Study On Wave Making Simulation Of Air Cushion Vehicle Based On Mass Source Method

Hovercraft is a type of high-performance ship supported by static air pressure.It forms an air cushion higher than atmospheric pressure between the bottom of the ship and the support surface（water or land）.As the air cushion vehicle（ACV）,the air cushion supports the whole weight of the hull,so that the whole hull can leave the supporting surface.Since the ACV is an important amphibious landing vehicle and special purpose ship platform,it is of great academic significance and practical value in engineering to conduct in-depth research on wave making characteristics of ACV.The motion of ACV is a multiple degree of freedom nonlinear complex system.It can be mainly composed of three parts: air cushion hydrodynamics,apron dynamics and air cushion aerodynamics.The air cushion hydrodynamics is the basis of the other.Without considering the wave effect,the air cushion hydrodynamics is mainly generated by the moving wave of air cushion pressure.The paper takes it as the research object,and studies the wave-making problem of direct navigation in different water depths and the hydrodynamic characteristics during oblique navigation of ACV.Firstly,the paper develops a wave making simulation technology of air cushion vehicle based on STAR-CCM+ platform,by simplifying the air chamber and using the mass source method to simulate the air supply.During the simulation a stable air cushion is generated and quite reasonable wave pattern is obtained.The air cushion wave-making resistance can be obtained by integrating pressure and waveform over the water surface under air cushion.The validity and accuracy of this method are verified by the research of grid independence and the comparison with the experimental data.The wave making motion of the air cushion model with specified size and pressure in the range of Fr=0.2 ～ 1.2 is simulated,and the curve of wave making resistance changing with the speed is obtained.The two peaks of wave-making resistance with speed variation are captured.Combined with the wave making shape and the change of water surface under the air cushion area,the reason for the change of resistance is revealed.The shallow water effect in the wave making of ACV is studied systematically by using the above methods.Four kinds of water depth limited channels and approximate infinite water depth channels for comparison are selected to simulate the wave making motion of ACV in direct navigation with Fr=0.2 ～ 1.0.The variation of wave making resistance coefficient with Froude number and water depth Froude number is obtained.The law of shallow water effect is analyzed combining with the deformation of water surface under the air cushion area.The results show that the water depth has a great influence on the second resistance peak of wave making resistance,and when the water is shallow,the water depth Froude number is 1 corresponds to the second resistance peak,which is similar to the shallow water effect of general drainage ships.The hydrodynamic characteristics of ACV in oblique navigation are studied by using the above methods.According to the combination of different Froude numbers and drift angles,the wave making resistance,lateral force and rotation moment,which are the three main control motion forces and their coefficients,are calculated.Combined with the average wave inclination of the water surface under the air cushion,the wave-making waveform,and the water surface change under the air cushion area,a systematic analysis is performed.In the range of speed studied,the lateral force coefficient is stable when the drift angle is large,and the centripetal force provided by it tends to be stable when the rotation moves to this angle.The ACV will have unstable heading at each speed,especially at high speeds and large drift angles.Finally,the paper summarizes the results of various studies using the method of wave making calculation.The simulation method based on mass source method is accurate and practical.In addition,the results of this paper have certain guiding significance for revealing the shallow water effect and the hydrodynamic characteristics of oblique motion of ACV.