To comprehensively assess fi＇actionated spacecraft, an assessment tool is developed based on lifecycle simulation under uncertainty driven by modular evolutionary stochastic models. First, fractionated spacecraft nom...To comprehensively assess fi＇actionated spacecraft, an assessment tool is developed based on lifecycle simulation under uncertainty driven by modular evolutionary stochastic models. First, fractionated spacecraft nomenclature and architecture are clarified, and assessment criteria are analyzed. The mean and standard deviation of risk adjusted lifecycle cost and net present value （NPV） are defined as assessment metrics. Second, fractionated spacecraft sizing models are briefly described, followed by detailed discussion on risk adjusted lifecycle cost and NPV models. Third, uncertainty sources over fractionated spacecraft life- cycle are analyzed and modeled with probability theory. Then the chronological lifecycle simulation process is expounded, and simulation modules are developed with object oriented methodology to build up the assessment tool. The preceding uncertainty models are integrated in these simulation modules, hence the random object status can be simulated and evolve with lifecycle timeline. A case study to investigate the fractionated spacecraft for a hypothetical earth observation mission is carried out with the proposed assessment tool, and the results show that fractionation degree and launch manifest have great influence on cost and NPV, and generally fractionated spacecraft is more advanced than its monolithic counterpart under uncertainty effect. Finally, some conclusions are given and future research topics are highlighted.展开更多
Various structures such as marine structures age over time. In order to always maintain safety conditions, maintenance processes including inspection and repair should be implemented on them. Corrosion and fatigue cra...Various structures such as marine structures age over time. In order to always maintain safety conditions, maintenance processes including inspection and repair should be implemented on them. Corrosion and fatigue cracks are two main factors that reduce the ultimate strength of the ship's hull girder over time and thus increase the probability and risk of failure. At the time of inspection,the structural conditions must be checked so that, if necessary, the required repairs can be done on it. The main objective of this paper is to provide optimized maintenance plans of the ship structure based on probabilistic concepts with regard to corrosion and fatigue cracks. Maintenance activities increase the operational costs of ships; therefore, it is advisable to inspect and repair in the optimal times. Optimal maintenance planning of the ship structure can be conducted by formulating and solving a multi-objective optimization problem. The use of risk as a structural performance indicator has become more common in recent years. The objective functions of the optimization problem include minimizing the structure's lifecycle maintenance costs, including inspection and repair costs, and also minimizing the maximum risk of structural failure during the ship's life. In the following,to achieve better responses, reliability index has been added to the problem as the third objective function. The multi-objective optimization problem is solved using genetic algorithms. The proposed risk-based approach is applied to the hull structure of a tanker ship.展开更多
基金Foundation items： National Natural Science Foundation of China （50975280, 61004094） Program for New Century Excellent Talents in University （NCET-08-0149）+1 种基金 Fund of Innovation by Graduate School of National University of Defense Technology （B090102） Hunan Provincial Innovation Foundation for Postgraduate, China.
文摘To comprehensively assess fi＇actionated spacecraft, an assessment tool is developed based on lifecycle simulation under uncertainty driven by modular evolutionary stochastic models. First, fractionated spacecraft nomenclature and architecture are clarified, and assessment criteria are analyzed. The mean and standard deviation of risk adjusted lifecycle cost and net present value （NPV） are defined as assessment metrics. Second, fractionated spacecraft sizing models are briefly described, followed by detailed discussion on risk adjusted lifecycle cost and NPV models. Third, uncertainty sources over fractionated spacecraft life- cycle are analyzed and modeled with probability theory. Then the chronological lifecycle simulation process is expounded, and simulation modules are developed with object oriented methodology to build up the assessment tool. The preceding uncertainty models are integrated in these simulation modules, hence the random object status can be simulated and evolve with lifecycle timeline. A case study to investigate the fractionated spacecraft for a hypothetical earth observation mission is carried out with the proposed assessment tool, and the results show that fractionation degree and launch manifest have great influence on cost and NPV, and generally fractionated spacecraft is more advanced than its monolithic counterpart under uncertainty effect. Finally, some conclusions are given and future research topics are highlighted.
文摘Various structures such as marine structures age over time. In order to always maintain safety conditions, maintenance processes including inspection and repair should be implemented on them. Corrosion and fatigue cracks are two main factors that reduce the ultimate strength of the ship's hull girder over time and thus increase the probability and risk of failure. At the time of inspection,the structural conditions must be checked so that, if necessary, the required repairs can be done on it. The main objective of this paper is to provide optimized maintenance plans of the ship structure based on probabilistic concepts with regard to corrosion and fatigue cracks. Maintenance activities increase the operational costs of ships; therefore, it is advisable to inspect and repair in the optimal times. Optimal maintenance planning of the ship structure can be conducted by formulating and solving a multi-objective optimization problem. The use of risk as a structural performance indicator has become more common in recent years. The objective functions of the optimization problem include minimizing the structure's lifecycle maintenance costs, including inspection and repair costs, and also minimizing the maximum risk of structural failure during the ship's life. In the following,to achieve better responses, reliability index has been added to the problem as the third objective function. The multi-objective optimization problem is solved using genetic algorithms. The proposed risk-based approach is applied to the hull structure of a tanker ship.
文摘由于在装备软件开发过程中存在大量的不确定性需求和许多未知因素，导致使用传统的寿命周期费用（lifecyclecose，LCC）评价方法很难处理评价中的模糊属性。为解决这一问题，提出了一种评价方法——模糊优劣指数评价法（fuzzy figure of merit，FFoM）。FFoM方法不仅能够处理定量的系统属性，而且能够处理模糊定性的系统属性。FFoM方法的主要思想是，用模糊隶属函数替代传统优劣指数评价法（FoM）中的效用函数，建立相应备择方案的模糊评判矩阵，使用中心点距离法对模糊数排序，求解最佳备择方案。最后用FFoM方法对一算例进行分析计算，结果表明此评价方法具有可行性。
