Using the reverse path multi-input-single-output method to identify nonlinear characteristics in the apparent mass: preliminary results

The study implements a classic analysis technique in dynamics to examine nonlinear characteristics seen in apparent mass of a recumbent person during whole-body horizontal random vibration. The nonlinearity under present context refers to the amount of ‘output’ that is not correlated to the ‘input’ usually indicated by values of a coherence function that is less than unity. The analysis is based on longitudinal horizontal inline and vertical cross-axis apparent mass measured with 0.25-20 Hz random vibration at 0.125 and 1.0 ms-2 r.m.s. Adding the vertical cross- axis output force as a ‘reversed’ mathematical input markedly increased the multiple coherence of the apparent mass in the frequencies where ordinary coherence between the longitudinal horizontal excitation acceleration and the inline longitudinal force was low. Little improvement in the multiple coherence was achieved by an arbitrarily constructed mathematical input from the inline force.