基于MIKE21、HEC-RAS及经验公式的桥梁壅水模拟及对比分析

摘要:

本文以镇巴至广安高速公路渠县北互通立交连接线2号大桥为工程实例,借助于MIKE21 FM模型及HEC-RAS模型,通过进行数值模拟和对比分析,对河道内的涉水建筑物对河道防洪流态的影响进行了研究,分别计算不同洪水频率条件下,河道中建桥前后,桥墩对河道行洪的影响,并将两种数值模拟成果与理论经验公式计算成果进行比较。通过计算比较分析,采用MIKE21 FM模型计算时,建桥后桥位上游水位壅高,流向变化较小,而流速增加值与流量成负相关；采用HEC-RAS模型计算时,水位壅高值小于MIKE21 FM模型,且无法分析整个流场的数值变化。在河道地形复杂或是所在河道防洪标准较高时,建议采用MIKE21 FM模型,并可采用HRC—RAS模型作为验证。经验公式与模型计算成果差距较大,陆浩公式计算得到的壅高值偏大,D’Aubuisson公式偏小。本研究可为实际桥梁工程设计及河道沿岸洪泛区防洪提供指导或参考作用。

Abstract:

With the aid of MIKE21 FM and HEC-RAS numerical model, this paper took the 2nd Bridge of Quxian North Interchange Connecting Line of Zhenba-Guangan Freeway as an example to analyse the influence on flood flow condition made by hydraulic engineering. Under circumstance of different flood frequencies, impact caused by piers was calculated by simulations and the numerical results were comparatively analysed with calculations of Theoretical experience formulas. Several conclusions could be drawn from the comparative analysis: based on the MIKE21 FM model, after the construction of bridge, water levels grew higher, flow directions varied little, and velocity increments were inverse ratio with river discharges; based on the HEC-RAS model which couldn’t simulate the whole flow field, the water level increments were less than the MIKE21 FM. Consequently, in condition of complex river topography or higher flood control standard, the MIKE21 FM model was recommended and the HEC-RAS model could be adopted as a validation. There was remarkable discrepancy between the theoretical experience formula results and simulations, where the Lu Hao formula results were higher and the D’Aubuisson formula results were lower than the simulations. In conclusion, This research could have a directive or referenced function for the practical bridge designs and the flood prevention along the inundation areas.