Underwater High-speed Supercavitation Projectile Modeling And Optimal Control

When the underwater object moving at a high-speed, the local pressure on its surface will decrease.With the increase of its speed, the pressure in liquid is reduced lower than the saturated vapor pressure, then the bubbles or cavities can be seen. The investigation shows that when the object is covered with bubbles, the fluid resistance on it will be greatly reduced, and the speed of the underwater object will have a qualitative leap in the future. Since the super-cavitation has great significant impact on the world underwater, more and more countries have stared the study on it. Depend on the current research, this paper established a six degrees of freedom control model for the underwater super-cavitation high-speed projectile, analyses the stability of the system, and also designed a stable feedback controller for it. The main works are as follows:According to the theory of the missile flight mechanics and torpedo flight mechanics, this paper defined the common coordinate systems and special coordinate systems for the super-cavitation projectile. And also give the transformation matrixes of each two coordinate systems. In this paper, we discussed the reason of the phenomenon of super-cavitation, and the way to maintain it, compared the simplified formula used in this paper with two other kinds of famous formula which used to describe the shape of a cavity. And give the finally formula of the cavity body we used in this paper, and also the axis drift formula is given.With the knowledge of the rigid body dynamics, this paper established a full ballistic six degrees of freedom kinematics equation and dynamic equation for the underwater high-speed super-cavitation projectile. This paper also discussed the reasons and gave the formula of the cavitation force, fin force and planning force.In this paper, we established a complete6DOF simulation model in the MATLAB. Using the M file to describe the force and moment, and also put them in the function to get a complete simulation model. In this paper, we also analysed the stability of the nonlinear system, and did the open loop simulation. And text the open loop sensitivity due to variations in system parameters.Then we linearizing the system at a trim condition, get a linear approximate model, and the state-space equation of this linearization model. And also compare the linear system and nonlinear system at the same inputs to see if they are matching.In this paper, we take the cavitator and the fins as the actuating mechanism. Designed a linear quadratic optimal controller of the system based on the state space equation, and test the stability of the system by a given input. To get an optimal control law, this paper use the genetic algorithm optimization, and test the stability of the close-loop system. The simulation results show that the genetic algorithm have a better...