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Attempts are being made to coordinate theory and design by means of reduction theory and nose shape numerical simulation in respect to micro-pressure waves, which constitute an environmental problem when a train enters a tunnel.

Nose shape optimization theory

Pressure waves generated when a high-speed train enters a tunnel turn into compressive waves shaped like shock waves as they are transmitted through the tunnel. When emitted from the outlet side, these are felt as explosive sounds. This is what we refer to as micro-pressure waves. One effective way of reducing micro-pressure waves is to even out the increasing rate of the cross section are of the nose section. A single-stage paraboloid of revolution is one way in which this can be done. However, previous studies have shown that the increasing rate of the central area of the nose has a considerable effect on the size of micro-pressure waves, and we have been able to come up with a three-stage paraboloid of revolution theory to create a practically realizable form.

Diagram of 3-stage paraboloid of revolution theory

Three-dimensional compressive fluid computation using unstructured grid
In order to discover the performance of micro-pressure waves, we have recourse to non-structural lattice three-dimensional compressive fluid analysis using unstructured grid. This method of analysis is characterized by the way in which it enables us to make models consisting of (1) compound lattices permitting superimposition of static and moving lattices and (2) complicated shapes consisting of combinations of tetrahedrons, triangular columns and square conical elements. Large-scale numerical simulation to the order of several million with element numbers is being carried out with the Hitachi SR8000 ultra high-speed parallel digital computer.

Image of example of unstructured grid on analysis of micro-pressure wave