Structural Dynamic Response Analysis Of Super-Large Container Under Spring Load

With the development of ships towards large-scale,the wave load forecasting methods based on rigid body theory and the structural strength assessment method based on quasi-static have been increasingly unable to meet the computational requirements.The wave loads calculation method based on the theory of hydroelasticity appears for large ships,and dynamic analysis methods are more and more used in structural strength assessment.However,it is still not perfect at present,for the wave load forecasting method based on the hydroelasticity theory,there are three-dimensional linear frequency domain and three-dimensional non-linear time-domain prediction method have high precision,however,the two methods have advantages and disadvantages and their optimal applicability.For structural strength assessment,the stress-strain response of the structure needs to be calculated first,the response magnitude due to the structure elastic effect can be comparable to the wave-frequency result for a very large ship.At present,there are few researches on the dynamic response of hull structures under the springing loads,but it is necessary to research the calculation method of the springing response for super large ships.The specific research contents are as follows:(1)Based on the study of ship wave loads frequency domain and time-domain hydroelasticity calculation method,two different calculation methods were used respectively to calculate the wave load of four sample ships,the vertical bending moment and the moving results in time domain are compared with the frequency domain results separately.Based on the differences of the results,the optimum ship types of the two calculation methods were explored,and the nonlinear effects caused by ship types were studied.(2)According to the ship structure dynamic response analysis method proposed in this paper.First,the structure of the load and deformation conditions are solved.In this paper,the calculation methods of hull structural elastic deformation are studied based on ship wave load frequency domain and time domain hydroelasticity respectively.Taking the 21000 TEU container ship as an example,the deformation results at certain positions of hull are calculated respectively,the frequency domain results are compared with the time domain results.Finally,the structural loads applied in the structural dynamic response analysis are analyzed,and the calculation methods of the frequency and time domain loads are given.(3)Due to the limitation of software and computer's computational ability,it is a difficult problem to analyze the dynamic response of the detailed whole ship model at present.Therefore,it is necessary to adopt a certain simplification when the calculation model is established.In this paper,two simplified models of local model and hybrid model are proposed for calculation.In order to study the dynamic response of different structural models under the springing loads,a three-dimensional beam is taken as the research object,the local,mixed and complete models are established respectively,and the structures frequency domain and time domain dynamic response under the unit amplitudes of the three models are calculated respectively.By comparing the three results,the method of structural dynamic response under the springing loads is validated.From the mixed model and the local model,it is confirmed that the hybrid model has the same vibration characteristics as the complete model.Finally,the total structural dynamic response of the hybrid model and the complete model under irregular wave is given,and the high frequency response caused by the projectile vibration is proposed.(4)According to the optimal modeling principle determined in this paper,21000 large container ships are modeled,and then the external forces and boundary conditions imposed by the structure are calculated through the solution of the load and the deformation conditions of the structure.Due to the large opening of a large container ship deck,the horizontal bending and torsional effects of the structure are taken into account in calculating the dynamic response of the structure in addition to calculating the vertical bending.Finally,the frequency dynamic response and the time-domain dynamic response of the structure are obtained respectively by calculation and solution,respectively.