大型空间变参数充液系统运动稳定性机理与自适应控制方法研究

Liquid sloshing in tanks has an unfavorable influence on spacecraft stability and performance. With the increasing amount of liquid onboard spacecraft, liquid sloshing and its influence on the spacecraft attitude dynamics and control are becoming increasingly important. During the processes of engine firing, the propellant will be consumed quickly, and the dynamical parameters of the spacecraft and the liquid in tanks varied consequently. The problem of liquid sloshing is more complicated. The stability principle and adaptive control of large variable-parametric spacecraft with multiple fuel tanks will be researched. A new equivalent mechanical model for large amplitude liquid sloshing under micro-gravity is developed. And the CFD (computational fluid dynamics) simulation method is used to demonstrate the validity of this equivalent mechanical model. Based on the compared results of two different methods, the equivalent mechanical model will be modified if necessary. The equations of motion of the system, which are derived using the Lagrangian method based on the equivalent mechanical model of liquid sloshing, are non-dimensionalized by choosing correct dynamical parameters. Motion stability for the spacecraft is analyzed, and condition for stability and instability are derived for a steady principal. Besides this, the nonlinear behavior of the system is analyzed under the influence of an external force. Based on the system model established, a simplified model used to attitude control system design is obtained under several reasonable assumptions. Finally, an adaptive attitude control method is designed for the large variable-parametric space system with liquid-filled tanks, and the Lyapunov theory is used to prove the close-loop stability of the control system. This research is useful for understanding the dynamical characteristic of complex spacecraft and helpful to study the stability and design the control subsystem of the spacecraft with liquid sloshing.

现代航天器的规模越来越大，需携带的化学推进剂也更多，储箱内推进剂的液体晃动成为影响航天器运动稳定性与控制精度的重要因素，为完成各种在轨任务，航天器需大量消耗推进剂，航天器的系统参数和动力学特性都呈典型的时变特征。本项目以上述空间变参数充液系统为研究对象，采用计算流体动力学与等效力学模型相结合的建模方法，研究其运动稳定性与控制问题；分析航天器的运动稳定性判据，揭示在不同运动状态下系统各参数对航天器运动稳定性的影响规律；并根据航天器的动力学特性，设计不依赖系统参数的自适应控制方法，实现对该类复杂充液航天器的高精度控制。重点解决多储箱充液系统的非线性变参数液体晃动动力学建模问题，时变空间系统的直接自适应控制律设计问题。本项目可为深入了解现代复杂充液航天器的动力学特性提供技术途径，并为其稳定性分析与控制系统设计提供理论依据。

本项目以我国正在研制的新型高轨卫星平台为应用背景，为解决多贮箱推进剂的大幅非线性液体晃动问题，提出了一种新型的三维质心面等效力学模型，该简化模型将贮箱内的液体等效为质量集中在质心处的质点，此质点只能在质心运动面内运动，而质心运动面是通过缓慢转动贮箱并测量贮箱内液体在各时刻的质心位置而得到的一个椭球面，通过建立与质心面相关的动力学方程组来求解液体晃动时的作用力大小。利用CFD商用软件对该模型的正确性进行了全面验证。基于上述模型，建立了贮箱液体晃动与卫星姿态运动的耦合动力学方程，利用SloshSat卫星在轨试验数据，对该耦合动力学模型的正确性进行了验证。提出了退步自适应姿态控制器以及退步直接自适应抗扰姿态控制器，设计了常系数反馈中间控制律，并采用Lyapunov稳定性理论验证了中间控制律对运动学子系统的稳定性证明，解决了该子系统非线性特性问题，设计了非线性自适应姿态控制器，通过数值仿真验证了所设计的自适应控制器对充液系统的高精度控制有效性。