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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.
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.
Projecting Boundaries to a Plane
The project to plane function can be used to modify a non-planar boundary on a 3D or 2D volume mesh and make it planar.

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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.
    - 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.
      - Projecting Boundaries to a Plane
        The project to plane function can be used to modify a non-planar boundary on a 3D or 2D volume mesh and make it planar.
      - Projecting Boundaries to an Axis
        The primary application for projecting boundaries to an axis is to ensure that the correct mesh definition is prescribed for an axis-symmetric type analysis.
    - 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.

Projecting Boundaries to a Plane

The project to plane function can be used to modify a non-planar boundary on a 3D or 2D volume mesh and make it planar.

This projection is shown schematically below:

A typical application would be to make an undulating boundary more planar so that it could better be used for either the creation of an interface or for extracting a two-dimensional mesh from a three-dimensional mesh.

The project to plane option should be used with caution since it has the potential for adversely affecting the quality of the adjacent cells. In fact, it is possible to severely distort a boundary (and the adjacent cells) by specifying the wrong plane for projection as illustrated below:

To project a boundary, open the region of interest in the Regions node. Then right-click on the boundary of interest from the Boundaries node. Select Project to Plane... from the pop-up menu:

This opens the Project Boundaries to Plane dialog with the selected boundaries already marked with a ticked checkbox.

The plane is defined by specifying the length vector, in the Plane group box, that is normal to the plane onto which you want the projection to take place. The Normal X, Normal Y and Normal Z inputs specify the direction of the vector and the Distance input specifies the length of the vector. The example above specifies a plane that is parallel to the X-Z plane and that is 0.5 meters from the origin. The parameters are illustrated for a general case below.

Click the Apply button to start the projection process. A progress bar will be displayed at the bottom of the simulation tree. Once the process has completed successfully, a message will be displayed in the Output window indicating the boundaries that were projected and the plane that was used.