STUDY OF WHOLE-BODY VIBRATION ON SEATED SUBJECTS

Abstract

When people are exposed to whole-body vibrations at work or in the travelling, they are often multi-axis vibrations that affect them in all directions at the same time. However, most biomechanical studies that look at how people react to such complex vibrations have used single-axis models in the lab. This thesis presents a study where 6 male subjects human subjects exposed to vibrations under two different conditions: vertical-only and combined vertical and rolling directions. The experiments were conducted using subjects seated on chairs without backrest support and exposed to three levels of vibration magnitudes using 6 DOF vibration simulator. All vibration magnitudes were 0.3 m/s2, 0.6 m/s2 and 0.9 m/s2 in vertical direction and in combined condition with 0.5 rad/s2 in rolling direction. The study focused on comparing the resonance frequencies and Seat-Transmissibility-Head (STH) responses between the two vibration conditions. Results indicated that the highest STH transmissibility occurred in both conditions within the frequency range of 5 to 6 Hz. However, the study found that STH transmissibility was lower for combined vertical and rolling vibrations compared to uniaxial vertical vibrations, despite the same vibration magnitudes. This was attributed to the concentration of energy along a single axis in uniaxial vibrations, enhancing resonance effects and transmission. In vibration dynamics, uniaxial vibrations concentrated energy along a single axis, resulting in higher vibration amplitudes and transmission along that axis. In contrast, biaxial or multiaxial vibrations spread energy across multiple axes, reducing resonance effects and lowering vibration amplitudes along any single axis. It is also Observed that weight and height have a considerable effect on transmissibility. Based on simulation results and graphical representations, the biodynamic model accurately estimated human responses to vibrations within the frequency range of 2-20 Hz. These findings underscore the importance of considering vibration direction and magnitude in assessing human biodynamic responses, which has implications for designing ergonomic and comfortable seating systems.