Design Wave Approach For The Fatigue Assessment Of Bulk Carrier Structures

Fatigue damage is one of the main failure modes of ship and marine structures. With the development of technology, fatigue damage problem has become a vital research field in ship building and ocean engineering. Presently, methods for the fatigue assessment proposed by classification society are divided into two parts, one is the simplified method, and the other is direct calculation method, which is based on FEM method. The direct calculation method includes the spectral-based analysis method and the design wave approach. The simplified method based on empirical formula, may leads to a large extent of errors, and it also cannot express the detail of the structural. The spectral-based analysis method cannot apply widely because of the quantity of work and the advanced technique, on account of those reasons the design wave approach for the fatigue assessment comes along. The most significant advantage of the design wave approach is it could consider the combination of various load components rationally.The aim of this paper is to do a research on the design wave approach of fatigue assessment for bulk carrier structures, the main contents are as follows:1) The damage and fatigue reference stress range of five bulk carrier are finally obtained by using the spectral-based analysis method. The main work includes the building of finite element models, the subtraction of corrosion, the application of wave loads and inertial cargo pressures, and the calculation of stress response.2) In the process of defining design waves, the design wave systems are determined by various dominant load parameters. After that the stress ranges of bulk carrier structures are obtained by each design wave.3) Taking the results calculated by the spectral-based analysis method as a target, then the structural stress ranges under the design waves are fitted to the fatigue reference stress ranges by the least square regression analysis and the combination factors of the stress ranges are obtained. The design wave approach for fatigue assessment is obtained.