The apparent mass of the seated human body: Vertical vibration

Fairley, Thomas E.; Griffin, Michael

doi:10.1016/0021-9290(89)90031-6

Cited by 250 publications

(232 citation statements)

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“…The findings seem partially consistent with the hypothesis of Shoenberger and Harris (1971) that the greatest exponents will occur at the whole-body resonance frequency; they determined exponents for vertical vibration at 3.5, 5, 7, 9, 11, 15, and 20 Hz and found that the exponent at 5 Hz (1.04) was significantly greater than that at 7, 15 and 20 Hz. The primary resonance frequencies for fore-and-aft, lateral and vertical whole-body vibration (without backrest) are in the region of 2.5, 2.0, and 4.0 Hz, respectively [24,25], which more-or-less coincide with the maximum exponent for fore-andaft vibration (at 2 Hz) and the maximum exponent for vertical vibration (at 4 Hz) in the present study. In the lateral direction, the study of Fairley and Griffin [25] had subjects with feet close together whereas in the present study the feet were further apart -this may have increased the resonance frequency of the body in the lateral direction in the present study and so a maximum exponent for lateral vibration in the 4 to 6 Hz range may also be associated (in some undefined way) with the biodynamic responses of the body during vibration.…”

Section: Fig 5 About Heresupporting

confidence: 71%

Magnitude-dependence of equivalent comfort contours for fore-and-aft, lateral and vertical whole-body vibration

Morioka¹,

Griffin²

2006

Journal of Sound and Vibration

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Section: Fig 5 About Heresupporting

confidence: 71%

Magnitude-dependence of equivalent comfort contours for fore-and-aft, lateral and vertical whole-body vibration

Morioka¹,

Griffin²

2006

Journal of Sound and Vibration

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“…For example, the seated body tends to be most sensitive to whole-body vertical acceleration around 5 Hz, consistent with an apparent mass resonance around 5 Hz (e.g. Fairley and Griffin, 1989).…”

Section: Introductionmentioning

confidence: 58%

“…A similar influence of a backrest can be seen in the physical responses of the body. With a vertical backrest, a general trend for increased resonance frequencies and increased apparent mass at frequencies greater than the resonance has been reported, probably due to changes in the dynamic responses of the body arising from differences in the vibration transmission paths to the body and the body posture (Fairley and Griffin, 1989). The transmission of vertical seat vibration to the head is also changed by the addition of a backrest: fore-and-aft head motion has been reported to increase at frequencies up to 25 Hz, with almost a doubling at the frequency of greatest transmissibility around 7 Hz; vertical head motion showed a more distinct peak around 6 Hz, and pitch head motion was increased at frequencies greater than principal resonance around 4 Hz (Paddan and Griffin, 1988).…”

Section: Introductionmentioning

confidence: 97%

“…Studies of physical responses (e.g., apparent mass, mechanical impedance, transmissibility) to whole-body vertical vibration when sitting with no backrest also show a strong dependence on the frequency of the vibration (e.g. Fairley and Griffin, 1989;Paddan and Griffin, 1988). Some similarities in the frequencydependence of subjective and physical responses suggest vibration discomfort is associated with physical responses of the body.…”

Section: Introductionmentioning

confidence: 99%

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Predicting discomfort from whole-body vertical vibration when sitting with an inclined backrest

Basri

Griffin

2013

Applied Ergonomics

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Current methods for evaluating seat vibration to predict vibration discomfort assume the same frequency weightings and axis multiplying factors can be used at the seat surface and the backrest irrespective of the backrest inclination. This experimental study investigated the discomfort arising from whole-body vertical vibration when sitting on a rigid seat with no backrest and with a backrest inclined at 0 (upright), 30, 60, and 90 (recumbent). Within each of these five postures, 12 subjects judged the discomfort caused by vertical sinusoidal whole-body vibration (at frequencies from 1 to 20 Hz at magnitudes from 0.2 to 2.0 ms -2 r.m.s.) relative to the discomfort produced by a reference vibration (8 Hz at 0.4 ms -2 r.m.s.). With 8-Hz vertical vibration, the subjects also judged vibration discomfort with each backrest condition relative to the vibration discomfort with no backrest. The locations in the body where discomfort was experienced were determined for each frequency at two vibration magnitudes.Equivalent comfort contours were determined for the five conditions of the backrest and show how discomfort depends on the frequency of vibration, the presence of the backrest, and the backrest inclination. At frequencies greater than about 8 Hz, the backrest increased vibration discomfort, especially when inclined to 30, 60, or 90, and there was greater discomfort at the head or neck. At frequencies around 5 and 6.3 Hz there was less vibration discomfort when sitting with an inclined backrest.

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“…the ratio of the force to the acceleration as a function of vibration frequency) around 4 Hz [5]. When the back is partially supported by an upright backrest, there is an increase in the resonance frequency of the apparent mass [6] and an increase in the apparent mass at frequencies greater than the resonance frequency [6,7].…”

Section: Introductionmentioning

confidence: 99%

The transmission of vertical vibration through seats: Influence of the characteristics of the human body

Toward

Griffin

2011

Journal of Sound and Vibration

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The transmission of vibration through a seat depends on the impedance of the seat and the apparent mass of the seat occupant. This study was designed to determine how factors affecting the apparent mass of the body (age, gender, physical characteristics, backrest contact, and magnitude of vibration) affect seat transmissibility. The transmission of vertical vibration through a car seat was measured with 80 adults (41 males and 39 females aged 18 to 65) at frequencies between 0.6 and 20 Hz with two backrest conditions (no backrest and backrest), and with three magnitudes of random vibration (0.5, 1.0, and 1.5 ms -2 r.m.s.). Linear regression models were used to study the effects of subject physical characteristics (age, gender, and anthropometry) and features of their apparent mass (resonance frequency, apparent mass at resonance and at 12 Hz) on the measured seat transmissibility. The strongest predictor of both the frequency of the principal resonance in seat transmissibility and the seat transmissibility at resonance was subject age, with other factors having only marginal effects. The transmissibility of the seat at 12 Hz depended on subject age, body mass index, and gender. Although subject weight was strongly associated with apparent mass, weight was not strongly associated with seat transmissibility. The resonance frequency of the seat decreased with increases in the magnitude of the vibration excitation and increased when subjects made contact with the backrest. Inter-subject variability in the resonance frequency and transmissibility at resonance was less with greater vibration excitation, but was largely unaffected by backrest contact. A lumped parameter seat-person model showed that changes in seat transmissibility with age can be predicted from changes in apparent mass with age, and that the dynamic stiffness of the seat appeared to increase with increased loading so as to compensate for increases in subject apparent mass associated with increased sitting weight.Author Keywords: seat transmissibility; biodynamics; seats; whole-body vibration; inter-subject variability; posture; age; weight; gender Published as: The transmission of vertical vibration through seats: influence of the characteristics of the human body. Toward, M. G. R. & Griffin, M. J. 19 Dec 2011 In : Journal of Sound and Vibration. 330, 26, p. 6526-6543. 3 Highlights > Transmissibility of a car seat measured with 80 subjects (of both genders, aged 18 to 65 years), with and without backrest. > Subject age was the strongest predictor of seat transmissibility -increased age was associated with increased resonance frequency and increased seat transmissibility at resonance. > Subject weight was not strongly associated with seat transmissibility. > Seat resonance frequency decreased with increased vibration magnitude and increased when using the backrest.

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The apparent mass of the seated human body: Vertical vibration

Cited by 250 publications

References 2 publications

Magnitude-dependence of equivalent comfort contours for fore-and-aft, lateral and vertical whole-body vibration

Magnitude-dependence of equivalent comfort contours for fore-and-aft, lateral and vertical whole-body vibration

Predicting discomfort from whole-body vertical vibration when sitting with an inclined backrest

The transmission of vertical vibration through seats: Influence of the characteristics of the human body

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