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To investigate the characteristics of the initial compression wave associated with tunnel sonic boom in long high-speed railway tunnels and analyze its correlation with the occurrence of tunnel sonic boom, full-scale tests were carried out in a long tunnel. Taking the formation mechanism of tunnel sonic boom and the propagation path of the initial compression wave as the starting point, the longitudinal distributions of the aerodynamic pressure and pressure-gradient peak of the initial compression wave inside the tunnel before and after the occurrence of sonic boom were comparatively analyzed. The influence of train speed on these peak values during sonic boom occurrence was clarified, and the effects of portal hood configuration and train type on tunnel sonic boom were discussed. The results show that, under the action of nonlinear effects, the initial compression wave is progressively steepened during propagation, thereby inducing tunnel sonic boom. For the tested tunnel, regardless of whether sonic boom occurs, the aerodynamic pressure peak of the initial compression wave along the tunnel longitudinal direction first increases and then decreases. When sonic boom occurs, the pressure peak of the initial compression wave near the train exit end is higher than that near the entry end. Taking a train speed of 340 km · h-1 as an example, the positive peak, negative peak, and peak-to-peak value of the aerodynamic pressure of the initial compression wave at the measurement point near the exit end increase by 36.53%, 11.22%, and 20.71%, respectively, compared with those near the entry end. With increasing speed, the probability of tunnel sonic boom increases, and the variation rate of the aerodynamic pressure peak of the initial compression wave from the train entry end to the middle section of the tunnel is higher than that at lower speeds. When sonic boom occurs, the pressure-gradient peak of the initial compression wave increases sharply after propagating a certain distance, and the increase near the train exit end is significantly greater than that near the entry end; at 340 km · h-1, the difference between the two reaches nearly ninefold in the tested tunnel. When sonic boom occurs, the pressure-gradient peak inside the tested tunnel is proportional to the train speed raised to the power of 6.5-9.6, whereas when sonic boom does not occur, it is proportional to the train speed raised to the power of 3.5-4.6. In addition, compared with the recessed portal hood, the oblique portal hood is more effective in mitigating the occurrence of tunnel sonic boom.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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