BIO-DYNAMIC RESPONSE AND BIO-DYNAMIC MODELING OF SEATED HUMAN SUBJECTS UNDER WHOLE BODY VIBRATION

Abstract

While traveling by vehicles: cars, buses, trains, ships and airplanes, there are many factors that causes discomfort, such as pressure at seat interface, sitting posture, vibration, noise, visual effect, humidity, temperature, etc. among this, exposure to whole body vibration causes a complex distribution of vibration within the body and unpleasant sensations giving rise to discomfort or annoyance result in impaired performance and health risk. This distribution vibration depends on extrinsic variables (those used to express the state or environment of the dynamics system such as magnitude, frequency, direction etc), intrinsic variables (which refers to the human subject natural behavior, characteristic and condition like age, posture, gender, weight, and etc) and interface between human body and the vibration environment. In this study effect of vibration posture, magnitude and frequency on seat-to-head (STH), floor-to-head (FTH), back-to-head (BTH) and floor-to-back (FTB) transfer function has been studied under fore-and-aft sinusoidal vibration. Six healthy male subjects participated in experimental work to measure fore-and-aft vibration transmitted to the occupants head and back in two representative postures (vertical backrest and 30 degree with vertical backrest ) under three magnitudes of vibration (0.4, 0.8 and 1.2 m/s2 r,m.s.) in frequency range of 4 to 12 Hz. From collected data seats, the effect of postures, magnitudes and frequency on STH, FTH, BTH and FTB transmissibility magnitude has been studied over the prescribed frequency range. And a six degree of freedom lumped parameter model was established for which the parameters where estimated to satisfied FTB transfer function characteristics. The parameter identification technique involves optimization by minimizing the square error sum of floor-to-back transmissibility. The experimental study reveals that FTB transmissibility peak value frequency occurs in frequency range 4-5 Hz for seated subject in both prescribed postures. The results showed that inclusion of all possible variables has great advantage in optimal design of vehicle seat, suspension and comfort analysis. Moreover the comparison of experimental and model response reveal that model matched with mean experimental data sets most closely and the provide best description about biodynamic response study of seated human subjects under fore-and-aft whole body vibration.