Seat Transmissibility Research Articles

An Investigation of the Effects of a Dynamic Vibration Absorber (DVA) to the Comfort of a Bus's Driver Seat

The frequency weighted acceleration, relative displacement, and Seat Effective Amplitude Transmissibility (SEAT) of a bus driver's seat are investigated by a 4 degrees of freedom (4DOF) vertical dynamic model, including a dynamic vibration absorber (DVA). The Root Mean Squared (RMS) values of the gain responses in the frequency domain are analyzed in the DVA damping ratio domain to help determine the optimal value of the DVA' s suspension. The obtained results show that the comfort evaluation index, in the case of a bus driver's seat with DVA, can be improved by more than 15% and nearly 10%, respectively, with the seat suspension natural frequency of 1~Hz and 4~Hz respectively. The comfort is better with the lower seat suspension natural frequency and vice versa. Especially in the case of both the seat and the DVA suspensions with low natural frequencies, all the three mean of evaluation indexes in the whole damping ratio domain of the DVA, have improved by more than 12%. This is the case with all three evaluation indexes which are the best when the damping ratio of the DVA is greater than 0.6.

THE EFFECT OF ANTHROPOMETRIC PARAMETERS ON THE SEAT TRANSMISSIBILITY DURING WHOLE-BODY VIBRATION: A HYBRID MODELING APPROACH BASED ON ARTIFICIAL NEURAL NETWORKS AND PRINCIPAL COMPONENT ANALYSIS

The modeling of the seat transmissibility is necessary to advance the understanding of the dynamic interactions between compliant seats and occupants. Within this investigation, an optimized artificial neural network (ANN) model was employed to clarify contributions associated with anthropometric parameters to the seat transmissibility. Anthropometric parameters underwent dimensionality reduction through the principal component analysis, and resultant principal components served as input features for the ANN model. Additionally, the ANN structure’s weights and biases values were adjusted using the genetic algorithm (GA), resulting in a PCA-GA-ANN model for the prediction of seat transmissibilities. The results indicated root mean square error (RMSE) values for predicting vertical in-line and horizontal cross-axis transmissibilities from the developed model were 0.061 and 0.055, respectively, demonstrating superior effectiveness in the prediction error and trends when compared with both the ANN and GA-ANN models. The seat transmissibility predicted from the PCA-GA-ANN model exhibited resonance behaviors similar to that observed in the whole-body vibration test. The sensitivity analysis showed that the subject’s age was the most predominant anthropometric parameter for the prediction, followed by gender and body mass index. The ANN model optimized with principal component analysis (PCA) and GA effectively eliminates the redundant information of anthropometric parameters, enhancing the generalization of the seat transmissibility prediction.

The seat transmissibility of an occupant-seat system: the influence of horizontal excitations with the additional vertical motion

The seat transmissibility of an occupant-seat system: the influence of horizontal excitations with the additional vertical motion

Dynamic characteristics of a compliant seat coupled with the human body and a manikin during the exposure to the whole-body vibration: Effect of the polyurethane foam, the track position, and the measurement location

Purpose Transmissibility is used to assess dynamic responses of the occupant-seat system, and most studies have exclusively assessed the transmissibility from the floor to the cushion or the backrest surface with the human body. Methods In this investigation, the vertical vibration transmitted from the floor to six specific locations both on the seat surface and the frame when the seat was fixed on three positions on the track was examined utilizing an SAE J826 manikin and 12 male adults (0.25 to 20 Hz) for a duration of 120 seconds at three vibration amplitudes. Results The transmissibility from the floor to the headrest frame, the cushion surface, the headrest surface, the seat back frame, and the seat back surface all exhibited a principal peak frequency within 4-5 Hz. With the exception of the cushion frame, the principal peak frequency and the peak transmissibility in transmissibilities to all positions decreased with increasing vibration amplitude, indicating the non-linearity within the occupant-seat system. It was also found modifying seat track positions minimally affected the seat transmissibility to either the surface or the frame of the seat. Conclusions Polyurethane foam amplified vibration at peak frequency, simultaneously enhancing static sitting comfort and reducing the vertical vibration transmission above peak frequency.

The Non-Linearity and Cross-Axis Effect of the Seat Transmissibility in Vertical and Dual-Axis Vibration Environments

The Non-Linearity and Cross-Axis Effect of the Seat Transmissibility in Vertical and Dual-Axis Vibration Environments

Nonlinear Dynamic Modelling of a Suspension Seat for Predicting the Vertical Seat Transmissibility

Suspension seats are widely used in heavy vehicles to reduce vibration transmitted to human body and promote ride comfort. Previous studies have shown that the dynamics of the suspension seat exhibits nonlinear behaviour with changed vibration magnitudes. Despite various linear seat models developed in the past, a nonlinear model of the suspension seat capturing the nonlinear dynamic behaviour of the seat suspension and cushion has not been developed for the prediction of the seat transmissibility. This paper proposes a nonlinear lumped parameter model of the suspension seat to predict the nonlinear dynamic response of the seat. The suspension seat model comprises of a nonlinear suspension submodel integrated with a nonlinear cushion submodel. The parameters of the submodels are determined by minimizing the error between the simulated and the measured transmissibility of the suspension mechanism and the force-deflection curve of the seat cushion, respectively. The model of the complete seat is then validated using the seat transmissibility measured with inert mass under vertical vibration excitation. The results show that the proposed suspension seat model can be used to predict the seat transmissibility with various excitation magnitudes.

Dynamic interaction between the human body and the seat during vertical vibration: effect of inclination of the seat pan and the backrest on seat transmissibilities

Seat inclinations at the seat pan and backrest may affect the sitting comfort. This study was designed to quantify the effect of inclination of a seat pan (0°, 10°, and 20°) and backrest (0°, 15°, and 30°), either foamed or rigid, on the transmissibilities measured at the seat pan and backrest. Seat transmissibilities were measured with fifteen subjects exposed to vertical random vibration between 1 and 15 Hz at 0.5 ms−2 r.m.s. It was found the resonance frequencies in transmissibilities measured at the seat pan and backrest increased with increasing the backrest inclination but were not affected by the seat pan angle. Increasing the foamed backrest inclination increased the peak transmissibilities. Inclination of the rigid seat pan or the rigid backrest reduced the transmissibilities measured at the backrest or the seat pan, respectively. Transmissibilities were more significantly affected by the backrest inclination than the seat pan inclination. Practitioner summary: Seat inclinations may alter the human-seat dynamic interaction and hence the riding discomfort. This study was designed to quantify the effect of inclined seats, either foamed or rigid, on the transmissibilities. It was found the backrest angle affected the transmissibilities more strongly than the seat pan angle.

Effect of the thickness of polyurethane foams at the seat pan and the backrest on fore-and-aft in-line and vertical cross-axis seat transmissibility when sitting with various contact conditions of backrest during fore-and-aft vibration

Ride comfort in vehicles can be affected by seat properties. While previous studies focused on the vertical whole-body vibration, this study was designed to understand the influence of the foam thickness at the seat pan and at the backrest on seat transmissibilities with fore-and-aft vibration. Twelve subjects sitting with or without a vertical backrest were exposed to random fore-and-aft vibration between 1 and 15 Hz with the magnitude of 0.5 ms−2 r.m.s.. It was found that there was no significant difference in the primary resonance frequencies in the fore-and-aft in-line and vertical cross-axis transmissibilities to the seat pan and to the backrest. The resonance frequency in the fore-and-aft in-line transmissibilities to the seat pan and the backrest decreased with increasing thickness of foam at the seat pan and the backrest. Altering the thickness of foam at the seat pan was more effective than changing that at the backrest.

Modeling and analysis of a train seat with occupant exposed to combined lateral, vertical and roll vibration

Considering the ride vibration of rail vehicles, a double-unit train seat model under exposure to combined lateral, vertical and roll vibrations was developed using multi-body dynamic modelling technique. Two coupled seat-occupant models, i.e. the double-unit seat with one occupant and two occupants, respectively, were then developed by integrating the seat model with a seated human model developed in a previous study. The corresponding seat transmissibilities measured in the laboratory experiment were used to calibrate the seat and seat-occupant models. The seat transmissibilities calculated with the models showed good agreement with the measured transmissibilities. Modal analyses with the models of the seat, human body, and seat-occupant systems, respectively, were carried out to find out the association between the resonances in the seat transmissibilities of the seat-occupant systems and the modal properties of the human body or the seat, and reveal the variation of the modal properties arising from the coupling between the seat and human body. The principal resonance around 5 Hz in the vertical transmissibility at the seat pan was found to arise from a vertical mode of the entire human body. A slight reduction of the modal frequency and modal damping of this mode was caused by the coupling between the seat and human body. It was further disclosed that the two resonances around 15 and 27 Hz in the seat transmissibilities resulted from two seat modes with close frequencies, respectively. The mode shape of the former (about 15 Hz) featured the in-phase motions of the two seat pans and backrests in lateral and roll directions, while that of the latter (about 27 Hz) was associated with the motions of the two backrests in lateral and roll directions. The results also showed that human bodies tended to increase the modal damping of the two seat modes.

The effect of posture and vibration magnitude on the vertical vibration transmissibility of tractor suspension system

The efficiency of suspension seat can be influenced by several factors such as the input vibration, the dynamic characteristics of the seat and the dynamic characteristics of the human body. The objective of this paper is to study the effect of sitting postures and vibration magnitude on the vibration transmissibility of a suspension system of an agricultural tractor seat. Eleven (11) healthy male subjects participated in the study. All subjects were asked to sit on the suspension system. Four (4) different sitting postures were investigated – i) “relax”, ii) “slouch”, iii) “tense”, and iv) “with backrest support”. All subjects were exposed to random vertical vibration in the range of 1–20 Hz, at three vibration magnitudes - 0.5, 1.0 and 2.0 m/s2 r.m.s for 60 s. The results showed that there were three pronounced peaks in the seat transmissibility, with the primary resonance was found at 1.75–2.5 Hz for every sitting postures. The “backrest” condition had the highest transmissibility resonance (1.46), while the “slouch” posture had the highest Seat Effective Amplitude Transmissibility (SEAT) values (64.7%). Changes in vibration magnitude for “relax” posture from 0.5 to 2.0 m/s2 r.m.s resulted in greater reduction in the primary resonance frequency of seat transmissibility. The SEAT values decreased with increased vibration magnitude. It can be suggested that variations in posture and vibration magnitude affected the vibration transmission through the suspension system, indicating the non-linear effect on the interaction between the human body and the suspension system.Relevance to industry: Investigating the posture adopted during agricultural activities, and the effects of various magnitudes of vibration on the suspension system's performance are beneficial to the industry. The findings regarding their influence on the human body may be used to optimize the suspension system's performance.

Approaches to Predicting the Vertical Transmissibility of a Suspension Seat With a Seated Subject

Abstract In this paper, four methods were put forward to predict the transmissibility of an air suspension seat with a seated subject. For characterizing the dynamics of the suspension seat, two of the methods were based on developing a model of the air suspension seat and calibrating the parameters using the transmissibilities of the suspension and complete seat respectively with an inert mass from the experiment. The other two methods substituted the detailed modeling of the seat by two dynamic stiffness connecting in series calculated from two same transmissibilities measured in the experiment. For characterizing the biodynamics of the human body, two of the methods took advantage of the normalized apparent mass from published papers to take the place of the human model, while the other two methods made use of one measured seat transmissibility with a subject to deduce the apparent masses of all the subjects. Good agreement was illustrated between the experiment and model prediction for all the four methods. In addition, it also exhibited that a large discrepancy can be resulted in, especially in the high-frequency range, if the seat model was substituted by one integrated dynamic stiffness.

The study of seat vibration transmission of a high-speed train based on an improved MISO method

The field measurement was carried out on a high-speed train for the vibration transmission of the seat. The transmissibilities and coherences from the accelerations at the seat base to those on the seat pan and backrest were studied by an improved multi-input and single-output (MISO) system newly proposed by the authors. The improved method has the advantage of calculating the partial coherence independently of the sequences of the inputs and evaluating the contribution of the coherent parts between the inputs to the output compared with the existing method. It was found that although the high-speed train seat was exposed to complex vibrations from different sources, when the three inputs (vertical, lateral and roll accelerations) at the seat base were used as the inputs for MISO models, good multiple coherence functions could be obtained when studying the seat transmissibility to the vertical, lateral or roll vibration at the seat pan and backrest except in the frequency range where the anti-resonances of the inputs located. In such an exceptional case, the unsatisfactory multiple coherence could be explained by the anti-resonances of the input signals, which was further verified by the laboratory experiment. Then the on-site measurement was compared with the laboratory measurement in terms of the estimation of the coherence and transmissibility. Due to the advantages of the laboratory experiment, the contribution from the coherent parts is smaller, and the multiple coherence is higher than the field measurement. In the field measurement, that the inputs were coherent with the ‘noise’ was the main reason for the erroneous estimation of frequency response function (FRF), but the erroneous estimation of FRF resulting from the coherence between the inputs can to some degree be figured out by adopting MISO system. Finally, it was found the peaks in the seat transmissibilities caused by seat modes usually got reduced by the neighboring subject because of the damping brought from the subject.

Seat cushions made of warp knitted spacer fabrics influence seat transmissibility

The aim of this study was to compare the application of different warp knitted spacer fabrics on a car seat shell to a standard seat in terms of vertical seat transmissibility. Furthermore, the results obtained by human subject tests were compared to results of an anthropodynamic dummy test. Experiments were conducted on a vertically actuated platform under laboratory conditions with 16 human subjects and an anthropodynamic dummy. Seat Effective Amplitude Transmissibility of the seat pan and the seat backrest were calculated to evaluate ride quality. Seat transmissibility ranged between 73.6% for backrest and 177.7% for pan. Based on the results of statistical tests, the hypothesis that the transmissibility of a seat would be influenced by seat cushion conditions was accepted (p < 0.05). It was also shown that an anthropodynamic dummy test could replace tests with human subjects (r2 = 0.907) if the target population was matched sufficiently.

The Effects of Posture on Suspension Seat Transmissibility during Exposure to Vertical Whole-Body Vibration

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/s2 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.

Mathematical Model of Suspension Seat-Person Exposed to Vertical Vibration for Off-Road Vehicles

Off-road drivers are exposed to a high magnitude of vibration at low frequency (0.5-25Hz), that can cause harm and possibly attribute to musculoskeletal disorder, particularly low-back pain. The suspension seat is commonly used on an off-road condition to isolate the vibration transmitted to the human body. Nevertheless, the suspension seat modelling that incorporates the human body is still scarce. The objective of this study is to develop a mathematical modelling to represent the suspension seat-person for off-road vehicles. This paper presents a three degrees-of-freedom lumped parameter model. A curve-fitting method is used for parameter identification, which includes the constraint variable function (fmincon()) from the optimisation toolbox of MATLAB(R2017a). The model parameters are optimised using experimentally measured of suspension seat transmissibility. It was found that the model provides a reasonable fit to the measured suspension seat transmissibility at the first peak of resonance frequency, around 2-3 Hz. The results of the study suggested that the human body forms a coupled system with the suspension seat and thus affects the overall performance of the suspension system. As a conclusion, the influence of the human body should not be ignored in the modelling, and a three-degrees degree-of-freedom lumped parameter model provides a better prediction of suspension seat transmissibility. This proposed model is recommended to predict vibration transmissibility for off-road suspension seat.

Modelling of a train seat with subject exposed to lateral, vertical and roll vibration

Considering the characteristics of ride vibration of a train, a multi-body dynamic model of a double-unit passenger seat exposed to lateral, vertical and roll vibrations was developed and calibrated using measured seat transmissibilities from the acceleration at the floor to the accelerations at both the seat pan and backrest in lateral, vertical and roll directions. With use of an existing seated human model, two coupled models of the double-unit seat with one and two subjects were then developed and calibrated using the corresponding measured seat transmissibilities. The models showed good agreement with the experimental data. Using these models, modal analysis was conducted to find out the modal properties of the human-seat system and facilitate discussions in relation to the resonances in the seat transmissibilities. It was found the primary peak in the vertical transmissibility of the seat pan may arise from the mode of human body. Two vibration modes around 15 and 30 Hz of the seat contributed to the peaks with approximate frequencies in the seat transmissibilities.

Effects of stretch reflex on back muscle response during sinusoidal whole body vibration in sitting posture: A model study

This study seeks to examine human vibration response using a musculoskeletal model that appropriately considers stretch reflex. The stretch reflex is modeled with a feedback control approach, and integrated into a generic musculoskeletal model to study the active muscle forces during seated whole body vibration. The model is used to investigate the effects of stretch reflex gain, vibration frequency and vibration magnitude on transmissibility from the seat to upper body and lower body and on muscle activations.The overall model is validated by comparison with thoracic and lumbar muscle activities measured in human participants during whole body vibration. The simulation results were consistent with the experimental results that the peak transmissibility occurred at resonance frequency of 5–6 Hz, and were in line with other experimental studies that found a primary resonance of 4–6 Hz. Furthermore, the peak normalized Electromyography (EMG) level accorded with the activation level for both thoracic and lumbar regions. What's more, an increase of primary resonance frequency was observed with increasing gains of stretch reflex. In contrary, the peak seat transmissibility of the upper body and lower body had a significant reduction.The major contribution of this model is that the proposed stretch reflex model provides a useful method to consider muscle active response in whole body vibration simulation. This may be used in future studies to better understand how stretch reflex affects spinal loading in a variety of conditions.

Whole-body vibration: Measurement of horizontal and vertical transmissibility of an agricultural tractor seat

The seats may significantly reduce the exposures levels transmitted to the driver, but the European Directive 2002/44/EC (2002) requires only tests on the damping seat capacity along the vertical direction, whereas nothing is required for the longitudinal and transversal directions.Field tests were carried out using a 93 kW tractor to verify the vibrational comfort values given by seat with pneumatic suspension. The tests were executed with the tractor running on different surfaces, at two different forward speed and tire pressures and with different tractor masses. Three repetition were carried out for each configuration. Accelerations were always measured on both the seat and the cabin platform and the calculations were done using the ISO 2631 standard suggestions. The vibration total values and the acceleration transmissibility along the 3 perpendicular axes were calculated and analysed.Despite different boundary conditions (surface, tire pressure, forward speed and tractor mass distribution), along the Z axis the transmissibility was constantly around 0.7, to confirm that the seat worked well to damp the vertical exposures. Different were the situations for the X and the Y axes. Excluding the asphalt, on the other crossed surfaces high transmissibility values were observed (never less than 1), especially along the X axis. Relevance to industry. This paper describes the vibration transmissibility of an agricultural tractor seat. Tests were carried out with the tractor running on different surfaces and with different configurations. The seat transmissibility along the three orthogonal directions was acquired.Results suggest that the tractor manufacturer should consider, during the machine design, also the rolling and pitching movements, because the seat accelerations along the X and Y axes are influenced by them. The seat manufacturer could reduce the rolling and pitching effects using specific suspension systems along the horizontal and lateral directions.

Vertical Suspension Seat Transmissibility and SEAT Values for Seated Person Exposed to Whole-body Vibration in Agricultural Tractor Preliminary Study

Agricultural tractor drivers have been exposed to high magnitude of whole-body vibration (WBV) exposure during their daily farm work activities due to many factors (e.g. uneven road surface, posture and apparent mass of the body). High vibration magnitude exposure may also lead to detrimental health of the driver such as low-back pain. The objectives of this study are to determine the vertical suspension seat transmissibility and Seat Effective Amplitude Transmissibility (SEAT) values for a seated person exposed to WBV in agricultural tractors. A healthy male subject participated in the field measurements. Two road surface conditions were tested - (i) tarmac and (ii) field (i.e. rough off-road). In the off-road condition, data were collected during mowing. The subject was seated in an upright posture with a backrest. The vertical vibrations (z-axis) on the seat base, beneath ischial tuberosities and at the thigh (i.e. top surface of the horizontal thigh during seated position) were measured. Three vertical vibration transmissibilities were calculated- i) suspension seat transmissibility (i.e. floor to beneath ischial tuberosities), ii) upper leg transmissibility (i.e. floor to thigh) and iii) seat to thigh transmissibility. In addition, the SEAT values were also calculated. The results show resonance frequency of the seat at around 2-3 Hz and the resonance at the thigh is higher than on the seat. The calculated SEAT values were 112.6% (with weighting Wk) and 103.6% (with weighting Wb). It is suggested that, the WBV is higher in the vertical direction when working on the off-road condition, and thus results in higher vibration energy absorbed by the operator's body.

Measuring, evaluating and assessing the transmission of vibration through the seats of railway vehicles

The transmission of vibration through a passenger train seat to the seat pan and to the backrest has been measured in the fore-and-aft, lateral and vertical directions with 12 subjects using 0.5–40 Hz random vibration (with both single-axis and tri-axial excitation) and using simulated tri-axial train vibration. There were small differences in transmissibilities obtained using single-axis and tri-axial random vibration but greater differences in transmissibilities between tri-axial random vibration and simulated train vibration. Seat effective amplitude transmissibilities (SEAT values) were similar for single-axis and tri-axial random vibration but differed between tri-axial random vibration and simulated train vibration. The SEAT values measured using both tri-axial random vibration and simulated train vibration were well predicted from the seat transmissibilities measured using single-axis random vibration. It is concluded that either single-axis or tri-axial vibration excitation can be used when quantifying the transmissibility of a seat and identifying seat resonances. A SEAT value depends on the vibration spectrum in the vehicle and so the SEAT value for a train seat cannot be obtained using vibration unlike that in a train. A useful SEAT value for a train seat can either be measured (by simulating tri-axial train vibration in a laboratory) or calculated (from measurements of vibration in a train and measurements of seat transmissibility obtained using random vibration in a laboratory). The findings of this study may assist the optimisation of seat testing standards including the laboratory method for evaluating the transmission of vibration through the seats of railway vehicles defined in a current international standard.