Study On Fatigue Strength And Its Influence Factors For Trimaran’s Typical Position

In the process of developing the sea the new demands for new ship have been proposed. As one of the best, the studies of trimaran are concerned. In order to improve its performance, the structure of trimaran has great difference with common ships. Compared with other parts, cross-structure of trimaran is weak in strength, endured great force and large deformation. So there is no doubt that cross-structure is the main part of trimaran which exist hidden danger. Safety assessment technology is significant for ship and marine design work. Once structural damage accident happened at the sea, it might cause serious economic loss and casualties. Thus, the safety and reliability of the trimaran structure research clearly has vital significance.Current research shows that fatigue damage is one of main failure mode of ship construction. Based on the basic tenets and approaches of fatigue evaluation and used the finite element method, this paper will research on structural strength model, fatigue load calculation, evaluation method of fatigue strength, uncertainties of fatigue loads and reliability of fatigue life of cross-structure of trimaran. The major research are as follow:(1)Briefly describe the existing methods of fatigue evaluation of ship structure. The basic principles, analysis steps and relative corrections of fatigue strength analysis method was discussed, which is based on Miner linear cumulative damage theory and S-N curve.(2)Established finite element model of the trimaran, and determined appropriate load cases to make the ship strength analysis according to the relevant specifications. And determined several fatigue hot spots on the cross-structure of trimaran according to the calculation results. On this basis, we will refine the grid near hotspots to get the model of analysis of trimaran fatigue strength.(3)Established trimaran hydrodynamic model, and calculated hydrodynamic parameters in different load case according to the requirements of fatigue evaluation. Then loaded the result into the trimaran fatigue strength model and got fatigue loads based on linear theory. Furthermore calculated the fatigue life of the corresponding hotspots by spectrum analysis method(SAM).(4)Investigated wave loads uncertainty influence of fatigue life, mainly consider the following aspects: wave spectrum, significant wave height, average zero crossing period, uncertainty of sea states and wave direction. Furthermore, the reliability of fatigue life was discussed with considering various uncertainties.