Method for Filtering Elastic Vibration Components of a Plate in the Measurement Signal of a Laser Doppler Vibrometer

Kurzfassung

This paper presents a method for filtering elastic vibration components of a plate from the measurement signal of a laser Doppler vibrometer (LDV). Motivated by the concept of flyable mirrors, in which a mirror attached to a drone enables LDV measurements in hard-to-reach places on large structures, but is disturbed by the elastically vibrating mirror, the mirror is modeled as a thin, isotropic plate in the sense of Kirchhoff-Love theory using the finite element method (FEM). After partitioning into free and excited degrees of freedom, a transformation into a base-excited system takes place. Using an implicit Newmark solver, transient numerical simulations are performed, from which the time and location-dependent influence of the plate vibration on the LDV signal is determined using shape function-based interpolation. The determined influence is subtracted from the LDV signal, thus providing a corrected measurement without elastic components. To validate the model, an experimental modal analysis of the plate was performed. The results were compared with the theoretically determined modal parameters of the model. To validate the method, it was applied to experimentally obtained LDV data obtained from the harmonic base excitation of a plate at 300 Hz, 500 Hz, and 700 Hz. The method reduced the root mean square error (RMSE) by 39-72 % compared to the uncorrected LDV signal and improved the agreement with the reference signal, particularly at 300 Hz. Potential for improvement became apparent for the base excitation at 500 Hz. The results demonstrate the general effectiveness of the method, although its applicability is currently limited to harmonic excitations, limited measurement durations, and restricted frequency ranges. Future work aims at phase-accurate simulation, transient excitations and the integration of different element sizes in the FE model to further reduce the computational effort and extend the method for realistic applications.