introduction to gambit 2 - freevincent.chapin.free.fr/cours cfd/doc/gambit-2.2-training.pdf ·...

Introduction to Gambit 2.2 Training Notes

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Introductory GAMBIT TrainingGAMBIT 2.2 December 2004

Introduction to GAMBIT

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What is GAMBIT?Geometry And Mesh Building Intelligent Toolkit

A single, integrated preprocessor for CFD analysis:Geometry construction and import

Using ACIS solid modeling capabilitiesUsing STEP, Parasolid, IGES, etc. import

Cleanup and modification of imported dataMesh generation for all Fluent solvers (including FIDAP and POLYFLOW)

Structured and Unstructured hexahedral, tetrahedral, pyramid, and prisms.Mesh quality examinationBoundary zone assignment

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OperationGeneral sequence of operations

Initial setupSolver selection, Mesh size, Defaults, etc.

Geometry Creation (ACIS, STEP, Parasolid, IGES or Mesh import)Create full geometryDecompose into mesh-able sections

MeshingLocal meshing: Edge, Boundary layers and Size FunctionsGlobal meshing: Face and/or Volume

Mesh examinationZone assignment

Continuum and Boundary attachmentMesh export

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GAMBIT Start-up

GAMBIT can be started up using the startup icon (Windows XP/2000 only). Gambit 2.2.13.lnk

Select working directory

Type in Session ID or select from previous stored sessions.

Startup Options

GAMBIT can be also started up from a DOS command prompt or LINUX/UNIX prompt by typing in “gambit Session Id”.

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Files (1) GAMBIT directory and files

When GAMBIT starts up, it creates a directory called GAMBIT.## = the process numberIt also creates a "lock" file, ident.lok, in the working directoryident.lok prevents any user from starting up another session using the same identifier in the same directory. If the code crashes, this file needs to be manually removed.

Three files are created inside this directoryident.dbs =

jou =

trn =

the database. All information will be saved in this file. This file is NOT retrievable upon a crash

the journal file. This file is directly accessible from the Run journal form

the transcript file. Output from GAMBIT

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Files (2) GAMBIT directory and files

GAMBIT permanently saves these files to your working directory as ident.dbs, ident.jou and ident.trn anytime you issue a "Save" option (equivalent to any standard word processor)

Upon Save, earlier versions of ident.dbs and ident.trn will be overwritten, while new commands are appended to the file ident.jou

Upon successful exit of GAMBIT:The directory GAMBIT.# is removedThe lock-file ident.lok is deleted

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Journal Files

Journal File:Executable list of Gambit commands

Created automatically by Gambit from GUI and TUI.Can be edited or created externally with text editor.

Journals are small - easy to transfer, e-mail, store Uses:

Can be parameterized, comments can be addedEasy recovery from a crash or power lossedit existing commands to create new ones

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Running Journal FilesJournal files can be processed in two ways:

Batch mode (Run)All commands processed without interruption."read pause" command will force interrupt with

resume option appearing.Interactive mode (Edit/Run)

Includes text editor for easy modificationsMark lines in process field to activate for processing.Editable text field.Right click text fieldfor more options.Auto or Step throughactivated process lines.

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GUIMain Menu bar

Global Control

Operation toolpad

Command line Description window

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Operation Tool Pads

VertexEdgeFace VolumeGroup

Boundary LayerEdgeFace VolumeGroup

Boundary TypesContinuum Types

Coordinate SystemsSizing FunctionG/TurboGeometry CleanupPlug-In Tools

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File Menu (1)

New, Open, Save, Save As and ExitStandard form of database operations

Print GraphicsPrints graphics to printer or to filePostScript, BMP, TIF, etc.

Run Journal / Clean JournalScreen editor/command processor for journal filesCommand processing:

Partial or global selection/de-selectionAutomatic or stepwise processing

Ability to load the current journalFile browserClean Journal removes unnecessary tags, undo’s, etc.

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File Menu (2)View File

View of the current output,ident.trn, the transcript fileAbility to view other files as well

ImportACIS, Parasolid -IGES, STEP, Catia V4 -add on)ICEM Input, Vertex DataCAD - Pro/E (STEP or DIRECT- add on), OptegraVisualizer, I-DEAS FTL Mesh - mesh and faceted geometry files.

ExportACIS, ParasolidIGES, STEPMesh - Export your mesh for your Solver.

Export 2D Mesh option guarantees 2D mesh

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Edit Menu (1)

Edit TitleTitle will be included on any printed graphics

Edit FileAbility to launch an editor within GAMBIT

Edit ParametersAbility to define, modify and list parameters

parameters: $numeric = 10, arrays: $array(3,4) = 5

Parameters and arrays can also be directly defined in the journal file using an editor (preferred option)

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Edit Menu (2)Edit Defaults

Modify a large range of defaults that effect: User EnvironmentMeshing CharacteristicsGeometry

Ability to load, modify and save a new set of defaults in $HOME/GAMBIT.ini which is loaded automatically at startup.

Undo/RedoTen levels of undo/redo (default)Reducing number of levels also reduces memory requirements.

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Solver Menu

The Solver selection will have an impact on the following input forms:

Available meshing algorithmsAvailable element types Continuum typesBoundary typesExport mesh file

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Graphical User InterfaceCommand:

Input of (non-GUI) commands, e.g.,reset: deletes all mesh and geometry in the current modelreset mesh: deletes mesh, keeps geometry

Transcript Output from GAMBIT is printed here as well as in ident.trnTranscript window can be expanded using arrow button in top right corner

DescriptionGives a short description of all global function buttons and screen areas

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Global Control (1)

Scale-to-Fit Pivot anchor forviewmanipulation

Four splitFour view

Light sourceSpecial LabelsAnnotate

Undo/Redo

Orient ModelJournal View

Modify (on/off) Label Visibility Rendering Show mesh Silhouette

Wire frameShadeHidden Line

Color coding Entity type Connectivity

Examine Mesh

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Global Control (2)Scale-to-fit resizes the model to fit the screenOrient Model - major axes , isometric and:

ReversePreviousJournal view

Select Pivot - around which the model rotates, zooms Body centerMouse position

Model display attributesTurn on/off visibility, label, silhouette, mesh and hidden line on all or selected geometrical entities

Preset configuration of the graphics window4-view and 4-splitOptions to return to any single view

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Global Control (3)The Window Attributes form

Modify the following attributes (defaults given)Render Wireframe on ; shaded and hidden offMesh Volume - offSilhouette All onLabel All off Visibility All on

Two ways of picking entities"All" - All entities are picked (Default)"Pick" - Individual picking includingthe use of pick lists

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Global (4)

Render Model - Wireframe , Shaded , HiddenModify Light/Label type

Change light source orientation and propertiesAdditional information on the entity labelInsert arrows and text for graphic presentations

Color ModeColor by entityColor by connectivity

Undo/Redo

Examine MeshDisplay different element types by quality, plane cuts, etc.

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Forms (1)Form - components

List box - (picking)active (yellow) - ready to pickinactive (white) - click to activate

Radio buttonsmutually exclusive options

Option buttonOption menu

Text boxClick-to-focus

Check boxnon-mutually exclusive options

Command buttons

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Forms (2)

Text box

Field for input of data, expressions, parametersThe cursor is blinking if active

To activate - left click in the text box (click-to-focus)Forms with several text boxes

The order of input is not importantUse "tab" to go to the next text box Use left click (click-to-focus) to go to any text box

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Forms (3)List box

Highlighted in yellow if activeTo activate - left click in the list box

Tells you the name of the latest picked itemThe item is highlighted in red on the screenAll previously picked items are pink

Individual pick lists for each list boxForms with several list boxes:

Depending on the form, the order of picking may be importantUse Shift right-click to go to the next list box Use left click (in the list box) to go to any list box

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Forms (4)Pick Lists

Open the Pick List by clicking on the arrow

The "Available" list is sorted in the order of pickingPick List functionality:

Pick or Un-pick, Selected or All entities by highlight in left column and by clicking on the arrowsHighlighted "picked" entities will appear red on the screen

edge.32, edge.33Non-highlighted “picked” entities will appear pink

edge.26, edge.28Right-click in lists area provides additional optionsFilter can be used to control which objects are picked.

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Mouse Operations (1) Left Middle Right

Drag x-y rotation Translation Zoom/ z-rotation

Shift + Click

Pick Next Accept/Next picker

Double Click

Previous View Save view to journal

Ctrl Drag zoom Stretch zoom Click points to grid

You can toggle between picking with or without "Shift":

Keep right mouse button down while doing a "left-click"The cursor now changes to another symbolNow, Pick/Next/Accept do not need a "Shift"The Rotation/Translation/Zoom now needs a "Shift"”

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Mouse Operations (2)The picking philosophy: Left - Middle - Right

Shift-Left: initial pickAlternative: click and hold, drag diagonally to pick several items at the same time –"window picking"

Upward diagonal picking will include everything fully included in the boxLower diagonal picking will include everything partially included in the box

The latest pick is highlighted in red, previously picked items are highlighted in pink

Picking Five FacesPicking One Face

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Mouse Operations (3)The picking philosophy: Left - Middle - Right

Shift-Middle: modify pickThe middle pick will behave differently depending on the mouse location:

Same: Cycle to the next available object within picking toleranceNew: Replace last pick with new pick at new locationBad: A Shift-Middle pick on "nothing"is equivalent to

"Un-select last pick”Shift-Right: Apply or go to the next list box

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Creating Geometry in GAMBIT

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Preliminaries-1Objective:

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 pointEdge - 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-2Color 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 systemCartesian, Cylindrical and Spherical systems

Using Offset/Angle or Vertices for location/orientation"Active" coordinate system is default in all formsGrid creation with "snapping" of vertices

-Recommended for simple geometries onlyCreation of rulers

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General Operations: Move/CopyMove/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 MovedMesh 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 axisTwo existing vertices An existing Edge Two points defined by coordinatesScreen View

Magnitude option allows size of vector to be defined.

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General Operations: Align

AlignAlign 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 31 1

2 2

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General Operations: Connect

Connect (Real)Vertices, Edges and Faces can be connectedThe operation eliminates all duplicate entities and reconnects upper topology Only entities within the ACIS tolerance will be connectedExisting 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 disconnectedThe operation recreates duplicate entities and reconnects upper topology Several options exists

Disconnect

Two EdgesOne EdgeEdge + Vertices

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General Operations: DeleteDelete

Select Lower Geometry (default)Deletes FacesDeletes Lower Geometry: Edges and Vertices

Deselect Lower GeometryDeletes Faces Does NOT delete Lower Geometry: Edges and Vertices

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Example: Deleting Entities that belong to higher order Entities

The selected face can NOT be deleted because it is connected to a volume.

Correct: Delete Volume (deselect Lower Geometry)

Volume is deleted. Faces, Edges and Vertices are not deleted. Any of the six faces can be deleted

Incorrect: Attempt to delete Face (of a Volume)

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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 geometryQuery: useful to associate geometrical objects with object namesGet total number of Entities

Modify Color/LabelModify entity colorsChange 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 byFace Primitives: Rectangle, Circle, EllipseVolume Primitives: Brick, Cylinder, Sphere, etc.Volume/Face Booleans: Unite, Subtract, IntersectVolume/Face Decompose: Split

Geometry creation typically involves use of all tools.

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"Bottom Up": Vertex Creation-1Real Vertex creation

By coordinates Cartesian, cylindrical and spherical coordinate systemsAlso available in virtual geometry

On edgeIf the intention is to split the edge, the Edge-Split form should be used instead

On faceUseful to create edges on surface for a virtual split

In volumesNot frequently used

At edge-edge intersectionsVertex is not connected to either edgeSplit edge with vertex for connectivity

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"Bottom Up": Vertex Creation-2

Import point data, FileFile format:

ICEM Input

Vertex DataFormat 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-1Real Edge creation

Straight lineMultiple edges can be created by selecting multiple vertices.

Arc, CircleCounterparts for face creation are also availableCreation Methods

Three vertices on the edgeUsing Center and End-pointsUsing Radius and Start/End Angles (Arc Only)

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Elliptical ArcCreated by three vertices

Conic ArcCreated by three vertices

+

+

+Major Vertex

On Edge VertexCenter VertexEnd Angle

Start Angle

+

+

+Shoulder Vertex

End Vertex

Start Vertex

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Fillet ArcCreates a fillet out of a corner

NURBSThird-order by defaultUse tolerance for the approximate option

+

++Edge 1

Edge 2

Radius

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"Bottom Up": Edge Creation-4

Real Edge creationRevolve Vertex

Select one or more vertices to rotateSpecify AngleAxis is defined using Vector Definition PanelInput Height for Spiral creation

Project Edge on SurfaceLimited to single edgeand faceDirection defined inVector DefinitionPanel

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"Bottom Up": Face Creation-1Real Face creation

Wire Frame Creates real and virtual facesAll edges have to be connected into one loopNumber of edges and order of picking are not importantIf all edges are co-planar — creation is always successful.For non-coplanar edges:

A real face will always be created if the number of edges is 3 or 4 and the tangents are not the same at connecting vertices.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 wire frame

co-planar edges real face

+

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"Bottom Up": Face Creation-2

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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"Bottom Up": Face Creation-3Real Face creation

Parallelogram defined by three vertices

PolygonSelection order is important.5 or more vertices must be coplanar.

Vertex rows Tolerance input

SkinTopologically parallel edgesEdges have to be picked in orderBoth ends of all edges can coincide

NetTopologically intersecting edges

++

+

++

+

++

++

++

++

++

+++

+

+ +++

+

+

++

+++

+

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"Bottom Up": Face Creation with RevolveReal Face creation

Revolve (With or without mesh)Using an edge, an angle and a revolving vectorUse vectors for definition of the axis of revolutionBasic edge can coincide with axis

axis of revolution

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"Bottom Up": Face Creation with Sweep

Path

Perpendicular Twist: Angle = 120

Perpendicular Draft: Angle = - 30, 0, 30

Rigid

PathEdge

Real Face Creation: Sweep (with or without mesh)Rigid sweep

Edge translated along sweep path without being rotatedPerpendicular sweep: Draft and Twist option

Angle edge makes with sweep path is maintained as edge swept along path

Be careful not to create degenerate facesSweep path start tangent vector parallel to edge tangent

Edge

RigidPerpendicular Draft: Angle=0

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Face PrimitivesFace Primitives

Dimensions and Plane/Direction must be specifiedRectangles

Circles

Ellipses

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"Bottom Up": Volume Creation-1Real Volume creation

Stitch Create single or multiple volumes out of connected faces

If a few faces are missing, GAMBIT automatically finds the missing faces.For multiple volumes, it discards any extra faces.

Available in virtual geometryOrder of picking not essentialCan handle voids and dangling faces.

Revolve (With or without mesh) Using a face, a revolving vector and an angleUse 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-2Real Volume creation

Wire Frame Create volumes from connected curvesNumber of edges and order of picking is not importantVoids and seamless volumes and faces cannot be createdSame limitation as face wire frame creation, for each face

36 connected edges one volume

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"Bottom Up": Volume Creation with SweepReal Volume creation

Sweep (With or without mesh)Rigid option

The driving edge/vector can be anywhere in the domain

Perpendicular optionThe driving edge/vector has to start in the "plane" of the curve or face

facepath

Draft Twist

face path face path

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Volume Primitives-1Real Volume Primitives

BrickWidth (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 FrustumHeight 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-2Real Volume Primitives

Prism and PyramidCorresponding to input of cylinder and frustumNumber of sides 9 different preset directions (three in each axis)

Sphere - only one radius

TorusMajor and cross-sectional radii Three axis locations

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Boolean Operations: UniteReal Face/Volume Boolean Unites

The order of picking is not important (except for labeling)Retain - keeps copies of the entitiesUnite Faces

All faces must be coplanar or havematching tangents.

Unite Volumes

AB A + B

AB A + B

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Boolean Operations: SubtractReal Face/Volume Boolean Subtract

The order of picking is importantRetain - keeps copies of entitiesSubtract Faces

All faces have to be coplanar

Subtract Volumes

A B A - B

B - A

A - B B - AA

BA

B

Multiple entities can be enteredin second list box.

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Boolean Operations: Intersection

Real Face/Volume Boolean IntersectThe 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 edgesResulting 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 createdBi-directional option results in both edges being split at point(s) of intersection.

Geometry Splitting- Edges

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Geometry Splitting- FacesReal Face Boolean Split

The order of picking is importantFaces do not need to be coplanarexample: coplanar face splits

In general, for all splits (edges, faces, volumes):"Tool" entities are, by default, deleted after split is performedRetain option prevents “Tool” entities from being deleted.By default, resulting objects are connected.

Split A with B

Split B with A

Two Faces

"Target Object"

"Tool"

Bidirectional split

Three Faces

connected

AA

Β∩Α)Β∩− (

connected

AB

Β∩Α)Β∩− (

)Β∩−Β∩Α

)Β∩−

AB

AA

(

(

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Geometry Splitting- VolumesReal Volume Boolean Split

The order of picking is importantVolume/Volume splits

two volumes

BidirectionalSplit

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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The appropriate operation to use can depend upon final geometry required.

SubtractCut-away shows one volume results

Cannot mesh core regionFlow/Heat Transfer in annular region only

SplitTwo 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 splitDuplicate faces appear at interface

Non-conformal mesh can resultUseful 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 conditionscontrolling meshing distribution

Bidirectional Split vs. Unite

UniteUnite

One volume resultsCut-away shows no interior faces

BiDirectionalSplit

Bidirectional splitThree connected volumes resultCut-away shows multiple interior faces which can be used to:

define internal boundarieshelp control mesh distribution in volume

Total represented volume is the same

Start with two

disconnected cylinders

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Boolean Characteristics: ImprintingUniting Connected Volumes Results in Imprinting

Unite A with B

A and C are connected cubes, B is a cylinder inside both

A C

Volume.1

Volume.2: face contains an imprint of the cylinder

B

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Volume BlendsReal Volume Blends

Blend - create fillet/rounded edgesPick a volumePick the edges that need a blend and specify radius Pick vertex (if needed) and specify radius using the Setback optionBulge option is not recommended for hexahedral meshing

Bulge option

Setback option

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Plug-in toolsPlug-in tools are extra tools which can be added to GAMBIT.

Download to the “FLUENT.INC/Gambit2.2.x/plugins” directory (Windows) or your home directory (Unix/linux)Load by import plugin file

File -> Import -> Plug-inAccess through the new Tools - Plug-in button

Currently developed Plug-ins:Create a Brick based on the bounding box for the current geometry Multiple splitting of edges based on equal spacing or actual lengthCalculate distances between two verticesConvex or concave pipe fittings

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Edge and Face Meshing

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Meshing - GeneralTo reduce overall mesh size, confine small cells to areas where they are needed (e.g., where high gradients are expected).

Controlling cell size distributionEdges, Faces and Volumes can be directly meshed

A uniform mesh is generated unless pre-meshing or sizing functions are used.Pre-meshing

Edge meshes can be graded (varying interval size on edge)Graded edge mesh can be used to control distribution of cell size in face mesh.Controlling distribution of cell size in face mesh also controls distribution of cell size in volume mesh.

Sizing FunctionsAllow direct control of cell size distribution in edges, faces and volumes directly for automatic meshing.

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Edge MeshingEdge mesh distribution is controlled through the spacing and grading parameters.Using the Edge meshing form

PickingTemporary graphicsLinks, Directions

Grading/SpacingSpecial characteristics

Apply and DefaultsInvert and Reverse

Options

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Picking Edges for Meshing

PickingTemporarily meshed edges

When you pick an edge, the edge is temporarily meshed using white nodesDisplayed edge mesh is based on current grading and spacing parametersIf you modify the scheme or spacing, the temporary mesh will be immediately updatedWhen you Apply, the mesh nodes will turn blue

SenseSense is used to show direction of gradingEvery picked edge will show its sense direction using an arrow The sense can be reversed by a shift-middle click on the last edge picked (this is in addition to the “next” functionality) or by clicking on the Reverse button

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Soft LinksPicking and soft links

Pick with linksBy enabling this option, Soft-linked edges can be selected in a single pickLinked edges share the same information and can be picked in a single pick

Modifying soft linksYou can anytime:

Form linksBreak linksMaintain links

By default, GAMBIT will form links between unmeshed edges that are picked togetherBy default, GAMBIT will maintain links between meshed edges that are picked together

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GradingControls mesh density distribution along an edge.Grading can produce single-sided or double-sided mesh

Doubled-sided mesh can be symmetric or asymmetric.Symmetric schemes produce symmetric mesh about edge center.Asymmetric schemes can produce asymmetric mesh about edge center.

Single-sided grading:Uses a multiplicative constant, R, to describe the ratio of the length of two adjacent mesh elements, i.e.,

R = l(i+1) / li

R can be specified explicitly (Successive Ratio) or determined indirectlyGambit also uses edge length and spacing information to determine R.

Single-sided grading

Symmetric grading

Asymmetric grading

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Double Sided Grading

Symmetric grading schemes implicitly generate double sided grading that is symmetric.Asymmetric schemes are accessible when Double-Sided Option is used with:

Successive Ratio, First Length, Last Length, First-Last Ratio, and Last-First RatioThe mesh is symmetric if R1 and R2 are equal.

The mesh is asymmetric if R1 and R2 are not equal.

Edge center is determined automatically.

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Spacing

SpacingIn all meshing forms, the following spacing functions can be specified:

Interval count - recommended for edge meshing onlyA value of 5 creates 5 intervals on the edge (6 nodes, including ends)

% of edge length - recommended for edge meshing onlyAn edge length of 10 and a value of 20 creates 5 intervals on the edge

Interval size - the default settingIdentifies the interval size relative to overall dimensions of geometry

– Identifies “average” interval size if used with gradingAn edge-length of 10 and a value of 2 creates 5 intervals on the edgeAverage size of elements/grid is 2

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First Edge Settings

Use first edge settings enabledFirst edge selected in pick list updates formUseful to copy settings from one meshededge to other edges.

Use first edge settings disabledAny time you pick two or more meshed edges where there is a difference in:

the Typethe Spacing

the local Apply button for that option will be turned offThis allows you to maintain pre-existing grading and/or spacing settings for each edge.Enforce a change in grading and/or spacing by enabling Apply button.

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Mesh OptionsApply without meshing

This option is useful in cases where you want to impose a scheme without fixing the number of intervalsThe higher level meshing scheme will decide (and match) the intervals

ExampleSpecify fixed interval and no gradingSpecify double sided grading andApply without Meshing on bottom edgesFace meshing will automatically match mesh

Remove Old MeshDeletes old mesh

Ignore Sizing FunctionSizing function has precedence on meshingunless this option is enabled.

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Face MeshingFace Meshing form

Upon picking a faceGAMBIT automatically chooses Quad elementsGAMBIT chooses the Type based on the Solver/face vertex types

Available element/scheme type combinationsQuad

MapSubmapTri-PrimitivePave

TriPave

Gambit also has quad-to-tri conversion utility.

Quad/TriMapPaveWedge

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Face Meshing - Quad Examples

Quad: Map

Quad: Submap

Quad: Tri-Primitive

Quad: Pave

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Face Meshing - Quad/Tri and Tri Examples

Quad/Tri: Map

Quad/Tri: Pave

Quad/Tri: Wedge

Tri: Pave

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Deleting Old MeshExisting mesh must be removed before remeshing.

Mesh can be deleted using delete mesh form.

Lower topology mesh can also be deleted (default)

Existing mesh can also be removed in all Create mesh forms without the need for Delete mesh

Remove meshLeaves all lower topology mesh

Remove mesh + lower meshRemoves all lower mesh that is not shared with another entity

Undo after meshing operation also works!

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Hard LinkingMesh Links (Hard Links)

Mesh linked entities have identical meshcreated for periodic boundary conditions

Applicable to Edge, Face, and Volume entitiesBest to use soft links for edge meshingTo link volume meshes, all faces must be hard linked first.

Setting up Hard Links for FacesSelect faces and reference vertices

Edge ‘sense’ will appearReverse orientation on by default for sensePeriodic option should be used for periodic boundary conditions, which creates a matched mesh even if the edges are split differently.

Mesh one face before or after hard link is definedmesh on second face generated automatically

Multiple pairs of hard links can be created.

+ + + +

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Mesh SmoothingFace and Volume meshes can be smoothed by moving interior nodes to obtain incremental improvement in quality.

The mesh at the boundary is not altered.Face and volume meshes are smoothed using a default scheme.

Different schemes can be selected and applied after meshing.Face mesh smoothing

Length-weighted Laplacian: Uses the average edge length of the elements surrounding each node to adjust the nodes.Centroid Area: Adjust node locations to equalize areas of adjacent elements. Winslow(for quad meshes only) : Optimizes element shapes with respect to perpendicularity.

Volume mesh smoothingLength-weighted Laplacian: same as for face mesh smoothingEquipotential: Adjusts node locations to equalize the volumesof the mesh elements surrounding each node.

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Face Vertex TypesAll vertices that are connected to a face are assigned initial face vertex types based on default angle criteria between the edges connected to the vertex.Combination of vertex types describes the face “shape” or topology.Face vertex types are used automatically to determine all quad face meshing schemes except the quad-pave scheme.

The tri meshing scheme also does not use face vertex types. Changing vertex types can help you create a structured mesh or help facilitate generating a hex mesh.

For the Cooper to work, the side faces must be either mappable or submapple and changing the vertex types may be required.

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Vertex Type CharacteristicsEnd (E)

0 < Default Angle < 120 zero internal grid lines

Side (S)120 < Default Angle < 216one internal grid line

Corner (C)216 < Default Angle < 309two internal grid lines

Reverse (R)309 < Default Angle < 360three internal grid lines

E

E E

S S S

CC C

R R

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Modifying Face Vertex TypesFace Vertex Types can be changed from default setting:

Automatically, by enforcing certain meshing schemes in face and volume meshing.

Can sometimes result in undesirable mesh.Manually, by direct modification in the Face Vertex Type form.

Select Facesymbols appear in graphics window

Select New Vertex TypeSelect Vertices to be affectedVertex Types can be applied to just Boundary Layers as option.

A vertex can have multiple Types; one per each associated face.For a given set of face vertex types, Gambit will choose which meshing scheme to use based on predefined "formulas".

S E

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Example: Using Vertex Types to make a Face Submappable

A face can be made submappableBy manually changing vertex types

Consider which vertex should be changed to "Side"In Set Face Vertex Type form, change vertex (default type) to “Side”

By enforcing the Submap schemeIn the Face Mesh form, change the scheme from default to "Submap" and "Apply"(GAMBIT will try to change the vertex types so the scheme is honored)User has less control - resulting mesh may be undesirable

R

E

E

EE

E

E

E

default

Submap: 4*End + Side + (2*End + Reverse)

R

E

E

SE

E

E

E

R

E

E S

E

E

E

E

?

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Formula for Map SchemeMap Scheme: 4*End + N*Side

Periodic Map Scheme: N*SideProject intervals can be specified for more mesh control.

E

E

E

ES+

E EEE

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By manually changing vertex types In Set Face Vertex Type form, change vertices (default) to "Side" (example)Open the Face Mesh form and pick the face

(GAMBIT should automatically select the map scheme)

By enforcing the Map schemeIn Face Mesh form, change the scheme from default to "Map"” and "Apply"

(GAMBIT will try to change the vertex types so the scheme is honored)

How to Make a Face Mappable

E

SS

E

S

EE

S

Map: 4*End + 4*Side

E

EE

E

C

EE

CDefault

E

E

E

Sdefault Map: 4*End

E

E E

E

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Formula for Submap SchemeSubmap Scheme: 4*End + L*Side + M*(End + Corner) + N*(2*End + Reverse)

additional terms when interior loops exist

Periodic Submap Scheme: N*Side + M*(End + Corner) where M >2additional terms when interior loops exist

E

EE

E

C

EE

CS

C

S

E

EE

E

E

C

C

C

CC

C E

E

E

C

E

E

CC

E

C

S S+ +

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Tri-Primitive Scheme

Tri-Primitive Scheme: 3*End + N*Side

To mesh a face with the tri-primitive scheme:Manually, change one of the vertex types to "Side" in this exampleThe Tri Primitive scheme can not be enforced

E

S

E

E

E

E

E

E

E

E

E

S

default

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Meshing Faces with Hybrid Quad/Tri SchemesQuad/Tri: Tri-Map formula: 2*Triangle

The face vertex types need to be manually changed to Triangle (T) and the “Tri-Map”scheme must be selected.

Quad/Tri: PaveAll vertex types are ignored except Trielement(T) and Notrielement (N)Trielement (T) will enforce a triangleNotrielement (N) will avoid a triangle

Quad/Tri: WedgeUsed for creating cylindrical/polar type meshesThe Vertex marked (T) is where rectangular elements are collapsed into triangles

T T

E

N

T

S

T

E

E

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Assessing Mesh QualityDefault measure of quality is based on EquiAngle Skew.Definition of EquiAngle Skew:

where:θmax = largest angle in face or cellθmin = smallest angle in face or cellθe = angle for equiangular face or cell

e.g., 60 for triangle, 90 for square

Range of skewness:

−

−−

e

mine

e

emax ,180

maxθθθ

θθθ

θ min

θ max

0 1best worst

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Examining the MeshExamine Mesh Form

Display TypePlane/Sphere

View mesh elements that fall in plane or sphere.Range

View mesh elements within quality range.Histogram shows quality distribution.Show worst element – automatically zooms into worst element

Select 2D/3D and Element TypeSelect Quality Type

Display ModeChange cell display attributes.

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Striving for QualityA poor quality grid will cause inaccurate solutions and/or slow convergence.Minimize EquiAngle Skew:

Hex and Quad CellsSkewness should not exceed 0.85.

Tri’sSkewness should not exceed 0.85.

Tet’sSkewness should not exceed 0.9

Minimize local variations in cell size:e.g., adjacent cells should not have ‘size ratio’ greater than 20%.

If Examine Mesh shows such violations:Delete meshPerform necessary decomposition and/or pre-mesh edges and faces.Remesh

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Volume Meshing

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Approach

To potentially reduce discretization errors, and to reduce cell count, a "high" quality hex mesh is preferred.

For a hex mesh, complicated geometries (volumes) typically need to be decomposed into simpler ones so that one of the hex meshing schemes can be used.In some instances, some geometries may be too complex and decomposition for hex meshing is impractical or impossible. In these instances use a tet/hybrid mesh.

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Volume MeshingVolume Meshing Form:

Upon picking a VolumeGAMBIT will automatically choose a Type based on the solver selected and the combination of the face Types of the volume.In ambiguous cases, GAMBIT chooses the Tet/Hybrid: TGrid combination

Available element/scheme type combinationsHex

MapSubmapTet-PrimitiveCooperStairstep

Hex/WedgeCooper

Tet/HybridTgridHex-Core

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Volume Meshes - Hex ExamplesHex: Map

Hex: Submap

Hex: Tet-Primitive

Hex: Cooper

Hex: Stairstep

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Hex/Wedge and Tet/Hybrid ExamplesHex/Wedge: Cooper

Tet/Hybrid: Tgrid

Tet/Hybrid: Hex-Core

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Hex Meshing - Map

Volumes that are mappable by default: A logical cube All faces map-able (or Submap-able) and mesh is matching

Map Scheme

mesh

mesh

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Hex Meshing - SubmapVolumes that are Submap-able by default:

All faces map-able or submap-able Topological matching of opposite faces

Submap Scheme

mesh

mesh

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Hex Meshing - Tet-Primitive

All hex elements in a four-sided (tet) volumeVolumes directly meshable using Tet-Primitive scheme

How the Tet Primitive Scheme worksConnect center points on edges, faces and the volumeMap the four sub-volumes

Tet-Primitive scheme

Tet Primitive

Mesh

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Hex Meshing - CooperThe Cooper Scheme, in essence, projects or extrudes a face mesh (or a set of face meshes) from one end of a volume to the other and then divides up the extruded mesh to form the volume mesh.

The projection direction is referred to as the Cooper direction.Faces topologically perpendicular to this direction are called Source faces.

Source faces do not have to be premeshed.In practice, at least one source face must not be meshed and must span across the entire cross section.

Faces that intersect the source faces are referred to as Side faces.Side faces must be Mappable or Submappable.

Cooper direction

Source Faces Side Faces

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Permissible Cooper Geometries

source faces

source faces

Volume containing multiple holes

Multiple source faces and multiple interior loops

Source faces are not parallel to each other

source faces

source faces

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Steps to Use the Cooper Tool

When the Cooper scheme is selected, a source face list box appears in the panel. If GAMBIT chooses the sources faces

Check the source face list and visually check for an intelligent selectionIf necessary, change the source faces selected by GAMBIT.

If GAMBIT fails to pick a set of source faces Manually select the source facesIf necessary, manually change the vertex types (discussed in lecture 3) on some of the side faces

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Getting the Cooper Tool to Work (1)

Problem: Mesh on Source Faces A and B can not be projected onto mesh on Source Face C

Work around: Remove Mesh on Face C. As a general rule, do not premesh all of the source faces.

A

B

C

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Problem: "Close" interior loops on opposing source Faces A and BThe Cooper tool fails if the interior loops (when projected onto a single face) intersect or are "close".

Work around: Split Face A. Neither of the faces A1 and A2 have interior loops.

A

B

Interior loops

A1 A2

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Problem: No logical cylinder exists: If Faces A and B are source faces, then Face C must be either mappable or submapple. Face C has a void and can only be paved.

Work around: Split the Volume with a Face. Use Face A1 as one source face for Volume 1 and use Face C2 as one source face for Volume 2.

AB

C

A1

C2

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How to Make a Volume CooperableThree options to cooper a volume:

Manually change the vertex types on the side faces so they are mappableand/or submappablePick the source facesEnforce the map or submap on the side faces

EE

S

SS

S

EE

E

E E

C

Example: manually change the vertex types

3 Source Faces

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Tetrahedral/Hybrid MeshingTetrahedral/Hybrid Mesh Scheme - TGrid

Automatic - most volumes can be meshed without decomposition.Use boundary layers to create hybrid grids (prism layers on boundaries to capture important viscous effects).Use on volumes that are adjacent to volumes that have been meshed with hex elements will automatically result in a transitional layer of pyramids.

Hex mesh first

Tet mesh second

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Tet/Hybrid Meshing: TroubleshootingQuality of the tetrahedral mesh is highly dependent on the quality of the triangular mesh on the boundaries.

Initialization process may fail or highly skewed tetrahedral cells may result if there exists:

highly skewed triangles on the boundaries.large cell size variation between adjacent boundary triangles.small gaps that are not properly resolved with appropriate sizedtriangular mesh.

Difficulties may arise in generation of hybrid mesh.Cannot grow pyramids from high aspect-ratio faces.Prism and pyramid generation may not work properly between surfaces forming very acute angles.

low quality pyramid

prism layer

acute angle

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Hex - Core MeshingTetrahedral/Hybrid Mesh Scheme –Hex - Core

Combines Tet/Hybrid mesh with core Cartesian meshFewer cells with full automation and geometric flexibilityNon Conformal Meshes Created with:

Size FunctionsHexcore_Quad_Surface_SplitDefault (split quads into tri elements)

The number of offset layers (cell layers between wall and hexahedral core is controlled by the GAMBIT Hexcore_Offset_Layers.

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Hex – Core Meshing : Surface Split

1 (default)Split boundary quad into 2

triangleshanging edges created

(NOT allowed in FIDAP)Smooth boundary hexes

with larger hexcore0

Boundary quads are NOT split

Pyramid (transition) elements created

Boundary hexes not smoothed

Geometry: CylinderEdit Default: Hexcore_Quad_Surface_Split = 1 (default) or 0

Hex Core Tets Pyramids

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Hex Core Meshing: Setting Offset LayersThe number of layers of cells between the boundaries of the domain and the hexcore is controlled by the GAMBIT default HEXCORE_OFFSET_LAYERS.

HEXCORE_OFFSET_LAYERS is set to 3 by default.Increasing HEXCORE_OFFSET_LAYERS provides flexibility in meshing with sizing functions, boundary layers and complex boundaries.

HEXCORE_OFFSET_LAYERS=3(default)

HEXCORE_OFFSET_LAYERS=5

3 cell layers

5 cell layers

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Assigning Boundary and Continuum Types The Boundary Type Form

Enter entities to be grouped into single zone in entity list box.

First choose entity type as face or edge.Select boundary type for zone (entity group).

Available types depend on SolverName zone if desired.Apply defines zone and boundary type.

Can also modify and delete zone/boundary.By default,

External faces/edges are wallsInternal faces/edges are interior

The Continuum Type FormSimilar operation.All continuum zones are by default, fluid.

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FLUENT 5/6 Example: Flow over a Heated Obstacle

Boundary: Name = inlet

Type = VELOCITY_INLET

Boundary: Name = outlet

Type = PRESSURE_OUTLET

Continuum: Name = step

Type = SOLID

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FIDAP 8: Example: Flow over a Heated Obstacle

Boundary: Name = inlet

Type = PLOT

Boundary: Name = outlet

Type = PLOT

Continuum: Name = step

Type = SOLID

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Defaults: Example: Flow over a Heated Obstacle

By default, the 4 remaining external faces have the Name and Type:

Boundary: Name = wall

Type = WALL

By default, the one remaining volume has the Name and Type

Continuum: Name = fluid

Type = FLUID

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Linear/Quadratic Elements (FIDAP/POLYFLOW USERS ONLY)

General toolsHigher-order elements

For FEM codes (FIDAP and POLYFLOW), the element order can be changed at all three meshing levelsOnly linear and quadratic elements are directly availableA change to quadratic element type at one level will automatically change the element type in other levels The following table presents the most commonly used and recommended quadratic element types for FEM - solvers

POLYFLOW FIDAPedge 3-node 3-nodeface 8-node quad 9-node quadvolume 21-node brick 27-node brick

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Volume Decomposition Examples

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Decomposition

Suggestions of how to decompose single volumes into multiple mesh-able volumes are shown in these examples. The following meshing tools are used:

MapSubmapTet-primitiveCooper

Volume decomposition is not needed for the Stairstep, Hex/Core or TGridTet/Hybrid meshing schemes.

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First Example (1)A spherical void inside a brick

ConstructionCreate a sphere, a brick and a cylinder using volume primitives. The cylinder diameter should be smaller than the sphere and its length extending outside the brickSubtract the sphere from the brick

DecompositionSplit the brick using the cylinderCreate edges going diagonally over the top and bottom face of the brick and use the edges to create a diagonal faceSplit the brick-like volume using this face

Last two steps are not necessary but create higher quality mesh.

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First Example (2)A spherical void inside a brick

Three of the four Cooper-able volumes

source faces

source faces

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Second Example (1)A handle

Construction:Create a torus and a brick using volume primitivesSplit the torus using the brick Face as a tool Delete the left part of the torus

Decomposition:Make a Bidirectional split of the remaining volumes

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Alternative Construction/Decomposition:Create a torus and a brick using volume primitivesPerform a bi-directional split using the two volumesDelete the part of the torus that is outside the back of the brickUnite back the block and the pipe section inside the block again

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The two volumes meshed by the Cooper - tool

source faces

source face

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Third Example (1)A box with rounded corners

ConstructionCreate a brick using volume primitivesUse the blend option to round off one corner and three edges using the same radius (Setback option)

Decomposition:Create a second brick of the same size as the radius of the blend and move it such that its corner coincides with the center point of the blended corner. Split off the the rounded cornerSweep out the three triangular faces created by the split to the opposite ends of the brickSplit off the three prismatic volumes from the main volume

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Third Example (2)A box with rounded corners

The volume can be meshed using the submap (1), the tet-primitive (not shown) and the Cooper (3) schemes.

source faces

source face

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Fourth Example (1)Pipe-pipe intersection (different radii)

Construction:Create the pipes using volume primitivesCreate a stretched brick with a rectangular cross-section, where the side length should be between the two pipe diameters.

DecompositionSplit the main pipe using the brick Unite the brick cut-out with the small cylinder

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Fourth Example (2)Pipe-pipe intersection (different radii)

The three volumes meshed using the Cooper tool

source faces

source faces

source faces

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Fifth Example (1)

A sphere in three volumesConstruction

Create a sphere using volume primitivesDecomposition:

Create a cylinder and split the sphere using the cylinderCreate a brick and move it such that one side of the brick is along the center of the cylinderSplit the annular remainder of the sphere into two volumesAll three volumes are basic Cooper-able volumes

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Fifth Example (2)A sphere

The final mesh for two of the volumes

source faces

source faces

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Fifth Example (3)A sphere in eight volumes

Alternative Construction/decompositionCreate a sphere and a brick using volume primitivesIntersect the two volumes to create a sphere octantMake a second copy by the use of Copy/Reflect and the z-planeMake six octants more using Copy/Rotate and 90 degree angle, twiceConnect all faces using Real Connect

The same geometry could also have been created by splitting a sphere in all three major planes This decomposition will create a better mesh quality

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Fifth Example (4)A sphere

The final mesh for seven out of the eight octants, all meshed using Tet Primitive

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Meshing Control using Sizing Functions and Boundary Layers

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Sizing Functions and Boundary Layers are meshing control tools available in GAMBIT.

Sizing functions can be used to smoothly control the growth in mesh size over any particular region of the geometry or the entire geometry, starting from a “source” or origin.

Sizing functions are used to smoothly transition from fine mesh needed to resolve flow physics, curved geometry and model flow in thin gaps.

Boundary layers are used to grow layers of cells of desired height from specified boundaries of 2-D/3-D geometry and are typically used to capture near wall phenomena such as turbulence and heat transfer.

Multiple Sizing Functions and Boundary Layers can be used to control mesh size distribution.

Sizing Functions and Boundary Layers

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Size FunctionsSize Functions control the mesh distribution in a region of space, including edges, faces, and volumes similar to the way gradingcontrols mesh distribution on edges.Size Functions are accessed through the Tools menu:Size Functions are designed to grade meshes with Tets even though they can be used with a hex mesh.

Multiple Size Functions: Curvature and Proximity

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Size Function TypesSize Function requires the specification of Type, Entities, and Parameters.Size Function "Type" controls method by which scope of sizing function is obeyed.

FixedScope is defined as a fixed region about a source.

CurvatureScope is defined as a region near highly curved surfaces.

ProximityScope is defined as a region within a specified distance from objects.

Meshed size FunctionEnsures that a mesh is radiated in a controlled manner from pre-meshed boundaries of the domain.

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Sizing Function DefinitionEach Size Function Type requires the specification of:

EntitiesSource entity defines shape and location of the "origin" of affected region.Attachment entities host the mesh that will be affected.

ParametersThree parameters define the characteristics of the size function, except the meshed size function. The two parameters common to all four size function types are the Growth rate and Size limit.The third (initialization) parameter is different for each of the first three size function types.The meshed size function does not use a initialization parameter.

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Fixed Size Function - SourceSource

Can be vertices, edges, faces, or volumesCan be internal or external to attachment entitiesSource entity defines shape of scope

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Size Function - AttachmentsThe attached entities host mesh to be affected.

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Fixed Size Function

ParametersStart size: Size adjacent to the sourceGrowth rate: Ratio of two adjacent mesh-element edge size

Size limit: Maximum allowable size for attachment entity

Small growth rate Large growth rate

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Curvature Size Function

Source Entities can only be FacesParameters

Angle: Specifies the maximum allowable angle between outward pointing normals for any two adjacent mesh elements.

Growth rate and Size limit: same as for Fixed

Large angle Small angle

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Proximity Size FunctionSpecifies number of cells in face gap (3D) and edge gap (2D)Parameters

Cells per gap : number of mesh layers in the gapGrowth rate and Size limit: same as for fixed

LimitationsBecomes slow on large modelsImproper use may result in abrupt change in sizeSolutions

Use multiple size functionsIncrease resolution by changing the defaults for background grids

Cells/gap = 2

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Meshed Size FunctionSource and attachment entities are specified similar to the fixed size function.Parameters:

No initialization parameter is needed.Growth rate and size limit need to be specified, though.

LimitationsThe source entities have to be pre-meshed.

Premeshedsource edges

Premeshed source face

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Background Grid GenerationSize functions work by generating a discrete map of mesh size on a background Cartesian grid that overlays the attachment geometry, which is used by the meshing algorithms in growing mesh with a size distribution.

A set of Cartesian boxes forming a grid that bounds the attachment geometry are generated and successively refined i.e. split into smaller boxes, until a maximum number of levels of refinement (or “tree depth”) are reached or the size variation in all the boxes is less than a specified percentage tolerance limit.

The GAMBIT Transcript window contains details of background grid generation for each size function.

The maximum allowable tree depth and the tolerance limits are set by GAMBIT Defaults, BGRID_MAX_TREE_DEPTH (=16 by default) and NONLINEAR_ERR_PERCENT (=25% deviation from linear variation, by default).

It may be necessary to increase BGRID_MAX_TREE_DEPTH to smoothly resolve size functions, and hence the mesh, on complex or large geometry.

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Increasing Background Tree Depth

Ideal background grid

Background grid level reached maximum value specified

Size Function not sufficiently resolved

Under-resolved Background Grid Resolved Background Grid

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Boundary LayersBoundary layers are layers of elements growing out from a boundary into the domain.

Produces high quality cells near boundary.Allows resolution of flow field effects with fewer cells than would be required without them.

In general, boundary layers are attached to:edges for 2D problemsfaces for 3D problems

complicated 3D shapes may require boundary layer attachments to edges.

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Specifying a Boundary LayerCreate Boundary Layer Form

AlgorithmsDefinition Inputs SettingsTransition PatternAttachment

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Boundary Layer Algorithms

Boundary Layers can be defined using Uniform or Aspect Ratio based algorithm.

Uniform Boundary Layer Aspect Ratio based Boundary Layer

Size is constant for each layer of cells

Aspect ratio/layer is constant for each layer of cells

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Boundary Layer Definition Inputs

Definition Inputs for Uniform Boundary Layer ( 3 out of 4 inputs are required, the fourth is calculated)

First row: height of first row of elements (a)Growth factor: factor for geometric series (b/a)Rows: total number of element rowsDepth: total height of boundary layer (D)

Definition Inputs for Aspect Ratio Based Boundary Layers are similar:

First percent: starting aspect ratioGrowth factor factor for geometric series (b/a)Number of rows

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Wedge Corner Shape

The Wedge corner shape option is used at corner or reversal vertices to create a rounded “wedge” of elements.

ON (Wedge Shape) OFF (Block Shape)

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Internal ContinuityThe Internal Continuity toggle allows boundary layers to be formed with no crossover or overlap regions.

Internal Continuity "ON"Internal Continuity “OFF”

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Boundary Layer AttachmentsBoundary layers attach to edges for 2D boundary layers and faces for 3D boundary layers.

A boundary layer is initially displayed in orange to indicate that it is temporary, and updates immediately with any changes.

An arrow points from the attachment edges towards the centroid of the corresponding face (for 2D boundary layers) or volume (for 3D boundary layers).

This can be misleading in some cases, e.g. in 3D case when the volume forms an annulus.

The boundary becomes white (permanent) upon clicking on Apply.

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Boundary Layers and Vertex Types2-D Boundary layers in regions near vertices are defined by the vertex type.

The vertex type for Boundary Layers can be changed in the Set Face Vertex Form in the Face meshing menu with the Boundary layer only option turned on.

Vertex types are also important for imprinting 3-D boundary layers on adjacent faces.

E

E

ES

CE

E

E

R

E

End: mesh overlaps

Corner: angle divided into thirds

Reverse: angle divided into fourths.

Side: angle bisected

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Imprinting Adjacent Faces with 3-D Boundary Layers

A 3-D boundary layer attached to a face may "imprint" the adjoining faces, depending on the vertex type of the vertices at the intersection of the boundary layer attachment face and adjoining faces.

If the vertex is an “End” type vertex, an imprint is created and displayed.If 3-D boundary layers are also attached to the adjoining faces, then the Internal Continuity toggle will determine the crossover region and imprint.

Imprint of 3-D boundary layer on adjacent faces with 3-D boundary layer attached to bottom face

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Imprinting 3-D Boundary Layers by Modifying Vertex Types

When the angle between adjacent and attachment faces in greater than 1200, a vertex type change to “End” can cause the 3-D boundary layer to imprint.

140

No imprinting of 3-D Boundary Layerand gaps due to Side Type vertices at the

intersection of the faces

Attachment Face

Vertex Types changed to ‘End’ closes the gap and imprints 3-D boundary layer

SS

EE

S

E

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Normal and Offset Smoothing

Normal smoothing of boundary layers is used to ensure a gradual change in growth direction of boundary layers wrapped around corners.Offset smoothing is used to reduce or eliminate spikes and dips in the boundary layer. Both kinds of smoothing are performed iteratively and are governed by GAMBIT defaults.

Without normal smoothing

With normal smoothing

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Boundary Layer DefaultsGAMBIT defaults set values for the critical parameters for growing boundary layers.

A knowledge of the important defaults will help control mesh on complex 2-D and 3-D geometry.

Boundary Layer Defaults are available in the in the BLAYER and BLAYERTGRID sections under the Mesh Tab in the Edit Defaults Menu.

The GAMBIT Command Reference Guide provides more information on defaults.

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Some Important Boundary Layer DefaultsUSE_FACET_EVALS (default = 1, 2-D and 3-D Boundary Layers)

1 = Surface boundary layers will use a faceted representation of the surface to calculate the growth direction.

The faceted representation is much faster, especially for complex surfaces, but less accurate.

0 = Surface boundary layers will use the exact representation of the surface (1e-6 tolerance) to calculate the growth direction for the boundary layer.

ANGLE_SMOOTH_FACTOR (default value=0, Maximum allowable value = 1, 2-D and 3-D boundary layers)

Nodes are projected perpendicular for a value of 0. Generates equidistant outer nodes for a value of 1. Intermediate values between 0 and 1 are allowable.

USE_FACET_EVALS=1

ANGLE_SMOOTH_FACTOR=0

USE_FACET_EVALS=0



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Some Important Boundary Layer DefaultsADJUST_EDGE_BL_HEIGHT (default = 0, 2-D boundary layers only)

0 = the boundary layer height at the edge is the distance grown from the vertex. If the adjacent edge is skewed, then the boundary layer height will be less than the perpendicular height.

1 = the boundary layer height is projected onto the skewed edge.

Other Important Defaults (Details in GAMBIT Command Reference Manual) :

QUICK_N_DIRTYHEIGHT_TRANSIT_RATIOSMOOTH_CONTINUOUS_SIDESDefaults for Normal and Offset Smoothing

ADJUST_EDGE_BL_HEIGHT=0

ADJUST_EDGE_BL_HEIGHT=1

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CAD/CAE Data Exchangeand Geometry Cleanup

(Virtual Geometry)

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IntroductionSeveral translation methods available to enable data exchange with CAD/CAE systems.

Appropriate approach depends upon source.Translation can:

return incomplete, corrupt, or disconnected geometryreturn geometry details unnecessary for CFD analysis

Geometry cleanup refers to processes required to prepare geometry for meshing.

Fix incomplete or corrupt geometry and connect disconnected geometryRemove unnecessary detailsDecompose geometry into meshable sections

Gambit's Virtual Geometry operations can help with the cleanup process.

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CAD Data Exchange - Direct Options

Direct Translation OptionsACIS-based CAD programs:

e.g., AutoCad, Cadkey, TurboCadcan export ACIS files (.sat or .sab) which can be imported into Gambit.

Parasolids-based CAD programs:e.g., Unigraphics, SolidWorks, PATRAN, ANSYScan export Parasolid files (.x_t and .xmt_txt) which can be imported into Gambit.

CAD programs using proprietary geometry kernelCatia V4 and Catia V5 (saved in Catia V4 format)Direct (single-stage) Catia V4.model file to ACIS translator

ADD-on (specific license key needed)Contact your account manager at Fluent for price information

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CAD Data Exchange - Standard OptionsStandard Translation Options

Translation uses an intermediate, neutral or standard, file format.Applicable for all CAD/CAE systemsthat can output:

STEP filesPro/E supports STEP export at no additional cost.Other systems support STEP as add-on.

IGES filesCommon format supported by most systems.

STEP (Standard for Exchange of Product model data)International standard defining format for geometry and model information.Gambit supports AP203 and AP214Preferred over IGES import

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CAD Data Exchange - Standard Options (2)Standard Translation Options (continued)

IGES (Initial Graphics Exchange Specification)Topology/connectivity information is lost when CAD programs export IGES surface data only.

e.g., faces associated with volume, etc.implies that volumes must be recreated from imported faces (tedious)

Some CAD packages export IGES-solids as well as IGES-surfaces.I-DEAS and CADDSTopology/connectivity information maintained.

Gambit provides two options for IGES importSpatial (Recommended)

– All imported geometry comes in as real, supports solidsNative (Fluent)

– Original IGES translator, does not support solids– Trimmed surfaces come in as virtual geometry

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Import Mesh and Import CADImport Mesh and some Import CAD options result in faceted geometry.

Least preferred approachImport/CAD Pro/E (Direct)

Gambit directly accesses Pro/E’s geometry engine

Eliminates geometry translation lossesUser works in Gambit environment

Need special Gambit and valid Pro/E licenseSolid models alone are supported

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Tolerant ModelingAutomatic "real" geometry connect using variable toleranceAvailable at

time of importinside the Heal Face (or Volume) Form

ApplicationAll Geometry filesRelatively large gapsReal ACIS volumes generated during import

Boolean operations subsequently possibleAdding/Subtracting additional geometryVolume ExtractionRetaining only ½ or ¼ of modelVolume Decomposition for better meshing

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Smoothing Real GeometrySmoothing can be used to remove discontinuities in geometry and simplify spline representations.Smoothing can aid in subsequent Boolean operations.There are two smoothing options:

Remove discontinuitiesReduce complexity to simplify NURB representation

Face smoothing

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Geometry imported from other CAD systems can lack the required accuracy and precision to render valid or connected ACIS geometry.

This results from numerical limitations in original CAD system, neutral file formats, or differences in tolerances between CAD systems and ACIS.

If Boolean operation fails on imported tolerant geometryProblems are usually resolved by smoothing or healing the geometry.

Healing can be done on either faces or volumesHealing can be invoked at time of import

If smoothing/healing fails to resolve the problem, Re-import the geometry without tolerant modeling or healingUse the check command to verify integrity of geometry/topology.Replace the corrupted faces using real optionsUse Tolerant modeling and Healing to re-connect the new face with the rest of the model.

Heal Real Geometry

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Virtual GeometryThree kinds of geometry in GAMBIT:

RealDefined by the ACIS library of geometry creation/modification routines.Geometry defined by mathematical formulae.

VirtualA Fluent Inc. library of routines providing additional functionality by redefining topology.Derive their geometrical descriptions by references to one or more real entities (called the Hosts).

Faceted geometryTreated like virtual geometry.Derived from importing a mesh or faceted geometry into GAMBIT, split mesh operations, or stairstep meshing scheme.

Two objects that share the same underlying geometry but different topologies.

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Virtual Geometry: Uses

Virtual geometry and the operations that create them are used tosimplify, clean, and connect existing geometry.

Simplify/Clean:remove details from the model unnecessary for CFD analysis.merge faces/edges to increase mesh quality.decompose geometry into smaller, meshable components.

Connect:Connect geometry that becomes disconnected during import process.

Virtual geometry provides additional flexibility in operations that affect geometry and mesh.

Merges edges to enable non-coplanar face to be created.Modify the mesh by repositioning nodes on virtual face.

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Creating Virtual Geometry

In general, virtual geometry is created as a result of a virtual geometry operation on a real entity.

Can also be created from a "native" IGES import operation.Virtual geometry operations:

are accessed:by selecting virtual option on a real geometry panel andthrough dedicated virtual operation panels.

employ any combination of real, virtual, and/or faceted entities.result in the creation or modification of virtual (typical) and real entities.Some real geometry operations will not work with virtual geometry.

e.g., boolean operations and some split operations will not work with virtual geometry Take care when planning to use virtual geometry operations.

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Characteristics

Virtual entities:entities are colored differently from real entities.naming convention: v_vertex, v_edge, v_face, v_volume.

When performing a virtual geometry operation:Directly connected lower and upper geometry will become virtualUnderlying real geometry (host) will become invisible and inaccessible (or put in the "background")

Deleting virtual geometry:Will not delete host geometry.Typically, lower order entities (virtual) remain undeleted.

Meshing and Boundary Assignments:Meshing and boundary assignment operations are unaffected by virtual geometry.

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Virtual Geometry Operations-1

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)

++

++

Example:

Example:

Example:

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Create - creates independent virtual entitiesUse host entities for shape definition

Collapse - splits a face and merges the resulting pieces with two or more neighboring faces


+ + + +

collapsethis face

betweenthese faces

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Convert - converts non-real entities to realApplicable to vertices, edges, faces, and volumes.Edges are sampled and real spline (NURBS) curve generated.

sampling controlled by geometry.edge.VIRTUAL_NUM_SAMPLING_POINTSFace conversions require that a map mesh first be generated on face (no Side vertices allowed).Volume conversions require that all lower topologies can be convertedTopology and any existing mesh are preserved.

Face SimplifyRemoves dangling edges and hard points from a face.Result is virtual faceThe face with dangling edge can also be split using face split (by location)


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Edge/Face MergeVirtual Edge/Face Merge options

Virtual (Forced) Create one single edge/face from all edges/faces

++

max. edge =

min. angle = 135

+ +

++

+

face merge

edge merge

Virtual (Tolerance)Merge all entities shorter than Max. Edge/Face Length Merge all entities of higher entity angle than Min. AngleNo input will merge all vertices connected to two edges only

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Boundary Defined Virtual Face Unite (1)Handles gross overlaps and gaps

Arbitrary shapesTolerance option

LimitationsOrder of picking Points is importantImportant locations must be picked by userGaps larger than the mesh size can create trouble during meshingCan not handle large distances between overlapping faces

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Boundary Defined Virtual Face Unite (2): Example

Select 6 points (a,b,c,d,e,f)c and e lie on square edge

Square face in z = 0 planeCircular face in z = .05 planeFaces can not be Real united

a b

fe

c

d

Straight edge constructed between points c and d (and between d and e) because they lie on different edges.

Select 6 points (a,b,c,d,e,f)c and e lie on circular arc

Arc shape retained between points c and d (and between d and e) because they lie on the same edge

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Face Splits (Virtual and Faceted)Split by

Face (Real or Virtual)Edge (Virtual)Vertices (Virtual)

Example using 2 vertices

Location (Virtual)Vertex locations can be adjusted after the splitLimitations (for both Face and Volume Split)

Split through voids, protrusions and dangling faces will create incorrect geometryOrder of picking is importantIf you do not Zoom in close to the object, the split might fail First and last location on a face must be on its boundary

++

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Volume Splits (Virtual and Faceted)Split by

Volume (Real)Face (Real or Virtual)

All edges of the face have to be connected to the volume

Locations (Virtual)

one volume two virtual volumes

connected face

virtual volume split

Pick (at least) two locations

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Comparison of Face Unite, Merge, and ConnectUnite

RealFaces must have matching tangents at edge

VirtualGaps or overlaps allowed

No unite for edgesMerges

Operates on real/non-real geometry virtualFaces must share edge but they need not be tangent

ConnectOperates on real/non-real geometry real or virtualReplaces selected entities with single entity

Merge

Real Unite

Connect

tolerance

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Edge Connect (Virtual)Edge Connect

Also available in Vertex and FaceVirtual (Forced)

Pick two or more edges you want to connectVirtual (Tolerance)

Every picked edge within the tolerance will be connected10 % of shortest edge is recommended (default)The shortest edge is shown by clicking the “Highlight shortest edge” buttonThe shape of the connected edge is aninterpolated ‘average’ of the picked edges.

Use Preserve first edge shape to force result toassume shape of first edge in pick list.

– Preserve first vertex location is available for vertex connects.

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T-Junctions OptionT-Junctions - splits edges by vertices that exist within a specified tolerance of the edges and then connects the split entities.

Use Preserve split-edge shape option to get following result:

connected virtual edges/facesunconnected real edges/faces

Edge Splits

Invoking too early may result in very small edges

Original Option Off Option On

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Virtual Face Connect with T-JunctionsVirtual (Tolerance) Face Connect includes a T-Junctions option.This helps overcome common geometry problems in imported models such as gaps, mismatches and overlaps.

Utilizes projections, splits, and connects to overcome problems.

Available for both real and virtual geometryThe resulting geometry is always virtual.

Virtual (Tolerance) Face connect using T-Junctions

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Importing IGES FilesFile Import IGES

SummaryReview important information in the form before importing the file.Validity of information varies.

OptionsNative or Spatial TranslatorAbility to scale the IGES file at import (Scale model between the dimensions of 1e-6 and 1e+4, preferably around 1)Remove stand alone entities

Virtual CleanupEnables automated cleanup sequence using:

connect toleranceedge merge toleranceangle merge tolerance

– geometry.edge.VIRTUAL_MERGE_MIN_ANGLE

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Virtual Geometry Cleanup Strategy-11. Delete all unnecessary geometry2. Check validity of imported geometry3. Correct invalid geometry (Heal and/or reconstruction)4. Check connectivity by color coding

Helps distinguish between connected and unconnected entities.White - Stand-alone entitiesOrange - Unconnected faces (Edge connected to one Face)Dark Blue - Connected faces (Edge connected to two Faces)Light Blue - Multiple connections (internal Face)

5. Connect Geometry (can be automated using Virtual Cleanup option)a. Merge edges based on length and angle tolerances to eliminate short edges.b. Real/Virtual connect of vertices, edges, and faces, in steps, based on increasing connect tolerancec. Connect with T-Junction Option.d. Use forced connect operation for entities out of tolerance

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Virtual Geometry Cleanup Strategy-26. Create additional geometry, if necessary, and form volume.

Some of this may need to be done before resorting to virtual geometry commands so that real boolean operations are available.Bridge real and existing virtual geometry together using virtualgeometry.In 3D, use face stitch command to create virtual volumes.

7. Simplify facesMerge small edges and faces with neighbors to eliminateRemove sharp angles for better meshing.

8. Decompose volume, if necessary.9. Mesh

Merge example:

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Clean up Imported Geometry

Imported geometry containing large number of faces

Why is Clean up important?Ensure connectivity: holes and cracksImprove mesh quality: Eliminate short edges, sliver faces, sharp angles, …

Clean up on models containing a large number of faces can be tedious without use of the cleanup toolsCleanup Tools can semi-automate this process

Finding the problem areasSuggesting fixes

Virtual Geometry createdChoose "Real" path to clean up if Boolean operations needed

Refer to Chapter 5.4 in the GAMBIT Modeling Guide for more information

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Meshed Geometry: With and Without CleanupInterval size = 2.5

Without Cleanup- Only theTet/Hybrid Scheme can be used

Tet mesh: 202,798 elements

With Cleanup- Cooper Tool can be used

Hex mesh: 43,778 elements

Number of elements reduced by a factor of 4.6

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Cleanup ToolsSequential, Semi-automatic Geometry Cleanup Tool resulting in connected geometry and a better meshQuickly identify, zoom-in, highlight areas that cause connectivity and mesh quality problems

Graphics color coding set to connectivityGraphics window pivot set to mouse

Appropriate tools to fix problems are givenAvailable Cleanup tools:

Clean up Short EdgesClean up HolesClean up CracksClean up Sharp AnglesClean up Large Angles

Clean Up Small FacesClean Up Hard EdgesClean Up FilletsCleanup Duplicate GeometrySelect Clean up Domain

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Clean Up Short Edges (1)

Tools to identify and highlight the problem spotCleanup domain

Select whole model or groupMaximum length: upper limit

Default: 10* shortest edge in the Cleanup domainItems List: candidates for cleanup operation based on Cleanup domain and Maximum lengthCurrent length: length of currently picked edgeUpdate: updates the Items list

Required when Maximum length is modified

ZoomIn/Out: quick auto zoom in on or from the picked items

Auto: automatically zooms in on selected item

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Tools to identify and highlight the problem spotLocal: current item + all faces connected to it

Visible: make everything else invisibleShade: shade the local objects

Options to Apply Cleanup ToolApply: applies appropriate fix to selected itemA/N: (Apply/Next) applies appropriate fix to selected item and automatically picks the next item in the list. The view is changed.Auto: entire list is processes automatically (only works for the Method: Edge merge)Ignore: removes selected item from list and selects next itemRestore: the list is restored

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Clean Up Short Edges (3)Methods to fix the problem spot

Vertex connect (least common)Average locationPreserve location: first vertexPreserve location: second vertex

Edge mergeMerge with (select edge)

Face mergeFaces to merge (select faces)

Edge merge pre-selected when at least one vertex has only one other connected edge. Appropriate methods and applicable entities are often pre-selected, however users may edit them.

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Clean Up Holes (1)Holes in the model are internal edge loops that do not constitute external boundaries of a face (or faces)Tools to identify and highlight the problem spot and Options to Apply Cleanup Tool

Similar to those for Cleanup Short edgeMethod to fix the problem spot

Create Face from Wireframe Real and Virtual options available

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Clean Up Cracks (1)

A Crack is defined as an edge pair that meets the following criteria

Each edge in the pair serves as a boundary edge for a separate face.The edges share common endpoint vertices at one or both ends.The edges are separated along their length by a small gap.

Defining angle: the angle at the endpoint vertex shared by the two edges.

If edges share common endpoint vertices at both ends, the minimum angle is used

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Clean Up Cracks (2)

Tools to identify and highlight the problem spot

Maximum angle: default is 20Other tools similar to those for Cleanup Short edge

Options to Apply Cleanup ToolSimilar to those for Cleanup Short edge

Method to fix the problem spotConnect edges

Tolerance: maximum distance between edges to be connected

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Clean Up Cracks (3)

The edges that define the crack share one vertex

The edges that define the crack share two vertices

Before Cleanup After Cleanup Before Cleanup After Cleanup

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Clean Up Sharp Angles (1)

A Sharp Angle is defined as an edge pair that meets the following criteriaThe edge pair shares a common endpoint vertex and serves as part of the boundary for an existing face.At least one of the edges in the sharp-angle edge pair serves as a common boundary edge between its bounded face and an adjacent face.The angle between the edges in the pair (computed at their common endpoint vertex) is less than a specified angle.

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Clean Up Sharp Angles (2)Tools to identify and highlight the problem spot

Maximum angle: default is 20Other tools similar to those for Cleanup Short edge

Options to Apply Cleanup ToolSimilar to those for Cleanup Short edge

Methods to fix the problem spot determined by face-face angle

If face-face angle > 135: Merge facesIf face-face angle < 135: With Options (to truncate)

Distance: length of shortest boundary edge of truncated face

Chop MergeBi-Chop Merge

face–face angle: 180 –

is the angle between the normals of the two faces (shaded in grey)

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Clean Up Sharp Angles without Chop (3)Before Cleanup

After cleanup: Merge with left face

After cleanup: Merge with right face

Virtual Virtual

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Clean Up Sharp Angles with Chop (4)

1 of 8 Sharp Angles:

Chop optionface - face angle < 135

truncated face

distance

Merge edges

merged face

Mesh: Cooper

Tri-primitive

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Clean Up Large Angles (1)

A Large angle is defined by a pair of faces that meets the following criteria

The faces are connected by a common boundary edge.The angle between the outward-pointing normals for the faces (the average of three different points along their common boundary edge) is less than a specified angle.

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Maximum angle: default is 5 degreesOther tools similar to those for Cleanup Short edge

Options to apply the Cleanup ToolSimilar to those for Cleanup Short edge

Method to fix the problem spotMerge faces

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Clean Up Small Faces (1)Tools to identify and highlight the problem spot

Maximum area: default value is 100 times the area of the smallest face in the Cleanup domainItems in the list contains all faces with areas less the maximum areaOther tools similar to those for Cleanup Short edge


Methods to fix the problem spot: Merge faceCollapse face

Candidate Faces to merge: all bounding faces with a face-face angle > 135 pre-picked

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Clean Up Small Faces (2)

After cleanup by Merge Face

Before cleanup

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Clean Up Hard Edges (1)

Hard edges are also know as dangling edges.Creation occurs:

as a result of a face split when the split tool only partially intersects target facefrom STL or mesh import

Tools to identify and highlight the problem spot and options to apply the cleanup tool

similar to those for Cleanup Short edgeMethod to fix the problem spot

Remove all hard edge

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Clean Up Fillets (1)A fillet is defined as a face that meets the following criteria:

The face lies between and is connected by means of common boundary edges to two or more faces.The faces to which the fillet face is connected are oriented at an angle with respect to each other.

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Clean Up Fillets (2)


Maximum angle: specifies the maximum deviation from 90o for outward-pointing normals computed at the boundaries of the fillet face.Other tools similar to those for Cleanup Short edge


Methods to fix the problem spotMerge faceCollapse face

Candidate Faces Faces to merge: all bounding faces with a face-face angle > 135 pre-pickedto collapse between: two opposite faces along the longest edges prepicked

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Cleanup Duplicate Edges Clean Up Duplicate Edges

Includes edges which are coincident in part (T-junction connect)

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Cleanup Duplicate FacesClean Up Duplicate Faces

Two search optionsTopology-based

All lower entities (edges or vertices) to be identical between the two faces.

Centroid-based The centroids of the two faces should be within tolerance.Less accurate, but helpful in detecting duplicate faces with different lower topology.

Method: Connect or delete faces

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Cleanup Duplicate VolumesClean Up Duplicate Volumes Method: Connects or deletes duplicate volumes

Duplicate entities due to modeling errors or problematic import

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Select Cleanup Domain

Specifies the domain to which the geometry cleanup operations apply.

Whole Model (default)Predefined geometry group

The Cleanup Domain is group2

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Demo

Import a Non-ACIS File (demo.igs)Apply Cleanup Tools

There are many different approaches. Mesh the Model using the Cooper Tool (Hexes).

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Where are the Problem Areas?

Fillet Short edge Orange edges: unconnected facesFaces can

be mergedSliver face

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Steps to Clean up Import the .iges file using the default settings (Make tolerant).Change color coding to connectivity.

Blue edges (2 connections) indicate connected geometry.Orange edges (1 connection) indicate unconnected geometry.

Try healing the faces (to retain Real Geometry)Delete the problematic faceApply Cleanup Tools (Virtual Geometry Created)

Short EdgesHolesLarge AnglesFillets

Create a Volume by stitchingMesh using the Cooper Tool

Source face

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Outline

Basis of Journal FilesParameters: Scalars and ArraysSpecial ConstantsExpressions: Arithmetic, Logical and StringFunctions: String and ArithmeticExamplesDO and IF-THEN-ELSE CommandsSummary of Journal File UsesDynamic GUI and Examples

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Journal Files

Journal File:Executable list of Gambit commands

Created automatically by Gambit from GUI and TUI.Can be edited or created externally with text editor.

Journals are small - easy to transfer, e-mail, store Uses:

Can be parameterized, comments can be addedEasy recovery from a crash or power lossedit existing commands to create new ones

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Running Journal FilesJournal files can be processed in two ways:

Batch mode (Run)All commands processed without interruption."read pause" command will force interrupt with

resume option appearing.Interactive mode (Edit/Run)

Includes text editor for easy modificationsMark lines in process field to activate for processing.Editable text field.Right click text fieldfor more options.Auto or Step throughactivated process lines.

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Journal File: Parametric ModelingParameters (including arrays), control-blocks, do-loops, arithmetic functions, etc., can be used in the Journal File for simplifying parametric studies.

Comment lines

Parameter names begin with $.Parameters are case sensitive.

GAMBIT Commands are not case sensitive

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Command Interpreter (1)

Commands are not case sensitiveComments begin with /

/ This is a comment line

Continue statements with \vertex create coordinates \0.0 1.0 2.0

All commands and arguments are documented in GAMBIT Command Reference GuideDO Loops, IF-THEN-ELSE blocks, constants, functions, expressions, etc. are documented in appendices of GAMBIT Users Guide (available in online help)

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Parameters

Scalar or ArrayNumeric or stringDefined by: $param = value

param = name of parametervalue = numeric or string value of parameter

Name of parameterMust start with $Is not case sensitive ($length same as $LENGTH)

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Scalar (1): Pipe (centered)

/original journal file

volume create height 10 radius1 2 radius3 2 zaxis frustum

/modified journal file with parameters for height ($h) and radius ($r)$h = 10$r = 2volume create height $10 radius1 $r radius3 $r zaxis frustum

Cylinder: Height = 10, Radius = 2

Axis Location: Centered Z

Center of the cylinder is at the origin of the active coordinate system

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Scalar (2): Pipe (not centered)

/original journal file

volume create height 10 radius1 2 radius3 2 offset 0 0 5 zaxis frustum

/modified journal file with parameters for height ($h) and radius ($r)$h = 10$r = 2volume create height $h radius1 $r radius3 $r offset 0 0 ($h/2) \zaxis frustum

Cylinder: Height = 10, Radius = 2

Axis Location: Positive Z

Center of the cylinder is offset (Height / 2) in the + z direction from the origin of the active coordinate system

offsets in the x, y and z directions

Use Parenthesis

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Array (1)Define arrays by declare $p[{n1}:m1, {n2}:m2, ...]

Where p is the name of the parametern is the starting index ({} indicate this is optional; default is 1)m is the range of the dimensionSquare brackets [] are necessary

Elements in the array still need to have values assigned to them$p[1,2]= 6.5

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Array (2): Examples

declare $sides[4] Creates $sides[1], $sides[2], $sides[3], $sides[4]

declare $tri[2:3] Creates $tri[2], $tri[3], $tri[4]

declare $sqr[3, 2] Creates $sqr[1,1], $sqr[1,2], $sqr[2,1] $sqr[2,2], $sqr[3,1], $sqr[3,2]

declare $matrix[0:3, 5:2] Creates $matrix[0,5], $matrix[0,6], $matrix[1,5], $matrix[1,6], $matrix[2,5], $matrix[2,6]

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Array (3): Multiple Pipes

$p[3,2] = 4$p[3,1] = 23

$p[2,2] = 3$p[2,1] = 12

$p[1,2] = 3$p[1,1] = .51

HeightRadiusPipe Number

Pipe 1, 2, 3

declare $p[3,2]

1st dimension is the pipe number (1, 2 or 3)

2nd dimension is the radius (1) or height (2)

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Special Constants

Available for use in any expressionPI 3.141592653590TWOPI 6.283185307180DEG2RAD 0.0174532925199RAD2DEG 57.29577951308

Examples4 * $rad * RAD2DEG$arclength = PI * $radius

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ExpressionsArithmetic, logical, or stringEnclose in parentheses when used as arguments to commands, IF statements, or DO conditionsvolume create height $h radius1 $r radius3 $r offset 0 0 ($h/2) \zaxis frustum

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Arithmetic Expressions (1)

Evaluate to numeric resultsFORTRAN-like syntax

E1 op E2where E1 and E2 can also be expressions, and op* is

+ (addition)- (subtraction)* (multiplication)/ (division)^ (exponentiation, note difference from FORTRAN)

Order of operations is ^ * / + -Use parentheses to override

*op refers to operations

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Arithmetic Expressions (2)

Examples:$x + 10-5.0 * $a / $b3^3.5 + 4 * $y(3^3.5 + 4) * $y

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Logical Expressions (1)

Evaluate to "true" or "false"FORTRAN syntax

E1 .op. E2where E1 and E2 are expressions, and .op. is

.GT. (greater than)

.LT. (less than)

.GE. (greater than or equal to)

.LE. (less than or equal to)

.EQ. (equal to)

.NE. (not equal to)

.AND. (true if both E1 and E2 are true)

.OR. (true if E1 is true or E2 is true, or both are true).NOT. E1 (true if E1 is false)

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Logical Expressions (2)

Examples:$x .lt. 5$y .gt. 10($a .eq. 4).and.(($b+$c) .lt. $d).not. $z

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String Expressions

String parameters defined as $name = “GAMBIT”Enclose string constants in double-quotes

"volume.1""fluid"

Concatenation: str1 + str2$base = “volume”$extension = “.one”$label = $base + $extension yields “volume.one”"/usr/" + "gambit" = "/usr/gambit”

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Functions

Can be used in any expressionReturn a single numerical, logical, or string valueNot case sensitiveArguments are constants or expressions enclosed in parentheses

ABS(exp)COS(exp)

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String Functions

Many string functions available, such as STRLEN and STRCMPSTRLEN: number of characters in a string

$x= STRLEN("title")$x=5

CSTRCMP: case sensitive string compare$y= CSTRCMP ("ABD","abd")$y=0

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Arithmetic Functions (1) : TrigonometricACOS(exp) arc-cosineASIN(exp) arc-sineATAN(exp) arc-tangentCOS(exp) cosineCOSH(exp) hyperbolic cosineSIN(exp) sineSINH(exp) hyperbolic sineTAN(exp) tangentTANH(exp) hyperbolic tangent

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Arithmetic Functions (2) : MiscellaneousABS(exp) absolute valueDIGSUM(exp) sum of digits of integer portion, i.e., DIGSUM(123)= 6EXP(exp) exponentialINT(exp) integer truncationLOG(exp) natural logarithmLOG10(exp) base 10 logarithmMAX(exp1,exp2) maximum of exp1 and exp2MIN(exp1,exp2) minimum of exp1 and exp2MOD(exp1,exp2) modulo (remainder) of exp1/exp2POW(exp1,exp2) same as exp1^exp2SIGN(exp) -1.0 if exp < 0, else 1.0SQRT(exp) square root

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Important String & Database FunctionsNTOS(exp) Converts a Number TO a String

Example: If $i = 1:"wall."+ NTOS ($i) = "wall.1"

LASTID(tag) ID of last-created entity, tag =ve_id or 1 (vertex)ed_id or 2 (edge)fa_id or 3 (face)vo_id or 4 (volume)gr_id or 5 (group)cs_id or 6 (coordinate system)bl_id or 7 (boundary layer)

Example: If five vertices has been created:LASTID(ve_id) or LASTID(1) = 5

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Example: Using Strings to Include Parameter value in the name of the exported .msh file

/journal file for creation of a pipe of varying height/parameter definition/$h is the height of the pipe$h= 6.4/commands for the creation of the pipe, meshing and definition /of boundary zones//end of the commands /commands to export the meshsolver select "FLUENT 5/6"$title = "pipe-"$end = ".msh"$id = $title + NTOS ($h) + $endexport fluent5 $id

/This journal file will export a file named: pipe-6.4.msh

FIDAP users: solver select "FIDAP"

$end = ".FDNEUT"

export fidap $id

Exported file: pipe-6.4.FDNEUT

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DO Loops (1)Syntax

DO PARA "$param" INIT exp1 COND(cond) INCR exp2commands

ENDDOWhere

PARA - loop parameter $param - must be defined before loopIts value is overwritten by the initialization of the DO Loop

INIT - initial value of the loop parameter COND - condition

Example: (cond) = ($param .le. 5)INCR - incrementINIT and INCR are optional; if one of them is not defined, its value is set to 1 (i.e. $param is initialized to be 1 or is incremented by 1)

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DO Loops (2): Example

The following GAMBIT journal creates 36 vertices at every integer position in the x-y plane, where 0 ≤ x,y ≤ 5

$i = 0$j = 0

$imax = 5$jmax = 5/do para "$i" init 0 cond ($i .le. $imax)do para "$j" init 0 cond ($j .le. $jmax)

vertex create coordinates $i $j 0enddo

enddo

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DO Loops (3): ExampleThe following GAMBIT journal creates a set of grid points (9 x 9) which are used to approximate a surface which is defined by

$i = 0$imax = 2$j = 0$jmax = 2$inc = .25$fact = .15do para "$i" init 0 cond ($i.le.$imax) incr $incdo para "$j" init 0 cond ($j.le.$jmax) incr $incvertex create coordinate $i $j ($fact*sin(RAD2DEG*PI*$i)\

*cos(RAD2DEG*PI*$j/2)) enddoenddoface create vertices "vertex.1" "vertex.2" … "vertex.81" rowdimension 9

)2/cos()sin(15. yxz ππ=

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IF-THEN-ELSE Blocks (1)

SyntaxIF COND (exp)

true-commandsELSE

false-commandsENDIF

WhereCOND - condition

Example: (exp) = ($param .le. 5) ELSE and false-commands are optionalCan be nestedNo ELSEIF defined (must use nested IF)

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IF-THEN-ELSE Blocks (2): Example

In the following Gambit journal the condition is false and a coarse grid is created

/coarse grid: a = - 1/fine grid: a = 1$a= -1if cond ($a .gt. 0)

volume mesh "volume.1" cooper source "face.1" "face.3" size 1else

volume mesh "volume.1" cooper source "face.1" "face.3" size 10endif

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Current LimitationsParameter definition in the Edit - Parameters form does not produce journal commandsParameters and expressions can NOT be used within the GUIJournals produced by GAMBIT contain the values of parameters and expressions, not the parameters/expressions themselves

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Steps to Use Parameters in Journal FilesBuild initial model with GUI

First use a set of basic numerical values.Mesh model and specify Boundary Types.Save journal file with unique name.

Editing the journal file:Define key parameters at the top of the file and include comments.Replace values with parameters throughout.

Check the journal file:Replay the journal to make sure that parameters were defined and used correctly.List of all parameters and their current values can be checked:

The parameter list - command The Parameter form

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Summary of Journal File Uses

Parameterized journals can save large amounts of time for parametric studiesDO loops and IF-ELSE blocks can be used control events in the journal file Time spent up-front thinking about how to best parameterize your journals can save time later in the processGAMBIT journal files can be combined with FIDAP journal files.

allows parameters to be defined only once if any of the boundaryconditions depend on the parameterized geometry.

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Dynamic GUI: Application-Specific TemplatesIncludes capabilities that enable us to create application-focused templates

Process automation toolsEasy-to-use, customized GUIsAddress specific applications, customized and fine-tuned for your specific processesAutomated geometry creation, meshing, solution, post-processing, and/or reporting

Facilitate the CFD process for both CFD engineers and non-CFD engineersDoes not replace roles of expert analyst in defining processes, exploring limits, and investigating problems

Contact Fluent's Consulting organization or your Technical Support Engineer

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