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Railway noise. Gijsjan van Blokland M+P Ard Kuijpers M+P sources: Müller-BBM (D), D. Thompson (GB), M.Dittrich (TNO) . topics. Relevance Sources Rolling noise Propulsion noise Aero dynamic noise Model of generation process of rolling noise Force generation in wheel/rail contact
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Railway noise Gijsjan van Blokland M+P Ard Kuijpers M+P sources: Müller-BBM (D), D. Thompson (GB), M.Dittrich (TNO)
topics • Relevance • Sources • Rolling noise • Propulsion noise • Aero dynamic noise • Model of generation process of rolling noise • Force generation in wheel/rail contact • Vibrational response of wheel and of rail • Effect of parameter changes in wheel system and rail system • Mitigation measures • Special constructions • Curve squeal • Generation process • Mitigation measures
Sources of railway noise (I) Areo-dynamic Propulsion system Rolling wheel/rail system
Bronnen en snelheid (II) aerodynamisch rolgeluid geluidniveau rolgeluid bijafscherming >350 km/h snelheid
Cast iron blocks lead to significant roughness of the wheel rolling surface due to local high temperatures during braking Disc brakes causes no roughness build-up Disc + blocks is the worst combination Replacing cast iron blocks with composite blocks improves noise characteristics Effect of braking system on wheel roughness and sound production Wavelength translated to frequency: f=v/λ
Rail surface is not completely flat, rail roughness increases by use Cause not fully understood Worst situation is periodic irregularity with a 4 cm wavelength f=v/λ: 4 cm at 40 m/s equals 1 kHz level of rail roughness
Wheel/rail force reception: mobility (velocity/force)wheel: modal systemrail: no boundery, regular support by sleepers
Calculated using FEM Showing exaggerated cross-section deformation of each mode Wheel: modes of vibration
Rail pad defines coupling between rail and sleeper • high stiffness pad strong coupling good energy transfer from (low damped) rail to (high damped) sleepers
Rail noise level difference (dB) Increased stiffnes baseplate pad Effect of pad stiffnes on vibration and noise level
Rail cross-section deformations - only relevant at higher frequencies- not relevant for total dB(A) level
Speed related wheel and rail contribution total rail Noise level wheel speed
Rail grinding • Reduces rail rougnes • Regular grinding: longer wavelengths • Acoustic grinding: 1mm – 63cm • Acoustic effect: 2-4 dB(A) • Effect depending on wheel rougness
Skirts (vehicle mounted barriers) • Only effective in combination with track mounted barriers
Mini barriers • mecahnism: • Mainly sheilding of rail radiation • Added absorption is essential (to prevent multiple reflections) • effect: 5 dB(A) for rail contribution
Results Metarail Project Influence on Noise
Rotterdam Köln 490 km Bettembourg 1177 km Basel Lyon Milano Total line length: 1667 km Cost-benefit study of mitigation measures Calculate costs & benefits for different noise control strategies. Strategies consist of combinations of noise control measures. Two major freight freeways chosen for study.
Instruments for strategic noise abatementCost-Benefit Analysis max. 4 m barriers track system improvement max. 2 m barriers Scenarios of Noise reduction due to rolling stock improvement - 10 dB - 5 dB none rolling stock improvement only
Non-standard rail construction (slab track) Preferred construction for high speed lines in Germany and Netherlands Stable system , even at soft soil Low maintenance High initial costs
Types of track construction • Elasticity in track system is essential to prevent cracks in rail Conventional ballast track Flexible mounted sleepers in concrete slab Rigid mounted sleeper in concrete slab Rail directly mounted in slab
Slab tracks are more noisy then conventional ballast tracks. Why? • Less tight rail to sleeper connection less damping • No acoustic absorption from ballast • Total effect +2 tot +5 dB(A