Settings for the Heat Transfer in Shells Interface
The Label is the default physics interface name.
The Name is used primarily as a scope prefix for variables defined by the physics interface. Refer to such physics interface variables in expressions using the pattern <name>.<variable_name>. In order to distinguish between variables belonging to different physics interfaces, the name string must be unique. Only letters, numbers, and underscores (_) are permitted in the Name field. The first character must be a letter.
The default Name (for the first physics interface in the model) is htlsh.
Boundary Selection
By default, all boundaries are available for the application of the Heat Transfer in Shells interface. Select the Restrict to layered boundaries checkbox to make the interface applicable only if a layered material is defined on the boundary. If a layered material (Material with Layer thickness specified, Single Layer Material, Layered Material Link, or Layered Material Stack) is available, its name is then displayed beside the boundary index (for example, slmat1), otherwise the boundary is marked as not applicable.
Shell Properties
Two options are available for the Shell type:
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When the Layered shell option is selected, the Extra Dimension tool is used to solve the equations through the thickness of a layered material. It is possible to consider several layers with different thermal properties varying through the thickness, by using the General option for Layer type in the Thin Layer (Heat Transfer Interface) and Solid (Heat Transfer in Shells Interface), Thin Film (Heat Transfer Interface) and Fluid (Heat Transfer in Shells Interface), or Fracture (Heat Transfer Interface) and Porous Medium (Heat Transfer in Shells Interface) nodes.
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When the Nonlayered shell option is selected, only the thermal properties need to be specified within the material. This option should be used for thermally thin layers, for which no through-thickness temperature variation is expected in the layered material. This lumped approach is available by using the Thermally thin approximation option for Layer type in the Thin Layer (Heat Transfer Interface) and Solid (Heat Transfer in Shells Interface), Thin Film (Heat Transfer Interface) and Fluid (Heat Transfer in Shells Interface), or Fracture (Heat Transfer Interface) and Porous Medium (Heat Transfer in Shells Interface) nodes.
Layered Shell
By default, the Shell type is Layered shell, and the thickness of the layered material should be set as follows, depending on the type of material:
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In a Material node, the Layer thickness can be in the table found under the Material Contents section of the material Settings window. This automatically adds a Shell subnode under the Material node, transforming it as a layered material.
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When the layered material is a Single Layer Material, the Thickness is set in the Layer Definition section of the Shell Property Group window.
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For a general Layered Material, added through a Layered Material Link or a Layered Material Stack, the Thickness is set in the Layer Definition section of the Settings window. Several layers may be defined in the table, and the Thickness should be defined for each of them. The total thickness of the layered material is the sum of all the layers thicknesses.
Note that the Layered shell option should be used whenever a layered material is applied on the boundaries, because the thickness is part of the material settings.
In the Solid, Fluid, and Porous Medium nodes, the same layered material is used, and this choice is not editable. And both the Thermally thin approximation and General options are available as Layer type in these nodes.
Clear the Use all layers checkbox to apply the Heat Transfer in Shells interface on some layers only. Select a Layered material from the list (the interface is then applicable only on the boundaries where this latter material is defined), and clear the checkboxes corresponding to layers where the interface should not be applied in the Selection table.
Nonlayered Shell
If the Restrict to layered boundaries checkbox is not selected in the Boundary Selection section, a nonlayered material may be defined on the selected boundaries, and the Thickness Lth can be set as a user defined value or expression. This value overrides the values set in the material nodes.
In the Solid, Fluid, and Porous Medium nodes, the Thickness is set by default to From physics interface, and is editable only in a manually added node. Only the Thermally thin approximation option is available as Layer type in these nodes.
You can visualize the selected layered materials and layers in each layered material by clicking the Layer cross section preview and Layer 3D preview buttons.
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The layer thickness variable, htlsh.ds, used in the weak equations, is the product of the thickness set in the Shell Properties section, htlsh.lth, and the scale factor htlsh.lsc, which is equal to 1 by default, and can be overridden by a user defined value in a single layer material.
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The layer thickness variable, htlsh.ds, is defined in all dimensions, and is unrelated to the Out-of-plane thickness of the layered material, htlsh.d, which is only available in 2D, and might be edited in the Out-of-Plane Thickness section.
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See Layer and Interface Selection Tools.
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You can provide material parameters with a through-thickness variation by explicitly or implicitly using expressions containing the extra dimension coordinate as described in Using the Extra Dimension Coordinates.
The desired selection for the physics interface may correspond to boundaries with different layered materials. This means that a single physics interface can accommodate several different stacking sequences.
See Layered Material, Layered Material Link, Layered Material Stack, Layered Material Link (Subnode), and Single Layer Materials in the COMSOL Multiphysics Reference Manual for details on the definition of layered materials.
Out-of-Plane Thickness
For 2D components, the cross-section of the layered material is modeled, and its Out-of-plane thickness, dz (SI unit: m), should be defined (see Equation 4-73). The default is 1 m.
When the Heat Transfer in Shells interface is coupled to a Surface-to-Surface Radiation interface through a Heat Transfer with Surface-to-Surface Radiation multiphysics coupling, these inputs are automatically defined from the multiphysics coupling. These variables are set to unit length of the component unit system. This corresponds to the assumption that the geometry is infinite in the out-of-plane direction and that the equations are defined per unit length. This assumption is required as it corresponds to the view factor computation in these dimensions.
Physical Model
Set the Reference temperature Tref. It is used in the definition of the reference enthalpy Href which is set to 0 J/kg at pref (1 atm) and Tref. The corresponding interface variable is htlsh.Tref.
This input is not overridden by the model input found in features like Solid, Porous Medium, Thin Layer (Heat Transfer Interface) and Solid (Heat Transfer in Shells Interface), and Fracture (Heat Transfer Interface) and Porous Medium (Heat Transfer in Shells Interface). It sets the ht.Tref variable.
Consistent Stabilization
This section is available by clicking the Show More Options button () and selecting Stabilization in the Show More Options dialog.
The Streamline diffusion checkbox is selected by default and should remain selected for optimal performance for heat transfer in fluids or other applications that include a convective or translational term. Crosswind diffusion provides extra diffusion in regions with sharp gradients. The added diffusion is orthogonal to the streamlines, so streamline diffusion and crosswind diffusion can be used simultaneously. The Crosswind diffusion checkbox is also selected by default and is only available when the Streamline diffusion checkbox is selected.
The Use dynamic subgrid time scale checkbox is selected by default. When selected, it estimates the influence of temporal variations in the temperature field instead of using the solver time step as a time scale in the consistent stabilization terms.
Inconsistent Stabilization
This section is available by clicking the Show More Options button () and selecting Stabilization in the Show More Options dialog.
The Isotropic diffusion option (not selected by default) adds an additional term to the diffusion coefficient to dampen spurious oscillations caused by convective terms. Increasing the Tuning parameter δid amplifies the effect of the isotropic diffusion. As a rule of thumb, the tuning parameter should be large enough to ensure convergence, while remaining as small as possible as it reduces the accuracy of the original problem.
Heat Transfer Consistent and Inconsistent Stabilization Methods
Discretization
To display all settings available in this section, click the Show More Options button () and select Advanced Physics Options in the Show More Options dialog. You can choose the type and order of the shape functions used for the variables solved by the Heat Transfer in Shells interfaces.
Temperature
For the temperature, you can choose not only the order of the discretization, but also the type of shape functions: Lagrange or serendipity. For highly distorted elements, Lagrange shape functions provide better accuracy than serendipity shape functions of the same order. The serendipity shape functions will however give significant reductions of the model size for a given mesh containing hexahedral, prism, or quadrilateral elements.
The shape functions used for the temperature are Quadratic Lagrange for the modeling of heat transfer in shells, and Linear for the modeling of heat transfer in films and heat transfer in fractures.
Dependent Variables
The Heat Transfer in Shells interfaces have the dependent variable Temperature T. The dependent variable names can be changed. Editing the name of a scalar dependent variable changes both its field name and the dependent variable name. If a new field name coincides with the name of another field of the same type, the fields share degrees of freedom and dependent variable names. A new field name must not coincide with the name of a field of another type or with a component name belonging to some other field.