On long-term prediction of stresses in principal members of ship hull structures

Abstract

The paper presents a discussion on the strength criteria and load cases required in the rules of classification societies for direct FEM strength analysis of ship hull structures, which show some differences to each other. The conclusion of it is that detail studies on stress values in ship structures are necessary to improve the requirements. With this end in view an effective method for long-term prediction of stresses in ship hull structure principal members is proposed. The method is based on the concept of influence coefficients and spectral analysis of wave loads. A FEM model of the principal member system in the form of 3D frame is applied to calculate values of the influence coefficients. Next, the concept is used of correlation factors for combining characteristic long-term stress values caused by global and local loads, with combined stresses due to general bending of the ship, zone bending of the principal members and local bending of longitudinals. As an example, results of stress prediction and correlation factors calculated in some points of hull structure of a panamax bulk carrier are presented and discussed.