Scanning vibrometry and modal analysis of growing, thin ice within a circular basin

Ice thickness is currently assessed by either drilling or coring, which can be hazardous. One stand-off method that has the potential to mitigate the risks of ice measurement is laser Doppler vibrometry, but vibrometer signals must be interpreted by a physics-based understanding of ice vibrations. For thick ice, it is appropriate to consider the medium as a viscoelastic plate. The vibrational response of growing, thin ice is largely unknown. It is hypothesized that thin ice responds in a fashion somewhere between an elastic membrane and a viscoelastic plate. A modal test of thin ice, grown within an insulated, circular steel basin, was conducted over the course of three tests. Scanning laser Doppler vibrometer data were gathered over the ice surface, with time-synchronized accelerometer measurements on the upper basin lip. The resulting dataset spans a range of ice thicknesses from approximately 2 to 41 mm. Modal analysis on the dataset follows the rational fraction polynomial method to identify modal parameters of the ice: resonance frequencies, damping ratios, and modal coefficients. Finite-element analysis calculations and analytical predictions are compared to experimental data.