Biodynamic response of seated human body to vertical and added lateral and roll vibrations.

The biodynamic response of 12 subjects to single-axis vertical and multi-axis vertical, lateral and roll excitations was studied to advance understanding of the biodynamics. Different from using single-input and single-output (SISO) method, the apparent masses with multiple inputs were estimated by multi-input and single-output (MISO) method, whose advantage was discussed. By studying the relationship between resonance frequencies and excitation magnitudes, the primary resonance frequencies of vertical apparent masses on seat pan and backrest and fore-and-aft cross-axis apparent masses from vertical acceleration on seat pan had a negative correlation with the weighted root-sum-of-square (r.s.s.) value of excitation magnitudes. Weighting factors of lateral and vertical magnitudes in r.s.s. value were comparable and were much larger than that of roll magnitude. However, the nonlinearity in the apparent mass was more significant or significant only under low r.s.s. value. MISO method appeared more suitable for estimating apparent masses with multiple inputs than SISO method. This paper experimentally studies the dependence of the resonance frequencies in the apparent masses of seated human body on the vibration magnitudes to advance understanding of the biodynamics. The sensitivities of resonance frequencies to lateral and vertical magnitudes are comparable, and much higher than that to roll magnitude. MISO: multi-input and single-output; SISO: single-input and single-output; r.s.s.: root-sum-of-square; SD: standard deviation; ISVR: Institute of Sound and Vibration Research; r.m.s.: root-mean-square; FRF: frequency response function.