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Experimental set-up (the locations of the two force transducers are in the red boxes, the side view is shown in the right subgraph).
Source publication
The biodynamic response of 12 subjects to single-axis vertical and multi-axis vertical, lateral and roll excitations was studied to advance understanding of the biodynamics. Different from using single-input and single-output (SISO) method, the apparent masses with multiple inputs were estimated by multi-input and single-output (MISO) method, whose...
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... rigid seat with a vertical backrest was used in the experiment in order to avoid the influence of the dynamics of the seat on the biodynamics of human body (Fig. 2). During the experiment, the participants were asked to sit in an upright posture in contact with the backrest, with the feet resting on the footrest (average thigh contact), one hand holding an emergency button and the other on the lap. Another emergency button was within the reachable distance of the experimenter. Table 1. The ...
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... the reachable distance of the experimenter. Table 1. The coherence between excitations in different directions in each pair was checked numerically and shown very small (less than 0.3). The rotational axis of roll excitation was defined as the intersection line between the upper surface of the seat pan and the symmetrical (x-z) plane of the seat (Fig. ...
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... stimulus lasted 60 s. As shown in Fig. 2 ) in x, y and z directions were measured by two tri-axial SIT-pads. The SITpad on the seat pan was positioned beneath the ischial tuberosity of the seated subject. The SIT-pad on the backrest was centrally located at d z 470 mm above the seat pan surface (Fig. 2). All the data were recorded by HVLab data acquisition system at 512 ...
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... stimulus lasted 60 s. As shown in Fig. 2 ) in x, y and z directions were measured by two tri-axial SIT-pads. The SITpad on the seat pan was positioned beneath the ischial tuberosity of the seated subject. The SIT-pad on the backrest was centrally located at d z 470 mm above the seat pan surface (Fig. 2). All the data were recorded by HVLab data acquisition system at 512 samples per second via an anti-aliasing filter set at 50 Hz. Data analysis was conducted with ...
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... View A c c e p t e d M a n u s c r i p t Fig. 2 Alt Text: Two SIT-pads at the seat pan and backrest are used to measure the tri-axial accelerations; a force plate and two force transducers between two plates of the backrest are used to measure the tri-axial ...
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... in total, Table 3), however, a smaller proportion of significant decreases were visible as the increase of magnitude in y direction ( Fig. A-2; 27/72 in total, Table A-1), and a very small proportion of significant decreases as the increasing magnitudes in roll direction (8/72 in total, not shown) were detected. Interestingly, the proportion of significant changes of resonance frequency with z-axis excitation magnitude decreased as the rise of y-axis excitation magnitude ...
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... rigid seat with a vertical backrest was used in the experiment in order to avoid the influence of the dynamics of the seat on the biodynamics of human body (Figure 2). During the experiment, the participants were asked to sit in an upright posture in contact with the backrest, with the feet resting on the footrest (average thigh contact), one hand holding an emergency button and the other on the lap. ...
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... coherence between excitations in different directions in each pair was checked numerically and shown very small (less than 0.3). The rotational axis of roll excitation was defined as the intersection line between the upper surface of the seat pan and the symmetrical (x-z) plane of the seat (Figure 2). Every stimulus lasted 60 s. ...
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... shown in Figure 2, the forces F sx , F sy and F sz at the seat pan were respectively the summations of the forces in x, y and z directions measured by a force plate (Kistler 9281 B) with four tri-axial transducers located at the four corners of the plate amplified by Kistler 5001 charger amplifiers. The forces F bx , F by and F bz at the backrest were respectively the summation of the forces in x, y and z directions measured by two tri-axial force transducers (Kistler 9602) placed at the two diagonal ends amplified by Kistler 5073 charger amplifiers. ...
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... SIT-pad on the seat pan was positioned beneath the ischial tuberosity of the seated subject. The SIT-pad on the backrest was centrally located at z d ¼ 470 mm above the seat pan surface ( Figure 2). All the data were recorded by HVLab data acquisition system at 512 samples per second via an anti-aliasing filter set at 50 Hz. ...
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... the apparent mass in z direction on the seat pan, the primary resonance frequencies for almost all the subjects lied in 4-7.5 Hz (Figure A-1). A large proportion of significant decreases of the resonance frequencies were found by Wilcoxon test as the increase of excitation magnitude in z direction (Figure 3; 30/48 in total, Table 3), however, a smaller proportion of significant decreases were visible as the increase of magnitude in y direction (Figure A-2; 27/72 in total, Table A-1), and a very small proportion of significant decreases as the increasing magnitudes in roll direction (8/72 in total, not shown) were detected. Interestingly, the proportion of significant changes of resonance frequency with z-axis excitation magnitude decreased as the rise of y-axis excitation magnitude (from 11/12 to 3/ 12, Table 3) and roll excitation magnitude (from 9/12 to 5/12, Table 3). ...
Citations
... Apart from causing the failure of mechanical constructions, unwanted vibration and deformation could spoil their capability to function properly; for example, in the case of wings, oscillations could result in poor aerodynamic performance [1,2]. These vibrations also create noise and heat, which reduces efficiency and may cause discomfort to anyone exposed to it for an excessive amount of time [3,4]. Therefore, it is essential for engineers to mitigate these vibrations as much as possible. ...
Hybrid vibration absorbers (HVAs) are an effective solution for vibration mitigation. They combine the passive vibration absorption mechanism of tuned mass dampers (TMDs) with feedback-controlled actuators, similar to active mass dampers. This enables them to overcome the performance of both systems in terms of vibration mitigation effectiveness and energy consumption, respectively. This study evaluates the vibration suppression capabilities of an HVA against self-excited oscillations. A single-degree-of-freedom host system encompassing a negative damping term is considered. First, the possibility of enhancing the stability properties of an optimally tuned TMD through a feedback controller is evaluated. The analysis shows that this approach cannot improve the absorber’s performance. Subsequently, simultaneous optimization of all the HVA parameters is considered. Our results reveal that this approach significantly enhances the system’s performance. All analysis is carried out analytically without resorting to approximations. Finally, the absorber is numerically applied to suppress friction-induced vibrations and galloping instabilities.
... The biodynamic response of the seated human body to combined lateral, vertical and roll vibrations was measured in a laboratory experiment using a 6-axis motion simulator in the Institute of Sound and Vibration Research (ISVR) at the University of Southampton. The experiment was also introduced in a previous paper [16,30]. ...
To study the coupled vibration of the seated human body in the sagittal plane and coronal plane exposed to lateral, vertical and roll excitations, a seated human body model consisting of abdomen , pelvis, two thighs, upper torso (including the shoulders, thorax, arms), and head (in-cluding neck) was proposed. The model was calibrated with the apparent masses measured in 0.5-20 Hz and proved to be applicable for subjects of different weights and heights and different excitation magnitudes in combined lateral, vertical and roll directions. This model was also potentially suitable for different backrest inclinations. Three modes of the human body associated with the resonances in the measured apparent masses were observed by means of modal analysis. The first and second modes with modal frequencies of 1.16 and 2.53 Hz, respectively, featured the vibration of the human body in the coronal plane. The former was dominated by the lateral and roll vibrations of the upper torso and head, while the latter by the lateral whole-body vibration accompanied by roll of the upper torso and head. The third mode with a modal frequency of 5.28 Hz featured the vibration of the human body in the sagittal plane. This mode exhibited a combination of the vertical vibration of the entire body and a bending motion of the upper body arising from the pitch of pelvis. These three modes showed good consistency with those identified in the modal test. The vibration coupling between the sagittal plane and coronal plane associated with these three modes was not significant. This model can be used to calculate the ride vibration and comfort of passengers in rail vehicles.
Ride comfort can be affected by the multi-axis vibrations. This research was designed to investigate how the seat transmissibility was affected by the variation of single-axis vertical vibration and dual-axis horizontal and vertical vibration. Twelve occupants were exposed to vertical vibration (0.2, 0.4, or 0.8 ms−2 r.m.s.) with and without additional horizontal vibration (0.2, 0.4, or 0.8 ms−2 r.m.s.). The peak frequencies of both vertical in-line and horizontal cross-axis seat transmissibilities to the seat back and the seat cushion reduced with increasing the amplitude of single-axis vibration and dual-axis vibration. And the peak frequencies in the seat transmissibilities measured with dual-axis vibration were lower than those measured with single-axis vibration. The seat transmissibilities measured with dual-axis vibration might exhibit similar resonant behaviour to those acquired with single-axis vibration. The peak frequencies of the seat transmissibilities to the interfaces between seat and occupant might be induced by the same vibration mode.
Most previous studies on the biodynamic response and the seating dynamics were limited to single axial excitations. How the suspension-seat-occupant system behaves in the multi-axial vibrational environment is less reported. The objective of this study is to advance the understanding of the effect of the excitation magnitude and the backrest inclination angle on the biodynamic response of the seated human body and the transmissibility of the suspension seat with tri-axial translational excitation. An experimental study was carried out with single-axial excitations at various magnitudes up to 1.0 ms-2 (r.m.s.) to examine the effect of the backrest inclination angles on the biodynamic response in fore-aft, lateral and vertical directions when the human body was sitting in the rigid seat. It was found that, at different excitation magnitudes, the apparent masses in the three translational directions were affected by the increased backrest inclination angle up to 20°. Such an inclination angle also affected the degree of the nonlinearity caused by changing excitation magnitude. The experimental study on the human body seated in the rigid seat also investigated under triaxial excitations the effect of the excitation magnitude in fore-aft, lateral and vertical directions (up to 1.0 ms-2 r.m.s. in each axis) and the backrest inclination angle on the biodynamic response. The increased excitation magnitude in one (named as “primary-axis”) of three translational axes and that in the other two (named as “secondary-axes”) axes both led to the decrease of the resonance frequency of the apparent mass in the “primary-axis” under the conditions tested. Interactive effects were found between the excitation magnitudes in different directions: the reduction of the resonance frequency of the apparent mass with the increased excitation magnitude in the “primary-axis” became smaller when the excitation magnitude in the “secondary-axes” was increased, and vice versa. Furthermore, the effect of backrest inclination angle under tri-axial vibration on the apparent mass was found to be comparable with that under single-axial vibration. Results showed that the backrest inclination and the excitation magnitude had combined effect on the degree of nonlinearity of the apparent mass. The effect of the excitation magnitude and the backrest inclination angle on the transmissibility of the suspension seat with the seated subject was further studied with tri-axial excitation. Under the conditions tested, the suspension seat with loaded inert mass exhibited nonlinear behaviour in all three translational directions subject to the change of the excitation magnitude in the “primary axis”. The interaction between the excitation magnitude in the “primary-axis” and that in the “secondary-axes” were observed in the transmissibilities of the suspension seat with seated occupant. The backrest inclination angle also affected the moduli of the seat transmissibilities at the backrest. Based on the experimental studies, a linear multi-body biodynamic model of the seated human body exposed to tri-axial vibration was developed. With a rigorous calibration procedure, the model was shown to be capable of representing the tri-axial biodynamic responses of human body supported by either upright or inclined backrest. Four vibration modes of the human body, which contributed to the resonances of the lateral, fore-aft and vertical apparent masses respectively, were identified through a modal analysis with the calibrated biodynamic model. Finally, linear multi-body models of the suspension mechanism with inert mass, the suspension seat with inert mass, and suspension seat with occupant under tri-axial excitation were developed. Results showed that the suspension-seat-occupant model was capable of predicting the fore-aft and vertical seat transmissibilities at the seat pan and backrest under tri-axial excitation when the subject was seated. The parameters of the seat model (e.g., the contact stiffness at the sea to occupant interface) to which the seat transmissibilities were most sensitive were identified, providing useful information for the seat design to improve ride comfort.
The biodynamic response of 14 subjects to sinusoidal dual-axis vibration in lateral and roll directions is studied. The root mean square of human response is detected by measuring the torque at the seat pan. The effects of phase difference, magnitude, and frequency on the biodynamic responses are investigated. The consistency between human responses to dual-axis and single-axis is studied. With increasing phase difference, human response is found to reach the maximum when the vibrations are anti-phase and then decrease to the minimum when they are in-phase. Besides, the dominance of the lateral excitation is confirmed in the dual-axis vibration. Finally, the principle of equivalence between lateral-roll dual-axis vibration and roll single-axis vibration is established. With the equivalence method, the biodynamic characteristics of the human body to multi-axis vibration are expected to be measured and represented with a much simpler test and dynamic model.
Practitioner summary: Proposed equivalence uses one index to evaluate the compound discomfort caused by the roll and lateral vibration. Overestimation of discomfort due by summing the effects of them calculated separately can be avoided. After the equivalence, evaluation of discomfort and modelling of the human body can be carried out only in roll direction.
