Robust expected violation criterion for constrained robust design problems and its application in automotive lightweight design

Metamodeling techniques are commonly used to replace expensive computer simulations in robust design problems. Due to the discrepancy between the simulation model and metamodel, a robust solution in the infeasible region can be found according to the prediction error in constraint responses. In deterministic optimizations, balancing the predicted constraint and metamodeling uncertainty, expected violation (EV) criterion can be used to explore the design space and add samples to adaptively improve the fitting accuracy of the constraint boundary. However in robust design problems, the predicted error of a robust design constraint cannot be represented by the metamodel prediction uncertainty directly. The conventional EV-based sequential sampling method cannot be used in robust design problems. In this paper, by investigating the effect of metamodeling uncertainty on the robust design responses, an extended robust expected violation (REV) function is proposed to improve the prediction accuracy of the robust design constraints. To validate the benefits of the proposed method, a crashworthiness-based lightweight design example, i.e. a highly nonlinear constrained robust design problem, is given. Results show that the proposed method can mitigate the prediction error in robust constraints and ensure the feasibility of the robust solution.     

Accommodating risk in the valuation of expected travel time savings

Valuation of travel time savings is a critical measure in transport infrastructure appraisal, traffic modelling and network performance. It has been recognised for some time that the travel times associated with repeated trips are subject to variation, and hence there is risk embedded in the treatment of expected travel time. In the context of the expected utility framework, we use a nonlinear probability weighting function to accommodate choice made under risk. Although the empirical findings suggest small differences between the value of expected travel time savings (VETTS) in the presence and absence of risk, the mean estimate does make a noticeable difference to time benefits when applied to real projects. By incorporating nonlinear probability weighting, our model reveals that the probabilities associated with specific travel times that are shown to respondents in the choice experiment are transformed, resulting in overweighting of outcomes with low probabilities and underweighting of outcomes with high probabilities. Copyright © 2011 John Wiley & Sons, Ltd.     

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城市公共交通财政补贴是落实优先发展公共交通战略的关键环节之一,由于城市公共交通财政补贴测算涉及面广,构建具有可操作性的测算模型和完善测算方法是城市交通可持续发展的一个重要课题。本文利用效用函数导出使用者乘坐公共交通的需求函数,建立使用者收入、企业经营成本和政府财政补贴之间的博弈模型,分析对公共交通使用者实行分类补贴的优势所在,并提出实际运用中具有可操作性的补贴测算模型。最后,文章结合北京市常规公交的调查数据进行案例分析,分析结果表明分类补贴的方法和补贴测算模型不仅能很好地满足使用者的公交出行需求,而且可以有效测算公交财政补贴金额,实现政府补贴的效用最大化,为城市公共交通补贴测算提供新的思路&;#61472;。     

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在城市交通系统中,动态交通和静态交通之间存在着密切的关系,两者之间既相互促进又相互制约。本文对城市交通网络中的道路及停车流量分配问题进行了探讨和研究。充分考虑了影响出行者停车选择的主要因素,包括车辆行驶费用、停车费用以及步行费用等,构造了停车场广义效用函数,采用Logit模型来描述出行者的停车选择概率,并假定出行者的路径选择行为满足Wardrop平衡准则。在此基础上,综合考虑交通网络中出行者的路径选择和停车选择问题,提出了具有能力约束的城市道路及停车流量分配的用户平衡模型,并给出了求解该模型的算法。最后通过一个简单算例,对模型及算法进行了验证,分析了不同交通需求及停车收费条件下停车流量的变化情况。     

机动车尾气污染对居民出行选择的影响

机动车尾气排放造成的空气污染对人体健康的危害逐渐被医学界证实。城市居民选择交通工具以及出行路线时,道路机动车尾气污染会影响其选择行为。文中通过居民出行问卷调查证实部分出行者会采取规避行为降低机动车尾气污染对个人健康的危害,建立表征出行者与污染气体接触程度的曝露指数模型,通过数据拟合建立增量时间转化模型,以出行时间增加值的形式定量得到机动车尾气污染对居民出行的影响程度,对离散选择模型的效用函数进行了修正,并给出了算例。     

水资源配置方案的相对有效性评价

将水资源配置定义为一种广义的投入产出问题,在给出水资源配置的基本投入产出指标后,探讨了应用GEM(群组特征根法)-MAUT(多属性效用理论)模型对配置方案的相对有效性进行评价.该模型运用群组特征根法确定指标权重,而后由多属性效用理论给出方案的优劣次序.相对于DEA(数据包络分析)或ANN(人工神经网络)法,该模型更适用于对评价指标有特别要求的情况.     

考虑异质性的经典随机后悔最小化模型改进研究

传统基于后悔理论的交通行为模型对异质性考虑不充分，对真实选择行为的解释存在不足.本文利用韦伯比率，考虑出行者对各方式属性变量感知的异质性，对经典随机后悔最小化模型进行改进，分别建立基于随机效用最大化，经典随机后悔最小化和改进经典随机后悔最小化的选择模型；以网约车选择行为为例进行实证研究，验证改进模型效果.结果表明：3种模型参数标定结果具有一致性，改进模型的拟合优度(0.271)和命中率(75.8%)相较于另外两个模型均较优；改进模型能更好地描述多维属性决策过程中的半补偿原则和折中效应，可以提高模型对真实选择行为的解释能力.     

Discussing the “positive utilities” of autonomous vehicles: will travellers really use their time productively?

ABSTRACT

Autonomous vehicles (AVs) are expected to reshape travel behaviour and demand in part by enabling productive uses of travel time—a primary component of the “positive utility of travel” concept—thus reducing subjective values of travel time savings (VOT). Many studies from industry and academia have assumed significant increases in travel time use and reductions in VOT for AVs. In this position paper, I argue that AVs’ VOT impacts may be more modest than anticipated and derive from a different source. Vehicle designs and operations may limit activity engagement during travel, with AV users feeling more like car passengers than train riders. Furthermore, shared AVs may attenuate travel time use benefits, and productivity gains could be limited to long-distance trips. Although AV riders will likely have greater activity participation during travel, many in-vehicle activities today may be more about coping with commuting burdens than productively using travel time. Instead, VOT reductions may be more likely to arise from a different “positive utility”—subjective well-being improvements through reduced stresses of driving or the ability to relax and mentally transition. Given high uncertainty, further empirical research on the experiential, time use, and VOT impacts of AVs is needed.     

国际理解教育的定义及内涵初探

在全球化背景下,国际理解教育目的是增进不同文化背景的、不同种族的、不同宗教信仰的和不同区域、国家的人们之间相互了解;加强他们之间相互合作,养成对多元文化的理解与尊重,拥有全球的胸怀与视野,理解世界各国相互依存的关系,遵守国际基本法则的意识,以便共同认识和处理全球社会存在的重大共同问题。     

功率变流器拓扑结构共模电压的比较和降低

所有由接地的电网系统供电并向可变输出系统供电的开关变流器拓扑结构,都会在负载装置上产生共模电压.系统地分析了用在交流传动装置上的各种变流器拓扑结构的共模电压,包括两点式电压源逆变器(VSI)、电流源逆变器(CSI)以及多点式逆变器.还分析了每种拓扑结构中使用的有源前端整流器.分析了共模电压的来源,并比较了由不同变流器拓扑结构产生的共模电压幅值.讨论了共模电压和降低共模电压技术的实际意义,并提供仿真和试验结果加以证明.