Extreme value distribution and reliability of nonlinear stochastic structures

A new approach to evaluate the extreme value distribution （EVD） of the response and reliability of general multi-DOF nonlinear stochastic structures is proposed. The approach is based on the recently developed probability density evolution method, which enables the instantaneous probability density functions of the stochastic responses to be captured. In the proposed method, a virtual stochastic process is first constructed to satisfy the condition that the extreme value of the response equals the value of the constructed process at a certain instant of time. The probability density evolution method is then applied to evaluate the instantaneous probability density function of the response, yielding the EVD. The reliability is therefore available through a simple integration over the safe domain. A numerical algorithm is developed using the Number Theoretical Method to select the discretized representative points. Further, a hyper-ball is imposed to sieve the points from the preceding point set in the hypercube. In the numerical examples, the EVD of random variables is evaluated and compared with the analytical solution. A frame structure is analyzed to capture the EVD of the response and the dynamic reliability. The investigations indicate that the proposed approach provides reasonable accuracy and efficiency.

Reliability Analysis of a Powerloom Plant Using Interval Valued Intuitionistic Fuzzy Sets

In this paper, we investigate the reliability analysis of a powerloom plant by using interval valued intuitionistic fuzzy sets (IVIFS). Herein, we modeled a powerloom plant as a gracefully degradable system having two units A(n) and B(m) connected in series. The reliability ofncomponents of unitAandmcomponents of unitBis assumed to be an IVIFS defined over the universe of discourse [0, 1]. Thus, the reliability of the system obtained is an IVIFS that covers the inherited uncertainty in data collection and reliability evaluation of a powerloom plant.

Evaluating the reliability of distributed photovoltaic energy system and storage against household blackout

Distributed energy resources have been proven to be an effective and promising solution to enhance power system resilience and improve household-level reliability.In this paper,we propose a method to evaluate the reliability value of a photovoltaic(PV)energy system with a battery storage system(BSS)by considering the probability of grid outages causing household blackouts.Considering this reliability value,which is the economic profit and capital cost of PV+BSS,a simple formula is derived to calculate the optimal planning strategy.This strategy can provide household-level customers with a simple and straightforward expression for invested PV+BSS capacity.Case studies on 600 households located in eight zones of the US for the period of 2006 to 2015 demonstrate that adding the reliability value to economic profit allows households to invest in a larger PV+BSS and avoid loss of load caused by blackouts.Owing to the differences in blackout hours,households from the 8 zones express distinct willingness to install PV+BSS.The greater the probability of blackout,the greater revenue that household can get from the PV+BSS.The simulation example shows that the planning strategy obtained by proposed model has good economy in the actual operation and able to reduce the economic risk of power failure of the household users.This model can provide household with an easy and straightforward investment strategy of PV+BSS capacity.

Multi-bit soft error tolerable L1 data cache based on characteristic of data value

Due to continuous decreasing feature size and increasing device density, on-chip caches have been becoming susceptible to single event upsets, which will result in multi-bit soft errors. The increasing rate of multi-bit errors could result in high risk of data corruption and even application program crashing. Traditionally, L1 D-caches have been protected from soft errors using simple parity to detect errors, and recover errors by reading correct data from L2 cache, which will induce performance penalty. This work proposes to exploit the redundancy based on the characteristic of data values. In the case of a small data value, the replica is stored in the upper half of the word. The replica of a big data value is stored in a dedicated cache line, which will sacrifice some capacity of the data cache. Experiment results show that the reliability of L1 D-cache has been improved by 65% at the cost of 1% in performance.

Development of contingent valuation method in evaluating non-market values of resources and environment in China

The contingent valuation method （CVM） is one of the main methods for evaluating non-market values of resources. It originated in the United States and was introduced into China during the 1980s and 1990s. However, application of CVM in China is highly controversial based on three primary aspects： （I） the appropriate guidelines for CVM; （2） the elicitation techniques for willingness to pay （WTP）; and （3） reliability and validity testing of CVM. The major objectives of this paper are to i^eview the recem devel- opments pertaining to guidelines, elicitation techniques, and reliability and validity testing for application of CVM, and to summa- rize the limitations of and measures for improving application of CVM in China. The applicability of CVM in China is discussed to enhance the future development of CVM in China.

Importance Analysis of a Multi-state System Based on Direct Partial Logic Derivatives and Multi-valued Decision Diagrams

Importance analysis quantifies the critical degree of individual component. Compared with the traditional binary state system,importance analysis of the multi-state system is more aligned with the practice. Because the multi-valued decision diagram( MDD) can reflect the relationship between the components and the system state bilaterally, it was introduced into the reliability calculation of the multi-state system( MSS). The building method,simplified criteria,and path search and probability algorithm of MSS structure function MDD were given,and the reliability of the system was calculated. The computing methods of importance based on MDD and direct partial logic derivatives( DPLD) were presented. The diesel engine fuel supply system was taken as an example to illustrate the proposed method. The results show that not only the probability of the system in each state can be easily obtained,but also the influence degree of each component and its state on the system reliability can be obtained,which is conducive to the condition monitoring and structure optimization of the system.

Improved Discrete Interval-Valued Stress-Strength Interference Model Based on Extended Universal Generating Function

In practical engineering,sometimes the probability density functions( PDFs) of stress and strength can not be exactly determined,or only limited experiment data are available. In these cases,the traditional stress-strength interference( SSI) model based on classical probabilistic approach can not be used to evaluate reliabilities of components. To solve this issue, the traditional universal generating function( UGF) is introduced and then it is extended to represent the discrete interval-valued random variable.Based on the extended UGF,an improved discrete interval-valued SSI model is proposed, which has higher calculation precision compared with the existing methods. Finally,an illustrative case is given to demonstrate the validity of the proposed model.

Efficient Bayesian networks for slope safety evaluation with large quantity monitoring information

New sensing and wireless technologies generate massive data. This paper proposes an efficient Bayesian network to evaluate the slope safety using large-quantity field monitoring information with underlying physical mechanisms. A Bayesian network for a slope involving correlated material properties and dozens of observational points is constructed.

CALCULATION OF FUZZY RELIABILITY IN THE CASE OF RANDOM STRESS AND FUZZY FATIGUE STRENGTH

The fuzzy sets theory is introduced into the fatigue reliability analysis. The concepts of maximizing set and minimizing set are developed to decide the ordering value of each fuzzy number, and these values can be used to determine the order of the fuzzy numbers. On the basis of the works mentioned above, the membership function defining the fuzzy safety event can be calculated, and then the fuzzy reliability in the case of stress and fuzzy fatigue strength is deduced. An example is given to illustrate the method.

Semi-Probabilistic Evaluation of System Redundancy for Existing Offshore Structures

In this paper, a new definition of structure system redundancy is proposed in view of the various measures for structure redundancy. By introducing the terms of structure system failure at the mechanism level and equivalent reliability index, the safety for existing offshore platforms can be evaluated by the semi-probabilistic method presented in this paper. Some numerical examples are given and satisfactory results have been obtained.

Reliability Analysis of Slope Stability Considering Temporal Variations of Rock Mass Properties

Temporal variation of rock mass properties,especially the strength degradation due to drying-wetting cycles as well as the acidic wetting fluid(rainfall or reservoir water)is crucial to stability of reservoir rock slopes.Based on a series of drying-wetting cycling and experiments considering the influences of pH values,the degradation degree models of the reduced cohesion𝑐𝑐′,friction angle𝜑𝜑′are developed.2D stability analysis of the slope is subsequently carried out to calculate the factor of safety(Fs)via limit equilibrium method(LEM)and a predictive model of Fs is built using multivariate adaptive regression splines(MARS),revealing the effect of the drying-wetting cycles and pH value.The reliability analysis by Monte Carlo simulation is performed to rationally consider the uncertainty and the temporal variation of the shear strength parameters of rock mass.Results indicate that the MARS-based model can estimate the Fs accurately.The Fs and the reliability indexβdecrease with increase of drying-wetting cycles,and the temporal variation of rock mass properties has significant influence on the slope reliability.Overlooking the temporal variation of rock properties may overestimate the Fs and reliability indexβin the longer term.

Target reliability index for serviceability limit state of single piles

The objective is to develop an approach for the determination of the target reliability index for serviceability limit state(SLS) of single piles. This contributes to conducting the SLS reliability-based design(RBD) of piles. Based on a two-parameter,hyperbolic curve-fitting equation describing the load-settlement relation of piles, the SLS model factor is defined. Then, taking into account the uncertainties of load-settlement model, load and bearing capacity of piles, the formula for computing the SLS reliability index(βsls) is obtained using the mean value first order second moment(MVFOSM) method. Meanwhile, the limit state function for conducting the SLS reliability analysis by the Monte Carlo simulation(MCS) method is established. These two methods are finally applied to determine the SLS target reliability index. Herein, the limiting tolerable settlement(slt) is treated as a random variable. For illustration, four load test databases from South Africa are compiled again to conduct reliability analysis and present the recommended target reliability indices. The results indicate that the MVFOSM method overestimates βsls compared to that computed by the MCS method. Besides, both factor of safety(FS) and slt are key factors influencing βsls, so the combination of FS and βsls is welcome to be used for the SLS reliability analysis of piles when slt is determined. For smaller slt, pile types and soils conditions have significant influence on the SLS target reliability indices; for larger slt, slt is the major factor having influence on the SLS target reliability indices. This proves that slt is the most key parameter for the determination of the SLS target reliability index.

Analysis of Reliability of CET Band4

CET Band 4 has been carried out for more than a decade. It becomes so large- scaled, so popular and so influential that many testing experts and foreign language teachers are willing to do research on it. In this paper, I will mainly analyse its reliability from the perspective of writing test and speaking test.

A Study of Quantitative Progress Evaluation Models for Open Source Projects

Open source software (OSS) has become an indispensable part of society, not only for personal use but also for corporate use. Projects developed and operated by OSS are called open source projects, and the number of such projects is increasing. On the other hand, because anyone can participate in an open source project, the progress of the project is uncertain due to differences in project members’ skills, development environments, and time zones of activity. Therefore, many users and companies need to understand the development and operation status of open source project. Then, the developers carefully make decisions on upgrading or installing new OSS. In this paper, we focus on the maintenance effort estimation for open source projects considering uncertainty. Also, we evaluate the project quantitatively using Earned Value Management (EVM). Moreover, we examine the appropriateness of the model for predicting the maintenance effort expeditures. Furthermore, we discuss the appropriateness of this EVM method.

一种拖拉机核心执行机构的可靠性分析

以拖拉机转向机构为研究对象,对不确定因素下转向机构的运动精度进行分析,并利用概率学相关理论对转向机构运动误差和可靠性进行建模,同时采用一次二阶矩阵进行可靠性模型求解。结果表明:受转向机构工作过程可靠性不确定因素影响,拖拉机转向机构结构件误差最大时,其失效概率并未达到最大值。

基于似然函数筛选法的旋转轴唇形密封可靠性关键设计因素研究

基于油封的有限元和数值计算模型,分析油封的设计参数对其静态和动态密封可靠性的影响规律。将油封的初始安装过盈量、油侧唇角、空气侧唇角、腰厚、腰长、理论接触宽度、卡紧弹簧的弹性模量、油封主体橡胶的硬度8个设计参数的标准化数据作为输入向量,将油封唇口最大接触压力、泵吸率和摩擦扭矩的标准化数据作为输出向量,建立响应面模型,以输出向量方差得到各设计因素的似然函数值作为评判指标,确定各设计参数对油封密封可靠性的影响程度。结果表明:橡胶硬度、理论接触宽度、弹簧弹性模量、过盈量、腰长对油封动态密封可靠性的影响较显著,油封唇口最大接触压力对弹簧弹性模量、理论接触宽度、橡胶硬度、腰厚、油侧唇角较敏感。综合考虑旋转轴唇形油封的静态和动态可靠性,得到影响其可靠性的关键设计因素为理论接触宽度、弹簧弹性模量和橡胶硬度。

3种跌倒风险自评工具在住院老年病人中应用的信效度及预测价值分析

目的探讨3种跌倒风险自评工具在住院老年病人中应用的信效度及预测价值。方法采用便利抽样法,选取2023年1—6月中南大学湘雅医院内符合纳排标准的420例住院老年病人为研究对象,分别接受中文版住院病人自我跌倒风险评估量表(CSAFR)、中文版i Engaging跌倒自主评估工具、中文版老年人跌倒风险自评量表(CFRQ)3种工具的评估。采用组内相关系数评价3种工具的调查员信度;采用Cronbach’sα系数评价3种工具的内部一致性;采用因子分析法评价3种工具的结构效度;以中文版Morse跌倒评估量表(CMFS)作为标准,比较3种工具与CMFS测定得分的相关系数,分析标准效度;采用ROC曲线分析比较3种量表对跌倒的预测价值。结果CSAFR、中文版i Engaging跌倒自主评估工具、CFRQ的组内相关系数分别为0.862、0.804和0.926,Cronbach’sα系数分别为0.515、0.726、0.742;效度KMO值分别为0.618、0.662、0.831,Bartlett’s球形度检验值P均<0.01。主成分分析法结果显示,CSAFR提取出2个公因子,累计方差贡献率为47.4%;中文版i Engaging跌倒自主评估工具提取出7个公因子,累计方差贡献率为58.2%;CFRQ提取出3个公因子,累计方差贡献率为43.3%。CSAFR、i Engagring跌倒自主评估工具、CFRQ与CMFS的相关系数分别为0.398、0.376、0.478。ROC分析结果显示:3种工具AUC值分别为0.814、0.689、0.821,当3种工具的截断点分别为3.5、5.5、4.5时,约登指数分别为0.469、0.259、0.503,敏感度分别为64.9%、88.3%、81.8%,特异度分别为82.1%、37.6%、68.5%。结论本研究认为3种跌倒风险自评工具均有一定的信效度,对住院老年病人跌倒风险的评估均有一定的预测价值,其中CFRQ的信效度及预测价值均较高,且评估时间不长,是进行老年人跌倒风险自评的有效工具和重要参考。

主客观结合的水下连接器拉近工具液压系统方案遴选方法

拉近工具需要合格的液压系统方案以克服连接器和跨接管的偏载,本文针对拉近工具液压系统的性能可靠性提出了一种主客观结合的方案遴选方法,以确保遴选方案的可信度和无偏性。采用层次分析法对拉近工具液压系统的关键性能确立了遴选目标,包括主观方面和客观方面的评估。主观方面通过专家经验和二元对比排序法比较各系统关键性能的对比度,建立了拉近工具失效造成的维修工期隶属函数,确定了各液压系统的功能指数。同时,通过计算各液压系统的搭建成本,确定了其价值指数。最终,结合价值工程理论,选定了分流集流阀和调速阀控制的同步回路作为拉近工具的液压系统方案。为了保证方案的可靠性,本文利用AMEsim仿真软件进行了仿真以及出厂试验,验证了该方案的实用性。

考虑基坑宽度及软弱土层厚度的基坑抗隆起稳定可靠度研究

坑底隆起破坏是导致基坑失稳的关键因素之一。对坑底隆起的影响因素展开研究工作,分析基坑宽度以及软弱土层厚度对坑底隆起变形以及基坑抗隆起稳定可靠度的影响规律。首先,建立不同工况的基坑开挖有限元模型,获取坑底不同特征点的隆起变形值,分析其变形规律,进而构建基于隆起变形限值的坑底抗隆起失效极限状态函数,最后采用蒙特卡罗法对坑底进行概率分析。数值模拟结果表明:当软弱土层厚度足以使隆起破坏滑动面贯通时,窄基坑的坑底两侧隆起变形大,中间小,宽基坑隆起变形规律与之相反;两种类型基坑坑底隆起变形都随基坑宽度增加而增大。改变软弱土层厚度,坑底各特征点隆起变形值随之变化,当为窄基坑时,坑底隆起变形依旧是中间小,两侧大;当基坑为宽基坑时,随软弱土层厚度增加,隆起变形随之增大,且坑底中心隆起变形逐渐超过两侧隆起变形;依据变形规律得到不同宽度基坑隆起破坏滑动面贯通时的软弱土层厚度。坑底抗隆起稳定可靠度与基坑宽度、特征点位置以及软弱土层厚度有关,坑底的稳定状态以及可靠度最低的特征点位置随基坑宽度以及软弱土层厚度变化而变化。

考虑拆卸结构的动车组系统动态机会维修策略

为研究拆卸结构对动车组系统维修计划的影响,运用拆卸混合图模型分析单部件最优拆卸序列。并基于效费比分析方法选择多级维修方式,计算考虑拆卸成本和安装调试成本的部件最优可靠度阈值。在此基础上,引入机会维修理念,针对系统内多部件维修前拆卸序列规划问题,提出多拆卸目标序列优化方法,建立考虑可靠度价值浪费的动态机会维修策略模型。算例分析表明,动态机会维修策略相较于传统顺序预防性维修策略,通过归并维修时机,停机次数减少16次,有效减少因预防性维修和拆卸时间冗长造成的停机成本损耗,且维修总成本节省16.6%,满足维修部门对经济性的要求,为动车组系统考虑复杂相关性的维修策略研究提供理论支持。