基于TrueGrid的起伏界面精准剖分及地震动模拟

利用谱元法的规则六面体单元进行网格剖分时，界面起伏较大处会出现阶梯状网格而导致模拟时产生数值散射。为消除阶梯状网格对起伏界面地震动模拟计算的影响，本文基于TrueGrid软件编写了应用程序，提出了起伏界面处六面体单元网格剖分方式，通过该程序可快速建立起伏界面处均匀的六面体网格模型。本文采取了删除四纵列拐角单元、删除一纵列拐角单元以及构造单元过渡环3种剖分方式，解决两个方向上（x-z与y-z方向）单元二合一过渡后拐角处产生扭曲单元的问题。将阶梯状网格经二合一处理后变为斜面网格，并投影至起伏界面，使得网格完全贴合起伏界面，改善了用台阶状网格近似描绘起伏界面的问题。将3种模型通过谱元法进行数值模拟计算验证了该剖分方式的正确性,对比结果发现删除拐角处一纵列单元方式与设置过渡环的方式均可使用，删除四纵列拐角单元方式不推荐使用，本文提出的方案有助于提高谱元法处理起伏界面问题的灵活性。

Accurate Mesh Generation of Undulating Interface Based on Truegrid and the Ground Motion Simulation

When the regular hexahedral element of the spectral element method is used for meshing, a stepped grid will appear where the interface fluctuates greatly, which leads to numerical scattering during simulation. In order to eliminate the influence of the stepped grid on the ground motion simulation calculation of the undulating interface, an application program is written based on the TrueGrid software, and a method of meshing hexahedral element at the undulating interface is proposed. By using this program, a uniform hexahedral mesh model at the undulating interface can be quickly established. This paper adopts three meshing methods: deleting four-column corner elements, deleting one-column corner elements, and constructing element transition rings to solve the problem of twisting elements at the corners after the two-in-one transition of the elements in the two directions (x-z and y-z directions). The stepped grid is transformed into an inclined grid after two-in-one processing, and projected to the undulating interface, so that the grid fits the undulating interface completely, and the problem of using a stepped grid to approximate the undulating interface is improved. Numerical simulations of the three models verify the correctness of the subdivision method. Comparing the results, it is found that both the method of deleting one column of elements at the corner and the method of setting a transition ring are effective,but the method of deleting four columns of corner elements is not recommended. The schemes proposed in this paper can help to improve the flexibility of the spectral element method to deal with undulating interface problems.