Study of RCM-based maintenance planning for complex structures using soft computing technique

To guarantee the efficiency of maintenance strategies for a complex structure, safety and cost limitations must be considered. This research introduces RCM-based (Reliability Centered Maintenance) life cycle optimization for reasonable maintenance. The design variable is the reliability of each part, which consists of a complex structure, while the objective is to minimize the total cost function in order to maintain the system within the desired system reliability. This research constructs the cost function that can reflect the current operating condition and maintenance characteristics of individual parts by generating essential cost factors. To identify the optimal reliability of each component in a system, this paper uses a Neuro-Evolutionary technique. Additionally, this research analyzes the reliability growth of a system by using the AMSAA (Army Material Systems Analysis Activity) model to estimate the failure rate of each part. The MTBF (Mean Time Between Failure) and the failure rate of the whole system, which is responding to the individual parts, are estimated based on the history data by using neural networks. Finally, this paper presents the optimal life cycle of a complex structure by applying the optimal reliability and the estimated MTBF to the RAMS (Reliability, Availability, Maintainability, and Safety) algorithm.     

MMFX-2钢筋性能综述和抗腐蚀性现场实验

水泥混凝土桥面钢筋腐蚀是一普遍且复杂的问题,采用替代钢筋能有效地预防或延缓钢筋腐蚀,而近年应用的MMFX-2钢被认为具有更好的抗锈蚀性能。印第安纳州交通厅对现有的MMFX-2钢的研究成果进行了综合分析,并修建了现场试验桥面以长期评价MMFX钢筋抗腐蚀能力。同普通碳钢相比,MMFX-2钢的屈服强度和抗拉强度更高、抗腐蚀性更好,但没有明显的屈服点。试验桥面铺装的实验结果表明,施工竣工不久至竣工两年期间,MMFX-2钢筋腐蚀很少,混凝土中氯化物含量没有达到钢筋去钝化水平,但在桥面铺装上部氯离子浓度显著增加。笔者建议对于氯化物影响较大场合的混凝土桥面铺装,如果希望提供二次腐蚀保护时,可考虑使用MMFX-2钢。     

The motion analysis of fire video images based on moment features and flicker frequency

In this paper, motion analysis methods based on the moment features and flicker frequency features for early fire flame from ordinary CCD video camera were proposed, and in order to describe the changing of flame and disturbance of non-flame phenomena further more, the average changing pixel number of the first-order moments of consecutive flames has been defined in the moment analysis as well. The first-order moments of all kinds of flames used in our experiments present irregularly flickering, and their average changing pixel numbers of first-order moments are greater than fire-like disturbances. For the analysis of flicker frequency of flame, which is extracted and calculated in spatial domain, and therefore it is computational simple and fast. The method of extracting flicker frequency from video images is not affected by the catalogues of combustion material and distance. In experiments, we adopted two kinds of flames, i.e. , fixed flame and movable flame. Many comparing and disturbing experiments were done and verified that the methods can be used as criteria for early fire detection.     

Multiple USV cooperative algorithm method for hunting intelligent escaped targets北大核心CSCD

[目的]针对无人艇协同围捕过程中逃跑目标具备智能性,现有无人艇策略难以围捕成功的问题,提出一种基于双层切换策略的多无人艇协同围捕算法。[方法]第1层围捕策略采用改进势点法,以无人艇与势点的总直线距离最小为优化目标,采用匈牙利算法为无人艇动态分配势点,并采用人工势场法实现无人艇的协同避碰;第2层围捕策略利用了阿波罗尼奥斯圆的性质,在两艘无人艇前往逃跑目标的目标点进行拦截,剩余无人艇运动方向保持与逃跑目标相同,以不断缩紧包围区域;为应对逃跑目标不同的逃跑方式,第1层围捕策略和第2层围捕策略可互相转化。[结果]仿真实验表明,该算法相较于顺序分配势点算法和极角分配势点算法,围捕时间更少或持平,证明了该算法的有效性和先进性。[结论]该多无人艇协同双层围捕算法,对具备典型智能性的逃跑目标具有围捕效果。     

欧洲客车设计案例剖析--伊利萨尔客车

旅游客车制造业是一个既专业又特殊的行业。乍一看,它理应归属于汽车制造业;但从产品的实际情形以及相对较小的年产量来看,它又应归属于手工艺品行业;在这里可以看到,机械制造结合了手工艺,汽车造型融入了建筑艺术。这篇文章概述了伊利萨尔旅游客车的设计过程:从与客户的第一次     

模拟流体-弹性结构相互作用分析的ISPH-TLSPH耦合方法研究（英文）

A fully Lagrangian algorithm for numerical simulation of fluid-elastic structure interaction(FSI) problems is developed based on the Smoothed Particle Hydrodynamics(SPH) method. The developed method corresponds to incompressible fluid flows and elastic structures. Divergence-free(projection based) incompressible SPH(ISPH) is used for the fluid phase, while the equations of motion for structural dynamics are solved using Total Lagrangian SPH(TLSPH) method.The temporal pressure noise can occur at ...     

砂灰比和砂的级配对CA砂浆抗压强度和流动性的影响

通过调整砂与水泥的质量比和调整2种单级配砂的质量比,研究了砂灰比和砂的级配对CA砂浆的抗压强度和流动性的影响。结果表明：随着m（S）／m（C）的增大,低强和高强CA砂浆的流动性都变差,但低强CA砂浆流动性的变化幅度较小;随着m（S）／m（C）的增大,高强CA砂浆的抗压强度降低,而低强CA砂浆的抗压强度呈升高的趋势;使用两级配砂能够提高CA砂浆的抗压强度并改善其流动性,粒径为0．42-0．21mm的砂与粒径0．85-0．30mm的砂的最佳质量比为6：4。     

A traffic analysis zone definition: a new methodology and algorithm

This paper develops a comprehensive approach to the definition of transportation analysis zones (TAZ), and therein, presents a new methodology and algorithm for the definition of TAZ embedded in geographic information systems software, improves the base algorithm with several local algorithms, and comprehensively analyses the obtained results. The results obtained are then compared to these presently used in the transportation analysis process of the Lisbon Metropolitan Area. The proposed algorithm presents a new methodology for TAZ design based on a smoothed density surface of geocoded travel demand data. The algorithm aims to minimise the loss of information when moving from a continuous representation of the origin and destination of each trip to their discrete representations through zones, and focuses on the trade-off between the statistical precision, geographical error, and the percentage of intra-zonal trips of the resulting OD matrix. The results for the Lisbon Metropolitan Area case study suggest a significant improvement in OD matrix estimates compared to current transportation analysis practises based on administrative units.

Inferring attribute non-attendance from stated choice data: implications for willingness to pay estimates and a warning for stated choice experiment design

There is a growing interest in traveller behaviour research to explore alternative information processing strategies (often referred to as heuristics or rules) adopted by individuals when assessing packages of attributes describing alternatives in a choice set, and making a choice. One popular attribute processing rule relates to attributes not being considered (i.e., being ignored), for all manner of reasons, referred to in the small but growing literature as attribute non-attendance or non-preservation. Researchers have used a mixture of methods to study the role of attribute non-attendance, including supplementary questions on whether each attribute is ignored or not, and methods in which the functional form of the utility expressions defining an alternative can recognise the possibility, up to a probability, of an attribute being ignored. Although supplementary questions are worthy of further consideration, despite the controversy as to the reliability of the response, recent interest has focused on ways to establish the incidence of attribute non-attendance without recourse to such evidence. In this paper we use an existing data set of choice amongst four attributes describing alternative car non-commuting trips, to illustrate the proposed method, and to compare values of travel time savings under each possible combination of non-attendance attributes relative to a model in which all attributes are assumed to be fully attended to. The paper reveals a major concern with the way that attribute levels and ranges are selected in the design of choice experiments, which can induce non-attendance situations where willingness to pay estimates cannot be obtained.     

Not bored yet - Revisiting respondent fatigue in stated choice experiments

Stated choice surveys are used extensively in the study of choice behaviour across many different areas of research, notably in transport. One of their main characteristics in comparison with most types of revealed preference (RP) surveys is the ability to capture behaviour by the same respondent under varying choice scenarios. While this ability to capture multiple choices is generally seen as an advantage, there is a certain amount of unease about survey length. The precise definition about what constitutes a large number of choice tasks however varies across disciplines, and it is not uncommon to see surveys with up to twenty tasks per respondent in some areas. The argument against this practice has always been one of reducing respondent engagement, which could be interpreted as a result of fatigue or boredom, with frequent reference to the findings of Bradley and Daly (1994) who showed a significant drop in utility scale, i.e. an increase in error, as a respondent moved from one choice experiment to the next, an effect they related to respondent fatigue. While the work by Bradley and Daly has become a standard reference in this context, it should be recognised that not only was the fatigue part of the work based on a single dataset, but the state-of-the-art and the state-of-practice in stated choice survey design and implementation has moved on significantly since their study. In this paper, we review other literature and present a more comprehensive study investigating evidence of respondent fatigue across a larger number of different surveys. Using a comprehensive testing framework employing both Logit and mixed Logit structures, we provide strong evidence that the concerns about fatigue in the literature are possibly overstated, with no clear decreasing trend in scale across choice tasks in any of our studies. For the data sets tested, we find that accommodating any scale heterogeneity has little or no impact on substantive model results, that the role of constants generally decreases as the survey progresses, and that there is evidence of significant attribute level (as opposed to scale) heterogeneity across choice tasks.