Reliability analysis of repairable systems using stochastic point processes

In order to analyze the failure data from repairable systems, the homogeneous Poisson process(HPP) is usually used. In general, HPP cannot be applied to analyze the entire life cycle of a complex, re-pairable system because the rate of occurrence of failures (ROCOF) of the system changes over time rather thanremains stable. However, from a practical point of view, it is always preferred to apply the simplest methodto address problems and to obtain useful practical results. Therefore, we attempted to use the HPP model toanalyze the failure data from real repairable systems. A graphic method and the Laplace test were also usedin the analysis. Results of numerical applications show that the HPP model may be a useful tool for the entirelife cycle of repairable systems.     

预应力高强混凝土T梁非线性结构行为研究

结合高强混凝土的特点，考虑材料非线性影响，计算了预应力高强混凝土T梁的极限承载力。在非线性有限元分析中，提出了合适的预应力钢筋建模方法。选择了适合于预应力高强混凝土梁非线性分析的一些基本理论，主要包括混凝土和钢筋的应力应变关系、整体式有限元模型、混凝土的破坏准则。计算结果表明：这些方法对预应力高强混凝土梁的非线性分析具有良好的适应性。基于上述理论，对影响预应力高强混凝土承载力的主要参数进行了对比分析，其结果可供工程设计参考使用。     

机车车辆运行平稳性指数的估测方法

运行平稳性是机车车辆的重要指标。一般而言,机车车辆运行平稳性随着速度提高而下降。为了便于设计我国高速铁路机车车辆,本文提出一种估测机车车辆运行平稳性的方法,作为机车车辆在设计过程中优化结构和方案比较的手段。本文以东风9内燃机车为例,分析了各种速度下的平稳性指数,并比较了线性模型和非线性模型的分析结果。     

树状结构网络在列车状态监测中的应用

为确保大数据量下列车状态数据传输有序、传输错误可修复,建立了列车状态监测设备树状组网模型,分析了树状拓扑列车在途监测系统应用的可行性,继而给出了支持自由挂载的车载设备组网算法,实现了基于以太网的数据传输和路由数据结构与算法在NS-2工具上的建模.仿真结果表明,树状网络延时主要受制于发送端与接收端所在网络的深度,相对于EXP流量模型和使用TCP协议,在树状网络中使用CBR流量模型与UDP协议能够获得更好的性能.     

随机选择修理工且修理延迟的可修系统的可靠性分析

研究了可随机选择修理工且修理延迟的可修系统．假定系统的寿命、延迟修理时间和修理时间均为广义指数分布．通过引进补充变量法并利用广义马尔可夫过程和拉普拉斯变换方法求出了系统的可用度、可靠度、维修频度和系统等待修理的概率等重要可靠性指标．     

推力桩非线性传力机理和计算模型的探讨

本文在分析推力桩非线性传力机理的基础上,提出了用微分方程式表达的计算推力桩非线性过程的系列化模型,并通过实例计算,说明能得到颇为满意的结果。     

3D Nonlinear Numerical Simulation of Intact and Debonded Reinforced Concrete Beams

To study the behaviour of reinforced concrete (RC) structures with sections of concrete removed and the reinforcement exposed, 3D nonlinear numerical analysis was performed upon both intact and debonded RC beams by using finite element techniques. The deformational characteristics and the ultimate loads were obtained through numerical models, as well as crack and stress distributions. The failure modes can also be deduced from computational results. Compared with intact beams, the normal assumptions of plane section behaviour is not hold true and the patterns of stress and strain are different in debonded RC beams. The numerical results show good consistency with experimental data. This kind of numerical simulation is a supplement to existing codes.     

基于形态学分形维数的输电线路故障选相方法

输电线路故障信号是一种典型的非线性信号,分形几何理论为描述非线性故障信号的特性提供了一个有力的分析工具。针对传统分形维数的局限性,本文提出了一种基于局域均值分解（local mean decomposition,LMD）-形态学的分形维数-Elman神经网络的输电线路故障选相新方法。该方法通过对故障电流进行相模转换后,对单一线模分量进行LMD分解得到若干乘积函数（product function,PF）分量,然后选取前4个PF分量进行数学形态学的分形维数估计,最后形成特征向量作为Elman神经网络的输入参数。仿真试验表明：提出的故障分类识别方法能快速、准确地识别各类故障,并且不易受故障初始角、故障位置和过渡电阻的影响,与传统的BP神经网络相比,Elman神经网络具有更好的效果,为准确判断输电线路故障选相提供了一种快速有效的新方法。     

考虑初始空隙压密的岩石变形全过程本构模型

为了建立能够准确模拟岩石变形全过程的本构模型,深入分析了现有统计损伤模型难以描述岩石初始非线性变形阶段的局限性.综合考虑岩石的变形机理,将岩石抽象为由空隙和骨架组成的材料,分析了岩石变形及空隙与骨架两部分变形之间的关系,提出了空隙应变比K的概念;利用岩石三轴试验结果,提出了岩石骨架和空隙两部分应变的计算方法,推导了K的...     

带劲性钢筋混凝土边框低剪力墙的试验研究

通过对４个劲性混凝土及１个钢筋混凝土边框低剪力墙的试验研究，探讨了低剪力墙的破坏特征及抗震性能，提出了劲性混凝土边框低剪力墙的震后可修复性。     

A New Nonlinear Yield Criterion

Introduction　　 The yield criteria and strength theories of ma-terials undercombined stresses are importantfoun-dations in the mechanics of solids and the strengthof structures.　　 Two presently popular yield criteria had beenproposed,i.e.those of Tresca and Von Mises.Since then yield criteria have been studied by anumber of investigators,i.e twin- shear stressyield criterion[1] ,energy based yield criterion[2 ] ,anisotropic criterion[3 ] ,Hoek- Brown criterion[4] .However,any conceivable …     

Estimation of Load-Induced Damage and Repair Cost in Post-Tensioned Concrete Rocking Walls

Post-tensioned concrete rocking walls might be used to avoid severe seismic damage at the base of structural walls, decrease residual drift, and lessen post-earthquake repair costs. The prediction of load-induced damage to the rocking wall resulting from seismic loading can provide an extremely valuable tool to evaluate the status and safety of structural concrete walls following earthquakes. In this study, the behavior and the damage state of monolithic, self-centering, rocking walls, as a new type of concrete rocking wall, are investigated. The nonlinear mechanical behavior of the wall is first modeled numerically, and subsequently the mechanical parameters from the numerical simulation are used to generate the local damage index. The results from the damage index model are compared with the full-scale test results, confirming the viability of the numerically based damage index method for estimating the seismically induced damage in concrete walls. Moreover, the estimated damage can be utilized as a qualitative and quantitative scale to assess the status of the wall following seismic loading events. Finally, an equation is proposed to estimate the repair cost based on the predicted damage state for the studied structural system.     

Multi-Point and Multi-Interval Availabilities for Markov Repairable Systems with History-Dependent Up and Down States

A Markov repairable system with history-dependent up and down states is presented. The state space of the repairable system is divided into three sets, which are up states, down states and changeable states.Using aggregated stochastic processes, we can get the multi-interval availability and multi-point availability for the Markov repairable system. Finally, numerical examples are given to illustrate the obtained results.     

Numerical simulation to reliability analysis of fault-tolerant repairable system

In the traditional method for the reliability analysis of fault-tolerant system, the system structure is described by means of binary decision diagram (BDD) and Markov process, and then the reliability indexes are calculated. However, as the size of system augments, the size of state space will increase exponentially. Additionally, Markov approach requires that the failure and repair time of the components obey an exponential distribution. In this study, by combining dynamic fault tree (DFT) and numerical simulation based on the minimal sequence cut set (MSCS), a new method to evaluate reliability of fault-tolerant system with repairable components is proposed. The method presented does not depend on Markov model, so that it can effectively solve the problem of the state-space combination explosion. Moreover, it is suitable for systems whose failure and repair time obey an arbitrary distribution. Therefore, our method is more flexible than the traditional method. At last, an example is given to verify the method.     

结构动力抗震可靠度理论的研究进展

从状态变量模型、基本变量模型和实用简化模型3个方面,对结构动力抗震可靠度理论的研究进展系统地进行了总结与评述.针对状态变量模型,结合随机振动理论,将随机振动分析方法分为两类:第1类是面向数字特征的方法,主要解决结构的随机反应从基本随机变量空间到状态变量空间的统计矩演化问题;第2类是面向概率密度的方法,主要解决结构的随机反应从基本随机变量空间到状态变量空间的概率密度演化问题.分别评述了两类方法中的代表性方法:等价线性化方法和概率密度演化方法.针对基本变量模型,分别总结了考虑系统参数随机性的结构动力抗震可靠度分析方法,以及将动力可靠度问题转化为静力可靠度问题的理论和方法,对近年来提出的尾部等效线性化方法、子集模拟法、等价极值法等进行了对比分析.针对实用简化模型,总结评述了3种方法:基于随机地震动模拟-确定性时程分析的直接方法、基于一致危险性反应谱和等效非线性体系的简化方法、基于可靠度简化解析表达式与数值模拟的半解析方法.最后,对新近提出的结构整体抗震可靠度理论及其存在的问题进行了归纳分析,并从地震作用的输入模型、主要失效模式的搜索、结构的破坏准则、结构失效模式的多重性、结构的整体极限状态方程等方面给出了研究建议.      

公路高切坡分类及其破坏模式

目前,公路高切坡缺乏一个统一的分类,从而造成其破坏模式分析混乱,降低了公路高切坡治理的针对性和有效性.因此,根据岩体结构面的控制性及现场易识性原则,将公路高切坡分成3大类9小类.依据岩性及其组合、岩体结构、岩体强度、结构面间距、走向与边坡走向的关系、结构面倾角与坡角的关系等各种不同组合情况具体分析了公路高切坡可能破坏的具体模式.在此基础上,提出了楔形体-平面滑动破坏模式、崩塌-滑动破坏模式、滑动-拉裂型破坏模式及滑动-压裂型破坏模式等4种复合破坏模式,对高切坡的稳定性分析及潜在破坏面的识别具有指导意义.     

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交通尾气排放宏观模型是进行广域尾气排放估测的重要工具,其功能是计算国家和区域范围内的有交通排放产生的排放因子与排放清单。目前,中国尚缺乏自己的宏观尾气排放模型,利用国外模型进行尾气排放估算误差较大。基于国内自己的尾气排放数据,利用国外的部分模型数据作为必要的补充,提出并实现了中国宏观尾气排放模型的建模方法与程序设计。首先,在总结国外机动车尾气排放模型优缺点的基础上,确定基于中国城市交通环境的机动车尾气排放宏观模型的目标、结构和建模方法,并对模型关键模块的数据获取、数据分析以及计算流程进行了详细的研究。其次,利用Visual Basic对模型进行了程序开发。最后,对北京市2008年尾气排放对交通环境的影响进行预测,并将其预测结果与MOBILE预测结果进行对比分析。     

公路高切坡分类及其破坏模式

目前,公路高切坡缺乏一个统一的分类,从而造成其破坏模式分析混乱,降低了公路高切坡治理的针对性和有效性.因此,根据岩体结构面的控制性及现场易识性原则,将公路高切坡分成3大类9小类.依据岩性及其组合、岩体结构、岩体强度、结构面间距、走向与边坡走向的关系、结构面倾角与坡角的关系等各种不同组合情况具体分析了公路高切坡可能破坏的具体模式.在此基础上,提出了楔形体-平面滑动破坏模式、崩塌-滑动破坏模式、滑动-拉裂型破坏模式及滑动-压裂型破坏模式等4种复合破坏模式,对高切坡的稳定性分析及潜在破坏面的识别具有指导意义.     

Application of Convex Optimization to Queuing Systems

On the basis of the queuing theory, a nonlinear optimal load allocation model is proposed. A novel transformafion method for the optimization variables is also presented, and the constraints are properly combined so as to make this model convex. The interior-point method for convex optimization is presented as an efficient computational tool. Finally, this model is evaluated by a real example,from which the following conclusions are drawn： the optimum result can ensure the full utilization of machines and the smallest amount of WIP （work-in-progress） in queuing systems; the interior-point method needs a few iterations with significant computational savings; other performance measures of queuing systems can also be optimized in a similar way.     

Fatigue Damage Modeling for Partially Prestressed Concrete Beams under Repeated Loadings with Variable Amplitude

Introduction Prestressedconcretestructuresfrequentlysub jectedtovariable amplituderepeatedloadingsare widelyusedinbridges,cranebeamsandoffshore structures.Repeatedloadingsmaycausetheprogres siveinternalstructuraldamagedegradingthereliabili tyofstructuresd…