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3.3 Face Meshing Commands

The following commands are available on the Mesh/Face subpad.

Symbol Command Description
Mesh Faces Creates mesh nodes on faces
Move Face Nodes
Split Quad Meshes
Adjusts mesh node positions on a face; splits quadrilateral face mesh elements into triangular elements
Smooth Face Meshes Adjusts face mesh node positions to improve uniformity of node spacing
Set Face Vertex Type Specifies the characteristics of a face mesh in the vicinity of a corner
Set Face Element Type Specifies face element types used throughout the model
Link Face Meshes
Unlink Face Meshes
Creates or removes mesh hard links between faces
Modify Meshed Face
Split Meshed Face
Converts mesh edges to topological equivalents; splits faces along boundaries defined by mesh node locations
Summarize Face Mesh
Check Face Meshes
Displays mesh information in the graphics window; summarizes face mesh quality information
Delete Face Meshes Deletes existing mesh nodes and/or elements from faces


3.3.1 Mesh Faces

The Mesh Faces operation (face mesh and face modify commands) creates the mesh for one or more faces in the model. When you mesh a face, GAMBIT creates mesh nodes on the face according to the currently specified meshing parameters.

The Mesh Faces operation requires the following input parameters:

Specifying the Faces

GAMBIT allows you to specify any face for a meshing operation; however, the shape and topological characteristics of the face, as well as the vertex types associated with the face, determine the type(s) of mesh scheme(s) that can be applied to the face.

Specifying the Meshing Scheme

To specify the face meshing scheme, you must specify two parameters:

The Elements parameter defines the shape(s) of the elements that are used to mesh the face. The Type parameter defines the pattern of mesh elements on the face. The Smoother specification determines the type of smoothing algorithm (if any) used to smooth a mapped mesh during the meshing operation.

The following sections describe the parameters listed above and their effects on the overall face mesh.

Specifying Scheme Elements

GAMBIT allows you to specify any of the following face meshing Elements options.

Option Description
Quad Specifies that the mesh includes only quadrilateral mesh elements
Tri Specifies that the mesh includes only triangular mesh elements
Quad/Tri Specifies that the mesh is composed primarily of quadrilateral mesh elements but includes triangular corner elements at user-specified locations (see "Set Face Vertex Type," below)

Each of the Elements options listed above is associated with a specific set of Type options (see below).

Specifying Scheme Type

GAMBIT provides the following face meshing Type options.

Option Description
Map Creates a regular, structured grid of mesh elements
Submap Divides an unmappable face into mappable regions and creates structured grids of mesh elements in each region
Pave Creates an unstructured grid of mesh elements
Tri Primitive Divides a three-sided face into three quadrilateral regions and creates a mapped mesh in each region
Map Split Creates a mapped mesh of quadrilateral elements and splits the elements to create triangular elements
Submap Split Creates a submapped mesh of quadrilateral elements and splits the elements to create triangular elements
Wedge Primitive Creates triangular elements at the tip of a wedge-shaped face and creates a radial mesh outward from the tip

As noted above, each of the Elements options is associated with a specific set of one or more of the Type options listed above. The following table shows the correspondence between each of the face meshing Elements and Type options. (NOTE: Shaded cells marked with an "X" represent allowable combinations of options.)

  Elements
Type Quad Tri Quad/Tri
Map X   X
Submap X    
Pave X X X
Tri Primitive X    
Map Split   X  
Submap Split   X  
Wedge Primitive     X

Each of the allowable combinations shown in the table above results in a specific pattern of mesh nodes for any given face. In addition, each is associated with a set of restrictions that govern when it can or cannot be applied. The following sections describe the patterns and restrictions associated with each of the allowable combinations of Elements and Type options listed above.

NOTE: When you specify a face on the Mesh Faces form, GAMBIT automatically evaluates the face with respect to its shape, topological characteristics, and vertex types and sets the Scheme option buttons to reflect a recommended face meshing scheme. If you specify more than one face for a meshing operation, the scheme represented by the Scheme option buttons reflects the recommended scheme for the most recently specified face. You can enforce a meshing scheme, and thereby override any recommended scheme, by means of the Scheme option buttons on the Mesh Faces form. When you enforce a meshing scheme, GAMBIT applies the specified scheme to all currently picked faces.

Quad:Map Meshing Scheme

When you apply the Quad:Map meshing scheme to a face, GAMBIT meshes the face using a regular grid of quadrilateral face mesh elements, such as those shown in Figure 3-32.

Figure 3-32: Quad:Map face meshing scheme—example mesh

The Quad:Map meshing scheme is applicable primarily to faces that are bounded by four or more edges, however not all such faces are suitable for mapping. To be "mappable," a face must not violate restrictions related to the following parameters:

The vertex-type and edge mesh interval restrictions for the Quad:Map meshing scheme are as follows.

Vertex Types

To be mappable, a face must represent a logical rectangle. (For the exception to this criterion, see NOTE (1), below.) To represent a logical rectangle, a face must include four End type vertices, and all other vertices associated with the face must be designated as Side type vertices.

Figure 3-33 shows four planar faces, two of which are mappable and two of which are not mappable. The faces shown in Figure 3-33(a) and (c) are mappable, because each includes four End type vertices and all other vertices associated with the face are Side type vertices. The face shown in Figure 3-33(b) is not mappable, because it includes only three End type vertices. The face shown in Figure 3-33(d) is not mappable, because one of its vertices is designated as a Reversal type vertex.

Figure 3-33: Quad:Map face meshing scheme—face suitability

NOTE (1): If a face is bounded by two closed-loop edges, GAMBIT can employ the Quad:Map meshing scheme even if the vertex type designations do not define a logical rectangle. For example, GAMBIT automatically applies the Quad:Map meshing scheme to a cylindrical face, even though the circular edges that bound the face possess only one vertex each and both vertices are, by default, designated as Side type vertices. Likewise, GAMBIT can use a Quad:Map scheme to mesh an annular face.
NOTE (2): If you enforce a Quad:Map meshing scheme on a face, GAMBIT evaluates the face with respect to its vertex type designations. If the vertex types do not meet the criteria outlined above, GAMBIT attempts to change the vertex types so that the face is rendered mappable.

If the specified face includes more than four vertices, there are multiple configurations of vertex types that satisfy the vertex-type criteria. For example, if the face includes five vertices, there are five possible vertex-type configurations that allow the creation of a Quad:Map mesh, because any of the five vertices can be designated as the Side vertex. When GAMBIT automatically changes vertex types, it attempts to employ the configuration that minimizes distortion in the mesh.

Each vertex-type configuration results in a unique node pattern for the mapped mesh. To enforce a specific node pattern on a mapped mesh, manually specify the vertex types such that they meet the Quad:Map scheme vertex-type criteria outlined above. (See "Set Face Vertex Type," below.)

Edge Mesh Intervals

If you grade or mesh the edges of a face prior to creating a mapped mesh, you must specify the edge mesh intervals such that the numbers of mesh intervals on opposing sides of the logical rectangle are equal. For meshing purposes, a single side of the logical rectangle consists of all edges that exist between any two End type vertices.

NOTE: If you do not grade or mesh the edges of a face prior to creating the mapped mesh, GAMBIT automatically assigns edge mesh intervals such that they satisfy the criteria described above.

As an example of the edge mesh interval restriction, consider the face shown in Figure 3-34. The face includes four End type vertices and one Side type vertex.

Figure 3-34: Mappable planar face consisting of five edges

The four sides of the logical rectangle that bounds the face can be defined as follows.

Side Edge
1 edge.2
2 edge.3
3 edge.4
4 edge.1 and edge.5

For the face to be mappable, the number of mesh intervals on edge.2 (Side 1) must be equal to that on edge.4 (Side 3). Likewise, the combined number of intervals on edge.1 and edge.5 (Side 4) must be equal to the number of intervals on edge.3 (Side 2).

NOTE (1): If you grade or mesh one or more edges of a face and apply a Quad:Map meshing scheme to the face, GAMBIT automatically meshes the remaining edges such that the numbers of intervals on opposing sides of the face satisfy the criteria outlined above. For example, if you grade or mesh edge.3 in Figure 3-34 such that it contains 10 intervals, GAMBIT meshes edge.1 and edge.5 such that they include a combined total of 10 intervals.
NOTE (2): GAMBIT does not include the edge mesh interval restriction when evaluating a face with respect to a recommended meshing scheme. As a result, GAMBIT may recommend a Quad:Map meshing scheme for a face that is mappable with respect to its vertex-type configuration but which cannot be mapped, because it violates the edge mesh interval restriction.
NOTE (3): If you create a mesh link between two edges that constitute opposing sides of a logical rectangle, the edges automatically satisfy the edge mesh interval restriction described above.
NOTE (4): If you mesh a face using the Quad:Map meshing scheme, you can smooth the mesh during its creation by means of the Smoother options (see "Specifying Scheme Smoother Algorithm," below).
NOTE (5): When you apply the Quad:Map scheme to a face bounded by two closed loops (for example, a cylindrical or annular face), GAMBIT allows you to specify the number of mesh intervals between the loops (see "Specifying Projection Intervals," below).

Quad:Submap Meshing Scheme

When you apply the Quad:Submap meshing scheme to a face, GAMBIT divides the face into one or more mappable regions and creates a mapped mesh in each region. Like the Quad:Map meshing scheme, the Quad:Submap meshing scheme is subject to restrictions related to vertex types and edge mesh intervals. The vertex-type and edge mesh interval restrictions for the Quad:Submap meshing scheme are as follows.

Vertex Types

To constitute a submappable face, a face must possess only End, Side, Corner, and Reversal vertices. In addition, the total number of End vertices, , must satisfy the following equation:

where and are the total numbers of Corner and Reversal type vertices, respectively, on the face. That is, for every Corner type vertex, the face must possess an additional End vertex, and for every Reversal vertex, the face must possess two additional End vertices.

The shape of the mesh generated by means of the Quad:Submap face meshing scheme depends on the type and arrangement of vertex types on the face. As an example of the effect of vertex types, consider the faces shown in Figure 3-35 and Figure 3-36, each of which consists of an identical planar L-shaped face, one corner of which is truncated at an angle.

Figure 3-35: Quad:Submap face meshing scheme-inside Corner vertex

Figure 3-36: Quad:Submap face meshing scheme-inside Reversal vertex

In Figure 3-35, the inside corner vertex (C) is designated as a Corner vertex, therefore, in order to be submappable, the face must possess five End type vertices (A, B, D, E, and F). The Quad:Submap meshing scheme divides the face into the following two mapped regions:

In Figure 3-36, the inside corner vertex (C) is designated as a Reversal vertex, therefore, in order to be submappable, the face must possess six End type vertices (A, B, D, E, F, and G). In this case, the Quad:Submap meshing scheme divides the face into the following two mapped regions:
NOTE: If you enforce a Quad:Submap meshing scheme on a face, GAMBIT evaluates the face with respect to its vertex type designations. If the vertex types do not meet the criteria outlined above, GAMBIT attempts to change the vertex types so that the face is submappable.

For most submappable faces, there are multiple configurations of vertex types that satisfy the vertex-type criteria. Each vertex-type configuration results in a unique node pattern for the submapped mesh. When GAMBIT automatically changes vertex types, it attempts to employ the configuration that minimizes distortion in the mesh. To enforce a specific node pattern on a submapped mesh, manually specify the vertex types such that they meet the Quad:Submap scheme vertex-type criteria outlined above. (See "Set Face Vertex Type," below.)

Edge Mesh Intervals

If you grade or mesh the edges of a face before applying the Quad:Submap scheme, the edge mesh grading schemes must be specified such that the total numbers of intervals on opposite sides of any given submapped region are equal. For example, in Figure 3-35, the number of intervals (I) on each side of the submapped regions can be expressed as follows:

and

.

Similarly, in Figure 3-36, the number of intervals (I) on each side of the submapped regions are:

and

.

NOTE (1): If you grade or mesh one or more edges of a face before applying a Quad:Submap meshing scheme to the face, GAMBIT automatically meshes the remaining edges such that the numbers of intervals on opposing sides of the face satisfy the criteria outlined above.
NOTE (2): GAMBIT does not include the edge mesh interval restriction when evaluating a face with respect to a recommended meshing scheme. As a result, GAMBIT may recommend a Quad:Submap meshing scheme for a face that is submappable with respect to its vertex-type configuration but which cannot be submapped, because it violates the edge mesh interval restriction outlined above.
NOTE (3): When you apply the Quad:Submap scheme to a face bounded by two closed loops (for example, a cylindrical or annular face), GAMBIT allows you to specify the number of mesh intervals between the loops (see "Specifying Projection Intervals," below).

Quad:Pave Meshing Scheme

When you apply the Quad:Pave meshing scheme, GAMBIT creates an unstructured face mesh consisting of quadrilateral mesh elements (see Figure 3-37).

Figure 3-37: Quad:Pave face meshing scheme—example mesh

NOTE: The Quad:Pave meshing algorithm can sometimes fail when pre-graded (or meshed) boundary edges possess interval lengths that vary widely along the edges. In such cases, it is often possible to help the meshing algorithm to succeed by applying a mesh-based size function to the face. (For a description of mesh-based size functions, see "Meshed Size Functions" in Section 5.2.2 in this guide.)

You can force GAMBIT to automatically apply mesh-based size functions where appropriate to successfully create a Quad:Pave mesh. The specification is made by means of two default variables:

  • MESH.PAVER.CREATE_OWN_SF
  • MESH.PAVER.SIZE_VARIATION_LIMIT
The CREATE_OWN_SF default variable can take on the following values:
  • -1—GAMBIT evaluates each edge and automatically applies a size function to any face the edges of which possess a wide variation in interval lengths.
  • 0—GAMBIT does not automatically apply any size functions.
  • 1—GAMBIT automatically applies a size function to every face to be meshed.
The SIZE_VARIATION_LIMIT default variable specifies the interval-length difference that triggers the automatic application of the size functions. Its value represents the ratio of the maximum interval length to the minimum interval length for any pre-graded/meshed edges associated with the face(s) to be meshed using the Quad:Pave algorithm.

You can apply the Quad:Pave meshing scheme to any face that consists of a closed loop of edges. The vertex-type and edge mesh interval restrictions for the Quad:Pave meshing scheme are as follows.

Vertex Types

There are no restrictions on vertex types associated with a Quad:Pave mesh.

Edge Mesh Intervals

If you grade or mesh all of the boundary edges of a face before applying the Quad:Pave meshing scheme, you must specify the grading such that the total number of mesh intervals on all edges is an even number. If you grade some, but not all, of the face boundary edges, GAMBIT automatically meshes the remaining edges such that the total number of edge mesh intervals is even.

Quad:Tri Primitive Meshing Scheme

The Quad:Tri Primitive meshing scheme allows you to create a submapped mesh on a three-sided face. (NOTE: Any side of the three-sided face may consist of more than one edge.) When you apply the Quad:Tri Primitive meshing scheme to a three-sided face, GAMBIT locates a point internal to the face that serves as a common endpoint for three mappable subregions.

Figure 3-38 shows a triangular, planar face meshed according to the Quad:Tri Primitive meshing scheme. Note that the face is divided into three mappable regions, each of which shares a common endpoint (D). The regions are defined by the quadrilaterals AFDE, FBGD, and EDGC.

Figure 3-38: Quad:Tri Primitive face meshing scheme—example mesh

The vertex-type and edge mesh interval restrictions for the Quad:Tri Primitive meshing scheme are as follows.

Vertex Types

The Quad:Tri Primitive meshing scheme requires that the vertices at the corners of the three sides of the face are specified as End vertices (see Figure 3-38, above) and that all other vertices are specified as Side vertices.

Edge Mesh Intervals

If you grade or mesh the sides of the face before applying the Quad:Tri Primitive meshing scheme, you must specify the grading such that the total number of intervals on the three sides of the face is an even number. In addition, the grading must satisfy the following criterion:

where and are the numbers of intervals on any two sides, and is the number of intervals on the remaining side.

Tri:Pave Meshing Scheme

When you apply the Tri:Pave meshing scheme, GAMBIT creates a face mesh consisting of irregular triangular mesh elements, such as that shown in Figure 3-39.

Figure 3-39: Tri:Pave face meshing scheme—example mesh

The vertex-type and edge mesh interval restrictions for the Tri:Pave meshing scheme are as follows.

Vertex Types

There are no restrictions on vertex types associated with the Tri:Pave meshing scheme.

Edge Mesh Intervals

There are no restrictions on the edge mesh intervals for the Tri:Pave meshing scheme.

Tri:Map Split Meshing Scheme

When you apply the Tri:Map Split meshing scheme, GAMBIT creates a Quad:Map mesh and splits the resulting quad elements diagonally to create a triangular mesh. For example, if you mesh a simple square face using the Tri:Map Split meshing scheme, GAMBIT creates a mesh such as that shown in Figure 3-40.

Figure 3-40: Tri:Map Split face meshing scheme

Any face to be meshed using the Tri:Map Split scheme must meet the mappabil­ity requirements that apply to the Quad:Map meshing scheme (see "Quad:Map Meshing Scheme," above). If the specified face does not meet the Quad:Map requirements, GAMBIT attempts to use a Tri:Submap Split scheme to mesh the face (see "Tri:Submap Split Meshing Scheme," below).

Excluding Boundary Layers

When you select the Tri:Map Split meshing scheme, GAMBIT activates the Exclude boundary layer faces option, which allows you to specify whether GAMBIT splits boundary layer elements when splitting the mesh. Figure 3-41 shows the effect of the Exclude boundary layer faces option on a simple square face with a fixed boundary layer attached to one side.

Figure 3-41: Tri:Map Split—effect of Exclude boundary layer faces option

Vertex Types

Vertex type restrictions for the Tri:Map Split meshing scheme are identical to those for the Quad:Map mesh scheme (see "Quad:Map Meshing Scheme," above). If the vertex types do not exactly meet the Quad:Map vertex type criteria, GAMBIT attempts to change vertex types where necessary to create the mapped mesh and execute the Tri:Map Split operation.

Edge Mesh Intervals

Edge mesh interval restrictions for the Tri:Map Split meshing scheme are identical to those for the Quad:Map mesh scheme (see "Quad:Map Meshing Scheme," above).

Tri:Submap Split Meshing Scheme

When you apply the Tri:Submap Split meshing scheme, GAMBIT creates a Quad:Submap mesh and splits the resulting quad elements diagonally to create a triangular mesh. For example, Figure 3-42 shows the results of the Tri:Submap Split scheme for a simple L-shaped face.

Figure 3-42: Tri:Submap Split face meshing scheme

Any face to be meshed using the Tri:Submap Split scheme must meet the mappabil­ity requirements that apply to the Quad:Submap meshing scheme (see "Quad:Submap Meshing Scheme," above).

Excluding Boundary Layers

When you select the Tri:Submap Split meshing scheme, GAMBIT activates the Exclude boundary layer faces option, which allows you to specify whether GAMBIT splits boundary layer elements when splitting the mesh. Figure 3-43 shows the effect of the Exclude boundary layer faces option on the face shown in Figure 3-42, above, with a fixed boundary layer attached to one side.

Figure 3-43: Tri:Submap Split—effect of Exclude boundary layer faces option

Vertex Types

Vertex type restrictions for the Tri:Submap Split meshing scheme are identical to those for the Quad:Submap mesh scheme (see "Quad:Submap Meshing Scheme," above). If the vertex types do not exactly meet the Quad:Submap vertex type criteria, GAMBIT attempts to change vertex types where necessary to create the submapped mesh and execute the Tri:Submap Split operation.

Edge Mesh Intervals

Edge mesh interval restrictions for the Tri:Submap Split meshing scheme are identical to those for the Quad:Submap mesh scheme ("Quad:Submap Meshing Scheme," above).

Quad/Tri:Map Meshing Scheme

The Quad/Tri:Map meshing scheme is applicable only to geometry that constitutes a narrow, logical sliver consisting of two sides-such as that shown in Figure 3-44. Either side may consist of more than one edge.

Figure 3-44: Quad/Tri:Map face meshing scheme—example mesh

When you apply the Quad/Tri:Map meshing scheme, GAMBIT creates triangular mesh elements at the two endpoints of the sides and creates quadrilateral elements across the rest of the face. The vertex-type and edge mesh interval restrictions for the Quad/Tri:Map meshing scheme are as follows.

Vertex Types

To employ the Quad/Tri:Map meshing scheme to a sliver-shaped face, you must specify the vertices as follows:

Edge Mesh Intervals

If you grade or mesh the edges that comprise the sides of a sliver-shaped face before applying the Quad/Tri:Map meshing scheme, you must specify the edge grading such that the sides possess identical numbers of intervals.

Quad/Tri:Pave Meshing Scheme

When you apply the Quad/Tri:Pave meshing scheme to a face, GAMBIT creates a paved mesh that consists primarily of quadrilateral elements but employs triangular mesh elements in any corners the edges of which form a very small angle with respect to each other. You can also impose the creation of triangular mesh elements in corners of the face by setting the associated vertices as Trielement vertices. Figure 3-45 shows a Quad/Tri:Pave mesh in which vertices A, D, and E are set as Trielement vertices.

Figure 3-45: Quad/Tri:Pave face meshing scheme—example mesh

The vertex-type and edge mesh interval restrictions for the Quad/Tri:Pave meshing scheme are as follows.

Vertex Types

There are no restrictions on vertex types associated with the Quad/Tri:Pave meshing scheme, however, you can enforce the creation of either triangular or quadrilateral corner elements by means of the Trielement or Notrielement vertex types, respectively, as follows:

Edge Mesh Intervals

If you grade or mesh all of the edges that comprise the boundary of a face before applying the Quad/Tri:Pave meshing scheme, you must specify the grading such that

is an even number, where is the total number of mesh intervals on all edges, and is the total number of triangle mesh elements. If you grade some, but not all, of the edges, GAMBIT automatically meshes the ungraded edges such that N is an even number.

Quad/Tri:Wedge Primitive Meshing Scheme

The Quad/Tri:Wedge Primitive meshing scheme allows you to create a radial mesh on a three-sided face. (NOTE: Any side of the three-sided face may consist of more than one edge.) When you apply the Quad/Tri:Wedge Primitive meshing scheme, GAMBIT creates a mapped mesh that includes a group of triangular mesh elements emanating from common endpoint (see Figure 3-46).

Figure 3-46: Quad/Tri:Wedge Primitive face meshing scheme—example mesh

The vertex-type and edge mesh interval restrictions for the Quad/Tri:Wedge Primitive meshing scheme are as follows.

Vertex Types

The Quad/Tri:Wedge Primitive meshing scheme requires that the vertices at the corners of the three sides of the face are specified as End vertices (see Figure 3-47) and that all other vertices are specified as Side vertices.

Figure 3-47: Quad/Tri:Wedge Primitive face meshing scheme—vertex-types

Face meshes created by means of the Quad/Tri:Wedge Primitive mesh scheme consist of regular quadrilateral mesh elements and a group of triangular mesh elements that share a common endpoint. The group of triangular elements exists at the Trielement type vertex. To create the mesh, GAMBIT constructs a series of mesh grid lines that emanate from the Trielement type vertex to the opposite side of the logical triangle-that is, to the edges that exist between the two End type vertices (see Figure 3-47, above).

Edge Mesh Intervals

If you grade or mesh the face boundary edges before applying the Quad/Tri:Wedge Primitive meshing scheme, you must specify the grading such that the total numbers of intervals on opposite sides of the logical triangle are equal. For meshing purposes, the opposite sides of the logical triangle are defined as all edges that exist between the Trielement type vertex and each End type vertex. For example, in Figure 3-47, the combined numbers of edge mesh intervals on the edges AB and BC must equal the total number of intervals on edge AE.

Specifying Scheme Smoother Algorithm

If you mesh a face with Quad element types using a Map meshing scheme, GAMBIT allows you to automatically smooth the mesh during meshing by means of Smoother options on the Mesh Faces form. (NOTE: You can also smooth any existing face mesh by means of the Smooth Face Meshes command (see Section 3.3.3, below).)

GAMBIT provides the following Smoother options for faces.

Option Algorithm
None No smoother applied during meshing
Thom-Mid Thomas-Middlecoff

The Thom-Mid option is useful when mesh nodes on the face boundary edges are bunched together in certain sections of the edges. Such bunching can affect the smoothness of the interior face mesh. The algorithm tends to smooth the face mesh only (or primarily) in those regions affected by the bunched edge nodes.

NOTE: The Thom-Mid option applies only to planar faces. If you specify the Thom-Mid option when meshing a non-planar face, GAMBIT meshes the face without smoothing and displays a warning message in the Transcript window.

Specifying Node Spacing

When you specify mesh node spacing on the Mesh Faces form, GAMBIT applies the specification to all edges associated with any specified faces that are not currently graded or meshed. GAMBIT provides three different ways to specify the number of intervals on the edges of a face.

For a description of the three edge mesh interval spacing options listed above, see "Specifying Node Spacing" in Section 3.2.1.

Specifying Projection Intervals

When you apply a Quad:Map or Quad:Submap scheme to a face that is bounded by two closed-loop edges, such as a cylindrical or annular face, GAMBIT allows you to specify the number of "projection" intervals between the bounding edges. The number of intervals is specified by means of the Proj Intervals text field on the Mesh Faces form.

As an example of the effect of the Proj Intervals value, consider the two faces shown in Figure 3-48. The cylindrical face (Figure 3-48(a)) has a height of 10 and a constant radius of 4. The annular face (Figure 3-48(b)) has inner and outer radii of 2 and 6, respectively.

Figure 3-48: Faces bounded by closed-loop edges

Figure 3-49 shows the effect of the Proj Intervals value on Quad:Map meshes for the two faces shown in Figure 3-48 when the Interval size is specified as 1. The meshes shown in Figure 3-49(a) and (b) represent Proj Intervals values of 10 and 20, respectively. The meshes shown in Figure 3-49(c) and (d) represent Proj Intervals values of 5 and 10, respectively.

Figure 3-49: Effect of Proj Intervals value

Specifying Face Meshing Options

GAMBIT includes the following primary options on the Mesh Faces form:

Mesh Option

If you select the Mesh option, GAMBIT meshes the picked face(s) according to the parameters as currently specified on the Mesh Faces form. If you Apply the meshing specifications without selecting the Mesh option, GAMBIT applies the currently specified mesh parameters to the face(s) but does not create the mesh.

Remove old mesh Option

If you select the Remove old mesh option, GAMBIT removes any currently existing mesh from the specified face(s) before creating the new face mesh(es). GAMBIT also enables the Remove lower mesh option (see below), which specifies whether or not to remove the mesh on pre-meshed boundary edges. If you do not select the Remove lower mesh option, GAMBIT retains any existing pre-assigned edge mesh(es) when meshing the face.

Remove lower mesh Option

As noted above, when you select the Remove old mesh option, GAMBIT enables the Remove lower mesh option, which allows you to specify whether or not to remove the mesh on pre-meshed boundary edges—that is, edges for which mesh intervals and grading specifications are assigned (using the Mesh Edges command) prior to meshing the face.

Ignore size functions Option

If you select the Ignore size functions option, GAMBIT ignores any existing size function specifications that would otherwise affect the face mesh.

Using the Mesh Faces Form

To open the Mesh Faces form (see below), click the Mesh command button on the Mesh/Face subpad.

The Mesh Faces form contains the following specifications.
Faces specifies the faces to be meshed.
Scheme:
Apply specifies that the meshing scheme indicated on the option button is applied to all currently picked faces.
Default resets the meshing scheme option button to its default algorithm value (Undetermined).
Elements:
Quad
Tri
Quad/Tri
specifies the mesh element shape. (NOTE: Each Elements option is associated with its own set of allowable Type options (see "Specifying Scheme Elements," above).)
Type:
Map
Submap
Pave
Tri Primitive
Map Split
Submap Split
Wedge Primitive
specifies the type of meshing scheme used to mesh the specified face(s).
Smoother:
None
Thom-Mid
specifies whether or not to smooth the face mesh while meshing. (NOTE: This option is available only when using Quad element types and the Map meshing scheme.)
Spacing:
Apply specifies that the current mesh node spacing parameters are applied to all currently picked faces.
Default resets the mesh node spacing parameters to their default values.
Value specifies the numerical component of the mesh node spacing parameters.
Interval size
Interval count
Shortest edge (%)
specifies the measurement unit component of the mesh node spacing parameters.
Proj Intervals specifies the number of projection intervals for any mapped or submapped face bounded by two closed-loop edges (see "Specifying Projection Intervals").
Options
Mesh specifies that a new mesh is created in the specified face(s).
Remove old mesh removes any existing mesh on the specified face(s).
Remove lower mesh removes pre-assigned edge-mesh interval information for the specified face(s). (NOTE: GAMBIT retains any pre-assigned grading specifications.)
Ignore size functions specifies that GAMBIT ignores any existing size-function specifications that would otherwise affect the face mesh.


3.3.2 Move Face Nodes/Split Quad Meshes

The Move Face Nodes/Split Quad Meshes command button allows you to perform the following operations.

Symbol Command Description
Move Face Nodes Adjusts face-element corner nodes within the interior of a meshed face
Split Quad Meshes Splits quadrilateral face mesh elements into triangular elements

The following sections describe the procedures and specifications required to execute the operations listed above.


Move Face Nodes

The Move Face Nodes operation (face move meshnodes command) repositions mesh nodes that exist in the interior of a meshed face. You can move the mesh nodes either by means of the Move Face Nodes form or by means of the mouse.

To move a face node, you must specify the following parameters and options:

The following paragraphs describe the specifications listed above as well as the procedure required to move face mesh nodes by means of the mouse.

Specifying the Face

When you specify a face for which mesh nodes are to be moved, GAMBIT highlights the face the graphics window and displays the corresponding mesh as a series of grid lines. Face nodes are located at the intersections of the grid lines.

Specifying the Node Number

To specify a node to be moved, you must input the corresponding node number on the Move Face Nodes form. To open a complete list of available node numbers associated with the specified face:

  1. Click the Node pick list button.
  2. Click All on the Node pick list form.
When you click the All command button, GAMBIT fills the Node pick list with the numbers of all nodes associated with the specified face and displays the nodes on the mesh grid in the graphics window. (NOTE: The Node list includes only face-element corner nodes that are interior to the face.) When you select a node number from the Node pick list, GAMBIT highlights the node in the graphics window.

To move a series of nodes, select and specify the coordinates of each node in turn. When you have selected and moved all nodes, click Apply on the Move Face Nodes form.

Specifying Node Coordinates

To specify the new coordinates of a face mesh node, you must specify the reference coordinate system and the coordinate parameters corresponding to the new node location. You can input the coordinate parameters with respect to either the Global or Local coordinate system. If you specify a node location that does not lie on the specified face, GAMBIT automatically adjusts the coordinate parameters so that the new node location lies on the face.

Using the Mouse to Move Face Nodes

To use the mouse to move face nodes:

  1. Pick the face upon which the nodes are to be moved.
  2. Shift-right-click in the graphics window to accept the selection.
  3. Pick (Shift-left-click) the node to be moved and drag it to its new location.
To move a series of mesh nodes, pick and drag each node in turn. When you have finished moving all nodes, Shift-right-click the mouse in the graphics window to accept and apply the new node positions.

Specifying the Smooth Option

If you specify the Smooth option when moving a node, GAMBIT smoothes the entire mesh by adjusting the positions of mesh nodes other than the moved node. If you specify the Smooth option for a face that includes a boundary layer, the effect of the smoothing operation depends on whether the node to be moved exists inside or outside the boundary layer, as follows:

As an example of the effect of the Smooth option, consider the square, meshed face shown in Figure 3-50, which includes a six-row boundary layer on its bottom edge.

Figure 3-50: Square meshed face with boundary layer

Figure 3-51 and Figure 3-52 show the effects of the Smooth option when moving a single node located either outside (node A) or inside (node B) the boundary layer.

Figure 3-51: Effect of Smooth option on node move outside boundary layer

Figure 3-52: Effect of Smooth option on node move inside boundary layer

Using the Move Face Nodes Form

To open the Move Face Nodes form (see below), click the Move Face Nodes command button on the Mesh/Face subpad.

The Move Face Nodes form contains the following specifications.

Face specifies the meshed face upon which nodes are to be moved.
Node specifies the node to be moved.
Smooth specifies that the face mesh is to be smoothed.
Coordinate Sys. specifies the reference coordinate system.
Type
Cartesian
Cylindrical
Spherical
specifies the reference coordinate system type.
Global | Local allows you to define the location of the node with respect to either the Global or Local coordinate system.


Split Quad Meshes

The Split Quad Meshes operation (face quadsplit command) splits quadrilateral face mesh elements into triangular elements. To accomplish the split operation, GAMBIT creates mesh edges between existing nodes of the quadrilateral mesh but does not alter the original positions of the mesh nodes in the process.

As an example of the Split Quad Meshes operation, consider the quad-meshed face shown in Figure 3-53(a). In this example, the face is bounded by an edge loop consisting of five edges and has been meshed by means of a Quad:Pave scheme.

Figure 3-53: Split Quad Meshes example

If you perform the Split Quad Meshes operation on the face shown in Figure 3-53(a), GAMBIT splits the quadrilateral mesh elements into triangular elements to create the mesh shown in Figure 3-53(b).

Excluding Boundary Layer Faces

The Split Quad Meshes form includes an Exclude boundary layer faces option that allows you to prohibit GAMBIT from splitting quad mesh elements in face boundary layers. As an example of the effect of the Exclude boundary layer faces option, consider the meshed face shown in Figure 3-54. The face is similar to that shown in Figure 3-53, above, but includes a boundary layer along the left side.

Figure 3-54: Quad-meshed face with boundary layer

Figure 3-55 shows the effect of the Exclude boundary layer faces option on the Split Quad Meshes operation for the face shown in Figure 3-54.

Figure 3-55: Effect of Exclude boundary layer faces option

The effects can be summarized as follows:

Using the Split Quad Meshes Form

To open the Split Quad Meshes form (see below), click the Split command button on the Mesh/Face subpad.

The Split Quad Meshes form contains the following specifications.

Faces specifies the meshed face(s) for which the quad mesh is to be split into triangular elements.
Exclude boundary layer faces specifies that quad face elements in boundary-layer regions are to be excluded from the split operation.


3.3.3 Smooth Face Meshes

The Smooth Face Meshes operation (face smooth command) adjusts the node locations for one or more face meshes. When you smooth a face mesh, GAMBIT automatically adjusts the mesh node locations to improve the uniformity of the spacing between nodes across the face. To smooth a face mesh, you must specify the following parameters:

Specifying the Smoothing Scheme

GAMBIT provides the following smoothing schemes:

The following table summarizes the basic features of the algorithm employed by each scheme.

Algorithm Features
Length-weighted Laplacian
  • Uses the average edge length of the elements surrounding each node
  • Tends to average element edge lengths
Centroid Area
  • Equalizes areas of adjacent elements
Winslow
  • Optimizes element shapes with respect to perpendicularity
  • Applies only to quadratic elements

Using the Smooth Face Meshes Form

To open the Smooth Face Meshes form (see below), click the Smooth Mesh command button on the Mesh/Face subpad.

The Smooth Face Meshes form contains the following specifications.

Faces specifies the face(s) for which the mesh is to be smoothed.
Scheme contains an option button that allows you to specify one of three smoothing algorithms (see above).
L-W Laplacian
Centroid Area
Winslow
specifies the mesh smoothing algorithm.


3.3.4 Set Face Vertex Type

The Set Face Vertex Type operation (face modify command) defines the characteristics of face meshing and/or boundary layer construction operations in the vicinity of a specified vertex. The vertex-type specifications also determine which face meshing scheme GAMBIT selects as the default scheme.

To set the type for one or more vertices, you must specify the following parameters.

The Face, Type, and Vertices parameters define the vertex type specification. The Boundary layer only option specifies whether the specification applies to meshing and/or boundary layer construction operations.

Specifying the Face

GAMBIT vertex types are specific to the faces upon which they are set; therefore, to specify the type designation of an individual vertex, you must also specify a face associated with that vertex. An individual vertex may possess as many vertex type designations as the number of faces to which it is attached. For example, it is possible for a vertex to possess a Side type designation with respect to one face and an End type designation with respect to another face.

Specifying Vertex Type

The structure of any face mesh in the vicinity of an individual vertex on its boundary is a function of the face meshing scheme and vertex type. GAMBIT provides six vertex types (see Figure 3-56):

Figure 3-56: Face vertex types

Each vertex type differs from the others in the following ways:

The following table summarizes the characteristics of the vertex types shown in Figure 3-56.

Vertex Type Intersecting Grid Lines Angle Between Edges Applicable Mesh Scheme
End 0 Quad:Map
Quad:Pave
Quad:Submap
Quad:Tri Primitive
Quad/Tri:Map
Quad/Tri:Pave
Quad/Tri:Wedge Primitive
Tri:Pave
Side 1 Quad:Map
Quad:Pave
Quad:Submap
Quad:Tri Primitive
Quad/Tri:Map
Quad/Tri:Wedge Primitive
Corner 2 Quad:Map
Quad:Submap
Reversal 3 Quad:Map
Quad:Submap
Trielement 0 Acute
(User specified)
Quad:Tri Primitive
Quad/Tri:Map
Quad/Tri:Wedge Primitive
Notrielement 0 Acute
(User specified)
Quad:Tri Primitive
Quad/Tri:Map
Quad/Tri:Wedge Primitive

NOTE: GAMBIT ignores vertex types when meshing a face according to the Pave mesh scheme.

The following sections describe the general effect of each vertex type on the shape of the face mesh in the vicinity of a specified vertex.

End Vertex Type

When you specify a vertex as the End vertex type and do not specify a Pave meshing scheme, GAMBIT creates the face mesh such that only two mesh element edges intersect at the vertex (see Figure 3-56(a)). As a result, the mapped and submapped face mesh patterns on both sides of the End vertex terminate at the edges adjacent to the vertex.

Side Vertex Type

When you specify a vertex as the Side vertex type and do not specify a Pave meshing scheme, GAMBIT creates the face mesh such that three mesh element edges intersect at the vertex (see Figure 3-56(b)). GAMBIT treats the two topological edges that are adjacent to the vertex as a single edge for the purposes of meshing.

Corner Vertex Type

When you specify a vertex as the Corner vertex type and do not specify a Pave meshing scheme, GAMBIT creates the face mesh such that four mesh element edges intersect at the vertex (see Figure 3-56(c)). The Corner vertex type cannot be applied to vertices the adjacent edges of which form angles less than 180.

Reversal Vertex Type

When you specify a vertex as the Reversal vertex type, GAMBIT creates the face mesh such that five mesh element edges intersect at the vertex (see Figure 3-56(d)). When you apply a Submap meshing scheme to a face that includes a Reversal vertex, GAMBIT creates a line of mesh edges that extends from the Reversal vertex to a topological edge on an opposite side of the face. GAMBIT treats the resulting line and each adjacent edge as a single edge for the purposes of meshing.

Trielement and Notrielement Vertex Types

When you specify a vertex as the Trielement vertex type, GAMBIT creates a triangular element (see Figure 3-56(e)) at the vertex, regardless of the default element type that would otherwise be created using either the Quad/Tri:Map, Tri:Primitive, or Quad/Tri:Wedge Primitive face meshing schemes.

When you specify a Notrielement vertex type, GAMBIT creates a quadrilateral element at the vertex, regardless of the default element type that would otherwise be created.

Effect of Vertex Type on Face Meshes

As an example of the general effects of vertex types on face meshes, consider the planar face shown in Figure 3-57. The following three examples illustrate the effects of different vertex-type specifications applied to vertices C, F, and G on the shape of the resulting mesh.

Figure 3-57: Seven-sided planar face

In Figure 3-58, vertices C, F, and G are specified as Side vertices; therefore, GAMBIT treats sides BCD and EFGA as if each were a single edge. As a result, the entire face represents a mappable region, and GAMBIT creates a single checkerboard pattern for the mesh.

Figure 3-58: Example face mesh—Side inside corner vertex

In Figure 3-59, vertices C, F, and G are specified as Corner, Side, and End type vertices, respectively. As a result, the face is submappable, and GAMBIT creates two separate checkerboard patterns for the mesh. The upper-left submapped region is defined by the polygon ABCHFG. The lower-right submapped region is defined by CDEH. For both regions, the node at point H serves as an End type vertex for the purposes of mesh creation.

Figure 3-59: Example face mesh—Corner inside corner vertex

In Figure 3-60, vertices C, F, and G are specified as Reversal, End, and End vertices, respectively. As a result, the face is submappable, similar to that shown in Figure 3-59. The upper-left submapped region is defined by the polygon ABCHG. The lower-right submapped region is defined by CDEFH.

Unlike the mesh shown in Figure 3-59, the mesh in Figure 3-60 does not terminate at vertex C. Instead, GAMBIT treats the sides BCH and HCD as single edges when creating the mesh.

Figure 3-60: Example face mesh—Reversal inside corner vertex

Meshing Vertex Types vs. Boundary Layer Vertex Types

Vertex type specifications affect two kinds of GAMBIT operations: The Set Face Vertex Type form allows you to specify the vertex type for each operation independently. For example, a given vertex can be specified as End type for meshing operations and Side type for boundary layer construction. The boundary layer characteristic affects the mesh only if a boundary layer is applied to the face prior to meshing.

As an example of the effect of independent specification of vertex types, consider the square planar face shown in Figure 3-61(a) and (b). For this face, vertex b is specified as an End vertex for meshing operations and as a Side vertex for boundary layer construction operations.

Figure 3-61: Effect of independent specification of vertex type

If you mesh the face without first applying a boundary layer, GAMBIT creates the mesh shown in Figure 3-61(a). However, if you apply a uniform, five-row boundary layer to edges a-b and b-c before meshing, GAMBIT creates the mesh shown in Figure 3-61(b). In this case, the boundary layer dovetails in the corner region because vertex b is specified as a Side vertex for boundary layer construction.

As noted above, the boundary layer vertex type affects the structure of the mesh only when a boundary layer is applied prior to meshing. As an example of the effect of boundary layer vertex type on mesh structure, consider the square planar face shown in Figure 3-62. In Figure 3-62(a), vertex b is specified as an End vertex for boundary layer operations; in Figure 3-62(b), vertex b is specified as a Side vertex for boundary layer operations. In both cases, vertex b is specified as an End vertex for meshing operations.

Figure 3-62: Effect of boundary layer vertex type

If you apply a uniform, five-row boundary layer to edges a-b and b-c before meshing the face, GAMBIT creates the meshes shown in Figure 3-62(a) and (b). In this case, the structure of the mesh in proximity to vertex b varies according to the specified vertex type. In both cases, if you do not apply a boundary layer to the edges prior to meshing the face, GAMBIT creates the mesh shown in Figure 3-61(a), above.

Specifying the Boundary layer only Option

The Boundary layer only option on the Set Face Vertex Type form operates according to the following rules:

Using the Set Face Vertex Type Form

To open the Set Face Vertex Type form (see below), click the Set Face Vertex Type command button on the Mesh/Face subpad.

The Set Face Vertex Type form contains the following options and specifications.

Face specifies the face upon which the vertex type is to be set.
Type contains a field of six radio buttons that specify the vertex type for all vertices selected by means of the Vertices list box in the lower part of the form. The available vertex types are End, Side, Corner, Reversal, Trielement, and Notrielement.
Vertices specifies one or more vertices to which the currently specified vertex type is applied.
Boundary layer only specifies that any change made to the vertex type specifications applies only to boundary layers adjacent to the specified vertices.


3.3.5 Set Face Element Type

The Set Face Element Type operation (default set command for the MESH.NODES.QUAD default variable) specifies the mesh node configuration associated with either of two available face element shapes.

To set the face element type, you must specify the node pattern associated with each of the face element shapes. There are two face element shapes available in GAMBIT:

Each face element shape is associated with three different node patterns, and each node pattern is characterized by the number of nodes in the pattern. Figure 3-63 and Figure 3-64 show the node patterns associated with the quadrilateral and triangular face element types, respectively.

Figure 3-63: Quadrilateral face element types

Figure 3-64: Triangular face element types

When you set a face element type, GAMBIT applies the type to all face elements of the specified shape. For example, if you specify 8-node quadrilateral face elements, GAMBIT locates mesh nodes according to the 8-node pattern for all quadrilateral face elements produced in the subsequent face meshing operation. (NOTE: For a description of the relationships between edge, face, and volume element types, see "Set Edge Element Type," above.)

NOTE: Finite-element solvers, such as the FIDAP solver, employ higher-order elements (for example, 8-node and 9-node quadrilateral elements). Finite-volume solvers, such as FLUENT/UNS, employ only linear elements (for example, 4-node quadrilateral elements).

Using the Set Face Element Type Form

To open the Set Face Element Type form (see below), click the Set Face Element Type command button on the Mesh/Face subpad.

The Set Face Element Type form contains the following specifications.

Quadrilateral allows you to specify the quadrilateral face element node pattern. The available node patterns include 4 node, 8 node, and 9 node.
Triangle allows you to specify the triangular face element node pattern. The available node patterns include 3 node and 6 node.


3.3.6 Link/Unlink Face Meshes

The Link/Unlink Face Meshes command button allows you to perform the following operations.

Symbol Command Description
Link Face Meshes Creates hard links between faces
Unlink Face Meshes Deletes hard links between faces

The following sections describe the procedures and specifications required to execute the operations listed above.

NOTE (1): Face-mesh linking is required for periodic and cyclic boundary zones, because it insures that meshes match on linked face pairs.
NOTE (2): When you mesh one of two faces that constitutes part of a linked pair of faces, GAMBIT stores only one copy of the mesh in the database as well as the transformation matrix. As a result, the linking of face meshes reduces memory use.


Link Face Meshes

The Link Face Meshes operation (face link command) creates a mesh hard link between two faces. When you create hard links between faces in a set, GAMBIT associates the faces with each other such that any meshing or splitting operation applied to one or more of the faces is similarly applied to all faces in the set. For example, if you mesh a face that is hard-linked to another face, GAMBIT meshes both faces according to the grading scheme and parameters applied to the specified face. Likewise, if you split the boundary edge of a face that is hard-linked to another face, GAMBIT splits the corresponding edge on the other face.

NOTE: When you select a face for the Link Face Meshes operation, GAM­BIT automatically highlights the graphic display of any faces to which the face is currently linked.

To create a mesh hard-link between two faces, you must specify the following parameters for each face:

Specifying Faces

When you hard-link two faces, the faces to be hard-linked must possess identical numbers of edges. In addition, if a face possesses more than one edge loop, any face to which it is hard-linked must possess an identical number of edge loops, and the edge loops that correspond to each other must possess identical numbers of edges.

As an example of this restriction, consider the six faces shown in Figure 3-65. Of all possible combinations represented by the faces in the figure, only the following faces may be hard-linked to each other:

Figure 3-65: Face edge loop hard-link examples

The rules governing the permissibility of hard-links for the faces shown in Figure 3-65 are as follows.

Specifying Reference Vertices

When you hard-link two faces, you must specify one reference vertex for each edge loop of each face. The reference vertex determines the relationship between the edges of each face with respect to meshing. As an example of the effect of reference vertex specification, consider the two hard-linked faces shown in Figure 3-66 and Figure 3-67. In both figures, face.1 possesses a boundary layer attached to its left edge.

Figure 3-66: Face hard-link—identical reference vertex positions

Figure 3-67: Face hard-link—differing reference vertex positions

In Figure 3-66, the reference vertices are located at identical positions on each face, therefore the mesh scheme applied to face.1 is exactly duplicated on face.2. In Figure 3-67, the reference vertex locations differ between faces, therefore the location of the boundary layer on face.2 is different from that on face.1.

Specifying Mesh Orientation

If you create a hard link between two faces the edge loop senses of which are reversed relative to each other, you must reverse the orientation of the linked mesh in order to create identical meshes on both faces. As an example of this constraint, consider the two hard-linked faces shown in Figure 3-68. The bottom edge of face.1is graded toward its left endpoint vertex, and the senses of the edge loops for the faces are reversed relative to each other.

Figure 3-68: Face hard-link—orientation relative to edge loop sense

If you specify reference vertices at identical positions on both faces, GAMBIT constructs a mesh on the linked face (for example, face.2) that is different in orientation from that constructed on the specified face (for example, face.1). To create identical meshes on both faces when you specify reference vertices as shown in Figure 3-68, you must specify the Reverse orientation option when you create the mesh hard link.

Specifying the Periodic Option

The Link Face Meshes command includes a Periodic option that allows you to specify that the faces are periodically linked. Periodically linked faces are constrained such that they must behave identically to each other with respect to any virtual edge-split and vertex-move operations. For a general description of the effect of periodic linking on the boundary edges of periodically linked faces, see "Link Edge Meshes," in Section 3.2.3, above.

Using the Link Face Meshes Form

To open the Link Face Meshes form (see below), click the Link command button on the Mesh/Face subpad.

The Link Face Meshes form contains the following specifications.

Face specifies the first of two faces to be hard-linked.
Vertices specifies one or more reference vertices on the first of the hard-linked faces. (NOTE: You must specify one reference vertex for each edge loop associated with the face.)
Link With
Face specifies the second of two faces to be hard-linked.
Vertices specifies one or more reference vertices on the second hard-linked face (see above).
Reverse orientation specifies that the edge meshing on the second of the two hard-linked faces is reversed relative to the first.
Periodic specifies that the faces are periodically linked.


Unlink Face Meshes

The Unlink Face Meshes operation (face unlink command) deletes existing hard links associated with two faces. To delete a hard link, you must specify both faces associated with the link.

NOTE: When you select a face for the Unlink Face Meshes operation, GAM­BIT automatically highlights the graphic display of any faces to which the face is currently linked.

Using the Unlink Face Meshes Form

To open the Unlink Face Meshes form (see below), click the Unlink command button on the Mesh/Face subpad.

The Unlink Face Meshes form contains the following specifications.

Faces specifies the face(s) for which the hard link is to be deleted.
Lower topology specifies that any edge hard links that are associated with the face hard link are deleted along with the face hard link.


3.3.7 Modify Meshed Face / Split Meshed Face

The Modify Meshed Face / Split Meshed Face command button allows you to perform the following operations.

Symbol Command Description
Modify Meshed Face Converts mesh edges to topological equivalents
Split Meshed Face Splits a face along lines defined by an existing mesh

The following sections describe each of these operations.


Modify Meshed Face

The Modify Meshed Face operation (face split command) converts mesh edges to faceted topological edges and creates faceted faces where appropriate. The command can be used to create faceted representations of existing geometry or to modify geometry associated with imported mesh information.

To perform a Modify Meshed Face operation, you must first create a Mesh edges conversion list—that is, a list of mesh edges that are to be converted to faceted geometric edges. To create the conversion list, you must specify the following parameters:

Specifying the Meshed Face

You can specify any meshed face for a Modify Meshed Face operation. The shape of the meshed face determines which mesh edges are added to the conversion list when using the automatic method of mesh-edge specification (see below).

Specifying the Mesh Edges

GAMBIT provides two methods of adding edges to the Mesh edges conversion list.

When you use the automatic method, GAMBIT automatically adds mesh edges to the conversion list based on the angle between the outward-pointing normals of any two adjacent mesh element faces. When you use the manual method, GAMBIT allows you to select specific mesh edges to be added to (or removed from) the list.

NOTE (1): To activate the Mesh edges conversion-list picker, you must first select a meshed face and Shift-right-click in the graphics window to accept the selection.
NOTE (2): When you perform a Modify Meshed Face operation, GAMBIT highlights mesh edges in the graphics window according to the following color code:
  • Pink—Detected/picked mesh edges
  • Light blue—Undetected/unpicked mesh edges

Using the Automatic Method

To employ the automatic method of adding mesh edges to the conversion list, you must specify an Angle parameter, . The Angle parameter represents the minimum angle (in degrees) between outward-pointing normals for any two faces the common edge of which is to be automatically added to the conversion list (see Figure 3-69).

Figure 3-69: Automatic-method angle criterion

When you employ the automatic method, GAMBIT applies the Angle () criterion to all mesh element faces associated with the meshed topological face. If for any two mesh element faces, GAMBIT adds their common mesh edge to the conversion list. If , GAMBIT does not add the mesh edge to the conversion list. If you specify Angle = 0 and employ the automatic method for the face, GAMBIT adds to the conversion list all of the mesh edges associated with the face.

As an example of the use of the automatic method, consider the meshed elliptical, cylindrical face shown in Figure 3-70. The face is meshed using a regular map mesh with 40 intervals on each of the elliptical boundary edges, resulting in 560 regular quadrilateral mesh elements.

Figure 3-70: Example meshed cylindrical face

If you employ the automatic method of mesh-edge selection and specify an Angle parameter of 10 (degrees), GAMBIT automatically adds to the conversion list the mesh edges highlighted in Figure 3-71(a). In this case, the selected edges form straight chains that run the entire length of the cylinder; therefore, the Modify Meshed Face operation results in the creation of 10 faceted faces, each of which is as long as the cylinder itself (see Figure 3-71(b)).

If you specify an Angle parameter of 5 (degrees), GAMBIT automatically adds to the conversion list the mesh edges highlighted in Figure 3-71(c). In this case, the list includes longitudinal edges that exist on the less-rounded regions of the cylinder, and the Modify Meshed Face operation results in the creation of 22 faceted faces (see Figure 3-71(d)).

Figure 3-71: Effect of Angle parameter on created faces

NOTE (1): GAMBIT does not include any lateral mesh edges in this example (that is, mesh edges that are perpendicular to the cylinder axis), because all adjacent faces that share common lateral edges are parallel to each other.
NOTE (2): All faces created by the Modify Meshed Face command are faceted faces. By default, GAMBIT labels all faceted faces with the prefix "f_"—for example, f_face.107.
NOTE (3): When you create faceted faces by means of the Modify Meshed Face command, GAMBIT does not delete the underlying face geometry. For example, the geometry shown in Figure 3-71(b), above, includes 10 faceted faces, as well as the original real elliptical face.

Using the Manual Method

When you use the manual method of managing the mesh-edge conversion list, GAMBIT allows you to per­form the following operations, each of which cor­responds to a separate option on the Modify Meshed Face form.

Adding and Removing Edges

To add or remove a mesh edge to or from the conversion list, you must select the Add or Remove option, respectively, and specify the mesh edge to be added or removed. You can specify the mesh edge to be added or removed in the following ways:

NOTE (1): The mesh edge conversion list automatically includes all mesh edges that exist on the boundary edges of the meshed face. GAMBIT does not allow you to remove such edges from the conversion list.
NOTE (2): If you click the Mesh edges pick-list button, GAMBIT displays the special Mesh Edge List (Multiple) pick-list form. The form differs from ordinary pick-list forms in that it does not include a list of Available mesh edges. (In most cases, the list of Available mesh edges is too long to be of practical use.) Otherwise, the form operates according to the principles that govern all pick-list forms.

Removing Spurs

Spurs are chains of connected mesh edges in the conversion list—such as those that form the longitudinal edges of the faceted faces shown in Figure 3-71, above. Spurs that do not attach at both ends to other topological edges constitute dangling spurs (see Figure 3-72).

Figure 3-72: Example dangling spurs

When you select the Remove spurs option and specify a mesh edge that constitutes any part of a spur, GAMBIT removes from the conversion list all edges associated with the spur.

Combining the Automatic and Manual Methods

The Modify Meshed Face command allows you to combine the automatic and manual methods to create the Mesh edges conversion list. For example, you can use the automatic method to create the overall conversion list and use the manual method to modify the list. Figure 3-73 shows the effect of a combined automatic/manual method on the meshed elliptical cylinder shown above. In this case, the conversion list is first created by using the automatic method with an Angle specification of 5 (degrees) then modified using the manual method to add and remove edges from the list as shown. Figure 3-73(b) shows the faceted faces created from the resulting Modify Meshed Face operation.

Figure 3-73: Combined use of automatic and manual methods

NOTE: To combine the automatic and manual methods, you must use the automatic method before using the manual method. Each time you input a value into the Angle input field (or use the Angle slider bar), GAMBIT resets the conversion list and populates it based only on mesh edges specified using the current Angle criterion.

Selecting the Entire Meshed Face

You can specify selection of the entire meshed face for conversion in either of the following ways.

Using the Modify Meshed Face Form

To open the Modify Meshed Face form (see below), click the Modify Meshed Face command button on the Mesh/Face subpad.

The Modify Meshed Face form contains the following options and specifications.

Face specifies the meshed face to which mesh-edge conversion operation is to be applied.
Mesh edges specifies the mesh edges in the conversion list.
Keep original edge specifies the retention of any topological edge associated with a removed mesh edge.
Automatic:
Angle specifies the minimum angle between normals for adjacent mesh-element faces for which the common mesh edge is to be added to the con­version list.
Manual:
Add specifies that the specified mesh edge is added to the conver­sion list.
Remove specifies that the specified mesh edge is removed from the conversion list.
Remove spurs specifies that all edges included in the spur associated with the specified mesh edge are removed from the conversion list.


Split Meshed Face

The Split Meshed Face operation (face split command) splits a meshed face into two virtual faces.

When you split a face by means of the Split Meshed Face command, GAMBIT creates two virtual faces that share a common virtual edge. The shape of the virtual edge is determined by the nodes that define the split path. Once the virtual faces are created, GAMBIT retains them even if you delete the mesh that was used to define their shapes.

To split a meshed face by means of the Split Meshed Face command, you must specify the following parameters.

Specifying the Face

You can use the Split Meshed Face command to split any real or virtual face that is currently meshed.

Specifying the Split Path Mesh Nodes

To split a face using mesh nodes, you must specify two or more mesh nodes that define the path of the split. Two of the mesh nodes must be located on the edges of the face. The other mesh nodes that define the split path may exist anywhere else internal to the face, but none of them may lie on one of the edges of the face.

Figure 3-75 illustrates the effect of splitting a real face by means of the Split Meshed Face form. Figure 3-75(a) shows the mesh and four mesh nodes that define the split path. Figure 3-75(b) shows the two virtual faces that result from the split operation.

Figure 3-74: Face split by mesh nodes

Specifying the Split edge angle Option

The Split edge angle option allows you to specify the characteristics of the chain of edges that separates the faces resulting from the split. When you select the Split edge angle option and specify a value, GAMBIT creates vertices only at those mesh nodes the adjacent mesh edges of which are separated by an angle (in degrees) less than the specified Split edge angle value.

As an example of the effect of the Split edge angle option, consider the meshed face shown in Figure 3-75(a). The face is square and is meshed using a triangular pave mesh.

Figure 3-75: Effect of Split edge angle option

If you split the face and do not specify the Split edge angle option, GAMBIT creates vertices at each mesh node along the split path and joins the vertices with a chain of straight edges that splits the face (Figure 3-75(b)). If you specify a Split edge angle value of 140, GAMBIT creates vertices only at those nodes the adjacent mesh edges of which are separated by an angle less than 140o (Figure 3-75(c)). If you specify a Split edge angle value of 90, GAMBIT splits the meshed face with a single edge (Figure 3-75(d)).

Using the Split Meshed Face Form

To open the Split Meshed Face form (see below), click the Split Meshed Face command button on the Mesh/Face subpad.

The Split Meshed Face form contains the following specifications.

Face specifies the face to be split.
Split With
Nodes specifies the mesh nodes that define the split path.
Split edge angle specifies that vertices are created only at mesh nodes the adjacent mesh edges of which are separated by an angle less than the Split edge angle value.


3.3.8 Summarize Face Mesh / Check Face Meshes

The Summarize Face Mesh / Check Face Meshes command button lets you perform the following operations.

Symbol Command Description
Summarize Face Mesh Summarizes general face mesh information in the Transcript window
Check Face Meshes Displays face mesh quality information in the Transcript window


Summarize Face Mesh

The Summarize Face Mesh operation (face msummarize command) displays edge mesh information in the Transcript window and allows you to highlight specific mesh nodes and/or mesh elements in the graphics window. The command requires three input parameters:

Specifying the Component Type

To summarize face mesh information in the Transcript window, you must specify the type of mesh components to be included in the summary. Each face mesh includes two component types:

The type of mesh summary information displayed in the Transcript window depends on the component type (see "Face Mesh Summary Information," below).

Selecting Specific Components

GAMBIT provides two methods for selecting specific components (elements or nodes) to be included in the face mesh summary:

In most cases, it is preferable to pick the components in the graphics window, rather than selecting them by means of a pick list, because the component labels (element or node numbers) are not known prior to component selection.

To pick the components in the graphics window:

  1. Select the appropriate Component option (Elements or Nodes).
  2. Click (to activate) the appropriate (Elements or Nodes) pick-list field.
  3. Shift-left-click in the graphics window to select each element or node to be included in the summary.
To select the components by means of a pick list:
  1. Select the appropriate Component option (Elements or Nodes).
  2. Click the appropriate (Elements or Nodes) pick-list button to open the Mesh Face List (Multiple) or Mesh Node List (Multiple) form.
  3. On the Mesh Face List (Multiple) or Mesh Node List (Multiple) form, click the All–> pushbutton to populate the list with all elements or nodes associated with the specified face.
  4. In the Mesh Face List (Multiple) or Mesh Node List (Multiple) list, select (highlight) the elements or nodes to be excluded from the summary.
  5. Click the <– – – pushbutton to remove the selected (highlighted) elements or nodes from the list.
NOTE: The Mesh Face List (Multiple) and Mesh Node List (Multiple) forms do not include the Available list field that is included on most pick-list forms because of the number of items that might need to be included in the list field. A fully meshed model can contain tens of thousands of mesh elements or nodes, each of which constitutes an Available component. If the Mesh Face List (Multiple) or Mesh Node List (Multiple) form included an Available list field, GAMBIT would need to compile the Available list before opening the form, thereby delaying the appearance of the form on the GUI.

When you specify any component (element or node) to be included in the mesh summary, GAMBIT highlights the component in the graphics window. If you select the Element labels and/or Node labels options, GAMBIT also displays the element and/or node numbers associated with the specified components (see Figure 3-76).

Figure 3-76: Face mesh element and node numbering display

Face Mesh Summary Information

As noted above, the type of mesh summary information displayed in the Transcript window depends on the type of component being summarized. For example, element summaries include node connectivity information, which is not available in node summaries.

Elements Summary Information

If you select the Elements option, the mesh summary includes the following information for each specified element.

For example, if you select an Elements summary for the face and highlighted elements shown in Figure 3-76, above, GAMBIT displays the following information in the Transcript window.
Summarizing mesh on face.4:
Total nodes: 25
Total elements: 16
 Element     Type         Count       Connectivity
----------- --------- ------------ ----------------------
      9       quad          4:        12   18   19   13
     10       quad          4:        18   21   22   19
     14       quad          4:        19   22    8    7
     15       quad          4:        22   25    9    8
In this case, the summary indicates that element 10 is an edge mesh element connected to nodes 18, 21, 22, and 19.

Nodes Summary Information
If you select the Nodes option, the mesh summary includes the following information for each specified node. For example, if you select a Nodes summary for the face and nodes 7, 13, and 19 shown in Figure 3-76, above, GAMBIT displays the following information in the Transcript window.

Summarizing mesh on face.4:
Total nodes: 25
Total elements: 16
Coordinate System: c_sys.1

   Node        x          y         z        Owner
----------- --------- ---------- --------- -------------
      7       5.0000     2.5000   -5.0000   edge.3
     13       5.0000     5.0000   -2.5000   edge.8
     19       5.0000     2.5000   -2.5000   face.4
In this case, the summary indicates that node 13 is located at the position (5, 5, -2.5) and is associated with ("owned by") face.4.

Using the Summarize Face Mesh Form

To open the Summarize Face Mesh form (see below), click the Summarize command button on the Mesh/Face subpad.

The Summarize Edge Mesh form contains the following options and specifications.

Edge specifies the face for which summary information is to be displayed.
Component
Elements displays summary information for specified elements.
All
Pick
specifies whether the mesh summary information includes all elements or only selected elements.
Pick specifies the elements for which mesh sum­mary information is to be displayed.
Element labels displays labels (numbers) in the graphics window for all specified elements.
Node labels displays labels (numbers) in the graphics window for all nodes associated with the specified elements.
Nodes displays summary information for specified nodes.
All
Pick
specifies whether the mesh summary information includes all nodes or only selected nodes.
Pick specifies the nodes for which mesh sum­mary information is to be displayed.
Node labels displays labels (numbers) in the graphics window for all specified nodes.


Using the Summarize Face Mesh Form

To open the Summarize Face Mesh form (see below), click the Summarize command button on the Mesh/Face subpad.

The Summarize Face Mesh form contains the following options and specifications.

Face specifies the face for which information is to be summarized.
Component
Elements specifies that the mesh summary display is based on mesh elements.
All
Pick
specifies whether GAMBIT displays all element and/ or node numbers or only those corresponding to selected elements.
Pick specifies the elements for which element and/or node numbers are to be displayed.
Element labels specifies that element numbers are displayed.
Node labels specifies that node numbers are displayed.
Nodes specifies that the face mesh summary display is based on mesh nodes.
All
Pick
specifies whether GAMBIT displays all node numbers or only those corresponding to selected nodes.
Pick specifies the nodes for which node numbers are displayed.
Node labels specifies that node numbers are to be displayed.


Check Face Meshes

The Check Face Meshes operation (face check quality command) displays 2-D mesh quality data. When you execute the Check Face Meshes command, GAMBIT displays the following elements in the Transcript window:

Tabular 2-D Mesh Quality

The Check Face Meshes tabular output represents the statistical distribution of element quality values for the current default 2-D quality metric. Table 3.1 shows an example of such output for a face mesh evaluated according to the EquiAngle Skew quality metric. Output such as that shown in Table 3.1 constitutes a numerical representation of the mesh quality histogram that is displayed on the Examine Mesh form when you choose the Display Type:Range option (see Section 3.4.2 of the GAMBIT User's Guide).

Table 3.1: Example Check Face Meshes tabular output

From value   To value   Count in range     % of total count (114)
-----------------------------------------------------------------
    0           0.1           36                31.58
    0.1         0.2           46                40.35
    0.2         0.3           20                17.54
    0.3         0.4            6                 5.26
    0.4         0.5            2                 1.75
    0.5         0.6            4                 3.51
    0.6         0.7            0                 0.00
    0.7         0.8            0                 0.00
    0.8         0.9            0                 0.00
    0.9         1              0                 0.00
----------------------------------------------------------------
    0           1            114               100.00
In addition to the tabular output shown in Table 3.1, the Check Face Meshes command displays the minimum and maximum values of element quality for the set of specified faces, thus:
Measured minimum value: 0.0286973
Measured maximum value: 0.587398
This minimum and maximum element quality information is not available by means of any other GAMBIT operation.

Specifying the Quality Metric

As noted above, the Check Face Meshes command evaluates 2-D mesh element quality according to the current default mesh quality metric. To change the metric used to evaluate element quality for the Check Face Meshes command, you must modify the default 2-D mesh quality metric by means of the Edit Defaults form. To do so:

  1. Open the Edit Defaults form.
  2. Click the MESH tab to open the MESH defaults subform.
  3. Select the EXAMINE radio button to display the EXAMINE variables.
  4. Modify the ELEMENT_2D_QUALITY variable.
(For a complete description of the procedures required to modify default variables by means of the Edit Defaults form, see Section 4.2.4 of the GAMBIT User's Guide.)

For example, to evaluate 2-D elements on the basis of the Aspect Ratio metric:

  1. Use the procedure described above to set Aspect Ratio as the default quality metric (ELEMENT_2D_QUALITY=2)
  2. Execute the Check Face Meshes command.
NOTE: Check Face Meshes command tabular output, such as that shown in Table 3.1, above, includes all 2-D elements that possess shapes for which the current default quality metric applies. For example, if you specify Aspect Ratio as the default quality metric, the tabular output includes all quadrilateral and triangular elements associated with the faces specified on the Check Face Meshes form. However, if you specify Diagonal Ratio as the default quality metric, the tabular output includes only quadrilateral elements, because the Diagonal Ratio metric does not apply to triangular elements.

Summary Statement

The Check Face Meshes summary statement indicates the number of specified faces that "fail" the mesh check-for example,

0 out of 2 meshed face(s)failed mesh check.
In the context of the Check Face Meshes command, any face that includes at least one inverted mesh element fails the mesh check.

Using the Check Face Meshes Form

To open the Check Face Meshes form (see below), click the Check command button on the Mesh/Face subpad.

The Check Face Meshes form contains the following specification.

Faces specifies the faces for which mesh element quality is to be evaluated.


3.3.9 Delete Face Meshes

The Delete Face Meshes operation (face delete onlymesh command) removes the mesh from one or more meshed faces. When you remove a face mesh, GAMBIT allows you to retain or remove all edge meshes associated with the face.

Using the Delete Face Meshes Form

To open the Delete Face Meshes form (see below), click the Delete command button on the Mesh/Face subpad.

The Delete Face Meshes form contains the following options and specifications.

Faces specifies the face(s) for which the mesh is deleted.
All
Pick
  • All specifies all faces in the model.
  • Pick specifies faces selected by means of the Faces list box.
Remove unused lower mesh removes all unused lower-topology meshes associated with the specified face(s).


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