Model experiments on area optimization of multiple openings of tunnel hoods to reduce micro-pressure waves

•Area optimization of windows of hoods for reducing micro-pressure waves was investigated.•Performance of the area optimization is almost the same as that of typical pattern optimization.•Area optimization converges within a few iterations.•Robustness to change of train speed is confirmed for area optimization. Optimization of tunnel hood openings is one of the most important technologies that has been developed to effectively reduce micro-pressure waves (MPWs) on high-speed railway lines. Two types of optimization techniques exist: “pattern optimization,” where the location of open windows is optimized, and “area optimization,” where the area distribution of windows is optimized. This paper presents an evaluation of the zeroth-order area optimization of multiple openings uniformly spaced of tunnel hoods for reducing MPWs. In the zeroth-order area distribution, all openings are assumed to have the same area. Model experiments were conducted using a train launcher facility, and the performances of the two types of optimizations were compared. The objective function to be minimized was the maximum value of the pressure gradient of a tunnel compression wave ∂p/∂tmax. The objective function was shown to be unimodal and can be easily optimized because the peak values of the pressure gradient either linearly increase or decrease with the area of the openings, specifically for typical Japanese hoods. This linear relationship between the peak values and area was demonstrated via theoretical and experimental analysis. The minimized values of ∂p/∂tmax for area optimization were almost the same as those for pattern optimization. The advantage of area optimization is that the optimization procedure ensures automated convergence within a small number of iterations based on the linear relationship.