Automatic simulation techniques for 3D wave propagation in geological media

本项目致力于大范围地质区域中波传播的高效数值模拟。这在一些与安全和可持续性相关的应用中至关重要，例如关键基础设施的地震故障、地质勘探或地下物体的探测。尽管相关的复杂波浪反射和折射现象本质上是空间的，但缺乏能够完全解决大规模动力学问题的模拟技术。在很大范围的土体中，出射变形波会产生辐射衰减，必须用有限元计算模型来精确表示。波传播模拟与特定的啮合要求相关联，具体取决于材料属性和频率内容。为包含非常不同规模的特征的不同地质域生成高质量的网格是高度劳动密集型的，需要相当多的经验。在现实地质区域中，与3D波传播的非线性时域分析相关的计算工作可能是令人望而却步的。这些挑战如下所述。主要目的是开发一种全自动网格划分和分析方法，用于三维非均匀土体区域中的波传播。在这里，由于问题的规模很大，效率至关重要。设计了一种高度灵活的网格划分方法，既减少了手动网格生成的负担，又在精度和效率方面导致了数值模型的优化。将使用结构化网格，从而可以快速高效地细化几何不连续区域或塑性区中的计算网格。同时，还将利用谱元素在波传播问题上的优越收敛性能。为了实现这一点，将制定一种策略，根据材料属性和频率含量自动分配不同区域的元素顺序。此外，我们寻求严格和有效地表示辐射衰减，以便将近场尺寸保持在所需的最小维度。为解决上述问题，将采用尺度边界有限元方法。后者在模拟无界域中的波浪方面表现出色。它可以直接用于结构化网格，从而为高效分析提供了一个潜在的框架。将开发一种自动八叉树/多面体网格技术，并专门为波传播的要求量身定做。所得到的模型将耦合到基于单位脉冲响应的SBFE公式来表示远场。最终的自动网格划分和分析工具将有助于逼真地模拟包括动态非线性现象在内的高度不均匀地质域中的三维波辐射和散射过程。

This project addresses the efficient numerical simulation of wave propagation in large geological regions. This is of crucial importance in a number of safety and sustainability related applications such as seismic failure of critical infrastructure, geological exploration or detection of underground objects. While the related complex wave reflection and refraction phenomena are inherently spatial, there is a lack of simulation techniques that can address the large-scale dynamic problem in its full complexity. In soil regions of very large extent radiation damping of outgoing deformation waves occurs, which must be represented accurately in finite computational models. Wave propagation simulation is associated with particular meshing requirements depending on the material properties and frequency content. The generation of high quality meshes for heterogeneous geological domains containing features of very different scale is highly labour intensive and requires considerable experience. The computational effort associated with nonlinear time-domain analysis of 3D wave propagation in realistic geological regions can be prohibitive.These challenges are addressed as follows. The main objective is to develop a fully automatic meshing and analysis approach for wave propagation in three-dimensional heterogeneous soil regions. Here, efficiency is of crucial importance due to the large scale of the problem. A highly flexible meshing approach will be devised, which both reduces the burden of manual mesh generation and leads to optimized numerical models both in terms of accuracy and efficiency. Structured meshes will be used, which allow for the rapid and thus highly efficient refinement of computational grids near geometrical discontinuities or in plastic zones. At the same time, the superior convergence behaviour of spectral elements for wave propagation problems will be exploited. To achieve this, a strategy for the automatic assignment of element orders in various regions based on the material properties and frequency content will be developed. Moreover, we seek to rigorously and efficiently represent radiation damping in order to keep the near field size to the required minimum dimensions. To address the above objectives, the scaled boundary finite element method (SBFEM) will be used. The latter excels in modelling waves in unbounded domains. It can be used on structured meshes straightforwardly and thus provides a potential framework for highly efficient analysis. An automatic octree / polyhedral meshing technique will be developed and specifically tailored to the requirements of wave propagation. The resulting model will be coupled to a unit-impulse-response-based formulation of the SBFEM to represent the far field. The final automatic meshing and analysis tool will facilitate the realistic simulation of three-dimensional wave radiation and scattering processes in highly heterogeneous geological domains including dynamic nonlinear phenomena.