Study on Dynamics and Modeling of Human Body Exposed to Multi Dimensional Excitation

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The purpose of this study is to understand dynamic characteristics of the sitting human body by performing multi-dimensional experiments, and to make up a three-dimensional dynamic model of the human body. Firstly vibrational experiments are performed by using a three-directional shaking table on which a wooden seat is installed. Experimental subjects sitting on the seat are excited with respect to three directions, i.e., fore-and-aft (x-axis), lateral (y-axis), vertical (z-axis) one after another. Paying attention to the head, vibrational characteristics of the sitting human body are clarified by transmissibilities between the seat's acceleration and the acceleration of the head with respect to three translational directions, i.e., 3x3=9 transmissibilites are measured. As a result, the head's motion has two dominant resonant peaks up to 20Hz in each translational directions, and the fore-and-aft motion and the vertical motion is coupled. It is supposed that the coupling is caused by the rotational motion of the head around y-axis (piching). Secondly a three-dimensional dynamic model of the human body is built up considering the experimental results. In the model, the body and the head are regarded as rigid bodies and they are connected to each other by the translational springs and dampers. The body is able to move in three translational directions, and the head is able to move in the vertical direction and in two rotational directions relatively to the body. The model has six dof's in total. Through the comparison of transmissibilities obtained by the experiment and those synthesized from the model, it is confirmed that the model reflects the fundamental dynamic properties of sitting human body.