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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.
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.
Understanding Geometry Parts
You can use the geometry parts manager node to control what parts are meshed and included in the simulation downstream.

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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.
  - Preparing the Geometry
    In general, a Simcenter STAR-CCM+ analysis requires one or more geometry parts from which you define the spatial construction of the regions. Simcenter STAR-CCM+ allows you to create geometry parts directly using the built-in 3D-CAD modeler, or import geometry from a wide range of source formats.
  - Importing Geometry
    One of the possible starting points for the meshing process is to import surface data.
  - Understanding Geometry Parts
    You can use the geometry parts manager node to control what parts are meshed and included in the simulation downstream.
    - Geometry Parts
      A geometry part is a collection of surfaces and curves that you wish to address as one object. Parts surfaces and curves can be defined by CAD data or discrete (surface mesh) data, depending on the type of geometry part. A single object is referred to as a leaf-level part; a collection of geometry parts is referred to as a composite part. A surface can contain one or more sets of faces and a curve can contain one or more sets of edges.
    - What Is Metadata?
      The metadata specifier can be used to associate a key and value with the part.
    - Creating and Importing Parts
      Geometry parts can be created in the following ways
    - Organizing Assemblies Using Composite Parts
      Composite parts allow other parts to be grouped into assemblies and subassemblies for easier organization.
    - Using Part Contact Data to Create Interfaces
      A geometry part has a Contacts property that provides a list of all other parts with which the part is in contact. This part contact data can be used to generate interfaces for meshing and physics coupling automatically without having to create and assign coincident faces manually.
    - Updating Part Interfaces
      Updating part interfaces between two regions becomes necessary when one or more interfacing parts have been modified or have changed region.
  - Manipulating Parts
    Simcenter STAR-CCM+ allows leaf-level parts to be manipulated in several different ways once they have been imported or created.
  - Part Contacts
    Part contacts define the connection between two part surfaces. The meshers aim to generate a conformal mesh at the contact, which then becomes an interface in the physics region.
  - Repairing CAD Geometry
    The Geometry Repair tool provides diagnostic checks for assessing the validity of geometry and the means to repair the geometry automatically.
  - Displaying the Geometry
- 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.

Understanding Geometry Parts

You can use the geometry parts manager node to control what parts are meshed and included in the simulation downstream.

Using the parts-based meshing approach allows a more flexible, re-playable, pipeline of operations, which is particularly useful for any or all of the following scenarios:

Where you want to mesh multiple parts in the same region with different types of volume mesh.
Where a hierarchical assembly of CAD assemblies and parts exist that must be maintained within the Simcenter STAR-CCM+ environment.
Where you want the control over the ability to repair or swap out individual parts without having to work with the entire surface.
Where you want to define a template .sim file, containing meshing and modeling settings so that geometries can be imported later.
Where you want to use a non-standard volumetric control shape that a closed volume part defines.
Where you want to use the 3D-CAD modeler within Simcenter STAR-CCM+ to design and parameterize a geometry so that an optimal flow solution is obtained.

This section covers how geometry parts are created or imported, how to organize them, and how to apply tags and filters to them. Geometry parts can be repaired and manipulated in a similar way to surface meshes. Once parts have been organized and prepared, they are assigned to regions and an initial surface mesh is created by initializing the meshing operations.

Although the parts-based meshing approach is recommended, you do not have to use parts to generate a mesh. You can import parts, assign parts to regions, then generate mesh at the regions level. However, if you are working with assemblies that contain dozens or hundreds of parts, using the parts-based meshing approach is beneficial. Furthermore, if you intend to use the 3D-CAD modeler to design the geometry from scratch or modify an existing CAD model, using geometry parts is a natural part of the process of going from CAD to flow solution.