A Simplified Method to Analyse the Strength of Double Hulled Structures in Collision

The strength of ship structures in collision is an important matter in terms of saving life, preventing pollution and from an economic point of view, especially in the case of hazardous cargo carriers, oil tankers and so on. So far, several analysis methods or formulae have been presented to estimate the collision strength of such ships. However, there are few papers in which the accuracy of the methods have been verified.In this paper, the collision strength of a typical double hulled structure was examined. The types of collisions were classified into five groups from a geometric view point between a colliding bow and a hull. Two kinds of experiment (which were considered to be more critical than others among those five groups), were carried out using large scale models. The first was an experiment in which a stem collided against the ship's side and in the other a bulbous bow collided against it. In both cases, the bow models were assumed to be rigid.A simplified method to analyse the damage of double hulled structures in collision was developed on the basis of the results from the experiments. As far as this method, is concerned, a double hulled structure is considered to consist of three main structural members, the side shell, trans web frames and side stringers. The side shell is modelled into plastic membrane plates, and trans webs and side stringers are assumed to support the side shell rigidly and buckle when critical load is imposed.The method was formulated in matrix form, where triangular membrane elements and buckling elements are used to model a double hulled structure.The accuracy of the analysis method was then examined by comparing the calculated values with the experimental ones. From these, a strong correlation emerged.