Waveform inversion of crosshole data based on acoustic wave equation is investigated in this paper. The inversion is set as an optimization problem with the Lagrange multiplier function. The Tikhonov regularization is...
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Waveform inversion of crosshole data based on acoustic wave equation is investigated in this paper. The inversion is set as an optimization problem with the Lagrange multiplier function. The Tikhonov regularization is adopted in objective function. The gradient of the objective function is generated by solving the adjoint equation of the forward problem with the finite difference method. In order to prevent the quasi-Newton method to trap in local optimal value, a suitable initial model is required. For comparison, the traveltime inversion or tomography is implemented which provide smooth features of the velocity model. Numerical computations are given which show the good ability of the new velocity inversion method.
The simulation of wave propagation has important applications in many problems such as in computational seismology. Here, we focus on boundary absorbing computations in wave simulation with the finite element method o...
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The simulation of wave propagation has important applications in many problems such as in computational seismology. Here, we focus on boundary absorbing computations in wave simulation with the finite element method on triangular mesh. The first-order and second-order absorbing boundary conditions based on wave decomposition are presented. Moreover, the absorbing conditions for corners are proposed. The weak formulations combined with absorbing conditions are derived. Numerical computations for a complex model show that boundary reflections are eliminated and the computational efficiency is high by using the mass-lumping technique.
The understanding of biological processes, e.g. related to cardio-vascular disease and treatment, can significantly be improved by numerical simulation. In this paper, we present an approach for a multiscale simulatio...
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作者：
L. YuanL. ZhangaLSEC
Institute of Computational Mathematics and Scientific/Engineering Computing Academy of Mathematics and Systems Science Chinese Academy of Sciences Beijing 100190 China bSchool of Science
China University of Mining and Technology (Beijing) Beijing 100083 China
We apply a Runge‐Kutta discontinuous Galerkin (RKDG) method to numerical solution of the reactive Euler equations. In order to keep conservation naturally, Taylor basis functions are utilized. We construct a new Tayl...
We apply a Runge‐Kutta discontinuous Galerkin (RKDG) method to numerical solution of the reactive Euler equations. In order to keep conservation naturally, Taylor basis functions are utilized. We construct a new Taylor basis function which has smaller numerical error than previous Taylor basis function when the TVD limiter is used. The program is written with MPI for parallel computation. Numerical results of two‐dimensional unstable detonation waves demonstrate that the resulting RKDG method performs well in resolving detonation wave structures. Load imbalance due to different stiffness in different subzones is discussed.
Recent increases in computational efficiency have enabled large-scale ab initio molecular dynamics simulations to be performed on molten eutectic Al1−xSix alloys (x = 0.12). Atomic forces were calculated using real-sp...
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Recent increases in computational efficiency have enabled large-scale ab initio molecular dynamics simulations to be performed on molten eutectic Al1−xSix alloys (x = 0.12). Atomic forces were calculated using real-space pseudopotential density-functional theory, and the pair correlation, structure factor, coordination number, velocity autocorrelation, and mean-square displacement were computed at temperatures 973 K, 1223 K, and 1473 K. The calculated structure factor agrees very well with data from neutron-diffraction experiments. In addition an analysis of partial coordination numbers suggests that Si and Al are well mixed. This finding does not support an earlier conjecture attributing anomalous density variations to Si-aggregation phenomena. For dynamical properties the velocity autocorrelation function calculated for Al atoms demonstrates a “cage effect” similar to that found in pure liquid Al. In addition, the diffusion constants of Al are consistently lower than that of Si over the temperature range we have studied.
Spatial interpolation is a widely used GIS function for estimating values at locations where observed values are not available or adequate. One popular method for spatial interpolation is inverse distance weighted, wh...
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In this paper,a two-scale finite element approach is proposed and analyzed for approximationsof Green's function in *** approach is based on a two-scale finite elementspace defined,respectively,on the whole domain...
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In this paper,a two-scale finite element approach is proposed and analyzed for approximationsof Green's function in *** approach is based on a two-scale finite elementspace defined,respectively,on the whole domain with size H and on some subdomain containing singularpoints with size h (h << H).It is shown that this two-scale discretization approach is very *** particular,the two-scale discretization approach is applied to solve Poisson-Boltzmann equationssuccessfully.
Cross-streamline migration of deformable entities is essential in many problems such as industrial particulate flows, DNA sorting, and blood rheology. Using two-dimensional numerical experiments, we have discovered th...
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Cross-streamline migration of deformable entities is essential in many problems such as industrial particulate flows, DNA sorting, and blood rheology. Using two-dimensional numerical experiments, we have discovered that vesicles suspended in a flow with curved flow lines migrate towards regions of high flowline curvature, which are regions of high shear rates. The migration velocity of a vesicle is found to be a universal function of the normal stress difference and the flow curvature. This finding quantitatively demonstrates a direct coupling between a microscopic quantity (migration) and a macroscopic one (normal stress difference). Furthermore, simulations with multiple vesicles revealed a self-organization, which corresponds to segregation, in a rim closer to the inner cylinder, resulting from a subtle interaction among vesicles. Such segregation effects could have a significant impact on the rheology of vesicle flows.
We have examined the properties of CdS-ZnS and ZnS-CdS core-shell nanocrystals over a range of shell thicknesses using a real-space pseudopotential-density functional theory approach. The effect of structural relaxati...
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We have examined the properties of CdS-ZnS and ZnS-CdS core-shell nanocrystals over a range of shell thicknesses using a real-space pseudopotential-density functional theory approach. The effect of structural relaxation was shown to be important as it leads to significant changes in the band-gap and frontier orbital localizations. It was also predicted that strains at the core-shell interface are only affected by addition of the first few shell layers, with subsequent layers producing small changes in the strain configuration. This strain saturation gives rise to a “thin” shell regime in which both confinement and strain effects contribute to the evolution of the band gap and a “thick” shell regime in which band-gap variations from bulk values are strongly dependent on confinement effects but approximately constant with respect to strain.
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