COMSOL 6.2 - The Geometry Node

) you define and create the geometry sequence for the model component. The node also contains some general settings for the geometry such as the length unit.

To add a new Component, which includes a Geometry node, right-click the root node of the , and select (or use the to create a new sequence as described in Creating a New Model). A node is added to the containing a (if it is the first Component) feature node with the start of a geometry sequence containing only a node (see Figure 7-2 for an example).

	See Geometric Primitives, Geometry Operations and Virtual Geometry and Mesh Control Operations for descriptions of the geometry features. The tables in each section link to the individual feature Settings window descriptions. To add features to a geometry sequence, use the buttons in The Geometry Toolbar or right-click the Geometry node () in the Model Builder and then select one of the available options.

To open the window for a geometry, click the node in the Model Builder and adjust the following settings sections.

Select the check box to scale the values for the geometric dimensions so that the geometric objects keep their physical size. The default setting is to not scale the values when changing units; the program then interprets the values for the geometric dimensions using the new units for length and angle. The values themselves do not change.

From the list select the length unit to use in fields for lengths and for visualization of the geometry. You can override the unit using the unit syntax to specify the length unit (for example, 13[mm]). When solving the model, all lengths are converted to the base unit for length. If you change the unit, COMSOL Multiphysics converts all pure numeric values in fields for lengths to the new unit, if you have selected the check box (see above).

	For information about available length units and prefixes, see Specifying Model Equation Settings.

From the list choose to use radians or degrees as the angular unit to use in fields for angles. You can override the unit by entering, for example, 0.3[rad]. The program assumes that numeric inputs and outputs of trigonometric functions are in radians. If you change the unit, all pure numeric values in fields for angles are converted to the new unit, if you have selected the check box (see above).

	This section is only visible in 2D and 2D Axisymmetric components and if your license includes the Design Module.

Use the list to enable or disable the use of geometric constraints and dimensions. The default for this setting is determined by a preference settings on the page in the dialog box: Select or clear the check box. This preference setting is On by default. In the dialog box, you can also specify the (the default value is 10,000 geometric entities). You can use this limit to prevent lengthy computations for very complex 2D geometries when using the constraints and dimensions solver.

If you have selected , the list determines what constraint and dimension features to include when building the geometry:

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. This means that no constraint and dimension feature are used. Note that there can be other constraints and dimensions, generated by the primitive features.

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. This means that only the constraint and dimension features up to the feature you are building up to are used.

The Status message informs you whether the constraints and dimensions define the geometry uniquely.

This list is only visible if you have a license for the CAD Import Module. The list controls which kernel (geometric modeler) that COMSOL uses to represent and operate on the geometry objects: the CAD Import Module’s kernel (Parasolid) or COMSOL’s own kernel.

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If you choose (requires the CAD Import Module), all objects and operations that support the CAD Import Module’s kernel use it. For example, Work Plane, Extrude, and Revolve operations do not support this kernel. You need to choose the CAD kernel to use the defeaturing and repair tools, such as the Cap Faces feature, as well as to import 3D geometries using various 3D CAD file formats.

When you change the setting, all nodes that support the CAD kernel are marked as edited with an asterisk (*) in the upper-right corner of the node’s icon. To rebuild the geometry using the new kernel, click the button (

). To avoid re-solving an already solved model, you can click the button (

) in the toolbar to map the solutions from the geometry represented by the CAD kernel to the new geometry represented by the COMSOL kernel.

	If you solve a model using the CAD kernel, it is not possible to view and postprocess the solution if you open it in a COMSOL Multiphysics session where a license for the CAD Import Module is not available, unless, before saving the model, you change the geometry representation to COMSOL kernel and update the solution.

When you create a new model, its default geometry representation is controlled by the preference setting .

When you open an existing model, you normally use the geometry representation used in the model. To always get the possibility to convert the geometry to the COMSOL kernel, change the preference setting to .

If your license includes the Design Module and the geometry representation is set to use the CAD kernel, you can select the check box in a 3D node’s window to use the 3D Boolean operations available with the Parasolid kernel. Those operations might perform better in some cases. When you open an existing model, you normally use the Boolean operations used in the model. To always get the possibility to use the Design Module Boolean operations, change the preference setting to .

This is the default value that is used when you add a feature that has a list (for example, Boolean operations and conversions):

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The default value in the list is , which for the COMSOL kernel is a relative repair tolerance of 10−6. For the CAD kernel, the automatic setting changes the representation of the input objects so they get a common scale factor, which is the maximum of the scale factors of the input objects; if the operation fails, the automatic setting uses the COMSOL kernel instead.

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Choose to enter a value for the field (the default is 10−6). This value is relative to the largest absolute value of the coordinates of all input objects.

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Choose to enter a value for the field (the default is 10−6; SI unit: m). This value uses the same unit as the geometry sequence’s length unit.

The check box controls if certain geometry operations will be built automatically when you add them, provided that you have preselected a sufficient number of entities or object. The default value is controlled by the preference setting . It is selected by default to always rebuild the geometry when using the factory settings. Clear it to prevent any geometry operations from being built automatically.

The check box controls if the geometry sequence is automatically rebuilt when clicking on a node in the model tree outside the geometry sequence. The default value is controlled by the preference setting . It is selected by default to always rebuild the geometry when using the factory settings. Clear it to prevent any automatic rebuilding of the geometry.