This paper describes the propagation of pressure waves in single or ramified tunnels. We use an unsteady one-dimensional model to describe the generated flow in this situation. This model takes into account the geometry of the train and tunnel, and also the compressibility effects. It is solved by the method of characteristics. The flow in the vicinity of train and tunnel ends or the tunnels junctions, is three-dimensional and must be considered as a boundary condition when using a one-dimensional model. So we introduce pressure loss coefficients in order to take into consideration three-dimensional effects.
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