134 results found
Song C, Wang Y, 2023, Simulating seismic multi-frequency wavefields with the Fourier feature physics-informed neural network, Geophysical Journal International, Vol: 232, Pages: 1503-1514, ISSN: 0956-540X
To simulate seismic wavefields with a frequency-domain wave equation, conventional numerical methods must solve the equation sequentially to obtain the wavefields for different frequencies. The monofrequency equation has the form of a Helmholtz equation. When solving the Helmholtz equation for seismic wavefields with multiple frequencies, a physics-informed neural network (PINN) can be used. However, the PINN suffers from the problem of spectral bias when approximating high-frequency components. We propose to simulate seismic multi-frequency wavefields using a PINN with an embedded Fourier feature. The input to the Fourier feature PINN for simulating multi-frequency wavefields is four-dimensional, namely the horizontal and vertical spatial coordinates of the model, the horizontal position of the source, and the frequency, and the output is multi-frequency wavefields at arbitrary source positions. While an effective Fourier feature initialization strategy can lead to optimal convergence in training this network, the Fourier feature PINN simulates multi-frequency wavefields with reasonable efficiency and accuracy.
Zhang H, Brito-Parada PR, Neethling SJ, et al., 2022, Yield stress of foam flow in porous media: The effect of bubble trapping, COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS, Vol: 655, ISSN: 0927-7757
Yao J, Warner M, Wang Y, 2022, Regularization of anisotropic full waveform inversion with multiple parameters by adversarial neural networks, Geophysics, Pages: 1-38, ISSN: 0016-8033
The anisotropic full waveform inversion (FWI) is a seismic inverse problem for multiple parameters, that aims to simultaneously reconstruct the vertical velocity and the anisotropic parameters of the Earth's subsurface. This multiparameter inverse problem suffers from two issues. First, the objective function of the data fitting is less sensitive to the anisotropic parameters. Second, the crosstalk effect between the different parameters worsens the model update in the iterative inversion. We proposed to statistically regularize the anisotropic FWI using Wasserstein adversarial networks, which penalize the Wasserstein distance between the distribution of the current model parameters and that of the parameters at the borehole locations. The proposed regularizer can mitigate the problems of anisotropic FWI with multiple parameters. Therefore, the method can also be applied to other inverse problems with multiple parameters.
Wang Y, 2022, Time–frequency Analysis of Seismic Signals, Publisher: Wiley, ISBN: 9781119892342
Time–frequency analysis of seismic signals aims to reveal the local properties of nonstationary signals. The local properties such as time-period, frequency, and spectral content are varying with time, and the time of a seismic signal is a proxy of geologic depth. Therefore, the time–frequency spectrum is composed of the frequency spectra that are generated by using the classic Fourier transform at different time positions. Different time–frequency analysis methods are distinguished in the construction of the local kernel prior to using the Fourier transform. Based on the difference in constructing the Fourier transform kernel, this book divides time–frequency analysis methods into two groups, the Gabor transform-type methods and the energy density distribution methods. This book provides a practical guide to geophysicists who attempt to generate geophysically meaningful time–frequency spectra, who attempt to process seismic data with time-dependent operations for the fidelity of nonstationary ...
Wang Y, 2022, Time–frequency domain local spectral analysis of seismic signals with multiple windows, Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol: 478, ISSN: 1364-5021
<jats:p>For a non-stationary seismic signal, time–frequency analysis methods often include a time window function that serves as a weighting function and by which the signal is multiplied to form a segment. The time window function often has the highest weighting coefficient for the central sample of the signal segment. For the rest of the segment, there is no adequate representation in the frequency spectrum. Here, I propose to use multiple orthogonal window functions to properly represent the local spectral property in the time–frequency plane and recover the information lost due to time windowing before applying the Fourier transform. First, I propose to construct multiple window functions directly using a stack of Gaussian functions. The weighted average spectrum of the multiple window functions has a flat passband, which is better than the conventional multiple windows. Taking advantage of the linearity of the Fourier transform, we can apply each window to the analytic signal to generate the instantaneous autocorrelation accordingly and form an averaged instantaneous autocorrelation by a weighted sum before performing the Fourier transform to generate the Wigner–Ville distribution (WVD). This multi-window WVD method successfully represents the local spectrum of the non-stationary seismic signal in the time–frequency plane.</jats:p>
Yu Y, Cilliers J, Hadler K, et al., 2022, A review of particle transport and separation by electrostatic traveling wave methods, Journal of Electrostatics, Vol: 119, Pages: 1-16, ISSN: 0304-3886
The controlled movement of dry particles using non-mechanical means is desirable in a number of different applications, including solar panel dust mitigation, toner particle motion and in the handling and beneficiation of regolith for In-Situ Resource Utilization (ISRU). The electric curtain, the electrostatic traveling wave (ETW) and the electro-dynamic screen (EDS) are examples of techniques that can transport and separate particles with no moving parts nor fluid medium. This review paper brings together the research carried out on these techniques.We provide a comprehensive review on the particle movement mechanisms and the development and application of ETW methods, featuring a diverse range of hardware and circuitry, particulate material and process objectives. We focus on the evaluation of experimental development in the area of dust mitigation, particle transport and ISRU processes. We also detail the current knowledge about theory and modelling methods. Moreover, we provide a guide for possible improvement of the effectiveness of ETW devices, by outlining the limitations in application, theoretical understanding and potential research aspects.
Guo X, Shi Y, Wang W, et al., 2022, Suppressing migration noise in reverse time migration of vertical seismic profiles by multiple stacking estimation, GEOPHYSICS, Vol: 87, Pages: S223-S235, ISSN: 0016-8033
XU QIANG, WANG YANGHUA, 2022, Spatial Filter for the Pseudo-spectral Implementation of Fractional Derivative Wave Equation, PURE AND APPLIED GEOPHYSICS, Vol: 179, Pages: 2831-2840, ISSN: 0033-4553
Yao J, Warner M, Wang Y, 2022, Generating surface-offset common-image gathers with backward wavefield synthesis, GEOPHYSICS, Vol: 87, Pages: S129-S135, ISSN: 0016-8033
Song C, Wang Y, 2022, High-frequency wavefield extrapolation using the Fourier neural operator, JOURNAL OF GEOPHYSICS AND ENGINEERING, Vol: 19, Pages: 269-282, ISSN: 1742-2132
Yao J, Wang Y, 2022, Building a full-waveform inversion starting model from wells with dynamic time warping and convolutional neural networks, GEOPHYSICS, Vol: 87, Pages: R223-R230, ISSN: 0016-8033
Ni J, Gu H, Wang Y, 2022, Seismic wave equation formulated by generalized viscoelasticity in fluid-saturated porous media, GEOPHYSICS, Vol: 87, Pages: T111-T121, ISSN: 0016-8033
<jats:p> Biot’s theory of poroelasticity describes seismic waves propagating through fluid-saturated porous media, so-called two-phase media. The classic Biot’s theory of poroelasticity considers the wave dissipation mechanism as being the friction of relative motion between the fluid in the pores and the solid rock skeleton. However, within the seismic frequency band, the friction has a major influence only on the slow P-wave and an insignificant influence on the fast P-wave. To represent the intrinsic viscoelasticity of the solid skeleton, we incorporate a generalized viscoelastic wave equation into Biot’s theory for the fluid-saturated porous media. The generalized equation that unifies the pure elastic and viscoelastic cases is constituted by a single viscoelastic parameter, presented as the fractional order of the wavefield derivative in the compact form of the wave equation. The generalized equation that includes the viscoelasticity appropriately describes the dissipation characteristics of the fast P-wave. Plane-wave analysis and numerical solutions of our wave equation reveal that (1) the viscoelasticity in the solid skeleton causes the energy attenuation on the fast P-wave and the slow P-wave at the same order of magnitude and (2) the generalized viscoelastic wave equation effectively describes the dissipation effect of the waves propagating through the fluid-saturated porous media. </jats:p>
OMalley CPB, Roberts GG, Mannion PD, et al., 2022, Coherence of Terrestrial Vertebrate Species Richness with External Drivers Across Scales and Taxonomic Groups, Publisher: Cold Spring Harbor Laboratory
<jats:title>Abstract</jats:title><jats:sec><jats:title>Aim</jats:title><jats:p>Understanding connections between environment and biodiversity is crucial for conservation, identifying causes of ecosystem stress, and predicting population responses to changing environments. Explaining biodiversity requires an understanding of how species richness and environment co-vary across scales. Here, we identify scales and locations at which biodiversity is generated and correlates with environment.</jats:p></jats:sec><jats:sec><jats:title>Location</jats:title><jats:p>Full latitudinal range per continent.</jats:p></jats:sec><jats:sec><jats:title>Time period</jats:title><jats:p>Present-day.</jats:p></jats:sec><jats:sec><jats:title>Major taxa studied</jats:title><jats:p>Terrestrial vertebrates: all mammals, carnivorans, bats, songbirds, humming-birds, amphibians.</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>We describe the use of wavelet power spectra, cross-power and coherence for identifying scale-dependent trends across Earth’s surface. Spectra reveal scale- and location-dependent coherence between species richness and topography (<jats:italic>E</jats:italic>), mean annual precipitation (<jats:italic>Pn</jats:italic>), temperature (<jats:italic>Tm</jats:italic>) and annual temperature range (Δ<jats:italic>T</jats:italic>).</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>> 97% of species richness of taxa studied is generated at large scales, i.e. wavelengths ≳ 10<jats:sup>3</jats:sup> km, with 30–69% generated at scales ≳ 10<jats:sup>4</jats:sup> km. At these scales, richness tends to be highly coherent and anti-correlated wit
Alsalmi H, Wang Y, 2021, Mask filtering to the Wigner-Ville distribution, GEOPHYSICS, Vol: 86, Pages: V489-V496, ISSN: 0016-8033
Jamali J, Javaherian A, Wang Y, et al., 2021, The behavior of elastic moduli with fluid content in the VTI media, JOURNAL OF PETROLEUM SCIENCE AND ENGINEERING, Vol: 208, ISSN: 0920-4105
Wu D, Wang Y, Cao J, et al., 2021, Least-squares reverse-time migration with sparsity constraints, JOURNAL OF GEOPHYSICS AND ENGINEERING, Vol: 18, Pages: 304-316, ISSN: 1742-2132
Izadian S, Aghazade K, Amini N, et al., 2021, Semi-exact local absorbing boundary condition for seismic wave simulation, JOURNAL OF GEOPHYSICS AND ENGINEERING, Vol: 18, Pages: 62-73, ISSN: 1742-2132
Wang Y, 2021, The W transform, GEOPHYSICS, Vol: 86, Pages: V31-V39, ISSN: 0016-8033
Rosa DR, Santos JMC, Souza RM, et al., 2020, Comparing different approaches of time-lapse seismic inversion, JOURNAL OF GEOPHYSICS AND ENGINEERING, Vol: 17, Pages: 929-939, ISSN: 1742-2132
Duarte EF, da Costa CAN, de Araujo JM, et al., 2020, Seismic shot-encoding schemes for waveform inversion, JOURNAL OF GEOPHYSICS AND ENGINEERING, Vol: 17, Pages: 906-913, ISSN: 1742-2132
Wang Y, Liu X, Gao F, et al., 2020, Robust vector median filtering with a structure-adaptive implementation, GEOPHYSICS, Vol: 85, Pages: V407-V414, ISSN: 0016-8033
Li H, Gao R, Wang Y, 2020, Predicting the thickness of sand strata in a sand-shale interbed reservoir based on seismic facies analysis, JOURNAL OF GEOPHYSICS AND ENGINEERING, Vol: 17, Pages: 592-601, ISSN: 1742-2132
Wang R, Wang Y, Rao Y, 2020, Seismic reflectivity inversion using an L1-norm basis-pursuit method and GPU parallelisation, JOURNAL OF GEOPHYSICS AND ENGINEERING, Vol: 17, Pages: 776-782, ISSN: 1742-2132
Wang Y, Rao Y, 2020, Seismic, Waveform Modeling and Tomography, Encyclopedia of Solid Earth Geophysics, 2nd edition, Editors: Gupta, Publisher: Springer, Cham, ISBN: 978-3-030-10475-7
Tomography. A seismic inversion method to produce slicing image of the internal structures of an object, by recording seismic wavefield propagating through and scattered-refracted-reflected back from the object and observing the difference in the effects on the wave energy impinging on those structures.
He F, Rao Y, Wang W, et al., 2020, Prediction of hydrocarbon reservoirs within coal-bearing formations, JOURNAL OF GEOPHYSICS AND ENGINEERING, Vol: 17, Pages: 484-492, ISSN: 1742-2132
Gao F, Wang Y, 2020, Radiation pattern analyses for seismic multi-parameter inversion of HTI anisotropic media, JOURNAL OF GEOPHYSICS AND ENGINEERING, Vol: 17, Pages: 65-75, ISSN: 1742-2132
Wang Y, Rao Y, Xu D, 2020, Multichannel maximum-entropy method for the Wigner-Ville distribution, GEOPHYSICS, Vol: 85, Pages: V25-V31, ISSN: 0016-8033
Liu J, Wang Y, 2020, Seismic simultaneous inversion using a multidamped subspace method, GEOPHYSICS, Vol: 85, Pages: R1-R10, ISSN: 0016-8033
Rao Y, Wang Y, 2020, Pore-pressure diffusion during water injection in fractured media, GEOPHYSICS, Vol: 85, Pages: MR51-MR56, ISSN: 0016-8033
Wang Y, 2019, A constant-Q model for general viscoelastic media, GEOPHYSICAL JOURNAL INTERNATIONAL, Vol: 219, Pages: 1562-1567, ISSN: 0956-540X
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