Research On Transmission Characteristic Of Energy Flows Of Micro-Vibrations In Spacecraft Structures

The on-orbit micro-vibrations of spacecraft structures,induced by moving devices such as reaction wheels and control moment gyros,will directly deteriorate the pinting stability and preision of the spacecraft bus and severely restrict the implements of high precision space missions.The propagation of micro-vibrations is essentially the transimission of vibrational energy in structures,and the displacement responses at focused points/positions are determined by the transimission characteristic in whole structures.For effectively reducing responses at focused points with proper passive control at pivotal positions,the micro-vibration transimission characteristic and relative vibrational transimission paths(VTPs)in spacecraft structures must be firstly analyzed.However,researches are mainly focused on the transimission characteristic of energy flows in simple beams,plates or assemblies at present.And for spacecraft structures,there isn't a general,efficacious analysis tools for vibrational energy flows in complex structures,and studies on the parameters sensitivities of energy flows are also shortly.Besides,due to the lack of judging method for VTPs,the obtained VTPs in whole structures are hard to be utilized for guiding the designs of micro-vibration reductions.The analysis and judging methods of micro-vibration energy flows in spacecraft structures are studied in this dissertation.Anf three aspects have been studied: analysis method of energy flows in complex sturctures,sensitivities of energy flows about structural paramenters and judging metheds of crucial VTPs in whole structures.The main work of this dissertation can be summarized as follows:1.Analysis method of micro-vibration energy flows are studied.(1)The configurations feature of the spacecraft structures are analyzed,then proper hypothesizes are made and simplied models are developed for typical components and connected assemblies,such as rods,beams,plates and jointed plates.(2)The governing equations of typical components are developed,and then the transimission characteristic of different kinds of structural micro-vibrations are studied.(3)Finite element energy flow method,streamlines representation technique,and the input/output transfer ratio of energy flows which can numerially measure the transimission characteristic of the whole structures are studied.Hereafter,an analysis methodology and relative software of micro-vibration transimission characteristic are developed for the computations of energy flows in complex structures.The above theoretical results have founded method bases for the transimission characteristic analysis of micro-vibration energy flows in spacecraft sturctures.2.Sensitivities of energy flows about structural parameters are studied.(1)Excitations sensitivities of energy flows are analyzed.And three aspects are focused: the effect of magnitude and phase of a single load,the coupled feature of energy flows for multiple loads and the effect of different phases of multiple loads.(2)A noval analysis method based on perturbations of finite element models for parameters sensitivities of energy flows in complex structures are proposed.Then,the analysis procedure is given and the proposed method is verified by the parameter sensitivity analysis of a beam-plate built-up structure.(3)For common change of structural configuration,such as rigid region and damping sheets,the effect of local rigidity and damping reinforcements to the local and global transimission characteristic of vibrational energy are studied.The theoretical results obtained above can provide theoretical supports for optimization designs of spacecraft stuctures in engineering practices.3.The judging principle of crucial VTPs in structures are studied.(1)For parallel rod/beams,the directly sorting method and significance test method are studied for judgments of crucial VTPs.Then,a progressively backwards picking method is proposed for judgments of crucial VTPs in rod/beam built-up structures.(2)For energy flows in plates/shelles,the similarity between energy flows and fluid motions is proved,and then an analysis method of VTPs in plates is proposed by analogy with fluid motions in two-dimension domains.Hereafter,the crucial VTPs and crucial effective regions are defined for focused points in plates/shells,and detailed judging methods are also proposed.(3)The complexity and loop feature of energy flows in plate/shell built-up structures are studied,and relative judging method of crucial VTPs are proposed.The above theoretical results can provide technical supports for passive control designs of micro-vibrations at pivotal positions in spacesraft sturctures.4.Test experiment of energy flows in a box structure is carried out.The test experiment system of micro-vibration energy flows is designed,then the transimission characteristic of energy flows in honeycomb plates of a box structures are measured.This test experiment has verified the proposed analysis methodology of transimission characteristic for complex structures and the developed software.In this thesis,analysis methods of energy flows,judging methods of crucial VTPs,and paramenters sensitivities of energy flows are studied.And based on the obtained theoretical results,it will be helpful for the design of micro-vibration reduction and the enhancements of spacecraft performance,so that it shall be widely uased in feature.