The Incentive Of The Wheel-rail Subway Truck Exterior Noise Prediction Theory

The noise property of subway train is an important quality index,its acoustical comfortableness is the essential factor that must be checked on. To forecast the exterior noise problem of train head under track excitement, in this paper the following aspects were thoroughly researched.Taken train head carriage,bogies and wheel sets as rigid ones,rail is handled as infinite long Timoshenko beam supported by dispersed sleepers, the coupling dynamics model of vehicle-track of subway has been established.The vehicle vibration was calculated caused by track irregularities,and three dimensional spatial vibration loads have been obtained at contact points between secondary air spring and car body,the conclusions were reached as follows:the vertical and lateral vibration amplitudes are greater,and the longitudinal ones are less.The longitudinal stiffness of the first suspension has much effect on steady coefficient,it is advisable for the stiffness to be taken as 5 MN/m.The lateral stiffness of the first suspension has little effect on train operation steadiness,but has great effect on derailment coefficient,it is advisable for the lateral stiffness to be taken as 4 MN/m.By harmonic analysis,vibration displacement of train panel was obtained,which was the excitement condition of sound field calculation, exterior sound pressures of train head were solved at different frequency,and sound pressure level was obtained outside train head.Outside cab,the maximal sound pressure level(SPL)is 61.5207dBA,the sound field point with maximal SPL is 7.5 m away from rail central line,1.2 m away from vehicle base,2.6 m away from the back panel of cab.At frequency 30 Hz, the noise contribution of the back panel of cab is the greatest for the point, whose acoustical contribution coefficient is 47.3%.At frequency 200 Hz,the noise contribution of the curved surface of train head is the greatest for the point,whose acoustical contribution coefficient is 87.6%.Outside passenger room,the maximal sound pressure level(SPL)is 60.91dBA,the sound field point with maximal SPL is 7.5 m away from rail central line,1.2 m away from vehicle base,3.9 m away from the back panel of passenger room.At frequency 30 Hz,the noise contribution of the back panel of passenger room is the greatest for the point,whose acoustical contribution coefficient is 76.9%.At frequency 200 Hz,the noise contribution of the fifth panel of top panel is the greatest,whose acoustical contribution coefficient is 47.19%.When the train runs with the speed of 60 km/h,the major noise radiated from wheel-rail is at the frequency of 500 Hz～4000 Hz;The major noise radiated from rail is at the frequency of 500 Hz～4000 Hz;The major noise radiated from wheel is at the frequency of 1250～4000 Hz.As for the contribution to total noise,rail is dominate,wheel is minor.The sound pressure level radiated from rail-wheel,rail,wheel,is 85 dBA,81 dBA,86 dBA,separately.The SPL radiated from rail is 4 dBA greater than that radiated from wheel,the contribution to total sound press of rail and wheel are 87.5%and 12.5%,separately.It is difficult to get ideal effect through improving wheel structure to reduce rail-wheel noise.In order to reduce the outside noise of head train to 80 dBA,measures must be taken to reduce roughness of rail and wheel surface.