Dynamic modeling and global modal analysis of symmetric/asymmetric flexible spatial structures

Symmetric and asymmetric structures dynamically alternate throughout the on-orbit assembly or deployment of the large flexible spacecrafts. To investigate the influences of the structural symmetry on the spacecraft dynamic behaviors, the T-shaped and L-shaped structural configurations appeared in the construction process of the China Space Station are adopted as geometric models in this paper. Firstly, the orbit-attitude-vibration coupled dynamic models for both structures are constructed based on Hamilton principle. Then, the global mode method (GMM) is employed to capture the global modes of the T-shaped and L-shaped flexible spatial structures. The validity of the global modal analysis results is demonstrated through comparison of the natural frequencies and mode shapes with the results of the finite element model. Based on the global modal analysis results, discrete dynamic models are established for both structures. From the global modal results, it is found that the strong attitude-vibration coupling effect in the L-shaped structure results in higher natural frequencies comparing with those of the T-shaped structure. In addition, different dynamic energy exchange characteristics for the T-shaped and L-shaped structures can be found from the numerical simulation results. This investigation is expected to provide valuable guidance for the on-orbit assembly strategies and attitude control schemes of large flexible spacecrafts.