The Fatigue Assessment Methods For Structures Of Naval Vessels

Fatigue damage is one of the main failure modes for naval architecture and ocean structurs and has been a vital research field for a long time.The major purpose of this thesis is to make the research on the method for fatigue assessment of structures of naval ships.The main contents are as follows:1) Research on the simplifid procedure by classification societies. The discussion concentrates on the wave induced hull girder bending moment, the external dynamic wave pressure, the calculation of ship accelerations and motions, the hull girder stress, the regulation on mean stress, S-N curves as well as the criterion of fatigue assessment. The differences between GJB, CCS rules and BV military rules are discussed.2) Research on the spectral-based fatigue analusis.The basic theory and procedures of the spetral based fatigue analysis is discussed. Further research is mainly on improve the efficiency of loading approach, boundary condition and local details such as hatch corners.3) Research on the design wave approach. Under the linear wave loads, the dominant load parameter and the selection of design wave in terms of dominant load parameters are discussed. Then the characteristics of the design wave approach for fatigue assessment are discussed. Based on concept of the design wave, a new method is present to select a design wave. Fatigue check for four ships is done and the results are compared with that of spectral based method.4) Fatigue check is a very particularity work for unsuitable deals with local details will cause errors. A unique definition and the numerical calculation of the structural stresses are poblematic, which has resulted in the development of different variants of the approach. These are discussed and compared with each other in the present paper.