Creating a Freeform Surface

Use the freeform tool to morph an existing CAD surface on the geometry.

Currently you can only use the freeform tool on a single surface or patch.

In this tutorial, the wing is symmetrical about the midpoint, and has therefore been already cut in half. The surface of the lower element of the wing is a single surface.

Here, you modify the shape of the lower wing element by sliding the profile on the symmetry plane. Currently, you can only do this on sheet bodies. For geometries that are symmetrical, such as in this case, you can convert a solid body into a sheet body by deleting the planar surface on the symmetry plane.

  1. Right-click the Geometry > 3D-CAD Models > Dual Element Wing and select Edit...
  2. In the 3D-CAD View scene, click (Save-Restore-Select Views) and choose Views > -X +Y +Z > Up +Z.


  3. Right-click the surface on the lower element of the wing that lies on the symmetry plane and select Face > Delete Faces.


  4. In the Delete Faces panel, to confirm the selection click OK.
    The selected surface on the symmetry plane is deleted and the lower element is converted to a sheet body.
  5. In the 3D-CAD View scene, right-click the surface of the lower element (shown below) and select Freeform Surface.


    The Freeform Surface panel appears. A UV grid (that is, a grid with U and V lines) is displayed on the selected surface.
  6. Increase the resolution of the UV grid:
    1. In the Freeform Surface panel, in Display Options group box, click (Set Number of Grid Rows and Columns).
    2. In the Grid Rows and Columns dialog:
      • Set Number of Grid Rows to 10.
      • Set Number of Grid Columns to 6.
      • Click OK.
      The grid updates with the new settings. Increasing the resolution of the grid provides more locations in which you can place control points. Later, you add further local U lines for local refinement.

  7. Modify the profile boundary:
    1. In the 3D-CAD View scene, click the constraint glyph/icon on the boundary that is located at the symmetry.
      Edges that surround the freeform surface are referred to as boundaries. After selecting the boundary constraint, the boundary becomes highlighted in the 3D-CAD View scene.
    2. In the Freeform Surface panel, in the Boundary Constraints group box:
      1. Set Boundary Constraint to Planar.
      2. Set Planar Condition to Normal.

        This option makes the freeform surface normal to the plane and is useful to maintain symmetry in geometries that are cut in half.

      As you have an edge selected in the 3D-CAD View scene, the change of boundary condition only applies to that edge.
      The constraint glyph changes to confirm the new boundary condition. A plane also appears and shows that the profile is constrained to a plane.
    3. Click (Create Point) and move the mouse cursor over the boundary edge. As you do so, the cursor changes to a green ball when it is over a U or V line, and changes into a pink ball when it is over a surface. Place the point at the position shown below and click once.


      Simcenter STAR-CCM+ creates a control point.
    4. Click the control point to select it.
      A triad appears in the scene. You can control the morphing of the shape using the three direction controls on the triad.
    5. Click and drag the blue, upwards-pointing arrow on the triad so that the profile moves downwards.
      The blue arrow restricts movement to the Z axis. As you move the triad down, the freeform surface deforms in that direction. A preview of the deformation is displayed alongside the original shape, making it easy to visualize the change. The displacement values are displayed in the Displacement of Points group box. You can adjust these values for more precise control over the deformation.


    6. Within the Displacement of Points group box, set Z to -0.0826 m.
      By default, the coordinate system is set to Local, where the axis directions are normal to the surface at the selected point. The values that you enter are absolute values, not relative to the original position. As you are modifying the profile on the symmetry plane, you can only make valid changes in the X and Z directions.
    7. Click Apply.
      The freeform surface updates to display the new input values.
  8. Create a design parameter to control the height of the wing:
    1. To switch to the 3D-CAD feature tree, click the 3D-CAD tab.
    2. Right-click the Design Parameters node and select New > Length.
    3. Rename the new design parameter to wingHeight.
      This design parameter is a scalar design parameter that you can use to define a specific vector direction for a control point. In this tutorial, you want to control the displacement of the wing in the Z direction.
    4. Select wingHeight and set Value to -0.0826 m.
    5. To switch back to the Freeform Surface panel, click the Edit tab.
    6. If not already selected, click the control point that you created previously. In the Freeform Surface panel, in the Displacement of Points group box, set Z to $wingHeight.
    7. Press <Enter>, then click Apply.
  9. Control the shape of the element using an additional U curve and two control points:
    1. Orient the geometry so that you are looking up at the underside of the lower element.
    2. Click (Create U Curve) and move the mouse cursor over the underside of the lower element. A line appears and moves with the mouse cursor. When the line is between the two existing gridlines as shown below, click to place the line.


    3. Using the same technique as previously described, place two control points on the new U curve.
      The points must lie approximately in the center of the two gridlines on the U curve as shown below.
      You can hold down the <Ctrl> key while clicking the left mouse button to place multiple points in succession.


    4. By default, the Coordinate System is set to Local.
      The axes of the local coordinate system match those of the global coordinate system.
    5. Set the control points to have the following coordinates, note that the units are in mm:
      Point Displacement
      1 (closest to symmetry plane) [8.955, 0.000, -102.397] mm
      2 (closest to end plate) [8.633, 0.000, -16.932] mm
      By default, the units when entering displacement are set to match the units in the geometry file. You can use custom units independently for each control point.
    6. Click Apply.
    The lower surface of the wing element is expanded.

  10. Add another control point to flatten the shape of the lower element:
    1. Click Create Point and place the point on the lower surface of the wing, as shown below.


    2. Set Displacement to [0.009, 0.000, -0.061] m and click Apply.
  11. Set up a design parameter to control the displacement of the previous control point:
    1. Click the control point from the previous step.
    2. In the Freeform Surface panel, within Displacement of Points, click (Expose Parameter).
    3. In the Design Parametre dialog, activate the Expose Parameter option, enter wingDepth as the Name, and click OK.
    The vector that controls the position of the control point is exposed as a vector design parameter under the Design Parameter node in the 3D-CAD feature tree.
  12. Click OK to complete the freeform operation.
  13. Use the fill hole tool to cap the end of the lower element and convert it to a solid body:
    1. In the 3D-CAD View scene, double-click the large free edge (displayed in green) to select all connected free edges.
    2. Right-click the selection and choose Fill Surface.
    3. In the Fill Surface panel, click OK.
    The missing surface on the sheet body is filled and the lower element is converted to a solid body. The completed wing geometry is shown below.