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# Initial Fluid Volumes

1. 1. Specify 8-point Regions

When the analysis type is Open Channel Flow, an important step in the setup is to indicate which portion of the model is initially filled with fluid (or which portion is filled with gas). This is done with the Initial Fluid Volumes branch in the tree view. Right-click the Initial Fluid Volumes branch and choose Add New Hexahedral Region. This accesses the Initial Fluid Volume (Hexahedral) dialog from which you specified an 8-point region in space which is initially fluid or gas.

On the Initial Fluid Volume (Hexahedral), set the Fluid options drop-down to one of the following options:

• Inside region indicates that the 8-point region created is initially filled with fluid. Elements outside the region will be filled with gas.
• Outside region indicates that the 8-point region created is initially filled with gas. Elements outside the region will be filled with fluid.

Multiple regions can be created. The union of all the regions determine where the fluid and gas starts at time 0. The Enable check box controls whether the region will be used in the computations (checked) or not (not checked).

## Specify 8-point Regions

The initial fluid volume is specified using 8-points that define a hexahedral region (see Figure 1). The points can be specified using either of these methods:

• Enter points one at a time: Using the Initial Fluid Volume (Hexahedral) dialog, enter the coordinates of each point (or click a vertex). The points are entered in the order A, B, C, D (which define one quadrilateral face), A', B', C', and D' (which defines the opposite quadrilateral face). After a point has been entered, use the Escape key to back up through the previous points. (The Escape key can be used while creating the original volume or while modifying an existing volume.)
• Enter all points at once: Click the Edit points button to display the coordinates of all 8 points. Either enter the coordinates of a point, or use the Select button to click a vertex.

Figure 1: 8-Point Initial Fluid Volume

When the analysis is started, each element is assigned a fluid volume between 0 (no fluid) and 1 (completely filled with fluid) based on the intersection of the element with each of the initial fluid volumes.

NoteThe Volume of Fluid result is only created when the analysis is performed. Doing a Check Model cannot be used to check the setup of the initial fluid volume.