Creating Geometry in GAMBIT

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Creating Geometry in GAMBIT
2
Preliminaries-1

• 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
• 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 (as in a solids
  model), also can be thought of as an "air tight"
  set of bounding faces.

Lowest order entity
Highest order entity
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Preliminaries-2

• Color Identification
• Vertices and Edges are colored according to the
  highest order entity to which they are connected.
  
• The coloring scheme is
• Vertex (white)
• Edge (yellow)
• Face (light blue)
• Volume (green)
• 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.

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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

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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 and/or Zone types can be copied linked or
  unlinked

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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.

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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

Rotation
Plane alignment
Translation
1
1


3
3








2
2
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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
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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
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General Operations Delete

• Delete
• Select Lower Geometry (default)
• Deletes Faces
• Deletes Lower Geometry Edges and Vertices
• Deselect Lower Geometry
• Deletes Faces
• Does NOT delete Lower Geometry Edges and Vertices

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Example Deleting Entities that belong to higher
order Entities
Incorrect Attempt to delete Face (of a Volume)
The selected face can NOT be deleted because it
is connected to a volume.
Volume is deleted. Faces, Edges and Vertices are
not deleted. Any of the six faces can be deleted
Correct Delete Volume (deselect Lower Geometry)
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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

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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.

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"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

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"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
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"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)

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"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
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"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
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"Bottom Up" Edge Creation-4

• Real Edge creation
• Revolve Vertex
• Select one or more vertices to rotate
• Specify Angle
• Axis is defined using Vector Definition Panel
• Input Height for Spiral creation
• Project Edge on Surface
• Limited to single edgeand face
• Direction defined inVector DefinitionPanel

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"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
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"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 coincide
• Net
• Topologically intersecting edges

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"Bottom Up" Face Creation with Revolve

• Real Face creation
• Revolve (With or without mesh)
• 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
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"Bottom Up" Face Creation with Sweep

• Real Face Creation Sweep (with or without mesh)
• Rigid sweep
• Edge translated along sweep path without being
  rotated
• Perpendicular sweep Draft and Twist option
• Angle edge makes with sweep path is maintained as
  edge swept along path
• Be careful not to create degenerate faces
• Sweep path start tangent vector parallel to edge
  tangent

Perpendicular Draft Angle - 30, 0, 30
Perpendicular Draft Angle0
Perpendicular Twist Angle 120
Rigid
Rigid
Edge
Path
Path
Edge
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Face Primitives

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

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"Bottom Up" Volume Creation-1

• Real Volume creation
• Stitch
• Create volumes out of connected faces
• If a few faces are missing, GAMBIT automatically
  finds the missing faces
• Available in virtual geometry
• Order of picking not essential
• Voids not allowed
• Revolve (With or without mesh)
• 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
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"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
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"Bottom Up" Volume Creation with Sweep

• Real Volume Creation Sweep (with or without
  mesh)
• Rigid sweep
• Edge translated along sweep path without being
  rotated
• Perpendicular sweep Draft and Twist option
• Angle edge makes with sweep path is maintained as
  edge swept along path
• Be careful not to create degenerate volumes
• Sweep path start tangent vector perpendicular to
  a face normal

Perpendicular Twist Angle 60
Perpendicular Draft Angle0
Rigid
Path
Face
Face
Path
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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)

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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

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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
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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
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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
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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.

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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
• 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.

Split A with B
"Tool"
Two Faces
Split B with A
Three Faces
Bidirectional split
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Geometry Splitting- Volumes

• Real Volume Boolean Split
• The order of picking is important
• Volume/Volume splits

"Target" Object
Split A with B
"Tool"
two volumes
Split B with A
two volumes

• Volume/Face splits

Bidirectional Split
two volumes
three volumes
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Split vs. Subtract

• 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)

Start with two disconnected cylinders
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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

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Boolean Characteristics Imprinting

• Uniting Connected Volumes Results in Imprinting

Volume.1
A
C
B
Unite A with B
Volume.2 face contains an imprint of the cylinder
A and C are connected cubes, B is a cylinder
inside both
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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