模糊二階可靠度應用於船體縱向結構之強度分析

The Fuzzy Reliability Analysis of Ship's Longitudinal Structures Based on the Second-Order Reliability Method

船舶及海洋結構物的破壞是一個受到大量隨機變數與不確定因子所影響的問題，在設計過程中相關的參數需考慮其模糊性的存在，假如都是以一些確定的數值來設計，則可能會造成不經濟或不安全之顧慮。事實上結構的強度與外力負荷是具有模糊性的。本研究之主要目的是引用模糊集合觀念於二階可靠度中。利用經驗二階可靠度方法結合模糊理論來進行船舶結構可靠度分析。對於船殼極限狀態函數中之各個隨機變數以及不確定因子，本文取三角形隸屬函數來將其隸屬程度予以量化，並以截集的方法來控制其容差大小，進而求得各種破壞模式不同α-截集下之破壞機率的置信區間。最後本研究針對兩艘實船，175700噸之雙殼散裝貨輪與26萬噸之單殼油輪，進行模糊二階可靠度分析。其目的是希望藉由模糊集合觀念應用於可靠度分析，提供船體結構設計者更多的設計參考資訊與更寬廣的設計空間。 Basically, the failure of marine structures is affected by several factors, which are random in natural. If deterministic values alone are used as design parameters to describe those random factors while ignoring fuzzy characteristics in design, this may cause some economical or safe concerns for marine structures. In fact, the fuzziness lies in both strengths and loads. The purpose of this study is to employ the fuzzy set concept into the Second-Order Reliability Method (SORM) to evaluate the fuzzy reliability of a ship Based on the empirical SORM and the fuzzy mathematics, the triangular member-ship function of the failure probability can be obtained for fuzzy reliability analysis of a ship. Two ships, a double-hull bulk carrier (175700 tons) and an oil tanker (260000 tons) are select as examples to analyze the fuzzy reliabilities based on both FORM and SORM. It is believed that this algorithm may provide more design information for ship structure designers.