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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.
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 Combination
To have two or more computational domains share physical properties, combine regions.
Combining Volume-Meshed Regions
You can combine two volume-meshed regions using the region pop-up menu.

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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 Combination
      To have two or more computational domains share physical properties, combine regions.
      - Combining Surface Meshed Regions
        You can immediately combine two surface-meshed regions using the region pop-up menu.
      - Combining Volume-Meshed Regions
        You can combine two volume-meshed regions using the region pop-up menu.
        Combine Regions Dialog
        The Combine Regions dialog provides properties for combining and fusing boundaries during the combination of volume meshes. This dialog also allows you to change the selected regions.
    - Region Splitting
      Region splitting allows you to modify the simulation topology by separating regions using several characteristics. Thereafter, you can apply different continua and conditions to different parts of the model.
    - Creating An Empty Region
      You can create an empty region and allocate parts to it for meshing.
    - Transforming Regions
      There are four types of transformations that you can apply to regions: Scale, Translate, Rotate, and Reflect.
    - Regions Manager Properties
      The Regions manager node provides information on the number of regions in the simulation.
    - Regions Manager Pop Up Menu
      Right-click the Regions manager node to add regions or group them.
  - 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.
  - 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.

Combining Volume-Meshed Regions

You can combine two volume-meshed regions using the region pop-up menu.

Note	The name of the combined region is the first region in the Combine Regions dialog (sorted in alphabetic order). This operation can require you to fuse adjacent boundaries.

To combine regions that have a volume mesh:

Multi-select two or more regions.
Right-click a selected region node and select Combine...
In the Combine Regions dialog, specify the region combination options.
You can also change the selected regions within the dialog.
Click OK to combine the regions.

Once the combine is complete, the Output window displays a summary of the operation.