The Geometry Node
Under a Geometry node () you define and create the geometry sequence for the model component. The Geometry node also contains some general settings for the geometry such as the length unit.
Adding a Component Geometry
To add a new Component, which includes a Geometry node, right-click the root node of the Model Builder, and select Add Component (or use the Model Wizard to create a new sequence as described in Creating a New Model). A Component node is added to the Model Builder containing a Geometry 1 (if it is the first Component) feature node with the start of a geometry sequence containing only a Form Union node (see Figure 7-1 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 Settings window for a geometry, click the Geometry node in the Model Builder and adjust the following settings sections.
Units
Select the Scale values when changing units 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 Length unit 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 Scale values when changing units check box (see above).
For information about available length units and prefixes, see Specifying Model Equation Settings.
Angular Unit
From the Angular unit 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 Scale values when changing units check box (see above).
Advanced
Geometry Representation (3D Only)
This list is only visible if you have a license for the CAD Import Module. The Geometry representation 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.
•
If you choose CAD kernel (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.
•
If you choose COMSOL kernel, all objects are represented using COMSOL’s kernel.
When you change the Geometry representation 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 Build All button ().
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.
When you create a new model, its default geometry representation is controlled by the preference setting Geometry>Geometry representation>In new models.
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 Geometry>Geometry representation>When opening an existing model to Convert to COMSOL kernel.
Default Repair Tolerance
This is the default value that is used when you add a feature that has a Repair tolerance list (for example, Boolean operations and conversions):
•
The default value in the Default repair tolerance list is Automatic, 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.
•
Choose Relative to enter a value for the Default relative repair tolerance field (the default is 10−6). This value is relative to the largest absolute value of the coordinates of all input objects.
•
Choose Absolute to enter a value for the Default absolute repair tolerance field (the default is 10−6; SI unit: m). This value uses the same unit as the geometry sequence’s length unit.
Automatic Rebuild
The Automatic rebuild 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 Geometry>Automatic rebuild>Default in new geometries. Select the Automatic rebuild check box to always rebuild the geometry, or clear it to prevent any automatic rebuilding of the geometry.