Traditional 3D Magnetotelluric(MT) forward modeling and inversions are mostly based on structured meshes that have limited accuracy when modeling undulating surfaces and arbitrary structures. By contrast, unstructured...Traditional 3D Magnetotelluric(MT) forward modeling and inversions are mostly based on structured meshes that have limited accuracy when modeling undulating surfaces and arbitrary structures. By contrast, unstructured-grid-based methods can model complex underground structures with high accuracy and overcome the defects of traditional methods, such as the high computational cost for improving model accuracy and the difficulty of inverting with topography. In this paper, we used the limited-memory quasi-Newton(L-BFGS) method with an unstructured finite-element grid to perform 3D MT inversions. This method avoids explicitly calculating Hessian matrices, which greatly reduces the memory requirements. After the first iteration, the approximate inverse Hessian matrix well approximates the true one, and the Newton step(set to 1) can meet the sufficient descent condition. Only one calculation of the objective function and its gradient are needed for each iteration, which greatly improves its computational efficiency. This approach is well-suited for large-scale 3D MT inversions. We have tested our algorithm on data with and without topography, and the results matched the real models well. We can recommend performing inversions based on an unstructured finite-element method and the L-BFGS method for situations with topography and complex underground structures.展开更多
We propose a new 3D inversion scheme to invert the near-and transition-zone data of CSAMT with topography accurately.In this new method,the earth was discretized into unstructured tetrahedra to fit the ragged topograp...We propose a new 3D inversion scheme to invert the near-and transition-zone data of CSAMT with topography accurately.In this new method,the earth was discretized into unstructured tetrahedra to fit the ragged topography and the vector fi nite-element method was adopted to obtain precise responses and good sensitivity.To simulate the attitude and shape of the transmitter,we divided a long-grounded transmitter into dipoles and integrated these dipoles to obtain good responses in the near-and transition-fi eld zones.Next,we designed an L2 norm-based objective functional and applied a standard quasi-Newton method as the optimization method to solve the inverse problem and guarantee steady convergence.We tested our 3D inversion method first on synthetic data and then on a field dataset acquired from select sites near Changbai Mountain,China.In both tests,the new inversion algorithm achieved excellent fitting between the predicted and observed data,even in near-and transition-fi eld zones,and the inversion results agreed well with the true model.These fi ndings reveal that the proposed algorithm is eff ective for 3D inversion of CSAMT data.展开更多
本文利用CiteSpace可视化软件对CNKI和ISI Web of Science数据库所收录的有限元技术在法医学中应用的研究文献进行统计和可视化对比分析,得出国内外法医领域有限元应用研究文献的关键词、机构合作、作者合作的可视化知识图谱。在此基础...本文利用CiteSpace可视化软件对CNKI和ISI Web of Science数据库所收录的有限元技术在法医学中应用的研究文献进行统计和可视化对比分析,得出国内外法医领域有限元应用研究文献的关键词、机构合作、作者合作的可视化知识图谱。在此基础上,作者对文献内容进行深入研究,发现有限元技术在法医学中的研究及应用主要集中在损伤机制分析方面,以车祸损伤、高坠损伤、钝器损伤、锐器损伤、枪弹损伤等为重点,研究方法主要是通过对人体、致伤物等建立高仿真模型,利用有限元技术,以数字化、可视化、可量化的方式研究各类损伤的生物力学机制。目前,国内外法医学者主要借助Mimics等软件将人体影像数据转换为分割化的三维模型,依托较为成熟的THUMS、ANSYS等有限元系统构建多种损伤模型,有效揭示了各类损伤的发生机制,在一定程度上推动了法医病理损伤专业的发展,为法医学者开展相关研究提供了参考和借鉴。同时,有限元技术在法医学中的应用属于学科交叉,但目前的研究人员多以法医为主,缺少相关学科专业技术人员的深度介入,在某种程度上限制了该技术在法医学中的应用发展,有必要加强与从事有限元等相关研究的专业技术人员之间的交流合作。展开更多
基金financially supported by the National Natural Science Foundation of China(No.41774125)Key Program of National Natural Science Foundation of China(No.41530320)+1 种基金the Key National Research Project of China(Nos.2016YFC0303100 and 2017YFC0601900)the Strategic Priority Research Program of Chinese Academy of Sciences Pilot Special(No.XDA 14020102)
文摘Traditional 3D Magnetotelluric(MT) forward modeling and inversions are mostly based on structured meshes that have limited accuracy when modeling undulating surfaces and arbitrary structures. By contrast, unstructured-grid-based methods can model complex underground structures with high accuracy and overcome the defects of traditional methods, such as the high computational cost for improving model accuracy and the difficulty of inverting with topography. In this paper, we used the limited-memory quasi-Newton(L-BFGS) method with an unstructured finite-element grid to perform 3D MT inversions. This method avoids explicitly calculating Hessian matrices, which greatly reduces the memory requirements. After the first iteration, the approximate inverse Hessian matrix well approximates the true one, and the Newton step(set to 1) can meet the sufficient descent condition. Only one calculation of the objective function and its gradient are needed for each iteration, which greatly improves its computational efficiency. This approach is well-suited for large-scale 3D MT inversions. We have tested our algorithm on data with and without topography, and the results matched the real models well. We can recommend performing inversions based on an unstructured finite-element method and the L-BFGS method for situations with topography and complex underground structures.
基金the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDA14020102)the National Natural Science Foundation of China(Nos.41774125,41530320,41904104)+1 种基金the Key National Research Project of China(No.2018YFC0603300)the S&T Program of Beijing(No.Z181100005718001).
文摘We propose a new 3D inversion scheme to invert the near-and transition-zone data of CSAMT with topography accurately.In this new method,the earth was discretized into unstructured tetrahedra to fit the ragged topography and the vector fi nite-element method was adopted to obtain precise responses and good sensitivity.To simulate the attitude and shape of the transmitter,we divided a long-grounded transmitter into dipoles and integrated these dipoles to obtain good responses in the near-and transition-fi eld zones.Next,we designed an L2 norm-based objective functional and applied a standard quasi-Newton method as the optimization method to solve the inverse problem and guarantee steady convergence.We tested our 3D inversion method first on synthetic data and then on a field dataset acquired from select sites near Changbai Mountain,China.In both tests,the new inversion algorithm achieved excellent fitting between the predicted and observed data,even in near-and transition-fi eld zones,and the inversion results agreed well with the true model.These fi ndings reveal that the proposed algorithm is eff ective for 3D inversion of CSAMT data.
文摘本文利用CiteSpace可视化软件对CNKI和ISI Web of Science数据库所收录的有限元技术在法医学中应用的研究文献进行统计和可视化对比分析,得出国内外法医领域有限元应用研究文献的关键词、机构合作、作者合作的可视化知识图谱。在此基础上,作者对文献内容进行深入研究,发现有限元技术在法医学中的研究及应用主要集中在损伤机制分析方面,以车祸损伤、高坠损伤、钝器损伤、锐器损伤、枪弹损伤等为重点,研究方法主要是通过对人体、致伤物等建立高仿真模型,利用有限元技术,以数字化、可视化、可量化的方式研究各类损伤的生物力学机制。目前,国内外法医学者主要借助Mimics等软件将人体影像数据转换为分割化的三维模型,依托较为成熟的THUMS、ANSYS等有限元系统构建多种损伤模型,有效揭示了各类损伤的发生机制,在一定程度上推动了法医病理损伤专业的发展,为法医学者开展相关研究提供了参考和借鉴。同时,有限元技术在法医学中的应用属于学科交叉,但目前的研究人员多以法医为主,缺少相关学科专业技术人员的深度介入,在某种程度上限制了该技术在法医学中的应用发展,有必要加强与从事有限元等相关研究的专业技术人员之间的交流合作。
