Sequential optimization and fuzzy reliability analysis for multidisciplinary systems

Structural and Multidisciplinary Optimization - To meet the rising demand for high reliability in complex multidisciplinary engineering systems, more attention has been paid to reliability-based...     

Sequential optimization and reliability assessment for multidisciplinary systems design

With higher reliability and safety requirements, reliability-based design has been increasingly applied in multidisciplinary design optimization (MDO). A direct integration of reliability-based design and MDO may present tremendous implementation and numerical difficulties. In this work, a methodology of sequential optimization and reliability assessment for MDO is proposed to improve the efficiency of reliability-based MDO. The central idea is to decouple the reliability analysis from MDO with sequential cycles of reliability analysis and deterministic MDO. The reliability analysis is based on the first-order reliability method (FORM). In the proposed method, the reliability analysis and the deterministic MDO use two MDO strategies, the multidisciplinary feasible approach and the individual disciplinary feasible approach. The effectiveness of the proposed method is illustrated with two example problems.     

Geometrically nonlinear finite element reliability analysis of structural systems. I: theory

This article reviews the theory of finite element reliability analysis of geometrically nonlinear elastic structures (GNS) based on the total lagrangian formulation. It also provides computer implementation developments and establishes the basis of understanding of the applications presented in the second part of this investigation. Because of the slenderness of GNS, the structural responses are nonlinear even if the strains are within the elastic range. For this reason, the nonlinear relationships between strains and displacements should be considered. Since the failure surface is nonlinear, this study reviews the evaluation of structural reliability of GNS by using both first-order and second-order reliability methods. To evaluate the structural reliability, the linkage of system reliability analysis program RELSYS with the finite element analysis program (FEAP) is presented. The computer code RELSYS–FEAP is readily applicable to the evaluation of system reliability of GNS.     

Geometrically nonlinear finite element reliability analysis of structural systems. II: applications

This is the second part of an investigation on finite element reliability analysis of geometrically nonlinear elastic structures (GNS). This study concentrates on applications. The linkage code RELSYS-FEAP presented in the companion paper is used for finding both component and system reliabilities of GNS. Structural reliabilities are evaluated for both geometrically linear and nonlinear elastic behaviors. Two geometrically nonlinear applications are presented, including a truss and a suspended structure. The stress and displacement reliabilities of the truss are computed considering both geometrically linear and nonlinear elastic behaviors. The system reliability of a geometrically nonlinear suspended structure is evaluated. The structure is modeled as a series of parallel subsystems according to three system failure criteria. The effects of correlation between loads, correlation between resistances, and material behavior (brittle or ductile) are evaluated and discussed. Finally, displacement reliability indices of the suspended structure are computed.     

A Lyapunov approach to analysis of discrete singular systems

In this paper, a new type generalized Lyapunov equation for discrete singular systems is proposed. Then it is applied to study problems such as pole clustering, controllability and observability for discrete singular systems. First, some necessary and sufficient conditions for pole clustering are derived via the solution of this new type Lyapunov equation. Further, the relationship between the solution of the Lyapunov equation and structure properties of discrete singular systems will be investigated based on these results. Finally, a type of generalized Riccati equation is proposed and its solution is used to design state feedback law for discrete singular systems such that all the finite poles of the closed-loop systems are clustered into a specified disk.     

基于ANSYS的静力问题结构可靠性分析方法

分别使用ANSYS中的拉丁超立方样本蒙特卡罗法、中心复合设计样本响应面法以及Box—Behnken矩阵样本响应面法进行结构可靠性分析和计算．比较分析结果证明,对于静力问题结构可靠性分析,响应面分析结果仅在输出参数的均值、最大值以及最小值上逼近蒙特卡罗法结果,确定目标的可靠度以及输出参数标准差结果偏差较大;对于灵敏度分析结果,仅有高灵敏度变量结果可信．     

用于软件可靠性分析的分解方法

随机Petri网(SPN)是一种有力的系统建模和分析工具.但SPN在应用中经常碰到状态空间爆炸问题.分解压缩技术是解决随机网状态空间指数性增长的有效方法之一.介绍了一种获得SPN可靠性模型瞬时状态的分解方法.该方法在保证评价和预测可靠性精确度的基础上,不仅能有效地降低可靠性描述与分析的复杂度,还扩大了分解压缩技术的适用范围.     

大规模存储系统可靠性参数最优化分析

在大规模存储系统中,数据的可靠性越来越受到人们的关注。已有的研究分析了在系统规模已知的条件下,某些系统参数,如副本分布策略、存储对象数目等,对可靠性的粗略影响,但较少提及它们的最优值或者最优组合。提出了一种基于对象粒度恢复的可靠性新模型;基于该模型,在分析三种主流的副本分布策略的基础上,分别计算出了各个系统参数的独立最优值及其组合最优值。与已有模型相比,该模型更易于求解,且获得了更加综合实用的最优值,这些最优参数值能直接有效地指导系统设计者构建更可靠的大规模存储系统。     

Modelling errors, entropy and the hydraulic reliability of water distribution systems

This paper reports on an investigation of the possible influence of modelling errors on the relationship between the entropy and hydraulic reliability of water distribution systems. The errors are due to minor differences between the design optimisation and subsequent simulation models, which lead to small discrepancies between the capacity of the network and the required supply. Pressure-dependent analysis was used for the hydraulic simulations. It is shown that any correlation between the redundancy or undercapacity due to the modelling errors and the hydraulic reliability is insignificant. The results, therefore, provide yet more evidence that the entropy-reliability relationship is strong.     

A delay-partitioning approach to the stability analysis of discrete-time systems

This paper revisits the problem of stability analysis for linear discrete-time systems with time-varying delay in the state. By utilizing the delay partitioning idea, new stability criteria are proposed in terms of linear matrix inequalities (LMIs). These conditions are developed based on a novel Lyapunov functional. In addition to delay dependence, the obtained conditions are also dependent on the partitioning size. We have also established that the conservatism of the conditions is a non-increasing function of the number of partitions. Numerical examples are given to illustrate the effectiveness and advantage of the proposed methods.