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.
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
WindWaveFloat (WWF): Final Scientific Report
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.
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.
Numerical simulation of a floating buoy in surface waves
NASA Astrophysics Data System (ADS)
Altazin, Thomas; Golay, Frédéric; Fraunié, Philippe
2016-04-01
A numerical method based on volumic penalization is developed to track a floating body in a two phase flows (air and water). Fast computations on parallel computer are performed thanks to an adaptative mesh refinement following a numerical entropy criterion together with a variable time step depending on the mesh size. Applications concern the motion of a floating buoy in a surface wave field and the induced perturbation of the wave and atmospheric fields by the buoy. Presented cases concern a breaking wave and a second order Stokes wave as initial conditions. Acknowledgements : This research was supported by the Modtercom and CHEF projects of Region PACA, when applications on windage of floating buoys are related to the SUBCORAD LEFE-INSU project.
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.
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.
Vibrations of a floating beam on marine waves
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.
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.
Imaging Rayleigh wave attenuation with USArray
NASA Astrophysics Data System (ADS)
Bao, Xueyang; Dalton, Colleen A.; Jin, Ge; Gaherty, James B.; Shen, Yang
2016-04-01
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 travel time 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 travel-time 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.
Relating P-wave attenuation to permeability
Akbar, N.; Dvorkin, J.; Nur, A. . Dept. of Geophysics)
1993-01-01
To relate P-wave attenuation to permeability, the authors examine a three-dimensional (3-D) theoretical model of a cylindrical pore filled with viscous fluid and embedded in an infinite isotropic elastic medium. They calculate both attenuation and permeability as functions of the direction of wave propagation. Attenuation estimates are based on the squirt flow mechanism; permeability is calculated using the Kozeny-Carmen relation. They find that in the case when a plane P-wave propagates parallel to this orientation (Q[sup [minus]1][delta] = 90[degree]), attenuation is always higher than when a wave propagates parallel to this orientation (Q[sup [minus]1][delta] = 0[degree]). The ratio of these two attenuation values Q[sup [minus]1][delta] = 90[degree]/Q[sup [minus]1] = 0[degree] increases with an increasing pore radius and decreasing frequency and saturation. By changing permeability, varying the radius of the pore, they find that the permeability-attenuation relation is characterized by a peak that shifts toward lower permeabilities as frequency decreases. Therefore, the attenuation of a low-frequency wave decreases with increasing permeability. They observe a similar trend on relations between attenuation and permeability experimentally obtained on sandstone samples.
Experimental study of nonlinear behaviors of a free-floating body in waves
NASA Astrophysics Data System (ADS)
He, Ming; Ren, Bing; Qiu, Da-hong
2016-04-01
Nonlinear behaviors of a free-floating body in waves were experimentally investigated in the present study. The experiments were carried out for 6 different wave heights and 6 different wave periods to cover a relatively wide range of wave nonlinearities. A charge-coupled device (CCD) camera was used to capture the real-time motion of the floating body. The measurement data show that the sway, heave and roll motions of the floating body are all harmonic oscillations while the equilibrium position of the sway motion drifts in the wave direction. The drift speed is proportional to wave steepness when the size of the floating body is comparable to the wavelength, while it is proportional to the square of wave steepness when the floating body is relatively small. In addition, the drift motion leads to a slightly longer oscillation period of the floating body than the wave period of nonlinear wave and the discrepancy increases with the increment of wave steepness.
Graphene-Based Waveguide Terahertz Wave Attenuator
NASA Astrophysics Data System (ADS)
Jian-rong, Hu; Jiu-sheng, Li; Guo-hua, Qiu
2016-07-01
We design an electrically controllable terahertz wave attenuator by using graphene. We show that terahertz wave can be confined and propagate on S-shaped graphene waveguide with little radiation losses, and the confined terahertz wave is further manipulated and controlled via external applied voltage bias. The simulated results show that, when chemical potential changes from 0.03 into 0.05 eV, the extinction ratio of the terahertz wave attenuator can be tuned from 1.28 to 39.42 dB. Besides the simplicity, this novel terahertz wave attenuator has advantages of small size (24 × 30 μm2), a low insertion loss, and good controllability. It has a potential application for forthcoming planar terahertz wave integrated circuit fields.
Compressional head waves in attenuative formations
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.
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.
Nonlinear dynamic behaviors of a floating structure in focused waves
NASA Astrophysics Data System (ADS)
Cao, Fei-feng; Zhao, Xi-zeng
2015-12-01
Floating structures are commonly seen in coastal and offshore engineering. They are often subjected to extreme waves and, therefore, their nonlinear dynamic behaviors are of great concern. In this paper, an in-house CFD code is developed to investigate the accurate prediction of nonlinear dynamic behaviors of a two-dimensional (2-D) box-shaped floating structure in focused waves. Computations are performed by an enhanced Constrained Interpolation Profile (CIP)-based Cartesian grid model, in which a more accurate VOF (Volume of Fluid) method, the THINC/SW scheme (THINC: tangent of hyperbola for interface capturing; SW: Slope Weighting), is used for interface capturing. A focusing wave theory is used for the focused wave generation. The wave component of constant steepness is chosen. Comparisons between predictions and physical measurements show good agreement including body motions and free surface profiles. Although the overall agreement is good, some discrepancies are observed for impact pressure on the superstructure due to water on deck. The effect of grid resolution on the results is checked. With a fine grid, no obvious improvement is seen in the global body motions and impact pressures due to water on deck. It is concluded that highly nonlinear phenomena, such as distorted free surface, large-amplitude body motions, and violent impact flow, have been predicted successfully.
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
Hydroelastic response of a floating runway to cnoidal waves
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.
Attenuation of sound waves in drill strings
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.
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.
Hydrodynamic responses of a thin floating disk to regular waves
NASA Astrophysics Data System (ADS)
Yiew, L. J.; Bennetts, L. G.; Meylan, M. H.; French, B. J.; Thomas, G. A.
2016-01-01
The surge, heave and pitch motions of two solitary, thin, floating disks, extracted from laboratory wave basin experiments are presented. The motions are forced by regular incident waves, for a range of wave amplitudes and frequencies. One disk has a barrier attached to its edge to stop the incident waves from washing across its upper surface. It is shown that the motions of the disk without the barrier are smaller than those of the disk with the barrier. Moreover, it is shown that the amplitudes of the motions, relative to the incident amplitude, decrease with increasing incident wave amplitude for the disk without a barrier and for short incident wavelengths. Two theoretical models of the disk motions are considered. One is based on slope-sliding theory and the other on combined linear potential-flow and thin-plate theories. The models are shown to have almost the same form in the long-wavelength regime. The potential-flow/thin-plate model is shown to capture the experimentally measured disk motions with reasonable accuracy.
Waves in fragmented geomaterials with impact attenuation
NASA Astrophysics Data System (ADS)
Dyskin, Arcady; Pasternak, Elena
2016-04-01
Attenuation of waves in geomaterials, such as seismic waves is usually attributed to energy dissipation due to the presence of viscous fluid and/or viscous cement between the constituents. In fragmented geomaterials such as blocky rock mass there is another possible source of energy dissipation - impacting between the fragments. This can be characterised by the coefficient of restitution, which is the ratio between the rotational velocities after and before the impact. In particular, this manifests itself in the process of mutual rotations of the fragments/blocks, whereby in the process of oscillation different ends of the contacting faces of the fragments are impacting. During the rotational oscillations the energy dissipation is concentrated in the neutral position that is the one in which the relative rotation between two fragments is zero. We show that in a simple system of two fragments this dissipation is equivalent, in a long run, to the presence of viscous damper between the fragments (the Voigt model of visco-elasticity). Generalisation of this concept to the material consisting of many fragments leads to a Voigt model of wave propagation where the attenuation coefficient is proportional to the logarithm of restitution coefficient. The waves in such a medium show slight dispersion caused by damping and strong dependence of the attenuation on the wave frequency.
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
A low-cost float method of harnessing wave energy
George, M.P.
1983-12-01
The author proposes in this paper a low-cost and simple method of harnessing wave energy that should enable coastal regions to be self-sufficient in electric power. The method is eminently applicable to India and such developing countries, being simple and involving a small capital investment. The method was evolved after study of the Indian West Coast fronting the Arabian Sea, and can harness about 50% of the wave energy. A log of wood about 5 metres long and 50 cm. in diameter, having a specific gravity of 0.8 to 0.9, is made to float parallel to the beach and about 50 metres away from it. Its movement is restricted to the vertical plane by means of poles. Two roller chains are attached to the ends of the log which pass over two sprocket free-wheels. When the log is lifted with the crest of the wave, the roller chain moves over the free-wheel. When the trough of the wave reaches the log, its weight is applied to the sprocket wheels through the roller chains. Each sprocket wheel rotates and the rotation is multiplied with a gear wheel. The torque from the high speed spindle of the gear is applied to a small alternating current generator. The AC output from the generator is rectified and used either for charging a battery bank, or connected to the lighting system, or supplied to electrolytic tank for producing hydrogen and other chemicals at the site. A chain of such systems along the coast can supply enough power to light the fishermen's hamlets stretching along the coast.
Attenuation of coda waves in southern Tibet
NASA Astrophysics Data System (ADS)
Reese, C. C.; Ni, J. F.
The alternation characteristics of the crust in the southernmost Tibetan plateau are determined from analysis of S-wave coda recorded at a temporary broadband station deployed during the 1994 INDEPTH-II experiment. A method for determining Qc is developed which utilizes the coda spectrogram observed at a single station. The average S-wave coda quality factor for this continent-continent collision zone is Qc(f) = (160 ± 69) (f/ f0)1.11±0.19, 1 < (f/f0) < 4, where f0 = 1Hz. The results are consistent with other measurements of Qc(f) in continental collisional environments which typically exhibit low values of Qc(f) at 1 Hz and a strong dependence on frequency. In particular, the attenuation characteristics obtained for the Arabian-Eurasian continental collisional boundary in western Turkey are quite similar to the results reported here for the southern Tibetan plateau.
Experimental study on behavior of an open bottom floating platform in wave, wind and current
Qi Xinyuan
1994-12-31
The behavior of a moored open bottom floating platform has been investigated by a series of model tests at the wave basin of CSSRC (69 x 46 x 4m). The model tests were divided into two versions, i.e., version 1 for a conventional semi-submersible and version 2 for an open bottom floating platform. Comparison was made under the same mooring and environmental conditions including waves, steady wind and current. The results of model tests indicate that the open bottom floating platform is more stable and with less mooring loads than the conventional semi-submersible.
RANS Simulation of the Heave Response of a Two-Body Floating Point Wave Absorber: Preprint
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.
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.
Shear wave speed dispersion and attenuation in granular marine sediments.
Kimura, Masao
2013-07-01
The reported compressional wave speed dispersion and attenuation could be explained by a modified gap stiffness model incorporated into the Biot model (the BIMGS model). In contrast, shear wave speed dispersion and attenuation have not been investigated in detail. No measurements of shear wave speed dispersion have been reported, and only Brunson's data provide the frequency characteristics of shear wave attenuation. In this study, Brunson's attenuation measurements are compared to predictions using the Biot-Stoll model and the BIMGS model. It is shown that the BIMGS model accurately predicts the frequency dependence of shear wave attenuation. Then, the shear wave speed dispersion and attenuation in water-saturated silica sand are measured in the frequency range of 4-20 kHz. The vertical stress applied to the sample is 17.6 kPa. The temperature of the sample is set to be 5 °C, 20 °C, and 35 °C in order to change the relaxation frequency in the BIMGS model. The measured results are compared with those calculated using the Biot-Stoll model and the BIMGS model. It is shown that the shear wave speed dispersion and attenuation are predicted accurately by using the BIMGS model. PMID:23862793
Damping factor estimation using spin wave attenuation in permalloy film
Manago, Takashi; Yamanoi, Kazuto; Kasai, Shinya; Mitani, Seiji
2015-05-07
Damping factor of a Permalloy (Py) thin film is estimated by using the magnetostatic spin wave propagation. The attenuation lengths are obtained by the dependence of the transmission intensity on the antenna distance, and decrease with increasing magnetic fields. The relationship between the attenuation length, damping factor, and external magnetic field is derived theoretically, and the damping factor was determined to be 0.0063 by fitting the magnetic field dependence of the attenuation length, using the derived equation. The obtained value is in good agreement with the general value of Py. Thus, this estimation method of the damping factor using spin waves attenuation can be useful tool for ferromagnetic thin films.
Simulation Of Attenuation Regularity Of Detonation Wave In Pmma
NASA Astrophysics Data System (ADS)
Lan, Wei; Xiaomian, Hu
2012-03-01
Polymethyl methacrylate (PMMA) is often used as clapboard or protective medium in the parameter measurement of detonation wave propagation. Theoretical and experimental researches show that the pressure of shock wave in condensed material has the regularity of exponential attenuation with the distance of propagation. Simulation of detonation produced shock wave propagation in PMMA was conducted using a two-dimensional Lagrangian computational fluid dynamics program, and results were compared with the experimental data. Different charge diameters and different angles between the direction of detonation wave propagation and the normal direction of confined boundary were considered during the calculation. Results show that the detonation produced shock wave propagation in PMMA accords with the exponential regularity of shock wave attenuation in condensed material, and several factors are relevant to the attenuation coefficient, such as charge diameter and interface angle.
Simulation of attenuation regularity of detonation wave in PMMA
NASA Astrophysics Data System (ADS)
Lan, Wei; Xiaomian, Hu
2011-06-01
Polymethyl methacrylate (PMMA) is often used as clapboard or protective medium in the parameter measurement of detonation wave propagation, due to its similar shock impedance with the explosive. Theoretical and experimental research show that the pressure of shock wave in condensed material has the regularity of exponential attenuation with the distance of propagation. Simulation of detonation wave propagation in PMMA is conducted using a two-dimensional Lagrangian computational fluid dynamics program, and results are compared with the experimental data. Different charge diameters and different angles between the direction of detonation wave propagation and the normal direction of confined boundary are considered during the calculation. Results show that the detonation wave propagation in PMMA accords with the exponential regularity of shock wave attenuation in condensed material, and several factors are relevant to the attenuation coefficient, such as charge diameter and interface angle.
Wind/Wave Misalignment in the Loads Analysis of a Floating Offshore Wind Turbine: Preprint
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.
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.
Attenuation layer for magnetostatic wave (MSW) absorbers
NASA Astrophysics Data System (ADS)
Glass, H. L.; Adkins, L. R.; Stearns, F. S.
1984-09-01
A new technique has been developed for the suppression of MSW end reflections which give rise to passband ripple. The basic idea is to provide a thin film of highly attenuating epitaxial material at the ends of a MSW delay line while preserving high quality YIG in the active region of the device. The GGG wafer preparation is a three step process which involves: (1) the growth of the attenuation layer, (2) the removal of this layer from the central region of the wafer and (3) the growth of high quality YIG on the remaining structure. Delay lines using the attenuation layer for end terminations have been evaluated experimentally and compared to devices utilizing other termination methods. The results indicate that the attenuation layer method produces ripple suppression characteristics which are the equal of those obtained with other termination techniques. The advantage of this new method lies in its suitability for large quantity fabrication requirements.
Attenuation of Seismic Waves by Grain Boundary Relaxation
Jackson, David D.
1971-01-01
Experimental observations of the attenuation of elastic waves in polycrystalline ceramics and rocks reveal an attenuation mechanism, called grain boundary relaxation, which is likely to be predominant cause of seismic attenuation in the earth's mantle. For this mechanism, the internal friction (the reciprocal of the “intrinsic Q” of the material) depends strongly upon frequency and is in good agreement with Walsh's theory of attenuation (J. Geophys. Res., 74, 4333, 1969) in partially melted rock. When Walsh's theory is extended to provide a model of the anelasticity of the earth, using the experimental values of physical parameters reported here, the results are in excellent agreement with seismic observations. PMID:16591937
Oceanic Rossby Waves Acting As a ``Hay Rake'' for Ecosystem Floating By-Products
NASA Astrophysics Data System (ADS)
Dandonneau, Yves; Vega, Andres; Loisel, Hubert; du Penhoat, Yves; Menkes, Christophe
2003-11-01
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.
Wave pressure acting on V-shaped floating breakwater in random seas
NASA Astrophysics Data System (ADS)
Yu, Yang; Ding, Ning; Lin, Jie; Hou, Jiajia
2015-12-01
Wave pressure on the wet surface of a V-shaped floating breakwater in random seas is investigated. Considering the diffraction effect, the unit velocity potential caused by the single regular waves around the breakwater is solved using the finite-depth Green function and boundary element method, in which the Green function is solved by integral method. The Response-Amplitude Operator (RAO) of wave pressure is acquired according to the Longuet-Higgins' wave model and the linear Bernoulli equation. Furthermore, the wave pressure's response spectrum is calculated according to the wave spectrum by discretizing the frequency domain. The wave pressure's characteristic value corresponding to certain cumulative probability is determined according to the Rayleigh distribution of wave heights. The numerical results and field test results are compared, which indicates that the wave pressure calculated in random seas agrees with that of field measurements. It is found that the bigger angle between legs will cause the bigger pressure response, while the increase in leg length does not influence the pressure significantly. The pressure at the side of head sea is larger than that of back waves. When the incident wave angle changes from 0° to 90°, the pressure at the side of back waves decreases clearly, while at the side of head sea, the situation is more complicated and there seems no obvious tendency. The concentration of wave energy around low frequency (long wavelength) will induce bigger wave pressure, and more attention should be paid to this situation for the structure safety.
Attenuation character of seismic waves in Sikkim Himalaya
NASA Astrophysics Data System (ADS)
Hazarika, Pinki; Kumar, M. Ravi; Kumar, Dinesh
2013-10-01
In this study, we investigate the seismic wave attenuation beneath Sikkim Himalaya using P, S and coda waves from 68 local earthquakes registered by eight broad-band stations of the SIKKIM network. The attenuation quality factor (Q) depends on frequency as well as lapse time and depth. The value of Q varies from (i) 141 to 639 for P waves, (ii) 143 to 1108 for S waves and (iii) 274 to 1678 for coda waves, at central frequencies of 1.5 Hz and 9 Hz, respectively. The relations that govern the attenuation versus frequency dependence are Qα = (96 ± 0.9) f (0.94 ± 0.01), Qβ = (100 ± 1.4) f (1.16 ± 0.01) and Qc = (189 ± 1.5) f (1.2 ± 0.01) for P, S and coda waves, respectively. The ratio between Qβ and Qα is larger than unity, implying larger attenuation of P compared to S waves. Also, the values of Qc are higher than Qβ. Estimation of the relative contribution of intrinsic (Qi) and scattering (Qs) attenuation reveals that the former mechanism is dominant in Sikkim Himalaya. We note that the estimates of Qc lie in between Qi and Qs and are very close to Qi at lower frequencies. This is in agreement with the theoretical and laboratory experiments. The strong frequency and depth dependence of the attenuation quality factor suggests a highly heterogeneous crust in the Sikkim Himalaya. Also, the high Q values estimated for this region compared to the other segments of Himalaya can be reconciled in terms of moderate seismic activity, unlike rest of the Himalaya, which is seismically more active.
On attenuation of seismic waves associated with flow in fractures
NASA Astrophysics Data System (ADS)
Vinci, C.; Renner, J.; Steeb, H.
2014-11-01
Heterogeneity of porous media induces a number of fluid-flow mechanisms causing attenuation of seismic waves. Attenuation induced by squirt-type mechanisms has previously been analyzed for aspect ratios smaller or equal to 103. Using a hybrid-dimensional modeling approach, particularly apt for large aspect ratio conduits, we numerically simulated deformation-induced fluid flow along two intersecting fractures to investigate the physics of attenuation related to the interaction of fracture-induced fluid flow and to leak-off. Attenuation related to fracture flow increases in magnitude with increasing geometrical aspect ratio of the fracture. The inherent time scales of both flow mechanisms do not influence each other, but the faster process is associated with stronger attenuation than the slower process. Models relying on simple diffusion equations have rather limited potential for approximation of pressure transients.
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.
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.
Efficiency of shock wave attenuation in ducts by various methods
NASA Astrophysics Data System (ADS)
Frolov, S. M.
1993-02-01
Different methods of shock wave attenuation in ducts are compared in terms of efficiency. The methods investigated include expansion of the duct cross section, the use of perforated side walls, and the use of porous screens and screen cascades. The attentuation of air shock waves is estimated by using a unified approach which provides satisfactory agreement with experimental data. Based on the results of the study, a nomogram is plotted which can be used for practical calculations.
Fault-zone attenuation of high-frequency seismic waves
Blakeslee, S.; Malin, P.; Alvarez, M. )
1989-11-01
The authors 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. The 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 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 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,{minus}5). If fault-zones are low-Q environments, then near-source attenuation of high-frequency seismic waves may help to explain phenomenon such as f{sub max}. 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.
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.
A new instrumentation to measure seismic waves attenuation
NASA Astrophysics Data System (ADS)
Tisato, N.; Madonna, C.; Boutareaud, S.; Burg, J.
2010-12-01
Attenuation of seismic waves is the general expression describing the loss of energy of an elastic perturbation during its propagation in a medium. As a geophysical method, measuring the attenuation of seismic waves is a key to uncover essential information about fluid saturation of buried rocks. Attenuation of seismic waves depends on several mechanisms. In the case of saturated rock, fluids play an important role. Seismic waves create zones of overpressure by mobilizing the fluids in the pores of the rock. Starting from Gassmann-Biot theory (Gassman, 1951), several models (e.g. White, 1975; Mavko and Jizba, 1991) have been formulated to describe the energy absorption by flow of fluids. According to Mavko et al. (1998) for rock with permeability equals or less than 1 D, fluid viscosity between 1 cP and 10 cP and low frequencies seismic wave (< 100 Hz), the most important processes that subtract energy from the seismic waves are squirt flow and patchy saturation. Numerical models like Quintal et al. (2009) calculate how a patchy saturated vertical rock section (25 cm height), after stress steps of several kPa (i.e. 30 kPa) show a dissimilar increase in pore pressure between gas-saturated and liquid-saturated layers. The Rock Deformation Laboratory at ETH-Zürich has designed and set up a new pressure vessel to measure seismic wave attenuation in rocks at frequencies between 0.1 and 100 Hz and to verify the predicted influence of seismic waves on the pore pressure in patchy saturated rocks. We present this pressure vessel which can reach confining pressures of 25 MPa and holds a 250 mm long and 76 mm diameter sample. Dynamic stress is applied at the top of the rock cylinder by a piezoelectric motor that can generate a stress of several kPa (> 100 KPa) in less than 10 ms. The vessel is equipped with 5 pressure sensors buried within the rock sample, a load cell and a strain sensor to measure axial shortening while the motor generates the seismic waves. The sensor
Estimates of millimeter wave attenuation for 18 United States cities
NASA Astrophysics Data System (ADS)
Allen, K. C.; Liebe, H. J.; Rush, C. M.
1983-05-01
Brief discussions of three mechanisms that attenuate millimeter waves in the atmosphere are presented: rain attenuation, clear air absorption, and atmospheric multipath. Propagation models were combined with meteorological statistics to obtain estimates of average year attenuation distributions for 18 cities in the United States. The estimates are presented in such a way to elucidate the restrictions on system parameters required for reliable operation, i.e. frequency, path length for terrestrial paths, and path elevation angle for earth-satellite paths. The variation imposed by the diverse climates within the United States is demonstrated. Generally, in regions that have humid climates, millimeter wave systems perform less favorably than in areas where arid or semi-arid conditions prevail.
Mantle-Lid P Wave Attenuation in the Korean Peninsula
NASA Astrophysics Data System (ADS)
Lee, K.; Hong, T.
2012-12-01
The mantle-lid P wave, Pn, is the first arrival phase in regional distances. The Pn waves are widely analyzed for estimation of event sizes. Also, it is known that analysis of Pn waves is effective for discrimination of nuclear explosions from natural earthquakes. The attenuation of Pn waves provides us information on medium properties in mantle lid. It is crucial to understand the nature of Pn attenuation for correct estimation of event sizes from Pn amplitudes. We investigate the lateral variation of Pn attenuation in the mantle lid of the Korean Peninsula from vertical regional seismograms for events around the Korean Peninsula and Japanese islands. The number of events is 149, and the focal depths are less than 50 km. The seismic records with signal-to-noise ratios greater than 1.5 are analyzed. The number of stations is 121. The Pn quality factors are calculated using a two-station method in which ratios of Pn displacement spectra of stations on the same azimuths are used. The power-law frequency dependence term is estimated using a least-squares fitting for quality factors at frequencies from 0.37 Hz to 25 Hz. The number of station pairs is 3317. The average quality factor at 1 Hz is determined to be about 67, which is consistent with previous studies. We present the resultant Pn attenuation model, and discuss the correlations with geological and geophysical properties in the medium.
Review of methods to attenuate shock/blast waves
NASA Astrophysics Data System (ADS)
Igra, O.; Falcovitz, J.; Houas, L.; Jourdan, G.
2013-04-01
Quick and reliable shock wave attenuation is the goal of every protection facility and therefore it is not surprising that achieving this has drawn much attention during the past hundred years. Different options have been suggested; their usefulness varying from a reasonable protection to the opposite, a shock enhancement. An example for a suggestion for shock mitigation that turned out to be an enhancement of the impinging shock wave was the idea to cover a protected object with a foam layer. While the pressure behind the reflected shock wave from the foam frontal surface was smaller than that recorded in a similar reflection from a rigid wall [25], the pressure on the “protected” surface, attached to the foam's rear-surface, was significantly higher than that recorded in a similar reflection from a bare, rigid wall [11]. In protecting humans and installations from destructive shock and/or blast waves the prime goal is to reduce the wave amplitude and the rate of pressure increase across the wave front. Both measures result in reducing the wave harmful effects. During the past six decades several approaches for achieving the desired protection have been offered in the open literature. We point out in this review that while some of the suggestions offered are practical, others are impractical. In our discussion we focus on recent schemes for shock/blast wave attenuation, characterized by the availability of reliable measurements (notably pressure and optical diagnostics) as well as high-resolution numerical simulations.
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
Generating attenuation-resistant frozen waves in absorbing fluid.
Dorrah, Ahmed H; Zamboni-Rached, Michel; Mojahedi, Mo
2016-08-15
We demonstrate a class of nondiffracting beams, called frozen waves, with a central spot that can be made to maintain a predefined intensity profile while propagating in an absorbing fluid. Frozen waves are composed of Bessel beams with different transverse and longitudinal wavenumbers, and are generated using a programmable spatial light modulator. The attenuation-resistant frozen waves demonstrated here address the problem of propagation losses in absorbing media. This development can be beneficial for many applications in particle micro-manipulation, data communications, remote sensing, and imaging. PMID:27519067
Wave transmission and mooring-force characteristics of pipe-tire floating breakwaters
Harms, Volker W.; Westerink, Joannes J.
1980-10-01
The results are presented of a series of prototype scale tests of a floating breakwater that incorporates massive cylindrical members (steel or concrete pipes, telephone poles, etc.) in a matrix of scrap truck or automobile tires, referred to as the Pipe-Tire Breakwater (PT-Breakwater). Tests were conducted in the large wave tank at the US Army Coastal Engineering Research Center (CERC). Breakwater modules were preassembled at SUNY in Buffalo, New York, and then transported to CERC by truck, where final assembly on location was again performed by SUNY personnel. Wave-tank tests were conducted jointly by CERC and SUNY personnel. A series of wave-tank experiments and mooring system load-deflection tests were performed, and are described. Wave-transmission and mooring-load characteristics, based on 402 separate tests, were established and are reported. (LCL)
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.
Wave Dispersion and Attenuation in Partially Saturated Sandstones
NASA Astrophysics Data System (ADS)
Nie, Jian-Xin; Yang, Ding-Hui; Yang, Hui-Zhu
2004-03-01
We investigate the wave dispersion and attenuation in partially water-saturated sandstones based on the improved Biot/squirt (BISQ) model in which the saturation is introduced. Numerical experiments indicate that the phase velocity of the fast P-wave decreases as the saturation increases in the low-frequency range (102-104 Hz), and reaches the minimum at the full-saturation state. The behaviour of the phase velocity varying with the saturation in the high-frequency range (104-106 Hz), however, is opposite to that in the low-frequency range. The peak value of P-wave attenuation increases with increasing saturation, and is the maximum at the fully saturated state. Numerical models and experiments show that the improved BISQ model is better than the traditional Gassmann-Biot model.
On the design of a prototype model of the floating wave power device ``Mighty Whale``
Hotta, H.; Washio, Y.; Yokozawa, H.; Pizer, D.J.
1996-12-31
The Mighty Whale is a floating wave power device to convert the wave energy to other convenient energy for the conservation of the sea, and to create the calm sea area such as a floating breakwater. JAMSTEC (Japan Marine Science and Technology Center) has been promoting the R and D on this Mighty Whale since 1986. Already, the authors have finished fundamental development by theoretical, numerical and experimental study on the basic Mighty Whale. By 1996, they will finish designing the prototype model of the Mighty Whale, will start to construct it, and will carry out the open sea test between 1998 and 1999 at the coastal sea of Japan. The dimensions of the Mighty Whale are 50m in length, 30m in breadth and it has 3 air chambers, 3 units of the air turbines and generators of 50 kW rated power. It will be moored by mooring chains and anchors at the site of about 35m water depth. The mechanism to absorb the wave energy is of the OWC (Oscillating Water Column) type with the Wells Turbine. Its efficiency to absorb the wave energy is about 40--50% on average in regular waves, and it can make in the lee zone the height of incident waves about one half under 8 sec of the significant wave period. Because of such behavior, and from the view point of sustainable development at the coastal zone, the authors recognize the Mighty Whale can be a convenient and beneficial structure for the coastal development. In this paper, they introduce this design, and discuss the utilization of the Mighty Whale for the coastal development.
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
Wave-induced fluid flow in random porous media: attenuation and dispersion of elastic waves.
Müller, Tobias M; Gurevich, Boris
2005-05-01
A detailed analysis of the relationship between elastic waves in inhomogeneous, porous media and the effect of wave-induced fluid flow is presented. Based on the results of the poroelastic first-order statistical smoothing approximation applied to Biot's equations of poroelasticity, a model for elastic wave attenuation and dispersion due to wave-induced fluid flow in 3-D randomly inhomogeneous poroelastic media is developed. Attenuation and dispersion depend on linear combinations of the spatial correlations of the fluctuating poroelastic parameters. The observed frequency dependence is typical for a relaxation phenomenon. Further, the analytic properties of attenuation and dispersion are analyzed. It is shown that the low-frequency asymptote of the attenuation coefficient of a plane compressional wave is proportional to the square of frequency. At high frequencies the attenuation coefficient becomes proportional to the square root of frequency. A comparison with the 1-D theory shows that attenuation is of the same order but slightly larger in 3-D random media. Several modeling choices of the approach including the effect of cross correlations between fluid and solid phase properties are demonstrated. The potential application of the results to real porous materials is discussed. PMID:15957744
Wave attenuation in the shallows of San Francisco Bay
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.
Riser tensioning wave and tide compensating system for a floating platform
Heeres, C.J.; Larsen, C.H.
1980-09-16
A riser tensioner cylinder is provided with a hollow piston rod which forms a second cylinder in which a ram is reciprocated. The free end of the ram is connected to a link which in turn is connected to the end of the riser for providing tension on the riser. The ram reciprocates in the second cylinder under constant pressure to compensate for wave action on the floating platform and the second cylinder is automatically positioned within the first cylinder for adjustment for tide, vessel offset or other infrequent but variable factors.
Spectral wave flow attenuation within submerged canopies: Implications for wave energy dissipation
NASA Astrophysics Data System (ADS)
Lowe, Ryan J.; Falter, James L.; Koseff, Jeffrey R.; Monismith, Stephen G.; Atkinson, Marlin J.
2007-05-01
Communities of benthic organisms can form very rough surfaces (canopies) on the seafloor. Previous studies have shown that an oscillatory flow induced by monochromatic surface waves will drive more flow inside a canopy than a comparable unidirectional current. This paper builds on these previous studies by investigating how wave energy is attenuated within canopies under spectral wave conditions, or random wave fields defined by many frequencies. A theoretical model is first developed to predict how flow attenuation within a canopy varies among the different wave components and predicts that shorter-period components will generally be more effective at driving flow within a canopy than longer-period components. To investigate the model performance, a field experiment was conducted on a shallow reef flat in which flow was measured both inside and above a model canopy array. Results confirm that longer-period components in the spectrum are significantly more attenuated than shorter-period components, in good agreement with the model prediction. This paper concludes by showing that the rate at which wave energy is dissipated by a canopy is closely linked to the flow structure within the canopy. Under spectral wave conditions, wave energy within a model canopy array is dissipated at a greater rate among the shorter-period wave components. These observations are consistent with previous observations of how wave energy is dissipated by the bottom roughness of a coral reef.
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.
Attenuation of shock waves in copper and stainless steel
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.
Seismic interferometry of scattered surface waves in attenuative media
NASA Astrophysics Data System (ADS)
Halliday, David; Curtis, Andrew
2009-07-01
Seismic interferometry can be used to estimate interreceiver surface wave signals by cross-correlation of signals recorded at each receiver that are emitted from a surrounding boundary of impulsive or uncorrelated noise sources. We study seismic interferometry for scattered surface waves using a stationary-phase analysis and surface wave Green's functions for isotropic point scatterers embedded in laterally homogeneous media. Our analysis reveals key differences between the interferometric construction of reflected and point-scattered body or surface waves, since point scatterers radiate energy in all directions but a reflection from a finite flat reflector is specular. In the case of surface waves, we find that additional cancelling terms are introduced in the stationary-phase analysis for scattered waves related to the constraint imposed by the optical theorem for surface waves. The additional terms are of second order even for single-scattered waves, and we show that these can be highly significant in multiple-scattering cases. In attenuative media errors are introduced due to amplitude errors in these additional terms. Further, we find that as the distribution of scatterers in a medium becomes more complex the errors in correlation-type interferometry caused by attenuation in the background medium become larger. Convolution-type interferometry has been shown to be effective when considering electromagnetic wavefields in lossy media, and we show that this is also true for scattered surface waves in attenuating elastic media. By adapting our stationary-phase approach to this case, we reveal why convolution-type interferometry performs well in such media: the second-order cancelling terms that appear in the correlation-type approach do not appear in convolution-type interferometry. Finally, we find that when using both correlation- and convolution-type interferometry with realistic source geometries (illustrative of both industrial seismics and `passive noise
P wave attenuation structure below the Tokyo Metropolitan area
NASA Astrophysics Data System (ADS)
Panayotopoulos, Y.; Sakai, S.; Nakagawa, S.; Kasahara, K.; Hirata, N.; Aketagawa, T.; Kimura, H.; Lee, C.
2010-12-01
The material properties of the complex subduction zone beneath the Tokyo Metropolitan can be estimated by the seismic attenuation Q-1 of seismic waves observed at local seismic stations. The attenuation of seismic waves is represented by the t* attenuation operator that can be estimated by fitting the observed P wave amplitude spectrum to a theoretical spectrum using an ω2 source model. The waveform data used in this study are recorded at the dense seismic array of the Metropolitan Seismic Observation network (MeSO-net). The station network is distributed on five lines with an average spacing of 3 km and in an area with a spacing of 5 km in the central part of Kanto plane. The MeSO-net stations are equipped with a three-component accelerometer at a bottom of a 20-m-deep borehole, signals from which are digitized at a sampling rate of 200 Hz with a dynamic range of 135 dB.The waveforms of 141 earthquakes observed at 226 stations were selected from the Japan Meteorological Agency (JMA) unified earthquake list from January 1st 2010 to August 4th 2010. Only high-quality amplitude spectra of earthquakes with M > 3 were used for the estimation of reliable attenuation parameters. The acceleration waveforms were integrated twice to yield the corresponding displacement vectors, applying a high pass filter to remove the effect of the low-frequency background noise. Taking into account that the majority of the events occurred at depth greater than 30 km a search window of 5 sec starting 1 sec before the P wave arrival was implemented for the creation of the dataset. The t* values were estimated from the amplitude spectra of approximately 33800 P wave waveforms conducting a fast Fourier transform analysis. The Q values for the Tokyo Metropolitan area estimate by this study range from 100 to 500 in the upper 30 km of the crust. A site effect on the attenuation near stations inside a densely populated area is also a possible reason for the large Q variations observed.
A Heterogeneous Nonlinear Attenuating Full-Wave Model of Ultrasound
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
On the concept of sloped motion for free-floating wave energy converters
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
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.
Seismic Attenuation Technology for the Advanced Virgo Gravitational Wave Detector
NASA Astrophysics Data System (ADS)
Beker, M. G.; Blom, M.; van den Brand, J. F. J.; Bulten, H. J.; Hennes, E.; Rabeling, D. S.
The current interferometric gravitational wave detectors are being upgraded to what are termed 'second generation' devices. Sensitivities will be increased by an order of magnitude and these new instruments are expected to uncover the field of gravitational astronomy. A main challenge in this endeavor is the mitigation of noise induced by seismic motion. Detailed studies with Virgo show that seismic noise can be reinjected into the dark fringe signal. For example, laser beam jitter and backscattered light limit the sensitivity of the interferometer. Here, we focus on seismic attenuators based on compact inverted pendulums in combination with geometric anti-prings to obtain 40 dB of attenuation above 4 Hz in six degrees of freedom. Low frequency resonances (< 0.5 Hz) are damped by using a control system based on input from LVDTs and geophones. Such systems are under development for the seismic attenuation of optical benches operated both in air and vacuum. The design and realization of the seismic attenuation system for the Virgo external injection bench, including its control scheme, will be discussed and stand-alone performance presented.
Wave Dispersion and Attenuation on Human Femur Tissue
Strantza, Maria; Louis, Olivia; Polyzos, Demosthenes; Boulpaep, Frans; van Hemelrijck, Danny; Aggelis, Dimitrios G.
2014-01-01
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. PMID:25196011
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
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.
Seismic attenuation due to wave-induced flow
Pride, S; Berryman, J; Harris, J
2003-10-17
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 field data.
Seismic attenuation due to wave-induced flow
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.
Seismic-wave attenuation associated with crustal faults in the New Madrid seismic zone
Hamilton, R.M.; Mooney, W.D.
1990-01-01
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.
Attenuation of coda waves in the Northeastern Region of India
NASA Astrophysics Data System (ADS)
Hazarika, Devajit; Baruah, Saurabh; Gogoi, Naba Kumar
2009-01-01
Coda wave attenuation quality factor Qc is estimated in the northeastern region of India using 45 local earthquakes recorded by regional seismic network. The quality factor Qc was estimated using the single backscattering model modified by Sato (J Phys Earth 25:27-41, 1977), in the frequency range 1-18 Hz. The attenuation and frequency dependence for different paths and the correlation of the results with geotectonics of the region are described in this paper. A total of 3,890 Qc measurements covering 187 varying paths are made for different lapse time window of 20, 30, 40, 50, 60, 70, 80, and 90 s in coda wave. The magnitudes of the analyzed events range from 1.2 to 3.9 and focal depths range between 7 and 38 km. The source-receiver distances of the selected events range between 16 and 270 km. For 30-s duration, the mean values of the estimated Qc vary from 50 ± 12 (at 1 Hz) to 2,078 ± 211(at 18 Hz) for the Arunachal Himalaya, 49 ± 14 (at 1 Hz) to 2,466 ± 197 (at 18 Hz) for the Indo-Burman, and 45 ± 13 (at 1 Hz) to 2,069 ± 198 (at 18 Hz) for Shillong group of earthquakes. It is observed that Qc increases with frequency portraying an average attenuation relation Qc=52.315± 1.07f ^{left( {1.32 ± 0.036} right)} for the region. Moreover, the pattern of Qc - 1 with frequency is analogous to the estimates obtained in other tectonic areas in the world, except with the observation that the Qc - 1 is much higher at 1 Hz for the northeastern region. The Qc - 1 is about 10 - 1.8 at 1 Hz and decreases to about 10 - 3.6 at 18 Hz indicating clear frequency dependence. Pertaining to the spatial distribution of Qc values, Mikir Hills and western part of Shillong Plateau are characterized by lower attenuation.
NASA Astrophysics Data System (ADS)
Wang, Ping; Lu, DongQiang
2013-11-01
An analytic approximation method known as the homotopy analysis method (HAM) is applied to study the nonlinear hydroelastic progressive waves traveling in an infinite elastic plate such as an ice sheet or a very large floating structure (VLFS) on the surface of deep water. A convergent analytical series solution for the plate deflection is derived by choosing the optimal convergencecontrol parameter. Based on the analytical solution the effects of different parameters are considered. We find that the plate deflection becomes lower with an increasing Young's modulus of the plate. The displacement tends to be flattened at the crest and be sharpened at the trough as the thickness of the plate increases, and the larger density of the plate also causes analogous results. Furthermore, it is shown that the hydroelastic response of the plate is greatly affected by the high-amplitude incident wave. The results obtained can help enrich our understanding of the nonlinear hydroelastic response of an ice sheet or a VLFS on the water surface.
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.
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.
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.
Wave-induced response of a floating two-dimensional body with a moonpool
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
Wave-induced response of a floating two-dimensional body with a moonpool.
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. PMID:25512594
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.
NASA Astrophysics Data System (ADS)
Ouyang, Huei-Tau; Chen, Kue-Hong; Tsai, Chi-Ming
2015-11-01
The water wave characteristics of Bragg reflections from a train of fixed floating pontoon breakwaters was studied numerically. A numerical model of boundary discretization type was developed to calculate the wave field. The model was verified by comparing to analytical data in literature and good agreements were achieved. Series of parametric studies were conducted systematically to investigate the dependence of the reflected coefficients by the Bragg scattering on the design variables, including the spacing between the breakwaters, the total number of installed breakwaters, the draft and width do the breakwater, and wave length. Certain wave characteristics of the Bragg reflections were observed and discussed in details which might be of help for practical engineering applications in shoreline protection from incident waves.
Subduction zone guided waves: 3D modelling and attenuation effects
NASA Astrophysics Data System (ADS)
Garth, T.; Rietbrock, A.
2013-12-01
Waveform modelling is an important tool for understanding complex seismic structures such as subduction zone waveguides. These structures are often simplified to 2D structures for modelling purposes to reduce computational costs. In the case of subduction zone waveguide affects, 2D models have shown that dispersed arrivals are caused by a low velocity waveguide, inferred to be subducted oceanic crust and/or hydrated outer rise normal faults. However, due to the 2D modelling limitations the inferred seismic properties such as velocity contrast and waveguide thickness are still debated. Here we test these limitations with full 3D waveform modelling. For waveguide effects to be observable the waveform must be accurately modelled to relatively high frequencies (> 2 Hz). This requires a small grid spacing due to the high seismic velocities present in subduction zones. A large area must be modelled as well due to the long propagation distances (400 - 600 km) of waves interacting with subduction zone waveguides. The combination of the large model area and small grid spacing required means that these simulations require a large amount of computational resources, only available at high performance computational centres like the UK National super computer HECTOR (used in this study). To minimize the cost of modelling for such a large area, the width of the model area perpendicular to the subduction trench (the y-direction) is made as small as possible. This reduces the overall volume of the 3D model domain. Therefore the wave field is simulated in a model ';corridor' of the subduction zone velocity structure. This introduces new potential sources of error particularly from grazing wave side reflections in the y-direction. Various dampening methods are explored to reduce these grazing side reflections, including perfectly matched layers (PML) and more traditional exponential dampening layers. Defining a corridor model allows waveguide affects to be modelled up to at least 2
A New Approach for Quantitative Evaluation of Ultrasonic Wave Attenuation in Composites
NASA Astrophysics Data System (ADS)
Ni, Qing-Qing; Li, Ran; Xia, Hong
2016-06-01
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.
Attenuation of P-Waves by Wave-Induced Fluid Flow
Pride, S R; Berryman, J G
2002-03-29
Analytical expressions for three P-wave attenuation mechanisms in rocks are given and numerically-compared. The mechanisms are: (1) Biot loss, in which flow occurs at the scale of the wavelength between the peaks and troughs of a P wave; (2) squirt loss, in which flow occurs at the grain scale between microcracks the grains and the adjacent pores; and (3) mesoscopic loss, in which flow occurs at intermediate scales between the various lithological bodies that are present in an averaging volume of earth material. Each mechanism is of importance over different frequency bands. Typically, Biot loss is only important at the highest of ultrasonic frequencies (> 1 MHz), squirt-loss (when it occurs) is important in the range of 10 kHz to 1 MHz, while mesoscale loss dominates at the lower frequencies (<10 kHz) employed in seismology.
Attenuation of an electromagnetic wave by charged dust particles in a sandstorm.
Xie, Li; Li, Xingcai; Zheng, Xiaojing
2010-12-10
We calculate the light scattering properties of the partially charged dust particles with the Mie theory for electromagnetic waves with different frequencies, and the attenuation coefficients of an electromagnetic wave propagating in a sandstorm are also calculated. The results show that the electric charges distributed on the sand surface have a significant effect on the attenuation of the electromagnetic wave, especially for a frequency lower than 40 GHz, and attenuation coefficients increase with the magnitude of charges carried by the dust particles (expressed by the charge-to-mass ratio in this paper). For the higher frequency electromagnetic wave, such as visible light, the effect of charges carried by sand particles on its attenuation is very little, which can be ignored. PMID:21151232
A poroelastic model for ultrasonic wave attenuation in partially frozen brines
NASA Astrophysics Data System (ADS)
Matsushima, Jun; Nibe, Takao; Suzuki, Makoto; Kato, Yoshibumi; Rokugawa, Shuichi
2011-02-01
Although there are many possible mechanisms for the intrinsic seismic attenuation in composite materials that include fluids, relative motion between solids and fluids during seismic wave propagation is one of the most important attenuation mechanisms. In our previous study, we conducted ultrasonic wave transmission measurements on an ice-brine coexisting system to examine the influence on ultrasonic waves of the unfrozen brine in the pore microstructure of ice. In order to elucidate the physical mechanism responsible for ultrasonic wave attenuation in the frequency range of 350-600kHz, measured at different temperatures in partially frozen brines, we employed a poroelastic model based on the Biot theory to describe the propagation of ultrasonic waves through partially frozen brines. By assuming that the solid phase is ice and the liquid phase is the unfrozen brine, fluid properties measured by a pulsed nuclear magnetic resonance technique were used to calculate porosities at different temperatures. The computed intrinsic attenuation at 500kHz cannot completely predict the measured attenuation results from the experimental study in an ice-brine coexisting system, which suggests that other attenuation mechanisms such as the squirt-flow mechanism and wave scattering effect should be taken into account.
Attenuation and distortion of compression waves propagating in very long tube
NASA Astrophysics Data System (ADS)
Nakamura, Shinya; Sasa, Daisuke; Aoki, Toshiyuki
2011-03-01
A lot of phenomena related to propagating various waves are seen when the high-speed train goes through the tunnel, the gas pipeline is broken due to an accident or the air brake of the wagon operates. For instance, a compression wave generated ahead of a high-speed train entering a tunnel propagates to the tunnel exit and spouts as a micro pressure wave, which causes an exploding sound. In order to estimate the magnitude correctly, the mechanism of the attenuation and distortion of a compression wave propagating along a very long tunnel must be understood and the experimental information on these phenomena is required. An experimental investigation is carried out to clarify the attenuation and distortion of the propagating compression wave in a very long tube. Experimental results show that the strength of a compression wave decreases with distance. The attenuation and distortion of compression waves are affected by the initial waveform of the compression wave and by the unsteady boundary layer induced by the propagating wave. The shape of a compression wave becomes different with the propagating distance; that is, a shock wave appears just head of a wavefront and an overshoot on pressure distribution is observed behind a shock wave due to the transition of the unsteady boundary layer.
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.
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.
NASA Astrophysics Data System (ADS)
Cal, Filipe S.; Dias, Gonçalo A. S.; Nazarov, Serguei A.; Videman, Juha H.
2015-04-01
We derive a linear system of equations governing the interaction of water waves with partially or totally submerged freely floating structures in a two-layer fluid. We establish conditions for the stability of equilibrium and, by considering time-harmonic motions, rewrite the problem as a spectral boundary-value problem consisting of a differential equation and an algebraic system, coupled through boundary conditions. We give also a suitable variational formulation for the problem and provide examples of configurations where the problem admits only the trivial solution.
NASA Astrophysics Data System (ADS)
Williams, Westin B.; Michaels, Thomas E.; Michaels, Jennifer E.
2016-02-01
The behavior of guided waves propagating in anisotropic composite panels can be substantially more complicated than for isotropic, metallic plates. The angular dependency of wave propagation characteristics need to be understood and quantified before applying methods for damage detection and characterization. This study experimentally investigates the anisotropy of wave speed and attenuation for the fundamental A0-like guided wave mode propagating in a solid laminate composite panel. A piezoelectric transducer is the wave source and a laser Doppler vibrometer is used to measure the outward propagating waves along radial lines originating at the source transducer. Group velocity, phase velocity and attenuation are characterized as a function of angle for a single center frequency. The methods shown in this paper serve as a framework for future adaptation to damage imaging methods using guided waves for structural health monitoring.
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.
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.
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. PMID:16180769
Attenuation of electromagnetic wave propagation in sandstorms incorporating charged sand particles
NASA Astrophysics Data System (ADS)
Zhou, You-He; Shu He, Qin; Zheng, Xiao Jing
2005-06-01
A theoretical approach for predicting the attenuation of microwave propagation in sandstorms is presented, with electric charges generated on the sand grains taken into account. It is found that the effect of electric charges distributed partially on the sand surface is notable. The calculated attenuation is in good agreement with that measured in certain conditions. The distribution of electric charges on the surface of sand grains, which is not easy to measure, can be approximately determined by measuring the attenuation value of electromagnetic waves. Some effects of sand radius, dielectric permittivity, frequency of electromagnetic wave, and visibility of sandstorms on the attenuation are also discussed quantitatively. Finally, a new electric parameter is introduced to describe the roles of scattering, absorption and effect of charges in attenuation.
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
Laboratory measurements of wave attenuation through model and live vegetation
Technology Transfer Automated Retrieval System (TEKTRAN)
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...
Dispersion and attenuation of acoustic guided waves in layered fluid-filled porous media
Parra, J.O.; Xu, P. )
1994-01-01
The analysis of acoustic wave propagation in fluid-filled porous media based on Biot and homogenization theories has been adapted to calculate dispersion and attenuation of guided waves trapped in low-velocity layered media. Constitutive relations, the balance equation, and the generalized Darcy law of the modified Biot theory yield a coupled system of differential equations which governs the wave motion in each layer. The displacement and stress fields satisfy the boundary conditions of continuity of displacements and tractions across each interface, and the radiation condition at infinity. To avoid precision problems caused by the growing exponential in individual matrices for large wave numbers, the global matrix method was implemented as an alternative to the traditional propagation approach to determine the periodic equations. The complex wave numbers of the guided wave modes were determined using a combination of two-dimensional bracketing and minimization techniques. The results of this work indicate that the acoustic guided wave attenuation is sensitive to the [ital in] [ital situ] permeability. In particular, the attenuation changes significantly as the [ital in] [ital situ] permeability of the low-velocity layer is varied at the frequency corresponding to the minimum group velocity (Airy phase). Alternatively, the attenuation of the wave modes are practically unaffected by those permeability variations in the layer at the frequency corresponding to the maximum group velocity.
Application of sound-absorbent plastic to weak-shock-wave attenuators
NASA Astrophysics Data System (ADS)
Ootsuta, Katsuhisa; Matsuoka, Kei; Sasoh, Akihiro; Takayama, Kazuyoshi
1998-04-01
A device for attenuating weak shock waves propagating in a duct has been developed utilizing sound-absorbent plastic which is usually used for attenuating sound waves. The device has a tube made of the sound-absorbent plastic installed coaxially to a surrounding metal tube with a clearance between them. The clearance acts as an air layer to enhance the performance of the shock wave attenuation. When a weak shock wave propagates through this device, the pressure gradient of the shock wave is gradually smeared and hence its overpressure is decreased. The performance of the device was examined using a 1/250-scaled train tunnel simulator which simulated the discharge of weak shock waves created by high-speed entry of trains to tunnels. The overpressure of the shock waves ranged up to 5 kPa. The shock wave overpressure was decreased by 90% with the present attenuator attached. This device can be applied to various industrial noise suppressions which are associated with unsteady compressible flows.
Effects of partial liquid/gas saturation on extensional wave attenuation in Berea sandstone
NASA Astrophysics Data System (ADS)
Yin, C.-S.; Batzle, M. L.; Smith, B. J.
1992-07-01
Extensional wave attenuation measurements on Berea sandstone were made during increasing (imbibition) and decreasing (drainage) brine saturations. Measurements on samples with both open-pore and closed-pore surfaces were made using the resonant-bar technique. The frequency dependence was examined using the forced-deformation method. The attenuation was found to be dependent on saturation history as well as degree of saturation and boundary flow conditions. The sample with open-pore surface had a larger attenuation which peaked at greater brine saturations than the sample with closed-pore surface. During drainage, the attenuation reached a maximum at about 90% brine saturation as opposed to about 97% brine saturation during imbibition. The variation of the size and number of air pockets within the rock can account for this discrepancy. The magnitude of the attenuation peak value decreases substantially with decreasing frequency to the extent that no attenuation peak with saturation was apparent at seismic frequencies, say, below 100 Hz.
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.
The large-scale influence of the Great Barrier Reef matrix on wave attenuation
NASA Astrophysics Data System (ADS)
Gallop, Shari L.; Young, Ian R.; Ranasinghe, Roshanka; Durrant, Tom H.; Haigh, Ivan D.
2014-12-01
Offshore reef systems consist of individual reefs, with spaces in between, which together constitute the reef matrix. This is the first comprehensive, large-scale study, of the influence of an offshore reef system on wave climate and wave transmission. The focus was on the Great Barrier Reef (GBR), Australia, utilizing a 16-yr record of wave height from seven satellite altimeters. Within the GBR matrix, the wave climate is not strongly dependent on reef matrix submergence. This suggests that after initial wave breaking at the seaward edge of the reef matrix, wave energy that penetrates the matrix has little depth modulation. There is no clear evidence to suggest that as reef matrix porosity (ratio of spaces between individual reefs to reef area) decreases, wave attenuation increases. This is because individual reefs cast a wave shadow much larger than the reef itself; thus, a matrix of isolated reefs is remarkably effective at attenuating wave energy. This weak dependence of transmitted wave energy on depth of reef submergence, and reef matrix porosity, is also evident in the lee of the GBR matrix. Here, wave conditions appear to be dependent largely on local wind speed, rather than wave conditions either seaward, or within the reef matrix. This is because the GBR matrix is a very effective wave absorber, irrespective of water depth and reef matrix porosity.
NASA Astrophysics Data System (ADS)
Sano, Yukio
1989-05-01
A qualitative analysis of the mechanical response of rate-dependent media caused by a one-dimensional plane smooth wave front and by a continuous wave front attenuating in the media is performed by an underdetermined system of nonlinear partial differential equations. The analysis reveals that smooth strain, particle velocity, and stress profiles, which the smooth wave front has, are not similar and that the wave front is composed of some partial waves having different properties. The property is represented by a set of strain rate, acceleration, and stress rate. The wave front derived here from the analysis is composed of four different partial waves. The front of the wave front is necessarily a contraction wave in which strain, particle velocity, and stress increase with time, while the rear is a rarefaction wave where they all decrease with time. Between these two wave fronts there are two remaining wave fronts. We call these wave fronts mesocontraction waves I and II. Wave front I is a wave in which stress decreases notwithstanding the increase in strain and particle velocity with time, which is followed by the other, i.e., wave front II, where with time, particle velocity, and stress decrease in spite of the increase in strain. The continuous wave front having continuous and nonsmooth profiles of strain, particle velocity, and stress can also be composed of four waves. These waves possess the same property as the corresponding waves in the smooth wave front mentioned above. The velocities at three boundaries that the waves have are discontinuous. Therefore, these four wave fronts are independent waves, just as a shock wave and a rarefraction wave. Specifically, the front wave, i.e., a contraction wave front is being outrun by a second wave front, the second one is being outrun by a third wave front, and the third is being outrun by a fourth wave front, i.e., a rarefaction wave. We call the second wave front degenerate contraction wave I. We also call the third
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. PMID:25583866
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
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.
The first direct measurements of upper oceanic crustal compressional wave attenuation
NASA Astrophysics Data System (ADS)
Jacobson, R. S.; Lewis, B. T. R.
1990-10-01
The first direct measurement of compressional wave attenuation of the uppermost 650 m of oceanic crust was performed using data recorded by seafloor hydrophones and large (56-116 kg), deep, explosive sources. The site was 13 km east of the southernmost Juan de Fuca Ridge on crust 0.4 m.y. old Spectral ratios were performed between bottom refracting waves and direct water waves, adjusted for spreading losses and transmission coefficient losses. Several tests of the data were performed, demonstrating that attenuation is linearly related to frequency between 15 and 140 Hz, but frequency-independent components of attenuation are also evident. Values of compressional wave Q cluster between 20 and 50 and do not show any systematic variation with depth over 650 m. The attenuation results also indicate the presence of heterogeneities within the crust, as the solutions for each receiver's data set are significantly different. No evidence for azimuthal variations of attenuation are supported by the data, although the data do not optimally sample a wide variation of azimuths. Our attenuation values are judged to be normal to higher than expected for the whole oceanic crust, based upon comparisons to results from synthetic seismogram modeling by others and by modeling signal to noise ratios of typical seismic refraction profiles. The results are consistent with recent laboratory measurements at ultrasonic frequencies for dry and saturated basalts at seafloor pressures and temperatures.
Electromagnetic wave attenuation measurements in a ring-shaped inductively coupled air plasma
NASA Astrophysics Data System (ADS)
Wei, Xiaolong; Xu, Haojun; Li, Jianhai; Lin, Min; Su; Chen
2015-05-01
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 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 cm3 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 e achieves nearly uniform within the electronegative core and sharply steepens in the edge. The N 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.
Imaging Rayleigh wave attenuation and phase velocity in the western and central United States
NASA Astrophysics Data System (ADS)
Bao, X.; Dalton, C. A.; Jin, G.; Gaherty, J. B.
2013-12-01
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, 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. We jointly invert Rayleigh wave phase and amplitude observations for phase velocity and attenuation maps for the western and central United States using USArray data. This approach exploits the amplitudes' sensitivity to velocity and the phase delays' sensitivity to attenuation. The phase and amplitude data are measured in the period range 20--100 s using a new interstation cross-correlation approach, based on the Generalized Seismological Data Functional algorithm, that takes advantage of waveform similarity at nearby stations. The Rayleigh waves are generated from 670 large teleseismic earthquakes that occurred between 2006 and 2012, and measured from all available Transportable Array stations. We consider two separate and complementary approaches for imaging attenuation variations: (1) the Helmholtz tomography (Lin et al., 2012) and (2) two-station path tomography. Results obtained from the two methods are contrasted. We provide a preliminary interpretation based on the observed relationship between Rayleigh wave attenuation and phase velocity.
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.
Experimental investigation of wave attenuation through model and live vegetation
Technology Transfer Automated Retrieval System (TEKTRAN)
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...
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.
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
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.
Attenuation of seismic waves in methane gas hydrate-bearing sand
NASA Astrophysics Data System (ADS)
Priest, Jeffrey A.; Best, Angus I.; Clayton, Christopher R. I.
2006-01-01
Compressional wave (P wave) and shear wave (S wave) velocities (Vp and Vs, respectively) from remote seismic methods have been used to infer the distribution and volume of gas hydrate within marine sediments. Recent advances in seismic methods now allow compressional and shear wave attenuations (Q-1p and Q-1s, respectively) to be measured. However, the interpretation of these data is problematic due to our limited understanding of the effects of gas hydrate on physical properties. Therefore, a laboratory gas hydrate resonant column was developed to simulate pressure and temperature conditions suitable for methane gas hydrate formation in sand specimens and the subsequent measurement of both Q-1p and Q-1s at frequencies and strains relevant to marine seismic surveys. 13 dry (gas saturated) sand specimens were investigated with different amounts of methane gas hydrate evenly dispersed throughout each specimen. The results show that for these dry specimens both Q-1p and Q-1s are highly sensitive to hydrate saturation with unexpected peaks observed between 3 and 5 per cent hydrate saturation. It is thought that viscous squirt flow of absorbed water or free gas within the pore space is enhanced by hydrate cement at grain contacts and by the nanoporosity of the hydrate itself. These results show for the first time the dramatic effect methane gas hydrate can have on seismic wave attenuation in sand, and provide insight into wave propagation mechanisms. These results will aid the interpretation of elastic wave attenuation data obtained using marine seismic prospecting methods.
P- and S-wave seismic attenuation for deep natural gas exploration and development
Walls, Joel; Uden, Richard; Singleton, Scott; Shu, Rone; Mavko, Gary
2005-04-12
Using current methods, oil and gas in the subsurface cannot be reliably predicted from seismic data. This causes domestic oil and gas fields to go undiscovered and unexploited, thereby increasing the need to import energy.The general objective of this study was to demonstrate a simple and effective methodology for estimating reservoir properties (gas saturation in particular, but also including lithology, net to gross ratios, and porosity) from seismic attenuation and other attributes using P- and S-waves. Phase I specific technical objectives: Develop Empirical or Theoretical Rock Physics Relations for Qp and Qs; Create P-wave and S-wave Synthetic Seismic Modeling Algorithms with Q; and, Compute P-wave and S-wave Q Attributes from Multi-component Seismic Data. All objectives defined in the Phase I proposal were accomplished. During the course of this project, a new class of seismic analysis was developed based on compressional and shear wave inelastic rock properties (attenuation). This method provides a better link between seismic data and the presence of hydrocarbons. The technique employs both P and S-wave data to better discriminate between attenuation due to hydrocarbons versus energy loss due to other factors such as scattering and geometric spreading. It was demonstrated that P and S attenuation can be computed from well log data and used to generate synthetic seismograms. Rock physics models for P and S attenuation were tested on a well from the Gulf of Mexico. The P- and S-wave Q attributes were computed on multi-component 2D seismic data intersecting this well. These methods generated reasonable results, and most importantly, the Q attributes indicated gas saturation.
Attenuative body wave dispersion at La Cerdanya, eastern Pyrenees
NASA Astrophysics Data System (ADS)
Correig, Antoni M.; Mitchell, Brian J.
1989-11-01
Coda- Q for P- and S-waves has been measured from digitally recorded events occurring in the La Cerdanya region of the eastern Pyrenees. Interpreted in terms of a power law, Q( f) = Q0fη, Q-coda for P-waves is characterized by Q0 = 14 and η = 1.07, and S-waves by Q0 = 14 and η = 1.13. Using a generalization of a model due to Dainty (1981), we obtain a Q model for S-waves in which intrinsic- Q is 23, the frequency dependence (ζ) of intrinsic- Q is 1.17, and the turbidity factor is 0.051. Interpreted in terms of a continuous relaxation model, where Qm is minimum Q, and τ1 and τ2 are high- and low-frequency cutoffs, respectively, the values of the parameters are Qm = 5 and τ1 = 0.37 when τ2 is assumed to be 10 000. Body wave dispersion, as computed from the differences in arrival times of the wave filtered at 3, 6, 12 and 24 Hz relative to that at 6 Hz has been measured and found to range from 0.067 at 3 Hz to -0.075 at 24 Hz. This dispersion constrains τ2 to be 43.
Attenuation Tomography of Body Waves in Thickness-varying Layered Media
NASA Astrophysics Data System (ADS)
Cao, H.; Zhou, H.
2006-12-01
The intrinsic attenuation of seismic waves, which is quantified as inverse to the quality factor (Q) of a medium, is a well-publicized and yet poorly studied subject. While it is common to deduce Q values from measured dispersion data for surface waves, previous studies on the intrinsic attenuation of body waves have relied on measurements of the waveform of first arrivals or reflections. Better understanding is needed for both solid Earth geophysics and applied seismology to quantify the contributing factors to seismic attenuation and decompose Q from other factors because Q is closely related to rock property and fluid saturation. This study focuses on forward modeling and tomographic inversion for the Q values in thickness-varying layered media. Many of the existing theoretical Q models work in such media. Our work is an extension of the deformable- layer tomography (Zhou, 2004) to dissipative media. In the first phase of this study, we evaluated, through numerical modeling the various factors contributing to the attenuation of body waves. Theoretically, there are intrinsic attenuation, which is related to rock and pore fluid properties, and attenuation due to wave propagation effects, such as geometrical spreading and energy partition across interfaces (transmission and reflection). We made several representative numerical models, and conducted forward modeling using both wave theory and ray theory to quantify the amount of the attenuation of body waves due to different factors. In the second phase, we are integrating the forward modeling with the deformable-layer tomography algorithm to develop means to invert for Q distribution in thickness-varying layer media. While the deformable-layer tomography determines layer velocities and geometry, the current work intends to invert for Q values of the thickness-varying model layers as well as parameters associated with interface energy partition and geometric spreading. In the third phase, we plan to apply the
Experimental and Numerical Investigation of Pressure Wave Attenuation due to Bubbly Layers
NASA Astrophysics Data System (ADS)
Jayaprakash, Arvind; Fourmeau, Tiffany; Hsiao, Chao-Tsung; Chahine, Georges; Dynaflow Inc. Team
2013-03-01
In this work, the effects of dispersed microbubbles on a steep pressure wave and its attenuation are investigated both numerically and experimentally. Numerical simulations were carried out using a compressible Euler equation solver, where the liquid-gas mixture was modeled using direct numerical simulations involving discrete deforming bubbles. To reduce computational costs a 1D configuration is used and the bubbles are assumed distributed in layers and the initial pressure profile is selected similar to that of a one-dimensional shock tube problem. Experimentally, the pressure pulse was generated using a submerged spark electric discharge, which generates a large vapor bubble, while the microbubbles in the bubbly layer are generated using electrolysis. High speed movies were recorded in tandem with high fidelity pressure measurements. The dependence of pressure wave attenuation on the bubble radii, the void fraction, and the bubbly layer thickness were parametrically studied. It has been found that the pressure wave attenuation can be seen as due to waves reflecting and dispersing in the inter-bubble regions, with the energy absorbed by bubble volume oscillations and re-radiation. Layer thickness and small bubble sizes were also seen as having a strong effect on the attenuation with enhanced attenuation as the bubble size is reduced for the same void fraction. This study was supported by the Department of Energy, under SBIR Phase II Contract DE-FG02-07ER84839.
Grain-size dependence of shear wave speed dispersion and attenuation in granular marine sediments.
Kimura, Masao
2014-07-01
The author has shown that measured shear wave speed dispersion and attenuation in water-saturated silica sand can be predicted by using a gap stiffness model incorporated into the Biot model (the BIMGS model) [Kimura, J. Acoust. Soc. Am. 134, 144-155 (2013)]. In this study, the grain-size dependence of shear wave speed dispersion and attenuation in four kinds of water-saturated silica sands with different grain sizes is measured and calculated. As a result, the grain-size dependence of the aspect ratio in the BIMGS model can be validated and the effects of multiple scattering for larger grain sizes are demonstrated. PMID:24993238
Dynamic aspects of apparent attenuation and wave localization in layered media
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.
Propagation and attenuation of Rayleigh waves in generalized thermoelastic media
NASA Astrophysics Data System (ADS)
Sharma, M. D.
2014-01-01
This study considers the propagation of Rayleigh waves in a generalized thermoelastic half-space with stress-free plane boundary. The boundary has the option of being either isothermal or thermally insulated. In either case, the dispersion equation is obtained in the form of a complex irrational expression due to the presence of radicals. This dispersion equation is rationalized into a polynomial equation, which is solvable, numerically, for exact complex roots. The roots of the dispersion equation are obtained after removing the extraneous zeros of this polynomial equation. Then, these roots are filtered out for the inhomogeneous propagation of waves decaying with depth. Numerical examples are solved to analyze the effects of thermal properties of elastic materials on the dispersion of existing surface waves. For these thermoelastic Rayleigh waves, the behavior of elliptical particle motion is studied inside and at the surface of the medium. Insulation of boundary does play a significant role in changing the speed, amplitude, and polarization of Rayleigh waves in thermoelastic media.
Poroelastic model to relate seismic wave attenuation and dispersion to permeability anisotropy
Parra, J.O.
2000-02-01
A transversely isotropic model with a horizontal axis of symmetry, based on the Biot and squirt-flow mechanisms, predicts seismic waves in poroelastic media. The model estimates velocity dispersion and attenuation of waves propagating in the frequency range of crosswell and high-resolution reverse vertical seismic profiling (VSP) (250--1,250 HZ) for vertical permeability value much greater than horizontal permeability parameters. The model assumes the principal axes of the stiffness constant tensor are aligned with the axes of the permeability and squirt-flow tensors. In addition, the unified Biot and squirt-flow mechanism (BISQ) model is adapted to simulate cracks in permeable media. Under these conditions, the model simulations demonstrate that the preferential direction of fluid flow in a reservoir containing fluid-filled cracks can be determined by analyzing the phase velocity and attenuation of seismic waves propagating at different azimuth and incident angles. As a result, the fast compressional wave can be related to permeability anisotropy in a reservoir. The model results demonstrate that for fast quasi-P-wave propagating perpendicular to fluid-filled cracks, the attenuation is greater than when the wave propagates parallel to the plane of the crack. Theoretical predictions and velocity dispersion of interwell seismic waves in the Kankakee Limestone Formation at the Buckhorn test site (Illinois) demonstrate that the permeable rock matrix surrounding a low-velocity heterogeneity contains vertical cracks.
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.
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.
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.
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
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. PMID:22326320
Shear wave velocity and attenuation from pulse-echo studies of Berea sandstone
NASA Astrophysics Data System (ADS)
Green, Douglas H.; Wang, Herbert F.
1994-06-01
The pulse-echo spectral-ratio technique has been adapted to the determination of ultrasonic shear wave attenuation in sandstone at variable states of saturation and pressure. The method can measure shear attenuation coefficients in the range 0.5 dB/cm to 8 dB/cm to within +/- 0.5 dB/cm. For the Berea sandstone, this range corresponds to values of the shear quality factor Q(sub s) between 10 and 100. Spectra Q(sub s) show that between 600 and 1110 kHz, Q(sub s) decreases with frequency, particularly at high pressures (up to 70 MPa). Ultrasonic shear wave attenuation in a 90% water-saturated sample was intermediate between that for dry samples and the relatively high attenuation in fully saturated rock. Strong pressure dependence is seen in the shear attentuation for all saturation states, indicating a dominant role of dissipation mechanisms operating within open and compliant cracks. Substantial shear attenuation remains at the highest effective pressure applied to the saturated sample, which may be due to a more 'global' fluid-flow loss mechanism. Scattering losses as described by weak scattering theories for compressional waves, do not appear to be dominant at these frequencies.
Study of transmission line attenuation in broad band millimeter wave frequency range
NASA Astrophysics Data System (ADS)
Pandya, Hitesh Kumar B.; Austin, M. E.; Ellis, R. F.
2013-10-01
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.
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
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.
NASA Astrophysics Data System (ADS)
Cui, Y.; Zou, D. H.
2006-08-01
In this paper, the guided ultrasonic wave propagating in grouted rock bolts was simulated with finite element method. An 800 mm partially grouted cylindrical rock bolt model was created. Dynamic input signals with frequency from 25 to 100 kHz were used to excite ultrasonic wave. The simulated waveform, group velocity and amplitude ratio matched well with the experimental results. This model made it possible to study the behaviour of the guided waves in the grouted bolt along its central axis. Analysis of the simulated results showed that the group velocity in grouted rock bolts is constant along the grouted length, and the boundary effect on the group velocity is negligible. This paper also presents methods to determine the attenuation coefficient from simulation and to determine the boundary effect on attenuation at the bolt ends. The analysis showed that the attenuation of the guided wave propagating inside the grouted bolts is similar to the theoretical solution in steel bar with infinite length. After correction for the boundary effects the grout length of a grouted rock bolt can be determined using the measured attenuation, with sufficient accuracy.
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.
Laboratory velocities and attenuation of p-waves in limestones during freeze-thaw cycles
Remy, J.M.; Bellanger, M.; Homand-Etienne, F. )
1994-02-01
The velocity and the attenuation of compressional P-waves, measured in the laboratory at ultrasonic frequencies during a series of freezing and thawing cycles, are used as a method for predicting frost damage in a bedded limestone. Pulse transmission and spectral ratio techniques are used to determine the P-wave velocities and the attenuation values relative to an aluminum reference samples with very low attenuation. Limestone samples were water saturated under vacuum conditions, jacketed with rubber sleeves, and immersed in an antifreeze bath (50 percent methanol solution). They were submitted to repeated 24-hour freezing and thawing cycles simulating natural environment conditions. During the freeze/thaw cycles, P-wave velocities and quality factor Q diminished rapidly in thawed rock samples, indicating modification of the pore space. Measurements of crack porosity were conducted by hydrostatic compression tests on cubic rock samples that had been submitted to these freeze/thaw cycles. These measurements are used as an index of crack formation. The hydrostatic compression tests confirmed the phases of rock damage that were shown by changes in the value of Q. Furthermore, comparison between Q values and crack porosity demonstrate that the variations of P-wave attenuation are caused by the creation of new cracks and not by the enlargement of pre-existing cracks.
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
Electromagnetic wave attenuation measurements in a ring-shaped inductively coupled air plasma
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.
Angular and Frequency-Dependent Wave Velocity and Attenuation in Fractured Porous Media
NASA Astrophysics Data System (ADS)
Carcione, José M.; Gurevich, Boris; Santos, Juan E.; Picotti, Stefano
2013-11-01
Wave-induced fluid flow generates a dominant attenuation mechanism in porous media. It consists of energy loss due to P-wave conversion to Biot (diffusive) modes at mesoscopic-scale inhomogeneities. Fractured poroelastic media show significant attenuation and velocity dispersion due to this mechanism. The theory has first been developed for the symmetry axis of the equivalent transversely isotropic (TI) medium corresponding to a poroelastic medium containing planar fractures. In this work, we consider the theory for all propagation angles by obtaining the five complex and frequency-dependent stiffnesses of the equivalent TI medium as a function of frequency. We assume that the flow direction is perpendicular to the layering plane and is independent of the loading direction. As a consequence, the behaviour of the medium can be described by a single relaxation function. We first consider the limiting case of an open (highly permeable) fracture of negligible thickness. We then compute the associated wave velocities and quality factors as a function of the propagation direction (phase and ray angles) and frequency. The location of the relaxation peak depends on the distance between fractures (the mesoscopic distance), viscosity, permeability and fractures compliances. The flow induced by wave propagation affects the quasi-shear (qS) wave with levels of attenuation similar to those of the quasi-compressional (qP) wave. On the other hand, a general fracture can be modeled as a sequence of poroelastic layers, where one of the layers is very thin. Modeling fractures of different thickness filled with CO2 embedded in a background medium saturated with a stiffer fluid also shows considerable attenuation and velocity dispersion. If the fracture and background frames are the same, the equivalent medium is isotropic, but strong wave anisotropy occurs in the case of a frameless and highly permeable fracture material, for instance a suspension of solid particles in the fluid.
Attenuation of Elastic Waves due to Scattering from Spherical Cavities and Elastic Inclusions.
NASA Astrophysics Data System (ADS)
Hinders, Mark Karl
1990-01-01
The attenuation of elastic waves due to scattering from a spherical inclusion of arbitrary size in an infinitely extended medium is investigated. The spherical scatterer and the exterior medium are isotropic, homogeneous, and linearly elastic, but of arbitrarily differing material parameters, with compressional and shear waves supported in both media. Exact expressions for scattered and transmitted fields caused by an incident plane compressional or shear wave of unit amplitude are calculated analytically and general expressions for extinction and scattering cross -sections are derived for both lossy and lossless scattering. Application to ultrasonic determination of porosity in cast aluminum is investigated.
Effects of microstructure on the speed and attenuation of elastic waves
Gubernatis, J.E.; Domany, E.
1982-01-01
A unified theory pertaining to the sensitivity of the propagation of an elastic wave to changes in the microstructural details of a material is discussed. In contrast to nearly all previous treatments a first principles approach, using developments from other multiple scattering problems and adapting them to the elastic wave case, is followed. We then present several simple, standard approximations. In the process the validity of the commonly made assumption that ..cap alpha.. = n anti sigma is clarified, and the effective speed, illustrating its complementary character to the attenuation, is computed. The principal objective is to present the formal analysis necessary to treat systematically the dependency of the wave propagation on microstructural statistics.
NASA Astrophysics Data System (ADS)
Jung, Heeok; Jang, Yong-seok; Lee, Jung Mo; Moon, Wooil M.; Baag, Chang-Eob; Kim, Ki Young; Jo, Bong Gon
2007-01-01
We analyzed the short period Rayleigh waves from the first crustal-scale seismic refraction experiment in the Korean peninsula, KCRUST2002, to determine the shear wave velocity and attenuation structure of the uppermost 1 km of the crust in different tectonic zones of the Korean peninsula and to examine if this can be related to the surface geology of the study area. The experiment was conducted with two large explosive sources along a 300-km long profile in 2002. The seismic traces, recorded on 170 vertical-component, 2-Hz portable seismometers, show distinct Rayleigh waves in the period range between 0.2 s and 1.2 s, which are easily recognizable up to 30-60 km from the sources. The seismic profiles, which traverse three tectonic regions (Gyeonggi massif, Okcheon fold belt and Yeongnam massif), were divided into five subsections based on tectonic boundaries as well as lithology. Group and phase velocities for the five subsections obtained by a continuous wavelet transform method and a slant stack method, respectively, were inverted for the shear wave models. We obtained shear wave velocity models up to a depth of 1.0 km. Overall, the shear wave velocity of the Okcheon fold belt is lower than that of the Gyeonggi and Yeongnam massifs by ˜ 0.4 km/s in the shallowmost 0.2 km and by 0.2 km/s at depths below 0.2 km. Attenuation coefficients, determined from the decay of the fundamental mode Rayleigh waves, were used to obtain the shear wave attenuation structures for three subsections (one for each of the three different tectonic regions). We obtained an average value of Qβ- 1 in the upper 0.5 km for each subsection. Qβ- 1 for the Okcheon fold belt (˜ 0.026) is approximately three times larger than Qβ- 1 for the massif areas (˜ 0.008). The low shear wave velocity in the Okcheon fold belt is consistent with the high attenuation in this region.
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.
Relating wave attenuation to pancake ice thickness, using field measurements and model results
NASA Astrophysics Data System (ADS)
Doble, Martin J.; De Carolis, Giacomo; Meylan, Michael H.; Bidlot, Jean-Raymond; Wadhams, Peter
2015-06-01
Wave attenuation coefficients (α, m-1) were calculated from in situ data transmitted by custom wave buoys deployed into the advancing pancake ice region of the Weddell Sea. Data cover a 12 day period as the buoy array was first compressed and then dilated under the influence of a passing low-pressure system. Attenuation was found to vary over more than 2 orders of magnitude and to be far higher than that observed in broken-floe marginal ice zones. A clear linear relation between α and ice thickness was demonstrated, using ice thickness from a novel dynamic/thermodynamic model. A simple expression for α in terms of wave period and ice thickness was derived, for application in research and operational models. The variation of α was further investigated with a two-layer viscous model, and a linear relation was found between eddy viscosity in the sub-ice boundary layer and ice thickness.
A multiscale poromicromechanical approach to wave propagation and attenuation in bone.
Morin, Claire; Hellmich, Christian
2014-07-01
Ultrasonics is an important diagnostic tool for bone diseases, as it allows for non-invasive assessment of bone tissue quality through mass density-elasticity relationships. The latter are, however, quite complex for fluid-filled porous media, which motivates us to develop a rigorous multiscale poromicrodynamics approach valid across the great variety of different bone tissues. Multiscale momentum and mass balance, as well as kinematics of a hierarchical double porous medium, together with Darcy's law for fluid flow and micro-poro-elasticity for the solid phase of bone, give access to the so-called dispersion relation, linking the complex wave numbers to corresponding wave frequencies. Experimentally validated results show that 2.25 MHz acoustical signals transmit healthy cortical bone (exhibiting a low vascular porosity) only in the form of fast waves, agreeing very well with experimental data, while both fast and slow waves transmit highly osteoporotic as well as trabecular bone (exhibiting a large vascular porosity). While velocities and wavelengths of both fast and slow waves, as well as attenuation lengths of slow waves, are always monotonously increasing with the permeability of the bone sample, the attenuation length of fast waves shows a minimum when considered as function of the permeability. PMID:24457030
Numerical investigation of wave attenuation by vegetation using a 3D RANS model
NASA Astrophysics Data System (ADS)
Marsooli, Reza; Wu, Weiming
2014-12-01
Vegetation has been recognized as an important natural shoreline protection against storm surges and waves. Understanding of wave-vegetation interaction is essential for assessing the ability of vegetation patches, such as wetlands, to mitigate storm damages. In this study the wave attenuation by vegetation is investigated numerically using a 3-D model which solves the Reynolds-Averaged Navier-Stokes equations (RANS) by means of a finite-volume method based on collocated hexahedron mesh. A mixing length model is used for turbulence closure of the RANS equations. The water surface boundary is tracked using the Volume-of-Fluid (VOF) method with the Compressive Interface Capturing Scheme for Arbitrary Meshes (CICSAM) to solve the VOF advection equation. The presence of vegetation is taken into account by adding the vegetation drag and inertia forces to the momentum equations. The model is validated by several laboratory experiments of short wave propagation through vegetation over flat and sloping beds. The comparisons show good agreement between the measured data and calculated results, but the swaying motion of flexible vegetation which is neglected in this study can influence the accuracy of the wave height predictions. The model is then applied to one of the validation tests with different vegetation properties, revealing that the wave height attenuation by vegetation depends not only on the wave conditions, but also the vegetation characteristics such as vegetation height and density.
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.
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.
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. PMID:22417882
Temporal change in coda wave attenuation observed during an eruption of Mount St. Helens
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
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
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
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.
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.
Attenuation of coda waves in the Garhwal Lesser Himalaya, India
NASA Astrophysics Data System (ADS)
Jain, S. K.; Gupta, S. C.; Kumar, Ashwani
2015-04-01
Qc estimates for the Uttarkashi and the Chamoli regions of the Garhwal Lesser Himalaya have been obtained by analyzing the coda waves of 159 local earthquakes recorded during 2008 and 2009 employing a 12-station seismological network. Earthquakes around the Uttarkashi region are located in the epicentral distance range of 5.0 to 93.9 km, focal depth range of 1.63 to 42.13 km, and coda magnitude range of 0.2 to 2.9, whereas earthquakes around Chamoli region are located in the epicentral distance range of 19.8-109.2 km, focal depth range of 1.36 to 40.72 km, and coda magnitude range of 1.0 to 3.0. The coda waves of 30 s duration, recorded on 982 seismograms, have been analyzed in seven frequencies range centered at 1.5, 3.0, 6.0, 9.0, 12.0, 18.0, and 24.0 Hz for four to five lapse time windows (LTW) using the single backscattering model given by Aki and Chouet (J Geophys Res 80:3322-3342, 1975). Mean value of Qc estimates vary from 76 at 1.5 Hz to 2201 at 24.0 Hz for LTW range of 10-40 s and from 216 at 1.5 Hz to 3243 at 24.0 Hz for LTW range of 50-80 s (for the Uttarkashi region) and from 147 at 1.5 Hz to 2273 at 24.0 Hz for LTW range of 20-50 s and from 188 at 1.5 Hz to 2826 at 24.0 Hz for LTW range of 50-80 s (for Chamoli region). The Qc values thus obtained showed a clear dependence on frequency and LTW and frequency dependence Qc relationships, Qc = Q0fη, for LTWs that have been obtained as Qc = 57f1.20 (10-40 s), Qc = 97f1.07 (20-50 s), Qc = 116f1.03 (30-60 s), Qc = 130f1.03 (40-70 s), and Qc = 162f0.95 (50-80 s) for Uttarkashi region and Qc = 107f0.95 (20-50 s), Qc = 115f0.96 (30-60 s), Qc = 128f0.95 (40-70 s), and Qc = 145f0.95 (50-80 s) for Chamoli region.
Scattering attenuation ratios of P and S waves in elastic media
NASA Astrophysics Data System (ADS)
Hong, Tae-Kyung
2004-07-01
The variation of scattering attenuation ratios of P and S waves (Q-1P/Q-1S) is investigated in elastic media by using numerical simulations and theoretical expressions based on the first-order Born approximation. Numerical results from stochastic random media (von Karman, exponential, Gaussian) with mild velocity perturbation (10 per cent in this study) are represented well by theoretical attenuation curves with a minimum scattering angle of 60-90°. The level of scattering attenuation ratios is dependent on the velocity ratio (γ=α0/β0) and the type of medium. The change of perturbation in the density introduces a relatively small variation in attenuation ratio. Attenuation ratios are proportional to normalized frequency (fa, frequency-by-correlation length) at the intermediate-frequency range (0.1 km s-1 < fa < 10 km s-1) and determined constant at the high-frequency (fa > 10 km s-1) and low-frequency (fa < 1 km s-1) regimes. The von Karman-type models look appropriate for the representation of small-scale variation in the Earth. The scattering attenuation ratios can be implemented for the investigation of small-scale heterogeneities in the Earth.
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.
NASA Astrophysics Data System (ADS)
Lemein, T.; Cox, D. T.; Albert, D.; Blackmar, P.
2012-12-01
Feedbacks between vegetation, wave climate, and sedimentation create stable ecosystem states within estuaries that provide ecosystem services such as wildlife habitat, erosion control, and pollution filtration. Flume and field studies conducted with cordgrass (Spartina spp.) and sea grasses (Zostera spp., Halodule spp.) have demonstrated that the presence of vegetation reduces wave energy and increases sediment retention. Since the spatial distribution of plant species and the presence of unique plant species differ between estuaries, there is a need to understand how individual plant species, or groups of species with similar morphology, influence wave characteristics and sedimentation. Within Tillamook Bay, Oregon, three species of emergent vascular vegetation species (Carex lyngbyei, Eleocharis sp., Schoenoplectus pungens) and one species of submergent vascular vegetation species (Zostera marina) are present in the high wave energy portion of the estuary at the border of open water and the start of vegetation. These species represent three distinct growth forms (emergent reeds, emergent grasses, submergent grasses) and occur at varying densities relative to each other, as well as within the estuary. Using paired acoustic Doppler velocimeters (ADVs), we quantify the relative attenuation of wave velocity between vegetation types and densities within the estuary and compare these results with published attenuation rates from flume and field studies in different environments. The effect of decreased wave velocity on sediment retention is measured using permanent sediment markers within and outside of vegetation stands and paired with ADV data. Sediment retention is predicted to vary seasonally with seasonal vegetation composition changes and remain constant in unvegetated areas. From this experiment we expect to identify like groups of plant species whose attenuation characteristics are the same, allowing for models of wave-vegetation-sediment interaction to be
Attenuation of shock waves propagating through nano-structured porous materials
NASA Astrophysics Data System (ADS)
Al-Qananwah, Ahmad K.; Koplik, Joel; Andreopoulos, Yiannis
2013-07-01
Porous materials have long been known to be effective in energy absorption and shock wave attenuation. These properties make them attractive in blast mitigation strategies. Nano-structured materials have an even greater potential for blast mitigation because of their high surface-to-volume ratio, a geometric parameter which substantially attenuates shock wave propagation. A molecular dynamics approach was used to explore the effects of this remarkable property on the behavior of traveling shocks impacting on solid materials. The computational setup included a moving piston, a gas region and a target solid wall with and without a porous structure. The gas and porous solid were modeled by Lennard-Jones-like and effective atom potentials, respectively. The shock wave is resolved in space and time and its reflection from a solid wall is gradual, due to the wave's finite thickness, and entails a self-interaction as the reflected wave travels through the incoming incident wave. Cases investigated include a free standing porous structure, a porous structure attached to a wall and porous structures with graded porosity. The effects of pore shape and orientation have been also documented. The results indicate that placing a nano-porous material layer in front of the target wall reduced the stress magnitude and the energy deposited inside the solid by about 30 percent, while at the same time substantially decreasing the loading rate.
NASA Astrophysics Data System (ADS)
Tisato, N.; Madonna, C.; Saenger, E. H.
2012-04-01
Seismic wave attenuation at low frequencies in the earth crust has been explained by partial saturation as well as permeability models. We present results obtained by the Broad Band Attenuation Vessel (BBAV) which measures seismic wave attenuation using the sub-resonance method in the frequency range 0.01 - 100 Hz. The apparatus also allows the investigation of attenuation mechanisms related to fluid flow by means of five pore pressure sensors placed in the specimen. This allows continuous local measurements of pore pressure changes generated by stress field changes. Measurements were performed on 76 mm diameter, 250 mm long, 20% porosity, and ~500 mD permeability Berea sandstone samples. The confining pressure was varied between 0 and 20 MPa, and the specimens were saturated with water between 0% and 90%. Attenuation measurements show dependence with saturation. For instance, when samples are at dry conditions they exhibit attenuation values around 0.01, the same sample saturated with 90% water shows attenuation values between 0.018 and 0.028 across the entire frequency range. Attenuation is also confining pressure dependent. For instance, variations of confining pressure ranging between 0 and 8 MPa lead to quality factors between 40 and 10 at 60 Hz and 60% water saturation. Best fits on these measurements reveal that the corner frequency of the attenuation mechanism decreases from ~800 to ~200 Hz with increasing confining pressure. Using calibration measurements with Aluminum the possibility of apparatus resonances can be ruled out. Local pore pressure measurements corroborate this observation showing pore pressure evolution as a function of saturation. The results are discussed and interpreted in light of known attenuation mechanisms for partially saturated rocks (patchy saturation and squirt flow). We rule out the possibility of patchy saturation occurrence, but squirt flow would offer an explanation. The confining pressure dependence could be the result of
Development of Floating Wave Barriers for Cost Effective Protection of Irrigation Pond Levees
Technology Transfer Automated Retrieval System (TEKTRAN)
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, ...
Fully nonlinear modeling of radiated waves generated by floating flared structures
NASA Astrophysics Data System (ADS)
Zhou, Bin-Zhen; Ning, De-Zhi; Teng, Bin; Zhao, Ming
2014-10-01
The nonlinear radiated waves generated by a structure in forced motion, are simulated numerically based on the potential theory. A fully nonlinear numerical model is developed by using a higher-order boundary element method (HOBEM). In this model, the instantaneous body position and the transient free surface are updated at each time step. A Lagrangian technique is employed as the time marching scheme on the free surface. The mesh regridding and interpolation methods are adopted to deal with the possible numerical instability. Several auxiliary functions are proposed to calculate the wave loads indirectly, instead of directly predicting the temporal derivative of the velocity potential. Numerical experiments are carried out to simulate the heave motions of a submerged sphere in infinite water depth, the heave and pitch motions of a truncated flared cylinder in finite depth. The results are verified against the published numerical results to ensure the effectiveness of the proposed model. Moreover, a series of higher harmonic waves and force components are obtained by the Fourier transformation to investigate the nonlinear effect of oscillation frequency. The difference among fully nonlinear, body-nonlinear and linear results is analyzed. It is found that the nonlinearity due to free surface and body surface has significant influences on the numerical results of the radiated waves and forces.
Design and Analysis for a Floating Oscillating Surge Wave Energy Converter: Preprint
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.
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…
NASA Astrophysics Data System (ADS)
Ardhuin, Fabrice; Sutherland, Peter; Doble, Martin; Wadhams, Peter
2016-06-01
The poorly understood attenuation of surface waves in sea ice is generally attributed to the combination of scattering and dissipation. Scattering and dissipation have very different effects on the directional and temporal distribution of wave energy, making it possible to better understand their relative importance by analysis of swell directional spreading and arrival times. Here we compare results of a spectral wave model—using adjustable scattering and dissipation attenuation formulations—with wave measurements far inside the ice pack. In this case, scattering plays a negligible role in the attenuation of long swells. Specifically, scattering-dominated attenuation would produce directional wave spectra much broader than the ones recorded, and swell events arriving later and lasting much longer than observed. Details of the dissipation process remain uncertain. Average dissipation rates are consistent with creep effects but are 12 times those expected for a laminar boundary layer under a smooth solid ice plate.
Potsika, Vassiliki T; Protopappas, Vasilios C; Vavva, Maria G; Polyzos, Demosthenes; Fotiadis, Dimitrios I
2013-01-01
The quantitative determination of wave dispersion and attenuation in bone is an open research area as the factors responsible for ultrasound absorption and scattering in composite biological tissues have not been completely explained. In this study, we use the iterative effective medium approximation (IEMA) proposed in [1] so as to calculate phase velocity and attenuation in media with properties similar to those of cancellous bones. Calculations are performed for a frequency range of 0.4-0.8 MHz and for different inclusions' volume concentrations and sizes. Our numerical results are compared with previous experimental findings so as to assess the effectiveness of IEMA. It was made clear that attenuation and phase velocity estimations could provide supplementary information for cancellous bone characterization. PMID:24111396
Seismic‐wave attenuation determined from tectonic tremor in multiple subduction zones
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.
Baksi, A John; Davies, Justin E; Hadjiloizou, Nearchos; Baruah, Resham; Unsworth, Beth; Foale, Rodney A; Korolkova, Olga; Siggers, Jennifer H; Francis, Darrel P; Mayet, Jamil; Parker, Kim H; Hughes, Alun D
2015-01-01
Background Wave reflection may be an important influence on blood pressure, but the extent to which reflections undergo attenuation during retrograde propagation has not been studied. We quantified retrograde transmission of a reflected wave created by occlusion of the left femoral artery in man. Methods 20 subjects (age 31-83 y; 14 male) underwent invasive measurement of pressure and flow velocity with a sensor-tipped intra-arterial wire at multiple locations distal to the proximal aorta before, during and following occlusion of the left femoral artery by thigh cuff inflation. A numerical model of the circulation was also used to predict reflected wave transmission. Wave reflection was measured as the ratio of backward to forward wave energy (WRI) and the ratio of peak backward to forward pressure (Pb/Pf). Results Cuff inflation caused a marked reflection which was largest 5-10cm from the cuff (change (Δ) in WRI = 0.50 (95% CI 0.38, 0.62); p<0.001, ΔPb/Pf = 0.23 (0.18 - 0.29); p<0.001). The magnitude of the cuff-induced reflection decreased progressively at more proximal locations and was barely discernible at sites >40cm from the cuff including in the proximal aorta. Numerical modelling gave similar predictions to those observed experimentally. Conclusions Reflections due to femoral artery occlusion are markedly attenuated by the time they reach the proximal aorta. This is due to impedance mismatches of bifurcations traversed in the backward direction. This degree of attenuation is inconsistent with the idea of a large discrete reflected wave arising from the lower limb and propagating back into the aorta. PMID:26436672
Rheological anisotropy of the Earth's mantle and attenuation of seismic waves
NASA Astrophysics Data System (ADS)
Birger, B. I.
2006-11-01
The nonlinear integral (having memory) model previously proposed by the author for the description of the dislocation rheology of mantle rocks is generalized to the case of crystals with anisotropic rheology. The latter is caused by a large difference between the effective viscosities associated with dislocation glide and dislocation climb (in the crystallographic coordinate system, the dislocation glide governs simple shear, whereas the dislocation climb governs pure shear). Since the mantle is polycrystalline and crystal grains an order of a millimeter in size are oriented chaotically, anisotropy vanishes with volume averaging. However, convective flows in the mantle produce large strains and lead to a preferred orientation of grains and, thereby, anisotropy of the upper mantle. The lower mantle is dominated by diffusion rheology, which cannot cause anisotropy. The mantle rheological anisotropy gives rise to anisotropic attenuation of seismic waves. It is shown that the attenuation depends on the polarization and direction of seismic waves and on the parameters of the rheological model.
Dislocation damping and anisotropic seismic wave attenuation in Earth's upper mantle.
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. PMID:22517856
Pore-Scale Modeling of Pore Structure Effects on P-Wave Scattering Attenuation in Dry Rocks
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
Pore-scale modeling of pore structure effects on P-wave scattering attenuation in dry rocks.
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. PMID:25961729
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.
NASA Astrophysics Data System (ADS)
Petrov, P. S.; Zakharenko, A. D.; Trofimov, M. Yu.
2012-11-01
A suitable tool for the simulation of low frequency acoustic pulse signals propagating in a shallow sea is the numerical integration of the nonstationary wave equation. The main feature of such simulation problems is that in this case the sound waves propagate in the geoacoustic waveguide formed by the upper layers of the bottom and the water column. By this reason, the correct dependence of the attenuation of sound waves in the bottom on their frequency must be taken into account. In this paper we obtain an integro-differential equation for the sound waves in the viscoelastic fluid, which allows to simulate the arbitrary dependence of acoustic wave attenuation on frequency in the time domain computations. The procedure of numerical solution of this equation based on its approximation by a system of differential equations is then considered and the methods of artificial limitation of computational domain are described. We also construct a simple finite-difference scheme for the proposed equation suitable for the numerical solution of nonstationary problems arising in the shallow-sea acoustics.
NASA Astrophysics Data System (ADS)
Zaslavsky, A.
2015-02-01
In situ observation of dust grains from various origins is routinely 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 collection by the spacecraft of electric charges generated by impact ionization. Here for the first time, a complete theoretical model of how pulses are generated by charge collection is proposed. In the solar wind at 1 AU, the pulses are shown to be shaped by local plasma and photoelectron parameters. However, the situation can be different in hotter or denser plasma environments. We use the data provided by the STEREO/WAVES (S/WAVES) radio instrument onboard the twin STEREO spacecraft to validate our model. We find that the observations indeed strongly support the theory. The proposed model is an important step forward, since it makes it possible 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 radio instruments onboard different spacecraft and can help the design of dust detection optimized radio instruments for future missions.
Attenuation and velocity structure from diffuse coda waves: Constraints from underground array data
NASA Astrophysics Data System (ADS)
Galluzzo, Danilo; La Rocca, Mario; Margerin, Ludovic; Del Pezzo, Edoardo; Scarpa, Roberto
2015-03-01
An analysis of coda waves excited in the 0.2-20 Hz frequency band and recorded by the underground array Underseis (central Italy) has been performed to constrain both seismic attenuation at regional scale and velocity structure in the Mount Gran Sasso area. Attenuation was estimated with the MLTWA method, and shows a predominance of scattering phenomena over intrinsic absorption. The values of Qi and Qs are compatible with other estimates obtained in similar tectonic environments. Array methods allowed for a detailed study of the propagation characteristics, demonstrating that earthquake coda at frequencies greater than about 6 Hz is composed of only body waves. Coherence and spectral characteristics of seismic waves measured along the coda of local and regional earthquakes indicate that the wavefield becomes fully diffuse only in the late coda. The frequency-dependent energy partitioning between horizontal and vertical components has been also estimated and compared with synthetic values computed in a layered half-space under the diffuse field assumption. This comparison confirms that, for frequencies higher than 6 Hz, the coda appears as a sum of body waves coming from all directions while, in the low frequency range (0.2-2 Hz), the observations can be well explained by a coda wavefield composed of an equipartition mixture of surface and body waves traveling in a multiple-layered medium. A Monte-Carlo inversion has been performed to obtain a set of acceptable velocity models of the upper crust. The present results show that a broadband coda wavefield recorded in an underground environment is useful to constrain both the regional attenuation and the velocity structure of the target area, thereby complementing the results of classical array analysis of the wavefield.
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.
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.
Transmission, attenuation and reflection of shear waves in the human brain.
Clayton, Erik H; Genin, Guy M; Bayly, Philip V
2012-11-01
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
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.
NASA Astrophysics Data System (ADS)
Houser, C.; Hill, P. R.
2010-12-01
This paper describes the results of two instrument field studies to examine sediment transport processes and wave attenuation across Roberts Bank, a sandy intertidal bank on the Fraser River Delta. The field work was completed as part of a three-year study of the sensitivity of Roberts Bank to sea level rise and changing storminess. It was hypothesized that the response of the mudflats and salt marshes along the landward margin of the delta were dependent on the ability of the fronting sand flat to attenuate wave height and energy. The attenuation of wave height and energy was monitored at four stations along a shore-normal transect between December 23, 2003 and February 10, 2004. The attenuation varied with the relative wave height ratio (Hs h-1) along the seaward margin, with dissipation increasing as water depths decrease and/or incident wave heights increase. Under the most dissipative conditions observed (Hs h-1 ≈ 0.25), the exponential decay coefficient reached 0.00045. This decay coefficient is an order of magnitude smaller than predicted by a simple wave transformation model due to the relatively large wind fetch over the sand flat. Despite the maintenance of wave energy, the range of wave heights remains constrained in the landward direction, with the frequency of waves capable of entraining sediment on the sand flat decreasing from 11% at the outer flat to 2% at the inner stations. In response, bed elevation change and depth of sediment activation are greatest at the seaward margin and decrease exponentially landward. It is argued that the sand flat provides a natural barrier that defines the extent of mudflat development by limiting the potential for sediment resuspension and morphological change on the mudflat. The ability of the sand flat to provide continued protection to the mudflats and salt marshes depends on how it will respond to change in sea level and storminess. A comparison of the dimensionless, current-induced skin friction with the
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.
Optimal Configuration of Large Arrays of Floating Bodies for Ocean Wave Energy Extraction
NASA Astrophysics Data System (ADS)
Tokic, Grgur; Yue, Dick K. P.
2015-11-01
We study the performance of large (O (100)) wave energy converter (WEC) arrays that are used for ocean energy harvesting. We developed a fast computational algorithm based on the multiple scattering framework that is capable of handling large arrays of different configurations (general finite-size arrays, periodic arrays, periodic arrays of subarrays); for axisymmetric bodies the algorithm imposes no constraints on the body-size-to-wavelength ratio or on the inter-body spacings. Using this fast algorithm, we optimize the spatial configurations of arrays of different types and with increasing number of bodies (up to 400), with the goal of maximizing energy extraction. The results show that employing non-uniform spacings between the bodies in ordered and non-ordered arrays can increase the array gain several times. This holds for body resonant and near-resonant frequencies, as well as for the full spectrum cases. The optimal configurations are analyzed from a physical standpoint and compared to other structured arrays in physics. These results give a guideline on the possible future design of WEC arrays.
NASA Astrophysics Data System (ADS)
Dalton, C. A.; Hjorleifsdottir, V.; Ekstrom, G.
2011-12-01
Surface-wave amplitudes provide the primary constraint on upper-mantle anelastic structure and are also sensitive to small-scale elastic structure through focusing effects. However, the use of amplitudes for seismic imaging presents several challenges. One, amplitudes are affected not only by propagation through anelastic and elastic heterogeneity but also by uncertainty in the source excitation, local receiver structure, and instrument response. Two, accounting for focusing and defocusing effects, which is important if amplitudes are to be used to study anelasticity, depends considerably on the chosen theoretical treatment. Three, multiple scattering of seismic energy by elastic heterogeneity can be mapped into attenuation, especially at high frequencies. With the objective of improving our ability to image mantle seismic attenuation using real amplitude observations, we investigate how approximations in the theoretical treatment of wave excitation and propagation influence the interpretation of amplitudes. We use a spectral-element wave-propagation solver (SPECFEM3D_GLOBE) to generate accurate seismograms for global Earth models containing one-dimensional attenuation structure and three-dimensional variations in seismic velocity. The seismograms are calculated for 42 realistically distributed earthquakes. Fundamental-mode Rayleigh wave amplitudes in the period range 50--200 seconds are measured using the approach of Ekström et al. (1997), for which PREM is the assumed Earth model. We show that using the appropriate local seismic structure at the source and receiver instead of PREM has a non-negligible effect on the amplitudes and improves their interpretation. The amplitudes due to focusing and defocusing effects are predicted for great-circle ray theory, exact ray theory (JWKB theory), and finite-frequency theory. We assess the ability of each theory to predict amplitudes that agree with those measured from the SPECFEM synthetics for an Earth model that
S-wave attenuation structure beneath the northern Izu-Bonin arc
NASA Astrophysics Data System (ADS)
Takahashi, Tsutomu; Obana, Koichiro; Kodaira, Shuichi
2016-04-01
To understand temperature structure or magma distribution in the crust and uppermost mantle, it is essential to know their attenuation structure. This study estimated the 3-D S-wave attenuation structure in the crust and uppermost mantle at the northern Izu-Bonin arc, taking into account the apparent attenuation due to multiple forward scattering. In the uppermost mantle, two areas of high seismic attenuation (high Q -1) imaged beneath the volcanic front were mostly colocated with low-velocity anomalies. This coincidence suggests that these high- Q -1 areas in low-velocity zones are the most likely candidates for high-temperature regions beneath volcanoes. The distribution of random inhomogeneities indicated the presence of three anomalies beneath the volcanic front: Two were in high- Q -1 areas but the third was in a moderate- Q -1 area, indicating a low correlation between random inhomogeneities and Q -1. All three anomalies of random inhomogeneities were rich in short-wavelength spectra. The most probable interpretation of such spectra is the presence of volcanic rock, which would be related to accumulated magma intrusion during episodes of volcanic activity. Therefore, the different distributions of Q -1 and random inhomogeneities imply that the positions of hot regions in the uppermost mantle beneath this arc have changed temporally; therefore, they may provide important constraints on the evolutionary processes of arc crust and volcanoes.
Wave-speed dispersion associated with an attenuation obeying a frequency power law.
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. PMID:26627763
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.
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 1.4
NASA Astrophysics Data System (ADS)
Yamanouchi, Kazuhiko; Ishii, Toru
2003-05-01
The important properties required for surface acoustic wave (SAW) substrates are large electromechanical coupling coefficients (k2), small temperature coefficient of frequency (TCF), low propagation loss, among other. LiNbO3 is a good SAW substrate because of its good properties and large size. We developed SiO2/rotated Y-cut, X-propagating LiNbO3 leaky SAW substrates with a large k2 (over 0.2) and zero TCF at a small thickness of SiO2 of H/λ=0.2 (H: SiO2 film thickness, λ: SAW wave-length) compared to those of other substrates and zero propagation attenuation in the case of metalized surface. In this paper, the theoretical and experimental results for SAW filters, resonators and resonator filters are described. The low-loss filters using floating electrode type unidirectional transducer (FEUDT) showed an insertion loss of below 1 dB at a center frequency of 400 MHz and bandwidth of 20 MHz. Also, the resonator showed the wide-band characteristics and resonator filters showed a bandwidth of 80 MHz at a center frequency of 500 MHz.
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.
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.
Seismic attenuation: effects of interfacial impedance on wave-induced pressure diffusion
NASA Astrophysics Data System (ADS)
Qi, Qiaomu; Müller, Tobias M.; Rubino, J. Germán
2014-12-01
Seismic attenuation and dispersion in layered sedimentary structures are often interpreted in terms of the classical White model for wave-induced pressure diffusion across the layers. However, this interlayer flow is severely dependent on the properties of the interface separating two layers. This interface behaviour can be described by a pressure jump boundary condition involving a non-vanishing interfacial impedance. In this paper, we incorporate the interfacial impedance into the White model by solving a boundary value problem in the framework of quasi-static poroelasticity. We show that the White model predictions for attenuation and dispersion substantially change. These changes can be attributed to petrophysically plausible scenarios such as imperfect hydraulic contacts or the presence of capillarity.
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.
Apparent Attenuation and Dispersion Arising in Seismic Body-Wave Velocity Retrieval
NASA Astrophysics Data System (ADS)
Wirgin, Armand
2016-04-01
The fact that seismologists often make measurements, using natural seismic solicitations, of properties of the Earth on rather large scales (laterally and in terms of depth) has led to interrogations as to whether attenuation of body waves is dispersive and even significant. The present study, whose aim is to clarify these complicated issues, via a controlled thought measurement, concerns the retrieval of a single, real body wave velocity of a simple geophysical configuration (involving two homogeneous, isotropic, non-dissipative media, one occupying the layer, the other the substratum), from its simulated response to pulsed plane wave probe radiation. This inverse problem is solved, at all frequencies within the bandwidth of the pulse. Due to discordance between the models associated with the assumed and trial responses, the imaginary part of the retrieved velocity turns out to be non-nil even when both the layer and substratum are non-lossy, and, in fact, to be all the greater, the larger is the discordance. The reason for this cannot be due to intrinsic attenuation, scattering, or geometrical spreading since these phenomena are absent in the chosen thought experiment, but rather to uncertainty in the measurement model.
Apparent Attenuation and Dispersion Arising in Seismic Body-Wave Velocity Retrieval
NASA Astrophysics Data System (ADS)
Wirgin, Armand
2016-07-01
The fact that seismologists often make measurements, using natural seismic solicitations, of properties of the Earth on rather large scales (laterally and in terms of depth) has led to interrogations as to whether attenuation of body waves is dispersive and even significant. The present study, whose aim is to clarify these complicated issues, via a controlled thought measurement, concerns the retrieval of a single, real body wave velocity of a simple geophysical configuration (involving two homogeneous, isotropic, non-dissipative media, one occupying the layer, the other the substratum), from its simulated response to pulsed plane wave probe radiation. This inverse problem is solved, at all frequencies within the bandwidth of the pulse. Due to discordance between the models associated with the assumed and trial responses, the imaginary part of the retrieved velocity turns out to be non-nil even when both the layer and substratum are non-lossy, and, in fact, to be all the greater, the larger is the discordance. The reason for this cannot be due to intrinsic attenuation, scattering, or geometrical spreading since these phenomena are absent in the chosen thought experiment, but rather to uncertainty in the measurement model.
Spatial variation of Lg-wave attenuation in the Iberian Peninsula
NASA Astrophysics Data System (ADS)
Noriega, Raquel; Ugalde, Arantza; Villaseñor, Antonio; José Jurado, María
2014-05-01
Within a global context, the Iberian Peninsula is a region where low to moderate (Mw < 5.5) earthquakes occur, most of them at shallow depths (h < 40 km). Seismicity concentrates mainly around the Pyrenean Range, the northwestern part of the peninsula, and the southern deformation zone that includes the Betics, the Alborán Sea and the Gulf of Cádiz. In recent years, considerable improvements in seismic data quality and geographic coverage have been made by the deployment of new permanent and portable broadband seismic stations in the Iberian Peninsula. The dense accumulation of seismic data has allowed us to investigate lateral variation of crustal seismic attenuation to develop the first regional 2D Lg-wave attenuation model for the entire Iberian Peninsula and its frequency dependence. Seismic data used consist of 71 events with magnitudes 3 ≤ mbLg ≤ 5.4 focal depths less than 30 km and epicentral distances from 100 to 1000 km which were recorded by 343 seismic stations between January 2008 and October 2013. To avoid confusion with fundamental-mode Love-wave energy on the transverse components, we only analyzed vertical component recordings. Among all the methods proposed to measure Lg attenuation, we considered the reliable Two-Station Method that allows removing the common source term by taking the ratio of Lg amplitudes recorded at two different stations along the same great-circle path from the same event. It requires, however, strict source-station configuration and dense event and station coverage. The spectral ratios collected over high-quality interstation paths were used to determine 1 Hz Lg Q (Q0) and its frequency dependence η. Then, the lateral variations of the attenuation parameters were mapped using inversion. Lg-wave propagation was found to be inefficient or blocked for most of the paths crossing the Mediterranean Sea, the western Alborán Sea and the Strait of Gibraltar. Our results reflect large variations in Q0 values across the Iberian
Lapse time dependence of coda wave attenuation in Central West Turkey
NASA Astrophysics Data System (ADS)
Akyol, Nihal
2015-09-01
The attenuation of coda waves has been inferred for Central West Turkey, which is characterized by a very complex tectonic evolution. The selected dataset is composed of 440 waveforms from 228 local earthquakes with a magnitude range of 2.9-4.9. The coda quality factor (Qc) was estimated for five central frequencies (fc = 1.5, 3, 5, 7, 10 Hz) and eight lapse times (tL, ranging from 25 to 60 s), based on the assumption of single isotropic scattering model. Estimated Qc values were strongly dependent on frequency and lapse time. The frequency dependence of Qc values for each lapse time was inferred from Qc(f) = Q0fn relationships. Q0 values change between 32.7 and 82.1, while n values changes between 0.91 and 0.79 for the lapse times of 25 and 60 s, respectively. The obtained low Q0 values show that the Central West Turkey region is characterized by a high seismic attenuation, in general. The whole region was divided into four subregions to examine spatial differences of attenuation characteristics. Obtained 1/Q0 and n values versus the lapse time for each subregion implies the tectonic complexity of the region. Lapse time dependencies of attenuation and n values were also examined for subdatasets from two different ranges of event depth (h < 10 km and h ≥ 10 km) and distance (r < 40 km and r ≥ 40 km). High attenuation and its high frequency dependence for long distances manifest the elevation of isotherms and increasing heterogeneity with depth. This could be associated with the extensional intra-continental plate setting, forming regional tectonics in the back-arc area.
NASA Astrophysics Data System (ADS)
Jeong, Hyunjo; Zhang, Shuzeng; Cho, Sungjong; Li, Xiongbing
2016-04-01
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.
Attenuation of High Frequency P and S Waves in the Gujarat Region, India
NASA Astrophysics Data System (ADS)
Chopra, Sumer; Kumar, Dinesh; Rastogi, B. K.
2011-05-01
The local earthquake waveforms recorded on broadband seismograph network of Institute of Seismological Research in Gujarat, India have been analyzed to understand the attenuation of high frequency (2-25 Hz) P and S waves in the region. The frequency dependent relationships for quality factors for P ( Q P) and S ( Q S) waves have been obtained using the spectral ratio method for three regions namely, Kachchh, Saurashtra and Mainland Gujarat. The earthquakes recorded at nine stations of Kachchh, five stations of Saurashtra and one station in mainland Gujarat have been used for this analysis. The estimated relations for average Q P and Q S are: Q P = (105 ± 2) f 0.82 ± 0.01, Q S = (74 ± 2) f 1.06 ± 0.01 for Kachchh region; Q P = (148 ± 2) f 0.92 ± 0.01, Q S = (149 ± 14) f 1.43 ± 0.05 for Saurashtra region and Q P = (163 ± 7) f 0.77 ± 0.03, Q S = (118 ± 34) f 0.65 ± 0.14 for mainland Gujarat region. The low Q (<200) and high exponent of f (>0.5) as obtained from present analysis indicate the predominant seismic activities in the region. The lowest Q values obtained for the Kachchh region implies that the area is relatively more attenuative and heterogeneous than other two regions. A comparison between Q S estimated in this study and coda Q ( Qc) previously reported by others for Kachchh region shows that Q C > Q S for the frequency range of interest showing the enrichment of coda waves and the importance of scattering attenuation to the attenuation of S waves in the Kachchh region infested with faults and fractures. The Q S/ Q P ratio is found to be less than 1 for Kachchh and Mainland Gujarat regions and close to unity for Saurashtra region. This reflects the difference in the geological composition of rocks in the regions. The frequency dependent relations developed in this study could be used for the estimation of earthquake source parameters as well as for simulating the strong earthquake ground motions in the region.
NASA Astrophysics Data System (ADS)
Lo, Wei-Cheng; Yeh, Chao-Lung; Jan, Chyan-Deng
2008-08-01
SummaryThe study of the propagation and dissipation of acoustic waves through a fluid-containing porous medium is crucial for the successful application of seismic methods to characterize subsurface hydrological properties. To gain a better understanding of changes in two important acoustic wave characteristics (speed and attenuation) due to the effect of soil texture and excitation frequency, a complex-valued dispersion relation obtained from the Biot theory of poroelasticity was solved numerically for eleven soil texture classes whose pore space is fully saturated by one of two very different fluids, air or water. Two modes of acoustic motion can be demonstrated to exist, known as the Biot fast and slow waves. Five lower excitation frequencies (100-500 Hz) were selected for numerical simulation, below which Darcy's law remains valid for describing porous media flow under wave perturbation. Numerical results show that in the frequency range we examined, the predicted phase speed of the Biot fast wave takes the same value as the Biot reference speed. The variation in speed is not obvious in a water-filled system, but becomes more significant in an air-filled system. When the pore fluid is water, an inverse linear relation exists between the phase speed of the Biot fast wave and porosity. An important physical parameter controlling its attenuation coefficient is intrinsic permeability, which renders a positive impact. A statistical analysis indicates that the attenuation coefficient of the Biot fast wave linearly increases with an increase in intrinsic permeability. In an air-saturated system, the phase speed of the Biot slow wave is found to be quadratically proportional to intrinsic permeability, whereas the attenuation coefficient of the Biot slow wave bears a quadratic relation with the inverse of intrinsic permeability. A study on the influence of pore fluid reveals that the Biot fast wave attenuates more in the water-saturated system than in the air
NASA Astrophysics Data System (ADS)
Jin, Jianxun; Zheng, Luhai
Traveling-wave magnetic field generated by a linear motor is a typical AC time-varying field. In order to identify the trapped magnetic flux attenuation characteristics of the high temperature superconducting (HTS) bulk magnet exposed to the external traveling-wave field generated by the primary of a developed HTS linear synchronous motor (HTSLSM), relevant experiments have been carried out through a built measurement system. As results, the relationships between the trapped magnetic flux attenuation of the HTS bulk magnet and the amplitude, frequency and direction of the external traveling-wave magnetic field are experimentally obtained to allow the HTSLSM characteristics to be practically verified.
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. PMID:22225009
Velocity and attenuation of scalar and elastic waves in random media: a spectral function approach.
Calvet, Marie; Margerin, Ludovic
2012-03-01
This paper investigates the scattering of scalar and elastic waves in two-phase materials and single-mineral-cubic, hexagonal, orthorhombic-polycrystalline aggregates with randomly oriented grains. Based on the Dyson equation for the mean field, explicit expressions for the imaginary part of Green's function in the frequency-wavenumber domain (ω, p), also known as the spectral function, are derived. This approach allows the identification of propagating modes with their relative contribution, and the computation of both attenuation and phase velocity for each mode. The results should be valid from the Rayleigh (low-frequency) to the geometrical optics (high-frequency) regime. Comparisons with other approaches are presented for both scalar and elastic waves. PMID:22423683
Attenuation of Higher Order Circumferential Thermoacoustic Waves in Viscous Fluid Lines
NASA Astrophysics Data System (ADS)
Liang, P. N.; Scarton, H. A.
1996-06-01
The acoustic waves propagation in viscous water, glycerin and air contained in a rigid wall, thermally insulated, infinite long, circular tube are studied using the exact three-dimensional thermal-fluid coupled equations for the vibrations in the n= 0, 1 circumferential modes. The first three axially symmetric modes at n= 0 and the first three non-axially symmetric modes at n= 1 are presented. The corresponding two-dimensional mode shapes are plotted so that the wave vibrations can be identified. It is found that the dispersion spectra, mode shapes and phase velocity dispersion plots of the three fluid mediums are very close. But the attenuation rates of glycerin and air are about 37 and 9 times higher than water, respectively.
Coda wave attenuation parallel and perpendicular to the Mexican Pacific coast
NASA Astrophysics Data System (ADS)
Novelo-Casanova, D. A.; Valdés-González, C.
2000-10-01
We calculated the quality factor, Qc, at frequencies from 6 to 24 Hz using coda waves of 97 aftershocks of the Petatlan, Mexico, earthquake (March 14, 1979; MS=7.6). The data were recorded parallel (between Acapulco and Playa Azul) and perpendicular (between Petatlan and Mexico City) to the coast. The results are the following: at 12 and 24 Hz there is no significant difference in the attenuation ( Qc-1) along the two paths; at 6 Hz, Qc-1 has a large scatter in both directions. This observation indicates strong site effects at this frequency; average Qc-1 is slightly higher between Petatlan-Acapulco (toward SE) than between Petatlan-Playa Azul (toward NW); and at high frequencies, Qc-1 remains essentially constant perpendicular to the coast. These results show that the large seismic wave amplifications in Mexico City are caused by shallow site effects.
NASA Astrophysics Data System (ADS)
Ma, Yong; Li, Teng-fei; Zhang, Liang; Sheng, Qi-hu; Zhang, Xue-wei; Jiang, Jin
2016-01-01
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.
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.
NASA Astrophysics Data System (ADS)
Bauer, K.; Haberland, Ch.; Pratt, R. G.; Ryberg, T.; Weber, M. H.; Mallik Working Group
2003-04-01
We present crosswell seismic data from the Mallik 2002 Production Research Well Program, an international research project on Gas Hydrates in the Northwest Territories of Canada. The program participants include 8 partners; The Geological Survey of Canada (GSC), The Japan National Oil Corporation (JNOC), GeoForschungsZentrum Potsdam (GFZ), United States Geological Survey (USGS), United States Department of the Energy (USDOE), India Ministry of Petroleum and Natural Gas (MOPNG)/Gas Authority of India (GAIL) and the Chevron-BP-Burlington joint venture group. The crosswell seismic measurements were carried out by making use of two 1160 m deep observation wells (Mallik 3L-38 and 4L-38) both 45 m from and co-planar with the 1188 m deep production research well (5L-38). A high power piezo-ceramic source was used to generate sweeped signals with frequencies between 100 and 2000 Hz recorded with arrays of 8 hydrophones per depth level. A depth range between 800 and 1150 m was covered, with shot and receiver spacings of 0.75 m. High quality data could be collected during the survey which allow for application of a wide range of crosswell seismic methods. The initial data analysis included suppression of tube wave energy and picking of first arrivals. A damped least-squares algorithm was used to derive P-wave velocities from the travel time data. Next, t* values were derived from the decay of the amplitude spectra, which served as input parameters for a damped least-squares attenuation tomography. The initial results of the P-wave velocity and attenuation tomography reveal significant features reflecting the stratigraphic environment and allow for detection and eventually quantification of gas hydrate bearing sediments. A prominent correlation between P velocity and attenuation was found for the gas hydrate layers. This contradicts to the apparently more meaningful inverse correlation as it was determined for the gas hydrates at the Blake Ridge but supports the results from
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.
Laser-generated shock wave attenuation aimed at microscale pyrotechnic device design
NASA Astrophysics Data System (ADS)
Yu, Hyeonju; Yoh, Jack J.
2016-05-01
To meet the rising demand for miniaturizing the pyrotechnic device that consists of donor/acceptor pair separated by a bulkhead or a thin gap, the shock initiation sensitivity in the microscale gap test configuration is investigated. For understanding the shock attenuation within a gap sample (304 stainless steel) thickness of 10˜800 μm, the laser-generated shock wave in water confinement is adopted. The shock properties are obtained from the free surface velocity by making use of a velocity interferometer system for any reflector (VISAR). Analytical models for plasma generation in a confined geometry and for evolution and decay of shock waves during the propagation are considered. The shape and amplitude of the laser-driven initial pressure load and its attenuation pattern in the gap are effectively controlled for targeting the microscale propagation distance and subsequent triggering pressure for the acceptor charge. The reported results are important in the precise controlling of the shock strength during the laser initiation of microscale pyrotechnic devices.
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.
Investigation of the Attenuation of Plane Shock Waves Moving over very Rough Surfaces
NASA Technical Reports Server (NTRS)
Huber, Paul W.; McFarland, Donald R.; Levine, Philip
1953-01-01
Experimental measurements of the attenuation of plane shock waves moving over rough walls have been made in a shock tube. Measurements of the boundary-layer characteristics, including thickness and velocity distribution behind the shock, have also been made with the aid of new cal techniques which provide direct information on the local boundary-layer conditions at the rough walls. Measurements of shock speed and shock pressure ratio are presented for both smooth-wall and rough-wall flow over lengths of machined-smooth and rough strips which lined all four walls of the shock tube. A simplified theory based on Von Karman's expression for skin-friction coefficient for flow over rough walls, along with a wave-model concept and extensions to include time effects, is presented. In this theory, the shock-tube flow is assumed to be one-dimensional at all times and the wave-model concept is used to relate the local layer growth to decreases in shock strength. This concept assumes that local boundary-layer growths act as local mass-flow sinks, which give rise to expansion waves which, in turn, overtake the shock and lower its mass flow accordingly.
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).
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.
NASA Astrophysics Data System (ADS)
Brissaud, Quentin; Martin, Roland; Garcia, Raphaël F.; Komatitsch, Dimitri
2016-07-01
Acoustic and gravity waves propagating in planetary atmospheres have been studied intensively as markers of specific phenomena such as tectonic events or explosions or as contributors to atmosphere dynamics. To get a better understanding of the physics behind these dynamic processes, both acoustic and gravity waves propagation should be modelled in a 3-D attenuating and windy atmosphere extending from the ground to the upper thermosphere. Thus, in order to provide an efficient numerical tool at the regional or global scale, we introduce a finite difference in the time domain (FDTD) approach that relies on the linearized compressible Navier-Stokes equations with a background flow (wind). One significant benefit of such a method is its versatility because it handles both acoustic and gravity waves in the same simulation, which enables one to observe interactions between them. Simulations can be performed for 2-D or 3-D realistic cases such as tsunamis in a full MSISE-00 atmosphere or gravity-wave generation by atmospheric explosions. We validate the computations by comparing them to analytical solutions based on dispersion relations in specific benchmark cases: an atmospheric explosion, and a ground displacement forcing.
NASA Astrophysics Data System (ADS)
Molyneux, Joseph Benedict
Laboratory velocity measurements are an integral component of solid earth seismic investigations. Typically, ultrasonic measurements from centimeter scale plug samples are used to model large sections of the crust, core and mantle. By using the laboratory determined velocities, the seismic arrival time can more accurately calibrate spatial physical properties of the solid-earth. A semi-automated picking procedure is presented which determines the velocity measured from recorded ultrasonic pulses propagated through laboratory samples. This procedure is quicker and more consistent than the standard hand picking method, allowing larger data sets to be accurately investigated. Furthermore, a series of common velocity analyses are compared to the physical properties of phase and group velocity in an attenuating medium of glycerol saturated glass bead packs (Q ˜ 3). It is found that the velocity determined from the first break of the waveform (signal velocity) is up to 13% different from group and phase velocities. This illustrates that signal velocity is unsuitable to determine rock properties in highly attenuating media. Also, greater than 81% velocity dispersion is observed when the dominant propagating wavelength is comparable to the bead size. More surprisingly, on propagation of the broad band input signal a bimodal amplitude spectrum becomes apparent. The low frequency peak is consistent with standard attenuation, whereas the high frequency peak is related to resonance of either the constituent beads or the interbead fluid cavity. Such resonance partitions energy of the main incoming signal. This phenomenon represents a new and fundamental attenuation mechanism that should be considered in many wave-propagation experiments.
NASA Astrophysics Data System (ADS)
Bellis, C.; Lin, P.; Holtzman, B. K.; Gaherty, J. B.; Roy, M.
2013-12-01
The upper mantle beneath the Colorado Plateau (CP) is characterized by high seismic velocities in the plateau interior and lower seismic velocities beneath the plateau margins, below the Basin and Range to the west and the Rio Grande Rift to the east. The seismic velocity contrast across the margins has been interpreted as a thermal- mechanical modification of the sub-CP lithospheric keel, by various mechanisms. Using teleseismic P- and S-wave spectra from the La Ristra 1.5 Array and EarthScope USArray Transportable Array (TA), we measure t*, the seismic parameter representing integrated attenuation along a ray path, across the western margin of the CP. For wave fields from two sets of earthquakes to the Northwest and Southeast of the CP, we measured the spectra of P- and S-waves at each station, relative to the spectra of the reference stations and extracted the differential attenuation factor (dt*) across the frequency band 0.2-4 Hz for P waves and 0.1-1.5 Hz for S waves for each event-station pair. To first order, both tp* and ts* varies from higher in the Basin and Range to lower on the CP, which suggests that coherent variations in attenuation are present across the Northwestern margin of the CP. However, the gradients of dt* for the two sets of NW and SE wave fields are significantly different, with a sharper gradient observed for the NW set. One of our primary questions concerns the origin of these variations: to what extent do they reflect the spatial distribution of intrinsic attenuation structure or wave propagation effects such as focusing and defocusing. To address these questions, our approach is to first build 1- and 2-D models for hypothetical spatial variations in state and compositional variables (T, water and melt content), and then calculate attenuation structures based on experimentally derived power-law frequency-dependent anelastic models. These structures are transferred into our anelastic finite difference wave propagation code, from which
Effects of fracture contact areas on seismic attenuation due to wave-induced fluid flow
NASA Astrophysics Data System (ADS)
Germán Rubino, J.; Müller, Tobias M.; Milani, Marco; Holliger, Klaus
2014-05-01
Wave-induced fluid flow (WIFF) between fractures and the embedding matrix is considered to be a predominant seismic attenuation mechanism in fractured rocks. That is, due to the strong compressibility contrast between fractures and embedding matrix, seismic waves induce strong fluid pressure gradients, followed by local fluid flow between such regions, which in turn produces significant energy dissipation. Natural fractures can be conceptualized as two surfaces in partial contact, containing very soft and highly permeable material in the inner region. It is known that the characteristics of the fracture contact areas control the mechanical properties of the rock sample, since as the contact area increases, the fracture becomes stiffer. Correspondingly, the detailed characteristics of the contact area of fractures are expected to play a major role in WIFF-related attenuation. To study this topic, we consider a simple model consisting of a horizontal fracture located at the center of a porous rock sample and represented by a number of rectangular cracks of constant height separated by contact areas. The cracks are modelled as highly compliant, porous, and permeable heterogeneities, which are hydraulically connected to the background material. We include a number of rectangular regions of background material separating the cracks, which represent the presence of contact areas of the fracture. In order to estimate the WIFF effects, we apply numerical oscillatory relaxation tests based on the quasi-static poro-elastic equations. The equivalent undrained, complex plane-wave modulus, which allows to estimate seismic attenuation and velocity dispersion for the vertical direction of propagation, is expressed in terms of the imposed displacement and the resulting average vertical stress at the top boundary. In order to explore the effects of the presence of fracture contact areas on WIFF effects, we perform an exhaustive sensitivity analysis considering different
S wave attenuation and site effects in the region of Friuli, Italy
NASA Astrophysics Data System (ADS)
Castro, Raúl R.; Pacor, Francesca; Sala, Alfio; Petrungaro, Carmine
1996-10-01
We used strong motion records from the 1976 Friuli earthquake (M 6.4) and 10 of the biggest aftershocks recorded by the National Accelerograph Network of the Electrical Power Company of Italy to estimate the quality factor Q of S waves in this region. The wide distance range of the recordings (10 < r < 190 km) permits us to analyze the spectral amplitude decay of the records using a nonparametric approach [e.g., Anderson and Quaas, 1988; Castro et al., 1990; Anderson, 1991]. We obtained attenuation functions for a set of 18 frequencies ranging between 0.4 and 25.0 Hz. The values of Q retrieved from the attenuation functions obtained follow the frequency-dependent relation Q = 20.4f. A test of the method was made using a second data set consisting of digital seismograms from the Friuli-Venezia Giulia Seismograph Network. In spite of the different size of the volume sampled by these data (10 < r < 131 km), the frequency dependence of Q obtained (Q = 16.1f0.92) is similar to that obtained with the strong motion data set. The near-surface attenuation was also estimated using the model proposed by Anderson and Hough [1984] and Anderson [1991]. We found that κ0 is smaller for the strong motion stations located on rock compared to stations located on either shallow or soft sediments. To estimate the site response of the strong motion stations, we corrected the spectral records for the attenuation effect and then inverted the corrected records to separate source and site effects using the inversion scheme proposed by Andrews [1986]. To verify the site amplification estimates obtained, we also calculated the transfer function of each site using Nakamura's [1989] method for S wave [e.g., Lermo and Chavez-García, 1993]. In general, the shapes of the site functions obtained with the inversion are consistent with the transfer functions obtained calculating the horizontal to vertical component ratio.
Body-wave Attenuation in the South-Central Region of the Gulf of California, México
NASA Astrophysics Data System (ADS)
Castro, R. R.; Vidales-Basurto, C. A.; Huerta, C. I.; Sumy, D. F.; Gaherty, J. B.; Collins, J. A.
2014-12-01
We present results from a recent study of seismic attenuation of body waves in the south-central region of the Gulf of California (GoC) obtained using records from the Network of Autonomously Recording Seismographs of Baja California (NARS-Baja), from the CICESE's Broadband Seismological Network of the GoC (RESBAN), and from the Ocean Bottom Seismographs (OBS) deployed as part of the Sea of Cortez Ocean Bottom Array experiment (SCOOBA). We examine 27 well-located earthquakes that occurred from October 2005 to October 2006 with magnitudes (Mw) between 3.5 and 4.8. We estimated S-wave site effects by calculating horizontal to vertical spectral ratios and determined attenuation functions with a nonparametric model by inverting the observed spectral amplitudes of 21 frequencies between 0.13 and 12.59 Hz for the SCOOBA (OBS) stations and 19 frequencies between 0.16 and 7.94 Hz for NARS-Baja and RESBAN stations. We calculated the geometrical spreading and the attenuation (1/Q) factors for two distance intervals (10-120 km and 120-220 km, respectively) for each frequency considered. The estimates of Q obtained with the SCOOBA (OBS) records for the interval 10-120 km indicate that the P waves attenuate more than S waves (QP=34 f 0.82, QS=59 f 0.90) for frequencies between 0.6 and 12.6 Hz; while for the 120-220 km interval, where ray-paths travel deeper, S waves attenuate more than P waves (QP=117 f 0.44, QS=51 f 1.12). The estimates of Q obtained using NARS-Baja and RESBAN records, within 10-120 km, indicate that P waves attenuate more than S waves (QP=69 f 0.87, QS=176 f 0.61) at frequencies between 0.3 and 6.3 Hz; while at the 120-220 km distance interval S waves attenuate slightly more than P waves (QP=39 f 0.64, QS=48 f 0.37) at high frequencies (f > 3 Hz). These results, based on a unique OBS dataset, provide an indirect mean to constrain future models of the thermal structure beneth the GoC.
NASA Astrophysics Data System (ADS)
Nusca, Michael Joseph, Jr.
The effects of various gasdynamic phenomena on the attenuation of an electromagnetic wave propagating through the nonequilibrium chemically reacting air flow field generated by an aerodynamic body travelling at high velocity is investigated. The nonequilibrium flow field is assumed to consist of seven species including nitric oxide ions and free electrons. The ionization of oxygen and nitrogen atoms is ignored. The aerodynamic body considered is a blunt wedge. The nonequilibrium chemically reacting flow field around this body is numerically simulated using a computer code based on computational fluid dynamics. The computer code solves the Navier-Stokes equations including mass diffusion and heat transfer, using a time-marching, explicit Runge-Kutta scheme. A nonequilibrium air kinetics model consisting of seven species and twenty-eight reactions as well as an equilibrium air model consisting of the same seven species are used. The body surface boundaries are considered as adiabatic or isothermal walls, as well as fully-catalytic and non-catalytic surfaces. Both laminar and turbulent flows are considered; wall generated flow turbulence is simulated using an algebraic mixing length model. An electromagnetic wave is considered as originating from an antenna within the body and is effected by the free electrons in the chemically reacting flow. Analysis of the electromagnetics is performed separately from the fluid dynamic analysis using a series solution of Maxwell's equations valid for the propagation of a long-wavelength plane electromagnetic wave through a thin (i.e., in comparison to wavelength) inhomogeneous plasma layer. The plasma layer is the chemically reacting shock layer around the body. The Navier-Stokes equations are uncoupled from Maxwell's equations. The results of this computational study demonstrate for the first time and in a systematic fashion, the importance of several parameters including equilibrium chemistry, nonequilibrium chemical kinetics, the
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. PMID:25669286
High-power gyrotron traveling-wave amplifier with distributed wall losses and attenuating severs
Yeh, Y.S.; Shin, Y.Y.; You, Y.C.; Chen, L.K.
2005-04-15
Distributed-loss gyrotron traveling-wave amplifiers (gyro-TWTs) with high-gain, broadband, and millimeter-wave capabilities have been demonstrated. Most structures with distributed wall losses 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. Simulation results show that gyrotron backward-wave oscillations (gyro-BWOs) are not effectively suppressed by the lossy section; in contrast, the severed sections can effectively enhance the start-oscillation threshold of gyro-BWOs in the proposed gyro-TWT. Meanwhile, localized reflective oscillations seem not to occur in the gyro-TWT unless it operates at a high magnetic field or with a high interaction length. The stable gyro-TWT, operating in the low-loss TE{sub 01} mode, is predicted to yield a peak output power of 405 kW at 33 GHz with an efficiency of 20%, a saturated gain of 77 dB and a 3 dB bandwidth of 2.5 GHz for a 100 kV, 20 A electron beam with an axial velocity spread of {delta}v{sub z}/v{sub z}=5%.
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.
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.
NASA Astrophysics Data System (ADS)
Lin, F.; Ritzwoller, M. H.
2011-12-01
The deployment of the EarthScope/USArray Transportable Array has promoted new and better ways to utilize the dense array configuration and to resolve higher resolution crustal and upper mantle structures beneath the US. Here, we present a local inversion method for surface wave that utilizes the USArray first to determine the surface wave wavefield empirically and then to directly measure the surface wave propagation characteristics such as isotropic velocity, azimuthal anisotropy, and intrinsic attenuation by solving the 2D Helmholtz wave equation. The method starts with single event analysis, where for each period and earthquake all measurements across the array are aggregated to determine maps of phase travel time and amplitude on a fine spatial grid, which essentially describes the surface wave wavefield. The solution of the 2D wave equation contains real and imaginary parts, which are relevant to velocity and attenuation measurements, respectively. For the real part, directionally dependent phase velocities at each location are estimated from the gradient of phase travel time along with the Laplacian of amplitude. For the imaginary part, on the other hand, intrinsic attenuation at each location is estimated from the dot product of the gradients of phase travel time and amplitude along with the Laplacian of phase travel time. In both cases, the terms that contain the gradient operator are directly related to traditional ray theoretic approaches (e.g., eikonal equation for velocity measurement) whereas the terms involving the Laplacian operator provide corrections for off-ray sensitivity. In principle, by applying the correction terms, finite frequency effects such as wave interference, wavefront healing, and backward scattering are accounted for in phase velocity measurements and focus/defocusing is accounted for in attenuation measurements. We apply the method to Rayleigh wave measurements between 30 and 100 sec period from more than 700 earthquakes and all
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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.
Shear wave attenuation and micro-fluidics in water-saturated sand and glass beads.
Chotiros, Nicholas P; Isakson, Marcia J
2014-06-01
An improvement in the modeling of shear wave attenuation and speed in water-saturated sand and glass beads is introduced. Some dry and water-saturated materials are known to follow a constant-Q model in which the attenuation, expressed as Q(-1), is independent of frequency. The associated loss mechanism is thought to lie within the solid frame. A second loss mechanism in fluid-saturated porous materials is the viscous loss due to relative motion between pore fluid and solid frame predicted by the Biot-Stoll model. It contains a relaxation process that makes the Q(-1) change with frequency, reaching a peak at a characteristic frequency. Examination of the published measurements above 1 kHz, particularly those of Brunson (Ph.D. thesis, Oregon State University, Corvalis, 1983), shows another peak, which is explained in terms of a relaxation process associated with the squirt flow process at the grain-grain contact. In the process of deriving a model for this phenomenon, it is necessary to consider the micro-fluidic effects associated with the flow within a thin film of water confined in the gap at the grain-grain contact and the resulting increase in the effective viscosity of water. The result is an extended Biot model that is applicable over a broad band of frequencies. PMID:24907791
Attenuation Characteristics of Body-Waves for the Bilaspur Region of Himachal Lesser Himalaya
NASA Astrophysics Data System (ADS)
Vandana; Kumar, Ashwani; Gupta, S. C.
2016-02-01
The attenuation characteristics around Bilaspur region of the Himachal Lesser Himalaya have been estimated adopting extended-coda-normalization method, and using a data set of 41 local events (0.5 < M L ≤ 2.9) that occurred in the region from May 2013 to March 2014. The frequency-dependent relations governing the quality factors of P-waves ( Q α ) and S-waves ( Q β ) in the frequency range from 1.5 to 24 Hz are: ( Q α ) = (43 ± 4) f 1.30±0.04 and Q β = (79 ± 6) f 1.25±0.02. The average estimates of ( Q α ) and ( Q β ) are found to vary from 71 and 125 at 1.5 Hz to 2901 and 4243 at 24 Hz, respectively. The ( Q α ) and ( Q β ) estimates are compared to the similar estimates obtained for the other seismically active regions of the Himalaya. It is found that for the various Himalayan regions, the ( Q α ) estimates at 1 Hz vary between 22 (for the Kumaon Himalaya) and 97 (for the northwest Himalaya), whereas ( Q β ) estimates range between 63 (for the Garhwal Himalaya) and 127 (for the northwest Himalaya). For the Bilaspur region, the ( Q β )/( Q α ) ratio is greater than unity and varies between 1.84 and 1.45 in the frequency range from 1 to 24 Hz. The region-specific attenuation relations can be adopted for estimating earthquake source parameters, simulating strong ground motion and assessing seismic hazard for the Bilaspur region of Himachal Lesser Himalaya.
NASA Astrophysics Data System (ADS)
Jackson, I.; Faul, U. H.; Fitz Gerald, J. D.
2001-12-01
The frequency-dependent mechanical behaviour expected of Earth materials at high temperature places a special premium on laboratory measurements of wave speeds and attenuation at seismic frequencies. The symposium in honour of Mervyn Paterson provides a welcome opportunity to acknowledge his vital role in the design of the specialised equipment for this purpose described by Jackson and Paterson (PEPI 45: 349-367, 1987; Pageoph 141: 445-466, 1993). This instrument allows the study of low-strain high-temperature viscoelastic behaviour through the application of torsional forced oscillation/ microcreep techniques within the P-T environment (200 MPa, 1600 K) provided by an internally heated gas apparatus. Application of these techniques to fine-grained synthetic olivine polycrystals is beginning to provide a robust basis for the understanding of seismic wave attenuation (and dispersion) in the upper mantle under sub-solidus conditions. More recently, we have begun to explore the effects of partial melting through the fabrication, characterisation and mechanical testing of a suite of fine-grained olivine polycrystals containing up to 4% basaltic melt. The most striking effect of the added melt is the appearance of a melt-related dissipation peak superimposed upon the dissipation background characteristic of melt-free materials - which varies monotonically with period and temperature. The melt-related dissipation peak is adequately modelled as a Gaussian in log X, where X = To exp(E/RT). The melt-related dissipation peak sweeps across the seismic band from period To > 100 s to To < 1 s as temperature increases across the range 1300 - 1600 K producing pronounced systematic changes in the frequency dependence of 1/Q, that may be seismologically observable. >http://rses.anu.adu.au/petrophysics/PetroHome.html
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.
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.
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.
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)
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.
NASA Astrophysics Data System (ADS)
Wang, Zhi-liang; Li, Yong-chi; Wang, J. G.
2006-12-01
The propagation and attenuation of blast-induced stress waves differs between geomedia such as rock or soil mass. This paper numerically studies the propagation and attenuation of blast-induced elastoplastic waves in deep geomedia by using a one-dimensional (1-D) finite-difference code. Firstly, the elastoplastic Cap models for rock and soil masses are introduced into the governing equations of spherical wave motion and a FORTRAN code based on the finite difference method is developed. Secondly, an underground spherical blast is simulated with this code and verified by software, RENEWTO. The propagation of stress-waves in rock and soil masses is numerically investigated, respectively. Finally, the effect of a soil cover layer on the attenuation of stress waves in the rear rock mass is studied. It is determined that large plastic deformation of geomedia can effectively dissipate the energy of stress-waves inward and the developed 1-D finite difference code coupled with elastoplastic Cap models is convenient and effective in the numerical simulations for underground spherical explosion.
NASA Astrophysics Data System (ADS)
Euler, G. G.; Wysession, M. E.; Huhmann, B.
2007-12-01
We investigate global differential travel-time dispersion and attenuation of core-diffracted phases from large, deep earthquakes. This technique aids in constraining radial velocity structure at the core-mantle interface in a manner analogous to surface wave observables constraining upper mantle structure. We confirm that there is noticeable differential dispersion and attenuation caused by diffraction on a global basis for both Pdiff and Sdiff. Variations in differential dispersion and attenuation are observed with both geographic location and between Pdiff and Sdiff along the same azimuth suggesting lateral variations in Vp, Vs and Vp/Vs ratio in the lowermost mantle. We attempt to utilize dispersion and attenuation characteristics to put bounds on the magnitude and distribution of large-scale velocity perturbations in the lowermost mantle and draw comparisons to variations found in several 3D whole-mantle models. Our dataset consists of broadband records available from the IRIS DMC for deep (>180 km), large (>5.6 mb) teleseismic events. Preprocessing of the records includes deconvolution of the instrument response, rotation of horizontal components, filtering using a set of bandpass filters, and sample-rate decimation (5 sps). Relative arrival times and amplitudes are found by computing cross correlegrams in the frequency domain, detecting and removing poor recordings with cluster analysis, and iteratively converging on a stable low-variance solution with a weighted least-squares inversion while automatically remediating phase-skips utilizing a database of potential relative arrivals. Raypath-approximated corrections for reciever-side differences in ellipticity, mantle, and crust are applied for the derivation of phase velocites in the lowermost mantle as a function of azimuth and frequency. Following previous studies of diffracted signals, we limit our analysis to station pairs located in narrow azimuthal windows spread over a considerable distance while
Shear wave velocity, seismic attenuation, and thermal structure of the continental upper mantle
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
NASA Astrophysics Data System (ADS)
Brajanovski, Miroslav; Müller, Tobias M.; Parra, Jorge O.
2010-08-01
In this work we interpret the data showing unusually strong velocity dispersion of P-waves (up to 30%) and attenuation in a relatively narrow frequency range. The cross-hole and VSP data were measured in a reservoir, which is in the porous zone of the Silurian Kankakee Limestone Formation formed by vertical fractures within a porous matrix saturated by oil, and gas patches. Such a medium exhibits significant attenuation due to wave-induced fluid flow across the interfaces between different types of inclusions (fractures, fluid patches) and background. Other models of intrinsic attenuation (in particular squirt flow models) cannot explain the amount of observed dispersion when using realistic rock properties. In order to interpret data in a satisfactory way we develop a superposition model for fractured porous rocks accounting also for the patchy saturation effect.
Braccini, S.; Bradaschia, C.; Cobal, M.; Del Fabbro, R.; Di Virgilio, A.; Flaminio, R.; Giazotto, A.; Kautzky, H.; Morganti, M.; Passuello, D. ); Calloni, E.; Di Fiore, L. ); Holloway, L.E. ); Montelatici, V. )
1993-02-01
We present a method of lowering below 2.5 Hz the vertical normal mode frequencies of the Pisa Super Attenuator by using permanent magnets which provide an antispring force. This method allows a more efficient suppression of the seismic noise decreasing the lower limit of the frequency region devoted to gravitational wave detection.
NASA Astrophysics Data System (ADS)
Ott, R. H.
1983-09-01
A method for calculating the ground wave field over irregular, inhomogeneous terrain was developed, and comparisons with alternative analytical methods were made for idealized terrain profiles such as concave parabolas, sea-land-sea paths, and single Gaussian ridges. This method employs a numerically efficient algorithm, PROGRAM WAGNER, based on an integral equation. PROGRAM WAGNER appears the only method general enough for calculating ground wave attenuation along detailed paths. The fundamentals of PROGRAM WAGNER to the user seeking to make path loss calculations are explained. A users guide, the complete FORTRAN IV program listing, and sample input and output are included. Comparisons of computed field strengths are presented, with measured values over a path in the Netherlands at 10 frequencies from 2 to 30 MHz. Also, PROGRAM WAGNER at 5 and 30 MHz is compared with a method based on scattering from multiple knife edges. Finally, reciprocity is shown to provide necessary and useful criteria for spacing the observation points along the terrain profile.
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. PMID:25287976
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.
2-D Coda and Direct Wave Attenuation Tomography in Northern Italy
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
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.
NASA Astrophysics Data System (ADS)
Ma, Zhitu; Masters, Guy; Mancinelli, Nicholas
2016-01-01
In this study, we obtain a set of 2-D global phase velocity and attenuation maps for Rayleigh waves between 5 and 25 mHz. Correcting the effect of focusing-defocusing is crucial in order to obtain reliable attenuation structure. Great circle linearized ray theory, which has been used to date, can give useful predictions of this effect if careful attention is paid to how the phase velocity model is smoothed. In contrast, predictions based on the 2-D finite-frequency kernels are quite robust in this frequency range and suggest that they are better suited as a basis for inversion. We use a large data set of Rayleigh wave phase and amplitude measurements to invert for the phase velocity, attenuation, source and receiver terms simultaneously. Our models provide 60-70 per cent variance reduction to the raw data though the source terms are the biggest contribution to the fit of the data. The attenuation maps show structures that correlate well with surface tectonics and the age progression trend of the attenuation is clearly seen in the ocean basins. We have also identified problematic stations and earthquake sources as a by-product of our data selection process.
NASA Astrophysics Data System (ADS)
Scherbaum, Frank; Wyss, Max
1990-08-01
A new method to simultaneously invert for Q structure and source parameters was used on a set of 635 microearthquakes (0.9 < M < 2.0) in the Kaoiki area of southern Hawaii. Approximately 2800 signals were analyzed which had been recorded by 6 short period vertical seismographs at epicentral distances of a few to 10 km. The hypocentral depths ranged from O to 14 km, with the bulk of the sources in the 7.5-10.5 km range. The hypothesis to be tested was that the source volume of the M = 6.6 Kaoiki main shock of November 16, 1983, may be heterogeneous in attenuation distribution. We assumed that the observed P wave displacement spectra could be modelled by a source spectrum with an ω-2 high-frequency decay, a single-layer resonance filler to account for local site resonances and whole path attenuation along the ray path. In a next step the attenuation factor Q was constrained by tomographically reconstructing the three-dimensional Q structure for the source region and using it as starting model for a nonlinear inversion of the corner frequency, the seismic moment M0, and a new Q value. This process was iterated until the results changed less than 0.1% and were accepted as final. The average Q was approximately constant and very low (105
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.