Passive reconstruction of dispersion curve in plates via flow-induced random vibration: The effect of boundary reflection and sensor placement

Flow-induced random vibration propagates throughout a plate-like structure and thus contains information about the structural properties and states. Previous research has shown that the group velocity under various frequencies can be estimated by the cross-correlation between two measurement points, in which the prominent peak signifies the travel time of the random guided wave. However, it is found that the performance of this method depends on the sensor placement and the plate size; in some cases, the cross-correlation is contaminated such that the extraction of dispersion curve is problematic. This is because the wave package in the cross-correlation corresponding to the direct propagation between the two sensors overlaps with the coda wave packages associated with complex boundary reflections. This hypothesis is justified by a passive experiment on an ellipse-shaped plate: in the cross-correlation between the foci of the ellipse, the imprints of the direct propagation and various orders of boundary reflections can be clearly separated and precisely predicted by the ray method. Based on these findings, a sensor placement criterion is proposed, by which a robust passive reconstruction of dispersion curve using flow-induced random vibration is guaranteed.