Understanding face pair creation

With the Midsurface by Face Pairs command, the quality and accuracy of the face pairs you define determines the quality of the resulting midsurface.

About face pairs

Each face pair has two sides: side 1 and side 2.

• The faces that comprise side 1 of a pair are the master faces for the pair. These faces define the shape and size of the resulting mid-sheets.

• The faces that comprise side 2 of a pair are the dependent faces for the pair.

Face pairing strategies

Use the Strategy list in the Face Pairing group of options to specify the method to use to pair the faces. You can select a different Strategy for different areas of the solid body.

Pairing strategy	Manual or Automatic	Description	Best method for...	Side definition rules
Progressive	Automatic	Creates face pairs based on a computed average thickness value.The Progressive strategy uses a rolling ball calculation. A rolling ball calculation is analogous to using a moving sphere, similar to an inflatable ball, that is constrained within the walls of the solid body. The ball contacts a solid face at one point and expands until it contacts the adjacent faces, creating the largest ball that can fit within the constraints of the faces.The diameter of the ball becomes larger or smaller automatically as it rolls through the different regions of the part. The software then uses the diameter of the ball at a given location as the thickness of the part at that location.	Bodies where the thickness is fairly constant and does not change abruptly.Tangent-continuous parts in which the angle between faces is less than 3°.	The software determines which faces belong on side 1 and side 2 of the pair.
Thickness	Automatic	Pairs two surfaces if the thickness between them is less than the specified thickness threshold value.	Variable thickness bodies.Note: When you specify the Thickness threshold value, you should specify the maximum thickness threshold value for pairing.Tangent-continuous parts in which the angle between faces is less than 3°.	The software determines which faces belong on side 1 and side 2 of the pair.Side 1 can only contain a single face, though side 2 can contain multiple faces.
Manual	Manual	Lets you manually select the faces that belong to side 1 and side 2 in a pair.With the manual option, you can use the Side 2 Search options to have the software search for candidate faces for side 2 within a specified distance from the side 1 faces. See Using the Side 2 Search option with manual pairing for more information.Note: For better performance, clear the Preview check box.	Bodies with tangent continuous faces.Bodies in which the automatic pairing strategies do not provide satisfactory results.Situations in which you want to control precisely how the faces are paired.	You specify which faces belong on side 1 and side 2 of the pair.Both side 1 and side 2 can contain multiple faces.

Rules for automatic face pairing

With the Progressive and Thickness automatic pairing methods, the software evaluates face pair candidates to try to determine the best possible pairs.

• For blend or fillet faces, the software only pairs faces with consistent blends. For example, the software does not pair blend (fillet) faces with non-blend faces. Additionally, the software does not pair blend faces with non-blend faces.

• The software ignores very small faces and does not include them in pairing. The software ignores any face whose width is less than 1/8th of its thickness.

• The software does not pair planar surfaces with curved surfaces.

• As the software creates face pairs, it determines which faces in the solid body are the side faces. The software does not create face pairs for side faces.

Excluding faces from pairing

When you use the Progressive or Thickness automatic pairing strategy, you can use the Faces to Exclude from Pairing option to specify any faces that you do not want the software to consider for pairing. For example, you can use this option to exclude blends, small fillets, and side faces that you do not want to include in the midsurface. Additionally, when you use the Progressive or Thickness pairing strategy, you can exclude faces to reduce the time it takes the software to create the face pairs.

You can use selection options to exclude all blend faces:

1. In the Midsurface by Face Pairs dialog box, click Faces to Exclude from Pairing.

2. With the selection Type filter set to Face, select Detailed Filtering from the General Selection Filtering list.

3. On the Detailed Types tab in the Detailed Filtering dialog box, ensure that only the Blended, Cylinder, Sphere, and Torus face types are selected.

4. Click Close.

5. Area select around the entire displayed part.

The following graphic shows the differences in the resulting midsurface depending on whether small fillets or blends are excluded from face pairing.

• (A) shows the resulting midsurface when the highlighted fillet surfaces are included in face pairing.

• (B) shows the resulting midsurfaces when the highlighted fillet surfaces are excluded from face pairing.

Using the Merge Angle tolerance to merge face pairs

You can use the Merge Angle Tolerance option to merge face pairs. Merging face pairs:

• Significantly reduces the overall number of face pairs that you have to manage.

• Decreases the number of individual mid-sheets that you must stitch together.

The Merge Angle Tolerance option merges face pairs when the angle between the individual pairs is less than the value you specify.

Using the Side 2 Search option with manual pairing

When you select the face pairing strategy, you can use the Side 2 Search options to have the software search for appropriate faces for side 2 of the pair. With the Side 2 Search option, the software tries to identify only appropriate faces. For example:

• The software does not pair blend (fillet) faces with non-blend faces.

• The software does not pair blend faces that have the same convexity.

• The software does not pair cylindrical faces that have the same convexity.

• The software only pairs faces where the difference in the radius of the blends is within acceptable limits when compared to the ray-casting distance between the blends.

How do I

Create a midsurface by face pairs

Modify the face pairs in an existing midsurface

Define a midsurface with the Offset method

Define a midsurface with the User Defined method

Insert a replacement mid-sheet into a face pair

Learn more

Creating midsurfaces before meshing

Selecting appropriate parts for midsurfacing

Creating a midsurface by pairing faces

Working with the Face Pair list

Understanding midsurface creation and trimming methods

Controlling midsurface display

Creating a midsurface with the Offset method

Creating user-defined midsurfaces

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Understanding face pair creation, Simcenter 3D 2021.1 Series

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