Import

) to import a mesh from a file, from another meshing sequence or mesh part, or from a or dataset. It is only possible to import a mesh to a meshing sequence under a node if the geometry sequence is empty. If the sequence already contains a mesh, the imported mesh is added to the existing mesh, forming an assembly. If you use this node in a mesh part, you can then use it in a geometry sequence through an node under a node.

To import a mesh, right-click a node or a node and select . Then enter the properties for the import using the following section:

In the list, choose the type of data to import: , (if applicable meshing sequences are available), and are always available. In addition to the native file formats, you can choose (stereolitography file), (Virtual Reality Modeling Language file), (Polygon File Format or Stanford Triangle Format file), and (3D Manufacturing Format file), and and in 2D and 3D. Choose to import the visualization mesh of a Filter or Partition dataset. This option is only available if there is at least one or node under in .

For file import, specify the filename in the field or click the button. For import from another mesh in the model, select a meshing sequence or mesh part from the list below. To import a meshing sequence, click the button. For a mesh part, the button is not needed and is therefore disabled. For import of a dataset in the model, select a Filter or Partition dataset from the list below.

If you have changed some property, the software automatically reimports the mesh when you click a build button.

	For information on remeshing an imported mesh, see Creating Geometry from Mesh.

In 3D, you can import 3D meshes and planar 2D meshes from COMSOL Multiphysics files (.mphtxt or .mphbin). Planar 2D meshes, imported to a 3D component, always appear at z = 0.

When you import a mesh from a COMSOL Multiphysics file that contains mesh selections, you need to select the check box (selected by default) to import the selections together with the mesh. If you choose to import mesh selections, corresponding selections are created and appear in the , , , or sections, depending on space dimension and the entity level for the imported selections. You can use the imported selections, for example, to add as a selection to a dataset or plot during postprocessing. See also Domain Selections, Boundary Selections, Edge Selections, and Point Selections below.

To import the second-order elements in 2D and 3D as linear elements (that is, ignoring node points not in element vertices), select the check box (not selected by default).

In 2D and 3D, it is possible to import the result of a Filter or Partition dataset evaluation. An example of where import of a dataset is used is when setting up a verification study for topology optimization results.

Select the check box (selected by default) to also import the selections defined by the component corresponding to the dataset. If you choose to import these selections, they will appear in the , , , or sections, depending on space dimension and the entity level for the imported selections. You can use the imported selections, for example, to add as a selection to a dataset or plot during postprocessing. See also Domain Selections, Boundary Selections, Edge Selections, and Point Selections below.

Select the check box (cleared by default) to import domain mesh elements from the dataset. Domain mesh elements can only be imported if the result that the dataset is evaluated on is defined a domain mesh.

	It is recommended to import the boundary mesh only. The operations Adapt or Free Triangular can be used to improve the quality or remesh the boundaries. Lastly, use the Free Tetrahedral operation to fill the domains with a tetrahedral mesh.

You can import 3D meshes (and planar 2D meshes) in the NASTRAN bulk data format, the most common format for exchanging 3D meshes among programs. This format supports hundreds of NASTRAN entries describing elements, loads, and materials, making it possible to define a complete finite element model. When you import a NASTRAN bulk data file into COMSOL Multiphysics, the software only imports mesh and material information, while creating appropriate selections.

To import mesh and material data from a NASTRAN file, select in the list. In this case, COMSOL Multiphysics creates nodes corresponding to the data in any MAT1 and MAT10 entries in the file. Furthermore, the thickness data of any PSHELL entry in the file is stored in a node as long as it is greater than zero. To simplify the use of this data in physics interfaces, such as the interface, an selection, which contains all boundary faces associated with PSHELL entries, also becomes available. If the material data is not required, select to import the mesh only.

Mesh information is read from different NASTRAN entries, including those for mesh elements of lower dimension. When this information is not complete in the file, COMSOL Multiphysics enriches the imported mesh data with boundary elements, edge elements, and vertex elements such that a valid mesh object is formed. Each element in the imported mesh receives a unique entity index.

	For information on the NASTRAN entries that COMSOL Multiphysics supports, see Import in the COMSOL Multiphysics Programming Reference Manual (Meshing).

To use material data in the file to determine the partitioning of the elements, select the check box (selected by default). The check box is selected by default to automatically generate selections deduced from the file. Domain, boundary, and edge selections are created for each property id (PID) of the elements in the file. Mesh elements associated with RBE entries (RBE2 and RBE3) can form selections of all geometric entity levels. The created selections appear in , , , and sections, depending on their entity levels. The origin of each created selection is described in the column. These selections become available for specifying geometric entities throughout the component — for instance, in Material nodes and physics interfaces. The check box is selected by default to allow the boundary partitioning algorithm to split the boundary entities that are defined based on the data in the file into smaller parts.

The import of NASTRAN files supports first-order (linear) and second-order elements. To import the second-order elements in the NASTRAN file as linear elements (that is, ignoring node points not in element vertices), select the check box (not selected by default).

These settings are available with the following options from the list: , , , , , , , and .

If the partitioning of the boundary elements in the mesh to import into boundaries (faces) is not complete, you can use the list to control the partitioning:

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Select to make a minimal boundary partitioning. This is useful when you import a mesh from a measured geometry or a NASTRAN mesh with a predefined boundary partitioning. The automatic face partitioning is not desired then.

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Select (in 2D) or (in 3D) to manually control the partitioning. Both choices add a set of parameters, which make it possible to influence the result of the partitioning algorithm; for the Detect boundaries case in 3D, the and sections appear, containing settings for controlling the face and edge partitioning, respectively.

These settings are available when the list is set to for import of stereolithography files in 3D. Such files contain data for an unstructured triangulated surface.

The check box is selected by default to create a boundary selection of every solid section in the file during import. Typically, there is only one such section. In that case, a selection of the entire boundary is created. This happens also when the STL file is binary and can by definition have no solid sections. The created selections appear in a table in the section that appears below the section. The table has two columns. In the right column, the name of the solid section that the selection has been created from appears. If the section is unnamed or if the file is binary, the name is empty. The selections appear in the same order as the corresponding sections in the file. In the left column, the name of the selection appears. By this name, which can be changed, as well as dimension of the selection, you can find the selection in the model.

The repair tolerance assures that the imported mesh contains no holes and no triangles with sides shorter that the tolerance. From the list, select one of these options:

The partitioning algorithm aims to split boundary elements (edge elements in 2D, face elements in 3D) into boundary entities in such a way that no large angles appear between neighboring elements within the same boundary entity. In 2D, you can limit the angle between any two elements within the same boundary entity using the field. The maximum accepted neighbor angle can be set using the field (default: 40 degrees).

If the check box (3D) or the check box (2D) is selected (both are selected by default), the mesh import detects (approximately) planar faces or straight edges, respectively. The minimum size of a straight or planar boundary entity, relative to the entire boundary, can be set using the field (2D) and field (3D). The maximum accepted angle (in degrees) between elements for a boundary to be considered straight or planar can be set using the field. If the check box (3D) is selected, the algorithm also searches for adjacent groups of boundary elements that form cylindrical faces.

The partitioning algorithm aims to split edge elements into edge entities in such a way that no large angles appear between neighboring elements within the same edge entity. The maximum accepted neighbor angle can be set using the field (default: 60 degrees).

If the check box is selected (it is selected by default), the mesh import detects (approximately) planar edges. The specifies to which extent the operation should search for planar edges. Use the slider to tune the detection level, where means that only fully planar edges are searched for, and means that the algorithm searches for planar edges with a wider tolerance. You can also enter the parameter value directly as a value between 0 (strict) and 1 (tolerant).

If the check box is selected (it is selected by default), the mesh import detects (approximately) straight edges. The specifies to which extent the operation should search for straight edges. Use the slider to tune the detection level, where means that only fully straight edges are searched for, and means that the algorithm searches for straight edges with a wider tolerance. You can also enter the parameter value directly as a value between 0 (strict) and 1 (tolerant).

From the list, choose one of the following options: (the default), , or to specify the minimum required length of an edge to be detected. If you select , specify a minimum relative length in the field that appears, and if you select , specify a minimum absolute length in the field that appears.

In these sections, imported mesh selection appear. In the column, the name of each selection appears. For COMSOL Multiphysics file import, each name is by default the name of the selection in the imported file, which appears in the column. For STL and NASTRAN import, the source of each selection appears in column (that is, which information in the imported file that was used to generate the selection). Select the name in the column to highlight the selection in the window. You can change the name of a selection by editing the corresponding table entry in the column. Note that not all of these selection sections are available for all space dimensions.