Research On Fatigue Strength Standardization Of Naval Vessels

More and more attention has been paid to the fatigue strength of ship structures due to the trend of navy ship upsizing and the application of special steel and high strength steel.The military standard only provides the simplified checking method of main longitudinal structure fatigue,and it only takes into account the effect of wave bending moment and the slamming bending moment of hull beam when calculating fatigue load.In recent years,the fatigue checking of many types of ships mainly refers to the methods of various civil regulations,and the new models are re-approved for analysis and verification.However,there is no unified standard for the fatigue evaluation of ships.Therefore,it is necessary to establish a set of fatigue assessment methods suitable for Chinese ships by referring to civilian standards.On account of the characteristics of ship structure and hull fatigue load,this paper adopts the direct calculation method of typical ship nodes to establish a reasonable and feasible direct calculation standard for the fatigue checking analysis of ship structure.The main research contents include:Through the comparative study of various specifications,a simplified calculation standard for ship fatigue assessment is established.By comparing the specific contents of the fatigue specifications for CCS and DNV,the standard method for simplified calculation of ships is obtained.Multiple specifications and standards established in this paper are used to evaluate the fatigue damage of longitudinal and transverse bones in ships,and the results are compared and analyzed to verify the accuracy and applicability of the standards to ships.The hot spot criteria for ship fatigue assessment is established.The fatigue damage of each typical structure is obtained based on the design wave,then the damage degree is sorted according to the type and size of the typical structure,and the nodes with larger damage degree of each typical structure are selected as the fatigue hotspots,and the ship fatigue evaluation standard based on the design wave is established.Then,based on spectral analysis,the hot spot screening of ships is studied.A large number of nodes of typical ship structures are selected for calculation,and the fatigue life of all selected nodes is obtained by sorting them according to damage degree.The standard of ship screen point based on spectral analysis is obtained and compared with the design wave method.According to the spectrum analysis principle and the ship’s own characteristics,the fatigue load,model building method,boundary condition and interpolation method are studied to establish the spectrum analysis standard applicable to the ship’s fatigue assessment.Taking a large warship as an example,the fatigue of spectrum analysis is evaluated.Based on the time domain,the ship fatigue damage is corrected by taking into account the slamming,and the nonlinear fatigue evaluation standard is established.The beam theory is used to calculate the bang damage and the wave frequency damage,then the nonlinear contribution degree and the nonlinear influence coefficient of each wave direction can be obtained,and then combined with the spectral analysis results,the direct calculation standard of ship including the bang can be obtained.