COMSOL 6.2 - Swept

) to generate a swept mesh on a domain in 3D by sweeping the mesh from the source faces along the domain to the opposite destination faces, as shown in Figure 8-102. A swept mesh is an example of a semistructured mesh since it is structured in the sweep direction and can be either structured or unstructured orthogonally to the direction of the sweep. A swept mesh is typically a hexahedral mesh (hex mesh) or a prism mesh.

Figure 8-102: Generation of a hexahedral mesh. A mapped mesh is built on the source face, highlighted in blue. This mesh is swept along the circular linking edges (highlighted in red), resulting in a hexahedral mesh, as shown to the right.


	See the Learning Center resource Using Swept Meshes for Model Geometries for more examples and animations: https://www.comsol.com/support/learning-center/article/48941/152

The operation is available both for meshing sequences that generate mesh for a geometry and for meshes that define their own geometric model.


	See The Mesh Node for more information about meshes that define their own geometric models.

You can control the number, size, and distribution of elements using the Size and Distribution subnodes. The operation only reads properties from nodes defined on the entire geometry or on the domain level and nodes defined on the domain level.

Classifications

Each face about a domain that is to be operated on by the swept mesher is classified as either a source face, a destination face, or a linking face. The linking faces are the faces connecting the source and destination faces, as shown in Figure 8-103.

The linking edges are the edges, or the chains of edges, that are approximately tangent to the sweep direction. The section edges are the edges, or chains of edges, that are approximately perpendicular to the sweep direction.

A section is a face component bounded by two loops of section edges.

Figure 8-103: Classification of the boundaries and edges about a domain used for swept meshing. The sections are depicted by the three shades of blue. If the number of faces differ on source and destination, the source will always have the larger number of faces. Two faces are hidden to show the inside of the domain.

Requirements

For the sweeping technique to work, the geometry must satisfy these criteria:

•

Each domain must not contain holes or isolated faces except if they penetrate both source and destination (see Figure 8-104). Also, the domains must not contain void regions.

Figure 8-104: Domains containing holes and isolated faces. Left: the domains are sweepable because the hole and face penetrate both source and destination. Right: the geometries do not fulfill the criteria but can be swept meshed if partitioned into smaller domains (see Figure 8-106).

•

For each domain, the source and destination must be connected face components.

Figure 8-105: The domains to the left in both images cannot be swept meshed due to the disconnected face components on the top. By partitioning the geometry, most or all domains can be swept meshed (exploded view of resulting domains with some faces hidden in the foreground).

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Each destination face must correspond to one or more source faces (see Figure 8-105 and Figure 8-105).

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Each source face must correspond to precisely one destination face or a subset of it (see Figure 8-103 and Figure 8-105). If needed, use a Cross Section operation to make an imprint of the source faces on the destination.

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Coincident source and destination faces are allowed, as when sweeping the mesh a full revolution around an axis.

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Each edge of a linking face must be either a linking edge or a section edge.

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There must be at least two chains of linking edges connecting the two loops of section edges of each section.

Even if the original geometry does not fulfill the above criteria, it is sometimes possible to partition the geometry in order to obtain domains where a swept mesh can be created, as shown in Figure 8-105 and Figure 8-106.

Figure 8-106: Left: Domains where a swept mesh cannot be created due to holes and isolated faces that do not penetrate source and destination (some faces are hidden). Right: Partitioning the domains results in smaller, sweepable domains (exploded view of the domains).

If any of the faces about a domain is meshed prior to the sweeping operation, the following must be fulfilled:

•

If the source and destination faces are meshed, these meshes must match.

•

If any of the linking faces are meshed, these must be meshed with structured quad meshes in such a way that one direction in the grid is aligned with the linking edges and the other direction is aligned with the section edges.

To add a node, select the domains to sweep or the boundaries to use as source faces in the window, then choose one of the following:

•

Right-click in the Graphics window and select (

) from The Graphics Context Menu.

•

In The Mesh Toolbar, click the (

) button.

•

Right-click a 3D node and select (

Domain Selection

Specify the domains where you want a swept mesh. Choose the level of the geometry from the list:

•

Choose to generate a swept mesh for the remaining, unmeshed domains.

•

Choose to specify swept mesh for the entire geometry.

•

Choose to specify the domains for which you want a swept mesh. Choose in the list to select the domains in the window, choose a named selection to refer to a previously defined selection, or choose to select all domains.

Source Faces

Click the button to toggle between turning ON

and OFF

selections.

In most cases the swept mesher can automatically identify source and destination faces from the geometry. To specify the source faces directly, activate the list and select the faces defining the source of the sweep operation in the window.

Click the button (

) to swap the faces in the source list above and the faces in the destination list in the section below.

Destination Faces

To specify the destination faces directly, activate the list and select the faces defining the destination of the sweep operation in the window.

Sweep Method

Face Meshing Method

In the list, you can specify how unmeshed source faces are automatically meshed by the Swept operation. For meshes defining their own geometric model, select the check box (selected by default) to remesh the source faces using the selected method:

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Select to generate a surface mesh with quadrilateral elements. This is the default meshing method.

•

Select to generate a surface mesh with triangular elements.

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Select any of the legacy versions to generate a surface mesh with quadrilateral elements using an algorithm used in earlier versions of the software.

Sweeping Path

Use the list if you want to specify the shape of the sweep path:

•

The default, , means that the sweeping algorithm automatically tries to determine if the sweep path is straight or circular; otherwise, a general approach is used.

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means that all interior mesh points are located on straight lines between the corresponding source and destination points.

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means that all interior mesh points are located on circular arcs between the corresponding source and destination points, as shown in Figure 8-102.

•

means that the positions of the interior mesh points are determined by a general interpolation procedure, as shown in Figure 8-107.

Figure 8-107: An hourglass-shaped geometry in which an unstructured quad mesh is swept using a general interpolation procedure.

Destination Mesh

Use the list if you want to specify the method to be used for transferring the source mesh to the destination:

•

The default, , means that the algorithm automatically tries to determine a suitable method for creating the destination mesh.

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when the source and destination have the same shape, up to a scaling factor.

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when the source and destination have different shape. For example, when going from a circular to a rectangular cross-section, or going from a planar source face to a curved destination face.

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means that the destination mesh is created from the source mesh by a projection technique. This is useful when the source and destination faces are close to each other and have different shape.

Control Entities

Select the check box to smooth the transition in element size across removed control entities. When selected, 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. Clear the check box to not adjust the mesh. You can specify the number of smoothing iterations in the field. In the field you can specify the maximum element depth for the mesh points to be smoothed.

Figure 8-108: Comparing meshes where Smooth across removed control entities has been used vs. not used.

Linking Faces

You can choose between two different interpolation methods for the linking faces in the list. This specifies how the mapped mesher, which is used by the swept mesher for the linking faces, determines the positions of the interior mesh points. For more information on the different options see Mapped.