Fatigue Analysis and Reliability Assessment for a 17K Oil Tanker

Abstract

오랜 기간동안 피로로 인한 균열 및 파괴는 선박과 해양구조물에 대한 가장 중요한 문제중의 하나로 인식되고 있다. 최근 10년동안, 고장력강(HTS)을 이용한 선박의 대형화로 인하여 피로 문제가 더욱 크게 대두되었다. 대부분 연구에서 선박의 피로 강도를 어떻게 합리적으로 평가하는지를 고민하고 있다. 이에 따라,세계 주요 선급에서도 적절한 피로 평가 지침을 발행하였다. 그러나 많은 복잡한 요소들이 피로 성능에 영향을 끼치고 있다. 예를 들어, 파랑 및 화물의 하중, 여러 가지 응력의 합성, 응력 집중, 평균응력과 부식 환경 등이 그러한 것들이다. 그리고 각 선급에 따라 기술지침서의 내용도 다르다. 본 논문에서는 DNV선급에 따른 피로 평가 절차 및 간략화한 계산방법을 이용하였고 이를 실제 선박에 적용하여 이에 대한 신뢰성을 평가하였다.

Fatigue cracks and damages have been an important issue for ship and offshore structure in a long times. Initially the obvious remedy was to improve detail design. However, in the last decades, with the introduction of higher tensile steels in hull structures and dimension of ships become larger than before, the greater attention should be paid to fatigue problem. Most of researches focus on how to access the fatigue strength of ships more reasonably. Also, the major classification societies have already released their fatigue assessment notes. But due to the complexity of factor influencing fatigue performances，such as, wave load and pressure from cargo，the combination of different stress components，stress on concentration of local structure details，means stress and the corrosive environments etc，there are different specifications with varying classification societies，so it will lead to the different of results from different fatigue assessment methods. This paper founds on the DNV classification notes “fatigue assessment of ship structures” that expatiates on process of fatigue assessment and simplified method. Finally, a fatigue analysis was taken by use data of a real ship and assesses the reliability of the result. The main aspects of this paper are as following: 1. Expatiation of elements of fatigue analysis and general method for fatigue strength analysis of ship structure----Focuses on base theory, analysis process and characteristic of S-N curves. 2. Simplified method of fatigue assessment----Expatiates the base theory and analysis process, and then, estimates the design life of the considered point by using simplified analysis provided by DNV fatigue assessment rules. 3. Reliability assessment---- Expatiates the base theory and analysis process, and assesses the reliability of result of fatigue analysis.