Structural design of mega LNG carrier

Abstract

Design of ship is a spiral of stages which highly effected by each others, where every step forward must be reviewed by previous stages to make the best combinations between requirements in all design stages and results. The initial design stage for ship depend on its mission and service, this functions determine the main characteristic and dimensions for the owner and shipyard. The final design should be arrived at taking into account not only present economic consideration but also those likely to develop within the ship life. This is especially for some trading like LNG where the ship will do the same work for all its working life. While spherical storage tanks are widely used in LNG carrier, this thesis aim to make hull structural design of mega LNG ship with spherical tanks type B, perform structural analysis based on the functional requirement of typical LNG carriers providing its main particulars, hull form as well as the general arrangements. The design is developed according to the GL rules integrated in Poseidon software. This work start by defining the structural concept of LNG carrier type B, where the spherical tank, which uniquely used in LNG ships, highly effect on the ship design, in way of providing enough space for huge tanks and ensure the hull rigidity. The second part is concerning the material selection for this kind of ships. To evaluate the scantling of structural members, Poseidon software was used to built numerical model, two approaches were considered, the first one analytical, where dimensioning of the structural elements has to confirm the requirements of the GL rules. The structural weight was estimated, section modulus, moment of inertia, was also calculated. In the second approach direct calculations were carried out with the use of the finite element method to verify that the stress level and buckling capability of primary structures under the applied load cases are within the acceptable limits. The 3D-FE model analysis and applied loading is to evaluate the loads and responses of all primary structural items including hull structure supporting the cargo containment system; inner and outer hull plating and associated structure; double bottom structures; cargo tank covers and their connections to upper deck. A buckling analysis is to consider the maximum construction tolerances.