A BIOMECHANICAL MODEL AS A SEATED HUMAN BODY FOR CALCULATION OF VERTICAL VIBRATION TRANSMISSIBILITY USING A GENETIC ALGORITHM

Abstract

Many biomechanical models of whole body vibrations have been developed, as part of the design, optimization, and vibrations control of vehicle seat systems, with the aim of achieving greater comfort. Most of these models are complex and result in large errors. In this paper, we introduce two new models, with and without backrest support, within a specific frequency domain. One is an optimized seven-degrees-of-freedom (7-DoF) lumped-parameter model with a unique structure to display vertical vibrations in one direction. The other is a new type of model called the coupled model, where the stiffness and damping matrices are employed instead of the spring and damper scalar parameters to present vertical vibrations in two directions — vertical and horizontal. The use of matrices not only simplifies and reduces DoF, but also gives more accurate results in comparison with the conventional multi-body models. With the help of a genetic algorithm (GA) through the global criterion method, we obtained numerical parameters of both models including mass, stiffness, and damping, which minimized the errors. The mean error for the 7-DoF model was 2.2%, while the best lumped-parameter models previously developed produced 12.6%. For the coupled model, we measured a mean error of 7%, a significant improvement over a well-known multi-body model with a mean error of 22.4%. Finally, we compared the transmissibility of vibrations in the human body applying the two models in the frequency range below 6 Hz, in both cases of with and without a backrest. These confirmed the importance of the backrest.