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1.
In petrochemical plant, the in-operation repairing is usually a repairing strategy with pressured inoperation repairing for avoiding huge economic losses caused by unplanned shutdown when some slight local leakage happens in pipes. This paper studies the effects of repairing strategies on the failure probability of the pipe systems in process industries based on the time-average fault tree approach, especially the in-operation repairing strategies including pressured in-operation repairing activities. The fault tree model can predict the effect of different repairing plans on the pipe failure probability, which is significant to the optimization of the repairing plans. At first pipes are distinguished into four states in this model, i.e., successive state, flaw state, leakage state and failure state. Then the fault tree approach, which is usually applied in the studies of dynamic equipment, is adopted to model the pipe failure. Moreover, the effect of pressured in-operation repairing is also considered in the model. In addition, this paper proposes a series of time-average parameters of the fault tree model, all of which are used to calculate node parameters of the fault tree model. At last, a practical case is calculated based on the fault tree model in a repairing activity of pipe thinning. 相似文献
2.
在英汉两种语言中,由于文化价值观和语言本身的差异,人们对英汉请求策略的选择不尽相同,形成了不同的交际风格,而请求策略的运用是否得当,直接影响到人们交际目的能否实现,这也为相应的大学英语教学带来了较大的困难。从跨文化的角度分析英汉两种请求行为的异同,结合大学英语教学,探讨在教学中,教师如何引导学生重视文化差异,避免语用失误,从而提高大学生在跨文化交际中的语用能力,增强中国英语学习者的文化感知力。 相似文献
3.
The lifeti me maintenance of a bridge can comprise amuch greater portion of the total lifeti me cost than theoriginal cost of construction because of deterioration.An opti mal maintenance programis the key to makingappropriate decisions to mini mize cost and maintain anappropriate level of safety.Life-cycle cost is a usefulconcept in reducing the overall cost and achieving anappropriate maintenance plan[1,2].It is difficult tomake a reliable esti mate of thelifeti me costs whenthefuture of the… 相似文献
4.
以进化算法为优化手段 ,疲劳累积失效概率增量为约束条件 ,检验费用为目标函数 ,检验时间间隔及检验方式为优化变量 ,根据船体构件本身的疲劳特性进行疲劳破损检验优化研究 ,选出检验费用最少的最优检验方案 ,给出了计算实例和检验方案的比较 .结果表明 ,本文提出的方法能选出兼顾安全性和经济性的最优检验方案 相似文献
5.
柴油机的可维修性研究 总被引：1，自引：0，他引：1
张丽萍 《南通职业大学学报》2002,16(2):33-35
建立了柴油机具有共性的可维修系统的失效率模型,论述了柴油机的可维修性理论,探讨了其最佳维修周期的界定问题,给出了计算实例。该方法对其他系统的可维修性问题也具有普遍意义。 相似文献
6.
Per Nilsson 《Educational Studies in Mathematics》2007,66(3):293-315
The purpose of this study is to investigate the ways in which Swedish seventh grade students (12 and 13 years old) handle
chance encounters. Four groups of students working in pairs participated in the study. In the group discussions, which were
tape-recorded and fully transcribed, the students were encouraged to explore strategies for winning a specifically designed
dice game based on the sum of two dice. The dice game included four different set-ups of dice designed to bring to the fore
different aspects of probability modelling and to offer the student the opportunity to encounter small differences in the
mathematical structure of the sample space and of the probability distribution between the four different set-ups. The study
describes strategies that the students use when confronted with these different set-ups, what their activities imply in terms
of resources in handling random phenomena and what the dice game offers in terms of opportunities for learning probability.
In order to explain such meaning-making processes the students’ activities are viewed from a perspective that takes into consideration
how the students’ understanding varies with their interpretations of the situation they are confronted with, i.e., how they
contextualize the different set-ups of the dice game. The results show how the students, during the course of the game, reorganize
their interpretations of the mathematical content confronting them, and how a variation of guiding principles becomes the
object of exploration. Approaches of extremes and a number model are described as a means for the students to identify and
assign probabilities for the total of two dice. 相似文献
7.
黄长征 《五邑大学学报(社会科学版)》2006,8(4):49-53
生物认知系统基于回避指数爆炸的天然倾向,经常采取限制分类深度和忽略小概率事件等降低认知成本的认知策略.根据模式识别专家渡边慧的“丑小鸭定理“,这些认知策略的执行并不取决于事实判断,而取决于价值观.多方证据显示,大时间尺度下的进化过程对生物价值观的形成、固化及再塑起决定作用. 相似文献
8.
介绍了汽车ABS系统的结构、原理和故障诊断方法.通过真实案例分析了汽车ABS系统故障的诊断及维修过程. 相似文献
9.
基于圆弧滑动模型确定的安全系数,将基坑隆起破坏的不利事件划分为5种情况,利用Monte Carlo模拟确定不利事件发生概率,提出了考虑基坑隆起破坏引起的不利事件发生概率及经济损失的风险评估模型。将所提方法应用于福州地铁2号线某基坑工程中,结果表明,当围护结构插入比小于1.2时,加固对基坑隆起破坏损失期望减小效果显著;当围护结构插入比大于1.2时,加固对基坑隆起破坏损失期望减小效果一般;当插入比小于0.8时,基坑隆起破坏的损失期望等级属于“严重”;当插入比介于0.8～1.2时,基坑隆起破坏的损失期望等级属于“需要考虑”;当插入比大于1.2时,基坑隆起破坏的损失期望等级属于“可忽略”。 相似文献
10.
本提出了移动通信越区优先动态信道保留及排队算法(DCA-GC-QH)并加以深入研究，通过建立M／M／M／T马尔可夫链模型，以及通话阻塞率和越区通话中断率的动态建模，从而进一步优化信道分配。与固定信道策略相比，动态信道保留及排队策略的通话阻塞率和越区掉话率分别下降了约20％和30％。理论分析和仿真结果相符合。 相似文献
11.
本文对二不同型部件热贮备可修系统在部件工作时间、贮备时间、维修时间均服从指数分布且各r.v.独立情形下作了可靠性分析,建立了该类系统模型,并给出了平稳状态下系统有效度等解析式. 相似文献
12.
The quantity discount contracts are investigated for a one-supplier-one-retailer supply chain with asymmetric information when the retailer‘s cost is disrupted. While the retailer‘s cost structure is asymmetric information, two all-unit quantity discount contract models, fixed expected-profit percentage discount(FEPD) and fixed wholesale-pricing percentage discount(FWPD) under asymmetric information are proposed in a regular scenario. When the retailer‘s cost distribution fluctuates due to disruptions, the ... 相似文献
13.
酸沉降成为全球性的重大区域环境问题,在我国已造成了极大的生态破坏和经济损失,每年仅森林损失一项就已经超过几百亿元。为了及时地避免土壤酸化所造成的损失,有必要对酸化的土壤进行修复。本文对修复剂的加入对土壤的影响进行综述,以期为将来修复剂在我国可能的大规模生产和使用提供参考。 相似文献
14.
《哈姆雷特》作为莎士比亚四大悲剧之首,将主人公哈姆雷特的性格特征刻画得淋漓尽致。哈姆雷特本身是个热情乐观的青年,对人类的明天满怀热爱和信心,但是父王的意外死亡,母亲的改嫁,王位的丢失使他忧郁,优柔寡断,多疑,性格上出现了矛盾,从而造成了他的悲剧人生。 相似文献
15.
目前对预防性维修策略的研究大多都基于固定的预防维修周期T,但实际生产中,每一次预防维修后设备的故障率不会降到零,且以更快的速度增长,因此预防维修周期也应相应地变化。本文运用故障率增加因子和役龄回退因子来刻画每一次预防维修后设备故障率的演变规律,以每周期内单位时间的最小成本为目标,并将每次预防维修前的可靠度进行最低的限制,以此来确定最佳的弹性周期预防维修策略,最后通过实例计算与定周期进行比较,说明其经济性,能够为实际生产提供决策支持。 相似文献
16.
The loss of life risk evaluation model for dam break is built in this paper.By using an improved Monte Carlo method,the overtopping probability induced by concurrent flood and wind is calculated,and the Latin Hypercube Sampling is used to generate random numbers.The Graham method is used to calculate the loss of life resulting from dam failure.With Dongwushi reservoir located at Hebei Province taken as an example,the overtopping probability induced by concurrent flood and wind is calculated as 4.77×10-6.Loss of life is 24 220 when the warning time is 0.25-1 h and flood severity understanding is vague,which indicates that the risk is intolerable.The losses of life under three other conditions are tolerable:warning time 0.25-1 h,and precise flood severity understanding;warning time more than 1 h,and vague flood severity understanding;warning time more than 1 h,and precise flood severity understanding. 相似文献
17.
本介绍一例在检修JD12型电视机故障时，运用基尔霍夫定律正确分析判断故障原因的过程。 相似文献
18.
研究了双寡头市场条件下,基于不完美定向的定向广告竞争模型.通过两阶段博弈来描述新产品或升级产品引入时不完美定向对企业广告及定价决策带来的影响.第一阶段通过价格竞争辨识消费者,第二阶段广告作为传递产品信息和价格歧视的工具.比较分析不完美定向与完美定向情况下企业的广告和定价策略,均衡结果显示:在不完美定向条件下,当广告成本足够低时,会出现在完美定向情境下不可能出现的均衡,即两企业均会选择向对方的优势市场投入广告.这一均衡的存在会导致2种相反的结果:当广告成本较高时,不完美定向能缓和价格竞争并增加企业利润;但当广告成本足够低时,随着不完美定向程度的增加,反而会加剧市场竞争并导致企业利润损失,因此,企业有动机降低定向误差的程度. 相似文献
19.
This paper evaluates if the excitement about school-based financial education is warranted. First, relying on recent experimental evidence, the paper takes stock of the impact of financial education programs aimed at reaching children and youth. Second, it complements existing studies by focusing on the potentially negative unintended effects of these programs. Relying on data from a large-scale randomized controlled trial (RCT) in Peru, this paper investigates whether financial education programs have spillover effects on academic outcomes or if they widen initial inequalities due to heterogeneous treatment impacts. While delivery models that incorporate a mandatory course requirement yield large and robust impacts on financial literacy, voluntary after-school programs yield meager effects. These gains do not come at the cost of pervasive effects on the probability to pass a grade. Moreover, the impact of school-based financial education seems to be very inclusive, as treatment effects tend to be uniform across different sub-samples. 相似文献
20.
Nonlinear vibration can cause serious problems in long span cable-stayed bridges.When the internal resonance threshold is reached between the excitation frequency and natural frequency,large amplitudes occur in the cable.Based on the current situation of lacking corresponding constraint criteria,a model was presented for analyzing the dynamic reliability of coupling oscillation between the cable and tower in a cable-stayed bridge.First of all,in the case of cable sag,the d'Alembert principle is applied to studying the nonlinear dynamic behavior of the structure,and resonance failure interval of parametric oscillation is calculated accordingly.Then the dynamic reliability model is set up using the JC method.An application of this model has been developed for the preliminary design of one cable-stayed bridge located on Hai River in Tianjin,and time histories analysis as well as reliability indexes have been obtained.When frequency ratio between the cable and tower is approaching 1∶2,the reliability index is 0.98,indicating high failure probability.And this is consistent with theoretical derivation and experimental results in reference.This model,which is capable of computing the reliability index of resonance failure,provides theoretical basis for the establishment of corresponding rule. 相似文献