Creating Geometry in GAMBIT

1. Creating Geometry in GAMBIT

2. Preliminaries-1 • Objective: • Create and mesh the fluid region for flow problems and solid regions for heat transfer (and structrual analysis for Fidap Users). • Typically accomplished by constructing and working with lower order entity objects and volume primitives. • Terminology: • Vertex - a point • 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 (in the case of 1 edge, the edge forms a loop) • Volume - a geometric solid (as in a solids model), also can be thought of as an “air tight” set of bounding faces.

3. Preliminaries-2 • Identification: • Standalone entities assume following color scheme: Vertex (white), Edge (yellow), Face (light blue), Volume (green), Group (dark green) • When an entity is connected, it is taking the highest (dimensionally) entity color • Undo/Redo: • 10 levels of undo by default. • Undoes geometry, meshing, and zoning commands. • Description window provides command to be undone when mouse is passed over undo button. • Left click to execute visible button operation. • Right click to access options.

4. General Operations: Coordinate System • Coordinate system Cartesian, Cylindrical and Spherical systems • Using Offset/Angle or Vertices for location/orientation “Active” coordinate system is default in all forms Grid creation with “snapping” of vertices -Recommended for simple geometries only Creation of rulers

5. Vector (x,y,z) Angle Vector General Operations: Move/Copy • Move/Copy • Operations: • Translate: (inputs are Ds) • Reflect: • Rotate: • Scale: Plane normal to vector • Options: • Connected geometry can also be Moved • Mesh can be copied linked or unlinked

6. General Operations: Vector Definition Form • Vector Definition form • is used in: • Rotate and Reflect (in Move/Copy) • Sweep and Revolve (in Face/Volume Create) • Methods: • Coordinate system axis • Two existing vertices • An existing Edge • Two points defined by coordinates • Screen View • Magnitude option allows size of vector to be defined.

7. General Operations: Align • Align • Align is an alternative to Move - translate (+rotate). • It uses vertices on the start and final position to move the object • Method of increased alignment with the use of vertex-pairs • Connected geometry can be included Translation Rotation Plane alignment 1 1 + + 3 3 + + + + + + + + 2 2

8. General Operations: Connect • Connect (Real) • 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 Edge Two Edges One Face

9. General Operations: Disconnect • Disconnect (Real) • Vertices, Edges and Faces can be disconnected • The operation recreates duplicate entities and reconnects upper topology • Several options exists Disconnect Edge + Vertices Two Edges One Edge

10. General Operations: Delete • Delete • Default deletes geometry and lower geometry. • Option to keep lower geometry (e.g., delete face but save edges)

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

12. Geometry Creation • ACIS - geometry engine (“kernel”) • Provides tools for “bottom-up” creation by: • Vertex: Add, Grid Snap, etc. • Edge: Line, Arc, Ellipse, Fillet, B-spline, etc. • Face: Wire Frame, Sweep, Net, etc. • Volume: Wire Frame, Sweep, Face Stitch, etc. • Provides tools for “top-down” creation by • Face Primitives: Rectangle, Circle, Ellipse • Volume Primitives: Brick, Cylinder, Sphere, etc. • Volume/Face Booleans: Unite, Subtract, Intersect • Volume/Face Decompose: Split • Geometry creation typically involves use of all tools.

13. “Bottom Up”: Vertex Creation-1 • Real Vertex creation By coordinates • Cartesian, cylindrical and spherical coordinate systems • Also available in virtual geometry On edge • If the intention is to split the edge, the Edge-Split form should be used instead On face • Useful to create edges on surface for a virtual split In volumes • Not frequently used At edge-edge intersections • Vertex is not connected to either edge • Split edge with vertex for connectivity

14. “Bottom Up”: Vertex Creation-2 • Import point data, File • File format: • ICEM Input • Vertex Data • Format is similar, curve information is not needed npc nc x1 y1 z1 x2 y2 z2 : xn yn zn Where: n = npc* nc is the total number of points npc is the number of points per curve nc is the number of curves xi yi zi are real or integer vertex coordinates

15. “Bottom Up”: Edge Creation-1 • Real Edge creation Straight line • Multiple edges can be created by selecting multiple vertices. Arc, Circle • Face create counterparts available • Creation Methods • Three vertices on the edge • Using Center and End-points • Using Radius and Start/End Angles (Arc Only)

16. “Bottom Up”: Edge Creation-2 • Real Edge creation Elliptical Arc • Created by three vertices Conic Arc • Created by three vertices Start Angle Major Vertex + + End Angle Center Vertex + On Edge Vertex Shoulder Vertex + Start Vertex + End Vertex +

17. “Bottom Up”: Edge Creation-3 • Real Edge creation Fillet Arc • Creates a fillet out of a corner NURBS • Third-order by default • Use tolerance for the approximate option + Edge 1 Radius + + Edge 2

18. “Bottom Up”: Edge Creation-4 • Real Edge creation Revolve Vertex • Select one or more vertices to rotate • Specify Angle • Axis is defined using Vector DefinitionPanel Project Edge on Surface • Limited to single edgeand face • Direction defined inVector DefinitionPanel

19. “Bottom Up”: Face Creation-1 • Real Face creation Wire Frame • Creates real and virtual faces • All edges have to be connected into one loop • Number of edges and order of picking are not important • If all edges are co-planar — creation is always successful • For non-coplanar edges: • The number of edges has to be 3 or 4 • Edges cannot have the same tangent at the connecting vertex + create real face by wire frame real face co-planar edges

20. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + “Bottom Up”: Face Creation-2 • Real Face creation Parallelogram • 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 have to be picked in order • Both ends of all edges can not coincide Net • Topologically intersecting edges

21. “Bottom Up”: Face Creation with Revolve • Real Face creation Revolve • Using an edge, an angle and a revolving vector • Use vectors for definition of the axis of revolution • Basic edge can coincide with axis axis of revolution

22. 30 deg “Bottom Up”: Face Creation with Sweep • Real Face creation Sweep • Rigid option • The driving Edge/vector can be anywhere in the domain • Perpendicular option • The driving edge/vector has to start in the “plane” of the curve or face edge path Draft Twist edge edge path path

23. Face Primitives • Face Primitives • Dimensions and Plane/Direction must be specified Rectangles Circles Ellipses

24. “Bottom Up”: Volume Creation-1 • Real Volume creation Stitch • Create volumes out of connected faces • Available in virtual geometry • Order of picking not essential • Voids not allowed Revolve • Using a face, a revolving vector and an angle • Use edges or vectors for definition of the axis of revolution one volume ten connected faces axis of revolution

25. “Bottom Up”: Volume Creation-2 • Real Volume creation Wire Frame • Create volumes from connected curves • 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 one volume 36 connected edges

26. “Bottom Up”: Volume Creation with Sweep • Real Volume creation Sweep • Rigid option • The driving edge/vector can be anywhere in the domain • Perpendicular option • The driving edge/vector has to start in the “plane” of the curve or face face path Draft Twist face path face path

27. Volume Primitives-1 • Real Volume Primitives Brick • Width (X), Depth (Y) and Height (Z) • The Width (X) value is used for Y and Z if no other input is given. • 10 different preset positions (each octant plus center) Cylinder and 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 different preset directions (three in each axis)

28. Volume Primitives-2 • Real Volume Primitives Prism and Pyramid • Corresponding to input of cylinder and frustum • Number of sides • 9 different preset directions (three in each axis) Sphere - only one radius Torus • Major and cross-sectional radii • Three axis locations

29. Boolean Operations: Unite • Real Face/Volume Boolean Unites • The order of picking is not important (except for labeling) • Retain - keeps copies of the entities Unite Faces • All faces must be coplanar or havematching tangents. Unite Volumes A A + B B A B A + B

30. Boolean Operations: Subtract • Real Face/Volume Boolean Subtract • The order of picking is important • Retain - keeps copies of entities Subtract Faces • All faces have to be coplanar Subtract Volumes A B A - B B - A Multiple entities can be entered in second list box. A A B B A - B B - A

31. A B Boolean Operations: Intersection • 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 have to be coplanar Intersect Volumes A B

32. Geometry 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 complicated geometries into smaller, simpler ones. • Edge Split • Split an edge into two or more edges • Resulting edges are, by default, connected. • Edges can be split with: • Point - specify U Value between 0 and 1 where 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.

33. A A A B B B Geometry Splitting- Volumes “Target” Object • Real Volume Boolean Split • The order of picking is important • Volume/Volume splits Split A with B “Tool” two volumes Split B with A two volumes • Volume/Face splits Bidirectional Split two volumes three volumes

34. Split A with B Two Faces Split B with A Geometry Splitting- Faces “Target Object” • Real Face Boolean Split • The order of picking is important • Faces do not need to be coplanar example: coplanar face splits • The Bidirectional Face split is not yet supported. • 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. “Tool”

35. Split vs. Subtract Start with two disconnected cylinders • The appropriate operation to use can depend upon final geometry required. • Subtract • Cut-away shows one volume results • Cannot mesh core region • Flow/Heat Transfer in annular region only • Split • Two connected volumes result • Cut-away shows that both annular and core regions can be meshed. • Flow/Heat Transfer possible in both regions • Subtract + Retain “Tool” (inner cylinder) • Two disconnected volumes result, appears same as split • Duplicate faces appear at interface • Non-conformal mesh can result • Useful for multiple reference frame problem (Fluent)

36. Bidirectional Split vs. Unite • The appropriate operation to use can depend upon the need to create additional surfaces for: • defining boundary conditions • controlling meshing distribution Unite • Unite • One volume results • Cut-away shows no interior faces BiDirectional Split Start with twodisconnected cylinders • Bidirectional split • Three connected volumes result • Cut-away shows multiple interior faces which can be used to: • define internal boundaries • help control mesh distribution in volume • Total represented volume is the same

37. Split/Boolean Characteristics: Imprinting • Special cases • For Unite or Bidirectional Split • Any other enclosed connected volume will get a bidirectional split • Special for volume or face split • GAMBIT will split the volume using all connected internal faces/volumes, even though only one was picked A + B Unite A with B B will make an “imprint” on C C B C A A and C connected, B separate two connected faces Split Volume with one Face two volumes one volume

38. Volume Blends • Real Volume Blends Blend - create fillet/rounded edges • Pick a volume • Pick the edges that need a blend and specify radius • Pick vertex (if needed) and specify radius using the Setback option • Bulge option is not recommended for hexahedral meshing Bulge option Setback option