| The high-speed water exit process of a vehicle is a typically trans-media process,which is strongly nonlinear and unsteady and involves strong turbulence,multiphase flow and multiphase fluid-solid interaction.The existence of brash ice certainly complicates the process,so it is necessary to establish the prediction model of interaction between a high-speed water-exit vehicle and brash ice,investigate the flow field and load characteristics as well as movement stability during this process to provide technical support and program strategies for launching underwater vehicles in polar regions.In this thesis,the computational fluid dynamics(CFD)and finite element method(FEM)coupling algorithm was firstly used to establish the prediction model for high-speed water exit process of a vehicle in a small amount of brash ice condition.Penalty function method was used to capture the collision process between the vehicle and ice,and the validity of the CFD-FEM coupling algorithm was verified by comparing with the results of water tunnel test and model test.The flow field,load characteristics and structural dynamic response of the vehicle in the water exit process were studied and the results show that in the case of collision between the vehicle and brash ice,the height of heave deformation of the free surface increases and then shrinks towards the tail when the tail of the vehicle exits water.Besides,the rupture of the liquid film on the head of the vehicle produces a large impact load in the crossing the water surface process.In the second place,a prediction model of the high-speed water-exit process of a vehicle in the brash ice zone considering the distribution of brash ice was established based on the coupling algorithm of CFD and discrete element method(DEM).The effectiveness of CFD-DEM coupling algorithm was verified by comparing with the results of water tunnel test,model test and empirical formula,and the evolution of flow field and load characteristics of the vehicle during water exit process were studied.The results indicate that the effect of brash ice on the crossing the water surface stage is mostly embodied in the number of bubbles,and there is a strong alternating load due to the high pressure caused by the collapse of bubbles.Finally,the test on the influence of brash ice on the water-exit dynamics of an underwater vehicle was designed and carried out,and the cavity evolution process,load and motion information were captured by high-speed cameras and sensors.The results display that the collapsed bubbles during the crossing the water surface process of the vehicle show a state of eruption,and the existence of brash ice changes the pressure distribution around the vehicle,making the pressure oscillation more severe. |
