A Dependent Variable Declaration node (
) declares a dependent variable used by the interface. This node does not make the interface add any shape functions for this variable, it just declares that a dependent variable exists. All dependent variables in a physics interface must have an unique identifier (or reference tag) within an interface. In most cases you only solve for one type of physical quantity per interface, so the physical quantity works fine as a reference tag. If you need two or more dependent variables for the same physical quantity, it is necessary to append a unique tag to the reference tag.
) declares a dependent variable used by the interface. This node does not make the interface add any shape functions for this variable, it just declares that a dependent variable exists. All dependent variables in a physics interface must have an unique identifier (or reference tag) within an interface. In most cases you only solve for one type of physical quantity per interface, so the physical quantity works fine as a reference tag. If you need two or more dependent variables for the same physical quantity, it is necessary to append a unique tag to the reference tag.
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Add these subnodes: Dependent Variable Declaration, Initial Values, Component Settings, Disable in Solvers, and Hide in GUI.
To add a Dependent Variable Declaration, first add a Physics Interface or Multiphysics Interface, then:
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Right-click the Physics Interface or Multiphysics Interface node and select it from the Variables submenu.
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To find the definitions of the variable, click the Find Declarations of this Variable button (
) on the Settings window, or click the node and press F7, or right-click the node and choose Search>Find Definitions.
) on the Settings window, or click the node and press F7, or right-click the node and choose Search>Find Definitions.The Settings window has the following sections:
Select a Dependent variable reference: Use physical quantity (the default) or Use physical quantity + tag.
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Keep the default Use physical quantity if you want to use the physical quantity as the reference.
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For Use physical quantity + tag you can specify an arbitrary unique tag. Enter the tag in the Unique tag field. This tag is added to the end of the name of the Physical quantity chosen. For example, if you choose Area (m^2) from the list and enter house in the Unique tag field, the name for the node (in brackets) in the Physics Builder changes to areahouse.
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The Physical quantity list defines what quantity the dependent variable represents, including the unit. As mentioned previously, the physical quantity is also used to generate the unique reference tag for the dependent variable. In addition to the predefined physical quantities you can use locally defined physical quantities or physical quantities imported from an external resource:
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Select Locally defined from the top of the Physical quantity list to use one of the locally defined physical quantities, which you choose from the Link list. Click the Go to Source button (
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Select Imported from external resource from the Physical quantity list to use physical quantities from another imported Physics Builder file, which you choose from the Imported file list. Click the Go to Source button (
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It you choose None from the list it is recommended to use the option Use physical quantity + tag in the Dependent variable reference list. As None is not a physical quantity, enter an explicit unit in the SI unit field.
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The Default variable name field declares the default name for the dependent variable, and the Description field has the descriptive text for the variable shown in analysis and variable listings.
Enter a LaTeX-encoded string in the Symbol (LaTeX encoded) field to define a symbol (\mu, for example, to display the Greek letter μ).
Select a Dimension: Scalar, Vector (3x1), Matrix (3x3), and Custom. For Custom, you can specify a nonstandard dimension (for example, 3x3x3 if you need a tensor of rank 3 with indices of dimension 3).
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Select or clear the check boxes Show in plot menu and Announce variable to feature inputs. See Preferences described for Variable Declaration.
This sections contains settings for defining the discretization levels that control the shape-function order used in the physics interface and the Discretization section of the physics interface instance. By default the parameter for the shape order is set automatically and includes five levels for order 1–5. You can also specify a default level (set to 2 by default). Use the Parameter list to specify if the discretization parameter name and description should be defined automatically (the default) or manually. This is the list in the physics interface instance that, in its automatic configuration, has the description Element order and has valid values Linear, Quadratic, and so on. Below the Parameter setting is a table with the following columns: Level, Level description, Shape order, and Lower level. This table controls the values that can be selected in the discretization parameter. Each row in this table represents a discretization level, which corresponds to a shape order for the dependent variable and an allowed value for the discretization parameter. Enter the value in the Level column and its description in the Level description column. Each level has a shape order, which you define in the Shape order column. The Lower level column’s value should point to a discretization level that has a shape order that is smaller than the current one, so it needs to be a value that is present in the Level column. The Lower level setting is used by the multigrid preconditioner.
In the Default level list you select the default level for the discretization parameter (default value: 2, for quadratic order of the shape functions).
Select the Enable accurate boundary flux option check box to make the Compute boundary fluxes check box visible in the Discretization section of the physics interface instance. The On by default check box (selected by default) controls the default value of that parameter. Note that to make the computation of accurate boundary fluxes work as well as possible it is also necessary to add Flux Definition nodes that define the flux for the dependent variable anywhere it is defined.
This section contains advanced options that you do not have to change in most cases. In the Base vector system list, you can override the base vector system specified by the parent (for example, a feature or property) by choosing something other that the option Same as parent.
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