以共同結構規範分析雙層船殼油輪疲勞強度之研究

Abstract

近年來，油輪結構損傷的事件時有所聞，因此各船級協會及船廠對於船體構件的疲勞強度逐漸重視。經調查顯示，船體結構在長期各種變動負荷的作用下，產生疲勞龜裂等現象，而無法維持其原有的強度。又因船舶輕量化的緣故，高張力鋼廣泛使用，使疲勞方面的課題更趨重要。 共同結構規範是由IACS(International Association of Classification Societies)所制定，目前IACS有十個國家的船級協會加入，吸取各方經驗並制定出法規，不但能提升船舶在海上的安全性，也能使法規更有一致性。 本文介紹一般疲勞分析方法及共同結構規範之疲勞分析方法。依據共同結構規範之疲勞分析方法，以一艘四萬噸的油輪為分析對象，並利用法國驗船協會所開發之VeriSTAR Hull程式，配合FEMAP有限元素分析軟體，進行船體的疲勞強度分析。包括船體運動、船體負荷、有限元素分析、船體長期應力分佈，並根據累積損傷法則(Miner’s damage rule)計算船體疲勞壽命。而後針對計算結果，嘗試改變應力集中處的結構來降低應力集中的現象，以提升船體疲勞壽命。

Recently, the damage of oil tankers have happened frequently. Therefore, classification societies and shipyards show increasing concern about the fatigue strength of the ship’s structure components. Data from investigation show that fatigue damage of ship structures are caused by stress range on structure members under long-term changeable wave loads. Because of increasing need for ship lightening, the high tensile steel is being widely used, broadening the risks of fatigue damage. The study of fatigue is hence becoming crucial and the knowledge is widely needed. Common Structural Rules (CSR) is formulated by IACS (International Association of Classification Societies). IACS has ten members, which are ten national classification societies. They absorb experience from all quarters and establish the regulations. They not only promote the marine security of ships, but also ensure the consistency of the rules. The general fatigue analysis method and CSR fatigue analysis method are introduced in this article. Based on the CSR fatigue analysis method, a 40000 DWT Oil Tanker is taken as the analysis object. The fatigue strength of the ship is analyzed by using the software --- VeriSTAR(developed by BV), in combination with finite element analysis software ---FEMAP. Analysis includes the ship motion, the ship hull loads, the finite element analysis, long-term distribution of stress, and estimates the fatigue life by cumulative damage rule (Miner’s damage rule). The aim of this study is to attempt to reduce the stress of hot spots by modifying the structure, and promote the fatigue life of the ship.