3.4 Volume Meshing Commands

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

The following sections describe the purpose and operation of each of the commands listed above.

3.4.1 Mesh Volumes

The Mesh Volumes command allows you to create a mesh for one or more volumes in the model. When you mesh a volume, GAMBIT creates mesh nodes throughout the volume according to the currently specified meshing parameters.

To mesh a volume, you must specify the following parameters:

• Volume(s) to be meshed
• Meshing scheme
• Mesh node spacing
• Meshing options

Specifying the Volume

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

Specifying the Meshing Scheme

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

• Elements
• Type

The Elements parameter defines the shape(s) of the elements that are used to mesh the volume. The Type parameter defines the meshing algorithm and, therefore, the overall pattern of mesh elements in the volume.

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

Specifying Scheme Elements

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

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 volume meshing Type options.

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

Each of the allowable combinations shown in the table above results in a unique pattern of mesh nodes for any given volume. In addition, each is associated with a set of restrictions that govern the types of volumes to which it can be applied. The following sections describe the patterns and restrictions associated with each of the allowable combinations of options listed above.

Map Meshing Scheme

When you apply the Map meshing scheme to a volume, GAMBIT meshes the volume using an array of hexahedral mesh elements, such as those shown in Figure 3-51.

Figure 3-51: Map volume meshing scheme-array of hexahedral elements

Each mesh element includes at least eight nodes-located at the corners of the element. If you specify an alternative volume element node pattern, GAMBIT creates either 20 or 27 nodes per mesh element (see "Set Volume Element Type," below).

General Applicability

The Map volume meshing scheme can only be applied to volumes that can be meshed such that the mesh represents a logical cube. To represent a logical cube, a volume mesh must satisfy the following general requirements.

1. There must exist exactly eight mesh nodes that are attached to only three mesh element faces. (These eight mesh nodes comprise the corners of the logical cube.)
2. Each of the eight corner mesh nodes must be connected to three other corner mesh nodes by means of a straight chain of mesh edges-that is, a chain of mesh edges all of which belong to a single logical row of mesh nodes.

According to the criteria described above, the most basic form of a mappable volume is a rectangular brick, such as that shown in Figure 3-51, above. For such a volume, the mesh nodes located at the corner vertices of the brick constitute the corners of the mesh cube.

Although the strict definition of volume mappability is best expressed in terms of the mesh itself, it is possible to state mappability requirements in terms of the general geometrical configuration of a given volume. Specifically, volume mappability criteria may be stated as follows:

To be mappable, a volume should contain six sides, each of which can be rendered mappable by the correct specification of vertex types.

(For an exception to the criteria described above, see "Mapping Volumes with Less Than Six Faces," below.)

As an example of the application of the general rule stated above, consider the volumes shown in Figure 3-52.

Figure 3-52: Map volume meshing scheme-example volumes

Of the volumes shown in the figure, only the brick shown in Figure 3-52(a) is mappable in its primitive form. However, it is possible to transform the other volumes into mappable volumes by means of vertex-type assignments and virtual geometry operations. The following sections describe the operations required to render each volume mappable.

Transforming Volumes Into Mappable Forms

As noted above, the volumes shown in Figure 3-52(b), (c), and (d) are not mappable in their primitive forms, but each can be transformed into a mappable volume by means of either vertex-type specifications or virtual geometry operations. Specifically, the operations that are required to transform each volume are as follows.

Pentagonal Prism-Specifying Vertex Types

To transform the pentagonal prism shown in Figure 3-52(b) into a mappable volume, you must specify its vertex types such that the top and bottom faces are mappable. To do so, you must specify one vertex on each of the top and bottom faces as a Side vertex and all other vertices as End vertices (see Figure 3-53(a)).

Figure 3-53: Mappable pentagonal prism volume

Figure 3-53(b) shows the Map volume mesh that results from the vertex specifications shown in Figure 3-53(a). Note that faces A and B in the figure comprise one side of the logical mesh cube and that face C, by itself, constitutes the opposing side.

When you assign vertex types to transform a prism into a mappable volume, you must specify the vertex types such that the Side vertices on the top and bottom faces are connected to each other by means of a single vertical edge. For example, if you assign vertex types according to the specifications shown in Figure 3-54, GAMBIT cannot create a Map volume mesh in the prism, because the configuration cannot be made to represent a logical mesh cube.

Figure 3-54: Unmappable pentagonal prism volume

Cylinder-Splitting Edges and Faces

The cylinder shown in Figure 3-52(c) is not mappable in its primitive form, but it is possible to transform the cylinder into a mappable volume by means of virtual edge-split and face-split operations. (For descriptions of the virtual edge-split and face-split operations, see the Appendix of this guide.)

If you split the edges that circumscribe the end caps and use the resulting vertices to split the cylindrical face into four separate faces, the end faces become mappable (see Figure 3-55(a)), and the cylinder becomes topologically equivalent to the brick shown in Figure 3-52(a). As a result, the cylinder can be meshed according to the Map meshing scheme (see Figure 3-55(b)).

Figure 3-55: Mappable cylinder

Clipped Cube-Collapsing a Face

The clipped cube shown in Figure 3-52(d) is not mappable in its primitive form, but it can be rendered mappable by means of a virtual face collapse operation. (For a description of the virtual face collapse operation, see the Appendix of this guide.) When you collapse the triangular face between its three neighboring faces, GAMBIT creates the virtual volume shown in Figure 3-56(a).

Figure 3-56: Mappable brick without corner

The volume shown in Figure 3-56(a) is topologically equivalent to the brick shown in Figure 3-52(a). If all of its vertices are specified as End vertices, the volume represents a logical meshing cube and can, therefore, be meshed according to a Map volume meshing scheme (see Figure 3-56(b)).

Mapping Volumes with Less Than Six Faces

As a general rule, the Map volume meshing scheme is applicable only to volumes that include six or more faces. It is possible, however, to transform some volumes that contain fewer than six faces into mappable volumes. As an example of such a transformation, consider the sliver-shaped volume shown in Figure 3-57(a). The volume is bounded by four faces and is not mappable in its primitive form.

Figure 3-57: Mappable volume with four faces

You can transform the sliver-shaped volume shown in Figure 3-57 into a mappable form by performing a virtual split operation on each of the curved edges and specifying the vertex types as follows (see Figure 3-57(b)):

• Vertices a, b, c, and d are End vertices with respect to all faces
• Vertices e, f, g, and h are Side vertices with respect to the curved faces and End vertices with respect to the sliver-shaped end caps

Figure 3-57(c) shows the final form of the Map volume mesh.

Submap Meshing Scheme

When you apply the Submap meshing scheme to a volume, GAMBIT subdivides the volume into logical mesh cubes each of which can be mapped according to a Map meshing scheme.

General Applicability

To be submappable, a volume must be configured such that it satisfies both of the following criteria:

• Each face must be either mappable or submappable
• Opposing submappable faces must be configured consistently with respect to their vertex types

The following sections illustrate each of these criteria.

Face Mappability and Submappability

In order for GAMBIT to apply a Submap meshing scheme to a volume, each face that bounds the volume must be either mappable or submappable. Figure 3-58 shows four volumes, three of which meet the criteria described above. The volumes shown in Figure 3-58(a), (b), and (c) are submappable, because the faces of each volume are, themselves, submappable. The volume shown in Figure 3-58(d) is not submappable, because the end face of the cylindrical protrusion on the top of the volume is neither mappable nor submappable.

Figure 3-58: Submap volume meshing scheme—submappability criterion

Opposing-Face Vertex Types

The face mappability/submappability criterion described above constitutes a necessary but insufficient condition for volume submappability. It is possible, for example, to construct a volume that cannot be meshed according to the Submap meshing scheme even though all of its faces are either mappable or submappable.

To apply the Submap meshing scheme to a volume, the face vertex types must be specified such that the face submap meshes on opposing faces of the volume are similar in shape and form. As an example of this requirement, consider the volume shown in Figure 3-59. The volume consists of an L-shaped brick the outside corner of which is truncated at an angle.

Figure 3-59: Submap volume meshing scheme—L-shaped volume

The L-shaped faces that comprise the top and bottom sides of the volume can be submapped in a number of ways, each of which is a function of the vertex types that are assigned to the faces. Figure 3-59 shows face submap meshes that result from three different configurations of vertex types.

The configurations shown in Figure 3-59(a) and (b) can be meshed according to the Submap volume meshing scheme, because the vertex types and meshes on the top and bottom faces of the volume are consistent with each other. By contrast, GAMBIT cannot apply the Submap volume meshing scheme to the volume shown in Figure 3-59(c), because the Submap meshes on the top and bottom faces differ in form.

Tet Primitive Meshing Scheme

The Tet Primitive volume meshing scheme applies only to volumes that constitute logical tetrahedra. To constitute a logical tetrahedron, a volume must include only four sides, each of which constitutes a logical triangle. (NOTE: Any side of the logical tetrahedron may consist of more than one face.) When you apply the Tet Primitive meshing scheme, GAMBIT creates Tri Primitive meshes on each of the faces of the tetrahedron, then subdivides the volume into four hexahedral quadrants and creates a Map-type volume mesh in each quadrant.

As an example of the Tet Primitive meshing scheme, consider the tetrahedral volume shown in Figure 3-60(a). If you apply the Tet Primitive meshing scheme to the volume, GAMBIT creates Tri Primitive meshes on each face (see Figure 3-60(b)), then subdivides the volume into four quadrants and meshes each quadrant with hexahedral mesh elements. Figure 3-60(c) shows a cutaway view of the final mesh.

Figure 3-60: Tet Primitive volume meshing scheme

Cooper Meshing Scheme

When you apply the Cooper meshing scheme to a volume, GAMBIT treats the volume as consisting of one or more logical cylinders each of which is composed of two end caps and a barrel (see Figure 3-61). Faces that comprise the caps of such cylinders are called "source" faces; faces that comprise the barrels of the cylinders are called "non-source" faces. (For restrictions related to the specification of faces for the Cooper meshing scheme, see "Face Characteristics," below.)

Figure 3-61: Cooper volume meshing scheme-logical cylinder

The Cooper meshing scheme involves the following operations.

As an example of the procedure outlined above, consider the volume shown in Figure 3-62. The volume represents the union of a cube, a cylinder, and a triangular prism.

Figure 3-62: Cooper volume meshing scheme-example volume

If you apply the Cooper meshing scheme to the volume shown in Figure 3-62, GAMBIT performs the following operations (see Figure 3-63).

Figure 3-63: Cooper volume meshing scheme-example volume

General Applicability

In general, the Cooper meshing scheme applies to volumes that demonstrate either of the following characteristics.

• At least one face is neither mappable nor submappable.
• All faces are mappable or submappable, but the vertex types are specified such that the volume cannot be divided into mappable subvolumes (see "Submap Meshing Scheme: Opposing-Face Vertex Types," above).

Faces that meet either of the criteria outlined above, as well as those that are logically parallel to such faces, constitute source faces for the volume and the end caps of the corresponding logical cylinder.

Face Characteristics

The Cooper volume meshing scheme imposes the following restrictions on the volumes to which it applies.

1. All non-source faces must be mappable or submappable.
2. Source faces onto which a mesh will be imprinted must not be previously meshed.
3. Source faces must not include dual enclosed loops (see NOTE, below).
4. Source faces that are linked to other faces must be linked such that they do not interfere with the Cooper meshing algorithm. (For a description of face mesh links, see "Link Face Meshes" in Section 3.3.6.)

Figure 3-64 shows four volumes that illustrate the application of the criteria outlined above.

Figure 3-64: Non-Cooper-able volumes

The volumes shown in Figure 3-64 violate the restrictions outlined above for the following reasons.

NOTE: To apply the Cooper meshing scheme to a volume such as that shown in Figure 3-64(c), you must first split the upper and lower rectangular source faces as shown in Figure 3-65. Figure 3-65: Cooper-able volume with internal edge loops

Specifying Source Faces

When you apply the Cooper volume meshing scheme to a volume, you must specify the source faces that define the end caps of the logical cylinder. The source faces also define the longitudinal direction of the logical cylinder. For certain volumes, there exist more than one valid set of source faces. For such volumes, the final form of the mesh depends, in part, on the selection of source faces.

NOTE: When you specify a Cooper meshing scheme for a volume, GAMBIT automatically determines which faces are likely source faces. To override the automatically selected set of source faces, specify an alternative set of faces on the Mesh Volumes form.

As an example of the effect of source-face selection on a mesh, consider the annular volume shown in Figure 3-66. The volume includes four faces-the end faces, labeled A and B, and the inner and outer cylindrical faces, labeled C, and D, respectively.

Figure 3-66: Annular volume

If you mesh the annular volume by means of a Cooper volume meshing scheme and specify faces A and B as the source faces, GAMBIT maps the inner and outer cylinders and paves the end faces, then sweeps the paved mesh through the annular volume along its axis. The resulting mesh appears as shown in Figure 3-67(a), below.

Figure 3-67: Cooper mesh of an annular volume, end source faces

If you specify faces C and D as the source faces, GAMBIT maps the end faces and paves the inner and outer cylindrical faces, then sweeps the paved mesh node pattern in a radial direction through the volume. The resulting mesh appears as shown in Figure 3-67(b).

TGrid Meshing Scheme

When you apply the TGrid meshing scheme to a volume, GAMBIT creates a mesh that consists primarily of tetrahedral mesh elements but which may also contain elements that possess other shapes. If you mesh one or more faces of the volume by means of a Quad or Quad/Tri scheme before applying the TGrid volume meshing scheme, GAMBIT creates hexahedral, pyramidal, and/or wedge elements where appropriate in proximity to the previously meshed faces.

The TGrid meshing algorithm may be summarized as follows.

As an example of effect of face meshes on the TGrid scheme, consider the rectangular brick volume shown in Figure 3-68. Figure 3-68(a) shows the general shape of the tetrahedral mesh elements that are created in the volume if none of the faces are meshed prior to the application of the TGrid scheme or if all pre-meshed faces are meshed by means of a Tri-Pave scheme. If you create a Quad-Map mesh on one of the faces of the brick prior to applying the TGrid meshing scheme (see Figure 3-68(b)), GAMBIT creates an array of pyramidal mesh elements in proximity of that face (see Figure 3-68(c)) and creates tetrahedral elements throughout the rest of the volume.

Figure 3-68: TGrid meshing scheme

Stairstep Meshing Scheme

The Stairstep meshing scheme creates and meshes a faceted volume the shape of which approximates the volume to be meshed. GAMBIT does not mesh the original volume itself, and the created faceted volume is not connected to any existing geometry—including geometry to which the original volume is connected.

As an example of the effect of the Stairstep meshing scheme, consider the volume (volume.1) shown in Figure 3-69. The volume is an elliptical cylinder 10 units long with major and minor axis radii of 5 and 3 units, respectively.

If you mesh the elliptical cylinder shown in Figure 3-69 by means of the Stairstep scheme using an overall interval size of 1, GAMBIT creates and meshes the faceted volume (f_volume.2) shown in Figure 3-70. Note that the shape of the faceted volume crudely approximates the shape of the original elliptical cylinder and that all mesh elements are cubic hexahedra of uniform size.

Using a Template Mesh Volume

In the general Stairstep meshing scheme described above, the created mesh consists entirely of cubic hexahedral mesh elements the sizes of which can vary according to user-specified default settings and any existing mesh information associated with edges and/or faces of the volume to be meshed. It is possible, however, to employ a template mesh volume that serves as an initial overlay grid to start the Stairstep meshing procedures. In some cases, the use of a template mesh volume can greatly improve the density and element quality of the Stairstep mesh. To employ a template mesh volume, you must create and mesh a volume that completely encloses the volume to be meshed by the Stairstep scheme. You can mesh the template mesh volume using any applicable volume meshing scheme—such as Cooper or Map—but the template mesh must consist of 8-node hexahedral elements and must not contain any hanging nodes. GAMBIT uses the mesh of the template mesh volume as the initial subdivision for the Stairstep scheme.

Stairstep Mesh Refinement

Overview

If you apply the Stairstep meshing scheme to a volume that includes edges and/or faces for which mesh interval size information exists, GAMBIT refines the hexahedral mesh in the region of the edges and/or faces. If the existing interval length for an edge is less than the overall length specified for the Stairstep scheme, GAMBIT creates smaller cubic hexahedral mesh elements in the proximity of the edge and also creates a transition region located near to the edge. For example, if you specify an interval size of 0.5 for the elliptical front face of volume.1 in Figure 3-69 and mesh the volume using the Stairstep scheme with an overall interval length specification of 1, GAMBIT creates the meshed, faceted volume shown in Figure 3-71.

Refinement Options

GAMBIT provides three different options for refining the mesh in the Stairstep scheme. One option allows the existence of hanging nodes such as those shown in Figure 3-71. The other two options disallow the existence of hanging nodes by propagating the refined mesh either across the volume in the directions of the coordinate axes to the limit of the volume boundaries or throughout the entire volume.

You can control the Stairstep mesh refinement algorithm by means of a GAMBIT default variable named STAIRSTEP_MESH_TYPE. To modify the STAIRSTEP_MESH_TYPE default variable:

1. Open the Edit Defaults form.
2. Access the MESH default definition subform.
3. Choose the GOCARTS option.
4. Select and modify the STAIRSTEP_MESH_TYPE default variable.

The value of the STAIRSTEP_MESH_TYPE default variable affects Stairstep mesh refinement in the following manner.

As an example of the effect of the STAIRSTEP_MESH_TYPE default variable on the Stairstep mesh, consider the volume shown in Figure 3-72. The volume consists of a cube with a spherical cut-out in one corner. Each edge of the cube is 10 units long, and the sphere radius is 4 units.

Figure 3-72: Stairstep meshing scheme—cube with cutout corner

Figure 3-73 shows the effect of the STAIRSTEP_MESH_TYPE default variable value on the final Stairstep mesh configuration. In each case, the edge interval lengths for the straight and curved edges are 1.0 and 0.25, respectively.

General Applicability

The Stairstep meshing scheme is applicable to all volumes.

Specifying Volume Meshing Options

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

• Mesh
• Remove old mesh
• Ignore size functions

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

Remove old mesh Option

If you select the Remove old mesh option, GAMBIT deletes any currently existing mesh from the specified volume(s). If you delete a volume mesh using the Remove old mesh option, GAMBIT enables the Remove lower mesh option—which allows you to specify whether or not to delete the mesh on the faces and edges that define the volume. If you select the Remove lower mesh option, GAMBIT deletes the face and edge mesh(es) when it deletes the volume mesh(es). If you do not select the option, GAMBIT deletes the volume mesh but retains any associated face and edge meshes.

Ignore size functions Option

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

Using the Mesh Volumes Form

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

The Mesh Volumes form contains the following options and specifications.

3.4.2 Smooth Volume Meshes

The Smooth Volume Meshes command allows you to smooth the spacing of mesh nodes throughout one or more volumes.

When you smooth a volume mesh, GAMBIT automatically adjusts mesh node locations in order to improve the uniformity of spacing between nodes throughout the mesh. To smooth a volume mesh, you must specify the following parameters:

• The volume for which the mesh is to be smoothed
• The smoothing scheme

Specifying the Smoothing Scheme

GAMBIT provides the following mesh smoothing schemes:

• Length-weighted Laplacian (L-W Laplacian)
• Equipotential (Equipotential)

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

Using the Smooth Volume Meshes Form

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

The Smooth Volume Meshes form contains the following options and specifications.

3.4.3 Set Volume Element Type

The Set Volume Element Type command allows you to specify the number of mesh nodes and the node pattern associated with any of four available volume element shapes.

To set the volume element type, you must specify the numbers of nodes associated with each of the volume element shapes. There are four volume element shapes available in GAMBIT:

• Hexahedron
• Wedge
• Tetrahedron
• Pyramid

Every volume element shape is associated with as many as five different node patterns. Each node pattern is characterized by the number of nodes in the pattern. The node patterns associated with each volume element shape are as follows:

When you set a volume element type, GAMBIT applies the specified mesh node pattern to all volume elements of the specified shape. For example, if you specify 20-node wedge volume elements, GAMBIT locates mesh nodes according to the 20-node pattern for all wedge volume elements produced in the subsequent volume meshing operation.

Figure 3-74, Figure 3-75, Figure 3-76, and Figure 3-77 show the placement of nodes for each of the node patterns listed above.

Figure 3-74: Hexahedron volume element node patterns

Figure 3-75: Wedge volume element node patterns

Figure 3-76: Tetrahedron volume element node patterns

Figure 3-77: Pyramid volume element node patterns

Using the Set Volume Element Type Form

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

The Set Volume Element Type form contains the following specifications.

3.4.4 Link/Unlink Volume Meshes

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

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

Link Volume Meshes

The Link Volume Meshes command allows you to create a hard link between two volumes. When you mesh a volume that is hard-linked to another volume, GAMBIT applies identical mesh parameters to both volumes. The volumes to be linked must satisfy the following criteria:

• They must be topologically identical to each other.
• The corresponding faces of each volume must be hard-linked to each other prior to execution of the Link Volume Meshes command.

Figure 3-78: Example volumes to be hard-linked

To create a hard link between the two volumes, you must first create hard links between face.1 and face.4, face.2 and face.5, and face.3 and face.6. (For instructions on the creation of hard links between faces, see "Link Face Meshes," in Section 3.3.6, above.)

Using the Link Volume Meshes Form

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

The Link Volume Meshes form contains the following specifications.

Unlink Volume Meshes

The Unlink Volume Meshes command allows you to delete an existing link between two volumes. To delete the link, you must specify both volumes associated with the link.

Using the Unlink Volume Meshes Form

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

The Unlink Volume Meshes form contains the following options and specifications.

3.4.5 Modify Meshed Geometry

The Modify Meshed Geometry command allows you to convert exterior mesh edges to topological edges. When you convert a mesh edge to a topological edge, GAMBIT creates a real straight edge the endpoints of which are located at the mesh-node endpoints of the mesh edge.

For a description of the procedures and specifications involved in creating a conversion list, see "Modify Meshed Geometry," in Section 3.3.7, above.

Using the Modify Meshed Geometry Form

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

For a general description of the procedures and specifications involved in using the Modify Meshed Geometry form, see "Using the Modify Meshed Geometry Form," in Section 3.3.7, above.

3.4.6 Summarize Volume Mesh / Check Volume Meshes

The Summarize Volume Mesh / Check Volume Meshes command buttons let you perform the following operations.

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

The Summarize Volume Mesh command displays a summary of volume mesh information in the Transcript window.

Using the Summarize Volume Mesh Form

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

For a general description of the use of the Summarize Volume Mesh form, see Section 3.3.8, above.

The Check Volume Meshes command displays 3-D mesh quality data. When you execute the Check Volume Meshes command, GAMBIT displays the following elements in the Transcript window:

• A table that summarizes 3-D mesh quality statistical information for all volumes specified on the Check Volume Meshes form
• A summary statement that includes the total number of inverted elements and the number of specified volumes that contain inverted mesh elements

The Check Volume Meshes tabular output represents the statistical distribution of element mesh quality values for the current default 3-D quality metric. Table 3.2 shows an example of such output for a volume mesh evaluated according to the EquiAngle Skew quality metric. Output such as that shown in Table 3.2 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).

From value   To value   Count in range     % of total count (1463)
-----------------------------------------------------------------
    0           0.1          286                19.55
    0.1         0.2          671                45.86
    0.2         0.3          341                23.31
    0.3         0.4           88                 6.02
    0.4         0.5           66                 4.51
    0.5         0.6           11                 0.75
    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         1463               100.00

In addition to the tabular output shown in Table 3.2, the Check Volume Meshes command displays the minimum and maximum values of element quality for the set of specified volumes, thus:

Measured minimum value: 0.0274079
Measured maximum value: 0.553874

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 Volume Meshescommand evaluates mesh element quality according to the current default 3-D mesh quality metric. To change the metric used to evaluate element quality for the Check Volume Meshes command, you must modify the default 3-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_3D_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 3-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_3D_QUALITY=2 )
2. Execute the Check Volume Meshes command.

Summary Statement

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

0 out of 2 meshed volumes(s)failed mesh check.

In the context of the Check Volume Meshes command, any volume that includes at least one inverted mesh element fails the mesh check.

Using the Check Volume Meshes Form

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

The Check Volume Meshes form contains the following specification.

Volumes

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

3.4.7 Delete Volume Meshes

The Delete Volume Meshes command allows you to delete the mesh from one or more volumes. When you delete a volume mesh, GAMBIT allows you to retain or delete all face meshes and edge meshes associated with the volume.

Using the Delete Volume Meshes Form

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

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

© Fluent, Inc. 12/21/01