Effects of rail dynamics and friction characteristics on curve squeal

Curve squeal in railway vehicles is an instability mechanism that arises in tight curves under certain running and environmental conditions. In developing a model the most important elements are the characterisation of friction coupled with an accurate representation of the structural dynamics of the wheel. However, the role played by the dynamics of the rail is not fully understood and it is unclear whether this should be included in a model or whether it can be safely neglected. This paper makes use of previously developed time domain and frequency domain curve squeal models to assess whether the presence of the rail and the falling characteristics of the friction force can modify the instability mechanisms and the final response. For this purpose, the time-domain model has been updated to include the rail dynamics in terms of its state space representation in various directions. Frequency domain and time domain analyses results show that falling friction is not the only reason for squeal and rail dynamics can play an important role, especially under constant friction conditions

Sound power and vibration levels for two different piano soundboards

This paper compares the sound power and vibration levels for two different soundboards for upright pianos. One of them is made of laminated spruce and the other of solid spruce (tone-wood). These differ also in the number of ribs and manufacturing procedure. The methodology used is defined in two major steps: (i) acoustic power due to a unit force is obtained reciprocally by measuring the acceleration response of the piano soundboards when excited by acoustic waves in reverberant field; (ii) impact tests are adopted to measure driving point and spatially-averaged mean-square transfer mobility. The results show that, in the mid-high frequency range, the soundboard made of solid spruce has a greater vibrational and acoustic response than the laminated soundboard. The effect of string tension is also addressed, showing that is only relevant at low frequencies

Development of a model to assess acoustic treatments to reduce railway noise

Porous materials have recently been used in absorptive treatments around railway tracks to reduce noise emissions. To investigate the effect of porous materials, a finite element model has been developed. 2D models for porous materials have been considered either as an equivalent fluid or as a poroelastic material based on the Biot theory. The two models have been validated and compared with each other to check the effect of the skeleton vibration. The poroelastic FE model has been coupled with a 2D acoustic boundary element model for use in railway applications. The results show that it may be necessary to include the frame vibration, especially at low frequencies where a frame resonance occurs. A method for the characterization of porous materials is also discussed. From this it is shown that the elastic properties of the material determine the resonance frequency and the magnitude

Method for obtaining the wheel-rail contact location and its application to the normal problem calculation through CONTACT

[EN] This work presents a robust methodology for calculating inter-penetration areas between railway wheel and rail surfaces, the profiles of which are defined by a series of points. The method allows general three-dimensional displacements of the wheelset to be considered, and its characteristics make it especially suitable for dynamic simulations where the wheel-rail contact is assumed to be flexible. The technique is based on the discretization of the geometries of the surfaces in contact, considering the wheel as a set of truncated cones and the rail as points. By means of this approach, it is possible to reduce the problem to the calculation of the intersections between cones and lines, the solution for which has a closed-form expression. The method has been used in conjunction with the CONTACT algorithm in order to solve the static normal contact problem when the lateral displacement of the wheelset, its yaw angle and the vertical force applied in the wheelset centroid are prescribed. The results consist of smooth functions when the dependent coordinates are represented as a function of the independent ones, lacking the jump discontinuities that are present when a rigid contact model is adopted. Example results are shown and assessed for the normal contact problem for different lateral and yaw positions of the wheelset on the track.This work was supported by the financial contribution of the European Union’s Shift2Rail programme (RUN2Rail project, grant number 777564), the Spanish Ministry of Economy, Industry and Competitiveness and the European Regional Development Fund (projects TRA2013-45596-C2-1-R and TRA2017-84701-R).Baeza González, LM.; Thompson, DJ.; Squicciarini, G.; Denia, FD. (2018). Method for obtaining the wheel-rail contact location and its application to the normal problem calculation through CONTACT. Vehicle System Dynamics. 56(11):1734-1746. https://doi.org/10.1080/00423114.2018.1439178S173417465611Garg, V. K., & Dukkipati, R. V. (1984). Wheel–Rail Rolling Contact Theories. Dynamics of Railway Vehicle Systems, 103-134. doi:10.1016/b978-0-12-275950-5.50009-2Wickens, A. H. (1965). The dynamic stability of railway vehicle wheelsets and bogies having profiled wheels. International Journal of Solids and Structures, 1(3), 319-341. doi:10.1016/0020-7683(65)90037-5DE PATER, A. D. (1988). The Geometrical Contact between Track and Wheelset. Vehicle System Dynamics, 17(3), 127-140. doi:10.1080/00423118808968898Yang G. Dynamic analysis of railway wheelsets and complete vehicle systems (PhD thesis). Delft: Delft University of Technology; 1993.Negretti, D. (2012). A third-order approximation method for three-dimensional wheel–rail contact. Vehicle System Dynamics, 50(3), 431-448. doi:10.1080/00423114.2011.595804Shabana AA, Zaazaa KE, Escalona JL, et al. Modeling two-point wheel/rail contacts using constraint and elastic-force approaches. In: Paidoussis MP, editor. ASME 2002 International Mechanical Engineering Congress and Exposition; 2002 Nov 17–22; New Orleans, Louisiana: American Society of Mechanical Engineers, Rail Transportation Division (Publication) RTD, p. 35–50.Netter, H., Schupp, G., Rulka, W., & Schroeder, K. (1998). NEW ASPECTS OF CONTACT MODELLING AND VALIDATION WITHIN MULTIBODY SYSTEM SIMULATION OF RAILWAY VEHICLES. Vehicle System Dynamics, 29(sup1), 246-269. doi:10.1080/00423119808969563Pombo, J., Ambrósio, J., & Silva, M. (2007). A new wheel–rail contact model for railway dynamics. Vehicle System Dynamics, 45(2), 165-189. doi:10.1080/00423110600996017Polach, O. (2010). Characteristic parameters of nonlinear wheel/rail contact geometry. Vehicle System Dynamics, 48(sup1), 19-36. doi:10.1080/00423111003668203Santamaría, J., Vadillo, E. G., & Gómez, J. (2006). A comprehensive method for the elastic calculation of the two-point wheel–rail contact. Vehicle System Dynamics, 44(sup1), 240-250. doi:10.1080/00423110600870337Cuperus, J. L., & Venter, G. (2016). Numerical simulation and parameterisation of rail–wheel normal contact. Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit, 231(4), 419-430. doi:10.1177/0954409716631009Chollet, H., Sébès, M., Maupu, J. L., & Ayasse, J. B. (2013). The VOCO multi-body software in the context of real-time simulation. Vehicle System Dynamics, 51(4), 570-580. doi:10.1080/00423114.2013.768771Pascal, J.-P., & Soua, B. (2016). Solving conformal contacts using multi-Hertzian techniques. Vehicle System Dynamics, 54(6), 784-813. doi:10.1080/00423114.2016.1161201Piotrowski, J., & Chollet, H. (2005). Wheel–rail contact models for vehicle system dynamics including multi-point contact. Vehicle System Dynamics, 43(6-7), 455-483. doi:10.1080/00423110500141144Vollebregt EAH, Weidemann C, Kienberger A. Use of “CONTACT” in multi-body vehicle dynamics and profile wear simulation: initial results. in: S. Iwinicki (Ed.) 22nd International Symposium on Dynamics of Vehicles on Roads and Tracks (IAVSD2011), Manchester: Manchester Metropolitan University; 2011.Liu, B., Bruni, S., & Vollebregt, E. (2016). A non-Hertzian method for solving wheel–rail normal contact problem taking into account the effect of yaw. Vehicle System Dynamics, 54(9), 1226-1246. doi:10.1080/00423114.2016.1196823Kalker, J. J. (1990). Three-Dimensional Elastic Bodies in Rolling Contact. Solid Mechanics and Its Applications. doi:10.1007/978-94-015-7889-9Pombo, J., & Ambrosio, J. (2005). A computational efficient general wheel-rail contact detection method. Journal of Mechanical Science and Technology, 19(S1), 411-421. doi:10.1007/bf02916162Kaiser, I., & Popp, K. (2006). Interaction of elastic wheelsets and elastic rails: modelling and simulation. Vehicle System Dynamics, 44(sup1), 932-939. doi:10.1080/00423110600907675Falomi, S., Malvezzi, M., & Meli, E. (2011). Multibody modeling of railway vehicles: Innovative algorithms for the detection of wheel–rail contact points. Wear, 271(1-2), 453-461. doi:10.1016/j.wear.2010.10.039Meli, E., Magheri, S., & Malvezzi, M. (2011). Development and implementation of a differential elastic wheel–rail contact model for multibody applications. Vehicle System Dynamics, 49(6), 969-1001. doi:10.1080/00423114.2010.504854Burgelman N. The wheel–rail contact problem in vehicle dynamic simulation, in: Railahead Group [PhD thesis]. Technische Universiteit Delft; 2016.Ren, Z., Iwnicki, S. D., & Xie, G. (2011). A new method for determining wheel–rail multi-point contact. Vehicle System Dynamics, 49(10), 1533-1551. doi:10.1080/00423114.2010.539237Yang, X., Gu, S., Zhou, S., Zhou, Y., & Lian, S. (2015). A method for improved accuracy in three dimensions for determining wheel/rail contact points. Vehicle System Dynamics, 53(11), 1620-1640. doi:10.1080/00423114.2015.1066508Johnson, K. L. (1985). Contact Mechanics. doi:10.1017/cbo9781139171731European Standards, Railway applications – testing for the acceptance of running characteristics of railway vehicles – testing of running behaviour and stationary tests, in: EN 14363:2005

Sound transmission loss of windows on high speed trains

The window is one of the main components of the high speed train car body structure through which noise can be transmitted. To study the windows’ acoustic properties, the vibration of one window of a high speed train has been measured for a running speed of 250 km/h. The corresponding interior noise and the noise in the wheel-rail area have been measured simultaneously. The experimental results show that the window vibration velocity has a similar spectral shape to the interior noise. Interior noise source identification further indicates that the window makes a contribution to the interior noise. Improvement of the window’s Sound Transmission Loss (STL) can reduce the interior noise from this transmission path. An STL model of the window is built based on wave propagation and modal superposition methods. From the theoretical results, the window’s STL property is studied and several factors affecting it are investigated, which provide indications for future low noise design of high speed train windows

Acute Delta Hepatitis in Italy spanning three decades (1991–2019): Evidence for the effectiveness of the hepatitis B vaccination campaign

Updated incidence data of acute Delta virus hepatitis (HDV) are lacking worldwide. Our aim was to evaluate incidence of and risk factors for acute HDV in Italy after the introduction of the compulsory vaccination against hepatitis B virus (HBV) in 1991. Data were obtained from the National Surveillance System of acute viral hepatitis (SEIEVA). Independent predictors of HDV were assessed by logistic-regression analysis. The incidence of acute HDV per 1-million population declined from 3.2 cases in 1987 to 0.04 in 2019, parallel to that of acute HBV per 100,000 from 10.0 to 0.39 cases during the same period. The median age of cases increased from 27 years in the decade 1991-1999 to 44 years in the decade 2010-2019 (p < .001). Over the same period, the male/female ratio decreased from 3.8 to 2.1, the proportion of coinfections increased from 55% to 75% (p = .003) and that of HBsAg positive acute hepatitis tested for by IgM anti-HDV linearly decreased from 50.1% to 34.1% (p < .001). People born abroad accounted for 24.6% of cases in 2004-2010 and 32.1% in 2011-2019. In the period 2010-2019, risky sexual behaviour (O.R. 4.2; 95%CI: 1.4-12.8) was the sole independent predictor of acute HDV; conversely intravenous drug use was no longer associated (O.R. 1.25; 95%CI: 0.15-10.22) with this. In conclusion, HBV vaccination was an effective measure to control acute HDV. Intravenous drug use is no longer an efficient mode of HDV spread. Testing for IgM-anti HDV is a grey area requiring alert. Acute HDV in foreigners should be monitored in the years to come

Use of a reciprocity technique to measure the radiation efficiency of a vibrating structure

The reciprocity principle is well-known and has many applications in acoustics and vibro-acoustics. This paper discusses a reciprocity measurement method to determine the radiation efficiency of a vibrating structure. The method comprises two steps: (i) measurements of the acceleration response of the structure induced by a sound field in a reverberation chamber and (ii) measurements of the spatially-averaged squared transfer mobility of the structure. The approach is more flexible than a direct method and has the advantage that no shaker is required to excite the structure in the acoustic measurements. To demonstrate the applicability of this method, experiments were conducted on rectangular flat plates, on two components of a railway track test-rig and on three different built-up structures. For the plates and the railway rig components, comparisons are also made with theoretical models. It is shown that the measured results for each arrangement obtained using this reciprocity method provide good agreement with conventional direct measurements and with theoretical modelling. However, in most of the examples presented, the direct method has been found to be less practical and sometimes even less accurate than the reciprocal one, mostly due to the structure-shaker connection and to the inherent uncertainty of acoustic intensity measurement

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

Noise and vibration

The public’s awareness of noise and vibration forms a significant barrier to further development of railways. This chapter begins with a short introduction to the main fundamental aspects of acoustics, including decibels, frequency analysis, the propagation of sound with distance and common measurement quantities. The main sources of railway noise are discussed, including rolling noise, impact noise, curve squeal and aerodynamic noise. Simple calculation procedures are described that can be used to assess the impact of railway noise and to compare it with legal limits. The final section is devoted to ground vibration, which is a related form of environmental disturbance

Rail vehicle dynamics

The vehicle–track interaction and the resulting dynamic response of the vehicle involve a number of complex wenonlinear problems. Large vertical loads act through a small contact patch leading to very high contact pressures. Transverse loads acting through this contact induce a relative velocity between wheel and rail expressed in non-dimensional form as a creepage. The wheel and rail profiles determine the contact patch shape and affect the ability of the vehicle to run stably. If the yaw stiffness of the axles is too low, the vehicle will become unstable at a relatively low speed; conversely, if the yaw stiffness is too high, the curving behaviour will be adversely affected. The vehicle suspension, especially the secondary suspension, also affects the ride comfort of passengers. Finally, it is shown how the speed profiles of accelerating and decelerating trains can be calculated from basic assumptions about the train power, adhesion and rolling resistance.</p