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本文基于广义样条子域法,在合理构造冷却域计算模型的基础上,建立了研究长期风荷载作用下冷却失效机理分析的数学模型。该模型采用矩阵逆摄动法考虑长期风荷载作用下冷却塔的失效过程。并通过引入一个“区域失效系数”来判断各区域的失效程度,为冷却塔在长期风荷载作用下的失峁机理分析奠定了理论基础。 相似文献
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钢筋混凝土结构正常使用极限状态可靠性分析 总被引:1,自引:0,他引:1
本文对钢筋混凝土结构正常使用极限状态(变形、裂缝控制)可靠度分析中的不确定性-随机性、模糊性进行了讨论。对于不同情况,建议了三种可靠度计算模式,指出将失效准则按确定值考虑,实质上是用具有某一阈值λ的水平截集代替模糊子集。正常使用失效准则具有强烈的模糊性,采用“模糊事件概率”来计算失效概率更为合理。 相似文献
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为了提高港口集疏运网络中转站选址布局的合理性并优化货流分配,本文考虑实际环境中节点失效因素和多货种货主选择偏好因素对港口集疏运网络的影响,建立了双层规划模型刻画选址配流决策和货主偏好行为之间的关系。上层决策加入中转站失效惩罚成本,下层模型建立考虑货主选择偏好的用户均衡(user-equilibrium,UE)配流模型,用于估算运输网络中各路段的均衡货流量。根据模型特点设计了基于遗传框架并融合Frank-Wolfe算法的启发式算法,通过案例分析对模型及算法的有效性进行验证。结果表明:在模型中考虑节点失效能够显著提高港口集疏运网络的可靠性,并有效降低网络惩罚成本;考虑多货种货主选择偏好能够优化集装箱中转站选址布局及货流分配。 相似文献
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《中国新技术新产品》2014,(12)
关于铝合金失效机理一般是通过材料成分和材料的硬度来进行分析,一般来说模具材料的合金元素含量不足,或存在着不可忽视的冶金缺陷,就会导致铝合金失效。事实上失效是一个很复杂的概念,一般特点的失效机理取决于材料或结构的缺陷、材料的制造和组装过程中导致的损伤和储存以及现场使用环境等。本文着重介绍了各种可以使铝合金特性退化的失效机理。 相似文献
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由于MEMS器件的可靠性成为MEMS产品商业化过程中一个重要问题,而冲击断裂是导致器件失效的一个重要原因.本文主要研究多晶硅微悬臂梁在冲击条件下的可靠性,文中阐述了断裂失效机理,并使用应力一强度模型对可靠度进行建模.通过实验统计在各种加速度冲击下的可靠度,并将实验实测值与理论值进行对比. 相似文献
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基于模糊综合判定的网壳结构强震失效模式研究 总被引:1,自引:0,他引:1
为合理判别单层网壳结构在强震下的两类失效模式,指导网壳工程在地震区的实践,该文采用考虑材料损伤累积的荷载域全程分析方法,对单层球面网壳和单层柱面网壳在动力荷载下(包括强震)的响应进行了系统的参数分析。简述了两类失效模式的结构表现及结构响应特征;引入模糊数学中的模糊综合判定理论,确定了网壳结构多项响应因素与模糊失效模式集合的关系,建立了基于模糊综合判定的网壳结构动力失效模式判别模型;通过分析表明:所建立的模型具有准确的判别效果,可对网壳结构在动力荷载下的失效模式进行判别。 相似文献
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Maintenance contract assessment for aging systems 总被引:1,自引:0,他引:1
Anatoly Lisnianski Ilia Frenkel Lev Khvatskin Yi Ding 《Quality and Reliability Engineering International》2008,24(5):519-531
This paper considers an aging system, where the system failure rate is known to be an increasing function. After any failure, maintenance is performed by an external repair team. Repair rate and cost of repair are determined by a corresponding maintenance contract with a repair team. There are many different maintenance contracts suggested by the service market to the system owner. In order to choose the best maintenance contract, a total expected cost during a specified time horizon should be evaluated for an aging system. In this paper, a method is suggested based on a piecewise constant approximation for the increasing failure rate function. Two different approximations are used. For both types of approximations, the general approach for building the Markov reward model is suggested in order to assess lower and upper bounds of the total expected cost. Failure and repair rates define the transition matrix of the corresponding Markov process. Operation cost, repair cost and penalty cost for system failures are taken into account by the corresponding reward matrix definition. A numerical example is presented in order to illustrate the approach. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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Measures that improve durability of a structure usually increase its initial cost. Thus, in order to make a decision about a cost-effective solution the life-cycle cost of a structure including cost of structural failure needs to be considered. Due to uncertainties associated with structural properties, loads and environmental conditions the cost of structural failure is a random variable. The paper derives probability distributions of the cost of failure of a single structure and a group of identical structures when single or multiple failures are possible during the service life of a structure. The probability distributions are based on cumulative probabilities of failure of a single structure over its service life. It is assumed that failures occur at discrete points in time, the cost of failure set at the time of decision making remains constant for a particular design solution and the discount rate is a deterministic parameter not changing with time. The probability distributions can be employed to evaluate the expected life-cycle cost or the expected utility, which is then used in decision making. An example, which considers the selection of durability specifications for a reinforced concrete structure built on the coast, illustrates the use of the derived probability distributions. 相似文献
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George Nenes Sofia Panagiotidou 《Quality and Reliability Engineering International》2011,27(2):149-163
We develop a model for the economic design of a Bayesian control chart for monitoring a process mean. The process may randomly suffer failures that result in a non‐operating state, and thus call for an immediate corrective maintenance action, as well as assignable causes that shift the process mean to an undesirable level. Quality shifts, apart from poorer quality outcome and higher operational cost, also result in higher failure rate. Consequently, their removal, besides improving the outcome quality and reducing the quality‐related cost, is also a preventive maintenance action since it reduces the probability of a failure. The proposed Bayesian model allows the determination of the design parameters that minimize the total expected quality and maintenance cost per time unit. The effectiveness of the proposed model is evaluated through the comparison of its expected cost against the optimum expected cost of the simpler variable‐parameter Shewhart chart. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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为同时保证设备承租方对租赁设备的可用度,以及优化设备出租方的设备维护成本,提出了基于故障状态的定周期检测的多维护方式策略。首先,对租赁设备进行定周期检测,基于设备故障率来选择相应的维护策略,采取役龄回退的方式描述采取不同的维护策略后设备状态的恢复情况。其次,综合考虑周期维护成本、小修成本、惩罚成本和租赁延迟成本,建立了以出租方成本最低为目标的多维护策略优化模型。通过数学建模和数理统计方法,利用MATLAB仿真进行算例分析,将其与定周期单一预防性维护策略进行对比,证明了对租赁设备进行定周期多策略维护,其维护效果较单一预防性维护有较大的提升。 相似文献
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The fatigue strength and its correct assessment play an important role in design and maintenance of marine crankshafts to obtain operational safety and reliability. Crankshafts are under alternating bending on crankpins and rotating bending combined with torsion on main journals, which mostly are responsible for fatigue failure. The commercial management success substantially depends on the main engine in service and of its design crankshaft, in particular. The crankshaft design strictly follows the rules of classification societies. The present study provides an overview on the assessment of fatigue life of marine engine crankshafts and its maintenance taking into account the design improving in the last decades, considering that accurate estimation of fatigue life is very important to ensure safety of components and its reliability. An example of a semi-built crankshaft failure is also presented and the probable root case of damage, and at the end some final remarks are presented. 相似文献
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In this paper, the effects of uncertainty and expected costs of failure on optimum structural design are investigated, by comparing three distinct formulations of structural optimization problems. Deterministic Design Optimization (DDO) allows one the find the shape or configuration of a structure that is optimum in terms of mechanics, but the formulation grossly neglects parameter uncertainty and its effects on structural safety. Reliability-based Design Optimization (RBDO) has emerged as an alternative to properly model the safety-under-uncertainty part of the problem. With RBDO, one can ensure that a minimum (and measurable) level of safety is achieved by the optimum structure. However, results are dependent on the failure probabilities used as constraints in the analysis. Risk optimization (RO) increases the scope of the problem by addressing the compromising goals of economy and safety. This is accomplished by quantifying the monetary consequences of failure, as well as the costs associated with construction, operation and maintenance. RO yields the optimum topology and the optimum point of balance between economy and safety. Results are compared for some example problems. The broader RO solution is found first, and optimum results are used as constraints in DDO and RBDO. Results show that even when optimum safety coefficients are used as constraints in DDO, the formulation leads to configurations which respect these design constraints, reduce manufacturing costs but increase total expected costs (including expected costs of failure). When (optimum) system failure probability is used as a constraint in RBDO, this solution also reduces manufacturing costs but by increasing total expected costs. This happens when the costs associated with different failure modes are distinct. Hence, a general equivalence between the formulations cannot be established. Optimum structural design considering expected costs of failure cannot be controlled solely by safety factors nor by failure probability constraints, but will depend on actual structural configuration. 相似文献
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An economically designed, integrated quality and maintenance model using an adaptive Shewhart chart 总被引:1,自引:0,他引:1
Sofia Panagiotidou Author Vitae Author Vitae 《Reliability Engineering & System Safety》2009,94(3):732-741
This paper proposes a model for the economic design of a variable-parameter (Vp) Shewhart control chart used to monitor the mean in a process, where, apart from quality shifts, failures may also occur. Quality shifts result in poorer quality outcome, higher operational cost and higher failure rate. Thus, removal of such quality shifts, besides improving the quality of the outcome and reducing the quality cost, is also a preventive maintenance (PM) action since it reduces the probability of a failure and improves the equipment reliability. The proposed model allows the determination of the scheme parameters that minimize the total expected quality and maintenance cost of the procedure. The monitoring mechanism of the process employs an adaptive Vp-Shewhart control chart. To evaluate the effectiveness of the proposed model, its optimal expected cost is compared against the optimum cost of a fixed-parameter (Fp) chart. 相似文献
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