Dynamic Analysis And Active Control Of Medium And High Jitters For Truss Structure In Spacecraft

The rapid development of the aerospace industry will make more stringent requirements for the accuracy and reliability of spacecraft in the future, but the work of high-speed rotating mechanism such as reaction wheels will cause the jitters in the medium and high frequency ranges for spacecraft structure, then it will influence the pointing accuracy and performance of spacecraft payload. Therefore, it has important theoretical value and engineering significance to analyze dynamic characteristics of medium and high frequency jitters in spacecraft and study the corresponding active control methods.For the problems of dynamic analysis and active control of medium and high frequency jitters in spacecraft structure, the conventional Finite Element Method based on modal superposition and Statistical Energy Analysis based on statistical analysis have encountered insurmountable difficulties. Therefore, the typical structure of the future spacecraft-truss structure is studied in the paper. The dynamic model is established by Travelling Wave Method, and the precise dynamic characteristics of medium and high frequency jitters and the corresponding active control methods are obtained. In this paper, the specific research works are as follows:Firstly, the vibration of truss structure in spacecraft is regarded as the superposition of different forms and frequencies of elastic waves. Travelling wave dynamic model of the basic member for truss is established which contains longitudinal, flexural and torsional waves, and junction scattering model is built considering the interconversion among the three types of waves at the junctions. The final system equations are acquired by assembling all members and junctions, and then travelling wave dynamic model of complex spacecraft truss structure is obtained. In the process of modeling, the complex Timoshenko beam model is used to study the medium and high frequency jitters, and the effects of rotary inertia and shear distortion are considered.Secondly, the dynamic analyses are made for the specific truss structure in spacecraft based on travelling wave dynamic model, and the general matrix solving method is given for natural frequencies, displacement frequency responses and power flow transmission characteristics. On this basis, numerical simulation analyses of truss structure in spacecraft are made. The simulation results show Travelling Wave Method can accurately calculate dynamic responses of medium and high frequency jitters in the spacecraft truss structure, and it has higher computational efficiency in comparison with the traditional Finite Element Method. Comparing the classical Euler-Bernoulli beam theory and Timoshenko beam theory, the results with complex Timoshenko beam theory is more accurate and more close to engineering practice for dynamic analyses of medium and high frequency jitters.Then, based on the travelling wave dynamic model and dynamic analysis of truss structure in spacecraft, when the wave propagate to the structural discontinuity (junctions and boundaries), it will transmit and reflect, and the wave transmission and reflection coefficients are derived. The controllers are designed to suppress medium and high frequency jitters of truss structure in spacecraft from a wave vibration standpoint. In this paper, the wave controllers are designed based on lateral displacement, vertical displacement, lateral bending angle and twist angle, respectively. Several different control strategies are studied, and the numerical simulation analyses and comparisons are made for different wave controllers and control algorithms. The results show wave control can well suppress the medium and high jitters for complex spacecraft truss structures, especially for around the resonance peak frequencies.Finally, on this basis of travelling wave dynamic model and the obtained power flow transmission characteristics, active control method of power flow for suppressing medium and high jitters is studied for truss structure in spacecraft, and this method is compared with the traditional active control method of acceleration. Then active control method of power flow with multiple control forces and error sensors is developed. The research results show that active control method of power flow can effectively suppress the jitters level of overall truss structure in spacecraft; Whether the error sensor is located in the far field or near field of the control source, active control method of power flow effectively suppress the acceleration and power flow transmission of spacecraft truss structure in comparison with active control method of acceleration. In addition, the effects of small error of optimal control forces, the location of optimal control forces and error sensors are analyzed, and the corresponding simulation analyses and discussions are made for active control of power flow with multiple control forces and error sensors.