Analytical and Numerical Investigations of Mechanical Vibration in the Vertical Direction of a Human Body in a Driving Vehicle using Biomechanical Vibration Model
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Abstract:
The main reason that affects the discomfort in a driving vehicle is the vibration response. The human body vibration leads to many malfunctions in both comfort and performance in human health. As a result, the human body’s simulation in sitting posture in the driving vehicle has a strategic relationship for all Tires and vehicles manufacturers. The digital process simulation of the human body seat vehicle vibration shows two significant advantages. The first advantage is the prevention of the high-cost modifications in the construction stage of the vehicle, while the second one describes the stability test during the undesirable vibrations. This study modelled the human body’s dynamic characterisations, natural frequency, and mechanical response when seated in the driving vehicle with vibration transmissibility in the vertical direction have been using the biomechanical vibration model. The vertical vibrations and the transmissibility of the human body dynamic response are presented in detail. Exciting results have been obtained, and they are significant for human health, which relates to sitting posture in the driving vehicle. It can assist in understanding the influences of low-frequency vibration on human health, comfort, and performance, and therefore it could be applied for ride comfort evaluation. An analytical solution to derive the general equations of motion for the human system was developed. Then, using the vibration analysis technique and the corresponding equations, the accurate dynamic response of the selected mode is identified. Furthermore, the mathematical modelling for free vibration using the finite element analysis has been performed to determine the appropriate values and set its description. Then, the comparison results of the two techniques have been carried out.Keywords:
Transmissibility (structural dynamics)
Whole body vibration
Sitting
Natural frequency
Transmissibility (structural dynamics)
Whole body vibration
Mechanical vibration
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"Effect of vibration frequency and angle knee flexion on muscular activity and transmissibility function during static whole body vibration exercise." Computer Methods in Biomechanics and Biomedical Engineering, 17(sup1), pp. 116–117Keywords:: mechanical vibrationpostureEMG AcknowledgementsThese investigations were financially supported by the Champagne-Ardenne region and the European Fund of Regional Development (FEDER).
Transmissibility (structural dynamics)
Whole body vibration
Biomechanics
Knee flexion
Mechanical vibration
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Although the exposure to whole-body vibrations (WBV) has been shown to be detrimental to seated humans, the vibration levels to which wheelchair (WC) users are exposed to in their communities have not been thoroughly examined. Furthermore, some evidence suggests that the cushions used in WCs, the first line of protection, may amplify WBV, although conclusive evidence has not been presented in the literature. The purpose of this work was twofold. First, to evaluate and compare the transmissibility of commercially WC cushions with two laboratory test methods: (1) direct measurement of transmissibility while human subjects propelled a WC over a road course with different cushions and (2) characterization of cushions with a material testing system (MTS) combined with mathematical models of the apparent mass of the human body. Second, to evaluate WBV exposure to WC users in their communities using ISO 2631-1 methods, and determine whether exposure levels are correlated with WC type and/or back pain, which is a physiological symptom of WBV exposures. Results showed that although dynamic characterization of WC cushions is possible with an MTS, the results did not correlate well with the transmissibility obtained in the WC road course. Significant differences were found for transmissibility among the cushions tested, with the air-based cushions having lower transmissibility than the foam- or gel-based cushions. All WC users who participated in this community-based trial were continuously exposed to WBV levels that were within and above the health caution zone specified by ISO 2631-1 during their day-to-day activities. Our evidence suggested that WCs with suspension did not significantly impact the WBV transmitted to WC users. Finally, we found that WC users are exposed to other risk factors to LBP such as prolonged sitting and transfers. WBV exposure to WC users may be an important contributor to LBP as it has been shown to exceed international standards. Suspension systems need to be improved to reduce vibrations transmitted to the users. More research is needed to understand the interplay between posture, WC configuration, and WBV.
Transmissibility (structural dynamics)
Whole body vibration
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Whole body vibration
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Abstract Suspension seat is used in the off-road condition to attenuate excessive vibration exposed to the human body. The efficiency of a seat reducing vibration not only depends on the dynamic characteristics of the seat, but the dynamic characteristics of human body and the characteristics of the input vibration as well. Tractor drivers adopted different postures during their farm work activities, which may influence the dynamic characteristics of the human body. However, the influenced of the driver’s posture on suspension seat transmissibility has received less systematic attention. Thus, this study is carried out with the objective to investigate the effect of different postures on seat transmissibility when seated on a suspension seat. Three male subjects were exposed to random vibration at 2.0 m/s 2 r.m.s with frequency ranging from 1-20 Hz, while seated on a vibration simulator for 60 seconds. The subjects adopted four seating postures: (i) relaxed, (ii) slouched, (iii) tensed and (iv) with backrest support. The study found that relaxed and slouched postures have a resonance frequency at 2.0 Hz. However, as the posture changed to backrest support, the resonance frequency of the seat transmissibility slightly increased by 0.25 Hz. This study suggested that changing the postures caused changes in the dynamics of human body, and thus affected the suspension seat transmissibility. It is concluded that, non-linearity in suspension seat transmissibility is influenced by the changes of body postures.
Transmissibility (structural dynamics)
Whole body vibration
Suspension
Tractor
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Whole body vibration has been postulated to contribute to the onset of back pain. However, little is known about the relationship between vibration exposure, the biomechanical response, and the physiological responses of the seated human. The aim of this study was to measure the frequency and corresponding muscle responses of seated male volunteers during whole body vibration exposures along the vertical and anteroposterior directions to define the transmissibility and associated muscle activation responses for relevant whole body vibration exposures. Seated human male volunteers underwent separate whole body vibration exposures in the vertical (Z-direction) and anteroposterior (X-direction) directions using sinusoidal sweeps ranging from 2 to 18 Hz, with a constant amplitude of 0.4 g. For each vibration exposure, the accelerations and displacements of the seat and lumbar and thoracic spines were recorded. In addition, muscle activity in the lumbar and thoracic spines was recorded using electromyography (EMG) and surface electrodes in the lumbar and thoracic region. Transmissibility was determined, and peak transmissibility, displacement, and muscle activity were compared in each of the lumbar and thoracic regions. The peak transmissibility for vertical vibrations occurred at 4 Hz for both the lumbar (1.55 ± 0.34) and thoracic (1.49 ± 0.21) regions. For X-directed seat vibrations, the transmissibility ratio in both spinal regions was highest at 2 Hz but never exceeded a value of 1. The peak muscle response in both spinal regions occurred at frequencies corresponding to the peak transmissibility, regardless of the direction of imposed seat vibration: 4 Hz for the Z-direction and 2–3 Hz for the X-direction. In both vibration directions, spinal displacements occurred primarily in the direction of seat vibration, with little off-axis motion. The occurrence of peak muscle responses at frequencies of peak transmissibility suggests that such frequencies may induce greater muscle activity, leading to muscle fatigue, which could be a contributing mechanism of back pain.
Transmissibility (structural dynamics)
Whole body vibration
Back muscles
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Laboratory-based whole-body vibration studies often involve complex experimental designs, dozens of vibration exposures and multiple sessions. Shortening the test vibration duration would increase experimental efficiency by permitting more trials in the same time period. This study evaluated reported discomfort based on different sinusoidal vibration durations and amounts of rest between successive vibrations. Ten subjects were exposed to four blocks of vibration trials (15/20 second vibration and 5/10 second rest durations). Each block of 37 trials included repeated single axis, planar, and 6 degree of freedom multi-axial vibrations. These repeated trials were analysed to evaluate whether discomfort varied between the different blocks. We did not observe any statistically significant differences in discomfort between the different vibration and rest durations. This finding is useful for designing future vibration experiments. Part II of this study evaluates the relationship between discomfort and vibration exposure.
Whole body vibration
Rest (music)
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Whole-body vibration training machines are used by both male and female users. However, studies investigating the biodynamic responses to vibration during training have used either mixed-gender subjects or male subjects. No study has investigated the effect of gender on the biodynamic responses under vibration training conditions. The objective of this study is to investigate the effect of gender on the apparent mass and the vibration of the head of standing people during exposure to vibration. A total of 40 subjects (20 females and 20 males) were exposed to vertical vibration at six frequencies in the range 20-45 Hz and vibration acceleration in the range 10.8-20.9 m/s2 (peak). The subjects stood on a force platform mounted on the vibrating plate of the machine adopting an upright standing posture with their knees unlocked and their arms straight along their bodies. The vertical acceleration and force at the interface between the vibrating plate and the feet were measured and used to calculate the apparent mass. The accelerations of the head in the x-, y- and z-directions were also measured and used to calculate the transmissibility to the head. The apparent mass of males was found higher than that of females. The transmissibility to the head in all directions was found higher in females than males. The differences in the biodynamic responses between males and females were attributed to the differences in body properties and structure of the two genders. The results of this study imply the need for gender-specific vibration training programmes.
Transmissibility (structural dynamics)
Whole body vibration
Mechanical vibration
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Biodynamic modelling of seat-occupant systems can assist in seat comfort design. A finite element (FE) model of the seated human body, including detailed modelling of the lumbar spine, was established to reflect the human response to vibration and biodynamic response of the lumbar spine under whole-body vibration (WBV). The lumbar spine model was established and validated against the in-vitro results and calculated data. The posture of the lumbar spine was adjusted according to the radiological research results, and the adjusted model was combined to establish a FE model of the seated human body. The present seated human model with backrest inclination angles of 10, 20, and 30°, validated by comparing the measured apparent mass and seat-to-lumbar spine transmissibility, was used to calculate the biodynamic response of the lumbar spine with three inclined backrests under WBV. The results showed that the model could characterise the apparent mass, seat-to-lumbar spine transmissibility, and the biodynamic response of the lumbar spine. Practitioner summary: Biodynamic models can represent dynamic characteristics of the human body exposed to vibration and assist in seat comfort design. The three-dimensional FE model of the human body can be used to explore the human response to vibration and the biodynamic response of the lumbar spine under WBV.
Whole body vibration
Transmissibility (structural dynamics)
Biomechanics
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Mobile machinery operators are exposed to whole-body vibrations (WBV) and unfavourable postures which may lead to adverse effects on the spine. 14 subjects were exposed to WBV on a rigid seat without a backrest. They adopted nine different postures. Apparent mass MA(f) and seat-to-head transmissibility T(f) were measured in the horizontal (X), lateral (Y) and vertical (Z) directions. They were compared to the reference posture from the ISO 2631-1 standard. Head and thorax inclinations in the sagittal plane had significant effects. An increase in the main resonant frequency fr, together with a decrease in |MA(f)|max were observed in the Z direction. A second lower frequency peak also appeared (fr≈1 Hz for X, fr≈2.5 Hz for Z). fr increased in the X and Z directions for |T(f)|. |T(f)|max increased in the X direction. Head and thorax inclinations in the frontal and the horizontal planes had weak or non-significant effects.Practitioner summary: Mobile machinery operators are exposed to whole-body vibration and unfavourable body posture. Laboratory measurements of the apparent mass MA(f) and the seat-to-head transmissibility T(f) in the horizontal (X), lateral (Y) and vertical (Z) directions are presented for 9 postures relevant to the exposure at the driving position and to the effects of vibration on the spine.
Whole body vibration
Transmissibility (structural dynamics)
Thorax (insect anatomy)
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