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  Optimization of Tunnel Portal shape for Pressure variation and Micro-pressure wave reduction

  When a train enters a tunnel at high-speed, a micro-pressure wave generates at a tunnel exit and air pressure in a tunnel changes largely and rapidly. This paper shows optimization process of tunnel portals to reduce both a micro-pressure wave and large pressure variation simultaneously. Firstly, the length and the radius of a hood are considered as design variables and the aerodynamic interactions between a train and a tunnel is simulated with an axi-symmetric numerical analysis. An approximation model with an artificial neural network is applied to find the length and the radius of a hood for the minimum micro-pressure wave. Secondly, the length of a dummy tunnel duct is defined to minimize the pressure variation using the superposition between a compression wave and an expansion wave. In order to show an effect on the reduction of a micro-pressure wave and pressure variation, a portal shape of a 570m long tunnel is optimized. Micro-pressure wave and pressure variation can be reduced by about 73 % and 74% respectively, when the tunnel has just about 26m long and 1.6times bigger radius of a hood than an equivalence radius of a tunnel with about 35m long dummy tunnel duct at each tunnel portal.

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