1. Mesh Control through Boundary Layers and Face Vertex Types

2. Face Vertex Type Basics
All vertices that are connected to a face are assigned initial face vertex types based on default angle criteria between the edges connected to the vertex.
Combination of vertex types describes the face ‘shape.’
Face vertex types are used automatically to determine all quad face meshing schemes except the quad-pave scheme.
The tri meshing scheme also does not use face vertex types.
Changing vertex types can help you create a structured mesh, control the mesh or help facilitate generating a hex mesh.
For the majority of models, vertex types don’t need to be changed.

3. Vertex Type Characteristics
End (E)
0 < Default Angle < 120
zero internal grid lines
Side (S)
120 < Default Angle < 216
one internal grid line
Corner (C)
216 < Default Angle < 309
two internal grid lines
Reverse (R)
309 < Default Angle < 360
three internal grid lines E E E S S S C C C R R

4. Modifying Face Vertex Types
Face Vertex Types can be changed from default setting:
Automatically, by enforcing certain meshing schemes in face and volume meshing.
Can sometimes result in undesirable mesh.
Manually, by direct modification in the Face Vertex Type form.
Select Face
symbols appear in graphics window
Select New Vertex Type
Select Vertices to be affected
Vertex Types can be applied to just Boundary Layers as option.
A vertex can have multiple Types; one per each associated face.
For a given set of face vertex types, Gambit will choose which meshing scheme to use based on predefined ‘formulas.’

5. Formula for Map Scheme Map Scheme: 4*End + N*Side
Periodic Map Scheme: N*Side
Project intervals can be specified for more mesh control. E S + E

6. How to Make a Face Mappable
By manually changing vertex types
In Set Face Vertex Type form, change vertices (default) to “Side” (example)
Open the Face Mesh form and pick the face
(GAMBIT should automatically select the map scheme)
By enforcing the Map scheme
In Face Mesh form, change the scheme from default to “Map” and “Apply”
(GAMBIT will try to change the vertex types so the scheme is honored)
Default E S
Map: 4*End + 4*Side E E S
Map: 4*End
default

7. Formula for Submap Scheme
Submap Scheme: 4*End + L*Side + M*(End + Corner) + N*(2*End + Reverse)
additional terms when interior loops exist
Periodic Submap Scheme: N*Side + M*(End + Corner) where M >2 E C E C S C E C E C S + + S

8. How to Make a Face Submappable
By manually changing vertex types
Consider which vertex should be changed to “Side”
In Set Face Vertex Type form, change vertex (default type) to “Side”
By enforcing the Submap scheme
In Face Mesh form, change the scheme from default to “Submap” and “Apply”
(GAMBIT will try to change the vertex types so the scheme is honored)
User has less control - resulting mesh may be undesirable R E S R E
Submap: 4*End + Side + (2*End + Reverse) ? R E S
default

9. Tri-Primitive Scheme Tri-Primitive Scheme: 3*End + N*Side
To mesh a face with the tri-primitive scheme:
Manually, change one of the vertex types to “Side” in this example
The Tri Primitive scheme can not be enforced E S E E S
default

10. Meshing Faces with Quad and Tri Pave Schemes
Quad:Pave Scheme
All vertex types of the face are ignored
The sum of all elements on the edges of the face must be even.
Mesh inner faces first if possible to prevent from ‘locking’ into odd number intervals on boundaries.
No guarantee of a symmetric mesh on a symmetric geometry
Tri:Pave Scheme
No even number restriction
Use boundary layers for better mesh near boundaries
Use sizing function and edge mesh grading for controlling cell size distribution.
Edge mesh grading alone results in poor quality mesh.

11. Meshing Faces with Hybrid Quad/Tri Schemes
Quad/Tri: Tri-Map formula: 2*Triangle
The face vertex types need to be manually changed to Triangle (T) and the “Tri-Map” scheme must be selected.
Quad/Tri: Pave
All vertex types are ignored except Trielement (T) and Notrielement (N)
Trielement (T) will enforce a triangle
Notrielement (N) will avoid a triangle
Quad/Tri: Wedge
Used for creating cylindrical/polar type meshes
The Vertex marked (T) is where rectangular elements are collapsed into triangles T E N T S T E

12. How to Make a Volume Mappable
Three options to map a volume:
Enforce the map
Manually change the vertex types on all faces so they are mappable
Enforce the map on the faces
Example: E
map the faces E E E E S E E
enforce the map E E
Map E S
default E
manually change the vertex types E E E

13. How to Make a Volume Submappable
Three options to submap a volume:
Enforce the submap
Manually change the vertex types on all faces so they are mappable and/or submappable
Enforce the submap on the faces
Example: manually change the vertex types E E E E E E C C E S S S E E

14. How to Make a Volume Cooperable
Three options to cooper a volume:
Manually change the vertex types on the side faces so they are mappable and/or submappable
Pick the source faces
Enforce the map or submap on the side faces
Example: manually change the vertex types S E E S S E E C E S E E

15. Boundary Layers
Boundary layers are layers of elements growing out from a boundary into the domain.
Produces high quality cells near boundary.
Allows resolution of flow field effects with fewer cells than would be required without them.
In general, boundary layers are attached to:
edges for 2D problems
faces for 3D problems
complicated 3D shapes may require boundary layer attachments to edges.

16. Create Boundary Layers
Create Boundary Layer Form
Show Option: toggles display of temp. boundary layer
Useful for complicated models
B.L. can be defined using Uniform or Aspect Ratio based algorithm
Definition Inputs (3 of 4 inputs required)
First row: height of first row of elements (a)
(or starting aspect ratio)
Growth factor: factor for geometric series (b/a)
Rows: total number of element rows
Depth: total height of boundary layer (D)
(or ending aspect ratio)
Internal continuity and Wedge corner shape
Transition Pattern
Reduces number of elements in ‘flow’ direction.
Not to be used with tets; watch for highly skewed cells.

17. Attachment General Edges Attach to:
Edges for 2d problems
Faces for 3d problems
Arrows point to center of associated face or volume.
Boundary layers are initially displayed in orange to indicate that it is temporary.
Temporary boundary layers update immediately with change in definition.
Boundary layer becomes permanent (displayed as white) upon Apply.
Edges
Boundary layer mesh in region near vertices is defined by vertex type.
End: mesh overlaps
Side: angle bisected
Corner: angle divided into thirds
Reverse: angle divided into fourths. E S C R
Internal continuity allows the boundary layers to be formed with no crossover regions (end, corner, or reversal treatments). Everything becomes a side. This is especially important for the meshing with prism layers using tgrid algorithms.

18. Boundary Layers and End Vertex Type
BL mesh butts up against adjoining edge
BL mesh uses adjoining edge’s mesh if pre-existing
If BL is attached to adjoining edge on a face, a block of “overlap” elements is created where the two BL meshes meet

19. Wedge Corner Shape ON OFF
At corner or reversal vertices, wedge corner shape option is applicable.
ON  Wedge shape
OFF  Block shape ON
OFF

20. Attachment to Faces
A boundary layer attached to a face may ‘imprint’ the adjoining faces.
The imprint is displayed graphically on adjoining faces.
Imprinting will depend upon b.l. attachments of adjoining faces and state of internal continuity.
If adjoining faces do not have b.l. attachments-
Attaching boundary layer to face:
Gambit checks angle bounded by attachment and adjoining faces.
Will imprint (become visible) the adjoining faces if angle is less than default angle (135o).
Will not imprint adjoining faces if angle is larger than default.
b.l. is still created but may not impact mesh.
If adjoining faces have b.l. attachments-
Imprinting and overlap region depends upon state of internal continuity.
Internal continuity allows the boundary layers to be formed with no crossover regions (end, corner, or reversal treatments). Everything becomes a side. This is especially important for the meshing with prism layers using tgrid algorithms.

21. Internal Continuity Internal Continuity Internal Continuity “ON”
Allows boundary layers to be formed with no crossover regions (vertices become sides)
Must be ON for tet/hybrid meshing
Internal Continuity “ON”
Prism Growth in Boundary Layer
Internal Continuity “OFF”