Studies On The Equivalent Mechanical Model Of Large Amplitude Liquid Slosh And Rigid-Liquid-Flex-Control Coupling Dynamics Of Spacecraft

Modern spacecrafts often carry a considerable amount of liquid propellant and flexible appendages.Large amplitude liquid slosh and flexible appendage vibration probably occur in some maneuvers,such as rapid large angle transition,docking,rendezvous and orbital transfer.Therefore,the dynamic coupling effects from rigid-liquid,rigid-liquid-controller,or rigid-liquid-flexible-controller can be resulted in,which can degrade the performance of the attitude and position control system.The traditional pendulum model and spring-mass model cannot imitate the dynamic behaviors of large amplitude liquid slosh,because they are based on a common theory about small amplitude liquid slosh.In this dissertation,the coupling dynamics and control of liquid-filled flexible spacecraft that takes account of large amplitude liquid slosh are systematically investigated based on the moving pulsating ball model.The specific research topics of this dissertation are shown as follows:(1)The research progress on the equivalent mechanical model for large amplitude liquid slosh is comprehensively and systematically introduced,and then more details on the theoretical basis of the moving pulsating ball model are provided.Moreover,the rigid-liquid coupling kinetic equations of spacecraft are derived based on the moving pulsating ball model,which is verified to be correct and effective by the computer numerical simulation results.(2)According to the experiment results of large amplitude liquid slosh and the phenomenon that surface tension can affect the static equilibrium position of liquid,the moving pulsating ball model is improved in two asepects:(a)an effective mass factor is added into the moving pulsating ball model to correct the liquid centrifugal acceleration force calculated by this model;(b)an static surface tension force is also added into the moving pulsating ball model to correct the influence of surface tension on the normal force obtained by this model.The effectiveness of these improvements is verified by the comparison between the numerical simulation results and the published experiment results.(3)Based on the moving pulsating ball model,the rigid-liquid-controller coupling kinetic equations of spacecraft that includes multiple liquid propellant tanks are derived.The attitude feedback control strategy is designed based on Lyapunov theory.Through numerical simulations,for spacecraft with a single tank,the effects of liquid sloshing damping,attitude maneuver completion time and tank position on the spacecraft attitude transition process are investigated,respectively.Moreover,for spacecraft with two tanks,the effects of the offset on sloshing torque,control torque and the minimum sloshing damping required for completing attitude maneuver are respectively investigated,when the major spinning axis of spacecraft moves away from ideal position.Lastly,for spacecraft with four tanks,the effects of various tank arrangements on sloshing torque,control torque and the minimum sloshing damping required for completing attitude maneuver are respectively investigated.(4)The rigid-liquid-flexible-controller coupling kinetic equations of spacecraft that take account of liquid slosh and flexible appendage vibration are derived through the moving pulsating ball model,the attitude feedback control strategy mentioned above and Bernoulli-Euler beam theory.Based on these kinetic equations,the related investigations are focused on three topics: the effects of liquid slosh and flexible appendage vibration on the attitude motion of the main rigid body;dynamic coupling behaviors between liquid propellant and flexible appendage;the reorientation process of liquid propellant under dynamic coupling effects in low Weber number environment.(5)An improved moving pulsating ball model that takes account of liquid propellant depletion is derived,and then the spacecraft position and attitude control is discussed when there exist large amplitude liquid slosh and propellant depletion simultaneously.Moreover,for a spacecraft with multiple tanks,the effects of three kinds of propellant depletion on position-attitude tracking control are investigated,and a related adaptive sliding mode control strategy is proposed.Through numerical simulation results,the hybrid controller is proved to be capable of increasing the efficiency of position-attitude tracking maneuver significantly and reducing the sensitivity of the controller on various kinds of propellant depletion effectively,by which improves the stability of the control system.