Railway systems presently under consideration are intended to employ higher speeds than systems in operation today. In these systems, undesirable waves are generated when the front and rear of a train enter and leave a tunnel. For example, nose entry causes a compression wave to pass along the tunnel and the rate of change of pressure at the wavefront is so large that it is sufficient to regard it as a step-wavefront. This disturbance moves along the tunnel at approximately sonic speed, reflects and discharges at the exit portal. One can easily understand that this sort of noise due to a discharge wave from the exit portal is similar to the blast pressure emerging from a gun muzzle or from a rocket venture and the exhaust noise of an internal combustion engine. However, the magnitude of the pressure level is generally large compared with those of blast overpressure and exhaust noise. Practical means of reducing the noise have not yet been suggested, although many passive controls, such as perforated and flared tube extensions, slotted tunnel portals and so on have been presented so far. In this case, an active noise cancellation, which is the cancelling of noise by the addition of an inverse wave, seems to be a useful technique for reducing impulsive noise. It is the main objective of the study to present the design for a negative impulse wave generator utilizing unsteady mass influx. In the research reported to, in order to clarify the relationship between the unsteady mass influx and the negative impulsive wave, numerical and aeroacustical analyses and experimental investigations were carried out using a shock tube.
A study of a negative impulse wave generator
Negativer Impulswellengenerator zur aktiven Schallauslöschung am Ausgang von Eisenbahntunneln
Journal of Sound and Vibration ; 197 , 5 ; 573-587
1996
15 Seiten, 19 Bilder, 24 Quellen
Article (Journal)
English
A study of a negative impulsive wave generator
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