Transverse Strength of Ships

The research study presented in this thesis is principally concerned with the transverse strength problem of ship structures. The main interest of the study lies in naval ships such as frigates and small destroyers which usually have a rise of floor in the range of 10 to 20 degrees and a relatively large radius of bilge, necessitated by comparatively high ship velocity to length (V/√L) ratios. Having outlined and historically reviewed the transverse strength problem of ships, the application of the finite element method to the analysis of a compartment of a frigate hull between major bulkheads under predominantly lateral loads is described. The fundamental aspects of the finite element modelling of structures are discussed from a general perspective along with an emphasis on the modelling of the plate-beam systems. The finite element modelling of the compartment of a frigate model hull, tested by Clarkson and Wallace(1967), for the linear elastic analysis of transverse strength is outlined. The results of the finite element analysis of the compartment and comparisons with the measurements are presented. In addition, the results of a parametric study on the effect of some geometrical features on the structural response for the hydrostatic pressure loading are discussed. Further, the analysis of the compartment with a different modelling strategy to account for the effect of the overall bending of the whole test hull girder is described. The results of the analysis and comparisons with the measurements are presented. The study further concentrates on the bottom structure of the compartment due to the characteristic nature of structural behaviour under lateral loading, arising from the geometrical configuration. The linear elastic behaviour of stiffened plates with vee-shaped geometry representing the bottom part of a ship's section under lateral loading is analysed by employing the orthotropic plate theory within the finite strip method. A finite strip formulation for the analysis of folded stiffened plates under lateral loading is given. The results of the analysis of an example stiffened plate are discussed. The analysis of the non-linear elasto-plastic behaviour of the bottom structure of the compartment, performed by using an incremental-iterative finite element solution procedure, under hydrostatic pressure loading is presented. The research effort presented endeavours to provide an improved understanding of the ship structural mechanics from the transverse strength point of view. It is hoped that the conclusions of the work will furnish the designer with a better understanding on overall as well as local structural behaviour of the type of ship structures under consideration subjected to mainly transverse loads