Slamming is a highly non-linear phenomenon between hull structure and wave. Due to the special structure of trimaran, the slamming mode is extremely different from that of traditional vessel. Besides bow emergence and enter, the slamming phenomenon of the out shell at the cross structure is also obvious. In conventional hull structure fatigue strength evaluation, the slamming load is usually not considered. However, the slamming problem is unavoidable at danger load cases, and the stress concentration of the trimaran cross structure is serious. So it is dangerous to ignore the existence of slamming in serious load cases when evaluating the structural fatigue strength. Therefore, it is necessary to study the contribution of slamming load to fatigue damage.

In this paper, a practical method for calculating and analyzing is presented to consider the effect of slamming on the fatigue strength of the trimaran cross structure to ensure that the fatigue life of the structure is closer to the true value. According to the linear theory, the relative motion and relative speed of the hull in wave and the stress response of the wave load on the structure are calculated firstly. Then, the stress response of the non-linear out shell slamming force is calculated. The linear response and non-linear response are combined. And the stress response time history under the combined action of slamming and wave load are obtained. Finally, the fatigue damage of the structure under dangerous operating conditions is calculated by the rain flow counting method. And the contribution value of the slamming load to the structural damage degree is calculated. The paper will put forward some reference suggestions for fatigue study calculation and evaluation of Trimaran cross structure with the influence of slamming.

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