Modal Identification Algorithm And Experimental Study Of Space Deployable Truss

Space deployable structure has the advantages of high receiving ratio,and it is widely used in the field of space.Accurate acquisition of dynamic characteristics of spatial deployable structures is the precondition of dynamic optimization design and vibration control.The modal identification algorithm and experimental research are carried out with the model of the truss structure shrinkage of the international space station as the research object.The main studies incluses three parts as follows:First of all,the research on the method of additional mass elimination based on Sherman-Morrison theory is carried out.In order to remove the coupling effects of transducers on each measurement point with the existence of multi-transducers,a hierarchical multi-transducers eliminations method based on Sherman-Morrison theory is investigated.The method consists of two steps:(1)by stratified processing,a dendrogram can be used to clearly express the coupling relationship between the frequency response functions of each layer;(2)according to the relationship between each layer in step(1),the Sherman-Morrison theory is used to modify the frequency response function in order to eliminate the transducers mass loading effect.A case study of the spring-mass system with multi-sensor mass is carried out to verify the effectiveness of the hierarchical elimination method.The robustness of this method is also verified by the noise-contamitated case.Secondly,the modal identification algorithms are studied,which include the Eigensystem Realization Algorithm(ERA)in time domain,and the Morlet Wavelet Identification Algorithm in time-frequency domain.To eliminate noise of the initial data,an improved Eigensystem Realization Algorithm is proposed based on singular value decomposition and Cadzow's algorithm.Meanwhile,a mode order indicator,called singular value percentage,is developed.According to the characteristics of the singular value percentage curve,a minimum prediction value is determined firstly,and then the order of modes is determined by using the characteristics of incremental ratio.The minimum value in the curve indicades the realistic mode order.The effectiveness of the proposed method is verified by a six degree-of-freedom spring-mass system and a 12 frame truss simulation.Finally,the experimental verification of the hierarchical multi-transducers eliminations method and the modal test are carried out.The multi-transducers mass elimination test is carried out in a three truss structure.The effect of multi-transducers mass is eliminated by processing the measured frequency response function data.Results verify the feasibility of the hierarchical elimination method.For the 12 frame trusses,the ground modal test is carried out.Firstly,the singular value indicator is used to determine the order of modes.Through the test data processing,the effectiveness of the improved Eigensystem Realization Algorithm is confirmed.A modal parameter identification software called MPIDS is realized based on MATLAB,which includes the function of truss geometric modeling,data processing and modal parameter identification.