Physics Interface
In the Model Builder you can add physics interfaces and physics features in the Model Wizard. Depending on your license, the Model Wizard can contain different physics interfaces grouped in different physics branches. The physics interfaces shipped with COMSOL are referred to as built-in physics interfaces.
With the Physics Builder you can create new physics interfaces that show up in the Model Wizard, either in an existing physics branch or in a new physics branch.
To add a Physics Interface () and create a single physics interface:
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On the Home or Physics Interface toolbar, click the Add Physics Interface button (), or
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Right-click the Root node (the top node) and choose Physics Interface.
You can add features to the Physics Interface node in these ways:
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On the Physics Interface toolbar, click the available buttons, or
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Right-click the Physics Interface node and choose features from the context menu.
For example, see Features, User Inputs, Properties, Mesh Defaults, Study and Solver Defaults, Result Defaults.
The Settings window has the following sections:
Physics Area
This section is initially collapsed. It contains a tree view of all physics areas (fluid flow, heat transfer, and so forth) and sub-areas available from built-in resources, areas defined in the current builder file, and areas defined in any imported file under the External Resources branch (). See Physics Areas to learn about adding physics areas.
To put a physics interface under a physics area in the tree, select the relevant physics area node and then click the Set as Parent () button below the tree. Or right-click the physics node and choose Set as Parent from the submenu. You can find the currently selected category under the Parent area divider.
Identifiers
The text written in the Description field is the text COMSOL Multiphysics displays for the physics interface in the Model Wizard. Click the Rename node using this text button () to update the node in the Physics Builder.
Select the Type check box to define a unique string to identify the physics interface. The string should not conflict with other names for the physics interfaces present in the Model Wizard.
The entry in the Default name and tag field is used to generate the scope of all variables that the physics interface adds in the Model Builder. It also defines the prefix for the tag of all newly created physics interfaces in the Model Builder. The tag of a physics interface is only important for references to a created interface in model files for Java®.
In the Model Wizard and for the physics instance in the Model Builder there is an icon displayed for the particular physics interface. Browse to an image file to add the Icon to display for the physics interface if the default icon is not applicable.
Restrictions
The Allowed space dimensions list specifies the geometry dimensions that the physics interface supports: 3D, 2D, 1D, Axial symmetry (2D), Axial symmetry (1D), and 0D. Click the Add button () to open the Allowed space dimensions list
Choose 0D to create a physics interface with a global scope (for example, a system of ODEs). The default is to support all space dimensions except 0D. Delete items from the list in cases where not all space dimensions are applicable.
The Allowed study types includes the study types that the physics interface can create equations for. The most important alternatives are Stationary, Time-dependent, Frequency domain, Eigenfrequency, and Eigenvalue. Click the Add button () to open the Allowed study types list to choose other study types. Some of these studies are only for specific physics interfaces. Use the Move Up , Move Down , and Delete buttons under the table to organize the list.
Study and Study Step Types in the COMSOL Multiphysics Reference Manual
Settings
From the Top geometric entity level list, choose the top level for the governing equations of the physics interface: Global, Domain (the default), Boundary, Edge, or Point. Domain is the most common, which means that the top level is the same as the geometry dimension.
It is also possible to define shell and wire interfaces that have dependent variables and equations defined on entity levels lower than the geometry dimension. For a Shell interface choose Boundary. The governing equations are then defined on faces in a 3D geometry or lines (edges) in a 2D geometry.
Select a Default frame to choose how the physics interface behaves together with mesh deformation. Select Spatial or Material (the default) if needed. Typically, the frame is decided by each feature or physics property.
Select the Deformed mesh check box to allow this physics interface to control frame motion, similarly to the Moving Mesh or Deformed Geometry interfaces. When this check box is selected, the Moving Frame Domain Condition and Moving Frame Boundary Condition nodes can be used in physics feature and physics properties to specify the frame motion. The frame control settings for this physics interface will also be available in study steps.
When the check box is selected,
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Select the Moving frame. controlled by this physics. If Spatial is selected (the default), the interface will control the spatial frame and use the material frame as reference frame (similarly to the Moving Mesh interface). If Material is selected, the interface will control the material frame and use the geometry frame as reference frame (similarly to the Deformed Geometry interface).
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The Geometry shape order setting controls the order of polynomials used for representing the geometry shape in the moving frame. Select Same as first dependent variable (the default) or Custom. For Custom, enter an Order. The default is 2.
GUI Option
Select an option from the Hide interface in the Model Wizard: No (the default) or Yes. This can be useful if you want to define an interface that is only used in another multiphysics interface, and does not make sense to use as a standalone interface.
Enter a List order weight in Model Wizard. The default is 2. The higher the weight, the lower position the physics interface gets in the tree of physics interfaces in the Model Wizard.
Override Rule
This section summarizes the override rules defined by all features of the interface. If two features uses different override rules, you can fill in the table with rules between override types in different override rules. See Override Rule.
Default Features
This section has no user input. It contains a list of all default features that you declare for the physics interface and what geometric entity level and domain type they exist on. When you create a new physics interface in the Model Builder, COMSOL Multiphysics always adds the default features in this list to the new physics interface. See Features.