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Reverse time migration imaging of tunnels via the finite element method using an unstructured mesh

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Applied Geophysics 2020年第2期17卷 267-276,316页

作者： Wang Jing Liu Jiang-Ping Cheng Fei Yang Huai-Jie Huang Yi-Fan School of Civil Engineering Shijiazhuang Tiedao UniversityShijiazhuang 050043China Key Laboratory of Roads and Railway Engineering Safety Control(Shijiazhuang Tiedao University) Ministry of EducationShijiazhuang 050043China Hebei Technology and innovation center on safe and efficient mining of metal mines Shijiazhuang Tiedao UniversityShijiazhuang 050043China Hubei Subsurface Multi-scale Imaging Key Laboratory Institute of Geophysics and GeomaticsChina University of GeosciencesWuhan 430074China College of Marine Science and Technology China University of GeosciencesWuhan 430074China Beijing Research Institute of Uranium Geology Beijing 100029China

Wavefield extrapolation is critical in reverse time migration(RTM).The finite diff erence method is primarily used to achieve wavefi eld extrapolation in case of the RTM imaging of ***,complex tunnel models,including those for karsts and fault fracture zones,are constructed using regular grids with straight curves,which can cause numerical dispersion and reduce the imaging *** this study,wavefi eld extrapolation was conducted for tunnel RTM using the finite element method,wherein an unstructured mesh was considered to be the body-fi tted partition in a complex ***,a Poynting vector calculation equation suitable for the unstructured mesh considered in the fi nite element method was established to suppress the interference owing to low-frequency *** tunnel space was considered during wavefi eld extrapolation to suppress the mirror artifacts based on the fl exibility of mesh ***,the infl uence of the survey layouts(one and two sidewalls)on the tunnel imaging results was *** RTM results obtained for a simple tunnel model with an inclined interface demonstrate that the method based on unstructured meshes can effectively suppress the low-frequency noise and mirror artifacts,obtaining clear imaging ***,the two-sidewall tunnel survey layout can be used to accurately obtain the real position of the inclined interface ahead of the tunnel *** complex tunnel numerical modeling and actual data migration results denote the eff ectiveness of the fi nite element method in which an unstructured mesh is used.

关键词： Tunnel advanced prediction fi nite element method unstructured mesh Poynting vector mirror artifacts

UPWIND SCHEME FOR IDEAL 2-D MHD FLOWS BASED ON unstructured mesh

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Transactions of Nanjing University of Aeronautics and Astronautics 2007年第1期24卷 1-7页

作者：潘勇王江峰伍贻兆南京航空航天大学航空宇航学院

An upwind scheme based on the unstructured mesh is developed to solve ideal 2-D magnetohydrodynamics （MHD） equations. The inviscid fluxes are approximated by using the modified advection upstream splitting method （AUSM） scheme, and a 5-stage explicit Runge-Kutta scheme is adopted in the time integration. To avoid the influence of the magnetic field divergence created during the simulation, the hyperbolic divergence cleaning method is introduced. The shock-capturing properties of the method are verified by solving the MHD shock-tube problem. Then the 2-D nozzle flow with the magnetic field is numerically simulated on the unstructured mesh. Computational results demonstrate the effects of the magnetic field and agree well with those from references.

关键词： ideal magnetohydrodynamics equation unstructured mesh advection upstream splitting method(AUSM) scheme divergence cleaning

2.5-D direct current resistivity forward modeling with unstructured mesh

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2.5-D direct current resistivity forward modeling with unstr...

An application of space-filling curves to improve results of turbulent aerodynamics modeling with convolutional neural networks

The 19th International Workshop on Electromagnetic Induction in the Earth

作者： TANG Jingtian WANG Feiyan School of info-physics and Geomatics Engineering,Central South University,Changsha,China

Considering the requirement of achieving economically numerical method under a given accuracy,we implemented unstructured 2D triangular generation adopted from the commercial software ANSYS for 2.5-D direct current forward *** comparing the results obtained from three different kinds of meshes (unstructured triangles, traditional quadrilaterals and rectangle triangles),it is obvious that the unstructured mesh owns a much better performance than the others with nearly the same nodes (actually,unstructured mesh has less nodes).And also results showed surprising priority of unstructured mesh on fitting terrains and complex *** we did comparison for terrain *** numerical results demonstrated that the algorithm of terrain correction has mostly eliminated influence caused by *** the singularities only brought by local ore-bodies have been obtained successfully.

关键词： unstructured mesh 2.5 dimensional ANSYS Finite Element Method

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Chinese Journal of Aeronautics 2024年第2期37卷 81-92页

作者： Mikhail PETROV Sofia ZIMINA Moscow Institute of Physics&Technology Dolgoprudny 141701Russia

When carrying out calculations for turbulent flow simulation,one inevitably has to face the choice between accuracy and speed of *** order to simultaneously obtain both a computationally efficient and more accurate model,a surrogate model can be built on the basis of some fast special model and knowledge of previous calculations obtained by more accurate base models from various test bases or some results of serial *** objective of this work is to construct a surrogate model which allows to improve the accuracy of turbulent calculations obtained by a special model on unstructured *** this purpose,we use 1D Convolutional Neural Network(CNN)of the encoder-decoder architecture and reduce the problem to a single dimension by applying space-filling *** an approach would have the benefit of being applicable to solutions obtained on unstructured *** this work,a non-local approach is applied where entire flow fields obtained by the special and base models are used as input and ground truth output ***-Allmaras(SA)model and Near-wall Domain Decomposition(NDD)method for SA are taken as the base and special models *** efficiency and accuracy of the obtained surrogate model are demonstrated in a case of supersonic flow over a compression corner with different values for angleαand Reynolds number *** conducted an investigation into interpolation and extrapolation by Re and also into interpolation byα.

关键词： Space-filling curves Convolutional neural network Domain decomposition Turbulent flows unstructured mesh

Effects of mesh loop modes on performance of unstructured finite volume GPU simulations

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Advances in Aerodynamics 2021年第1期3卷 357-379页

作者： Yue Weng Xi Zhang Xiaohu Guo Xianwei Zhang Yutong Lu Yang Liu School of Computer Science and Engineering Sun Yat-sen UniversityGuangzhouChina Hartree Centre STFC Daresbury LaboratoryWarringtonUK. China Aerodynamics Research and Development Center MianyangChina.

In unstructured finite volume method,loop on different mesh components such as cells,faces,nodes,etc is used widely for the traversal of *** loop results in direct or indirect data access that affects data locality *** loop on mesh,many threads accessing the same data lead to data *** data locality and data dependence play an important part in the performance of GPU *** optimizing a GPU-accelerated unstructured finite volume Computational Fluid Dynamics(CFD)program,the performance of hot spots under different loops on cells,faces,and nodes is evaluated on Nvidia Tesla V100 and *** tests under different mesh scales show that the effects of mesh loop modes are different on data locality and data ***,face loop makes the best data locality,so long as access to face data exists in *** loop brings the smallest overheads due to non-coalescing data access,when both cell and node data are used in computing without face *** loop owns the best performance in the condition that only indirect access of cell data exists in *** operations reduced the performance of kernels largely in K80,which is not obvious on *** the suitable mesh loop mode in all kernels,the overall performance of GPU simulations can be increased by 15%-20%.Finally,the program on a single GPU V100 can achieve maximum 21.7 and average 14.1 speed up compared with 28 MPI tasks on two Intel CPUs Xeon Gold 6132.

关键词： GPU CFD Finite volume unstructured mesh mesh loop modes Data locality Data dependence

High-order Lagrangian cell-centered conservative scheme on unstructured meshes

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Applied Mathematics and Mechanics(English Edition) 2014年第9期35卷 1203-1222页

作者：葛全文 Institute of Applied Physics and Computational Mathematics

A high-order Lagrangian cell-centered conservative gas dynamics scheme is presented on unstructured meshes. A high-order piecewise pressure of the cell is intro- duced. With the high-order piecewise pressure of the cell, the high-order spatial discretiza- tion fluxes are constructed. The time discretization of the spatial fluxes is performed by means of the Taylor expansions of the spatial discretization fluxes. The vertex velocities are evaluated in a consistent manner due to an original solver located at the nodes by means of momentum conservation. Many numerical tests are presented to demonstrate the robustness and the accuracy of the scheme.

关键词： high-order sub-cell force high-order Lagrangian cell-centered conservativescheme high-order piecewise pressure of cell unstructured mesh

Three-dimensional magnetotellurics modeling using edgebased finite-element unstructured meshes

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Applied Geophysics 2008年第3期5卷 170-180页

作者：刘长生任政勇汤井田严艳中南大学信息物理工程学院中南大学高等教育研究所

Three-dimensional forward modeling magnetotellurics （MT） problems. We present a is a challenge for geometrically complex new edge-based finite-element algorithm using an unstructured mesh for accurately and efficiently simulating 3D MT responses. The electric field curl-curl equation in the frequency domain was used to deduce the H （curl） variation weak form of the MT forward problem, the Galerkin rule was used to derive a linear finite-element equation on the linear-edge tetrahedroid space, and, finally, a BI-CGSTAB solver was used to estimate the unknown electric fields. A local mesh refinement technique in the neighbor of the measuring MT stations was used to greatly improve the accuracies of the numerical solutions. Four synthetic models validated the powerful performance of our algorithms. We believe that our method will effectively contribute to processing more complex MT studies.

关键词： Magnetotelluric modeling edge-based finite-element unstructured mesh local mesh refinement

Runge-Kutta Discontinuous Galerkin Method with Front Tracking Method for Solving the Compressible Two-Medium Flow on unstructured meshes

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Advances in Applied Mathematics and Mechanics 2017年第1期9卷 73-91页

作者： Haitian Lu Jun Zhu Chunwu Wang Ning Zhao College of Aerospace Engineering Nanjing University of Aeronautics and AstronauticsNanjingJiangsu 210016China College of Science Nanjing University of Aeronautics and AstronauticsNanjingJiangsu 210016China

In this paper,we extend using the Runge-Kutta discontinuous Galerkin method together with the front tracking method to simulate the compressible twomedium flow on unstructured meshes.A Riemann problem is constructed in the normal direction in the material interfacial region,with the goal of obtaining a compact,robust and efficient procedure to track the explicit sharp interface *** numerical tests including the gas-gas and gas-liquid flows are provided to show the proposed methodologies possess the capability of enhancing the resolutions nearby the discontinuities inside of the single medium flow and the interfacial vicinities of the two-medium flow in many occasions.

关键词： Runge-Kutta discontinuous Galerkin method front tracking method two-medium flow Riemann problem unstructured mesh

mesh Deformation Method Based on Mean Value Coordinates Interpolation

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Acta Mechanica Solida Sinica 2016年第1期29卷 1-12页

作者： Shuli Sun Shuming Lv Yuan Yuan Mingwu Yuan LTCS Department of Mechanics and Engineering ScienceCollege of EngineeringPeking University

mesh deformation technique is widely used in many application fields, and has re- ceived a lot of attentions in recent years. This paper focuses on the methodology and algorithm of algebraic type mesh deformation for unstructured mesh in numerical discretization. To preserve mesh quality effectively, an algebraic approach for two and three dimensional unstructured mesh is developed based on mean value coordinates interpolation combined with node visibility analysis. The proposed approach firstly performs node visibility analysis to find out the visible boundary for each grid point to be moved, then evaluates the mean value coordinates of each grid point with respect to all vertices on its visible boundary. Thus the displacements of grid points can be calculated by interpolating the boundary movement by the mean value coordinates. Compared with other methods, the proposed method has good deformation capability and predictable com- putational cost, with no need to select parameters or functions. Applications of mesh deformation in different fields are presented to demonstrate the effectiveness of the proposed approach. The results of numerical experiments exhibit not only superior deformation capability of the method in traditional applications of fluid dynamic grid, but also great potential in modeling for large deformation analysis and inverse design problems.

关键词： unstructured mesh mesh deformation mean value coordinates (MVC) visibilityanalysis domain partition