Global FEM Strength and Fatigue Analysis of Large LNG Vessel

Abstract

Due to the dangers of liquefied natural gas and the high price of a liquefied natural gas (LNG) vessel, there are high reliability and safety requirements with the structure design of large LNG vessels. Taking a large LNG Vessel designed by Hudong-Zhonghua shipbuilding group as a research object, global finite element model (FEM) strength and fatigue analysis was carried out by DLA/SFA software. Five typical load conditions, including fully loaded, ballast, one tank empty, two adjacent tanks empty and three adjacent tanks empty conditions, were considered in the global strength analysis (Dynamic Loading Approach, simplified as DLA), following the Guide for Safehull-dynamic Loading Approach for Vessels (DLA Guide). For the fatigue analysis spectral-based fatigue analysis, simplified as SFA, two typical operational load conditions, including homogeneous load condition at summer draught departure and ballast load condition arrival, were considered to achieve at least 40 years fatigue life requirement with north Atlantic wave spectrum, following Guidance Notes on Spectral-based Fatigue Analysis for Vessels (SFA Guide). Some special design details were taken to solve the local stress concentration yielding and fatigue problems. Some analysis methods and design experiences are discussed and proposed. The analysis procedure and solutions of global FEM strength and fatigue analysis in this paper for a large LNG ship can be a reference to analysis for other large vessels.