A WAVELET THRESHOLDING DENSITY-BASED ADAPTIVE IMPORTANCE SAMPING METHOD

提出了一种基于小波阈值密度估计的结构可靠性分析高效自适应重要抽样方法.该方法利用非线性小波收缩方法对结构失效域样本进行密度估计,并以此作为重要抽样密度进行可靠性分析.与传统基于核密度估计的重要抽样方法比,由于非线性小波阈值密度估计具有较好局部适应性和最优收敛速度,且克服了核密度估计中计算精度严重依赖于参数选择的缺陷,因此以较少的预抽样样本就能获得与传统方法相当的精度,有效提高计算效率.数值算例表明所提方法对工程中常遇到的多设计点及噪音功能函数可靠性问题具有良好适应性.     

基于凸模型的复杂多学科系统可靠性设计研究

复杂工程系统通常涉及到多个相互耦合的学科,而且其中往往存在不确定性因素。本文采用凸模型描述不确定性变量,将序列优化和可靠性评价方法应用于多学科可靠性优化之中,提出了一种新的多学科系统可靠性设计方法。在该方法中,可靠性分析采用功能度量法,多学科优化方法采用多学科可行方法或者二级系统一体化合成优化方法。数值算例和工程算例说明,该方法求解效率较常规嵌套求解方法效率高,为复杂工程系统的可靠性设计提供了一种新型求解算法。     

基于Nataf变换的层递响应面法分析结构可靠度

针对现有的随机响应面法(SRSM)和层递响应面法(CRSM)存在的局限性,本文结合预处理随机Krylov子空间法,建立了基于Nataf变换的向量型层递响应面法,并应用于含非高斯型互相关随机变量的结构可靠度分析。首先,利用预处理随机Krylov子空间的层递基向量近似展开结构的总体节点位移向量,建立向量型层递响应面;然后,根据Nataf变换建立非高斯型互相关随机变量与独立标准正态随机变量之间的关系式,将独立标准正态空间内由Hermite多项式的根组合形成的概率配点变换成非高斯空间内的概率配点,并通过回归分析确定层递响应面的待定系数。计算结果表明,本文建立的CRSM属于向量型响应面法,能较好地处理含非高斯型互相关随机变量的结构可靠度分析问题,计算精度和效率均较高,且具有良好的全域性。     

Nonparametric predictive reliability of series of voting systems

Nonparametric Predictive Inference (NPI) for system reliability reflects the dependence of reliabilities of similar components due to limited knowledge from testing. NPI has recently been presented for reliability of a single voting system consisting of multiple types of components. The components are all assumed to play the same role within the system, but with regard to their reliability components of different types are assumed to be independent. The information from tests is available per type of component. This paper presents NPI for systems with subsystems in a series structure, where all subsystems are voting systems and components of the same type can be in different subsystems. As NPI uses only few modelling assumptions, system reliability is quantified by lower and upper probabilities, reflecting the limited information in the test data. The results are illustrated by examples, which also illustrate important aspects of redundancy and diversity for system reliability.     

基于M~x/G/1排队模型的信息系统软件失效风险分析方法研究

研究首先对信息系统软件节点进行数学建模,然后根据M^x/G/1排队模型及分布函数,针对信息系统软件的可靠性,给出了由威胁利用软件脆弱性所导致的信息系统节点失效,以及由此所带来的损失风险计算模型,并以银行的柜面业务系统所安装的Windows和Linux操作系统为例,给出了详细的计算过程.风险分析模型突破了目前沿用的经典六因素模型,将系统可靠性的定量分析方法引入其中,从而有效的避免了风险分析方法中对主观因素的依赖.     

爆炸药间隙零门可靠性窗口分析

可靠性窗口的区间长度是爆炸药间隙零门设计过程中重点考虑的问题,它直接影响间隙零门能否成功作用.在固定装药密度和通道截面的情况下,将可靠性窗口问题转化为基于间隙长度的三元响应问题,并把窗口端点的阈值视为随机变量,给出了基于可靠性窗口两个端点的联合响应分布模型.为估计模型的参数,结合得分检验统计量,给出了判断三元响应分布中两阈值变量相关性的准则和模型参数估计方法.为了说明方法的有效性,结合试验数据,利用极大似然估计,给出了一类间隙零门可靠性窗口端点和区间长度的估计结果.     

An appropriate and systematized procedure for validating qualitative methods: Its application in the detection of sulfonamide residues in raw milk

The lack of well-established references for the validation of qualitative analyses and the increasing demand for reliable binary responses were the main motivating factors for this study. A detailed procedure for single-laboratory validation of qualitative methods is proposed. The experimental design and the tools for data analysis were based on the theoretical background, as well as the aspects of efficiency, convenience and simplicity. Four experimental steps were defined, as follows: (i) preliminary tests for the determination of the concentration range, (ii) a study of the rates, unreliability region, detection limit, and the accordance and concordance values, (iii) a study of the selectivity in the presence of known interferences, and (iv) a study of robustness. The applicability of the procedure was demonstrated by the validation of a qualitative commercial kit for detecting sulfonamide residues in raw milk using both the visual and instrumental reading techniques. Reliability rates of 100% were obtained for the blank samples. For the samples spiked with sulfamethazine at 10.8 and 108 μg L⁻¹ and with sulfadimethoxine or sulfathiazole at 10 and 100 μg L⁻¹, the reliability rates ranged from 93.3 to 100%. Selectivity was demonstrated using trimethoprim as a potential interferent. The method was considered robust for the factors of the temperature (54 and 58 °C) and time (6 and 10 min) for incubating the test strips. The estimated detection limits and unreliability regions confirmed the suitability of the kit for this purpose, based on the legislated residue limits.     

数控车床可靠性分配中的单准则排序方法

数控车床可靠性分配模型是一个层次结构,可靠性分配的关键技术是确定结构底层指标关于顶层目标的重要度排序,其前提条件是单准则排序已知.AHP通过构造"两两比较"的"1~9"比例标度判断矩阵A_n为单准则排序提供了合理的数据条件;但是基于A_n一致性检验的特征根排序法因临界值的确定缺乏必要理论基础而受到质疑.改进AHP的FAHP因为没有摆脱"一致性检验"的干扰所以改进并不成功.为了建立与"一致性"无关的单准则排序方法定义具有可加性的评分标度概念,通过标度转换将比例标度判断矩阵A_n转化为评分标度判断矩阵B_n,利用评分标度的可加性在准则C下对n个比较对象排序.因为B_n不是正矩阵所以不存在"一致性概念",因此基于评分标度判断矩阵的排序与"一致性"无关.     

修复率可变化的表决系统可靠性分析

研究了具有维修速率可变化的k/n(G)表决可修系统,其中部件的工作时间和修理时间均服从负指数分布.开始时,当系统中的故障部件数小于某一阈值L时,修理工以较低的维修率修理故障的部件.如果修理工修理工作进展不顺利,故障部件数增加到阈值L时,将立即以较快的速度修理故障部件,此状态一直持续到系统中没有故障部件为止.使用马尔可夫过程理论和分析方法,得到了系统可用度、故障频度、系统首次故障前的平均时间等指标的表达式.进一步,讨论了不同条件下系统相关指标随系统参数变化的情况,并通过对特殊情形的讨论数值验证了所得结果的正确性.     

Hierarchical differential evolution for minimal cut sets identification: Application to nuclear safety systems

In this paper, we present a Hierarchical Differential Evolution (HDE) algorithm for minimal cut set (mcs) identification of coherent and non-coherent Fault Trees (FTs). In realistic application of large-size systems, problems may be encountered in handling a large number of gates and events. In this work, to avoid any approximation, mcs identification is originally transformed into a hierarchical optimization problem, stated as the search for the minimum combination of cut sets that can guarantee the best coverage of all the minterms that make the system fail: during the first step of the iterative search, a multiple-population, parallel search policy is used to expedite the convergence of the second step of the exploration algorithm. The proposed hierarchical method is applied to the Reactor Protection System (RPS) of a Pressurized Water Reactor (PWR) and to the the Airlock System (AS) of a CANadian Deuterium Uranium (CANDU) reactor. Results are evaluated with respect to the accuracy and computational demand of the solution found.