The compression wave generated when a high-speed train enters a tunnel at Mach numbers smaller than 0.4 can be described in good approximation by a linear theory of a inviscid compressible fluid. The wave equation for the acoustic potential becomes the governing equation. It is solved by a three dimensional boundary element method in time domain which forces a vanishing normal component of the velocity at the tunnel wall. It is assumed that the elements are compact in time. This leads to a linear equation in which a special matrix-vector multiplication has to be evaluated for every time-step. The aim is to create a fast method which sets as few constraints on the geometry as possible while still beeing accurate enough to be used as a first estimate of the occuring wave propagation. In a first step the elements are assumed to be rectangles and a cylinder of finite length with infinitely thin walls is taken as the geometry of the tunnel. The train is modeled by a single moving mass source of monopole type. It defines a semi-infinite body whose shape slightly changes when entering the tunnel. The results of this simple model along with the comparison with analytical solutions and experimental data are shown and discussed.
Keywords
- Linear Theory
- Boundary Element Method
- Compression Wave
- Pressure Amplitude
- Tunnel Wall
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