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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.
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.
Manipulating Boundaries
It is often convenient to modify boundaries in the simulation without having to modify the mesh and re-import it.
Splitting Boundaries
It is useful to split boundaries if the original mesh contains too few of them for modeling or analysis purposes.
Splitting by Patch
The split by patch function allows you to split a boundary based on the underlying patch definition of the imported surface geometry.

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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.
- 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.
  - Regions Layout Workflow
    In defining the regions layout you map between the geometrical definition of the problem and the computational (or physical) definition.
  - Assigning Parts to Regions
    Before a leaf-level part can be used in the meshing process, it must be assigned to a region.
  - Assigning Part Surfaces to Boundaries
    As with parts and regions, a bi-directional relationship exists between part surfaces and boundaries.
  - Using the Assign Parts to Regions Dialog
    The Assign Parts to Regions dialog lets you assign several part-level objects to region-level objects in one action. This dialog is the recommended method of assigning parts to regions.
  - Initial Assignment of Boundary Types
  - Interfaces Overview
    Interfaces are used in Simcenter STAR-CCM+ to transfer solution quantities between regions in a simulation. Certain types of interfaces modify quantities passing across them, such as a porous baffle interface that presents resistance to fluid flow. Periodic and repeating interfaces allow you to reduce the scope of the solution domain.
  - Region Manipulation
    To fix surface or volume meshes that are not suitable for obtaining a valid solution, choose from among various techniques for manipulating regions.
  - Region Reposition
    The Reposition Model adds a transformation to the volume mesh representation of a region at the point of simulation initialization. That is, the transformation applies in the case of a new simulation or a simulation with cleared solution. In some automated simulation or design exploration studies, your objective is to obtain results for a series of simulations in which the relative positioning of one part changes in each simulation. An example is an airfoil with a changing angle of attack. Using the Reposition Model, you can wrap the geometry that changes in an overset region, and then use the Reposition Specification on the region to define the orientation at the start of each new simulation run.
  - Manipulating Boundaries
    It is often convenient to modify boundaries in the simulation without having to modify the mesh and re-import it.
    - Combining Boundaries
      Combining two or more boundaries into a single boundary is useful when the imported surface or volume mesh contains separate boundaries which should have identical types, conditions, and values.
    - Fusing Boundaries
      The fuse command can be used to combine a pair of boundaries from the same volume mesh region and replace them with interior faces.
    - Merging Boundaries
      Boundaries that belong to a surface mesh can be merged together if they are in the same region and have surfaces intersecting one another.
    - Splitting Boundaries
      It is useful to split boundaries if the original mesh contains too few of them for modeling or analysis purposes.
      - Splitting Non-Contiguous Boundaries
        This function will split a surface or volume mesh boundary into its non-contiguous pieces.
      - Splitting by Angle
        This function enables surface or volume mesh boundaries to be split according to the included angle between faces.
      - Splitting by Function
        This operation splits volume mesh boundaries according to the rounded integral value of a specified field function.
      - Splitting by Patch
        The split by patch function allows you to split a boundary based on the underlying patch definition of the imported surface geometry.
    - Creating New Boundaries
      New empty boundaries can be created at any time so that part surfaces can be allocated to them as required in order to form regions for meshing purposes.
    - Projecting Boundaries
      Boundaries belonging to a volume mesh can be projected in order to modify an existing boundary surface to conform to a given plane.
    - Selecting Boundaries
      A dialog is available for selecting boundaries for various operations.
    - Copying Boundary Properties
      If you have two (or more) boundaries that you want to have exactly the same Type property, but you have chosen not to combine them, then you can copy that property from one boundary to another.
    - Properties of the Boundaries Manager
      The Boundaries manager node provides information on the number of boundaries in the simulation.
    - Pop-Up Menu of the Boundaries Manager
      Right-click the Boundaries manager node to add boundaries or group them.
  - Performing Boolean Operations on Regions
    Boolean operations can be performed between two or more intersecting, closed, manifold regions to create a single region made up of a single surface. The new surface is also closed and manifold and can be used as part of the meshing process or as the starting point for additional Boolean operations.
- 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 by Patch

The split by patch function allows you to split a boundary based on the underlying patch definition of the imported surface geometry.

A patch represents a cell table, group, family or some other similar entity used in the original surface pre-processing software to differentiate one surface from another. This information is read into Simcenter STAR-CCM+ as part of the surface import process and is maintained as part of the import representation. All surface file formats other than STL support patch definitions.

Patches are useful in Simcenter STAR-CCM+ as they allow a quick and easy method of reconstructing the boundaries to match the original surface definitions should they not initially be imported this way. A boundary can contain multiple patches but a patch cannot be shared among two or more boundaries. The patch definitions can change depending on how the boundaries are manipulated. For example, if a boundary is split up (based on an angle or part curves etc), then each new boundary will have its own patch definition.

To split boundaries by patch:

Right-click on the boundary name or names (using multiple selection) in the Boundaries node and select Split By Patch...

Note You must have a scene open to use this feature.

The Split Boundary by Patch window appears in the edit tab in the explorer pane.

Here, the patches that are contained in the import surface are listed numerically. The surfaces on the geometry in the scene window will also be color-coded to represent each patch number.
Select the patches from the list box or directly using the mouse in the scene display. To select multiple patches, press the <Ctrl> key, or use the zone selection tool from the Selection toolbar. Selecting a patch will result in it being highlighted in the scene window.
Enter the new Boundary Name.
Click Create. The relevant patch or patches will be removed from the dialog and scene so that only the remaining patches are shown.
Repeat the process as many times as required until only one patch is left.
Click Close when done.

Note	When only one patch remains, the Create button is disabled. The source name will be used for the remaining boundary.

The new boundaries appear in the simulation tree. In the following example, the boundaries were created based on 6 patches.