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Pre-Processing
Simcenter STAR-CCM+ solves physics problems on a computational mesh. To provide this mesh, you first define geometry using internal or external tools, and then create a mesh pipeline whose operations generate the mesh in repeatable steps.
Modeling Geometry
This part of the User Guide describes how to use 3D-CAD, the parametric solid modeler available within Simcenter STAR-CCM+. It also describes the features and tools available for further preparation of the geometry model and its surfaces.
Importing Geometry
One of the possible starting points for the meshing process is to import surface data.
Checking the Surface Validity
The validity of the surface can be checked using one of two different methods:

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Pre-Processing
Simcenter STAR-CCM+ solves physics problems on a computational mesh. To provide this mesh, you first define geometry using internal or external tools, and then create a mesh pipeline whose operations generate the mesh in repeatable steps.
- 3D-CAD
  3D-CAD is a feature-based parametric modeler within Simcenter STAR-CCM+ that allows you to build geometries from scratch. The geometries that you create with 3D-CAD are stored as 3D-CAD models, which you can then convert to geometry parts for integration with the meshing and simulation process.
- Modeling Geometry
  This part of the User Guide describes how to use 3D-CAD, the parametric solid modeler available within Simcenter STAR-CCM+. It also describes the features and tools available for further preparation of the geometry model and its surfaces.
  - Preparing the Geometry
    In general, a Simcenter STAR-CCM+ analysis requires one or more geometry parts from which you define the spatial construction of the regions. Simcenter STAR-CCM+ allows you to create geometry parts directly using the built-in 3D-CAD modeler, or import geometry from a wide range of source formats.
  - Importing Geometry
    One of the possible starting points for the meshing process is to import surface data.
    - Surface Mesh Formats
      A surface mesh is a discrete representation of the geometry of individual regions that are used for the volume mesh generation.
    - Neutral Formats
      Neutral format data files allow CAD model data to be exchanged between different programs while still maintaining the model integrity.
    - Native CAD Formats
      Native CAD data files are created with parametric based CAD programs and contain all the relevant solid model information for that program.
    - XML Formats
      XML files are top-level data files that typically describe the assembly structure and components of a product.
    - CAD Package Support
      This section contains a list of supported CAD Clients, the CAD import versions, and the CAD export versions.
    - Importing Surface Data into Simcenter STAR-CCM+
      All surface data (except for XML-based imports) for use in the meshing pipeline is imported into Simcenter STAR-CCM+ using the Import Surface Mesh... menu item:
    - Importing Surfaces Using an XML File
      XML-based data files can be used to import many parts with a given hierarchy, such as a CAD assembly.
    - Importing Multiple Surface Data Files
      STAR-CCM+ allows multiple surface input files of the same format to be imported simultaneously using the File > Import Surface option.
    - Reviewing the Surface Data Import Report
      A summary of the surface statistics for the imported file is reported in the Output window.
    - Using Surface Data Import Representations
      When importing surfaces as regions, an Import representation is created under the Representations node in the simulation tree.
    - Checking the Surface Validity
      The validity of the surface can be checked using one of two different methods:
  - Understanding Geometry Parts
    You can use the geometry parts manager node to control what parts are meshed and included in the simulation downstream.
  - Manipulating Parts
    Simcenter STAR-CCM+ allows leaf-level parts to be manipulated in several different ways once they have been imported or created.
  - Part Contacts
    Part contacts define the connection between two part surfaces. The meshers aim to generate a conformal mesh at the contact, which then becomes an interface in the physics region.
  - Repairing CAD Geometry
    The Geometry Repair tool provides diagnostic checks for assessing the validity of geometry and the means to repair the geometry automatically.
  - Displaying the Geometry
- The Surface Repair Tool
  The Surface Repair tool diagnoses errors in, and provides repair tools for, tessellated surfaces and part curves. The same tool allows you to reorganize discretized geometry by searching for face-based features and attributes then assigning the results to new or existing part surfaces or curves.
- Defining the Regions Layout
  An essential part of the process in setting up your simulation is to define the relationship between geometry parts and regions, boundaries, and interfaces.
- Meshing
  A mesh is a discretized representation of a geometric domain. This domain can include real-world geometry, its content, and its surrounding environment.

Checking the Surface Validity

The validity of the surface can be checked using one of two different methods:

Using the surface preparation options dialog.
Using thresholds.

Three different derived part threshold scalars can be used to check the quality. The checks are:

Free edges
Non-manifold edges
Pierced Faces

Free edges refer to cell faces that are not connected to a neighboring face. A non-manifold edge refers to a cell face edge that is connected to two (or more) other edges. A pierced face is one that has one or more edges of another surface cell piercing it.

To create the above threshold checks, do the following:

In the Input Parts list, specify the boundary surfaces that you want to check. It is not sufficient to include only the region part.
Select the appropriate Scalar for the desired surface check (either Free Edges, Non-manifold Edges, or Pierced Faces).
Set the Extraction Mode to All Above.
Set the threshold value to 0 and press the Create button.

A new derived part is created containing the cell faces next to the problem areas which allows you to investigate the problems further.

If you have any doubts over the validity of the starting surface, then run these checks as a precaution. Fix any problems that are found: the volume meshers cannot proceed until all problems are fixed. Currently, free edges can be fixed by using the hole filler, the edge zipper, or the manual fixing tools, depending the nature of the problem. A non-manifold edge is sometimes valid depending on whether the surface cells causing the problem are supposed to be a part of the geometry or not. For example, consider a geometry that contains a baffle surface that is joined to the exterior surface. This geometry is not a problem as long as the surface is converted to an interface before proceeding with the volume meshing. If the non-manifold edge is not expected, then you can delete the faces that are causing the problem. Hand fixing tools to remove pierced faces are now supported in STAR-CCM+ and as such can be fixed directly within the software itself.