Revision as of 20:18, 27 February 2025 view source Pavlina Monhartova (talk \| contribs) Bureaucrats, Administrators 5,372 edits →What FLC values should be used for 2d_bg bridge if hB/T is below 2 or above 6? ← Older edit		Revision as of 17:00, 27 March 2025 view source Chris Huxley (talk \| contribs) Bureaucrats, Administrators 7,776 edits →2D Bridges Line vs Polygon Layer Newer edit →
Line 158: The form loss coefficient (FLC) is applied differently when using a line compared to a polygon. The FLC is applied at cell sides (u and v faces) as this is where velocities are calculated.<br> When using a polyline, the FLC attribute depends on the type of the polyline: Thin line (width attribute of zero) - The FLC attribute in the GIS object should reflect the total form loss value for the bridge. A thin 2d_lfcsh line will apply the FLC to a single row of cell sides. As such, this approach is cell size independent. Thin line lfcsh are the easiest setup, and isthe ~~the~~preferred ~~preferable~~/ recommended approach. Thick line (width attribute between zero and 1.5 times the cell size) - The FLC attribute is half of the total loss as the form loss is applied on each cell side of the selected cells. A cell is selected if the polyline intersects the cell crosshair. Caution should be taken when using a "thick" line, due to the fact changes in cell size can trigger a "thick" line to become a "wide" line. If this were to occur the FLC attribute would need to be recalculated to not overestimate losses. * Wide line (only supported for 2d_lfcsh, width attribute larger than 1.5 times the cell size) - The FLC attribute is a portion of the total loss based on number of cell sides in the predominant direction of flow. Caution should be taken when using a "wide" line due to the fact changes in cell size can trigger the need to recalculate and define losses. Line 167: </ol> For larger bridges that spread across multiple cells, it is recommended to use a polygon layer, which selects all u and v faces falling within the polygon. Caution should be taken when specifying the FLC values for the two different 2d bridge features: 2d_lfcsh: FLC attribute is the total loss '''per unit length''' (meters or feet) in the direction of flow. The FLC is applied to each face as 'FLC cell size' 2d_bg: FLC attribute is still the '''total form loss'''. Instead of converting it to "form loss per meter", the "Deck_Width" attribute is used to automatically distribute the total FLC to the selected faces, i.e. FLC<sub>face</sub> = FLC / Deck_Width cell size. For bridges modelled using a 2d_bg polygon, the relative ratio of the bridge width to the 2D cell size should be 4 or greater. For more information on this see <u>[https://downloads.tuflow.com/Other/2d_bg_R_Bridge_Configuration_Advice_202503.pdf 2d_bg_R_Bridge_Configuration_Advice.pdf]</u>. ~~:Note: For bridges modelled using a 2d_bg polygon, the number of cells across the width of the bridge should be 4 or more.~~ [[File:2d_lfcsh_polygon.png\|450px]] [[File:2d_bg_polygon.png\|450px]]

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