Size
Use the Size () attribute to specify the size of mesh elements, as shown in Figure 8-100. It is possible to add Size nodes both as global nodes and as local nodes. If there are several Size nodes in the sequence with a nonempty selection intersection, the mesher uses properties corresponding to the last Size node in the sequence.
Figure 8-100: Meshing an imported CAD geometry with the predefined size Normal (left). Meshing the same geometry with the predefined size Finer resolves the fillets and other curved boundaries better.
A meshing sequence corresponding to a nonempty geometry contains a Size node at the first position in the sequence. This Size node, referred to as the default Size node, is defined for the entire geometry and cannot be removed. To override the mesh size settings defined by this Size node, add another Size node to the sequence.
To add Size () as a global node, choose one of the following:
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Right-click a Mesh node and select Size ().
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Click Sizing () in The Mesh Toolbar and select Size.
To add Size () as a local attribute, right-click a mesh operation in the Model Builder and select Size.
Global vs. Local Attributes
Geometric Entity Selection
This section is not available for the default Size node.
In this section you define the geometric entities where you want to specify a size. Choose the level of the geometry from the Geometric entity level list:
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Choose Entire geometry to specify the size for the entire geometry.
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Choose Domain, Boundary, Edge (3D), or Point (2D and 3D) to specify the domains, boundaries, edges, or points for which you want to refine the mesh. Choose Manual from the Selection list to select the domains, boundaries, edges, or points in the Graphics window, choose a named selection to refer to a previously defined selection, or choose All domains, All boundaries, All edges, or All Points to select all domains, all boundaries, all edges, or all points, respectively.
Element Size
Different types of physics typically require different mesh resolutions. You can use the Calibrate for list to adapt the element sizing to a specific physics area or application. The default values of the parameters under Element Size Parameters will be adjusted according to the selected options in the Calibrate for and Predefined lists. The Calibrate for list contains the following options:
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 General physics
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 Fluid dynamics
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 Plasma
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 Semiconductor
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 Coarse mesh for adaptation
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Time-explicit wave propagation
The default element size is Predefined and set as Normal. See Controlling the Mesh Size Using Attributes and Predefined Mesh Element Sizes for details about the options. This automatically determines the parameters that you can otherwise customize under Element Size Parameters.
Select Custom if you want to change the value for any parameters in the Element Size Parameters section.
Element Size Parameters
This section is available when Custom is selected as the Element Size. Specify all element size parameters using numerical values or user-defined parameters.
Except for the default Size node, if you select a Custom element size above, the check boxes are automatically added next to each field. Click to select a check box to activate, and edit, the corresponding parameter.
The following parameters control the mesh element size (the parameters where you define a size use the geometry’s length unit). Defaults vary based on whether it is a default node or not. Edit the default values as required for the following fields:
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Maximum element size: Use this parameter to limit the allowed element size, for example, if you want to limit the maximum element size to a fraction of the wavelength to make sure that the wave propagation is fully resolved. By using a parametric sweep to vary the maximum element size, you can solve the model using meshes with different mesh density to study how it affects the solution.
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Minimum element size: Use this parameter to specify the minimum allowed element size. You can use this value to, for example, prevent the generation of many elements around small curved parts of the geometry. If some details of the geometry are smaller than the minimum element size, the mesh will contain elements of a smaller size in order to resolve the geometry. This parameter is not available in 1D.
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Maximum element growth rate: Use this parameter to determine the maximum rate at which the element size can grow from a region with small elements to a region with larger elements. The value must be greater or equal to one. For example, with a maximum element growth rate of 1.5, the element size can grow by at most 50% (approximately) from one element to another.
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Curvature factor. Use this parameter to determine the size of boundary elements compared to the curvature of the geometric boundary (that is, the ratio between the boundary element size and the curvature radius). The curvature radius multiplied by the curvature factor, which must be a positive scalar, gives the maximum allowed element size along the boundary. A smaller curvature factor gives a finer mesh along curved boundaries. This parameter is not available in 1D.
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Resolution of narrow regions: Use this parameter to control the number of layers of elements that are created in narrow regions (approximately). The value must be a nonnegative scalar. A higher value gives a finer mesh in narrow regions. If the value of this parameter is less than one, the mesh generator might create elements that are anisotropic in size in narrow regions.
There is no guarantee that all mesh elements in the generated mesh strictly fulfill the size constraints given by the specified element size parameters.
It is not possible to use a coarser mesh size setting on a geometric entity adjacent to a higher dimensional entity with a finer mesh size setting; the finer setting on a geometric entity overrides the coarser setting on its boundary. A warning is given when coarser settings are overridden.
For a tutorial about adjusting the mesh size, see
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Adjusting the Element Size for the Unstructured Mesh Generator:
Application Library path COMSOL_Multiphysics/Meshing_Tutorials/piston_mesh.
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Using Meshing Sequences:
Application Library path COMSOL_Multiphysics/Meshing_Tutorials/meshing_sequence.
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Meshing Operations and Attributes
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Free Tetrahedral
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Free Triangular
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Free Quad