Meshing Control changing Vertex Types, using Boundary Layers

and Smoothing the Mesh

Face Vertex Types Vertices connected to faces are

assigned face vertex types Based on default angle criteria

between the edges connected to the vertex.

Face vertex types determine face meshing schemes, except quad-pave scheme Tri-pave scheme

Vertex Type Characteristics End (E)

0 < Default Angle < 120

zero internal grid lines

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

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

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

E E

E

SSS

CC C

R R

Modifying Face Vertex Types Face Vertex Types can be changed from

default setting: Automatically: enforcing certain meshing

scheme Manually: direct modification in the Face Vertex

Type form A vertex can have multiple

Types; one per each associated face Meshing schemes are based on "formulas"

S E

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

Periodic Map Scheme: N*Side Project intervals can be specified

for more mesh control.

E

E

E

ES+

E EEE

How to Make a Face MappableManually changing vertex types

By enforcing the Map scheme

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

Formula for Submap Scheme Submap 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 >2

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+ +

Example: Using Vertex Types to make a Face Submappable

A face can be made submappable By manually changing

vertex types Consider which vertex

should be changed to "Side"

By enforcing the Submap scheme

Less control

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

?

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

E

E

E

E

E

E

E

S

E

S

E

E

default

Tri-Primitive Scheme: 3*End + N*Side The face vertex types need to be manually

changed to Triangle (T) T T

Meshing Faces with Hybrid Quad/Tri Schemes

Quad/Tri: Pave All vertex types are

ignored except Trielement (T) and Notrielement (N)

Trielement (T) will enforce a triangle

Notrielement (N) will avoid a triangle

E

N

T

ST

E

E

Quad/Tri: Wedge The Vertex marked

(T) is where rectangular elements are collapsed into triangles

Boundary Layers Boundary 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

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

Specifying a Boundary Layer Create Boundary

Layer Form Algorithms Definition Inputs Settings Transition Pattern Attachment

Boundary Layer Algorithms

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

Uniform Boundary Layer Aspect Ratio based Boundary Layer

Aspect ratio/layer is constant for each layer of cells

Size is constant for each layer of cells

Boundary Layer Definition Inputs

3 out of 4 inputs are required, the fourth is calculated

Uniform Aspect Ratio Based

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)

Internal Continuity The Internal Continuity toggle allows

boundary layers to be formed with no crossover or overlap regions.

Internal Continuity "ON"Internal Continuity OFF

Boundary Layer Attachments Boundary layers attach to edges for 2D boundary

layers and faces for 3D boundary layers.

Temporary boundary layer is displayed in orange and updates immediately with any changes.

Permanent boundary becomes white

An arrow indicates direction This can be misleading in some cases, e.g. in 3D case when

the volume forms an annulus.

Boundary Layers and Vertex Types

2-D Boundary layers in regions near vertices are defined by the vertex type.

E

E

ES

CE

E

E

R

E

End: mesh overlaps

Corner: angle divided into thirds

Reverse: angle divided into fourths.

Side: angle bisected

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.

Imprinting Adjacent Faces with 3-D Boundary Layers

Vertex types are important for imprinting3-D boundary layers on adjacent faces.

End type vertex creates an imprint

If 3-D boundary layers are attached to the adjoining faces Internal Continuity toggle will determine the crossover

region and imprint.

Imprinting 3-D Boundary Layers by Modifying Vertex Types

Angle > 1200, an End vertex type can cause an imprint.

140No imprinting of 3-D Boundary Layerand gaps due to Side Type vertices at the

intersection of the facesAttachment Face

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

SS

EE

S

E

Normal and Offset Smoothing

Normal smoothing Ensure a gradual change in

growth direction of B.L. wrapped around corners

Offset smoothing Reduce or eliminate spikes and

dips in the boundary layer

Iteratively and governed by GAMBIT defaults SMOOTH_CONTINUOUS_SIDES

Without normal smoothing

With normal smoothing

Boundary Layer Defaults Help control mesh on

complex 2-D and 3-D geometry. Edit->Defaults->

Mesh/BLAYER and BLAYERTGRID resp.

The GAMBIT Command Reference Guide provides more information

Some Important Boundary Layer Defaults

USE_FACET_EVALS 1 = Use of faceted representation of the

surface (default) 0 = Use of exact representation of the

surface (1e-6 tolerance) Faceted is much faster, but less accurate

ANGLE_SMOOTH_FACTOR 0 = Nodes are projected perpendicular

(default) 1 = Generates equidistant outer nodes Intermediate values between 0 and 1 are

allowable.

USE_FACET_EVALS=1

ANGLE_SMOOTH_FACTOR=0

USE_FACET_EVALS=0

ANGLE_SMOOTH_FACTOR=0

ANGLE_SMOOTH_FACTOR=1

Some Important Boundary Layer Defaults

ADJUST_EDGE_BL_HEIGHT (2-D B.L. only) 0 = boundary layer height will

be less than the perpendicular height (default)

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

ADJUST_EDGE_BL_HEIGHT=0

ADJUST_EDGE_BL_HEIGHT=1

Mesh Smoothing

Smooth meshes to obtain incremental improvement in quality. The mesh at the boundary is not altered

Smoothing schemes Face mesh smoothing

Length-weighted Laplacian Centroid Area Winslow(for quad meshes only)

Volume mesh smoothing Length-weighted Laplacian Equipotential

Mesh nodes adjustments

Bigger changes on surface mesh

Move indivually nodes seperataly

Meshing Control changing Vertex Types, using Boundary Layers and Smoothing the MeshFace Vertex TypesVertex Type CharacteristicsModifying Face Vertex TypesFormula for Map SchemeHow to Make a Face MappableFormula for Submap SchemeExample: Using Vertex Types to make a Face SubmappableTri-Primitive SchemeMeshing Faces with Hybrid Quad/Tri SchemesBoundary LayersSpecifying a Boundary LayerBoundary Layer AlgorithmsBoundary Layer Definition InputsWedge Corner ShapeInternal ContinuityBoundary Layer AttachmentsBoundary Layers and Vertex TypesImprinting Adjacent Faces with 3-D Boundary LayersImprinting 3-D Boundary Layers by Modifying Vertex TypesNormal and Offset SmoothingBoundary Layer DefaultsSome Important Boundary Layer DefaultsSome Important Boundary Layer DefaultsMesh SmoothingMesh nodes adjustments