The Analysis Of Ultimate Longitudinal Strength Of Ship Hull Girders

It is very important to estimate the load carrying capacity of a ship's hull as a whole from the viewpoints of safety and economy.The concept of the longitudinal strength of ship hulls has changed and advanced greatly as the study on the failure mechanism of the hull is getting deep. By taking account the failure modes of yielding, buckling and their combination, as well as the non-linear interactions between structural members, the ultimate longitudinal bending moment is defined by the moment corresponding to the point with zero slope on the moment-curvature curve of the ship hull. The definition has considered as the most reasonable so far.The calculation of the ultimate longitudinal bending moment is extremely complicated because of the non-linearity both in material properties and in geometry of deformations. There are three main methods by far, nonlinear finite element method, idealized structural unit method and simple method.With great developments in modern mechanics, computational mathematics and computer technology in hardware and software, finite element analysis has made rapid progress in both theory and computational technology. More and more general-purpose or specialized programs have been in use, costs on performing FEA are reduced shapely. The most popular software around the word are such as MSC/MARC, MSC/NASTRAN, ANSYS, ABAQUS and ADINA, etc.. They both supply the user with user-friendly interface, strong analysis capability and powerful pre- and post-processing functions. Currently, FEA and its programs have become the standard tool for engineering design.Some calculation indicated, general-purpose programs can forecast load carrying capacity of a ship's hull accurately if we take sufficiently into account every load and boundary combination, structure imperfections and initial stresses, together with geometric and material non-linearity.In this article, we have analyzed the load carrying capacity of several hull or hull models by using the general-purpose programs MSC/MARC, and gainedsome detailed results. Through comparing FEA results with foregoing calculation results or experiment data, we put forward some suggestions, which may be useful for future FEA.