Equivalent magnitude-dependent discomfort under vertical vibration up to 100 Hz.

The effect of vibration magnitude on frequency-dependence of discomfort of human body is always overlooked with respect to the comfort equivalence contours, particularly for high-magnitude vibration in wideband frequency. In this study, the magnitude effect of vertical vibration on discomfort of human body is investigated experimentally. Nineteen male subjects are involved in the jury test of vibration discomfort in the vertical direction with 2-5 m/s2 in magnitude up to 100 Hz. It is shown that the growth rate of discomfort may exceed 1 due to the high-magnitude vibration employed. In this condition that the rate varies around 1, the Stevens' power law is not capable to properly represent the relationship between the subjective discomfort and the vibration magnitude. It means the equivalent comfort contours are not only dependent on the frequency range but also related to the vibration magnitude. Frequency weightings of vibration discomfort are influenced by the excitation magnitude. Practitioner summary: The occupant comfort to vertical whole-body vibration is affected by vibration magnitude. This study provides the effect of vibration magnitude on frequency-dependence of discomfort to whole-body vibration. It is suggested to propose variable frequency weightings for vibration discomfort evaluation under different magnitudes to achieve better comfort design.

Subjective discomfort analysis of human body in semi-supine posture caused by vertical sinusoidal vibration.

The vibration discomfort to the human body in semi-supine posture is currently evaluated as per ISO 2631-1, although it is recommended for sitting, standing and recumbent posture. The present study investigated the frequency-dependence of subjective responses of semi-supine humans to vertical vibration (0.5-1.5 m s-2 r.m.s.) across the frequency range 2.0-16.0 Hz. The subjects (14 males) judged the discomfort caused due to sinusoidal vibration using a modified absolute magnitude estimation method. The significant variation of rate of growth of discomfort across the frequency spectra caused the shape of equivalent comfort contour to vary with the vibration magnitude. The equivalent comfort contours illustrated significant discomfort between 8.0 and 10.0 Hz. Moreover, for frequencies above 10.0 Hz, substantial vibration acceleration was required to cause discomfort of the same intensity, implying that the frequency dependence of semi-supine posture is distinct from other postures. The frequency weighting obtained for semi-supine posture suggested that the discomfort estimation based on ISO 2631-1 was relatively accurate though conservative. Practitioner Summary: The discomfort caused by vertical vibration to the human in semi-supine posture was quite different from other postures. The present study provided the frequency-dependence of vibration discomfort for humans in semi-supine posture. Further, it investigated the suitability of frequency weightings defined in ISO 2631-1 for the acceleration measurements. Abbreviations: ISO: International Organization for Standardization; BS: British Standard; NASA: National Aeronautics and Space Administration; BMI: body mass index; AME: absolute magnitude estimation.

Subjective discomfort caused by vertical whole-body vibration in the frequency range 2-100 Hz.

Current standards assume the same frequency weightings for discomfort at all magnitudes of vibration, whereas biodynamic and psychological studies show that the frequency-dependence of objective and subjective responses of the human body depends on the magnitude of vibration. This study investigated the discomfort of seated human body caused by vertical whole-body vibration over the frequency range 2-100 Hz at relatively high magnitudes from 1.0 to 2.5 ms-2 r.m.s. Twenty-eight subjects (15 males and 13 females) judged the discomfort using the absolute magnitude estimation method. The rate of growth of discomfort with increasing vibration magnitude was highly dependent on the frequency, so the shapes of the equivalent comfort contours depended on the magnitude of vibration and no single frequency weighting would be appropriate for all magnitudes. The equivalent comfort contours indicated that the standards and previous relevant studies underestimated the vibration discomfort at frequencies greater than about 30 Hz. Practitioner Summary: The discomfort caused by vertical vibration at relatively high frequencies can be severe, particularly at relatively great magnitudes in transport. This study provides the frequency-dependence of vibration discomfort at 2-100 Hz, and shows how the frequency weightings in the current standards can be improved at relatively high frequencies.

Response of the seated human body to whole-body vertical vibration: discomfort caused by sinusoidal vibration.

Frequency weightings for predicting vibration discomfort assume the same frequency-dependence at all magnitudes of vibration, whereas biodynamic studies show that the frequency-dependence of the human body depends on the magnitude of vibration. This study investigated how the frequency-dependence of vibration discomfort depends on the acceleration and the force at the subject-seat interface. Using magnitude estimation, 20 males and 20 females judged their discomfort caused by sinusoidal vertical acceleration at 13 frequencies (1-16 Hz) at magnitudes from 0.1 to 4.0 ms(-2) r.m.s. The frequency-dependence of their equivalent comfort contours depended on the magnitude of vibration, but was less dependent on the magnitude of dynamic force than the magnitude of acceleration, consistent with the biodynamic non-linearity of the body causing some of the magnitude-dependence of equivalent comfort contours. There were significant associations between the biodynamic responses and subjective responses at all frequencies in the range 1-16 Hz. Practitioner Summary: Vertical seat vibration causes discomfort in many forms of transport. This study provides the frequency-dependence of vibration discomfort over a range of vibration magnitudes and shows how the frequency weightings in the current standards can be improved.

Response of the seated human body to whole-body vertical vibration: biodynamic responses to sinusoidal and random vibration.

The dependence of biodynamic responses of the seated human body on the frequency, magnitude and waveform of vertical vibration has been studied in 20 males and 20 females. With sinusoidal vibration (13 frequencies from 1 to 16 Hz) at five magnitudes (0.1-1.6 ms(-2) r.m.s.) and with random vibration (1-16 Hz) at the same magnitudes, the apparent mass of the body was similar with random and sinusoidal vibration of the same overall magnitude. With increasing magnitude of vibration, the stiffness and damping of a model fitted to the apparent mass reduced and the resonance frequency decreased (from 6.5 to 4.5 Hz). Male and female subjects had similar apparent mass (after adjusting for subject weight) and a similar principal resonance frequency with both random and sinusoidal vibration. The change in biodynamic response with increasing vibration magnitude depends on the frequency of the vibration excitation, but is similar with sinusoidal and random excitation.

A systematic review of studies investigating the effects of controlled whole-body vibration intervention on peripheral circulation.

The findings of the published studies investigating the changes in peripheral circulation induced by exposure to whole-body vibration (WBV) are not consensual or conclusive. Also, those studies did not consider the role of vibration magnitude on the peripheral circulatory responses making the interpretation of the observed findings difficult. We aimed to review the published literature investigating the effects of controlled WBV intervention on peripheral circulation by characterizing the relevant exposure conditions including vibration magnitudes, and ascertain the specific patterns of responses in peripheral circulation of the lower extremity from such exposure. A computerized search was performed in PubMed and Scopus using selected key search terms, and the relevant data were extracted. The vibration magnitude in the included studies frequently exceeded the limit specified in the International Standard ISO 2631-1 (1997) for such exposure. As observed, exposure to WBV with frequencies ≤30 Hz caused an improvement in peripheral blood flow (BF) and/or skin temperature (ST) of the lower extremity. In contrast, the responses in BF and ST from exposure to WBV of higher frequencies (31 Hz-50 Hz) produced conflicting results. The findings of this review indicate that WBV exposure with relatively lower frequency and magnitude can be safely and effectively used to induce improvements in peripheral circulation. For this purpose, the limits recommended by the ISO 2631-1 (1997) should be considered till safe and effective vibration-related parameters are established.

Effect of simulated transportation vibration on suspended erythrocyte quality / 军事医学

Objective To investigate the effect of vibration on the quality of suspended erythrocytes during transportation, and explore suitable experimental vibration conditions.Methods Three intensities(highway truck vibration, random vibration of fixed goods in a caterpillar, and combined wheeled vehicle vibration)were selected to simulate suspended erythrocyte transportation using electromagnetic vibration test system.Suspended erythrocytes of the same storage were randomly divided into three groups:highway truck vibration(group1),random vibration of fixed goods in a caterpillar(group 2),and combined wheeled vehicle vibration(group 3).The suspended erythrocytes were stored for 11 days and 26 days.The control group was stored with conventional methods.Suspended erythrocytes were vibrated for 1 hour,samples were collected before and after vibration,while free hemoglobin(FHb),K+,and LDH were tested.Results The changes in FHb and LDH after vibration were gradually increased with the magnitude of vibration(P<0.05).There was no significant difference in K +between the three vibration levels.The increase in FHb in suspended erythrocytes stored for 26 days was higher than 11days after random vibration of fixed goods in a caterpillar and combined wheeled vehicle vibration(P<0.05).There was no significant difference in the change in FHb between day(d)26 and d 11 after highway truck vibration.Under the same magnitude of vibration,the change in LDH in the d 26 suspended erythrocytes was more significant than that of the d 11, and no significant difference was found in the change in K +between d 26 and d 11. Conclusion The damage to suspended erythrocytes after combined wheeled vehicle vibration is more obvious than that by the other two vibrations.The vibration environment of combined wheel vehicles is more suitable for simulating the vibration damage to suspended erythrocyte vibration.Suspended erythrocytes with a longer storage time have significant changes in FHb and LDH after transportation vibration, and the length of storage time of suspended red blood cells might affect the vibration injury.