1. Geometry Operations in GAMBIT

2. Introduction Objective: Terminology:
Create and mesh the fluid region for flow problems and solid regions for heat transfer (and structural analysis for FIDAP Users).
Typically accomplished by constructing and working with lower order entity objects and volume primitives.
Terminology:
Vertex – A point in space.
Edge – A curve that is defined by at least 1 vertex (in the case of 1 vertex, the edge forms a loop).
Face – A surface (not necessarily planar) bounded by at least 1 edge (except for sphere and torus).
Volume – A geometric solid, can be thought of as an air-tight set of connected faces.
Lowest order
Highest order

3. Introduction Color by entity Color by connectivity
Vertices and edges are colored according to the highest order entity to which they are connected.
Coloring scheme:
Vertex: White
Edge: Yellow
Face: Blue
Volume: Green
Color by connectivity
Vertices and edges are colored according to the number of edges and faces to which they are connected:
White: Connected to 0 parent entities
Orange: Connected to 1 parent entity
Blue: Connected to 2 parent entities
Magenta: Connected to 3 or more parent entities

4. Introduction Undo/Redo: 10 levels of undo by default.
Applies to all geometry, meshing, and zoning commands.
Rolling the mouse over any button provides a description of any command. This also applies to the Undo/Redo buttons.
Number of undo/redo levels controlled by the variable global.undo.LEVEL
Left-click to execute the visible button operation.
Right-click to select between undo/redo.

5. Real, Virtual, and Faceted Geometry
Three kinds of geometry in GAMBIT:
Real
Defined by the ACIS library of geometry creation/modification routines.
Geometry defined by mathematical formulae.
Virtual
A library of routines (created by FLUENT) which provides additional functionality by redefining the topology.
Geometry is defined using references to one or more real entities (referred to as host entities).
Faceted geometry
Treated like virtual geometry.
Derived from importing a mesh or faceted geometry into GAMBIT
Two objects that share the same underlying geometry but have different topology.

6. Coordinate Systems
Create coordinate system. Cartesian, cylindrical, and spherical are possible with either Offset/Angle or Vertices for location/orientation.
Modify a user-created coordinate system.
Set the active coordinate system. The selected coordinate system will be used in all panels.
Snap vertex creation onto grid (recommended only for simple geometries)
Creation of rulers

7. General Operations – Move/Copy
Move/Copy is available for all geometric entities.
Translate
Reflect
Rotate
Scale
Vector
Plane normal to vector
Options:
Move connected geometry (Move tool only)
Copy mesh and/or zone types (either linked or unlinked)

8. General Operations – Define Vector
Vector Definition form
is used in:
Rotate and Reflect (in Move/Copy)
Sweep and Revolve (in Edge/Face/Volume Create)
Methods:
Coordinate system axis
Edge
2 Vertices
2 Points
Screen View
Magnitude option allows size of vector to be defined.

9. General Operations – Align
The align tool combines one translation and two rotation commands into one tool.
Can operate on any geometric entity.
It uses vertices on the start and end position to move the object.
Method of increased alignment with the use of vertex pairs
Connected geometry can be included 1 2
Plane alignment 3 1 3 2
Plane Alignment
Translation 2
Rotation 3

10. Non-Conformal Interface (Faces are not connected)
Connectivity
It is very important to understand the concept of connectivity.
In order for flow to pass from one face/volume to another, the two entities must be connected.
Conformal mesh – Nodes are shared at the interface between entities
Non-Conformal mesh – Nodes are not shared at the interface.
Conformal Interface
(Faces are connected)
Non-Conformal Interface
(Faces are not connected)

11. General Operations – Connect
Vertices, edges and faces can be connected.
The operation eliminates all duplicate entities and reconnects upper topology.
Only entities within the ACIS tolerance will be connected.
Existing mesh will be preserved
Copy +
Translate
Connect
Edges
One Face
Two Edges
One Edge

12. General Operations – Disconnect
Vertices, edges and faces can be disconnected
The operation recreates duplicate entities and reconnects upper topology
Several options exist
Edge + vertices
Edge only
Edge + selected vertex
Disconnect
Edge + Vertices
One edge shared by two faces
Two edges
(one for each face)

13. General Operations – Delete
The delete tool can be used to delete any geometry.
Lower Geometry option
If selected, will delete the selected entity plus any lower order geometry.
This option defaults to ON.
Will delete the selected entity plus all available lower geometry (that does not belong to another entity).
If not selected, the lower order geometry will be retained.
Useful for deleting an edge/face/volume for purposes of cleaning up splits in faces and edges.
An entity CANNOT be deleted if it is referenced by another higher order entity.
A vertex that belongs to an edge, an edge that belongs to a face, etc.

14. General Operations – Miscellaneous
Summarize/Query/Total
Summary of vertex coordinates,lower topology, mesh information, element/node labels, etc.
Checks for valid ACIS geometry
Query: useful to associate geometric objects with object names
Get total number of entities
Modify Color/Label
Modify entity colors
Change entity label

15. Geometry Creation

16. Geometry Creation GAMBIT uses the ACIS geometry engine.
Provides tools for bottom-up geometry creation:
Vertex creation: From coordinates, grid snap, etc.
Edge creation : Straight, vertex sweep/revolve, arc, ellipse, spline, etc.
Face creation : Wireframe, edge sweep/revolve, etc.
Volume creation : Wireframe, face sweep/revolve, face stitch, etc.
Provides tools for top-down geometry creation by:
Face creation: Rectangle, circle, ellipse, etc.
Volume creation: Brick, cylinder, sphere, etc.
Boolean operation: Unite, subtract, intersect
Decomposition: Split
Geometry creation typically involves use of all tools.

17. Vertex Creation Commonly used vertex creation methods:
By coordinates (Cartesian, cylindrical, spherical)
On edge (if the intent is to split the edge, the edge split tool should be used instead).
At the intersection of two edges (resulting vertex is not connected to either edge)
Vertex is not connected to either edge
At the centroid of an edge/face/volume
Project onto an edge
Other vertex creation methods are presented in the Appendix
On face or volume
Read coordinates from data file

18. Edge Creation – Straight and Arcs
Straight line
Multiple edges can be created by selecting multiple vertices.
Arc
Circle
Three vertices on the arc/circle OR
Center and two endpoints OR
Radius and start/end angles (arc only)

19. Edge Creation – Vertex Sweep and Revolve
Sweep vertex
Select a vertex to sweep.
Choose edge or vector option.
Revolve vertex
Select one or more vertices to rotate
Specify angle of revolution
Define the axis of revolution using the vector definition form.
Input the Height for spiral creation.

20. Edge Creation – Other Tools
Other edge creation tools are available:
Elliptical arc
Conic arc
Fillet arc
Create edge from vertices (NURBS)
Project edge(s) onto a face
Details on each of these tools can be found in the Appendix.

21. Face Creation – Wireframe
Creates both real and virtual faces
All edges must be connected into a closed loop.
Number of edges and pick order are not important.
If all edges are coplanar then the face creation is always successful.
For non-coplanar edges:
A real face will be created if the edges form a convex shape.
A planar tolerant face can also be created if the edges are close to being coplanar and within a specified tolerance.
6 coplanar edges
Real or virtual face
Create real face
by wireframe

22. Face Creation – Wireframe
Real face creation from convex non-coplanar edges
Tolerant real face creation from non-coplanar edges (Tolerance is calculated automatically and printed in the transcript window)

23. Advanced Covering
Advanced Covering technology allows construction of new, real geometry based on existing geometry or mesh.
Better quality faces result from using existing faces, edges or vertices as guides.
Virtual-to-Real conversion is possible using an existing triangular surface mesh on any arbitrarily-shaped single loop face.
Face creation without Advanced Covering
Face creation with Advanced Covering

24. Face Creation – Revolve Edge
Revolve Edge (with or without mesh)
Using an edge, an angle and an axis definition.
Use vectors for definition of the axis.
Source edge can intersect the axis.
Axis
Axis
Source edge
Rotation
Axis and rotation direction determined by right-hand rule
Source edge

25. Face Creation – Sweep Edge
Sweep Edge (with or without mesh)
Rigid – edge is translated along sweep path, edge maintains orientation throughout the sweep.
Perpendicular – Edge orientation is rotated with the path.
Draft and Twist option
Be careful not to create degenerate faces
Sweep path start tangent vector parallel to edge tangent
Path
Perpendicular,
Draft = 0, ± 30
Rigid
Perpendicular,
Draft = 0
Perpendicular,
Twist = 120
Edge

26. Face Creation – Other Tools
Other bottom-up face creation tools are available:
Parallelogram
Polygon
Vertex rows
Skin
Net
Details on each of these tools can be found in the Appendix.

27. Face Primitives Dimensions and Plane/Direction must be specified
Rectangle
Circle
Ellipse

28. Volume Creation – Face Stitch
Can create single or multiple volumes from a set of connected faces
For a single volume, if a few faces are missing, GAMBIT can automatically find the missing faces.
For multiple volumes, any extra faces are discarded.
Tolerant volume stitch can create a single volume from disconnected faces with gap(s) within a small tolerance.
Tolerance can be Auto or Specified.
Real and virtual options are available.
Order of picking is not important.
Can handle voids and dangling faces.
Ten Connected Faces
One Volume

29. Volume Creation – Face Stitch
Single Volume Stitch
Multiple Volume Stitch
…and creates one volume
2 faces selected, GAMBIT locates other faces automatically… F
11 faces selected, GAMBIT ignores two faces…
…and creates two volumes

30. Volume Creation –Sweep Face and Revolve Face
Rigid option (analogous to face sweep)
Perpendicular option
Draft
Twist
Revolve Face (with or without mesh)
Using a face, a revolving vector and an angle
Use either edge or vector to define the axis.
Axis

31. Volume Primitives GAMBIT can create volumes using primitives.
The following are available:
Brick Frustum
Cylinder Sphere
Prism Torus
Pyramid
Details of each can be found in the Appendix.

32. Real Geometry Operations

33. Boolean Operations – Unite
The order of picking is not important (except for labeling)
Retain option – keeps copies of the entity
Unite Faces
All faces must be coplanar or have matching tangents.
Unite Volumes
1 face
2 faces
1 volume
2 intersecting volumes

34. Boolean Operations – Subtract
The order of picking is important
Retain option – keeps copies of the entity
Subtract Faces
All faces must be coplanar
Subtract Volumes
2 faces
Multiple entities can be entered
in second list box.
2 intersecting volumes

35. Boolean Operations – Intersect
Real Face/Volume Boolean Intersect
The order of picking is not important (except for labeling)
Retain - keeps copies of entities.
All entities must intersect each other.
Intersect Faces (All faces must be coplanar)
Intersect Volumes

36. Splitting Edges
The Split operation: Employs the intersection of two geometric entities to divide one or both objects into two or more pieces.
Useful for decomposing geometries into smaller, simpler ones.
Edge Split
Split an edge into two or more edges
Resulting edges are connected by default.
Edges can be split with:
Point – specify a value between 0 and 1 where the edge will be split.
Use 0.5 to split edge in half.
Vertex - must already be created.
Edge
Must already be created
Bi-directional option results in both edges being split at point(s) of intersection.

37. Splitting Faces "Target" "Tool" 2 Faces: Split A with B 2 Faces:
Real Face Split
The order of picking is important
Faces do not need to be coplanar
In general, for all splits (edges, faces, volumes):
"Tool" entities are, by default, deleted after split is performed.
Retain option prevents “Tool” entities from being deleted.
By default, resulting objects are connected.
"Target"
Split A with B
2 Faces:
Split B with A
2 Faces:
Bidirectional split
3 Faces:
"Tool"

38. Splitting Volumes Real Volume Boolean Split "Target" "Tool"
The order of picking is important
Volume/Volume splits
"Target" B A
Split A with B
2 volumes B A
"Tool"
Split B with A
2 volumes
Volume/Face splits B A
Bidirectional split
2 volumes
3 volumes

39. Clarification – Subtract vs. Split
Result is one volume.
Cut-away shows one volume results
Cannot mesh core region.
Flow/Heat Transfer in annular region only
Split
Result is two connected volumes.
Both annulus and core can be meshed.
Flow/Heat Transfer possible in both regions
Subtract + Retain option (inner cylinder)
Result is two disconnected volumes.
Appears same as split
Duplicate faces result at the interface
Non-conformal mesh
Useful for multiple reference frame problem.
Two cylinders (disconnected)

40. Clarification – Bidirectional Split vs. Unite
The appropriate operation to use depends on the need to create additional surfaces for:
Defining boundary conditions
Controlling the mesh
One Volume
Unite
One volume results
No interior faces
Two cylinders (disconnected)
Three Volumes
Bidirectional Split
Three volumes result
Multiple interior faces

41. Virtual Geometry Operations

42. Virtual Geometry Operations
Merge – replaces two connected entities with a single virtual entity
Split – partitions an individual entity into two separate, connected virtual entities
Connect – combines two individual, unconnected entities such that the lower geometry is shared at common interfaces (unrestricted by ACIS tolerances)
2 faces
(real or virtual)
Virtual face
One face
(real or virtual)
2 virtual faces
2 virtual, connected faces
2 faces
(real or virtual)

43. Virtual Geometry Operations
Create - creates independent virtual entities
Use host entities for shape definition
Collapse - splits a face and merges the resulting pieces with two or more neighboring faces
Virtual edge conforms to face
3 faces
(real or virtual)
2 virtual faces

44. Plug-In Tools Plug-ins are extra tools which can be added to GAMBIT.
Download plugins to:
\FLUENT.INC\Gambit2.2.x\plugins (Windows)
Home directory (UNIX/LINUX)
Load by importing a plugin file
Currently developed plugins
Split multiple faces with a face
Create a face via offset
Control visibility by zone
Create a brick based on the bounding box for the current geometry
Multiple splitting of edges based on equal spacing or actual length
Calculate distance between two vertices
Convex or concave pipe size transitions
Project multiple edges onto multiple faces

45. Appendix

46. Example – Deleting Entities that Belong to Other Entities
Incorrect:
Attempt to delete one face of a volume
An error results. The selected face cannot be deleted since it is part of a volume (a higher order entity).
Correct:
Delete the volume with Lower Geometry option turned OFF.
The volume is deleted and the faces are left behind. Any of the remaining faces can be deleted.

47. Vertex Creation – Other Methods
On a face
Useful to create edges on a surface for use in a virtual face split
Select a face, enter a U or V value (or enter coordinates)
On a volume
Rarely used

48. Vertex Creation – Read From Data File
Vertices can be created by reading a data file.
Both ICEM input and generic vertex data file are supported.
ICEM Input
File → Import → ICEM Input…
Vertex data file
File → Import → Vertex Data…
Format same as ICEM input except only the coordinates are required.
Npc Nc
x1 y1 z1
x2 y2 z2 .
xN yN zN
N = Total number of points
Npc = number of points per curve
Nc = number of curves
xi yi zi = Real or integer vertex coordinates

49. Edge Creation Elliptical Arc – created using 3 vertices
Conic Arc – created using 3 vertices
Center vertex
Major
vertex
Start angle
End angle
On-edge vertex
Shoulder
vertex
End
Start

50. Edge Creation Fillet Arc Create Edge from Vertices (NURBS)
Creates a fillet out of a corner
Create Edge from Vertices (NURBS)
Third-order by default
Use tolerance for the approximate option
Edge 1
Edge 2 R
Continuous edge

51. Edge Creation Project Edge on Surface
Limited to a single edge projection onto a single face
Direction defined in the Vector Definition form.
Face
Projection vector
Edge
Projected edge

52. Face Creation Parallelogram Polygon Vertex rows Skin Net
defined by three vertices
Polygon
Selection order is important.
5 or more vertices must be coplanar.
Vertex rows
Tolerance input
Skin
Topologically parallel edges
Edges must be picked in order
Both ends of all edges can coincide
Net
Topologically intersecting edges

53. Volume Creation – Wireframe
Create volume from wireframe
Create volumes from connected edges
Number of edges and order of picking is not important
Voids and seamless volumes and faces cannot be created
Same limitation as face wire frame creation, for each face
36 connected edges
One volume

54. Volume Creation – Sweep Faces
Sweep (with or without mesh)
Rigid option
Perpendicular option
Draft
Twist
face
path
volume
volume
Draft
face
path
volume
Twist
path
face

55. Volume Primitives Brick Cylinder, Frustum
Width (X), Depth (Y) and Height (Z)
The width (X) value is also used for Y and Z if no other input is given.
9 preset positions (each octant plus centered)
Cylinder, Frustum
Height and two cross-sectional radii (3rd radius for frustum)
The Radius 1 value is used for remaining radii if no other radius input is given.
9 preset directions (three in each axis)

56. Volume Primitives Prism, Pyramid Sphere Torus
Similar inputs as cylinder and frustum.
Number of sides
9 different preset directions (three for each axis)
Sphere
Only one radius is required
Torus
Major and cross-sectional radii
Three axis locations

57. Volume Blends Blend - create fillet/rounded edges
Pick a volume
Pick the edges that need a blend and enter the desired radius.
Pick vertex (if needed) and specify the setback
Bulge specifies the surface bulge with range from 0–2 (0 = no bulge, 2 = highly bulged).
Bulge is not recommended for hex meshing.
Setback > Radius
Setback < Radius

58. Boolean Characteristics: Imprinting
Uniting connected volumes results in imprinting A B C
Unite A
with B
Face contains an imprint of the cylinder
A and C are connected
B is a cylinder inside both