About Selecting Geometric Entities

Throughout COMSOL Multiphysics there are many lists of selected geometric entities, all based on the same principle — pick a domain, boundary, edge, or point 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, and other parts of the model’s design, or 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 on the Graphics toolbar (The Graphics Window Toolbar Buttons), 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 click the button (

in 3D) in the window toolbar.

The Geometry 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

and 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.

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: 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.

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

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

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

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: 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.

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

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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 of the applicable pairs (typically identity pairs). 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. Select one or more pairs from the list to specify where to apply the pair condition. 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.

Settings Window Toolbar

Table 6-2: Geometric Entity Selection Buttons on various Settings windows
Button	Name	Description
	Active ON	Click the Active button ON to make the selection of geometric entities to the Selection list active for that particular node.
	Active OFF	Click the Active 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.
	Paste Selection	Use this button if you have a list of geometric entities in a file or document 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 directly 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.
	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. Clearing the selection also activates the selection for that node.
	Zoom to Selection	Use this button to zoom into the selected geometric entities. This zoom operation also updates the center of rotation, which will stay active until you click the Zoom Extents or the Go to Default 3D View button to reset it.