Creating Blended Surfaces

You can create a blended surface, that is a surface between two wireframe elements, taking a number of constraints into account, such as tension, continuity, and so forth.

This task shows you how to:

Before you begin: Create a 3D shape containing open or closed curves.

Create a Blend Between Curves

You can create a blended surface between curves.

  1. From the SurfaceCreate section of the action bar, click Blend .
    The Blend Definition dialog box appears.
  2. Successively select the first curve and its support, then the second curve and its support.

    These can be surface edges, or any curve.



  3. In the Basic tab, set the continuity type.
    It defines the continuity connection between the newly created surface and the curves on which it lies. The illustration above, shows the Tangency continuity, and the following illustrations show the Point and Curvature continuity types:
    Point continuity on both limits

    Curvature

  4. Select the Trim first support/Trim second support check boxes, on one or both support surfaces to trim them by the curve and assemble them to the blend surface:
    By default, the blend surface borders are tangent to the support surface borders.



    You can also specify whether and where the blend boundaries must be tangent to the supports boundaries:

    • Both extremities: the tangency constraint applies at both ends of the curve.
    • None: the tangency constraint is disregarded.
    • Start extremity only: the tangency constraint applies at the start endpoint of the curve only.
    • End extremity only: the tangency constraint applies at the end endpoint of the curve only.

    The Start and End extremities are defined according to the arrows in the blended surface's preview.

  5. In the Tension tab, define the tension type.
    It defines the tension of the blend at its limits. It can be Constant or Linear, and can be set for each limit independently. A third tension type is available: S Type. It enables to set a variable tension.
    Important: If you select any of the tension types in the list, the Default option is cleared.
  6. Click OK to create the blended surface.
    The surface (identified as Blend.xxx) is added to the tree.

Create a Blend Between Closed Contours

You can create blend surface between closed contours.

  1. Click Blend .

    The Blend Definition dialog box appears.

  2. Successively select two contours.


  3. Click Preview.
    The surface to be generated is twisted.

    To avoid this you need to define a closing point.
    Important: By default, the system detects and highlights a vertex on each curve that can be used as a closing point, or it creates an extremum point (you can also manually select another one if you want).
    Warning: This capability only applies to closed curves.
  4. In the Closing Points tab, right-click in the First closing point box and select Create Projection.

    The Projection Definition dialog box appears.

  5. Select the closing point on the second contour, then the first curve onto which the point is to be projected.
  6. Click OK in the Projection Definition dialog box.
  7. Click OK in the Blend Definition dialog box to create the blended surface.
    The surface (identified as Blend.xxx) is added to the tree.

Create a Coupling Blend

You can create a blend surface between a coupling.

  1. Click Blend .

    The Blend Definition dialog box appears.

  2. Select the elements to be blended and click Preview.


  3. Select the Coupling / Spine tab and define the coupling type.

    • Ratio: the curves are coupled according to the curvilinear abscissa ratio.

    • Tangency : the curves are coupled according to their tangency discontinuity points. If they do not have the same number of points, they cannot be coupled using this option.

    • Tangency then curvature: the curves are coupled according to their tangency continuity first then curvature discontinuity points. If they do not have the same number of points, they cannot be coupled using this option.

    • Vertices: the curves are coupled according to their vertices. If they do not have the same number of vertices, they cannot be coupled using this option.

    • Spine: the curve are coupled using a spine curve. This curve can either be a new curve or one of the curves already specified. If no spine is explicitly selected, the first curve is used as the default one. Here is how the blended surface is computed using this coupling mode: at any given point on the spine, a plane normal to the spine is first computed then coupling points corresponding to the intersection of this plane with the limit curves are computed. The blended surface corresponds to the set of lines created with the coupled points. This construction is similar to the one used when creating swept surfaces using a linear profile and two guide curves. In the Spine box, select the spine curve. When using this option, the Display coupling curves option is disabled and any manual coupling is removed.
    • Avoid Twists: The coupling points are automatically computed hence avoiding possibilities of twisted geometry. When using this option, the Display coupling curves option is disabled, as well as the manual coupling and developable modes.
    Important: The Spine box is enabled only when selecting the Spine coupling type.
  4. Double-click in the coupling list or select Add in the context menu and manually select a point on the first section.
    The Coupling dialog box appears.
  5. Select a corresponding coupling point on each section.
    The Coupling dialog box is updated consequently, and the coupling curve is previewed, provided the Display coupling curves option is active. When a coupling point has been defined on each section, this dialog box automatically disappears.

  6. Click OK in the Blend Definition dialog box to create the blended surface.
    The surface (identified as Blend.xxx) is added to the tree.

Create a Ruled Developable Surface

You can create a blend surface by defining the start and end connection points.

  1. Click Blend .

    The Blend Definition dialog box appears.

  2. Successively select the first curve, then the second curve.
    Warning: They cannot form closed contour.


  3. In the Developable tab, select the Create a ruled developable surface check box.

    The Start and End lists are enabled.

    The options available under the Start drop-down list are:

    • Connect Both Extremities: connects the extremities of both curves.

    • First Curve Origin: lets you to free the first curve origin.

    • Free Second Curve Origin: lets you to free the second curve origin.

    The options available under the End list are:

    • Connect Both Extremities: connects the extremities of both curves

    • First Curve End: lets you free the first curve end.

    • Free Second Curve End: lets you free the second curve end.

    Important: The icons depicting the chosen options are represented in the work area as follows:
    • : indicates that both extremities are connected.
    • : indicates that the first curve origin/end is free.
    • : indicates that the second curve origin/end is free. You can click on the icons to change the options.
  4. Click Preview.

    The maximum value of the Gaussian curve appears in the work area.

  5. Click OK to generate the ruled developed surface.
    The surface (identified as Blend.xxx) is added to the tree.

Define Smooth Parameters

You can define the smoothing parameters on the blend surface.

In the Smooth parameters area, select the:
  • Angular Correction check box to smooth the blending motion along the reference guide curves. This may be necessary when small discontinuities are detected with regards to the spine tangency or the reference guide curves' normal. The smoothing is done for any discontinuity which angular deviation is smaller than the input value, and therefore helps generating better quality for the resulting blended surface. Over 0.01 degree, the smoothing is cancelled. By default, the angular correction is set to 0.5 degree.
  • Deviation check box to smooth the blending motion by deviating from the guide curve(s). A smoothing is performed using correction default parameters in tangency and curvature. By default, the deviation is set to 0.001mm.
Important:
  • Selecting a support is not compulsory.
  • You can create closing points using the context menu directly on one of the selected curves, providing no closing point already exists.
  • Use the Replace, Remove or Reverse buttons, to manage the selected elements (curves, support, closing and coupling points).
  • You can use the context menu on the texts displayed on the geometry to set the continuities, trim the supports or manage the curves and support in general.