基于区域叠合有限元技术预测三维编织复合材料弹性性能

本文基于区域叠合有限元技术预测三维四向编织复合材料弹性性能。在该方法中,分别建立相互独立的纤维增强相有限元模型和复合材料整体区域(包括所有增强相和基体相所占几何空间)有限元模型,两相模型在空间叠合组成复合材料模型,运用节点自由度耦合技术使两相模型满足变形协调关系,通过对两相模型赋予适当的材料属性以使所建复合材料模型具有与实际复合材料等效的力学特性。该方法较传统方法显著缩短了建模时间,降低了建模难度。区域叠合法的数值模拟结果与传统方法预测结果一致。本文的研究为进一步研究编织复合材料非线性宏观力学特性和渐进损伤过程模拟奠定基础。

三维非均匀电大目标散射的有限元撕接区域分解法计算

针对非均匀电大目标的散射问题,将有限元撕接区域分解方法(finite element tearing and interconnecting,FETI)应用于非均匀电大目标散射的精确计算模型.该计算模型以各向异性完全匹配吸收层作为吸收边界.数值实验表明,该计算模型比一般吸收边界条件模型精度高.更为重要的是,虽然该模型由于使用各向异性完全匹配吸收层导致计算效率略有降低,但降低十分有限,有限元撕接区域分解方法对于电大尺寸目标的该模型仍然具有很高的计算效率.结果表明,有限元撕接区域分解方法是计算非均匀电大目标散射的一种有效方法.

基于多区多求解器的金属-介质复合目标电磁散射特性分析

在导弹类金属-介质复合目标电磁散射特性求解过程中,采用常规迭代求解方法存在难以收敛以及内迭代边界积分区域重复求解的问题。针对该问题,在传统有限元边界积分区域分解法(finite element boundary integral domain decomposition method,FE-BI-DDM)的基础上,采用了更为灵活的多区多求解器的方法(multi domain multi solver method,MDMSM)。该方法对导弹类金属-介质复合目标中难以收敛的金属区域,使用快速直接求逆的方法求解,由于可以使用独立的网格模型进行电磁建模,避免了内迭代部分的模型重复建立过程,从而大幅减少了整体模型求解时间。实验结果表明:所提方法可以在相同计算精度的条件下,以不过多增加内存空间为前提,大幅缩短了导弹类目标的金属-介质复合模型的电磁求解时间。该方法为开展导弹类目标特性分析提供了一条可行的技术途径。

基岩地震波作用下隧道计算模型分析

针对隧道的地震计算模型,详细分析了地震波、有限元区域及边界条件、有限单元尺寸等3个关键问题,指出:隧道的地震分析应采用平原基岩地震波;在地震波作用分析中计算模型应采用底部固定边界条件,侧面具有无限边界时,不宜采用有限截断后添加具有透射功能的边界,而宜根据圣维南原理采用大范围的截断边界;有限元尺寸应根据地震波的频谱关系确定。

A FICTITIOUS DOMAIN METHOD FOR DIRICHLET PROBLEM AND ITS APPLICATIONS TO GENER ALIZED STOKES PROBLEM

This paper discusses a fictitious domain method for the linear Dirichlet problem and its applications to the generalized Stokes problem. This method treats Dirichlet boundary condit ion via a Lagrange multiplier technique and is well suited to the no-slip bound ary condition in viscous flow problems. In order to improve the accuracy of solu tions, meshes are refined according to the a posteriori error estimate. The mini -element discretization is applied to solve the generalized Stokes problem. Fin ally, some numerical results to validate this method are presented for partial d ifferential equations with Dirichlet boundary condition.

Origin of the regional stress field along the Liquine-Ofqui Fault Zone(LOFZ),Southern Chilean Andes by means of FE Simulation

The Liquine-Ofqui Fault Zone(LOFZ) of southern Chilean Andes is one of the largest active strike-slip fault zones.There is an ongoing debate regarding the origin of the stress field along the LOFZ due to its complex geometry.This paper represents a study of the origins of the LOFZ regional stress field.Stress fields are calculated by finite element(FE) analysis.The two possible stress origins, i.e., oblique plate convergence and ridge collision/indenter tectonics of Chile ridge against Peru-Chile trench, have been emphasized in the present study.Three types of boundary conditions for the three particular models have been applied to calculate stress fields.Models are assumed to be elastic and plane stress condition.Modeling results are presented in terms of four parameters, i.e., orientation of maximum horizontal stress(σ H max ), displacement vector, s train distribution, and maximum shear stress(τmax ) contour line within the model.The results of the first model with oblique plate convergence show inconsistency between the geometric shape of the LOFZ and the distribution of the four parameters.Although more realistic results are obtained from the second model with normal ridge collision, there are few coincident in the LOFZ geometry and regional stress field.The third model with normal and oblique ridge collision is reasonable in understanding the origin of stress field and geometrical condition in the lithosphere of the LOFZ.

边界元方法的一些研究进展

本文旨在综述我们小组近二十年来在边界元方法这一领域的一些研究成果,在简要介绍边界元方法的基本思想后,主要介绍了一类非线性界面问题的有限元-边界元耦合方法、求解电磁散射问题的有限元-边界元耦合方法和超奇异积分的一类计算方法.

Contact stress non-uniformity of wafer surface for multi-zone chemical mechanical polishing process

A finite element analysis(FEA)model is developed for the chemical-mechanical polishing(CMP)process on the basis of a 12-in five-zone polishing head.The proposed FEA model shows that the contact stress non-uniformity is less dependent on the material property of the membrane and the geometry of the retaining ring.The larger the elastic modulus of the pad,the larger contact stress non-uniformity of the wafer.The applied loads on retaining ring and zone of the polishing head significantly affect the contact stress distribution.The stress adjustment ability of a zone depends on its position.In particular,the inner-side zone has a high stress adjustment ability,whereas the outer-side zone has a low stress adjustment ability.The predicted results by the model are shown to be consistent with the experimental data.Analysis results have revealed some insights regarding the performance of the multi-zone CMP.