Research On The Dynamics And Control Of Liquid-filled Quadrotor Disturbed By Sloshing

Liquid load could be easily seen in astronautical and aeronautical engineering.For example,the multi-rotor UAV for plant protecting,AG600 amphibious plane for fire-fighting in the forest,or liquid rocket thrust by liquid propellant.During the mission,the violent liquid sloshing in the tank may lead to sloshing force and sloshing moment,disturbed position of Co G,uncertain parameters and so on,which may lead to a worse dynamics performance of the flight vehicle,or even more disastrous consequences like unstability.The key point of predicting the dynamics responses of liquid-filled flight vehicle is the numerically model of sloshing phenomenon.Hence,systematically and in-depth study on the numerical algorithm of liquid sloshing has its important theoretical meaning and engineering value.This dissertation focuses on the sloshing and fluid/structure interaction(FSI)problem by numerical method.The dissertation mainly talks about the dynamics performance of the liquid-filled quadrotor by Smoothed Particle Hydrodynamics(SPH),and expand its application in non-inertial frame.The single-phase and multi-phase sloshing in the liquid-filled tank and their effects to the quadrotor system are studied,which could be summarized as following contents and conclusions,Aiming at the sloshing problem,this dissertation uses kernel approximation and particle approximation method to describe the Navier-Stokes equations for flows,and studies the dry-friction-induced self-excitation of a mass-spring system effected by sloshing,an FSI problem as an example.Three models with constant load,sloshing load by SPH,and sloshing load by equivalent method are studied and compared to make the mechanism clear,which affects the nonlinear dynamics behaviors.Simulation results show that the super-critical Hopf bifurcation in original case will convert to sub-critical Hopf bifurcation if the liquid sloshes violently,and the nonlinear characteristics like hysteresis range and jump phenomenon could also be observed under this condition.Aiming at the liquid-filled quadrotor UAV during in-plane maneuvering,the composite motion of liquid particle and Navier-Stokes equations in SPH scheme based on incompressible assumption are introduced first.After comparing with some numerical cases to verify its reliability and correctness,the extraction method of sloshing force and moment is proposed,and based on this method,the dynamics model of in-plane liquid-filled quadrotor UAV with PID+Backstepping dual-channel controller is built.Numerical results show that the trajectory tracking performance of quadrotor under sloshing will deteriorate obviously with high-frequency vibration caused by the liquid.The rotation speed of rotor also vibrates,which is difficult to be damped.Based on the research above,the algorithm is extended to 3-D problems.The research on attitude/liquid/control coupled modelling and dynamics responses of liquid-filled quadrotor UAV during 3-D maneuvering are conducted.By numerical simulation it could be found that sloshing force in horizontal direction is about 20%of the liquid gravity.Sloshing force in vertical direction vibrates around the liquid gravity,and the amplitude is about 5% of the liquid gravity.During maneuvering,the trajectory tracking performance obviously deteriorates thanks to the sloshing,and even ‘backward motion’.The actual velocity output also vibrates,and the overshoot of three attitude angles are 40% higher than the cases without sloshing.Considering the liquid/air multi-phase sloshing in the tank,based on weakly compressible assumption,the single-phase and multi-phase sloshing models based on Riemann SPH are built,which markedly improved the efficiency and accuracy.By taking the dam-break problem as an example,the correctness and precision of single-/multi-phase model are verified.Aiming at the maneuvering of quadrotor,a attitude/liquid coupled model is built and its numerical simulation is also conducted.Results show that the inherent problem of volume expand in SPH is well restrained when taken the multi-phase into consideration.The sloshing in horizontal direction is always in dominant whatever the filling ratio is.The sloshing forces in horizontal direction are similar when the filling ratios are 50% and 75%,respectively,which are higher than the case with only 25% filling liquid.The sloshing moment reaches its minimum when the filling ratio is around 50%.