Research On Direct Strength Analysis Of Ship Structure

Direct strength analysis of ship structure is an important means to evaluate the safety of ship structure.Owing to the fact that the method can reflect the effect of various load combinations on the hull structure and fully reflect the stress levels of various components of the hull.Applicability has been recognized by the ship industry and has been incorporated into the ship structure safety specification system.According to the structural modeling method and the simplified degree of the model,the direct strength analysis can be divided into direct strength analysis of the plate-beam combination model and a direct strength analysis of the cross beam system.Although the more detailed structural modeling,the more accurately the structure details,component connection relationships,plate thickness distribution,etc.,Establishing a highly-simulated finite element model requires a relatively long period of time even for designers with rich modeling experience.The long cycle will also impose higher requirements on designers.Therefore,it is particularly important to choose structural analysis model and computing tool flexibly according to manpower,time and resource cost.This paper starts from two direct strength analysiss and systematically studies several problems in the direct strength analysis.Cross beam calculation methods play an important role in the synthesis of stress methods.In this paper,the simplified box girder model of a 27 000 DWT tanker is taken as an example.The comparison of the stress components of the plate-beam combination model method and the composite stress method is the entry point,and a multi-level refinement strategy on grid is adopted in the analysis of the plate-beam combination model.The convergence of stress in the calculation method is analyzed,and the convergence solution is selected to be compared with the calculated results of the composite stress method.The quantitative analysis of the difference in stress components between the two calculation methods is carried out.Then,the key issues involved in the plate-beam combination model method of the local model,cabin model,whole ship model are summarized,including the application object,main purpose and calculation method.Combine the grid division technology,modeling process and modeling method applied to the plate-beam combination model method.Taking a deck transportation ship as an example,the key technical measures for the direct calculation of the plate-beam combination model using the entire ship model is described,including the whole ship static load calculation method,static balance adjustment method(i.e.float state adjustment),wave dynamic pressure calculation method,dynamic balance adjustment method(i.e.inertial force calculation method)and so on.Finally,based on the characteristics of ship cross-beam calculation and the finite element displacement method,the static calculation tool applicable to ship cross-beam system is developed.According to the preliminary completed cross-beam calculation tool,from the perspective of program design,versatile procedural methods are discussed,including calculation of element stiffness matrix,calculation of equivalent nodal forces of beam element loads and self-weight loads,define operating conditions,define boundary conditions,freedom of release,calculation of internal forces and internal force curves parameters,and other important functions.