Local scour in the vicinity of bridge piers under ice-covered conditions - experimental study and numerical simulation

冰雪条件下桥墩附近局部冲刷试验研究与数值模拟

• 批准号: RGPIN-2014-05242
• 负责人: Sui, Jueyi
• 金额: $ 1.6万
• 依托单位: University of Northern British Columbia
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2014
• 资助国家: 加拿大
• 起止时间: 2014-01-01 至 2015-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=567039
• 关键词: Local; scour; vicinity; bridge; piers

Local scour in the vicinity of bridge piers has been identified as one issue with potentially catastrophic results. Excessive scour can cause bridge pier damage, which can result in bridge failure and may cause loss of life. The proposed research will address some important gaps in the scientific literature, such as (a) assessing local scour processes around bridge piers under ice cover, (b) establishing associated equations describing the dependence of scour processes on flow intensity, particle grain size and boundary conditions, (c) understanding how ice cover alters the geometry of scour holes and deposition mounds, (d) investigating the impacts of the dimension/shape of bridge piers on local scour processes under ice cover, and (e) developing a numerical model for simulating local scour processes around bridge piers under ice-covered conditions. Extensive experiments will be carried out in a flume which is 80-m long, 2-m wide and 1.3-m deep at the Quesnel River Research Center of the University of Northern British Columbia. An acoustic doppler velocimeter will be used to determine the flow field around bridge piers. Styrofoam sheets will be used as simulated ice cover (smooth, rough and very rough). Analyses of the experimental data collected from clear-water experiments under both open-flow and ice-covered conditions will be focused on non-dimensional variables, such as shear Reynolds number, Shields parameter, and bridge pier dimensions. Equations will be established to determine scour depth around bridge piers under ice-covered conditions. Modeling the scour process includes modeling a strongly coupled system involving flow field, sediment transport and bed morphology. In this proposed research, the numerical model will consist of three modules: a hydrodynamic module for the simulation of the flow field around a bridge pier, a sediment module for the modeling of suspended sediment transport, and a bed variation module to account for the change in the bed topography. Numerical studies of the local scour around bridge piers will also be undertaken in the present research. RANS models will be applied to simulate the flow field around bridge piers under ice-covered conditions. One of the priorities for the simulation of flow fields around bridge piers is to solve the vortex systems around the infrastructure. To solve the vortex systems, either unsteady RANS or Large Eddy Simulation (LES) will be used to resolve the horseshoe vortex. In this study, the standard k-epsilon turbulence model will be used first in the simulation for the flow field around a bridge pier under ice cover. The RNG-based k-epsilon turbulence model will also be used in the simulation. Suspended load and bed load will be simulated separately under both open-flow and ice-covered conditions. For suspended-load transport, based on the hypothesis that the interaction between different size fractions of suspended load is negligible (Wu et al. 2000), the transport will be governed by the universal advection-diffusion equation. For bed-load transport, the formula proposed by van Rijn (1987) will be used. In the event that van Rijn’s approach does not work, other approaches should be attempted such as Ashida-Michiue’s empirical formula. Once the suspended load and bed load is determined, the bed deformation can be calculated by applying the mass balance equation to the bed layer. The proposed research will help us to better understand local scour processes around bridge piers under ice cover. Results will provide civil engineers with reliable results regarding local scour around bridge piers that can be used to modify guidelines for bridge design considering the impact of ice cover.

桥墩附近的局部冲刷已被确定为可能造成灾难性后果的问题之一，过度冲刷可能会导致桥墩损坏，从而导致桥梁故障并可能导致人员伤亡。科学文献，例如（a）评估冰盖下桥墩周围的局部冲刷过程，（b）建立描述冲刷过程对水流强度、颗粒粒径和边界条件的依赖性的相关方程，（c）了解冰盖如何变化几何学冲孔和沉积丘的研究，(d) 研究桥墩尺寸/形状对冰盖下局部冲刷过程的影响，以及 (e) 开发数值模型，用于模拟冰盖条件下桥墩周围的局部冲刷过程大量实验将在北不列颠哥伦比亚大学克内尔河研究中心的一个长80米、宽2米、深1.3米的水槽中进行。速度计将用于确定桥墩周围的流场，并将用作模拟冰盖（光滑、粗糙和非常粗糙）的实验数据。覆盖条件将侧重于无量纲变量，例如剪力雷诺数、屏蔽参数和桥墩尺寸，将建立方程来确定冰覆盖条件下桥墩周围的冲刷深度。冲刷过程包括对涉及流场、沉积物输送和河床形态的强耦合系统进行建模。在本项研究中，数值模型将由三个模块组成：用于模拟桥墩周围流场的水动力模块、沉积物模块。本研究还将应用 RANS 模型来模拟悬浮泥沙输送，并采用河床变化模块来解释桥墩周围局部冲刷的数值研究。桥墩周围的田地桥墩周围流场模拟的首要任务之一是解决基础设施周围的涡系统，要解决涡系统，将使用非定常RANS或大涡模拟（LES）来解决。在本研究中，将首先使用标准 k-epsilon 湍流模型来模拟冰层下桥墩周围的流场。还将在模拟中使用悬载和床载，对于悬载运输，基于悬载不同大小部分之间的相互作用可以忽略不计的假设。 （Wu et al. 2000），输送将由通用平流扩散方程控制。对于床荷输送，将使用 van Rijn (1987) 提出的公式。 Rijn 的方法不起作用，应尝试其他方法，例如 Ashida-Michiue 的经验公式。一旦确定了悬浮载荷和床层载荷，就可以通过将质量平衡方程应用于床层来计算床层变形。帮助我们更好地了解冰盖下桥墩周围的局部冲刷过程，结果将为土木工程师提供有关桥墩周围局部冲刷的可​​靠结果，可用于修改考虑冰盖影响的桥梁设计指南。