Fatigue Assessment Of6900Cars PCTC Ship

Fatigue damage is one of the main failure modes for ships and offshore structures. It will affect the safety of structure and cause property losses. This issue have been paid great attention by the foreign and domestic researchers in this field. So it is necessary to assess the fatigue strength of ships and offshore structures reasonably.As a special type of ship, PCTC has several layers of decks to meet demand of loading. And these decks are all light and thin. There is no transverse bulkhead in the ship, so that cars can embark and debark easily. So flexible design is adopted to resist transverse distortion. There is no specific regulatory requirements about fatigue assessment for PCTC. So fatigue assessment is performed for it, which will make great practical significance in the design and construction of PCTC in the future.The main aspects studied in this paper are as follows:1. The basic theory of fatigue analysis and general methods for fatigue strength analysis of ship structures are expatiated. The fatigue cumulative damage method which based on S-N curve and Miner’s linear cumulative damage theory is introduced. And crack mechanics based on Paris crack propagation law and reliability assessment method are described.2. Distribution law of wave-induced load of6900cars PCTC ship is simulated. Ship model is built and wave-induced loads of the ship in different load cases, different incoming waves, different wave frequencies is studied using module of HydroD of Sesam software which is developed by DNV(DET NORSKE VERITAS). And long term prediction in different given return-period and exceed probability is studied as well.3. The parameters selection method of design wave for6900cars PCTC ship is introduced.Based on the value of transfer function and long term wave-induced loads, six groups of design wave are selected. And structural strength of ship hull in typical load cases is analyzed via the FE method.4. Fatigue strength assessment is performed for6900cars PCTC ship. Based the stress distribution of the structure and the engineer experience, three fatigue check points are selected and the corresponding meshes are refined. The fatigue strength assessment at these check points is performed using the stofat module of the Sesam software via the submod method.