151 results found
Yu Y, Cilliers J, Hadler K, et al., 2024, Dry particle size separation using electrostatic traveling wave methods, Separation and Purification Technology, Vol: 336, ISSN: 0950-4214
Electrostatic traveling wave (ETW) methods have grown in popularity as a method to manipulate and separate fine particles. This is of interest to mineral processing and In-situ Space Resource Utilization. Here, we demonstrate that ETW can be used to separate particles by size. First, our numerical calculation and simulation results show the competing effect of DEP and Coulomb force on particle motion direction, which depends on the frequency, particle size and charge. Then we define the “crossover frequency” allowing prediction of operating parameters to separate particles. At the “crossover frequency” – a particle is equally likely to move forward or backward. The crossover frequency decreases as particle size increases, and the proportion of particles moving backward increases as frequency increases. Four size groups of ballotini particles (glass) were transported and collected at different wave field frequencies. Finally, we have demonstrated experimentally the separation of particles between 30–50 µm and 75–110 µm. Simulation and experiment results revealed the effects of frequency, particle size and charge on particle motions. And the model can be used to guide the design of separation systems.
Zhang H, An S, Brito-Parada PR, et al., 2024, Investigation into three-dimensional dry foam modelling using the boundary integral method, Journal of Computational Physics, Vol: 499, ISSN: 0021-9991
Understanding foam rheology relies on predictions of the foam structure and physical quantities associated with foam dynamics. In this work, we explore the modelling of dry foam dynamics using the boundary integral method, which can be used to predict the behaviour of dry foam in bulk or in confined geometries. The resultant equation for dry foam shows that the movement of foam films or lamellae is governed by the film curvature and the normal stress that the wall imposes on the fluid phase in bubbles and is characterized by three distinct motion modes: the background flow, the imposed flow due to the deformation of wall and the relaxation process of films. The singular integrals involved in the model are handled using a combined method of singularity subtraction and nonsingular contour integral. To demonstrate the validity of the method in potential applications, we consider two scenarios, for foam in bulk and in confined geometries, respectively. Dynamic foam motion is tracked using the model. The results show that the dry foam model has potentials applied in a variety of applications, such as foam flow in microfluidic devices and porous media.
Xu Q, Wang Y, 2024, Seismic reverse time migration based on biaxial wavefield decomposition, GEOPHYSICS, Vol: 89, Pages: S61-S70, ISSN: 0016-8033
<jats:p> Seismic images generated by reverse time migration (RTM) are often contaminated by low-wavenumber artifacts. Decomposition of up- and downgoing waves during propagation can effectively reduce these artifacts. However, decomposition along the vertical axis is not sufficient to eliminate the migration artifacts. We introduce biaxial wavefield decomposition to decompose seismic wavefields in the lateral and vertical directions. After decomposition, there are 16 crosscorrelation terms between different components, and there are only four crosscorrelation terms that can be used separately to image flat layers and tilted interfaces. Within these four terms, the remaining artifacts can be easily identified and reduced by other methods, and the resolution can be further improved by adjusting the weights of the four terms. The decomposition method based on the analytic wavefield via the Hilbert transform has been shown to agree with the viscoacoustic wave equation with fractional spatial derivatives. Therefore, this biaxial wavefield decomposition method is suitable for decomposing the wavefields for the attenuation-compensated RTM. The decomposed and recombined migration results can better image a complex subsurface structure with high resolution. </jats:p>
Zhang B, Wang Y, 2024, Seismic attribute-assisted seismic fault interpretation, GEOPHYSICS, Vol: 89, Pages: N1-N13, ISSN: 0016-8033
<jats:p> Fault mapping is one of the main tasks of 3D seismic interpretation, and seismic discontinuity attributes are often used to support fault mapping in vertical sections and time slices. The most commonly used fault mapping procedure involves three passes/generations. First, the approximate positions of faults (generation I) on some vertical sections are interpreted manually. Second, the generation I faults are projected on some time slices, and the individual fault traces (generation II) are picked on time slices. Finally, the generation II faults are projected onto the vertical sections and the fault sticks (generation III) are picked in the vertical sections. To speed up the fault mapping process, we use the seismic discontinuity attribute as input to automatically extract the generation III faults in the vertical sections under the generation I and II fault mapping conditions. A quality control (QC) step is essential to improve the accuracy of the automatically generated fault sticks. To reduce the time required for QC, we propose to output the fault sticks on the seismic vertical sections defined by the interpreters. The workflow is applied to a real seismic survey to demonstrate its effectiveness. </jats:p>
Zhang H, Torres-Ulloa C, An S, et al., 2024, A comparative study of a viscous froth lens in two and three dimensions, Physics of Fluids, Vol: 36, ISSN: 1070-6631
The two-dimensional (2D) viscous froth model was initially designed to capture the dynamic behavior of dry foams within a Hele–Shaw cell, characterized by two parallel covering plates separated by a small gap. However, due to its inherent 2D nature, this model does not explicitly account for the dimension across the gap. To address this limitation, we have opted for a three-dimensional (3D) version of the viscous froth model. In this 3D model, the dynamic effect is introduced through the motion of the surface Plateau borders, while the configurations of films in bulk are determined via surface energy minimization subject to specified bubble volumes and surface Plateau border locations. We use this 3D model to simulate the motion of a viscous froth lens within a straight channel. The steady states of the viscous froth lens in 3D are primarily influenced by the driving velocity-to-gap size ratio, particularly at relatively small values of this ratio. By contrast, as the ratio becomes relatively large, the gap size begins to play a significant role in influencing the behavior of the viscous froth lens in 3D. Differences are observed in the steady-state configurations of the viscous froth lens in 3D when compared to those in 2D. However, the behavior of the viscous froth lens in 2D can be better aligned with the results in 3D by treating the drag coefficient required in the 2D viscous froth model as a fitting parameter. A further quantitative analysis indicates that the drag coefficient needed in the 2D viscous froth model may not serve as a uniform parameter for the entire foam structure. Instead, it may depend on the specific location along the evolving foam films over time.
Zhao Z, Rao Y, Wang Y, 2024, The Fractional-Order W-Transform, IEEE Geoscience and Remote Sensing Letters, Vol: 21, Pages: 1-5, ISSN: 1545-598X
Song C, Wang Y, 2023, Simulating seismic multifrequency wavefields with the Fourier feature physics-informed neural network, GEOPHYSICAL JOURNAL INTERNATIONAL, Vol: 232, Pages: 1503-1514, ISSN: 0956-540X
Wang G, Chen S, Wang Y, 2023, Direct inversion for the equivalent pore aspect ratio based on the theory of ellipsoid modelling, Geophysical Prospecting, Vol: 71, Pages: 1821-1834, ISSN: 0016-8025
Pore aspect ratio, together with porosity, is a structural parameter that represents the geometric property of rock reservoirs. We have adopted the theory of ellipsoid modelling in material mechanics to derive the dry rock modulus. Based on this derivation, the Gassmann equation, which is a constitutional equation for a fully saturated rock model, can be linearized in terms of the pore structure parameters and the elastic parameters. We have established a relationship between the seismic reflection coefficient and the pore structure parameters, where the equivalent pore aspect ratio and porosity are two key parameters. Based on this relationship, the equivalent pore aspect ratio can be inverted directly from seismic reflection data instead of being converted from the intermediate parameters of conventional seismic inversion. Therefore, seismic inversion is a simultaneous inversion in which seven parameters are inverted: the elastic moduli (matrix bulk modulus and shear modulus, fluid bulk modulus), the densities (matrix and fluid densities) and the pore structure parameters (the equivalent pore aspect ratio and porosity). We applied this direct inversion scheme to a carbonate reservoir to predict the fracture development zone with low porosity and low aspect ratio.
Hao Y, Bell R, Rao Y, et al., 2023, Prediction of Permian karst reservoirs in the Yuanba gas field, northern Sichuan Basin, China, MARINE AND PETROLEUM GEOLOGY, Vol: 154, ISSN: 0264-8172
Yu Y, Cilliers J, Hadler K, et al., 2023, The motion of small particles in electrostatic travelling waves for transport and separation, POWDER TECHNOLOGY, Vol: 425, ISSN: 0032-5910
Gao F, Wang Y, 2023, Seismic Waveform Tomography for 3D Impedance Model with Salt Structure, Pure and Applied Geophysics, Vol: 180, Pages: 2577-2587, ISSN: 0033-4553
<jats:title>Abstract</jats:title><jats:p>Conventional impedance inversion from post-stack zero-offset seismic data is usually based on the convolution model, and wave-equation based inversion is rarely used, although it is capable to precisely describe seismic wave propagation and invert impedance model with higher resolution. That is because there are more than one physical parameters involved in the conventional wave equation, making impedance inversion complicated. In this study, a one-dimensional (1D) wave equation, containing only the impedance parameter, is adopted and applied for the inversion of 1D impedance model by seismic waveform tomography. However, for a three-dimensional (3D) model, direct application of the 1D waveform tomography may lead to lateral discontinuities. Therefore, we propose to utilize a truncated Fourier series to parameterize the 3D impedance model, and then invert for the Fourier coefficients. With this parameterization scheme, the large- and small-scale components of the impedance model can be reconstructed stepwise by gradually increasing the number of Fourier coefficients. To efficiently and effectively invert the coefficients for the 3D model with salt structure, we propose a joint strategy, in which the low-frequency seismic data is used to invert for the Fourier coefficients representing the large-scale components of the model, while the high-frequency seismic data is applied to invert for the Fourier coefficients representing the small-scale components of the model. Tests on a 3D impedance model with salt structure result in models with high resolution and good spatial continuity, proving the feasibility and stability of the impedance inversion procedure.</jats:p>
Yu Y, Luo Y, Cilliers J, et al., 2023, Numerical solution of the electric field and dielectrophoresis force of electrostatic traveling wave system, Micromachines, Vol: 14, Pages: 1347-1347, ISSN: 2072-666X
Electrostatic traveling wave (ETW) methods have shown promising performance in dust mitigation of solar panels, particle transport and separation in in situ space resource utilization, cell manipulation, and separation in biology. The ETW field distribution is required to analyze the forces applied to particles and to evaluate ETW design parameters. This study presents the numerical results of the ETW field distribution generated by a parallel electrode array using both the charge simulation method (CSM) and the boundary element method (BEM). A low accumulated error of the CSM is achieved by properly arranging the positions and numbers of contour points and fictitious charges. The BEM can avoid the inconvenience of the charge position required in the CSM. The numerical results show extremely close agreement between the CSM and BEM. For simplification, the method of images is introduced in the implementation of the CSM and BEM. Moreover, analytical formulas are obtained for the integral of Green’s function along boundary elements. For further validation, the results are cross-checked using the finite element method (FEM). It is found that discrepancies occur at the ends of the electrode array. Finally, analyses are provided of the electric field and dielectrophoretic (DEP) components. Emphasis is given to the regions close to the electrode surfaces. These results provide guidance for the fabrication of ETW systems for various applications.
O'Malley CPB, Roberts GG, Mannion PD, et al., 2023, Coherence of terrestrial vertebrate species richness with external drivers across scales and taxonomic groups, Global Ecology and Biogeography, Vol: 32, Pages: 1285-1301, ISSN: 1466-822X
Aim: 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 under-standing of how species richness and environment covary across scales. Here, we identify scales and locations at which biodiversity is generated and correlates with environment.Location: Full latitudinal range per continent.Time Period: Present day.Major Taxa Studied: Terrestrial vertebrates: all mammals, carnivorans, bats, song-birds, hummingbirds, amphibians.Methods: 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 (E), mean annual precipitation (Pn), temperature (Tm) and annual temperature range (ΔT).Results: >97% of species richness of taxa studied is generated at large scales, that is, wavelengths ≳103 km, with 30%–69% generated at scales ≳104 km. At these scales, richness tends to be highly coherent and anti-correlated with E and ΔT, and positively correlated with Pn and Tm. Coherence between carnivoran richness and ΔT is low across scales, implying insensitivity to seasonal temperature variations. Conversely, amphibian richness is strongly anti-correlated with ΔT at large scales. At scales ≲103 km, examined taxa, except carnivorans, show highest richness within the trop-ics. Terrestrial plateaux exhibit high coherence between carnivorans and E at scales ∼103 km, consistent with contribution of large-scale tectonic processes to biodiver-sity. Results are similar across different continents and for global latitudinal averages. Spectral admittance permits derivation of rules-of- thumb relating long-wavelength environmental and species richness trends.Main Conclusions: Sensitivities of ma
Cai S, Fang F, Wang Y, 2023, Nonstationary seismic-well tying with time-varying wavelets, GEOPHYSICS, Vol: 88, Pages: M145-M155, ISSN: 0016-8033
Zhao Z, Rao Y, Wang Y, 2023, The W transform with a chirp-modulated window, GEOPHYSICS, Vol: 88, Pages: V93-V100, ISSN: 0016-8033
Zhao Z, Rao Y, Wang Y, 2023, Structure-adapted Multichannel Matching Pursuit for Seismic Trace Decomposition, PURE AND APPLIED GEOPHYSICS, Vol: 180, Pages: 851-861, ISSN: 0033-4553
Yao J, Warner M, Wang Y, 2023, Regularization of anisotropic full-waveform inversion with multiple parameters by adversarial neural networks, GEOPHYSICS, Vol: 88, Pages: R95-R103, ISSN: 0016-8033
Xu Q, Wang Y, 2023, Determination of the viscoelastic parameters for the generalized viscoelastic wave equation, GEOPHYSICAL JOURNAL INTERNATIONAL, Vol: 233, Pages: 875-884, ISSN: 0956-540X
Gao F, Rao Y, Zhu T, et al., 2023, 3-D Seismic Inversion by Model Parameterization With Fourier Coefficients, IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, Vol: 61, ISSN: 0196-2892
Song C, Wang Y, Richardson A, et al., 2023, Weighted Envelope Correlation-Based Waveform Inversion Using Automatic Differentiation, IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, Vol: 61, ISSN: 0196-2892
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
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
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.
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
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
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
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
Jamali J, Javaherian A, Wang Y, et al., 2022, The behavior of elastic moduli with fluid content in the VTI media, JOURNAL OF PETROLEUM SCIENCE AND ENGINEERING, Vol: 208, ISSN: 0920-4105
Yao J, Wang Y, 2021, 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
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