Utilization of Subjective Information to the Problem of Structural Maintenance

船舶结构在役检测对维护船舶抗疲劳损伤安全具有重要作用。然而，当我们想要进行合理的检测时，有必要明确目前结构构件的可靠性水平以及期望的水平。从这个角度出发，对散货船的6个结构构件进行了重复检测下的疲劳可靠性分析。通过对肚脐工程师的问卷调查，收集了构件的裂纹萌生和扩展特性、目视检测到裂纹的概率、构件的目标失效概率等可靠性分析的基本信息，并利用问卷结果进行了疲劳可靠性分析和灵敏度分析。为此，采用马尔可夫链模型，将裂纹长度超过200 mm或500 mm定义为失效事件。通过计算，研究了现有条件下重复检测对疲劳可靠性的影响，以及达到目标失效概率所需的检测间隔。主要结论如下：(1)通过问卷调查得到了散货船六个部位的疲劳特性和目视检测的POD曲线。(2)如果使用两年一次的ISI，在20年内，ISI至少能检测到60%-70%的启裂裂纹。(3)两年一次的ISI可以将未检测的失效概率PF(200)降低到1/3，将PF(500)降低到1/5，(4)目标PF(200)的实现间隔为6个月，PF(500)目标的实现间隔为1.5年。(5)针对可靠性提高、重量减轻、检查简化等设计要求，提出了满足要求的解决方案。

In-service inspection on ship structure plays an important role for maintaining safety against fatigue damage. However, when we want to perform reasonable inspection, it is necessary to clarify the present reliability level of structural members as well as the desirable level.From this point of view, fatigue reliability analysis under repeated inspections is carried out for the six structural members of bulk carrier. Crack initiation and propagation properties of the members, probability of crack detection by the visual inspection, target failure probabilities of the members and etc., which are essential information in the reliability analysis, are collected by the questionnaire asked to the navel engineers.Then fatigue reliability analysis and sensitivity analysis are carried out using the questionnaire results. Markov Chain Model is employed for this purpose, in which crack length exceeding 200mm or 500mm was defined as the failure event. Through the calculations, effect of repeated inspections at the present condition on fatigue reliability, and the inspection intervals necessary to achieve the target failure probability are investigated for the six members. The major conclusions are drawn as follows :(1) Fatigue characteristics and POD curves by visual inspection were obtained for the six locations of bulk carrier by the questionnaire.(2) If ISI of two years interval is applied, al least 60 to 70% of initiated cracks are detected by the ISI during 20 years.(3) ISI of two years interval can reduce the failure probability Pf (200) under no inspection to 1/3 and the Pf (500) to 1/5, respectively.(4) Inspection interval of 6 months is necessary for the achievement of target Pf (200) and 1.5 years for target Pf (500).(5) For the design requirements such as the improvement of reliability, reduction of weight and simplification of inspection, the solutions to respond to the requirements were extracted.