Click Close

14. Right-click the mouse to exit the Draw regions mode. The cursor will change from a cross-hair back to an arrow and the node numbers will appear.

Notice that both the nodes and the elements have been automatically sorted in the vertical direction. After you have completed the above steps, your screen should look like the following picture.

The above procedure will now be repeated to generate elements in the remaining two regions.

¾ To generate the second region:

1. Choose Regions from the Draw menu. The cursor will change to a crosshair. Move the cursor near (7,0) and click.

2. Move the cursor near (7,3) and click.

3. Move the cursor near (8,3) and click.

4. Move the cursor near (8,0) and click.

5. Move the cursor back to (7,0), and click. The second region will be created, a default mesh will be generated within the region and the Region Properties dialogue box will appear

6. Click Close to accept the mesh. This time, do not right-click to exit the Draw regions mode, just continue onto the next step to draw the third and final region.

¾ To generate the last region:

1. Move the cursor near and click at the following locations (8,0), (8,3), (8,6), (15,6), (15,0), (8,0). The Regions Properties dialogue will appear and a default mesh will be generated.

2. Click on the Edges Tab to adjust the number of subdivisions on each edge of the region.

3. Click on the line between Region points 6 and 8. Note that the corresponding Edge Subdivision has been selected in the Region Properties dialogue box. Type 6 in the Min. edit field. Click Copy.

4. Click on Edge 8,9 either on the screen or within the dialogue box.

Type 14 in the Min. edit field. Click Copy.

5. Click Close. Right click the mouse to exit the Draw regions mode.

After you have completed the above steps, your screen should look like the following:

Set view preferences

When defining a problem, the default values are automatically selected in the View Preferences dialog box.

¾ To change or set the view preferences for the drawing:

1. Choose Preferences from the View menu.

The Preferences group box can be used to check or un-check any of the options in the Items to View group box.

The Font size and type can be set for node, point, region and element numbers as well as the axes using the Font Size group box options. Checking the Convert All Sketch Text Fonts option and selecting a font will convert all of the sketch text to the corresponding font. The check box will remain inactive unless a sketch text has been created and placed.

2. Under Geometry Information, click in the check box for Point Numbers and Region Numbers to turn off the Point and Region Numbers on the profile.

3. Under Mesh Information, click in the check box and unselect Element Numbers. Select OK.

You can also select and unselect the View Preferences by clicking on the icons in the View Preferences toolbar. You can learn about each of the icons by placing the cursor over the icon. A tool tip will appear for a few seconds and a description is displayed on the status bar at the bottom of the window.

Specify node boundary conditions

Boundary conditions may be specified as total head (H), total nodal flow or flux (Q), or flow per unit length along the side of an element (q).

The boundary conditions for this problem are:

• Total head of 9 m at the base of the reservoir.

• Total head of 6 m at the ground surface downstream of the dam.

¾ To specify the node boundary conditions:

1. Choose Boundary Conditions from the Draw menu. The cursor changes from an arrow to a cross-hair and the status bar indicates that

"Draw Boundary Conditions" is the current mode. The following dialog box appears:

2. Select H from the drop down Type menu.

3. Type 9 in the Action edit box to specify the total head at the base of the reservoir,.

4. Click the left mouse button near Node 13 which is the top, left corner of the mesh. The cursor snaps to Node 13 and the node symbol is changed to a red circle, indicating the node is a head boundary.

5. The remaining reservoir boundary nodes will be defined by dragging a rectangle around a group of nodes. Move the cursor above and to the left of Node 26. Hold the left mouse button down, but do not release it.

Now move the mouse to the right, and a rectangle appears. "Drag" the mouse until the rectangle encompasses Nodes 26, 29, 57, 65, 78, 91, 104, 117, 130, 143, 156, 169. Now release the left mouse button, and all of these nodes are redrawn as red circles.

Node boundary conditions can therefore be defined both by clicking on each node individually and by dragging a rectangle around a group of nodes. Another way of specifying boundary nodes is to hold down the SHIFT key and select nodes along

any straight line. See the Draw Boundary Conditions command reference in the on-line help for more information.

6. Type 6 in the Action edit box to specify the total head at the ground surface downstream of the dam

7. Use the procedure described in Step 5 to drag a rectangle around Nodes 267, 280, 293, 306, 319, 332, 345, 358, 371, 384 and 397. You may need to move the dialog box if it overlaps these nodes. All of these nodes are redrawn as red circles, indicating each node is a head boundary.

The other boundary conditions for this simulation include a total flux of zero across every external node that does not have an assigned head boundary. Since all nodes are Q=0 nodes by default, meaning that the flow into the nodes must equal the flow out of these nodes, it is unnecessary to define Q = 0 boundaries around the perimeter of the problem. There is no harm in assigning this boundary condition, it just is not required.

Draw flux sections

A flux section is desired for this problem to compute the total seepage flow through the foundation of the dam. Flux sections must be drawn completely across an element in order to include the flux through that element. Flux sections must not pass through nodes, which is why the snap to grid feature must be disabled.

¾ To define a flux section:

1. Turn off the grid by choosing Grid under the Set Menu and un-checking the Snap to Grid option or by clicking on the Snap Grid button on the Grid toolbar. You do not have to turn off the display grid feature if using the Set Grid approach so the grid will still appear on the screen but the snap feature will be disabled. If you use Snap Grid Button on the toolbar, both the display grid and snap to grid features will be disabled

2. Choose Flux Sections from the Draw menu. The following dialog box appears: