TUFLOW 2D Hydraulic Structures: Difference between revisions
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= 2D Structure Modelling Theory =
The theory behind the modelling of energy losses and affluxes of hydraulic structures is presented in the following webinars by Bill Syme and Greg Collecutt (
*<u>[https://www.tuflow.com/library/webinars/#structures Webinar Link: Modelling Energy Losses at Structures]</u><br>
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<ol>
<li>Calculate the ratio of the water area occupied by piers to the gross water area of the constriction (both based on the normal water surface) and the angularity of the piers. These inputs are used to calculate "J" in the FHA documentation.</li>
<li>Use the Figure
[[File:incremental_backwater_coefficient_2018_pier_losses.png]]
<br>
'''NOTE''': the pier form loss coefficients in Hydraulics of Bridge Waterways are derived based on the cross-sectional averaged velocity through the bridge opening in the absence of piers. It's not necessary to specify a blockage value if a pier form loss coefficient estimated from this method is used.
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Four flow constriction layers are represented in a 2d_lfcsh layer. The lower three layers represents the pier, the bridge deck and the rails. Each layer has its own attributes to specify the blockage and the form loss coefficient. The top (fourth) layer assumes the flow is unimpeded, representative of flow over the top of a bridge. Within the same shape, the invert of the bed, and thickness of each layer can vary in 3D.
The following table provides an overview for how to determine the blockage and form loss coefficient for each layer
{| style="text-align: left; margin-left: 0; " class="wikitable" width="80%"
!colspan="1" style="background-color:#005581; font-weight:bold; color:white;"| Layer
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[[File:
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<br>
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2D BG Shape is similar to the Layered Flow Constriction, but has several updates to simplify the input based on the findings from the joint study with TMR <u>[https://tuflow.com/media/7554/2022-bridge-deck-afflux-modelling-benchmarking-of-cfd-and-swe-codes-to-real-world-data-collecutt-et-al-hwrs.pdf (Collecutt et al, 2022)]</u>.
The following table provides an overview of how to determine the blockage and form loss coefficient for each layer
{| style="text-align: left; margin-left: 0; " class="wikitable" width="80%"
!colspan="1" style="background-color:#005581; font-weight:bold; color:white;"| Layer
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[[File:
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===Inflection Point===
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TUFLOW is a 2D solution (not 3D), in the 2d_lfcsh layer the percent blockage and form loss coefficient applied to the cell faces is depth averaged across the entire cell face (across Layer 1, 2 and 3):<br>
*For bridges, where Layer 2 has a 100% blockage applied, the minimum flow width factor of 0.
*Layered flow constriction works by adjusting the flow area of the cell faces by any blockages to generate the correct depth averaged velocity at each face at which the form losses are applied as a fraction of the V<sup>2</sup>/2g kinetic energy. Calculating the correct velocity is critical for determining the losses as the losses are proportional to the velocity squared. <br>
*For a layered flow constriction cell face the flow area cannot be zero above the invert of Layer 1 to avoid a divide by zero in the computations, therefore after applying blockages, a minimum
*If this is unacceptable, and a 2d_lfcsh is intended to be 100% blocked, or even just Layer 1 100% blocked in the case of a fence with a solid base, then the preferred approach is to raise the ground elevation by setting the 2d_lfcsh invert attribute higher or using a 2d_zsh Z Shape modification (e.g. a breakline). <br>
<ol>
[[File:100% Blockage Diagram.png | 500px]]
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