Dynamic Analysis Of Liquid-Filled Flexible Systems And Its Application Studies On Aerospace Engineering

Liquid and flexible bodies constitute the distributed parameter systems on spacecraft. Their dynamic behaviors directly influence the capability of control systems. With the continuous development of aerospace engineering, the spacecraft structures increasingly become more complex, the motion factors present diversity, and the control requirements are enhanced greatly. Then further studies are required on the liquid sloshing and the vibration of flexible bodies on spacecraft and their effects on the system dynamics. Therefore, from the practical needs of aerospace engineering, this thesis carries out theoretical analyses and application studies on liquid-filled flexible systems.In respect of the theoretical analyses, the equivalent mechanical model for 3D liquid sloshing is polished, the parametric stability of a rigid-liquid coupled system is analyzed, and the mechanism of impact and nonlinear vibration of flexible bodies is studied.For the dynamic modeling of liquid sloshing in complex shaped tanks, the equivalent mechanical model for liquid sloshing in an arbitrary 3D tank undergoing 3D translational and rotational motions is theoretically derived. A numerical model for calculating the parameters of equivalent mechanical model is built using 3D finite element method. Accordingly, a high efficient numerical algorithm is proposed. The characteristic of the equivalent mechanical model for liquid sloshing in non-axisymmetric tanks is studied. The validity of the equivalent mechanical model is verified with analytical solutions and CFD method.For the stability analysis of a liquid-filled spacecraft subject to vertical parametric excitations, a translational rigid-liquid coupled system is established using an equivalent pendulum model of liquid sloshing. Differences of the parametric stability between the coupled system and the uncoupled system are analyzed. It is discovered that a vertical-lateral coupling vibration may take place when a liquid-filled spacecraft is suffering vertical excitations. The geometric nonlinear effects due to the foreshortening deformations under external excitations are studied. It is illuminated that the axial load induced stiffness effects during an oblique excitation or impact are quite responsible for the nonlinear vibration. The influence of using different floating frames of reference on the simulation results is discussed. It is illustrated that the key to improve the simulation accuracy is not depending on the choice of floating frame of reference, but to consider the geometric nonlinear effects and increase the modal orders, properly.In respect of the application studies, the achievements made in the theoretical analyses are used to build a simulation method for the liquid sloshing dynamics with a varying fill ratio due to draining, and propose a reduced-order dynamic model for a flexible solar sail.For solving the liquid sloshing problem during draining, a simulation method using an equivalent mechanical model with varying parameters is proposed. Compared and verified with CFD method, the range of applicable conditions of the proposed method is analyzed.Using the mixed coordinates method considering foreshortening deformations, dynamic modeling of a flexible solar sail is conducted. The model is reduced using pre-stressed modes. The varying eigenfrequencies of the solar sail with the solar pressure load can be considered in the model. The validity of the proposed model is verified with nonlinear finite element method.