Supercaviting Vehicle Control

Supercavitation can significantly reduce drag of underwater torpedo,which enabling a dramatic increase of velocity and attack power for underwater weapons.Therefore,study of the underwater high-speed supercavitating vehicle(HSSV)have great strategic significance and military application value.Because the HSSV is almost entire enveloped by a supercavity,the hydrodynamic problems of the HSSV is complex.The dynamic equtions of HSSV has coupling effect and lightly-damped characteristics,any small disturbances will make the HSSV drift away,so the HSSV must have feedback control to work.In this paper,the hydrodynamic forces including the cavitator,fin,and the planing force in the longitude plane of the underwater HSST are analyzed.According to the basic dynamic equtions of the longitude plane,this paper studyed about the control design of HSSV,and the specific work and results as follow:Because of the coupling effect and lightly damped dynamics of the HSSV,a decoupling inner-outer loop design is proposed.In the design,the dynamic characteristics of the weak damping are stabilized by the pitch angle feedback fristly,and decoupled with the kinematics.And then the kinematic loop was designed in which the depth signal is used as the output.The Nyquist method is used to analyze the design of the system.This method of determining the feedback gain with loop and bandwidth can satisfy the good performance requirement of depth control and ensure the stability of the attitude loop.Each step of this design has a clear physical explanation,for the state feedback design provides a new idea,bu t also for the supercavity of the classic control law gives a perfect comment.For the planing force when the tail of the the HSSV into contact with the cavity,the H? control is proposed.The channel of the planing force is also taken into account in this control design to ensure that the system has good performance under sustained planing force disturbances.According to the two-input characteristics of the cavitator deflection and fins deflection and the special stability requirements of HSSV,and based on the considerations of the ill-conditioned problems in solving Riccati equations,the requirement in the low-frequency domain as well as the attitude stabilization problems,the choice of weighting coefficients is discussed in detail,a comprehensive solution to this weight slection problem is presented and the H? state feedback controller which satisfies the many requirements is given.Because of delay characteristic of cavitation,the delay characteristic of planing force and the performance affect of delay characteristic in control is analyzed.It is pointed out that the delay characteristic of supercavitating almost no affection in qualitative.Because the planing force with time-delay is a multivariable nonlinear function,in order to simplify the analysis,the banchmark model can be used in control design firstly,and then the time delay model can be use to verify in the simulation.When the underwater high-speed supercavitation vehicle aft end pierces the bubble generated planing force,for the phenomenon of periodic collisions,planing avoid control mothod is discussed,based on observer will be used to compensate and eliminate the influence of constant disturbance.The disturbance observer equation was deduced and the compensator is given.The observer and compensation degined in this paper can avoid the problem of the HSSV slapping the cavity wall and actuator stroke too large.The predecessor's unsuccessful cases which use direct compensation is analyed,and provides a feasible scheme for the future control design for planing avoid control of HSSV.