Kinematic and dynamic analysis of a sit-ski to improve vibrational comfort

This paper reports both procedures for the kinematic design and the results of dynamic analyses of three models of sit-ski in order to evaluate their vibrational comfort. The model described in the US Patent US 6,019,380 has been assumed as a reference in the following kinematic and dynamic analyses of the new models proposed. The two main features to be considered while designing a sit-ski are the manoeuvrability and the range of vision of the driver. These two features appear to be important considering that the sit-ski is generally used by disabled people (e.g. paraplegic). Thus the kinematic design phase should account for the fulfillment of these requirements. On the basis of these, three new models have been proposed and herein named: Flex, modified Flex and eight-bar linkage (Smarrini 2003). Once the kinematic synthesis and analysis have been completed the dynamic performance of each model is investigated. For this purpose two kinds of slope profiles are simulated in order to reproduce the stresses which may likely occur during a downhill race. In particular the position and the acceleration of the seat have been monitored during the simulations. This is important in order to test the range of vision and handling requirements. The seat acceleration is also important to evaluate the vibrational comfort of the sit-ski according to the British standard BS 6841 (Griffin 1990). The dynamic simulation is first executed by means of the multibody dynamics code NumDyn3D, then the vibrational comfort analysis is performed using in-house developed software (Vita 2001, Valentini and Vita 2003).