Comprehensive Study Of Wave Induced Load And Structural Strength Analysis Of Trimaran

The trimaran ship consisting of a main hull stabilised by two smaller side hulls is akind of HPV ship with low resisitence and good seakeeping performance at high speed.MoD of UK has done extensive R&D work about it since the beginning of this centuryand prepared it to be one of the main warcraft types in FSC plan. The trimaran ship hasbeen gaining high currency since then and a lot of institutes worldwide began to do awide range of research on that newborn ship. The basic design philosophy of trimaranis to get good seagoing performance with slender central main hull and to get sufficienttransverse stability and large cargo area with two small side hulls placed on both side ofit. Generally speaking, researches in recent years mainly focused on the theoreticalstudy on the calculation of wave resistence and the optimum sidehull’s layout tominimum it. These R&D achivements are the preliminary study which contributesmuch to the ship hull form design. There are few studies about the wave induced loadon trimaran and the existing reseach results are scattered and far less than systematic,and due to the lack of detailed structural design information, current study on thestructural performance of trimaran is fewer.This thesis deal with the wave induced load and the structural performance on thetrimaran, aiming at doing a systemtic study on the characteristics of the primary waveloads on trimaran and get an overview of the special structural response of trimaranunder hydrodynamic pressure. Details about the implementation and mainachievements of the reseach are presented in the following paragraghs:Firstly,3-D Rankine panel method was applied to calculate the response functionsof the wave load on typical sections along the mainhull and on the crossdeck. Thenlong term prediction results based on statistical wave information of North Atlantic were used to demonstrate their distribution characteristics along ship length as well asover wave directions. Sensitivity analysis of wave loads with different sidehull’slayouts and different ship speeds was investigated respectively. Sidehull’s layouts havesignificant impacts on longitudinal torsion moment and crossdeck’s transverse load andhave little influence on the longditidinal bending moment and vertical shear force.While the main hull has an opposite effect on these wave loads. Optimum design canbe executed to the main hull form and the side hull form individually with respect totheir severe load conditons. Desirable position of sidehull is about35%~40%of shiplength from the aft. Speed within (0.25≤Fn <0.4) is good for wave load on trimaran.Reducing the distance between center of mass and buoyancy of sidehull is good forcrossdeck’s structural performance.Research on the trimaran’s structural performance was the performed based on theequivalent design wave method. The stess distribution and deformation feature can begained through a linear quasi-static analysis by directly transfer the hydrodynamicpressure on the wet surface under the designed regular wave environment to thestructural finite element model. The reseach results showed that the connection point ofthe mainhull with the crossdeck is a hot stress point and it has to be reinforced or shapeoptimized to reduce the stress. Beam sea condition is bad for the structural strength ofthe crossdeck, especially in the area where the crossdeck connected to the mainhull.Optimum position of sidehull for trimaran’s structural performance is about1/3L~1/2L from the aft.