A New Simple Equation Governing Distortion of Compression Wave Propagating Through Shinkansen Tunnel with Slab Tracks

Abstract

A high-speed train entering a tunnel generates a compression wave that propagates through the tunnel toward its exit. When the compression wave reaches the tunnel exit, a pressure pulse causing environmental problems (the micro-pressure wave) is radiated from the exit portal. The magnitude of the micro-pressure wave is approximately proportional to the maximum pressure gradient of the compression wave arriving at the tunnel exit. In a long Shinkansen tunnel with concrete slab tracks the compression wavefront steepens due to the nonlinear effect during its propagation because the whole surfaces of the tunnel being smooth. Hence, it is necessary to investigate the distortion of the compression wave in a tunnel and clarify the characteristics of compression wave propagation for estimating and reducing the micro-pressure wave. In this paper, we introduce a new simple equation governing the distortion of the compression wave propagating through a Shinkansen tunnel with concrete slab-tracks and propose a new simple scheme for a numerical calculation. A space evolution type equation with one variable is derived from the three conservation equations (mass, momentum, and energy including the wall friction and heat transfer terms) of the 1D CFD by assuming small disturbances excited by the compression wave. The numerical calculation scheme based on the simple equation remarkably reduces the computing time because its CFL condition is relaxed. The calculation results by the present scheme agree well with those by a conventional scheme based on the 1D CFD and the accuracy of the simple equation is verified.