Collaborative Research: Physics-Based Modeling of Bridge Foundation Scour: Numerical Simulations and Experiments

该项目由NSF和陆军研究办公室（ARO）共同资助，旨在开发和验证第一个能够准确再现桥梁基础冲刷的三维非稳态数值模型。这项工作的基本前提是，波动的水动力，由于基础引起的非定常相干涡驱动泥沙输移和冲刷，需要正确建模。现有的方法是无法捕捉固有的不稳定的物理问题，因为它们要么依赖于定性描述，经验相关性或采用统计稳定的计算模型。为了克服这些缺点，在圣安东尼福尔斯实验室（SAFL）、弗吉尼亚理工大学（VT）和美国陆军工程兵团（USACE）WES设施之间建立了研究伙伴关系。其目的是将三维相干结构解析湍流结流数值模拟的最新发展与最先进的实验室能力和仪器相结合，从而可以同时测量瞬时流量和压力以及冲刷坑的相应空间和时间发展。一个新的欧拉模型的推移质输运将开发，采用拉格朗日的想法来考虑到近床波动水动力的影响到Exner的方程。 初步工作表明，该模型能够再现冲刷坑的高度动态演变，包括复杂底形的形成。 本项目将完成以下任务：a）水动力模型的实验验证，B）在桥墩直径、沉积物尺寸和水流特性的大范围内，同时监测水流结构和冲刷坑演变、桥墩和沉积物颗粒上的瞬时压力的实验，其中一些实验代表了近原型条件，以及c）进一步发展和验证新的非恒定推移质输移模型。实验室实验将在13个基于桥墩直径的雷诺数（范围从4x104到6.7x105）下进行，而数值模型将探索这些以及更宽范围的雷诺数。 该项目将通过合作努力，推进能够在实际水流条件下预测冲刷的计算模型的开发，并推进我们对这一现象的认识和理解，包括尺度效应。 该项目的成果将通过提供一个强大的计算工具来造福社会，该工具可用于研究和制定桥梁冲刷问题的缓解策略，这导致了比近代历史上所有其他原因更多的桥梁故障，并有可能严重损害国家的交通基础设施。 数值模型也将大大提高我们的研究基础设施，提供了一个工具，可用于解决广泛的流恢复问题。 在这方面，该模型可以应用于制定改进的标准流恢复研究，占周围的巨石和其他障碍物的流动结构影响流栖息地的质量。 这项工作的潜在影响流恢复和推广活动将大大促进通过跨学科的互动与美国国家科学基金会国家中心地球表面动力学设在SAFL。

This project is jointly funded by NSF and the Army Research Office (ARO) and seeks to develop and validate the first 3D, unsteady, numerical model capable of accurately reproducing bridge foundation scour. The basic premise of this work is that fluctuating hydrodynamic forces due to the foundation-induced unsteady coherent vortices drive sediment transport and scour and need to be modeled correctly. Available methods are incapable of capturing the inherently unsteady physics of the problem as they either rely on qualitative descriptions, empirical correlations or employ statistically stationary computational models. To overcome these shortcomings, a research partnership is established among St. Anthony Falls Laboratory (SAFL), Virginia Tech (VT), and the US Army Corps of Engineers (USACE) WES facility. The objective is to integrate the latest developments in 3D coherent-structure resolving numerical modeling of turbulent junction flows with state-of-the-art laboratory capabilities and instrumentation, which permit simultaneous measurements of instantaneous flow quantities and pressures with the corresponding spatial and temporal development of the scour hole. A novel Eulerian model of bedload transport will be developed, which employs Lagrangian ideas to account for the effect of near-bed fluctuating hydrodynamic forces into Exner's equation. Preliminary work has demonstrated the ability of this model to reproduce the highly dynamic evolution of the scour hole including the formation of complex bedforms. The following tasks will be accomplished in this project: a) experimental validation of the hydrodynamic model, b) experiments for monitoring the flow structures simultaneously with the scour hole evolution, instantaneous pressures on the pier and on sediment particles over a wide range of pier diameters, sediment sizes, and flow characteristics, with some of them representative of near-prototype conditions, and c) further development and validation of the new unsteady model of bedload transport. The laboratory experiments will be carried out at thirteen pier-diameter based Reynolds numbers (ranging from 4x104 to 6.7x105), while the numerical model will explore these as well as a wider range of Reynolds numbers. This project will advance, in a collaborative effort, the development of a computational model capable of scour prediction in practical flow conditions, as well as advance our knowledge and understanding of the phenomenon, including upscaling effects. The outcomes of the project will benefit society by providing a powerful computational tool that can be used to study and develop mitigation strategies for the bridge scour problem, which has resulted in more bridge failures than all other causes in recent history and has the potential to seriously impair the nation's transportation infrastructure. The numerical model will also enhance significantly our research infrastructure by providing a tool that can be used to tackle a wide range of stream restoration problems. In this regard the model can be applied to develop improved criteria for stream restoration studies that account for the flow structures around boulders and other obstructions affecting stream habitat quality. The potential impact of this work to stream restoration and outreach activities will be greatly facilitated through cross-disciplinary interactions with the NSF National Center for Earth Surface Dynamics housed at SAFL.