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Editing of Contraction and Expansion Coefficients

Contraction or expansion of flow due to changes in the cross section is a common cause of energy losses within reach (between two cross sections). Whenever this occurs, the loss is computed from the contraction and expansion coefficients specified in the cross section data. To learn more about contraction and expansion losses, refer to this article in our knowledge base.

In GeoHECRAS, the Edit Contraction & Expansion Coefficients command allows the user to view and edit contraction and expansion coefficients in a tabular format. The user can modify a group of contraction or expansion coefficient values as follows:

  • By adding a constant to coefficient values
  • By multiplying coefficient values by a factor
  • By changing coefficient values to a specific value

The user can also go directly into the table and change any individual values.

In addition, cut, copy, and paste commands are provided to pass data to and from the Windows clipboard. The contraction and expansion coefficients are shaded in different colors to make it easier to distinguish between contraction and expansion coefficients in the table.

Follow the steps below to use the Edit Contraction & Expansion Coefficients command:

  1. From the Input ribbon menu, click the Cross Sections dropdown menu and then select the Edit Contraction & Expansion Coefficients command.
    Edit Contraction & Expansion Coefficients Input ribbon menu command
  2. The Edit Contraction & Expansion Coefficients dialog box will be displayed.
    Edit Contraction & Expansion Coefficients dialog box

The following sections describe the Edit Contraction & Expansion Coefficients command and how to interact with the above dialog box.

Cross Section Contraction & Expansion Coefficients

This section is used to select the river and the corresponding reach for editing the contraction and expansion coefficients. The user can select the river and the reach from the River and Reach dropdown combo boxes, respectively. Alternatively, the user can click the [Pick] button to select the river reach from the Map View.

The data grid will list all the corresponding cross sections of the selected river reach and their contraction and expansion coefficients values.

Note that structures such as culverts, lateral structures, and roadway crossings falling within the reach are identified in the Type column. The corresponding rows for the Contraction and Expansion columns will be disabled.

The right-click context menu of the data grid displays the commands to cut, copy, and paste data to and from the Windows clipboard. In addition, the user can export the grid data to excel or pdf format and delete the grid data.
data grid right-click context menu commands

Selected Cells Group Editing

This section provides different options for the user to edit the grid data. The user must first select the values that the user would like to change. To select a group of values, place the mouse in the upper-left cell of the desired cells to select, then press the left mouse button and drag the cursor to the lower-left corner of the desired cells. When the left mouse button is released, the selected cells will be highlighted.
Selected Cells Group Editing section

After selecting the desired cells to be modified, use one of the following options:

  • No change
    This is the default option. No changes will be made in the contraction and expansion coefficient values when this radio button option is selected.
  • Add constant
    Select this radio button option to add a constant value to a group of contraction and expansion coefficient values. After selecting this option, the user must enter a constant value in the entry field provided next to this option. This value will be added to all the cells that are selected.
  • Multiply by factor
    Select this radio button option to multiply a group of contraction and expansion coefficient values by a factor. The user must enter a value in the entry field provided next to this option. This value will be multiplied by each of the selected cells’ values.
  • Apply value
    Select this radio button option to set a group of contraction or expansion coefficient values to the same number. The user must enter a specific contraction or expansion coefficient value in the entry field provided next to this option. This value will replace all of the selected values. The user can click the […] lookup button to display the Expansion Contraction Coefficients lookup dialog box.
    Expansion Contraction Coefficients dialog box

After selecting the desired option and entering the required value, the user can click the [Apply Change] button to modify the values in the data grid.

Note that the [Apply Change] button will be disabled (i.e., grayed out) when the No change radio button option is selected.

The user can click the [Default] button to restore the values of the coefficients to the default values.

When the grid data has been modified, click the [OK] button to save the changes and close the dialog box.

About the Author Chris Maeder

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