Research On Loads Equilibrium In Ship Direct Assessment By FEM

While the increasing demand for ship safety from major ship classification societies,the direct strength assessment by finite element method has gained more and more applications in the field of ships.At the same time,the requirements of direct strength assessment are more and more strict,especially for the loads of ship's finite element model.For the full ship model calculation,the ship body needs to be in static equilibrium state according to the rules.Therefore,it is necessary to calculate the balanced floating state of the ship on the assumption that the load case is static floating on the wave.For the ship in the state of acceleration,it is necessary to calculate and apply the ship's inertia force and the dynamic load of the cargo.As for the direct strength assessment of cabin model,sometimes the loads of finite element model need to be calculated by bending moment and shear force curve,so a useful method to calculate the loads is needed.At present,the methods to solve the above three problems still have some shortcoming and deficiencies.Therefore,in order to meet the requirements of rules and research,it is needed to create better ways to solve the key problems in finite element analysis of ship structure.The wet surface model and full ship mass model need to be created to calculate the floating state of ship,which will increase the workload of finite element analysis of ship structure.In order to simplify the calculation process,a calculation method for calculating the floating state of the ship which only needs the finite element model of ship structure is proposed in this paper.This method is based on the approximate response relationship between the floating state and buoyancy,trim moment and heel moment,and calculates the balanced floating state of ship by iterative method.In order to calculate and apply the ship's inertial force under acceleration,the response relationship between the inertial force and acceleration is deduced.As for the cargo's dynamic load,based on the approximate formula of dynamic load of bulk cargo and liquid cargo given by HCSR rule,considering the shape and location of cargo hold,the response relationship between dynamic load and acceleration is deduced.Through the above response relations,the acceleration of the hull under external force,as well as the ship's inertia force and the dynamic load of the cargo under this acceleration can be obtained.As for the calculation of loads on cabin model,firstly,through theoretical deduction proved that by applying vertical force to cross section of cabin model,and applying moments to the ends of cabin model can make the bending moment and shear force curves meet the target value.In order to complete the above calculation quickly and accurately,the computer programs are coded for the above three methods respectively.Some target ships are selected to verify these three methods.The results show that these three load calculation and application methods can meet the precision requirements of rules,and they have obvious advantages over the previous methods and can significantly reduce the working time of applying loads.The above three load calculation and application methods have great engineering value and can be widely applied in the field of finite element analysis of ship structure.