Study On Fatigue Strength Assessment Method Of Large Marine Pressure Vessels

The fatigue failure of ships and offshore engineering structures has always been the focus that cannot be ignored,but the fatigue problem of marine pressure vessels in the marine environment is still needs improvement.This paper mainly studies how to evaluate the fatigue strength and predict the fatigue life of large marine pressure vessels in the marine environment,puts forward a fatigue evaluation method suitable for marine pressure vessels,and analyzes the feasibility of using this method to evaluate the fatigue of a marine pressure vessel through numerical simulation.Taking a ship-shaped floating structure with pressure vessels as an example,a method for fatigue assessment of marine pressure vessels using finite element analysis software is formed on this basis.The specific research contents are as follows:(1)The basic principle and calculation steps of the fatigue assessment method for marine pressure vessels are discussed.This article uses a direct calculation method based on spectral analysis to evaluate the fatigue of marine pressure vessels,and provides a brief explanation of the basic principles of fatigue assessment.The principle and calculation process of three transfer function calibration methods are introduced,and the regular wave experimental simulation method which is more suitable for marine pressure vessels and more accurate and reasonable is proposed.The principle and method for determining the short-term and long-term distribution of stress range are briefly described,and the formula for calculating fatigue cumulative damage is given.(2)A complete fatigue evaluation calculation of a marine pressure vessel was carried out by using ANSYS software.First,the finite element model of the whole ship is established in the classic ANSYS,and the hydrodynamic analysis of the ship is performed on the Workbench platform.The wave load file of the ship is extracted with the help of the AqwaWave program.After the loading calculation,select the fatigue damage assessment location,obtain and compare the stress response transfer functions of each wave direction and frequency with three methods,then determine the short-term and long-term distribution of the stress range,and finally calculate the fatigue cumulative damage.Through the fatigue assessment of the example,a set of fatigue assessment methods for marine pressure vessels from structural finite element modeling to fatigue cumulative damage calculation are formed.(3)The feasibility of the method is verified by comparing the fatigue evaluation results.This paper discusses the methods of revising the fatigue evaluation results according to the norms in each field,and discusses the influence of the norms in each field on the fatigue evaluation results.The time-domain fatigue evaluation method was used to calculate the fatigue damage of part of sea state and part of wave direction.Transient time-domain analysis was carried out on the whole ship on Workbench platform,and the results were compared with the method proposed in this paper.It was concluded that the calculated results of the method proposed in this paper could accurately reflect the fatigue damage of the structure,and the results were safer than the time-domain method.