Hydroelastic Response Analysis And Compliance Control Of Fin Stabilizer Under Cavitation Conditions

When a ship sails in a complex Marine environment,it is disturbed by waves and currents,it produces six degrees of freedom motion,of which roll is the most violent.With the application of fin stabilizer,ship roll motion has been significantly reduced,and the conventional control methods of fin stabilizer system are abundant.However,the related research on its compliant control is not enough.Simple mechanical position control cannot meet the current working requirements of fin stabilizer,and even reduces its service efficiency and shortens its service life.In order to meet the requirements of roll reduction performance,the realization of fin stabilizer compliance control has become an urgent problem to be solved,and the analysis of the hydroelasticity and cavitation response of the fin stabilizer is an important part of the force control and the compliance control.Based on the wave energy spectrum theory,kinematics law and wavelength distribution law,the long-peak wave disturbance model is analyzed and established,Carry out force analysis on the hull and the ship roll model and the fin stabilizer system model are also established.On this basis,the hydroelastic response of the fin stabilizer was analyzed,and a dynamic model of the fin stabilizer based on the fluid-structure coupling principle is established,using the calculation function of the additional load of the fin stabilizer in the flow field environment and the complete coupling algorithm.Considering the application environment of fin stabilizer engineering,the cavitation response is incorporated into the design of fin stabilizer dynamics model.The homogeneous flow model method is adopted to equivalent the flow field around the fin,which considers flow field with cavitation as homogeneous and equal density environment.The corresponding flow field density is calculated according to the different degrees of cavitation,and the additional load of fin stabilizer is modified to achieve the goal of optimizing fin stabilizer dynamics model.Then,an impedance-based control strategy is proposed to solve the control problem that the fin is not compliant and has no force under the conventional control method.Taking the output of the classical PID controller as the expected signal,on the basis of the hydrodynamic analysis of the fin stabilizer,the impedance controller of the fin stabilizer system is designed by using the rotary resistance of fin stabilizer as the external disturbance torque,and the smooth optimization of the fin stabilizer control system is obtained.Then the impedance control parameter design rules are used to optimize and debug the impedance parameters.Finally,the goal of flexible fin movement around the axis is realized by using the force position conversion relation of impedance controller.Finally,the dynamic model of fin stabilizer considering cavitation effect and based on fluid-structure coupling analysis is combined with impedance controller.It solves the problem of the influence of cavitation phenomenon and additional load of flow field on the motion state of fin body,so as to achieve the compliant control of fin stabilizer under complex environment.Taking "Yukun" wheel fin stabilizer as an example,the simulation environment is built and the evaluation index of fin stabilizer working condition is designed.Through the simulation experiment,it can be seen that the control strategy in this paper can improve the flexibility of the fin stabilizer system,it improves the stress condition of the fin body on the premise of ensuring the effect of the system’s fin stabilizer.