Research On Simplified Vibration Model Of Ship Hull Girder

Aiming at the practical engineering problem that the traditional ship natural frequency prediction method is difficult to be applied to high-order frequency prediction,this paper deals with the shear effect involved in the one-dimensional beam simplified model in the study of hull natural vibration characteristics and the simplification in the three-dimensional finite element modal calculation A series of studies have been conducted on modeling methods.In order to study the effect of shear deformation on the vibration characteristics of ships,the shear lag theory and Levinson high-order shear beam theory in the field of highway and bridge were used to derive the vertical vibration control differential equations of simply supported beams with box sections based on the energy variation method.Assuming a simplified displacement function,using Hamilton variational principle to solve the analytical solution of the natural vibration frequency of a box-shaped straight beam with a straight section under the simplified displacement function under the MATLAB environment.A straight-walled box girder model was designed and its natural frequency was calculated.The Levinson beam theoretical solution,the Timoshenko beam theoretical solution and the finite element numerical solution of the box beam at different half-wavelengths were compared.Deviation ratio.The calculation results show that the Levinson beam theory has better applicability than the traditional method in high-order vibration,that is,when the pitch of the vibration nodes is small,and the stability is better than the calculated value of the Timoshenko beam theory.In order to study the influence of local structural simplification on the vibration analysis results of hull girder,the unidirectional stiffened plate is taken as the main research object,and the orthotropic plate method and the equivalent plate thickness method are combined to propose an equivalent thickness orthotropic for vibration analysis Board simplified method,and compared with the commonly used simplified method.The natural frequency formula of the simplified model of the stiffened plate under three kinds is deduced,and the natural frequency of the four-sided simply supported unidirectional stiffened plate is calculated.The results show that the simplified method proposed in this paper is used to obtain the low-order natural frequencies of unidirectional stiffened plates,and the calculation results are superior to the commonly used stiffened plates.In this paper,the simplified method is used to calculate the natural frequency of the hull girder.While the simplified model reduces the workload of finite element modeling,the calculation results fit well with the finite element simulation results.It shows that the simplified method of equivalent thickness orthotropic plates can be used in the modeling of ship vibration finite element model,and it has certain advantages over the previous method.In order to compare the influence of local structure and shear effects on the higher-order vibration of the hull girder,the orthotropic plate method and the equivalent plate thickness method were used to simplify the reinforcement on the wing-plate stiffened box girder,and the simplification was programmed in MATLAB The natural frequency of the model.The results show that the selection of the appropriate shear deformation mode is particularly critical in higher-order vibrations,while the influence of the local structure on the overall vibration is relatively small.