gambit 2.3 lecture 02a creatinggeometry

Fluent User Services Center

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Introductory GAMBIT Training

GAMBIT 2.3 June 2006

Geometry Operations in GAMBIT

2-1 © 2006 Fluent Inc.

Geometry Operations in GAMBIT


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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:


� 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


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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


� 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


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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


global.undo.LEVEL

� Left-click to execute the visible button operation.

� Right-click to select between undo/redo.


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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


� 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.


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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


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General Operations – Move/Copy

� Translate � Rotate

zyx ∆∆∆ ,,

� Move/Copy is available for all geometric entities.


� Reflect � Scale

Plane normal

to vector

Vector

� Options:

� Move connected geometry (Move tool only)

� Copy mesh and/or zone types (either linked or unlinked)


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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


� Coordinate system axis

� Edge

� 2 Vertices

� 2 Points

� Screen View

� Magnitude option allows size of vector to be defined.


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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

1

2


� Method of increased alignment with the use of

vertex pairs

� Connected geometry can be included

Plane alignment

Translation RotationPlane

Alignment

1 1

3

2

3

22

2

3 3

2

3


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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.

2-10 © 2006 Fluent Inc.

Non-Conformal Interface

(Faces are not connected)

Conformal Interface

(Faces are connected)


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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.

2-11 © 2006 Fluent Inc.

� Existing mesh will be preserved

Two EdgesOne Face

Copy+

Translate

Connect

Edges

One Edge


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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

2-12 © 2006 Fluent Inc.

� Edge only

� Edge + selected vertex

One edge shared

by two faces

Disconnect

Edge + Vertices

Two edges

(one for each face)


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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

2-13 © 2006 Fluent Inc.

� 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.


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General Operations – Miscellaneous

� Summarize/Query/Total

� Summary of vertex coordinates,lower topology, mesh information,

element/node labels, etc.

� Checks for valid ACIS geometry

2-14 © 2006 Fluent Inc.

� Query: useful to associate geometric objects with object names

� Get total number of entities

� Modify Color/Label

� Modify entity colors

� Change entity label


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Geometry Creation

2-15 © 2006 Fluent Inc.

Geometry Creation


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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.

2-16 © 2006 Fluent Inc.

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.


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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)

2-17 © 2006 Fluent Inc.

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


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Edge Creation – Straight and Arcs

� Straight line

� Multiple edges can be created by selecting

multiple vertices.

� Arc

� Circle

2-18 © 2006 Fluent Inc.

� Circle

� Three vertices on the arc/circle OR

� Center and two endpoints OR

� Radius and start/end angles (arc only)


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Edge Creation – Vertex Sweep and Revolve

� Sweep vertex

� Select a vertex to sweep.

� Choose edge or vector option.

2-19 © 2006 Fluent Inc.

� 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.


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Edge Creation – Other Tools

� Other edge creation tools are available:

� Elliptical arc

� Conic arc

2-20 © 2006 Fluent Inc.

� 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.


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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.

2-21 © 2006 Fluent Inc.

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.

Create real face

by wireframe

Real or virtual face 6 coplanar edges


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Face Creation – Wireframe

2-22 © 2006 Fluent Inc.

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)


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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

2-23 © 2006 Fluent Inc.

� Virtual-to-Real conversion is possible using an

existing triangular surface mesh on any

arbitrarily-shaped single loop face.

Face creation with

Advanced Covering

Face creation without

Advanced Covering


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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

2-24 © 2006 Fluent Inc.

Source

edge

Source

edge

Axis

Axis and rotation direction

determined by right-hand rule

Rotation


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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

2-25 © 2006 Fluent Inc.

� Be careful not to create degenerate faces

� Sweep path start tangent vector parallel to edge

tangent

Edge

Perpendicular,

Draft = 0Perpendicular,

Draft = 0, ± 30

Perpendicular,

Twist = 120Rigid

Path


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Face Creation – Other Tools

� Other bottom-up face creation tools are available:

� Parallelogram

� Polygon

2-26 © 2006 Fluent Inc.

� Vertex rows

� Skin

� Net

� Details on each of these tools can be found in the Appendix.


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Face Primitives

� Dimensions and Plane/Direction must be specified

� Rectangle

� Circle

2-27 © 2006 Fluent Inc.

� Circle

� Ellipse


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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

2-28 © 2006 Fluent Inc.

� 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


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� Single Volume Stitch

Volume Creation – Face Stitch

2-29 © 2006 Fluent Inc.

� Multiple Volume Stitch

…and creates one volume

…and creates

two volumes

2 faces selected, GAMBIT locates

other faces automatically…

11 faces selected, GAMBIT

ignores two faces…


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� Sweep Face

� Rigid option (analogous to face sweep)

� Perpendicular option

� Draft

Volume Creation –Sweep Face and Revolve Face

2-30 © 2006 Fluent Inc.

� 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


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Volume Primitives

� GAMBIT can create volumes using primitives.

� The following are available:

� Brick Frustum

� Cylinder Sphere

2-31 © 2006 Fluent Inc.

� Cylinder Sphere

� Prism Torus

� Pyramid

� Details of each can be found in the Appendix.


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Real Geometry Operations

2-32 © 2006 Fluent Inc.

Real Geometry Operations


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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

2-33 © 2006 Fluent Inc.

� All faces must be coplanar or have matching

tangents.

� Unite Volumes

BA+

A

B

BA+A

B

2 faces

1 face

2 intersecting volumes

1 volume


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Boolean Operations – Subtract

� The order of picking is important

� Retain option – keeps copies of the entity

� Subtract Faces

� All faces must be coplanar

BA−

2-34 © 2006 Fluent Inc.

� Subtract Volumes Multiple entities can be entered

in second list box.

BA−

A

B

AB −

BA−AB −

AB

2 faces

2 intersecting volumes


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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)

2-35 © 2006 Fluent Inc.

� Intersect Faces (All faces must be coplanar)

� Intersect Volumes

IBA

AB IBA

BA


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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

2-36 © 2006 Fluent Inc.

� 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.


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� Real Face Split� The order of picking is important

� Faces do not need to be coplanar

Splitting Faces

"Target"

Split A

with B

2 Faces: ( )

I

I

BA

BAA

)2

)1 −1 2

2-37 © 2006 Fluent Inc.

� 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"Bidirectional

split

3 Faces:

( )

( )I

I

I

BAB

BA

BAA

−

−

)3

)2

)1321

Split B

with A

2 Faces: ( )

I

I

BA

BAB

)2

)1 −12BA


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Splitting Volumes

� Real Volume Boolean Split

� The order of picking is important

� Volume/Volume splits

B

A

"Target"

Split A

with B

2-38 © 2006 Fluent Inc.

2 volumes3 volumes

2 volumes

2 volumes� Volume/Face splits

B

A

B

A

"Tool"

with B

Bidirectional

split

Split B

with A


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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

Two cylinders

(disconnected)

2-39 © 2006 Fluent Inc.

� 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.


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Clarification – Bidirectional Split vs. Unite

� The appropriate operation to use depends on the need to create

additional surfaces for:

� Defining boundary conditions

� Controlling the meshOne Volume

2-40 © 2006 Fluent Inc.

Unite

� One volume results

� No interior faces

Two cylinders

(disconnected)

Bidirectional Split

� Three volumes

result

� Multiple interior

faces

Three Volumes


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� Merge – replaces two connected entities with a single virtual entity

� Split – partitions an individual entity into two separate, connected virtual

entities

2 faces

(real or virtual) Virtual face

2-42 © 2006 Fluent Inc.

entities

� Connect – combines two individual, unconnected entities such that the

lower geometry is shared at common interfaces (unrestricted by ACIS

tolerances)

One face

(real or virtual) 2 virtual

faces

2 faces

(real or virtual)

2 virtual,

connected

faces


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� Create - creates independent virtual entities

� Use host entities for shape definition

Virtual edge

conforms to

face

2-43 © 2006 Fluent Inc.

� Collapse - splits a face and merges the resulting pieces with two or

more neighboring faces

3 faces

(real or virtual)

2 virtual faces


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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

2-44 © 2006 Fluent Inc.

� 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


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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

2-46 © 2006 Fluent Inc.

Attempt to delete one face of a volume

Correct:

Delete the volume with Lower Geometry

option turned OFF.

deleted since it is part of a volume (a higher

order entity).

The volume is deleted and the faces are left

behind. Any of the remaining faces can be

deleted.


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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)

2-47 © 2006 Fluent Inc.

� On a volume

� Rarely used


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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…

2-48 © 2006 Fluent Inc.

� 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


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Edge Creation

� Elliptical Arc – created using 3 vertices

Major

vertex

Center

vertex

Start angle

End

2-49 © 2006 Fluent Inc.

� Conic Arc – created using 3 vertices

On-edge

vertex

End

angle

Shoulder

vertex

End

vertex

Start

vertex


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Edge Creation

� Fillet Arc

� Creates a fillet out of a corner

Edge 1

Edge 2

R

2-50 © 2006 Fluent Inc.

� Create Edge from Vertices (NURBS)

� Third-order by default

� Use tolerance for the approximate option

Continuous edge


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Edge Creation

� Project Edge on Surface

� Limited to a single edge projection onto a single

face

� Direction defined in the Vector Definition form.

Edge

2-51 © 2006 Fluent Inc.

Face

Projection

vector

Edge

Projected

edge


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Face Creation

� Parallelogram

� defined by three vertices

� Polygon

� Selection order is important.

� 5 or more vertices must be coplanar.

� Vertex rows

2-52 © 2006 Fluent Inc.

� 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


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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

2-53 © 2006 Fluent Inc.

36 connected

edges

One volume


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Volume Creation – Sweep Faces

� Sweep (with or without mesh)

� Rigid option

face path volume

2-54 © 2006 Fluent Inc.

� Perpendicular option

� Draft

� Twist

Draftface path

volume

facepath

Twist

volume


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Volume Primitives

� Brick

� 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)

2-55 © 2006 Fluent Inc.

� 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)


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Volume Primitives

� Prism, Pyramid

� Similar inputs as cylinder and frustum.

� Number of sides

� 9 different preset directions (three for

each axis)

2-56 © 2006 Fluent Inc.

� Sphere

� Only one radius is required

� Torus

� Major and cross-sectional radii

� Three axis locations


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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

2-57 © 2006 Fluent Inc.

� 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


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Boolean Characteristics: Imprinting

� Uniting connected volumes results in imprinting

A CB

2-58 © 2006 Fluent Inc.

Unite A

with B

A and C are connected

B is a cylinder inside both

Face contains an

imprint of the cylinder

gambit 2.3 lecture 02a creatinggeometry

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