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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.
Meshing
A mesh is a discretized representation of a geometric domain. This domain can include real-world geometry, its content, and its surrounding environment.
Mesh Operations
Mesh operations perform actions on geometry parts that you can easily repeat whenever their input parts or properties are changed.
Unite Parts
The unite mesh operation performs a boolean unite on all input parts that are in contact with or overlap each other.

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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.
- Meshing
  A mesh is a discretized representation of a geometric domain. This domain can include real-world geometry, its content, and its surrounding environment.
  - Mesh Construction
    Within a bounding volume defined by geometrical surfaces, Simcenter STAR-CCM+ can construct meshes for finite volume and finite element solvers.
  - Meshers in Simcenter STAR-CCM+
    The meshers in Simcenter STAR-CCM+ generate surface and volume meshes for geometry parts that are assigned to regions and make them ready for analysis.
  - Parts-Based Meshing
    Parts-based meshing (PBM) is a meshing strategy in which you create one or more mesh operations that define workflows for preparing, fixing, and processing geometry. A major benefit of PBM is that every mesh operation you create forms part of a linear and repeatable process.
  - The Meshing Workflow
    This section contains the recommended workflow for setting up and generating the volume mesh at the parts level.
  - Mesh Operations
    Mesh operations perform actions on geometry parts that you can easily repeat whenever their input parts or properties are changed.
    - Creating Mesh Operations
    - Selecting Input Parts for Mesh Operations
    - Executing Operations
      Executing operations mean that you tell Simcenter STAR-CCM+ to perform the actions that the operation defines—such as volume extraction, transformation, or meshing. The operation right-click menu also lets you select the output parts that result from executing the operation.
    - Inherited Parts
      Inherited parts are the input parts to an operation, which are categorized separately from any new surface and curves that the operation creates. This categorization makes it easier to find and apply the input parts to other operations and mesh controls.
    - Copying Controls Between Mesh Operations
    - Mesh Operation Errors
    - Fill Holes
      You can use the Fill Holes operation to fill gaps in the geometry with a closed surface.
    - Extract Volume
      The extract volume mesh operation finds enclosed volumes within selected parts and generates a part to fill the volume.
    - Surface Extruder
      The surface extruder extends the edges of the input surface to form the bounding surfaces of the extruded region. You specify the extrusion distance in the surface extruder operation.
    - Transform
      The Transform operation allows you to perform transformations on parts and coordinate systems. The available transformations include translate, rotate, reflect, scale and coordinate system transform.
    - Zip Edges
      Use the Zip Edges operation to fix minor issues on a surface—such as the closing of small gaps, or stitching multiple parts together.
    - Contact Creator
      You can create contacts as part of the pipeline using the contact creator operation.
    - Part Pattern
      Two operations allow you to create patterns of parts—the linear pattern operation and the circular pattern operation. These operations reproduce one or more source parts in the specified formation.
    - Offset Parts
      This operation generates a surface on the outside of parts, at a specified distance away from the part surfaces. The offset operation also supports thin-walled structures known as shells.
    - Part Curve Creator
      The part curve creator operation creates and maintains part curves in the parts-based meshing pipeline. Within the operation, you add one or more part curve controls each of which acts on their own selection of part surfaces.
    - Morph Surface Mesh
      The Morph Surface Mesh operation allows you to morph (deform) a surface mesh based on a displacement field that you supply. The resulting surface is stored as a new description for the selected input parts.
    - Attached Shells Creator
      The Attached Shells Creator operation creates attached shell parts from parts and part surfaces.
    - Unite Parts
      The unite mesh operation performs a boolean unite on all input parts that are in contact with or overlap each other.
    - Intersect Parts
      The intersect mesh operation performs a boolean intersect on all input parts that overlap each other.
    - Subtract Parts
      The subtract mesh operation removes geometry parts from the target geometry part.
    - Imprint Parts
      The Imprint operation imprints geometrically close surfaces, or geometrically close surfaces and edges, within a defined tolerance. Part contacts are created between the surfaces that are coincident and you can choose to create a conformal or non-conformal surface mesh between parts.
    - Bounded Shapes
      Use bounded shapes to define your simulation domain or to refine the mesh in certain locations. Bounded shapes are shape parts that are bound to existing geometry, and resize to maintain their relative shape and size according to the reference geometry.
    - Boolean Mesh Operation Properties
      Some boolean mesh operations have common properties which are described in this section.
    - Priority Indexing
      When imprinting parts, at least one part is designated as the destination part and any other parts are designated as source parts. Priority Indexing lets you control which parts are the destination or source parts. The part or parts with the lowest index value have the highest priority. So any parts with the priority index of 1 are the destination parts.
    - Intersection Curve Remeshing
    - Automated Mesh
      The automated mesh operation generates surface and volumes meshes for its input parts. It manages all of the meshers, default controls, and custom controls.
    - Volume Mesh Pattern
      To generate an identical volume mesh for all segments in periodic geometries, use the Volume Mesh Pattern operation.
    - Detaching Parts from Operations
      Some operations create parts that contain the output of that operation. The output parts are linked to the operation so that when you make a change to the operation, the output parts are updated. You can break the link between the part and the operation by detaching the parts.
    - Identifying Out-of-Date Parts in an Operation
      Parts that will be meshed when you execute an operation, that is, parts that are newly added to an operation, have failed from previous operations, or are that were modified, are marked as "dirty" or out-of-date.
  - Mesh Descriptions
    A mesh description is a version of a surface or volume mesh belonging to a geometry part. Geometry parts can have more than one surface mesh description associated with them. You create and change descriptions by importing surfaces or executing operations.
  - Custom Mesh Controls
    Custom controls override any default controls for the surface and volume meshers. This facility allows you to refine or coarsen the mesh for part curves, part surfaces, geometry parts, and specified volumes.
  - Surface Meshers
    Simcenter STAR-CCM+ contains meshing tools which can be used to help prepare a high-quality surface mesh before a volume mesh can be generated.
  - Volume Meshers
    Simcenter STAR-CCM+ contains different types of meshers that can be used to generate a volume mesh starting from a suitably prepared surface mesh.
  - Mesh Refinement
    Simcenter STAR-CCM+ can refine the mesh by approximating the wake region or using solution-based approach. These features allow you to achieve efficient refinement by reducing the cell size in areas of interest.
  - Directed Meshing
    Directed meshing is a method for generating high quality swept meshes on geometries in Simcenter STAR-CCM+. The method operates by sweeping a mesh from the surfaces of a geometry through its volume onto a facing target surface.
  - Two Dimensional and Axisymmetric Meshes
    The use of a one-cell-thick three-dimensional mesh is much less efficient than using a real two-dimensional mesh for two-dimensional and axisymmetric simulations. When circumstances allow, use real two-dimensional meshes.
  - Turbomachinery Mesh
    Turbomachinery applications with axial blades typically require a flow-aligned, structured mesh. This type of mesh has implicit connectivity and a fixed number of vertex or face neighbors, leading to a more accurate solution.
  - Mesh Visualization
    You can visualize any mesh representation in Simcenter STAR-CCM+. After you have imported or generated a mesh, you visualize it to check the cell quality and mesh validity.
  - Checking the Surface Mesh
    The volume mesh quality is directly dependent on the surface mesh quality. Therefore, it is crucial to make sure that all surface meshes are of good quality.
  - Checking the Volume Mesh
    This section describes the tools available for checking the validity and quality of the volume mesh, and for diagnosing problem areas. Such problems can then be fixed, either inside Simcenter STAR-CCM+ or in the originating mesh generator.
  - Meshing Field Functions Reference
    This section contains a list of field functions that are related to meshing.
  - Working With Representations
    This section provides information on representations as a useful part of the meshing process.
  - Scaling the Entire Mesh
    Scaling the mesh is important as the units of the model must be in meters before running an analysis.
  - Working with Baffles
  - Exporting Mesh and Solution Data
    This section outlines the steps for exporting Simcenter STAR-CCM+ mesh and solution data to formats that can be used in other CAE packages.
  - Multi-Region Meshing
    This section outlines the surface requirements for performing multi-region meshing, as well as step-by-step instructions when starting from surface imports that result in single region and multiple regions definitions. Additionally, guidelines are provided on what the best approaches are for exporting surface data from CAD packages when multiple regions are required.

Unite Parts

The unite mesh operation performs a boolean unite on all input parts that are in contact with or overlap each other.

Selecting the Operations > Unite node allows you to set properties for the unite mesh operation in the properties window.

Example of the Unite Parts Operation

The following diagram illustrates the behavior of the unite parts operation.