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  A Numerical Study on the Pressure Relief by a Vertical Shaft in a Tunnel

  Many countries have planned high-speed railways in order to shorten time to transport passengers and commodities. Many European countries and Japan have a state art of technologies of high-speed railways [1]. These days, United States and China have started numerous researches and planned a lot of high-speed railway transportation systems [2] [3]. South Korea is also planning and constructing many high-speed railways [4]. In order to construct a high-speed railway, it is required to optimize the shape of a train and develop many kinds of related infrastructures for high-speed railway. In addition, route ways should be as straight as possible because of the speed of high-speed trains [5]. Therefore, there are many tunnels and bridges in the routeway of a high-speed railway. Most high-speed trains have a nose of streamlined shape to minimize air pressure created in front of a tunnel head during drive. The shape of a train head is designed considering air drag coefficient but the distribution of air pressure around a train is very complicated [6]. Especially, when a train passes through a tunnel which has a very small cross-sectional area, the distribution of air pressure around a train becomes much more complicated [7]. Various problems such as ear discomfort and micro pressure wave can be caused because of a high-speed train entering a tunnel. Improving the air-tightness of a train can relieve ear discomfort caused by a train that is passing through a tunnel [8]. Ear discomfort can be relieved by improving the air-tightness of a train because it has close relationship with the tightness of a train [9]. Micro pressure wave generated inside a tunnel travels through the tunnel with speed of sound and the pressure is reflected when it meets the stationary air outside the tunnel. Partial pressure from reflected micro wave pressure is discharged from a tunnel and released outside the tunnel with low frequency [10]. The other micro wave pressure reflected into the tunnel is overlapped with other pressure waves created from a running train and very complex pressure changes in the tunnel happens. Micro pressure wave is very closely related to various aspects of tunnel and the shape of a train, so it is difficult to resolve problems caused by micro pressure wave. There have been lots of profound researches to solve these problems. Pressure change between outside and inside of a tunnel was analyzed by experimental testing [11]. Similar studies were conducted using numerical analysis in order to investigate the effect of air pressure changes through a tunnel [12]. Kikuchi proposed a solution to reduce micro pressure wave and pressure changes through a tunnel [13]. He represented various solutions to alleviate these pressure changes with modifying the shape of tunnel portals. In this study, a numerical analysis was carried out in order to investigate the effect of a vertical shaft on alleviating air pressure in a tunnel. Additionally, a methodology of reliable numerical analysis is proposed.

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