浅谈索引失效原因、对策及其应用

针在银行金融业应用系统中往往涉及大数据量的查询与操作,其中索引对系统的性能起到了至关重要的作用。本文分析了索引的基本概念及数据库内部优化器的工作机制,科学分析了导致索引失效地各种情况,提出了隐式失效、主动失效、累积失效的定义,同时也给出了避免索引失效的各种对策及其在银行第三方存管系统中的实际应用案例,对开发高性能数据库应用有一定的指导意义。     

Mesolevel Modeling of Failure in Composite Laminates: Constitutive, Kinematic and Algorithmic Aspects

In this paper recent developments for mesolevel modeling of failure in composite laminates are reviewed. The complexity of failure processes in composite laminates presses the need for reliable computational tools that can predict strength and damage tolerance. In mesolevel modeling, where individual layers are modeled separately but individual fibers are not, different failure processes are distinguished such as delamination, fiber failure and matrix failure. This paper deals with the question how these different processes should be treated for efficient and realistic computational modeling of failure. The development that is central in this review is the use of the extended finite element method (XFEM) for matrix cracks. Much attention is also paid to algorithmic aspects of implicit analysis of complex failure mechanisms, particularly but not exclusively in relation to XFEM. Furthermore, the remaining limitations and challenges for mesolevel analysis of composite failure are discussed.     

A computational and experimental analysis of the buckling,postbuckling and initial failure of pultruded GRP columns

A two-dimensional finite element (FE) model was developed and nonlinear FE analyses were carried out, using the ANSYS software, to predict the buckling, postbuckling and initial failure loads of pultruded glass reinforced plastic (GRP) wide flange (WF) columns. Phenomenological failure criteria were proposed to predict failure initiation at the web-flange junctions of pultruded GRP WF columns, whereas the Tsai–Wu failure criterion was used for the web and flanges. Initial failure analysis was carried out with reasonable success as a post-processing operation on the nonlinear analysis results. The numerical predictions of the buckling, postbuckling and initial failure loads of pultruded GRP WF columns were in reasonably good agreement with the experimental results.     

Optimum preventive maintenance policies for systems subject to random working times,replacement, and minimal repair

This paper proposes, from the economical viewpoint of preventive maintenance in reliability theory, several preventive maintenance policies for an operating system that works for jobs at random times and is imperfectly maintained upon failure. As a failure occurs, the system suffers one of two types of failure based on a specific random mechanism: type-I (repairable) failure is rectified by a minimal repair, and type-II (non-repairable) failure is removed by a corrective replacement. First, a modified random and age replacement policy is considered in which the system is replaced at a planned time T, at a random working time, or at the first type-II failure, whichever occurs first. Next, as one extended model, the system may work continuously for N jobs with random working times. Finally, as another extended model, we might consider replacing an operating system at the first working time completion over a planned time T. For each policy, the optimal schedule of preventive replacement that minimizes the mean cost rate is presented analytically and discussed numerically. Because the framework and analysis are general, the proposed models extend several existing results.     

Software Reliability Models: Assumptions, Limitations, and Applicability

A number of analytical models have been proposed during the past 15 years for assessing the reliability of a software system. In this paper we present an overview of the key modeling approaches, provide a critical analysis of the underlying assumptions, and assess the limitations and applicability of these models during the software development cycle. We also propose a step-by-step procedure for fitting a model and illustrate it via an analysis of failure data from a medium-sized real-time command and control software system.     

Survey of expert systems for fault detection, test generation and maintenance

Abstract: The use of knowledge engineering in diagnostic systems, is aimed primarily at exploiting procedural knowledge (about: systems operations, configuration, observations, calibration, maintenance), in connection with failure detection and test generation tasks. Next, the goal is to devise knowledge representation schemes whereby the failure events can be analyzed by merging highly diverse sources of information: analog/digital signals, logical variables and test outcomes, text from verbal reports, and inspection images. The final goal is to ease the operator workload when interfacing with the system under test and/or the test equipment, or with reliability assessment software packages. The paper will present key notions, methods and tools from: knowledge representation, inference procedures, pattern analysis. This will be illustrated by reference to a number of current and potential applications for e.g.: electronics failure detection, control systems testing, analysis of intermittent failures, false alarm reduction, test generation, maintenance trainers.     

Hands-Free,Speech-Based Navigation During Dictation: Difficulties,Consequences, and Solutions

Speech recognition technology continues to improve, but users still experience significant difficulty using the software to create and edit documents. In fact, a recent study confirmed that users spent 66% of their time on correction activities and only 33% on dictation. Of particular interest is the fact that one third of the users' time was spent simply navigating from one location to another. In this article, we investigate the efficacy of hands-free, speech-based navigation in the context of dictation-oriented activities. We provide detailed data regarding failure rates, reasons for failures, and the consequences of these failures. Our results confirm that direction-oriented navigation (e.g., Move up two lines) is less effective than target-oriented navigation (e.g. Select target). We identify the three most common reasons behind the failure of speech-based navigation commands: recognition errors, issuing of invalid commands, and pausing in the middle of issuing a command. We also document the consequences of failed speech-based navigation commands. As a result of this analysis, we identify changes that will reduce failure rates and lessen the consequences of some remaining failures. We also propose a more substantial set of changes to simplify direction-based navigation and enhance the target-based navigation. The efficacy of this final set of recommendations must be evaluated through future empirical studies.     

Constitutive ply damage modeling, FEM implementation, and analyses of laminated structures

The present work is concerned with the modeling of progressive damage in fiber reinforced polymer laminates and its implementation into a finite element code as constitutive material law. The objective is to predict damage evolution and material degradation due to matrix dominated failure modes (“matrix cracking”). In a previous work, a ply-level continuum damage model based on ply failure mechanisms postulated by Puck has been presented. This model predicts the evolution of the complete tensor of elasticity for the damaged material and is able to capture the effects of stiffness recovery and slanted cracking under transverse compression. In the current work, this damage model is adapted for arbitrary loading paths and implemented within the finite element method in order to analyze complex structures and study their damage behavior including load redistribution due to damage. To demonstrate some key features and the application of the damage model in structural analysis, it is applied in a single element analysis as well as in the simulation of Open Hole Compression tests for which results are compared to experimental data from the literature.     

梦想与艺术的追求者——阿莱西(Alessi)设计成功简评

作为代表意大利设计的阿莱西在其发展历程中追求设计至上,渐渐形成了自己独特的设计评价体系,创建了内涵梦想与诗意的企业文化,但其成功背后也有隐藏着失败。本文将重点探讨分析阿莱西企业经历的得与失,以此来为国内正在成长的工业设计相关企业提供业界的成功经验。     

Homogenised limit analysis of masonry walls,Part I: Failure surfaces

A simple micro-mechanical model for the homogenised limit analysis of in-plane loaded masonry is proposed. Assuming brickwork under plane stress condition and adopting a polynomial expansion for the 2D stress field, a linear optimisation problem is derived on the elementary cell in order to recover the homogenised failure surface of the brickwork. Different models of higher accuracy are obtained by increasing the degree of the polynomial approximation. Several cases of technical interest are treated in detail, varying both the geometrical characteristics of the cell and the mechanical properties of the components. The model is validated through comparisons with experimental data and kinematic approaches; the comparison with experimental data has the aim to reproduce in a qualitative way the shape of the failure surface, since 3D effects and brittle behaviour of bricks can not be taken into consideration with the model proposed.In an accompanying paper, the homogenised failure surfaces here obtained are implemented in a finite element limit analysis code and relevant structural examples are treated both with a lower and an upper bound approach.     

Human Factors Analysis,Design, and Evaluation of Engage,a Consumer Health IT Application for Geriatric Heart Failure Self-Care

ABSTRACT

Human factors and ergonomics (HFE) and related approaches can be used to enhance research and development of consumer-facing health information technology (IT) systems, including technologies supporting the needs of people with chronic disease. A multiphase HFE study of health IT supporting self-care of chronic heart failure by older adults is described. The study was based on HFE frameworks of “patient work” and incorporated the three broad phases of user-centered design: study or analysis, design, and evaluation. In the study phase, data from observations, interviews, surveys, and other methods were analyzed to identify gaps in and requirements for supporting heart failure self-care. The design phase applied findings from the study phase throughout an iterative process, culminating in the design of the Engage application, a product intended for continuous use over 30 days to stimulate self-care engagement, behavior, and knowledge. During the evaluation phase, a variety of usability issues through expert heuristic evaluation and laboratory-based usability testing were identified. The implications of our findings regarding heart failure self-care in older adults and the methodological challenges of rapid translational field research and development in this domain are discussed.     

基于视情维修的涡轴发动机维修保障辅助决策体系研究

复杂装备科学的维修保障策略是保证装备合理使用与适时修理的基础,是有效实施复杂装备全寿命保障的前提,关系着装备任务效能的有效发挥;文中立足于航空装备的视情维修策略,以直升机中广泛采用的涡轴发动机为研究对象,首先基于装备维保过程的大量信息提出了构建涡轴发动机涡轴发动机及其关键部件寿命与健康管理综合知识库的方法、策略;其后结合涡轴发动机循环寿命统计法与基于K均值聚类算法等各类使用条件下的寿命损耗研究方法,阐明了涡轴发动机不同应用条件下的备件量化分析策略;更进一步地,以涡轴发动机关键部件典型故障模式梳理与成因分析(FMECA)与考虑故障概率的发动机核心备件的量化分析为基础,给出了涡轴发动机关键部件备件量化方法与策略;最后基于上述方法的研究成果,阐述了涡轴发动机维修保障辅助决策软件平台的体系架构;文中的相关研究成果可被用于航空发动机等复杂装备系统的维修保障策略构建与工程化应用.     

Ends,Means and Innovation Management

The management of innovation inevitably implies the management of uncertainty. Research and practise clearly indicate that judgements about the size and the nature of this are often inaccurate. This can result in poor performance against expectations and in some cases in complete failure. In this paper it is argued that prior analysis of the type of uncertainty can help to improve the success rate and/or reduce the time to completion. Early signs that discontinuation, or a significant change in direction, might be called for are also highlighted by this analysis.     

Musculoskeletal disorders as a fatigue failure process: evidence,implications and research needs

Abstract

Mounting evidence suggests that musculoskeletal disorders (MSDs) may be the result of a fatigue failure process in musculoskeletal tissues. Evaluations of MSD risk in epidemiological studies and current MSD risk assessment tools, however, have not yet incorporated important principles of fatigue failure analysis in their appraisals of MSD risk. This article examines the evidence suggesting that fatigue failure may play an important role in the aetiology of MSDs, assesses important implications with respect to MSD risk assessment and discusses research needs that may be required to advance the scientific community’s ability to more effectively prevent the development of MSDs.

Practitioner Summary: Evidence suggests that musculoskeletal disorders (MSDs) may result from a fatigue failure process. This article proposes a unifying framework that aims to explain why exposure to physical risk factors contributes to the development of work-related MSDs. Implications of that framework are discussed.     

Structured design,consistency analysis and failure reasoning of business workflows with activity-control templates and causal ordering

The design, analysis, control and diagnosis of business workflows have been major challenges for enterprise information system designers. We propose a structured framework for workflow design, formal semantics, consistency analysis, execution automation and failure reasoning targeting E-commerce applications. A business workflow is modeled by using a visual tool named activity-control (AC) diagram. Frequently occurring business procedures are captured by the adoptions of reusable AC templates. With formally defined semantics by a combination of first-order logic and happen-before causal ordering in distributed system theory, workflow consistency can be mechanically analyzed at design time while failure reasoning can be applied at execution time for problem diagnosis. A completely specified model is automatically converted to a workflow by an iterative traversal algorithm that maps an AC diagram to an XML workflow specification which can then be executed automatically by an XML workflow engine. A failure reasoning and diagnosis algorithm is devised to find all possible causes of a failed execution when problems occur. Preliminary proof-of-concept implementation and evaluation results demonstrate the feasibility and effectiveness of our framework and techniques.     

一种基于失效传播模型的危害分析方法

嵌入式实时系统越来越多地应用于交通、航空、核能等安全关键环境。尽管系统设计可能没有任何缺陷,但由于物理组件的磨损或环境的突变而导致的随机故障在运行时仍可能导致系统发生危险。目前基于失效传播模型的危害分析方法要么仅考虑失效传播时间,要么仅考虑失效概率,缺少综合分析失效传播时间及失效概率对危害分析的影响。时间失效传播图TFPGs模型用于建模安全关键系统设计阶段中失效传播过程,该模型包含失效传播时延建模。考虑到失效传播路径的不确定对危害发生的概率影响,提出了一种危害分析方法,用概率 时间失效传播图P-TFPGs模型建模失效传播过程,并基于该模型设计了一种分析 危害发生时间与发生概率之间关系的方法;最后,给出了一个案例来说明方法的可行性。     

运载火箭姿态控制系统的一种故障分析法

本篇论文研究提出了一种运载火箭姿态控制系统的故障分析法,称为故障-功能分析法(简称为F-FAM).F-FAM 由故障-功能树分析和故障模式分析两部分内容组成,后者是前者的延伸.在故障模式分析中,着重讨论了姿态控制系统各个环节的故障模型参数估计问题.最后,用实例说明了该方法用于姿态控制系统故障分析的有效性和快速性.     

The Conversion of Dynamic Fault Trees to Stochastic Petri Nets, as a case of Graph Transformation

A model-to-model transformation from Dynamic Fault Trees to Stochastic Petri Nets, by means of graph transformation rules, is presented in this paper. Dynamic Fault Trees (DFT) are used for the reliability analysis of complex and large systems and represent by means of gates, how combinations or sequences of component failure events, lead to the failure of the system. DFTs need the state space solution which can be obtained by converting a DFT to a Stochastic Petri Net: this task is expressed by means of graph transformation rules, and is applied to a case of system.     

复合材料π接头渐进失效分析

针对复合材料π接头复杂的失效形式,采用材料刚度退化的方法模拟结构的渐进失效过程,用Abaqus建立某复合材料π接头的三维有限元模型;采用三维Hashin失效准则和Ye分层准则判别复合材料层合板的5种失效形式,将理想弹塑性材料模型应用于胶层材料来模拟胶层材料的失效,在Abaqus中建立考虑复合材料层合板和胶层失效的分析子...     

基于联合事件概率定义的序列失效分析

基于Petri网的失效序列分析能较好拓展序列失效分析的应用范围。针对一种基于Petri网序列失效分析方法,通过仿真手段对其有效性进行检验,检验表明该方法对系统运行时间不敏感。对此,提出了一种基于联合事件概率定义的序列失效分析方法,给出了计算失效序列发生概率的精确解。从中也可得出启示：对于近似计算方法,为严谨周密起见,需对其有效性检验。