So the economic dependency among units is analyzed , and the recursion relationship of failure rate between pre and post imperfect preventive maintenance is built up concerning with the concept of age reduction factor , furthermore , the optimal maintenance model is proposed to minimize the maintenance cost rate , and the model is subject to the reliability 该模型分析了复杂系统中存在的维修经济相关性，并考虑了实际预防维修中的不完备性，为此引入了役龄回退因子对预防维修活动前后系统性能的动态变化进行了描述。
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In this paper i calculate the reasonable possession quantity of port handling machineries with chance - constrained linear programming . first in the paper is the background and meaning of this research ; then analysis present situation of port machinery management both in practice and theory ; in chapter 3 , i qualitatively discusses characters influencing machinery quantity , which include lifting ton , intact rate and using rate , age of machinery , machinery purchase and working cost and so on . in chapter 4 , i take the influencing characters to mathematic model of chance - constrained linear programming , aiming to maintain the need of production and reduce machinery cost 文章首先介绍了选题的背景、意义以及主要工作；第2章介绍了港口机械管理在港口企业管理中的地位与作用，以及我国港口机械设备管理与配置现状，并简要介绍目前港机合理拥有量的理论研究方法；第3章从技术与经济角度定性分析了各种因素对港机拥有量的影响，其中主要包括机械起运量、完好率与利用率、机械设备役龄、购置与营运成本等；第4章将各种影响因素引入模犁，提出以完成生产任务、机械成本最低为目标，应用随机线性规划模型计算港口流动机械合理拥有量的方法；第5章以大连港大港区为例对模型进行应用，选择四种型号叉车为研究对象，对其历史经济与技术数据进行统计分析，其中重点对随机变量单位台时维修费用进行了正态分布拟合。
