关键词: 振动与波, 应变模态, 模态参数辨识, 最小二乘复频域法, 模态实验

Abstract:

Due to its sensitivity to structural state, strain mode has more advantages than displacement mode in online structural health monitoring and damage identification. Take advantage to the relationship between strain and displacement, apply Least Squares Complex Frequency-domain method (LSCF) into the analysis of structural stress and strain, then establish the frequency domain identification method of structural dynamics parameter based on strain measurement data. Since the strain mode and displacement mode are different expressions of the same physical state, they are similar in mathematical expression. First, establish a parameterized common denominator model with strain as its variable, then on this basis, make the nonlinear least squares problem linearized and obtain the error of the weighted least squares linear equation. Then solve the equation using the algorithm based on the reduction of regular equations and in this way reduce the amount of computation, and avoid redundancy by imposing restriction on the modal parameters. After that, design an experimental system of a free beam structure and use Fiber Bragg Grating strain sensors to measure the structural dynamic strain data, then identify the frequency and damping ratio according to LSCF based on the measured strain data, which fit the results identified by the traditional mothed based on acceleration measurement data well. Besides, the strain mode shapes obtained from the identification are also consistent with the simulation results. Therefore, numerical simulation and the experiment show that the method based on LSCF in this paper can accurately identify the strain modes.