The Effectiveness Research Of Side Hull And Cross Deck Of Trimaran On Longitudinal Strength

The trimaran,as a new type of high-performance ship,has drawn attention in worldwide and own abroad application in military and civilian markets with its special ship hull and excellent hydrodynamic performance.But,the introduction of the side hull of trimaran complicates the structural form,which adds difficulty in the analysis of ship's structural strength.In current researches,it is common practice to ignore the contribution of the side hull and cross deck structure to the longitudinal bending,and only consider the participation of the main hull in longitudinal strength.Although the side hull and cross deck structure are shorter than the main hull,they still have quite big effects on the section's longitudinal strength in certain ship types and section areas,and these influences cannot be ignored.Therefore,the study on the effectiveness of the side hull and cross deck of the trimaran on the longitudinal bending is beneficial to the rational distribution of materials,which could optimize the structure and performance of the ship.In this paper,theory method and numerical simulation method are both employed to investigated the effectiveness of the side hull and cross deck of the trimaran on the longitudinal bending.The main contents and conclusions of this paper are as follow:(1)By applying theory method and finite element method(FEM),based on simplified trimaran model of a certain length and layout,the effectiveness of the side hull and cross deck are calculated with five different definitions of the effectiveness of superstructures.The advantages and disadvantages of these five definition methods on the trimaran are analyzed.It is founded that the five definitions of effective all have their own limitations in the calculation of side hull and cross deck's effectiveness in longitudinal strength.Thus,a new method,based on hull beam theory and named modulus reduction method,is proposed in this paper.(2)Based on the simplified model and the pure bending load,the deformation characteristics between the side hull and cross deck and the main hull are investigated.The contributions of different structures in resisting ship longitudinal bending are obtained by analyzing the components of the side hull and cross structures' longitudinal stress variation with different lengths of the side hull.The results show that the contribution of components in ship's longitudinal bending are higher when the side hull is closer to the main hull.By comparing the influence of side hull and cross deck on longitudinal stress of the main hull's deck and bottom,the linear relationship between ship bottom's longitudinal stress and the length of side hull are identified.The trend of longitudinal stress of ship deck varying with the length of side hull is different with that of ship's bottom.When the length of side hull is larger than 40% of the main hull's length,the change of ship deck's longitudinal stress is smaller.(3)Simplified models are adopted to study how the length and layout of the side hull effect the effectiveness of the side hull and cross structure.Different effectiveness definitions are applied to calculate the effectiveness of the side hull and cross structure and the changing characteristic of effectiveness with different length and layout of side hull and cross deck are obtained.The rationality of the modulus reduction method for calculating the effectiveness of the side hull and cross deck is verified.The variation of how the effectiveness of the side hull and cross deck vary with the length and layout of the side hull is obtained.(4)Based on a real trimaran model,a simplified trimaran external force balance method is proposed.The calculation of the longitudinal bending stress under the actual wave load is carried out and the longitudinal stress distribution characteristics of the main deck of the trimaran are analyzed.The modulus reduction method is used to calculate the effectiveness of the side hull and cross deck on longitudinal bending,and the effectiveness distribution of the side hull and cross deck along the length of the side hull is also obtained,which provide a reference for the structural design of the trimaran.