Revised Clear-Water and Live-Bed Contraction Scour Analysis (2021) / Chapter Skim
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Pages 95-108
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From page 95... ...
7-1 Computational Applications 7.1 Overview The design of the laboratory experiments and diagnostic interpretation of results from the experiments was aided and extended using computational modeling. As noted in Section 3.5, the 1D numerical model HEC-RAS was used to confirm the hydraulics of flow through the test setup (i.e., to check on adequacy of lengths of the two channel sections that constitute the setup, and to develop a discharge versus flow depth rating curve for the approach channel upstream of, and at, the contraction)
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From page 96... ...
7-2 Revised Clear-Water and Live-Bed Contraction Scour Analysis Figure 7-1 identifies items (a) through (c)
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From page 97... ...
Computational Applications 7-3 dataset was adjusted downwards by 110.1426 ft for Test CW_0.25-0.75 and by 110.1160 ft for Test LB_0.50-2.0, such that the pre-scour bed elevation equaled zero elevation. These adjusted post-scour datasets were then used to define the elevations of the numerically modeled terrain.
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From page 98... ...
7-4 Revised Clear-Water and Live-Bed Contraction Scour Analysis 7.3 Calibration to Clear-Water Contraction Scour Test CW_0.25-0.75 Conditions for Test CW_0.25-0.75 are summarized in Table 7-2. 7.3.1 1D Model: Coarse Resolution The 1D HEC-RAS was used with a cross section spacing corresponding to the predetermined data collection stations used to define the water surface as measured from the data collection carriage.
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From page 99... ...
Figure 7-3. Typical HEC-RAS cross section, Test CW_0.25-0.75 using the fine resolution model.
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From page 100... ...
7-6 Revised Clear-Water and Live-Bed Contraction Scour Analysis -1.5 -1.0 -0.5 0.0 0.5 1.0 10 20 30 40 50 60 70 80 El ev ati on (ft ) Station (ft)
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From page 101... ...
Computational Applications 7-7 Figure 7-6 shows the calibration results from SRH-2D for clear-water Test CW_0.25-0.75. Comparing Figure 7-6 with Figure 7-2 (1D coarse resolution model)
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From page 102... ...
7-8 Revised Clear-Water and Live-Bed Contraction Scour Analysis Calibration to observed water surface elevations using FLOW-3D produces nearly identical results compared with the 1D and 2D models discussed previously. In addition, the difference between pre-scour and post-scour water surface elevations are very similar for all the models.
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From page 103... ...
Computational Applications 7-9 was used to define the bathymetry at each HEC-RAS cross section to a typical resolution of 0.1 ft. The initial and final water surface and bed profiles as determined from the HEC-RAS model with the fine cross section spacing are shown in Figure 7-10.
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From page 104... ...
7-10 Revised Clear-Water and Live-Bed Contraction Scour Analysis 7.4.4 3D Model: Fine Resolution FLOW-3D was used to create a 3D hydraulic model of the post-scour laboratory conditions for Test LB_0.50-2.0. The structured grid of cubic elements was uniformly spaced at 0.1 ft.
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From page 105... ...
Computational Applications 7-11 Calibration to observed water surface elevations using FLOW-3D produces nearly identical results compared with the 1D and 2D models discussed previously. In addition, the difference between pre-scour and post-scour water surface elevations is similar for all the models.
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From page 106... ...
7-12 Revised Clear-Water and Live-Bed Contraction Scour Analysis between the results of 1D, 2D, and 3D numerical models. This confirms that the prevailing hydraulics of the long-contraction problem can be reliably modeled with the assumptions of a 1D model if water surface profile and cross section averaged velocity are the variables of concern.
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From page 107... ...
Computational Applications 7-13 7.6 3D Flow Visualization Figure 7-15 presents a streamline flow visualization of Test LB_0.50-2.0. The figure was created using FLOW-3D CFD software, the laboratory flow boundary conditions, and the post-scour LiDAR dataset.
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From page 108... ...
7-14 Revised Clear-Water and Live-Bed Contraction Scour Analysis Figure 7-16. Test LB_0.50-2.0 CFD Model (FLOW-3D)
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