Rail Dampers Research Articles

Parametric Study on the Effect of Rail Dampers on Track Decay Rate

Track decay rate (TDR), meaning the rate of attenuation of bending waves through the rail, is the most important indicator of a track’s dynamic characteristic impacting the rail noise emission. TDR depends on various parameters related to the construction of the track, and it can be increased using rail dampers. These are mechanical devices working on the principle of dynamic absorbers and are attached to the rail. This paper addresses the track with light rails needing improvements to reduce the rail noise emission using a particular rail damper with a mixed damping system (rubber–oil). The bending waves that propagate through the rail, the frequency response function of the rail, and TDR are investigated considering different scenarios regarding the parameters of the track: soft/stiff rail pad, tampered/settled ballast, and sleeper bay. To this end, an analytic model of the track featuring rail dampers consisting of an infinite Timoshenko beam with discrete attached oscillators is used. Numerical results show the possibility to increase TDR of railway track with light rails for both soft/stiff rail pads from 4 to 500 Hz up to 1250–1600 Hz using rail dampers with a mixed damping system.

Determination of the dynamic stiffness matrix of a rail damper and application to vibration decay rate

In this paper, the 6×6 dynamic stiffness matrix of a rail damper seen by a short section of rail is defined based on the force simplification theory, and a method to determine the matrix is presented. According to the method, frequency response functions (FRFs) between specific points on the rail as a rigid body are measured with hammer testing. These FRFs are then used to express the acceleration of the mass center of the rail as well as the rail's angular acceleration. As the third step, the equations of motion of the rail are established based on the laws of momentum and moment of momentum, from which the dynamic stiffness matrix can be worked out. The method is then applied to determine the dynamic stiffnesses of a typical damper, and the determined dynamic striffnesses are combined with an infinite periodic track model to stduy the effect of the damper on the verical and lateral vibration decay rates of the rail.

Research on the effect of rail vibration suppression using the stiffness-damping interventional rail vibration reduction device

This study introduces the Stiffness-Damping Interventional Rail Vibration Reduction Device (SDIRVRD) as a means to enhance rail vibration suppression. It compares the SDIRVRD with the traditional tuned rail damper (TRD) in terms of their vibration suppression mechanisms. The research investigates the influence of the SDIRVRD’s stiffness and damping parameters on the dynamic response of the vehicle and track. It also conducts a comparative analysis of track and vehicle vibration responses before and after the installation of the SDIRVRD, evaluating its effectiveness in reducing both track system and vehicle vibrations. The field test validates the theoretical calculations, and the vibration reduction efficiency is quantified using the insertion loss value. Key findings include the superiority of the SDIRVRD over the TRD in vibration reduction under equivalent damping ratio conditions. The SDIRVRD significantly reduces rail acceleration, displacement, and velocity admittances, with a notable suppression effect on pinned-pinned rail vibration. The stiffness and damping of the SDIRVRD play a crucial role in enhancing its vibration reduction effect, but after the stiffness exceeds 2 kN/mm and further increases the stiffness of the SDIRVRD, the enhancement of its damping effect on the vehicle-track system’s vibration diminishes significantly. The SDIRVRD reduces acceleration vibration levels in the vehicle and track system by approximately 2–3 dB. Insertion Loss measurements show significant vibration reduction in the rail across most frequency domains.

Auralization and Visualization for Infrastructure Planning in the Joint Project "EAV-Infra"

Within the joint research project "Real-time Calculation, Auralization and Visualization of Sound Propagation and Noise Protection Measures for Infrastructure Projects" (EAV-Infra), funded by the Federal Ministry for Economic Affairs, the potentials of digital infrastructure planning based on Building Information Modeling (BIM) and the auralization of different states of planning will be combined. In this contribution, the objectives of the project will be presented with particular focus on the auralization. Currently, the effectiveness of noise mitigation measures like acoustic barriers or rail dampers is evaluated and communicated mostly by means of SPL values. Through auralization, a more vivid impression of different states of planning can be given during the whole planning process. In EAV-Infra, the auralization will be based on audio data of partial sound sources taken from real train passings. The data will be collected at various sites using a newly developed MEMS microphone array. To achieve a realistic hearing impression at the receiver position, a suitable model of the sound propagation will be implemented, which allows for a simulation in real time. In a last step, the partial sound source's signals will be convolved with the calculated sound propagation to synthesize the signal at the receiver position.

Laboratory Vibration Studies of Metro Tracks Equipped with Tuned Rail Dampers

Laboratory Vibration Studies of Metro Tracks Equipped with Tuned Rail Dampers

Five Years' Monitoring Data on Rail Damper Performance

Roughness in rail surface accumulates with train operations and grows faster on curved tracks than tangent tracks. Higher roughness leads to higher noise radiation. In Hong Kong, railway noise prediction includes a 3dB correction for rail surface deterioration. Depending on rate of deterioration, different rail grinding cycles (typically between 3 and 24 months) are scheduled to ensure train operations without excessive noise radiation. Before rail dampers installation, noise levels were monitored for 1.5 years and around the noise limit with variation +/- 3dB(A) due to rail roughness variation. After installation of rail damper, railway noise was generally maintained at 7dB(A) below the noise limit with variation +/-1.5dB(A) for more than 3 years. Noise reduction at dominant frequencies 630 Hz and 800 Hz were more than 10dB in 1/3 Octave analysis. The rail dampers were installed at alternative spaces such that additional rail dampers can be installed to double the amount in case further noise reduction is required. This paper examines the five years' monitoring data in detail, showing the noise levels with smaller variations over grinding cycles after rail damper installation, and explores rail damper potential ability to slow down the growth rate of rail roughness levels.

Assessment of the Noise Reduction Impact from Application Restrictions on Rail Dampers

In the last decades, rail dampers had become a commonly used rolling noise abatement measure at several mainline and metro networks. Rolling noise reductions outdoor/indoor up to 4/8 dB had been found. While the beginning of damper application was started with multiple test sections, infrastructure managers had raised installation restrictions from other related technology departments like signaling and communication. This is leading to defined sections where one rail has to remain partially free from dampers or the track has to remain completely free from dampers. These sections become relevant when the damper application is caused by noise tackling action plans. Therefore, the acoustic impact was assessed by a) laboratory test track analysis (partially free) and b) environmental noise prognosis software (completely free). It is shown, that also for a partially free rail, a cancellation of the noise reduction can be expected for single 1/3 octave frequencies. This can be relevant for the overall noise emission. The effect from the completely free rail is much larger due to noise increases at several immission points. Railway noise mitigation has to consider these results or, if possible, the rail damper technology has to be improved to avoid these restricted sections.

Railway Ground Borne Noise (GBN) Reduction by Rail Dampers

Railway GBN impact has raised increasing concerns due to underground transportation expansion. Reducing train speed or replacing standard baseplates with high resilient ones are adopted for GBN control. Both mitigations are not satisfactory considering the installation difficulty and limited performance, e.g., only ~3dB noise reduction for 30% train speed reduction. On the other hand, FST (Floating Slab Track) are commonly used. In many cases, to accommodate the FST, tunnel diameter is enlarged for the TBM (Tunnel Boring Machine) tunnel section. Also, rail dampers are used for air-borne noise control, but never used for GBN control due to its relatively small mass. P2 resonance is a main cause of railway GBN. It is a simple harmonic motion of a lump mass (wheel and rail combined) oscillating on top of resilient baseplates. Laboratory test was conducted with a 6m fastened rail and a ~450kg mass to simulate train wheel and track system. A retrofit rail damper with TMD (Tuned Mass Damping) oscillators was tested. The mass of TMD oscillators along the rail with ~2m effective length of P2 resonance is more than 10% of the wheel. Around 7dB vibration reduction was recorded at the rail and floor when allowing the TMD oscillation.

Track Decay Rate (TDR) Measurement Method for Reactive Damping by Tuned Mass Damper (TMD)

TDR measures the rate of vibration decay along rail in dB/m. Higher TDR leads to lower noise radiation. However, new railways are often having low TDR due to the use of resilient fasteners (to provide vibration isolation between rail and supporting structure for ground borne noise concerns), which leads to high noise radiation. Rail damper is used to increase TDR (thus reduces railway noise), where TMD is an efficient damping mechanism dissipating the vibration energy of the rail. TMD provides reactive damping force, maximised after a few cycles of oscillations. TMD force is stronger with continuous excitation than impulse excitation. For convenient purposes in the industry, TDR measurements are primarily conducted by impulse method, which do not allow sufficient time to include reactive TMD force. Therefore, impulse excitation TDR is smaller than continuous excitation TDR. Continuous excitation TDR is considered to reflect more of the real case of wheel/rail interaction excitation during train running. Besides, TDR in terms of time decay in dB/s is an alternative approach for evaluating noise performance of the rail. This paper presents TDR measurement results under different conditions, e.g., impulse excitation against continuous excitation; freely supported short rail (~6m), short rail (~6m) with resilient fastener support as well as site measurements in continuous welded rails.

Auralisation of combined mitigation measures in railway pass-by noise

To reduce noise exposure along railway lines various combinations of noise mitigation measures can be considered. However, predicting and assessing their effects is non-trivial and the potential need for multiple measures is difficult to communicate to stakeholders. Auralisation is a promising tool that can help to support communication and decision-making, and enable psychoacoustic evaluations. This paper presents developments of a physics-based auralisation model for train pass-bys that allows various mitigation measures to be included. The work is conducted within the European research project SILVARSTAR. The proposed model includes contribution from rolling noise, impact noise, traction, auxiliary systems, and aerodynamic noise. It is physically based and allows a direct assessment of pass-by parameters such as speed, roughness, wheel flats and track design. Based on the TWINS model, five structural transfer paths for rolling noise are considered to integrate mitigation measures such as wheel and rail dampers. Shielding by noise barriers is simulated with analytical models. Reflection at different ground types is considered and can account for track embankments. The results can be coupled to an immersive Virtual Reality environment, by first panning the synthesised sounds to a small virtual speaker array and subsequently dynamic binaural rendering for headphones.

The mechanism of wheel polygonal wear based on rotor dynamics

A rotor dynamic model of wheel-rail coupling system was established taking wheel eccentricity and initial polygon into consideration in order to investigate the mechanism of wheel polygonal wear. Considering the complex wheel-rail contact relationship, the equivalent yaw angle was proposed and the wheel-rail relative speed model was established. The law of wheel-rail self-excited vibration and its effect on polygonal wear were studied. The possibility of variable speed operation was investigated together with the sensitivity of the system parameters. The results show that the periodic longitudinal and lateral creep forces are essential for the wheel polygonal wear, which have the characteristics of supercritical Hopf bifurcation and ‘fixed wavelength’ and ‘fixed frequency’. While in some circumstances, longitudinal and lateral creep forces jointly cause polygonal wear, in other cases, longitudinal creep forces have almost no effect. By adjusting the longitudinal and lateral stiffness, primary suspension stiffness, and rail damping parameters, as well as by selecting an appropriate speed for variable speed operation, the wheel polygonal wear may be effectively suppressed. The findings offer a fresh viewpoint for the study of mechanisms and the prevention of wheel polygonal wear.

Prediction and mitigation of train-induced vibrations of over-track buildings on a metro depot: Field measurement and numerical simulation

To predict the vibration transmission of over-track buildings and investigate the effectiveness of countermeasures, a fully coupled three-dimensional vibration prediction model for over-track buildings with consideration of the pile–soil interaction (PSI) was proposed. The accuracy of this prediction model was validated with field data from in-situ vibration monitoring in a metro depot. The consideration of PSI improved prediction accuracy about the vibration of over-track buildings. Then the effectiveness of different mitigation measures (rail damper and ballast mat) was investigated by this prediction model. It was found that the vibration of over-track buildings was dominated by vertical vibration components. Rail dampers significantly reduced the vibration in the high-frequency range above 80 Hz, while the vibration in the low-frequency range below 10 Hz was amplificated. The insertion loss of ballast mats reached 10 dB in the frequency range above 40 Hz except at the resonance frequency of the track, and mitigation effectiveness gradually decreased with increasing story height. This proposed method can predict the vibration level within over-track buildings and is an effective tool to guide the vibration mitigation design of over-track buildings.

Study on Possible Application of Rubber Granulate from the Recycled Tires as an Elastic Cover of Prototype Rail Dampers, with a Focus on Their Operational Durability.

This study is an attempt to investigate possible applications of rubber granulate SBR (styrene-butadiene rubber) produced from recycled waste tires as an elastic cover for prototype rail dampers, which are aimed at reducing the level of railway noise emitted in the environment. The authors present laboratory procedures and discuss the results of several experimental tests performed on seven different SBR materials with the following densities: 1100, 1050, 1000, 850, 750, 700 and 650 kg/m3. It is proven that rubber granulate SBR produced from recycled waste tires, can be used as an elastic cover in steel inserts in rail dampers, provided that the material density is not lower than 1000 kg/m3. In the conducted tests, samples of the materials with high densities exhibited good static and dynamic elastic characteristics and had sufficient operational durability.

Development of multi-band tuned rail damper for rail vibration control

The intense interaction force between the wheel-rail causes the vibration of wheel and rail, and generates rolling noise. Increasing the rail damper is an effective way to suppress rail vibration. In this paper, a shear-type multi-band tuned rail damper (MTRD) consist of internal mass bars and external resilient layer to reduce rail vibration is proposed. Mass bars are wrapped inside resilient layer and placed along the length of rail. Resilient layer between two adjacent mass bars can enforce them perform shearing motion corresponding to the layer along the main vibration direction of rail. Different oscillation frequencies corresponding to different mass bars can be tuned by adjusting the structure of MTRD. It achieves an increase in the operating frequency band and a widening of the operating frequency range of MTRD. The influence of parameters of MTRD on its performance is investigated by the finite element method (FEM). One of three designed MTRD models is selected for prototype production after comparative analysis. Laboratory measurements are conducted on a rail specimen and 12 m track platform. Results show the main operating frequency band of designed MTRD is in the range of 200 Hz–800 Hz, achieves the goal of the desired frequency band. Frequency response function tests of rail on 12 m platform show the MTRD could suppress rail vibration in the range of 100–2000 Hz. To estimate the practical reduction effects of MTRD on vibration, a small radius curve of metro line is selected for field measurements. The measured track decay rate (DR) shows MTRD could increase DR at frequencies above 80 Hz with a max increment of 5 dB/m and 9.3 dB/m in vertical and lateral direction respectively. Reduction of rail vibration and rolling noise when trains pass is also measured. The overall vibration level of rail achieves a max reduction of 10.9 dB and 6.3 dB in vertical and lateral directions respectively. The overall sound pressure level is reduced by 5.9 dB(A) at the speed of 60 km/h.

Noise Reduction by Rail Damper Tunable for Individual Rails in Curve

Tuned mass rail dampers are cost effective for the mitigation of the airborne noise and vibration with the ability to be tuned for individual site. TMDs have been developed and installed at a single rail in a curve tunnel and achieve more than 4dB(A) noise reduction in many cases. According to the on-site noise reduction performance during damper installation, half, one, two or three dampers can be installed at each spacing between two baseplates. TMDs with only half-installation provides more than 10dB reduction at vertical pin-pin resonance (~1kHz). With the standard installation, they provide the strong damping to half the corrugation growth rate. The stick-slip phenomena which causes the corrugation will be affected by the damping effect from TMDs. On the other hand, they can also be tuned to the low-frequency (p2 resonance) for grandborne noise control. The high reduction of the grand borne noise proved our claim for effectiveness of the TMDs besides many other studies on the other parameters like the type of the baseplates or the soil types. According to the test results TMDs achieve strong performance in different range of the frequencies.

Decay rate of rail with egg fastening system using tuned rail damper

In order to study the decay rate of the rail in some section of Beijing metro using the egg fastening system, a cellular rail model based on the spectral element method is established. In combination with Bloch theorem, the decay rate of the rail with the egg fastening system is hereby studied. On this basis, the influence of tuned rail damper (TRD) on the decay rate of the rail is analyzed. At present, the decay rate of the rail with the egg fastening system is relatively low, in the frequency range from 200 Hz to 400 Hz. The influence of the egg fastening system on the decay rate of the rail is mainly reflected in the frequency range below 450 Hz. TRD can greatly increase the decay rate of the rail in the vicinity of its operating frequency. Moreover, TRD damping can increase the decay rate of the rail, which is beneficial in controlling rail vibration. Rail vibration can be better controlled by increasing the weight of TRD when the operating frequency is constant. The installation position of TRD also affects the decay rate of the rail. Appropriate adjustment of this position can more effectively suppress rail vibrations over a wider frequency range.

The influence of track design on the rolling noise from trams

Tramway noise can be significant even though the speeds are relatively low. The influence of track design on the rolling noise is studied through a systematic comparison of different tracks on a single network. These include a slab track with embedded sleeper blocks, a ballasted track and a track with embedded rails. Measurements have been taken of rail vibration and noise during tram passages at approximately 55 km/h; the rail and wheel roughness have also been measured. Comparisons are made in terms of track decay rate, rail vibration and pass-by noise. After normalising to the same roughness, the slab track is found to be the noisiest and the ballasted track the quietest. Theoretical models of the various track forms are also presented to give insight into the differences in acoustic performance. The models allow the relative contributions of the track and wheels to the pass-by noise to be identified. In addition the effect of rail dampers added to the slab track is assessed. These attenuate the noise at higher frequencies due to the increase in decay rate, but an increase in radiation is noted at 500 Hz and below, possibly linked to differences in effective roughness.

Examination of Rail Dampers with Respect to Noise and Vibration Mitigation

Nowadays there are more and more possibilities to mitigate noise and vibration emitted by railway transport to the lower levels. Among them, rail dampers with highly viscous properties placed on the rail web, fixed with adhesives or other methods, appeared as a new element in the railway superstructure. The elements are applied to reduce noise and vibration by transforming the vibration energy of the rail web into heat, through their large internal friction. Many companies produce rail web elements and apply them with success abroad. Domestic manufacturers have already appeared in Hungary; however, the installation of these elements is still very limited. This publication is intended to introduce the rail dampers and to demonstrate their efficiency through laboratory and field measurements. Experimental modal analysis was used during the laboratory test to determine the eigenfrequencies, the damping factors and the mode shapes of an experimental rail section, thus analyzing the vibration damping and noise reduction effect of the elements. Field measurements were also carried out at a segment installed with rail web elements in Hungary and its vicinity, under standardized conditions. By averaging measured noise level values for various types of trains, comparable noise reduction of the investigated rail web element can be achieved. The laboratory and field test results confirmed that the rail web elements can be suitable for rolling noise reduction and vibration damping in most of the cases. The results of the measurements provide guidance and information for future development of the elements.

Parametric Investigation of a Rail Damper Design Based on a Lab-Scaled Model

BackgroundTrack noise is one of the main issues in the development of railway networks. It is well known that rail dampers, as a cost-effective, passive means of vibration reduction, do reduce the noise; still, neither the mechanism behind their action nor the influential parameters are well understood.PurposeThe main purpose of this work is to investigate the efficiency and influential parameters of a rail damper design based on a lab-scaled model of the rail-damper system and an accurate FE model.MethodsBased on experimental and numerical modal analyses and the Modal Assurance Criteria (MAC) analysis, the FE model updating technique was applied to develop a highly accurate FE model of the rail-damper system for the investigated frequency range. In a further step, the developed FE model is used in a parametric analysis to assess various damper parameters with respect to the efficiency of damping rail vibrations and, therewith, radiated noise.ResultsThe investigation performed based on FE simulations demonstrates how different material and geometric parameters of the damper influence the mobility decay rate of rail vertical vibrations. The investigated parameters are the thickness of still and rubber layers, stiffness and damping loss factor of rubber layers, and pre-force in the bolts that press the layers together.ConclusionsIt is shown that the FE model updating technique was capable of producing a highly accurate FE model despite the challenging properties of the real structure and that a combination of the lab-scaled model and the FE model represents a cost-effective approach.

Ways of protection from noise pollution in railway and tramway infrastructure

The paper presents various ways of protection from traffic noise used in railway infrastructure in Poland. The sources of noise in rail and tram transport were discussed. Also commonly found solutions on the railway network were analyzed such as noise barriers and rail dampers. Modern tram surfaces have been presented as one of the noise protection methods in the tram infrastructure. In the tram infrastructure a noise protection method was presented in the form of tram track lubricators on sharp curves. In addition, the effectiveness of noise protection methods was assessed on the basis of tests and research.