Field measurement and numerical simulation were performed on the distortion of the compression wave generated by train entry and propagating through a slab track Shinkansen tunnel, which is the longest mountain tunnel in the world as of 2004. The compression wave was measured at twelve different locations. In the numerical simulation, the distortion of the compression waveform were calculated by one-dimensional compressible flow analysis, which takes account of steady and unsteady friction, combined with acoustic analysis on the effect of side branches in the tunnel. The results of numerical simulation are consistent with those of the field measurement. Furthermore, the results indicate that the compression wavefront steepens in the early stage and smoothes down in the later stage of propagation, and the maximum value of the pressure gradient of the compression wavefront reaches a peak under certain conditions of the initial compression wave and a tunnel length.
In order to determine the actual circumstances of wayside low-frequency noise and infrasound generated by high-speed trains (Shinkansen), field measurements were performed at two sites, one near a tunnel portal and the other in a fully open section. The measurements were based upon the manual issued by the Ministry of the Environment of Japan in October 2000 and conducted to obtain G-weighted SPL, 1/3-octave band spectra, velocity dependence and distance attenuation of SPL. The measured results show that major components of the low-frequency noise from the tunnel portal are impulsive micro-pressure waves and continuous pressure waves, while those in the open section are near-field hydrodynamic pressure variations and far-field acoustic pressure waves.
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