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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.
Assigning Part Surfaces to Boundaries
As with parts and regions, a bi-directional relationship exists between part surfaces and boundaries.
Assigning Surfaces to Boundaries Using the Part Surface Nodes
The Set Boundary option lets you assign surfaces to boundaries.

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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.
    - Assigning Surfaces to Boundaries Using the Part Surface Nodes
      The Set Boundary option lets you assign surfaces to boundaries.
    - Assigning Surfaces to Boundaries Using the Region Boundary Nodes
      The part faces that are assigned to a boundary can be set using the boundary node Properties window.
  - 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.
  - 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.

Assigning Surfaces to Boundaries Using the Part Surface Nodes

The Set Boundary option lets you assign surfaces to boundaries.

To assign a surface face directly to a boundary, right-click the face node and use the Set Boundary menu item. For a small set of boundaries, a list of the boundaries is available as a submenu. For a larger set, the Existing submenu item activates the object selector (see Activating the Object Selection Dialog):

More than one face node can be selected and assigned to the same boundary using the above method.

A new region always contains one boundary by default, usually with the name Default. If a new boundary is preferred for the selected face, then the Set Boundary > New... option can be selected instead, as shown below:

A dialog appears with a text box for you to name the new boundary. The boundary name matches the selected face node by default.

After you click OK, a new boundary is created and is automatically assigned the face. The new boundary is shown below:

If two or more face nodes are selected for the new boundary option, then the boundary name is based on the keyword Boundary instead of the face node name.

If the region to which the parent part is assigned has no boundaries existing for it, only the New suboption is available.

Alternatively, the boundary that a face node is assigned to can be reviewed or modified using the face node properties. Selecting the face node of interest shows the properties for that node:

Click the right half of the property to activate the object selector, which only shows boundaries belonging to the region to which the parent leaf-level part is assigned. A new boundary cannot be created using this method.