基于PVM的网络并行有限元面向对象的设计

子结构是有限元并行计算常用的一种方法，本文采用面向对象的方法，首先对子结构进行了面向对象的设计，得到了其类层次结构图；然后针对工作站网络有限元并行计算环境。提出了基于PVM消息传递平台上的Shadow—Mirror数据传输模型，该模型在有限元并行计算数据传输时，充分发挥数据面向对象的特性，采用设置数据缓冲区、短消息合并等方法以缩短数据通信时间，并据此编制了相应的程序。计算结果表明，使用文中提出的面向对象的Shadow—Mirror数据传输模型可以得到较为理想的并行加速比，而且随着问题规模增大，并行加速比增高。本文研究内容为进一步开展基于工作站网络的并行有限元研究提供了一个可参考的基础。     

基于区域分解的并行有限元程序及其在水下爆炸中的应用

基于MPI标准定义的消息传递接口实现了显式动力学有限元程序的并行计算.通过基于Hilbert空间填充曲线的区域分解算法,实现各区域的独立运算和区域之间共享数据的相互通信.利用程序对水下爆炸自由场中的冲击波传播规律进行了数值模拟,并通过对不同进程数下的并行加速比进行测试,验证了程序的并行效率.     

有限元分析的并行计算方法

文章介绍有限元方法的并行化研究是今后计算力学发展的重要趋势之一，分析了国内外有限元并行计算方法的研究现状与发展，并对国内在这一新兴领域研究工作的开展从技术和管理两方面提出了一些有益的建议。     

A HIERARCHICAL PARALLEL COMPUTING APPROACH FOR STRUCTURAL STATIC FINITE ELEMENT ANALYSIS

根据分布式存储并行计算机的体系结构特点,提出了一种结构静力有限元分层并行计算方法. 该方法在两级分区两次缩聚策略的基础上不仅实现了大量数据的分布式存储,提高了数据的内存访问速率;而且实现了计算过程的三层并行,有效提高了通信效率;此外,它还进一步降低了界面方程的规模,大幅度减少了界面方程的求解时间. 因此,它能够充分利用分布式存储并行计算机的体系结构特点提升大规模并行计算效率. 最后通过典型数值算例验证了该方法的正确性和有效性.     

基于集群的并行有限元分析研究

利用面向对象的方法实现了基于集群的并行有限元分析.首先介绍构建高性能计算集群的系统分析新方法,并针对建成集群系统的特点,对并行消息传递库MPI进行了并行语义分析,进而对其主要的实现函数进行面向对象的重构而建立起OO消息传递库,以此为基础分别利用两种不同的策略实现了面向对象的并行有限元分析(OOParaFEA: Object-Oriented Parallel FEA),一种是通过对传统的基于域分解方法的并行PCG算法进行改造而在集群平台实现,另一种是对已有的基于子结构方法的串行有限元分析程序加以扩展,加入系统方程组并行求解器而达到有限元分析并行化的目的.多个分析算例表明,基于集群进行面向对象的并行有限元分析可以有效提高计算效率,为进一步的网络化CAD/CAE研究奠定良好基础.     

一种有限元并行计算前处理方法

本文研究一种有限元并行计算前处理方法,只需将各子结构的超单元信息发送给各处理机,就可并行自动剖分各子结构和并行优化各子结构单元编号,以达到极小最大波宽和波宽的均主根,算例表明,该方法可大大减少有限元并行计算前处理时间。     

结构静力有限元分层并行计算方法

根据分布式存储并行计算机的体系结构特点,提出了一种结构静力有限元分层并行计算方法. 该方法在两级分区两次缩聚策略的基础上不仅实现了大量数据的分布式存储,提高了数据的内存访问速率;而且实现了计算过程的三层并行,有效提高了通信效率;此外,它还进一步降低了界面方程的规模,大幅度减少了界面方程的求解时间. 因此,它能够充分利用分布式存储并行计算机的体系结构特点提升大规模并行计算效率. 最后通过典型数值算例验证了该方法的正确性和有效性.      

大规模并行结构动力分析分层计算方法

多核分布式存储超级计算机的兴起为大规模并行结构动力分析提供了强有力的计算工具。根据多核分布式计算环境的特点,提出了一种大规模并行结构动力分析分层计算方法。该方法在传统隐式动力分析的区域分解法的基础上,利用两级分区和两次缩聚策略进行求解。不但通过进一步缩减求解问题规模有效提高了界面方程的收敛速度,而且通过三层并行计算有效提高了通信效率。该方法并不对有限元模型引入近似,属于精确的动力子区域分层计算方法。典型数值算例表明,该方法计算精度与商业软件ANSYS完全法求解精度相当;同传统区域分解法相比,该方法能够获得较高的并行计算性能。     

断裂过程的有限元模拟

讨论了材料断裂过程的有限元模拟技术。基于自适应有限元的一般原理，并针对多相材料的裂纹扩展的特点，提出了一种简化的高精度和高效率有限元网格的动态重新划分策略。裂纹被假设沿着单元之间的路径连续扩展，利用节点力释放技术生成新的裂纹自由表面，发展了一种可随裂尖连续移动的网格动态加密和释放方法。这种方法已在各种裂纹问题中得以实现与应用。     

基于并行计算和遗传算法的钢-UHPC华夫板组合梁优化设计

为实现钢-超高性能混凝土(UHPC)华夫板组合梁结构快速经济合理的设计，提出了基于并行计算与遗传算法的结构优化设计方法。通过Python建立了并行计算平台，使Abaqus和Python能够执行同步数值模拟和数据处理，以成本最小化为目标，采用遗传算法对钢-UHPC华夫板组合梁进行了优化，验证了所提方法的可行性。结果表明，遗传算法中密集的分析任务可以并行化并分配给不同的计算资源以提高计算效率；使用并行计算可以提高8.6倍的优化效率；并行计算和串行计算的CPU平均使用率分别为82%和18%。本文方法的成功应用可为其他类型结构的优化设计提供参考。     

Parallel SOR methods with a parabolic-diffusion acceleration technique for solving an unstructured-grid Poisson equation on 3D arbitrary geometries

This paper presents a parallel algorithm for the finite-volume discretisation of the Poisson equation on three-dimensional arbitrary geometries. The proposed method is formulated by using a 2D horizontal block domain decomposition and interprocessor data communication techniques with message passing interface. The horizontal unstructured-grid cells are reordered according to the neighbouring relations and decomposed into blocks using a load-balanced distribution to give all processors an equal amount of elements. In this algorithm, two parallel successive over-relaxation methods are presented: a multi-colour ordering technique for unstructured grids based on distributed memory and a block method using reordering index following similar ideas of the partitioning for structured grids. In all cases, the parallel algorithms are implemented with a combination of an acceleration iterative solver. This solver is based on a parabolic-diffusion equation introduced to obtain faster solutions of the linear systems arising from the discretisation. Numerical results are given to evaluate the performances of the methods showing speedups better than linear.     

Parallel implementation of a non‐hydrostatic model for free surface flows with semi‐Lagrangian advection treatment

The parallel implementation of an unstructured‐grid, three‐dimensional, semi‐implicit finite difference and finite volume model for the free surface Navier–Stokes equations (UnTRIM ) is presented and discussed. The new developments are aimed to make the code available for high‐performance computing in order to address larger, complex problems in environmental free surface flows. The parallelization is based on the mesh partitioning method and message passing and has been achieved without negatively affecting any of the advantageous properties of the serial code, such as its robustness, accuracy and efficiency. The key issue is a new, autonomous parallel streamline backtracking algorithm, which allows using semi‐Lagrangian methods in decomposed meshes without compromising the scalability of the code. The implementation has been carefully verified not only with simple, abstract test cases illustrating the application domain of the code but also with advanced, high‐resolution models presently applied for research and engineering projects. The scheme performance and accuracy aspects are researched and discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Aerodynamic shape optimization on overset grids using the adjoint method

This paper deals with the use of the continuous adjoint equation for aerodynamic shape optimization of complex configurations with overset grids methods. While the use of overset grid eases the grid generation process, the non‐trivial task of ensuring communication between overlapping grids needs careful attention. This need is effectively addressed by using a practically useful technique known as the implicit hole cutting (IHC) method. The method depends on a simple cell selection process based on the criterion of cell size, and all grid points including interior points and fringe points are treated indiscriminately in the computation of the flow field. This paper demonstrates the simplicity of the IHC method for the adjoint equation. Similar to the flow solver, the adjoint equations are solved on conventional point‐matched and overlapped grids within a multi‐block framework. Parallel computing with message passing interface is also used to improve the overall efficiency of the optimization process. The method is successfully demonstrated in several two‐ and a three‐dimensional shape optimization cases for both external and internal flow problems. Copyright © 2009 John Wiley & Sons, Ltd.     

Large-scale high performance computation on 3D explosion and shock problems

Explosion and shock often involve large deformation, interface treatment between multi-material, and strong discontinuity. The Eulerian method has advantages for solving these problems. In parallel computation of the Eulerian method, the physical quantities of the computaional cells do not change before the disturbance reaches to these cells. Computational efficiency is low when using fixed partition because of load imbalance. To solve this problem, a dynamic parallel method in which the computation domain expands with disturbance is used. The dynamic parallel program is designed based on the generally used message passing interface model. The numerical test of dynamic parallel program agrees well with that of the original parallel program, also agrees with the actual situation.     

Optimal control applied to water flow using second order adjoint method

This paper presents an optimal control applied to water flow using the first and second order adjoint equations. The gradient of the performance function with respect to control variables is analytically obtained by the first order adjoint equation. It is not necessary to compute the Hessian matrix directly using the second order adjoint equation. Two numerical studies have been performed to show the adaptability of the present method. The performance of the second order adjoint method is compared with that of the weighted gradient method, Broyden–Fletcher–Goldfarb–Shanno method and Lanczos method. The precise forms of the adjoint equations and the gradient to use for the minimisation algorithm are derived. The computation by the Lanczos method is shown as superior to those of the other methods discussed in this paper. The message passing interface library is used for the communication of parallel computing.     

Automatic unstructured surface mesh generation for complex configurations

In this paper a new object‐oriented (OO) approach is presented for automatic parallel advancing front based surface mesh generation and adaptive remeshing for complex configurations. Based on the ST++‐system the advantages of the OO design and implementation compared to the traditional structural approach are described. Algorithmic enhancements to the advancing front method are explained, enabling a robust NURBS based triangulation process directly on B‐rep CAD data. The message passing (MPI) parallelization strategy together with the achievable performance improvements are demonstrated. With the outlined parallel geometry analysis/rasterization a powerful method is described to derive automatically a well suited mesh size specification without any user‐interaction from scratch. The application of this method to a complex ‘real world’ example finishes this paper. Copyright © 2004 John Wiley & Sons, Ltd.     

Vectorized Directional Sweep Based Parallelization Method for Factored Alternating Direction Implicit (ADI) Schemes

A new parallelization method is proposed for factored alternating direction implicit (ADI) schemes based on the vectorized global domain directional sweep. This approach, when combined with multi-partitioning domain decomposition, significantly reduces the frequency of necessary communication calls and minimizes processor idling during the sweeping processes. The present parallelization approach is applied to a number of vectorized two-dimensional compressible Navier-Stokes solvers. The codes vary in complexity from laminar to algebraic turbulence closure model and finally the strongly coupled Navier-Stokes and K-e equations. Implementation is conducted using PVM (Parallel Virtual Machine) message passing tool on the Cray T3D massively parallel processing (MPP) machine. The implemented parallel codes are assessed in terms of accuracy and parallel performance.     

GLONASS星历电文特征及其解算方法

针对飞行试验中由于GLONASS星历解算错误导致的定位结果异常问题,研究了GLONASS星历电文下传的基本特征,即通过第1~4串电文下传,并且一个更新周期内下传60组数据完全相同的星历。基于此,提出了基于电文串标识的GLONASS星历解算基本算法,但发现该算法在电文串丢失且发生星历更新时解算出错误星历的问题。为确保星历来源于连续的1~4串电文,提出了基于时间比较的星历解算改进算法,发现GLONASS星历更新时,不保证从第1串开始,也不保证在连续的1~4串电文中更新完毕,改进算法依然无法确保获取到正确星历。最后分析了星历电文误码时的特征,提出了基于星历合法性检测的星历解算可靠算法,该算法综合考虑卫星不健康、星历更新以及电文误码等异常情况,采用轨道特性检测法和原码比对检测法验证星历合法性,采用电文串标识法充分利用有效电文数据。试验结果表明,该算法的星历误码识别率达到100%,星历更新异常识别率达到100%,获取的GLONASS星历数据正确率到100%。