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Using the flow acceleration parameter flows are now squared and multiplied by an acceleration factor when passing through an inlet.
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Figure 1 Hydraulic Structure Boundary Conditions: Low Chord Option.
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It is recommended that users set a common low chord elevation for adjoining cells and pay attention to the bathymetry for those cells. While it is possible to set a different low chord elevation for adjoining cells, if they have different values then flow will pass from cell to cell across the bridge and cause model instability. In the same way, sudden change of bathymetry between the cells may also create oscillations. To prevent this it is suggested to use masks.
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Figure 2 Hydraulic Structure Editing Form: Low Chord.
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Figure 3 Bridge (Low Chord) Hydraulic Structure in View3D.
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In another example, P Outlet uses a control type with flow derived from both upstream and downstream elevations as shown in Hydraulic Structures Boundary Condition Editor – Flow Derived. In this case it is necessary to have a matrix to describe the relationship between head and flow as shown in Hydraulic Structures Boundary Condition Editor – Flow Derived. Most data tables, such as those by the US Corp of Engineers, use the same downstream and upstream head. Therefore, if the user wants to change the table, they should select Edit Heads, and add a new table. When Accept Heads is selected a new row and column will be created.
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Figure 4 Structure Boundary Conditions: Flow from US and DS Elevations.
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Figure 5 Hydraulic Structure BC Editing: Flow from US and DS Elevations.
This matrix may be plotted by selecting the View Series | Current option. This displays the graph as shown in Hydraulic Structures Boundary Condition Editor – Flow Derived. As there are often too many series to plot, the user is prompted for a skip interval so that some lines are not displayed. The user may also select a specific upstream head to plot.
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Figure 6 Flow from US and DS Elevations.