where A is the mean amplitude (m); x is the angular fre- quency, x = 2pf; t is the time (s). The
vibrational accel- eration was used for determining the dimensionless vibration given by Eq. (3),
which is defined as the ratio between the maximum vibrational acceleration and the gravitational
acceleration. A simplified method for cal- culation of the dimensionless vibration is given by Eq.
(4) (Thomas, Liu, Chan, & Squires, 1987; Thomson & Dahleh, 1998).