COMSOL 6.4 - Free Quad

) to generate an unstructured quadrilateral mesh on boundaries in 3D and domains in 2D, as shown in Figure 8-69. The operation can also be used to remesh faces of imported surface meshes in 3D.

Figure 8-69: An unstructured quad-dominant mesh in a 2D geometry with three domains (left). The Free Quad mesher inserts triangles (yellow) to aid element size transition. The quad mesh on the face in the 3D geometry (colored in blue to the right) is swept together with the triangular face mesh (gray) on adjacent faces, resulting in a mixed prism and hexahedral mesh.


	The quadrilateral mesh generator does not strictly create only quadrilateral elements. In places of the geometry where it judges it as necessary, it can also create triangular elements, as shown in Figure 8-69.

You can control the number, size, distribution, and refinement of elements by using Distribution, Size Expression, Size, and Corner Refinement subnodes (only and subnodes are available for Finalizing the Mesh).

For imported meshes, use to remesh one or several faces. The operation separates the selected boundaries from the mesh, creates geometry from the separated mesh, meshes the geometry, and then copies the new generated mesh onto the original mesh. Edges adjacent to faces outside the selection are kept unchanged, while other edges are remeshed.


	Only surface meshes with first-order elements can be remeshed. Clear the Import domain elements checkbox in the mesh Import node to import only boundary elements. Select checkbox Import as linear elements to ignore second-order mesh data. See Importing Meshes for more information.

To add a (

) node, select boundaries (3D) or domains (2D) in the , then choose one of the following:

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Right-click in the window and select (

) from The Graphics Context Menu.

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In The Mesh Toolbar, choose (

) from the (

) menu (3D components and parts) or click the (

) button (2D).

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Right-click a node and choose (

). For 3D components and parts, this is selected from the menu.

Then enter the properties for the quadrilateral meshing operation using the following sections:

Entity Selection

Define the boundaries (3D) or domains (2D) where you want to create an unstructured quad mesh. Choose the level of the geometry from the list:

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Choose to specify unstructured quad mesh for remaining, unmeshed faces (3D) or domains (2D).

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Choose to create an unstructured quad mesh in the entire geometry.


	In 2D and 2D Axial symmetry, for the options Entire geometry and Remaining, the operation will mesh all remaining entities, even those that are not adjacent to a domain.

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Choose (3D) or (2D) to specify the geometric entities for which you want to create an unstructured quad mesh. Choose in the list to select the boundaries or domains in the window, choose a named selection to refer to a previously defined selection, or choose (3D) or (2D) to select all entities.

For imported meshes in 3D, the available options in the list are and .

Scale Geometry

To scale the geometry during the meshing operation, change the x-scale, y-scale, and z-scale in 3D to positive real numbers. If any of the scale factors are not equal to one, the software scales the geometry in those directions before meshing; after meshing, it restores the geometry and mesh to fit the original size, as shown in Figure 8-70.

The scale factors make it possible to generate meshes that are anisotropic. They are also useful if the mesh generator creates many elements due to a thin geometry or due to large aspect ratios in the geometry (compare the first and last meshes in Figure 8-71). Compare this to changing the parameter in a mesh Size attribute to only affect the mesh size in narrow regions.

Figure 8-70: Three copies of the same geometry, where the quad mesh is more or less resolved in the y direction by scaling the geometry in the background before it is meshed. The top geometry is not scaled. The one in the middle is scaled with a factor 2 in the y direction. The geometry at the bottom is scaled with a factor 0.5 in the y direction.

Control Entities


	This section is visible when there are mesh control entities in the geometry. See Mesh Control Operations for more information.

Use the setting to smooth the transition in element size across removed control entities. Use (default) to let the algorithm decide if to apply smoothing or not. Smoothing will be applied if, for example, 2D domains adjacent to removed edges contain triangular elements only. When set to , the mesher adjusts the sizes of the mesh elements to get a smoother transition from large to small elements by adjusting the locations of the mesh vertices on the entity that is removed. Select to not adjust the mesh. When set to , you can specify the number of smoothing iterations in the field. In the field you can specify the maximum element depth for the mesh vertices to be smoothed.

Figure 8-71: Comparing meshes where Smooth across removed control entities has been used vs. not used. The thin domain (highlighted in blue in left image) is designated as Mesh Control Domains. When all domains are meshed, the edges are removed, leaving only one domain. With the Smooth across removed control entities set to On, the sizes of the edge elements are adjusted (upper-right image) and with the option set to Off, the edge mesh is not adjusted (lower-right image). As the adjacent domains are meshed with a quad mesh, the Automatic option gives the same result as Off.

Mesh Generation

From the list, choose the tessellation method to use for generating an unstructured quadrilateral mesh:

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Select (the default) to generate a quad-dominant mesh where triangles are inserted to aid element size transition, as shown in Figure 8-72.

Figure 8-72: A quad-dominant mesh where the colors indicate the element type.

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Select to generate an unstructured quadrilateral mesh.

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Select any of the legacy versions to use a specific version of the algorithm.

Mesh Preprocessing


	This section is only available for imported 3D meshes when Method is set to Quad or any of the legacy versions. Refer to the section Creating a Computational Mesh for Imported Mesh Data for more information and related tutorials.

You can optionally simplify the mesh when remeshing faces in an imported mesh. The simplification can remove small defects typically present in mesh data from measurements, such as tomography, and it can speed up the process by removing unnecessary elements. The checkbox is selected by default to enable simplification.

The (default value: 0.01) is relative to the dimensions of the entire geometry and specifies a global limit for how much the mesh can be modified. The (default value: 1) is relative to the local feature size, as estimated by the algorithm, and is combined with the global limit to produce a limit for how much the mesh can be modified at a certain location. If the mesh contains many defects that you want to remove, you could try to increase the value of the . If the mesh describes the desired geometry with high accuracy, you might want to decrease this factor instead.

Information

For information, see Generated and Modified Elements.

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For a tutorial about the mesh size parameters, see
Adjusting the Element Size for the Unstructured Mesh Generator:
Application Library path .

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For a tutorial showing the operation used in 3D, see
Forced Convection Cooling of an Enclosure with Fan and Grille: Application Library path .

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For a tutorial showing a swept quad mesh, see
Steam Reformer: Application Library path .

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For a tutorial showing the operation used in 2D, see
Brittle Fracture of a Holed Plate: Application Library path .

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Information, Warnings, and Errors for Meshing Operations

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