How to Select Surfaces with the "Neighbor Objects" Command

For a curved shape (such as a cylinder or hollow shell), if you want to apply a pressure loading or boundary conditions to only the exterior (or interior) surfaces, then you must select all of the surfaces. However, Superdraw III's "Neighbor Objects" command enables you to select the surfaces quickly and conveniently.

Consider the cylinder model shown in Figure 1. The cylinder has a surface mesh (but no solid mesh) where the only connections between the exterior surface and the interior surface are the end surfaces. The exterior surface can be selected by using "Neighbor Objects" in the following step-by-step procedure.

1. Put the cylinder in a view where you are looking at its side. In this case, the "View:Pre-Defined Views:XY Top" and "View:Enclose" command sequences were used.
2. Select the ends of the cylinder. "Select:Box..." was used to access the "Box Select" pop-up menu. Then, "Add Mode" was specified and selection boxes were drawn around first one end of the cylinder and then the other as is shown in Figure 2.
3. Put the ends of the cylinder on a unique layer. "Modify:Update Object Parameters:Layer Number..." was used to access the "LAYER" pop-up screen. (See Figure 3.) Layer 2 was chosen as the new layer number for the selected lines.

Figure 2: Drawing a selection box around one end of the cylinder.	Figure 3: Modifying the layer number of the selected lines.

4. Hide the layer of the end surfaces. "Tools:Layer Control..." was used to access the "Layer Control" window. The "Inactive" option was chosen for layer 2, which hid the end surfaces. Thus, the exterior and interior surfaces of the cylinder were not connected as is shown in Figure 4.
5. Select one line on the exterior surface. "Select:Point..." was used to access the "Point Select" pop-up menu and then clicking on any line of the exterior surface selected a line.
6. Use "Neighbor Objects" to select all of the exterior surface lines. In the "Point Select" menu, clicking on the "Neighbor Objects" button selected all objects connected to the selected line. Repeatedly clicking the "Neighbor Objects" button eventually selected all of the lines of the exterior surface as is shown in Figure 5. Notice that none of the lines on the interior surface were selected, because the interior and exterior surfaces were not connected.

Figure 4: Making layer 2 inactive to hide the end surfaces.	Figure 5: Using "Neighbor Objects" to select all of the lines of the exterior surface.

7. Modify the surface number of the selected exterior surface lines, which will be convenient for specifying a surface pressure or other finite element data. "Modify:Update Object Parameters:Surface Number..." was used to access the "SURFACE" pop-up screen. Surface 10 was chosen as the new surface number for the selected lines. "Tools:Surface Control..." was used to access the "Surface Control" window and surfaces 1 and 2 were deactivated to display only surface 10. (See Figure 6.)

While the cylinder model is a simple example, this procedure can also be used for models that have complex, multi-faceted portions with many surfaces. Superdraw III's "Neighbor Objects" command enables quick and convenient selection of such surfaces. Then, the surface number can be modified, which will enable easy application of finite element objects such as forces, pressures or constraints.

Note: Here are some additional considerations for using the "Neighbor Objects" command:

• The "Neighbor Objects" command selects all objects (lines, arcs and splines) connected to the selected objects. This can be particularly useful in a wire-mesh model for identifying elements connected to a problem element.
• The current selection mode (Normal, Toggle, Add or Subtract) has no effect on the "Neighbor Objects" command. Adjacent objects are always added to the current selection set.
• The "Neighbor Objects" command can also be accessed from the SELECT pull-down menu in addition to the "Point Select" pop-up menu.
• The keyboard shortcut key for the "Neighbor Objects" command is "e". Hence, instead of clicking on the "Neighbor Objects" button in the "Point Select" menu, alternatively, you can press "e".