This document provides an overview of meshing tools in GAMBIT including edge meshing, face meshing, examining mesh quality, assigning boundary conditions, and using linear and quadratic elements. Key topics covered include controlling mesh density through grading and spacing, various face meshing schemes for quads and tris, assessing mesh quality using equiangle skew, and assigning boundary and material types.

1. © Fluent Inc. 4/8/20143-1
Introductory GAMBIT Notes
GAMBIT v2.0 Jan 2002
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Edge and Face Meshing

2. © Fluent Inc. 4/8/20143-2
Introductory GAMBIT Notes
GAMBIT v2.0 Jan 2002
Fluent User Services Center
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Meshing - General
 To reduce overall mesh size, confine small cells to areas where
they are needed (e.g., where high gradients are expected).
 Controlling cell size distribution
 Edges, 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 Functions
 New feature to control cell size in faces and volumes directly.

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Introductory GAMBIT Notes
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Edge Meshing
 Edge mesh distribution is controlled through
the spacing and grading parameters.
 Using the Edge meshing form
 Picking
 Temporary graphics
 Links, Directions
 Grading/Spacing
 Special characteristics
 Apply and Defaults
 Invert and Reverse
 Options

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Introductory GAMBIT Notes
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Picking Edges for Meshing
 Picking
 Temporarily meshed edges
 When you pick an edge, the edge is
temporarily meshed using white nodes
 Displayed edge mesh is based on current grading and spacing parameters
 If you modify the scheme or spacing, the temporary mesh will be
immediately updated
 When you Apply, the mesh nodes will turn blue
 Sense
 Sense is used to show direction of grading
 Every 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 Links
 Picking and soft links
 Pick with links
 By enabling this option, Soft-linked edges can be selected in a single pick
 Linked edges share the same information and can be picked in a single
pick
 Modifying soft links
 You can anytime:
 Form links
 Break links
 Maintain links
 By default, GAMBIT will form links between unmeshed edges that are
picked together
 By default, GAMBIT will maintain links between meshed edges that are
picked together

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Introductory GAMBIT Notes
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Grading
 Controls 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 indirectly
 Gambit 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 Ratio
 The 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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Introductory GAMBIT Notes
GAMBIT v2.0 Jan 2002
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Spacing
 Spacing
 In all meshing forms, the following spacing functions can be specified:
 Interval count - recommended for edge meshing only
 A value of 5 creates 5 intervals on the edge (6 nodes, including
ends)
 % of edge length - recommended for edge meshing only
 An edge length of 10 and a value of 20 creates 5 intervals on the edge
 Interval size - the default setting
 Identifies the interval size relative to overall dimensions of geometry
– Identifies “average” interval size if used with grading
 An edge-length of 10 and a value of 2 creates 5 intervals on the edge
 Average size of elements/grid is 2

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Introductory GAMBIT Notes
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First Edge Settings
 Use first edge settings enabled
 First edge selected in pick list updates form
 Useful to copy settings from one meshed
edge to other edges.
 Use first edge settings disabled
 Any time you pick two or more meshed edges
where there is a difference in:
 the Type
 the Spacing
the local Apply button for that option will
be turned off
 This 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 Options
 Apply without meshing
 This option is useful in cases where you
want to impose a scheme without fixing
the number of intervals
 The higher level meshing scheme will decide
(and match) the intervals
 Example
 Specify fixed interval and no grading
 Specify double sided grading and
Apply without Meshing on bottom edges
 Face meshing will automatically match mesh
 Remove Old Mesh
 Deletes old mesh
 Ignore Sizing Function
 Sizing function has precedence on meshing
unless this option is enabled.

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Face Meshing
 Face Meshing form
 Upon picking a face
 GAMBIT automatically chooses Quad elements
 GAMBIT chooses the Type based on the
Solver/face vertex types
 Available element/scheme type combinations
 Quad
 Map
 Submap
 Tri-Primitive
 Pave
 Tri
 Pave
 Gambit also has quad-to-tri conversion utility.
 Quad/Tri
 Map
 Pave
 Wedge

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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 Mesh
 Existing 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 mesh
 Leaves all lower topology mesh
 Remove mesh + lower mesh
 Removes all lower mesh that is not shared
with another entity
 Undo after meshing operation also works!

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Hard Linking
 Mesh Links (Hard Links)
 Mesh linked entities have identical mesh
 created for periodic boundary conditions
 Applicable to Edge, Face, and Volume entities
 Best to use soft links for edge meshing
 To link volume meshes, all faces must be mesh
hard linked first.
 Setting up Hard Links for Faces
 Select faces and reference vertices
 Edge „sense‟ will appear
 Reverse orientation on by default for sense
 Periodic option can be used for split edges
 Mesh one face before or after hard link is defined
 mesh on second face generated automatically
 Multiple pairs of hard links can be created.
+ + + +

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Introductory GAMBIT Notes
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Assessing Mesh Quality
 Default measure of quality is based on EquiAngle Skew.
 Definition of EquiAngle Skew:
 where:
 max = largest angle in face or cell
 min = smallest angle in face or cell
 e = angle for equiangular face or cell
 e.g., 60 for triangle, 90 for square
 Range of skewness:





 


e
mine
e
emax ,
180
max




 min
 max
0 1
best worst

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Examining the Mesh
Examine Mesh Form
 Display Type
 Plane/Sphere
 View mesh elements that fall in plane or sphere.
 Range
 View mesh elements within quality range.
 Histogram shows quality distribution.
 Select 2D/3D and Element Type
 Select Quality Type
 Display Mode
 Change cell display attributes.

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Striving for Quality
 A poor quality grid will cause inaccurate solutions and/or slow convergence.
 Minimize EquiAngle Skew:
 Hex and Quad Cells
 Skewness should not exceed 0.85.
 Tri‟s
 Skewness should not exceed 0.85.
 Tet‟s
 Skewness 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 mesh
 Perform necessary decomposition and/or pre-mesh edges and faces.
 Remesh

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Introductory GAMBIT Notes
GAMBIT v2.0 Jan 2002
Fluent User Services Center
www.fluentusers.com
Mesh Smoothing
 Gambit generally incorporates default smoothing scheme after initial
mesh on face or in volume is created.
 Default scheme can be changed in Edit - Defaults
 Different scheme can be selected and
applied after meshing.
 Face mesh smoothing
 Length-weighted Laplacian
 Centroid Area
 Winslow
 Volume mesh smoothing
 Length-weighted Laplacian
 Equipotential
 Boundary mesh by default is fixed.
 Option allows frees boundary mesh.

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Introductory GAMBIT Notes
GAMBIT v2.0 Jan 2002
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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 Solver
 Name zone if desired.
 Apply defines zone and boundary type.
 Can also modify and delete zone/boundary.
 By default,
 External faces/edges are walls
 Internal faces/edges are interior
 The Continuum Type Form
 Similar operation.
 All continuum zones are by default, fluid.

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Introductory GAMBIT Notes
GAMBIT v2.0 Jan 2002
Fluent User Services Center
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Linear/Quadratic Elements
(FIDAP/POLYFLOW USERS ONLY)
 General tools
 Higher-order elements
 For FEM codes (FIDAP and POLYFLOW), the element order can be
changed at all three meshing levels
 Only linear and quadratic elements are directly available
 A 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 FIDAP
edge 3-node 3-node
face 8-node quad 9-node quad
volume 21-node brick 27-node brick