Fatigue Assessment Ofshipbased On 3D Hydroelasticity

In recent years,with the increase of the main scale of ships and the use of high strength steel,the stiffness of the hull decreased been continually.The amplitude of the elastic deformation of the hull structure in waves should notbe ignored,compared with that of the rigid body.The traditional wave load theory and the ship rules gradually show their limitations in the calculation of hull motion and wave loads.Therefore,in order to safely and rationally design a large ship structure and ensure its safety and reliability,it is necessary to combine the fluid dynamics with the hull structure dynamics to deal with the fluid-structureinteraction problem in a unified manner when the seakeeping performance prediction and structural assessment of a large ship are carried out.The three dimensional hydroelastic theory shows more and more extensive development potential and application prospects in these areas.However,the commercial computing software at home and abroad can not yet consider the effect of hydroelasticity.THAFTS,a three dimensional hydro-elasticity analysis software,came into being under this background.Based on the three dimensional hydro-elasticity theory and the THAFTS software system,this paper studies the application of THAFTS in structural design and fatigue analysis of large ships.Firstly,the finite element model and hydrodynamic panel model of a large bulk carriers and container ships were established.The modal analysis results of the dry hull structure in vacuum were given.On this basis,the hydrodynamic coefficients,wave excitation forces and the principal coordinate response were studied.At the same time,the AQWA rigid body calculation results are given for comparison and the influence of speed is discussed.Secondly,the springing of the principal coordinates response of the hull and amplitude-frequency response of the midship section load are analyzed and studied.The influences of speed and wave direction on springing are discussed.At the same time,the mechanism of springing is studied.Thirdly,short-term and long-term prediction are carried out for ship motion response and section loads.The influence of speed on the long-term prediction results of hull section loads is discussed,and the long-term prediction results of section load distribution along the ship are compared with rules of CCS.Finally,a fatigue spectrum analysis method considering springing was established to evaluate the fatigue damage of large bulk carriers and large container ships.The hot spot stress and fatigue life of typical nodes were calculated.The calculation results are compared with the results obtained from the traditional fatigue method and the effects of springing on fatigue damage of the hull structure are discussed.In summary,the motions,loads,and fatigue damage arestudied based on three-dimensional hydroelasticitytheory and THAFTS software.The influence of springing on wave loads and fatigue strength are analyzed preliminarily.The conclusions obtained from the paper will provide important reference value for the structural design and fatigue analysis of large vessels.