Seat Effective Amplitude Transmissibility Values Research Articles

COMFORT ANALYSIS COMPARISON BETWEEN ALFAPENDULAR AND INTERCITY PORTUGUESE TRAINS AT THE NORTH RAIL

Nowadays, trains are one of the most used public transportation modes. Comfort is the key to keeping and attracting new users. Vibration highly influences comfort levels and, once it is derived from the train motion it is stated as a primary concern. Due to contact with the seat and floor, passengers are subjected to whole-body vibration. ISO 2631 standard is fully dedicated to the evaluation of this type of vibration. Following its approach, the present research evaluates the comfort levels of Alfapendular and Intercity trains operating in Portugal at the Porto Campanhã – Lisbon Oriente connection. Measurements were performed at the beginning, middle, and end of the train, allowing a comparison between seat types within the same train and the same types from different trains. Results showed higher comfort levels for the Alfapendular trains, while for the Intercity train, both middle and end of train locations were ranked as “Little uncomfortable”. As a complementary analysis, it was observed the vibration transmission of the seat based on the Seat Effective Amplitude Transmissibility (SEAT). Results were above 100%, showing vibration amplification by all tested seats. Higher SEAT values were found for the Intercity train seat. This was the first study conducted on Portuguese trains regarding comfort analysis and vibration transmission. Keywords: Railways, Whole-body vibration, Vibration transmission, SEAT.

Transmission of vertical vibration through a seat cushion at the seat pan: Effect of foam physical properties during different excitation magnitudes

The vibration characteristics of car seats directly influence the ride comfort. Polyurethane foam is the key part of a seat, and its physical parameters have an important impact on the seat. In this study, the influence of the foam thickness and foam hardness on the vibration characteristics of seat cushion with different excitation magnitudes was investigated by using transmissibility and seat effective amplitude transmissibility (SEAT) value. First, vibration tests were carried out at a vertical vibration simulator with width-limited white noise vibration frequencies from 0.5 to 20 Hz with root-mean-square (r.m.s.) values of 0.4, 0.8, and 1.2 m/s2, the acceleration at the platform and the body-foam interfaces were measured to calculate the transmissibility, and the influence of the foam physical properties on the transmissibility was analyzed. Then, the SEAT value was introduced to assess the vibration isolation efficiency of the foam cushion, and the influence of the foam physical properties of the foam cushion on the vibration isolation efficiency was analyzed. With increasing thickness of the foam and decreasing hardness of the foam at the seat pan, the peak transmissibility increased and the resonance frequency decreased. The SEAT values show that increasing the foam thickness is beneficial to the improvement of the vibration isolation efficiency of the seat, but there is a diminishing return; the combination of physical parameters of low hardness and high thickness could make the vibration isolation performance of the seat better. In addition, the nonlinearity of human-seat system during different vibration magnitude was found.

Transforming farming with intelligence: Smart vibration monitoring and alert system

During the evolution towards digital agriculture, the pivotal role of tractor riding necessitates a focus on improving operator performance and well-being. While most research has centered around vibration analysis, tangible solutions to control elevated vibration levels remain rare. The study aims to introduce an intelligent ThingSpeak-Enabled IoT (Internet of Things) solution that provides real-time monitoring and generates prompt warning alerts for tractor operators when vibrations exceed safe thresholds. The initial phase involved the real-time measurement of WBV (whole-body vibration) and SEAT (seat effective amplitude transmissibility). Following this, the secondary phase encompassed the analysis and validation of the system in cases where WBV and SEAT exceeded the recommended limits. The experimental design comprised 135 trials by systematically varying tractor ride parameters, including average speed (m/s), average depth (m), and pulling force (kN) levels. Daily vibration exposure response ranged from 0.43 m/s² to 0.87 m/s² with a mean exposure of 0.64 m/s2, surpassing the EAV (exposure action value) threshold of 0.5 m/s². The SEAT values ranged between 91.37 and 133.08 with a mean of 108.35, that indicates insufficient seat isolation capacity, i.e., < 100. Statistically, the study ascertained a significant influence of average speed and average depth WBV and SEAT responses at a 5% significance level. It underscores the potential efficacy of altering speed and depth parameters to attenuate vibration exposure levels. Further, the effectiveness of the system was tested through the automatic transmission of warning alerts via emails, text messages, and flashing red LED light on the IoT system. This critical feature provides considerable utility for tractor operators to adjust ride settings, ensuring that the ride remains within safe vibration limits. Furthermore, adopting such an advanced warning system in tractor manufacturing signifies a pioneering step towards sustainably enhancing operator well-being.

Prediction of the driver’s head acceleration and vibration isolation performance of the seating suspension system using the time and frequency domain modeling

Long-time exposure to low-frequency vibration will negatively impact human health.A rapid biodynamic system modeling method has been proposed to study the human body’s response to the low-frequency vibration excitation in the whole vehicle environment. The sensitivity of design parameters of the seating suspension system to the vibration isolation performance will be studied. The dynamic model consists of a lumped parameter mass-spring-dashpot model of seven degrees of freedom (7DOF) and used for the prediction of the head acceleration in the time domain and peak transmissibility ratio in the frequency domain under a sinusoidal wave excitation and random road profile excitations of different road classes and vehicle speeds. A calculation formula has been established to predict the seat effective amplitude transmissibility (SEAT) from the transmissibility ratios and frequency weighting function of the ISO 8606, while the transmissibility ratios can be calculated from the frequency response analysis of the seven degrees of freedom system dynamic equations. The simulation results in the frequency domain have been verified by those in the time domain for the linear system assumption. The change trends of the driver’s head acceleration, SEAT value, and peak transmissibility ratio from the driver’s head to the seat base with respect to the stiffness and damping coefficients of the seat and cushion have been compared with and verified by one another.It is proved that in the vehicle system, individually, reducing the individual stiffness and damping coefficients of the seat structure, reducing the individual seat cushion stiffness, and increasing the individual seat cushion damping coefficient one by one will be able to reduce the driver’s head acceleration, peak transmissibility ratio, and SEAT value from the head to seat base, and improve the ride comfort. Simultaneously reducing the stiffness and damping coefficients of the seat and cushion will be able to reduce the driver’s head acceleration, peak transmissibility ratio, and SEAT value from the head to seat base and improve the ride comfort. The reduction effect of the driver’s head acceleration is more substantial under the Class E road profile of a large profile roughness than that under the other road classes.

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.

A comparative study of transmissibility factors of traditional and pneumatic dumper seats using one-third octave band analysis

Severity of exposure to whole-body vibration of vehicle drivers depends on multiple factors including type of vehicle suspension or quality of seats. The study presents analysis of seat vibrations of two different types of dumpers in opencast mines. Since health guidance provided in ISO 2631-1997 are only indicative, seat effective amplitude transmissibility factors along with one-third octave-band analysis of vibration signals have been considered as more effective information for control measures. Vibration characteristics of conventional seats ( n = 3) with rigid frame and those with pneumatic suspensions ( n = 3) have been compared during their use in mines. A(8) values ranged from 0.66 to 1.41 m/s2. All the six operators had shown moderate to higher health risk but this may vary since both intensity and durations of exposure frequently change during the operators’ employment. Vibration signals from a mono-axial accelerometer (z′) placed on the cabin floor was captured in addition to three channel vibration data (x, y and z) of a seat pad accelerometer placed on the vehicle seat. Transmissibility analysis of vibration signals from cabin floor to seat surface showed that the three pneumatic seats resonated in the range of 1.6–2.5 Hz in the z axis. There was significant attenuation of vibration energy ranging from 37% to 63% at 4 Hz which is important in the context of spinal injuries. The seat effective amplitude transmissibility values (%) in the resonating frequencies ranged from 119% to 173%. Interestingly, the conventional seats resonated at 4–5 Hz and the corresponding seat effective amplitude transmissibility (%) values were varying from 128% to 163%. This resonance at 4 Hz is in sharp contrast with the behaviour of pneumatic seats. It is recommended that vibration transmissibility should be considered as a major design parameter for mining vehicle seats.

Kineto-dynamic design optimisation for vehicle-specific seat-suspension systems

ABSTRACTDesigns and analyses of seat-suspension systems are invariably performed considering effective vertical spring rate and damping properties, while neglecting important contributions due to kinematics of the widely used cross-linkage mechanism. In this study, a kineto-dynamic model of a seat-suspension is formulated to obtain relations for effective vertical suspension stiffness and damping characteristics as functions of those of the air spring and the hydraulic damper, respectively. The proposed relations are verified through simulations of the multi-body dynamic model of the cross-linkage seat-suspension in the ADAMS platform. The validity of the kineto-dynamic model is also demonstrated through comparisons of its vibration transmission response with the experimental data. The model is used to identify optimal air spring coordinates to attain nearly constant natural frequency of the suspension, irrespective of the seated body mass and seated height. A methodology is further proposed to identify optimal damping requirements for vehicle-specific suspension designs to achieve minimal seat effective amplitude transmissibility (SEAT) and vibration dose value (VDV) considering vibration spectra of different classes of earthmoving vehicles. The shock and vibration isolation performance potentials of the optimal designs are evaluated under selected vehicle vibration superimposed with shock motions. Results show that the vehicle-specific optimal designs could provide substantial reductions in the SEAT and VDV values for the vehicle classes considered.

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.

Assessment of the whole body vibration exposure and the dynamic seat comfort in passenger aircraft

This paper describes the study performed to investigate and assess the whole body vibration (WBV) and the dynamic seat comfort of aircraft seats under three different flight conditions. The WBV exposures were assessed based on the international standard ISO-2631-1 (1997) and the British Standard BS-6841 (1987). The seat effective amplitude transmissibility (SEAT) value was then calculated and used as a measure of comfort. Three different methods were used to calculate the SEAT value; these methods include using average weighted vibration (Aw), vibration dose values (VDV) and using the transmissibility data. The experiments were performed using a multi-axis shaker table simulating takeoff, landing and cruise through turbulence vibration levels. The vibration levels were modeled closely to recordings obtained onboard an actual aircraft during flight. The effect of passenger weight and cushion material on the vibration transmissibility are also discussed. Relevance to IndustryOne of the customer's top priorities when looking to travel in an airplane is comfort. Assessing the WBV exposure and the dynamic seat comfort on passenger aircraft seats in laboratory will allow for better development of aircraft seats at much lower costs which, in turn, will provide the customer with high quality products.

Numerical and experimental characterisation of the dynamic behaviour of a passenger aircraft seat during a takeoff condition

This paper investigates the dynamic response of an aircraft seat structure. The study involved the use of a finite element software to predict aircraft seat vibrations during takeoff-like flight conditions. The described model is validated by performing experimental dynamic response measurements of an aircraft seat subjected to actual take off excitation recordings obtained onboard an aircraft. The accuracy of the model is investigated by comparing the simulated properties with experimental modal analysis and seat plate dynamics data. Moreover, the severity of the transmitted vibrations to the seat surface is assessed using the seat effective amplitude transmissibility (SEAT) method. Results show that the numerical model is able to replicate the dynamic and modal properties of the aircraft seat. The numerical and experimental SEAT values computed through different methods were also found to be in good agreement. This developed model can be used to predict and improve the dynamic comfort of aircraft seats.

Assessment of Passenger Ride Comfort during Vertical Vibration of Mid-size Saloon and Off-road Vehicles on Asphalt Roads

Ride comfort in road vehicles is related to vehicle vibration levels and the perception of passenger fatigue. In this study, vibration in vertical direction on the seat and floor are measured to characterise the ride comfort based on standard formulae and frequency analysis. A mid-size saloon vehicle and an off-road vehicle are driven on smooth, spalled and coarse asphalt road surfaces. To assess the vertical vibrations transmitted to the passengers, vibration dose values, Kurtosis, frequency response functions and power spectral densities of the compartment recorded signals were evaluated. Seat effective amplitude transmissibility value based on vibration RMS and vibration dose values were also evaluated. The results indicate that the vibration dose value increases in proportional to the vehicle speed and road roughness.

Investigation of the effect of safety belt on the seat transmissibility

Seat transmissibility is used to evaluate the vibration attenuation performance of seats. Because the seat and the driver interact with each other, the seat transmissibility is affected by the dynamic characteristics of the driver. The constraint on the movement of the driver caused by the safety belt results in the change of the seat–driver dynamics and the seat transmissibility. Vibration accelerations were measured on the seat cushion and at the seat base on a medium size wheel loader when the driver wore a lap belt or a four-point seat harness. The seat effective amplitude transmissibility value and the seat transmissibility derived from the cross spectral density method were analysed to investigate the effect of safety belt on the seat transmissibility. Two multi-body models of the seat–driver system were built in MATLAB and their parameters were identified in cases where the driver wore the lap belt or the four-point seat harness. Based on the analysis of these parameters, the way how the safety belt affects the seat–driver dynamics and the seat transmissibility is studied.

Selecting seats for steel industry mobile machines based on seat effective amplitude transmissibility and comfort

The purpose of this work was to help a steel industry partner select the most appropriate of three high end heavy equipment seats to retrofit a number of their heavy mobile machines used in the steel making process. The participants included 8 males (22.3 ± 2.0 yrs.) and 8 females (23.5 ± 1.8 yrs.) with no experience operating heavy mobile equipment. Previously recorded 6-DOF chassis acceleration data from a Pot Hauler (a machine which picks up and transports pots of slag) were used to extract six, 20 second representative profiles for implementation on a lab-based heavy machine simulator (6-DOF Parallel Robotics System Corporation robot). Subjects sat on three heavy equipment seats (BeGe7150, Grammar MSG 95G1721, and a 6801 Isringhausen with the seat pan cushion retrofitted with a Skydex cushion) mounted on the simulator. Each subject completed three trials for each combination of seat (n=3) and vibration profile (n=6). Chassis and operator/seat interface vibration were measured by 2, 6-DOF vibration transducers. Variables included Seat Effective Amplitude Transmissibility (SEAT) (X,Y,Z,Roll,Pitch,Yaw,6DOF Vector Sum) to determine if the seat was attenuating or amplifying the vibration, 6-degree of freedom (DOF) vibration total value weighted predicted comfort (Avc) (according to ISO 2631-1) and operator reported comfort (ORC). Factorial ANOVAs revealed significant differences (p < or = 0.05) between seats for all SEAT variables but different seats performed better than others depending on the axis. Significant differences between males and females were observed for SEAT in X,Y, and Pitch as well as for Avs. As expected there were significant differences between vibration profiles for all assessed variables. A number of interaction effects were observed, the most frequently occurring of which was between seat and vibration profile. Based upon the number of seat and vibration profile interactions, results suggest that a single seat is not suited for all tested conditions. However, SEAT values for all of the seats tested were extremely low (e.g., 6-DOF SEAT < 30%) indicating that all of the seats were capable of providing good vibration attenuation.

Assessments of two dynamic manikins for laboratory testing of seats under whole-body vibration

The aptness of two anthropodynamic manikins for assessing vibration isolation effectiveness of suspension seats is evaluated through laboratory measurements. The evaluations were performed using five different suspension seats exposed to idealized white noise (0.5–20 Hz) and target vehicle excitations along the vertical axis using a whole-body vehicular vibration simulator. The measurements were performed to derive acceleration transmissibility and seat effective amplitude transmissibility (SEAT) characteristics of seats loaded with: human subjects of body masses in the vicinity of 55, 75 and 98 kg; manikins configured to same masses; and equivalent rigid masses. The dynamic responses of the manikins were also measured under different magnitudes of white-noise excitations and expressed in terms of apparent mass. The relative applicability of the manikins for selected seats was evaluated by comparing the measures with those obtained for the seat–human and seat–mass systems. The comparisons suggested that the SEAT measures attained with manikins are comparable with those obtained with equivalent rigid mass, irrespective of the body mass, for the low natural frequency seats (⩽2 Hz) considered in the study. Both the manikins and the equivalent rigid masses, however, provided an overestimate of isolation effectiveness of seats, when compared to those with human subjects. The manikins resulted in better estimates of SEAT values for high natural frequency seats than the rigid mass. The dynamic responses of manikins were also compared with the ranges of standardized values reported in ISO-5982 and DIN-45676. The results revealed considerable differences between the biodynamic responses of manikins and the standardized ranges.

Transmission characteristics of suspension seats in multi-axis vibration environments

The multi-axis vibration transmission characteristics of selected suspension seats were investigated in the laboratory. Subjects were exposed to a flat acceleration spectrum and two low frequency signals extracted from multi-axis acceleration data recorded at the floor of a passenger locomotive. Triaxial accelerations were measured at the floor of the vibration table and at the interfaces between the subject and mounted seat (seat pan and seat back). The transmission ratios between the overall seat pan and seat back accelerations and floor accelerations provided an effective tool for evaluating the effects of measurement site, vibration direction, and posture among the selected seating systems. The results showed that the system transfer matrix, estimated using a multiple-input/single-output model, would be less than ideal for predicting low frequency operational seat vibration when using suspension seats. The Seat Effective Amplitude Transmissibility (SEAT), estimated for the tested locomotive seats, was used to predict the weighted seat pan accelerations and Vibration Total Values for assessing a 1-h operational exposure in accordance with ISO 2631-1: 1997. Relevance to industry Multi-axis SEAT values can be estimated for seating systems tested in the laboratory using representative operational exposures. These values can be applied to monitored vehicle floor accelerations to target potentially harmful vibration in accordance with ISO 2631-1: 1997, assuming the operational exposures have similar frequency and magnitude characteristics. The transmission at the seat back should be considered when substantial low frequency multi-axis vibration is present.

Verification of seat effective amplitude transmissibility (SEAT) value as a reliable metric to predict dynamic seat comfort

A rough road vibration stimulus was reconstructed on a shaker platform to verify if seat effective amplitude transmissibility (SEAT) values can be used as a reliable metric to determine dynamic seat comfort using seven seats and six subjects. The virtual seat method was combined with a paired comparison procedure to obtain reliable subjective dynamic seat comfort data. The psychometric method of constants, a 1-up-1-down Levitt procedure and a 2-up-1-down Levitt procedure were compared experimentally to find the most accurate and efficient paired comparison scheme. A two-track, interleaved, 2-up-1-down Levitt procedure was used for the subjective dynamic seat comfort assessment. SEAT value is an objective metric and has been widely used to determine seat vibration isolation efficiency. There was excellent correlation ( R 2 = 0.97 ) between the subjective ratings and estimated SEAT values on the seat-top when the values are averaged over the six subjects. This study suggests that SEAT values, estimated from averaged seat-top transmissibility functions of six carefully selected subjects, could be used as a reliable metric to select the best seat for a specific road vibration input.

The use of seat effective amplitude transmissibility (SEAT) values to predict dynamic seat comfort

The Seat Effective Amplitude Transmissibility (SEAT) value is the ratio of the vibration experienced on top of the seat and the vibration that one would be exposed to when sitting directly on the vibrating floor. SEAT values have been widely used to determine the vibration isolation efficiency of a seat. In this article the subjective evaluations of six persons were compared to the SEAT values estimated from experimentally obtained transmissibility curves for 16 different automobile seats ranging from sedans to SUVs and pickups. A vertical rough road stimulus was used as input for both the subjective testing and the SEAT calculations. The SEAT values were estimated using the power spectral density of the vertical vibration input at the seat track and the measured transmissibility data to compute the response in the vertical direction at the seat top. The averaged, estimated SEAT values were compared to averaged measured values and significant correlation ( R 2=0.94) was obtained. The subjective ratings were obtained on the Ford Vehicle Vibration Simulator using a paired comparison methodology that eliminated static comfort bias during the evaluation. The results indicated that there is good correlation ( R 2=0.94) between the subjective ratings and the SEAT values when the subjective ratings and transmissibilities are averaged over the six subjects.