Specifying Selections

Specifying the selection where a certain variable definition is valid works in the same way for all types of definitions throughout the Physics Builder. You find these settings under the section of all nodes that support a selection.

It is not possible to give an absolute selection, because you do not know enough about the geometry that the physics interface is used in. Instead, set up the selection relative to selections that are known in the Model Builder.

In the list specify what selection to start from. The bullets below explain the list options, assuming that the selection belongs to a variable, but this is also valid for all other types of nodes that support selections.

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. The selection becomes identical to the selection of the feature. If the variable belongs to a property or a physics interfaces, the selection becomes identical to the selection of the physics interface.

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. The selection is taken from the selection input.

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. The variable gets a global selection. This option can disable other settings, like shape selection, for example. A shape selection does not make sense for global selections because the only valid degree of freedom is an ODE variable.

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. Only available for selection components. The selection is taken from the physics interface.

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. Only available for periodic condition features and pair features. The selection is identical to the source selection of the periodic condition or pair.

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. Only available for periodic condition features and pair features. The selection is identical to the destination selection of the periodic condition or pair.

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. Performs an operation between several selection components defined under the branch (

). The supported operations are the same as for selections in the Model Builder; see Visualization and Selection Tools in the COMSOL Multiphysics Reference Manual.

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. Use this option to select a link to a selection definition from an external resource. To define the selection, choose an and a . The list is the list of nodes that has been defined and imported from the external resource.

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. Use this option to define a link to a built-in Java maker, which you defined using the , , and lists.

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. The selection become the top level entities applicable to the parent node (domains or boundaries, for example).

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. Searches for sibling features with a specific type in the list containing the current feature, or if the current entity is a property or physics interface, it searches the feature list under the physics interface. Then performs the selected operation on the selections of the found features. With this option in a Selection node, you can select the check box. When this check box is selected, a field becomes available. Here you can enter a conditional expression that is evaluated for all siblings that match the criteria. The condition must evaluate to 0 (false) or 1 (true). You can also press Ctrl+space to get a list of supported operators, prefixes, and functions. Only when the condition evaluates to 1 (or true) the selection of the sibling feature will be included in the total selection operation.

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. The selection refers to a selection component under the branch that defines the selection; see Selection.

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. The selection is taken from the moving domains.

For all options except , you can also choose the output entity from the list. This list has the following options:

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. The variable’s selection contains the adjacent boundaries to the selection, which typically is a domain selection. If the selection is a boundary selection, this option returns the boundaries adjacent to the selection.

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. The variable’s selection contains the adjacent domains to the selection.

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. The variable’s selection contains the adjacent edges to the selection.

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. The variable’s selection contains the adjacent points to the selection.

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. Specifies that the selection is of a special kind where the entities represents the boundaries of each mesh element in a domain selection.

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. The selected entities undergo a filtering only including the entity types selected in the , such as , , or (in axial symmetry). See Selection Terminology for more details.

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. Restrict the use of the selected entities to the frame type selected from the list. A frame type can vary across the selected entities of a feature when the list of a feature uses the option ; see Using Coordinate Systems.

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. With this option, the output selection only contains the base selection.

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. The output selection contains only the extra dimension that was attached to the production selection.

For the option you get another option to restrict the output boundaries to certain conditions. Some restrictions only make sense if the original selection (determined by the list) is a domain selection. In the list, you can choose among the following options:

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. This option returns all adjacent boundaries, and this is the only option that makes sense for non-domain original selections.

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. All boundaries that only has one of the upside domain or downside domain belonging to the domain selection.

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. The boundaries where the upside domain and downside domain both belong to the domain selection.

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. Include exterior boundaries that has the upside domain in the domain selection.

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. Include exterior boundaries that has the downside domain in the domain selection.

Figure 2-5: A schematic of a domain selection with highlighted exterior and interior boundaries. Note that some exterior boundaries are not highlighted.