| The detuning caused by errors and defects is inevitable in the reticulated shell structures with high dense modes, and this might lead to the vibration mode localization, vibration mode jumping, frequency loci veering phenomenon and so on. Therefore, the analysis of the dynamic characteristics of detuned reticulated shell structure has important theoretical significance and practical value to deepen the understanding of the structural working state and improve the accuracy, reliability of structural damage identification and health monitoring. In this paper, on the basis of domestic and foreign relevant research, under the consideration of many factors affect the structural dynamic characteristics, by theoretical analysis, numerical simulation and model test as a means, combined with modal analysis theory and modal parameter identification methods, a more systematic and in-depth study on the vibration mode localization, vibration mode jumping and frequency curve veering induced by the structural detuning and the modal parameter identification problem is carried out in reticulated shell structures. The main research contents and achievements are as follows:First of all, the existence, mechanism analysis and solving method of vibration mode localization, vibration mode jumping and frequency loci veering of reticulated shell structures are analyzed. The occurrence mechanisms of them are revealed by the perturbation analysis. At the same time, the finite element method is used to establish the computing model of simulated antenna reticulated shell, and the structural detuning cases are simulated according to the structure characteristics. The vibration mode and frequency characteristics of the structure under different boundary conditions are discussed, and the basic model of the vibration mode localization and mode jumping analysis of reticulated shell structures is determined.Secondly, the simulation analysis is carried out on the vibration mode jumping and mode localization of reticulated shell structure, which reveals the influence law of the detuning of the stiffness and equivalent nodal mass distribution on the two phenomena.Taking the spherical shell of the spherical shell as an example, the research is focus on the analysis of vibration mode jumping and mode localization of reticulated shell for the stiffness detuning cases of longitudinal ribs using the finite element method. According to the correlation between the modes, the differences and the similarities and differences between the modes are analyzed, and the criterion for determining whether the vibration mode jumping occurs is given. Then, the quantitative description method of vibration mode localization is put forward, and the criterion of vibration mode localization for reticulated shell structure is established. And an in-depth study of vibration mode localization characteristics of reticulated shell is carried out for three detuned patterns that the radial member stiffness detuning, circumferential member stiffness detuning and equivalent nodal mass distribution detuning. The variation law of the proposed localization factors of the reticulated shell structures with the three different detuned patterns is summarized, and the qualitative conclusions are given. In addition, the similar analysis of arch-supported reticulated shell is made to verify the relevant conclusions.Thirdly, the frequency loci veering and the vibration mode of veering region are analyzed. Taking a simple spring mass system as an example, the phenomenon of frequency loci veering is analyzed, and the correlation of vibration modes in the veering regions are calculated. To seek the inner link between the frequency curve veering and mode jumping phenomenon, a simplified analysis model of reticulated shell is established to study the two phenomena. The study of frequency curve veering phenomenon is extended to the complex reticulated shell structure, the similarities and differences of the frequency loci veering and vibration mode jumping phenomenon under different detuning cases are analyzed and the evaluation index of frequency curve veering is established. Then, the perturbation method is used to explain the occurrence mechanism of them.Finally, the experimental verification of reticulated shell model is carried out. By simplified the single-layer ribbed reticulated shell used in the finite element analysis, the experimental model of reticulated shell is designed and produced, the relevant dynamic test of the model is completed. The modal parameters of the structure are identified by Poly MAX method based on the test data. The vibration mode localization and the vibration mode jumping are verified from the mode shape. Then, the two kinds of local factors proposed in the paper are used to quantitatively evaluate the experimental results,and the results of finite element calculation are compared and verified. |
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