sandstones with aligned penny-shaped voids (fracture density of 0.0298 ± 0.0077), chosen to simulate the effect of natural fractures in the Earth according to theoretical models. Our results show, for the first time, contrasting variations in the attenuation (Q-1) of P and S waves with water saturation in samples with and without fractures. The observed Qs/Qp ratios are indicative of saturation state and the presence or absence of fractures, offering an important new possibility for remote fluid detection and characterization.

  13. Attenuation of seismic waves in rocks saturated with multiphase fluids: theory and experiments

    NASA Astrophysics Data System (ADS)

    Tisato, N.; Quintal, B.; Chapman, S.; Podladchikov, Y.; Burg, J. P.

    2016-12-01

    Albeit seismic tomography could provide a detailed image of subsurface fluid distribution, the interpretation of the tomographic signals is often controversial and fails in providing a conclusive map of the subsurface saturation. However, tomographic information is important because the upward migration of multiphase fluids through the crust of the Earth can cause hazardous events such as eruptions, explosions, soil-pollution and earthquakes. In addition, multiphase fluids, such as hydrocarbons, represent important resources for economy. Seismic tomography can be improved considering complex elastic moduli and the attenuation of seismic waves (1/Q) that quantifies the energy lost by propagating elastic waves. In particular, a significant portion of the energy carried by the propagating wave is dissipated in saturated media by the wave-induced-fluid-flow (WIFF) and the wave-induced-gas-exsolution-dissolution (WIGED) mechanism. The latter describes how a propagating wave modifies the thermodynamic equilibrium between different fluid phases causing exsolution and dissolution of gas bubbles in the liquid, which in turn causes a significant frequency-dependent 1/Q and moduli dispersion. The WIGED theory was initially postulated for bubbly magmas but was only recently demonstrated and extended to bubbly water. We report the theory and laboratory experiments that have been performed to confirm the WIGED theory. In particular, we present i) attenuation measurements performed by means of the Broad Band Attenuation Vessel on porous media saturated with water and different gases, and ii) numerical experiments validating the laboratory observations. Then, we extend the theory to fluids and pressure-temperature conditions which are typical of phreatomagmatic and hydrocarbon domains and we compare the propagation of seismic waves in bubble-free and bubble-bearing subsurface domains. This work etends the knowledge of attenuation in rocks saturated with multiphase fluid and

  14. Electromagnetic wave attenuation measurements in a ring-shaped inductively coupled air plasma

    SciTech Connect

    Xiaolong, Wei; Haojun, Xu; Min, Lin; Chen, Su; Jianhai, Li

    2015-05-28

    An aerocraft with the surface, inlet and radome covered large-area inductive coupled plasma (ICP) can attenuate its radar echo effectively. The shape, thickness, and electron density (N{sub e}) distribution of ICP are critical to electromagnetic wave attenuation. In the paper, an air all-quartz ICP generator in size of 20 × 20 × 7 cm{sup 3} without magnetic confinement is designed. The discharge results show that the ICP is amorphous in E-mode and ring-shaped in H-mode. The structure of ICP stratifies into core region and edge halo in H-mode, and its width and thickness changes from power and pressure. Such phenomena are explained by the distribution of RF magnetic field, the diffusion of negative ions plasma and the variation of skin depth. In addition, the theoretical analysis shows that the N{sub e} achieves nearly uniform within the electronegative core and sharply steepens in the edge. The N{sub e} of core region is diagnosed by microwave interferometer under varied conditions (pressure in range of 10–50 Pa, power in 300–700 W). Furthermore, the electromagnetic wave attenuation measurements were carried out with the air ICP in the frequencies of 4–5 GHz. The results show that the interspaced ICP is still effective to wave attenuation, and the wave attenuation increases with the power and pressure. The measured attenuation is approximately in accordance with the calculation data of finite-different time-domain simulations.

  15. Anelastic Attenuation and Elastic Scattering of Seismic Waves in the Los Angeles Region

    NASA Astrophysics Data System (ADS)

    Song, X.; Jordan, T. H.

    2013-12-01

    The accuracy of earthquake simulations needed for physics-based seismic hazard analysis depends on good information about crustal structure. For low-frequency (f < 0.3 Hz) simulations, the most important structural parameters are the seismic wave velocities, but as the frequencies increase, seismic wave attenuation becomes more important. We compare attenuation models that have been recently used in the CyberShake hazard model (Graves et al., 2011) and other simulation studies for the Los Angeles region (Olsen et al., 2009; Taborda & Bielak, 2013) with constraints from local earthquake data out to 10 Hz, which include those from Hauksson & Shearer's (2006) attenuation tomography as well as our own measurements. We show that the velocity-attenuation scaling relationship for shear waves employed by CyberShake (QS = 50VS, where VS is in km/s) provides a good approximation to the average crustal structure at f = 0.3 Hz, but it does not capture the lateral variations in QS at shallow depths. Moreover, this frequency-independent model is inconsistent with the high QS values observed throughout most of the crust at f > 1 Hz. The data indicate a frequency-dependent attenuation of the form QS ~ f γ, where 0.5 ≤ γ ≤ 0.8. Anomalously low QS factors are observed at very shallow depths, which can be explained by a combination of anelastic attenuation and elastic scattering. The scattering parameters are roughly consistent with small-scale, near-surface heterogeneities observed in well-logs and seismic reflection surveys in the Los Angeles basin. High-frequency scattering may also play a role in explaining Hauksson & Shearer's (2006) observation that the QP/QS ratio is anomalously low (~ unity). We summarize the observations in a new attenuation and scattering model for the CyberShake region that is laterally heterogeneous and frequency dependent.

  16. Amplitude-frequency dependencies of wave attenuation in single-crystal quartz: Experimental study

    NASA Astrophysics Data System (ADS)

    Mashinskii, E. I.

    2008-11-01

    The experiments have been conducted to investigate the effect of strain amplitude and frequency on the compressional and shear wave attenuation in quartz samples of three types: the intact quartz, fractured quartz, and smoky quartz. The measurements were performed using the reflection method on a pulse frequency of 1 MHz with changing strain in the range 0.3 ≤ ɛ ≤ 2.0 μstrain under a confining pressure of 10 MPa and at ambient temperature. The essential difference in amplitude-frequency characteristics of wave attenuation in three quartz types has been detected. The intact quartz shows the more "simple" behavior in comparison with the fractured and smoky quartz. The attenuation (the inverse quality factor Q) depends on strain amplitude as Q-1(ɛ) ˜ ɛ-n, where n ≅ 0.005-0.085, with the greatest decrease in the smoky and fractured quartz reaching of about 15%. Relaxation spectra of attenuation are presented in the frequency range from 0.4 to 1.4 MHz. The dependence Qp-1(f) ˜ f-1.2 characterizes the intact and fractured quartz, whereas the smoky quartz has the relaxation peak. The dependence Qs-1(f) ˜ f-0.84 presents S wave relaxation spectrum in the intact quartz; in the fractured and smoky quartz, the attenuation peaks take place. The strain amplitude variation exerts influence on the relaxation strength, the peak frequency, and the width of the relaxation peak. Such behavior of attenuation can be explained by a joint action of viscoelastic and microplastic mechanisms. These results can be considered as a contribution for providing the experimental background to the theory of attenuation in rocks. They can also be used in solving applied problems in material science, seismic prospecting, etc.

  17. 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.

  18. Measurement of the speed and attenuation of the Biot slow wave using a large ultrasonic transmitter

    NASA Astrophysics Data System (ADS)

    Bouzidi, Youcef; Schmitt, Douglas R.

    2009-08-01

    Two compressional wave modes, a fast P1 and a slow P2, propagate through fluid-saturated porous and permeable media. This contribution focuses on new experimental tests of existing theories describing wave propagation in such media. Updated observations of this P2 mode are obtained through a water-loaded, porous sintered glass bead plate with a novel pair of ultrasonic transducers consisting of a large transmitter and a near-point receiver. The properties of the porous plate are measured in independent laboratory experiments. Waveforms are acquired as a function of the angle of incidence over the range from -50° to +50° with respect to the normal. The porous plate is fully characterized, and the physical properties are used to calculate the wave speeds and attenuations of the P1, the P2, and the shear S waves. Comparisons of theory and observation are further facilitated by numerically modeling the observed waveforms. This modeling method incorporates the frequency and angle of incidence-dependent reflectivity, transmissivity, and transducer edge effects; the modeled waveforms match well those observed. Taken together, this study provides further support for existing poroelastic bulk wave propagation and boundary condition theory. However, observed transmitted P1 and S mode amplitudes could not be adequately described unless the attenuation of the medium's frame was also included. The observed P2 amplitudes could be explained without any knowledge of the solid frame attenuation.

  19. Characterisation of the biofouling community on a floating wave energy device.

    PubMed

    Nall, Christopher R; Schläppy, Marie-Lise; Guerin, Andrew J

    2017-05-01

    Wave energy devices are novel structures in the marine environment and, as such, provide a unique habitat for biofouling organisms. In this study, destructive scrape samples and photoquadrats were used to characterise the temperate epibenthic community present on prototypes of the Pelamis wave energy converter. The biofouling observed was extensive and diverse with 115 taxa recorded including four non-native species. Vertical zonation was identified on the sides of the device, with an algae-dominated shallow subtidal area and a deeper area characterised by a high proportion of suspension-feeding invertebrates. Differences in species composition and biomass were also observed between devices, along the length of the device and between sampling dates. This research provides an insight into the variation of biofouling assemblages on a wave energy device as well as the potential technical and ecological implications associated with biofouling on marine renewable energy structures.

  20. Characteristics of vibrational wave propagation and attenuation in submarine fluid-filled pipelines

    NASA Astrophysics Data System (ADS)

    Yan, Jin; Zhang, Juan

    2015-04-01

    As an important part of lifeline engineering in the development and utilization of marine resources, the submarine fluid-filled pipeline is a complex coupling system which is subjected to both internal and external flow fields. By utilizing Kennard's shell equations and combining with Helmholtz equations of flow field, the coupling equations of submarine fluid-filled pipeline for n=0 axisymmetrical wave motion are set up. Analytical expressions of wave speed are obtained for both s=1 and s=2 waves, which correspond to a fluid-dominated wave and an axial shell wave, respectively. The numerical results for wave speed and wave attenuation are obtained and discussed subsequently. It shows that the frequency depends on phase velocity, and the attenuation of this mode depends strongly on material parameters of the pipe and the internal and the external fluid fields. The characteristics of PVC pipe are studied for a comparison. The effects of shell thickness/radius ratio and density of the contained fluid on the model are also discussed. The study provides a theoretical basis and helps to accurately predict the situation of submarine pipelines, which also has practical application prospect in the field of pipeline leakage detection.

  1. Influence of reef geometry on wave attenuation on a Brazilian coral reef

    NASA Astrophysics Data System (ADS)

    Costa, Mirella B. S. F.; Araújo, Moacyr; Araújo, Tereza C. M.; Siegle, Eduardo

    2016-01-01

    This study presents data from field experiments that focus on the influence of coral reef geometry on wave transformation in the Metropolitan Area of Recife (MAR) on the northeast coast of Brazil. First, a detailed bathymetric survey was conducted, revealing a submerged reef bank, measuring 18 km long by 1 km wide, parallel to the coastline with a quasi-horizontal top that varies from 0.5 m to 4 m in depth at low tide. Cluster similarity between 180 reef profiles indicates that in 75% of the area, the reef geometry has a configuration similar to a platform reef, whereas in 25% of the area it resembles a fringing reef. Measurements of wave pressure fluctuations were made at two stations (experiments E1 and E2) across the reef profile. The results indicate that wave height was tidally modulated at both experimental sites. Up to 67% (E1) and 99.9% (E2) of the incident wave height is attenuated by the reef top at low tide. This tidal modulation is most apparent at E2 due to reef geometry. At this location, the reef top is only approximately 0.5 m deep during mean low spring water, and almost all incident waves break on the outer reef edge. At E1, the reef top depth is 4 m, and waves with height ratios smaller than the critical breaking limit are free to pass onto the reef and are primarily attenuated by bottom friction. These results highlight the importance of reef geometry in controlling wave characteristics of the MAR beaches and demonstrate its effect on the morphology of the adjacent coast. Implications of differences in wave attenuation and the level of protection provided by the reefs to the adjacent shoreline are discussed.

  2. Development of Floating Wave Barriers for Cost Effective Protection of Irrigation Pond Levees

    USDA-ARS?s Scientific Manuscript database

    The earth levees commonly used for irrigation reservoirs are subjected to significant embankment erosion due to wind-generated waves. Large seasonal fluctuations in water level make vegetative bank protection impractical, and other stabilization methods, such as the use of stone or discarded tires, ...

  3. Design and Analysis for a Floating Oscillating Surge Wave Energy Converter: Preprint

    SciTech Connect

    Yu, Y. H.; Li, Y.; Hallett, K.; Hotimsky, C.

    2014-03-01

    This paper presents a recent study on the design and analysis of an oscillating surge wave energy converter. A successful wave energy conversion design requires the balance between the design performance and cost. The cost of energy is often used as the metric to judge the design of the wave energy conversion system. It is often determined based on the device power performance, the cost for manufacturing, deployment, operation and maintenance, as well as the effort to ensure the environmental compliance. The objective of this study is to demonstrate the importance of a cost driven design strategy and how it can affect a WEC design. Three oscillating surge wave energy converter (OSWEC) designs were used as the example. The power generation performance of the design was modeled using a time-domain numerical simulation tool, and the mass properties of the design were determined based on a simple structure analysis. The results of those power performance simulations, the structure analysis and a simple economic assessment were then used to determine the cost-efficiency of selected OSWEC designs. Finally, a discussion on the environmental barrier, integrated design strategy and the key areas that need further investigation is also presented.

  4. Do Parent Co-Op Preschools Float on Kondratieff's Economic Waves?

    ERIC Educational Resources Information Center

    Hewes, Dorothy W.

    Certain economic theories can help explain the rise to prominence of parent participation preschools in the 1950s and help to make predictions about their future. Specifically, the long-wave cycle of economic behavior and its explanation of social systems and innovations can be useful. One popular approach is that of the Soviet economist Nikolai…

  5. Analysis of coherent surface wave dispersion and attenuation for non-destructive testing of concrete.

    PubMed

    Chekroun, M; Le Marrec, L; Abraham, O; Durand, O; Villain, G

    2009-12-01

    Rayleigh waves measurements are used to characterise cover concrete and mortar in the frequency range 60-180 kHz. At these frequencies, the wavelength is comparable to the size of the aggregates, and waves propagate in a multiple scattering regime. Acquired signals are then difficult to interpret due to an important incoherent part. The method proposed here is the study of the coherent waves, obtained by averaging signals over several configurations of disorder. Coherent waves give information on an equivalent homogeneous medium. To acquire a large amount of measurements with accuracy, an optimised piezoelectric source is used with a laser interferometer for reception. Adapted signal processing technique are presented to evaluate the coherent phase and group velocities and also the coherent attenuation parameter. The sensitivity of these three parameters with the properties of concrete is discussed, as well as the necessity to use coherent waves to obtain accurate results.

  6. Attenuation of Slab determined from T-wave generation by deep earthquakes

    NASA Astrophysics Data System (ADS)

    Huang, J.; Ni, S.

    2006-05-01

    T-wave are seismically generated acoustic waves that propagate over great distance in the ocean sound channel (SOFAR). Because of the high attenuation in both the upper mantle and the ocean crust, T wave is rarely observed for earthquakes deeper than 80 km. However some deep earthquakes deeper than 80km indeed generate apparent T-waves if the subducted slab is continuous Okal et al. (1997) . We studied the deep earthquakes in the Fiji/Tonga region, where the subducted lithosphere is old and thus with small attenuation. After analyzing 33 earthquakes with the depth from 10 Km to 650 Km in Fiji/Tonga, we observed and modeled obvious T-phases from these earthquakes observed at station RAR. We used the T-wave generated by deep earthquakes to compute the quality factor of the Fiji/Tonga slab. The method used in this study is followed the equation (1) by [Groot-Hedlin et al,2001][1]. A=A0/(1+(Ω0/Ω)2)×exp(-LΩ/Qv)×Ωn where the A is the amplitude computed by the practicable data, amplitude depending on the earthquakes, and A0 is the inherent frequency related with the earthquake's half duration, L is the length of ray path that P wave or S travel in the slab, and the V is the velocity of P-wave. In this study, we fix the n=2, by assuming the T- wave scattering points in the Fiji/Tonga island arc having the same attribution as the continental shelf. After some computing and careful analysis, we determined the quality factor of the Fiji/Tonga to be around 1000, Such result is consistent with results from the traditional P,S-wave data[Roth & Wiens,1999][2] . Okal et al. (1997) pointed out that the slab in the part of central South America was also a continuous slab, by modeling apparent T-waves from the great 1994 Bolivian deep earthquake in relation to channeling of S wave energy propagating upward through the slab[3]. [1]Catherine D. de Groot-Hedlin, John A. Orcutt, excitation of T-phases by seafloor scattering, J. Acoust. Soc, 109,1944-1954,2001. [2]Erich G.Roth and

  7. Temporal change in coda wave attenuation observed during an eruption of Mount St. Helens

    SciTech Connect

    Fehler, M.; Roberts, P.; Fairbanks, T.

    1988-05-10

    During the past few years there have been numerous reports of changes in coda wave attenuation occurring before major earthquakes. These observations are important because they may provide insight into stress-related structural changes taking place in the focal region prior to the occurrence of large earthquakes. The results of these studies led us to suspect that temporal changes in coda wave attenuation might also accompany volcanic eruptions. By measuring power decay envelopes for earthquakes at Mount St. Helens recorded before, during, and after an eruption that took place during September 3--6, 1981, we found that coda Q/sup -1/ for frequencies between 6 and 30 Hz was 20--30% higher before the eruption than after. The change is attributed to an increase in the density of open microcracks in the rock associated with inflation of the volcano prior to the eruption. Q/sup -1/ was found to be only weakly dependent on frequency and displayed a slight peak near 10 Hz. The weak frequency dependence is attributed to the dominance of intrinsic attenuation over scattering attenuation, since it is generally accepted that intrinsic attenuation is constant with frequency, whereas scattering attenuation decreases strongly at higher frequencies. The weak frequency dependence of Q/sup -1/ at Mount St. Helens contrasts with results reported for studies in nonvolcanic regions. The peak in Q/sup -1/ near 10 Hz at Mount St. Helens is attributed to the scale length of heterogeneity responsible for generating backscattered waves. Results for nonvolcanic regions have shown this peak to occur near 0.5 Hz. Thus a smaller scale length of heterogeneity is required to explain the 10-Hz peak at Mount St. Helens. copyright American Geophysical Union 1988

  8. Numerical wave modelling for seismo-acoustic noise sources: wave model accuracy issues and evidence for variable seismic attenuation

    NASA Astrophysics Data System (ADS)

    Ardhuin, F.; Lavanant, T.; Obrebski, M. J.; Marié, L.; Royer, J.

    2012-12-01

    Nonlinear wave-wave interactions generate noise that numerical ocean wave models may simulate. The accuracy of the noise source predicted by the theory of Longuet-Higgins (1950) and Hasselmann (1963) depends on the realism of the directional wave distribution, which is generally not very well known. Numerical noise models developed by Kedar et al. (2008) and Ardhuin et al. (2010) also suffer from poorly known seismic wave propagation and attenuation properties. Here, several seismic and ocean pressure records are used here to assess the effects of wave modelling errors on the magnitude of noise sources. Measurements within 200~m from the sea surface are dominated by acoustic-gravity modes, for which bottom effects are negligible. These data show that directional wave spectra are well enough reproduced to estimate seismo-acoustic noise sources at frequencies below 0.3~Hz, whith an underestimation of the noise level by about 50%. In larger water depths, the comparison of a numerical noise model with hydrophone records from two open-ocean sites near Hawaii and Kerguelen islands reveal that a) deep ocean acoustic noise at frequencies 0.1 to 1 Hz is consistent with the Rayleigh wave theory, and is well predicted up to 0.4~Hz. b) In particular, evidence of the vertical modes expected theoretically is given by the local maxima in the noise spectrum. c) noise above 0.6 Hz is not well modeled probably due to a poor estimate of the directional properties of high frequency wind-waves, d) the noise level is strongly influenced by bottom properties, in particular the presence of sediments. Further, for continental coastal seismic stations, an accurate model of noise level variability near the noise spectral peak requires an accurate modelling of coastal reflection (Ardhuin and Roland JGR 2012). In cases where noise sources are confined to a small area (e.g. Obrebski et al. GRL 2012), the source amplitude may be factored out, allowing an estimate of seismic attenuation rates

  9. The attenuation of Love waves and toroidal oscillations of the earth.

    NASA Technical Reports Server (NTRS)

    Jackson, D. D.

    1971-01-01

    An attempt has been made to invert a large set of attenuation data for Love waves and toroidal oscillations in the earth, using a recent method by Backus and Gilbert. The difficulty in finding an acceptable model of internal friction which explains the data, under the assumption that the internal friction is independent of frequency, casts doubt on the validity of this assumption. A frequency-dependent model of internal friction is presented which is in good agreement with the seismic data and with recent experimental measurements of attenuation in rocks.

  10. Imaging Rayleigh Wave Attenuation and Phase Velocity beneath North America with USArray

    NASA Astrophysics Data System (ADS)

    Bao, X.; Dalton, C. A.; Jin, G.; Gaherty, J. B.

    2014-12-01

    The EarthScope USArray provides an opportunity to obtain detailed images of the continental upper mantle of United States at a novel scale. The majority of mantle models derived from USArray data contain spatial variations in velocity; however, little is known about the attenuation structure of the North American upper mantle. Joint interpretation of seismic attenuation and velocity models can improve upon the interpretations based only on velocity, and provide important constraints on the temperature, composition, melt content, and volatile content of the mantle. In this study, Rayleigh wave travel time and amplitude are measured using an interstation cross-correlation version of the Generalized Seismological Data Functional algorithm, which takes advantage of waveform similarity at nearby stations. Our data are from 670 large teleseismic earthquakes that occurred from 2006 to 2014 and were recorded by 1,764 Transportable Array stations. More than 4.8 million measurements at periods between 20 and 100 s are collected into our database. Isolating the signal of attenuation in the amplitude observations is challenging because amplitudes are sensitive to a number of factors in addition to attenuation, such as focusing/defocusing and local site amplification. We generate several Rayleigh wave attenuation maps at each period, using several different approaches to account for source and receiver effects on amplitude. This suite of attenuation maps allows us to distinguish between the robust features in the maps and the features that are sensitive to the treatment of source and receiver effects. We apply Helmholtz surface-wave tomography (Lin et al., 2012) to determine velocity and attenuation maps. A significant contrast in velocity and attenuation is observed in the transition between the western and central United States along the Rocky Mountain front. We find low Q values in the western US, along the eastern coast, and the Gulf plain. These areas are also

  11. Natural attenuation of contaminated marine sediments from an old floating dock Part II: changes of sediment microbial community structure and its relationship with environmental variables.

    PubMed

    Wang, Ya-Fen; Tam, Nora Fung-Yee

    2012-04-15

    Changes of microbial community structure and its relationship with various environmental variables in surface marine sediments were examined for a one-year period after the removal of an old floating dock in Hong Kong SAR, South China. Temporal variations in the microbial community structure were clearly revealed by principal component analysis (PCA) of the microbial ester-linked fatty acid methyl ester (EL-FAME) profiles. The most obvious shift in microbial community structure was detected 6 months after the removal of the dock, although no significant decline in the levels of pollutants could be detected. As determined by EL-FAME profiles, the microbial diversity recovered and the predominance of gram-negative bacteria was gradually replaced by gram-positive bacteria and fungi in the impacted stations. With redundancy analysis (RDA), the concentration of total polycyclic aromatic hydrocarbons (PAHs) was found to be the second important determinant of microbial community structure, next to Time. The relative abundance of 18:1ω9c and hydroxyl fatty acids enriched in the PAH hot spots, whereas 16:1ω9 and 18:1ω9t were negatively correlated to total PAH concentration. The significant relationships observed between microbial EL-FAME profiles and pollutants, exampled by PAHs in the present study, suggested the potential of microbial community analysis in the assessment of the natural attenuation process in contaminated environments. Copyright © 2012 Elsevier B.V. All rights reserved.

  12. Electromagnetic wave attenuation due to the charged particles in dust&sand (DUSA) storms

    NASA Astrophysics Data System (ADS)

    Dou, X. Q.; Xie, L.

    2017-07-01

    In this paper, we calculated the attenuation of the electromagnetic waves (EMWs) propagating through the dust&sand (DUSA) storms using the predicting model based on Mie theory, in which the charges carried on the DUSA particles, the ambient relative humidity (RH) and the particle size distribution are considered simultaneously. It can be found that the charges carried on the DUSA particles and the RH can change the value of the absorption and scattering efficiency, but they can't change the domain attenuation mechanism caused by the DUSA storms in the EMWs frequency regions (3 GHz, 4 GHz), (8 GHz, 40 GHz) and (75 GHz, 100 GHz). Whatever the DUSA storms are formed by equal-size particles or the mixed-size particles, the charge carried on the particle surface and the RH have a significant impact on the attenuation caused by the DUSA storms, and the change ratio of the attenuation caused by the charge or RH depends on the particle size. By the comparison of the calculated attenuation with the measured one, we found that the charges carried on the particles and the RH will be important factors to affect the attenuation of the EMWs.

  13. Strong Lg-wave attenuation in the Middle East continental collision orogenic belt

    NASA Astrophysics Data System (ADS)

    Zhao, Lian-Feng; Xie, Xiao-Bi

    2016-04-01

    Using Lg-wave Q tomography, we construct a broadband crustal attenuation model for the Middle East. The QLg images reveal a relationship between attenuation and geological structures. Strong attenuation is found in the continental collision orogenic belt that extends from the Turkish and Iranian plateau to the Pamir plateau. We investigate the frequency dependence of QLg in different geologic formations. The results illustrate that QLg values generally increase with increasing frequency but exhibit complex relationships both with frequency and between regions. An average QLg value between 0.2 and 2.0 Hz, QLg (0.2-2.0 Hz), may be a critical index for crustal attenuation and is used to infer the regional geology. Low-QLg anomalies are present in the eastern Turkish plateau and correlate well with low Pn-velocities and Cenozoic volcanic activity, thus indicating possible partial melting within the crust in this region. Very strong attenuation is also observed in central Iran, the Afghanistan block, and the southern Caspian Sea. This in line with the previously observed high crustal temperature, high-conductivity layers, and thick marine sediments in these areas, suggests the high Lg attenuation is caused by abnormally high tectonic and thermal activities.

  14. Enhancing the sensitivity of three-axis detectable surface acoustic wave gyroscope by using a floating thin piezoelectric membrane

    NASA Astrophysics Data System (ADS)

    Lee, Munhwan; Lee, Keekeun

    2017-06-01

    A new type of surface acoustic wave (SAW) gyroscope was developed on a floating thin piezoelectric membrane to enhance sensitivity and reliability by removing a bulk noise effect and by importing a higher amplitude of SAW. The developed device constitutes a two-port SAW resonator with a metallic dot array between two interdigital transducers (IDTs), and a one-port SAW delay line. The bulk silicon was completely etched away, leaving only a thin piezoelectric membrane with a thickness of one wavelength. A voltage controlled oscillator (VCO) was connected to a SAW resonator to activate the SAW resonator, while the SAW delay line was connected to the oscilloscope to monitor any variations caused by the Coriolis force. When the device was rotated, a secondary wave was generated, changing the amplitude of the SAW delay line. The highest sensitivity was observed in a device with a full acoustic wavelength thickness of the membrane because most of the acoustic field is confined within an acoustic wavelength thickness from the top surface; moreover, the thin-membrane-based gyroscope eliminates the bulk noise effect flowing along the bulk substrate. The obtained sensitivity and linearity of the SAW gyroscope were ˜27.5 µV deg-1 s-1 and ˜4.3%, respectively. Superior directivity was observed. The device surface was vacuum-sealed using poly(dimethylsiloxane) (PDMS) bonding to eliminate environmental interference. A three-axis detectable gyroscope was also implemented by placing three gyrosensors with the same configuration at right angles to each other on a printed circuit board.

  15. Seismic Wave Attenuation in Fractured Reservoir: Application on Abu Dhabi Oil Fields.

    NASA Astrophysics Data System (ADS)

    Bouchaala, F.; Ali, M.; Matsushima, J.

    2016-12-01

    There is a close link between fractures network and fluids circulation so information about nature and geometry of fractures in the reservoir zone is benificial for the petroleum industry. However the immaturity of the methodology and the complication of fractures network in some reservoirs like those of Abu Dhabi oil fields, make getting such information challenging. Since several studies showed the close link between physical properties of the subsurface and seismic wave attenuation (eg. Müller et al. 2010), we use this parameter in this study to assess its potentiality on fractures detection and characterization, even though its use is not common for reservoir characterization and even less for fractures characterization. To get an accurate attenuation profiles, we use a robust methods recently developed to estimate accurately attenuation from Vertical Seismic Profiling (VSP) (Matsushima et al. 2016) and sonic waveforms (Suziki and Matsushima 2013) in the reservoir zones. The data were acquired from many wells located in offshore and onshore oil fields of Abu Dhabi region. The subsurface of this region is mainly composed of carbonate rocks, such media are known to be highly heterogeneous. Scattering and intrinsic attenuation profiles were compared to interpreted fractures by using Formation Micro-imager (FMI). The comparison shows a correlation between these two parameters and fractures characteristic, such as their density and dipping. We also performed Alford rotation on dipole data to estimate the attenuation from fast and slow shear waveforms. The anisotropy is proportional to the dispersion of the points plotted from the ratio between the intrinsic attenuation of fast and slow shear over the depth, from the line (Qslow /Qfast=1), which corresponds to the isotropic case. We noticed that the zones with low fractures density display less dispersion than those of high density. Even though our results show potentiality of the attenuation for fractured

  16. Wave propagation in double-porosity dual-permeability materials: Velocity and attenuation

    NASA Astrophysics Data System (ADS)

    Sharma, M. D.

    2017-08-01

    This study considers the propagation of harmonic plane waves in a double-porosity solid saturated by a viscous fluid. Two different porosities are supported with different permeabilities to facilitate the wave-induced fluid-flow in this composite material. The variation of the fluid content in the pores due to the wave-induced flow is expressed in terms of the dilatation of constituent particles in the porous aggregate. This fluid-flow can be considered through the constitutive relations with modified anelastic coefficients. The modified coefficients, being frequency dependent and complex, illustrate the dispersive and anelastic behaviour of double-porosity dual-permeability materials. Relevant equations of motion are solved to explain the propagation of three longitudinal waves and one transverse wave in double-porosity dual-permeability medium. A numerical example is considered to illustrate dispersion in velocity and attenuation of the four waves. Effect of wave-induced fluid-flow is analysed with changes in wave-inhomogeneity, pore-fluid viscosity and double-porosity structure.

  17. Microscopic mechanism of attenuation of compressional ultrasonic waves in tissue-mimicking phantom materials.

    PubMed

    Wu, E X; Goodsitt, M M; Madsen, E L

    1992-04-01

    An investigation was performed to determine whether the sound-attenuation-insuspensions theory of Allegra and Hawley can be used to explain the compressional (longitudinal wave) attenuation of ultrasonically tissue-mimicking materials commonly used in phantoms for testing the performance of medical ultrasound systems. These materials are composed of microscopic graphite particles suspended in a gel. The theory was first tested using materials containing spherical glass beads instead of graphite particles because these materials more closely fit the geometric conditions assumed in the theory. For the glass bead type materials as well as the graphite particle type materials, the attenuation coefficients predicted using the Allegra and Hawley model agreed rather well with experimental measurements over the diagnostic frequency range.

  18. An observation related to directional attenuation of SKS waves propagating in anisotropic media

    NASA Astrophysics Data System (ADS)

    Zhao, Liang; Xue, Mei

    2015-04-01

    Azimuthal anisotropy of attenuation is a physical phenomenon related to the directional change of attenuation. This study examines the frequency properties and directional attenuation of SKS waves. The directional frequency-dependent characteristics of SKS waves are investigated in the frequency band of 0.02-0.5 Hz using data from 53 permanent seismic stations located throughout the northern Yangtze Craton, the southern North China Craton and adjacent areas. In addition to normal splitting behavior, the analysis reveals that many SKS splitting measurements exhibit a lemniscate shape, reflecting frequency differences along fast and slow polarization directions. Frequency analysis shows that spectral ratios between fast/slow components of the lemniscate-type splitting results fluctuate strongly in a higher frequency band of 0.2-0.5 Hz, and fluctuate less within the main frequency band of 0.02-0.2 Hz. For each station, the ratio of the peak amplitude of the fast/slow components can be represented as a cotangential function of event backazimuth multiplying with a constant = 0.42 ± 0.10. This transformation shows that the regional average angles consistently fall within the relatively narrow range of -46.5 ± 3° with respect to the north, suggesting that a regional tectonic controlling factor dictates the relatively uniform directional attenuation of SKS waves within the frequency band of 0.02-0.2 Hz. Further analysis is performed by projecting the SKS waves onto the components along and perpendicular to the regional average angles. The calculation also shows that, in the 0.02-0.2 Hz band, the relationship between amplitude ratio and event backazimuth matches a cotangential functions with the same best matching angles and constant a < 1. Synthetic calculations demonstrate that although different filters influence the splitting parameters, attenuation anisotropy cannot be explained by elastic anisotropic media, including multilayer anisotropy and anisotropy with a

  19. Dislocation damping and anisotropic seismic wave attenuation in Earth's upper mantle.

    PubMed

    Farla, Robert J M; Jackson, Ian; Fitz Gerald, John D; Faul, Ulrich H; Zimmerman, Mark E

    2012-04-20

    Crystal defects form during tectonic deformation and are reactivated by the shear stress associated with passing seismic waves. Although these defects, known as dislocations, potentially contribute to the attenuation of seismic waves in Earth's upper mantle, evidence for dislocation damping from laboratory studies has been circumstantial. We experimentally determined the shear modulus and associated strain-energy dissipation in pre-deformed synthetic olivine aggregates under high pressures and temperatures. Enhanced high-temperature background dissipation occurred in specimens pre-deformed by dislocation creep in either compression or torsion, the enhancement being greater for prior deformation in torsion. These observations suggest the possibility of anisotropic attenuation in relatively coarse-grained rocks where olivine is or was deformed at relatively high stress by dislocation creep in Earth's upper mantle.

  20. The propagation and attenuation of complex acoustic waves in treated circular and annular ducts

    NASA Technical Reports Server (NTRS)

    Reethof, G.

    1976-01-01

    The propagation of plane waves and higher order acoustic modes in a circular multisectioned duct was studied. A unique source array consisting of two concentric rings of sources, providing phase and amplitude control in the radial, as well as circumferential direction, was developed to generate plane waves and both spinning and nonspinning higher order modes. Measurements of attenuation and radial mode shapes were taken with finite length liners between the hard wall sections of an anechoically terminated duct. Materials tested as liners included a glass fiber material and both sintered fiber metals and perforated sheet metals with a honeycomb backing. The fundamental acoustic properties of these materials were studied with emphasis on the attenuation of sound by the liners and the determination of local versus extended reaction behavior for the boundary condition. The experimental results were compared with a mathematical model for the multisectioned duct.

  1. Alfvén waves and current relaxation: attenuation at high frequencies and large resistivity

    NASA Astrophysics Data System (ADS)

    Silveira, F. E. M.

    2012-06-01

    The dispersion relations of Alfvén waves propagating in a resistive plasma are explored by assuming a finite relaxation time for the current density. It is shown that the proposed approach is consistent with the hydromagnetic approximation. An extension for the equation governing the space and time evolution of Alfvén waves is provided. New results are found at high values of the wave frequency ω: for a small resistivity, the wavelength increases as the cube of the equilibrium magnetic field but decreases with the cube of ω for a large resistivity, the wave attenuation does not depend on ω, saturating to a finite value which is fully determined by the relaxation time of the current density. A transition frequency, ωt, between two sharply distinct regimes of the perturbation is identified: for ω < ωt, the disturbance propagates in the resistive plasma as an attenuated oscillation; for ω > ωt the wave ceases very rapidly to oscillate (in space), its amplitude saturating to a finite value. The results presented here may be relevant for investigations of some transient phenomena in plasma physics such as the reconnection of magnetic field lines.

  2. Intensity noise enhancement in the half-wave plate/polarizer attenuator.

    PubMed

    Kolner, B H

    1991-06-01

    The conventional optical attenuator for linearly polarized light is usually constructed with a half-wave retardation plate and a polarizer. With one axis of the polarizer aligned so as to transmit the incident beam fully, the addition of the half-wave plate causes the output power to follow a cos(2) 2theta dependence, where theta is the angle between the optic axis of the wave plate and the incident polarization. When the incident light has an additional orthogonal polarization component, the output power dependence becomes more complex and depends on the correlation between the two polarization fields ?E(x)E(y)?. More significantly, if amplitude noise in the polarization fields is correlated, the attenuator will couple the noise processes, which results in relative power fluctuations that increase as the optical power is reduced. The noise produced by this coupling may even exceed the noise of either polarization state alone. Measurements of the statistical behavior of the relative intensity noise of a cw modelocked Nd:YAG laser as a function of the wave-plate angle showed more than a tenfold increase when the output power was reduced to near minimum. In addition, the noise was found to be asymmetrical about the minimum power point, theta = 45 degrees . It is shown that the simple addition of a polarizer ahead of the wave plate strips off the unwanted polarization field and virtually eliminates this added noise effect.

  3. Seismic‐wave attenuation determined from tectonic tremor in multiple subduction zones

    USGS Publications Warehouse

    Yabe, Suguru; Baltay, Annemarie S.; Ide, Satoshi; Beroza, Gregory C.

    2014-01-01

    Tectonic tremor provides a new source of observations that can be used to constrain the seismic attenuation parameter for ground‐motion prediction and hazard mapping. Traditionally, recorded earthquakes of magnitude ∼3–8 are used to develop ground‐motion prediction equations; however, typical earthquake records may be sparse in areas of high hazard. In this study, we constrain the distance decay of seismic waves using measurements of the amplitude decay of tectonic tremor, which is plentiful in some regions. Tectonic tremor occurs in the frequency band of interest for ground‐motion prediction (i.e., ∼2–8  Hz) and is located on the subducting plate interface, at the lower boundary of where future large earthquakes are expected. We empirically fit the distance decay of peak ground velocity from tremor to determine the attenuation parameter in four subduction zones: Nankai, Japan; Cascadia, United States–Canada; Jalisco, Mexico; and southern Chile. With the large amount of data available from tremor, we show that in the upper plate, the lower crust is less attenuating than the upper crust. We apply the same analysis to intraslab events in Nankai and show the possibility that waves traveling from deeper intraslab events experience more attenuation than those from the shallower tremor due to ray paths that pass through the subducting and highly attenuating oceanic crust. This suggests that high pore‐fluid pressure is present in the tremor source region. These differences imply that the attenuation parameter determined from intraslab earthquakes may underestimate ground motion for future large earthquakes on the plate interface.

  4. Pore-scale modeling of pore structure effects on P-wave scattering attenuation in dry rocks.

    PubMed

    Wang, Zizhen; Wang, Ruihe; Li, Tianyang; Qiu, Hao; Wang, Feifei

    2015-01-01

    Underground rocks usually have complex pore system with a variety of pore types and a wide range of pore size. The effects of pore structure on elastic wave attenuation cannot be neglected. We investigated the pore structure effects on P-wave scattering attenuation in dry rocks by pore-scale modeling based on the wave theory and the similarity principle. Our modeling results indicate that pore size, pore shape (such as aspect ratio), and pore density are important factors influencing P-wave scattering attenuation in porous rocks, and can explain the variation of scattering attenuation at the same porosity. From the perspective of scattering attenuation, porous rocks can safely suit to the long wavelength assumption when the ratio of wavelength to pore size is larger than 15. Under the long wavelength condition, the scattering attenuation coefficient increases as a power function as the pore density increases, and it increases exponentially with the increase in aspect ratio. For a certain porosity, rocks with smaller aspect ratio and/or larger pore size have stronger scattering attenuation. When the pore aspect ratio is larger than 0.5, the variation of scattering attenuation at the same porosity is dominantly caused by pore size and almost independent of the pore aspect ratio. These results lay a foundation for pore structure inversion from elastic wave responses in porous rocks.

  5. Pore-Scale Modeling of Pore Structure Effects on P-Wave Scattering Attenuation in Dry Rocks

    PubMed Central

    Li, Tianyang; Qiu, Hao; Wang, Feifei

    2015-01-01

    Underground rocks usually have complex pore system with a variety of pore types and a wide range of pore size. The effects of pore structure on elastic wave attenuation cannot be neglected. We investigated the pore structure effects on P-wave scattering attenuation in dry rocks by pore-scale modeling based on the wave theory and the similarity principle. Our modeling results indicate that pore size, pore shape (such as aspect ratio), and pore density are important factors influencing P-wave scattering attenuation in porous rocks, and can explain the variation of scattering attenuation at the same porosity. From the perspective of scattering attenuation, porous rocks can safely suit to the long wavelength assumption when the ratio of wavelength to pore size is larger than 15. Under the long wavelength condition, the scattering attenuation coefficient increases as a power function as the pore density increases, and it increases exponentially with the increase in aspect ratio. For a certain porosity, rocks with smaller aspect ratio and/or larger pore size have stronger scattering attenuation. When the pore aspect ratio is larger than 0.5, the variation of scattering attenuation at the same porosity is dominantly caused by pore size and almost independent of the pore aspect ratio. These results lay a foundation for pore structure inversion from elastic wave responses in porous rocks. PMID:25961729

  6. A novel protocol to measure the attenuation of electromagnetic waves through smoke

    NASA Astrophysics Data System (ADS)

    Yan-wu, Li; Hong-yong, Yuan; Yang, Lu; Xiaoxiang, Zhang; Ru-feng, Xu; Ming, Fu

    2016-06-01

    The electromagnetic properties of smoke from a structure fire are important in terms of their relation to the stability of wireless communication systems used in fire rescue. As it is hard to make a measurable electromagnetic environment for particles in the air, compressed and bulk samples are used instead to measure sand storms and smoke plumes. In this paper, an experiment system was designed to measure smoke particles in the air, in consideration of both smoke control and electromagnetic measurement. Several measures had been taken to create a fulfilled smoke environment. The simulated and measured transmission parameters of the electromagnetic testing area were approximate and the electromagnetic wave frequencies were set from 350 to 400 MHz. Repeated experiments have been conducted to test the stability of the results and they showed that there was no obvious attenuation until the smoke concentration was more than 10 dB m-1. It was found that the frequency around 355 and 360 MHz had a larger attenuation coefficient. The relationship between the attenuation coefficient and the smoke concentration was concluded to be linear. The results may help us understand the attenuation of electromagnetic waves within a smoke column.

  7. Features of HF Radio Wave Attenuation in the Midlatitude Ionosphere Near the Skip Zone Boundary

    NASA Astrophysics Data System (ADS)

    Denisenko, P. F.; Skazik, A. I.

    2017-06-01

    We briefly describe the history of studying the decameter radio wave attenuation by different methods in the midlatitude ionosphere. A new method of estimating the attenuation of HF radio waves in the ionospheric F region near the skip zone boundary is presented. This method is based on an analysis of the time structure of the interference field generated by highly stable monochromatic X-mode radio waves at the observation point. The main parameter is the effective electron collision frequency νeff, which allows for all energy losses in the form of equivalent heat loss. The frequency νeff is estimated by matching the assumed (model) and the experimentally observed structures. Model calculations are performed using the geometrical-optics approximation. The spatial attenuation caused by the influence of the medium-scale traveling ionospheric disturbances is taken into account. Spherical shape of the ionosphere and the Earth's magnetic field are roughly allowed for. The results of recording of the level of signals from the RWM (Moscow) station at a frequency of 9.996 MHz at point Rostov are used.

  8. Errors and uncertainties in the measurement of ultrasonic wave attenuation and phase velocity.

    PubMed

    Kalashnikov, Alexander N; Challis, Richard E

    2005-10-01

    This paper presents an analysis of the error generation mechanisms that affect the accuracy of measurements of ultrasonic wave attenuation coefficient and phase velocity as functions of frequency. In the first stage of the analysis we show that electronic system noise, expressed in the frequency domain, maps into errors in the attenuation and the phase velocity spectra in a highly nonlinear way; the condition for minimum error is when the total measured attenuation is around 1 Neper. The maximum measurable total attenuation has a practical limit of around 6 Nepers and the minimum measurable value is around 0.1 Neper. In the second part of the paper we consider electronic noise as the primary source of measurement error; errors in attenuation result from additive noise whereas errors in phase velocity result from both additive noise and system timing jitter. Quantization noise can be neglected if the amplitude of the additive noise is comparable with the quantization step, and coherent averaging is employed. Experimental results are presented which confirm the relationship between electronic noise and measurement errors. The analytical technique is applicable to the design of ultrasonic spectrometers, formal assessment of the accuracy of ultrasonic measurements, and the optimization of signal processing procedures to achieve a specified accuracy.

  9. Crustal intrinsic and scattering attenuation of high-frequency shear waves in the contiguous United States

    NASA Astrophysics Data System (ADS)

    Eulenfeld, Tom; Wegler, Ulrich

    2017-06-01

    We use 10 years of data of the USArray project to estimate the areal distribution of crustal intrinsic and scattering attenuation of shear waves for frequencies between 1 Hz and 20 Hz in the contiguous United States. Additionally, we report energy site amplification factors and estimate moment magnitudes for small earthquakes (M 1.5 to M 3.5). The Qopen method is used to invert for intrinsic and scattering attenuation for each event and nearby stations. Observations are collected for around 25,000 events, averaged at each station and interpolated between station locations. In a second inversion, energy site amplifications and moment magnitudes are corrected by assuming that site amplifications for one station and frequency are the same for different earthquakes. We observe a west-east decline of intrinsic attenuation for high frequencies which reflects the west-east transition from young, hot to old and cold crust. Scattering attenuation for high frequencies is stronger in the east with an extraordinary high attenuation around the southern part of the Appalachian Highlands and the Interior Low Plateaus. Results at low frequencies do not show clear trends. A large site amplification is observed at high frequencies in parts of the eastern United States. Estimated moment magnitudes show a good agreement to moment magnitudes independently derived from moment tensor inversion. Moment magnitudes in the west are higher than in the east for the same Richter magnitudes.

  10. Estimates of ocean wave heights and attenuation in sea ice using the SAR wave mode on Sentinel-1A

    NASA Astrophysics Data System (ADS)

    Ardhuin, Fabrice; Collard, Fabrice; Chapron, Bertrand; Girard-Ardhuin, Fanny; Guitton, Gilles; Mouche, Alexis; Stopa, Justin

    2015-04-01

    Swell evolution from the open ocean into sea ice is poorly understood, in particular the amplitude attenuation expected from scattering and dissipation. New synthetic aperture radar (SAR) data from Sentinel-1 wave mode reveal intriguing patterns of bright oscillating lines shaped like instant noodles. We investigate cases in which the oscillations are in the azimuth direction, around a straight line in the range direction. This observation is interpreted as the distortion by the SAR processing of crests from a first swell, due to the presence of a second swell. As deviations from a straight line should be proportional to the orbital velocity towards the satellite, swell height can be estimated, from 1.5 to 5 m in the present case. This evolution of this 13 s period swell across the ice pack is consistent with an exponential attenuation on a length scale of 200 km.

  11. Estimates of ocean wave heights and attenuation in sea ice using the SAR wave mode on Sentinel-1A

    NASA Astrophysics Data System (ADS)

    Ardhuin, Fabrice; Collard, Fabrice; Chapron, Bertrand; Girard-Ardhuin, Fanny; Guitton, Gilles; Mouche, Alexis; Stopa, Justin E.

    2015-04-01

    Swell evolution from the open ocean into sea ice is poorly understood, in particular the amplitude attenuation expected from scattering and dissipation. New synthetic aperture radar (SAR) data from Sentinel-1A wave mode reveal intriguing patterns of bright oscillating lines shaped like instant noodles. We investigate cases in which the oscillations are in the azimuth direction, around a straight line in the range direction. This observation is interpreted as the distortion by the SAR processing of crests from a first swell, due to the presence of a second swell. Since deviations from a straight line should be proportional to the orbital velocity toward the satellite, swell height can be estimated, from 1.5 to 5 m in the present case. The evolution of this 13 s period swell across the ice pack is consistent with an exponential attenuation on a length scale of 200 km.

  12. Seismic Attenuation of Teleseismic Body Waves in Cascadia, Measured on the Amphibious Array

    NASA Astrophysics Data System (ADS)

    Eilon, Z.; Abers, G. A.

    2015-12-01

    Fundamental questions remain about the nature of the asthenosphere, including its dynamical relationship to overlying lithosphere, melt content, and entrainment in subduction zones. We examine the evolution of this low-velocity, highly attenuating layer using data from the Cascadia Initiative's Amphibious Array, which provides unprecedented coverage of an oceanic plate from ridge crest to trench to sub-arc. Our study extends the suite of measurements achievable with OBS data, augmenting traditional travel time analysis with integrated attenuation data that are a powerful tool for imaging melt/fluids and the variation of asthenospheric character with age. Cooling models, coupled with experimentally-derived anelastic scaling relationships, indicate that thermal gradients should cause appreciable decrease in attenuation of teleseismic body waves with increasing age. This long-wavelength cooling trend may be perturbed by highly attenuating melt or volatiles concentrated at the ridge axis or beneath the Cascades arc, depending on melt fraction and pore geometry. Attenuation beyond the trench should be a strong function of the fate of asthenospheric entrainment beneath subducted plates, with implications for mass transfer to the deep mantle as well as recent models of sub-slab anisotropy. The Amphibious Array, with <70 km spacing of OBS and on-land broadband seismometers deployed between 2011 and 2015, provides a dataset of ~1 x 105 arrivals from ~700 Mw>6.0 teleseismic earthquakes. We use a spectral ratio method to compute differential attenuation (Δt*) from body wave teleseisms recorded at OBS and land stations, allowing us to estimate path-integrated quality factor in the upper mantle. Preliminary results reveal variations of ~3 s in differential travel time and >0.5 s in ΔtS* across the 0-10 Ma oceanic plate, demonstrating the strong thermal control on anelasticity. Large values of Δt* observed east of the trench may indicate entrainment of highly attenuating

  13. Meso-scale Computational Investigation of Shock-Wave Attenuation by Trailing Release Wave in Different Grades of Polyurea

    NASA Astrophysics Data System (ADS)

    Grujicic, Mica; Snipes, J. S.; Ramaswami, S.; Yavari, R.; Ramasubramanian, M. K.

    2014-01-01

    Over the past several years, considerable research efforts have been made toward investigating polyurea, a segmented thermoplastic elastomer, and particularly its shock-mitigation capacity, i.e., an ability to attenuate and disperse shock-waves. These research efforts have clearly established that the shock-mitigation capacity of polyurea is closely related to its chemistry, processing route, and the resulting microstructure. Polyurea typically possesses a nano-segregated microstructure consisting of (high glass transition temperature, T g) hydrogen-bonded discrete hard domains and a (low T g) contiguous soft matrix. While the effect of polyurea microstructure on its shock-mitigation capacity is well-established, it is not presently clear what microstructure-dependent phenomena and processes control its shock-mitigation capacity. To help identify these phenomena and processes, meso-scale simulations of the formation of nano-segregated microstructure and its interaction with a leading shock-wave and a trailing release-wave is analyzed in the present work. The results obtained revealed that shock-induced hard-domain densification makes an important contribution to the superior shock-mitigation capacity of polyurea, and that the extent of densification is a sensitive function of the polyurea soft-segment molecular weight. In particular, the ability of release-waves to capture and neutralize shock-waves has been found to depend strongly on the extent of shock-induced hard-domain densification and, thus, on the polyurea soft-segment molecular weight.

  14. Transmission, attenuation and reflection of shear waves in the human brain.

    PubMed

    Clayton, Erik H; Genin, Guy M; Bayly, Philip V

    2012-11-07

    Traumatic brain injuries (TBIs) are caused by acceleration of the skull or exposure to explosive blast, but the processes by which mechanical loads lead to neurological injury remain poorly understood. We adapted motion-sensitive magnetic resonance imaging methods to measure the motion of the human brain in vivo as the skull was exposed to harmonic pressure excitation (45, 60 and 80 Hz). We analysed displacement fields to quantify the transmission, attenuation and reflection of distortional (shear) waves as well as viscoelastic material properties. Results suggest that internal membranes, such as the falx cerebri and the tentorium cerebelli, play a key role in reflecting and focusing shear waves within the brain. The skull acts as a low-pass filter over the range of frequencies studied. Transmissibility of pressure waves through the skull decreases and shear wave attenuation increases with increasing frequency. The skull and brain function mechanically as an integral structure that insulates internal anatomic features; these results are valuable for building and validating mathematical models of this complex and important structural system.

  15. Transmission, attenuation and reflection of shear waves in the human brain

    PubMed Central

    Clayton, Erik H.; Genin, Guy M.; Bayly, Philip V.

    2012-01-01

    Traumatic brain injuries (TBIs) are caused by acceleration of the skull or exposure to explosive blast, but the processes by which mechanical loads lead to neurological injury remain poorly understood. We adapted motion-sensitive magnetic resonance imaging methods to measure the motion of the human brain in vivo as the skull was exposed to harmonic pressure excitation (45, 60 and 80 Hz). We analysed displacement fields to quantify the transmission, attenuation and reflection of distortional (shear) waves as well as viscoelastic material properties. Results suggest that internal membranes, such as the falx cerebri and the tentorium cerebelli, play a key role in reflecting and focusing shear waves within the brain. The skull acts as a low-pass filter over the range of frequencies studied. Transmissibility of pressure waves through the skull decreases and shear wave attenuation increases with increasing frequency. The skull and brain function mechanically as an integral structure that insulates internal anatomic features; these results are valuable for building and validating mathematical models of this complex and important structural system. PMID:22675163

  16. Bio-optical anomalies in the world's oceans: An investigation on the diffuse attenuation coefficients for downward irradiance derived from Biogeochemical Argo float measurements

    NASA Astrophysics Data System (ADS)

    Organelli, Emanuele; Claustre, Hervé; Bricaud, Annick; Barbieux, Marie; Uitz, Julia; D'Ortenzio, Fabrizio; Dall'Olmo, Giorgio

    2017-05-01

    Identification of oceanic regions characterized by particular optical properties is extremely important for ocean color applications. The departure from globally established bio-optical models (i.e., anomaly) introduces uncertainties in the retrieval of biogeochemical quantities from satellite observations. Thanks to an array of 105 Biogeochemical Argo floats acquiring almost daily downward irradiance measurements at selected wavelengths in the UV and blue region of the spectrum, we reexamined the natural variability of the spectral diffuse attenuation coefficients, Kd(λ), among the world's oceans and compared them to previously established bio-optical models. The analysis of 2847 measurements of Kd(λ) at 380 and 490 nm, within the first optical depth, provided a classification of the examined regions into three groups. The first one included the Black Sea, a water body characterized by a very high content of colored dissolved organic matter (CDOM). The second group was essentially composed by the subtropical gyres (Atlantic and Pacific Oceans), with optical properties consistent with previous models (i.e., no anomalies). High latitude (North Atlantic and Southern oceans) and temperate (Mediterranean Sea) seas formed the third group, in which optical properties departed from existing bio-optical models. Annual climatologies of the Kd(380)/Kd(490) ratio evidenced a persistent anomaly in the Mediterranean Sea, that we attributed to a higher-than-average CDOM contribution to total light absorption. In the North Atlantic subpolar gyre, anomalies were observed only in wintertime and were also attributed to high CDOM concentrations. In the Southern Ocean, the anomaly was likely related to high phytoplankton pigment packaging rather than to CDOM.

  17. Q-structure beneath the Tibetan Plateau from the inversion of Love- and Rayleigh-wave attenuation data

    NASA Astrophysics Data System (ADS)

    Singh, D. D.; Gupta, Harsh K.

    1982-08-01

    The fundamental mode Love and Rayleigh waves generated by ten earthquakes and recorded across the Tibet Plateau, at QUE, LAH, NDI, NIL, KBL, SHL, CHG, SNG and HKG are analysed. Love- and Rayleigh-wave attenuation coefficients are obtained at time periods of 5-120 s using the spectral amplitudes of these waves for 23 different paths. Love wave attenuation coefficient varies from 0.0021 km -1, at a period of 10 s, to 0.0002 km -1 at a period of 90 s, attaining two maxima at time periods of 10 and 115 s, and two minima at time periods of 25 and 90 s. The Rayleigh-wave attenuation coefficient also shows a similar trend. The very low value for the dissipation factor, Qβ, obtained in this study suggests high dissipation across the Tibetan paths. Backus-Gilbert inversion theory is applied to these surface wave attenuation data to obtain average Qβ-1 models for the crust and uppermost mantle beneath the Tibetan Plateau. Independent inversion of Love- and Rayleigh-wave attenuation data shows very high attenuation at a depth of ˜50-120 km ( Q β ⋍ 10 ). The simultaneous inversion of the Love and Rayleigh wave data yields a model which includes alternating regions of high and low Qβ-1 values. This model also shows a zone of high attenuating material at a depth of ˜40-120 km. The very high inferred attenuation at a depth of ˜40-120 km supports the hypothesis that the Tibetan Plateau was formed by horizontal compression, and that thickening occurred after the collision of the Indian and Eurasian plates.

  18. Spatial variations of P wave attenuation in the mantle beneath North America

    NASA Astrophysics Data System (ADS)

    Hwang, Yong Keun; Ritsema, Jeroen; Goes, Saskia

    2009-06-01

    We estimate the spatial variation of the seismic parameter t* using teleseismic (epicentral distance = 30°-85°) P wave spectra of about 200 deep (focal depths > 200 km) earthquakes recorded by 378 broadband seismometers in the United States and Canada. Relative P wave spectral ratios up to 1 Hz for about 63,000 station pairs with high signal-to-noise ratio and impulsive P waveforms are inverted for t*P by least squares inversion. The continental-scale t*P pattern correlates to the age of geological terrains and the seismic, heat flow, gravity, and magnetic variations across North America. Predominantly low values of t*P are obtained in stable central North America (SNA), and high t*P values are obtained for stations in the tectonically active western part of the continent (TNA). This variation is similar to that observed previously in short-period amplitude anomalies, spectral ratio variations, and ScS reverberations. On average, we resolve a contrast in t*P between SNA and TNA of about 0.2 s. We resolve regional variations in t*P, which correlate with tectonics. Relatively low t*P is associated with currently active subduction below Alaska. Relatively high t*P is found in SNA below the Appalachians and the Gulf Coast. The consistency between t*P and tectonics suggests that the observed variations in t*P are, on the scale of around 200-500 km, predominantly due to intrinsic attenuation. The similar patterns in t*P and predicted values for a recent global attenuation model confirm this further. The compatibility with the t*P computed for attenuation estimated via a thermal interpretation of shear wave velocity anomalies illustrates that variations in seismic velocity are predominantly due to physical effects with a strong attenuation signature, most likely temperature or a combination of temperature and water content.

  19. Analysis of dispersion and attenuation of surface waves in poroelastic media in the exploration-seismic frequency band

    USGS Publications Warehouse

    Zhang, Y.; Xu, Y.; Xia, J.

    2011-01-01

    We analyse dispersion and attenuation of surface waves at free surfaces of possible vacuum/poroelastic media: permeable-'open pore', impermeable-'closed pore' and partially permeable boundaries, which have not been previously reported in detail by researchers, under different surface-permeable, viscous-damping, elastic and fluid-flowing conditions. Our discussion is focused on their characteristics in the exploration-seismic frequency band (a few through 200 Hz) for near-surface applications. We find two surface-wave modes exist, R1 waves for all conditions, and R2 waves for closed-pore and partially permeable conditions. For R1 waves, velocities disperse most under partially permeable conditions and least under the open-pore condition. High-coupling damping coefficients move the main dispersion frequency range to high frequencies. There is an f1 frequency dependence as a constant-Q model for attenuation at high frequencies. R1 waves for the open pore are most sensitive to elastic modulus variation, but least sensitive to tortuosities variation. R1 waves for partially permeable surface radiate as non-physical waves (Im(k) < 0) at low frequencies. For R2 waves, velocities are slightly lower than the bulk slow P2 waves. At low frequencies, both velocity and attenuation are diffusive of f1/2 frequency dependence, as P2 waves. It is found that for partially permeable surfaces, the attenuation displays -f1 frequency dependence as frequency increasing. High surface permeability, low-coupling damping coefficients, low Poisson's ratios, and low tortuosities increase the slope of the -f1 dependence. When the attenuation coefficients reach 0, R2 waves for partially permeable surface begin to radiate as non-physical waves. ?? 2011 The Authors Geophysical Journal International ?? 2011 RAS.

  20. Numerical simulation of ultrasonic wave propagation in anisotropic and attenuative solid materials

    NASA Astrophysics Data System (ADS)

    You, Zhongqing; Lusk, M.; Ludwig, Reinhold; Lord, William

    1991-09-01

    The axisymmetric elastodynamic finite element code developed is capable of predicting quantitatively accurate displacement fields for elastic wave propagation in isotropic and transversely isotropic materials. The numerical algorithm incorporates viscous damping by adding a time-dependent tensor to Hooke's law. Amplitude comparisons are made between the geometric attenuation in the far field and the corresponding finite element predictions to investigate the quality and validity of the code. Through-transmission experimental measurements made with a 1-MHz L-wave transducer attached to an aluminum sample support the code predictions. The algorithm successfully models geometric beam spreading dispersion and energy absorption due to viscous damping. Extension of the model to include anisotropy, inhomogeneities and the awkward boundaries associated with finite aperture transducers, and realistic defect shapes makes this numerical model a viable tool for the study of elastic wave propagation in nondestructive testing applications.

  1. A highly attenuating and frequency tailorable annular hole phononic crystal for surface acoustic waves.

    PubMed

    Ash, B J; Worsfold, S R; Vukusic, P; Nash, G R

    2017-08-02

    Surface acoustic wave (SAW) devices are widely used for signal processing, sensing and increasingly for lab-on-a-chip applications. Phononic crystals can control the propagation of SAW, analogous to photonic crystals, enabling components such as waveguides and cavities. Here we present an approach for the realisation of robust, tailorable SAW phononic crystals, based on annular holes patterned in a SAW substrate. Using simulations and experiments, we show that this geometry supports local resonances which create highly attenuating phononic bandgaps at frequencies with negligible coupling of SAWs into other modes, even for relatively shallow features. The enormous bandgap attenuation is up to an order-of-magnitude larger than that achieved with a pillar phononic crystal of the same size, enabling effective phononic crystals to be made up of smaller numbers of elements. This work transforms the ability to exploit phononic crystals for developing novel SAW device concepts, mirroring contemporary progress in photonic crystals.The control and manipulation of propagating sound waves on a surface has applications in on-chip signal processing and sensing. Here, Ash et al. deviate from standard designs and fabricate frequency tailorable phononic crystals with an order-of-magnitude increase in attenuation.

  2. Crustal attenuation characteristics of S-waves beneath the Eastern Tohoku region, Japan

    NASA Astrophysics Data System (ADS)

    Arshad, Muhammad Adeel

    2016-10-01

    An inversion method was applied to crustal earthquakes dataset to find S-wave attenuation characteristics beneath the Eastern Tohoku region of Japan. Accelerograms from 85 shallow crustal earthquakes up to 25 km depth and magnitude range between 3.5 and 5.5 were analyzed to estimate the seismic quality factor Q s. A homogeneous attenuation model Q s for the wave propagation path was evaluated from spectral amplitudes, at 24 different frequencies between 0.5 and 20 Hz by using generalized inversion technique. To do this, non-parametric attenuation functions were calculated to observe spectral amplitude decay with hypocentral distance. Then, these functions were parameterized to estimate Q s. It was found that in Eastern Tohoku region, the Q s frequency dependence can be approximated with the function 33 f 1.22 within a frequency range between 0.5 and 20 Hz. However, the frequency dependence of Q s in the frequency range between 0.5 and 6 Hz is best approximated by Q s ( f) = 36 f 0.94 showing relatively weaker frequency dependence as compared to the relation Q s ( f) = 6 f 2.09 for the frequency range between 6 and 15 Hz. These results could be used to estimate source and site parameters for seismic hazard assessment in the region.

  3. A Rayleigh-Wave Attenuation Method for Crack Depth Determination in Asphalt Beams

    NASA Astrophysics Data System (ADS)

    Gibson, Alex; Gallo, Gonzalo E.

    2004-02-01

    It has been established through research on concrete structures that the attenuation of surface waves is sensitive to the presence of a surface-breaking obstructing its path. This is the basis for a non-destructive crack depth measurement technique to quantitatively establish the extent of damage on a pavement subject to of top-down cracking. A previously developed self-compensating technique was applied to asphalt concrete beams constructed with a variety of crack and notch configurations. In the study different notch geometries and the effect of crack width, by comparing results from saw-cut notches to those of narrow cracks, were examined. Two types of impact sources were used and the results obtained were compared to each other. The frequency-dependent signal transmission coefficient was measured at 30 and 50 mm spacing for both undamaged and cracked beams. A single relationship between signal attenuation and crack depth can be attained by normalizing the crack depth with respect to the wavelength. Although the frequency response of a beam is different to that of a slab, the viability of Rayleigh wave attenuation measurements in asphalt pavement surfaces was proved if certain corrections are considered. The method may provide a non-destructive means to determine the depth of cracks in asphalt, such as it does in concrete, with the future understanding of certain phenomena encountered in this work.

  4. A Split of Direction of Propagation and Attenuation of P Waves in the Po Valley

    NASA Astrophysics Data System (ADS)

    Daminelli, R.; Tento, A.; Marcellini, A.

    2013-12-01

    On July 17, 2011 a ML 4.8 earthquake occurred in the PO valley at a 48 km epicentral distance from a seismic station located at Palazzo Te (Mantova). The station is situated on deep quaternary sediments: the uppermost layers are mainly composed of clay and silty clay with interbedded sands; the Robertson index is 1.4wave particle motion, that appears rather difficult to explain if we assume the homogeneity of the P waves (that means attenuation is scalar). Note that the degree of nonlinearity is very low given that the maximum strain can be roughly estimated as 10-5 on the basis of maximum ground velocity of the P wave train considered and the Vp. On the contrary we show that P wave particle motion can be fully (and easily) described by a Homogeneous Isotropic Linear Viscoelastic model (HILV). HILV, as in the 2009 Borcherdt formulation adopted here, allows two different directions of propagation and attenuation; in other words attenuation becomes a vector that is not necessarily parallel to the propagation vector. The results evidence that the incidence angle and the inhomogeneity angle (it is the angle between propagation and attenuation vectors and it is closely related to Q factor) are in good agreement with the geological conditions of the site. Finally, we observed that these results are very similar to the ones obtained when we analyzed two explosions recorded by a seismic station in Milano, also situated in the Po valley at some 140 km from Mantova (Marcellini & Tento, 2011). Borcherdt, R.D. (2009) 'Viscoelastic Waves in Layered Media', Cambridge University Press, Cambridge, United Kingdom, 305 pp. Marcellini, A. and A. Tento (2011) ' Explosive Sources Prove the Validity of Homogeneous Isotropic Linear Viscoelastic Models', BSSA, Vol. 101, No. 4, pp. 1576-1583.

  5. Estimation of the intrinsic absorption and scattering attenuation in Northeastern Venezuela (Southeastern Caribbean) using coda waves

    USGS Publications Warehouse

    Ugalde, A.; Pujades, L.G.; Canas, J.A.; Villasenor, A.

    1998-01-01

    Northeastern Venezuela has been studied in terms of coda wave attenuation using seismograms from local earthquakes recorded by a temporary short-period seismic network. The studied area has been separated into two subregions in order to investigate lateral variations in the attenuation parameters. Coda-Q-1 (Q(c)-1) has been obtained using the single-scattering theory. The contribution of the intrinsic absorption (Q(i)-1) and scattering (Q(s)-1) to total attenuation (Q(t)-1) has been estimated by means of a multiple lapse time window method, based on the hypothesis of multiple isotropic scattering with uniform distribution of scatterers. Results show significant spatial variations of attenuation: the estimates for intermediate depth events and for shallow events present major differences. This fact may be related to different tectonic characteristics that may be due to the presence of the Lesser Antilles subduction zone, because the intermediate depth seismic zone may be coincident with the southern continuation of the subducting slab under the arc.

  6. Wave-speed dispersion associated with an attenuation obeying a frequency power law.

    PubMed

    Buckingham, Michael J

    2015-11-01

    An attenuation scaling as a power of frequency, |ω|(β), over an infinite bandwidth is neither analytic nor square-integrable, thus calling into question the application of the Kramers-Krönig dispersion relations for determining the frequency dependence of the associated phase speed. In this paper, three different approaches are developed, all of which return the dispersion formula for the wavenumber, K(ω). The first analysis relies on the properties of generalized functions and the causality requirement that the impulse response, k(t), the inverse Fourier transform of -iK(ω), must vanish for t < 0. Second, a wave equation is introduced that yields the phase-speed dispersion associated with a frequency-power-law attenuation. Finally, it is shown that, with minor modification, the Kramers-Krönig dispersion relations with no subtractions (the Plemelj formulas) do in fact hold for an attenuation scaling as |ω|(β), yielding the same dispersion formula as the other two derivations. From this dispersion formula, admissible values of the exponent β are established. Physically, the inadmissible values of β, which include all the integers, correspond to attenuation-dispersion pairs whose Fourier components cannot combine in such a way as to make the impulse response, k(t), vanish for t < 0. There is no upper or lower limit on the value that β may take.

  7. First evidence for high anelastic attenuation beneath the Red Sea from Love wave analysis

    NASA Astrophysics Data System (ADS)

    1990-10-01

    Attenuation coefficients of Love waves are determined for two seismic paths along the Red sea. The attenuation coefficients are obtained using the multiple filter method for periods from 25 to 130 s alone one path and from 40 to 130 s along the second one. The two sets of observations are in good agreement with anomalously high attenuation coefficients similar to those reported across a young part of the Pacific ocean. Indeed, the values lie on average between 3.3+/-0.6 and 1.1+/-0.3 (10-4km-1), higher values being observed at shorter periods. In a second part of the paper, these apparent attenuation observations are interpreted in terms of a distribution of intrinsic absorption in the upper mantle. A frequency independent Qβ model is obtained using a trial-and-error method. The best fit to the data required a large and very low Qβ (30-50) zone below a depth of 50 km, underlying a thin and high Qβ (200-300) lid. These results are consistent with high heat flows and low velocities which characterize this tectonically active area, and corroborate the inference of anomalously high temperatures and low viscosity in the upper mantle beneath the Red Sea from recent seismological results.

  8. Iterative methods for solving coefficient inverse problems of wave tomography in models with attenuation

    NASA Astrophysics Data System (ADS)

    Goncharsky, Alexander V.; Romanov, Sergey Y.

    2017-02-01

    We develop efficient iterative methods for solving inverse problems of wave tomography in models incorporating both diffraction effects and attenuation. In the inverse problem the aim is to reconstruct the velocity structure and the function that characterizes the distribution of attenuation properties in the object studied. We prove mathematically and rigorously the differentiability of the residual functional in normed spaces, and derive the corresponding formula for the Fréchet derivative. The computation of the Fréchet derivative includes solving both the direct problem with the Neumann boundary condition and the reversed-time conjugate problem. We develop efficient methods for numerical computations where the approximate solution is found using the detector measurements of the wave field and its normal derivative. The wave field derivative values at detector locations are found by solving the exterior boundary value problem with the Dirichlet boundary conditions. We illustrate the efficiency of this approach by applying it to model problems. The algorithms developed are highly parallelizable and designed to be run on supercomputers. Among the most promising medical applications of our results is the development of ultrasonic tomographs for differential diagnosis of breast cancer.

  9. Plate-type elastic metamaterials for low-frequency broadband elastic wave attenuation.

    PubMed

    Li, Yinggang; Zhu, Ling; Chen, Tianning

    2017-01-01

    In this paper, we numerically and experimentally demonstrate the low-frequency broadband elastic wave attenuation and vibration suppression by using plate-type elastic metamaterial, which is constituted of periodic double-sides stepped resonators deposited on a two-dimensional phononic plate with steel matrix. The dispersion relations, the power transmission spectra, and the displacement fields of the eigenmodes are calculated by using the finite element method. In contrast to the typical phononic plates consisting of periodic stepped resonators deposited on a homogeneous steel plate, the proposed elastic metamaterial can yield large band gap in the low-frequency range, resulting in the low-frequency broadband elastic wave attenuation. The formation mechanisms of the band gap as well as the effects of material and geometrical parameters on the band gap are further explored numerically. Numerical results show that, the formation mechanism of opening the low-frequency band gap is attributed to the coupling between the local resonant Lamb modes of two-dimensional phononic plate and the resonant modes of the stepped resonators. The band gap can be significantly modulated by the material and geometrical parameters. The properties of broadband gaps of the proposed subwavelength scale elastic metamaterials can potentially be applied to vibration and noise reduction in the audio regime as well as broadband elastic wave confinement and modulation in ultrasonic region. Copyright © 2016 Elsevier B.V. All rights reserved.

  10. The attenuation of seismic shear waves in quaternary alluvium in Santa Clara Valley, California

    USGS Publications Warehouse

    Gibbs, James F.; Boore, David M.; Joyner, William B.; Fumal, Thomas E.

    1994-01-01

    We used shear waves, generated by an air-powered source at the ground surface and recorded in a borehole, to estimate the shear-wave quality factor at strong-motion station Gilroy no. 2. We find similar values of Q using both the decay of the spectra with depth and the slope of the spectral ratio at two depths; we find no evidence of a frequency dependence of Q. The mean value of Q over the depth range 10 to 115 m is close to 10. The use of this value over the depth of the borehole and the observed travel time of 0.358 sec gives a cumulative attenuation factor t* of 0.036 sec for the upper 180 m of the Quaternary alluvium. This is comparable to the differential decay between Gilroy no. 2 and a rock site 1.9 km away (Gilroy no. 1), as measured from the decay of the high-frequency spectra of accelerograms from large earthquakes, plotted on a log-linear scale: t* = 0.05, 0.04, and 0.03 sec for the 1979 Coyote Lake, 1984 Morgan Hill, and 1989 Loma Prieta earthquakes, respectively. The similarity between the attenuations measured from the low-strain surface source and those from the larger amplitude earthquake sources suggests that increases of damping due to nonlinear wave propagation effects are limited.

  11. Traveling waves in trimer granular lattice II: Asymptotic prediction of weakly attenuated pulses

    NASA Astrophysics Data System (ADS)

    Shiffer, A.; Jayaprakash, K. R.; Starosvetsky, Y.

    2017-02-01

    In the present study we consider the impulsive response of perfectly aligned, uncompressed, tri-atomic (trimer) granular lattice. In this study, we demonstrate that under particular choice of the system parameters - impulsively loaded, trimer granular lattice can support formation of highly localized, weakly attenuated pulses. These pulses are manifested by the completely non-symmetric wave profiles and can be attributed to the special family of solitary like waves forming in the non-homogenous, periodic trimer granular lattice in the state of acoustic vacuum. Using the recently developed analytical procedure based on the singular, multi-scale perturbation analysis, we derive a simplified reduced order model predicting the special regions in the space of the system parameters corresponding to the formation of the weakly attenuated pulses. Predictions of the asymptotical model are found to be in very good agreement with the results of numerical simulations of the full trimer granular lattice. From a practical point of view, these results can have important implications in complex, structural optimization problems of wave manipulation in the repetitive granular metamaterials.

  12. Technological cost-reduction pathways for attenuator wave energy converters in the marine hydrokinetic environment.

    SciTech Connect

    Bull, Diana L; Ochs, Margaret Ellen

    2013-09-01

    This report considers and prioritizes the primary potential technical costreduction pathways for offshore wave activated body attenuators designed for ocean resources. This report focuses on technical research and development costreduction pathways related to the device technology rather than environmental monitoring or permitting opportunities. Three sources of information were used to understand current cost drivers and develop a prioritized list of potential costreduction pathways: a literature review of technical work related to attenuators, a reference device compiled from literature sources, and a webinar with each of three industry device developers. Data from these information sources were aggregated and prioritized with respect to the potential impact on the lifetime levelized cost of energy, the potential for progress, the potential for success, and the confidence in success. Results indicate the five most promising costreduction pathways include advanced controls, an optimized structural design, improved power conversion, planned maintenance scheduling, and an optimized device profile.

  13. Stress wave attenuation in thin structures by ultrasonic through-transmission

    NASA Technical Reports Server (NTRS)

    Lee, S. S.; Williams, J. H., Jr.

    1980-01-01

    The steady state amplitude of the output of an ultrasonic through transmission measurement is analyzed and the result is given in closed form. Provided that the product of the input and output transduction ratios; the specimen-transducer reflection coefficient; the specimen-transducer phase shift parameter; and the material phase velocity are known, this analysis gives a means for determining the through-thickness attenuation of an individual thin sample. Multiple stress wave reflections are taken into account and so signal echoes do not represent a difficulty. An example is presented for a graphite fiber epoxy composite (Hercules AS/3501-6). A direct method for continuous or intermittent monitoring of through thickness attenuation of plate structures which may be subject to service structural degradation is provided.

  14. Stress-wave attenuation in thin structures by ultrasonic through-transmission

    NASA Technical Reports Server (NTRS)

    Lee, S. S.; Williams, J. H., Jr.

    1980-01-01

    The steady-state amplitude of the output of an ultrasonic through-transmission measurement is analyzed and the result is given in closed form. Provided that the product of the input and output transduction ratios, the specimen-transducer reflection coefficient, the specimen-transducer phase-shift parameter, and the material phase velocity are known, this analysis gives a means for determining the through-thickness attenuation of an individual thin sample. Multiple stress-wave reflections are taken into account, and so signal echoes do not represent a difficulty. An example is presented for a graphite fiber epoxy composite (Hercules AS/3501-6). Thus, the technique provides a direct method for continuous or intermittent monitoring of through-thickness attenuation of plate structures which may be subject to service structural degradation.

  15. High-sensitivity attenuated total internal reflection continuous-wave terahertz imaging

    NASA Astrophysics Data System (ADS)

    Liu, Hongxiang; Wang, Yuye; Xu, Degang; Wu, Limin; Yan, Chao; Yan, Dexian; Tang, Longhuang; He, Yixin; Feng, Hua; Yao, Jianquan

    2017-09-01

    We demonstrate an attenuated total internal reflection imaging system. The surface information of the sample on top of a prism can be acquired by two-dimensionally scanning this prism moving in the vertical plane with horizontally incident continuous terahertz waves at a fixed height. The principles and feasibility of this method are investigated. The effective imaging area on the prism, image resolution and polarization dependence of contrast enhancement and stability improvement are analyzed. Examples including solid agar, distilled water and porcine tissue are presented, demonstrating the method’s advantages of high sensitivity and simple sample preparation. The experimental and theoretical results consistently show that p-polarization contributes to enhanced image contrast and more stable intensity of the attenuated total internal reflected signal.

  16. Producing acoustic 'Frozen Waves': simulated experiments with diffraction/attenuation resistant beams in lossy media.

    PubMed

    Prego-Borges, José L; Zamboni-Rached, Michel; Recami, Erasmo; Costa, Eduardo Tavares

    2014-08-01

    The so-called Localized Waves (LW), and the "Frozen Waves" (FW), have raised significant attention in the areas of Optics and Ultrasound, because of their surprising energy localization properties. The LWs resist the effects of diffraction for large distances, and possess an interesting self-reconstruction -self-healing- property (after obstacles with size smaller than the antenna's); while the FWs, a sub-class of LWs, offer the possibility of arbitrarily modeling the longitudinal field intensity pattern inside a prefixed interval, for instance 0⩽z⩽L, of the wave propagation axis. More specifically, the FWs are localized fields "at rest", that is, with a static envelope (within which only the carrier wave propagates), and can be endowed moreover with a high transverse localization. In this paper we investigate, by simulated experiments, various cases of generation of ultrasonic FW fields, with the frequency of f0=1 MHz in a water-like medium, taking account of the effects of attenuation. We present results of FWs for distances up to L=80 mm, in attenuating media with absorption coefficient α in the range 70⩽α⩽170 dB/m. Such simulated FW fields are constructed by using a procedure developed by us, via appropriate finite superpositions of monochromatic ultrasonic Bessel beams. We pay due attention to the selection of the FW parameters, constrained by the rather tight restrictions imposed by experimental Acoustics, as well as to some practical implications of the transducer design. The energy localization properties of the Frozen Waves can find application even in many medical apparatus, such as bistouries or acoustic tweezers, as well as for treatment of diseased tissues (in particular, for the destruction of tumor cells, without affecting the surrounding tissues; also for kidney stone shuttering, etc.).

  17. Development of attenuation and diffraction corrections for linear and nonlinear Rayleigh surface waves radiating from a uniform line source

    SciTech Connect

    Jeong, Hyunjo Cho, Sungjong; Zhang, Shuzeng; Li, Xiongbing

    2016-04-15

    In recent studies with nonlinear Rayleigh surface waves, harmonic generation measurements have been successfully employed to characterize material damage and microstructural changes, and found to be sensitive to early stages of damage process. A nonlinearity parameter of Rayleigh surface waves was derived and frequently measured to quantify the level of damage. The accurate measurement of the nonlinearity parameter generally requires making corrections for beam diffraction and medium attenuation. These effects are not generally known for nonlinear Rayleigh waves, and therefore not properly considered in most of previous studies. In this paper, the nonlinearity parameter for a Rayleigh surface wave is defined from the plane wave displacement solutions. We explicitly define the attenuation and diffraction corrections for fundamental and second harmonic Rayleigh wave beams radiated from a uniform line source. Attenuation corrections are obtained from the quasilinear theory of plane Rayleigh wave equations. To obtain closed-form expressions for diffraction corrections, multi-Gaussian beam (MGB) models are employed to represent the integral solutions derived from the quasilinear theory of the full two-dimensional wave equation without parabolic approximation. Diffraction corrections are presented for a couple of transmitter-receiver geometries, and the effects of making attenuation and diffraction corrections are examined through the simulation of nonlinearity parameter determination in a solid sample.

  18. Teleseismic Body Wave Attenuation in the Upper Mantle beneath the United States

    NASA Astrophysics Data System (ADS)

    Cafferky, S.; Schmandt, B.

    2014-12-01

    EarthScope seismic data provide opportunities to examine mantle properties on a continental scale as the Transportable Array (TA) nears the end of its traverse across the contiguous United States. We use P- and S-wave amplitude spectra from all >M5.7 deep earthquakes recorded by the TA to examine seismic attenuation patterns in the upper mantle. More than 2 million inter-station P-wave spectral ratios were inverted for maps of relative tP* variations across the U.S. in multiple frequency bands between 0.08 - 2 Hz. We plan to have corresponding S-wave results by meeting time. Maps of tP* are strongly correlated (>0.8) for frequency bands of 0.08 - 2 Hz, 0.25 - 2 Hz, 0.08 - 1 Hz, and 0.25 - 1 Hz. The broader the frequency band examined (e.g. 0.08 - 2 Hz), the lower the magnitude in variations of tP*; however, those broader frequency bands still exhibited geographic patterns similar to the narrow frequency bands. We compare our maps' tP* with seismic velocity models and constraints on crustal scattering to assess the physical origin of apparent attenuation. In the tectonically active and high heat flow domain of the western U.S., tP* variations are moderately correlated with thermal variations predicted by tomography studies of seismic velocity. However, contrast in tP* between western Cordillera and the cratonic interior is weaker than predicted by tomography. Additionally some areas of high attenuation are correlated with Precambrian tectonic boundaries within the Laurentian craton. The weak contrast between the western and eastern U.S. and correlations with Precambrian tectonics suggest that elastic scattering due to small-scale (~10 - 100 km) heterogeneity or compositional variations in the lithosphere are major contributors to tP* estimates from deep earthquake spectral ratios. Moderate correlation of tP* with estimates of mantle temperature within the western U.S. suggests deep earthquake spectral ratios do carry some evidence of intrinsic attenuation, but

  19. Numerical upscaling in 2-D heterogeneous poroelastic rocks: Anisotropic attenuation and dispersion of seismic waves

    NASA Astrophysics Data System (ADS)

    Rubino, J. Germán.; Caspari, Eva; Müller, Tobias M.; Milani, Marco; Barbosa, Nicolás. D.; Holliger, Klaus

    2016-09-01

    The presence of stiffness contrasts at scales larger than the typical pore sizes but smaller than the predominant seismic wavelengths can produce seismic attenuation and velocity dispersion in fluid-saturated porous rocks. This energy dissipation mechanism is caused by wave-induced fluid pressure diffusion among the different components of the probed geological formations. In many cases, heterogeneities have elongated shapes and preferential orientations, which implies that the overall response of the medium is anisotropic. In this work, we propose a numerical upscaling procedure that permits to quantify seismic attenuation and phase velocity considering fluid pressure diffusion effects as well as generic anisotropy at the sample's scale. The methodology is based on a set of three relaxation tests performed on a 2-D synthetic rock sample representative of the medium of interest. It provides a complex-valued frequency-dependent equivalent stiffness matrix through a least squares procedure. We also derive an approach for computing various poroelastic fields associated with the considered sample in response to the propagation of a seismic wave with arbitrary incidence angle. Using this approach, we provide an energy-based estimation of seismic attenuation. A comprehensive numerical analysis indicates that the methodology is suitable for handling complex media and different levels of overall anisotropy. Comparisons with the energy-based estimations demonstrate that the dynamic-equivalent viscoelastic medium assumption made by the numerical upscaling procedure is reasonable even in the presence of high levels of overall anisotropy. This work also highlights the usefulness of poroelastic fields for the physical interpretation of seismic wave phenomena in strongly heterogeneous and complex media.

  20. Compressional wave velocity and attenuation at ultrasonic and sonic frequencies in near-surface sedimentary rocks

    SciTech Connect

    Best, A.I.; Sams, M.S.

    1997-03-01

    Laboratory ultrasonic measurements of compressional wave velocity and attenuation were made as a function of effective pressure on samples of limestone, sandstone and siltstone taken from a shallow borehole test site. The results indicate that the sandstones are pervaded by grain contact microcracks which dramatically affect their compressional wave attenuations. Clean sandstone shows a compressional wave quality factor (Q{sub p}) of 24 {+-} 2 at 5 MPa effective pressure (close to the estimated in situ burial pressure) and a Q{sub p} of 83 {+-} 29 at 60 MPa. The Q{sub p} of limestones and siltstones at the site show negligible and small increases with pressure in the laboratory, respectively. The strong pressure dependence of Q{sub p} in clean sandstone was used to infer the presence of in situ microcracks. Sediment velocities measured in the laboratory at about 1 MHz were compared with those from the full waveform sonic log at about 10 kHz implies that they must also be highly attenuating over a significant part of the frequency range 10 kHz to 1 MHz, to account for the magnitude of the observed velocity dispersion. Assuming the laboratory Q{sub p} values measured at 5 MPa remain constant down to 10 kHz predicts the observed dispersion quite well. Furthermore, the sonic log velocities of sandstones, limestones and siltstones (after normalizing each lithology for porosity and clay content) were found to reflect the same pressure (depth) trends observed in the laboratory. The results provide evidence for the existence of in situ microcracks in near-surface sediments.

  1. Shear wave velocity and attenuation in the upper layer of ocean bottoms from long-range acoustic field measurements.

    PubMed

    Zhou, Ji-Xun; Zhang, Xue-Zhen

    2012-12-01

    Several physics-based seabed geoacoustic models (including the Biot theory) predict that compressional wave attenuation α(2) in sandy marine sediments approximately follows quadratic frequency dependence at low frequencies, i.e., α(2)≈kf(n) (dB/m), n=2. A recent paper on broadband geoacoustic inversions from low frequency (LF) field measurements, made at 20 locations around the world, has indicated that the frequency exponent of the effective sound attenuation n≈1.80 in a frequency band of 50-1000 Hz [Zhou et al., J. Acoust. Soc. Am. 125, 2847-2866 (2009)]. Carey and Pierce hypothesize that the discrepancy is due to the inversion models' neglect of shear wave effects [J. Acoust. Soc. Am. 124, EL271-EL277 (2008)]. The broadband geoacoustic inversions assume that the seabottom is an equivalent fluid and sound waves interact with the bottom at small grazing angles. The shear wave velocity and attenuation in the upper layer of ocean bottoms are estimated from the LF field-inverted effective bottom attenuations using a near-grazing bottom reflection expression for the equivalent fluid model, derived by Zhang and Tindle [J. Acoust. Soc. Am. 98, 3391-3396 (1995)]. The resultant shear wave velocity and attenuation are consistent with the SAX99 measurement at 25 Hz and 1000 Hz. The results are helpful for the analysis of shear wave effects on long-range sound propagation in shallow water.

  2. Experimental study on hydrodynamic characteristics of vertical-axis floating tidal current energy power generation device

    NASA Astrophysics Data System (ADS)

    Ma, Yong; Li, Teng-fei; Zhang, Liang; Sheng, Qi-hu; Zhang, Xue-wei; Jiang, Jin

    2016-10-01

    To study the characteristics of attenuation, hydrostatic towage and wave response of the vertical-axis floating tidal current energy power generation device (VAFTCEPGD), a prototype is designed and experiment is carried out in the towing tank. Free decay is conducted to obtain attenuation characteristics of the VAFTCEPGD, and characteristics of mooring forces and motion response, floating condition, especially the lateral displacement of the VAFTCEPGD are obtained from the towing in still water. Tension response of the #1 mooring line and vibration characteristics of the VAFTCEPGD in regular waves as well as in level 4 irregular wave sea state with the current velocity of 0.6 m/s. The results can be reference for theoretical study and engineering applications related to VAFTCEPGD.

  3. Velocity and attenuation of ultrasound waves under cyclic loading of low-carbon steel

    NASA Astrophysics Data System (ADS)

    Lunev, Alexey; Nadezhkin, Mikhail; Zuev, Lev

    2016-11-01

    The results of the research of ultrasound wave velocity and attenuation in low-carbon steel during low-cycle fatigue tests have been presented in this work. It has been found that the dependencies of acoustic parameters on the number of cycles have three stages. The first stage is connected with dislocation density growth in a specimen. The transition from the second stage to the third one can be used as a criterion of fatigue wear of metalworks and implemented for nondestructive ultrasound lifetime estimation.

  4. Viscous effects on the attenuation of a plane wave by an acoustic lining in shear flow.

    PubMed

    Khamis, Doran; Brambley, Edward James

    2017-04-01

    The attenuation of a plane acoustic wave incident on a flat impedance surface in a sheared and viscous fluid is investigated numerically and asymptotically. Predictions of various boundary models of impedance surfaces in shear flow are tested by comparing their predicted reflection coefficient. It is found that viscosity has a significant effect, reducing the reflection of upstream propagating sound while increasing the reflection of cross-stream propagating sound. The classical Ingard-Myers boundary condition is shown to incorrectly predict the damping rate of sound in many cases, and in some cases viscous effects are shown to be comparable to shear effects.

  5. Development of Surface Wave Dispersion and Attenuation Maps and Improved Methods for Measuring Surface Waves

    DTIC Science & Technology

    2008-05-30

    waves at KNET stations due to Lop Nor explosions .........................26 3.6. 3D Calculations of Lop Nor to KNET and comparison with the Born...out of Lop Nor. Right – same, but the velocity model has been smoothed by modeling it as a bilinear rather than piecewise discontinuous function...attributed to the effects of the propagation near the basin boundary. ............ 25 Figure 3.10. Paths (top) and data (bottom) for the Lop Nor explosion of

  6. Electrocardiogram voltage attenuation and shortening of the duration of P-waves, QRS complexes, and QT intervals.

    PubMed

    Madias, John E

    2013-01-01

    Multiple pathologies in concert may lead to attenuation of the electrocardiogram (ECG) voltage. A case of a patient illustrating the above is presented, who showed marked attenuation of the ECG voltage. Automated values of the amplitude of the ECG QRS complexes, P-waves, and T-waves (in mm), duration of the QRS complexes, P-waves, and QT intervals (in ms), in 2 ECGs were compared. The patient was a 64-year-old woman who developed in the setting of a fatal illness, pleural and pericardial effusions, pneumomediastinum, pneumoperitoneum, subcutaneous emphysema in the neck and chest, peripheral edema with weight gain of 43.4 lbs, marked hypoalbuminemia, abnormal liver tests, and renal failure. All the above pathologies led to a marked attenuation of the ECG voltage, and shortening of the mean P-wave, QRS complexes, and QTc interval durations. The postulated mechanism of the observed ECG phenomena is discussed.

  7. Phase velocities and attenuations of shear, Lamb, and Rayleigh waves in plate-like tissues submerged in a fluid (L).

    PubMed

    Nenadic, Ivan Z; Urban, Matthew W; Bernal, Miguel; Greenleaf, James F

    2011-12-01

    In the past several decades, the fields of ultrasound and magnetic resonance elastography have shown promising results in noninvasive estimates of mechanical properties of soft tissues. These techniques often rely on measuring shear wave velocity due to an external or internal source of force and relating the velocity to viscoelasticity of the tissue. The mathematical relationship between the measured velocity and material properties of the myocardial wall, arteries, and other organs with non-negligible boundary conditions is often complicated and computationally expensive. A simple relationship between the Lamb-Rayleigh dispersion and the shear wave dispersion is derived for both the velocity and attenuation. The relationship shows that the shear wave velocity is around 20% higher than the Lamb-Rayleigh velocity and that the shear wave attenuation is about 20% lower than the Lamb-Rayleigh attenuation. Results of numerical simulations in the frequency range 0-500 Hz are presented.

  8. Seismic waves attenuation in the lithosphere of the northern Basin and Range Province

    NASA Astrophysics Data System (ADS)

    Dobrynina, Anna

    2013-04-01

    The seismic quality factor of the direct body waves (P- and S-waves) and coda and their frequency dependence (n) were estimated for the northern Basin and Range Province using traces of 66 local earthquakes and explosions recorded during 1988-1989 PASSCAL Basin and Range Passive Seismic Experiment. For calculation of Q-coda the single backscattering model by Aki was used. Q-coda values were estimated for six central frequencies (f): 0.3±0.1, 0.75±0.25, 1.5±0.5, 3.0±1.0, 6.0±2.0 and 12.0±4.0 Hz and for 18 lapse time windows (W) - from 10 to 95 sec with a step 5 sec. The Qp and Qs values were obtained by the method of the maximum amplitudes for the frequency bands 0.5-1.0, 1.0-2.0, 2.0-4.0 ? 4.0-8.0 Hz. Also we tired to evaluate the part of the intrinsic and scattering attenuation (Qi and Qsc respectively) in the total attenuation using Wennerberg's method. The Q-coda increases and the frequency parameter n and the attenuation coefficient δ decrease with increasing of frequency and lapse time windows. This fact shows that the upper part of the lithosphere is more heterogeneous compared to its lower layers. The deep variations of the frequency parameter n and the attenuation coefficient δ show the sharp change at the depth about 150 km - at the same depth the boundary of the low velocity anomaly is observed (Bensen et al., 2009; Wagner et al., 2012; Shen et al., 2012). The Qs and Qp values also increase with frequency: Qs varies from 42 (0.84 Hz) to 298 (5.52 Hz) and Qp - from 60 (0.84 Hz) to 279 (6.05 Hz). The following empirical relations of Q vs. f are deduced for P- and S-waves respectively: Qp(f)=69*f0.78 and Qs(f)=53*f1.08. The Q-values, describing the intrinsic and scattering attenuation, also show a significant dependence on frequency and lapse time windows: the empirical relations of Q vs. f are: Qi(f)=8*f1.2 and Qsc(f)=13*f1.1 (for W=10 sec) and Qi(f)=5*f1.2 and Qsc(f)=102*f1.0 (for W=95 sec) respectively. The comparison of the intrinsic and

  9. Influence of spin wave attenuation on a ferromagnetic nanowire-based magnonic Bragg mirror

    NASA Astrophysics Data System (ADS)

    Parsons, L. C.

    2017-03-01

    A theoretical study of classical spin waves propagating in axially magnetized, lossy ferromagnetic nanowires is considered, resulting in a model for a magnonic Bragg mirror based on an axially periodic arrangement of identical nanowire segments. While the system shows evidence of one-dimensional magnonic band gaps, with widths increasing as the inter-nanowire exchange coupling strength decreases, spin wave attenuation effects can be quite dramatic for magnetic damping constants within the range 0.001-0.1. In fact, calculated reflectance spectra for nanowire structures with a damping constant on the order of 0.01 exhibit relatively intense Bragg peaks only when the nanowire segment length is no more than an order of magnitude larger than the exchange length.

  10. Broadband attenuation of Lamb waves through a periodic array of thin rectangular junctions

    NASA Astrophysics Data System (ADS)

    Moiseyenko, Rayisa P.; Pennec, Yan; Marchal, Rémi; Bonello, Bernard; Djafari-Rouhani, Bahram

    2014-10-01

    We study theoretically subwavelength physical phenomena, such as resonant transmission and broadband sound shielding for Lamb waves propagating in an acoustic metamaterial made of a thin plate drilled with one or two row(s) of rectangular holes. The resonances and antiresonances of periodically arranged rectangular junctions separated by holes are investigated as a function of the geometrical parameters of the junctions. With one and two row(s) of holes, high frequency specific features in the transmission coefficient are explained in terms of a coupling of incident waves with both Fabry-Perot oscillations inside the junctions and induced surface acoustic waves between the homogeneous part of the plate and the row of holes. With two rows of holes, low frequency peaks and dips appear in the transmission spectrum. The choice of the distance between the two rows of holes allows the realization of a broadband low frequency acoustic shielding with attenuation over 99% for symmetric waves in a wide low frequency range and over 90% for antisymmetric ones. The origin of the transmission gap is discussed in terms of localized modes of the "H" element made by the junctions, connecting the two homogeneous parts of the plate.

  11. Finite Difference Numerical Modeling of Gravito-Acoustic Wave Propagation in a Windy and Attenuating Atmosphere

    NASA Astrophysics Data System (ADS)

    Brissaud, Q.; Garcia, R.; Martin, R.; Komatitsch, D.

    2015-12-01

    The acoustic and gravity waves propagating in the planetary atmospheres have been studied intensively as markers of specific phenomena (tectonic events, explosions) or as contributors to the atmosphere dynamics. To get a better understanding of the physic behind these dynamic processes, both acoustic and gravity waves propagation should be modeled in an attenuating and windy 3D atmosphere from the ground to the upper thermosphere. Thus, In order to provide an efficient numerical tool at the regional or the global scale a high order finite difference time domain (FDTD) approach is proposed that relies on the linearized compressible Navier-Stokes equations (Landau 1959) with non constant physical parameters (density, viscosities and speed of sound) and background velocities (wind). One significant benefit from this code is its versatility. Indeed, it handles both acoustic and gravity waves in the same simulation that enables one to observe correlations between the two. Simulations will also be performed on 2D/3D realistic cases such as tsunamis in a full MSISE-00 atmosphere and gravity-wave generation through atmospheric explosions. Computations are validated by comparison to well-known analytical solutions based on dispersion relations in specific benchmark cases (atmospheric explosion and bottom displacement forcing).

  12. Input-dependent wave attenuation in a critically-balanced model of cortex.

    PubMed

    Yan, Xiao-Hu; Magnasco, Marcelo O

    2012-01-01

    A number of studies have suggested that many properties of brain activity can be understood in terms of critical systems. However it is still not known how the long-range susceptibilities characteristic of criticality arise in the living brain from its local connectivity structures. Here we prove that a dynamically critically-poised model of cortex acquires an infinitely-long ranged susceptibility in the absence of input. When an input is presented, the susceptibility attenuates exponentially as a function of distance, with an increasing spatial attenuation constant (i.e., decreasing range) the larger the input. This is in direct agreement with recent results that show that waves of local field potential activity evoked by single spikes in primary visual cortex of cat and macaque attenuate with a characteristic length that also increases with decreasing contrast of the visual stimulus. A susceptibility that changes spatial range with input strength can be thought to implement an input-dependent spatial integration: when the input is large, no additional evidence is needed in addition to the local input; when the input is weak, evidence needs to be integrated over a larger spatial domain to achieve a decision. Such input-strength-dependent strategies have been demonstrated in visual processing. Our results suggest that input-strength dependent spatial integration may be a natural feature of a critically-balanced cortical network.

  13. Differential shear wave attenuation and its lateral variation in the North Atlantic region

    NASA Technical Reports Server (NTRS)

    Sheehan, Anne F.; Solomon, Sean C.

    1992-01-01

    A digital data base of over 150 seismograms and a spectral radio technique are used to measure SS-S differential attenuation in the North Atlantic region. Differential attenuation is positively correlated with SS-S travel time residual, and both differential attentuation and travel time residual decrease with increasing seafloor age. Models are developed for seismic Q in which lateral variations include contributions from the asthenospheric low-Q zone as well as from lithospheric cooling. The Q models obtained under this assumption are in good agreement with those obtained from surface wave studies and are therefore preferred over those models with lateral variations confined to the upper 125 km. Systematic long-wavelength (1000-7000 km) variations in differential attenuation, corrected for seafloor age, are evident along the axis of the Mid-Atlantic Ridge. These variations can be qualitatively correlated with long-wavelength variations in SS-S differential travel time residuals and are attributed to along-axis differences in upper mantle temperature.

  14. First evidence for high anelastic attenuation beneath the Red Sea from Love Wave Analysis

    NASA Astrophysics Data System (ADS)

    Hadiouche, Ouiza

    1990-10-01

    Attenuation coefficients of Love waves are determined for two seismic paths along the Red sea. The attenuation coefficients are obtained using the multiple filter method for periods from 25 to 130 s along one path and from 40 to 130 s along the second one. The two sets of observations are in good agreement with anomalously high attenuation coefficients similar to those reported across a young part of the Pacific ocean. Indeed, the values lie on average between 3.3 ± 0.6 and 1.1 ± 0.3(10-4km-1), higher values being observed at shorter periods. In a second part of the paper, these apparent attenution observations are interpreted in terms of a distribution of intrinsic absorption in the upper mantle. A frequency independent Qβ model is obtained using a trial-and-error method. The best fit to the data required a large and very low Qβ (30-50) zone below a depth of 50 km, underlying a thin and high Qβ (200-300) lid. These results are consistent with high heat flows and low velocities which characterize this tectonically active area, and corroborate the inference of anomalously high temperatures and low viscosity in the upper mantle beneath the Red Sea from recent seismological results.

  15. Estimation of Coda Wave Attenuation for the National Capital Region, Delhi, India Using Local Earthquakes

    NASA Astrophysics Data System (ADS)

    Mohanty, William K.; Prakash, Rajesh; Suresh, G.; Shukla, A. K.; Yanger Walling, M.; Srivastava, J. P.

    2009-03-01

    Attenuation of seismic waves is very essential for the study of earthquake source parameters and also for ground-motion simulations, and this is important for the seismic hazard estimation of a region. The digital data acquired by 16 short-period seismic stations of the Delhi Telemetric Network for 55 earthquakes of magnitude 1.5 to 4.2, which occurred within an epicentral distance of 100 km in an area around Delhi, have been used to estimate the coda attenuation Q c . Using the Single Backscattering Model, the seismograms have been analyzed at 10 central frequencies. The frequency dependence average attenuation relationship Q c = 142 f 1.04 has been attained. Four Lapse-Time windows from 20 to 50 seconds duration with a difference of 10 seconds have been analyzed to study the lapse time dependence of Q c . The Q c values show that frequency dependence (exponent n) remains similar at all the lapse time window lengths. While the change in Q 0 values is significant, change in Q 0 with larger lapsetime reflects the rate of homogeneity at the depth. The variation of Q c indicates a definitive trend from west to east in accordance with the geology of the region.

  16. Investigation of the Maule, Chile rupture zone using seismic attenuation tomography and shear wave splitting methods

    NASA Astrophysics Data System (ADS)

    Torpey, Megan Elizabeth

    The Maule, Chile 2010 Mw 8.8 earthquake afforded the opportunity to study the rupture zone (33°S-38°S) in detail using aftershocks recorded by the rapid-response IRIS CHAMP seismic network. We used measurements of differential S to P seismic attenuation to characterize the attenuation structure of the South American crust and upper mantle wedge. We implemented an evolving time window to determine Qs-1 values using a spectral ratio method and incorporated these measurements into a bounded linear inequality least squares inversion to solve for Qs -1 in a 3D volume. On a large-scale, we observe an east-dipping low attenuation feature, consistent with the location of the Nazca oceanic slab, and image progressively greater attenuation as we move towards the surface of our model. A dramatic feature in our model is a large, low-attenuation body in the same location where Hicks et al. (2014) resolved a high P wave velocity anomaly in their velocity tomography model. We calculated the shear wave splitting intensity of the Maule rupture zone by implementing the multichannel method of Chevrot (2000) which calculates the splitting intensity of teleseismic SK(K)S phases and splitting parameters, ϕ and deltat. The results we obtained show an overall fast direction with a strong component of trench parallel splitting and very few trench normal splits. The fast directions do not parallel the Nazca APM, but are instead dominated by splits rotated 40°-50° counter-clockwise from Nazca APM. Based on these data, we see little evidence for sub-slab entrained mantle flow and invoke the trench-parallel retrograde flow model as an explanation for our measurements. We developed an extended splitting intensity method to allow for use of the upgoing S phase from Maule aftershocks, utilizing the initial event polarization. For this local dataset, we observe three dominant fast directions oriented N20°W, N40°E, and N10°W-20°E and a subset of fast directions trending N60°-90°E which

  17. Structure-preserving spectral element method in attenuating seismic wave modeling

    NASA Astrophysics Data System (ADS)

    Cai, Wenjun; Zhang, Huai

    2016-04-01

    This work describes the extension of the conformal symplectic method to solve the damped acoustic wave equation and the elastic wave equations in the framework of the spectral element method. The conformal symplectic method is a variation of conventional symplectic methods to treat non-conservative time evolution problems which has superior behaviors in long-time stability and dissipation preservation. To construct the conformal symplectic method, we first reformulate the damped acoustic wave equation and the elastic wave equations in their equivalent conformal multi-symplectic structures, which naturally reveal the intrinsic properties of the original systems, especially, the dissipation laws. We thereafter separate each structures into a conservative Hamiltonian system and a purely dissipative ordinary differential equation system. Based on the splitting methodology, we solve the two subsystems respectively. The dissipative one is cheaply solved by its analytic solution. While for the conservative system, we combine a fourth-order symplectic Nyström method in time and the spectral element method in space to cover the circumstances in realistic geological structures involving complex free-surface topography. The Strang composition method is adopted thereby to concatenate the corresponding two parts of solutions and generate the completed numerical scheme, which is conformal symplectic and can therefore guarantee the numerical stability and dissipation preservation after a large time modeling. Additionally, a relative larger Courant number than that of the traditional Newmark scheme is found in the numerical experiments in conjunction with a spatial sampling of approximately 5 points per wavelength. A benchmark test for the damped acoustic wave equation validates the effectiveness of our proposed method in precisely capturing dissipation rate. The classical Lamb problem is used to demonstrate the ability of modeling Rayleigh-wave propagation. More comprehensive

  18. Seismic tomography of compressional wave attenuation structure for Kı¯lauea Volcano, Hawai`i

    NASA Astrophysics Data System (ADS)

    Lin, Guoqing; Shearer, Peter M.; Amelung, Falk; Okubo, Paul G.

    2015-04-01

    We present a frequency-independent three-dimensional (3-D) compressional wave attenuation model (indicated by the reciprocal of quality factor Qp) for Kı¯lauea Volcano in Hawai`i. We apply the simul2000 tomographic algorithm to the attenuation operator t* values for the inversion of Qp perturbations through a recent 3-D seismic velocity model and earthquake location catalog. The t* values are measured from amplitude spectra of 26708 P wave arrivals of 1036 events recorded by 61 seismic stations at the Hawaiian Volcanology Observatory. The 3-D Qp model has a uniform horizontal grid spacing of 3 km, and the vertical node intervals range between 2 and 10 km down to 35 km depth. In general, the resolved Qp values increase with depth, and there is a correlation between seismic activity and low-Qp values. The area beneath the summit caldera is dominated by low-Qp anomalies throughout the entire resolved depth range. The Southwest Rift Zone and the East Rift Zone exhibit very high Qp values at about 9 km depth, whereas the shallow depths are characterized with low-Qp anomalies comparable with those in the summit area. The seismic zones and fault systems generally display relatively high Qp values relative to the summit. The newly developed Qp model provides an important complement to the existing velocity models for exploring the magmatic system and evaluating and interpreting intrinsic physical properties of the rocks in the study area.

  19. Stable harmonic multiplying gyrotron traveling-wave amplifier with distributed wall losses and attenuating severs

    SciTech Connect

    Yeh, Y. S.; Cheng, J. H.; Chen, L. K.; Hung, C. W.; Lo, C. Y.; Liao, C. W.

    2008-02-15

    Harmonic multiplying gyrotron traveling-wave amplifiers (gyro-TWTs) provide magnetic field reduction and frequency multiplication. However, spurious oscillations may reduce the amplification of the gyro-TWT. Most distributed-loss structures are stabilized in gyro-TWTs that operate at low beam currents. Attenuating severs are added to the interaction circuit of a distributed-loss gyro-TWT to prevent high beam currents that result in mode competition. This study proposes a Ka-band harmonic multiplying gyro-TWT, using distributed wall losses and attenuating severs, to improve the stability of the amplification and the performance of the amplifier. Simulation results reveal that the absolute instabilities are effectively suppressed by wall losses of the lossy and severed sections, especially in the low-k{sub z} and high-order modes. Meanwhile, the severed section, dividing an interaction circuit into several short sections, reduces the effective interaction lengths of the absolute instabilities. The stable harmonic multiplying gyro-TWT is predicted to yield a peak output power of 230 kW at 33.65 GHz with an efficiency of 30%, a saturated gain of 40 dB, and a 3 dB bandwidth of 0.8 GHz for a 60 kV, 13 A electron beam with an axial velocity spread of {delta}v{sub z}/v{sub z}=8%. The power/gain scaling and phase relation between the drive and the output waves are elucidated.

  20. Quantifying Regional Body Wave Attenuation in a Seismic Prone Zone of Northeast India

    NASA Astrophysics Data System (ADS)

    Bora, Nilutpal; Biswas, Rajib

    2017-03-01

    We evaluated the body wave attenuation parameter in Kopili region of northeast India. Using the modified algorithm of coda normalization method, we delineated frequency-dependent attenuation for both P and S waves. Taking more than 300 seismograms as input, we comprehensively studied microearthquake spectra in the frequency range of 1.5-12 Hz. The estimated values of {Q}_{P}^{-1} and {Q}_{S}^{-1} show strong frequency dependence. Based on this, we formulated empirical relationships corresponding to {Q}_{P}^{-1} and {Q}_{S}^{-1} for the study region. The relationships emerge to be {Q}_{P}^{-1} = ( {23.8 ± 6} ) × 10^{-3} {f}^{{( {-1.2 ± 0.008} )}} and {Q}_{S}^{-1} = ( {10.2 ± 2} ) × 10^{-3} {f}^{{( {-1.3 ± 0.02} )}} , respectively. The ratio {Q}_{P}^{-1} /{Q}_{S}^{-1} is found to be larger than unity for the entire frequency band which implies profound seismic activity and macroscale heterogeneity prevailing in the region. The study may act as the building block towards determination of source parameter and hazard-related studies in the region.

  1. Variability of crustal attenuation in the northeastern United States from Lg waves

    NASA Astrophysics Data System (ADS)

    Shi, Jinghua; Kim, Won-Young; Richards, Paul G.

    1996-11-01

    High-quality, digital seismograms from eight pairs of collocated earthquakes in the northeastern United States were analyzed to determine accurate source spectrum corner frequencies. This was accomplished by applying the empirical Green's function method to regional Pg and Lg (or Sg) phases recorded by vertical component seismographs of the U.S. National Seismographic Network (USNSN) and the Lamont-Doherty Cooperative Seismographic Network (LCSN) stations. The frequency band used was 0.5-16 Hz for USNSN and 1-30 Hz for LCSN records. The source spectrum corner frequencies for the eight larger earthquakes of the event pairs (magnitudes between mb(Lg) = 2.5 - 4.1) range from about 4.3 to 16.3 Hz. Based on the comer frequencies obtained independently from the empirical Green's function analysis, Sg or Lg wave displacement amplitude spectra up to 30 Hz were used to determine the crustal average Q factors along 87 event-station paths. These paths crossed diverse tectonic features in the northeastern United States and were in the epicentral distance range of 41 to 1394 km. We found that within the northeastern United States, the crustal average QLg we obtained was frequency dependent and showed spatial variability which correlated fairly well with the major tectonic features in the region. Our attenuation measurements indicated low Lg attenuation in the Adirondack Mountains with exposed Precambrian Grenville basement with QLg = 905 f0.40, high Lg attenuation in the central Appalachian Province with QLg = 561-586 f0.46-0.47, and an intermediate Lg attenuation in northern New England Appalachians with Q = 705 f0.41.

  2. Seismic wave attenuation and dispersion due to wave-induced fluid flow in rocks with strong permeability fluctuations.

    PubMed

    Germán Rubino, J; Monachesi, Leonardo B; Müller, Tobias M; Guarracino, Luis; Holliger, Klaus

    2013-12-01

    Oscillatory fluid movements in heterogeneous porous rocks induced by seismic waves cause dissipation of wave field energy. The resulting seismic signature depends not only on the rock compressibility distribution, but also on a statistically averaged permeability. This so-called equivalent seismic permeability does not, however, coincide with the respective equivalent flow permeability. While this issue has been analyzed for one-dimensional (1D) media, the corresponding two-dimensional (2D) and three-dimensional (3D) cases remain unexplored. In this work, this topic is analyzed for 2D random medium realizations having strong permeability fluctuations. With this objective, oscillatory compressibility simulations based on the quasi-static poroelasticity equations are performed. Numerical analysis shows that strong permeability fluctuations diminish the magnitude of attenuation and velocity dispersion due to fluid flow, while the frequency range where these effects are significant gets broader. By comparing the acoustic responses obtained using different permeability averages, it is also shown that at very low frequencies the equivalent seismic permeability is similar to the equivalent flow permeability, while for very high frequencies this parameter approaches the arithmetic average of the permeability field. These seemingly generic findings have potentially important implications with regard to the estimation of equivalent flow permeability from seismic data.

  3. Wave Transformation and Attenuation near the Submerged Breakwater and Vegetation: Field investigation and Numerical simulation

    NASA Astrophysics Data System (ADS)

    Shin, S.; Kim, I.; Hur, D.; Lee, W.; Kim, J.; Lee, J. L.; Lee, H. S.; Kim, H. G.

    2016-12-01

    The large scale decreasing of beach width in the Anmok beach had occurred due to the coastal erosion caused by the short-term events, such as unexpected high waves and storms. Hence, the city officials decided the installation of hard construction, and the first submerged breakwater, which is a structure that parallels the beach and support as a wave absorber, was constructed on this beach in September 2014. In order to deduce the correlation equation of the transmitted wave heights (TWH) after the breakwater installed, we have observed the transmitted wave height at four sites nearby the breakwater, two wave gauges were mounted on the front side of the breakwater, and the others were placed in the behind side of it. We found that the TWH using the formula suggested by Takayama et al. (1985) for the submerged breakwaters (crown elevation: D.L. (-)0.5 m, crown width: 18.5 m, bottom width: 22.8 m) was 0.501, whereas the value which was measured by the wave gauge showed 0.547. Therefore, we suggested a formula for estimating the TWH based on the field observation data. 3D numerical model (LES-WASS-3D) was employed to estimate hydrodynamic chracteristics near the submerged breakwater. The results showed that the predicted TWH agreed well with the field field observation data results. In order to consider evironmet-friendly measure, the model also simulated the wave transformation and attenuation phenomina near the area of submerged vegetation. The model was already verified in two-dimensional laboratory experiments. In this study, the numerical model is used to predict the three-dimensional wave transformation and attenucation through the underwater vegetation. The results are compared with those in the case of submerged breakwater. This research was partially supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2016R1A2B4015419) and Korean Institute of Marine Science and Technology

  4. High-resolution 3-D P wave attenuation structure of the New Madrid Seismic Zone using local earthquake tomography

    NASA Astrophysics Data System (ADS)

    Bisrat, Shishay T.; DeShon, Heather R.; Pesicek, Jeremy; Thurber, Clifford

    2014-01-01

    A three-dimensional (3-D), high-resolution P wave seismic attenuation model for the New Madrid Seismic Zone (NMSZ) is determined using P wave path attenuation (t*) values of small-magnitude earthquakes (MD < 3.9). Events were recorded at 89 broadband and short-period seismometers of the Cooperative New Madrid Seismic Zone Network and 40 short-period seismometers of the Portable Array for Numerical Data Acquisition experiment. The amplitude spectra of all the earthquakes are simultaneously inverted for source, path (t*), and site parameters. The t* values are inverted for QP using local earthquake tomography methods and a known 3-D P wave velocity model for the region. The four major seismicity arms of the NMSZ exhibit reduced QP (higher attenuation) than the surrounding crust. The highest attenuation anomalies coincide with areas of previously reported high swarm activity attributed to fluid-rich fractures along the southeast extension of the Reelfoot fault. The QP results are consistent with previous attenuation studies in the region, which showed that active fault zones and fractured crust in the NMSZ are highly attenuating.

  5. S wave attenuation structure on the western side of the Nankai subduction zone: Implications for fluid distribution and dynamics

    NASA Astrophysics Data System (ADS)

    Takahashi, Tsutomu; Obana, Koichiro; Yamamoto, Yojiro; Nakanishi, Ayako; Kodaira, Shuichi; Kaneda, Yoshiyuki

    2014-10-01

    We estimated the S wave attenuation structure in southwestern Japan and the western Nankai Trough by analyzing maximum S wave amplitudes at 4-8, 8-16, and 16-32 Hz with a correction term for apparent amplitude attenuation due to multiple forward scattering. Because the estimated attenuation (Q-1) in our tomographic study was much larger than Q-1 due to wide-angle scattering, our estimated Q-1 was composed mainly of intrinsic attenuation. High-attenuation areas (Q-1 > 1/300 at 4-8 Hz) were imaged beneath Quaternary volcanoes and south off Shikoku. Low (<1/1500 at 4-8 Hz) or moderate Q-1 (1/500-1/1000 at 4-8 Hz) was imaged beneath Shikoku and nonvolcanic areas of Chugoku. High and moderate Q-1 in and around Shikoku are located near the top of subducting Philippine Sea Plate. This correspondence implies that these high and moderate Q-1 reflect fluid in the subducting slab. By applying a theoretical model of attenuation in water-saturated porous random media, we examined wave-induced fluid flow induced by lower frequency (<1 Hz) seismic waves that may be related with triggering of nonvolcanic tremor by surface waves. Even though Q-1 structure in this study cannot fully explain the tremor triggering by wave-induced fluid flow, large uncertainties of Q-1 in tremor zone suggest that high resolution imaging of Q-1 and random inhomogeneities would give some constraints for the spatial variation of permeability and other medium properties.

  6. Attenuation, source parameters and site effects of SH waves in Taiwan

    NASA Astrophysics Data System (ADS)

    Chang, Shun-Chiang; Wen, Kuo-Liang

    2016-04-01

    Generalized inversion technique (GIT) (Castro et al., 1990) was used to derive SH-wave in the frequency range 0.2-25 Hz (interval 0.1 Hz). The inversion results can find attenuation characteristics, earthquake source parameters and site amplification functions. The characteristics of the site amplification are referred to horizontal-to-vertical (H/V) Fourier spectral ratios of microtremor for a referent rock site. The SH-wave from 28 earthquakes with magnitude ranging from ML 5 to 7, of 1319 earthquake records at 146 TSMIP strong motion stations in Jianan Plain, southwestern Taiwan are used in this analysis. The SH-wave quality factor Q(f) is estimated as 52.83f0.77 for 0.2<= f < =25 Hz. The stress drops can be found from source spectra by using the omega-square model. The results of site amplification are similar to horizontal-to-vertical spectral ratio of the microtremor which have clearly and similar predominant peaks.

  7. On the onset of multi-wave patterns in laterally heated floating zones for slightly supercritical conditions

    NASA Astrophysics Data System (ADS)

    Lappa, Marcello

    2016-12-01

    This analysis follows and integrates the line of inquiry started in past author's works [M. Lappa, "Three-dimensional numerical simulation of Marangoni flow instabilities in floating zones laterally heated by an equatorial ring," Phys. Fluids 15(3), 776-789 (2003) and "Combined effect of volume and gravity on the three-dimensional flow instability in non-cylindrical floating zones heated by an equatorial ring," ibid. 16(2), 331-343 (2004)] about the typical instabilities of the Marangoni flow and associated hierarchy of bifurcations in laterally heated floating zones with various shapes and aspect ratios. The main motivation for re-examining this kind of problems, which have attracted so much attention over the last twenty years, is the recent discovery [M. Kudo et al., "Transition of thermocapillary convection in a full-zone liquid bridge," Trans. JSME (in Japanese) 80(812), TEP0095 (2014)] of a chaotic state in the region of the space of parameters where on the basis of existing theories and earlier results for the classical liquid-bridge problem with organic fluids, the flow should be relatively regular in time and with a simple structure in space. Axisymmetric computations are used to obtain the steady basic state, and then the Navier Stokes equations are solved in their complete, three-dimensional, time-dependent, and non-linear formulation to investigate the evolution of azimuthal disturbances. It is shown that the "apparent" doubling or quadrupling of the azimuthal wavenumber in the equatorial plane, previously reported for the case of floating zones of liquid metals, is replaced for high-Prandtl-number liquids by the complex interaction of disturbances with distinct spatial and temporal scales. These disturbances become critical at relatively comparable values of the Marangoni number. The unexpected multiplicity of waveforms and competition of spatial modes are explained according to the increased complexity of the considered system in terms of flow

  8. A method based on reflection theory to test the attenuation performance of an absorption coat to 8mm waves

    NASA Astrophysics Data System (ADS)

    Wang, Xuanyu

    2016-09-01

    A testing method has been set up to evaluate the attenuation performance of an absorption coat to 8mm waves, which is based on a set of detecting system included by an 8mm wave emitter, a millimeter power meter, a point to point collimator and a reflecting plate. The power meter was aimed at the 8 mm wave emitter along the reflection optical path instead of the direction observation between incident and reflected millimeter wave. Some Al, Fe and aluminum alloy sample plates were made and painted by the dope which was complexed with chopped carbon fibers. A naked metal plate was first used to adjust the transmission path of the millimeter wave. Then the power meter was adjusted to phase locking after preheating, and the millimeter wave power was sampled as the background value. Then the other painted plates were tested under the same conditions. When the concentration of chopped carbon fibers is 0.5mg/ml and the thickness of the absorption coat is 0.5mm, the attenuation percentages of Al, Fe and aluminum alloy painted plates respectively is 54.29%, 58.31% and 41.12%. By the result, the reflection testing method may be widely used to measure the reflection capacity or attenuation performance of various surfaces to millimeter waves.

  9. Stools - floating

    MedlinePlus

    ... absorption of nutrients ( malabsorption ) or too much gas (flatulence). Considerations Most causes of floating stools are harmless. ... Elsevier Saunders; 2016:chap 140. Read More Gas - flatulence Malabsorption Review Date 5/11/2016 Updated by: ...

  10. Seismic modelling study of P-wave attenuation and velocity dispersion in patchy-saturated porous media

    NASA Astrophysics Data System (ADS)

    Li, Xiaobo; Dong, Liangguo; Zhao, Qun

    2014-12-01

    Seismic wave propagation in patchy-saturated porous media is studied by numerical simulation in time domain at the seismic frequency band (1-1000 Hz). The models consist of hundreds of representative elementary volumes (REVs), where the REV is partially saturated with water and gas pockets. Seismic modelling experiments are implemented in a traditional way, with ‘periodic’ boundary conditions applied to get rid of undrained boundary conditions at the outer edges of the REVs. The characteristics of confining pressure, induced pore pressure, solid particle velocities and Darcy filtration velocities are analysed. The snapshots show that strong pore pressure gradients are generated across the interface between gas and water phases, and significant fluid flow occurs. The conversion of a fast P-wave into a dissipating slow P-wave takes place at seismic frequencies, and the converted slow P-wave diffuses strongly in both gas- and water-saturated phases. These numerical results can help us to understand the loss mechanism at seismic frequencies. Then, P-wave attenuation and velocity dispersion of a heterogeneous REV are calculated during traditional seismic modelling at seismic frequencies. The numerical results show good agreement with theoretical predictions obtained from patchy saturation theory. Furthermore, the effects of different fluid distributions on P-wave attenuation and velocity dispersion are analysed numerically. A series of experiments are implemented by considering large, small and random gas-patchy inclusions. The decrease of gas pocket size makes the peak frequency move towards high frequencies. Random distribution of gas patches may affect both the peak attenuation and peak frequencies. Seismic attenuation caused by Biot global flow, elastic scattering and wave-induced fluid flow (WIFF) associated with patchy saturation are computed numerically. The results show that the contribution of Biot’s global flow and scattering to the overall attenuation

  11. Frequency dependent attenuation characteristics of coda waves in the Northwestern Himalayan (India) region

    NASA Astrophysics Data System (ADS)

    Kumar, Sushil; Singh, Priyamvada; Singh, Pitam; Biswal, Shubhasmita; Parija, Mahesh Prasad

    2016-03-01

    Digital seismogram data of 82 earthquakes from the Northwestern Himalayan (India) region recorded at different stations during 2004-2006 were analyzed to study the seismic coda wave attenuation characteristics in this region. We used 132 seismic observations from local earthquakes with a hypocentral distance <240 km and a magnitude range of 1.2-4.9 to study the coda QC using the single isotropic scattering model. These earthquakes were recorded at 20 temporary seismic stations installed in the Northwestern Himalayas (India) by the Wadia institute of Himalayan Geology, Dehradun. The QC values were estimated at 10 central frequencies: 1.5, 3, 5, 7, 9, 12, 16, 20, 24, and 28 Hz using starting lapse-times of 10, 20, 30, 40, 50, and 60 s and coda window-lengths of 10, 20, 30, 40, and 50 s. The QC fits the frequency dependent power-law, QC =Q0fn . For a 10 s lapse time with a 10-s coda window length QC = 47.42f1.012 and for a 50 s lapse time with a 50 s coda window length, QC = 204.1f0.934 . Q0 (QC at 1 Hz) varied from ∼47 for a 10 s lapse time and a 10 s window length, to ∼204 for a 50 s lapse time and a 50 s window length. An average frequency dependent power law fit for the study region may be given as QC = 116.716f0.9943 . The exponent of the frequency dependence law n ranged from 1.08 to 0.9, which correlates well with values obtained in other seismically and tectonically active and heterogeneous regions of the world. In our study region, QC increases both with respect to lapse time and frequency, i.e., the attenuation decreases as the quality factor is inversely proportional to attenuation. The low QC values or high attenuation at lower frequencies and high QC values or low attenuation at higher frequencies suggest that the heterogeneity decreases with increasing depth in our study region.

  12. High S-wave attenuation anomalies and ringlike seismogenic structures in the lithosphere beneath Altai: Possible precursors of large earthquakes

    NASA Astrophysics Data System (ADS)

    Kopnichev, Yu. F.; Sokolova, I. N.

    2016-12-01

    This paper addresses inhomogeneities in the short-period S-wave attenuation field in the lithosphere beneath Altai. A technique based on the analysis of the amplitude ratios of Sn and Pn waves is used. High S-wave attenuation areas are identified in the West Altai, which are related to the source zones of recent large earthquakes, viz., the 1990 Zaisan earthquake and the 2003 Chuya earthquake. Associated with the Chuya earthquake, a large ringlike seismogenic structure had been formed since 1976. It is also found that ringlike seismogenic structures are confined to high S-wave attenuation areas unrelated to large historical earthquakes. It is supposed that processes paving the way for strong earthquakes are taking place in these areas. The magnitudes of probable earthquakes are estimated using the earlier derived correlation dependences of the sizes of ringlike seismogenic structures and the threshold values of magnitudes on the energy of principal earthquakes with prevailing focal mechanisms taken into consideration. The sources of some earthquakes are likely to occur near to the planned gas pipeline route from Western Siberia to China, which should be taken into account. The relationship of anomalies in the S-wave attenuation field and the ringlike seismogenic structures to a high content of deep-seated fluids in the lithosphere is discussed.

  13. Attenuation of stress waves in single and multi-layered structures. [mitigation of elastic and plastic stress waves during spacecraft landing

    NASA Technical Reports Server (NTRS)

    Yang, J. C. S.; Tsui, C. Y.

    1972-01-01

    Analytical and experimental studies were made of the attenuation of the stress waves during passage through single and multilayer structures. The investigation included studies on elastic and plastic stress wave propagation in the composites and those on shock mitigating material characteristics such as dynamic stress-strain relations and energy absorbing properties. The results of the studies are applied to methods for reducing the stresses imposed on a spacecraft during planetary or ocean landings.

  14. Differential shear-wave attenuation (δt*) across the East Pacific Rise

    NASA Astrophysics Data System (ADS)

    Schlue, J. W.

    SS phases from earthquakes on fracture zones near the Easter Island Cordillera and the West Chile Rise which are recorded in the United States have reflection points on either side of the East Pacific Rise (EPR) near the equator. The east-west records from seven WWSSN stations of seven events in this region were used to obtain spectral amplitudes of horizontally polarized S and SS waves. SS-to-S amplitude ratios were formed, and differential attenuation (δt*) computed within the frequency band 0.01 to 0.11 Hz. The values of δt* vary between -0.1 sec and +35.8 sec for the 23 station-event pairs used. However, the change in δt* with distance from the axis of the EPR does not reflect the smooth variation expected using a model of a simple cooling slab.

  15. Stability of coda wave attenuation during the Loma Prieta, California, earthquake sequence

    NASA Astrophysics Data System (ADS)

    Beroza, Gregory C.; Cole, Alex T.; Ellsworth, William L.

    1995-03-01

    The Loma Prieta, California, earthquake occurred in a densely instrumented region with a history of microearthquake recording beginning more than a decade before the October 1989 mainshock. This affords an unprecedented opportunity to detect changes in seismic wave propagation in the Earth's crust associated with a major earthquake. In this study we use pairs of nearly identical earthquakes (doublets) to search for temporal changes of coda attenuation in the vicinity of the Loma Prieta earthquake. We analyze 21 earthquake doublets recorded from 1978 to 1991 that span the preseismic, coseismic, and postseismic intervals and measure the change in coda Q using a running window ratio of the doublet spectral amplitudes in three frequency bands from 2 to 15 Hz. This method provides an estimate of changes in coda Q that is insensitive to other factors that influence coda amplitudes.

  16. Differential shear-wave attenuation (deltat) across the East Pacific Rise

    SciTech Connect

    Schlue, J.W.

    1981-08-01

    SS phases from earthquakes on fracture zones near the Easter Island Cordillera and the West Chile Rise which are recorded in the United States have reflection points on either side of the East Pacific Rise (EPR) near the equator. The east-west records from seven WWSSN stations of seven events in this region were used to obtain spectral amplitudes of horizontally polarized S and SS waves. SS-to-S amplitude ratios were formed, and differential attenuation (deltat) computed within the frequency band 0.01 to 0.11 Hz. The values of deltat vary between -0.1 sec and +35.8 sec for the 23 station-event paris used. However, the change in deltat with distance from the axis of the EPR does not reflect the smooth variation expected using a model of a simple cooling slab.

  17. Experimental Measurements Of Seismic Wave Speeds And Attenuation In CO2 Saturated Porous Rocks

    NASA Astrophysics Data System (ADS)

    Njiekak, G.; Yam, H.; Kofman, R. S.; Chowdhury, M.; Schmitt, D. R.

    2011-12-01

    Due to the sensitivity of seismic waves to pore fluid contents, time lapse seismology is regarded as a promising monitoring method for geological CO2 sequestration projects and is employed in all industrial scale projects (Sleipner, Weyburn, In Salah). Therefore, understanding the effect of CO2 as a pore fluid on the overall rock seismic response is critical, and it is particularly interesting as CO2 can be in gas, liquid, or supercritical phases even at the relatively modest pore pressures and temperatures in the uppermost kilometer of the earth's crust. To address this issue, ultrasonic P- and S-wave pulse transmission experiments were carried out on fully CO2 saturated samples of a synthetic porous ceramic, Berea and Fontainebleau sandstones, and carbonates under a variety of temperatures and pressures representative of conditions expected in volcanic edifices and geological sequestration projects. The synthetic sample was chosen because of its lack of microcracks, which can complicate the acoustic behavior of real rocks. Although this sample is extremely porous (58%) and is not reflective of real reservoir rocks, its large porosity allows the overall rock behavior to be more susceptible to the changes in the physical properties of the pore fluid; this could provide an extreme end member understanding on the rock physics involved with CO2 as the pore fluid. Laboratory results show waveform variations (velocity, amplitude, attenuation) in response to CO2's varying phase state. For the ceramic rod, CO2 phase changes (gas to liquid and gas to supercritical fluid) are marked by a drop in velocities of 4-5% likely due to the increased density of the liquid or the supercritical fluid relative to the gas. Wave attenuation increases with pore pressure and with frequency. The measured elastic wave velocities showed good agreement with Biot's model in this highly porous sample. The real sandstones, in contrast, display more complicated behaviour at the point of the phase

  18. The Attenuation of a Detonation Wave by an Aircraft Engine Axial Turbine Stage

    NASA Technical Reports Server (NTRS)

    VanZante, Dale; Envia, Edmane; Turner, Mark G.

    2007-01-01

    A Constant Volume Combustion Cycle Engine concept consisting of a Pulse Detonation Combustor (PDC) followed by a conventional axial turbine was simulated numerically to determine the attenuation and reflection of a notional PDC pulse by the turbine. The multi-stage, time-accurate, turbomachinery solver TURBO was used to perform the calculation. The solution domain consisted of one notional detonation tube coupled to 5 vane passages and 8 rotor passages representing 1/8th of the annulus. The detonation tube was implemented as an initial value problem with the thermodynamic state of the tube contents, when the detonation wave is about to exit, provided by a 1D code. Pressure time history data from the numerical simulation was compared to experimental data from a similar configuration to verify that the simulation is giving reasonable results. Analysis of the pressure data showed a spectrally averaged attenuation of about 15 dB across the turbine stage. An evaluation of turbine performance is also presented.

  19. Controls of Seismic Attenuation System (SAS) for the LIGO II Gravitational Wave Detector

    NASA Astrophysics Data System (ADS)

    Sannibale, Virginio; Bertolini, Alessandro; Cella, Giancarlo; Kovalik, Joseph; Tariq, Hareem; Desalvo, Riccardo; Takamori, Akiteru; Marka, Szabolcz; Viboud, Nicolas

    2000-04-01

    The Seismic Attenuation System (SAS) has to be actively controlled over a frequency band of up to several Hz in order to damp its own rigid body modes (inertial damping), to generate DC local and global positioning, and to reduce residual rms motion to acquire the locking of the interferometer. The control system incorporates signals from local sensors (for displacement and acceleration) and the interferometer and generates adequate feedback signals for various actuators on different levels of the SAS chain. The control system is organized in a hierarchical scheme. With a large dynamic range at higher stages of the SAS, it damps internal modes of the system which minimizes requirements for the suspension control. The control system is a Multiple Input and Multiple Output (MIMO) that can be separated to simple Single Input and Single Output (SISO) feedback loops by using fast DSP boards. SAS controls are limited to a frequency band well below 10 Hz, to avoid noise injection in the gravitational wave band. Above this frequency, the SAS behaves as a completely passive seismic attenuator. According to simulated SAS performance based on measured seismic noise, achievable residual r.m.s. motion of SAS is a few tens of nm above 100 mHz. A similar system for VIRGO has already achieved 50 nm r.m.s. displacement.

  20. Regional wave attenuation and seismic moment from the inversion of NORESS spectra

    NASA Astrophysics Data System (ADS)

    Sereno, Thomas J., Jr.; Bratt, Steven R.; Bache, Thomas C.

    1987-07-01

    Frequency-dependent regional wave attenuation along continental paths to the NORESS array in Norway is investigated. Regional Lg and Pn spectra from 190 events, at distances between 200 and 1300 km, have been inverted for seismic moment and apparent attenuation. Our method uses both the spectral and spatial decay of observed signal amplitudes to separate source and path contributions. Based on adequate signal/noise, the Lg spectra were inverted between 1 and 7 Hz and the Pn spectra between 1 and 15 Hz. The data are parameterized by an omega - sq source spectrum with cube-root corner frequency scaling and an assumed geometric spreading function. Most events considered have local magnitudes less than 3.0, so the corner frequencies are near or beyond the upper limit of the bandwidth inverted. The spectra are inverted for source moment, a constant relating corner frequency and moment, and two parameters describing a power-law frequency dependence of Q. For fixed source and spreading assumptions, the inversion defines clear trade-offs among model parameters. To resolve these trade-offs, constraints are added to the separately derived source parameters Lg and Pn that they be consistent. The inversion results for seismic moment as a function of local magnitude are generally consistent with near-field studies.

  1. The Influence of Water on Seismic Wave Attenuation in the Upper Mantle

    NASA Astrophysics Data System (ADS)

    David, E. C.; Jackson, I.; Faul, U.; Berry, A.

    2014-12-01

    Trace amounts of water, present as protons structurally bound in olivine crystal defects, are inferred to significantly enhance the low-strain solid-state viscoelastic relaxation responsible for attenuation and dispersion of seismic waves in the upper mantle. This inferrence is supported by recent observation of water weakening at moderate compressive strains in synthetic, water-undersaturated aggregates (Faul et al., in preparation). In these fine-grained olivine polycrystals of Fo90 composition, doped with 0.02wt% TiO2, "water" is incorporated in the remarkably stable Ti-clinohumite defect. Such synthetic olivine specimens reproduce the infrared spectra of natural mantle olivines (Berry et al., 2005), and present the advantage of being melt-free and of low dislocation density. The water contents in such synthetic polycrystalline olivine aggregates, which can be quantitatively measured by Fourier Transform Infrared Spectroscopy (FTIR), range up to 90 ppm, and are thus representative of water-undersaturated conditions in the upper mantle. We will report here the outcome of torsional-oscillation tests,in which attenuation and shear modulus were measured at seismic frequencies (mHz-Hz) and various temperatures up to 1300C on Pt-encapsulated, Ti-doped olivine specimens, enclosed within a mild-steel jacket.

  2. Q c and Q S wave attenuation of South African earthquakes

    NASA Astrophysics Data System (ADS)

    Brandt, Martin B. C.

    2016-04-01

    Quality factor Q, which describes the attenuation of seismic waves with distance, was determined for South Africa using data recorded by the South African National Seismograph Network. Because of an objective paucity of seismicity in South Africa and modernisation of the seismograph network only in 2007, I carried out a coda wave decay analysis on only 13 tectonic earthquakes and 7 mine-related events for the magnitude range 3.6 ≤ M L ≤ 4.4. Up to five seismograph stations were utilised to determine Q c for frequencies at 2, 4, 8 and 16 Hz resulting in 84 individual measurements. The constants Q 0 and α were determined for the attenuation relation Q c( f) = Q 0 f α . The result was Q 0 = 396 ± 29 and α = 0.72 ± 0.04 for a lapse time of 1.9*( t s - t 0) (time from origin time t 0 to the start of coda analysis window is 1.9 times the S-travel time, t s) and a coda window length of 80 s. This lapse time and coda window length were found to fit the most individual frequencies for a signal-to-noise ratio of at least 3 and a minimum absolute correlation coefficient for the envelope of 0.5. For a positive correlation coefficient, the envelope amplitude increases with time and Q c was not calculated. The derived Q c was verified using the spectral ratio method on a smaller data set consisting of nine earthquakes and one mine-related event recorded by up to four seismograph stations. Since the spectral ratio method requires absolute amplitudes in its calculations, site response tests were performed to select four appropriate stations without soil amplification and/or signal distortion. The result obtained for Q S was Q 0 = 391 ± 130 and α = 0.60 ± 0.16, which agrees well with the coda Q c result.

  3. Numerical and Experimental Investigation on the Attenuation of Electromagnetic Waves in Unmagnetized Plasmas Using Inductively Coupled Plasma Actuator

    NASA Astrophysics Data System (ADS)

    Lin, Min; Xu, Haojun; Wei, Xiaolong; Liang, Hua; Song, Huimin; Sun, Quan; Zhang, Yanhua

    2015-10-01

    The attenuation of electromagnetic (EM) waves in unmagnetized plasma generated by an inductively coupled plasma (ICP) actuator has been investigated both theoretically and experimentally. A numerical study is conducted to investigate the propagation of EM waves in multilayer plasma structures which cover a square flat plate. Experimentally, an ICP actuator with dimensions of 20 cm×20 cm×4 cm is designed to produce a steady plasma slab. The attenuation of EM waves in the plasma generated by the ICP actuator is measured by a reflectivity arch test method at incident waves of 2.3 GHz and 10.1 GHz, respectively. A contrastive analysis of calculated and measured results of these incident wave frequencies is presented, which suggests that the experiment accords well with our theory. As expected, the plasma slab generated by the ICP actuator can effectively attenuate the EM waves, which may have great potential application prospects in aircraft stealth. supported by National Natural Science Foundation of China (Nos. 51276197, 11472306 and 11402301)

  4. A Simultaneous Multi-phase Approach to Determine P-wave and S-wave Attenuation of the Crust and Upper Mantle

    SciTech Connect

    Pasyanos, M E; Walter, W R; Matzel, E M

    2009-02-26

    We have generalized the methodology of our regional amplitude tomography from the Lg phase to the four primary regional phases (Pn, Pg, Sn, Lg). Differences in the geometrical spreading, source term, site term, and travel paths are accounted for, while event source parameters such as seismic moment are consistent among phases. In the process, we have developed the first regional attenuation model that uses the amplitudes of four regional phases to determine a comprehensive P-wave and S-wave attenuation model of the crust and upper mantle. When applied to an area encompassing the Middle East, eastern Europe, western Asia, south Asia, and northeast Africa for the 1-2 Hz passband, we find large differences in the attenuation of the lithosphere across the region. The tectonic Tethys collision zone has high attenuation, while stable outlying regions have low attenuation. While crust and mantle Q variations are often consistent, we do find several notable areas where they differ considerably, but are appropriate given the region's tectonic history. Lastly, the relative values of Qp and Qs indicate that scattering Q is likely the dominant source of attenuation in the crust at these frequencies.

  5. Measurement of intrinsic and scattering attenuation of shear waves in two sedimentary basins and comparison to crystalline sites in Germany

    NASA Astrophysics Data System (ADS)

    Eulenfeld, Tom; Wegler, Ulrich

    2016-05-01

    We developed an improved method for the separation of intrinsic and scattering attenuation of seismic shear waves by envelope inversion called Qopen. The method optimizes the fit between Green's functions for the acoustic, isotropic radiative transfer theory and observed energy densities of earthquakes. The inversion allows the determination of scattering and intrinsic attenuation, site corrections and spectral source energies for the investigated frequency bands. Source displacement spectrum and the seismic moment of the analysed events can be estimated from the obtained spectral source energies. We report intrinsic and scattering attenuation coefficients of shear waves near three geothermal reservoirs in Germany for frequencies between 1 and 70 Hz. The geothermal reservoirs are located in Insheim, Landau (both Upper Rhine Graben) and Unterhaching (Molasse basin). We compare these three sedimentary sites to two sites located in crystalline rock with respect to scattering and intrinsic attenuation. The inverse quality factor for intrinsic attenuation is constant in sediments for frequencies smaller than 10 Hz and decreasing for higher frequencies. For crystalline rock, it is on a lower level and strictly monotonic decreasing with frequency. Intrinsic attenuation dominates scattering except for the Upper Rhine Graben, where scattering is dominant for frequencies below 10 Hz. Observed source displacement spectra show a high-frequency fall-off greater than or equal to 3.

  6. Shear wave velocity, seismic attenuation, and thermal structure of the continental upper mantle

    USGS Publications Warehouse

    Artemieva, I.M.; Billien, M.; Leveque, J.-J.; Mooney, W.D.

    2004-01-01

    Seismic velocity and attenuation anomalies in the mantle are commonly interpreted in terms of temperature variations on the basis of laboratory studies of elastic and anelastic properties of rocks. In order to evaluate the relative contributions of thermal and non-thermal effects on anomalies of attenuation of seismic shear waves, QS-1, and seismic velocity, VS, we compare global maps of the thermal structure of the continental upper mantle with global QS-1 and Vs maps as determined from Rayleigh waves at periods between 40 and 150 S. We limit the comparison to three continental mantle depths (50, 100 and 150 km), where model resolution is relatively high. The available data set does not indicate that, at a global scale, seismic anomalies in the upper mantle are controlled solely by temperature variations. Continental maps have correlation coefficients of <0.56 between VS and T and of <0.47 between QS and T at any depth. Such low correlation coefficients can partially be attributed to modelling arrefacts; however, they also suggest that not all of the VS and QS anomalies in the continental upper mantle can be explained by T variations. Global maps show that, by the sign of the anomaly, VS and QS usually inversely correlate with lithospheric temperatures: most cratonic regions show high VS and QS and low T, while most active regions have seismic and thermal anomalies of the opposite sign. The strongest inverse correlation is found at a depth of 100 km, where the attenuation model is best resolved. Significantly, at this depth, the contours of near-zero QS anomalies approximately correspond to the 1000 ??C isotherm, in agreement with laboratory measurements that show a pronounced increase in seismic attenuation in upper mantle rocks at 1000-1100 ??C. East-west profiles of VS, QS and T where continental data coverage is best (50??N latitude for North America and 60??N latitude for Eurasia) further demonstrate that temperature plays a dominant, but non-unique, role in

  7. Intrinsic and scattering attenuation of high-frequency S-waves in the central part of the External Dinarides

    NASA Astrophysics Data System (ADS)

    Majstorović, Josipa; Belinić, Tena; Namjesnik, Dalija; Dasović, Iva; Herak, Davorka; Herak, Marijan

    2017-09-01

    The central part of the External Dinarides (CED) is a geologically and tectonically complex region formed in the collision between the Adriatic microplate and the European plate. In this study, the contributions of intrinsic and scattering attenuation ( Q i - 1 and Q sc - 1 , respectively) to the total S-wave attenuation were calculated for the first time. The multiple lapse-time window analysis (MLTWA method), based on the assumptions of multiple isotropic scattering in a homogeneous medium with uniformly distributed scatterers, was applied to seismograms of 450 earthquakes recorded at six seismic stations. Selected events have hypocentral distances between 40 and 90 km with local magnitudes between 1.5 and 4.7. The analysis was performed over 11 frequency bands with central frequencies between 1.5 and 16 Hz. Results show that the seismic albedo of the studied area is less than 0.5 and Q i - 1 > Q sc - 1 at all central frequencies and for all stations. These imply that the intrinsic attenuation dominates over scattering attenuation in the whole study area. Calculated total S-wave and expected coda wave attenuation for CED are in a very good agreement with the ones measured in previous studies using the coda normalization and the coda-Q methods. All estimated attenuation factors decrease with increasing frequency. The intrinsic attenuation for CED is among the highest observed elsewhere, which could be due to the highly fractured and fluid-filled carbonates in the upper crust. The scattering and the total S-wave attenuation for CED are close to the average values obtained in other studies performed worldwide. In particular, good agreement of frequency dependence of total attenuation in CED and in the regions that contributed most strong-motion records for ground motion prediction equations used in PSHA in Croatia indicates that those were well chosen and applicable to this area as far as their attenuation

  8. Attenuation of standing waves in a large water tank using arrays of large tethered encapsulated bubbles.

    PubMed

    Lee, Kevin M; Wilson, Preston S; Wochner, Mark S

    2014-04-01

    The use of bubble resonance effects to attenuate low-frequency underwater sound was investigated experimentally in a large water tank. A compact electromechanical sound source was used to excite standing wave fields at frequencies ranging between 50 and 200 Hz in the tank. The source was then surrounded by a stationary array of tethered encapsulated air bubbles, and reduction in standing wave amplitude by as much as 26 dB was observed. The bubbles consisted of either thin-shelled latex balloons with approximately 5 cm radii or thicker-shelled vinyl boat fenders with 6.9 cm radii. The effects of changing the material and thickness of the bubble shells were found to be in qualitative agreement with predictions from Church's model for sound propagation in a liquid containing encapsulated bubbles [J. Acoust. Soc. Am. 97, 1510-1521 (1995)]. Although demonstrated here for low frequency noise abatement within a tank, which is useful for quieting acoustic test facilities and large tanks used for marine life husbandry, the eventual aim of this work is to use stationary arrays of large tethered encapsulated bubbles to abate low frequency underwater noise from anthropogenic sources in the marine environment.

  9. Diffraction, attenuation, and source corrections for nonlinear Rayleigh wave ultrasonic measurements.

    PubMed

    Torello, David; Thiele, Sebastian; Matlack, Kathryn H; Kim, Jin-Yeon; Qu, Jianmin; Jacobs, Laurence J

    2015-02-01

    This research considers the effects of diffraction, attenuation, and the nonlinearity of generating sources on measurements of nonlinear ultrasonic Rayleigh wave propagation. A new theoretical framework for correcting measurements made with air-coupled and contact piezoelectric receivers for the aforementioned effects is provided based on analytical models and experimental considerations. A method for extracting the nonlinearity parameter β11 is proposed based on a nonlinear least squares curve-fitting algorithm that is tailored for Rayleigh wave measurements. Quantitative experiments are conducted to confirm the predictions for the nonlinearity of the piezoelectric source and to demonstrate the effectiveness of the curve-fitting procedure. These experiments are conducted on aluminum 2024 and 7075 specimens and a β11(7075)/β11(2024) measure of 1.363 agrees well with previous literature and earlier work. The proposed work is also applied to a set of 2205 duplex stainless steel specimens that underwent various degrees of heat-treatment over 24h, and the results improve upon conclusions drawn from previous analysis.

  10. Viscoacoustic wave form inversion of transmission data for velocity and attenuation

    NASA Astrophysics Data System (ADS)

    Watanabe, Toshiki; Nihei, Kurt T.; Nakagawa, Seiji; Myer, Larry R.

    2004-06-01

    This study investigates the performance of a frequency domain viscoacoustic full wave form nonlinear inversion to obtain high resolution images of velocity and attenuation. An efficient frequency domain implementation is applied that consists of performing a series of single frequency inversions sweeping from low to high frequency. A cascaded inversion was adopted in which the real part of the velocity is first imaged using the phase information, then the quality factor (Q) is imaged using the amplitude information. Tests with synthetic data indicate that our approach yielded better images than the simultaneous determination of the real and imaginary parts of the complex velocity. The method is applied to laboratory data obtained in a water tank with suspended acrylic bars. Broadband 200 kHz data are obtained for a crosshole configuration with a computer-controlled scanning system and piezofilm source and detector. The velocity image produced by the full wave form inversion is compared to a curved ray travel time tomography velocity image, and was observed to possess higher resolution and more precise locations of the acrylic bars. The Q image shows a lower resolution than the velocity image, but recovers the correct Q for acrylic. This method can be applied for geophysical applications targeted to soil, unconsolidated rocks, and marine sediments and also nondestructive evaluation and medical applications.

  11. Some Remarks on the Microscopic Physics of Seismic Wave Attenuation and Tidal Dissipation (Invited)

    NASA Astrophysics Data System (ADS)

    Karato, S.

    2009-12-01

    There are a number of questions on the Q of planetary bodies. They include: (1) Seismic Q of Earth’s interior varies from one region to another. What is the cause for lateral and depth variation of seismic Q? Is it due to the variation in temperature, grain-size, partial melting and/or water content? (2) What is the relationship between seismic Q and long-term rheology? (3) The Moon’s seismic Q is large (>1000) at least for waves passing the shallow part. However, the tidal Q reflecting energy dissipation in the deep part of the Moon is small (~50). If the Moon is a “dry” body, why is tidal Q of the Moon so small? (4) Exo-solar planets are usually found close to their parent stars. But these planets likely have undergone orbital evolution that is controlled by tidal energy dissipation. What controls the magnitude of tidal dissipation in these planets? I will provide a brief review to address some of these questions with a focus on the microscopic physics of anelastic energy dissipation. The most important message from recent lab studies is that solid materials show large energy dissipation (Q of ~100 or less) at modestly high temperatures (T/Tm>0.5, Tm: melting temperature). This implies that the majority of seismic wave attenuation is likely attributed to solid-state processes and energy loss in many of the exo-solar planets might be due to small rocky cores. Some details of solid-state mechanisms of energy dissipation in solids will be reviewed including the influence of frequency, temperature, grain-size, strain amplitude and some impurities such as hydrogen. A common observation among many solids so far studied at high T/Tm is power-law frequency dependence of Q with a modest frequency exponent (~0.3+/-0.1) with a gradual change to the Maxwell body (viscous) behavior at lower frequencies. The transition frequency to the Maxwell body behavior is also dependent on strain amplitude, causing larger energy dissipation at higher strain amplitudes. These

  12. 2-D Coda and Direct Wave Attenuation Tomography in Northern Italy

    SciTech Connect

    Morasca, P; Mayeda, K; Gok, R; Phillips, W S; Malagnini, L

    2007-10-17

    A 1-D coda method was proposed by Mayeda et al. (2003) in order to obtain stable seismic source moment-rate spectra using narrowband coda envelope measurements. That study took advantage of the averaging nature of coda waves to derive stable amplitude measurements taking into account all propagation, site, and Sto-coda transfer function effects. Recently this methodology was applied to micro earthquake data sets from three sub-regions of northern Italy (i.e., western Alps, northern Apennines and eastern Alps). Since the study regions were small, ranging between local-to-near-regional distances, the simple 1-D path assumptions used in the coda method worked very well. The lateral complexity of this region would suggest, however, that a 2-D path correction might provide even better results if the datasets were combined, especially when paths traverse larger distances and complicated regions. The structural heterogeneity of northern Italy makes the region ideal to test the extent to which coda variance can be reduced further by using a 2-D Q tomography technique. The approach we use has been developed by Phillips et al. (2005) and is an extension of previous amplitude ratio techniques to remove source effects from the inversion. The method requires some assumptions such as isotropic source radiation which is generally true for coda waves. Our results are compared against direct Swave inversions for 1/Q and results from both share very similar attenuation features that coincide with known geologic structures. We compare our results with those derived from direct waves as well as some recent results from northern California obtained by Mayeda et al. (2005) which tested the same tomographic methodology applied in this study to invert for 1/Q. We find that 2-D coda path corrections for this region significantly improve upon the 1-D corrections, in contrast to California where only a marginal improvement was observed. We attribute this difference to stronger lateral

  13. Analysis of the Attenuation Characteristics of an Elastic Wave Due to the Wave-Induced Fluid Flow in Fractured Porous Media

    NASA Astrophysics Data System (ADS)

    Wang, Ding; Wang, Li-Ji; Zhang, Mei-Gen

    2014-04-01

    A theoretical model is presented to describe the elastic wave propagation characteristics in porous media of periodically arranged fractures. The effects of fracture geometric parameters on a compressional wave (p-wave) are considered through analysis of the wave induced fluid flow (WIFF) process between the fractures and the background media. The diffusion equation in porous media is used to reveal how the entire diffusion process affects the wave propagation. When the thickness proportion of fractures tends to 0 and 1, the WIFF does not take place almost between fractures and background matrix porosity, and therefore the media elasticity modulus is perfectly elastic. When the fracture thickness fraction achieves a certain value, the peak of the attenuation curve reaches the maximum value at a particular frequency, which is controlled by the fluid mass conservation and stress continuity conditions on each fracture boundary. That is, the inter-coupling of fluid diffusion between the adjacent layers is important for waves attenuation. Physically speaking, the dissipation of a wave is associated with the fluid flux essentially.

  14. CodaNorm: A software package for the body-wave attenuation calculation by the coda-normalization method

    NASA Astrophysics Data System (ADS)

    Predein, Peter A.; Dobrynina, Anna A.; Tubanov, Tsyren A.; German, Eugeny I.

    The presented software package CodaNorm is an open source seismological software and allows the estimation of the seismic quality factor (QP, QS), its frequency dependence (n) and attenuation decrement (γ) for body P- and S-waves by the coda-normalization method for different frequency ranges selected by a user. Obtained data about the seismic wave attenuation are necessary to correct the decay shake model from the earthquakes on the traces from the seismically active zones in the main urban areas, as well as for the further calculation of synthetic accelerograms and the evaluation of the parameters of the vibration for the possible strong earthquakes and etc. The software package CodaNorm was applied for the estimation of the attenuation of the body P- and S-waves in the area of the South and Central Baikal (Baikal rift system, Southern Siberia, Russia) using 185 regional earthquakes with magnitude Ml =2-5. The calculations were carried out for eight traces crossing the rift system in different directions and for the frequency range from 0.5 to 16 Hz. In the low frequency area the coincidence of the values of the seismic quality factor for P- and S-waves (QP and QS, respectively) is observed while for the high frequencies (8-16 Hz) the ratio between quality factors is QS ≈ 1.7QP. Such difference is the evidence of different absorption of longitudinal and transverse waves by geological medium. The comparison of the attenuation parameters for different azimuthal traces showed that higher attenuation is observed for the traces crossing the rift system in normal direction to the main tectonic structures. This fact may reflects the differences between the local elastic properties of the crust of the Baikal rift system and the high heterogeneity of the medium.

  15. Modeling of the attenuation of stress waves in concrete based on the Rayleigh damping model using time-reversal and PZT transducers

    NASA Astrophysics Data System (ADS)

    Tian, Zhen; Huo, Linsheng; Gao, Weihang; Li, Hongnan; Song, Gangbing

    2017-10-01

    Wave-based concrete structural health monitoring has attracted much attention. A stress wave experiences significant attenuation in concrete, however there is a lack of a unified method for predicting the attenuation coefficient of the stress wave. In this paper, a simple and effective absorption attenuation model of stress waves in concrete is developed based on the Rayleigh damping model, which indicates that the absorption attenuation coefficient of stress waves in concrete is directly proportional to the square of the stress wave frequency when the damping ratio is small. In order to verify the theoretical model, related experiments were carried out. During the experiments, a concrete beam was designed in which the d33-model piezoelectric smart aggregates were embedded to detect the propagation of stress waves. It is difficult to distinguish direct stress waves due to the complex propagation paths and the reflection and scattering of stress waves in concrete. Hence, as another innovation of this paper, a new method for computing the absorption attenuation coefficient based on the time-reversal method is developed. Due to the self-adaptive focusing properties of the time-reversal method, the time-reversed stress wave focuses and generates a peak value. The time-reversal method eliminates the adverse effects of multipaths, reflection, and scattering. The absorption attenuation coefficient is computed by analyzing the peak value changes of the time-reversal focused signal. Finally, the experimental results are found to be in good agreement with the theoretical model.

  16. Numerical and experimental study on the wave attenuation in bone--FDTD simulation of ultrasound propagation in cancellous bone.

    PubMed

    Nagatani, Yoshiki; Mizuno, Katsunori; Saeki, Takashi; Matsukawa, Mami; Sakaguchi, Takefumi; Hosoi, Hiroshi

    2008-11-01

    In cancellous bone, longitudinal waves often separate into fast and slow waves depending on the alignment of bone trabeculae in the propagation path. This interesting phenomenon becomes an effective tool for the diagnosis of osteoporosis because wave propagation behavior depends on the bone structure. Since the fast wave mainly propagates in trabeculae, this wave is considered to reflect the structure of trabeculae. For a new diagnosis method using the information of this fast wave, therefore, it is necessary to understand the generation mechanism and propagation behavior precisely. In this study, the generation process of fast wave was examined by numerical simulations using elastic finite-difference time-domain (FDTD) method and experimental measurements. As simulation models, three-dimensional X-ray computer tomography (CT) data of actual bone samples were used. Simulation and experimental results showed that the attenuation of fast wave was always higher in the early state of propagation, and they gradually decreased as the wave propagated in bone. This phenomenon is supposed to come from the complicated propagating paths of fast waves in cancellous bone.

  17. Teleseismic P wave spectra from USArray and implications for upper mantle attenuation and scattering

    NASA Astrophysics Data System (ADS)

    Cafferky, Samantha; Schmandt, Brandon

    2015-10-01

    Teleseismic P wave amplitude spectra from deep earthquakes recorded by USArray are inverted for maps of upper mantle Δt* for multiple frequency bands within 0.08-2 Hz. All frequency bands show high Δt* regions in the southwestern U.S., southern Rocky Mountains, and Appalachian margin. Low Δt* is more common across the cratonic interior. Inversions with narrower frequency bands yield similar patterns, but greater Δt* magnitudes. Even the two standard deviation Δt* magnitude for the widest band is ˜2-7 times greater than predicted by global QS tomography or an anelastic olivine thermal model, suggesting that much of the Δt* signal is nonthermal in origin. Nonthermal contributions are further indicated by only a moderate correlation between Δt* and P travel times. Some geographic variations, such as high Δt* in parts of the cratonic interior with high mantle velocities and low heat flow, demonstrate that the influence of temperature is regionally overwhelmed. Transverse spectra are used to investigate the importance of scattering because they would receive no P energy in the absence of 3-D heterogeneity or anisotropy. Transverse to vertical (T/Z) spectral ratios for stations with high Δt* are higher and exhibit steeper increases with frequency compared to T/Z spectra for low Δt* stations. The large magnitude of Δt* estimates and the T/Z spectra are consistent with major contributions to Δt* from scattering. A weak positive correlation between intrinsic attenuation and apparent attenuation due to scattering may contribute to Δt* magnitude and the moderate correlation of Δt* with travel times.

  18. Vibration and wave propagation attenuation for metamaterials by periodic piezoelectric arrays with high-order resonant circuit shunts

    NASA Astrophysics Data System (ADS)

    Zhou, Wanlu; Wu, You; Zuo, Lei

    2015-06-01

    Beam or plate metamaterials with periodic piezoelectric arrays have attracted more and more attention in recent years for wave propagation attenuation and the corresponding vibration reduction. Conventional designs use resistive shunt (R-shunt) and resistor-inductor shunt (RL-shunt). An innovative metamaterial with a high-order resonant shunt circuit is proposed and investigated for vibration and wave propagation attenuation in this paper. The proposed high-order resonant shunt circuit can introduce two local resonances in series around the tuning frequency to broaden the attenuation bandwidth, or can create two separate resonances to achieve two separate bandgaps. Finite element modeling of the beam metamaterial with wave propagation and vibration in the transverse direction is established. Simulations have been conducted to compare the vibration attenuation performances among R-shunt, RL-shunt, and the proposed high-order shunt. An impedance-based method has been presented for the parameter design of electrical components in the proposed high-order shunt for bandgaps at two desired frequencies.

  19. The Velocity and Attenuation of Acoustic Emission Waves in SiC/SiC Composites Loaded in Tension

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.; Gyekenyesi, Andrew L.; Gray, Hugh R. (Technical Monitor)

    2002-01-01

    The behavior of acoustic waves produced by microfracture events and from pencil lead breaks was studied for two different silicon carbide fiber-reinforced silicon carbide matrix composites. The two composite systems both consisted of Hi-Nicalon (trademark) fibers and carbon interfaces but had different matrix compositions that led to considerable differences in damage accumulation and acoustic response. This behavior was primarily due to an order of magnitude difference in the interfacial shear stress for the two composite systems. Load/unload/reload tensile tests were performed and measurements were made over the entire stress range in order to determine the stress-dependence of acoustic activity for increasing damage states. It was found that using the extensional wave velocities from acoustic emission (AE) events produced from pencil lead breaks performed outside of the transducers enabled accurate measurements of the stiffness of the composite. The extensional wave velocities changed as a function of the damage state and the stress where the measurement was taken. Attenuation for AE waveforms from the pencil lead breaks occurred only for the composite possessing the lower interfacial shear stress and only at significantly high stresses. At zero stress after unloading from a peak stress, no attenuation occurred for this composite because of crack closure. For the high interfacial stress composite no attenuation was discernable at peak or zero stress over the entire stress-range of the composite. From these observations, it is believed that attenuation of AE waveforms is dependent on the magnitude of matrix crack opening.

  20. Three-dimensional P- and S-wave attenuation structures around the source region of the 2016 Kumamoto earthquakes

    NASA Astrophysics Data System (ADS)

    Komatsu, Masanao; Takenaka, Hiroshi; Oda, Hitoshi

    2017-07-01

    We investigate the three-dimensional P- and S-wave attenuation (QP^{ - 1} and QS^{ - 1} ) structures of the crust around the source region of the 2016 Kumamoto earthquakes, Japan. To estimate the attenuation structures, the path-averaged attenuation factor t^{*} is estimated from the amplitude decay rate of the P- and S-wave spectra corrected for the source spectrum. The QP^{ - 1} and QS^{ - 1} structures are estimated by tomography using t^{*} for the P- and S-waves, respectively. Several features are found in the attenuation structures as follows: In the source region, two high-QP and high-QS zones exist along the Futagawa and the Hinagu fault segments in the upper crust. The high-QP and high-QS zone along the Futagawa fault segment is found to include the large-slip area of the mainshock obtained from a source inversion study. In the lower crust, the low QP is distributed beneath the entire source region. A low-QP and low-QS zone also exists beneath the Kuju and Aso volcanoes, which is consistent with the shallow limited depth extent of the seismogenic zone due to high temperature. The western edge of this zone adjoins the eastern edge of the high-QP and high-QS area, including the large-slip area.[Figure not available: see fulltext.

  1. Seismic Wave Amplification, Attenuation, and Scattering at the UZ-16 Borehole, Yucca Mountain, Nevada

    NASA Astrophysics Data System (ADS)

    Preston, L.; Smith, K.

    2006-12-01

    The UE#25 UZ-16 borehole array at Yucca Mountain, Nevada (designated site for the nation's high-level nuclear waste repository), provides a prime opportunity to investigate near surface effects on seismic waveforms as a function of depth. The borehole 3-component geophone array consists of 96 depth levels of 4.5 Hz sensors from about 30 m to 500 m depth below the surface. Currently we are recording at 18 approximately equally spaced depth levels and the array was recently augmented with three 3-component matching surface sensors (totaling 63 16-bit 200 sps data channels). The time stamped continuous digital data stream is telemetered in real-time to the Nevada Seismological Laboratory where it is visually inspected and event data is subset and integrated with regional network data when necessary; system check calibrations have been performed on all recorded sensors. Therefore, we have high resolution time-depth local and regional earthquake waveform histories from 500 m to the surface within the Yucca Mountain block. Due to the thick cover of Miocene volcanic tuffs at Yucca Mountain, the borehole does not penetrate into the underlying Paleozoic basement but samples tuff horizons of varying thicknesses and properties. Ground motion design criteria for the repository and surface facilities are based, in part, on characterizing the near surface velocities and the amplification, intrinsic attenuation, and scattering of seismic waves from local earthquakes. We present results from several investigations of local earthquake recordings including spectral ratios and attenuation as a function of depth and characterize scattering in the tuff layers. Preliminary results indicate differences in spectral ratios depending on component, with E-W components indicating higher ratios relative to N-S and Z components as compared to the bottom most geophone, most likely due to the structural fabric of Yucca Mountain. Also, most observed amplification from spectral ratios (from about 3

  2. Feasibility of using P- and S-wave Attenuation for Monitoring of Bacterial Clogging in Unconsolidated Sediments

    NASA Astrophysics Data System (ADS)

    Noh, D. H.

    2015-12-01

    Accumulation of bacterial biopolymers in porous media is known to decrease permeability by several orders of magnitude, referred to as bioclogging, thereby altering the hydraulic flow systems of porous media. Successful microbial bioclogging treatments require geophysical monitoring techniques to provide appropriate spatial and temporal information on bacterial growth and activities in the subsurface; such monitoring datasets can be used to evaluate the status of plugged reservoir sections and optimize re-treatment if the plug degrades. This study investigated the variations of P- and S-wave attenuation of porous media for monitoring in-situ accumulation of bacterial biopolymers in sediments. Column experiments, where Leuconostoc mesenterorides were stimulated to produce the insoluble polysaccharide biopolymer (referred to as dextran) in a sand pack, were performed while monitoring changes in permeability as well as P- and S-wave responses. P-wave responses at ultrasonic and sub-ultrasonic frequency ranges (i.e., hundreds of kHz and tens of kHz) and S-wave responses at several kHz were acquired using ultrasonic transducers and bender elements during accumulation of the biopolymer. The permeability of the sand pack was reduced by more than one order of magnitude while the insoluble biopolymer, dextran, produced by Leuconostoc mesenteroides occupied ~10% pore volume. The amplitude of the P-wave signals decreased at the both ultrasonic (hundreds of kHz) and sub-ultrasonic (tens of kHz) frequency ranges; and the spectral ratio calculations confirmed an increase in P-wave attenuation (1/QP) in the both frequency ranges. The amplitude of the S-wave signals significantly increased during the increase in S-wave velocity, possibly due to the increased shear stiffness of the medium. However, the spectral ratio calculation suggested an increase in S-wave attenuation (1/QS) in the several kHz band. The observed changes in permeability and P- and S-wave attenuation were

  3. Regional Body-Wave Attenuation Using a Coda Source Normalization Method: Application to MEDNET Records of Earthquakes in Italy

    SciTech Connect

    Walter, W R; Mayeda, K; Malagnini, L; Scognamiglio, L

    2007-02-01

    We develop a new methodology to determine apparent attenuation for the regional seismic phases Pn, Pg, Sn, and Lg using coda-derived source spectra. The local-to-regional coda methodology (Mayeda, 1993; Mayeda and Walter, 1996; Mayeda et al., 2003) is a very stable way to obtain source spectra from sparse networks using as few as one station, even if direct waves are clipped. We develop a two-step process to isolate the frequency-dependent Q. First, we correct the observed direct wave amplitudes for an assumed geometrical spreading. Next, an apparent Q, combining path and site attenuation, is determined from the difference between the spreading-corrected amplitude and the independently determined source spectra derived from the coda methodology. We apply the technique to 50 earthquakes with magnitudes greater than 4.0 in central Italy as recorded by MEDNET broadband stations around the Mediterranean at local-to-regional distances. This is an ideal test region due to its high attenuation, complex propagation, and availability of many moderate sized earthquakes. We find that a power law attenuation of the form Q(f) = Q{sub 0}f{sup Y} fit all the phases quite well over the 0.5 to 8 Hz band. At most stations, the measured apparent Q values are quite repeatable from event to event. Finding the attenuation function in this manner guarantees a close match between inferred source spectra from direct waves and coda techniques. This is important if coda and direct wave amplitudes are to produce consistent seismic results.

  4. Measurements of seismic wave attenuation for frequencies between 0.1 and 100 Hz in a Paterson Rig

    NASA Astrophysics Data System (ADS)

    Madonna, C.; Tisato, N.; Delle Piane, C.; Saenger, E. H.

    2012-04-01

    The study of wave attenuation in partially saturated porous rocks over a broad frequency range provides valuable information about reservoir fluid systems, which are inherently composed of multiple phase fluid. Following an original idea initiated by Luigi, we designed and set up a specific instrument, the Seismic Wave Attenuation Module (SWAM), to experimentally measure the bulk attenuation on partially saturated rocks at frequencies between 0.01 and 100 Hz, using natural rock samples under in situ conditions. We present its bench-top calibration, a series of data collected from different kind of rocks at different confing pressure and the numerical simulations, supporting the obtained results. We employ the sub-resonance test. Assuming that the rock behaves as a linear time invariant (LTI) system, the attenuation factor 1/Q (Q is the quality factor) is equal to the tangent of the phase shift between the stress and the strain signal. The new attenuation measurement equipment is calibrated in a gas apparatus (Paterson rig) using aluminum as elastic standard and Plexiglas as a viscoelastic standard. Measurements were performed on 25.4 mm diameter, 60 mm long samples. Berea sandstone samples with 20% porosity, and ~500 mD permeability have been measured at different saturation conditions. Attenuation measurements show dependence upon saturation. Moreover, measurements on two well-characterized shale samples have been performed. The two shales have significantly different quality factors; which result to be dependent on both the saturation state of the samples and the propagation direction of the oscillatory signal with respect to the sedimentary bedding. The attenuation coefficient parallel to bedding is less than that vertical to bedding. Thanks to Luigi's initiative and inspiration two generations of his Ph.D. students are now able to jointly present these new challenging experimental results.

  5. Body wave attenuation characteristics in the crust of Alborz region and North Central Iran

    NASA Astrophysics Data System (ADS)

    Farrokhi, M.; Hamzehloo, H.

    2016-11-01

    Attenuation of P and S waves has been investigated in Alborz and north central part of Iran using the data recorded by two permanent and one temporary networks during October 20, 2009, to December 22, 2010. The dataset consists of 14,000 waveforms from 380 local earthquakes (2 < M L < 5.6). The extended coda normalization method (CNM) was used to estimate quality factor of P (Q P) and S waves (Q S) at seven frequency bands (0.375, 0.75, 1.5, 3, 6, 12, 24 Hz). The Q P and Q S values have been estimated at lapse times from 40 to 100 s. It has been observed that the estimated values of Q P and Q S are time independent; therefore, the mean values of Q P and Q S at different lapse times have been considered. The frequency dependence of quality factor was determined by using a power-law relationship. The frequency-dependent relationship for Q P was estimated in the form of (62 ± 7)f (1.03 ± 0.07) and (48 ± 5)f (0.95 ± 0.07) in Alborz region and North Central Iran, respectively. These relations for Q S for Alborz region and North Central Iran have estimated as (83 ± 8)f (0.99 ± 0.07) and (68 ± 5)f (0.96 ± 0.05), respectively. The observed low Q values could be the results of thermoelastic effects and/or existing fracture. The estimated frequency-dependent relationships are comparable with tectonically active regions.

  6. Body wave attenuation characteristics in the crust of Alborz region and North Central Iran

    NASA Astrophysics Data System (ADS)

    Farrokhi, M.; Hamzehloo, H.

    2017-07-01

    Attenuation of P and S waves has been investigated in Alborz and north central part of Iran using the data recorded by two permanent and one temporary networks during October 20, 2009, to December 22, 2010. The dataset consists of 14,000 waveforms from 380 local earthquakes (2 < M L < 5.6). The extended coda normalization method (CNM) was used to estimate quality factor of P ( Q P) and S waves ( Q S) at seven frequency bands (0.375, 0.75, 1.5, 3, 6, 12, 24 Hz). The Q P and Q S values have been estimated at lapse times from 40 to 100 s. It has been observed that the estimated values of Q P and Q S are time independent; therefore, the mean values of Q P and Q S at different lapse times have been considered. The frequency dependence of quality factor was determined by using a power-law relationship. The frequency-dependent relationship for Q P was estimated in the form of (62 ± 7) f (1.03 ± 0.07) and (48 ± 5) f (0.95 ± 0.07) in Alborz region and North Central Iran, respectively. These relations for Q S for Alborz region and North Central Iran have estimated as (83 ± 8) f (0.99 ± 0.07) and (68 ± 5) f (0.96 ± 0.05), respectively. The observed low Q values could be the results of thermoelastic effects and/or existing fracture. The estimated frequency-dependent relationships are comparable with tectonically active regions.

  7. Frequency scaling of rain attenuation at centimeter and millimeter waves using a path-averaged drop size distribution

    NASA Astrophysics Data System (ADS)

    Ihara, Toshio; Furuhama, Yoji

    1981-11-01

    The applicability of several frequency scaling methods of rain attenuation is discussed based upon the cumulative distributions of rain attenuations at 81.8, 34.5, and 11.5 GHz measured in the same horizontal propagation path of 1.3 km for 1 year. A frequency scaling method (MISD) based upon the concept of a path-averaged raindrop size distribution N-(D) is newly applied to statistical prediction of the attenuation and is shown to be effective at millimeter wave bands where attenuation changes remarkably depending upon the raindrop size distribution, although the usefulness of MISD has been verified for time-sequential data. The size distribution determined from the statistical data at the three frequencies is given by N-(D) = 26,000 R-(-0.294)exp [-(5.6 R-0.283D)], 10 ≤ R- ≤ 70 mm/h, where R- is the path-averaged rainfall rate in millimeters per hour and D is the diameter of a raindrop in millimeters. Frequency dependence of attenuation calculated by using this size distribution shows that the prediction of rain attenuation based upon the Laws and Parsons size distribution results in an underestimation at frequencies above 80 GHz.

  8. Thermal elastic-wave attenuation in low-dimensional SiNx bars at low temperatures

    NASA Astrophysics Data System (ADS)

    Withington, S.; Williams, E.; Goldie, D. J.; Thomas, C. N.; Schneiderman, M.

    2017-08-01

    At low temperatures, <200 mK, the thermal flux through low-dimensional amorphous dielectric bars, <2 μm wide and 200 nm thick, is transported by a small number of low-order elastic modes. For long bars, L > 400 μm, it is known that the conductance scales as 1/L, where L is the length, but for short bars, 1 μm < L < 400 μm, the length dependence is poorly known. Although it is assumed that the transport must exhibit a diffusive to ballistic transition, the functional form of the transition and the scale size over which the transition occurs have not, to our knowledge, been measured. In this paper, we use ultra-low-noise superconducting Transition Edge Sensors to measure the heat flux through a set of SiNx bars to establish the characteristic scale size of the ballistic to diffusive transition. For bars supporting 6 to 7 modes, we measure a thermal elastic-wave attenuation length of 20 μm. The measurement is important because it sheds light on the scattering processes, which in turn are closely related to the generation of thermal fluctuation noise. Our own interest lies in creating patterned phononic filters for controlling heat flow and thermal noise in ultra-low-noise devices, but the work will be of interest to others trying to isolate devices from their environments and studying loss mechanisms in micro-mechanical resonators.

  9. Complex Contact-Based Dynamics of Microsphere Monolayers Revealed by Resonant Attenuation of Surface Acoustic Waves

    NASA Astrophysics Data System (ADS)

    Hiraiwa, M.; Abi Ghanem, M.; Wallen, S. P.; Khanolkar, A.; Maznev, A. A.; Boechler, N.

    2016-05-01

    Contact-based vibrations play an essential role in the dynamics of granular materials. Significant insights into vibrational granular dynamics have previously been obtained with reduced-dimensional systems containing macroscale particles. We study contact-based vibrations of a two-dimensional monolayer of micron-sized spheres on a solid substrate that forms a microscale granular crystal. Measurements of the resonant attenuation of laser-generated surface acoustic waves reveal three collective vibrational modes that involve displacements and rotations of the microspheres, as well as interparticle and particle-substrate interactions. To identify the modes, we tune the interparticle stiffness, which shifts the frequency of the horizontal-rotational resonances while leaving the vertical resonance unaffected. From the measured contact resonance frequencies we determine both particle-substrate and interparticle contact stiffnesses and find that the former is an order of magnitude larger than the latter. This study paves the way for investigating complex contact-based dynamics of microscale granular crystals and yields a new approach to studying micro- to nanoscale contact mechanics in multiparticle networks.

  10. P wave attenuation of the Yellowstone Caldera from three-dimensional inversion of spectral decay using explosion source seismic data

    NASA Astrophysics Data System (ADS)

    Clawson, Steven R.; Smith, Robert B.; Benz, Harley M.

    1989-06-01

    Using explosion source, seismic refraction data, recorded in the 1978 and 1980 Yellowstone-Snake River Plain seismic experiments, a three-dimensional inversion of differential P wave attenuation was used to assess the relative variations in Q-1 in and around the volcanically active, 45 km by 70 km, Yellowstone caldera, northwestern Wyoming. Differential attenuation was derived from spectral decay of upper crustal Pg phases, observed from six explosions and recorded at 90 temporary stations. Because of the relatively short time windows used to determine the spectral content, a maximum entropy technique was employed to estimate the spectra that yielded an optimally small variance. Differential P wave attenuation was calculated from least squares determinations of the spectral ratios corrected for source and path effects. The observed differential attenuation parameters were then inverted using a weighted least squares technique for a discretized, 70×105 km, three-dimensional surface and upper crustal Q-1 model of the Yellowstone caldera and surrounding region. Results showed that the surface layer, to depths of 2 km within the Yellowstone caldera, is characterized by relatively high attenuation with low Q values less than 30, compared to values of 38 to 50 outside the caldera. The higher attenuation in the caldera's surface layer is thought to be associated with Quaternary lake sediments, highly altered rhyolites, and the possible influence of steam in areas of hydrothermal activity. In the crystalline upper crust, at depths of 2 km to 12 km, Q values of 40 to 70 were observed in areas of thick sedimentary fill northwest of the caldera and in areas of hydrothermal activity. Within the caldera, upper crustal attenuation generally corresponded to Q of 200 in areas that are interpreted to be associated with hot but now solidified granitic material. In comparison, relatively high attenuation, Q = 40, was observed in the upper crust of the northeastern Yellowstone

  11. On floats and float tests

    NASA Technical Reports Server (NTRS)

    Seewald, Friedrich

    1931-01-01

    The principal source of information on float resistance is the model test. In view of the insuperable difficulties opposing any attempt at theoretical treatment of the resistance problem, particularly at attitudes which tend toward satisfactory take-off, such as the transitory stage to planing, the towing test is and will remain the primary method for some time.

  12. Attenuation of elastic waves in bentonite and monitoring of radioactive waste repositories

    NASA Astrophysics Data System (ADS)

    Biryukov, A.; Tisato, N.; Grasselli, G.

    2016-04-01

    Deep geological repositories, isolated from the geosphere by an engineered bentonite barrier, are currently considered the safest solution for high-level radioactive waste (HLRW) disposal. As the physical conditions and properties of the bentonite barrier are anticipated to change with time, seismic tomography was suggested as a viable technique to monitor the physical state and integrity of the barrier and to timely detect any unforeseen failure. To do so, the seismic monitoring system needs to be optimized, and this can be achieved by conducting numerical simulations of wave propagation in the repository geometry. Previous studies treated bentonite as an elastic medium, whereas recent experimental investigations indicate its pronounced viscoelastic behaviour. The aims of this contribution are (i) to numerically estimate the effective attenuation of bentonite as a function of temperature T and water content Wc, so that synthetic data can accurately reproduce experimental traces and (ii) assess the feasibility and limitation of the HLRW repository monitoring by simulating the propagation of sonic waves in a realistic repository geometry. A finite difference method was utilized to simulate the wave propagation in experimental and repository setups. First, the input of the viscoelastic model was varied to achieve a match between experimental and numerical traces. The routine was repeated for several values of Wc and T, so that quality factors Qp(Wc, T) and Qs(Wc, T) were obtained. Then, the full-scale monitoring procedure was simulated for six scenarios, representing the evolution of bentonite's physical state. The estimated Qp and Qs exhibited a minimum at Wc = 20 per cent and higher sensitivity to Wc, rather than T, suggesting that pronounced inelasticity of the clay has to be taken into account in geophysical modelling and analysis. The repository-model traces confirm that active seismic monitoring is, in principle, capable of depicting physical changes in the

  13. Preparation, Characterization, and Millimeter Wave Attenuation of Carbon Fibers Coated with Ni-Cu-P and Ni-Co-P Alloys

    NASA Astrophysics Data System (ADS)

    Ye, Mingquan; Li, Zhitao; Wang, Chen; Han, Aijun

    2015-12-01

    Composite carbon fibers (CFs) coated with Ni-X-P (X = Cu, Co, none) alloys were prepared by electroless plating. The morphology, crystal structure, elemental composition, and millimeter wave (MMW) attenuation performance of the alloy-coated CFs were characterized by scanning electron microscopy, x-ray diffractometry, energy-dispersive spectrometry, and microwave attenuation. CFs were coated with a layer of alloy particles. The P content in the Ni-Cu-P or Ni-Co-P-coated alloy was lower than that in the Ni-P alloy, and coating alloy Ni-P was amorphous. Coating alloys exhibited crystal characteristics after Cu or Co introduction. MMW-attenuation performance of alloy-coated CFs showed that the 3 and 8 mm wave-attenuation effects of CF/Ni-Cu-P and CF/Ni-Co-P were better than those of CF/Ni-P and CFs. The 8 mm wave-attenuation values and their increases were larger than those of the 3 mm wave. The MMW-attenuation performance is attributable to the alloy bulk resistivity and P content. The 3 mm wave-attenuation effects of wavelength-coated CF samples were slightly larger than those of the half wavelength samples. An optimal weight gain value existed for the MMW-attenuation performance of alloy-coated CFs.

  14. High-performance near-field electromagnetic wave attenuation in ultra-thin and transparent graphene films

    NASA Astrophysics Data System (ADS)

    Kang, Junmo; Kim, Donggyun; Kim, Youngsoo; Choi, Jae-Boong; Hong, Byung Hee; Kim, Sang Woo

    2017-06-01

    Ultra-thin and transparent electromagnetic interference (EMI) shielding and absorbing materials are in increasing demand for near-field electromagnetic wave attenuation in transparent electronic devices that get thinner and lighter. Here, we report chemical-doped and undoped graphene as the thinnest and transparent shield for high-performance near-field electromagnetic wave attenuation. The electromagnetic loss characterization demonstrate that a single layer graphene film exhibits a giant magnetic field transmission loss normalized to the film thickness that is at least two orders of magnitude higher than those of conventional EMI shielding and absorbing materials, which is attributed to the outstanding magnetic field mirroring in graphene. The doped and double-layer graphene films exhibit superior power and transmission losses than the commercial transparent indium tin oxide shield over the frequency range from 0.1 GHz to 6 GHz. The high-performance near-field electromagnetic wave attenuation in graphene enables broad range applications such as futuristic transparent display devices.

  15. Heterogeneities of the shear wave attenuation field in the lithosphere of East Tien Shan and their relationship with seismicity

    NASA Astrophysics Data System (ADS)

    Kopnichev, Yu. F.; Sokolova, I. N.

    2012-02-01

    The shear wave attenuation field in the lithosphere of Eastern Tien Shan has been mapped. The method based on analysis of the ratio between amplitudes of Sn and Pn waves was used. On aggregate, about 120 seismograms made at the Makanchi station (MKAR), mainly in the period of 2003-2009, at epicentral distances of about 350-1200 km were analyzed. It was found that shear wave attenuation in the lithosphere of Eastern Tien Shan is weaker than that in the region of Central Tien Shan. This agrees with the fact that the rate of deformation of the Earth's crust in Eastern Tien Shan is lower (based on GPS data), as is the seismicity level, in comparison to Central Tien Shan. The zones of high attenuation, where strong earthquakes with M > 7.0 have not occurred for the last 200 years, have been identified: first of all, these are the area west of Urumqi and that of the Lop Nur test site. It is suggested that in the first zone, where an annular seismicity structure has formed over the last 30 years, a strong earthquake may be being prepared. The second zone is most probably related to the uplift of mantle fluids resulting from a long-term intensive technogenic effect, analogous to what has occurred in areas of other nuclear test sites (Nevada and Semipalatinsk).

  16. Spatial variations of seismic attenuation in the North West of Iranian plateau from analysis of coda waves

    NASA Astrophysics Data System (ADS)

    Naghavi, M.; Rahimi, H.; Moradi, A.; Mukhopadhyay, S.

    2017-06-01

    In this study, spatial variation of coda wave attenuation in the north western (NW) Iranian Plateau is explored using local earthquakes. Single backscattering method is used to map the spatial variations of coda Q (Qc) using 14,969 earthquakes which are recorded digitally by sixteen permanent stations. Observed spatial attenuation maps are well correlated with geological setting of study area. North West of Iranian plateau is dominated with high attenuation which is well correlated with Quaternary deposits as well as the Sahnad, Sabalan volcanic zone and Tabriz fault. These observation is in accordance with numerous 2D velocity tomograms which have shown very low velocity in the NW Iran. The region characterized by volcanic structures exhibits mainly higher seismic attenuation than the surrounding regions whereas, Paleo Tethys basin in the eastern part of covered area are categorized by smaller attenuation than the other zone. Our observation shows good correlation with reported lower crustal low-velocity region beneath the Sahand and Sabalan volcanos. The Sahand and Sabalan volcanoes are very large structures and they dominate the Pliocene-Quaternary magmatic landscape of NW Iran. In addition, our observation has clearly shown existence of a probable fault zone trending in NE - SW direction between Tabriz city and Urmia Lake which is consistent with the trend of meizoseismal zone of the Deh-Khareqan (modern Azarshahr) earthquake (M 6.8) in 1641.

  17. Accurate and efficient modeling of global seismic wave propagation for an attenuative Earth model including the center

    NASA Astrophysics Data System (ADS)

    Toyokuni, Genti; Takenaka, Hiroshi

    2012-06-01

    We propose a method for modeling global seismic wave propagation through an attenuative Earth model including the center. This method enables accurate and efficient computations since it is based on the 2.5-D approach, which solves wave equations only on a 2-D cross section of the whole Earth and can correctly model 3-D geometrical spreading. We extend a numerical scheme for the elastic waves in spherical coordinates using the finite-difference method (FDM), to solve the viscoelastodynamic equation. For computation of realistic seismic wave propagation, incorporation of anelastic attenuation is crucial. Since the nature of Earth material is both elastic solid and viscous fluid, we should solve stress-strain relations of viscoelastic material, including attenuative structures. These relations represent the stress as a convolution integral in time, which has had difficulty treating viscoelasticity in time-domain computation such as the FDM. However, we now have a method using so-called memory variables, invented in the 1980s, followed by improvements in Cartesian coordinates. Arbitrary values of the quality factor (Q) can be incorporated into the wave equation via an array of Zener bodies. We also introduce the multi-domain, an FD grid of several layers with different grid spacings, into our FDM scheme. This allows wider lateral grid spacings with depth, so as not to perturb the FD stability criterion around the Earth center. In addition, we propose a technique to avoid the singularity problem of the wave equation in spherical coordinates at the Earth center. We develop a scheme to calculate wavefield variables on this point, based on linear interpolation for the velocity-stress, staggered-grid FDM. This scheme is validated through a comparison of synthetic seismograms with those obtained by the Direct Solution Method for a spherically symmetric Earth model, showing excellent accuracy for our FDM scheme. As a numerical example, we apply the method to simulate seismic

  18. Effects of CO2 on P-wave attenuation in porous media with micro-cracks: A synthetic modelling study

    NASA Astrophysics Data System (ADS)

    Ekanem, A. M.; Li, X. Y.; Chapman, M.; Main, I. G.

    2016-12-01

    The presence of CO2 in hydrocarbon reservoirs can cause significant changes in seismic wave properties. In turn these properties can be used to map CO2 saturation in hydrocarbon reservoirs or aquifers - either from natural sources or by injection from the surface. We present the results of a synthetic modelling study of the effects of supercritical CO2 saturation on P-wave attenuation in a medium consisting of four horizontal layers, including a target aquifer. The target aquifer is modelled fully by an effective medium containing pores saturated with brine and/or CO2 and randomly-aligned microcracks at different densities. The other layers are modelled solely by their bulk seismic velocities and densities. We first compute synthetic seismograms for a reference case where the third layer is completely isotropic with no cracks, no pores and no fluid saturation. We then calculate synthetic seismograms for finite crack densities of 0.01, 0.02 and 0.03 at varying degrees of CO2 saturation in the third layer. The results of our analysis indicate that attenuation is sensitive both to CO2 saturation and the crack density. For a given crack density, attenuation increases gradually with decreasing percentage of CO2 saturation and reaches a maximum at around 10% saturation. The induced attenuation increases with crack density and with offset. These observations hold out the potential of using seismic attenuation as an additional diagnostic in the characterisation of rock formations for a variety of applications, including hydrocarbon exploration and production, subsurface storage of CO2 or geothermal energy extraction.

  19. Development of a floating photobioreactor with internal partitions for efficient utilization of ocean wave into improved mass transfer and algal culture mixing.

    PubMed

    Kim, Z-Hun; Park, Hanwool; Hong, Seong-Joo; Lim, Sang-Min; Lee, Choul-Gyun

    2016-05-01

    Culturing microalgae in the ocean has potentials that may reduce the production cost and provide an option for an economic biofuel production from microalgae. The ocean holds great potentials for mass microalgal cultivation with its high specific heat, mixing energy from waves, and large cultivable area. Suitable photobioreactors (PBRs) that are capable of integrating marine energy into the culture systems need to be developed for the successful ocean cultivation. In this study, prototype floating PBRs were designed and constructed using transparent low-density polyethylene film for microalgal culture in the ocean. To improve the mixing efficiency, various types of internal partitions were introduced within PBRs. Three different types of internal partitions were evaluated for their effects on the mixing efficiency in terms of mass transfer (k(L)a) and mixing time in the PBRs. The partition type with the best mixing efficiency was selected, and the number of partitions was varied from one to three for investigation of its effect on mixing efficiency. When the number of partitions is increased, mass transfer increased in proportion to the number of partitions. However, mixing time was not directly related to the number of partitions. When a green microalga, Tetraselmis sp. was cultivated using PBRs with the selected partition under semi-continuous mode in the ocean, biomass and fatty acid productivities in the PBRs were increased by up to 50 % and 44% at high initial cell density, respectively, compared to non-partitioned ones. The results of internally partitioned PBRs demonstrated potentials for culturing microalgae by efficiently utilizing ocean wave energy into culture mixing in the ocean.

  20. Rapid Near-inertial Internal Wave Group Propagation Through the Transition Layer from Float and Glider Observations in the Bay of Bengal

    NASA Astrophysics Data System (ADS)

    Johnston, S.; Rudnick, D. L.; Sherman, J. T.

    2016-02-01

    Two Spray gliders and 1 SOLO-II float were deployed in 2013 and 2014 as components of ONR's Air-Sea Interactions in the Northern Indian Ocean (ASIRI) experiment. Shallow (10-50 m) salinity-controlled mixed layers in the Bay of Bengal isolate the rest of the deeper isothermal layer and ocean interior from winds. The transition layer is a deeper stratification maximum (20-100 m), which separates the upper ocean from the interior. Downward near-inertial internal wave (NIW) groups are observed here in potential density fluctuations and can rapidly (a few inertial periods) transfer energy out of the mixed layer into the stratified interior. (Inertial periods are T = 2*pi/f = 2 - 3 days from 9 - 17°N, where f is the Coriolis frequency.) When isopycnals shoal at fronts, the transition layer is brought closer to the mixed layer allowing for faster downward group speed due to the higher stratification. With about 10 inertial wind events in the NCEP reanalysis over the observation period of about 21 weeks, we find 3 NIW groups with clear downward energy (upward phase) propagation into the interior. The groups reach 200 m within 2-3 T and have vertical wavelengths of about 200 m. This implies horizontal wavelengths of about 200 km if the waves have a frequency of 1.1f. This horizontal wavelength and propagation time scale appear consistent with surface wind forcing correlation scales from 3-day highpassed wind products and decay estimates from surface drifters and theory (Park et al., 2009). Our results extend this previous work by making subsurface observations and measuring further equatorward. The mesoscale appears to mediate: (a) the conversion from mixed layer inertial oscillations into propagating NIW and (b) NIW propagation into the interior.

  1. Effect of P-wave scattering on velocity and attenuation in unconsolidated sand saturated with immiscible liquids

    SciTech Connect

    Seifert, P.K.; Geller, J.T.; Johnson, L.R.

    1998-01-01

    Seismic wave tomography is a potentially powerful tool for detecting and delineating nonaqueous phase liquid (NAPL) contaminants in the shallow subsurface. To develop this application, the authors are conducted laboratory and numerical studies to understand the mechanisms of P-wave transmission through NAPL-water-sand systems. P-wave measurements of traveltime and amplitude were taken in the 100--900 kHz frequency range through saturated sand with variable NAPL content. To simulate the stress conditions of the shallow surface, a low confining and axial pressure of 60 and 140 kPa, respectively, was applied. The measurements show a significant change in the traveltime and amplitude of the primary arrival as a function of NAPL saturation. To simulate the laboratory measurements, the authors performed numerical calculations of P-wave propagation through a 1-D medium. The results show that the main behavior of traveltime and amplitude variation can be explained by P-wave scattering. This represents an alternative explanation to the theories that describe local fluid flow as the dominant mechanism for seismic wave attenuation and velocity dispersion.

  2. An energy-based approach to estimate seismic attenuation due to wave-induced fluid flow in heterogeneous poroelastic media

    NASA Astrophysics Data System (ADS)

    Solazzi, Santiago G.; Rubino, J. Germán; Müller, Tobias M.; Milani, Marco; Guarracino, Luis; Holliger, Klaus

    2016-11-01

    Wave-induced fluid flow (WIFF) due to the presence of mesoscopic heterogeneities is considered as one of the main seismic attenuation mechanisms in the shallower parts of the Earth's crust. For this reason, several models have been developed to quantify seismic attenuation in the presence of heterogeneities of varying complexity, ranging from periodically layered media to rocks containing fractures and highly irregular distributions of fluid patches. Most of these models are based on Biot's theory of poroelasticity and make use of the assumption that the upscaled counterpart of a heterogeneous poroelastic medium can be represented by a homogeneous viscoelastic solid. Under this dynamic-equivalent viscoelastic medium (DEVM) assumption, attenuation is quantified in terms of the ratio of the imaginary and real parts of a frequency-dependent, complex-valued viscoelastic modulus. Laboratory measurements on fluid-saturated rock samples also rely on this DEVM assumption when inferring attenuation from the phase shift between the applied stress and the resulting strain. However, whether it is correct to use an effective viscoelastic medium to represent the attenuation arising from WIFF at mesoscopic scales in heterogeneous poroelastic media remains largely unexplored. In this work, we present an alternative approach to estimate seismic attenuation due to WIFF. It is fully rooted in the framework of poroelasticity and is based on the quantification of the dissipated power and stored strain energy resulting from numerical oscillatory relaxation tests. We employ this methodology to compare different definitions of the inverse quality factor for a set of pertinent scenarios, including patchy saturation and fractured rocks. This numerical analysis allows us to verify the correctness of the DEVM assumption in the presence of different kinds of heterogeneities. The proposed methodology has the key advantage of providing the local contributions of energy dissipation to the overall

  3. An explicit formula for the coherent SH waves' attenuation coefficient in random porous materials with low porosities.

    PubMed

    Zhang, Jun; Ye, Wenjing

    2015-09-01

    In this paper, the attenuation coefficient of coherent SH waves in random porous material with uniformly randomly distributed elliptical cavities of different aspect ratios is studied. Based on an analysis of the mechanism for attenuation, a simple macro model for the attenuation coefficient is proposed. The macro model says that the attenuation coefficient can be expressed as a function of the mean scattering cross section and the number density of cavities at low porosities. Then, large-scale numerical simulations using the pre-corrected Fast Fourier Transform (pFFT) algorithm accelerated Boundary Element Method (BEM) are conducted to specify this macro model. Finally, this macro model is compared with four theoretical models derived for composite/porous materials with circular inclusions at the porosity p=3.17% and 5%. Results show this macro model agree well with three of them. Compared to the existing theoretical models, the form of this macro model is simple and has a clear physical meaning. In addition, it is applicable to cases with relatively complex cavities.

  4. The Use of Ultrasonic Seismic Wave Attenuation (Q) for Better Subsurface Imaging, Energy Exploration, and Tracking of Sequestrated Carbon Dioxide

    NASA Astrophysics Data System (ADS)

    Delaney, D.; Purcell, C. C.; Mur, A. J.; Haljasmaa, I.; Soong, Y.; Harbert, W.

    2012-12-01

    Parameters related to seismic and ultrasonic elastic waves traveling through a porous rock material with compliant pores, cracks and isometric pores are subject to variations which are dependent on the physical properties of the rock such as density, porosity, permeability, frame work moduli, fluid moduli, micro structural variation, and effective pressure. Our goal is to understand these variations through experiments completed using Berea sandstone, rhyolites, coal, and carbonate samples. Understanding these lithologies are relevant to enhanced oil recovery, enhanced geothermal, and CO2 storage activities. Working in the COREFLOW laboratory at the National Energy Technology Laboratory (NETL) of the United States Department of Energy (DOE) we performed several experiments on these rock types with various different pore filling fluids, effective pressures, and temperatures. We measured P, S1 and S2 ultrasonic velocities using an New England Research (NER) Autolab 1500 device and calculated the lame parameters (Bulk modulus (K), Young's modulus (E), Lamè's first parameter (λ), Shear modulus (G), Poisson's ratio ( ), P-wave modulus (M)). Using an aluminum reference core and the P, S1, and S2 ultrasonic waveform data collected, we employed the spectral ratio method to estimate Q. This method uses the ratio of the amplitude-frequency spectrum (obtained via fast Fourier Transform and processed using Matlab) of the rock core compared with the amplitude-frequency spectrum of the aluminum reference core to calculate the quality factor (Q). The quality factor is a dimensionless value that represents the attenuation of a seismic wave as it travels through a rock. Seismic attenuation is dependent on wave velocity, the path length or time the wave is in the rock, and of course the physical properties of the rock through which the wave travels. Effective pressures used in our experiments varied between 0.01 MPa and 50 MPa and temperatures varied between 21 C to 80 C which

  5. Wave intensity amplification and attenuation in non-linear flow: implications for the calculation of local reflection coefficients.

    PubMed

    Mynard, Jonathan; Penny, Daniel J; Smolich, Joseph J

    2008-12-05

    Local reflection coefficients (R) provide important insights into the influence of wave reflection on vascular haemodynamics. Using the relatively new time-domain method of wave intensity analysis, R has been calculated as the ratio of the peak intensities (R(PI)) or areas (R(CI)) of incident and reflected waves, or as the ratio of the changes in pressure caused by these waves (R(DeltaP)). While these methods have not yet been compared, it is likely that elastic non-linearities present in large arteries will lead to changes in the size of waves as they propagate and thus errors in the calculation of R(PI) and R(CI). To test this proposition, R(PI), R(CI) and R(DeltaP) were calculated in a non-linear computer model of a single vessel with various degrees of elastic non-linearity, determined by wave speed and pulse amplitude (DeltaP(+)), and a terminal admittance to produce reflections. Results obtained from this model demonstrated that under linear flow conditions (i.e. as DeltaP(+)-->0), R(DeltaP) is equivalent to the square-root of R(PI) and R(CI) (denoted by R(PI)(p) and R(CI)(p)). However for non-linear flow, pressure-increasing (compression) waves undergo amplification while pressure-reducing (expansion) waves undergo attenuation as they propagate. Consequently, significant errors related to the degree of elastic non-linearity arise in R(PI) and R(CI), and also R(PI)(p) and R(CI)(p), with greater errors associated with larger reflections. Conversely, R(Delta)(P) is unaffected by the degree of non-linearity and is thus more accurate than R(PI) and R(CI).

  6. The contribution of activated processes to Q. [stress corrosion cracking in seismic wave attenuation

    NASA Technical Reports Server (NTRS)

    Spetzler, H. A.; Getting, I. C.; Swanson, P. L.

    1980-01-01

    The possible role of activated processes in seismic attenuation is investigated. In this study, a solid is modeled by a parallel and series configuration of dashpots and springs. The contribution of stress and temperature activated processes to the long term dissipative behavior of this system is analyzed. Data from brittle rock deformation experiments suggest that one such process, stress corrosion cracking, may make a significant contribution to the attenuation factor, Q, especially for long period oscillations under significant tectonic stress.

  7. The contribution of activated processes to Q. [stress corrosion cracking in seismic wave attenuation

    NASA Technical Reports Server (NTRS)

    Spetzler, H. A.; Getting, I. C.; Swanson, P. L.

    1980-01-01

    The possible role of activated processes in seismic attenuation is investigated. In this study, a solid is modeled by a parallel and series configuration of dashpots and springs. The contribution of stress and temperature activated processes to the long term dissipative behavior of this system is analyzed. Data from brittle rock deformation experiments suggest that one such process, stress corrosion cracking, may make a significant contribution to the attenuation factor, Q, especially for long period oscillations under significant tectonic stress.

  8. Theoretical modeling insights into elastic wave attenuation mechanisms in marine sediments with pore-filling methane hydrate

    NASA Astrophysics Data System (ADS)

    Marín-Moreno, H.; Sahoo, S. K.; Best, A. I.

    2017-03-01

    The majority of presently exploitable marine methane hydrate reservoirs are likely to host hydrate in disseminated form in coarse grain sediments. For hydrate concentrations below 25-40%, disseminated or pore-filling hydrate does not increase elastic frame moduli, thus making impotent traditional seismic velocity-based methods. Here, we present a theoretical model to calculate frequency-dependent P and S wave velocity and attenuation of an effective porous medium composed of solid mineral grains, methane hydrate, methane gas, and water. The model considers elastic wave energy losses caused by local viscous flow both (i) between fluid inclusions in hydrate and pores and (ii) between different aspect ratio pores (created when hydrate grows); the inertial motion of the frame with respect to the pore fluid (Biot's type fluid flow); and gas bubble damping. The sole presence of pore-filling hydrate in the sediment reduces the available porosity and intrinsic permeability of the sediment affecting Biot's type attenuation at high frequencies. Our model shows that attenuation maxima due to fluid inclusions in hydrate are possible over the entire frequency range of interest to exploration seismology (1-106 Hz), depending on the aspect ratio of the inclusions, whereas maxima due to different aspect ratio pores occur only at sonic to ultrasound frequencies (104-106 Hz). This frequency response imposes further constraints on possible hydrate saturations able to reproduce broadband elastic measurements of velocity and attenuation. Our results provide a physical basis for detecting the presence and amount of pore-filling hydrate in seafloor sediments using conventional seismic surveys.

  9. Floating Potential Peturbations due to Micro-Meteoroids Impacts : Theory and Application to STEREO/WAVES data

    NASA Astrophysics Data System (ADS)

    Zaslavsky, A.

    2014-12-01

    In-situ observation of dust grains from various origins is continuously performed by space missions equipped with radio instruments. These measurements consist in observations of voltage pulses, or their spectral signature. It has for long been proposed that one of the mechanisms able to produce these pulses is the recollection by the spacecraft of electric charges generated by impact ionization. Here for the first time, on the basis of this charge recollection assumption, a complete theoretical model of how pulses are generated is proposed. This model makes it possible to reproduce the precise shape of a voltage pulse, including the sometimes observed "voltage undershoot" following the pulse, knowing the local plasma parameters. We use the data provided by S/WAVES and show that it strongly supports the model proposed. Even though other processes may be responsible for radio pulses generation, we show here that recollection process is unambiguously observed. The model proposed is an important step forward, in that it enables us to reproduce the shape, timescales and amplitudes of pulses generated by dust impacts in various space environments. Such a model can be used to infer the dust-detection abilities of different radio instruments onboard different spacecraft, including future missions Solar Orbiter and Solar Probe Plus.

  10. Study of Spectral Attenuation Laws of Seismic Waves for Michoacán state, México

    NASA Astrophysics Data System (ADS)

    Vazquez Rosas, R.; Aguirre, J.; Mijares Arellano, H.

    2009-12-01

    Several attenuation relationships have been developed for Mexico, mostly after the earthquake of September 19, 1985, an event that gave great impetus to the development of engineering seismology in Mexico. Since 1985, the number of seismic stations in the country has increased significantly, especially between the Coast of Guerrero and Mexico City. This is due to the infamous large amplifications observed in the lake area of Mexico City with respect to hard ground sites. Some studies have analyzed how seismic waves are attenuated or amplified from the Pacific Coast toward the inland. The attenuation relationship used for seismic hazard assessment in Mexico is that of Ordaz (1989), which uses data from the Guerrero acceleration network. Another recent study is that of García et al. (2005), which uses more recent data from intraplate earthquakes recorded at the Guerrero acceleration network. It is important to note that, since these relations were derived for only part of the Mexican subduction zone and for certain types of seismic sources, caution should be exercised when using them for earthquake risk studies in other regions of Mexico. In the present work, we study the state of Michoacán, one of the most important seimogenic zones in Mexico. Three kinds of sources exist in the state, producing tectonic earthquakes, volcanic earthquakes, and events due to local faults in the region. For this reason, it is of vital importance to study the propagation of seismic waves within Michoacán state, and in this paper in particular we study their attenuation. We installed a temporary network consisting of 7 accelerograph stations across the state, at the following locations: Faro de Brucerías, Aguililla, Apatzingán, Taretán, Pátzcuaro, Morelia, and Maravatío. The stations form a line that is perpendicular to the coastline and has a total length of 366 km, while the distance between neighboring stations varies from 60 to 80 km. Among all the seismic events recorded at

  11. A method to overcome the diffraction limit in infrared microscopy using standing waves in an attenuated total reflection configuration

    NASA Astrophysics Data System (ADS)

    Hendaoui, Nordine; Mani, Aladin; Liu, Ning; Tofail, Syed M.; Silien, Christophe; Peremans, André

    2017-01-01

    A method is proposed to overcome the diffraction limit of spatial resolution in infrared microscopy. To achieve this, standing waves in an attenuated total reflection configuration were generated to spatially modulate the absorbance of adsorbate vibrational transitions. A numerical simulation was undertaken. It showed that chemical imaging with a spatial resolution of approximately 100 nm is achievable in the case of self-assembled patterns (ofoctdecyltrichlorosilane [CH3-(CH2)17-SiCl3]), when probing the methyl modes located near 3.5 micrometres.

  12. Attenuation and Shock Waves in Linear Hereditary Viscoelastic Media; Strick-Mainardi, Jeffreys-Lomnitz-Strick and Andrade Creep Compliances

    NASA Astrophysics Data System (ADS)

    Hanyga, Andrzej

    2014-09-01

    Dispersion, attenuation and wavefronts in a class of linear viscoelastic media proposed by Strick and Mainardi (Geophys J R Astr Soc 69:415-429, 1982) and a related class of models due to Lomnitz, Jeffreys and Strick are studied by a new method due to the author. Unlike the previously studied explicit models of relaxation modulus or creep compliance, these two classes support propagation of discontinuities. Due to an extension made by Strick, either of these two classes of models comprise both viscoelastic solids and fluids. We also discuss the Andrade viscoelastic media. The Andrade media do not support discontinuity waves and exhibit the pedestal effect.

  13. Frequency scaling of slant-path atmospheric attenuation in the absence of rain for millimeter-wave links

    NASA Astrophysics Data System (ADS)

    Lucas-Vegas, María. José; Riera, José Manuel

    2016-11-01

    Broadband satellite communications systems, either used for broadcast or fixed satellite services, have grown continuously in recent years. This has led to the use of higher frequency bands, from the Ku (14/11 GHz) to the Ka band (30/20 GHz) in the last decade, and with the expectation of using the Q/V band (50/40 GHz) and even the W band (75-110 GHz) in the future. As frequency increases, radio wave propagation effects in the slant-path within the troposphere are becoming more and more relevant. The objective of this research is the proposal of frequency scaling approximations for the total attenuation in the absence of rain, a condition that occurs during the highest percentages of time, usually more than 95% in temperate climates. There is a strong relationship between total attenuation at different frequencies, as it arises from the same physical phenomena, namely, the presence of oxygen, water vapor, and clouds in the slant path. This strong relationship allows frequency scaling estimations to be proposed. In particular, polynomials for instantaneous frequency scaling of total attenuation under these conditions have been calculated for a set of frequencies in the range 10-100 GHz, based on atmospheric profiles of 60 sites from all over the world and physical models of attenuation. Global polynomials are provided for the 72 combinations of nine significant frequencies, which can be used to estimate attenuation at a frequency band from its known value at a different one. Refined expressions have also been calculated for different climatic zones, providing more precise estimations.

  14. Floating Point Control Library

    SciTech Connect

    Lee, G. L.; Shereda, C.

    2007-08-02

    Floating Point Control is a Library that allows for the manipulation of floating point unit exception masking funtions control exceptions in both the Streaming "Single Instruction, Multiple Data" Extension 2 (SSE2) unit and the floating point unit simultaneously. FPC also provides macros to set floating point rounding and precision control.

  15. Bottom attenuation estimation using sound intensity fluctuations due to mode coupling by nonlinear internal waves in shallow water.

    PubMed

    Grigorev, Valery A; Katsnelson, Boris G; Lynch, James F

    2016-11-01

    Analyses of fluctuations of low frequency signals (300 ± 30 Hz) propagating in shallow water in the presence of nonlinear internal waves (NIWs) in the Shallow Water 2006 experiment are carried out. Signals were received by a vertical line array at a distance of ∼20 km from the source. A NIW train was moving totally inside of the acoustic track, and the angle between the wave front of the NIW and the acoustic track in the horizontal plane was ∼10°. It is shown that the spectrum of the sound intensity fluctuations contains peaks corresponding to the coupling of pairs of propagating modes. Analysis of spectra at different hydrophone depths, and also summed over depth allows the authors to estimate attenuation in the bottom sediments.

  16. Attenuation distance of low frequency waves upstream of the pre-dawn bow shock: GEOTAIL and ISEE 3 comparison

    NASA Technical Reports Server (NTRS)

    Sugiyama, T.; Terasawa, T.; Kawano, H.; Yamamoto, T.; Kokubun, S.; Frank, L. A.; Ackerson, K.; Tsurutani, B. T.

    1995-01-01

    We have made a statistical study of the spatial distribution of low frequency waves (approx. 0.01-0.1 Hz) in the region upstream of the pre-dawn to dawn side bow shock (-50 Re less than X less than 15 Re) using both GEOTAIL and international sun earth explorer 3 (ISEE-3) magnetometer data. We have found that the wave amplitude dependence on D and X(sub s), where D is the distance from the bow shock and X(sub s) the x-coordinate position of shock foot point of the IMF, can be described by a functional form of A exp (X(sub s)/L(sub X)-D/L(sub D), with the characteristic attenuation distances, L(sub X) = 62 +/- 12 Re and L(sub D) = 59 +/- 38 Re.

  17. Shallow S wave attenuation and actively degassing magma beneath Taal Volcano, Philippines

    NASA Astrophysics Data System (ADS)

    Kumagai, Hiroyuki; Lacson, Rudy; Maeda, Yuta; Figueroa, Melquiades S.; Yamashina, Tadashi

    2014-10-01

    Taal Volcano, Philippines, is one of the world's most dangerous volcanoes given its history of explosive eruptions and its close proximity to populated areas. A real-time broadband seismic network was recently deployed and has detected volcano-tectonic events beneath Taal. Our source location analysis of these volcano-tectonic events, using onset arrival times and high-frequency seismic amplitudes, points to the existence of a region of strong attenuation near the ground surface beneath the east flank of Volcano Island in Taal Lake. This region is beneath the active fumarolic area and above sources of pressure contributing inflation and deflation, and it coincides with a region of high electrical conductivity. The high-attenuation region matches that inferred from an active-seismic survey conducted at Taal in 1993. These features strongly suggest that the high-attenuation region represents an actively degassing magma body near the surface that has existed for more than 20 years.

  18. Propagation of Biot slow waves in heterogeneous pipe networks: Effect of the pipe radius distribution on the effective wave velocity and attenuation

    NASA Astrophysics Data System (ADS)

    Bernabé, Y.

    2009-11-01

    This paper extends a previous study of the harmonic (or AC) flow of a compressible fluid through a single, elastic, thick-wall pipe. The model previously developed is used to investigate propagation of pore-scale Biot slow waves through heterogeneous one-, two- and three-dimensional networks of pipes. A novel method is applied to the results of the network simulations to numerically determine the dispersion equation of the upscaled Biot slow waves and investigate its dependence on pore-scale heterogeneity. As a function of frequency, the phase velocity of the macroscale Biot slow waves displays an S-shaped curve, increasing from zero at low frequencies (i.e., nonpropagative regime) to C? at high frequencies (i.e., propagative regime with C? lower than the sound velocity in the fluid). The transition between these two regimes is marked by the inflection point at the frequency ωB (where ωB is inversely proportional to the length scale Λ characteristic of fluid flow and permeability). The high-frequency phase velocity C? depends on the dimensionality of the network considered and decreases with increasing heterogeneity. The wave attenuation (as measured by the inverse quality factor) also presents an S-shaped curve, decreasing from 2 (i.e., critical damping) to zero, with the same inflection point at ωB. This behavior is approximately independent on the pore radius distribution, provided that ωB (or the corresponding fluid flow length scale Λ) is held constant. A mechanism based on wave scattering and interferences of forward and backward traveling (pore-scale) Biot slow waves is proposed to explain the observations.

  19. Centimeter and millimeter wave attenuation and brightness temperature due to atmospheric oxygen and water vapor

    NASA Technical Reports Server (NTRS)

    Smith, E. K.

    1982-01-01

    Calculations are presented for atmospheric absorption and radiation emission for several atmospheric conditions and elevation angles. The calculations are for frequencies in the 1 to 340 GHz frequency range. The calculations are compared to those from other models. Agreement is found to within 15% for absorption coefficient (7.5 g/m/cubed water vapor at 290 K) and approximately the same for total zenithal attenuation. The attenuation and gaseous emission noise curves defined by the International Radio Consultative Committee are found to have minor inconsistencies.

  20. Seismic-wave attenuation and yield determination at regional distances. Final report, 1 May 1987-30 April 1989

    SciTech Connect

    Mitchell, B.J.; Nuttli, O.W.; Xie, J.K.; Al-Shukri, H.; Correig, A.

    1989-05-25

    Work was completed on yield determination at the Soviet test site on Novaya Zemlya. Magnitudes and yields, determined for 30 explosions using Lg amplitudes recorded in northwestern Europe, ranged between 2.5 and 4900 kt, the largest since April 1976 being about 145 kt. Studies were completed on seismic wave attenuation of surface waves at intermediate periods and of Lg waves at 1 Hz in several regions of the world. Limits were determined for the degree of frequency dependence of Q (sub beta) which can occur in the crust in stable and tectonically active regions. A stochastic convolution model was proposed for Lg coda at distances > 200 km which considers the effects of dispersion scattering and mode conversions at those distances. A back-projection tomographic method was developed to regionalize large-scale lateral variations of coda Q for Lg waves which traverse long continental paths. A seismically active region in the New Madrid seismic zone was found to be characterized by lower than normal Q values. In the western United States, Q values in the upper mantle vary laterally, becoming smaller from east to west. Crust of the Basin and Range province has a low-Q upper crust overlying a lower crust with higher Q values.

  1. Toward a Rayleigh Wave Attenuation Model for Asia and Surrounding Regions

    DTIC Science & Technology

    2008-09-01

    Yangtze Craton, and others. High attenuation is observed in tectonically active regions such as the Himalayas, the Tian Shan, Pamir and Zagros ...active regions such as the Himalayas, the Tian Shan, Pamir, and Zagros mountains. We estimated variance reductions achieved with our tomographic

  2. Pn wave geometrical spreading and attenuation in Northeast China and the Korean Peninsula constrained by observations from North Korean nuclear explosions

    NASA Astrophysics Data System (ADS)

    Zhao, Lian-Feng; Xie, Xiao-Bi; Tian, Bao-Feng; Chen, Qi-Fu; Hao, Tian-Yao; Yao, Zhen-Xing

    2015-11-01

    We investigate the geometric spreading and attenuation of seismic Pn waves in Northeast China and the Korean Peninsula. A high-quality broadband Pn wave data set generated by North Korean nuclear tests is used to constrain the parameters of a frequency-dependent log-quadratic geometric spreading function and a power law Pn Q model. The geometric spreading function and apparent Pn wave Q are obtained for Northeast China and the Korean Peninsula between 2.0 and 10.0 Hz. Using the two-station amplitude ratios of the Pn spectra and correcting them with the known spreading function, we remove the contributions of the source and crust from the apparent Pn Q and retrieve the P wave attenuation information along the pure upper mantle path. We then use both Pn amplitudes and amplitude ratios in a tomographic approach to obtain the upper mantle P wave attenuation in the studied area. The Pn wave spectra observed in China are compared with those recorded in Japan, and the result reveals that the high-frequency Pn signal across the oceanic path attenuated faster compared with those through the continental path.

  3. Preparation and electromagnetic waves attenuation performances of infrared-interfering composite smog

    NASA Astrophysics Data System (ADS)

    Liu, Xiang-cui; Liu, Qing-hai; Dai, Meng-yan; Shi, Wei-dong; Fang, Guo-feng; Zhang, Tong

    2016-10-01

    The infrared-interfering composite smog material is prepared by a heating and agitating device in aqueous solutions and then sprayed into a cloud chamber for six minutes to form smog using gas-water mixing spray system. The attenuation performances of the smog to visible light, 1.06μm laser, 3-5μm infrared and 8-14μm infrared are evaluated, and compared with those of other testing materials. The results show that the sprayed smog have the best attenuation performances and the longest interfering time to visible light, 1.06μm laser, 3-5μm infrared and 8-14μm infrared. Therefore, the infrared-interfering composite smog material in the form of aqueous solution is the new smoke obscurant materials that are environment-friendly and possess broad application prospects in some aspects such as visible light, laser and infrared countermeasures.

  4. On Wave-Ice Interaction in the Arctic Marginal Ice Zone: Dispersion, Attenuation, and Ice Response

    DTIC Science & Technology

    2016-06-01

    Ice Interaction in the Arctic Marginal Ice Zone: Dispersion, Attenuation, and Ice Response ClarenCe O. COllins iii ASEE Postdoctoral Fellow Ocean ...Dynamics and Prediction Branch Oceanography Division W. eriCk rOgers Ocean Dynamics and Prediction Branch Oceanography Division aleksey MarChenkO The...focus of this report, is quite distinct from the Antarctic. In simple terms, the Arctic is ocean surrounded by land and the Antarctic is land surrounded

  5. Variation of coda wave attenuation in the Alborz region and central Iran

    NASA Astrophysics Data System (ADS)

    Rahimi, H.; Motaghi, K.; Mukhopadhyay, S.; Hamzehloo, H.

    2010-06-01

    More than 340 earthquakes recorded by the Institute of Geophysics, University of Tehran (IGUT) short period stations from 1996 to 2004 were analysed to estimate the S-coda attenuation in the Alborz region, the northern part of the Alpine-Himalayan orogen in western Asia, and in central Iran, which is the foreland of this orogen. The coda quality factor, Qc, was estimated using the single backscattering model in frequency bands of 1-25 Hz. In this research, lateral and depth variation of Qc in the Alborz region and central Iran are studied. It is observed that in the Alborz region there is absence of significant lateral variation in Qc. The average frequency relation for this region is Qc = 79 +/- 2f1.07+/-0.08. Two anomalous high-attenuation areas in central Iran are recognized around the stations LAS and RAZ. The average frequency relation for central Iran excluding the values of these two stations is Qc = 94 +/- 2f0.97+/-0.12. To investigate the attenuation variation with depth, Qc value was calculated for 14 lapse times (25, 30, 35,... 90s) for two data sets having epicentral distance range R < 100 km (data set 1) and 100 < R < 200 km (data set 2) in each area. It is observed that Qc increases with depth. However, the rate of increase of Qc with depth is not uniform in our study area. Beneath central Iran the rate of increase of Qc is greater at depths less than 100 km compared to that at larger depths indicating the existence of a high attenuation anomalous structure under the lithosphere of central Iran. In addition, below ~180 km, the Qc value does not vary much with depth under both study areas, indicating the presence of a transparent mantle under them.

  6. Modeling Attenuation and Phase of Radio Waves in Air at Frequencies Below 1000 GHz

    DTIC Science & Technology

    1981-12-01

    center frequency for each line; (2) an empirical 1 water vapor continuum spectrum: and (3) a liquid water attenuation term for haze and cloud conditions...INTRODUCTION penetrate a somewhat opaque atmosphere (haze, The physical properties of the neutral atmosphere fog, clouds , dust, smoke, light rain) under...responsible-a kind of ’invisible’ hydrogen-bonded dimers and/or clusters of selec- cloud (Nilsson, 19791. tive size distributions (10-30 H 20 molecules

  7. High-frequency seismic wave propagation within the heterogeneous crust: effects of seismic scattering and intrinsic attenuation on ground motion modelling

    NASA Astrophysics Data System (ADS)

    Takemura, Shunsuke; Kobayashi, Manabu; Yoshimoto, Kazuo

    2017-09-01

    For practical modelling of high-frequency (>1 Hz) seismic wave propagation, we analysed the apparent radiation patterns and attenuations of P and S waves using observed Hi-net velocity seismograms for small-to-moderate crustal earthquakes in the Chugoku region, southwestern Japan. By comparing observed and simulated seismograms, we estimated practical parameter sets of crustal small-scale velocity heterogeneity and intrinsic attenuations of P and S waves (QP.int-1 and QS.int-1). Numerical simulations of seismic wave propagation were conducted via the finite-difference method using a 1-D crustal velocity structure model with additional 3-D small-scale velocity heterogeneity and intrinsic attenuation. The estimated crustal small-scale velocity heterogeneity is stochastically characterized by an exponential-type power spectral density function with correlation length of 1 km and root-mean-square value of 0.03. Estimated QP.int-1 and QS.int-1 values range from 10-2.6 to 10-2.0 and 10-2.8 to 10-2.4, respectively, indicating QP.int-1 > QS.int-1 for high frequencies (>1 Hz). Intrinsic attenuation dominates over scattering attenuation, which is caused by small-scale velocity heterogeneity. The crustal parameters obtained in this study are useful for evaluating peak ground velocities and coda envelopes for moderate crustal earthquakes via physical-based simulations using a 3-D heterogeneous structure model.

  8. Time-domain comparisons of power law attenuation in causal and noncausal time-fractional wave equations

    PubMed Central

    Zhao, Xiaofeng; McGough, Robert J.

    2016-01-01

    The attenuation of ultrasound propagating in human tissue follows a power law with respect to frequency that is modeled by several different causal and noncausal fractional partial differential equations. To demonstrate some of the similarities and differences that are observed in three related time-fractional partial differential equations, time-domain Green's functions are calculated numerically for the power law wave equation, the Szabo wave equation, and for the Caputo wave equation. These Green's functions are evaluated for water with a power law exponent of y = 2, breast with a power law exponent of y = 1.5, and liver with a power law exponent of y = 1.139. Simulation results show that the noncausal features of the numerically calculated time-domain response are only evident very close to the source and that these causal and noncausal time-domain Green's functions converge to the same result away from the source. When noncausal time-domain Green's functions are convolved with a short pulse, no evidence of noncausal behavior remains in the time-domain, which suggests that these causal and noncausal time-fractional models are equally effective for these numerical calculations. PMID:27250193

  9. Time-domain comparisons of power law attenuation in causal and noncausal time-fractional wave equations.

    PubMed

    Zhao, Xiaofeng; McGough, Robert J

    2016-05-01

    The attenuation of ultrasound propagating in human tissue follows a power law with respect to frequency that is modeled by several different causal and noncausal fractional partial differential equations. To demonstrate some of the similarities and differences that are observed in three related time-fractional partial differential equations, time-domain Green's functions are calculated numerically for the power law wave equation, the Szabo wave equation, and for the Caputo wave equation. These Green's functions are evaluated for water with a power law exponent of y = 2, breast with a power law exponent of y = 1.5, and liver with a power law exponent of y = 1.139. Simulation results show that the noncausal features of the numerically calculated time-domain response are only evident very close to the source and that these causal and noncausal time-domain Green's functions converge to the same result away from the source. When noncausal time-domain Green's functions are convolved with a short pulse, no evidence of noncausal behavior remains in the time-domain, which suggests that these causal and noncausal time-fractional models are equally effective for these numerical calculations.

  10. Communication: Singularity-free hybrid functional with a Gaussian-attenuating exact exchange in a plane-wave basis.

    PubMed

    Song, Jong-Won; Giorgi, Giacomo; Yamashita, Koichi; Hirao, Kimihiko

    2013-06-28

    Integrable singularity in the exact exchange calculations in hybrid functionals is an old and well-known problem in plane-wave basis. Recently, we developed a hybrid functional named Gaussian-attenuating Perdew-Burke-Ernzerhof (Gau-PBE), which uses a Gaussian function as a modified Coulomb potential for the exact exchange. We found that the modified Coulomb potential of Gaussian function enables the exact exchange calculation in plane-wave basis to be singularity-free and, as a result, the Gau-PBE functional shows faster energy convergence on k and q grids for the exact exchange calculations. Also, a tight comparison (same k and q meshes) between Gau-PBE and two other hybrid functionals, i.e., PBE0 and HSE06, indicates Gau-PBE functional as the least computational time consuming. The Gau-PBE functional employed in conjunction with a plane wave basis provides bandgaps with higher accuracy than the PBE0 and HSE06 in agreement with bandgaps previously calculated using Gaussian-type-orbitals.

  11. "Floating shoulder" injuries.

    PubMed

    Heng, Kenneth

    2016-12-01

    "Floating shoulder" is a rare injury complex resulting from high-energy blunt force trauma to the shoulder, resulting in scapulothoracic dissociation. It is commonly associated with catastrophic neurovascular injury. Two cases of motorcyclists with floating shoulder injuries are described.

  12. Regional Wave Attenuation and Seismic Moment from the Inversion of NORESS Spectra.

    DTIC Science & Technology

    1987-07-31

    earthquake moment versus NORESS local magnitude for L9 03.1.9). The solid line is the best-fittng straight line to L~ ogM 0 . !!43 4 1f 4 -"rP f ti " % ’%’ d ...Blake US Dept of Energy/DP 331 Forrestal Bailding 1000 Independence Ave. Washington, D . C. 20585 Dr. S. Bratt Science Applications Int’l Cbrp. 10210...407B 299 REGIONA NAVE ATTENUATION AND SEISMIC WOENT FROM THE 112 INVERSION OF NORESS (U) SCIENCE APPLICATIONS INTERNATIONAL CORP SAN DIEGO CA T J

  13. Sound attenuation on an ocean shelf at short ranges from a source in the presence of surface waves

    NASA Astrophysics Data System (ADS)

    Lunkov, A. A.; Petnikov, V. G.; Chernousov, A. D.

    2017-03-01

    The effect of surface roughness on the attenuation of low-frequency acoustic waves on a shallow ocean shelf is analyzed using numerical simulation. We focus here on transmission loss during propagation at short (less than 50 water layer depths) ranges from the sound source. The effect is considered both for a soft and hard bottom, when the sound velocity in the bottom is, respectively, lower or higher than the sound velocity in seawater. It is shown that to correctly predict losses at a short range in the presence of a rough upper boundary, it is necessary to take into account the interaction of both propagation and leaky modes. In the case of a hard bottom compared to a low-velocity one, the effect of surface roughness on propagation turned out to be the most pronounced.

  14. Modelling of wave propagation and attenuation in the Osaka sedimentary basin, western Japan, during the 2013 Awaji Island earthquake

    NASA Astrophysics Data System (ADS)

    Asano, Kimiyuki; Sekiguchi, Haruko; Iwata, Tomotaka; Yoshimi, Masayuki; Hayashida, Takumi; Saomoto, Hidetaka; Horikawa, Haruo

    2016-03-01

    On 2013 April 13, an inland earthquake of Mw 5.8 occurred in Awaji Island, which forms the western boundary of the Osaka sedimentary basin in western Japan. The strong ground motion data were collected from more than 100 stations within the basin and it was found that in the Osaka Plain, the pseudo velocity response spectra at a period of around 6.5 s were significantly larger than at other stations of similar epicentral distance outside the basin. The ground motion lasted longer than 3 min in the Osaka Plain where its bedrock depth spatially varies from approximately 1 to 2 km. We modelled long-period (higher than 2 s) ground motions excited by this earthquake, using the finite difference method assuming a point source, to validate the present velocity structure model and to obtain better constraint of the attenuation factor of the sedimentary part of the basin. The effect of attenuation in the simulation was included in the form of Q(f) = Q0(f/f0), where Q0 at a reference frequency f0 was given by a function of the S-wave velocity, Q0 = αVS. We searched for appropriate Q0 values by changing α for a fixed value of f0 = 0.2 Hz. It was found that values of α from 0.2 to 0.5 fitted the observations reasonably well, but that the value of α = 0.3 performed best. Good agreement between the observed and simulated velocity waveforms was obtained for most stations within the Osaka Basin in terms of both amplitude and ground motion duration. However, underestimation of the pseudo velocity response spectra in the period range of 5-7 s was recognized in the central part of the Osaka Plain, which was caused by the inadequate modelling of later phases or wave packets in this period range observed approximately 2 min after the direct S-wave arrival. We analysed this observed later phase and concluded that it was a Love wave originating from the direction of the east coast of Awaji Island.

  15. Floating: sink or swim.

    PubMed

    Pronger, L

    1995-12-01

    Budget restrictions, fewer human resources and fluctuating patient populations have combined to increase the practice of floating general duty nurses. Floating occurs when a nurse from an overstaffed unit, based on patient load, is required to work in another unit that is understaffed. Floating is not a new practice, but it has always been an emotionally charged issue. Today, with more float pool nurses seeking the security of a permanent position in a home unit, the issue has increased in intensity.

  16. The Design of Floats

    NASA Technical Reports Server (NTRS)

    Sottorf, W

    1938-01-01

    Following a summary of the multiplicity of domestic and foreign floats and a brief enumeration of the requirements of floats, the essential form parameters and their effect on the qualities of floats are detailed. On this basis a standard float design is developed which in model families with varying length/beam ratio and angle of dead rise is analyzed by an experimental method which permits its best utilization on any airplane.

  17. Measuring sea ice permeability as a function of the attenuation and phase velocity shift of an acoustic wave

    NASA Astrophysics Data System (ADS)

    Hudier, E. J.; Bahoura, M.

    2012-12-01

    Sea ice is a two-phase porous medium consisting of a solid matrix of pure ice and a salty liquid phase. At spring when ice permeability increases, it has been observed that pressure gradients induced at the ice-water interface upstream and downstream of pressure ridge keels can cause sea water and brine to be forced through the ice water boundary. It suggests that salt and heat fluxes through the bottom ice layers may be a major factor controlling the decay of an ice sheet. Knowing how water flows through the ice matrix is fundamental to a modeling of ocean-ice heat exchanges integrating the advective import/export of latent heat that result from melting/freezing within the ice. Permeability is the measurement of the ease with which fluids flow through a porous medium, however one of the most tricky to measure without altering the porosity of the sampled medium. To further complicate the challenge, horizontal and vertical permeability of the ice, referred as ice anisotropy, is significant. Acoustic wave propagation through porous media have been theorized to relate the acoustic velocity and attenuation to the physical properties of the tested material. It is a non-invasive technique, and as such could provide more reliable measurements of sea ice permeability than anything presently used. Simulations combining the Biot's and squirt flow mechanisms are performed to investigate the effect of permeability on the attenuation and phase velocity as a function of frequency. We first present the attenuation dispersion curves for an isotropic sea ice, then low-frequency and high-frequency limits are determined. Optimal frequency range and resolution requirements are evaluated for testing.

  18. Radiometric observations of atmospheric attenuation at 20.6 and 31.65 GHz: The Wave Propagation Laboratory data base

    NASA Technical Reports Server (NTRS)

    Jacobson, Mark D.; Snider, J. B.; Westwater, E. R.

    1993-01-01

    The National Oceanic and Atmospheric Administration (NOAA) Wave Propagation Laboratory (WPL) presently operates five dual-channel microwave radiometers, one triple-channel microwave radiometer, and one six-channel microwave radiometer. The dual-channel radiometers operate at frequencies of 20.6 or 23.87 GHz and 31.4 or 31.65 GHz. The triple-channel radiometer operates at 20.6, 31.65, and 90.0 GHz. The six-channel radiometer operates at frequencies of 20.6, 31.65, 52.85, 53.85, 55.45, and 58.8 GHz. Recent brightness temperature measurements and attenuation values from some of the above radiometers are presented. These radiometric measurements, taken in different locations throughout the world, have given WPL a diverse set of measurements under a variety of atmospheric conditions. We propose to do a more complete attenuation analysis on these measurements in the future. In addition, a new spinning reflector was installed recently for the dual-channel radiometer at the Platteville, Colorado site. This reflector will extend our measurement capabilities during precipating conditions. Locating the three-channel and portable dual-channel radiometers at or near Greeley, Colorado to support the Advanced Communications Technology Satellite (ACTS) program is discussed.

  19. Preparation, characterization and millimetre wave attenuation performance of carbon fibers coated with nickel-wolfram-phosphorus and nickel-cobalt-wolfram- phosphorus

    SciTech Connect

    Ye, Mingquan; Li, Zhitao; Wang, Chen; Han, Aijun

    2016-04-15

    Highlights: • SEM, XRD, EDS and MMW attenuation performances of alloys coated CFs were studied. • Resistivity and P content in alloys were main factors on MMW attenuation property. • The weight gain of coated CFs has effects on the MMW attenuation performance. - Abstract: Carbon fibers (CFs) coated with Ni–X–P (X = W, Co–W or none) alloys were prepared by electroless plating. The morphology, crystal structure, and element composition of alloy-coated CFs were characterized by scanning electron microscopy, X-ray diffractometry, energy-dispersive spectrometry and microwave attenuation. The results showed that CFs were coated with a layer of alloy particles. P content in Ni–Co–W–P or Ni–W–P alloys was lower than that in Ni–P alloy, and coating alloy Ni–P was amorphous. After W or Co introduction, coating alloys exhibited crystal characteristics. MMW-attenuation performance analysis showed that the 3 mm wave attenuation performance of CFs/Ni–Co–W–P, CFs/Ni–W–P and CFs/Ni–P increased by 7.27 dBm, 4.88 dBm and 3.55 dBm, and the 8 mm wave attenuation effects increased by 11.61 dBm, 6.11 dBm, and 4.06 dBm respectively, compared with those of CFs. MMW-attenuation performance is attributable to the sample bulk resistivity and P content in the alloy. Moreover, an optimal weight gain value existed for the MMW-attenuation performance of alloy-coated CFs.

  20. Shear wave attenuation estimated from the spectral decay rate in the vicinity of the Petropavlovsk station, Kamchatka

    NASA Astrophysics Data System (ADS)

    Gusev, A. A.; Guseva, E. M.

    2016-07-01

    The parameters of S-wave attenuation (the total effect of absorption and scattering) near the Petropavlovsk (PET) station in Kamchatka were estimated by means of the spectral method through an original procedure. The spectral method typically analyzes the changes with distance of the shape of spectra of the acceleration records assuming that the acceleration spectrum at the earthquake source is flat. In reality, this assumption is violated: the source acceleration spectra often have a high-frequency cutoff (the source-controlled f max) which limits the spectral working bandwidth. Ignoring this phenomenon not only leads to a broad scatter of the individual estimates but also causes systematic errors in the form of overestimation of losses. In the approach applied in the present study, we primarily estimated the frequency of the mentioned high-frequency cutoff and then constructed the loss estimates only within the frequency range where the source spectrum is approximately flat. The shape of the source spectrum was preliminarily assessed by the approximate loss compensation technique. For this purpose, we used the tentative attenuation estimates which are close to the final ones. The difference in the logarithms of the spectral amplitudes at the edges of the working bandwidth is the input for calculating the attenuation. We used the digital accelerograms from the PET station, with 80 samples per second digitization rate, and based on them, we calculated the averaged spectrum of the S-waves as the root mean square along two horizontal components. Our analysis incorporates 384 spectra from the local earthquakes with M = 4-6.5 at the hypocentral distances ranging from 80 to 220 km. By applying the nonlinear least-square method, we found the following parameters of the loss model: the Q-factor Q 0 = 156 ± 33 at frequency f = 1 Hz for the distance interval r = 0-100 km; the exponent in the power-law relationship describing the growth of the Q-factor with frequency,

  1. Separation attenuation in swept shock wave-boundary-layer interactions using different microvortex generator geometries

    NASA Astrophysics Data System (ADS)

    Martis, R. R.; Misra, A.

    2017-09-01

    A numerical study is conducted to determine the effectiveness of six different microvortex generator geometries in controlling swept shock wave/boundary-layer interactions. The geometries considered are base ramp, base ramp with declining angle of 45°, blunt ramp, split ramp, thick vanes, and ramped vanes. Microvortex generators with a gap were found to be better suited for delaying the separation. Thick vanes showed the largest delay in separation among the devices studied.

  2. A Waveform Inversion Technique for Measuring Elastic Wave Attenuation in Cylindrical Bars

    DTIC Science & Technology

    1991-07-23

    rise to a numoer ()f extensional wave modes in the bar (Kolsky, 1953), the fundamental mode is of the most interest to us. At very low frequencies (w...sample using spectral ratio method around 800 kllz. ’[he ultrasonic extensional attenmat ion value was derived from the measured coinpressional and shear...Thorne Lay Department of Earth & Atmospheric Sciences Institute of Tectonics St. Louis University Earth Science Board St. Louis, MO 63156 University

  3. Separation attenuation in swept shock wave-boundary-layer interactions using different microvortex generator geometries

    NASA Astrophysics Data System (ADS)

    Martis, R. R.; Misra, A.

    2017-03-01

    A numerical study is conducted to determine the effectiveness of six different microvortex generator geometries in controlling swept shock wave/boundary-layer interactions. The geometries considered are base ramp, base ramp with declining angle of 45°, blunt ramp, split ramp, thick vanes, and ramped vanes. Microvortex generators with a gap were found to be better suited for delaying the separation. Thick vanes showed the largest delay in separation among the devices studied.

  4. Video and Field Observations of Wave Attenuation in a Muddy Surf Zone

    DTIC Science & Technology

    2011-01-01

    Southern Brazil—Rio Grande to Chui. RS. Land and Ocean Interaction in Coastal Zone (LOICZ) Meeting. Sao Paulo. SP. Brazil, pp . 231-247. Calliari, L.J...Coastal Sediments󈧋, New Orleans, MS. pp . 1-11. Calliari. L. Winterwerp, J.. Fernandes, E., Vinzon, S.. Cuchiara, D.. Holland. K., Sperle. M., 2009...Shargfi, Z.. 2008. Water waves propagating over mud. International Conference on Coastal Engineering. Hamburg, Germany, pp . 314-323. Dean. R

  5. Atmospheric Attenuation of Millimeter and Submillimeter Waves: Models and Computer Code

    DTIC Science & Technology

    1979-10-15

    17 5. Attenuon!ion vs ]Frequenex- for Rainfall liates 18 (:(Coinl pa ri aoil of the I-oll M1i e Ait enuat ion (dash1) to Rlayle igh Attenuation (solid...sno0w art’ highly Itrillfl)ý,ctenlt 1.o pa -ss iVC rad ic ace nlt’asut’etill (is. It is s it’ to say that the( theory of ealtC-ult ionl of sc~atterhipl hi...tlorizontal Path 50 Im References 1. AllcClatcllev, 1. A., Fenn, R.W. Selby, J., Volz , F. E., and Garing, ..S. (1972) Optical Properties of thie At m osphere

  6. Float launch system

    SciTech Connect

    Ayers, R.R.

    1989-09-26

    This patent describes a method for deploying a seismic subarray, which includes a float, seismic gun support beam and umbilical cable, from a vessel. It comprises: putting the vessel underway; connecting the subarray to the vessel by a detachable saddle rigged via a cable from a boom; moving the subarray along the length of the boom outboard of the vessel; deploying the seismic gun support beam from the float into the water, whereby the beam stabilizes the subarray; lowering the float to the water; releasing the detachable saddle from the float; towing the released float with the vessel by the umbilical cable; and raising the detached saddle.

  7. Solving the problem of shock wave attenuation in an obstacle during a contact explosion of a high-energy material charge

    NASA Astrophysics Data System (ADS)

    Kuzin, E. N.; Zagarskih, V. I.; Efanov, V. V.

    2016-12-01

    A problem of estimation of shock wave attenuation in an obstacle under an explosion of a high-energy material (explosive) charge on its surface is considered. An algorithm for its solution is proposed using the analytical and semiempirical dependences generally recognized in explosion physics.

  8. Role of vegetation on the attenuation of forces on structures due to cnoidal waves

    NASA Astrophysics Data System (ADS)

    2009-04-01

    The evaluation of forces on structures in the marine environment due to ocean waves is absolutely essential in the planning and development of mitigation measures against natural coastal hazards and dictates their design. Further, studies on the forces on coastal structures due to regular and random waves are well entrenched in literature, whereas, that due to shallow water waves are rather scanty. The recent tsunami has added a new dimension on the role of vegetation on the forces on structures. Due the propagation of tsunami, a number of signature studies have revealed that structures fronted by vegetation have suffered minimum damage compared to that in its absence and as also reported by Yanagisawa (2008). In the present paper, the results from an experimental study to investigate the effect of vegetation on a typical structure located onshore over a slope of 1:30 are reported. The tests were carried out in a wave flume of length 72m, width 2m and 2.7m depth. The water depth at the toe of the slope was 1m. Slender flexible cylindrical members that represent plantation along the coast have been adopted for the tests. Experiments were carried out for different G/B ratios of 0, 0.5,1 and 1.5. (Where G is the distance between front face of vegetation/ green belt and the rear face of the building and B is width of the building). Experiments were repeated for three widths of Green belts (BG) and for each of the green belt, two different diameters of the cylinders of 10mm and 3.0mm were used. The forces on structure were measured with load cells in the presence and absence of the green belt. The Cnoidal waves covering a range of Ursell parameter between 18 and 700 were employed for the experiments. The different vegetal and flow parameters in a non-dimensional form have been identified. The variation of non-dimensionalised force over the slope in the presence and absence of vegetation as a function of the Ursell parameter, Relative rigidity and Reduced velocity for

  9. Role of vegetation on the attenuation of forces on structures due to Cnoidal waves

    NASA Astrophysics Data System (ADS)

    Sundar, V.; Norayanan, L.; Murali, K.

    2009-04-01

    The evaluation of forces on structures in the marine environment due to ocean waves is absolutely essential in the planning and development of mitigation measures against natural coastal hazards and dictates their design. Further, studies on the forces on coastal structures due to regular and random waves are well entrenched in literature, whereas, that due to shallow water waves are rather scanty. The recent tsunami has added a new dimension on the role of vegetation on the forces on structures. Due the propagation of tsunami, a number of signature studies have revealed that structures fronted by vegetation have suffered minimum damage compared to that in its absence and as also reported by Yanagisawa (2008). In the present paper, the results from an experimental study to investigate the effect of vegetation on a typical structure located onshore over a slope of 1:30 are reported. The tests were carried out in a wave flume of length 72m, width 2m and 2.7m depth. The water depth at the toe of the slope was 1m. Slender flexible cylindrical members that represent plantation along the coast have been adopted for the tests. Experiments were carried out for different G/B ratios of 0, 0.5,1 and 1.5. (Where G is the distance between front face of vegetation/ green belt and the rear face of the building and B is width of the building). Experiments were repeated for three widths of Green belts (BG) and for each of the green belt, two different diameters of the cylinders of 10mm and 3.0mm were used. The forces on structure were measured with load cells in the presence and absence of the green belt. The Cnoidal waves covering a range of Ursell parameter between 18 and 700 were employed for the experiments. The different vegetal and flow parameters in a non-dimensional form have been identified. The variation of non-dimensionalised force over the slope in the presence and absence of vegetation as a function of the Ursell parameter, Relative rigidity and Reduced velocity for

  10. Electromagnetic Waves Attenuation due to Rain: A Prediction Model for Terrestrial or L.O.S SHF and EHF Radio Communication Links

    NASA Astrophysics Data System (ADS)

    Moupfouma, Fidèle

    2009-06-01

    Because of the interest raised for SHF and EHF radio communications, the attenuation of electromagnetic waves by rain will always constitute a major concern for telecommunication engineers and scientists. The rain attenuation prediction models exposed in literature calculate the attenuation related to a given rain rate or else to a given percentage of time. The new model proposed in this paper, predicts with a good accuracy the percentage of time for which any given rain attenuation will be exceeded on terrestrial SHF, EHF radiowaves links, provided the rain rate R001 (mm/h) that represents rain rate value exceeded for 0.01% of time in the locality of interest is available. R001 (mm/h) data being available for most of the localities across the world in ITU-R data base, we may conclude that this new model proposed here, can be broadly and successfully used.

  11. Simulation of stress waves in attenuating drill strings, including piezoelectric sources and sensors

    PubMed

    Carcione; Poletto

    2000-07-01

    A key element in drill steering and prediction of lithology ahead-of-the-bit is the transmission of while-drilling information from the bottom of the well to the rig operator and the geophysicists. Mud-pulse telemetry, based on pressure pulses along the drilling mud and extensional waves through the drill string, is the most used technique. The last method, properly designed, could transmit data rates up to 100 bits per second, against the 1 or 2 bits per second achieved with pressure pulses. In this work, a time-domain algorithm is developed for the propagation of one-dimensional axial, torsional, and flexural stress waves, including transducer sources and sensors. In addition, the equations include relaxation mechanisms simulating the viscoelastic behavior of the steel, dielectric losses, and any other losses, such as those produced by the presence of the drilling mud, the casing, and the formation. Moreover, the algorithm simulates the passbands and stopbands due to the presence of the coupling joints and pulse distortion and delay due to nonuniform cross-section areas. Acoustic and electric pulses, generated at one location in the string, can be propagated and detected at any other location by piezoelectric and acoustic sensors, such as PCB accelerometers, clamp-on ammeters, force, and strain transducers.

  12. Attenuation of the S+Lg+Surface Wave Group out to 600 km in Northeastern North America: A Baseline Study?

    NASA Astrophysics Data System (ADS)

    Boatwright, J.; Seekins, L. C.

    2009-12-01

    We analyze the S+Lg+surface wave groups radiated out to 600 km by four moderate (4 ≤ M ≤ 5) earthquakes in Quebec, New York, and Maine: the 1997 Cap Rouge, 2002 Ausable Forks, 2005 Rivière du Loup, and 2006 Bar Harbor earthquakes. The raypaths predominately sample the Appalacian Province, and the crustal velocity structure is roughly homogeneous across the study area. We compute spectra using 20-60 s windows of the horizontal broadband components. We restrict our analysis to hard-rock (Vs > 1500 m/s) and soft-rock (Vs > 700 m/s) sites, avoiding resonant sedimentary sites; we model site amplification using average 1D impedance functions (Boore and Joyner, 1997). We use ro = 50 km instead of ro = 100 km for the crossover distance in the Street et al. (1975) function for geometrical spreading: this distance adjusts the corrected spectra at 10 s to the moment tensor estimates. This simple correction scheme allows us to regress for Q directly as a function of frequency: the source spectral shape is entirely unconstrained. Fitting a Qo f q function to the Q estimates from 0.2 to 25 Hz yields Q = 410 f 0.5 for a group velocity of 3.5 km/s. This attenuation is stronger than the Lg attenuation of 650 f 0.36 obtained by Erickson et al. (2004). The Q estimates are consistent for individual events. For f > 20 Hz, the Q estimates increase more rapidly than f 0.5: this deviation from the Qo f q form appears characteristic. To gauge how these Q estimates depend on the distance limit, we will rerun the analysis using broadband data out to 1000 km, adding 30% more recordings to the dataset.

  13. Extracellular Space Attenuates the Effect of Gap Junctional Remodeling on Wave Propagation: A Computational Study

    PubMed Central

    Cabo, Candido; Boyden, Penelope A.

    2009-01-01

    Abstract Ionic channels and gap junctions are remodeled in cells from the 5-day epicardial border zone (EBZ) of the healing canine infarct. The main objective of the study was to determine the effect of gap junctional conductance (Gj) remodeling and Cx43 redistribution to the lateral membrane on conduction velocity (θ) and anisotropic ratio, and how gap junctional remodeling is modulated by the extracellular space. We first implemented subcellular monodomain and two-domain computer models of normal epicardium (NZ) to understand how extracellular space modulates the relationship between Gj and θ in NZ. We found that the extracellular space flattens the Gj-θ relationship, thus θ becomes less sensitive to changes in Gj. We then investigated the functional consequences of Gj remodeling and Cx43 distribution in subcellular computer models of cells of the outer pathway (IZo) and central pathway (IZc) of reentrant circuits. In IZo cells, side-to-side (transverse) Gj is 10% the value in NZ cells. Such Gj remodeling causes a 45% decrease in transverse θ (θT). Inclusion of an extracellular space reduces the decrease in θT to 31%. In IZc cells, Cx43 redistribution along the lateral membrane results in a 29% increase in θT. That increase in θT is a consequence of the decrease in access resistance to the Cx43 plaques that occur with the Cx43 redistribution. Extracellular space reduces the increase in θT to 10%. In conclusion: 1), The extracellular space included in normal epicardial simulations flattens the Gj-θ relationship with θ becoming less sensitive to changes in Gj. 2), The extracellular space attenuates the effects of gap junction epicardial border zone remodeling (i.e., Gj reduction and Cx43 lateralization) on θT. PMID:19383455

  14. Q-structure beneath the north and central Indian Ocean from the inversion of observed Love and Rayleigh wave attenuation data

    NASA Astrophysics Data System (ADS)

    Singh, D. D.

    The fundamental-mode Love and Rayleigh waves generated by 57 earthquakes which occurred in the north and central Indian Ocean (extending to 40°S) and recorded at Indian seismograph and other WWSSN stations such as HOW, SHL, VIS, MDR, HYB, KOD, CHG, TRD, POO, BOM, GOA, NDI, NIL and QUE are analysed. Love and Rayleigh wave attenuation coefficients are estimated at periods of 15-100 s using the spectral amplitude of these waves for 98 different paths across the Bay of Bengal Fan, the Arabian Fan, and the north and central Indian Ocean. The large standard deviations observed in the surface wave attenuation coefficients may be a result of regional variation of the attenuative properties of the crust and upper mantle beneath these regions. Love wave attenuation coefficients are found to vary from 0.000 03 to 0.000 45 km -1 for the Bay of Bengal Fan; from 0.000 03 to 0.000 85 km -1 for the Arabian Fan; and from 0.000 03 to 0.000 35 km -1 for the north and central Indian Ocean. Similarly, Rayleigh wave attenuation coefficients vary from 0.000 03 to 0.0004 km -1 for the Bay of Bengal Fan; from 0.000 06 to 0.0007 km -1 for the Arabian Fan; and from 0.000 03 to 0.0007 km -1 for the north and central Indian Ocean. Backus and Gilbert inversion theory is applied to these surface wave attenuation data to obtain average Q-1 models for the crust and upper mantle beneath the Bay of Bengal, the Arabian Fan, and the north and central Indian Ocean. Inversion of Love and Rayleigh wave attenuation data shows a high-attenuation zone centred at a depth of > 120 km ( Qβ ≈ 125) for the Bay of Bengal Fan. Similarly, a high-attenuation zone ( Qβ ≈ 40-70) occurs at a depth of 60-160 km for the Arabian Fan at 100-160 km ( Qβ ≈ 115) for the Indian Ocean off Ninetyeast Ridge, and at 80-160 km ( Qβ ≈ 80) for the Indian Ocean across the Ninetyeast Ridge. The Qβ-1 models show a lithosphere thickness of 120 km beneath the Bay of Bengal Fan. Similarly, lithosphere thickness of 70, 100 and

  15. Attenuation of low-frequency electromagnetic wave in the thin sheath enveloping a high-speed vehicle upon re-entry

    NASA Astrophysics Data System (ADS)

    Liu, DongLin; Li, XiaoPing; Liu, YanMing; Xie, Kai; Bai, BoWen

    2017-02-01

    Low-frequency (LF) electromagnetic (EM) waves are suggested as potentially solving "radio blackout" caused by a plasma sheath enveloping a high-speed vehicle on re-entry. However, the traditional plasma absorption theory neglects the fact that the plasma sheath is electrically small compared to LF EM wavelengths. To understand clearly the attenuation of such waves through the plasma sheath, different attenuation mechanisms for the electric field (SE) and magnetic field (SH) were studied using the equivalent circuit approach. Analytical expressions were derived by modeling the plasma sheath as a spherical shell, and numerical simulations were performed to validate the effectiveness of the expressions. SE and SH are calculated for various plasma parameter settings; the EM wave attenuations obtained from plasma absorption theory are used for comparison. Results show that, instead of SE and SH being equal in the plasma absorption theory, SE and SH are no longer the same for electrically small sizes. Whereas |SH| is close to that from plasma absorption theory, |SE| is much higher. Further analysis shows that |SH| is a function of the ratio of electron density (ne) and collision frequency (ve) and increases with increasing ne/ve. Numerical simulations with radio-attenuation-measurement-C-like vehicle's plasma sheath parameters are performed and the results show that the magnetic field attenuation in the front part of the vehicle is much lower than in the rear. So it is suggested to place the magnetic loop antenna in the very front part of the vehicle. Finally, SH at different frequencies are calculated using plasma sheath parameter values simulating the re-entry phase of a radio-attenuation measurement-C vehicle and results show that such a vehicle might overcome radio blackout during the entire re-entry phase if systems operating below 3 MHz and above the L-band are combined with a lower-frequency system working below Earth's ionosphere and a higher-frequency system

  16. Full Wave Analysis of RF Signal Attenuation in a Lossy Cave using a High Order Time Domain Vector Finite Element Method

    SciTech Connect

    Pingenot, J; Rieben, R; White, D

    2004-12-06

    We present a computational study of signal propagation and attenuation of a 200 MHz dipole antenna in a cave environment. The cave is modeled as a straight and lossy random rough wall. To simulate a broad frequency band, the full wave Maxwell equations are solved directly in the time domain via a high order vector finite element discretization using the massively parallel CEM code EMSolve. The simulation is performed for a series of random meshes in order to generate statistical data for the propagation and attenuation properties of the cave environment. Results for the power spectral density and phase of the electric field vector components are presented and discussed.

  17. Multi-resonant piezoelectric shunting induced by digital controllers for subwavelength elastic wave attenuation in smart metamaterial

    NASA Astrophysics Data System (ADS)

    Wang, Gang; Cheng, Jianqing; Chen, Jingwei; He, Yunze

    2017-02-01

    Instead of analog electronic circuits and components, digital controllers that are capable of active multi-resonant piezoelectric shunting are applied to elastic metamaterials integrated with piezoelectric patches. Thanks to recently introduced digital control techniques, shunting strategies are possible now with transfer functions that can hardly be realized with analog circuits. As an example, the ‘pole-zero’ method is developed to design single- or multi-resonant bandgaps by adjusting poles and zeros in the transfer function of piezoelectric shunting directly. Large simultaneous attenuations in up to three frequency bands at deep subwavelength scale (with normalized frequency as low as 0.077) are achieved. The underlying physical mechanism is attributable to the negative group velocity of the flexural wave within bandgaps. As digital controllers can be readily adapted via wireless broadcasting, the bandgaps can be tuned easily unlike the electric components in analog shunting circuits, which must be tuned one by one manually. The theoretical results are verified experimentally with the measured vibration transmission properties, where large insulations of up to 20 dB in low-frequency ranges are observed.

  18. Attenuation of high frequency P and S waves in the crust of the East-Central Iran

    NASA Astrophysics Data System (ADS)

    Ma'hood, M.; Hamzehloo, H.; Doloei, G. J.

    2009-12-01

    We simultaneously estimated Qp-1 and Qs-1 by applying the extended coda-normalization method at 39 stations of three local networks in the East-Central Iran. We measured frequency-dependent attenuation of both P and S waves for the frequency range of 1.5, 3.0, 6.0, 12 and 24 Hz. We have analysed 266 three-component seismograms of 53 local earthquakes, having focal depths less than 25 km, which occurred from 2003 December 28 to 2005 April 11. By fitting power-law frequency dependence to the estimated values over the whole stations, we obtained Qp-1 = (25 +/- 3) × 10-3 f (-0.99+/-0.04) and Qs-1 = (19 +/- 2) × 10-3 f(-1.02+/-0.06) in the upper crust of the East-Central Iran, where f is frequency in Hz. Our results are in the range of those estimated for Qp-1 and Qs-1 of the other seismically active regions.

  19. Numerical simulation of wave-induced fluid flow seismic attenuation based on the Cole-Cole model.

    PubMed

    Picotti, Stefano; Carcione, José M

    2017-07-01

    The acoustic behavior of porous media can be simulated more realistically using a stress-strain relation based on the Cole-Cole model. In particular, seismic velocity dispersion and attenuation in porous rocks is well described by mesoscopic-loss models. Using the Zener model to simulate wave propagation is a rough approximation, while the Cole-Cole model provides an optimal description of the physics. Here, a time-domain algorithm is proposed based on the Grünwald-Letnikov numerical approximation of the fractional derivative involved in the time-domain representation of the Cole-Cole model, while the spatial derivatives are computed with the Fourier pseudospectral method. The numerical solution is successfully tested against an analytical solution. The methodology is applied to a model of saline aquifer, where carbon dioxide (CO2) is injected. To follow the migration of the gas and detect possible leakages, seismic monitoring surveys should be carried out periodically. To this aim, the sensitivity of the seismic method must be carefully assessed for the specific case. The simulated test considers a possible leakage in the overburden, above the caprock, where the sandstone is partially saturated with gas and brine. The numerical examples illustrate the implementation of the theory.

  20. A Nonlinear Theory for Predicting the Effects of Unsteady Laminar, Turbulent, or Transitional Boundary Layers on the Attenuation of Shock Waves in a Shock Tube with Experimental Comparison

    NASA Technical Reports Server (NTRS)

    Trimpi, Robert L.; Cohen, Nathaniel B.

    1961-01-01

    The linearized attenuation theory of NACA Technical Note 3375 is modified in the following manner: (a) an unsteady compressible local skin-friction coefficient is employed rather than the equivalent steady-flow incompressible coefficient; (b) a nonlinear approach is used to permit application of the theory to large attenuations; and (c) transition effects are considered. Curves are presented for predicting attenuation for a shock pressure ratio up to 20 and a range of shock-tube Reynolds numbers. Comparison of theory and experimental data for shock-wave strengths between 1.5 and 10 over a wide range of Reynolds numbers shows good agreement with the nonlinear theory evaluated for a transition Reynolds number of 2.5 X 10(exp 5).

  1. S-wave attenuation in northeastern Sonora, Mexico, near the faults that ruptured during the earthquake of 3 May 1887 Mw 7.5.

    PubMed

    Villalobos-Escobar, Gina P; Castro, Raúl R

    2014-01-01

    We used a new data set of relocated earthquakes recorded by the Seismic Network of Northeastern Sonora, Mexico (RESNES) to characterize the attenuation of S-waves in the fault zone of the 1887 Sonora earthquake (M w 7.5). We determined spectral attenuation functions for hypocentral distances (r) between 10 and 140 km using a nonparametric approach and found that in this fault zone the spectral amplitudes decay slower with distance at low frequencies (f < 4 Hz) compared to those reported in previous studies in the region using more distant recordings. The attenuation functions obtained for 23 frequencies (0.4 ≤ f ≤ 63.1 Hz) permit us estimating the average quality factor Q S  = (141 ± 1.1 )f ((0.74 ± 0.04)) and a geometrical spreading term G(r) = 1/r (0.21). The values of Q estimated for S-wave paths traveling along the fault system that rupture during the 1887 event, in the north-south direction, are considerably lower than the average Q estimated using source-station paths from multiple stations and directions. These results indicate that near the fault zone S waves attenuate considerably more than at regional scale, particularly at low frequencies. This may be the result of strong scattering near the faults due to the fractured upper crust and higher intrinsic attenuation due to stress concentration near the faults.

  2. Float Zone Workshop

    NASA Technical Reports Server (NTRS)

    Naumann, R. J.

    1980-01-01

    A summary of the Analytical Float Zone Experiment System (AFZES) concept is presented. The types of experiments considered for such a facility are discussed. Reports from various industrial producers and users of float zone material are presented. Special emphasis is placed on state-of-the-art developments in low gravity manufacturing and their applications to space processing.

  3. Estimating Attenuation Coefficients and P-Wave Velocities of the Shallow San Jacinto Fault Zone from Betsy Gunshots Data Recorded by a Spatially Dense Array with 1108 Sensors

    NASA Astrophysics Data System (ADS)

    Ozakin, Yaman; Ben-Zion, Yehuda

    2016-04-01

    We estimate values of P wave velocity and P attenuation coefficients (QP) for the subsurface material at the Sage Brush Flat site along the Clark branch of the San Jacinto Fault Zone. The data are generated by 33 Betsy gunshots and recorded by a spatially dense array of 1108 vertical component geophones deployed in a rectangular grid that is approximately 600 m x 600 m. We automatically pick the arrival times of the seismic body waves from each explosion arriving at stations within 200 m. These measurements are used to derive an average velocity map with velocity values ranging from 500 m/s to 1250 m/s. We estimate the energy of the early P waves by squaring the amplitudes in a short window relative to the automatic picks. These energies are fitted to a decay function representing the geometrical spreading and intrinsic attenuation. By separating the stations into spatial bins and calculating attenuation values for each by linear regression, we construct a QP values map. Most of the QP values are in 5-20 range, which is consistent with other studies of shallow fault zone regions.

  4. Effects of heterogeneities on the propagation, scattering and attenuation of seismic waves and the characterization of seismic source. Final report, 1 December 1982-30 November 1985

    SciTech Connect

    Aki, K.; Cormier, V.F.; Toksoz, M.N.

    1985-01-01

    During this reporting period, work was completed on testing alternative measures of body-wave magnitude. It was found that alternative measures of body waves magnitude often exhibit as much scatter as classical measures of magnitude, although coda magnitudes usually have slightly less scatter than spectral and classical magnitudes. In the cases investigated, these differences were usually not statistically significant. Another completed task was an investigation of the intrinsic attenuation of the Earth's mantle selected paths from the Sea of Okhotsk to Regional Seismic Test Network (RSTN) and Global Digital Seismic Network (GDSN) Stations in North America. It was concluded that the intrinsic attenuation in the mantle beneath eastern North America is both depth and frequency dependent and that spectral and time domain studies of attenuation can be reconciled in the frequency band up to 2 Hz. The focus of the project was then divided between source problems related to scattering and seismic wave propagation in three-dimensional, heterogeneous media. A significant result was that short period and broadband waveforms can improve the depth-resolution-determined earthquakes and underground nuclear explosions, forming a powerful discriminant. Scattering was studied theoretically and observationally. The significant result of that work is that the Earth's lithosphere must possess multiple scales of heterogeneity in order to explain both the amplitude and phase fluctuations at large arrays as well as the shapes of local S coda.

  5. The Influence of Water on Seismic Wave Speeds and Attenuation in the Upper Mantle: an update from the Laboratory

    NASA Astrophysics Data System (ADS)

    Cline, C. J., II; David, E. C.; Jackson, I.; Faul, U.; Berry, A.

    2015-12-01

    A fine-grained synthetic olivine (Fo90) polycrystal, doped with ~0.04 wt. % TiO2, has been prepared with ~70 wt. ppm H2O accommodated in the remarkably stable Ti-clinohumite defect typical of natural olivines from the Earth's generally water-undersaturated upper mantle (Berry et al., 2005). A precision-ground specimen of this material, sleeved in Pt tubing within a mild-steel jacket, was tested in torsional forced oscillation at seismic frequencies (mHz-Hz) and temperatures to 1200 °C, under 200 MPa confining pressure. The shear modulus was observed to decrease systematically with increasing oscillation period and temperature, accompanied by monotonically increasing dissipation, which are characteristic of absorption band or high-temperature-background behaviour. In a previous preliminary report, the new data were compared with the model of Jackson and Faul (Phys. Earth Planet. Interiors, 2010) for a suite of essentially anhydrous Ti-free olivine polycrystals, evaluated at the 25 μm grain size of the hydrous titaniferous olivine specimen, showing that the latter is vastly more dissipative than its anhydrous equivalent (by an order of magnitude at 1200 °C) and correspondingly lower in shear modulus. The results of additional experiments now better constrain the mechanical behaviour of the enclosing Pt sleeve and allow direct comparison with data for an anhydrous titaniferous olivine of comparable grain size. The latest results confirm a very strong influence of water on seismic wave attenuation, even under the water-undersaturated conditions expected to prevail in the Earth's upper mantle.

  6. Surface Drift of RAFOS Floats in the California Current System

    NASA Astrophysics Data System (ADS)

    Gates, D. C.; Collins, C. A.; Margolina, T.

    2011-12-01

    The patterns of surface drift of ninety RAFOS floats in the California Current System have been studied. The floats were launched in the California Undercurrent during 1992-2010 and were tracked by the ARGOS system when they surfaced at the end of their subsurface mission. The float hulls were glass cylinders which were 8.6 cm wide by 1.52 m long and floated with the upper 30 cm of the hull above water. The surface drift of these floats was typically equatorward in the California Current. However, some floats would flow poleward, others would drift westward into the North Pacific Gyre, and others with orbital cyclonic and/or anti-cyclonic motions. The duration of surface trajectories varied from as short as a period of days to approximately ten months. Forces on the floats included wind stress on the exposed hull and the drag of ocean currents on the subsurface hull. The latter included the Stokes drift associated with surface wind waves, Ekman flow caused by the stress of the wind on the ocean surface, and the currents associated with the general circulation of the ocean. Surface currents can be explained by calculating current direction and velocity from wind stress data. As a first step, the relationship between observed wind stress and the motion of the float is determined by assuming Ekman balance. Mesoscale effects, including eddies, are also considered in explaining the surface drift of the floats.

  7. The amplitude of the cross-covariance function of solar oscillations as a diagnostic tool for wave attenuation and geometrical spreading

    NASA Astrophysics Data System (ADS)

    Nagashima, Kaori; Fournier, Damien; Birch, Aaron C.; Gizon, Laurent

    2017-03-01

    Context. In time-distance helioseismology, wave travel times are measured from the two-point cross-covariance function of solar oscillations and are used to image the solar convection zone in three dimensions. There is, however, also information in the amplitude of the cross-covariance function, for example, about seismic wave attenuation. Aims: We develop a convenient procedure to measure the amplitude of the cross-covariance function of solar oscillations. Methods: In this procedure, the amplitude of the cross-covariance function is linearly related to the cross-covariance function and can be measured even for high levels of noise. Results: As an example application, we measure the amplitude perturbations of the seismic waves that propagate through the sunspot in active region NOAA 9787. We can recover the amplitude variations due to the scattering and attenuation of the waves by the sunspot and associated finite-wavelength effects. Conclusions: The proposed definition of cross-covariance amplitude is robust to noise, can be used to relate measured amplitudes to 3D perturbations in the solar interior under the Born approximation, and provides independent information from the travel times.

  8. Floating emitter solar cell

    NASA Technical Reports Server (NTRS)

    Chih, Sah (Inventor); Cheng, Li-Jen (Inventor)

    1987-01-01

    A front surface contact floating emitter solar cell transistor is provided in a semiconductor body (n-type), in which floating emitter sections (p-type) are diffused or implanted in the front surface. Between the emitter sections, a further section is diffused or implanted in the front surface, but isolated from the floating emitter sections, for use either as a base contact to the n-type semiconductor body, in which case the section is doped n+, or as a collector for the adjacent emitter sections.

  9. Micromechanisms with floating pivot

    DOEpatents

    Garcia, Ernest J.

    2001-03-06

    A new class of tilting micromechanical mechanisms have been developed. These new mechanisms use floating pivot structures to relieve some of the problems encountered in the use of solid flexible pivots.

  10. Floating Magnet Demonstration.

    ERIC Educational Resources Information Center

    Wake, Masayoshi

    1990-01-01

    A room-temperature demonstration of a floating magnet using a high-temperature superconductor is described. The setup and operation of the apparatus are described. The technical details of the effect are discussed. (CW)

  11. Commercial Float Zone Furnace

    NASA Image and Video Library

    1996-05-25

    S77-E-5094 (25 May 1996) --- Astronaut Marc Garneau, mission specialist representing the Canadian Space Agency (CSA), stands at the Commercial Float Zone Furnace (CFZF) in the Spacehab Module onboard the Earth-orbiting Space Shuttle Endeavour.

  12. Floating Magnet Demonstration.

    ERIC Educational Resources Information Center

    Wake, Masayoshi

    1990-01-01

    A room-temperature demonstration of a floating magnet using a high-temperature superconductor is described. The setup and operation of the apparatus are described. The technical details of the effect are discussed. (CW)

  13. The Floating Reference Librarian

    ERIC Educational Resources Information Center

    Hernon, Peter; Pastine, Maureen

    1972-01-01

    The floating librarian'' is one who interprets and adjusts the formal library structure to meet legitimate needs. This is one of the ways the academic reference librarian can gain greater acceptance with students and faculty. (9 references) (Author/NH)

  14. Reducing float coal dust

    PubMed Central

    Patts, J.R.; Colinet, J.F.; Janisko, S.J.; Barone, T.L.; Patts, L.D.

    2016-01-01

    Controlling float coal dust in underground coal mines before dispersal into the general airstream can reduce the risk of mine explosions while potentially achieving a more effective and efficient use of rock dust. A prototype flooded-bed scrubber was evaluated for float coal dust control in the return of a continuous miner section. The scrubber was installed inline between the face ventilation tubing and an exhausting auxiliary fan. Airborne and deposited dust mass measurements were collected over three days at set distances from the fan exhaust to assess changes in float coal dust levels in the return due to operation of the scrubber. Mass-based measurements were collected on a per-cut basis and normalized on the basis of per ton mined by the continuous miner. The results show that average float coal dust levels measured under baseline conditions were reduced by more than 90 percent when operating the scrubber. PMID:28018004

  15. Attenuation of Bragg backscattering of electromagnetic waves from density fluctuations near the region of polarization degeneracy in magnetoactive plasma

    SciTech Connect

    Gospodchikov, E. D. Khusainov, T. A.; Shalashov, A. G.

    2016-08-15

    Specific features of Bragg backscattering under conditions of strong polarization degeneracy near the cutoff surface in an anisotropic medium are studied analytically and numerically. It is shown that the linear interaction of normal waves can substantially affect wave scattering by suppressing the amplification of Bragg backscattering near the cutoff region in the case of weak coupling between normal waves.

  16. Full Wave Analysis of RF Signal Attenuation in a Lossy Rough Surface Cave using a High Order Time Domain Vector Finite Element Method

    SciTech Connect

    Pingenot, J; Rieben, R; White, D; Dudley, D

    2005-10-31

    We present a computational study of signal propagation and attenuation of a 200 MHz planar loop antenna in a cave environment. The cave is modeled as a straight and lossy random rough wall. To simulate a broad frequency band, the full wave Maxwell equations are solved directly in the time domain via a high order vector finite element discretization using the massively parallel CEM code EMSolve. The numerical technique is first verified against theoretical results for a planar loop antenna in a smooth lossy cave. The simulation is then performed for a series of random rough surface meshes in order to generate statistical data for the propagation and attenuation properties of the antenna in a cave environment. Results for the mean and variance of the power spectral density of the electric field are presented and discussed.

  17. l-Citrulline supplementation attenuates blood pressure, wave reflection and arterial stiffness responses to metaboreflex and cold stress in overweight men.

    PubMed

    Figueroa, Arturo; Alvarez-Alvarado, Stacey; Jaime, Salvador J; Kalfon, Roy

    2016-07-01

    Combined isometric exercise or metaboreflex activation (post-exercise muscle ischaemia (PEMI)) and cold pressor test (CPT) increase cardiac afterload, which may lead to adverse cardiovascular events. l-Citrulline supplementation (l-CIT) reduces systemic arterial stiffness (brachial-ankle pulse wave velocity (baPWV)) at rest and aortic haemodynamic responses to CPT. The aim of this study was to determine the effect of l-CIT on aortic haemodynamic and baPWV responses to PEMI+CPT. In all, sixteen healthy, overweight/obese males (age 24 (sem 6) years; BMI 29·3 (sem 4·0) kg/m2) were randomly assigned to placebo or l-CIT (6 g/d) for 14 d in a cross-over design. Brachial and aortic systolic blood pressure (SBP), diastolic blood pressure (DBP) and mean arterial pressure (MAP), aortic augmented pressure (AP), augmentation index (AIx), baPWV, reflection timing (Tr) and heart rate (HR) were evaluated at rest and during isometric handgrip exercise (IHG), PEMI and PEMI+CPT at baseline and after 14 d. No significant effects were evident after l-CIT at rest. l-CIT attenuated the increases in aortic SBP and wave reflection (AP and AIx) during IHG, aortic DBP, MAP and AIx during PEMI, and aortic SBP, DBP, MAP, AP, AIx and baPWV during PEMI+CPT compared with placebo. HR and Tr were unaffected by l-CIT in all conditions. Our findings demonstrate that l-CIT attenuates aortic blood pressure and wave reflection responses to exercise-related metabolites. Moreover, l-CIT attenuates the exaggerated arterial stiffness response to combined metaboreflex activation and cold exposure, suggesting a protective effect against increased cardiac afterload during physical stress.

  18. Effects of Ionospheric Reflection Height and Ground Conductivity on Earth-Ionosphere Waveguide Mode and Ground-Wave Attenuation Rates.

    DTIC Science & Technology

    1980-06-01

    except that for the diffraction model the free-space region is infinite. It can be shown ( Budden 9 ) that, for certain complex angles of wave normals...minimum possible signal may be incorrect for certain combinations of radio frequency., ground conductivity, and ionospheric height. 9- Budden , K.G...VLF Radio Waves, US Dept of Commerce, National Bureau of Standards, Technical Note 300. 9. Budden , K.G., The Waveguide Mode Theory of Wave Propagation

  19. Floating Versus Sinking

    NASA Astrophysics Data System (ADS)

    Vella, Dominic

    2015-01-01

    Small objects that are more dense than water may still float at the air-water interface because of surface tension. Whether this is possible depends not only on the density and size of the object, but also on its shape and surface properties, whether other objects are nearby, and how gently the object is placed at the interface. This review surveys recent work to quantify when objects can float and when they must sink. Much interest in this area has been driven by studies of the adaptations of water-walking insects to life at interfaces. I therefore discuss these results in the context of this and other applications.

  20. Floating nut retention system

    NASA Technical Reports Server (NTRS)

    Charles, J. F.; Theakston, H. A. (Inventor)

    1980-01-01

    A floating nut retention system includes a nut with a central aperture. An inner retainer plate has an opening which is fixedly aligned with the nut aperture. An outer retainer member is formed of a base plate having an opening and a surface adjacent to a surface of the inner retainer plate. The outer retainer member includes a securing mechanism for retaining the inner retainer plate adjacent to the outer retainer member. The securing mechanism enables the inner retainer plate to float with respect to the outer retainer number, while simultaneously forming a bearing surface for inner retainer plate.

  1. Attenuated direct and scattered wave propagation on simulated land mobile satellite service paths in the presence of trees

    NASA Technical Reports Server (NTRS)

    Campbell, Richard L.; Estus, Robert

    1988-01-01

    Measurements were made of direct path with no trees, attenuated direct, and tree scattered signal levels at 1.3 GHz. Signals were received in two small groves of mixed hardwood trees. In the groves studied, average total signal levels were about 13 dB below adjacent no-trees locations, with attenuated direct signal levels about 14.6 dB below the no-trees case and scattered signals about 17.3 dB below the no-trees case. A simple model for land mobile satellite service (LMSS) propagation in groves of trees is proposed. The model assumes a constant scattered signal contribution at 17 dB below no-trees levels added to an attenuated direct signal which varies, depending on the number and density of trees in the direct path. When total signal levels are strong, the attenuated direct signal dominates. When total signal levels are more than 15 dB below no-trees levels, the scattered signals dominate.

  2. An Evaluation of Two Millimeter Wave Propagation Models for Horizontal Atmospheric Attenuation at 70-115 GHZ

    DTIC Science & Technology

    1988-02-01

    vations inappropiate . Thus, the emphasis in this section 󈧏 be on the assessment of the qualitative agreement between model prediction and observation...39-46. Hogg, D.C., 1969: Statistics on Attenuation of Microwaves by Intense Rain, Bell System Technical Journal, Vol. 48, pp 2949-2963. Hogg, D.C

  3. Floated gravity gradiometer and method

    SciTech Connect

    Lautzenhiser, T.V.; Eisner, M.

    1990-09-11

    This patent describes a gravity gradiometer. It comprises: a housing containing a fluid; a float buoyantly supported within the fluid; means for varying the metacentric height of the float; and means for obtaining a measure of the gravitational gradient acting on the float resulting from varying the metacentric height.

  4. Tethered float liquid level sensor

    SciTech Connect

    Daily, III, William Dean

    2016-09-06

    An apparatus for sensing the level of a liquid includes a float, a tether attached to the float, a pulley attached to the tether, a rotation sensor connected to the pulley that senses vertical movement of said float and senses the level of the liquid.

  5. Compound floating pivot micromechanisms

    DOEpatents

    Garcia, Ernest J.

    2001-04-24

    A new class of tilting micromechanical mechanisms have been developed. These new mechanisms use compound floating pivot structures to attain far greater tilt angles than are practical using other micromechanical techniques. The new mechanisms are also capable of bi-directional tilt about multiple axes.

  6. Thomas floats through Zvezda

    NASA Image and Video Library

    2005-07-28

    S114-E-5588 (28 July 2005) --- Astronaut Andrew S.W. Thomas may be reminiscing about his long duration stay aboard Russia's late Mir space station as he floats about the International Space Station during STS-114 flight day three activities.

  7. Commercial Float Zone Furnace

    NASA Image and Video Library

    1996-05-25

    S77-E-5093 (25 May 1996) --- Astronaut Marc Garneau, mission specialist representing the Canadian Space Agency (CSA), makes a visual check of the Commercial Float Zone Furnace (CFZF), a single-rack-mounted facility in the Spacehab Module onboard the Earth-orbiting Space Shuttle Endeavour. The scene was recorded with an Electronic Still Camera (ESC).

  8. The floating anchored craniotomy.

    PubMed

    Gutman, Matthew J; How, Elena; Withers, Teresa

    2017-01-01

    The "floating anchored" craniotomy is a technique utilized at our tertiary neurosurgery institution in which a traditional decompressive craniectomy has been substituted for a floating craniotomy. The hypothesized advantages of this technique include adequate decompression, reduction in the intracranial pressure, obviating the need for a secondary cranioplasty, maintained bone protection, preventing the syndrome of the trephined, and a potential reduction in axonal stretching. The bone plate is re-attached via multiple loosely affixed vicryl sutures, enabling decompression, but then ensuring the bone returns to its anatomical position once cerebral edema has subsided. From the analysis of 57 consecutive patients analyzed at our institution, we have found that the floating anchored craniotomy is comparable to decompressive craniectomy for intracranial pressure reduction and has some significant theoretical advantages. Despite the potential advantages of techniques that avoid the need for a second cranioplasty, they have not been widely adopted and have been omitted from trials examining the utility of decompressive surgery. This retrospective analysis of prospectively collected data suggests that the floating anchored craniotomy may be applicable instead of decompressive craniectomy.

  9. Why Do Things Float?

    ERIC Educational Resources Information Center

    Selley, Nicholas

    1993-01-01

    Combines two strands: one being an exposition of the variety of explanations which are given for the phenomenon of floating; the other being the pedagogical implications which arise from the use of alternative models in science. Attention is drawn to the ethical questions that may arise when primary science seems to conflict with accepted…

  10. Attenuation Distance of Low Frequency Waves Upstream of the Pre-Dawn Bow Shock: GEOTAIL snd ISEE-3 Comparison

    NASA Technical Reports Server (NTRS)

    Sugiyama, T.; Terasawa, T.; Kawano, H.; Yamamoto, T.; Kokubun, S.; Frank, L.; Ackerson, K.; Tsurutani, B.

    1994-01-01

    This paper presents a statistical study of the spatial distribution of low frequency waves in the region upstream of the pre-dawn to dawn side bow shock using both GEOTAIL and ISEE-3 magnetometer data.

  11. Anomalies in Giant Quantum Attenuation of Sound Waves in Bismuth at High Magnetic Fields. I. Temperature and Frequency Dependences

    NASA Astrophysics Data System (ADS)

    Mase, Shoichi; Fukami, Takeshi; Mori, Masatoshi; Akinaga, Masahiro; Yamaguchi, Toshinobu; Shiraishi, Naotaka

    1980-04-01

    A reinvestigation has been made of an anomaly in the temperature dependence of the ultrasonic attenuation in bismuth, which is observed when an electron Landau level and a hole Landau level approach simultaneously to the Fermi level at high magnetic fields and at low temperatures. It has been found that in the most anomalous case the anomaly in the temperature dependence accompanies an anomalous frequency dependence and these are quite sensitive to physical imperfections in bismuth. On the basis if Kuramoto’s theory of sound attenuation which is taking account of the short-range electron-hole correlation, the experimental results are analyzed, and it is suggested that one more additional term is required to explain the present anomalous data.

  12. The upper mantle structure of the central Rio Grande rift region from teleseismic P and S wave travel time delays and attenuation

    USGS Publications Warehouse

    Slack, P.D.; Davis, P.M.; Baldridge, W.S.; Olsen, K.H.; Glahn, A.; Achauer, U.; Spence, W.

    1996-01-01

    The lithosphere beneath a continental rift should be significantly modified due to extension. To image the lithosphere beneath the Rio Grande rift (RGR), we analyzed teleseismic travel time delays of both P and S wave arrivals and solved for the attenuation of P and S waves for four seismic experiments spanning the Rio Grande rift. Two tomographic inversions of the P wave travel time data are given: an Aki-Christofferson-Husebye (ACH) block model inversion and a downward projection inversion. The tomographic inversions reveal a NE-SW to NNE-SSW trending feature at depths of 35 to 145 km with a velocity reduction of 7 to 8% relative to mantle velocities beneath the Great Plains. This region correlates with the transition zone between the Colorado Plateau and the Rio Grande rift and is bounded on the NW by the Jemez lineament, a N52??E trending zone of late Miocene to Holocene volcanism. S wave delays plotted against P wave delays are fit with a straight line giving a slope of 3.0??0.4. This correlation and the absolute velocity reduction imply that temperatures in the lithosphere are close to the solidus, consistent with, but not requiring, the presence of partial melt in the mantle beneath the Rio Grande rift. The attenuation data could imply the presence of partial melt. We compare our results with other geophysical and geologic data. We propose that any north-south trending thermal (velocity) anomaly that may have existed in the upper mantle during earlier (Oligocene to late Miocene) phases of rifting and that may have correlated with the axis of the rift has diminished with time and has been overprinted with more recent structure. The anomalously low-velocity body presently underlying the transition zone between the core of the Colorado Plateau and the rift may reflect processes resulting from the modern (Pliocene to present) regional stress field (oriented WNW-ESE), possibly heralding future extension across the Jemez lineament and transition zone.

  13. A new multi-domain method based on an analytical control surface for linear and second-order mean drift wave loads on floating bodies

    NASA Astrophysics Data System (ADS)

    Liang, Hui; Chen, Xiaobo

    2017-10-01

    A novel multi-domain method based on an analytical control surface is proposed by combining the use of free-surface Green function and Rankine source function. A cylindrical control surface is introduced to subdivide the fluid domain into external and internal domains. Unlike the traditional domain decomposition strategy or multi-block method, the control surface here is not panelized, on which the velocity potential and normal velocity components are analytically expressed as a series of base functions composed of Laguerre function in vertical coordinate and Fourier series in the circumference. Free-surface Green function is applied in the external domain, and the boundary integral equation is constructed on the control surface in the sense of Galerkin collocation via integrating test functions orthogonal to base functions over the control surface. The external solution gives rise to the so-called Dirichlet-to-Neumann [DN2] and Neumann-to-Dirichlet [ND2] relations on the control surface. Irregular frequencies, which are only dependent on the radius of the control surface, are present in the external solution, and they are removed by extending the boundary integral equation to the interior free surface (circular disc) on which the null normal derivative of potential is imposed, and the dipole distribution is expressed as Fourier-Bessel expansion on the disc. In the internal domain, where the Rankine source function is adopted, new boundary integral equations are formulated. The point collocation is imposed over the body surface and free surface, while the collocation of the Galerkin type is applied on the control surface. The present method is valid in the computation of both linear and second-order mean drift wave loads. Furthermore, the second-order mean drift force based on the middle-field formulation can be calculated analytically by using the coefficients of the Fourier-Laguerre expansion.

  14. Microwave variable waveguide attenuator.

    PubMed

    Fabeni, P; Mugnai, D; Pazzi, G P; Ranfagni, A

    2008-06-01

    A new type of cutoff attenuator is presented. The attenuator works in the X-band in conditions of almost perfect matching. This means that the phase of the wave, which propagates inside the guide, does not suffer sensible variation in the passage between X- and K(u)-bands. Moreover, the attenuator works directly in the X-band, avoiding the passage between waveguide and cable, thus eliminating spurious effects due to this (double) passage. Experimental results of attenuation and dephasing using a prototype are also presented.

  15. Prototype Scale Mooring Load and Transmission Tests for a Floating Tire Breakwater.

    DTIC Science & Technology

    1978-04-01

    laboratory research into the wave transmission and mooring load characteristics of floating tire breakwaters. Kame l and Davidson (1968) conducted model...Floating Tire Break- waters ,” Marine Technical Report No. 54, University of Rhode Island, Kings ton , R.L , Apr. 1977. KAME L, A.M ., and DAVIDSON , D.D

  16. Three-dimensional P wave attenuation and velocity upper mantle tomography of the southern Apennines-Calabrian Arc subduction zone

    NASA Astrophysics Data System (ADS)

    Monna, Stephen; Dahm, Torsten

    2009-06-01

    We propose a 3-D crust-upper mantle seismic attenuation (QP) model of the southern Apennines-Calabrian Arc subduction zone together with a 3-D velocity (VP) model. The QP model is calculated from relative t* using the spectral ratio method and the VP from traveltime data. The final data set used for the inversion of the VP model consists of 2400 traveltime arrivals recorded by 34 short-period stations that are part of the Italian National Seismic Network, and for the QP model, 2178 Pn phases recorded by a subset of 32 stations. Traveltimes and waveforms come from 272 intermediate-depth Calabrian slab events. This 3-D model of attenuation, together with the 3-D velocity model, improves our knowledge of the slab/mantle wedge structure and can be a starting point in determining the physical state of the asthenosphere (i.e., its temperature, the presence of melt and/or fluids) and its relation to volcanism found in the study area. Main features of the QP and VP models show that the mantle wedge/slab, in particular, the area of highest attenuation, is located in a volume underlying the Marsili Basin. The existence and shape of this main low-QP (and low-VP) anomaly points to slab dehydration and fluid/material flow, a process that may explain the strong geochemical affinities between the subduction-related magmas from Stromboli and Vesuvius. Other interesting features in the models are strong lateral variations in QP and VP that are put in relation with known important tectonic structures and volcanic centers in the area.

  17. Dispersion and attenuation on the Brillouin sound waves of a lubricant: Di(2-ethylhexyl) sebacate under high pressures

    NASA Astrophysics Data System (ADS)

    Fujita, Yoshitaka; Kobayashi, Hiroshi

    2011-08-01

    The Brillouin spectra of di(2-ethylhexyl) sebacate, which is a liquid lubricant known as DOS, were measured at up to 5 GPa at 25 °C and up to 2.5 GPa at 80 °C. At 25 °C, the Brillouin frequency linewidth (acoustic attenuation) has a large maximum at 0.1 MPa, and at 80 °C, it has a large broad maximum at 0.8 GPa. The Brillouin frequency shift (sound velocity) and linewidth obtained indicate that the large dispersion of the sound velocities of DOS occurs from 0.1 MPa at 25 °C and from 0.8 GPa at 80 °C. The origins of this attenuation and dispersion are discussed on the basis of the theory for a viscoelastic liquid. It is proposed that the large acoustic attenuation and dispersion of DOS are due to the production of higher-rank structures with nano-order domains in a polymeric liquid by pressurization. The results show that DOS is strongly viscoelastic above 0.8 GPa at 80 °C, but it is not viscous below 0.8 GPa at 80 °C, with the disappearance of the frequency dispersion. The result obtained is used to explain a limiting shear stress observed in a traction oil. Above a given sliding speed, the oil reaches the region of temperature and pressure in which its viscosity decreases with increasing shear rate and conveys a constant torque above some high shear rate. Then, the oil flows as a plastic solid at a limiting shear stress. These findings regarding the dynamical properties of DOS under high pressures are very useful for the production and analysis of lubricants and traction oils.

  18. Effects of atmospheric turbulence on microwave and millimeter wave satellite communications systems. [attenuation statistics and antenna design

    NASA Technical Reports Server (NTRS)

    Devasirvatham, D. M. J.; Hodge, D. B.

    1981-01-01

    A model of the microwave and millimeter wave link in the presence of atmospheric turbulence is presented with emphasis on satellite communications systems. The analysis is based on standard methods of statistical theory. The results are directly usable by the design engineer.

  19. Model-data comparison of high frequency compressional wave attenuation in water-saturated granular medium with bimodal grain size distribution.

    PubMed

    Yang, Haesang; Seong, Woojae; Lee, Keunhwa

    2017-08-19

    Several acoustic models, such as the poro-elastic model, visco-elastic model, and multiple scattering model, have been used for describing the dispersion relation in a porous granular medium. However, these models are based on continuum or scattering theory, and therefore cannot explain the broadband measurements in cases where scattering and non-scattering losses co-exist. Additionally, since the models assume that the porous granular medium consists of grains of identical size (unimodal size distribution), the models does not account for the behavior of wave dispersion in a medium that has a distribution of differing grain sizes. As an alternative approach, this study proposes a new broadband attenuation model that describes the high frequency dispersion relation for the p-wave in the case of elastic grain scatterers existing in the background fluid medium. The broadband model combines the Biot-Stoll plus grain contact squirt and shear flow (BICSQS) model and the quasicrystalline approximation (QCA) multiple scattering model. Additionally, distribution of grain size effect is examined rudimentarily through consideration of bimodal grain size distribution. Through the quantitative analysis of the broadband model and measured data, it is shown that the model can explain the attenuation dependencies of frequency and grain size distribution for a water-saturated granular medium in the frequency range from 350kHz to 1.1MHz. This study can be applied to the high frequency acoustic SONAR modeling and design in the water-saturated environment. Copyright © 2017 Elsevier B.V. All rights reserved.

  20. Attenuation of Lg waves in the New Madrid seismic zone of the central United States using the coda normalization method

    NASA Astrophysics Data System (ADS)

    Nazemi, Nima; Pezeshk, Shahram; Sedaghati, Farhad

    2017-08-01

    Unique properties of coda waves are employed to evaluate the frequency dependent quality factor of Lg waves using the coda normalization method in the New Madrid seismic zone of the central United States. Instrument and site responses are eliminated and source functions are isolated to construct the inversion problem. For this purpose, we used 121 seismograms from 37 events with moment magnitudes, M, ranging from 2.5 to 5.2 and hypocentral distances from 120 to 440 km recorded by 11 broadband stations. A singular value decomposition (SVD) algorithm is used to extract Q values from the data, while the geometric spreading exponent is assumed to be a constant. Inversion results are then fitted with a power law equation from 3 to 12 Hz to derive the frequency dependent quality factor function. The final results of the analysis are QVLg (f) = (410 ± 38) f0.49 ± 0.05 for the vertical component and QHLg (f) = (390 ± 26) f0.56 ± 0.04 for the horizontal component, where the term after ± sign represents one standard error. For stations within the Mississippi embayment with an average sediment depth of 1 km around the Memphis metropolitan area, estimation of quality factor using the coda normalization method is not well-constrained at low frequencies (f < 3 Hz). There may be several reasons contributing to this issue, such as low frequency surface wave contamination, site effects, or even a change in coda wave scattering regime which can exacerbate the scatter of the data.

  1. Effects of Heterogeneities on the Propagation, Scattering and Attenuation of Seismic Waves and the Characterization of Seismic Source

    DTIC Science & Technology

    1985-01-01

    applications of the Gaussian beam method. The Gaussian beam method is a variation of both the asymptotic ray method [Cerveny et . al .. 1977] and the...Popov [1981], Popov [1981. 19821 and Cerveny et . al . [1982]. These studies were based on th«? scalar wave equation The elastic case was first derived...for which the examples are given, and follows the results of Cerveny et . al . [1982], Cerveny and Psencik [1983a]. and Cerveny [1983]. Before solving

  2. Velocity and attenuation of shear waves in the phantom of a muscle-soft tissue matrix with embedded stretched fibers

    NASA Astrophysics Data System (ADS)

    Rudenko, O. V.; Tsyuryupa, S. N.; Sarvazyan, A. P.

    2016-09-01

    We develop a theory of the elasticity moduli and dissipative properties of a composite material: a phantom simulating muscle tissue anisotropy. The model used in the experiments was made of a waterlike polymer with embedded elastic filaments imitating muscle fiber. In contrast to the earlier developed phenomenological theory of the anisotropic properties of muscle tissue, here we obtain the relationship of the moduli with characteristic sizes and moduli making up the composite. We introduce the effective elasticity moduli and viscosity tensor components, which depend on stretching of the fibers. We measure the propagation velocity of shear waves and the shear viscosity of the model for regulated tension. Waves were excited by pulsed radiation pressure generated by modulated focused ultrasound. We show that with increased stretching of fibers imitating muscle contraction, an increase in both elasticity and viscosity takes place, and this effect depends on the wave propagation direction. The results of theoretical and experimental studies support our hypothesis on the protective function of stretched skeletal muscle, which protects bones and joints from trauma.

  3. T-wave amplitude attenuation/augmentation in patients with changing edematous states: implications for patients with congestive heart failure.

    PubMed

    Madias, John E

    2007-01-01

    Since peripheral edema impacts the entire electrocardiographic curve, it was hypothesized that it would also affect T waves. The amplitude of T waves were measured in all electrocardiographic leads and a sum (SigmaT) was calculated in 28 patients with and 28 patients without peripheral edema (controls). For patients with peripheral edema, SigmaT on admission was 21.9+/-10.6 mm and SigmaT at peak weight was 8.3+/-6.3 mm (P=.0005). For patients with peripheral edema who subsequently lost weight, SigmaT at peak weight was 7.2+/-6.1 mm and SigmaT at the lowest weight was 14.1+/-12.2 (P=.006). For controls, SigmaT from admission and SigmaT from discharge were 24.4+/-16.9 mm and 24.7+/-15.7 mm (P=.82), respectively. Percent change (Delta%SigmaT) from admission to peak weight correlated with Delta% in weight (r=0.58; P=.001) and Delta% in the sum of QRS complexes (SigmaQRS) (r=0.71; P=.00005). Delta%SigmaT from peak weight to the lowest weight correlated with the corresponding Delta%SigmaQRS (r=0.65; P=.02). Changes in T waves with development and alleviation of peripheral edema mirror the changes shown by the QRS complexes and may be useful in the treatment of patients with congestive heart failure or other edematous states.

  4. FLOPAK: FLOATING POINT PROGRAMING PACKAGE,

    DTIC Science & Technology

    FLOPAK is a Packard-Bell 250 Computer semi-automatic, floating - point programing system which may be operated simultaneously in either of two modes...250 floating - point system available which may be used in real-time control. The system was originally designed to solve a real-time communication problem....The first is a non-time optimized mode which may be used by inex perienced coders; the second mode is a high-speed, fully time-optimized floating

  5. Air-Deployable Profiling Floats for Tropical Cyclone Research

    NASA Astrophysics Data System (ADS)

    Jayne, S. R.; Robbins, P.; Owens, B.; Ekholm, A.; Dufour, J. E.; Sanabia, E.

    2016-02-01

    The development of a smaller profiling float that can be launched from Hurricane Hunter aircraft offers the opportunity to monitor the upper-ocean thermal structure over a time span of many months. These Argo-type profiling floats can be deployed in advance of, or during, a tropical cyclone from any aircraft equipped with an A-sized (AXBT) launch tube, or from the stern ramp of a C-130. The floats have the same dimensions as an AXBT and weigh about 8.5 kg. Upon deployment, the floats parachute to the surface, detach and automatically begin their programmed mission. The recorded temperature data is averaged over 1-meter bins that are reported back via the Iridium satellite phone network, which is then automatically processed and posted to the GTS. The floats are also reprogrammable via the 2-way communication afforded by Iridium. We report on the results of deployments during the 2014 and 2015 hurricane seasons. Unique observations of the ocean response from Hurricane Ignacio are particularly noteworthy and will be presented. Further plans for continued development of floats include measuring salinity (from an inductive conductivity sensor) and observations of the surface wave field (measured by an onboard accelerometer) will also be described.

  6. Floating-diffusion electrometer with adjustable sensitivity

    NASA Technical Reports Server (NTRS)

    Tower, John R. (Inventor)

    1989-01-01

    The effective capacitance of the floating diffusion in a floating-diffusion electrometer is modified to adjust electrometer sensitivity. This is done by changing the direct potential applied to a gate electrode proximate to the floating diffusion.

  7. Floating Oil-Spill Containment Device

    NASA Technical Reports Server (NTRS)

    Jones, Jack A.

    2012-01-01

    Previous oil containment booms have an open top that allows natural gas to escape, and have significant oil leakage due to wave action. Also, a subsea pyramid oil trap exists, but cannot move relative to moving oil plumes from deepsea oil leaks. The solution is to have large, moveable oil traps. One version floats on the sea surface and has a flexible tarp cover and a lower weighted skirt to completely entrap the floating oil and natural gas. The device must have at least three sides with boats pulling at each apex, and sonar or other system to track the slowly moving oil plume, so that the boats can properly locate the booms. The oil trap device must also have a means for removal of the oil and the natural gas. A second design version has a flexible pyramid cover that is attached by lines to ballast on the ocean floor. This is similar to fixed, metal pyramid oil capture devices in the Santa Barbara Channel off the coast of California. The ballast lines for the improved design, however, would have winches that can move the pyramid to always be located above the oil and gas plume. A third design is a combination of the first two. It uses a submerged pyramid to trap oil, but has no anchor and uses boats to locate the trap. It has ballast weights located along the bottom of the tarp and/or at the corners of the trap. The improved floating oil-spill containment device has a large floating boom and weighted skirt surrounding the oil and gas entrapment area. The device is triangular (or more than three sides) and has a flexible tarp cover with a raised gas vent area. Boats pull on the apex of the triangles to maintain tension and to allow the device to move to optimum locations to trap oil and gas. The gas is retrieved from a higher buoyant part of the tarp, and oil is retrieved from the floating oil layer contained in the device. These devices can be operated in relatively severe weather, since waves will break over the devices without causing oil leaking. Also, natural

  8. Wave simulation in 2D heterogeneous transversely isotropic porous media with fractional attenuation: A Cartesian grid approach

    NASA Astrophysics Data System (ADS)

    Blanc, Emilie; Chiavassa, Guillaume; Lombard, Bruno

    2014-10-01

    A time-domain numerical modeling of transversely isotropic Biot poroelastic waves is proposed in two dimensions. The viscous dissipation occurring in the pores is described using the dynamic permeability model developed by Johnson-Koplik-Dashen (JKD). Some of the coefficients in the Biot-JKD model are proportional to the square root of the frequency. In the time-domain, these coefficients introduce shifted fractional derivatives of order 1/2, involving a convolution product. Based on a diffusive representation, the convolution kernel is replaced by a finite number of memory variables that satisfy local-in-time ordinary differential equations, resulting in the Biot-DA (diffusive approximation) model. The properties of both the Biot-JKD and the Biot-DA models are analyzed: hyperbolicity, decrease of energy, dispersion. To determine the coefficients of the diffusive approximation, two approaches are analyzed: Gaussian quadratures and optimization methods in the frequency range of interest. The nonlinear optimization is shown to be the better way of determination. A splitting strategy is then applied to approximate numerically the Biot-DA equations. The propagative part is discretized using a fourth-order ADER scheme on a Cartesian grid, whereas the diffusive part is solved exactly. An immersed interface method is implemented to take into account heterogeneous media on a Cartesian grid and to discretize the jump conditions at interfaces. Numerical experiments are presented. Comparisons with analytical solutions show the efficiency and the accuracy of the approach, and some numerical experiments are performed to investigate wave phenomena in complex media, such as multiple scattering across a set of random scatterers.

  9. Performance of floating oil booms in unsheltered waters

    NASA Astrophysics Data System (ADS)

    Iglesias, Gregorio; Castro, Alberte

    2013-04-01

    Oil booms are a fundamental tool to diminish the impact of an oil spill. They tend to perform reasonably well in sheltered waters, e.g. within a harbour. However, their performance is often inadequate in open water conditions, under waves, winds and currents. And it is precisely in those conditions that they are needed if oil slicks are to be prevented from reaching certain particularly sensitive areas, such as estuaries, rias, etc. (Castro et al., 2010; Iglesias et al., 2010). In this work the performance of floating oil booms under waves and currents is assessed on the basis of laboratory experiments carried out in a state-of-the-art wave-current flume. Different oil boom models are used, representative of booms with long and short skirts and with different weights. The results show that different booms behave very differently under waves and currents, hence the importance of selecting the boom design that is appropriate for the actual conditions under which it will have to contain the oil slick. Thus, different oil booms should be used for different areas. References A. Castro, G. Iglesias, R. Carballo, J.A. Fraguela, 2010. Floating boom performance under waves and currents, Journal of Hazardous Materials 174, 226-235 G. Iglesias, A.Castro, J.A.Fraguela, 2010. Artificial intelligence applied to floating boom behavior under waves and currents, Ocean Engineering 37, 1513-1521.

  10. Does It Sink or Float?

    ERIC Educational Resources Information Center

    McDonald, Judith Richards

    2012-01-01

    This activity is designed to teach prekindergarten to second grade students about the concept of sink or float through an inquiry activity. Students will use familiar objects to predict and test the properties of sink and float. Background information is offered to teachers to assist them with this activity. This lesson begins with an engaging…

  11. BEST POSSIBLE FLOATING POINT ARITHMETIC.

    DTIC Science & Technology

    The report presents an algorithm for floating point arithmetic, using single-length arithmetic registers, which yields the most accurate...approximation which can be expressed in the given floating point format, the greatest lower bound, or the least upper bound for the result of the operation

  12. Does It Sink or Float?

    ERIC Educational Resources Information Center

    McDonald, Judith Richards

    2012-01-01

    This activity is designed to teach prekindergarten to second grade students about the concept of sink or float through an inquiry activity. Students will use familiar objects to predict and test the properties of sink and float. Background information is offered to teachers to assist them with this activity. This lesson begins with an engaging…

  13. RADIO FREQUENCY ATTENUATOR

    DOEpatents

    Giordano, S.

    1963-11-12

    A high peak power level r-f attenuator that is readily and easily insertable along a coaxial cable having an inner conductor and an outer annular conductor without breaking the ends thereof is presented. Spaced first and second flares in the outer conductor face each other with a slidable cylindrical outer conductor portion therebetween. Dielectric means, such as water, contact the cable between the flares to attenuate the radio-frequency energy received thereby. The cylindrical outer conductor portion is slidable to adjust the voltage standing wave ratio to a low level, and one of the flares is slidable to adjust the attenuation level. An integral dielectric container is also provided. (AFC)

  14. Ground Motion Attenuation and Shear-Wave Splitting Analyses for the November 2011 M5.7 Prague, Oklahoma Earthquake

    NASA Astrophysics Data System (ADS)

    Sumy, D. F.; Cochran, E. S.; Keranen, K. M.; Neighbors, C.; Atkinson, G. M.

    2014-12-01

    During November 2011, three M≥5.0 earthquakes and thousands of aftershocks occurred on and near the Wilzetta fault, a structurally complex ~200 km long, Pennsylvanian-aged fault near Prague, Oklahoma, in close proximity to several active wastewater injection wells. All three M≥5.0 earthquakes had strike-slip mechanisms consistent with rupture on three independent focal planes, suggesting activation of three different strands of the Wilzetta fault. Wastewater injection can cause a buildup of pore fluid pressure along the fault, which decreases the fault strength and may induce earthquakes. Based on the proximity of earthquakes to active fluid injection wells, the unilateral progression of aftershocks away from the initial M5.0 event, and shallow earthquake depths, Keranen et al. [2013] concluded that fluid injection was responsible for inducing the first M5.0 event. Furthermore, Sumy et al. [2014] found that the initial M5.0 event increased the Coulomb stress in the region of the M5.7 mainshock, triggering a cascade of earthquakes along the Wilzetta fault. Thus, while nearby wastewater injection directly induced the initial M5.0 event, this earthquake triggered successive failure along the Wilzetta fault; however, it remains unclear if the additional ruptured fault strands are also influenced by fluid injection. In this study, we explore instrumental ground motions and shear-wave splitting of the November 2011 Prague, Oklahoma sequence, in order to construct ground motion prediction equations (GMPEs) and understand the local stress regime, respectively. We examine ~1,000 earthquakes recorded by a total of 47 seismometers, located within ~150 km of the Wilzetta fault. With respect to GMPEs, initial results suggest that the ground motions are smaller than similar magnitude earthquakes of natural/tectonic origins, and these lower intensities may be a result of lower stress drops [e.g. Hough, 2014]. With respect to shear-wave splitting, we examine quality graded

  15. Circumferentially segmented duct lines optimized for axisymmetric and standing wave sources. [reducing noise from turbofan engines galerkin method acoustic attenuation

    NASA Technical Reports Server (NTRS)

    Watson, W. R.

    1982-01-01

    Optimum and off-optimum properties of circumferentially segmented duct liners are compared with those of uniform liners to identify any potential benefits of circumferentially segmented liners. High- and low-order spinning-mode sources are considered in the study. The solution for the segmented liner is obtained by a multimodal expansion of the segmented-liner eigenmodes in terms of a series of hardwall duct models. The coefficients in the hard-wall series are obtained by using Galerkin's method. Results show that for some frequencies and duct lengths, circumferentially segmented liners scatter energy equally between a higher and lower order circumferential wave number. Studies for higher order spinning-mode sources show that an optimized segmented liner with a hard-wall/soft-wal admittance variation representing an optimum configuration gives better performance than an optimized uniform liner. Overall, the greatest benefit of the segmented liner over the uniform liner occurs under off-optimum conditions. The optimized segmented liner gives more effective broadband performance than the optimized uniform liner.

  16. Experiment study of the motion of the floating offshore turbine

    NASA Astrophysics Data System (ADS)

    Chuang, Tzu-Ching; Hsu, Wen-Yang; Yang, Ray-Yeng; Chen, Yang-Yi

    2016-04-01

    Recently the wind industry moved to offshore areas. The floating wind turbine combined the platform and the mooring system. This research focuses on studying the motion of the floating offshore turbine with a mooring system. The platform, which was developed by the Ship and Ocean Industries R&D Center, had been test in a wave-wind flume in the Tainan Hydraulics Laboratory by using a 1:50 Froude scaling model. In the experiment, the floating offshore turbine was placed in a water flume and exposed to periodic waves at frequencies ranging from 0.22 rad/s - 0.875 rad/s, the wave amplitude is about 2.5 meter, and with the different pretension of the mooring lines. The experiment includes the measurement of damping coefficient from the free decay test and the dynamic response in a sea state. This research compares the motion of the floating offshore turbine with the different pretension of the mooring lines, and the model provides comprehensive data for the operational, design, and survival seas states, as well as the calibration and improvement of the existing design and performance of numerical models.

  17. Water wave energy transducer

    SciTech Connect

    Lamberti, J.

    1980-01-22

    A water wave energy transducer for converting the motion of a water wave into a controlled mechanical movement such as rotational motion suitable for actuating an electrical generator is disclosed. The transducer comprises a float member floatingly moored in a water body having waves and/or tidal movement, such as a seashore. A power gear is rotatably mounted in a swing block on the float with a power shaft extending from the power gear to laterally spaced drive bevel gears mounted for rotation with the power gear. These drive bevel gears are coupled to a transmission on the float comprising one-way drive clutches transmitting rotational energy to the drive shaft of a generator or the like to provide rotational energy on both up and down movement of the float. A rack is pivotally anchored in the water body, extends up through the float and is slideable with respect to the power gear of the swing block, so that movement of the float with respect to the rack will provide rotation of the power gear.

  18. Floating Silicon Method

    SciTech Connect

    Kellerman, Peter

    2013-12-21

    The Floating Silicon Method (FSM) project at Applied Materials (formerly Varian Semiconductor Equipment Associates), has been funded, in part, by the DOE under a “Photovoltaic Supply Chain and Cross Cutting Technologies” grant (number DE-EE0000595) for the past four years. The original intent of the project was to develop the FSM process from concept to a commercially viable tool. This new manufacturing equipment would support the photovoltaic industry in following ways: eliminate kerf losses and the consumable costs associated with wafer sawing, allow optimal photovoltaic efficiency by producing high-quality silicon sheets, reduce the cost of assembling photovoltaic modules by creating large-area silicon cells which are free of micro-cracks, and would be a drop-in replacement in existing high efficiency cell production process thereby allowing rapid fan-out into the industry.

  19. Floating on oil.

    PubMed

    Zhang, Jihua; Deng, Xu; Butt, Hans-Jürgen; Vollmer, Doris

    2014-09-09

    We demonstrate that disk-shaped steel meshes coated with a superamphiphobic layer are able to float on water and on organic liquids. A coated disk-shaped steel mesh of 1 cm radius has a loading capacity of 17 mN in water and still remarkable 9 mN in n-hexadecane. Experimentally measured supporting forces and loading capacities agree well with theoretical predictions. Inspired by the giant water lily, pan-shaped "oil lilies" with even higher loading capacity and artificial oil striders carrying more than 10 times their own weight are designed. Even after the artificial devices are fully immersed into different liquids, they show self-draining properties due to capillary forces.

  20. Floating into Deep Space

    NASA Astrophysics Data System (ADS)

    La Frenais, R.; Saraceno, T.; Powell, J.

    2014-04-01

    Is it possible for spaceflight to become more sustainable? Artist and architect Tomas Saraceno proposes a long-term artscience research project based on his initial work with solar balloons to join with the efforts of engineers such as John Powell, working on the Airship to Orbit experiments, which describe a three stage process of using airships to fly to a large suborbital "Dark Sky Station' then literally floating into orbit with additional electrical and chemical propulsion. (See: http://www.jpaerospace.com) In his artworks Tomás Saraceno proposes cell-like flying cities as possible architectonic living spaces in direct reference to Buckminster Fuller's Cloud Nine (circa 1960). The fantastic architectural utopia Cloud Nine consists of a freely floating sphere measuring one mile in diameter that offers living space to several autonomous communities encompassing thousands of inhabitants each. The notion of the cloud is essential to the artist's work. The cloud as metaphor stands for artistic intention, for the meaning of territory and border in today's (urban) society, and for exploring possibilities for the sustainable development of the human living environment. In Saraceno's work this environment is not limited to the earth, but is explicitly conceived to reach into outer space. (Biomimetic Constructions- On the works of Tomás Saraceno By Katharina Schlüter) Saraceno is also interested in human factors experiments using his existing constructions as analogue environments for living on Mars and is proposing carry out a series of workshops, experiments and solar balloon launces in White Sands desert in early 2016 in collaboration with the curator Dr Rob La Frenais, the Rubin Center at The University of Texas at El Paso and various scientific partners.

  1. Calculation Of Pneumatic Attenuation In Pressure Sensors

    NASA Technical Reports Server (NTRS)

    Whitmore, Stephen A.

    1991-01-01

    Errors caused by attenuation of air-pressure waves in narrow tubes calculated by method based on fundamental equations of flow. Changes in ambient pressure transmitted along narrow tube to sensor. Attenuation of high-frequency components of pressure wave calculated from wave equation derived from Navier-Stokes equations of viscous flow in tube. Developed to understand and compensate for frictional attenuation in narrow tubes used to connect aircraft pressure sensors with pressure taps on affected surfaces.

  2. Calculation Of Pneumatic Attenuation In Pressure Sensors

    NASA Technical Reports Server (NTRS)

    Whitmore, Stephen A.

    1991-01-01

    Errors caused by attenuation of air-pressure waves in narrow tubes calculated by method based on fundamental equations of flow. Changes in ambient pressure transmitted along narrow tube to sensor. Attenuation of high-frequency components of pressure wave calculated from wave equation derived from Navier-Stokes equations of viscous flow in tube. Developed to understand and compensate for frictional attenuation in narrow tubes used to connect aircraft pressure sensors with pressure taps on affected surfaces.

  3. Floating gate circuits in MOSIS

    NASA Astrophysics Data System (ADS)

    Mann, James R.

    1990-11-01

    The MOSIS foundry offers a two-poly CMOS process that can be used as a floating gate technology, albeit not with the same performance as commercial EEPROM foundries. This report characterizes the structures and programming techniques necessary to build floating gate structures and associated high-voltage addressing circuitry on the low-noise analog process available through MOSIS. Techniques that are used include Fowler-Nordheim tunneling, channel hot-electron injection, and avalanche injection. The dielectric materials between the floating gate and both the control gate and substrate are characterized. Unconventional lightly doped drain FET devices and additional circuit techniques for handling the high-voltage programming signals are presented.

  4. Boat powered by sea waves

    SciTech Connect

    Gargos, G.

    1984-11-06

    A boat having an external float pivotally fixed to the boat. Through linkage, the motion of the float relative to the boat resulting from wave motion drives a dual cylinder pump. The pump admits water from the body of water in which the boat is suspended and pressurizes that water for direction aft as a means for propulsion.

  5. Ipsilateral Floating Hip and Floating Knee - A Rare Entity.

    PubMed

    Yashavantha Kumar, C; Nalini, K B; Nagaraj, Prashanth; Jawali, Abhijith

    2013-01-01

    Ipsilateral floating hip and floating knee are very rare injuries. These injuries so uncommon that only three cases of similar kind have been reported. These injuries are due to high velocity injuries following motor vehicle accidents. Management of such complex injuries is a challenging task even in experienced hands as there are no standard treatment guidelines for such fractures. We hereby report a 20 yr old male who sustained ipsilateral floating hip and ipsilateral floating knee injuries following motor vehicle accident. Patient was stabilized initially and later taken up for surgery. Patient was treated with interlocking nail for femur and tibia in the same sitting whereas acetabulam fracture was managed conservatively. At five months all the fractures united well with restoration of good range of motion in both hip and knee. Ipsilateral floating knee and floating hip are very rare injuries seen following high velocity motor vehicle accidents. There are no standard guidelines for treatment of those fractures as only a few cases of similar kind have been reported in literature. Early fixation and aggressive mobilization ensures fracture union and fewer complications.

  6. Ultrasonic Attenuation in Zircaloy-4

    SciTech Connect

    Gomez, M.P.; Banchik, A.D.; Lopez Pumarega, M.I.; Ruzzante, J.E.

    2005-04-09

    In this work the relationship between Zircaloy-4 grain size and ultrasonic attenuation behavior was studied for longitudinal waves in the frequency range of 10-90 MHz. The attenuation was analyzed as a function of frequency for samples with different mechanical and heat treatments having recrystallized and Widmanstatten structures with different grain size. The attenuation behavior was analyzed by different scattering models, depending on grain size, wavelength and frequency.

  7. Sellers floats into Node 1

    NASA Image and Video Library

    2010-05-16

    ISS023-E-041819 (16 May 2010) --- NASA astronaut Piers Sellers, STS-132 mission specialist, floats through a hatch on the International Space Station while space shuttle Atlantis remains docked with the station.

  8. De Winne floats through FGB

    NASA Image and Video Library

    2009-06-14

    ISS020-E-008936 (14 June 2009) --- European Space Agency astronaut Frank De Winne, Expedition 20 flight engineer, floats through the Zarya functional cargo block (FGB) of the International Space Station.

  9. De Winne floats through FGB

    NASA Image and Video Library

    2009-06-14

    ISS020-E-008938 (14 June 2009) --- European Space Agency astronaut Frank De Winne, Expedition 20 flight engineer, floats through the Zarya functional cargo block (FGB) of the International Space Station.

  10. NULL Convention Floating Point Multiplier

    PubMed Central

    Ramachandran, Seshasayanan

    2015-01-01

    Floating point multiplication is a critical part in high dynamic range and computational intensive digital signal processing applications which require high precision and low power. This paper presents the design of an IEEE 754 single precision floating point multiplier using asynchronous NULL convention logic paradigm. Rounding has not been implemented to suit high precision applications. The novelty of the research is that it is the first ever NULL convention logic multiplier, designed to perform floating point multiplication. The proposed multiplier offers substantial decrease in power consumption when compared with its synchronous version. Performance attributes of the NULL convention logic floating point multiplier, obtained from Xilinx simulation and Cadence, are compared with its equivalent synchronous implementation. PMID:25879069

  11. NULL convention floating point multiplier.

    PubMed

    Albert, Anitha Juliette; Ramachandran, Seshasayanan

    2015-01-01

    Floating point multiplication is a critical part in high dynamic range and computational intensive digital signal processing applications which require high precision and low power. This paper presents the design of an IEEE 754 single precision floating point multiplier using asynchronous NULL convention logic paradigm. Rounding has not been implemented to suit high precision applications. The novelty of the research is that it is the first ever NULL convention logic multiplier, designed to perform floating point multiplication. The proposed multiplier offers substantial decrease in power consumption when compared with its synchronous version. Performance attributes of the NULL convention logic floating point multiplier, obtained from Xilinx simulation and Cadence, are compared with its equivalent synchronous implementation.

  12. Control development for floating wind

    NASA Astrophysics Data System (ADS)

    Savenije, Feike; Peeringa, Johan

    2014-06-01

    Control of a floating wind turbine has proven to be challenging, but essential for lowering the cost of floating wind energy. Topic of a recent joint R&D project by GustoMSC, MARIN and ECN, is the concept design and verification with coupled simulations and model tests of the GustoMSC Tri-Floater. Only using an integral design approach, including mooring and control design, a cost effective system can be obtained. In this project, ECN developed a general floating wind turbine control strategy and applied this in a case study to the GustoMSC Tri-Floater and the OC3Hywind spar, both equipped with the NREL 5MW RWT. The designed controller ensures stable operation, while maintaining proper speed and power regulation. The motions of the floating support are reduced and substantial load reduction has been achieved.

  13. Floating orbital molecular dynamics simulations.

    PubMed

    Perlt, Eva; Brüssel, Marc; Kirchner, Barbara

    2014-04-21

    We introduce an alternative ab initio molecular dynamics simulation as a unification of Hartree-Fock molecular dynamics and the floating orbital approach. The general scheme of the floating orbital molecular dynamics method is presented. Moreover, a simple but sophisticated guess for the orbital centers is provided to reduce the number of electronic structure optimization steps at each molecular dynamics step. The conservation of total energy and angular momentum is investigated in order to validate the floating orbital molecular dynamics approach with and without application of the initial guess. Finally, a water monomer and a water dimer are simulated, and the influence of the orbital floating on certain properties like the dipole moment is investigated.

  14. Electrically floating, near vertical incidence, skywave antenna

    SciTech Connect

    Anderson, Allen A.; Kaser, Timothy G.; Tremblay, Paul A.; Mays, Belva L.

    2014-07-08

    An Electrically Floating, Near Vertical Incidence, Skywave (NVIS) Antenna comprising an antenna element, a floating ground element, and a grounding element. At least part of said floating ground element is positioned between said antenna element and said grounding element. The antenna is separated from the floating ground element and the grounding element by one or more electrical insulators. The floating ground element is separated from said antenna and said grounding element by one or more electrical insulators.

  15. The quasi-Lagrangian nature of SOFAR floats

    NASA Astrophysics Data System (ADS)

    Riser, Stephen C.

    1982-12-01

    From several simple numerical and analytical model experiments, estimates are made of the times over which quasi-Lagrangian (constant pressure) SOFAR floats are useful followers of truly Lagrangian fluid parcels. A simple, three-dimensional, analytical, time-dependent model, the MCWILLIAMS and FLIERL (1976 Deep-Sea Research, 23, 285-300) Rossby wave fit to the MODE data set, is used as the prototype mid-ocean eddy field. Twenty initially coincident Lagrangian-quasi-Lagrangian pairs of tracers were released at random locations in the field and tracked as a function of time and the root-mean-square amplitude of the field. When the field has an r.m.s. amplitude of 20 cm s -1 at 700 m, an isobaric SOFAR float represents fluid parcel motion for times of the order of the period of the fastest Rossby wave in the field, 129 days. When a field of internal gravity waves (a spectrum of inertial oscillations and baroclinic semidiurnal tides) is added to the Rossby wave field, the representative time is reduced by about 30%. The 700-m results provide a lower bound on estimates of the time that float motion is representative of parcel motion at greater depths.

  16. Floating wind turbine system

    NASA Technical Reports Server (NTRS)

    Viterna, Larry A. (Inventor)

    2009-01-01

    A floating wind turbine system with a tower structure that includes at least one stability arm extending therefrom and that is anchored to the sea floor with a rotatable position retention device that facilitates deep water installations. Variable buoyancy for the wind turbine system is provided by buoyancy chambers that are integral to the tower itself as well as the stability arm. Pumps are included for adjusting the buoyancy as an aid in system transport, installation, repair and removal. The wind turbine rotor is located downwind of the tower structure to allow the wind turbine to follow the wind direction without an active yaw drive system. The support tower and stability arm structure is designed to balance tension in the tether with buoyancy, gravity and wind forces in such a way that the top of the support tower leans downwind, providing a large clearance between the support tower and the rotor blade tips. This large clearance facilitates the use of articulated rotor hubs to reduced damaging structural dynamic loads. Major components of the turbine can be assembled at the shore and transported to an offshore installation site.

  17. Skylab floating ice experiment

    NASA Technical Reports Server (NTRS)

    Campbell, W. J. (Principal Investigator); Ramseier, R. O.; Weaver, R. J.; Weeks, W. F.

    1975-01-01

    The author has identified the following significant results. Coupling of the aircraft data with the ground truth observations proved to be highly successful with interesting results being obtained with IR and SLAR passive microwave techniques, and standard photography. Of particular interest were the results of the PMIS system which operated at 10.69 GHz with both vertical and horizontal polarizations. This was the first time that dual polarized images were obtained from floating ice. In both sea and lake ice, it was possible to distinguish a wide variety of thin ice types because of their large differences in brightness temperatures. It was found that the higher brightness temperature was invariably obtained in the vertically polarized mode, and as the age of the ice increases the brightness temperature increases in both polarizations. Associated with this change in age, the difference in temperature was observed as the different polarizations decreased. It appears that the horizontally polarized data is the most sensitive to variations in ice type for both fresh water and sea ice. The study also showed the great amount of information on ice surface roughness and deformation patterns that can be obtained from X-band SLAR observations.

  18. Floating into Thin Air

    SciTech Connect

    Hazi, A U

    2007-02-06

    On May 18, 2005, a giant helium balloon carrying the High Energy Focusing Telescope (HEFT) sailed into the spring sky over the deserts of New Mexico. The spindly steel and aluminum gondola that houses the optics, detectors, and other components of the telescope floated for 25 hours after its launch from Fort Sumner, New Mexico. For 21 of those hours, the balloon was nearly 40 kilometers above Earth's surface--almost four times higher than the altitude routinely flown by commercial jet aircraft. In the upper reaches of Earth's atmosphere, HEFT searched the universe for x-ray sources from highly energetic objects such as binary stars, galaxy clusters, and supermassive black holes. Before landing in Arizona, the telescope observed and imaged a dozen scientific targets by capturing photons emitted from these objects in the high-energy (hard) x-ray range (above 10 kiloelectronvolts). Among these targets were the Crab synchrotron nebula, the black hole Cygnus X-1 (one of the brightest x-ray sources in the sky), and the blazar 3C454.3. The scientific data gathered from these targets are among the first focused hard x-ray images returned from high altitudes.

  19. Active high-resolution seismic tomography of compressional wave velocity and attenuation structure at Medicine Lake Volcano, Northern California Cascade Range

    NASA Astrophysics Data System (ADS)

    Evans, John R.; Zucca, John J.

    1988-12-01

    We determine compressional wave velocity and attenuation structures for the upper crust beneath Medicine Lake volcano in northeast California using a high-resolution active source seismic tomography method. Medicine Lake volcano is a basalt through rhyolite shield volcano of the Cascade Range, lying east of the range axis. The Pg wave from eight explosive sources which has traveled upward through the target volume to a dense array of 140 seismographs provides 1- to 2-km resolution in the upper 5 to 7 km of the crust beneath the volcano. The experiment tests the hypothesis that Cascade Range volcanoes of this type are underlain only by small silicic magma chambers. We image a low-velocity low-Q region not larger than a few tens of cubic kilometers in volume beneath the summit caldera, supporting the hypothesis. A shallower high-velocity high-density feature, previously known to be present, is imaged for the first time in full plan view; it is east-west elongate, paralleling a topographic lineament between Medicine Lake volcano and Mount Shasta. This lineament is interpreted to be the result of an old crustal weakness now affecting the emplacement of magma, both on direct ascent from the lower crust and mantle and in migration from the shallow silicic chamber to summit vents. Differences between this high-velocity feature and the equivalent feature at Newbeny volcano, a volcano in central Oregon resembling Medicine Lake volcano, may partly explain the scarcity of surface hydrothermal features at Medicine Lake volcano. A major low-velocity low-Q feature beneath the southeast flank of the volcano, in an area with no Holocene vents, is interpreted as tephra, flows, and sediments from the volcano deeply ponded on the downthrown side of the Gillem fault, a normal fault mapped at the surface north of the volcano. A high-Q normal-velocity feature beneath the north rim of the summit caldera may be a small, possibly hot, subsolidus intrusion. A high-velocity low-Q region

  20. Ultrasonic attenuation in pearlitic steel.

    PubMed

    Du, Hualong; Turner, Joseph A

    2014-03-01

    Expressions for the attenuation coefficients of longitudinal and transverse ultrasonic waves are developed for steel with pearlitic microstructure. This type of lamellar duplex microstructure influences attenuation because of the lamellar spacing. In addition, longitudinal attenuation measurements were conducted using an unfocused transducer with 10 MHz central frequency on the cross section of a quenched railroad wheel sample. The dependence of longitudinal attenuation on the pearlite microstructure is observed from the changes of longitudinal attenuation from the quenched tread surface to deeper locations. The results show that the attenuation value is lowest and relatively constant within the quench depth, then increases linearly. The experimental results demonstrate a reasonable agreement with results from the theoretical model. Ultrasonic attenuation provides an important non-destructive method to evaluate duplex microstructure within grains which can be implemented for quality control in conjunction with other manufacturing processes.

  1. Wave action power plant

    SciTech Connect

    Lucia, L.V.

    1982-03-16

    A wave action power plant powered by the action of water waves has a drive shaft rotated by a plurality of drive units, each having a lever pivotally mounted on and extending from said shaft and carrying a weight, in the form of a float, which floats on the waves and rocks the lever up and down on the shaft. A ratchet mechanism causes said shaft to be rotated in one direction by the weight of said float after it has been raised by wave and the wave has passed, leaving said float free to move downwardly by gravity and apply its full weight to pull down on the lever and rotate the drive shaft. There being a large number of said drive units so that there are always some of the weights pulling down on their respective levers while other weights are being lifted by waves and thereby causing continuous rotation of the drive shaft in one direction. The said levers are so mounted that they may be easily raised to bring the weights into a position wherein they are readily accessible for cleaning the bottoms thereof to remove any accumulation of barnacles, mollusks and the like. There is also provided means for preventing the weights from colliding with each other as they independently move up and down on the waves.

  2. Discrete Element Modelling of Floating Debris

    NASA Astrophysics Data System (ADS)

    Mahaffey, Samantha; Liang, Qiuhua; Parkin, Geoff; Large, Andy; Rouainia, Mohamed

    2016-04-01

    Flash flooding is characterised by high velocity flows which impact vulnerable catchments with little warning time and as such, result in complex flow dynamics which are difficult to replicate through modelling. The impacts of flash flooding can be made yet more severe by the transport of both natural and anthropogenic debris, ranging from tree trunks to vehicles, wheelie bins and even storage containers, the effects of which have been clearly evident during recent UK flooding. This cargo of debris can have wide reaching effects and result in actual flood impacts which diverge from those predicted. A build-up of debris may lead to partial channel blockage and potential flow rerouting through urban centres. Build-up at bridges and river structures also leads to increased hydraulic loading which may result in damage and possible structural failure. Predicting the impacts of debris transport; however, is difficult as conventional hydrodynamic modelling schemes do not intrinsically include floating debris within their calculations. Subsequently a new tool has been developed using an emerging approach, which incorporates debris transport through the coupling of two existing modelling techniques. A 1D hydrodynamic modelling scheme has here been coupled with a 2D discrete element scheme to form a new modelling tool which predicts the motion and flow-interaction of floating debris. Hydraulic forces arising from flow around the object are applied to instigate its motion. Likewise, an equivalent opposing force is applied to fluid cells, enabling backwater effects to be simulated. Shock capturing capabilities make the tool applicable to predicting the complex flow dynamics associated with flash flooding. The modelling scheme has been applied to experimental case studies where cylindrical wooden dowels are transported by a dam-break wave. These case studies enable validation of the tool's shock capturing capabilities and the coupling technique applied between the two numerical

  3. Detection of Floating Inputs in Logic Circuits

    NASA Technical Reports Server (NTRS)

    Cash, B.; Thornton, M. G.

    1984-01-01

    Simple modification of oscilloscope probe allows easy detection of floating inputs or tristate outputs in digital-IC's. Oscilloscope probe easily modified with 1/4 W resistor and switch for detecting floating inputs in CMOS logic circuits.

  4. Detection of Floating Inputs in Logic Circuits

    NASA Technical Reports Server (NTRS)

    Cash, B.; Thornton, M. G.

    1984-01-01

    Simple modification of oscilloscope probe allows easy detection of floating inputs or tristate outputs in digital-IC's. Oscilloscope probe easily modified with 1/4 W resistor and switch for detecting floating inputs in CMOS logic circuits.

  5. 40 CFR 65.45 - External floating roof converted into an internal floating roof.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 15 2011-07-01 2011-07-01 false External floating roof converted into an internal floating roof. 65.45 Section 65.45 Protection of Environment ENVIRONMENTAL PROTECTION... External floating roof converted into an internal floating roof. The owner or operator who elects to...

  6. 40 CFR 65.45 - External floating roof converted into an internal floating roof.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 40 Protection of Environment 16 2014-07-01 2014-07-01 false External floating roof converted into an internal floating roof. 65.45 Section 65.45 Protection of Environment ENVIRONMENTAL PROTECTION... External floating roof converted into an internal floating roof. The owner or operator who elects to...

  7. 40 CFR 65.45 - External floating roof converted into an internal floating roof.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 40 Protection of Environment 16 2013-07-01 2013-07-01 false External floating roof converted into an internal floating roof. 65.45 Section 65.45 Protection of Environment ENVIRONMENTAL PROTECTION... External floating roof converted into an internal floating roof. The owner or operator who elects to...

  8. 40 CFR 65.45 - External floating roof converted into an internal floating roof.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 40 Protection of Environment 16 2012-07-01 2012-07-01 false External floating roof converted into an internal floating roof. 65.45 Section 65.45 Protection of Environment ENVIRONMENTAL PROTECTION... External floating roof converted into an internal floating roof. The owner or operator who elects to...

  9. 40 CFR 65.45 - External floating roof converted into an internal floating roof.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 15 2010-07-01 2010-07-01 false External floating roof converted into an internal floating roof. 65.45 Section 65.45 Protection of Environment ENVIRONMENTAL PROTECTION... External floating roof converted into an internal floating roof. The owner or operator who elects...

  10. 32 CFR 935.165 - Floating objects.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 32 National Defense 6 2010-07-01 2010-07-01 false Floating objects. 935.165 Section 935.165... REGULATIONS WAKE ISLAND CODE Public Safety § 935.165 Floating objects. No person may anchor, moor, or beach any boat, barge, or other floating object on Wake Island in any location or manner other than as...

  11. Have Floating Rates Been a Success?

    ERIC Educational Resources Information Center

    Higham, David

    1983-01-01

    Floating exchange rates have not lived up to all expectations, but neither have they performed as badly as some critics have suggested. Examined are the impact of floating rates on balance of payments adjustment, domestic economic policy, and inflation and the claim that floating rates have displayed excessive fluctuations. (Author/RM)

  12. New Directions in Floating-Point Arithmetic

    NASA Astrophysics Data System (ADS)

    Beebe, Nelson H. F.

    2007-12-01

    This article briefly describes the history of floating-point arithmetic, the development and features of IEEE standards for such arithmetic, desirable features of new implementations of floating-point hardware, and discusses work-in-progress aimed at making decimal floating-point arithmetic widely available across many architectures, operating systems, and programming languages.

  13. Have Floating Rates Been a Success?

    ERIC Educational Resources Information Center

    Higham, David

    1983-01-01

    Floating exchange rates have not lived up to all expectations, but neither have they performed as badly as some critics have suggested. Examined are the impact of floating rates on balance of payments adjustment, domestic economic policy, and inflation and the claim that floating rates have displayed excessive fluctuations. (Author/RM)

  14. Float It Down the River.

    ERIC Educational Resources Information Center

    Brendzel, Sharon; Orfan, Lucy; Schuhmacher, Robert

    2000-01-01

    Presents an activity that involves students in a hands-on, creative project in which they use higher order thinking skills while designing and studying the basics of floating devices. Focuses on inquiry, a number of scientific principles, and the relationship between mathematics and science. (ASK)

  15. Floating Ring-Groove Lapper

    NASA Technical Reports Server (NTRS)

    Williams, Robert L., Sr.; Williams, Robert L., Jr.; Chase, Timothy L.

    1992-01-01

    Tool fits out-of-round seal groove and laps it to fine finish without binding. Includes floating lapping pieces riding freely in groove, and are curved to match nominal diameter of groove. One lapping piece tightened so it does not move relative to disk.

  16. Flinking: Neither Floating nor Sinking.

    ERIC Educational Resources Information Center

    Wilson, Roger B.

    1993-01-01

    Describes an activity that challenges students to make an object that, when released under water, does not float up or sink down. The main concept this activity investigates is the density of ordinary objects in comparison to the density of water. (PR)

  17. Flinking: Neither Floating nor Sinking.

    ERIC Educational Resources Information Center

    Wilson, Roger B.

    1993-01-01

    Describes an activity that challenges students to make an object that, when released under water, does not float up or sink down. The main concept this activity investigates is the density of ordinary objects in comparison to the density of water. (PR)

  18. Designing seaplane hulls and