Scalable and portable implementation of the fast multipole method on parallel computers

A scalable and portable Fortran code is developed to calculate Coulomb interaction potentials of charged particles on parallel computers, based on the fast multipole method. The code has a unique feature to calculate microscopic stress tensors due to the Coulomb interactions, which is useful in constant-pressure simulations and local stress analyses. The code is applicable to various boundary conditions, including periodic boundary conditions in two and three dimensions, corresponding to slab and bulk systems, respectively. Numerical accuracy of the code is tested through comparison of its results with those obtained by the Ewald summation method and by direct calculations. Scalability tests show the parallel efficiency of 0.98 for 512 million charged particles on 512 IBM SP3 processors. The timing results on IBM SP3 are also compared with those on IBM SP4.     

模拟板金冲压成形的计算机软件系统

ＳＭＦＳＳ１由模具设计的ＣＡＤ模块、前处理模块、成形过程仿真模块和后处理模块及接口组成。仿真模块使用有限元方法对成形过程中的接触问题采用了接触搜寻法确定接触对，并使用罚参数法快速准确地求出接触力。前后处理模块使ＣＡＤ系统与仿真模块构成统一的应用系统，应用效率与方便性良好。通过应用实例说明软件的实用性及可应用性。     

基于模式化知识和人工神经网络的智能设计系统框架研究

阐述了将神经网络和模式识别引入智能设计系统的模型－集成转换模型,在该模型中,对智能系统与设计的实现系统的结合进行了探讨,提出了数值编译器与反编译器、图形／编码转换器等将神经网络引入设计系统来的工具和方法。     

Simulation of flowfields induced by wind blades based on a parallelized low-speed flow solver

In this study, a parallel computing technology is applied on the simulation of a wind turbine flow problem. A third-order Roe type flux limited splitting based on a pre-conditioning matrix with an explicit time marching method is used to solve the Navier–Stokes equations. The original FORTRAN code was parallelized with Message Passing Interface (MPI) language and tested on a 64-CPU IBM SP2 parallel computer. The test results show that a significant reduction of computing time in running the model and a super-linear speed up rate is achieved up to 32 CPUs at IBM SP2 processors. The speed up rate is as high as 49 for using IBM SP2 64 processors. The test shows very promising potential of parallel processing to provide prompt simulation of the current wind turbine problems.     

Parallel performance of a lattice-Boltzmann/finite element cellular blood flow solver on the IBM Blue Gene/P architecture

We discuss the parallel implementation and scaling results of a hybrid lattice-Boltzmann/finite element code for suspension flow simulations. This code allows the direct numerical simulation of cellular blood flow, fully resolving the two-phase nature of blood and the deformation of the suspended phase. A brief introduction to the numerical methods employed is given followed by an outline of the code structure. Scaling results obtained on Argonne National Laboratories IBM Blue Gene/P (BG/P) are presented. Details include performance characteristics on 512 to 65,536 processor cores.     

Parallel boundary and best neighbor searching sampling algorithm for drawbead design optimization in sheet metal forming

In the present paper, a Kriging-based metamodeling technique is used to minimize the risk of failure in a sheet metal forming process. The Kriging-based models are fitted to data that are obtained for larger experimental areas than the areas used in low-order polynomial regression metamodels. Therefore, computational time and memory requirement can be an obstacle for Kriging for data sets with many observations. To improve the usability of the Kriging-based metamodeling techniques, a parallel intelligent sampling approach: boundary and best neighbor searching (BBNS) (Wang et al., J Mater Process Technol 197(1–3):77–88, 2008a) is suggested. Compared with the serial BBNS version, the sampling procedure is performed synchronously. Thus, larger sample size should be considered for real-life problems when multiple processors are available. Furthermore, the parallel strategy is prone to converge based on more samples. The performance of the parallel approached is verified by means of nonlinear test functions. Moreover, the drawbead design in sheet metal forming is successfully optimized by the parallel BBNS approach and Kriging metamodeling technique. The optimization results demonstrate that the parallel BBNS approach improves the applicability of the Kriging metamodeling technique substantially.     

Parallel multigrid finite volume computation of three-dimensional thermal convection

A parallel implementation of the finite volume method for three-dimensional, time-dependent, thermal convective flows is presented. The algebraic equations resulting from the finite volume discretization, including a pressure equation which consumes most of the computation time, are solved by a parallel multigrid method. A flexible parallel code has been implemented on the Intel Paragon, the Cray T3D, and the IBM SP2 by using domain decomposition techniques and the MPI communication software. The code can use 1D, 2D, or 3D partitions as required by different geometries, and is easily ported to other parallel systems. Numerical solutions for air (Prandtl number Pr = 0.733) with various Rayleigh numbers up to 10⁷ are discussed.     

Tool path optimization for single point incremental sheet forming using response surface method

Incremental sheet forming (ISF) process is based on localized plastic deformation in a thin sheet metal blank. It consists to deform progressively and locally the sheet metal using spherical forming tool controlled by a CNC machine-tool. Although it is a slow process compared to conventional forming technique such as stamping. The cost reduction linked to the fact that punches and dies are avoided which makes it a very attractive process for small batch production and rapid prototyping. However, ISF process depends strongly on the forming tool path which influences greatly the part geometry and sheet thickness distribution. A homogeneous thickness distribution requires a rigorous optimization of the parameter settings, and an optimal parameterization of the forming strategy. This paper shows an optimization procedure tested for a given forming strategy, in order to reduce the manufacturing time and homogenize thickness distribution of an asymmetric part. The optimal forming strategy was determined by finite element analyses (FEA) in combination with response surface method (RMS) and sequential quadratic programming (SQP) algorithm.     

Parameter optimization of the sheet metal forming process using an iterative parallel Kriging algorithm

Different numerical optimization strategies were used to find an optimized parameter setting for the sheet metal forming process. A parameterization of a time-dependent blank-holder force was used to control the deep-drawing simulation. Besides the already well-established gradient and direct search algorithms and the response surface method the novel Kriging approach was used as an optimization strategy. Results for two analytical and two sheet metal forming test problems reveal that the new Kriging approach leads to a fast and stable convergence of the optimization process. Parallel simulation is perfectly supported by this method.     

Large strain solutions of rubber components

A Mooney-Rivlin material model for plane strain and axisymmetric analyses of rubber has been implemented in the ADINA computer code.

Using a consistent penalty method, derived from a regularized mixed formulation, the nonlinear incompressibility constraint is weakened by a properly chosen projection procedure. The hydrostatic pressure (proportional to the penalty function and discontinuous at interelement boundaries) may assume constant or linear elementwise variation, optimally matching the assumed displacement fields in four or nine node elements, respectively. Numerical studies on convergence rates and stability properties of pressure solutions give results that agree well with predictions made on the basis of the theory for the linear constraint case.

The code has been used in the practical design of a highly strained rubber diaphragm in a sheet metal forming press. The pressure load was kept perpendicular to deformed surfaces and the growth of contact areas between rubber and metal boundaries during the forming process was simulated by introducing successive constraints in repeated restart runs.     

Towards a three-dimensional moving body incompressible flow solver with a linear deformable model

In this study, a three-dimensional fluid–structured parallelized solver is extended from the previous work (Niu et al., 2009 [1]) for moving body simulations. Based on the unified Eulerian and Lagrangian coordinate transformations, the unsteady three-dimensional incompressible Navier–Stokes equations with artificial compressibility (Chorin, 1967 [2]) in a dual-time stepping approach are first derived. To implement unsteady flow calculations, the dual-time stepping strategy including the LU decomposition method is used in the pseudo-time iteration and the second-order accurate backward difference is adopted to discretize the unsteady flow terms. Also, a third-order Roe type flux limited splitting is derived to evaluate the spatial difference of the convective fluxes. The original FORTRAN code is converted to the MPI code and tested on a 64-CPU IBM SP2. The parallel strategy here is based on the partitions of all do-loops in the original FORTRAN code and transferring the calculations inside the do-loop into different CPUs. The partition of the do-loop can be applied on the innermost loop, only or the last two inner loops depending on two-dimensional or three-dimensional problems. This kind of the parallel data partition of the loops is independent of what kind of the explicit or implicit type numerical algorithm used. Therefore, the current parallel approach can take advantage of the MPI language fully to transfer data efficiently among CPUs even for solving the governing equation implicitly. The test results show that a significant reduction of computing time in running the model and a near-linear speed up rate is achieved up to 32 CPUs at IBM SP2. The speed up rate is as high as 31 for using 64 IBM SP2 processors The test shows efficient parallel processing to provide prompt simulation of 3D cavity, unsteady dropping airfoil and blood flows in an aortic tube with a linear elastic modeling of wall motion is included here.     

Using surrogate models and response surfaces in structural optimization – with application to crashworthiness design and sheet metal forming

The aim of this paper is to determine if the Space Mapping technique using surrogate models together with response surfaces is useful in the optimization of crashworthiness and sheet metal forming. In addition, the efficiency of optimization using Space Mapping will be compared to traditional structural optimization using the Response Surface Methodology (RSM). Five examples are used to study the algorithm: one optimization of an analytic function and four structural optimization problems. All examples are constrained optimization problems. In all examples, the algorithm converged to an improved design with all constraints fulfilled, even when a conventional RSM optimization failed to converge. For the crashworthiness design problems, the total computing time for convergence was reduced by 53% using Space Mapping compared to conventional RSM. For the sheet metal forming problems the total computing time was reduced by 63%. The conclusions are that optimization using Space Mapping and surrogate models can be used for optimization in crashworthiness design and sheet metal forming applications with a significant reduction in computing time.     

Linear-scaling parallelization of the WIEN package with MPI

A parallel version of the WIEN package, the full-potential linearized Augmented Planewave (FP-LAPW) code for ab initio electron structure calculation, has been developed using the message passing interface (MPI). All time-consuming parts of the self-consistent cycle, namely, the matrix setting, the eigen-solver, and the charge density and potential generators, have been parallelized on the level of the plane-wave basis, wherever possible, and/or of atomic loops. Test calculations done on Linux commodity cluster and the IBM power3 supercomputers show that the parallel code attains nearly linear scaling for almost all the time-consuming calculations. It opens the possibility to handle large systems with the full-potential method on the parallel platforms.     

A large scale molecular dynamics simulation code using the fast multipole algorithm (FMD): performance and application

We present the performance of the fast classical molecular dynamics (MD) code, fast molecular dynamics (FMD), designed for efficient, object-oriented, and scalable large scale simulations, and summarize its application to a liquid crystalline cluster. FMD uses an implementation of the three-dimensional fast multipole method, developed in our group. The fast multipole method offers an efficient way (order O(N)) to handle long range electrostatic interactions, thus, enabling more realistic simulations of large molecular systems. Performance testing was carried out on IBM SP2, SGI Origin 2000, and CRAY T3E massively parallel systems using the MPI massage passing library. The electrostatic forces were tested on models of up to 100,000 randomly placed charges, and on protein and liquid crystalline molecular systems of over 99,000 atoms. Tests on the stability of the method are presented, along with comparisons with direct calculations, the NAMD2 code, and the physical multipole-based cell-multipole method.     

Relating wear stages in sheet metal forming based on short- and long-term force signal variations

Journal of Intelligent Manufacturing - Monitoring systems in sheet metal forming cannot rely on direct measurements of the physical condition of interest because the space between the die component...     

A parallel finite element procedure for contact-impact problems

An efficient parallel finite element procedure for contact-impact problems is presented within the framework of explicit finite element analysis with thepenalty method. The procedure concerned includes a parallel Belytschko-Lin-Tsay shell element generation algorithm and a parallel contact-impact algorithm based on the master-slave slideline algorithm. An element-wise domain decomposition strategy and a communication minimization strategy are featured to achieve almost perfect load balancing among processors and to show scalability of the parallel performance. Throughout this work, a prototype code, named GT-PARADYN, is developed on the IBM SP2 to implement the procedure presented, under message-passing paradigm. Some examples are provided to demonstrate the timing results of the algorithms, discussing the accuracy and efficiency of the code.     

一种基于高压水射流的金属板材柔性渐进成形技术

本文提出了一种新型的金属板材无模成形方法,即高压水射流柔性渐进成形方法,并基于此方法设计出一套五轴成形装置,其中喷嘴具有二个旋转自由度,工作台具有三个平动自由度,具有很好的柔性,非常适合多品种小批量产品的生产和新产品的试制。对高压水射流柔性渐进成形装置的各个子系统进行了详细的介绍,并对成形过程提出了一种新的仿真分析方法,将比较复杂的流固耦合问题,简化为加载等效压强的方法。最后通过单点水柱成形的仿真分析,揭示射流压力和板厚对金属板材成形性能的影响。     

Tool path programming optimization for incremental sheet forming applications

Incremental sheet forming is an emerging process to manufacture sheet metal parts that is well adapted for small batch production or prototypes. The adjustment time is short, as it is sufficient to modify the tool motions to optimize the manufacturing process. Tool path generation therefore becomes a key topic linked to incremental sheet forming, and process characteristics ask for dedicated tool paths. Hence, this paper first discusses the impact of tool path types and other programming parameters on process implementation through an experimental campaign performed on a parallel kinematics machine tool. Then, a new approach to generate and control Intelligent CAM programmed tool paths is proposed. The major purpose of this innovative concept is to use process constraints for programming and controlling the tool path, which are adapted during the running of the CNC program according to real-time process data evaluation. Validation studies and an industrial implementation are finally presented to assess the efficiency of the proposed approach.     

Fracture in sheet metal forming: Effect of ductile damage evolution

This work deals with the virtual simulation of the sheet metal stamping process. The main objective is to predict when and where the cracks can appear in the workpiece during the forming operation. A local approach based on the strong coupling between anisotropic elastoplasticity with mixed nonlinear work hardening (isotropic and kinematic) and an isotropic ductile damage is proposed. The theoretical and numerical aspects of the constitutive equations are, first, presented. The resolution of the resulting system of equations is carried out via a Vumat user material, using ABAQUS/Explicit finite element code. The results obtained, in the context of Swift’s benchmark deep-drawing test show the efficiency and the potential interest of the proposed damage model.