Research On Model Updating Of Base Excitation Structure

With the development of the finite element technology, much more attention has been attached to the accuracy problem of finite element model. The influencing factor, such as all kinds of theoretical assumptions, the approximation of boundary conditions and the uncertainty of material parameters, which would cause certain error between the established finite element model and the actual structure. The model updating method based on experimental modal analysis is an effective way to increase the precision of finite element model. The finite element model updating method was first introduced in the 1970 s, the one which based on modal parameters or complete frequency response function(FRF) data is the most mature. The unknown base excitation, which influence the large complex structure frequently, make it difficult to acquire the complete FRF data and modal parameters in model updating. In order to improve the precision of finite element model, the model updating method based on incomplete FRF data and the indirect updating method based on transmissibility are mainly studied. What the paper described is as follows:(1) A new iterative model updating method using incomplete FRF data and the concept of pseudo master degree of freedom(DOF) were established, which increased the convergence. On the basis of the model updating method based on complete FRF data, we used the sensitivity equation of FRF, then took a study on the model updating method based on incomplete FRF data and a new iterative format was presented. In the model updating method based on incomplete FRF data, constructed pseudo master DOF FRFs can markedly improve the convergence performance of the finite element model. At the end, a 25 truss structure was used to validate the effectiveness of the proposed method.(2) The indirect updating method based on transmissibility was put forward. For large complex structures, the structural parameters or FRFs cannot be measured, for this reason, the methods based on modal parameters or FRF data cannot be used. Aim at this problem, the indirect updating method based on transmissibility functions has been proposed in this paper. The transmissibility functions were used to solve related FRFs, then the model updating method based on incomplete FRF data were adopted to modify the model. Finally, a numerical example was used to validate the feasibility of the proposed method.(3) The model updating method about complex parameters was studied, which took the damping characteristic into consideration. Compared with the step damping updating method, the results of the former has been proved to have better accuracy. In the numerical example, the applicability of general damping type about the proposed method was proved by the comparison of adding structure damping property or viscous damping property to the finite element model.