Passive Control of Micro-Pressure Wave from High-Speed Railway Tunnel

靠近隧道出口入口的简单膨胀室可以显著降低在隧道外传播的微压力波的振幅。这种腔室的最佳形状取决于反射波前的陡峭度。在最陡的波前，实现了最大的百分比降低。当入射波前的陡度范围被期望时，腔室的形状应该针对被认为是可行的最陡度的情况进行优化。这将在最需要的时候提供最大的好处。在大多数情况下，这种形状也会表现得很好，即使不太陡峭的波前。对于任何特定的入射波前陡度，腔室的最佳形状取决于腔室的大小。然而，对于此处最相关的陡峭波前，相关性并不强。通常，设计良好的具有单位体积隧道的腔室可以使微压力波的大小减小30%左右。这是由于其他修改（例如在隧道入口）而减少的。

Simple expansion chambers close to a tunnel exit portal can cause significant reductions in the amplitudes of micro-pressure waves propagating outside the tunnel.1. The optimum shape of such chambers depends upon the steepness of the reflecting wavefront. Greatest percentage reductions are achieved for the steepest wavefronts.2. When a range of steepnesses of incident wavefronts is expected, the chamber shape should be optimized for the steepest case that is considered feasible. This will provide greatest benefit when it is most needed. In most cases, this shape will also perform well with less steep wavefronts even though it is not optimum.3. For any particular incident wavefront steepness, the optimum shape of the chambers is dependent on the chamber size. For the steep wavefronts of greatest relevance herein, however, the dependence is not strong.4. Typically, a well-designed chamber with a unit volume of tunnel may cause a reduction of about 30% in the magnitudes of micro-pressure waves. This is in addition to reductions resulting from other modifications (e.g., at the tunnel entry).