© Fluent Inc. 10/20/20152-1 Introductory GAMBIT Notes GAMBIT v2.0 Jan 2002 Fluent User Services Center Creating Geometry in GAMBIT

© Fluent Inc. 04/20/232-1

Introductory GAMBIT Notes GAMBIT v2.0 Jan 2002

Fluent User Services Center

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Creating Geometry in GAMBIT

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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.

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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.

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General Operations: Coordinate System

Coordinate systemCartesian, 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 s)

Reflect:

Plane normal to vector

(x,y,z)

Angle

Vector

Vector

Rotate:

Scale:

Options: Connected geometry can also be Moved Mesh 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 alignmentwith the use of vertex-pairs

Connected geometry can be included

Rotation Plane alignmentTranslation++

++ ++++ + +

3 3

1 1

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

Connect EdgesCopy +Translate

Two Edges One EdgeOne 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

Two EdgesOne EdgeEdge + Vertices

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General Operations: Delete Delete

Default deletes geometry and lower geometry.

Option to keep lower geometry (e.g., delete face but save edges)

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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 pointsnpc is the number of points per curvenc is the number of curvesxi 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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Elliptical Arc Created by three vertices

Conic Arc Created by three vertices

+

+

+Major Vertex

On Edge VertexCenter Vertex

End Angle

Start Angle

+

+

+Shoulder Vertex

End Vertex

Start Vertex

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Fillet Arc Creates a fillet out of a corner

NURBS Third-order by default Use tolerance for the approximate option

+

++Edge 1

Edge 2

Radius

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Revolve Vertex Select one or more vertices to rotate Specify Angle Axis is defined using Vector Definition

Panel

Project Edge on Surface Limited to single edge

and face Direction defined in

Vector 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

co-planar edges real face

+

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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 not

coincide

Net Topologically intersecting edges

+

+

+

++

+

+

+

+

+

+

++

+

+

+

+

++

+

+ +

++

+

+

+

+

++

+

+

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“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

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“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

edge path

Draft

edgepath

Twist30 deg

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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 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

ten connected faces one volume

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

36 connected edges one volume

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“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

facepath

Draft Twist

facepath 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 have

matching tangents.

Unite Volumes

AB A + B

AB 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

AB A - B

B - A

A - B B - A A

BA

B

Multiple entities can be enteredin second list box.

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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

BA

BA

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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.

Geometry Splitting- Edges

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Geometry Splitting- Volumes Real Volume Boolean Split

The order of picking is important Volume/Volume splits

two volumes

Bidirectional Split

three volumes

Split A with B

B A

two volumes

Split B with A

two volumes Volume/Face splits

“Target” Object

“Tool”

B A

B A

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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.

Geometry Splitting- Faces

Split A

with B

Split B with A

Two Faces

“Target Object”

“Tool”

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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)

Split vs. Subtract

Start with two disconnected

cylinders

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The appropriate operation to use can depend upon the need to create additional surfaces for:

defining boundary conditions controlling meshing distribution

Bidirectional Split vs. Unite

Unite Unite

One volume results Cut-away shows no

interior faces

BiDirectional Split

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

Start with two

disconnected cylinders

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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

one volume two volumes

Unite A with BB

A

C B will make an “imprint” on C

two connected faces

Split Volume with one Face

A + B

A and C connected, B separate

C

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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

Documents

© Fluent Inc. 10/20/20152-1 Introductory GAMBIT Notes GAMBIT v2.0 Jan 2002 Fluent User Services Center Creating Geometry in GAMBIT