Geometry representation issues associated with p-version finite element computations

This paper addresses issues related to accurate geometry representation for p-version finite elements on curved three-dimensional domains. Specific options to account for domain geometry information during element-level computation are identified. Accuracy requirements on the geometry related approximations to preserve the optimal rate of finite element error convergence for second-order elliptic boundary value problems are given. An element geometric mapping scheme based on blending the exact shape of the domain boundary is described that can either be used directly during element integrations, or used to construct element-level geometric approximations of required accuracy. Smoothness issues of the rational blends on simplex topologies are discussed and a numerical example based on the solution of Poisson's equation in three dimensions is presented to illustrate the impact of the rational blends on the optimal rate of finite element error convergence.     

The generation of airframe finite element models using an expert system

This paper presents an expert system-based procedure for the creation of airframe finite element models from the geometric model available in a computer-aided design system. The objectives of the approach presented is the computerization of a process that is currently carried out in a semimanual manner, include previous modeling knowledge into the system, and provide a clear path for an ever-increasing level of automation in the process of creating analysis models for this class of structure. A main feature of the system developed is the combined use of algorithmic procedures and expert knowledge operating on data provided by previously run design software to produce an entirely different form of model to be used as input to a numerical analysis.     

Free-Form Solid Modeling with Trimmed Surface Patches

Solid modelers store a more complete representation than wireframe or surtace modelers. This completeness permits the automation of such tasks as interference analysis, mass property calculation, and finite element mesh generation. But the denser information content and complex algorithms needed to perform these tasks complicate the support of free-form geometry, especially Boolean operations. Consequently, the high degree of geometric coverage traditionally found in surface modeling systems has not, for the most part, been equaled in modern solid modelers. This article explores some of the difficulties encountered in Boolean combinations of free-from solids and presents a geometric representation designed to circumvent them.     

Octree-based automatic mesh generation for non-manifold domains

Automatic mesh generation within the context of non-manifold geometric models is far from a commercial reality. While manifold objects are the most commonly encountered domains in many applications, other applications such as those requiring multiple material models and mixedmodel representations (combination of 1-D, 2-D and 3-D domains) fall beyond the realm of the existing automatic meshing procedures as they require a non-conventional modeling enviroment, namely the non-manifold topology (NMT) based environment. This paper focuses on automatic mesh generation issues in the context of two such applications: (i) finite element modeling for multiple material models and (ii) geometric abstractions requiring a mixed-model representation. Specifically, the paper describes a geometry utility system, built around an NMT data structure and geometry-based meshing algorithms that ensure the validity of the mesh for non-manifold domains.GE Consulting Services.     

A hybrid and automated approach to adapt geometry model for CAD/CAE integration

Traditional adaption of CAD geometry, which plays an important role in generating effective and fit-for-purpose finite element models, is usually carried out manually and optionally with excessive dependence on engineer’s experience. Automatic and efficient geometry modification before simulation evidently improves design efficiency and quality, and cuts down product life cycle. This paper represents an automatic approach to generate simplified and idealized geometry models for CAE simulation, which consists of hybrid model simplification criteria, feature-based model simplification, and simulation intent driven geometry modification. Hybrid adaption criteria takes detailed features geometric dimension, geometry topology, design intent into consideration synthetically. Simulation intent-driven modification with the help of virtual topology operators helps to deal with geometry at a higher level to get an ameliorative boundary for mesh without perturbing the original design model with constructing history for down-stream manufacture-oriented application, such as machining feature recognition and process planning. Development of plug-in toolkit guarantees automation of the simplification process and helps generate simulation-fitted geometry for subsequent analysis and simulation process. Prototype system and cases are implemented to demonstrate the result and efficiency of the proposed approach.     

Finite element modeling within an integrated geometric modeling environment: part I—Mesh generation

This is the first of a two part paper that addresses the integration of finite element modeling and geometric modeling. Instead of considering the integration of currently available systems, this paper addresses both modeling techniques in general terms and identifies the functions that are needed to integrate them, taking full advantage of the capabilities of both. A set of geometric communication operators are identified and defined for use in carrying out this integration process. This first part considers the integration of geometric modeling and mesh generation, whereas the second part considers the specification of analysis attributes, accounting for domain differences between the geometric and finite element models and generating finite element models using element types that are of a lesser dimension than the geometry they represent.     

High-level operations dedicated to the integration of mechanical analysis within a design process

Here we present the high-level operators of the Mechanical Analysis Module, which is a software architecture dedicated to a better integration of the structural analysis phase within an integrated Computer-Aided Design environment. This generic module is independent of the mechanical analysis method used, and takes place in a distributed software architecture of an integrated design environment. The paper shows that the mechanical operators defined are split among geometric and mechanical treatments in order to enforce this distributed architecture. Thus, the interface between the geometric treatments and the mechanical analysis environment shows the adequacy of the boolean operators when used with mechanical analysis treatments. However, this is demonstrated for a restricted domain of the mechanical analysis, and open ended questions still exist as to when the geometry of the models is diversified. Also, requirements for new geometric treatments and extensions of the current geometric representation are listed.     

An object-oriented blackboard based approach for automated finite element modeling and analysis of multichip modules

This paper addresses the application of the blackboard system architecture and object-oriented data abstraction techniques to the domain of finite element modeling and analysis. Specifically, a hierarchical object-oriented database was used to represent the physical system at different levels of abstraction including the user-defined physical system level, a computer-generated, simplified physical model level, and the finite element model level. Object link relationships within a given abstraction level and across different abstraction levels resulted in seamless bidirectional information exchange. The blackboard system architecture employed provided a framework for distributed cooperative problem solving, for the application of simplifying domain-specific modeling assumptions, and for integrating the various software modules that are involved in the entire finite element modeling and analysis process. These methodologies were implemented in a prototype computational tool calledIMCMA theIntelligentMultichipModuleAnalyzer. An example illustrates howIMCMA automates finite element thermal analysis of small integrated circuit features in multichip modules through a two-step finite element submodeling process.     

Towards Realistic Automated 3D Modelling of Metal Forming Problems

This paper focuses on the issues dealing with automation of the 3D modelling of forming processes, specifically addressing (i) automatic remeshing of the deformed workpiece, (ii) the use of the CAD geometry of die for contact checks (within the analysis), and (iii) curvature compensation of nodes on the free surface to make the simulations more realistic. The procedures developed have been used with commercial software products including a CAD system, finite element solver and an automatic mesh generator to demonstrate the modelling of two forging processes.     

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.     

Finite element mesh generation

The capabilities of a geometric modeller are extended towards finite element analysis by a mesh generator which extracts all its geometric and topological information from the model. A coarse mesh is created and subsequently refined to a suitable finite element mesh, which accomodates material properties, loadcase and analysis requirements. The mesh may be optimized by adaptive refinement, ie according to estimates of the discretization errors.A survey of research and development in geometric modelling and finite element analysis is presented, then an implementation of a mesh generator for 3D curvilinear and solid objects is described in detail.     

Variational geometry: A new method for modifying part geometry for finite element analysis

Interactive graphic methods have the potential to significantly reduce the cost associated with pre- and post-processing of finite element analyses. One area of particular importance is the creation and modification of part geometry.

This paper describes a powerful method for modification of geometry for finite element analysis pre-processors. The method, called “Variational Geometry”, uses a single representation to describe the entire family of geometries that share a generic shape.

A solid geometric model of a component is defined with respect to a set of scalar parameters. Dimensions, such as those which appear on a mechanical drawing, are treated as constraints on the permissible values of these parameters. Constraints on the geometry are expressed as a set of non-linear algebraic equations. The values of the parameters and hence the geometry may be determined by solving the set of non-linear constraint equations.

A procedure for minimizing the computational requirements is presented. For a part with n degrees of freedom, the solution time is shown to be O(n).     

Intelligent finite element mesh generation

A knowledge-based and automatic finite element mesh generator (INTELMESH) for two-dimensional linear elasticity problems is presented. Unlike other approaches, the proposed technique incorporates the information about the object geometry as well as the boundary and loading conditions to generate an a priori finite element mesh which is more refined around the critical regions of the problem domain. INTELMESH uses a blackboard architecture expert system and the new concept of substracting to locate the critical regions in the domain and to assign priority and mesh size to them. This involves the decomposition of the original structure into substructures (or primitives) for which an initial and approximate analysis can be performed by using analytical solutions and heuristics. It then uses the concept of wave propagation to generate graded nodes in the whole domain with proper density distribution. INTELMESH is fully automatic and allows the user to define the problem domain with minimum amount of input such as object geometry and boundary and loading conditions. Once nodes have been generated for the entire domain, they are automatically connected to form well-shaped triangular elements ensuring the Delaunay property. Several examples are presented and discussed. When incorporated into and compared with the traditional approach to the adaptive finite element analysis, it is expected that the proposed approach, which starts the process with near optimal initial meshes, will be more accurate and efficient.     

Finite element analysis of spiral strands with different shapes subjected to axial loads

In this paper a new mathematical geometric model of spiral one or two-layered oval wire strands are proposed and an accurate computational two-layered oval strand 3D solid model, which is used for a finite element analysis, is presented. The three dimensional curve geometry of wires axes in the individual layers of the oval strand consists of straight linear and helical segments. The present geometric model fully considers the spatial configuration of individual wires in the right and left hand lay strand. Derived geometric equations were used for the generation of accurate 3D geometric and computational models for different types of strands. This study develops 3D finite element models of two-layer spiral round, triangular and oval strands subjected to axial loads using ABAQUS/Explicit software. Accurate modelling and understanding of their mechanical behaviour is complicated due to the complex contact interactions and conditions that exist between individual spirally wound wires. Comparisons of predicted responses for the strands with different shapes and constructions are presented. Resultant stress and/or deformation behaviours are discussed.     

Analysis automation with paving: A new quadrilateral meshing technique

This paper describes the impact of paving, a new automatic mesh generation algorithm, on the analysis portion of the design process. Paving generates an all-quadrilateral mesh in arbitrary 2D geometries. The paving technique significantly impacts the analysis process by drastically reducing the time and expertise requirements of traditional mesh generation. Paving produces a high quality mesh based on geometric boundary definitions and user specified element sizing constraints. In this paper we describe the paving algorithm, discuss varying aspects of the impact of the technique on design automation, and elaborate on current research into 3D all-hexahedral mesh generation.     

A new scheme for mesh generation and mesh refinement using graph theory

There are an extensive number of algorithms available from graph theory, some of which, for problems with geometric content, make graphs an attractive framework in which to model an object from its geometry to its discretization into a finite element mesh. This paper presents a new scheme for finite element mesh generation and mesh refinement using concepts from graph theory. This new technique, which is suitable for an interactive graphical environment, can also be used efficiently for fully automatic remeshing in association with self-adaptive schemes. Problems of mesh refinement around holes and local mesh refinement are treated. The suitability of the algorithms presented in this paper is demonstrated by some examples.     

Realization of an integrated structural design process: analysis-suitable geometric modelling and isogeometric analysis

Increasing complexity in structural shapes, the need for more detailed and precise numerical simulations, and shorter product development times request a tightly connected interaction within the design software environment since both fields, geometric design and structural analysis, rely on the results of each other. Therefore, this paper proposes an integrated design process, which is predicated on a NURBS-based CAD environment as well as on the NURBS-based isogeometric analysis, and substantiates in a mechanical point of view. The presented investigations are concentrated on thin-walled structures. In this paper several issues, e.g. continuity conditions associated with the applied finite element type, arising from the increased challenges for the geometric modelling within an integrated design process are identified and solution strategies are discussed. Furthermore, general analysis-aware modelling guidelines are derived. The paper concludes by exemplifying the complete integrated structural design process for a structural part.     

电子商务安全体系结构

1 引言电子商务将成为21世纪人类对信息世界关注的一个焦点,也将是网络应用中极为重要的一个发展方向。但是,网络欺诈、窃听、病毒和非法入侵都在威胁着电子商务的使用。电子商务安全技术是电子商务得以推广和应用的关键,是必须考虑的核心问题。同时,由于安全技术的特殊性,以及出于别国封锁和自身安全性的考虑,安全技术必须自主研究。随着我国电子商务的发展,电子商务安全技术将会有巨大的市场需     

Integration of topology and shape optimization for design of structural components

This paper presents an integrated approach that supports the topology optimization and CAD-based shape optimization. The main contribution of the paper is using the geometric reconstruction technique that is mathematically sound and error bounded for creating solid models of the topologically optimized structures with smooth geometric boundary. This geometric reconstruction method extends the integration to 3-D applications. In addition, commercial Computer-Aided Design (CAD), finite element analysis (FEA), optimization, and application software tools are incorporated to support the integrated optimization process. The integration is carried out by first converting the geometry of the topologically optimized structure into smooth and parametric B-spline curves and surfaces. The B-spline curves and surfaces are then imported into a parametric CAD environment to build solid models of the structure. The control point movements of the B-spline curves or surfaces are defined as design variables for shape optimization, in which CAD-based design velocity field computations, design sensitivity analysis (DSA), and nonlinear programming are performed. Both 2-D plane stress and 3-D solid examples are presented to demonstrate the proposed approach. Received January 27, 2000 Communicated by J. Sobieski