On the mechanical vibrator-earth contact geometry and its dynamics

The geometry of the contact between a vibrator and the earth underneath influences the dynamics of the vibrator. Although a vibrator might appear to be well-coupled with the earth on a macroscale, perfect coupling certainly does not occur on the microscale. With the aid of contact mechanical modeling and concepts, it can be shown that this lack of contact at the microscale, or rather the change thereof during a sweep, can have a significant effect on the dynamics of the vibrator-earth system. Modeling of such changing contact predicts that the dynamic behavior varies considerably with the vibrator drive level. The most significant effect predicted by the model is a decrease in the base-plate resonance frequency with an increasing drive level. Extensive drive-level tests carried out in a field experiment confirm this change of resonance behavior with drive level.