Apparent mass of seated men—Determination with single- and multi-axis excitations at different magnitudes

Apparent mass data describing the biodynamic responses of the human body during whole-body vibration in vertical direction using rigid seats has often been published and standardized. Such data has been used as a target function for developing models. At present there is no adequate database for the apparent mass during whole-body vibration in horizontal direction and in more than one vibration axis. Experiments and subsequent data analysis can be used to improve the database for modelling. An experimental study was performed with 13 male subjects sitting on a rigid seat without backrest, and with a hand resting on a support. They were exposed to random whole-body vibration with root-mean square (rms) values of about 0.25, 1.0 and 2.0 m s−2 in vertical, fore-and-aft, and lateral direction, and additionally in two horizontal vibration axes and all three vibration axes simultaneously. The forces and accelerations were measured in x-, y-, and z-directions for each condition tested. With an increase of the vibration magnitude in the three directions measured, the apparent mass functions shifted to lower frequencies. At the same vibration magnitude, the apparent mass functions shifted to the lower frequencies with an increasing number of vibration axes. The effects of the factors vibration magnitude and number of axes on the apparent mass curves were tested. The method of the modal description was applied to all individual apparent mass functions in order to obtain representative target functions. Recommendations for the revision of ISO 5982 were summarized.