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: 2016
• 资助国家: 加拿大
• 起止时间: 2016-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=611521
• 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.

在桥墩附近的局部冲刷已被确定为潜在灾难性结果的一个问题。过度的冲刷会造成桥梁的损坏，这可能导致桥梁故障并可能导致生命损失。 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覆盖，（e）开发一个数值模型，用于在冰覆盖的条件下模拟桥墩周围的本地冲刷过程。 在不列颠哥伦比亚省北部的Quesnel River Research Center中，将进行广泛的实验，该水槽长80米，宽2米，深1.3米。声学多普勒速度计将用于确定桥墩周围的流场。聚苯乙烯泡沫塑料板将用作模拟冰盖（光滑，粗糙和非常粗糙）。从开放流和冰覆盖的条件下从透明水实验中收集的实验数据的分析将集中在非二维变量上，例如剪切雷诺数，Shields参数和桥梁码头尺寸。将建立方程式以确定在冰覆盖的条件下桥梁周围的冲刷深度。 建模冲洗过程包括对涉及流场，沉积物传输和床形态的强耦合系统进行建模。在这项拟议的研究中，数值模型将由三个模块组成：用于模拟桥梁码头周围流场的流体动力模块，用于建模悬挂沉积物传输的沉积物模块以及一个床变化模块，以说明床地图的变化。 本研究还将对桥墩周围的当地冲刷进行数值研究。将应用兰斯模型来模拟在冰覆盖的条件下桥梁周围的流场。模拟桥墩周围流场的优先事项之一是解决基础架构周围的涡流系统。为了解决涡流系统，将使用Unsteady Rans或大型涡流模拟（LES）来解决Hornshoe涡流。这项研究，标准的K-Epsilon湍流模型将首先在冰盖下的桥码头周围的流场的模拟中使用。基于RNG的K-Epsilon湍流模型也将用于模拟中。 悬浮的负载和床负荷将在开放流和冰覆盖的条件下分别模拟。对于悬挂负载的运输，基于以下假设：悬浮负载的不同大小分数之间的相互作用可以忽略不计（Wu等，2000），运输将由通用的广告扩散方程支配。对于床负载的运输，将使用Van Rijn（1987）提出的公式。如果Van Rijn的方法不起作用，则应尝试采用其他方法，例如Ashida-Michiue的经验公式。一旦确定了悬浮的负载和床负荷，就可以通过将质量平衡方程式应用于床层来计算床变形。 拟议的研究将帮助我们更好地了解冰盖下的桥墩周围的当地冲刷过程。结果将为土木工程师在桥墩周围的本地冲刷中提供可靠的结果，这些结果可用于修改桥梁设计的指南，以考虑冰盖的影响。