Multibody Dynamics Approaches for Study on Good and Bad Whole-Body Vibrations

Whole-body vibrations (WBV) have been used for enhancing muscle strength and bone density of human bodies, training athletes and dancers, and helping people with disabling conditions and rehabilitations. On the other hand, WBV-induced occupational diseases have been reported. Researchers in automotive, farm equipment, and heavy machinery have put forward a few models for studying harmful vibrations on human bodies. This paper will review the effects of frequencies and magnitudes of WBV on a human body. Discussion of effects of frequencies and magnitudes on a human body will provide a preliminary boundary line between good and bad whole-body vibrations. Two multibody dynamics models and associated application cases will be proposed to show how the models may be used to represent whole-body vibrations under both good and bad vibrations. Three basic vibration elements associated with whole-body vibrations of the human body are handled as follows: (1) ligaments are modeled as spring elements; (2) muscles and tendons are modeled as damping elements; (3) bones are modeled as rigid bodies with masses/inertias and connected by idealized massless joints. In such a biomechanical vibration system, the spring elements (ligaments) help hold the human body skeleton structure in a stable condition, pass spring forces and potential energy to rigid bodies (bones) for bone vibrational motions. The damping elements (muscles and tendons) play roles of a damper and absorb energy input from the whole-body vibration resource. Based on the proposed multibody dynamics models, Kane's method is then used to develop equations of motion. The equations will be further used for development of simulation algorithms to understand frequencies and magnitudes of both good and bad whole-body vibrations. The models may be utilized to understand why frequencies and magnitudes of whole-body vibrations will provide benefits to human health under one situation but cause occupational diseases under another scenario.