Once a dam-break incident occurs in cascade reservoirs, it may lead to continuous dam-break in downstream cascade reservoirs. Clarifying the evolution law of dam-break flood in the downstream reservoir area is the basis for revealing the peak discharge enhancement mechanisms of cascade dam-break flood, but it has not been extensively studied. In this study, based on the Eulerian-Lagrangian theory, a model coupling computational fluid dynamics (CFD) and discrete element method (DEM) was established, considering the sediment concentration of dam-break flood, and it was verified that the model can accurately simulate the motion law of fluid phase and particle phase in dam-break flood through the benchmarking tests and existing experimental data. It was then applied to simulate the effects of different flood sediment concentration, upstream and downstream water levels, dam-dam spacing, and upstream slope ratio of the earth-rock dam on the evolution process of dam-break flood in the downstream reservoir area. The evolution law of upstream dam-break flood in the downstream reservoir area was revealed from the perspectives of wave climbing height and dam surface pressure. The results showed that compared with not considering the sediment concentration, when the sediment concentration of the dam-break flood was 40%, the maximum climbing height increased by 33.2%, and the peak pressure on the dam surface increased by 41.8%. The main reason was that the increase in sediment particle content improves the viscosity and density of flood. In addition, three typical flood evolution patterns were observed for different upstream and downstream water levels: climbing, leaping, and pushing patterns. In the climbing and leaping patterns, the impact pressure generated by the dam-break flood on the upstream dam heel of the earth-rock dam cannot be ignored. In the pushing pattern, the impact force of the dam-break flood has little effect on the dam surface pressure, but the climbing height at the dam crest increases significantly. The sediment concentration and upstream and downstream water levels were the key factors affecting the evolution law of dam-break flood, while the dam-dam spacing and the upstream slope ratio of the earth-rock dam has little effect.

中文翻译：

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基于CFD-DEM耦合的下游土石坝库区梯级溃坝洪水演化过程数值研究

一旦梯级水库发生溃坝事件，可能会导致下游梯级水库连续溃坝。明确下游库区溃坝洪水演化规律是揭示梯级溃坝洪水增洪机制的基础，但尚未得到广泛研究。本研究基于欧拉-拉格朗日理论，考虑溃坝洪水泥沙浓度，建立了计算流体力学（CFD）与离散元法（DEM）耦合的模型，并验证了该模型能够准确地预测溃坝洪水的泥沙浓度。通过基准测试和现有实验数据，模拟溃坝洪水中流体相和颗粒相的运动规律。模拟土石坝不同洪水含沙量、上下游水位、坝距、上游坡比等对下游库区溃坝洪水演化过程的影响。从波浪爬高高度和坝面压力的角度揭示了下游库区上游溃坝洪水的演化规律。结果表明，与不考虑含沙量相比，当溃坝洪水含沙量为40%时，最大爬高高度增加33.2%，坝面峰值压力增加41.8%。主要原因是泥沙颗粒含量的增加提高了洪水的粘度和密度。此外，针对上下游不同水位，观察到三种典型的洪水演化模式：爬升型、跳跃型和推挤型。在爬跃形态中，溃坝洪水对土石坝上游坝踵产生的冲击压力不可忽视。在推挤模式下，溃坝洪水的冲击力对坝面压力影响不大，但坝顶爬升高度显着增加。泥沙浓度和上下游水位是影响溃坝洪水演化规律的关键因素，而坝坝间距和土石坝上游坡比影响不大。