Research On Nonlinear Similarity Method Under Torsion Moment For Hull Structure

Ultimate strength represents the max bearing capacity,which can ensure the safety and reliability of ship structure.Model test is the most fundamental and effective way to reveal its ultimate capacity.While conducting model test,only if there is a similar relationship between prototype and test model,the ultimate strength of prototype can be predicted through model test result.However,the linear similarity criterion can only guarantee the similar relationship in the linear stage.In order to obtain the ultimate strength of real ship through model test,the nonlinear similarity method between model and real ship must be investigated.Until now,nonlinear similarity method under bending moment has almost been completed,while nonlinear similarity method under torsion moment is still needing further research.With the trend of large-scale ship and the increasing of ship openings,the load of torsion moment has been an indispensable part of ultimate strength calculation for hull structure.Due to the lack of reasonable and reliable nonlinear similarity method under torsion moment,the ultimate strength of real ship under torsion moment can't be obtained.In order to solve the problem,the linear and nonlinear similarity characteristics and methods between test model and real ship are discussed in this paper.Then,the nonlinear similarity method under torsion moment for hull structure collapse test is proposed.Combined with nonlinear similarity method under bending,the test model designed under the guidance of nonlinear similarity method can be used to predict real ship's ultimate strength.The main work in the present paper is as follows:1)The collapse behavior of hull structure under torsion moment is investigated,and the buckling characteristics of plate and stiffened plate under shear load are analyzed.The main parameters which can represent its collapse characteristics are discussed and the nonlinear similarity method for hull structure under torsion moment is proposed.2)In order to verify the accuracy of nonlinear similarity method under torsion moment,a series of stiffened plate structure and box girder structure are designed based on the method.The ultimate strength of series stiffened plates under shear and box girders under torsion moment are calculated and analyzed.3)Based on the proposed nonlinear similarity method under torsion moment,combined with nonlinear similarity method under bending moment,a similar model of one developed flat type river-sea-going container ship is designed.The progressive collapse test under combined bending and torsion moment is carried out,and the ultimate strength of real ship is predicted by the model test result.4)The finite element model of real ship is established.The ultimate strength of real ship under bending and torsion moment is calculated and analyzed.The calculated result and the predicted result are compared and analyzed.Model designed under the guidance of nonlinear similarity method can be used to conduct hull structure collapse test and the ultimate strength of real ship can be predicted through test result.The proposed nonlinear similarity method under torsion moment makes up the deficiency in the field of ultimate strength model test.It has positive significance for the safety and reliability research of hull structure.