Research On Dynamic Modeling And Suppression Strategy Of Propellant Sloshing In Spacecraft

The problem of liquid fuel sloshing in integrated design of modern large spacecrafts is drawing more and more attention. This is due to the increasing requirements of spacecraft mission executing abilities and thus the increase of fuel portion to overall mass of a spacecraft. Large scale liquid fuel sloshing may interfere overall dynamic characters of a spacecraft, putting structure safety or system stability under threatening. With respect to this problem, this study establishes coupled dynamic sloshing model with mechanic equivalent method and liquid sloshing module theory, and analyzes dynamic affection of fuel sloshing to spacecraft. In addition, practical methods are discussed in terms of anti-sloshing structure design and forward feedback control. Detailed research contents and results are as follows:Combining aeronautic application backgrounds, such three aspects as basic theories, research methodology, and achievement applications about liquid sloshing both domestic and abroad are reviewed. Research contents and implementation procedure are determined: the foundation of this research is modal theories, implementation means mechanics equivalent method, and the purpose to evaluate coupling effect of propellant sloshing and spacecraft control system and establish methodology for propellant sloshing inhibition.Based on fluid dynamic basics and variation principles, a mathematic description is established of fuel sloshing with liquid flow velocity potential as undermined functions. Via separating time variable of the function, description equation can be transformed from original partial differential equations to ordinary differential equations about modal functions. This transformation lays foundation for research of sloshing dynamics utilizing modal theories.Applying modal response theories and mechanical equivalent principles, models are built to replace liquid system equivalent mechanic modeling with simple mechanical system. Modeling efficiency and feasibility are improved during modeling process where solid finite element universal computation program is used. Several computational cases and comparison to corresponding research data validate the accuracy of this method. Open-looped analyzing results of equivalent model are used to summarize necessary exciting conditions of non-linear sloshing modules. These conclusions are research foundation of research on coupling effects between propellant sloshing and spacecraft control system dynamics.From the view of multi-body dynamics, based on equivalent mechanic model research results, analyzing model of liquid-solid-control of a spacecraft large system is established and a real-time simulation module is constructed. The numerical simulation results indicate that the control algorithm, which was designed based on rigid model of spacecraft, may be unable to achieve the control objective due to the sloshing disturbance. Especially when the centroid of the sloshing mass above the centroid of the spacecraft, the necessary condition for a stable system is that the sloshing mass must satisfy the constraint depends on moment of inertia of spacecraft and location of propellant vessel.Analytically, the sloshing inhibition structure mechanism is analyzed applying the circumferential flow theory in fluid dynamics. Quantity analysis model of the sloshing inhibition effect is founded. Comparison to experiments in literature validates the analytical results. Also, sloshing inhibiting structure improved was realized with combination of analytical methods and CFD simulation technology. This work has positive value to assist overall design of spacecraft.Finally, input shaping technique is adopted in this liquid propellant sloshing inhibition research. In specific, considering liquid sloshing primary frequency and inclusive factors as sloshing amplitudes, spacecraft thrust levels, time or energy optimization, input shaper for forward feedback control is designed. Numerical simulation validates the efficiency of inhibiting propellant sloshing of this method. Compare to common feedback controller, input shaper is simple in design process, and has a broad and promising application foreground.