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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.
Transforming Regions
There are four types of transformations that you can apply to regions: Scale, Translate, Rotate, and Reflect.

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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.
    - 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.
      - Scaling Regions
        Scaling regions is especially useful when the mesh has been created in non-SI units.
      - Translating Regions
        Translating regions is useful if you import multiple regions separately and you want to move them relative to each other.
      - Rotating Regions
        Region rotation can be used if the orientation of the imported mesh is not suitable for viewing, or if one region does not match the orientation of other regions.
      - Reflect Regions
        You can use the reflection option to reposition the region according to its mirror reflection about an axis or combination of axes.
    - 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.

Transforming Regions

There are four types of transformations that you can apply to regions: Scale, Translate, Rotate, and Reflect.

The transformations are typically used to create separate regions when more than one mesh is imported, and these regions would not match spatially without some sort of transformation.

The transformations can be done on a single region or on multiple regions at the same time. The transformations that you apply to a region also affect the interfaces and boundaries that are attached to the region.

When regions have one of the following assigned to them–and no volume mesh, interfaces form between the surface meshes of the regions:

geometry part
imported part
surface wrapper
remeshed surface

Interfaces between surface meshes require physical contact between the parts that contain the regions, however, interfaces between volume meshes do not. Interfaces can exist between widely spaced regions of parts with volume meshes. For this reason, you can transform regions of parts with volume meshes without affecting the interfaces.

Requirements when Transforming Regions:

You can transform a region that is connected to another region through an interface without affecting that interface as long as both regions have a volume mesh.

When you transform regions that have volume meshes and are connected through an interface:

There are no part contacts between the regions
No errors occur
The transformation is successful

If you attempt to transform a region that is connected to another region through an interface and one or both regions are assigned to parts without a volume mesh, an error occurs. The following error message is displayed:

When you transform regions that are assigned to parts without a volume mesh:

Interfaces are created from part contacts between the surface meshes of the parts
Part contacts can not be broken
The transformation fails

When you transform regions and one or more (but not all) regions are assigned to parts without a volume mesh:

The transformation is successful
The interface is not maintained

To Meet Requirements when Transforming Regions:

Create volume meshes for all regions that are connected through an interface.
Translate all coincident parts with the region that you want to translate. Then imprint the parts and re-create the part contacts.