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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.
Geometry Repair and Preparation
Simcenter STAR-CCM+ provides a suite of tools in 3D-CAD that helps you to prepare your CAD geometry so that it is suitable for meshing. CAD that is designed for manufacture can have gaps or inaccuracies that cause problems when trying to generate a watertight mesh.
Working with Repair Tools
The repair tools option simplifies the way you access features to repair a geometry in Simcenter STAR-CCM+.
Remove Gashes
In 3D-CAD, a gash is a tear or disconnection between edges that ought to form a matching seam between two connected faces. Gashes generally appear as loops having a high aspect ratio but small area. If left untouched, gashes can affect the behavior of other features downstream in the 3D-CAD simulation tree.

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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.
  - 3D-CAD Environment
    The 3D-CAD environment provides you with a feature tree from which you can activate all steps for creating and modifying geometry, and a 3D-CAD View scene in which you interact with the geometry. Many of the same feature actions are available for selection in the 3D-CAD View scene.
  - Sketches in 3D-CAD
    3D-CAD supports two types of sketch—2D sketches that are created on a planar surface and 3D sketches that are built from points located anywhere in geometric space. You can use both types of sketch in 3D geometry operations such as extrude, revolve, or sweep.
  - 3D-CAD Geometry Modeling
    Bodies represent the individual objects that make up the 3D-CAD model. Imported CAD geometry appears as bodies in 3D-CAD, and you can also create your own bodies directly using 3D-CAD features.
  - Freeform Surface Modeling
    Freeform surface modeling is a modeling technique in 3D-CAD that allows you to deform existing surfaces for desired shapes.
  - Importing and Exporting Geometry
  - Working with 3D-CAD Models
  - Geometry Repair and Preparation
    Simcenter STAR-CCM+ provides a suite of tools in 3D-CAD that helps you to prepare your CAD geometry so that it is suitable for meshing. CAD that is designed for manufacture can have gaps or inaccuracies that cause problems when trying to generate a watertight mesh.
    - Repairing CAD Geometry
      The Repair CAD tool provides diagnostic checks for assessing the validity of bodies and attempts to repair them automatically. You can typically use this tool first in order to assess the extent and location of problems, and then use specific repair tools to resolve them.
    - Search Tool
      The Search Tool is a feature in 3D-CAD that helps you to find and organize geometric entities, (that is, body groups, bodies, faces, edges, or vertices) using search criteria based on geometry, features, or similarities. The tool can also search for entities that clash or are in close proximity.
    - Working with Repair Tools
      The repair tools option simplifies the way you access features to repair a geometry in Simcenter STAR-CCM+.
      - Merging Multiple Faces into a Single Face
        In 3D-CAD, the Merge Faces feature allows you to combine two or more faces into a single face. This operation is useful when fixing poorly tessellated patch surfaces which affect the mesh.
      - Merging Edges
        In some geometries an edge can be composed of multiple shorter edges rather being one continuous edge. This composition can negatively impact meshing, freeform constraints, and 3D-CAD operations.
      - Splitting Faces by Edge Points
        The split operation allows you to split a face into multiple sections by choosing edge points that define a splitting line across the face.
      - Splitting Face by UV Point
        The Split Face by UV Points action allows you to split a single face through a chosen point using iso-parametric curves.
      - Splitting Faces by Edge Projection
        The Split Faces by Edge Projection feature allows you to split a face by imprinting edges onto it.
      - Removing Redundant Edges
        Redundant edges can appear after you execute a defeature or imprint operation. If left untouched, these free edges can affect mesh generation.
      - Zipping Edges
        In 3D-CAD, the edge zipper tool can be used to remove gaps. These gaps are usually found on parts imported from CAD systems where the native format permits faces to fit together loosely.
      - Optimizing Edges
        The optimize edges tool attempts to repair tolerant edges and vertices. Symptoms of tolerant edges are those that appear deviated or jagged or whose end vertices are not precisely where you expect them to be.
      - Filling Multiple Holes on a Sheet Body
        The fill holes operation identifies holes and boundary cut outs on a surface of a sheet body and allows you to fill them in a single operation.
      - Repairing Invalid Faces
        The repair faces tool attempts to fix invalid faces in a geometry when you discover these using the Search Tool.
      - Repairing Invalid Bodies
        The repair bodies tool attempts to repair invalid bodies automatically when you detect them using the Search Tool.
      - Removing Sliver Faces
        Sliver faces are small unwanted faces with a high aspect ratio (the ratio of length to width). If left untouched, these sliver faces can affect Boolean operations and internal volume extraction.
      - Remove Gashes
        In 3D-CAD, a gash is a tear or disconnection between edges that ought to form a matching seam between two connected faces. Gashes generally appear as loops having a high aspect ratio but small area. If left untouched, gashes can affect the behavior of other features downstream in the 3D-CAD simulation tree.
    - Removing Unwanted Features
      The defeature function in 3D-CAD allows you to remove unwanted features from a geometry. Unwanted features can include faces, holes, protrusions, chamfers, and fillets. The defeature function can also merge split surfaces into a single surface.
    - Working with Volume Extraction
      3D-CAD can automatically extract the volume of space surrounding a model or volume of space inside a model, and use it to form a new, separate solid body.
  - Design Parameters
    Design parameters allow Simcenter STAR-CCM+ to update geometry designs during design exploration studies. Although you define them within the 3D-CAD environment, they are exposed outside 3D-CAD for manual or automatic update.
- 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.

Remove Gashes

In 3D-CAD, a gash is a tear or disconnection between edges that ought to form a matching seam between two connected faces. Gashes generally appear as loops having a high aspect ratio but small area. If left untouched, gashes can affect the behavior of other features downstream in the 3D-CAD simulation tree.

As shown in the image below, a gash can either be open or closed, and are expected to lie between at least two distinct faces. Gashes are usually found on parts imported from CAD systems where the native format permits faces to fit together loosely.

For this feature to work as expected, the edges on either side of a gash must lie within the specified tolerance.

To launch the tool, do one of the following:
- Right-click the Features node in the 3D-CAD simulation tree and select Repair Tools > Remove Gashes.
- In the graphics window, right-click a body, face or edge and select Repair Tools > Remove Gashes.
The Remove Gashes panel appears on the left of the graphics window.
To select other bodies, body groups, or design filters, click the (Object Selector) icon on the right of the selection box. Make further selections in the object selection panel then click the icon again when done.
To remove one or all of your selections, right-click the selection in the list and choose the corresponding action.
In the Gash Width box, enter the tolerance value (default 1.0E-4 m).
In the Gash Aspect Ratio box, enter the value of the ratio (default 0.2).
Gash Aspect Ratio is the ratio of gash length to gash width.
The Attempt to Form Solid option is activated by default and it attempts to form a solid body after executing the Remove Gashes operation.
Click OK.

After the repair, a table appears in the Output window showing the end result of the operation.