Seat Forces Research Articles

Research on inversion of wheel-rail force based on neural network framework

Wheel-rail force is a critical parameter for vehicle-track-bridge (VTB) structure system, playing a pivotal role in ensuring the safe operation of trains and service performance of track and bridge structures. This paper proposes a methodological framework for efficient and accurate prediction of wheel-rail force, that bidirectional gated recurrent unit (Bi-GRU) neural network is developed and the hyperparameters of networks are optimized through grey wolf optimization (GWO). Based on the developed VTB system model, numerical experiments are carried out to produce datasets which are verified through field test. In order to make the data more universal and comprehensive, Latin hypercube sampling (LHS) is introduced to randomize the parameters of VTB model. The datasets generated from VTB system, with rail seat force as input and wheel-rail force as output, serve as the training data for framework. Additionally, the inversion effects under various working conditions are examined and discussed. The results indicate that the model can precisely inverse continuous wheel-rail forces from the moment the wheels enter the first test rail seat until leave the last test point of rail seat. When the neural network learns from the features of at least three or more rail seats on each track slab (with intervals not exceeding 2 rail seats), it can accurately inverse the time history curve of wheel-rail forces. The framework presents a viable alternative for the wheel-rail force analysis, and promising potential for the realization of online monitoring of wheel-rail force.

THOR-05F Response in Sled Tests Inducing Submarining and Comparison with PMHS Response Corridors.

The Test Device for Human Occupant Restraint (THOR) is an advanced crash test dummy designed for frontal impact. Originally released in a 50th percentile male version (THOR-50M), a female 5th version (THOR-05F) was prototyped in 2017 (Wang et al., 2017) and compared with biofidelity sub-system tests (Wang et al., 2018). The same year, Trosseille et al. (2018) published response corridors using nine 5th percentile female Post Mortem Human Subjects (PMHS) tested in three sled configurations, including both submarining and non-submarining cases. The goal of this paper is to provide an initial evaluation of the THOR-05F biofidelity in a full-scale sled test, by comparing its response with the PMHS corridors published by Trosseille et al. (2018). Significant similarities between PMHS and THOR-05F were observed: as in Trosseille et al. (2018), the THOR-05F did not submarine in configuration 1, and submarined in configurations 2 and 3. The lap belt tension and seat forces were similar in magnitude. For configurations 2 and 3, the pelvis excursions were of the same order of magnitude between both human surrogates. However, significant differences were also observed: compared to the PMHS, the THOR-05F showed shoulder belt forces that were 1.6 to 2.1 times higher in magnitude, and lap belt force time histories that were delayed by 10 to 20 ms. In configuration 1, the chest and pelvis resultant accelerations of the dummy were delayed as well, and the pelvis excursion and rotation more than doubled that of the PMHS.

A bi-block sleeper dynamic strain monitoring method based on embedded FRP-OF sensor

The traditional surface contact monitoring, in which sensors and wires are exposed outside, has a great risk on long-term monitoring at high-speed railway (HSR). This paper proposed a method that embedding the Fiber Reinforced Polymer-Optical Fiber (FRP-OF) sensor into the bi-block sleeper, which was designed for long-term monitoring of sleeper dynamic strain at high-speed railway. Sleeper is the key component of bi-block ballastless track that bears and transmits the load from wheel. Its internal dynamic strain somehow reflects the wheel/rail force under the high-speed train load. Considering the symmetry of bi-block sleeper, a single block of sleeper was selected for this research. To validate the feasibility of monitoring sleeper strain by embedding FRP-OF sensor in sleeper, both laboratory static test and field dynamic test have been conducted. The results showed that there was a linear relationship between the sensor response and the applied load in the laboratory static test. The wheel load ratio assigned to each sleeper and the mechanical behavior is verified theoretically and experimentally. The single wheel load is mainly borne by five sleepers below the rail, which bearing 8%, 22%, 32%, 22%, 8%. Then, the load of different train can be sensed by the sensors in the field dynamic test, which clearly identified the process of wheel action and showed good repeatability. The dynamic strain in sleeper was about 3-7με with 150kN axle load at 350 km/h, which was converted to rail seat force of 33-35kN, and 7-18με with 230kN axle load at 160 km/h which was converted to rail seat force of 89-96kN. The impact factors on the track are different since the difference of the vechicles load. In general, the vertical transient strain level of sleeper is low, but the trend of strain variation is obvious and accords with the characteristics of wheel load distribution ratio. It can be seen that the sensors had good performance on dynamic strain monitoring of bi-block sleeper, which will be used as the important supplementary means of the future wheel/rail force monitoring.

Experimental Study on Dynamic Interaction between Large U-Shape Aqueduct and Water

Hydrodynamic interaction between water and structure plays an important role in the evaluation of seismic response of aqueducts in area of high seismicity. This interaction differs in axial, lateral and vertical direction of aqueduct. Both impulsive and convective effects of water exist in lateral direction. In presented study, shaking table tests were conducted with a 1/10 model of U-shape aqueduct, of 30 m long, to study the hydrodynamic interaction. With the analyses of aqueduct and water responses to stationary White Noise excitations as well as non-stationary excitations, impulsive and convective effects of water were deduced quantitatively. Characteristic frequencies and corresponding modes of aqueduct were identified with the transfer functions of acceleration, sloshing frequencies in lateral direction were recognized with the transfer functions of seat force. Impulsive mass was deduced from the alteration in fundamental frequency and the corresponding modal seat forces of the aqueduct with and without water. Convective mass was obtained from the wave height of sloshing and lateral seat forces recorded, or the lateral modal seat force and damping ratio. Comparison was made with those given in simplified methods for rigid structure. Observed hydrodynamic pressure on the structure in the test was smaller than that based on the rigid assumption.

Geometrical and Mechanical Characterization of the Abdominal Fold of Obese Post Mortem Human Subjects for Use in Human Body Modelling.

Obese vehicle occupants sustain specific injury patterns in case of accidents in which the interaction between the seat belt and the abdomen may play a role. This study aimed to collect geometrical characteristics and to investigate the mechanical responses of the abdomen of obese subjects. Four Post Mortem Human Subjects (PMHS) with BMI ranging from 31 to 46 kg/m2 were collected. CT-scans performed in the seated position revealed that the antero-posterior depth of the abdominal fold (from the inguinal region to the most anterior point of the abdominal surface) was much greater (170 mm max., 127 mm average) than the thickness of subcutaneous adipose tissues (85 max., 38 mm in average). Each PMHS was subjected to three infra-injurious antero-posterior belt pulls in a seated posture with a lap belt positioned (C1) superior to the umbilicus, (C2) inferior to the umbilicus, (C3) inside the abdominal fold between the abdomen and the thigh. During the C1 and C2 tests, the belt moved cranially, and the abdominal fold opened widely especially in C2. Forces remained below 1800 N, for maximum applied displacements ranging from 89 to 151 mm for C1 and C2, and 37 to 66 mm for C3. Finally, sled tests were conducted on two PMHS seated on a semi-rigid seat and restrained by a three-point belt equipped with pretensioners and a 3.5 kN force limitation at the shoulder. The first PMHS (BMI 39 kg/m2) was tested at 49 km/h (39 g peak) and sustained severe injuries (AIS 4 pelvis dislocation, AIS 3 bilateral femur fractures) attributed to the combined loading of the seat and lap belt force (about 11 kN and 7 kN, respectively). The second PMHS (BMI 46 kg/m2) was subjected to a 29 km/h test (8 g plateau) and sustained no injury. The lap belt slid inside the abdominal fold in the first case and deformed the lower abdomen in the second, providing limited restraint forces during that interaction and leading to a large body excursion for the first test. The results highlight the possible relevance of the abdominal fold at the abdomen thigh junction to model and study the restraint conditions of obese occupants using Human Body Models (HBM).

Track Modulus Assessment of Engineered Interspersed Concrete Sleepers in Ballasted Track

Ballasted railway track is typically constructed using sleepers that are manufactured from a common material type within a given length of track. Timber and concrete are the two most common sleeper materials used internationally. Evidence from historical installations of interspersed concrete sleepers in timber sleeper track in North America has indicated inadequate performance, due largely to the heterogeneity in stiffnesses among sleepers. Theoretical calculations reveal that interspersed installation, assuming rigid concrete sleepers and supports, can result in rail seat forces more than five times as large as the force supported by the adjacent timber sleepers. Recently, engineered interspersed concrete (EIC) sleepers were developed using an optimized design and additional layers of resiliency to replace timber sleepers that have reached the end of their service lives while maintaining sleeper-to-sleeper stiffness homogeneity. To confirm that the concrete sleepers can successfully replicate the stiffness properties of the timber sleepers installed in track, field instrumentation was installed under revenue-service train operations on a North American commuter rail transit agency to measure the wheel–rail vertical loads and track displacement. The results indicated that there are minimal differences in median track displacements between timber (2.26 mm, 0.089 in.) and EIC sleepers (2.21 mm, 0.087 in). Using wheel-load data and the corresponding track displacements associated with each wheel load, track modulus values were calculated using the single-point load method based on beam on elastic foundation (BOEF) fundamentals. The calculated values for the track modulus indicated similar performances between the two sleeper types, with median values of 12.95 N/mm/mm (1878 lbs./in./in.) and 12.79 N/mm/mm (1855 lbs./in./in.) for timber sleepers and EIC sleepers, respectively. The field results confirmed the suitability of the new EIC sleeper design in maintaining a consistent track modulus for the location studied, thus evenly sharing loads between and among sleepers manufactured from both concrete and timber.

Influence of Non-Homogeneous Foundations on the Dynamic Responses of Railway Sleepers

In a railway track, the sleeper’s responses on a non-homogeneous foundation have been investigated by researchers focusing on the foundation behavior along the rails. However, the foundation can also vary along the sleeper length, particularly when the track is newly tamped. The foundation at the sleeper center is often weaker than those under the rails and this non-homogeneity directly affects the sleeper responses. This paper presents a new model to calculate the influence of such foundations on the dynamic responses of the railway sleepers. This model is developed by combining a finite element model for the sleepers and foundation and a model of periodically supported beams subjected to moving loads for the rails. In this paper, the foundation contains three parts with different mechanical behaviors. The sleeper’s responses can be calculated by transforming the finite-element dynamic stiffness matrix to the one considering the boundary conditions and the relation between the rail seat forces and rail displacements governed by the beam model. This method reduces all the degrees of freedom of the railway track to its one period which gives a substantial reduction in computational time. The numerical applications show that the more homogeneous (so-called consolidated) the foundation is, the larger the sleeper strain is at its center. This result shows the potential application of the sleeper responses to estimating the consolidation level of the foundation.

Use of fiber optic sensing to measure distributed rail strains and determine rail seat forces under a moving train

Rayleigh backscatter fiber optic sensing permits dynamic strains to be measured along an optical fiber with a gauge spacing and temporal resolution sufficient for rail applications. However, this sensing technology is highly sensitive to vibration. A 7.5 m long section of rail was instrumented with optical fiber and strain measurements were recorded during passage of a freight train slowed to 8–11 km/h. This strategy to minimize rail vibration was successful in permitting distributed dynamic rail strains to be measured under freight car loading. The measured rail strains were used to determine the rail shear forces, which were then used with the static wheel loads to determine the rail seat load for 14 consecutive sleepers as the train passed over the field monitoring site. These data were then combined with measurements of dynamic rail displacement captured using digital image correlation to infer the rail seat load–deflection relationships for individual sleepers. These relationships were observed to provide significantly more detailed information about unsupported voids and the sleeper contact stiffnesses than the traditional consideration of the relationship between applied load and rail deflection and highlights how track behavior at a monitored location can be dependent on the conditions and behavior of neighbouring sleeper.

New Devices for Measuring Forces on the Kayak Foot Bar and on the Seat During Flat-Water Kayak Paddling: A Technical Report

The purpose was to develop and validate portable force-measurement devices for recording push and pull forces applied by each foot to the foot bar of a kayak and the horizontal force at the seat. A foot plate on a single-point force transducer mounted on the kayak foot bar underneath each foot allowed the push and pull forces to be recorded. Two metal frames interconnected with 4 linear ball bearings, and a force transducer allowed recording of horizontal seat force. The foot-bar-force device was calibrated by loading each foot plate with weights in the push-pull direction perpendicular to the foot plate surface, while the seat-force device was calibrated to horizontal forces with and without weights on the seat. A strong linearity (r2 = .99-1.0) was found between transducer output signal and load force in the push and pull directions for both foot-bar transducers perpendicular to the foot plate and the seat-force-measuring device. Reliability of both devices was tested by means of a test-retest design. The coefficient of variation (CV) for foot-bar push and pull forces ranged from 0.1% to 1.1%, and the CV for the seat forces varied from 0.6% to 2.2%. The current study opens up a field for new investigations of the forces generated in the kayak and ways to optimize kayak-paddling performance.

Kinematic Asymmetries of the Lower Limbs during Ergometer Rowing

Rowing injuries, particularly of the lumbar spine, are often attributed to poor technique. Rowing technique comprises a series of coordinated movements between the back, upper limbs, and lower limbs, and abnormalities in these may lead to injury. The aim of this study was to test the hypothesis that ergometer rowing is symmetrical with respect to lower limb motion and that deviations from symmetry result from rowing experience, work rate, or stroke position. Twenty-two rowers in three levels of ability participated in this study. A motion analysis system was used with an instrumented rowing ergometer, which incorporated load cells at the handle and seat. Kinematic measurements of the knees, hips, lumbar-pelvic joints, and pelvic twist, in addition to measures of handle force, seat force, stroke length, mediolateral seat drift, and mean external power, were made during an incremental step test. Elite rowers exhibited the largest handle force and mean external power (P < 0.01) and least mediolateral seat drift (P < 0.01). All groups demonstrated lower limb asymmetries, with hip asymmetries significantly greater than knee asymmetries (P < 0.01). Regression analysis indicated that both hip and knee range of motion (ROM) asymmetry was significant (P < 0.05) in predicting lumbar-pelvic flexion at the catch and maximum handle force of the stroke. However, hip ROM asymmetry showed a better relation with lumbar-pelvic flexion compared with knee ROM asymmetry, explaining a greater proportion of the variance. Bilateral asymmetries during the rowing stroke, particularly at the hips, can contribute to suboptimal kinematics of the lumbar-pelvic region. Quantification of hip ROM asymmetries may therefore be a useful tool in predicting the development of low back pain in rowers.

Observer Based Method for Joint Torque Estimation in Active Orthoses

AbstractThis contribution presents a new approach of estimating the joint torques for an active orthosis. The new approach combines inverse dynamics and measured ground reaction forces. The joint torques can easily be computed from the ground reaction forces, but the measurement is usually flawed. An obsererver is employed to estimate the disturbance of the measurements and restore the original joint torques.A model of the human lower extremity is presented and additional seat forces are introduced to model the seat. Simulation results on the Sit-to-Stand movement illustrate the effectivity of the new approach.

Dynamics Optimization for the Valve Train of a Diesel Engine

The parameterized multi-body system dynamics model of the valve train of a diesel engine is built in ADAMS. The spring stiffness, spring force, valve mass and valve stiffness are set as experimental factors, and valve seat force and maximum acceleration are set as responses. Dynamic simulation experiments are carried out using design of experiment (DOE) method, from which the notable factors are obtained. The functions of response surfaces on notable factors are gotten, and then optimization design is implemented based on response surfaces.

Strapping rowers to their sliding seat improves performance during the start of ergometer rowing

Rowers sit on a seat that slides relative to the boat/ergometer. If a rower lifts him or herself from this sliding seat at any time, the seat will move away from under them and the rowing action is disrupted. From a mechanical perspective, it is clear that the need for the rower to remain in contact with the sliding seat at all times imposes position-dependent constraints on the forces exerted at the oar handle and the footstretcher. Here we investigate if the mechanical power output during rowing, which is strongly related to these forces, might be improved if the contact with the sliding seat was of no concern to the rower. In particular, we examine if elimination of these constraints by strapping the rower to the sliding seat leads to an increase in performance during the start on a standard rowing ergometer. Eleven well-trained female rowers performed 5-stroke starts in normal and strapped conditions. Handle force, vertical seat force, footstretcher force, and handle kinematics were recorded, from which mechanical power and work output were calculated. Most of the relevant mechanical variables differed significantly between the normal and strapped conditions. Most importantly, mechanical power output (averaged over the 5-stroke start) in the strapped condition was 12% higher than in the normal condition. We conclude that strapping a rower's pelvis to the sliding seat allows more vigorous execution of the stroke phases, resulting in a substantial improvement in performance during the start of ergometer rowing.

Influence of hand-rim wheelchairs with rear suspension on seat forces and head acceleration during curb descent landings

Shocks and vibrations experienced while using a hand-rim wheelchair can contribute to discomfort, fatigue and injury. The aim of this study was to compare the seat forces and head accelerations experienced by manual wheelchair users during independent curb descent landings in a standard and 3 suspension-type rigid-frame wheelchairs. repeated measures analysis of variance. Eight men with paraplegia due to spinal cord injury. Participants performed independently-controlled curb descent maneuvers with 4 wheelchairs. The seat force and head accelerations were compared across wheelchairs. The suspension-type wheelchairs decreased the seat force and head accelerations by significantly (p < 0.05) extending the force rise time. Also, the seat force and head accelerations were inversely related to the seat force at initial contact. The monoshock-based suspension wheelchairs showed the least seat force and longest force rise time. Suspension systems result in softer landings by attenuating the magnitude and time duration of the force and reducing head accelerations. Hand-rim wheelchair users can also soften landings by utilizing a "pull-up" strategy that reduces the force and head accelerations. Softer landings can contribute to improved ride quality.

Effect of rear suspension and speed on seat forces and head accelerations experienced by manual wheelchair riders with spinal cord injury

Whole-body shocks and vibrations experienced during manual wheelchair use can decrease an individual's comfort, increase the rate of fatigue, result in injury, and consequently limit mobility and community participation. We used a wheelchair-vibration simulator to examine whether the seat reaction forces experienced by wheelchair users were differentially influenced by wheelchair suspension, trunk-muscle innervations, and ground speed. We used wheelchairs instrumented with load cells and accelerometers to determine the forces transmitted from the seat frame and the head accelerations experienced by riders. We determined that self-selected speed, seat force, and head accelerations differed between subjects with and without trunk-muscle innervations and between rigid and suspension wheelchairs. Seat force and head accelerations were greatest in the rigid-frame wheelchair and lowest in the spring-type suspension-frame wheelchairs. Those participants without trunk-muscle innervations preferred slower speeds than those with trunk-muscle innervations. Forward head accelerations were greater in those without than with trunk-muscle innervations. Wheelchair rear-suspension systems may improve wheelchair mobility function in terms of comfort at higher velocity by minimizing the seat forces and head accelerations experienced by the riders, especially those with higher level spinal cord injury and diminished postural control.

Deficits in Surface Force Production During Seated Reaching in People After Stroke

In order to design effective treatment strategies for the rehabilitation of reaching after stroke, it is necessary to understand the underlying deficits. Although the kinematic aspects of reaching after stroke have been studied frequently, little attention has been paid to the surface force production underlying this behavior. The purpose of this study was to investigate surface force production and its coordination with arm movement during seated reaching in a group of people with hemiparesis. Seven people with mild right hemiparesis after stroke and 7 people who were neurologically healthy participated. Subjects performed seated reaching at 160% their normal speed toward ipsilateral and contralateral targets placed 160% beyond arm reach. Surface forces beneath the seat and feet and 3-dimensional hand movement and joint motions of the upper extremity and trunk were recorded. A weight shift from seat to feet occurred earlier whereas the onset of medial-lateral seat force was delayed and smaller in magnitude in people with hemiparesis. The results suggest that the normal magnitude and timing of surface force production during reaching beyond arm's length are altered in people with even mild hemiparesis after stroke, particularly during reaching toward the hemiparetic side.

Differences between Grab Rail Position and Orientation during the Assisted Sit-to-Stand for Able-Bodied Older Adults

The aim of this study was to compare the effects of grab rail position, orientation, and number of hands used on the kinetics of assisted sit-to-stand transfers. Participants were 12 able-bodied older adults between the ages of 69 and 88 years. While each one performed the sit-to-stand transfer, a motion analysis system with 9 cameras recording at 60 Hz tracked the 3-D trajectories of retroreflective markers. Bilateral 37-D platform, grab rail, and seat force data were collected at 200 Hz and normalized to participant body weight. Four lateral conditions were tested: vertical, 45 degrees inclined, and horizontal with the hand placed at 150 mm and 400 mm forward of the seat front edge. Four anterior conditions were tested: vertical and horizontal orientations with the use of one hand and two hands. Posterior grab rail force increased with anterior assistance and with two-hand use compared to lateral assistance and single hand use, respectively. The selection of grab rail position and the number of hands incorporated during assistance also determined the symmetry of anteroposterior net joint forces, net joint moments, and joint powers. Grab rail orientation determined the height of the gripping hand which influenced the assistance strategy. Grab rail position, orientation, and the amount of upper body contribution influenced the assisted sit-to-stand transfer. These kinetic responses to grab rail location require careful consideration in order to optimize grab rail assistance during the sit-to-stand transfer.

Measurement on Dynamic Behaviour of Track near Rail Joints and Prediction of Track Settlement

We measured factors relating to track dynamic behaviour, such as dynamic wheel loads and rail seat forces near a rail joint induced by running vehicles. We also proposed a track dynamic model to consider the excitation by wheels passing over discontinuous fish plate rail joints. We then compared the measured and analytical results, and found a close agreement between them. We also proposed a prediction model of ballast settlement near rail joints and calculated the effects of countermeasures against joint dips on ballast settlement.

Rising from a chair by a spring-loaded flap seat: a biomechanical analysis

Nine healthy male subjects and 8 patients with unilateral knee osteoarthrosis were studied while rising from a chair with and without the aid of a spring-loaded flap seat. The seat force started at 216 N and decreased with increasing seat angle. Ground reaction forces and motion were recorded using a force plate and video. EMG of the left vastus lateralis muscle was recorded. The effort when rising was estimated by the Borg scale. The use of the flap seat reduced the mean peak knee moment for the healthy subjects from 73 to 41 Nm and for the patients from 55 to 33 Nm. The decreases were significant at a p &lt; 0.001 level. The patients also reduced their hip moment significantly from 50 to 35 Nm (p &lt; 0.005). The muscle activity in the vastus lateralis was also significantly lower when the flap seat was used (p &lt; 0.005). When the theoretically maximal friction force between seat and subject was added, the effective seat force decreased more slowly, and the relation between its horizontal and vertical force components was more advantageous. The patients estimated greater effort reduction than the healthy subjects comparing the ordinary chair and the flap seat. CONCLUSION: a spring-loaded flap seat can reduce knee and hip load and can thus be useful for people with knee osteoarthrosis.

Thirty-minute continuous sitting force measurements with different support surfaces in the spinal cord injured and able-bodied

Able-bodied, paraplegic, and quadriplegic subjects sat for 30-minute intervals on various surfaces in a wheelchair with a forceplate mounted on the seat in order to determine factors that could contribute to the formation of decubitus ulcers. All three groups of subjects sat on ROHO and Jay cushions; in addition to sitting on the two cushions, the able-bodied subjects sat on a hard surface. Factors studied were: normal and shear seat forces, the location of the center of mass, and armrest force. The forceplate was under the cushions; therefore, the values reflect average forces over the buttocks and posterior thighs. These factors were compared between disability levels as well as between surface types. Larger, normal, and forward shear forces and a more anterior position of the center of mass were observed with the ROHO cushion. More frequent and larger lateral weight shifts occurred with the Jay cushion. The armrests tended to support from 5 percent of the body weight for quadriplegics to 9 percent for paraplegics. The results suggest that armrests reduce seat forces by carrying some of the body weight.