映射半解析边界元法解瞬态弹性动力问题的有关问题

提出了映射半解析边界元法解百轴对称瞬态弹性动力问题时存在解析方向不能正确反映波的传播现象的问题，产生该问题的原因和如何解决该问题的建议。     

具有初曲率板弯曲的边界元分析

由于具有初曲率板弯曲问题的控制微分方程较复杂，直接求解原问题基本解推导边界积分方程较为困难。本文通过引入等效荷载，将此问题的控制微分方程化成与普通板弯曲基本方程形式相同的微分方程，利用一般求解板弯曲问题的边界元法迭代求解，建立了分析具有初曲率板弯曲问题的边界元法。算例表明本方法理论准确、精度良好。     

Exploiting partial or complete geometrical symmetry in 3D symmetric Galerkin indirect BEM formulations

Procedures based on group representation theory, allowing the exploitation of geometrical symmetry in symmetric Galerkin BEM formulations, are investigated. In particular, this investigation is based on the weaker assumption of partial geometrical symmetry, where the boundary has two disconnected components, one of which is symmetric; e.g. this can be very useful for defect identification problems. The main development is expounded in the context of 3D Neumann elastostatic problems, considered as model problems; and then extended to SGBIE formulations for Dirichlet and/or scalar problems. Both Abelian and non‐Abelian finite symmetry groups are considered. The effectiveness of the present approach is demonstrated through numerical examples, where both partial and complete symmetry are considered, in connection with both Abelian and non‐Abelian symmetry groups. Copyright © 2003 John Wiley & Sons, Ltd.     

New approaches for error estimation and adaptivity for 2D potential boundary element methods

This work presents two new error estimation approaches for the BEM applied to 2D potential problems. The first approach involves a local error estimator based on a gradient recovery procedure in which the error function is generated from differences between smoothed and non‐smoothed rates of change of boundary variables in the local tangential direction. The second approach involves the external problem formulation and gives both local and global measures of error, depending on a choice of the external evaluation point. These approaches are post‐processing procedures. Both estimators show consistency with mesh refinement and give similar qualitative results. The error estimator using the gradient recovery approach is more general, as this formulation does not rely on an ‘optimal’ choice of an external parameter. This work presents also the use of a local error estimator in an adaptive mesh refinement procedure. This r‐refinement approach is based on the minimization of the standard deviation of the local error estimate. A non‐linear programming procedure using a feasible‐point method is employed using Lagrange multipliers and a set of active constraints. The optimization procedure produces finer meshes close to a singularity and results that are consistent with the problem physics. Copyright © 2002 John Wiley & Sons, Ltd.     

无限深透水坝基悬挂式垂直防渗体保角变换-边界元渗流计算

无限深透水坝基轮廓复杂,透水层深度大,其渗流计算精度难以保证。本文提出用保角变换-边界元法计算含有无限域渗流计算问题。保角变换将复杂的坝基轮廓线边值问题变换为水平线边值问题,使渗流计算边界问题大大简化;边界元法在求解边界简单的无限域渗流方面优势明显,两种方法联合使用进行求解,能充分发挥保角变换和边界元法各自优点。通过组合法计算结果表明：联合法计算更加快捷、简单,计算结果更加符合无限域的实际情况,可为解决无限域渗流问题提供一条途径。     

边界元法在汽车室内噪声建模中的应用

为探讨汽车室内噪声建模的方法,应用边界元法描述汽车车身室内的噪声水平。首先基于Hypermesh有限元软件建立汽车车室空腔有限元模型,然后以NASTRAN的格式导入到SYSNOISE环境中构建单区域边界元计算模型。引进车内座椅吸音材料对室内声场的影响,重新构建包含座椅的汽车室内多区域边界元计算模型。通过在车身室内安置一个点声源进行激励,分别采用单一和多区域边界元法模拟车身室内声场响应,获得在频率0~1 000 Hz范围内车身室内声场的频响函数。经试验验证,通过对比分析可知多区域边界元法计算结论与试验结果较好吻合,这表明多区域法比单区域法具有更高的精度。     

分析轧件流动速度的刚塑性边界单元法

边界单元法作为一种数值方法，具有降低维数、减小计算量及计算精度高等特点，非常适合于有塑性变形问题的分析。本文建立了刚塑性边界单元法，并用该方法计算了平板轧制中轧件的流动速度，验证了中性面的存在，从而证明该方法是有效的。     

二维任意形状寄生电阻电容的边界元计算

由于集成电路技术高速发展,精确提取任意形状寄生电阻电容变得十分重要,本文以直接边界元素法为基础,利用圆弧样条插值近似任意曲线边界,使插值曲线具有整体一阶连续性,并克服了大挠度与多值的困扰。在直线边界使用线性连续元,在曲线边界使用二次连续无。对两邻国为直线的角点,我们曾提出处理角点处存在多重法的导数的一种方法。这里,它被推广到角点邻边含曲线段的情形。数值结果表明模拟器是可行的。     

基于无迹卡尔曼滤波的双选信道估计方法

针对高速移动场景中由于信道存在时频域选择性衰落(双选衰落)导致正交频分复用(orthogonal frequency division multiplexing, OFDM)通信系统受到子载波间干扰而使通信质量下降的问题,采用基扩展信道模型,在消除子载波间干扰(inter carrier interference, ICI)影响的同时节约信道估计算法的空间复杂度。针对基扩展模型(basis expansion model, BEM)下的非线性信道状态空间模型,采用无迹卡尔曼滤波(unscented Kalman filter, UKF)方法进一步跟踪信道响应提升信道估计精度。仿真分析表明,本研究所提方法能够有效提升信道估计的精度,相对于传统算法具有更好的误码率性能和鲁棒性。     

Large deflection analysis of elastic space membranes

In this paper a solution to the problem of elastic space (initially non‐flat) membranes is presented. A new formulation of the governing differential equations is presented in terms of the displacements in the Cartesian co‐ordinates. The reference surface of the membrane is the minimal surface. The problem is solved by direct integration of the differential equations using the analogue equation method (AEM). According to this method the three coupled non‐linear partial differential equations with variable coefficients are replaced with three uncoupled equivalent linear flat membrane equations (Poisson's equations) subjected to unknown sources under the same boundary conditions. Subsequently, the unknown sources are established using a procedure based on the BEM. The displacements as well as the stress resultants are evaluated at any point of the membrane from their integral representations of the solution of the substitute problems, which are used as mathematical formulae. Several membranes are analysed which illustrate the method and demonstrate its efficiency and accuracy as compared with analytical and existing numerical methods. Copyright © 2005 John Wiley & Sons, Ltd.