Surface Repair Error Categories

If an edge pierces a face, the surface diagnostics color the face red in the Graphics window. If an edge is piercing a face, the surface diagnostics color the edge red.

You can fix pierced faces by using the surface wrapper, or by deleting one set of erroneous faces, using the surface repair tools. Deleting faces typically leaves free edges, which you must also fix.

Interaction Mode Specifics

A per-part pierced face is one that has at least one edge from another face intersecting it and that face belongs to the same part. If the pierced face is in a contact, then it is considered to belong to the per-part result if faces attached to the piercing edges belong to either part making up the contact face.

A part to part pierced face is one that has at least one edge from another face intersecting it and that edge has at least one or more faces attached to it that belong to a different part. If the pierced face is in a contact (and therefore belongs to two parts), then it is considered a part to part pierced face.

The surface diagnostics calculate face quality as the ratio of the in-circle radius to the circum-circle radius, multiplied by a factor of 2. The in-circle of a face is the largest circle that fits inside the face, while the circum-circle is the circle that passes through the three points of the face. The diagram below illustrates these definitions for an ideal face.

Face quality ranges from 0 to 1, with 0 being a line (that is, no in-circle radius) and 1 being an equilateral triangle (that is, in-circle radius is half of circum-circle radius).

Faces that have a quality below 0.01 (by default) are considered poor quality faces. In Surface Repair mode, poor quality faces are colored in yellow when you activate the Poor Quality Face diagnostic.

There are instances when you do not need to fix poor quality faces, depending on how the surface is used. For example, if you use the surface with the surface wrapper or surface remesher, poor quality faces do not usually cause a problem.

However, if you use the surface directly for volume meshing, poor quality faces lead to poor quality or invalid volume cells. In this case, you can improve face quality by locally remeshing the poor quality faces, using the surface repair tools.

Face proximity ranges from 0 to 1, with low values indicating one of the following problems:

• Folds in the surface, for example, “V” or “Z” shaped kinks in the surface causing localized overlaps
• Surfaces in close proximity, for example, two surfaces that are almost touching, such as either side of a thin baffle

Faces that have a face proximity below 0.05 (by default) are considered to be close proximity faces. In Surface Repair mode, close proximity faces are colored in orange when you activate the Close Proximity Faces diagnostic.

Depending on the nature of the problem, you can fix close proximity faces either by moving the faces further apart, or by smoothing the mesh locally, using the surface repair tools.

There are instances when you do not need to fix close proximity faces (for example, when you expect close proximity faces due to the nature of the geometry). However, pay attention to these areas during surface and volume meshing, to identify and correct any mesh quality problems.

Interaction Mode Specifics

When performing the face proximity calculation, Simcenter STAR-CCM+ starts with one face and then considers all other neighbouring faces one at a time. If a face pair meets the proximity criteria, then the starting face is considered to be the "original" face and the other face in the pair is considered to be the "opposing" face.

A per-part close proximity face is one that has the opposing face belonging to the same part as the original face. If either the original face and/or opposing face are in a contact, then the result is considered per-part if a common part is found between the two faces.

A part-to-part proximity face is one that has the opposing face belonging to a different part to the original face. If either the original face and/or opposing face belong to a contact, then the face is considered to belong to the part to part result.

Bi-Directional Proximity

By default, face proximity is calculated for inward opposing normals only. In some cases, where faces are extremely close together, the checks in the volume mesher pipeline can fail. These close faces can pass the default proximity check, where the inward face normals are not opposing. Activate the Use Bi-Directional Proximity option, in the diagnostic slide-out, to calculate the face proximity for both directions (inward and outward facing normals). The bi-directional proximity check will then flag these close faces.

You can visualize the direction of face normals using the Face Normal color mode. Face normals that point outward are colored green, while those that point inward are colored red. See Embedded Tools Reference: Color Modes.

Duplicate Faces

Duplicate faces exist when the three vertices of a given triangle are shared by another triangle, potentially in a different part. All duplicate faces are close proximity faces. To view duplicate faces only, create a custom diagnostic and set the Type to Duplicate Faces. See Custom Threshold Options.

For example, edges around a surface hole are marked as free edges, as is illustrated below:

The surface diagnostic colors Free Edges green in the Graphics window.

Double-clicking a free edge selects all connected free edges. This feature is useful when fixing free edges using the fill holes tool.

An understanding of how the free edges are calculated is required when you are diagnosing multiple parts.

You can fix free edges by filling or patching the hole using the surface repair tools.

There are instances when you do not need to fix free edges. For example, a free-floating baffle has the outside edges marked as free edges, until you convert the baffle to an interface. As long as you are aware of the error, and convert the baffle to an interface before surface and volume meshing, you can ignore the free edges.

You can create a custom control to show global free edges. A global free edge is one that belongs to one face only and considers edges at part-to-part perimeters to be connected. See Custom Thresholds: Global Free Edges.

For example, an interior surface joined to an exterior surface has non-manifold edges where the interior and exterior faces share an edge, as illustrated below:

The surface diagnostics color Non-manifold Edges blue in the Graphics window.

An understanding of how non-manifold edges are calculated is required when you are diagnosing multiple parts.

You can fix non-manifold edges by deleting the faces that are causing the additional edges, using the surface repair tools.

There are instances when you do not need to fix non-manifold edges. For example, a baffle joined to the surface of a body has the shared edges marked as non-manifold edges, until you convert the baffle to an interface. As long as you are aware of the error, and convert the baffle to an interface before surface and volume meshing, you can ignore the non-manifold edges.

Interaction Mode Specifics

A per-part non-manifold edge is one where at least three faces attached to the edge belong to the same part. If one or more of the faces belongs to a contact, then either part that the contact face belongs to can be considered.

For example, the diagnostics identify a non-manifold vertex when one surface joins another at a single vertex, as illustrated below.

The surface diagnostics color Non-manifold Vertices blue in the Graphics window.

If the geometry requires connected surfaces, you can fix non-manifold vertices by filling holes or zipping edges, using the surface repair tools.

If the geometry requires disconnected surfaces, you can fix non-manifold vertices by disconnecting the faces that are causing the non-manifold vertex, using the surface repair tools.

Interaction Mode Specifics

A per-part non-manifold vertex is one where at least two faces attached to the vertex belong to the same part. If one or more of the faces belongs to a contact then, either part that the contact face belongs to can be considered.

• An excess of part curves converging on a point
• Disconnected or isolated curves
• Over-constrained curves close to one another
• Missing part curves