Journal articles on the topic 'Elastic wave conversion'
To see the other types of publications on this topic, follow the link: Elastic wave conversion.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 journal articles for your research on the topic 'Elastic wave conversion.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse journal articles on a wide variety of disciplines and organise your bibliography correctly.
1
Paul, Anne, and Michel Campillo. "Diffraction and conversion of elastic waves at a corrugated interface." GEOPHYSICS 53, no. 11 (November 1988): 1415–24. http://dx.doi.org/10.1190/1.1442421.
Full textAbstract:
Numerical modeling is used to investigate the effect of small‐scale irregularities of a reflecting boundary on elastic wave reflections. The scattered wave field is computed by using a discretized form of boundary integral equations and a plane‐wave decomposition of seismic wave fields. For various values of incidence angle of the P wave, we compute the distribution of diffracted energy for both P waves and S waves as a function of reflection angle. We show that corrugations with mean wavelength of the order of, or smaller than, the seismic wavelength have little effect on the reflected P wave. However, the pattern of P‐to‐S conversion is very different from that with a plane boundary. Scattered S waves appear at postcritical angles for any angle of incidence of the P wave. The amplitude of these nongeometrical shear waves decreases rapidly with decreasing amplitude of the corrugations, or when the mean wavelength of the corrugations becomes larger than the dominant seismic wavelength. The local geometry of the irregularities has a negligible effect on the scattered S waves. By analogy with perturbation theory, we propose interpreting the postcritically scattered S waves as the contribution to the shear wave field of converted inhomogeneous P waves diffracted along the boundary.
2
Xu, Shibo, and Alexey Stovas. "Estimation of the conversion point position in elastic orthorhombic media." GEOPHYSICS 84, no. 1 (January 1, 2019): C15—C25. http://dx.doi.org/10.1190/geo2018-0375.1.
Full textAbstract:
Determination of the conversion point position is very important to carry out seismic processing in the common conversion point gather of converted wave data. The anisotropic effect is very obvious for a converted wave when estimating the physical and processing parameters from real data. To estimate the conversion point in an elastic orthorhombic (ORT) medium, we have defined an explicit rational form approximation for the radial coordinate of the conversion point for converted [Formula: see text], [Formula: see text], and [Formula: see text] waves. To obtain the approximation coefficients, the Taylor series approximation in the corresponding vertical slowness for three pure wave modes is applied. The coefficients in our proposed approximation are computed within two vertical symmetry planes. The difference between the acquisition azimuth and the azimuth of the conversion point position is analyzed for different combinations of the wave modes. The accuracy of the conversion point position estimation for three ORT models is illustrated in the numerical examples. One can see from the results that for converted [Formula: see text] and [Formula: see text] waves, our approximation is very accurate in estimating the conversion point position regardless of the tested ORT model. For a converted [Formula: see text] wave, due to the existence of cusps, triplications, and shear singularities, the error in conversion point estimation is relatively larger compared with PS-waves in the vicinity of the singularity point.
3
Belyayev, Yu N., E. I. Yashin, and O. Y. Yashina. "Conversion of Elastic Wave Polarization in Calcium Molybdate Layer." Solid State Phenomena 284 (October 2018): 95–100. http://dx.doi.org/10.4028/www.scientific.net/ssp.284.95.
Full textAbstract:
Scattering of elastic waves in calcium molybdate films is considered. The transformation of elastic waves as a result of six-beam diffraction in an anisotropic layer is analyzed. This analysis is based on the transfer matrix method. The distribution of incident wave energy between six scattered waves is characterized by conversion coefficients. The method for conversion coefficients calculations is presented. It does not require solving algebraic problem on eigenvalues for waves in an anisotropic layer. Features of dependencies of conversion coefficients of CaMoO4 layers on angles of incidence, frequency and the thickness of the layer are demonstrated.
4
Zeng, Yuehua. "Theory of scattered P- and S-wave energy in a random isotropic scattering medium." Bulletin of the Seismological Society of America 83, no. 4 (August 1, 1993): 1264–76. http://dx.doi.org/10.1785/bssa0830041264.
Full textAbstract:
Abstract A new theory is presented to study the scattered elastic wave energy propagation in a random isotropic scattering medium. It is based on a scattered elastic wave energy equation that extends the work of Zeng et al. (1991) on multiple scattering by considering S to P and P to S wave scattering conversions. We obtain a complete solution of the scattered elastic wave energy equation by solving the equation in the frequency/wave-number domain. Using a discrete wave-number sum technique combined with a modified repeated averaging and the FFT method, we compute numerically the complete solution. By considering that the scattering conversion from P- to S-wave energy is about (α/β)4 times greater than that from S to P waves (Aki, 1992), we found that the P-wave scattering field was converted quickly to the S-wave scattering field, leading to the conclusion that coda waves generated from both P- and S-wave sources are actually dominated by scattered S waves. We also compared our result with that obtained under the acoustic wave assumption. The acoustic wave assumption for seismic coda works quite well for the scattered S-wave field but fails for the scattered P-wave field. Our scattered elastic wave energy equation provides a theoretical foundation for studying the scattered wave field generated by a P-wave source such as an explosion. The scattered elastic wave energy equation can be easily generalized to an inhomogeneous random scattering medium by considering variable scattering and absorption coefficients and elastic wave velocities in the earth.
5
De Ponti, Jacopo Maria, Luca Iorio, and Raffaele Ardito. "Graded elastic meta-waveguides for rainbow reflection, trapping and mode conversion." EPJ Applied Metamaterials 9 (2022): 6. http://dx.doi.org/10.1051/epjam/2022004.
Full textAbstract:
Precise control of elastic waves is a challenge for many applications in the field of mechanical vibrations, ultrasonic inspection, and energy harvesting. Graded arrays of resonators on elastic substrates recently revealed superior performances for broadband wave trapping and mode conversion. In this study we present elastic waveguides able to govern waves at different scales exploiting rainbow reflection, trapping and mode conversion. We investigate whether these mechanisms, and the associated control, can be used for energy harvesting or signal conversion devices.
6
Lee, Jin Kyung, Sang Ll Lee, Joon Hyun Lee, and Young Chul Park. "Propagation Characteristic of Elastic Wave in Pipe." Key Engineering Materials 345-346 (August 2007): 1323–26. http://dx.doi.org/10.4028/www.scientific.net/kem.345-346.1323.
Full textAbstract:
In this study, elastic waves of ultrasonic and acoustic emission were used to evaluate the propagation characteristic of the wave in pipe, and study on mode conversion of the elastic wave due to the cracks in the pipe was also performed. An acoustic emission (AE) sensor was used to receive the propagated ultrasonic wave. AE technique has a merit that it can identify the received ultrasonic wave by the analysis of the AE parameters such as count, energy, frequency, duration time and amplitude. For transmitting and receiving of the wave, a wedge for universal angle was manufactured. The optimum angles for transmitting of ultrasonic wave and signal receiving at the attached AE sensor on the pipe were determined. Theoretical dispersion curve was compared with the results of the time-frequency analysis based on the wavelet transformation. The received modes showed a good agreement with theoretical one. The used ultrasonic sensor was 1MHz, and AE sensor was broadband (100kHz – 1200kHz). The artificial cracks were induced in the pipe to measure the propagation characteristics of the elastic wave for the cracks. AE parameters for the received signals were also varied with the crack types in the pipe. AE parameters of amplitude and duration time were more effective factors than the analysis of mode conversion for evaluation of the cracks in the pipe.
7
Li, Ke, Shuangxi Jing, Jiangong Yu, and Bo Zhang. "Complex Rayleigh Waves in Nonhomogeneous Magneto-Electro-Elastic Half-Spaces." Materials 14, no. 4 (February 21, 2021): 1011. http://dx.doi.org/10.3390/ma14041011.
Full textAbstract:
The complex Rayleigh waves play an important role in the energy conversion efficiency of magneto-electro-elastic devices, so it is necessary to explore the wave propagation characteristics for the better applications in engineering. This paper modifies the Laguerre orthogonal polynomial to investigate the complex Rayleigh waves propagating in nonhomogeneous magneto-electro-elastic half-spaces. The improved method simplifies the calculation process by incorporating boundary conditions into the constitutive relations, shortens the solving time by transforming the solution of wave equation to an eigenvalue problem, and obtains all wave modes, including real and imaginary and complex wavenumbers. The three-dimensional curves of full frequency spectrum and phase velocities are presented for the better description of the conversion from complex Rayleigh wave modes to real wave ones; besides, the displacement distributions, electric and magnetic potential curves are obtained in thickness and propagation directions, respectively. Numerical results are analyzed and discussed elaborately in three cases: variation of nonhomogeneous coefficients, absence of magnetism, and absence of electricity. The results can be used to optimize and fabricate the acoustic surface wave devices of the nonhomogeneous magneto-electro-elastic materials.
8
Parker, Samuel D., Michael R. Haberman, and Daniel R. Roettgen. "Time-varying elastic wave mode conversion in vibrating elastic beams with subwavelength nonlinearity." Journal of the Acoustical Society of America 152, no. 4 (October 2022): A294. http://dx.doi.org/10.1121/10.0016326.
Full textAbstract:
Introduction of time-varying properties in a background medium can enable unconventional wave behavior. Furthermore, it is well-known that subjecting nonlinear materials to time-varying stress can be used for material characterization [Appl. Phys. Lett. 94, 011905 (2009)]. We propose a technique called Dynamic Asymmetric Transmission Measurement (DATM) that combines structural dynamic (SD) and ultrasonic (US) testing modalities in an elastic waveguide to detect and characterize changes in the global stress state of a structure that result in local time-varying stress conditions due to local nonlinearity. Asymmetric geometric features in beams and plates, paired with time-varying stress conditions, result in asymmetric mode conversion of guided US waves that depend on large-scale structural dynamics. The DATM technique is explored through finite element modeling, semi-analytical methods, and experiments and discussed in a structural health monitoring context. We also discuss the use of dynamic structures with engineered defects to introduce time-varying stress conditions for the purpose of manipulating elastic waves. [Sandia National Laboratories is a multimission laboratory managed and operated by the National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.]
9
Belyayev, Yuriy N. "Calculation of the Six-Beam Diffraction in Layered Media Using Polynomials of Principal Minors." Journal of Theoretical and Computational Acoustics 26, no. 02 (June 2018): 1850017. http://dx.doi.org/10.1142/s2591728518500172.
Full textAbstract:
The scattering of plane elastic waves by an anisotropic layered medium in the case of the six-beam diffraction is considered. The matrix method for solving wave equations is developed. The conversion coefficients [Formula: see text] for the three types of incident waves (horizontally polarized shear wave, vertically polarized shear wave and longitudinal wave) are defined. Representations of coefficients [Formula: see text] through elements of transfer matrix are found. The method for coefficients [Formula: see text] calculations is presented. It does not require the solving of algebraic problem on eigenvalues for waves in an anisotropic layer. Some features of the functional dependencies of [Formula: see text] on the angles of incidence, wave frequency and layer thickness are demonstrated on several examples of the crystals in a three-layer model. It is shown that the conversions SH wave into SV waves and SV wave into SH waves are equivalent.
10
Wandowski, Tomasz, Pawel Malinowski, and Wieslaw Ostachowicz. "Analysis of S0/A0 elastic wave mode conversion phenomenon in glass fibre reinforced polymers." MATEC Web of Conferences 188 (2018): 01009. http://dx.doi.org/10.1051/matecconf/201818801009.
Full textAbstract:
In this paper results of experimental analysis of elastic guided wave mode conversion phenomenon in glass fibre reinforced polymers GFRP are presented. Results of research presented in this paper are strictly focused on S0/A0' mode conversion caused by discontinuities in the form of circular teflon insert simulating damage and impact damage. Experimental research is based on non-contact elastic wave sensing with utilisation of scanning laser Doppler vibrometer SLDV and full wave-field measurements. In presented research influence of location of circular teflon insert on S0/A0' mode conversion is investigated. Teflon inserts were located between layers of composite material at different depth. Moreover influence of impact damage with different energy on S0/A0' mode conversion is investigated. Analysis of influence of investigated discontinuities on S0/A0' mode conversion are based on the elastic wave mode filtration in frequency-wavenumber domain. Mode filtration process allows to remove effects of unwanted type of mode propagation in forward or backward direction. Effects of S0/A0' mode conversion are characterise by mode conversion indicator based on amplitude of new mode A0'.
11
Wandowski, Tomasz, Pawel Malinowski, and Wieslaw Ostachowicz. "Elastic wave mode conversion phenomenon in glass fiber-reinforced polymers." International Journal of Structural Integrity 10, no. 3 (June 10, 2019): 337–55. http://dx.doi.org/10.1108/ijsi-10-2018-0061.
Full textAbstract:
Purpose The purpose of this paper is to present the results of experimental analysis of the elastic-guided wave mode conversion phenomenon in glass fiber-reinforced polymers. The results of this research presented in this paper are strictly focused on S0/A0’ mode conversion phenomenon caused by discontinuities in the form of circular Teflon inserts (artificial delaminations) and impact damage. Results of this research could be useful in problems of damage detection and localization. Design/methodology/approach In the research, guided waves are excited using a piezoelectric transducer and sensed in a non-contact manner using a scanning laser Doppler vibrometer. Full wavefield measurements are analyzed. Analysis of the influence of investigated discontinuities on S0/A0’ mode conversion is based on the elastic wave mode filtration in frequency-wavenumber domain. Mode filtration process allows us to remove the effects of the propagation of unwanted type of mode in forward or backward direction. Effects of S0/A0’ mode conversion are characterized by a mode conversion indicator (MCI) based on the amplitude of new mode A0’ and the amplitude of incident S0 mode. Findings It was noticed that the magnitude of MCI depends on the depth at which the Teflon inserts were located for all analyzed excitation frequencies and diameters of inserts (10 and 20 mm). The magnitude of MCI also increases with increasing impact energies. The S0/A0’ mode conversion phenomenon could be utilized for the detection of surface and internal located discontinuities. Originality/value This paper presents the original results of this research related to the influence of discontinuity location with respect to the sample thickness and severity of discontinuity on S0/A0’ mode conversion.
12
Elita Li, Yunyue, Yue Du, Jizhong Yang, Arthur Cheng, and Xinding Fang. "Elastic reverse time migration using acoustic propagators." GEOPHYSICS 83, no. 5 (September 1, 2018): S399—S408. http://dx.doi.org/10.1190/geo2017-0687.1.
Full textAbstract:
Elastic wave imaging has been a significant challenge in the exploration industry due to the complexities in wave physics and numerical implementation. We have separated the governing equations for P- and S-wave propagation without the assumptions of homogeneous Lamé parameters to capture the mode conversion between the two body waves in an isotropic, constant-density medium. The resulting set of two coupled second-order equations for P- and S-potentials clearly demonstrates that mode conversion only occurs at the discontinuities of the shear modulus. Applying the Born approximation to the new equations, we derive the PP, PS, SP, and SS imaging conditions from the first gradients of waveform matching objective functions. The resulting images are consistent with the physical perturbations of the elastic parameters, and, hence, they are automatically free of the polarity reversal artifacts in the converted images. When implementing elastic reverse time migration (RTM), we find that scalar wave equations can be used to back propagate the recorded P-potential, as well as individual components in the vector field of the S-potential. Compared with conventional elastic RTM, the proposed elastic RTM implementation using acoustic propagators not only simplifies the imaging condition, it but also reduces the computational cost and the artifacts in the images. We have determined the accuracy of our method using 2D and 3D numerical examples.
13
Nassar, H., H. Chen, A. N. Norris, M. R. Haberman, and G. L. Huang. "Non-reciprocal wave propagation in modulated elastic metamaterials." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 473, no. 2202 (June 2017): 20170188. http://dx.doi.org/10.1098/rspa.2017.0188.
Full textAbstract:
Time-reversal symmetry for elastic wave propagation breaks down in a resonant mass-in-mass lattice whose inner-stiffness is weakly modulated in space and in time in a wave-like fashion. Specifically, one-way wave transmission, conversion and amplification as well as unidirectional wave blocking are demonstrated analytically through an asymptotic analysis based on coupled mode theory and numerically thanks to a series of simulations in harmonic and transient regimes. High-amplitude modulations are then explored in the homogenization limit where a non-standard effective mass operator is recovered and shown to take negative values over unusually large frequency bands. These modulated metamaterials, which exhibit either non-reciprocal behaviours or non-standard effective mass operators, offer promise for applications in the field of elastic wave control in general and in one-way conversion/amplification in particular.
14
Wandowski, T., P. Kudela, and W. M. Ostachowicz. "Numerical analysis of elastic wave mode conversion on discontinuities." Composite Structures 215 (May 2019): 317–30. http://dx.doi.org/10.1016/j.compstruct.2019.02.076.
Full text
15
Tol, Serife. "Electromechanical metastructures for simultaneous wave attenuation and energy harvesting." Journal of the Acoustical Society of America 151, no. 4 (April 2022): A156. http://dx.doi.org/10.1121/10.0010957.
Full textAbstract:
Periodic architectures designed with piezoelectric materials are favorable due to their potential to control waves without any need for structural modifications and also due to their multifunctional abilities, such as energy harvesting and vibration mitigation. This talk focuses on the latter and introduces a piezoelectric-based metastructure with broadband capability of low-frequency elastic wave energy conversion. Unlike the phononic crystal concepts consisting of piezoelectric patch arrays with heavy masses or resonance-based piezoelectric cantilever harvester arrays with tip mass attachments used for harvesting standing waves, our goal is to exploit the properties of locally-resonant metamaterials and phononic crystals within the same structure and harvest energy from travelling elastic waves. Specifically, we merge locally resonant and Bragg band gaps to achieve a multifunctional metastructure, which is capable for maximum energy conversion and wave attenuation in a broadband fashion. To this end, we develop a new wave-based fully coupled electroelastic transfer matrix method and study multifunctional harvesting and attenuation performance of the electromechanical metastructure. The theoretical frameworks and the applicability of the proposed metastructure are also validated using a full-scale experimental setup.
16
Geilen, Moritz, Alexandra Nicoloiu, Daniele Narducci, Morteza Mohseni, Moritz Bechberger, Milan Ender, Florin Ciubotaru, et al. "Fully resonant magneto-elastic spin-wave excitation by surface acoustic waves under conservation of energy and linear momentum." Applied Physics Letters 120, no. 24 (June 13, 2022): 242404. http://dx.doi.org/10.1063/5.0088924.
Full textAbstract:
We report on the resonant excitation of spin waves in micro-structured magnetic thin films by short-wavelength surface acoustic waves (SAWs). The spin waves as well as the acoustic waves are studied by micro-focused Brillouin light scattering spectroscopy. At low magnetic bias fields, a resonant phonon–magnon conversion is possible, which results in the excitation of short-wavelength spin waves. Using micromagnetic simulations, we verify that during this excitation both energy and linear momentum are conserved and fully transferred from the SAW to the spin wave. This conversion can already be detected after an interaction length of a few micrometers. Thus, our findings pave the way for miniaturized magneto-elastic spin-wave emitters for magnon computing.
17
Wapenaar, C. P. A., N. A. Kinneging, and A. J. Berkhout. "Principle of prestack migration based on the full elastic two‐way wave equation." GEOPHYSICS 52, no. 2 (February 1987): 151–73. http://dx.doi.org/10.1190/1.1442291.
Full textAbstract:
The acoustic approximation in seismic migration is not allowed when the effects of wave conversion cannot be neglected, as is often the case in data with large offsets. Hence, seismic migration should ideally be founded on the full elastic wave equation, which describes compressional as well as shear waves in solid media (such as rock layers, in which shear stresses may play an important role). In order to cope with conversions between those wave types, the full elastic wave equation should be expressed in terms of the particle velocity and the traction, because these field quantities are continuous across layer boundaries where the main interaction takes place. Therefore, the full elastic wave equation should be expressed as a matrix differential equation, in which a matrix operator acts on a full wave vector which contains both the particle velocity and the traction. The solution of this equation yields another matrix operator. This full elastic two‐way wave field extrapolation operator describes the relation between the total (two‐way) wave fields (in terms of the particle velocity and the traction) at two different depth levels. Therefore it can be used in prestack migration to perform recursive downward extrapolation of the surface data into the subsurface (at a “traction‐free” surface, the total wave field can be described in terms of the detected particle velocity and the source traction). Results from synthetic data for a simplified subsurface configuration show that a multiple‐free image of the subsurface can be obtained, from which the angle‐dependent P-P and P-SV reflection functions can be recovered independently. For more complicated subsurface configurations, full elastic migration is possible in principle, but it becomes computationally complex. Nevertheless, particularly for the 3-D case, our proposal has improved the feasibility of full elastic migration significantly compared with other proposed full elastic migration or inversion schemes, because our method is carried out per shot record and per frequency component.
18
Rokhlin, Stanislav I., and Theodore E. Matikas. "Ultrasonic Characterization of Surfaces and Interphases." MRS Bulletin 21, no. 10 (October 1996): 22–29. http://dx.doi.org/10.1557/s0883769400031602.
Full textAbstract:
Ultrasonic waves have been used extensively for material characterization and for sensing in material process control. The waves produce small-amplitude mechanical vibrations and, depending on the mode being used, may induce both longitudinal and shear stresses in the solid. Information on the structural properties of a substance can be obtained by measuring both the velocity and the attenuation of the ultrasonic wave. The phase velocity of the wave depends on the elastic constants and density of the body while attenuation depends on microstructure and crystalline defects.In an isotropic solid medium, which has only two independent elastic moduli, there exist two elastic waves: the longitudinal and the shear. Three kinds of bulk elastic waves may propagate in an anisotropic solid: a quasilongitudinal and two quasitransverse waves, differing in polarization and velocity. To determine the set of elastic constants, one must measure the phase velocity in several different directions relative to the crystallographic axes.The attenuation of an ultrasonic wave is associated with absorption of elastic waves (inelastic effect) and the scattering of elastic waves by structural inhomogeneities. Scattering may be the governing attenuation mechanism in polycrystalline, composite, and ceramic materials. As a result of scattering, elastic energy is lost by the prime ultrasonic beam in the form of a stochastically scattered field, which is gradually absorbed in the material. The latter is associated with conversion of elastic into thermal energy as a result of various inelastic effects termed internal friction.
19
Riva, Emanuele. "Dynamics of temporally modulated materials: Adiabatic transformations and frequency conversion." Journal of the Acoustical Society of America 151, no. 4 (April 2022): A156. http://dx.doi.org/10.1121/10.0010955.
Full textAbstract:
The recent progress in the context of elastic metamaterials and modulated waveguides with digitally controllable properties has spurred the research in the context of time-varying and space-time varying mechanical systems. In other words, the search of new functionalities, such as nonreciprocity, frequency conversion, parametric amplification, and edge-to-edge pumping, to name a few, requires advanced space-time control of the material parameters, which justifies the emergence of active times in phononics. The work presented herein discusses temporal modulations in the context of stiffness-modulated elastic structures, with emphasis on frequency conversion and wave steering. It is shown that slow temporal modulations, compliant with the adiabatic theorem, can be functionally employed to change the frequency content and the propagation direction of incident wave packets. At the same time, adiabatic variations avoid the scattering of back-propagating waves, which are instead present in case of fast modulations and, in many cases, can be undesired from a practical perspective. Both transient and steady-state behaviors of stiffness-modulated waveguides are discussed with the goal of achieving controllable transmission of elastic signals between an emitter and a receiver.
20
Wang, Chenlong, Jiubing Cheng, Wiktor Waldemar Weibull, and Børge Arntsen. "Elastic wave-equation migration velocity analysis preconditioned through mode decoupling." GEOPHYSICS 84, no. 3 (May 1, 2019): R341—R353. http://dx.doi.org/10.1190/geo2018-0181.1.
Full textAbstract:
Multicomponent seismic data acquisition can reveal more information about geologic structures and rock properties than single component acquisition. Full elastic wave seismic imaging, which uses multicomponent seismic to its full potential, is promising because it provides more opportunities to understand the material properties of the earth by the joint use of P- and S-waves. A prerequisite of seismic imaging is the availability of a reliable macrovelocity model. Migration velocity analysis for P-waves, which can fill that requirement for the P-wave velocity, has been well-studied, especially under the acoustic approximation. However, a reliable estimation of the S-wave velocities remains troublesome. Elastic wave-equation migration velocity analysis has the potential to build P- and S-wave velocity models together, but it inevitably suffers from the effects of mode coupling and conversion in the forward and adjoint wavefield reconstructions. We have developed a differential semblance optimization approach to sequentially invert the background P- and S-wave velocity models from extended PP- and PS-images in the subsurface offset domain. Preconditioning of the gradients with respect to the S-wave velocity through mode decoupling can improve the reliability of the optimization. Numerical investigations with synthetic examples demonstrate the effectiveness of gradient preconditioning and the feasibility of our migration velocity analysis approach for elastic wave imaging.
21
Kim, Noh Yu, and Sang Soon Lee. "Elastic Property Measurement of High-Tension Bolt Based on Mode Converted Ultrasound." Key Engineering Materials 326-328 (December 2006): 709–12. http://dx.doi.org/10.4028/www.scientific.net/kem.326-328.709.
Full textAbstract:
Elastic properties of high tension bolt are evaluated non-destructively by measuring acoustic longitudinal and shear wave velocities using mode-converted ultrasound. Mode-converted longitudinal and shear waves along bolt are captured to calculate acoustic wave velocities and determine elastic constants such as Young’s modulus and Bulk modulus based on acoustoelasticity. Ray analysis to select a specific mode conversion from longitudinal mode to shear mode is carried out and discussed with experimental results. From experiment results of maximum 5% of measurement error, it is shown that the proposed mode-converted ultrasonic technique is very effective and sensitive enough to characterize mechanical modulus of high-tension bolts quantitatively.
22
Hestholm, Stig, and Bent Ruud. "3-D finite‐difference elastic wave modeling including surface topography." GEOPHYSICS 63, no. 2 (March 1998): 613–22. http://dx.doi.org/10.1190/1.1444360.
Full textAbstract:
Three‐dimensional finite‐difference (FD) modeling of seismic scattering from free surface topography has been pursued. We have developed exact 3-D free surface topography boundary conditions for the particle velocities. A velocity‐stress formulation of the full elastic wave equations together with the boundary conditions has been numerically modeled by an eighth‐order FD method on a staggered grid. We give a numerical stability criterion for combining the boundary conditions with curved‐grid wave equations, where a curved grid represents the physical medium with topography. Implementation of this stability criterion stops instabilities from arising in areas of steep and rough topographies. We have simulated scattering from teleseismic P-waves using a plane, vertically incident wavefront and real topography from a 40 × 40 km area centered at the NORESS array of seismic receiver stations in southeastern Norway. Synthetic snapshots and seismograms of the wavefield show clear conversion from P-waves to Rg (short period fundamental mode Rayleigh) waves in an area of rough topography approximately 10 km east of NORESS. This result is consistent with numerous observations.
23
Shabelansky, Andrey H., Alison Malcolm, and Michael Fehler. "Converted-wave seismic imaging: Amplitude-balancing source-independent imaging conditions." GEOPHYSICS 82, no. 2 (March 1, 2017): S99—S109. http://dx.doi.org/10.1190/geo2015-0167.1.
Full textAbstract:
We have developed crosscorrelational and deconvolutional forms of a source-independent converted-wave imaging condition (SICW-IC) and show the relationship between them using a concept of conversion ratio coefficient, a concept that we developed through reflection, transmission, and conversion coefficients. We applied the SICW-ICs to a two half-space model and the synthetic Marmousi I and II models and show the sensitivity of the SICW-ICs to incorrect wave speed models. We also compare the SICW-ICs and source-dependent elastic reverse time migration. The results of SICW-ICs highlight the improvements in spatial resolution and amplitude balancing with the deconvolutional forms. This is an attractive alternative to active and passive source elastic imaging.
24
Kurniawan, Adi, Scott Brown, David Forehand, and Hugh Wolgamot. "Wave–Structure Interactions of Flexible Bags with Elastic Tendons: Application to Wave Energy Conversion." Journal of Waterway, Port, Coastal, and Ocean Engineering 147, no. 1 (January 2021): 04020045. http://dx.doi.org/10.1061/(asce)ww.1943-5460.0000607.
Full text
25
Mei, Jun, Lijuan Fan, and Xiaobin Hong. "Elastic Metagratings with Simultaneous Modulation of Reflected and Transmitted Waves." Crystals 12, no. 7 (June 24, 2022): 901. http://dx.doi.org/10.3390/cryst12070901.
Full textAbstract:
Elastic metagratings enabling independent and complete control of both reflection and transmission of bulk longitudinal and transverse waves are highly desired in application scenarios such as non-destructive assessment and structural health monitoring. In this work, we propose a kind of simply structured metagrating composed only of elliptical hollow cylinders carved periodically in a steel background. By utilizing the grating diffraction theory and genetic algorithm, we endow these metagratings with the attractive functionality of simultaneous and high-efficiency modulation of every reflection and transmission channel of both longitudinal and transverse waves. Interesting wave-front manipulation effects including pure mode conversion and anomalous deflection along the desired direction are clearly demonstrated through full-wave numerical simulations. Due to its subwavelength thickness and high manipulation efficiency, the proposed metagrating is expected to be useful in the design of multifunctional elastic planar devices.
26
Bian, Chunlei, Ji Wang, Bin Huang, Longtao Xie, Lijun Yi, Lili Yuan, Honglang Li, and Yahui Tian. "An analysis of axisymmetric Sezawa waves in elastic solids." Physica Scripta 96, no. 12 (December 1, 2021): 125272. http://dx.doi.org/10.1088/1402-4896/ac418f.
Full textAbstract:
Abstract The wave propagation in elastic solids covered by a thin layer has received significant attention due to the existence of Sezawa waves in many applications such as medical imaging. With a Helmholtz decomposition in cylindrical coordinates and subsequent solutions with Bessel functions, it is found that the velocity of such Sezawa waves is the same as the one in Cartesian coordinates, but the displacement will be decaying along the radius with eventual conversion to plane waves. The decaying with radius exhibits a strong contrast to the uniform displacement in the Cartesian formulation, and the asymptotic approximation is accurate in the range about one wavelength away from the origin. The displacement components in the vicinity of origin are naturally given in Bessel functions which can be singular, making it more suitable to analyze waves excited by a point source with solutions from cylindrical coordinates. This is particularly important in extracting vital wave properties and reconstructing the waveform in the vicinity of source of excitation with measurement data from the outer region.
27
KAWASHITA, Mishio, and Hideo SOGA. "Mode-conversion of the scattering kernel for the elastic wave equation." Journal of the Mathematical Society of Japan 42, no. 4 (October 1990): 691–712. http://dx.doi.org/10.2969/jmsj/04240691.
Full text
28
Minin, Igor, and Oleg Minin. "Mesoscale Acoustical Cylindrical Superlens." MATEC Web of Conferences 155 (2018): 01029. http://dx.doi.org/10.1051/matecconf/201815501029.
Full textAbstract:
We demonstrate experimentally for the first time the acoustojet (acoustic jets) formed from acoustic plane wave scattering by a penetrable cylindrical particle with dimensions of several wavelengths. It acts as a superlens with subwavelength localization of acoustical wave. During the scattering by elastic solid particles, additional internal shear waves are excited due to modes conversion. This mechanism allows achieving sharp focusing in the near-field zone. Such mesoscale single particle cylindrical lens may be considered as acoustic metamaterials free superlenses with resolution beyond the diffraction limit.
29
Rajput, Sanjeev, and Michael Ring. "Examining the processing differences between P and P-S waves in a Rocky Mountain Foothills model." APPEA Journal 54, no. 2 (2014): 504. http://dx.doi.org/10.1071/aj13077.
Full textAbstract:
For the past two decades, most of the shear-wave (S-wave) or converted wave (P-S) acquisitions were performed with P-wave source by making the use of downgoing P-waves converting to upgoing S-waves at the mode conversion boundaries. The processing of converted waves requires studying asymmetric reflection at the conversion point, difference in geometries and conditions of source and receiver, and the partitioning of energy into orthogonally polarised components. Interpretation of P-S sections incorporates the identification of P-S waves, full waveform modeling, correlation with P-wave sections and depth migration. The main applications of P-S wave imaging are to obtain a measure of subsurface S-wave properties relating to rock type and fluid saturation (in addition to the P-wave values), imaging through gas clouds and shale diapers, and imaging interfaces with low P-wave contrast but significant S-wave changes. This study examines the major differences in processing of P and P-S wave surveys and the feasibility of identifying converted mode reflections by P-wave sources in anisotropic media. Two-dimensional synthetic seismograms for a realistic rocky mountain foothills model were studied. A Kirchhoff-based technique that includes anisotropic velocities is used for depth migration of converted waves. The results from depth imaging show that P-S section help in distinguishing amplitude associated with hydrocarbons from those caused by localised stratigraphic changes. In addition, the full waveform elastic modeling is useful in finding an appropriate balance between capturing high-quality P-wave data and P-S data challenges in a survey.
30
Rajput, Sanjeev, and Michael Ring. "Examining the processing differences between P and P-S waves in a Rocky Mountain Foothills model." APPEA Journal 54, no. 2 (2014): 536. http://dx.doi.org/10.1071/aj13109.
Full textAbstract:
For the past two decades, most of the shear-wave (S-wave) or converted wave (P-S) acquisitions were performed with P-wave source by making the use of downgoing P-waves converting to upgoing S-waves at the mode conversion boundaries. The processing of converted waves requires studying asymmetric reflection at the conversion point, difference in geometries and conditions of source and receiver, and the partitioning of energy into orthogonally polarised components. Interpretation of P-S sections incorporates the identification of P-S waves, full waveform modeling, correlation with P-wave sections and depth migration. The main applications of P-S wave imaging are to obtain a measure of subsurface S-wave properties relating to rock type and fluid saturation (in addition to the P-wave values), imaging through gas clouds and shale diapers, and imaging interfaces with low P-wave contrast but significant S-wave changes. This study examines the major differences in processing of P and P-S wave surveys and the feasibility of identifying converted mode reflections by P-wave sources in anisotropic media. Two-dimensional synthetic seismograms for a realistic rocky mountain foothills model were studied. A Kirchhoff-based technique that includes anisotropic velocities is used for depth migration of converted waves. The results from depth imaging show that P-S section help in distinguishing amplitude associated with hydrocarbons from those caused by localised stratigraphic changes. In addition, the full waveform elastic modeling is useful in finding an appropriate balance between capturing high-quality P-wave data and P-S data challenges in a survey.
31
Zhu, Wenhao. "An FEM Simulation for Guided Elastic Wave Generation and Reflection in Hollow Cylinders With Corrosion Defects." Journal of Pressure Vessel Technology 124, no. 1 (September 12, 2001): 108–17. http://dx.doi.org/10.1115/1.1428331.
Full textAbstract:
The generation and reflection of guided elastic waves in hollow cylinders with corrosion defects have been investigated numerically for the purpose of nondestructive evaluation (NDE) of tubular structures. A new guided wave transducer model, time-delay periodic ring arrays (TDPRAs), has been used to generate the axisymmetric guided wave modes in hollow cylinders, and this is simulated by a finite element calculation. Unidirectional guided wave emission can be achieved by arranging a TDPRA’s parameters according to the principle of constructive and destructive interference. The guided wave reflections by axisymetric and nonaxisymmetric corrosion defects are analyzed using a 2-D and a 3-D FE simulation, respectively. The reflection features as well as mode conversion under the L0,1 and L0,2 mode incidences are discussed in association with the corrosion depth, the axial and circumferential extents in hollow cylinders.
32
Li, Xiaopeng, Yangyang Chen, Xiaodong Zhang, and Guoliang Huang. "Shaping elastic wave mode conversion with a piezoelectric-based programmable meta-boundary." Extreme Mechanics Letters 39 (September 2020): 100837. http://dx.doi.org/10.1016/j.eml.2020.100837.
Full text
33
Wen, Li Ping, Guan Xiu Wu, and Lan Li Zuo. "Influence of Ancient River Covering Layer Shear-Wave Velocity Variation on Plane Primary Waves." Advanced Materials Research 838-841 (November 2013): 948–52. http://dx.doi.org/10.4028/www.scientific.net/amr.838-841.948.
Full textAbstract:
While using the big circle method, Fourier Bessel series expansion technique, and the coordinate conversion of Graf's addition formula, an analytical solution for the scattering of non concentric arc layered alluvial valleys subjected to plane primary waves was derived. Then the precision of the numerical result was checked up and analyzed. Finally, by using the analytic solution, the surface displacement was analyzed at different shear wave velocity of covering layer. The analysis results show that shear wave velocity change has little effect on the crest value of displacement at lower frequency incidence, however the influence becomes significant with the increase of incident frequency. In general, lower the shear wave velocity is, higher the crest value of displacement will be. Compared with the existing conclusions, the covering thickness variation has little effect on the influence of shear wave velocity change on the scattering of elastic waves.
34
Ogilvie, Jeff S., and Guy W. Purnell. "Effects of salt‐related mode conversions on subsalt prospecting." GEOPHYSICS 61, no. 2 (March 1996): 331–48. http://dx.doi.org/10.1190/1.1443962.
Full textAbstract:
Mode conversion of waves during seismic reflection surveys has generally been considered a small phenomenon that could be neglected in data processing and interpretation. However, in subsalt prospecting, the contrast in material properties at the salt/sediment interface is often great enough that significant P‐to‐S and/or S‐to‐P conversion occurs. The resulting converted waves can be both a help and a hinderance for subsalt prospecting. A case history from the Mississippi Canyon area of the Gulf of Mexico demonstrates strong converted‐wave reflections from the base‐of‐salt that complicate the evaluation of a subsalt prospect using 3-D seismic data. Before and after stack, the converted‐wave reflections are evident in 2-D and 3-D surveys across the prospect. Ray‐tracing synthetic common midpoint (CMP) gathers provides some useful insights about the occurrence of these waves, but elastic‐wave‐equation modeling is even more useful. While the latter is more time‐consuming, even in 2-D, it also provides a more realistic simulated seismic survey across the prospect, which helps to reveal how some converted waves survive the processes of CMP stack and migration, and thereby present possible pitfalls to an unwary interpreter. The insights gained from the synthetic‐data study suggest some simple techniques that can assist an interpreter in the 3-D interpretation of subsalt events.
35
Ziyi, Guo, Hu Yongquan, Zhang Yong, Xiong Tingsong, Mao Chun, Lin Hai, Wan Youyu, and Liu Shiduo. "Study on the Acoustic Characteristics of Rocks and Fracability in Wunan Oilfield." E3S Web of Conferences 53 (2018): 03068. http://dx.doi.org/10.1051/e3sconf/20185303068.
Full textAbstract:
The acoustic characteristics under P&S wave velocity of 56 samples from Low Youshashan Formation in Wunan Oilfield were tested by SCMS-E high temperature and high pressure core multi parameter test instrument, the measured velocity ratio of P wave and S wave is 1.32-1.67 and the conversion between the P and S wave velocity of rock sample was established. The corresponding dynamic elastic modulus and Poisson's ratio were obtained on the base of the elastic wave propagation theory formula. So, according to the transformation relationship between static and dynamic mechanical parameters, rock brittleness index is calculated and average value is only equal to 38. Therefore, it is difficult to form a fully developed network model during the hydraulic fracturing. These achievements provide a guiding significance for fracturing development at Low Youshashan Formation in Wunan Oilfield.
36
Ravasi, Matteo, and Andrew Curtis. "Nonlinear scattering based imaging in elastic media: Theory, theorems, and imaging conditions." GEOPHYSICS 78, no. 3 (May 1, 2013): S137—S155. http://dx.doi.org/10.1190/geo2012-0286.1.
Full textAbstract:
With the more widespread introduction of multicomponent recording devices in land and marine ocean-bottom seismic acquisition, elastic imaging may become mainstream in coming years. We have derived new, nonlinear, elastic imaging conditions. A correlation-type representation theorem for perturbed elastic media, commonly used in seismic interferometry to explain how a scattered wave response between two receivers/sources may be predicted given a boundary of sources/receivers, can be considered as a starting point for the derivation. Here, we use this theorem to derive and interpret imaging conditions for elastic migration by wavefield extrapolation (e.g., elastic reverse-time migration). Some approximations lead to a known, heuristically derived imaging condition that crosscorrelates P- and S-wave potentials that are separated in the subsurface after full-wavefield extrapolation. This formal connection reveals that the nonapproximated correlation-type representation theorem can be interpreted as a nonlinear imaging condition, that accounts also for multiply scattered and multiply converted waves, properly focusing such energy at each image point. We present a synthetic data example using either an ideal (acquisition on a full, closed boundary) or a real (partial boundary) seismic exploration survey, and we demonstrate the importance of nonlinearities in pure- and converted-mode imaging. In PP imaging, they result in better illumination and artifact reduction, whereas in PS imaging they show how zero time-lag and zero space-lag crosscorrelation imaging conditions are not ideal for imaging of converted-mode waves because no conversion arises from zero-offset experiments.
37
Zhao, Dan, Xinxin Shi, Shaogang Liu, and Feihao Wang. "Theoretical and experimental investigation on wave propagation in the periodic impedance layered structure modulated by magnetorheological fluid." Journal of Intelligent Material Systems and Structures 31, no. 6 (February 17, 2020): 882–96. http://dx.doi.org/10.1177/1045389x20905972.
Full textAbstract:
This work aims to investigate the elastic wave propagation in the periodic impedance layered structure filled with magnetorheological fluid. The periodic impedance layered structure with high and low impedance layers is constructed by using the magnetorheological fluid with the controllability of liquid–solid conversion. The principle of the periodic impedance layered structure is presented. The transfer model of elastic wave in the proposed structure is established, and the propagation velocity and attenuation coefficient of elastic wave curves of the periodic impedance layered structures with different distribution modes are obtained. The prototype of experimental setup is designed and fabricated, and the experimental testing of the vibration transmissibility is conducted. The theoretical model is validated by comparing the results with the experimental measurements. The results suggest that appropriate distribution modes and also applied magnetic field are validly showing greater attenuation for elastic wave propagation in the periodic layered structures. Theoretical and experimental studies are conducted to investigate on the vibration transmissibility of the proposed structure, the findings of which contribute to provide guidance for the future vibration isolation platforms of the power systems in aerospace and marine engineering practical applications.
38
Hagino, Naoto, Seiji Komiya, Jinichi Endou, and Masao Ishihama. "Ultrasonic Wave Propagation Analysis for In-Process Monitoring of Stamping." Key Engineering Materials 716 (October 2016): 528–35. http://dx.doi.org/10.4028/www.scientific.net/kem.716.528.
Full textAbstract:
The servo press has high potential for producing high precision mechanical parts. However, small gaps between dies and workpieces tend to exist even in servo press stamping, and the potential of the servo press has not yet been fully utilized. The reason for this is conventional presses do not have feedback control systems, and the lack of a suitable method of sensing contact information in real time causes deterioration in the accuracy of products. If slide motion could be controlled by contact information, the small gaps could be removed. To solve this problem, the authors have developed a method of monitoring the contact states between dies and workpieces during the stamping process. The method uses ultrasonic wave reflection and transmission at the contact surfaces and was proved to be able to monitor contact pressure by using a simple geometry experimental die apparatus. Finite-difference time-domain (FDTD) numerical simulation was conducted in this study to obtain better understanding of wave propagation through dies and workpieces. The results obtained from this FDTD simulation visualized wave propagation that could not be experimentally measured. Some of the major results obtained are as follows. 1) When a thin metal sheet is pressed between dies that have inclined stamping surfaces, ultrasonic elastic waves are reflected and transmitted multiple times. 2) Modal conversion occurs at the die-workpiece boundary in such a way that normal waves with an inclined incident angle are transformed into normal and shear waves. 3) Elastic waves sent out from an ultrasonic transducer are mixtures of normal waves with flat wave fronts along the propagation path axis, normal waves with circular or spherical wave fronts expanding from both sides of the transducer, and shear waves. These results brought about much useful information for setting ultrasonic transducers and analyzing collected signals.
39
Song, Yongjia, Hengshan Hu, and Bo Han. "Effective properties of a porous medium with aligned cracks containing compressible fluid." Geophysical Journal International 221, no. 1 (December 27, 2019): 60–76. http://dx.doi.org/10.1093/gji/ggz576.
Full textAbstract:
SUMMARY Understanding the wave propagation in fluid-saturated cracked rocks is important for detecting and characterizing cracked reservoirs and fault zones with applications in geomechanics, hydrogeology, exploration geophysics and reservoir engineering. In sedimentary rocks, microscopic-scale pores are usually filled with fluid. One logical means of modelling the essential features of such rocks is to use poroelasticity theory. But previous models of wave propagation in cracked porous medium are either restricted to low frequencies at which effects of the elastic scattering (scattering into fast-P and S waves via mode conversion at the crack faces) are negligible or to the case that the crack-filling fluid is assumed to be incompressible. To overcome these restrictions, we consider the effects of crack fluid compressibility by extending spring condition into poroelasticity and derive exact solutions of the scattering problem of an incident P wave by a circular crack containing compressible fluid in a porous medium. Based on the solutions, we develop two different effective medium models to estimate frequency-dependent effective velocity and attenuation in a fluid-saturated porous rock with a set of aligned cracks. The mixed-boundary value problem reveals that both the wave-induced fluid flow (WIFF) and elastic wave scattering can cause important velocity dispersion and attenuation. The diffusion-type WIFF dominates the velocity change and attenuation for the low frequency range, while the elastic scattering dominates them for the relatively higher frequency range. The dependences of the P-wave velocity on the crack fluid compressibility are different at different frequencies. For the WIFF-dominated frequency range and Rayleigh-scattering frequency range, the P-wave velocity decreases with the crack fluid compressibility. In contrast, for the Mie scattering frequency range, the opposite occurs (the P-wave velocity increases with the crack fluid compressibility).
40
Turner, Joseph A. "Scattering and diffusion of seismic waves." Bulletin of the Seismological Society of America 88, no. 1 (February 1, 1998): 276–83. http://dx.doi.org/10.1785/bssa0880010276.
Full textAbstract:
Abstract Elastic radiative transfer equations have recently been derived to describe the evolution of seismic energy in the crust of the earth (Ryzhik et al., 1996). These equations are derived from a rigorous statistical treatment of the elastic-wave equation and include both shear polarizations and mode conversion between the P and S modes. Calculations of attenuations ratios and diffusion constants based upon these theories are made and compared with values used in the literature. Equivalent elastic radiative transfer equations have also been previously derived for ultrasonic materials characterization purposes using a different method. Observations made from numerical solutions of these ultrasonic radiative transfer equations are discussed with application to seismology. Both the steady-state and time-dependent solutions have been examined including effects from boundaries, depolarization of S waves approach to isotropy of energy, and validity of the diffusion approximation. Similar results are expected for seismology.
41
Nobili, A., E. Radi, and C. Signorini. "A new Rayleigh-like wave in guided propagation of antiplane waves in couple stress materials." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 476, no. 2235 (March 2020): 20190822. http://dx.doi.org/10.1098/rspa.2019.0822.
Full textAbstract:
Motivated by the unexpected appearance of shear horizontal Rayleigh surface waves, we investigate the mechanics of antiplane wave reflection and propagation in couple stress (CS) elastic materials. Surface waves arise by mode conversion at a free surface, whereby bulk travelling waves trigger inhomogeneous modes. Indeed, Rayleigh waves are perturbations of the travelling mode and stem from its reflection at grazing incidence. As is well known, they correspond to the real zeros of the Rayleigh function. Interestingly, we show that the same generating mechanism sustains a new inhomogeneous wave, corresponding to a purely imaginary zero of the Rayleigh function. This wave emerges from ‘reflection’ of a bulk standing mode: This produces a new type of Rayleigh-like wave that travels away from , as opposed to along, the free surface, with a speed lower than that of bulk shear waves. Besides, a third complex zero of the Rayleigh function may exist, which represents waves attenuating/exploding both along and away from the surface. Since none of these zeros correspond to leaky waves, a new classification of the Rayleigh zeros is proposed. Furthermore, we extend to CS elasticity Mindlin’s boundary conditions, by which partial waves are identified, whose interference lends Rayleigh–Lamb guided waves. Finally, asymptotic analysis in the thin-plate limit provides equivalent one-dimensional models.
42
Morozov, Igor B. "Exact elastic P/SV impedance." GEOPHYSICS 75, no. 2 (March 2010): C7—C13. http://dx.doi.org/10.1190/1.3318268.
Full textAbstract:
Several extensions of the concept of acoustic impedance (AI) to oblique incidence exist and are known as elastic impedances (EI). These quantities are constructed by heuristic integrations of reflectivity series but still involve approximations and do not represent a unique medium property. Nevertheless, for unambiguous interpretation, it is desirable to have an EI that would (1) be a mechanical property of the medium and (2) yield exact reflection coefficients at all angles of incidence. Here, such a definition is given for P- and/or SV-wave propagation in an arbitrary isotropic medium. The exact elastic P/SV impedance is a matrix quantity and represents the differential operator relating the stress and strain boundary conditions. With the use of the matrix form of the reflectivity problem, no approximations are required for accurate modeling of reflection (P/P and SV/SV) and mode-conversion (P/SV and SV/P) coefficients at all angles and for any contrasts in elastic properties. The matrix EI can be computed from real well logs and inverted from ray-parameter-dependent seismic reflectivity. Known limiting cases of P- and S-wave acoustic impedances are accurately reproduced and the approach also allows the extension of the concept of impedance to an attenuative medium. The matrix impedance readily lends itself to inversion with uncertainties typical of the standard acoustic-impedance inversion problem.
43
Maurel, Agnès, Vincent Pagneux, Denis Boyer, and Fernando Lund. "Propagation of elastic waves through polycrystals: the effects of scattering from dislocation arrays." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 462, no. 2073 (March 30, 2006): 2607–23. http://dx.doi.org/10.1098/rspa.2006.1696.
Full textAbstract:
We address the problem of an elastic wave coherently propagating through a two-dimensional polycrystal. The main source of scattering is taken to be the interaction with grain boundaries that are in turn modelled as line distribution of dislocations—a good approximation for low angle grain boundaries. First, the scattering due to a single linear array is worked out in detail in a Born approximation, both for longitudinal and transverse polarization and allowing for mode conversion. Next, the polycrystal is modelled as a continuum medium filled with such lines that are in turn assumed to be randomly distributed. The properties of the coherent wave are worked out in a multiple scattering formalism, with the calculation of a mass operator, the main technical ingredient. Expansion of this operator to second-order in perturbation theory gives expressions for the index of refraction and attenuation length. This work is motivated by two sources of recent experiments: firstly, the experiments of Zhang et al . (Zhang, G., Simpson Jr, W. A., Vitek, J. M., Barnard, D. J., Tweed, L. J. & Foley J. 2004 J. Acoust. Soc. Am. 116 , 109–116.) suggesting that current understanding of wave propagation in polycrystalline material fails to interpret experimental results; secondly, the experiments of Zolotoyabko & Shilo who show that dislocations are potentially strong scatterers for elastic waves.
44
QI, XUELE, LI LIU, C. STEVE SUH, and RAVI CHONA. "ELASTO-VISCOPLASTIC WAVE THERMOMETRY FOR SINGLE CRYSTALLINE SILICON PROCESSING." International Journal of Applied Mechanics 02, no. 04 (December 2010): 827–49. http://dx.doi.org/10.1142/s1758825110000779.
Full textAbstract:
Laser-induced stress wave thermometry (LISWT) is a non-contact thermal diagnostic technique for the rapid thermal processing (RTP) of silicon wafers using laser-generated, ultrasonic, dispersive stress waves. The required knowledge base for establishing LISWT as a viable alternative to current pyrometric technology for temperature measurement up to 1000°C with ±1°C resolution is presented. A 3D elasto-viscoplastic wave model is developed for describing wave behaviors from being elastic to viscoplastic subject to the RTP annealing temperature ranging from room temperature to exceeding 1000°C. The model is a system of nine coupled first-order hyperbolic equations formulated based on the kinematics of elasto-plastic deformation, conversion of linear momentum and a temperature-dependent viscoplastic constitutive law for single crystalline silicon derived from the material models developed by Hassen–Sumino and Tsai. The group velocity of the wave propagating in silicon wafer is a nonlinear function of temperature. As nonlinearity becomes prominent at high temperature for high frequency components, low frequency components are preferably exploited to achieve the desired thermal resolution at high temperature.
45
Elbaz, Guy, Adi Pick, Nimrod Moiseyev, and Gal Shmuel. "Encircling exceptional points of Bloch waves: mode conversion and anomalous scattering." Journal of Physics D: Applied Physics 55, no. 23 (March 11, 2022): 235301. http://dx.doi.org/10.1088/1361-6463/ac5859.
Full textAbstract:
Abstract The normal modes of nonconservative systems coalesce at the so-called exceptional points (EPs) of their spectrum. These degeneracy points are the source of unusual phenomena, some of which are accessed by encircling the points in a suitable space. Here, we encircle the EPs of the transfer matrix of a periodic laminate, using a spatial perturbation in its stiffness. We investigate how, collectively, mode conversion in the laminate and the fields it scatters depend on the parameters of the loop. We find that the starting point of the loop has a significant effect on various counterintuitive phenomena: it determines if the laminate acts as a source or a sink of energy; how mode conversion takes place; if the reflectance is greater than one; and if there is spatial asymmetry in the energy flow with respect to the direction of the incident waves. Our findings are relevant for the development of devices for elastic wave manipulation.
46
Krishnasamy, G., L. W. Schmerr, T. J. Rudolphi, and F. J. Rizzo. "Hypersingular Boundary Integral Equations: Some Applications in Acoustic and Elastic Wave Scattering." Journal of Applied Mechanics 57, no. 2 (June 1, 1990): 404–14. http://dx.doi.org/10.1115/1.2892004.
Full textAbstract:
The properties of hypersingular integrals, which arise when the gradient of conventional boundary integrals is taken, are discussed. Interpretation in terms of Hadamard finite-part integrals, even for integrals in three dimensions, is given, and this concept is compared with the Cauchy Principal Value, which, by itself, is insufficient to render meaning to the hypersingular integrals. It is shown that the finite-part integrals may be avoided, if desired, by conversion to regular line and surface integrals through a novel use of Stokes’ theorem. Motivation for this work is given in the context of scattering of time-harmonic waves by cracks. Static crack analysis of linear elastic fracture mechanics is included as an important special case in the zero-frequency limit. A numerical example is given for the problem of acoustic scattering by a rigid screen in three spatial dimensions.
47
Sherman, Christopher S., James Rector, and Steven Glaser. "The effects of near-source heterogeneity on shear-wave evolution." GEOPHYSICS 79, no. 4 (July 1, 2014): T233—T241. http://dx.doi.org/10.1190/geo2013-0199.1.
Full textAbstract:
The Born and Rytov approximation, radiative transfer theory, and other related techniques are commonly used to model features of wave propagation through heterogeneous geologic media such as scattering, attenuation, and pulse-broadening. However, due to the underlying assumptions about the scattering direction and the reference Green’s function, these methods overlook important features of the wavefield such as mode conversion and near-field term coupling. These effects are particularly important within the predicted S-wave nodes of a seismic source, so we analyzed the problem of wave propagation beneath a vertical-point force on the surface of a heterogeneous, elastic half space. To do this, we generated a suite of 3D synthetic heterogeneous geologic models using fractal statistics and simulated the wave propagation using the finite-difference method. We derived an estimate for the effective source radiation patterns, and we used these to compare the results of the models. Our numerical results showed that, due to a combination of mode conversion and near-source coupling effects, S-wave energy on the order of 10% of the P-wave energy is generated within the shear-radiation node. In some cases, this S-wave energy may occur as a coherent pulse and may be used to enhance seismic imaging.
48
Shoro, Takuya, Hiroki Kishikawa, and Nobuo Goto. "Analysis of optical OAM mode conversion using elastic vortex wave in graded-index optical fiber." Japanese Journal of Applied Physics 58, SG (June 10, 2019): SGGA04. http://dx.doi.org/10.7567/1347-4065/ab0ba0.
Full text
49
Lee, Tae-Gon, Soo-Ho Jo, Hong Min Seung, Sun-Woo Kim, Eun-Ji Kim, Byeng D. Youn, Sahn Nahm, and Miso Kim. "Enhanced energy transfer and conversion for high performance phononic crystal-assisted elastic wave energy harvesting." Nano Energy 78 (December 2020): 105226. http://dx.doi.org/10.1016/j.nanoen.2020.105226.
Full text
50
Tang, Chen, and George A. McMechan. "Multidirectional-vector-based elastic reverse time migration and angle-domain common-image gathers with approximate wavefield decomposition of P- and S-waves." GEOPHYSICS 83, no. 1 (January 1, 2018): S57—S79. http://dx.doi.org/10.1190/geo2017-0119.1.
Full textAbstract:
Elastic reverse time migration (E-RTM) has limitations when the migration velocities contain strong contrasts. First, the traditional scheme of P/S-wave mode separation is based on Helmholtz’s equations, which ignore the conversion between P- and S-waves at the current separation time. Thus, it contains an implicit assumption of the constant shear modulus and requires smoothing the heterogeneous model to approximately satisfy a locally constant condition. Second, the vector-based imaging condition needs to use the reflection-image normal, and it also cannot give the correct polarity of the PP image in all possible conditions. Third, the angle-domain common-image gathers (ADCIGs) calculated using the Poynting vectors (PVs) do not consider the wave interferences that happen at each reflector. Therefore, smooth models are often used for E-RTM. We relax this condition by proposing an improved data flow that involves three new contributions. The first contribution is an improved system of P/S-wave mode separation that considers the converted wave generated at the current time, and thus it does not require the constant-shear-modulus assumption. The second contribution is the new elastic imaging conditions based on multidirectional vectors; they can give the correct image polarity in all possible conditions without knowledge of the reflection-image normal. The third contribution is two methods to calculate multidirectional propagation vectors (PRVs) for RTM images and ADCIGs: One is the elastic multidirectional PV, and the other uses the sign of wavenumber-over-frequency ([Formula: see text]) ratio obtained from an amplitude-preserved approximate-propagation-angle-based wavefield decomposition to convert the particle velocities into multidirectional PRVs. The robustness of the improved data flow is determined by several 2D numerical examples. Extension of the schemes into 3D and amplitude-preserved imaging conditions is also possible.