Research On Fatigue Strength Of Pctc Ship Considering Forward Speed

With the factor of large-scale vessel, using of high-strength material and research and development of new form of structure, the question of ship hull structure's fatigue strength is becoming more outstanding, fatigue damage become one of the main failure modes for ship and ocean structures. In the past of application of engineering, fatigue assessment is always caught out by simplified method or the combination of finite element method and simplified method, cumulative fatigue damage is calculated in zero forward speed in crucial spot. The major purpose of this thesis is to make research on fatigue assessment of ship structure under linear wave-induced loads. The key point is the effect of forward speed in calculation of cumulative fatigue damage. The main contents are as follows:1) The basic theory and principal method of fatigue of ship structure is expatiated. It contains S-N curve and Miner's rule of cumulative damage, simplified method of fatigue assessment, spectral fatigue analysis in direct method of fatigue assessment.2) The research on the calculation of wave-induced motions and loads in a harmonic wave with a forward speed which based on three-dimensional potential theory, method of long-term and short-term predictions for wave-induced motions and loads, basic theory of Rankine panel method.3) The predictions of a 5000car PCTC's motion performance and sectional loads in typical loading conditions based on three-dimensional time domain full speed theory. By analyzing the law of change between forward speed and motions and loads, we find the speed effect of surge, sway, roll and wave-induced moment is very remarkable.4) Strength analysis of overall ship's structure based on design wave approach. The basic theory of design wave approach and method of design wave parameters selection are expatiated. The six groups of design wave parameters are selected based on RAO and long-term predictions for wave-induced motions and loads. Finite element analysis in typical loading conditions is performed. The selection of fatigue point is according to the calculation result.5) The research on the cumulative fatigue damage and fatigue life of structure based on spectral fatigue analysis. The compare of cumulative fatigue damage in different forward speed is carried out. The conclusion is necessity of consideration of forward speed in fatigue assessment of high-speed vessel.