Continuous/discrete modeling and analysis of elastic planar multi-body systems

The modeling and analysis of continuous/discrete multi-body systems are described, with emphasis on applications to elastic planar closed-loop systems. Whereas the continuous formulations presented can be applied to simplified models (with less effort) to help isolate the dominant factors for parametric evaluations in preliminary analysis studies, on the other hand, the finite element formulations described are, in general, applicable for more complex geometries and larger problems. In this regard, an explicit self-starting velocity-based time integration architecture is employed for the numerical simulation of multi-body dynamics with several inherent attractive features. Numerical test cases for planar multi-body dynamic situations employing the Timoshenko beam theory are presented from a generalized viewpoint in conjunction with the present formulations to validate the applicability of the proposed formulations.     

An optimizing compiler for an SPAP architecture using AI tools

A methodology that allows users to efficiently bridge the gap between high-level language and low-level microcode when implementing intensive mathematical operations and manipulations algorithms is discussed. The use of an optimized special-purpose array processor (SPAP) architecture for numerical computation and a host microprocessor for nonnumerical computation operations is described. The advantages of the optimizing compiler, the target architecture, and the compiler's implementation using AI tools are examined     

Analysis of continuous beams on discrete elastic supports by the five moment equation

The analysis of continuous beams on discrete elastic supports is a complex problem frequently encountered in structural engineering. In structures of this type, the supports displace in direct proportion to the support reactions. These support displacements result in moment redistribution in the beam. The methods in current use for solving this type of problem arc generally complex and in most cases are developed for analysis of more complicated structures.This paper illustrates a technique for computer analysis of continuous beams on discrete elastic supports by the five moment equation. The objective is to present a viable example for electronic computation consistent with the nature of the problem, and which will tend to contribute to the basic understanding of the use of computers in reducing the amount of computation.The five moment equation is an extension of the familiar three moment equation and results in the same simple form of analysis. The solution of the five moment equation for the analysis of continuous beams on elastic supports permits direct determination of the redundant moments at the supports. The result of this simplified form provides practicing engineers with an efficient analysis easily handled on small office computers. For the student of civil engineering, the method illustrated will significantly contribute to development of effective early progress of programming skills.     

Evolutionary Computation in Structural Design

The paper provides the results of preliminary research on the application of evolutionary computation to integrated structural design in which a complex design support tool automatically conducts both conceptual and detailed design. In the paper, a brief overview of the state of the art in evolutionary computation and its applications to structural design is provided. Next, Inventor 2000 is described, a unique research and structural design tool developed by the authors at George Mason University that combines an evolutionary computation component with a system for wind forces analysis, and a system for the analysis, design and optimisation of steel structures. The paper also presents the results of four structural design experiments conducted with Inventor 2000. The objective of experiments was to investigate various forms of evolutionary computation as applied to structure design. Finally, the paper provides the initial research conclusions and recommendations for further research.     

Structural optimization and system dynamics

The paper presents an alternative solution methodology for the optimization of continuous structures described in terms of one spatial coordinate. Using a control systems state variable formulation for the structural model, Pontryagin's principle reduces the optimization problem to simultaneously satisfying the state, costate and optimality condition together with any constraints on the problem. System dynamics methodology is then used to obtain the numerical solution. This is achieved by constructing graphically a flow diagram representing the necessary optimality conditions; contraints are included through the use of logical relationships. The associated (DYNAMO) equations are then solved numerically as part of the standard system dynamics package.     

The stochastic central difference method in structural dynamics

The stochastic central difference method is introduced for the computation of response of complex structures, discretized by the finite element method, to stationary and nonstationary random excitations. The method can be regarded as the stochastic equivalent of the deterministic central difference scheme employed for the direct integration of the equations of motion of discretized structures in structural dynamics. A systematic procedure for the stability and accuracy analysis of the proposed stochastic central difference method is also presented. Applications and advantages of the latter are made and discussed.     

Parallel computation of manipulator inverse dynamics

In this article, parallel computation of manipulator inverse dynamics is investigated. A hierarchical graph-based mapping approach is devised to analyze the inherent parallelism in the Newton-Euler formulation at several computational levels, and to derive the features of an abstract architecture for exploitation of parallelism. At each level, a parallel algorithm represents the application of a parallel model of computation that transforms the computation into a graph whose structure defines the features of an abstract architecture, i.e., number of processors, communication structure, etc. Data flow analysis is employed to derive the time lower bound in the computation as well as the sequencing of the abstract architecture. The features of the target architecture are defined by optimization of the abstract architecture to exploit maximum parallelism while minimizing various overheads and architectural complexity. An algorithmically specialized, highly parallel, MIMD-SIMD architecture is designed and implemented that is capable of efficient exploitation of parallelism at several computational levels. The computation time of the Newton-Euler formulation for a 6-degree-of-freedom (dof) general manipulator is measured as 187 μs. The increase in computation time for each additional dof is 23 μs, which leads to a computation time of less than 500 μs, even for a 12-dof redundant arm.     

Identification of structural systems by neural networks

A method based on the use of neural networks is developed for the identification of systems encountered in the field of structural dynamics. The methodology is applied to the identification of linear and nonlinear dynamic systems such as the damped Duffing oscillator and the Van der Pol equation. The “generalization” ability of the neural networks is used to predict the response of the identified systems under deterministic and stochastic excitations. It is shown that neural networks provide high fidelity models of unknown structural dynamic systems, which are used in applications such as structural control, health monitoring of structures, earthquake engineering, etc.     

Fifth generation and VLSI architectures

Most Western Governments (USA, Japan, EEC, etc.) have now launched national programmes to develop computer systems for use in the 1990s. These so-called Fifth Generation computers are viewed as “knowledge” processing systems which support the symbolic computation underlying Artificial Intelligence applications. The major driving force in Fifth Generation computer design is to efficiently support very high level programming languages (i.e. VHLL architecture).

Historycally, however, commercial VHLL architectures have been largely unsuccesful. The driving force in computer designs has principally been advances in hardware which at the present time means architectures to exploit very large scale integration (i.e. VLSI architecture).

This paper examines VHLL architectures and VLSI architectures and their probable influences on Fifth Generation computers. Interestingly the major problem for both architecture classes is parallelism; how to orchestrate a single parallel computation so that it can be distributed across an ensemble of processors.     

基于WebGIS的交互式缓冲区分析查询

基于ArcGIS的WebGIS汕头环境保护局建设了污染源管理系统。环保局在环境规划和污染源控制工作中经常需要交互式的缓冲区分析。首先介绍基于Flash的WebGIS的优势,接着讲述汕头环保局污染源管理系统的体系结构,包括污染源导入、非地理相关表的操作和地理信息系统的体系结构,再详细介绍用ArcGIS API for Flex实现缓冲区分析的三个步骤:用DrawTool动态绘制地理要素作为缓冲区分析的输入参数,用GeometryService进行缓冲区计算,查询计算结果内的点污染源。     

GO法在软件体系结构可靠性分析中的应用

GO法是一种系统可靠性分析方法,可将GO法应用到软件体系结构的可靠性分析中。根据软件体系结构自身的特点及构件之间的关系,分别建立了软件体系结构六种基本结构的GO模型,并进行了定量GO运算。通过一个实例,说明了应用GO法对软件体系结构的可靠性进行分析的全过程。实践表明:运用定量GO运算能够方便地计算出整个软件体系结构的可靠度,通过定性GO分析还可评估各构件及连接件的重要性,对后期系统的设计与开发具有一定的指导意义。     

A formal approach to automating conceptual structural design,Part I: Methology

In the conceptual phase of structural design a designer develops and investigates many potential alternatives for safe and economic transfer of loads that are to be carried by the structure. A methodology for automating conceptual structural design is presented in this paper. Some of the salient aspects of the methodology are: (1) an explicit representation of the structural form, function, and behavior; (2) modeling the structural engineering domain as well as the strategy employed by expert designers; (3) usingcost/value ratio as an intrinsic measure of the merit of a design alternative; and (4) reduced reliance on heuristics with more emphasis on first principles and fundamental knowledge. The categories of knowledge that need to be represented in a computer system to support the reasoning for conceptual structural design are identified. The use of such knowledge is illustrated through examples based on several different types of structures. A constraint classification system (to organize the constraints that arise from structural and exogenous considerations) is also proposed.     

Sensitivity analysis for hysteretic dynamic systems: Theory and applications

Sensitivity analysis — calculation of the rate of change of response variables with respect to design variables — is a critical component in the process of re-analysis for improvement of trial designs or in seeking an optimum design. This paper presents necessary theorems and provides details for numerical computation of sensitivity matrices for spatially discretized structural systems subjected to dynamic excitation. General results are presented for nonlinear (hysteretic) structures, and explicit numerical examples illustrate the methodology applied to multi-story shear frames whose force-displacement relationship is bilinear hysteretic.     

Reduced-order forward dynamics of multiclosed-loop systems

In this work, a reduced-order forward dynamics of multiclosed-loop systems is proposed by exploiting the associated inherent kinematic constraints at acceleration level. First, a closed-loop system is divided into an equivalent open architecture consisting of several serial and tree-type subsystems by introducing cuts at appropriate joints. The resulting cut joints are replaced by appropriate constraint forces also referred to as Lagrange multipliers. Next, for each subsystem, the governing equations of motion are derived in terms of the Lagrange multipliers, which are based on the Newton–Euler formulation coupled with the concept of Decoupled Natural Orthogonal Complement (DeNOC) matrices, introduced elsewhere. In the proposed forward dynamics formulation, Lagrange multipliers are calculated sequentially at the subsystem level, and later treated as external forces to the resulting serial or tree-type systems of the original closed-loop system, for the recursive computation of joint accelerations. Note that such subsystem-level treatment allows one to use already existing algorithms for serial and tree-type systems. Hence, one can perform the dynamic analyses relatively quickly without rewriting the complete model of the closed-loop system at hand. The proposed methodology is in contrast to the conventional approaches, where the Lagrange multipliers are calculated together at the system level or simultaneously along with the joint accelerations, both of which incur higher order computational complexities, and thereby a greater number of arithmetic operations. Due to the smaller size of matrices involved in evaluating Lagrange multipliers in the proposed methodology, and the recursive computation of the joint accelerations, the overall numerical performances like computational efficiency, etc., are likely to improve. The proposed reduced-order forward dynamics formulation is illustrated with two multiclosed-loop systems, namely, a 7-bar carpet scrapping mechanism and a 3-RRR parallel manipulator.     

一种基于XML的系统结构管理模型

介绍了在基于多角度的系统结构描述和与接口有关的系统结构外部特性这两个概念的基础上开发的一个实用工具,用来支持系统结构的管理。同时,又进一步地将XML用于所开发的模型工具中,用XML来描述、管理和分析系统结构视图、系统接口和有关的部件连接关系,并使之适用于分布式系统的设计。文章结合实例,阐述了将系统结构的研究与XML相结合的研究思路与实现方法。     

Knowledge-based control for finite element analysis

This paper shows that control logic may be separated from analysis software and that a knowledge-based expert system can use this logic to perform interactive computation. Heuristics that control a simple interactive finite element analysis program are represented using a rule-based format and are used by a goal-driven logic processor to invoke analysis activity.Traditional algorithm-oriented control and the proposed knowledge-based control are compared in a simple displacement computation scenario to identify the advantages/disadvantages of the two approaches. General activities and constraints, practical methods of reasoning and representation, and knowledge-based expert systems are discussed with emphasis on applications to interactive finite element analysis.An analysis control expert system has been developed for use in the numerical analysis of two-dimensional linear problems in solid and structural mechanics. An example problem is used to clarify the methods used to direct activity and to identify the problems associated with conditional task processing for interactive analysis.The main difference between the analysis program described in this paper and conventional analysis programs is related to the control architecture. The general conclusion of this paper is that knowledge-based control is more effective and flexible than algorithm-oriented control.     

Full resources utilization seismic design of irregular structures using multiple tuned mass dampers

This paper presents a methodology for the design of peripheral multiple tuned mass dampers (MTMD) in 3D irregular buildings. A Performance-Based Design (PBD) control strategy is proposed to reduce structural response to a desired acceptable level. Therefore, a limit is assigned to the accelerations experienced at the floors’ edges for a specific seismic hazard. In parallel, an attempt is made to keep the total mass of the added TMDs to its lowest possible level. The formulation of the design methodology relies on full utilization of control resources as presented herein; hence, a two stage iterative analysis/redesign procedure that is based on analysis tools is developed. The solution is compared to a formal gradient-based optimization solution, showing that the solution obtained by the analysis/redesign process is close to optimal, while it is much more computationally efficient than formal optimization and requires no gradient computation. The methodology applies to all types of structural irregularities, which allows its application in a practical design process of any structure.     

The stochastic finite-element method

A generic stochastic finite-element method for modeling structures is proposed as a means to analyze and design structures in a probabilistic framework. Stochastic differential and difference equation theory is applied in structures discretized with the finite-element methodology.Transient structural loads, idealized as stochastic processes, are incorporated into finite-element dynamic models with uncertain parameters. An estimate of the probability of failure based on known and established procedures in second-moment reliability analysis can be made with the aid of a transformation to gaussian space of the random variables that define structural reliability.The stochastic finite-element method will facilitate the use of probabilistic mathematical structural models for structural code development or design of important structures. It will also permit better estimation of structural reliability, which, when combined with risk analysis, could lead to improved decision-making processes.     

A Methodology for Programming Scalable Architectures

In scalable concurrent architectures, the performance of a parallel algorithm depends on the resource management policies used. Such policies determine, for example, how data is partitioned and distributed and how processes are scheduled. In particular, the performance of a parallel algorithm obtained by using a particular policy can be affected by increasing the size of the architecture or the input. In order to support scalability, we are developing a methodology for modular specification of partition and distribution strategies (PDSs). As a consequence, a PDS may be changed without modifying the code specifying the logic of a parallel algorithm. We illustrate our methodology for parallel algorithms that use dynamic data structures.