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TUFLOW 2D Hydraulic Structures: Difference between revisions

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==I don't see results that I expect when using 2d_lfcsh layer==
== Why am I seeing flow through a 2d_lfcsh with 100% blockage applied? ==
The 2d_lfcsh layer is a versatile feature that was designed to model bridges in 2D, but can also be used for other applications like fences, buildings raised on pillars and so on.
When using 2d_lfcsh, the blockage attribute of any layer can be set to 100%. This is useful when modelling structures such as bridge decks.
Some of the unexpected results could be:
However, as TUFLOW is a 2D solution (i.e. not 3D), the percent blockage applied to the cell faces is depth averaged across the entire cell face.<br>▼
* Water level going through the bridge deck in 2D map output.
 
* Water transiting through 100% blocked Layer 1, e.g. fences with solid base.
Layered FC’s function 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>▼
* SHMax.csv reporting values above the bridge deck when 2D map output reports water level lower than the top of the bridge deck.
 
For a Layered FC cell face the flow area cannot be zero above the invert of Layer 1 to avoid a divide by zero in the computations, therefore a minimum average flow width after applying blockages of 0.001 m is applied. if Layer 1 is 100% blocked, a very small amount of water will flow through Layer 1. If this is unacceptable, instead of applying 100% blockage of Layer 1, the preferred approach is to start the Layered FC at the top of Layer 1 or raise the ground elevation to the top of Layer 1 using one of the Z Shape modification functions (e.g. a breakline). <br>▼
 
For bridges, where Layer 2 has a 100% blockage applied, the minimum flow width of 0.001m is used and is averaged with the Layer 1 blockage (based on the depth of the water). This may result in a water level being reported within or above the bridge deck, which would represent the pressure head.▼
 
▲However, as TUFLOW is a 2D solution (i.e. 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 of 0.001m is used and is averaged with the Layer 1 blockage (based on the depth of the water). This may result in a water level being reported within or above the bridge deck, which would represent the pressure head.
▲*Layered FC’sflow constriction functionworks 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 Layeredlayered FCflow 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 a minimum average flow width after applying blockages of 0.001 m is applied. if Layer 1 is 100% blocked, a very small amount of water will flow through Layer 1. If this is unacceptable, instead of applying 100% blockage of Layer 1, the preferred approach is to start the Layeredlayered flow FCconstriction at the top of Layer 1 or raise the ground elevation to the top of Layer 1 using one of the Z Shape modification functions (e.g. a breakline). <br>
<ol>
[[File:100% Blockage Diagram.png | 500px]]
</ol>
 
== Can I model bridge piers explicitly in 2D using very small cells? ==
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