About Selecting Geometric Entities

Throughout COMSOL Multiphysics there are many lists of selected geometric entities, all based on the same principle — pick domains, boundaries, edges, or points and use methods to add or remove these geometric entities to create selections that define, for example, the parts of the geometry where a material or boundary condition is active. Such lists appear in windows for defining equations and material properties, boundary conditions, sources, mesh features, and other parts of the model’s design, and in the Variables node (

) definitions for variables that are not defined in the entire model.

All levels of geometry can be treated individually. You can add and remove 3D geometric entities (domains, boundaries, edges, or points) to selection lists in different ways, including buttons in the toolbar (The Graphics Window Toolbar Buttons and Navigation), using The Selection List Window, clicking directly on the geometry, or clicking buttons in the window. You can also select entities in the list to then remove them from the selection, for example. Ctrl+A selects all entities in the list. Table 6-2 lists the buttons that display on every window with a geometric entity selection list as displayed in Figure 6-6.

Figure 6-6: The selection list and toolbar on a physics node Settings window. The geometric entity level for the top Settings window is domains. The bottom Settings window is for a default boundary condition node where the selection cannot be changed, although a boundary can be overridden.

Figure 6-7: The Geometric entity level selection list and toolbar on a Settings window for Material (left) and the Settings window for Variables (right).

In The Graphics Window, the geometric entities are color highlighted as you make the selections, and you can lock the selections by turning off the active selection (at most one selection can be active at a time) or select (

in 3D) in the window toolbar.

The Geometric Entity Selection Sections

The name of the section where the list of selected geometric entities is managed depends on the geometric entity level. For example, Figure 6-6 displays a section.

Every geometric entity selection section also has an button to toggle between turning on

or off

selections for that node.

For physics nodes that are default nodes (see Physics Interface Default Nodes) the selection defaults to all geometric entities on the applicable level (all domains or all boundaries, for example, in Figure 6-6), and the list is not active. You can add other nodes that override the default nodes for some or all entities. Those entities are then marked in the selection list for the default node.

•

: For Materials and Variables nodes, where you first select the level (domain, boundary, and so on), from a list. See Figure 6-7 for an example using the “Diagonal Mounting Detail of a Communication Mast” model.

•

: For nodes that define, for example, material models, sources, and body loads in domains. See Figure 6-6 for an example.

•

: For nodes that define, for example, boundary conditions.

•

: For nodes that define, for example, conditions and forces on edges. This is applicable to 3D models only.

•

: For nodes that define, for example, point sources and point loads.

From the list you can choose one of the following options:

•

(the default): Select the geometric entities directly in the window, using The Selection List Window, or using the button. See below for more information about those selection methods.


	If you start by setting the Geometric entity level to Domain, and then select All domains, the Selection list displays all domains. If you make any changes to this list (for example, remove a domain) the Selection list reverts to Manual.

•

, , , : Depending on the geometric entity level, you can choose one of these options to select all entities. See Figure 6-6 for example.

•

Defined named selections: Selection nodes added in the geometry sequence or under (as well as selections created from Boolean operations, for example) are available in the lists for nodes that define model properties for the same geometric entity level. You can rename such selection nodes to better reflect what the selected entities represent. A named selection can consist of, for example, the domains where a volume force acts, the boundaries where an inflow occurs, or points that are grounded. Named selections are useful for reusing selections in a model component and to clearly indicate what parts of geometry that the selected entities include or represent. See Creating Named Selections.

In the lists of selected entities, and can display next to the label (the number) of a selected entity. See Figure 6-6 and Physics Node Status for more information about these status indicators. There is also an section in all physics nodes. It provides an overview of how the physics nodes and their selections interact. See Physics Exclusive and Contributing Node Types.

Pair Selection

If the geometry is an assembly you have access to specific pair conditions (typically on boundaries) that you choose from a submenu on the main physics nodes’ context menus. In the window for such pair nodes, a section contains a list (initially empty) of the selected pairs (typically identity pairs). Select the pairs where you want to include by clicking the button (

) and choose the pairs to add from the list in the dialog box that opens; then click . The section (or another standard selection section) is then not possible to modify and shows the entity numbers for the boundaries, for example, that the selected pairs include. See Identity and Contact Pairs.


	See Table 6-3 for the many ways to select geometric entities using toolbar buttons, mouse click options, page settings, and keyboard shortcuts.

Right-Clicking to Select Geometric Entities and Add Physics Features

You can right-click anywhere in the window to define a preselection of some geometric entities and the add some physics feature with that selection. On the context menu, when a physics interface node is selected in the model tree, choose , , , or , depending on the domain level that you want to make a selection for (not all levels are available for all space dimensions).

Figure 6-8: Right-click in the Graphics window to create a new selection for some physics.

For the geometry in the figure above, which is taken from the Stiffness Analysis of a Communication Mast's Diagonal Mounting model in the COMSOL Multiphysics Application Library, say that you want to add a boundary load to the four bottom boundaries (faces). Then with a Solid Mechanics interface node selected, add a new boundary selection for those boundaries and then right-click and select from the context menu.

Figure 6-9: The context menu for adding a physics feature to the preselection (for Solid Mechanics).

A node is then added to the Solid Mechanics interface in the model tree with its selection being the four bottom boundaries. You are still in the preselection mode and can make a new boundary selection, for example. The added selection appears in yellow. If you want to add more boundaries to this Boundary Load mode, select them, and then right-click and choose (for example).

Figure 6-10: The added Boundary Load node’s Settings window and its selection highlighted in yellow.

By selecting the (for example) item om the context menu, you can turn the yellow highlighting of that selection on and off. To activate the selection in the window, turn on the button in the window’s setting, or move to another node in the tree and then back.

Settings Window Toolbar

Table 6-2: Geometric Entity Selection Buttons on various Settings windows
Button	Name	Description
	Activate Selection (on)	Click the Activate Selection button on to make the selection of geometric entities to the Selection list active for that particular node.
	Activate Selection (off)	Click the Activate Selection button off to lock/deactivate the geometric entities in the Selection list for that particular node. The selected entities in the geometry are highlighted in yellow in the Graphics window. See Figure 6-3 for an example. The Graphics window is then available for preselection of entities for a new node.
	Create Selection	Use this button to create selection nodes under Definitions to represent various parts of the geometry and simplify the process of assigning materials, model equations, boundary conditions, and model properties. See Creating Named Selections. This button is also on The Selection List Window.
	Copy Selection	Use this button to copy the selection from the list in the Settings window to the clipboard. See Copying and Pasting Selection Lists. This button is also on The Selection List Window (except when in the Geometry mode).
	Paste Selection	Use this button if you have a list of geometry objects or geometric entities in a file or document, or that you have copied using Copy Selection, that you want to type in and then paste into a selection list. If you copy a selection from a document to the clipboard, you can paste the selection using Ctrl+V. An example is a list of geometric entity numbers described as a step in a modeling instruction. See Copying and Pasting Selection Lists. This button is also on The Selection List Window (except when in the Geometry mode).
	Add to Selection	Use this button to add a geometric entity to a selection list. See Table 6-3. This button is also on The Selection List Window.
	Remove from Selection	Use this button to remove a geometric entity from the Selection list. See Table 6-3. This button is also on The Selection List Window.
	Clear Selection	Use this button to clear a selection.
	Zoom to Selection	Use this button to zoom into the selected geometric entities. This zoom operation also updates the center of rotation and sets a manual rotation center, which will stay active until you click the Zoom Extents or the Go to Default 3D View button to reset it or switch to an automatic rotation center in some other way.