Study On Slamming Of High-speed Trimaran

The study on slamming of high-speed trimaran is a very complicated and significative topic,it has boon supported by 863 program of China(Name:Key technique research of high-speed trimaran,No.2006AA11Z227).In this thesis, the topic has been studied with methods of simulation and experimentation,and the following efforts have been made and the conclusions are presented:1,Some existing water entry theories were introduced,including the theory of two-dimensional water entry of wedge bodies,the numerical method of two-dimensional water entry of wedge bodies,the air cushion theory of flat bottom structures and the inverse method of three-dimensional blunt bodies and so on.Finally,the shortage of these theories were analyzed.2,Some studies on the key techniques of LS-DYNA software simulation on the slamming of high-speed trimaran have been carried out,the solutions of non-reflection boundary condition,the symmetry boundary condition and fluid initial condition at simulation have boon brought forward.And also the mesh size and precision control has been studied in order to get optimal model scale of simulation calculation.3,The water entry of flat bottom structures has been simulated with LS-DYNA software.The results have been compared with the existent experimental study,and it has approved correctness and validity of simulation calculation on slamming by the LS-DYNA soft ware.Accordingly,the slamming of the trimaran cross-deck structure has been simulated.Some conclusions have been obtained:(a)The air between hulls was brought out by wave splashed by main hull, the effect of air cushion was weakened.So,the peak value of pressure on the cross-deck was increased comparing with flat bottom slamming.(b)The formula of peak value of slamming pressure on the cross-deck has been regressed.The peak value is directly proportional to quadratic in velocity of water entry.The effect of air cushion on the peak value decays in the form of second order exponential with increasing of velocity.When the velocity is lower,the effect decreases rapidly with increasing of velocity;when the velocity is higher,the effect changes inconspicuously.(c)The maximum peak value of slamming pressure on cross-deck locates 0.7b from the broadside of the main hull and the secondly locates 0.3b.(d)The continuance of slamming pressure peak value decays in the form of first order exponential with increasing of velocity.When the velocity is lower, the continuance decreases with increasing of velocity;when the velocity is higher,the continuance changes inconspicuously.(e)The air cushion can decrease the peak value of slamming pressure on cross-deck,the effect of air cushion on peak value decreases with increasing of velocity.The effect of trimaran mass on the peak value increases with increasing of mass.When the mass arrives at the threshold value,the peak value is kept inconspicuously.The peak value is directly proportional to cross-deck width,and increases with increasing deadrise angle.When the deadrise angle arrives at the first threshold value,the peak value increases rapidly.When the angle arrives at the second threshold value,the peak value is kept inconspicuously.4,The slamming of the trimaran main hull has been simulated with LS-DYNA software.Some conclusions have been obtained:(a)The formula of the peak value on the main hull has been regressed.As a result,the peak value is directly proportional to quadratic in velocity of water entry.The effect of air cushion on the peak value decays in the form of second order exponential with increasing of velocity.The maximum peak value locates 3/8B from the midship of main hull.The continuance of peak value decays in the form of first order exponential with increasing of velocity.(b)The air cushion can decrease the peak value of pressure on the main hull,the effect of air cushion on peak value decreases with increasing of velocity.The effect of trimaran mass and cross-deck width on the peak value is lessness.The slamming peak value increases with increasing of deadrise angle. 5,Experimental achivements in hydrodynamics impact were introduced, including Chuang's slamming experimentations of flat bottom structure and wedge body,MARINTEK's slamming experimentations of wedge body and bow flare,international comparative studies on slamming of wedge body, slamming experimentation of SWATH and VISBY's experimentation with real situation.In this thesis,test equipment and trimaran model were designed and carried out.Slamming experimentation of high-speed trimaran has been processed.Salmming phenomenon of the high-speed trimaran was recorded. The peak value of slamming pressure,the responses of acceleration and deformation were obtained with different velocity.The formula of the peak value on the main hull and cross-deck has been regressed.The peak values is directly proportional to quadratic in velocity of water entry.The effect of air cushion on the peak value decays in the form of second order exponential with increasing of velocity.These have proved correctness of rules about slamming simulation of the high-speed trimaran.6,The veracity and creditability of simulation method has proved with comparing experimental conclusion with 3-D slamming simulation.The errors between experimental method and simulation method have been analyzed,and the slamming responses of the high-speed trimaran have been simulated.