Study On The Slamming Load Of Trimaran

Trimaran, with its large deck area and excellent navigation performance, more and more world-widespread attention is arisen by the shipping industry. Meanwhile, trimaran suffers wave slamming load during the high-speed sailing caused by frequent water entry and exit. Especially in the cross structure, which were seriously impact by the sputtered wave.In order to investigate the slamming load distribution and the relationship between the impact velocity and the slamming load, a small scale trimaran model test campaign of water entry from a series of heights is performed based on the similarity theory, and the peak pressure of the main hull, side hull and cross-deck are obtained. Meanwhile, a numerical study on the experiment process is carried out through the nonlinear finite element software MSC.DYTRAN. The results of simulation analysis are compared with the experiment results, and help to determine the relevant parameters used in numerical simulation. The emphasis in the present paper is to put forward a reasonable and effective prediction method of the trimaran slamming loads. and the following efforts have been made and the conclusions are presented:1. The background and significance of the study on the slamming loads of trimaran are introduced in this paper, which includes water entry theories, experimental study and numerical simulation research progress. The development of the slamming load research on the trimaran is presented.2. A small scale trimaran model test campaign of water entry from a series of heights is performed based on the similarity theory, and the peak pressure of the main hull, and cross-deck are obtained. Some conclusions have been obtained:a) In terms of the experimental results and the regression analysis, elicit the prediction formula of slamming peak pressure of trimaran and obtain the law as follow:peak pressure is proportional to the square of the impact speed, and the effects of nonlinear factors, such as air cushion and splashing, is quadratic declining with increasing of impact speed.b)Slamming pressure of main hull and cross structure increase with the increasing of the impact speed, while the pressure of main hull is greater than cross structure.c) The maximum of slamming pressure is at the place which is at a distance of B/10 from longitudinal section in center plane, and the maximum slamming pressure of cross cross-deck is at the place of 5b/8 in the width of cross structure.3. Some studies on the key techniques of simulation on the slamming of trimaran within MSC.DYTRAN software have been carried out, such as the coupling methods, the parameters of the materials, the solutions of non-reflection boundary condition, the symmetry boundary condition and fluid initial condition etc.4. The slamming of the trimaran has been simulated with MSC.DYTRAN software. Some conclusions have been obtained:a) Based on comparison with the experiment, the simulation of a series of scale trimaran model slamming into the water, proved that it could simulate the water entry problem effectively within the MSC.DYTRAN software, and the correlation coefficient values were determined through the experiment;b) The processes of trimaran slamming with different speed are researched by numerical simulation. The slamming peak pressure formula of the main-body and cross-deck of the trimaran are regressed. Slamming pressure is directly proportional to the square of the entry water speed. Other nonlinear influence factors, such as spray and air-cussion etc., are described in the impact factor k of the formula. The value of K presents quadratic index diminishing with the impact speed increase. At low speed, the K value decreases rapidly and it have little influence at the higher. The peak value of slamming pressure on the wet-slamming is at the 5b/8 distant from main hull, and the second largest value is at the 7b/8 from it.c) Basing on the dynamic similarity, the results of the scale model simulate the real trimaran verify the proportional similarity relation which is deduced by similarity theory.The impact speed of the real ship and the model meet the below relationship, VS=Vm(?).Ann the slamming external loads is meet the below relationship, CP=CpCV2=CL or PS/Pm=CL=6.The error of two simulations within 20%, which can be provided as a guidance for the practical project. d) Under the predict slamming loads, the strength of the cross-deck of trimaran can meet the requirements of relevant rules and regulations.