Free Tetrahedral
Add a Free Tetrahedral node () to create an unstructured tetrahedral mesh. If no selection is specified, this feature creates a mesh on the remaining domains, boundaries, edges and points. You can control the number, size, and distribution of elements by using Size and Distribution subnodes.
To create an unstructured tetrahedral mesh for a domain selection:
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In the Graphics window, select the domains. On the Mesh ribbon toolbar (Windows) or from the Mesh contextual toolbar (Mac and Linux), click the Free Tetrahedral () button.
Then choose the menu item corresponding to the desired predefined element size, for example, Normal. The software creates the resulting tetrahedral mesh by adding and building a Free Tetrahedral node, using the selected domains with a Size node, and using the selected predefined element size added as a subnode. Alternatively, you can click the button associated with the menu button. Then COMSOL Multiphysics uses the last selected menu item (or Free Tetrahedral (Normal)), as indicated by the tooltip. If you use this menu button with an empty selection, the software meshes the remaining, unmeshed geometry.
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Right-click a Mesh node and choose Free Tetrahedral.
Then define the properties for the tetrahedral meshing operation using the following sections:
Domain Selection
Define the domains where you want to create an unstructured tetrahedral mesh. Choose the level of the geometry from the Geometric entity level list:
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Choose Remaining to specify unstructured tetrahedral mesh for remaining, unmeshed domains.
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Choose Entire geometry to create an unstructured tetrahedral mesh in the entire geometry.
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Choose Domain to specify the domains for which you want to create an unstructured tetrahedral mesh. Choose Manual in the Selection list to select the domains in the Graphics window or choose All domains to select all domains.
Scale Geometry
To scale the geometry during the meshing operation, change the x-scale, y-scale, and z-scale to positive real numbers. If any of the scale factors are not equal to one (1), the software scales the geometry in the x, y, and z directions before meshing. After meshing, it restores the geometry and mesh to fit the original size. The scale factors make it possible to generate meshes that are anisotropic, and they are useful if the mesh generator creates many elements due to a thin geometry or if the mesh generation fails due to large aspect ratios in the geometry.
Control Entities
Select the Smooth across removed control entities check box to smooth the transition in element size across removed control entities. You can specify the number of smoothing iterations in the Number of iterations field. In the Maximum element depth to process field you can specify the maximum element depth, from the boundary layer interface, for the mesh points to be smoothed.
Tessellation
From the Method list, choose the Delaunay tessellation method to use for creating a tetrahedral mesh:
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Select Automatic (the default) to make the mesh generator determine the best algorithm to use for each domain.
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Select Delaunay to use a version of the Delaunay algorithm that under some conditions can modify the boundary mesh to simplify the meshing.
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Select Delaunay (legacy version) to use the Delaunay algorithm available in earlier versions of COMSOL Multiphysics. This is also the method that will be used if you open a model created using an earlier version of COMSOL Multiphysics.
Element Quality Optimization
In this section, you can control how much effort COMSOL Multiphysics puts into optimizing the element quality and tuning the optimization for certain situations. From the Optimization level list, choose one of the following levels:
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Basic (the default), which makes basic optimizations aiming at a minimal element quality of 0.2.
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Medium, which makes more optimization and aims at a minimal element quality of 0.35,
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High, which attempts all available optimization operations. If the quality of the surface mesh is low (typically due to small details or narrow corners in the geometry), this setting can take a significant amount of time.
There are two additional settings that you can use if you then accept a lower mesh element quality:
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If the geometry includes fillets or other curved regions with a relatively coarse mesh, and you solve with a geometry shape order higher than one, you can select the Avoid inverted curved elements check box. This setting makes the optimization try to reduce the number of mesh elements that become inverted when they are curved. The cost of this optimization is longer meshing time and often a slightly higher number of mesh elements and a lower element quality.
If curved mesh elements become inverted, the following message appears in the Messages window: Used linear geometry shape in N mesh elements to avoid inverted curved elements (where N is the number of inverted elements).
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If the computation is sensitive to too large mesh elements, you can select the Avoid too large elements check box. For each mesh element, there is a desired element size (h), specified by the mesh size parameters, and if the element is larger than that, COMSOL Multiphysics tries to make it smaller. The cost for this option is longer meshing time and a lower element quality. If you evaluate the maximum of h on a sufficiently large mesh of uniform size, this value is typically decreased by 10 percent if you have selected this option.
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Select the Avoid too small elements check box to optimize the mesh so that the diameter of the inscribed sphere of each element is maximized while still trying to respect the desired local element size. Optimizing this parameter can improve performance when solving problems using the discontinuous Galerkin method. The optimization level controls how much effort is put into this optimization.
For a tutorial about free meshing and mesh sizing, see Free Tetrahedral Meshing of a Piston Geometry, Application Library path: COMSOL_Multiphysics/Meshing_Tutorials/piston_mesh.