The Study On Transient Hydrodynamic Characteristics And Spray Resistance Of Planing Craft

When the ship is sailing at high speed,the dynamic loads and motion response of the ship hull have very complicated and strong nonlinear characteristics.When encountering raging waves,the ship hull may experience serious slamming and sometimes accompanied by flying wave phenomenon,these loads have great influence on the safety performance and motion response of the ship.Therefore,It is of great theoretical significance and practical value to study on hydrodynamic characteristics and spray characteristics of bluff body in wave and current to hydrodynamic performance and motion prediction of planing craft and other high performance ships.In view of different constraint navigation models of bluff bodies in the hydrostatic and the dynamic response of the three dimensional model of planing craft under self navigation mode in the static water and waves,we carried out related numerical simulation and also programmed to extract spray resistance.Based on Fine/Marine software,the research carry out numerical calculation on three different types of planing crafts with the trim angle τ=3.0°,the speed V=2.0m/s,and the deadrise angles β =10°,15°,20°,25° for a total of 12 cases.Analysis on the hydrodynamic performance and transient flow field variation of the bluff body was done and a post-processing program was written for parameters of splash area,the splash zone grid node was reconstructed through self-programming,spray resistance of the bluff body and splash area under different lateral oblique angles was gained.When the navigational speed is high,Inner concave inclined type bluff body is not conducive to lowering the ratio of splash resistance to total resistance.A high-speed planing craft model in self-navigation mode was selected to do the research.There were a total of 12 working conditions,as the distance from the center of gravity of the boat to the boat-tail was chosen as 38.1%L or 35.1%L(L is the total length),and the speed range of the planing craft was 2m/s to 7m/s.With the motion response prediction of the three degree of freedom of planing craft,the relationship among hydrodynamic characteristics,motion response characteristics,spray characteristics and navigation speed was finished.Compared with the experimental data,the two are in good agreement.Spray characteristic parameters were obtained through self-programming software,at the same time the spray resistance and the instantaneous magnitude of the average area steady state under different speed and center of gravity were gained.When the planing boat is in the sliding mode((V≥4m/s))and the centre of gravity lg=38.1%L,splash resistance accounted for 14.05%~21.42% of the total drag.While lg=35.1%L,splash resistance accounted for 10.02%~16.20% of the total drag.Based on the wave-generating method of velocity inlet,numerical prediction of both the flow field and the performance of the planing craft under the self-navigation mode of the high speed planing craft was done,here the wave height(H)is 0.2 meters and the value set for wavelengths(λ)are 0.5L、1L、1.5L、2L.The relationship between planing craft’s motion response and wave period was found and study on the distribution of pressure,velocity and water in the bottom of the boat was done at the same time.What’s more,the characteristic parameters of splash area were obtained by dealing with the splash zone through self-programming.The Fluid motion characteristic of splash area was analyzed and the spray resistance during the period of encounter was calculated.When λ≥1L,the planing craft was often accompanied by slight slamming,which led to the jumping increase of spray resistance,the crest value of spray resistance accounted for about 40% of the total drag.According to the internal mechanism of spray phenomenon and the empirical formula derived from experiments at home and abroad,based on Matlab and Delaunay triangulation,the post-processing program was written to calculate the spray resistance and a feasible analysis method for the research on spray resistance of planing craft was provided in this paper.