Research On Slamming Load Forecasting Method Of Trimaran Cross-deck

With its excellent performance in terms of rapidity and seakeeping performance,the trimaran has been widely used in military and civilian areas in recent years.With the continuous maturity of technology and ever-increasing requirements for use,the trimaran has the tendency of maximizing and lightweighting.This makes the trimaran slamming particularly problematic,especially for bridge structures where the profile line is flat and relatively weak.The severity of the slamming problem places higher demands on the anti-slamming design of the local structure and the evaluation of the strength of the structure under the slamming load,the key and basis for doing so is to accurately predict the slamming load.Due to the complex structure of the trimaran coupled with the strong non-linearity of the slamming problem,it is difficult to give sufficiently precise solutions by theoretical methods.In addition,the current standard system for determining the slamming design load of trimarans remains to be improved.Based on the above background,this paper mainly studies the following aspects:(1)The numerical simulation method based on explicit finite element method to solve the impact problem of structural water entry was studied.The basic principle of the simulation method,the setting of the key parameters and the main procedures were introduced.Then,the method was used to simulate the water entry impact problem of the wedge and the flat bottom structure.The results were compared with the published experimental data to verify the accuracy of the simulation method introduced in this thesis.(2)The free-drop model test technology for predicting the slamming load of the trimaran cross-deck was studied.The characteristic parameters of the slamming process,such as time history characteristics of slamming load,peak value of slamming pressure and dimensionless peak pressure coefficient and their distribution law along the structure surface,model acceleration,and the law of those parameters change with water entry velocity were studied by free-drop model test.The influence of main hull sputtering and air cushion effect on the slamming load at cross-deck was analyzed.(3)A more reasonable design method of test model in the case of main hull not out of water during slamming process was discussed preliminarily.Considering that the flow field severely disturbed by main hull water entry process in real hull profile model free-drop test and the actual flow filed when the cross-deck is slamming under the condition of main hull not out of water during slamming process is quite different,the main body weakening model conception was proposed and corresponding test was carried out.And then a new idea was given to more targeted study the problem of cross-deck slamming in the case of main hull not out of water.(4)The numerical simulation method to forecast the slamming load on trimaran cross-deck was studied.The 2D and 3D simulation methods were respectively used to forecast the slamming load on cross-deck and the applicability of those two methods was discussed by comparison with the experimental data.The disadvantages of 2D method were pointed out and then the effect of model weight on cross-deck slamming load was studied by 3D simulation method.(5)The direct calculation method of trimaran cross-deck design slamming loads was studied.Based on detailed study of the dimensionless peak pressure coefficient k,combining with the forecast of relative motion between hull and wave surface,a method with strong engineering applicability to determine the slamming loads design value of trimaran cross-deck was given.