Surface Mesh Formats

A surface mesh is a discrete representation of the geometry of individual regions that are used for the volume mesh generation.

A surface mesh is constructed from faces (triangles) and vertices. Additionally, part curves are included in surfaces that are created in some pre-processing packages. Internal feature surfaces such as baffles or interfaces are allowed.

The ideal surface mesh has the following properties:

Closed - Contains no free edges or mismatches
Manifold - Edges are shared between no more than two triangles
Non-intersecting - The surface does not self-intersect

The quality of triangle faces is also important. The ideal surface contains:

Equilateral sized triangles
Gradual variation in triangle size from one to the next
No sharp angles, surface folds, or other such characteristics within the triangle proximity sphere

Surface meshes traditionally originate from CAD packages directly or through third-party pre-processing/surfacing software, and are saved in specific formats. Consider carefully the method that you use to generate the surface mesh, as it directly influences the quality of the resulting volume mesh and the effort it takes to get to this step. In cases where a bad quality starting surface is the only option available, the surface wrapper and/or surface remesher tools can be used to improve the surface as defined above. In cases where the import surface contains quads or other elements with more than three sides, the face is automatically triangulated.

Supported Surface Mesh Input Formats

You can import the following surface mesh formats into Simcenter STAR-CCM+:


Format Name	File Extension	Binary/ASCII	Part Curves	Part Surface Names
pro-STAR Database	.dbs	Binary	Yes	Yes
pro-STAR Cell/Vertex/Shell Input	.cell/.vrt/.inp	Both	Yes	Yes
NASTRAN	.nas, .bdf, .dat	ASCII	No	Yes
PATRAN	.pat, .ntl, .neu	ASCII	No	Yes
STL	.stl, .STL	Both	No	Yes
FELISA Front Surface	.fro	Both	No	Yes
JT Open	.jt	Binary	No	No
Rhino 3D Model	.3dm	Binary	No	No
CATIA Graphics	.cgr	Binary	Yes	Yes
Parasolid Transmit	.x_t, .x_b	ASCII (.x_t), Binary (x_b)	No	Yes

All of the above formats support single or multiple region definitions but always result in a single region definition when geometries are imported from a single file. When importing multiple files, you can choose to generate either a single region or multiple regions. When importing as parts, the original hierarchy is maintained. For more information on the various import options, see Importing Surface Data into Simcenter STAR-CCM+.

If part curves exist in the original surfacing package, they are useful to maintain. Refer to the table below to see whether part curves are maintained on import.

pro-STAR Database Format

The pro-STAR database format is native to the pro-STAR pre-processing software by Siemens Digital Industries Software and can store either surface type or volume type meshes (or in combination if desired). Simcenter STAR-CCM+, however, can only read surface meshes from this file. More than one geometry can be stored in the file, with each being identified from a numerical database ID value and an optional descriptive name. Part curves that are supported and boundary names that are used in the pre-processing software are preserved when read into Simcenter STAR-CCM+. Cell table indexes in pro-STAR produce the equivalent patch definitions when read into Simcenter STAR-CCM+. The file is binary to preserve file size and is the recommended file format to use when transferring surface data from other Siemens Digital Industries Software pre-processing programs to Simcenter STAR-CCM+.

Surfaces that are imported from a database file are always represented as surface mesh parts.

pro-STAR Cell and Vertex Shell Input Format

The pro-STAR cell/vertex shell input format is a combination of three files which together reconstruct the surface geometry details. The three files are:

.cel- Cell file
.vrt- Vertex file
.inp- pro-STAR command input file

The input (.inp) file is always ASCII and contains pro-STAR commands that define the cell table entries for the mesh, as well as commands to read in the other two files with the appropriate ASCII or binary format option. Part curves are supported and boundary names are read from the cell table entries when available. Different cell table indexes in the cell file result in the equivalent patch definitions when read into Simcenter STAR-CCM+.

Surfaces that are imported from pro-STAR cell/vertex/input files are always represented as surface mesh parts. Additionally, when exporting a surface mesh to the .inp format, any spaces within boundary names are replaced with underscores.

NASTRAN Format

The NASTRAN format is an ASCII-based file that is commonly used by a number of CAD packages and pre-processing software. This format supports patch definitions but does not support part curves. The surface importer only recognizes shell (two-dimensional face) type elements. Volume meshes cannot be imported using the surface mesh importer. When preparing the NASTRAN file, it is recommended that the Free Field Format is used to export bulk data.

Surfaces that are imported from Nastran files are always represented as surface mesh parts. Surface names are preserved on import.

PATRAN Format

The PATRAN format is an ASCII-based file that is commonly used by a number of CAD packages and pre-processing software. It does not support part curves. The current importer only recognizes shell (two-dimensional face) type elements so volume meshes cannot be imported using this format. Patch definitions are supported.

Surfaces that are imported from PATRAN files are always represented as surface mesh parts.

STL Format

Stereolithography (STL) files can be binary or ASCII and are a universal method of transferring surface data using the least possible number of triangles. As such, the quality of the surface data is usually not good and some additional work is required before the geometry is usable. Part curves are also not supported and all surface patches are always placed into one boundary definition.

You can import multiple-surface binary files as a single STL binary file by concatenating multiple STL binary data. To preserve any surface names defined in the STL file, activate Read Part Surface Names From Binary Data Headers. This option allows Simcenter STAR-CCM+ to create surface names from the first word of the binary data header.

Surfaces that are imported from STL files are always represented as surface mesh parts. There is no limit to the file size when importing an STL file.

FELISA Front Surface Format

The Front Surface .fro file contains 3D surface triangulation data that is produced by the SURFACE module from the FELISA collection of programs. The SURFACE module accepts geometric curve and surface components as its input (generated by hand or from CAD software). The surface triangulation data can be used as a starting point for surface and volume meshing within Simcenter STAR-CCM+.

Surfaces that are imported from Front Surface files are always represented as surface mesh parts.

JT Open Surface Format

JT Open is a 3D data format provided by Siemens PLM Software. It is commonly used for product visualization and data exchange. It can contain a combination of tessellated and B-rep data to represent surfaces. Simcenter STAR-CCM+ supports both JT B-rep and Parasolid (XT) B-rep formats. The Simcenter STAR-CCM+ import process recognizes units specifications in the JT Open file.

If the JT Open file contains both a tessellation representation and B-rep representation, the JT Import Options box appears. From here, you can choose what representation you want to import into Simcenter STAR-CCM+. The import dialog presents options that are relevant to the type of data that is contained in the file.

To import tessellated data from a JT Open file, you require a JTOpen feature license. To import B-rep data from a JT Open file, you require a CAD Exchange license.

When importing in Part Mode, if the JT Open file does not contain units, you can select the desired units from the drop-down menu. If the JT Open file contains units, then those units are used instead of the units specified by the user.

When importing in Regions Mode, you can select the units from the drop down menu. The selected units are applied to all the JT Open files, even if they contain different units. If a hierarchy of parts is being imported in the JT format, and one or more of the parts have units specified, it is essential for all units to be the same.

Tessellated surfaces that are imported from JT Open files are represented as surface mesh parts. B-rep surfaces are represented as CAD parts.

Rhinoceros 3D Model File

Rhino 3D Model file format was originally designed to accurately transmit NURBS geometries between applications and is commonly used by the marine industry.

Rhino files can contain a combination of tessellated and B-rep data. If the geometry contains both types of data, you must import the geometry twice, changing the Import Type each time.

Surfaces that are imported from Rhino 3D Model files are always represented as surface mesh parts.

CATIA Graphics Format

CATIA Graphical Representation (CGR) is a stripped-down version of the CATIA .catpart and .catproduct formats. CGR files are typically used to view assemblies in a light-weight manner, and only contain the geometric information that is required to view the model. CAD data is not contained in this format.

Surfaces that are imported from CGR files are always represented as surface mesh parts.

Parasolid Transmit Format

Parasolid is a geometric modeling kernel that is owned by Siemens PLM. It is used as the basis of many CAD, CAM, and CAE packages for modeling three-dimensional solid objects. Parasolid Transmit files can be binary (.x_b) or ASCII (.x_t). You select the format required during the export process.

Parasolid Transmit files can contain CAD and faceted geometry. CAD data imported from Parasolid Transmit files are represented as 3D-CAD parts () while faceted data are imported as surface mesh parts (). Parasolid Transmit files that contain a mixture of CAD and faceted geometry can also be imported into geomerty parts or 3D-CAD. No units specification option is provided as this information is automatically preserved by the file.