Nondimensional maximum pressure gradient of tunnel compression waves generated by offset running axisymmetric trains

A high-speed train entering a tunnel generates a compression wave in the tunnel and a micro-pressure wave. The magnitude of the micro-pressure wave is approximately proportional to the maximum pressure gradient of the compression wave (∂p/∂t)max. High-speed railway operations require the consideration of the nose shape of the train in order to reduce (∂p/∂t)max generated by a train entering a tunnel. In this study, the compression waves generated by axisymmetric trains running at the offset position in double-track tunnels were investigated using a train launcher facility. Paraboloids of revolution, ellipsoids of revolution, and cones were used as the simplest nose shapes. The cone-nose train generated the largest value of (∂p/∂t)max, and the paraboloid-nose train generated the smallest value of (∂p/∂t)max among the three nose shapes. Although this tendency is the same as that for center running, the ratio of (∂p/∂t)max for the cone-nose train to that for the paraboloid-nose train became larger for offset running than center running. Moreover, the maximum value for the generation time of the compression wave was derived from acoustic theory, and the nondimensionalization of (∂p/∂t)max considering the nose length was proposed using it. Since the inverse of the nondimensionalized (∂p/∂t)max denotes the ratio of the generation time of the compression wave to its maximum value, it was defined as the efficiency of a train nose in the range of zero to unity. The values of the efficiency were almost constant with the nose length and 0.7, 0.6, and 0.5 for paraboloid-, ellipsoid-, and cone-nose shapes, respectively.