Bridge Hydraulics Analysis using Computational Fluid Dynamics
The flow field around an inundated bridge deck based on the hydraulics experiments conducted at the Turner-Fairbank Highway Research Center
The flow field around an inundated bridge deck based on the hydraulics experiments conducted at the Turner-Fairbank Highway Research Center
Bridges are the critical components of our nation’s transportation network. Evaluation of bridge stability after flooding events, including the integrity of the bridge itself and the erosion of the riverbed surrounding bridge support structures, is critical for highway safety. In coastal regions, the study of structural response of the bridges to hurricane-category winds is also of interest. Such evaluations have relied heavily on scaled experiments to provide measurements for flow field and structural response. However, the availability of parallel computers and analysis capabilities of commercially available software provide an opportunity to shift the focus of these evaluations to computational fluid dynamics (CFD). When validated with the broad experimental database, the use of CFD simulations allow expanded parametric analysis and provide a means of evaluating directly the effects of scaling.
The analysis support for hydraulics research, with an emphasis on bridge flooding and scouring, is one of the several identified area of study to support Federal Highway Administration programs. Through collaborations among Argonne National Laboratory, Turner-Fairbank Highway Research Center (TFHRC), University of Nebraska (UNeb), and Northern Illinois University (NIU), CFD-based simulation techniques are being evaluated for open-channel flow. Analysts from these four organizations are pursuing simulations of the reduced-scale experiments conducted at the TFHRC hydraulics laboratory to validate the CFD models. The overall objective of this effort is to establish validated computational practices to address the research needs of the transportation community in bridge hydraulics via simulations. The CFD simulations are expected to address a range of hydraulics research, including the assessment of lift and drag forces on bridge decks when flooded, optimization of bridge deck shapes to minimize pressure scour, analysis of sediment transport and its influence on scouring, evaluation of active or passive scour countermeasures to mitigate the damage, and environmental issues such as fish passage through culverts.
The first task pursued under this program is the analysis of lift and drag forces on inundated bridge decks under various flow configurations. The applicability of commercial CFD software for prediction of flow field and evaluation of drag and lift forces is being investigated. The Argonne and NIU teams are using STAR-CD, while the TFHRC and UNeb teams are using FLUENT software. The CFD model predictions are being compared with the laboratory data for force balance measurements of lift and drag forces for various inundation ratios, as well as particle image velocimetry measurements. The agreement between the code predictions and experimental data is being examined for various modeling options.
Since the form of the free surface in open-channel flow influences the flow field and other quantities of interest, the volume of fluid computational technique is being pursued to capture it accurately. Since this technique is an inherently transient solution scheme, even when only the equilibrium state is of interest, each case is studied with a time-dependent solution scheme requiring significant computational resources. The results to date indicate that a steady solution can generally be reached within a five-minute simulation time; however, the wall-clock time required for computations for that five-minute simulation can be significantly longer depending on the specified time-step size and number of processors used.
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