Martin Toward

The effect of temperature on railway rolling noise

The stiffness and damping of railpads in a railway track are affected by changes in the temperature of the surrounding environment. This results in the rolling noise radiated by trains increasing as the temperature increases. This paper quantifies this effect for a ballasted track equipped with natural rubber railpads and also studies the behaviour of a cork-reinforced rubber railpad. By means of measurements in a temperature-controlled environment, it is shown that the shear modulus of the natural rubber increases by a factor of six when the temperature is reduced from 40 ℃ to −20 ℃. The loss factor increases from 0.15 at 40 ℃ to 0.65 at −20 ℃. The shear modulus of the cork-reinforced rubber increases by a factor of 10, and the loss factor shows the typical trend of transition between rubbery and glassy regions. The railpad stiffness estimated from decay rate measurements at different temperatures is shown to follow the same trend. Field measurements of the noise from passing trains are performed for temperatures between 0 ℃ and 35 ℃; they show an increase of about 3–4 dB. Similar results are obtained from predictions of noise using the measured dependence of pad stiffness.

Reducing Railway Induced Ground-Borne Vibration by Using Trenches and Buried Soft Barriers

To reduce railway induced low frequency vibration, two mitigation measures - open trenches and buried soft wall barriers have been studied in this paper by using coupled finite element-boundary element models. These models were developed at KU Leuven and ISVR, and have been cross-validated within the EU FP7 project RIVAS (Railway Induced Vibration Abatement Solutions). Variations in the width, depth, location of trench and properties of soft barrier material are considered under various soil conditions. Results show that in all ground conditions, the notional rectangular open trench performs better than the other constructions. The width of an open trench has little influence on its performance, whereas increasing the width of a filled trench reduces the stiffness of the barrier, improving the performance of the trench. Likewise, fill materials with lower Young’s modulus give higher insertion losses.

Estimating the performance of rail dampers using laboratory methods and software predictions

Rail dampers are designed to reduce the rail component of rolling noise by increasing the attenuation with distance along the rail (decay rate, DR). There is no standardized method to assess the performance of rail dampers. The method described here, developed during the Franco-German STARDAMP project, uses laboratory tests and computer simulation to avoid the need for expensive and time-consuming field trials. The premise of the method is that the DRs of a damped track can be found from summing the DRs of a short-section of damped ‘freely supported’ rail and the DRs of an undamped track. Reasonable predictions of the decay rates of a test track have been made using this method. Software has been produced that implements TWINS-like predictions of rolling noise with and without rail dampers to predict the damper effect. The effect of rail pad stiffness on the effectiveness of rail dampers has been considered for track constructions typical in the UK and a regional train travelling at 120 km/h. For track fitted with ‘soft’ 120 MN/m rail pads, the dampers are predicted to reduce the total level by 2.5 dB(A) while with the ‘stiff’ 800 MN/m pads a 0.7 dB(A) reduction is expected.

Is the infant car seat challenge useful? A pilot study in a simulated moving vehicle

Background and objective The American Academy of Pediatrics recommends that preterm infants complete a predischarge ‘car seat challenge’ observation for cardiorespiratory compromise while in a car seat. This static challenge does not consider the more upright position in a car or the vibration of the seat when the car is moving. This pilot study was designed to assess the cardiorespiratory effects of vibration, mimicking the effect of being in a moving car, on preterm and term infants. Methods A simulator was designed to reproduce vertical vibration similar to that in a rear-facing car seat at 30 mph. 19 healthy newborn term and 21 preterm infants, ready for hospital discharge, underwent cardiorespiratory measurements while lying flat in a cot (baseline), static in the seat (30°), simulator (40°) and during motion (vibration 40°). Results Median test age was 13 days (range 1–65 days) and median weight was 2.5 kg (IQR: 2.1–3.1 kg). Compared with baseline observations, only the total number of desaturations was significantly increased when infants were placed at 30° (p=0.03). At 40°, or with vibration, respiratory and heart rates increased and oxygen saturation decreased significantly. Profound desaturations <85% significantly increased during motion, regardless of gestational age. Conclusions This is the first study to assess the effect of motion on infants seated in a car safety seat. Term and preterm infants showed significant signs of potentially adverse cardiorespiratory effects in the upright position at 40°, particularly with simulated motion, not identified in the standard challenge. A larger study is required to investigate the significance of these results.

Statistical description of wheel roughness

Wheel roughness measurements available from several different campaigns are presented in terms of average levels and dispersion. The dependence on factors such as brake type and whether the wheel is powered or trailing is also addressed. A method to decide how many wheels from a train are to be measured is then presented. Finally, the main outcomes are described from a round robin test aimed at assessing the effect on wheel roughness measurements of adopting different equipment, used independently by different teams.

Estimation of track parameters and wheel–rail combined roughness from rail vibration

Rolling noise from running trains is significantly influenced by the wheel–rail combined roughness and the dynamic properties of the track. To facilitate predictions of vibration and noise, it is desirable to be able to determine these parameters accurately from field measurements. In this study, an inverse method for the determination of these parameters is adopted and enhanced. A track model that is based on a wavenumber finite element model of the free rail coupled to discrete supports, which allows for the pinned–pinned mode and cross–sectional deformation of the rail, has been used. The rail vibration induced by hammer impacts and the vibration during train passages are simulated using this model, and these results are then applied to illustrate the accuracy of the direct and indirect methods for the estimation of track decay rate. These methods are compared in a case study for a ballasted track for which hammer impact and train pass–by measurements have been obtained. Other track parameters can also be extracted from the measured data by using the advanced track model. Thereafter, a more complete method is adopted to estimate the wheel–rail combined roughness from the measured rail vibration under train passages. A comparison is made among the estimated roughness levels obtained from this full method, an existing simplified method and the direct measurement method. It is found that the simplified method overestimates the roughness around the pinned–pinned resonance frequency, but gives a good estimation if the track decay rates of the loaded track are used.

Dataset for paper "A 2.5D finite element and boundary element model for the ground vibration from trains in tunnels and validation using measurement data"

Dataset supports: Jin, Q., et al. (2017). A 2.5D finite element and boundary element model for the ground vibration from trains in tunnels and validation using measurement data. Journal of Sound and Vibration.

Dataset for paper "Estimation of track parameters and wheel–rail combined roughness from rail vibration"

Dataset for: Li, Q., Thompson, D., and Toward, M. (2017). Estimation of track parameters and wheel–rail combined roughness from rail vibration. Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit.

Dataset for the figures in 'Reducing railway-induced ground-borne vibration by using open trenches and soft-filled barriers'

Data for the figures in the paper by Thompson, D., Jiang, J., Toward, M.G.R, Hussein, M.F.M., Ntotsios, E., Dickmans, A., Coulier, P., Lombaert, G. and Degrande, G. (2016) Reducing railway-induced ground-borne vibration by using open trenches and soft-filled barriers. Soil Dynamics and Earthquake Engineering

G531(P) Effect on cardiorespiratory function in term and preterm infants sitting in a car safety seat, in a simulated moving vehicle (pilot study)

Introduction The AAP recommends preterm infants undergo a “car seat challenge” before discharge, to observe for any differences in cardiorespiratory function whilst seated in a car seat compared to lying flat in a cot. The infant can be discharged if there is no compromise. This static (30°) challenge does not take into account the more vertical positioning of the seat or effects of vibration when it is secured in a moving vehicle. Aim To investigate the effect of vibration, mimicking that experienced in a moving car, on cardio-respiratory function, compared to the standard challenge. Methods A novel simulator was designed to represent the vibrations felt in a rear facing car seat during a normal urban cycle. 40 term & preterm babies, ready for discharge after birth, were recruited. The babies were their own control. Observations of heart & respiratory rates, saturation & end tidal CO2 levels were recorded flat in a cot, static in the seat (30°) & simulator (40°) & during vibration (motion). Results 19 term & 21 preterm infants were tested; 22 were male (55%). Gestation range was 25+2 weeks to 41+5 weeks (median 35+5). Median birthweight was 2.5 kg (range 0.8 kg to 4.8 kg). Age at testing was 1 to 65 days (median 13 days). There were no significant differences in outcome variables for infants in the cot & 30° position. However, compared to rest, in the static 40° position infants had significantly faster heartbeats, lower oxygen saturation & higher respiratory rates. When in motion these differences persisted & the number of desaturations below 85% were significantly higher. Conclusions Testing all infants at 30° would suggest they could travel. However both term & preterm babies showed signs of cardio-respiratory distress in the 40° position with a significant increase in profound desaturations during motion, which were underestimated by the standard challenge. A larger study is required to confirm these results. This may lead to revision of the current car seat challenge or the design of infant car seats.