Apparent mass of the human body in the vertical direction: Effect of seat backrest

Toward, Martin; Griffin, Michael J.

doi:10.1016/j.jsv.2009.07.012

Cited by 40 publications

(32 citation statements)

References 21 publications

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“…There is evidence of an increase in the resonance frequency of the vertical apparent mass measured at the seat surface as the inclination of a backrest increases: from 5 or 5.5 Hz with an upright backrest to 6.5 or 7.5 Hz with a backrest inclined by 30 (Shibata and Maeda, 2009;Toward and Griffin, 2009). An increase in the resonance frequency of the vertical apparent mass on the seat as a backrest inclines is consistent with a greater percentage of the body mass being supported by the inclined backrest, and the backrest becoming a more important source of vibration.…”

Section: Effect Of Backrest Inclinationmentioning

confidence: 99%

“…An upright backrest tends to stiffen the body: the resonance frequencies in the vertical apparent mass measured at the seat surface increase when sitting with a rigid upright backrest: from around 5 Hz without a backrest to 5.5 Hz with a backrest (Toward and Griffin, 2009). The backrest therefore tends to increase the apparent mass at frequencies greater than the principal resonance frequency and reduce the apparent mass at frequencies less than the principal resonance.…”

Section: Figure 8 About Herementioning

confidence: 99%

“…Shibata and Maeda, 2009;Toward and Griffin, 2009), and to 7.0 or 9.4 Hz with maximum contact of the semi-supine body with a horizontal backrest (Huang and Griffin, 2008).…”

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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Section: Effect Of Backrest Inclinationmentioning

confidence: 99%

Section: Figure 8 About Herementioning

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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“…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]. The resonance frequency in the apparent mass of the body increases when a rigid backrest is reclined [6,8] but decreases when a foam backrest is reclined [6].…”

Section: Introductionmentioning

confidence: 99%

“…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]. The resonance frequency in the apparent mass of the body increases when a rigid backrest is reclined [6,8] but decreases when a foam backrest is reclined [6]. The vibration transmitted through a seat cushion can also be affected by backrest contact: the resonance frequency and the transmissibility at resonance increased when contact was made with the backrest of a reclined train seat [3].…”

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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Vibration Transmission at Seat Cushion and Sitting Comfort in Next-Generation Cars

d’Amore

Qiu

2021

Proceedings of the 21st Congress of the International Ergonomics Association (IEA 2021)

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Apparent mass of the human body in the vertical direction: Effect of seat backrest

Cited by 40 publications

References 21 publications

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

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

Vibration Transmission at Seat Cushion and Sitting Comfort in Next-Generation Cars

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