Presentation on theme: "Mesh Control through Boundary Layers and Face Vertex Types"— Presentation transcript:
1Mesh Control through Boundary Layers and Face Vertex Types
2Face Vertex Type Basics All 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.’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, control the mesh or help facilitate generating a hex mesh.For the majority of models, vertex types don’t need to be changed.
4Modifying Face Vertex Types Face 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 windowSelect 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.’
5Formula for Map Scheme Map Scheme: 4*End + N*Side Periodic Map Scheme: N*SideProject intervals can be specified for more mesh control.ES+E
6How to Make a Face Mappable By manually changing vertex typesIn 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)DefaultESMap: 4*End + 4*SideEESMap: 4*Enddefault
7Formula for Submap Scheme Submap Scheme: 4*End + L*Side + M*(End + Corner) + N*(2*End + Reverse)additional terms when interior loops existPeriodic Submap Scheme: N*Side + M*(End + Corner) where M >2ECECSCECECS++S
8How to Make a Face Submappable By manually changing vertex typesConsider which vertex should be changed to “Side”In Set Face Vertex Type form, change vertex (default type) to “Side”By enforcing the Submap schemeIn 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 undesirableRESRESubmap: 4*End + Side + (2*End + Reverse)?RESdefault
9Tri-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 enforcedESEESdefault
10Meshing Faces with Quad and Tri Pave Schemes Quad:Pave SchemeAll vertex types of the face are ignoredThe sum of all elements on the edges of the face must be even.Mesh inner faces first if possible to prevent from ‘locking’ into odd number intervals on boundaries.No guarantee of a symmetric mesh on a symmetric geometryTri:Pave SchemeNo even number restrictionUse boundary layers for better mesh near boundariesUse sizing function and edge mesh grading for controlling cell size distribution.Edge mesh grading alone results in poor quality mesh.
11Meshing Faces with Hybrid Quad/Tri Schemes Quad/Tri: Tri-Map formula: 2*TriangleThe 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 triangleQuad/Tri: WedgeUsed for creating cylindrical/polar type meshesThe Vertex marked (T) is where rectangular elements are collapsed into trianglesTENTSTE
12How to Make a Volume Mappable Three options to map a volume:Enforce the mapManually change the vertex types on all faces so they are mappableEnforce the map on the facesExample:Emap the facesEEEESEEenforce the mapEEMapESdefaultEmanually change the vertex typesEEE
13How to Make a Volume Submappable Three options to submap a volume:Enforce the submapManually change the vertex types on all faces so they are mappable and/or submappableEnforce the submap on the facesExample: manually change the vertex typesEEEEEECCESSSEE
14How to Make a Volume Cooperable Three options to cooper a volume:Manually change the vertex types on the side faces so they are mappable and/or submappablePick the source facesEnforce the map or submap on the side facesExample: manually change the vertex typesSEESSEECESEE
15Boundary 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 problemscomplicated 3D shapes may require boundary layer attachments to edges.
16Create Boundary Layers Create Boundary Layer FormShow Option: toggles display of temp. boundary layerUseful for complicated modelsB.L. can be defined using Uniform or Aspect Ratio based algorithmDefinition Inputs (3 of 4 inputs required)First row: height of first row of elements (a)(or starting aspect ratio)Growth factor: factor for geometric series (b/a)Rows: total number of element rowsDepth: total height of boundary layer (D)(or ending aspect ratio)Internal continuity and Wedge corner shapeTransition PatternReduces number of elements in ‘flow’ direction.Not to be used with tets; watch for highly skewed cells.
17Attachment General Edges Attach to: Edges for 2d problemsFaces for 3d problemsArrows point to center of associated face or volume.Boundary layers are initially displayed in orange to indicate that it is temporary.Temporary boundary layers update immediately with change in definition.Boundary layer becomes permanent (displayed as white) upon Apply.EdgesBoundary layer mesh in region near vertices is defined by vertex type.End: mesh overlapsSide: angle bisectedCorner: angle divided into thirdsReverse: angle divided into fourths.ESCRInternal continuity allows the boundary layers to be formed with no crossover regions (end, corner, or reversal treatments). Everything becomes a side. This is especially important for the meshing with prism layers using tgrid algorithms.
18Boundary Layers and End Vertex Type BL mesh butts up against adjoining edgeBL mesh uses adjoining edge’s mesh if pre-existingIf BL is attached to adjoining edge on a face, a block of “overlap” elements is created where the two BL meshes meet
19Wedge Corner Shape ON OFF At corner or reversal vertices, wedge corner shape option is applicable.ON Wedge shapeOFF Block shapeONOFF
20Attachment to FacesA boundary layer attached to a face may ‘imprint’ the adjoining faces.The imprint is displayed graphically on adjoining faces.Imprinting will depend upon b.l. attachments of adjoining faces and state of internal continuity.If adjoining faces do not have b.l. attachments-Attaching boundary layer to face:Gambit checks angle bounded by attachment and adjoining faces.Will imprint (become visible) the adjoining faces if angle is less than default angle (135o).Will not imprint adjoining faces if angle is larger than default.b.l. is still created but may not impact mesh.If adjoining faces have b.l. attachments-Imprinting and overlap region depends upon state of internal continuity.Internal continuity allows the boundary layers to be formed with no crossover regions (end, corner, or reversal treatments). Everything becomes a side. This is especially important for the meshing with prism layers using tgrid algorithms.
21Internal Continuity Internal Continuity Internal Continuity “ON” Allows boundary layers to be formed with no crossover regions (vertices become sides)Must be ON for tet/hybrid meshingInternal Continuity “ON”Prism Growth in Boundary LayerInternal Continuity “OFF”