EFFECT OF LOW FREUQUENCY VIBRATION ON READING ACTIVITY IN STANDING POSTURE

Abstract

It is a common observation that vibration can interfere with human activities. Most evidently affected are the ability to see detail quickly and easily as in case of reading activity. People use rail and road vehicles as a daily means of transport and often spend a significant amount time while doing so and some field studies suggests reading is one of the most preferred and done activities while travelling. To understand the behavior of human body in standing posture and reading posture while standing, biodynamic model for 50th percentile Indian male subject is made and effects of vibration on various body parts were studies to investigate the frequency and acceleration dependencies on the head and forearm which in turn affects reading activity. To model the human body in the two standing postures, truncated ellipsoids were combined to make the model and analyzed the dynamic characteristics of the models with finite element approach using software simulations in different vibration conditions. To validate the present biodynamic model, comparison of natural frequencies and displacements is compared with the existing models. The reading posture biodynamic model in standing condition is made to assess the effect of vertical base excitation on the head and forearm in 1 m/s2 and 1.5 m/s2 from the range 1 to 40 Hz frequencies and their frequency response and force transmissibility is studied. It is found that on some frequencies, the applied force was in phase with the exciting force but transmissibility of force was not considerable as seen at 34 Hz for both 1 and 1.5 m/s2 for head and similarly at 28 Hz for both 1 and 1.5 m/s2 in the case of forearm. Transmissibility ratios is found to be greater than unity under attenuation of exciting frequencies and the applied acceleration was out of phase by 180º on these frequencies. By increasing base acceleration, the maximum transmissibility is seen to decrease. The inertia force of the body tries to overcome the effect of excitation frequencies and this is seen to be in accordance with the previous studies done experimentally. The frequencies on which large displacement are sought to occur remains almost the same when the applied acceleration is changed and these frequencies can be considered to be affecting reading activity in standing posture.