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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.
Manipulating Parts
Simcenter STAR-CCM+ allows leaf-level parts to be manipulated in several different ways once they have been imported or created.
Splitting a Part by Surface Topology
The split by surface topology method can be used to split and combine parts that can be defined as distinct geometrical regions.

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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.
    - Retessellating a Part
      The surfaces of a geometry part are represented using triangles which come from a process that is known as tessellation.
    - Transforming a Part
      Five different types of transformations are provided to transform parts.
    - Duplicating a Part
      You can duplicate a part in instances where only a half, quarter, or some fraction of a symmetrical or axis-symmetric model has been imported and the full geometry is desired instead.
    - Combining Parts
      Two or more parts can be combined to create a single mesh part.
    - Performing Boolean Operations
      This section describes the basic Boolean operations that can be performed on geometry parts.
    - Splitting Non-Contiguous Parts
      A non-contiguous mesh part (that is, a mesh part that has faces that are not connected to other faces in the part) can be split into its individual component parts if necessary.
    - Splitting a Part by Surface Topology
      The split by surface topology method can be used to split and combine parts that can be defined as distinct geometrical regions.
    - Replacing a Part
      You can replace a single CAD or mesh part at any time. Replacing a part lets you provide new geometrical input for the meshing pipeline without affecting any of the other data input required to generate a mesh.
    - Manipulating Part Surfaces
      Simcenter STAR-CCM+ allows leaf-level part surfaces to be manipulated in several different ways.
    - Deleting Empty Entities
      This option allows you to delete empty part surfaces and part curves. Empty part surfaces do not have face definitions in any of the descriptions in the simulation. Similarly, empty part curves do not have any feature edges in any of the descriptions in the simulation.
    - Manipulating Part Curves
      Simcenter STAR-CCM+ allows leaf-level part curves to be manipulated in several different ways.
    - Manipulating Part Points
      In addition to part surfaces and part curves, Simcenter STAR-CCM+ allows you to create part points. Part points are intended for specific applications that allow you to set quantities at point locations. For example, in solid stress simulations you can define loads and constraints at specific points.
    - Repairing Part Surfaces and Curves
      Repairs can be made to leaf-level parts at any time before surface initialization. They can be required to close a surface or fix some other non-valid entity that the translation process created.
    - Exporting Parts
      This section describes how to export the data that is contained in the geometry parts tree.
    - Getting the Face Count of a Part
      This section describes how to obtain the number of faces of a geometry part.
    - Editing Imported Parts in 3D CAD
      This section describes how to modify your imported geometry parts using 3D-CAD.
    - Part Operations Reference Page
      This section contains a list of available operations that appear when right-clicking a part.
  - 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.

Splitting a Part by Surface Topology

The split by surface topology method can be used to split and combine parts that can be defined as distinct geometrical regions.

It is similar to the method used to split regions. The operation is based on the topology of closed, manifold, non-intersecting surfaces that the parts define. When assessing the surfaces, Simcenter STAR-CCM+ considers the surfaces that are contained within one part to be a single surface. You do not need to combine or split any surfaces before carrying out the operation.

The technique allows you to:

Separate two or more closed surfaces that are not in contact into two or more parts.
Separate two or more closed surfaces that share a common interface.
Create new parts from internal voids.
Redefine the surfaces of parts that contain closed surfaces or other whole parts.
Combine parts with shared part surfaces.

When this technique is used for multiple parts, Simcenter STAR-CCM+ internally combines all the parts and treats them as a single part. If a part is not modified in the operation, it is returned as a CAD part with the same name as it had previously. If a part is modified, for example it gained extra surfaces from other selected parts, it is returned as a Mesh part.

To split a part by surface topology:

Right-click the part and select Split by Surface Topology.
If you wish to include several parts in the operation, select the parts using <Ctrl><Click>.
If you want to split parts by surface topology but combine parts that share a part surface, in the Split Parts Options dialog that appears, activate Combine Parts With Shared Part Surfaces.

Using Split by Surface Topology

An example where a part contains an inner void and one wishes to create another part from the inner surface is illustrated below.

Identify parts that can be split into one or more separate parts.

In the figure below, the single part Body 1 contains a cylindrical void.
Right-click the part that you want to split and choose Split by Surface Topology:
In the Split Parts Options dialog, click OK.

The result can be viewed in a geometry scene as shown below:

If separate part surfaces surrounded the inner void in the original part, these surfaces would be replicated in the splitting process. The source part (Body 1 in the example above) is removed in the splitting process.