Difference
To subtract geometry objects from other geometry objects to make a set difference, in the Geometry toolbar, from the Boolean and Partitions () menu, select Difference (). You can also right-click the Geometry node to add this node from the Boolean and Partitions submenu. Then enter the properties of the difference operation using the following section:
Difference
Activate the Objects to add list by clicking the Active button to toggle between turning ON and OFF selections. When set to ON, select the objects that you want to add in the Graphics window. If the geometry sequence includes user-defined selections above the Difference node, choose Manual to select objects, or choose one of the selection nodes from the list next to Objects to add.
Activate the Objects to subtract list by clicking the Active button to toggle ON and OFF. When set to ON, select the objects that you want to subtract in the Graphics window. If the geometry sequence includes user-defined selections above the Difference node, choose Manual to select objects, or choose one of the selection nodes from the list next to Objects to subtract.
Click the Swap Objects to Add and Objects to Subtract button () to swap the objects in the two lists.
Select the Keep objects to add to use the geometry objects to add for further geometry operations. Select the Keep objects to subtract to use the geometry objects to subtract for further geometry operations.
Create a geometry object without interior boundaries by clearing the Keep interior boundaries check box. This can be useful to simplify a geometry where the interior boundaries do not separate domains with different physics nodes or materials, for example.
You can change the settings for the Repair tolerance list if you experience problems with the difference operation. Geometric entities that have a distance less than the repair tolerance are merged.
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The default value in the Repair tolerance list is Automatic, which for 3D objects represented using the CAD kernel determines the repair tolerance internally. For 3D objects represented using the COMSOL kernel, and for 2D and 1D objects, Automatic means a relative repair tolerance of 10−6.
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Choose Relative to enter a value for the Relative repair tolerance field (the default is determined by the main Geometry node’s setting). This value is relative to the largest absolute value of the coordinates of all input objects.
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Choose Absolute to enter a value for the Absolute repair tolerance field (the default is determined by the main Geometry node’s setting; SI unit: m). This value uses the same unit as the geometry sequence’s length unit.
When you build this feature, the relative and absolute repair tolerances are set to the values that are used (with a precision of two digits), which can be useful when you have set Repair tolerance to Automatic.
Selections of Resulting Entities
Select the Resulting objects selection check box to create predefined selections (for all levels — objects, domains, boundaries, edges, and points — that are applicable) in subsequent nodes in the geometry sequence. To also make all or one of the types of resulting entities (domains, boundaries, edges, and points) that the resulting objects consist of available as selections in all applicable selection lists (in physics and materials settings, for example), choose an option from the Show in physics (Show in instances if in a geometry part; Show in 3D in a plane geometry under a work plane in a 3D component) list: All levels, Domain selection, Boundary selection, Edge selection, or Point selection. The default is Domain selection, which is suitable for use with materials and physics defined in domains. For use with a boundary condition, for example, choose Boundary selection. These selections do not appear as separate selection nodes in the model tree. Select Off to not make any selection available outside of the geometry sequence. From the Color list, choose a color for highlighting the resulting objects selection. See Selection Colors.
Cumulative Selection
If you want to make the resulting entities contribute to a cumulative selection, select a cumulative selection from the Contribute to list (the default, None, gives no contribution), or click the New button to create a new cumulative selection (see Cumulative Selections).
Assigned Attributes
From the Construction geometry list choose On to make the resulting objects available only in the feature’s geometry sequence. The default option Inherit means that the resulting objects become construction geometry if all input objects are construction geometry. Choose Off to never output construction geometry objects. For more information see Construction Geometry.