A model analysis of the effects of wobbling mass on whole-body vibration

Abstract

The effects of wobbling mass on the whole-body vibration are studied in terms of the comparison between two models A and B regarding their detailed behavior during the ‘whole-body vibration,’ where Model A is a system of four degrees of freedom with rigid and wobbling masses in both lower body and upper body, while Model B is a system of three degrees of freedom with a rigid upper body and is otherwise identical to Model A. Various quantities are calculated for both models. It is found that for the frequency range where the foot-to-upper-body transmission is important, the wobbling mass is able to reduce the transmissibility, to reduce the amplitude of the oscillation of the center of mass of the body, and therefore to reduce the amplitude of the fluctuation of the external force from the source of vibration. The model analysis reveals the mechanism for these reductions as follows: The oscillation of the wobbling mass in the upper body is carried by the oscillation of the rigid mass of the upper body and therefore the phase of the wobbling mass lags behind the phase of the rigid mass. For this reason, the average power which the wobbling mass in the upper body gives to the rigid mass of the upper body is negative.

Keywords:

• biomechanics
• vibration
• wobbling mass
• model analysis
• dynamic responses