Tute M06 MI 2D lfsch Archive: Difference between revisions
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Created page with " In the following steps we will be adjusting the elevations of the road crest as well as using a 2D zsh layer to lower the zpt elevations at the location of the 2D bridge.<br>..." |
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<ol><li>Copy the '''2d_zsh_M06_NorthRd_001''' from '''Module_Data\Module_06\2D_Bridge''' folder into the '''TUFLOW\model\mi''' folder. We will use this layer to remove the road embankment at the 2D Bridge location.</li>
<li>Open the newly saved layer '''2d_zsh_M06_NorthRd_001''' in MapInfo and make it editable.</li>
Observe the shape contained in this GIS layer. The polygon intersects the zpts where we want to modify the elevations and remove the road embankment. We will remove the embankment at this location by creating a GIS layer that tells TUFLOW to interpolate zpt elevations within the shape using the zpt elevations either side of the embankment. Additionally, the GIS layer will be designed such that TUFLOW does not use the zpt elevations where the two shapes intersect with the embankment. Refer to
<li> Digitise four points snapped to each of the polygon nodes that are circled in the image below.</li>
'''''Tip:''''' It is helpful to make nodes along the polygon perimeter visible by customising the layer properties in layer control. Before digitising points, ensure snap mode is turned on by hitting the S key. <br>
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<li> Use the ''Table >> Update Column'' tool to update the Z attribute of the points. Ensure the ''Table to Update:'' is '''Selection''' (the default) and the ''Column to Update'' is '''Z'''. Enter '''-99999''' in the ''Value:'' box. Click 'OK' and you should see that the eight points in the browser table now show -99,999 as their Z attribute. These points tell TUFLOW to ignore the zpt elevations where the polygons intersect the embankment.</li>
[[File:M06_MI_2D_Road_Update_Points.png]]
<li>Save and export the table
</ol>
===Create the 2D Layered Flow Constriction===
The following steps are used to create the 2D layered flow constriction - ''2d_lfsch'' - that will represent the bridge in the 2D domain. The flow constriction layers provided here are mostly completed. If these were not provided, the method would be to import the "2d_lfsch_empty.mif" and "2d_lfsch_empty_pts.mif" files from the TUFLOW\model\mi\empty folder and save them in the TUFLOW\model\mi\ folder, renaming the files and beginning the edits in these new layers.<br>
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</li>
The attributes are described
* Enter an "Invert" value of 99999 to leave the Zpt levels unchanged (ie. use the Zpt elevations modified by the 2d_zsh layer above).
* Percentage blockage below the obvert of layer 1 to account for any blockages perpendicular to the direction of flow (in this case 6% to account for the average blockage due to the bridge piers).
* A Form Loss Coefficient (FLC) below the obvert of layer 1 (in this case to account for sub-grid scale losses around piers). Note that the treatment of the FLC is different depending on the object used to define the flow constriction, i.e. a line or a polygon. The reason for this is to permit the flow constriction to be independent of the model cell size. See
* Blockage from the obvert level to the top of layer 2 (in this case 100% to account for the bridge deck).
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<li> The above edits and layers result in the below bridge configuration:
<br>[[File:M06BridgeLayeredFlowConstriction.jpg|500px]]
<li>Save and export the table
</ol>
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