Classifying Surfaces

In many cases, different surfaces of a geometry part require different mesh settings, for example, a different number of prism layers for internal and external surfaces. In Surface Repair, you can Classify faces based on specified criteria and create corresponding part surfaces. This classification process is suitable for regular geometries with well defined angles.

To classify a collection of faces on a surface, you define target points on the surface along with the geometrical criteria that determine which faces, around the target points, are included in the classification subset. The faces that satisfy the specified criteria form a subset that you can convert to a part surface. The criteria used to form the classification subset include the:
  • Source Distance
  • Visibility Angle
  • Sharp Angle

You can construct the Classified Faces subset gradually using multiple target points or you can use a single target point. The number of target points you require depends on the surface you want to cover and the specified classification settings. You are recommended to classify one part at a time.

For every target point, Simcenter STAR-CCM+ automatically determines a source point based on the Source Distance you specify. The source point is used to define which faces are included in the classification subset — any faces where the face center can been seen by the source point, at an angle less than the Visibility Angle, are included in the classification subset.

If, however, the dihedral angle between adjacent faces is greater than the Sharp Angle, those faces are not included in the classification subset. For more information, see Classify Surfaces.

  1. Launch Surface Repair.
  2. In the Surface Repair scene, display the surfaces that you want to classify.
    To reduce the time it takes to visualize the geometry in the Surface Repair scene and speed up the classification process, only display the parts that you wish to classify.
  3. In the Surface Repair tab, select Classify.


For an accurate classification, all faces must have either a positive or negative face normal. To check the orientation of the faces:
  1. Set Color Mode to Face Normal.
    The Face Normal color mode colors all faces with a positive face normal in green and faces with a negative face normal in red. For more information, see Color Modes.
  2. If the surface is oriented incorrectly, activate Show Advanced Options, then activate Invert Source Direction.
To classify a surface:
  1. Select Pick Target... and, in the Surface Repair scene, place target points on the surface you wish to classify.
    In the scene, target points appear in green, source points in red, and the faces included in the Classified Faces subset are highlighted in magenta.To completely cover the desired surface area, you can use one of the following methods:
    • Place multiple target points along the surface.

      For each local point you can define an individual Source Distance, Visibility Angle, and Sharp Angle.

      To classify the surface, start from the center of the surface and trace a path around its edge. When you trace the path, maintain a symmetrical pattern and the same distance between points along the geometry edge. In general, curved surfaces require a smaller Visibility Angle compared to planar surfaces. This ensures the required faces are included in the classification subset. For enclosed or tight areas in the geometry, it is recommended you reduce the Source Distance to around one or two face edge lengths. For more information, see Classification Tool Reference.

      注New target points can be positioned on faces already included in the Classified Faces subset.
    • Specify a single target point at the center of the surface.
      To maximize the number of faces included in the classification subset it is recommended you set the source distance (see Source Distance) to a distance greater than, but approximately on the same scale, as the maximum dimension of the part assembly, and set the Visibility Angle to 90.0 deg.

      注Simcenter STAR-CCM+ automatically clears the classification subset if you use any mesh repair tools during the classification process.
  2. To cancel the Pick Target... operation, press Esc.
  3. If the outcome of the classification is not as expected:
    • Modify the classification settings, and select (Re)Classify.
    • Select Undo Last, and select a new target point location.
If you want to visualize the location of the source and target points before you classify the faces:
  1. Deactivate Auto Classify on Pick.
    If Auto Classify on Pick is deactivated, to classify the surface, select (Re)Classify.
  2. To improve the visibility of the surfaces with faces selected, activate (Toggle face, edge, and vertex selection depth control).
    For more information, see Embedded Tools Reference.
When you classify a surface, sometimes a small number of closed loops faces are not included in the classification subset.
  1. To identify and add these faces:
    1. In the Classification Surface Cleanup Tools, select either % Limit or Face Limit and the corresponding values.
      The % Limit or Face Limit value you require depends on the size of gap you are trying to fill. To ensure you are capturing the correct closed loop gaps, it is recommended you use a % Limit less than 50.0 or a Face Limit less than 1000.
    2. Select Fill Gaps.


      Any closed loop gaps with a face count lower than the threshold specified are identified and automatically added to the face subset. The gap fill scheme uses the same methodology as the classification process. However, it ignores the visibility requirement allowing for the restricted faces to be identified. For gap filling, to prevent faces leaking into the opposite side of the surface, keep the Break at Sharp Angle criterion activated.
    3. If the required gaps in the classification subset are not filled, select Undo Last and redefine the surface cleanup settings.
    Alternatively, to fill the gaps automatically during classification, activate the Auto Fill Gaps advanced option. When using this option, set the correct face count properties before you select the target points. If you select Undo Last with Auto Fill Gaps activated, Simcenter STAR-CCM+ undoes both the fill gaps and classification result.
  2. If some gaps remain unfilled, repeat the process.
The classification process often produces an uneven boundary between the classified and unclassified faces. These uneven boundaries can impact the quality of the final volume mesh. To improve the boundaries:
  1. Select Cleanup Boundary.


    This option adds or removes faces along the boundary. A face is only identified by the clean-up process if:
    • The face has more than two (triangle) or three (quadrilateral) adjacent faces which do not belong to the same subset (classified or unclassified) as the face in question.
    • The classification subset contains more than ten perimeter edges.
    For more information, see Classification Surface Cleanup Tools.
  2. During the classification process, Simcenter STAR-CCM+ can also include isolated faces (islands) in the classification subset. To identify and remove any unwanted isolated faces from the classification subset:
    1. Define the correct Find Isolated face count, and select Find Isolated.


      The isolated faces are highlighted in the Surface Repair scene.
    2. To remove these faces from the classification subset, select Remove Selection.
  3. To include individual faces or entire surfaces in the classification subset, in the Surface Repair scene, select the required surface and select Add Selection.
  4. To create a new part surface from the classification subset, choose one of the following options:
    • Set the New Part Surface name and Part Surface Color, then select Modify.

      This method creates a single part surface for all faces in the Classified Faces subset.

    • Activate Append and set the Append Name, then select Modify.

      This approach maintains the existing part surface distribution, as it creates a new part surface for each classified surface. The name of the new part surfaces is the format [part surface name]_[append name]. The state of the append options is saved and restored in the simulation file.

  5. To delete the source and target points from the Surface Repair scene, select Clear Points.
  6. To restart the classification process, select Clear Classified.
You can record the complete classification process to a java macro. By default, if you are recording a macro, the target point is journalled automatically. However, for design variations, this can be problematic as the surface either may not exist in the same location or have the same orientation as the original surface. For cases where you are applying the java macro to a design variant, it is recommended you record the location of the source points instead of the locations of the target points.
By choosing to record the source point location, if the design contains a hole in the original target point location or a valid face is not present, the classification tool reverts to the nearest face to the source point whilst satisfying the classification settings. For example:

  1. To record the source point, in the Advanced Options, activate Journal Source Point.
    With the Journal Source Point property activated, the Invert Source Direction is ignored and Simcenter STAR-CCM+ automatically determines the normal direction of target surface and automatically inverts the results for each classification as required.