Numerical Simulation On The Ultimate Strength Of Hull Girder Under Dynamic Bending Moment

The ultimate load carrying capacity of the hull girder is of importance to reflect the safety and reliability of the ship structure.To ensure the safety and reliability of ship structure in the ship structure design and assessment,it is necessary to evaluate ultimate strength and post-ultimate strength behavior under the ultimate load,especially under the dynamic bending moment.With the development of the shipbuilding industry,the design of ships tends to be larger,more speedy and lighter.The ships may encounter more harsh marine environments during operation,and the requirements of the ship structures will be further enhanced.In engineering design,the ultimate strength of the ship structure is evaluated by the static method at present stage.However,the response of the ship structure under the action of the ultimate dynamic load will be more intense,and the ship structures meet the requirement of more severe ocean environment is a problem that the shipping industry workers urgently need to solve.Due to the incompatibility of the analytic method and empirical formula to the ultimate strength of hull girder and the difficulties and uneconomies of the actual ship experiment,this paper aims to analyze the dynamic response of hull girder under the dynamic ultimate moment load from the viewpoint of numerical simulation.The nonlinear finite element method is used to study the dynamic response of the stiffened plate,deck plate frame and hull girder structure,the material nonlinearity and geometric nonlinearity are considered in the simulations.The main contents are listed as follows:(1)The failure modes,ultimate strength and the difference of static load and dynamic load for a typical stiffened plate under axial load are studied.The nonlinear finite element method is utilized to calculate the failure mode of the stiffened plate with the influence of the initial geometric imperfections and the boundary conditions.The stress-strain curve of the stiffened plate under extreme conditions is obtained.At the same time,based on the concept of traditional ultimate strength and dynamic calculation method,the ultimate strength values under dynamic time-history loads with axial displacement and axial force are respectively calculated and compared;(2)The static and dynamic response process of deck structure under ultimate load is studied.The ultimate strength of the deck slab was calculated by the traditional method of static ultimate strength calculation,and the static failure process and ultimate strength of the deck slab structure were obtained.Considering the actual dynamic load acting on the deck plate structure,the dynamic load history is divided into the dynamic load changing with the wave period and the slamming load in a very short period of time,and the dynamics of the deck plate structure under two dynamic loads response;(3)The ultimate strength values of hull girder structures and the failure modes and ultimate strength values under dynamic loads are studied.The section with the largest central bending moment and the extension on both sides are selected as the finite element model of the hull girder section.The ultimate strength and failure modes of hull girder structures in mid-arch and sagging are studied respectively based on the traditional static analysis method and dynamic method.The dynamic response and stress-strain distribution of the hull girder beams under ultimate and failure conditions are studied.The difference of response of hull girder under static and dynamic load is analyzed.The evaluation method of hull ultimate strength under dynamic load is proposed.(4)The sensitivity of parameters affecting the dynamic response of hull girder structures is studied,such as different load cycles,slamming and dynamic load peaks,initial geometric imperfections of hull girder structures,and structural dimensions.Based on the criterion of static ultimate strength assessment,a method to determine the dynamic ultimate bending capacity of hull girder under dynamic load and the evaluation method of dynamic ultimate strength are proposed.