Research On Water-entry Ballistics And Stability Of The Supercavitating Vehicle

Combining the advantage of high-speed underwater navigation of supercavitating vehicles with the ability of trans-media penetration of airdrop vehicles,a new type of trans-media supercavitating vehicle is born with great application potential of high-speed water entry and striking underwater targets,of which there is a coupling between strong nonlinear loads and an unsteady evolutionary cavity during the water-entry process.Both force characteristics of the vehicle and evolution characteristics of the cavity are significantly different from those of general underwater vehicles,which further affects the trajectory stability and attitude control methods during the water-entry process.In this thesis,methods of theoretical derivation and program simulation are used to study load characteristics of the supercavitating vehicle and evolution characteristics of the waterentry cavity during the water-entry process.A dynamical model of the supercavitating vehicle during the water-entry process is established and trajectory and attitude characteristics of the supercavitating vehicle during the water-entry process are analyzed.The specific research contents and results are as follows:Based on the Russian “Shkval” torpedo,a simplified model of supercavitating vehicle is designed.Based on the principle of independence of cavity sections expansion,contour of the water-entry cavity is predicted and evolution characteristics of the waterentry cavity are calculated with track of the cavitator assumed as the cavity centerline.Based on momentum theorem,the impact force received by the disc cavitator during the flow formation stage is derived and the water-entry impact force is corrected.During the cavity opening stage,connection between the cavity and the atmosphere is considered to correct expression of cavitation number by assuming the atmospheric pressure as the pressure inside the cavity.Based on the related theories and methods of classical mechanics,the dynamical model of the supercavitating vehicle during the water-entry process is established.Considering geometric topology of the unsteady evolution of the water-entry cavity,force characteristics of the vehicle under different relative positions between the cavity and the vehicle are analyzed and the dynamical equations in the velocity coordinate system with geometric center of the vehicle as the origin are derived.According to axisymmetric characteristics of the vehicle,the dynamical model is simplified to the longitudinal plane.A method for predicting trajectory of the supercavitating vehicle during the waterentry precess is established.Force,trajectory and attitude characteristics of the supercavitating vehicle during the water-entry process under the typical case are analyzed.By analyzing cavity characteristics,a study on the influence of water-entry disturbance on the force characteristics of the vehicle is carried out.By changing the parameters of cavitator diameter,center of mass,water-entry velocity and water-entry pitch angle,a study on the influence of the parameters of vehicle body and initial conditions on the trajectory and attitude characteristics and force and cavity characteristics of the supercavitating vehicle during the water-entry process is carried out.Under uncontrolled conditions,the supercavitating vehicle may quickly float upward until above the water after oblique water entry and diving to the deepest position.In order to satisfy the requirement of initial attitude during the underwater cruise stage,the thesis carries out a study on the open loop control method of water-entry leveling.The open loop control law of the cavitator and rudder angles under a certain engine thrust is given.After Simulation,it is found that the vehicle can maintain dynamic balance at a depth of about 30 meters,and the depth and velocity remain basically stable,but its attitude stability is weaker than its trajectory stability.