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When using 2d_lfcsh, 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 points) as this is where velocities are calculated.
* When using a polyline, the FLC attribute depends on the type of the polyline:
** Thin line (width attribute of zero) - theThe FLC attribute isin the GIS object should reflect the total form loss thatvalue is applied tofor the bridge. ThinA thin 2d_lfcsh line will apply the FLC to a single row of cell sides,. asAs such, itthos approach is cell size independent. Thin line lfcsh isare easierthe toeasiest setup, and preferable if it is sufficientthe for thepreferable modellingrecommended taskapproach.
** Thick line (width attribute between zero and 1.5 times the cell size) - theThe 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, asdue withto the fact changes in cell size changecan trigger a "thick" line couldto become a "wide" line. If this were to andoccur the FLC attribute would need to be recalculated to not overestimate the losses.
** Wide line (width attribute larger than 1.5 times the cell size) - theThe FLC attribute is a portion of the total loss based on number of cell sides in the predominant direction of flow. The number of cell sides can be checked in the <u>[[Check_Files_2d_lfcsh_uvpt | 2d_lfcsh_uvpt_check file]]</u> file. Caution should be taken when using a "wide" line asdue withto cellthe sizefact changechanges widein linecell couldsize becomecan thick line andtrigger the FLC attribute would need to berecalculate recalculatedand to not underestimate thedefine losses.
* When using a polygon, the value entered in the FLC attribute is the total loss per unit length (meters or feet) in the predominant direction of flow. The FLC is applied to all u and v points that fall within the polygon. A polygon lfcsh is mostly used for larger bridges to spread the effect of the FLC across multiple cells. The benefit of this method is that it is cell size independent.
The <u>[[Check_Files_2d_lfcsh_uvpt | 2d_lfcsh_uvpt_check file]]</u> can be used to review the location of the applied lfcsh and its attributes.<br>
It is always a good modelling practice to undertake a sensitivity analysis on the applied form losses in the model to check if it makes any difference to the results and/or double check against other methods (hand calculations, other software, CFD modelling), especially if the bridge is anywhere near the area of interest. If calibration data is available, this should take precedencebe overused simulationto outputsguide orthe calculationsform loss value specification.<br>
== What form loss coefficient (FLC) values should I use for 2d_lfcsh bridge? ==
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