Geometry Operations in GAMBIT

1. Geometry Operations in GAMBIT

2. Introduction • Objective: • 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 • 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. Translate Reflect Rotate Scale General Operations – Move/Copy • Move/Copy is available for all geometric entities. 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. 1 1 Plane Alignment Translation Rotation 2 2 2 2 3 3 3 3 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

10. 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. Copy + Translate Connect Edges General Operations – Connect • 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 Two Edges One Edge One Face

12. Disconnect Edge + Vertices 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 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. Create real face by wireframe 6 coplanar edges Real or virtual face Face Creation – Wireframe • 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.

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. Path Perpendicular, Draft = 0 Perpendicular, Twist = 120 Perpendicular, Draft = 0, ± 30 Rigid 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 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. One Volume Ten Connected Faces

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

30. Axis Volume Creation –Sweep Face and Revolve Face • Sweep 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.

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. 2 Faces: 2 Faces: 3 Faces: Split A with B Split B with A Bidirectional split Splitting 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" "Tool"

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

39. Clarification – Subtract vs. Split • Subtract • 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. Shoulder vertex Start vertex End vertex 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

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