On the infrasound generated when a train enters a tunnel

摘要

An analysis is made of the 'open air infrasound' generated when a train enters a tunnel. For a tunnel of nominal radius R and train speed U the acoustic frequency ～U/R and wavelength ～R/M R, where M is the train Mach number. Infrasound is inaudible, hut the pressure fluctuations generated by a high-speed train (M>0.2) can cause annoying vibrations and rattles' in dwellings and other buildings close to a tunnel portal. Detailed calculations are presented in this paper for a hood-like' portal modelled analytically by the end of a circular cylindrical, thin-walled duct, and for an axisymmetric train' entering along the axis of the duct. A slender body approximation is used to model the influence of the moving train, and the acoustic problem is solved using the exact Green's function for a semi-infinite cylinder. Predictions are in good agreement with recent track-side measurements reported by Iida et al. (Proceedings of the 50th Japan National Congress on Theoretical and Applied Mechanics) for model scale experiments conducted at Mach numbers M as large as 0.33. However, both measurements and theory indicate that in applications at full scale it may be important to include in estimates of the infrasound the nonacoustic 'near-field' pressures produced by the passing train.