An improved three-dimensional multibody model of the human spine for vibrational investigations

In this paper, a three dimensional numerical model of the human spine, specialized for vibrational investigations, is presented. The model has been built using multibody dynamics techniques and includes the entire set of vertebrae, considered as rigid bodies. The interaction between vertebrae has been simulated using six component bushings, without the need of any kinematic constraint. This methodology allows a very relevant flexibility, and the fully three-dimensional deformation modes of the spine may be studied. The investigation has been focused on the assessment of the vibration modes and the computation of the transmissibility functions buttocks-to-head for acceleration inputs along three main directions. It has been observed that the first torsional modes with a relevant mass participation factors are present at very low frequencies. Most of the relevant modes, which involve the deformation of the spine with relevant participation factor, are within the range 0÷5 Hz. These peaks are also visible in the transmissibility functions. Results have been also compared to those of other experimental and numerical studies.