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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.
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.
Periodic Contact
A periodic contact defines two part surfaces that are spatially detached, but a rotation and/or translation can make them coincident.

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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.
  - 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.
    - Part Contacts Properties and Context Menus
      The Contacts manager node and the part contact subnodes provide several properties and right-click actions that allow you to check and edit the connections between parts.
    - Creating Part Contacts
      Use mesh contacts to define a connection between two part surfaces.
    - In-Place Contact
      An in-place contact is a direct connection between two part surfaces.
    - Periodic Contact
      A periodic contact defines two part surfaces that are spatially detached, but a rotation and/or translation can make them coincident.
      - Periodic Contact Properties
    - Baffle Contact
      A baffle contact is a zero-thickness surface that the meshers maintain in the surface and volume meshes.
  - 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.

Periodic Contact

A periodic contact defines two part surfaces that are spatially detached, but a rotation and/or translation can make them coincident.

When you create a periodic contact, the surface that you select first is the primary surface and the other surface is the secondary. Simcenter STAR-CCM+ calculates the rotation and/or translation as relative to the primary surface.

Some geometry configurations require a conformal surface and volume mesh between regions. The periodic contact helps achieve a conformal mesh between the desired regions. However, using this type of contact can lead to unwanted interfaces being generated when you assign parts to regions as by default, periodic contacts generate periodic interfaces. In some cases, periodic contacts are only required to achieve a conformal mesh between regions and a periodic interface is not required. For such cases, you can activate the Mesh Only Contact option on individual contacts to stop the contact from generating an interface.

To make sure that the mesher can generate a conformal mesh, the size and shape of the periodic surfaces must be identical. If you are using a rotation and translation transformation, make sure that the rotation and translation vectors are parallel to each other. If these transformation vectors are not parallel, the resulting mesh may not be conformal. If the mesher cannot generate a conformal mesh, the meshers continue, but the Output window displays a warning message.

To make sure that the periodic surfaces maintain their original shape, they are excluded from the automatic surface repair operations. Similarly, any manual repairs that you make to the periodic surface after remeshing are not maintained during volume meshing.

Examples of Periodic Contacts

The following examples show two types of periodic contacts. The green and red dashed lines represent the primary and secondary surfaces respectively.

The first diagram illustrates a rotational periodic contact.

The second diagram illustrates a translational periodic contact.