A model of nonlinear behavior of ice cracks

A work presented at the previous ASA meeting has demonstrated that the cracks may provide anomalously strong vibroacoustic nonlinearity in ice. Experimental data were obtained from the field experiments on a fresh-water lake, where a strong subharmonic signal was, in particular, registered. Here, a theoretical model is suggested for the description of the effects observed and possible use of them for characterizing the crack parameters. The model is based on consideration of nonlinear flexural oscillations of the ice plate with a crack which may be ‘‘opened’’ from its upper or lower part due to flexural oscillations. Together with the added mass of the surrounding area of the plate, a nonlinear oscillator may be formed which admits both higher harmonic and subharmonic generation (a parametric effect). The oscillator has a strong nonlinearity and relatively low Q factor which may provide a possibility of parametric excitation if there is a rather wide frequency range. The model considered seems to be applicable for real sea conditions.