Showing papers on "Wave propagation published in 2014"
Book•
21 Aug 2014
TL;DR: A survey of surface wave methods can be found in this article, where surface wave propagation in vertically inhomogeneous, inelastic continua measurements of surface waves are performed using a combination of velocity and dispersion analysis.
Abstract: Overview of surface wave methods Seismic waves Test methodology Historical perspective Challenges of surface wave methods Typical applications Advantages and limitations Linear wave propagation in verticallyinhomogeneous continua Basic notions of wave propagation Rayleigh waves in homogeneous elastic half-spaces Existence of Love waves Surface waves in vertically inhomogeneouselastic continua Surface waves in vertically inhomogeneous, inelastic continua Measurement of surface waves Seismic data acquisition The wave field as a signal in time and space Acquisition of digital seismic signals Acquisition of surface waves Equipment Dispersion analysis Phase and group velocity Steady-state method Spectral analysis of surface waves Multi-offset phase analysis Spatial autocorrelation Transform-based methods Group velocity analysis Errors and uncertainties in dispersion analyses Attenuation analysis Attenuation of surface waves Univariate regression of amplitude versus offset data Transfer function technique and complex wavenumbers Multichannel multimode complex wavenumber estimation Other simplified approaches Uncertainty in the attenuation measurement Inversion Conceptual issues Forward modeling Surface wave inversion by empirical methods Surface wave inversion by analytical methods Uncertainty Case histories Comparison among processing techniques with active-source methods Comparison among inversion strategies Examples for determining Vs and Ds profiles Dealing with higher modes Surface wave inversion of seismic reflection data Advanced surface wave methods Love waves Offshore and nearshore surface wave testing Joint inversion with other geophysical data Passive seismic interferometry Multicomponent surface wave analysis, polarization studies, and horizontal-to-vertical spectral ratio References Index
231 citations
TL;DR: In this article, a wave equation was derived from Kjartansson's constant-Q constitutive stress-strain relation in combination with the mass and momentum conservation equations for modeling acoustic wave propagation in attenuating media.
Abstract: We evaluated a time-domain wave equation for modeling acoustic wave propagation in attenuating media. The wave equation was derived from Kjartansson’s constant-Q constitutive stress-strain relation in combination with the mass and momentum conservation equations. Our wave equation, expressed by a second-order temporal derivative and two fractional Laplacian operators, described very nearly constant-Q attenuation and dispersion effects. The advantage of using our formulation of two fractional Laplacians over the traditional fractional time derivative approach was the avoidance of time history memory variables and thus it offered more economic computations. In numerical simulations, we formulated the first-order constitutive equations with the perfectly matched layer absorbing boundaries. The temporal derivative was calculated with a staggered-grid finite-difference approach. The fractional Laplacians are calculated in the spatial frequency domain using a Fourier pseudospectral implementation. We validated our numerical results through comparisons with theoretical constant-Q attenuation and dispersion solutions, field measurements from the Pierre Shale, and results from 2D viscoacoustic analytical modeling for the homogeneous Pierre Shale. We also evaluated different formulations to show separated amplitude loss and dispersion effects on wavefields. Furthermore, we generalized our rigorous formulation for homogeneous media to an approximate equation for viscoacoustic waves in heterogeneous media. We then investigated the accuracy of numerical modeling in attenuating media with different Q-values and its stability in largecontrast heterogeneous media. Finally, we tested the applicability of our time-domain formulation in a heterogeneous medium with high attenuation.
220 citations
TL;DR: In this paper, a 2D phase gradient metasurface (PGM) was designed using a square combination of 49 split-ring subunit cells to provide additional wave-vectors along the two in-plane directions simultaneously, leading to either surface wave conversion, deflected reflection, or diffuse reflection.
Abstract: Phase gradient metasurface (PGMs) are artificial surfaces that can provide pre-defined in-plane wave-vectors to manipulate the directions of refracted/reflected waves. In this Letter, we propose to achieve wideband radar cross section (RCS) reduction using two-dimensional (2D) PGMs. A 2D PGM was designed using a square combination of 49 split-ring sub-unit cells. The PGM can provide additional wave-vectors along the two in-plane directions simultaneously, leading to either surface wave conversion, deflected reflection, or diffuse reflection. Both the simulation and experiment results verified the wide-band, polarization-independent, high-efficiency RCS reduction induced by the 2D PGM.
197 citations
TL;DR: Spatial coherent compounding provided a strong improvement of the imaging quality, even with a small number of transmitted diverging waves and a high frame rate, which allows imaging of the propagation of electromechanical and shear waves with good image quality.
Abstract: Noninvasive ultrafast imaging of intrinsic waves such as electromechanical waves or remotely induced shear waves in elastography imaging techniques for human cardiac applications remains challenging. In this paper, we propose ultrafast imaging of the heart with adapted sector size by coherently compounding diverging waves emitted from a standard transthoracic cardiac phased-array probe. As in ultrafast imaging with plane wave coherent compounding, diverging waves can be summed coherently to obtain high-quality images of the entire heart at high frame rate in a full field of view. To image the propagation of shear waves with a large SNR, the field of view can be adapted by changing the angular aperture of the transmitted wave. Backscattered echoes from successive circular wave acquisitions are coherently summed at every location in the image to improve the image quality while maintaining very high frame rates. The transmitted diverging waves, angular apertures, and subaperture sizes were tested in simulation, and ultrafast coherent compounding was implemented in a commercial scanner. The improvement of the imaging quality was quantified in phantoms and in one human heart, in vivo. Imaging shear wave propagation at 2500 frames/s using 5 diverging waves provided a large increase of the SNR of the tissue velocity estimates while maintaining a high frame rate. Finally, ultrafast imaging with 1 to 5 diverging waves was used to image the human heart at a frame rate of 4500 to 900 frames/s over an entire cardiac cycle. Spatial coherent compounding provided a strong improvement of the imaging quality, even with a small number of transmitted diverging waves and a high frame rate, which allows imaging of the propagation of electromechanical and shear waves with good image quality.
193 citations
TL;DR: In this article, the theory necessary to model the propagation of light through an atomic vapour is presented, and analytical solutions to the theory are found, based on approximations to the numerical work.
Abstract: This tutorial presents the theory necessary to model the propagation of light through an atomic vapour. The history of atom–light interaction theories is reviewed, and examples of resulting applications are provided. A numerical model is developed and results presented. Analytic solutions to the theory are found, based on approximations to the numerical work. These solutions are found to be in excellent agreement with experimental measurements.
190 citations
TL;DR: In this study, shear wave velocity dispersion was measured in vivo in ten Achilles tendons parallel and perpendicular to the tendon fibre orientation and it is shown that parallel to fibres the shear waves dispersion is not influenced by viscosity, while it is perpendicularly to fibre.
Abstract: Non-invasive evaluation of the Achilles tendon elastic properties may enhance diagnosis of tendon injury and the assessment of recovery treatments. Shear wave elastography has shown to be a powerful tool to estimate tissue mechanical properties. However, its applicability to quantitatively evaluate tendon stiffness is limited by the understanding of the physics on the shear wave propagation in such a complex medium. First, tendon tissue is transverse isotropic. Second, tendons are characterized by a marked stiffness in the 400 to 1300 kPa range (i.e. fast shear waves). Hence, the shear wavelengths are greater than the tendon thickness leading to guided wave propagation. Thus, to better understand shear wave propagation in tendons and consequently to properly estimate its mechanical properties, a dispersion analysis is required. In this study, shear wave velocity dispersion was measured in vivo in ten Achilles tendons parallel and perpendicular to the tendon fibre orientation. By modelling the tendon as a transverse isotropic viscoelastic plate immersed in fluid it was possible to fully describe the experimental data (deviation<1.4%). We show that parallel to fibres the shear wave velocity dispersion is not influenced by viscosity, while it is perpendicularly to fibres. Elasticity (found to be in the range from 473 to 1537 kPa) and viscosity (found to be in the range from 1.7 to 4 Pa.s) values were retrieved from the model in good agreement with reported results.
167 citations
TL;DR: Li et al. as discussed by the authors investigated the effect of following currents on vegetation-induced wave attenuation and found that following currents can either increase or decrease wave dissipation depending on the velocity ratio, which explains the seeming inconsistency in previous studies.
162 citations
TL;DR: In this article, the authors proposed the first true optical Huygens' surface, which explicitly utilizes orthogonal electric and magnetic responses to realize total control on an optical surface's local reflection coefficients.
Abstract: Implementation of abrupt phase discontinuities along a surface has been the theme of recent research on electromagnetic metasurfaces. Simple functionalities such as reflecting, refracting, or focusing plane waves have been demonstrated with devices featuring phase discontinuities, but optical surfaces allowing independent magnitude and phase control on the scattered waves have yet to emerge. In this paper, we propose the first true optical Huygens’ surface, which explicitly utilizes orthogonal electric and magnetic responses to realize total control on an optical surface’s local reflection coefficients. This extends the functionality of metasurfaces to an unprecedented level. We first demonstrate that a nanorod gap-surface plasmon resonator can act as a Huygens’ source. Thereafter, by properly tuning and rotating these resonators, we realize arbitrary reflection optical metasurfaces—surfaces for which the local reflection coefficients can be independently tailored in both magnitude and phase. We demonstrate the versatility of this approach through designs of a metasurface that asymmetrically reflects two copolarized beams and a Dolph-Tschebyscheff optical reflectarray.
155 citations
TL;DR: In this article, the authors used normal-mode splitting functions in addition to surface wave phase anomalies, body wave traveltimes and long-period waveforms to construct a 3D model of anisotropic shear wave velocity in the Earth's mantle.
Abstract: S U M M A R Y We use normal-mode splitting functions in addition to surface wave phase anomalies, body wave traveltimes and long-period waveforms to construct a 3-D model of anisotropic shear wave velocity in the Earth’s mantle. Our modelling approach inverts for mantle velocity and anisotropy as well as transition-zone discontinuity topographies, and incorporates new crustal corrections for the splitting functions that are consistent with the non-linear corrections we employ for the waveforms. Our preferred anisotropic model, S362ANI+M, is an update to the earlier model S362ANI, which did not include normal-mode splitting functions in its derivation. The new model has stronger isotropic velocity anomalies in the transition zone and slightly smaller anomalies in the lowermost mantle, as compared with S362ANI. The differences in the midto lowermost mantle are primarily restricted to features in the Southern Hemisphere. We compare the isotropic part of S362ANI+M with other recent global tomographic models and show that the level of agreement is higher now than in the earlier generation of models, especially in the transition zone and the lower mantle. The anisotropic part of S362ANI+M is restricted to the upper 300 km in the mantle and is similar to S362ANI. When radial anisotropy is allowed throughout the mantle, large-scale anisotropic patterns are observed in the lowermost mantle with vSV > vSH beneath Africa and South Pacific and vSH > vSV beneath several circum-Pacific regions. The transition zone exhibits localized anisotropic anomalies of ∼3 per cent vSH > vSV beneath North America and the Northwest Pacific and ∼2 per cent vSV > vSH beneath South America. However, small improvements in fits to the data on adding anisotropy at depth leave the question open on whether large-scale radial anisotropy is required in the transition zone and in the lower mantle. We demonstrate the potential of mode-splitting data in reducing the trade-offs between isotropic velocity and anisotropy in the lowermost mantle for the even-degree variations. Spurious anisotropic variations in the mid-mantle are also suppressed with the addition of mode-splitting data.
148 citations
TL;DR: In this paper, reflection and transmission of compression and shear waves at structured interfaces between second-gradient continua is investigated, and two semi-infinite spaces filled with the same semidefinite spaces are modeled.
Abstract: In this paper reflection and transmission of compression and shear waves at structured interfaces between second-gradient continua is investigated. Two semi-infinite spaces filled with the same sec...
147 citations
TL;DR: It is demonstrated that the topology of wrinkling interfacial layers can be controlled by deformation and used to produce band gaps in wave propagation and, hence, to selectively filter frequencies.
Abstract: The ability to control wave propagation in highly deformable layered media with elastic instability-induced wrinkling of interfacial layers is presented. The onset of a wrinkling instability in initially straight interfacial layers occurs when a critical compressive strain is achieved. Further compression beyond the critical strain leads to an increase in the wrinkle amplitude of the interfacial layer. This, in turn, gives rise to the formation of a system of periodic scatterers, which reflect and interfere with wave propagation. We demonstrate that the topology of wrinkling interfacial layers can be controlled by deformation and used to produce band gaps in wave propagation and, hence, to selectively filter frequencies. Remarkably, the mechanism of frequency filtering is effective even for composites with similar or identical densities, such as polymer-polymer composites. Since the microstructure change is reversible, the mechanism can be used for tuning and controlling wave propagation by deformation.
TL;DR: This study has yielded a quantitative characterization strategy for fatigue cracks using embeddable piezoelectric sensor networks, facilitating deployment of structural health monitoring which is capable of identifying small-scale damage at an embryo stage and surveilling its growth continuously.
TL;DR: Numerical results of sample tests in one and two space dimensions are presented that show the ability of the proposed model to describe cavitation mechanisms and evaporation wave dynamics.
TL;DR: In this article, a set of algorithms for automatic detection and picking of direct P and S waves, as well as fault zone head waves (FZHW), generated by earthquakes on faults that separate different lithologies and recorded by local seismic networks.
Abstract: S U M M A R Y We develop a set of algorithms for automatic detection and picking of direct P and S waves, as well as fault zone head waves (FZHW), generated by earthquakes on faults that separate different lithologies and recorded by local seismic networks. The S-wave picks are performed using polarization analysis and related filters to remove P-wave energy from the seismograms, and utilize STA/LTA and kurtosis detectors in tandem to lock on the phase arrival. The early portions of P waveforms are processed with STA/LTA, kurtosis and skewness detectors for possible first-arriving FZHW. Identification and picking of direct P and FZHW is performed by a multistage algorithm that accounts for basic characteristics (motion polarities, time difference, sharpness and amplitudes) of the two phases. The algorithm is shown to perform well on synthetic seismograms produced by a model with a velocity contrast across the fault, and observed data generated by earthquakes along the Parkfield section of the San Andreas fault and the Hayward fault. The developed techniques can be used for systematic processing of large seismic waveform data sets recorded near major faults.
TL;DR: The investigated nonlinear dynamics of a periodic chain of bistable elements consisting of masses connected by elastic springs whose constraint arrangement gives rise to a large-deformation snap-through instability produces three different regimes of wave propagation in the periodic medium, depending on the wave amplitude.
Abstract: We investigate the nonlinear dynamics of a periodic chain of bistable elements consisting of masses connected by elastic springs whose constraint arrangement gives rise to a large-deformation snap-through instability. We show that the resulting negative-stiffness effect produces three different regimes of (linear and nonlinear) wave propagation in the periodic medium, depending on the wave amplitude. At small amplitudes, linear elastic waves experience dispersion that is controllable by the geometry and by the level of precompression. At moderate to large amplitudes, solitary waves arise in the weakly and strongly nonlinear regime. For each case, we present closed-form analytical solutions and we confirm our theoretical findings by specific numerical examples. The precompression reveals a class of wave propagation for a partially positive and negative potential. The presented results highlight opportunities in the design of mechanical metamaterials based on negative-stiffness elements, which go beyond current concepts primarily based on linear elastic wave propagation. Our findings shed light on the rich effective dynamics achievable by nonlinear small-scale instabilities in solids and structures.
TL;DR: Results show that as in the atmosphere, also in underwater media the plane wave is more affected by turbulence as compared to the spherical wave, and Salinity-induced turbulence strongly dominates the scintillations compared to temperature- induced turbulence.
Abstract: The scintillation indices of optical plane and spherical waves propagating in underwater turbulent media are evaluated by using the Rytov method, and the variations in the scintillation indices are investigated when the rate of dissipation of mean squared temperature, the temperature and salinity fluctuations, the propagation distance, the wavelength, the Kolmogorov microscale length, and the rate of dissipation of the turbulent kinetic energy are varied. Results show that as in the atmosphere, also in underwater media the plane wave is more affected by turbulence as compared to the spherical wave. The underwater turbulence effect becomes significant at 5-10 m for a plane wave and at 20-25 m for a spherical wave. The turbulence effect is relatively small in deep water and is large at the surface of the water. Salinity-induced turbulence strongly dominates the scintillations compared to temperature-induced turbulence.
TL;DR: In this article, a multichannel analysis of high-frequency surface (Rayleigh and Love) waves developed mainly by research scientists at the Kansas Geological Survey, the University of Kansas and China University of Geosciences (Wuhan) during the last eighteen years by discussing dispersion imaging techniques, inversion systems, and real-world examples.
TL;DR: In this article, the dispersion characteristics of elastic waves propagating in a monolayer piezoelectric nanoplate are investigated with consideration of the surface PAs as well as the nonlocal small-scale effect.
Abstract: In this paper, the dispersion characteristics of elastic waves propagating in a monolayer piezoelectric nanoplate is investigated with consideration of the surface piezoelectricity as well as the nonlocal small-scale effect. Nonlocal electroelasticity theory is used to derive the general governing equations by introducing an intrinsic length, and the surface effects exerting on the boundary conditions of the piezoelectric nanoplate are taken into account through incorporation of the surface piezoelectricity model and the generalized Young–Laplace equations. The dispersion relations of elastic waves based on the current formulation are obtained in an explicit closed form. Numerical results show that both the nonlocal scale parameter and surface piezoelectricity have significant influence on the size-dependent properties of dispersion behaviors. It is also found that there exists an escape frequency above which the waves may not propagate in the piezoelectric plate with nanoscale thickness.
Book•
01 Aug 2014
TL;DR: A brief history of the field of plasma physics can be found in this article, where DeBroglie et al. describe a collision operator for two-body elastic collisions and a collisional conservation law for collision operators.
Abstract: Introduction What is Plasma? Brief History of Plasma Physics Fundamental Parameters Plasma Frequency Debye Shielding Plasma Parameter Collisions Magnetized Plasmas Plasma Beta DeBroglie Wavelength Exercises Charged Particle Motion Introduction Motion in Uniform Fields Method of Averaging Guiding Center Motion Magnetic Drifts Invariance of Magnetic Moment Poincar'e Invariants Adiabatic Invariants Magnetic Mirrors Van Allen Radiation Belts Equatorial Ring Current Second Adiabatic Invariant Third Adiabatic Invariant Motion in Oscillating Fields Exercises Collisions Introduction Collision Operator Two-Body Elastic Collisions Boltzmann Collision Operator Collisional Conservation Laws Boltzmann H-Theorem Two-Body Coulomb Collisions Rutherford Scattering Cross-Section Landau Collision Operator Coulomb Logarithm Rosenbluth Potentials Collision Times Exercises Plasma Fluid Theory Introduction Moments of Distribution Function Moments of Collision Operator Moments of Kinetic Equation Fluid Equations Entropy Production Fluid Closure Chapman-Enskog Closure Normalization of Neutral Gas Equations Braginskii Equations Normalization of Braginskii Equations Cold-Plasma Equations MHD Equations Drift Equations Closure in Collisionless Magnetized Plasmas Langmuir Sheaths Exercises Waves in Cold Plasmas Introduction Plane Waves in homogeneous Plasmas Cold-Plasma Dielectric Permittivity Cold-Plasma Dispersion Relation Wave Polarization Cutoff and Resonance Waves in Unmagnetized Plasmas Low-Frequency Wave Propagation Parallel Wave Propagation Perpendicular Wave Propagation Exercises Wave Propagation Through Inhomogeneous Plasmas Introduction WKB Solutions Cutoffs Resonances Resonant Layers Collisional Damping Pulse Propagation Ray Tracing Ionospheric Radio Wave Propagation Exercises Magnetohydrodynamic Fluids Introduction Magnetic Pressure Flux Freezing MHD Waves Solar Wind Parker Model of Solar Wind Interplanetary Magnetic Field Mass and Angular Momentum Loss MHD Dynamo Theory Homopolar Disk Dynamo Slow and Fast Dynamos Cowling Anti-Dynamo Theorem Ponomarenko Dynamo Magnetic Reconnection Linear Tearing Mode Theory Nonlinear Tearing Mode Theory Fast Magnetic Reconnection MHD Shocks Parallel MHD Shocks Perpendicular MHD Shocks Oblique MHD Shocks Exercises Waves in Warm Plasmas Introduction Landau Damping Physics of Landau Damping Plasma Dispersion Function Ion Acoustic Waves Waves in Magnetized Plasmas Parallel Wave Propagation Perpendicular Wave Propagation Electrostatic Waves Velocity-Space Instabilities Counter-Propagating Beam Instability Current-Driven Ion Acoustic Instability Harris Instability Exercises Bibliography Index
Book•
17 Mar 2014
TL;DR: The Fractional Calculus and its Applications: Applications in physics, part A and BFractional Differential Equations: Theory and Applications as mentioned in this paper Theory and Applications of FF Equations.
Abstract: Fractional Calculus for Hydrology, Soil Science and GeomechanicsFunctional Fractional CalculusKindergarten of Fractional CalculusFractional CalculusFractional Calculus with Applications for Nuclear Reactor DynamicsThe Analysis of Fractional Differential EquationsGeneralized Fractional CalculusFractional Calculus with Applications in MechanicsFractional CalculusHandbook of Fractional Calculus with Applications/ Numerical MethodsTheory And Applications of Fractional Differential EquationsApplications of Fractional Calculus in PhysicsFractional Calculus and Its ApplicationsGeneral Fractional DerivativesHandbook of Fractional Calculus with Applications: Applications in physics, part AThe Fractional CalculusFractional Order Analysisq-Fractional Calculus and EquationsHandbook of Fractional Calculus with Applications: Applications in physics, part BFractional Calculus: Theory and ApplicationsHandbook of Fractional Calculus with Applications: Applications in engineering, life and social sciences, part BFractional CalculusFractional Calculus: Models And Numerical MethodsOn Fractional Calculus and Applications and Fractional Differential EquationsHandbook of Fractional Calculus with Applications: Applications in controlFractional CalculusAdvances in Fractional CalculusFractional CalculusFractional Derivatives with Mittag-Leffler KernelGeneral Fractional Derivatives with Applications in ViscoelasticityThe Fractional Calculus Theory and Applications of Differentiation and Integration to Arbitrary OrderFractional Differential EquationsFractional Calculus with Applications in MechanicsDiscrete Fractional CalculusFractional Calculus and its Applications in PhysicsFractional Calculus: Theory and ApplicationsUnivalent Functions, Fractional Calculus, and Their ApplicationsFunctional Fractional Calculus for System Identification and ControlsFractional Calculus and Its ApplicationsHandbook of Fractional Calculus with Applications: Applications in engineering, life and social sciences, part A
TL;DR: The proposed model provides unprecedented accuracy for describing near-field radar measurements collected over a water layer, the frequency-dependent electrical properties of which were described using the Debye model.
Abstract: A new near-field radar modeling approach for wave propagation in planar layered media is presented. The radar antennas are intrinsically modeled using an equivalent set of infinitesimal electric dipoles and characteristic, frequency-dependent, global reflection, and transmission coefficients. These coefficients determine through a plane wave decomposition wave propagation between the radar reference plane, point sources, and field points. The interactions between the antenna and layered medium are thereby inherently accounted for. The fields are calculated using 3-D Green's functions. We validated the model using an ultrawideband frequency-domain radar with a transmitting and receiving Vivaldi antenna operating in the range 0.8-4 GHz. The antenna characteristic coefficients are obtained from near- and far-field measurements over a copper plane. The proposed model provides unprecedented accuracy for describing near-field radar measurements collected over a water layer, the frequency-dependent electrical properties of which were described using the Debye model. Layer thicknesses could be retrieved through full-wave inversion. The proposed approach demonstrated great promise for nondestructive testing of planar materials and digital soil mapping using ground-penetrating radar.
TL;DR: Efendiev et al. as discussed by the authors proposed a multiscale finite element method for wave propagation on a coarse grid, which is based on the generalized multi-scale finite element (GMsFEM).
Abstract: Numerical modeling of wave propagation in heterogeneous media is important in many applications. Due to their complex nature, direct numerical simulations on the fine grid are prohibitively expensive. It is therefore important to develop efficient and accurate methods that allow the use of coarse grids. In this paper, we present a multiscale finite element method for wave propagation on a coarse grid. The proposed method is based on the generalized multiscale finite element method (GMsFEM) (see [Y. Efendiev, J. Galvis, and T. Hou, J. Comput. Phys., 251 (2012), pp. 116--135]). To construct multiscale basis functions, we start with two snapshot spaces in each coarse-grid block, where one represents the degrees of freedom on the boundary and the other represents the degrees of freedom in the interior. We use local spectral problems to identify important modes in each snapshot space. These local spectral problems are different from each other and their formulations are based on the analysis. To the best of kn...
TL;DR: In this paper, the authors examined the impact of a wave farm on the beach profile through a case study based on two coupled numerical models: a nearshore wave propagation model and a morphodynamic model, which are run in two scenarios, both with and without the wave farm.
TL;DR: In this paper, the authors compare simulations with SWASH to flume observations of random, unidirectional waves, incident on a 1:30 planar beach, and show that the model accurately predicts second-order bulk parameters such as wave height and period, the details of the spectral evolution, and higher-order statistics, such as skewness and asymmetry of the waves.
TL;DR: In this paper, the authors present the observations of a chain of winking filaments and a subsequent jet that are observed right after the X2.1 flare in AR11283, and they conclude that the EUV wave is a good agent for triggering and connecting successive but separated solar activities in the solar atmosphere.
Abstract: Winking (oscillating) filaments have been observed for many years. However, observations of successive winking filaments in one event have not yet been reported. In this paper, we present the observations of a chain of winking filaments and a subsequent jet that are observed right after the X2.1 flare in AR11283. The event also produced an extreme-ultraviolet (EUV) wave that has two components: an upward dome-like wave (850 km s(-1)) and a lateral surface wave (554 km s(-1)) that was very weak (or invisible) in imaging observations. By analyzing the temporal and spatial relationships between the oscillating filaments and the EUV waves, we propose that all the winking filaments and the jet were triggered by the weak (or invisible) lateral surface EUV wave. The oscillation of the filaments last for two or three cycles, and their periods, Doppler velocity amplitudes, and damping times are 11-22 minutes, 6-14 km s(-1), and 25-60 minutes, respectively. We further estimate the radial component magnetic field and the maximum kinetic energy of the filaments, and they are 5-10 G and similar to 10(19) J, respectively. The estimated maximum kinetic energy is comparable to the minimum energy of ordinary EUV waves, suggesting that EUV waves can efficiently launch filament oscillations on their path. Based on our analysis results, we conclude that the EUV wave is a good agent for triggering and connecting successive but separated solar activities in the solar atmosphere, and it is also important for producing solar sympathetic eruptions.
TL;DR: In this article, a hybrid model is proposed to simulate the induced shock waves in the gas together with wave propagation in the rock material, and the model successfully mimics crack propagation in rock.
TL;DR: In this article, the spectral cell method is proposed to combine the finite cell method with the spectral element method for the analysis of wave propagation phenomena, which is referred to as the spectralcell method.
Abstract: SUMMARY
An accurate and efficient simulation of wave propagation phenomena plays an important role in different engineering disciplines. In structural health monitoring, for example, ultrasonic guided waves are used to detect and localize damage and to assess the structural integrity of the component part under consideration. Because of the complexity of real structures, the numerical simulation of structural health monitoring systems is a computationally demanding task. Therefore, to facilitate the analysis of wave propagation phenomena, the authors propose to combine the finite cell method with the spectral element method. The ensuing novel method is referred to as the spectral cell method. Because it does not rely on body-fitted meshes, the resulting approach eliminates all discretization difficulties encountered in conventional finite element methods. Moreover, with the aid of mass lumping, it paves the way for the use of explicit time-integration algorithms. In the first part of the paper, we show that using a lumped mass matrix instead of the consistent one has no detrimental effect on the accuracy of the spectral element method. We introduce the spectral cell method in the second part, showing that, when applied to wave propagation analysis, the spectral cell method yields results comparable with other standard higher order finite element approaches.Copyright © 2014 John Wiley & Sons, Ltd.
TL;DR: In this paper, the authors investigated the role of ambient temperature in causing changes to the structural wave propagation, as sensed by piezoelectric transducers, in a newer perspective.
Abstract: This article investigates the role of ambient temperature in causing changes to the structural wave propagation, as sensed by piezoelectric transducers, in a newer perspective. A novel approach is proposed to compensate the influence of temperature on piezo-sensor response using both analytical models and numerical simulations. Parametric studies using numerical simulations for plates with surface-mounted piezoelectric transducers establish linear functional relationship between change in sensor signals and specific combination of material properties, within certain temperature range. A numerical temperature compensation model is developed based on this functional relationship to reconstruct piezo-sensor signals at elevated temperatures. Matching pursuit–based signal analysis and reconstruction schemes are used in this study. Practical efficacy of the compensation model is tested for metallic structures with both simple and complex geometries. Model-based reconstruction of first wave packets in the sensor...