V.H. Saran

Stiffness properties of small-sized pneumatic tyres

Abstract The vertical, longitudinal and lateral dynamic behaviour of road vehicles is largely influenced by the dynamic characteristics of tyres. The tyre characteristics have been modelled by researchers as functions of the tyre elastic properties which are characterized by tyre vertical, lateral, longitudinal and torsional stiffnesses. Design details of an experimental rig for measurement of tyre static stiffnesses are presented, and experimental data on these stiffness values in the form of a power law as functions of tyre size, ply rating, normal load and inflation pressure are reported. Using tyre models, the tyre force and moment characteristics necessary for vertical dynamic simulation can be predicted.

Measurement and bio-dynamic model development of seated human subjects exposed to low frequency vibration environment

In this study, the effect of posture, vibration magnitude and frequency on seat-to-head (STH) and back support-to-head (BTH) transfer functions has been studied under vertical sinusoidal vibration. Twelve healthy male subjects participated in experimental work to measure vertical vibration transmitted to the occupants’ heads in three representative postures (erect, vertical backrest and forward lean on table) under three magnitudes of vibration (0.4, 0.8 and 1.2 m/s2 r.m.s.) in frequency range 1 to 20 Hz. From collected data sets, the effects of vibration magnitude, vibration frequency and postures on STH and BTH transmissibility and phase were measured over the prescribed frequency range. The result suggested that inclusion of all possible variables in optimal design of vehicle seat, suspension and comfort analysis would improve the design and analysis. The comparison of experimental and model response reveals that both models matched with mean experimental data sets most closely and the models provide t...

Effect of magnitudes and directions (mono-axis and multi-axis) of whole body-vibration exposures and subjects postures on the sketching performance

Whole-body vibrations in trains are known to affect the performance of sedentary activities such as reading, writing, sketching, working on a computer, etc. The objective of the study was to investigate the extent of disturbance perceived in sketching task by seated subjects in two postures under mono- and multi-axis Gaussian random vibration environment. The study involved 21 healthy male subjects in the age group of 23—32 years. Random vibrations were generated both in mono- and multi-axial directions in the frequency range of 1—10 Hz at 0.5, 1.0, and 1.5 m/s2 rms (root mean square) amplitude. The subjects were required to sketch given geometric figures such as a circle, triangle, rectangle, and square with the help of ball-point pen under given vibration stimuli in two postures (sketch pad on lap and sketch pad on table). The deviation in distortion with respect to the given figure is represented in terms of percentage distortion. The influence of vibrations on the sketching activity was investigated both subjectively and by two specifically designed objective methods, namely, RMS (root mean square methodology) and area methods. The judgements of perceived difficulty to sketch were rated using seven-point semantic judgement scale. The percentage distortion and difficulty in sketching activity increased with an increase in vibration magnitude. Both subjective evaluation and the RMS method revealed that the task was affected more while sketching on the table. The percentage distortion was affected similarly and maximum in all the vibration directions except for the vertical, while sketching difficulty was found to be higher only with longitudinal and multi-axis vibration direction. The subjective evaluation also revealed that there was no effect of the type of entity chosen on the sketching difficulty.

Modal analysis of human body vibration model for Indian subjects under sitting posture

Need and importance of modelling in human body vibration research studies are well established. The study of biodynamic responses of human beings can be classified into experimental and analytical methods. In the past few decades, plenty of mathematical models have been developed based on the diverse field measurements to describe the biodynamic responses of human beings. In this paper, a complete study on lumped parameter model derived from 50th percentile anthropometric data for a seated 54- kg Indian male subject without backrest support under free un-damped conditions has been carried out considering human body segments to be of ellipsoidal shape. Conventional lumped parameter modelling considers the human body as several rigid masses interconnected by springs and dampers. In this study, concept of mass of interconnecting springs has been incorporated and eigenvalues thus obtained are found to be closer to the values reported in the literature. Results obtained clearly establish decoupling of vertical and fore-and-aft oscillations. Practitioner Summary: The mathematical modelling of human body vibration studies help in validating the experimental investigations for ride comfort of a sitting subject. This study clearly establishes the decoupling of vertical and fore-and-aft vibrations and helps in better understanding of possible human response to single and multi-axial excitations.

Effects of Vibration Magnitude and Posture on Seat-to-head-transmissibility Responses of Seated Occupants Exposed to Lateral Vibration

In an attempt to define how train vibration and motion affect passenger comfort, an experimental study has been conducted to show the effect of variations in posture and vibration magnitude on head motion in three translational directions (fore-and-aft, lateral and vertical) with seat vibration in lateral direction. Thirty healthy male subjects were exposed to random vibration in lateral axis with three excitation magnitudes of 0.4, 0.8 and 1.2 m/s2 rms over the frequency range of 1-20 Hz. The data results are analysed in terms of seat-to-head-transmissibility response, phase and coherence for head motions in two sitting postures (backrest and forward lean). The seat-to-head-transmissibility response registered maximum head motion in lateral direction with single peak at 2 Hz in both the sitting posture. The response also reported an additional peak near 6 Hz in forward lean postures. The broad peak converged to a single peak at 2 Hz with reduction in seat-to-head-transmissibility response under the higher magnitude of lateral vibration, which was attributed to the softening effect of the human body. The STHT response yields only minimal effect on posture, particularly in the vicinity of the resonance only.

Effects of posture and vibration magnitude on seat to head transmissibility during exposure to fore-and-aft vibration

An experimental study has been conducted on the vibration simulator, developed as a mockup of a railway vehicle. In this paper, the effect of variations in the posture and vibration magnitude on head motions in three translational directions (fore-and-aft, lateral and vertical) are studied with seat vibration in fore-and-aft direction. Thirty healthy male subjects are exposed to random vibration with three vibration magnitudes of 0.4, 0.8 and 1.2 m/s2 r.m.s. over the frequency range 1–20 Hz. The data results are analyzed in terms of seat-to-head transmissibility (STHT) in two sitting postures; backrest and forward lean. Vibration measurements of the head motions are made with an apparatus (bite-bar). The study confirms that the measured responses to single fore-and-aft axis vibration have shown notable cross-axis responses. An increase in the excitation magnitude consistently revealed a decrease in the response peak magnitude and the corresponding resonant frequency, particularly in the presence of a back support. Such non-linear behavior has been interpreted as a non-linear softening effect in the muscle tension under increasing intensity of vibration. The use of a back support significantly alters the biodynamic responses of the seated body, which is attributable to the constraint due to the backrest support.

Interference in Writing Performance Under Whole-Body Vibration Exposure Together with Subject Posture

Train passengers often experience difficulty in performing various sedentary activities such as writing during travel. This study identifies the influence of three primary parameters viz., vibration level, vibration direction and sitting posture on writing performance for an improved activity comfort in trains. Therefore, an experimental study was conducted on a mock up of rail vehicle to examine the interference in writing task under random vibrations excited in mono, dual and multi axis in low frequency range of 1-20 Hz at 0.4, 0.8 and 1.2 m/s2 amplitudes. Thirty healthy male subjects were assigned the task to write the given characters in two seated postures (on lap and table posture). The performance was evaluated subjectively using Borgs CR-10 scale and quantifying the distortion in writing. The results revealed that the degradation in writing performance was found to increase with vibration stimuli and reported maximum in both lateral and vertical direction equally. Similarly, the effects of multi axis vibration were found similar to dual axes vibration and greater than mono axes vibration. While higher degradation in performance was found while working on lap than on table in X-direction, however, all other mono and multi axis vibration reported maximum in table posture.