面向集成化CAE软件开发的SiPESC研发工作进展

针对我国自主CAE软件发展缓慢的事实,根据现代工程领域的科学研究和产品研发对CAE建模、分析和设计能力提出的需求,研发自主的面向CAE工程与科学计算集成化软件平台SiPESC（Software Integration Platform for Engineering and Scientific Computation...     

Interactive-adaptive geometrically nonlinear analysis of shell structures

This paper presents an investigation of interactive-adaptive techniques for nonlinear finite element structural analysis. In particular, effective methods leading to reliable automated, finite element solutions of nonlinear shell problems are of primary interest here. This includes automated adaptive nonlinear solution procedures based on error estimation and adaptive step length control, reliable finite elements that account for finite deformations and finite rotations, three-dimensional finite element modeling, and an easy-to-use, easy-to-learn graphical user interface with three-dimensional graphics. A computational environment, which interactively couples a comprehensive geometric modeler, an automatic three-dimensional mesh generator and an advanced nonlinear finite element analysis program with real-time computer graphics and animation tools, is presented. Three examples illustrate the merit and potential of the approaches adopted here and confirm the feasibility of developing fully automated computer aided engineering environments.     

A mixed variational formulation for shape optimization of solids with contact conditions

This paper is concerned with the development of a mixed variational formulation and computational procedure for the shape optimization problem of linear elastic solids in possible contact with a rigid foundation. The objective is to minimize the maximum value of the von Mises equivalent stress in a body (non-differentiable objective function), subject to a constraint on its volume and bound constraints on the design. For design purposes, the contact boundary is considered fixed.A finite element model that is appropriate for the mixed formulation is utilized in the discretization of the state and adjoint state equations. An elliptical mesh generator was used to generate the finite element mesh at each new design. The computational model is tested in several example problems.     

Symbolic integration of multibody system dynamics with the finite element method

With the widespread use of computer-aided engineering (CAE) to solve computational mechanics problems, engineering design has become more accurate and efficient. The integration of the finite element method (FEM) and flexible multibody dynamics (FMD) is a typical application of computational mechanics. It constitutes an important contribution to engineering development, but its potential is restrained by numerical computation. Computational time is a critical factor that influences the efficiency and cost of design and analysis. The advent of symbolic computation enables faster simulation code, but the symbolic integration of FEM and FMD is at the initial stages. A general symbolic integration procedure is presented in this paper. The performance of the symbolic model is compared with models from the literature and numerically-based commercial software.     

Design parameterization and tool integration for CAD-based mechanism optimization

This paper presents an open and integrated tool environment that enables engineers to effectively search, in a CAD solid model form, for a mechanism design with optimal kinematic and dynamic performance. In order to demonstrate the feasibility of such an environment, design parameterization that supports capturing design intents in product solid models must be available, and advanced modeling, simulation, and optimization technologies implemented in engineering software tools must be incorporated. In this paper, the design parameterization capabilities developed previously have been applied to support design optimization of engineering products, including a High Mobility Multi-purpose Wheeled Vehicle (HMMWV). In the proposed environment, Pro/ENGINEER and SolidWorks are supported for product model representation, DADS (Dynamic Analysis and Design System) is employed for dynamic simulation of mechanical systems including ground vehicles, and DOT (Design Optimization Tool) is included for a batch mode design optimization. In addition to the commercial tools, a number of software modules have been implemented to support the integration; e.g., interface modules for data retrieval, and model update modules for updating CAD and simulation models in accordance with design changes. Note that in this research, the overall finite difference method has been adopted to support design sensitivity analysis.     

A computer algebra based finite element development environment

A finite element development environment based on the technical computing program Mathematica is described. The environment is used to automatically program standard element formulations and develop new elements with novel features. Source code can also be exported in a format compatible with commercial finite element program user-element facilities. The development environment is demonstrated for three mixed Petrov–Galerkin plane stress elements: a standard formulation, an advanced formulation incorporating rotational degrees of freedom and a standard formulation in which the stiffness matrix is integrated analytically, before being exported as ANSYS user elements. The results presented illustrate the accuracy of the standard mixed formulation element and the enhancement of performance when rotational degrees of freedom are added. Further, the analytically integrated element shows that computational requirements can be greatly reduced when analytical integration schemes are used in the formation.     

A knowledge base for finite element mesh design

The finite element method (FEM) is the most successful numerical method, that is used extensively by engineers to analyse stresses and deformations in physical structures. These structures should be represented as a finite element mesh. Defining an appropriate geometric mesh model that ensures low approximation errors and avoids unnecessary computational overheads is a very difficult and time consuming task. It is the major bottleneck in the FEM analysis process. The inductive logic programming system GOLEM has been employed to construct the rules for deciding about the appropriate mesh resolution. Five cylindrical mesh models have been used as a source of training examples. The evaluation of the resulting knowledge base shows that conditions in the domain are well represented by the rules, which specify the required number of the finite elements on the edges of the structures to be analysed using FEM. A comparison between the results obtained by this knowledge base and conventional mesh generation techniques confirms that the application of inductive logic programming is an effective approach to solving the problem of mesh design.     

A component-oriented software toolkit for patient-specific finite element model generation

A component-oriented software system, i.BioMech (image-based biomechanical modeling) is proposed for generation of patient-specific finite element model. It applies a systematic software engineering approach to patient/subject-specific meshing and assignment of material properties. The prototype program is based on the component object model (COM), which enables ease of combination of existing mesh generation algorithms and material property assignment schemes, and incorporation of new ones. It also facilitates utilization by other programming languages or platforms. Data input comprises a series of medical images captured from the patient. The output is a patient-specific finite element model for computational analysis using commercially available finite element software. The prototype software system provides a framework to compare the different finite element mesh generation methods as well as schemes for material property assignment. Our focus is on patient/subject-specific modeling of the human vertebrae.     

An in-core grid index for transferring finite element data across dissimilar meshes

The simulation of a manufacturing process chain with the finite element method requires the selection of an appropriate finite element solver, element type and mesh density for each process of the chain. When the simulation results of one step are needed in a subsequent one, they have to be interpolated and transferred to another model. This paper presents an in-core grid index that can be created on a mesh represented by a list of nodes/elements. Finite element data can thus be transferred across different models in a process chain by mapping nodes or elements in indexed meshes. For each nodal or integration point of the target mesh, the index on the source mesh is searched for a specific node or element satisfying certain conditions, based on the mapping method. The underlying space of an indexed mesh is decomposed into a grid of variable-sized cells. The index allows local searches to be performed in a small subset of the cells, instead of linear searches in the entire mesh which are computationally expensive. This work focuses on the implementation and computational efficiency of indexing, searching and mapping. An experimental evaluation on medium-sized meshes suggests that the combination of index creation and mapping using the index is much faster than mapping through sequential searches.     

Feature-based modeling for automatic mesh generation

Automatic meshing algorithms for finite element analysis are based on a computer understanding of the geometry of the part to be discretized. Current mesh generators understand the part as either a boundary representation, an octree, or a point set. A higher-level understanding of the part can be achieved by associating engineering significance and engineering data, such as loading and boundary conditions, with generic shapes in the part. This technique, called feature-based modeling, is a popular approach to integrating computer-aided design (CAD) and computer-aided manufacturing through the use of machinable shapes in the CAD model. It would seem that feature-based design also could aid in the finite element mesh generation process by making engineering information explicit in the model.This paper describes an approach to feature-based mesh generation. The feature representation of a fully functioning feature-based system that does automatic process planning and inspection was extended to include finite element mesh generation. This approach is based on a single feature representation that can be used for design, finite element analysis, process planning, and inspection of prismatic parts. The paper describes several advantages that features provide to the meshing process, such as improved point sets and a convenient method of simplifying the geometry of the model. Also discussed are possible extensions to features to enhance the finite element meshing process.     

Concepts and implementation of parallel finite element analysis

The design of complex engineering systems such as advanced aircraft structures and offshore platforms requires continually increasing levels of detail in supporting analysis. The finite element method is widely used as a computational method with which to model physical systems in various engineering problems. For detailed analyses of complex designs, structural models composed of several thousands of degrees of freedom are no longer uncommon. Such design activities require large order finite element and/or finite difference models and excessive computation demands in both calculation speed and information management. The computer simulation of the nonlinear dynamic response of structures and the implementation of parallel FEM systems on a high speed multiprocessor have received considerable attention in recent years. The driving forces of these activities included the reliable simulation of automotive and aircraft crash phenomena, and the increased performance of computers. Most existing major structural analysis software systems were designed 10–20 years ago and have been optimized for current sequential computers. Such systems often are not well structured to take maximum advantage of the recent and continuing revolution in parallel vector computing capabilities. These parallel vector computer architectures not only occur in the form of large supercomputers, but are now also occurring for minicomputers and even engineering workstations. To benefit from advances in parallel computers, software must be developed which takes maximum advantage of the parallel processing feature.     

Meshing complexity: predicting meshing difficulty for single part CAD models

This paper proposes a method for predicting the complexity of meshing computer aided design (CAD) geometries with unstructured, hexahedral, finite elements. Meshing complexity refers to the relative level of effort required to generate a valid finite element mesh on a given CAD geometry. A function is proposed to approximate the meshing complexity for single part CAD models. The function is dependent on a user defined element size as well as on data extracted from the geometry and topology of the CAD part. Several geometry and topology measures are proposed, which both characterize the shape of the CAD part and detect configurations that complicate mesh generation. Based on a test suite of CAD models, the function is demonstrated to be accurate within a certain range of error. The solution proposed here is intended to provide managers and users of meshing software a method of predicting the difficulty in meshing a CAD model. This will enable them to make decisions about model simplification and analysis approaches prior to mesh generation.     

齿轮齿根应力和轮齿变形的三维整轮仿真

使用高性能并行计算机和ANSYS有限元软件,通过精确产生齿根过渡曲线和齿轮三维实体模型,建立可靠的高精度的有限元网格模型和计算模型.使用三维20节点等参单元计算,仿真一个真实齿轮整体模型的三维齿根应力和轮齿变形.二维模型和三维等效模型的仿真计算误差和可靠性对比表明,该方法可为计算齿根应力和轮齿变形提供参考.     

Performance analysis tools applied to a finite element adaptive mesh free boundary seepage parallel algorithm

A finite element, adaptive mesh, free surface seepage parallel algorithm is studied using performance analysis tools in order to optimize its performance. The physical problem being solved is a free boundary seepage problem which is nonlinear and whose free surface is unknown a priori. A fixed domain formulation of the problem is discretized and the parallel solution algorithm is of successive over-relaxation type. During the iteration process there is message-passing of data between the processors in order to update the calculations along the interfaces of the decomposed domains. A key theoretical aspect of the approach is the application of a projection operator onto the positive solution domain. This operation has to be applied at each iteration at each computational point.The VAMPIR and PARAVER performance analysis software are used to analyze and understand the execution behavior of the parallel algorithm such as: communication patterns, processor load balance, computation versus communication ratios, timing characteristics, and processor idle time. This is all done by displays of post-mortem trace-files. Performance bottlenecks can easily be identified at the appropriate level of detail. This will numerically be demonstrated using example test data and comparisons of software capabilities that will be made using the Blue Horizon parallel computer at the San Diego Supercomputer Center.     

面向数据库的化工软件集成环境的设计

对于化工领域,用户若能够在一个软件集成环境上对现有的化工软件进行集成,则可以很大程度上节省用户软件二次开发或掌握集成技术所耗费的人力物力。本文试图研究开发一种化工软件集成的环境。利用Windows自身的特点,以及其管理应用程序的一般方法,设计了化工软件的集成环境。该集成环境由界面集成模块、代码集成模块、数据集成模块和数据库管理子系统4个模块组成,对于4个模块分别给出了界面集成策略、代码集成策略、数据集成策略、数据库和数据库管理子系统的建立策略。     

Adaptive finite element mesh triangulation using self-organizing neural networks

The finite element method is a computationally intensive method. Effective use of the method requires setting up the computational framework in an appropriate manner, which typically requires expertise. The computational cost of generating the mesh may be much lower, comparable, or in some cases higher than the cost associated with the numeric solver of the partial differential equations, depending on the application and the specific numeric scheme at hand.The aim of this paper is to present a mesh generation approach using the application of self-organizing artificial neural networks through adaptive finite element computations. The problem domain is initially constructed using the self-organizing neural networks. This domain is used as the background mesh which forms the input for finite element analysis and from which adaptive parameters are calculated through adaptivity analysis. Subsequently, self-organizing neural network is used again to adjust the location of randomly selected mesh nodes as is the coordinates of all nodes within a certain neighborhood of the chosen node. The adjustment is a movement of the selected nodes toward a specific input point on the mesh. Thus, based on the results obtained from the adaptivity analysis, the movement of nodal points adjusts the element sizes in a way that the concentration of elements will occur in the regions of high stresses. The methods and experiments developed here are for two-dimensional triangular elements but seem naturally extendible to quadrilateral elements.     

A general purpose adaptivity driver for FE software

This paper describes a tool that serves as an automatic mesh adaptivity driver program for general purpose finite element (FE) software packages. Many commercially available FE programs lack a feature to control the numerical solution's accuracy properly. Our tool implements a mesh adaptive method that, in conjunction with separate finite element software, allows one to fully automatically improve the quality of the numerical solution up to a user specified accuracy. We demonstrate the use of the package with selected computational examples performed with a commercial FE package, ANSYS, and with our FE program FEMEngine. Copyright © 2003 John Wiley & Sons, Ltd.