3.4 Using the Global Control Toolpad

The Global Control toolpad (Figure 3-8 and below) allows you to control the layout and operation of the graphics window as well as the appearance of the model as displayed in any individual quadrant. In addition, the Global Control toolpad includes an Undo/Redo button that undoes the most recently executed GAMBIT operation or re-executes the most recently undone operation.

The Global Control toolpad contains two types of command buttons:

• Quadrant
• Control

Global Control toolpad

• Change the overall layout of the graphics window
• Alter the appearance of the model in any individual quadrant
• Undo or redo GAMBIT operations

3.4.1 Quadrant Command Buttons

Quadrant command buttons allow you to enable and disable any or all of the graphics-window quadrants with respect to changes in the model appearance. From left to right on the Global Control toolpad, the quadrant command buttons correspond to the following quadrants:

• Upper left
• Upper right
• Lower left
• Lower right
• All four quadrants (enable only)

Each quadrant command button toggles its corresponding quadrant between the enabled and disabled states. Enabled quadrants are displayed in red on their corresponding command buttons. Disabled quadrants are displayed in gray.

To enable a disabled quadrant or disable an enabled quadrant, click the corresponding quadrant command button. To enable all quadrants, click All.

3.4.2 Control Command Buttons

Control command buttons allow you to specify the appearance of the graphics window itself and of the model as viewed in any individual quadrant. In addition, the Undo/Redo control command button undoes the most recently executed GAMBIT operation or re-executes the most recently undone operation. The Global Control toolpad contains the following control command buttons.

The following sections describe the function and use of the command buttons listed above.

Fit to Window

The Fit to Window command button scales the graphics display to fit in each of the enabled quadrants.

Select Pivot

The Select Pivot command button allows you to change the pivot point around which the model turns when you rotate and/or revolve it using the left and right mouse buttons (see "Rotating the Model (Left-drag)" and "Revolve/Zoom the Model (Right-drag)," above).

GAMBIT allows you to specify either of two points about which to pivot the model.

To define a user-specified pivot point, click the Select Pivot command button to display the user-specified point symbol, then left-click at the selection point in the graphics window to identify the new pivot point location. GAMBIT locates the pivot point according to the following hierarchy of rules:

1. If the selection point intersects one or more coordinate systems, GAMBIT locates the pivot point at the coordinate system closest to the viewer.
2. If the selection point intersects one or more vertices, GAMBIT locates the pivot at the vertex closest to the viewer.
3. If the selection point intersects one or more edges, GAMBIT locates the pivot in reference to the selection point and the nearest edge. GAMBIT uses either the point of intersection as the anchor point or the tangent to the edge at that point as an axis of rotation.
4. If the selection point intersects one or more faces, GAMBIT locates the pivot at the point of intersection with the closest face.
5. If the selection point does not intersect any model components, GAMBIT sets the center of the viewing volume as the pivot point.

To restore the pivot point to its default (quadrant centroid) location, click Select Pivot command button to display the quadrant centroid symbol.

Select Preset Configuration

The Select Preset Configuration command button allows you to modify the overall configuration of the graphics window and the orientation of the model as displayed in the enabled quadrants.

To open the menu of preset configuration options, right-click the Select Preset Configuration button. The preset configuration options include the following configurations and orientations.

Modify Lights

When you click the Modify Lights command button, GAMBIT opens the Modify Lights form. The Modify Lights form allows you to customize the appearance of model shading.

Using the Modify Lights Form

The Modify Lights form (see below) allows you to specify the direction and brightness of eight different light sources used to determine model shading. Each light source is represented on the Modify Lights form by one of eight colors: white, cyan, magenta, blue, yellow, green, red, and black.

The Modify Lights form consists of the following components:

• Status buttons
• Orientation globe

Status Buttons

The Modify Lights form contains eight sets of status buttons corresponding to each of the eight light sources. Each set of status buttons includes the following buttons:

• Light command button
• Ambient and Distant radio buttons

Each Light command button toggles the state of its associated light source between the active (On) and inactive (Off) states. The Ambient and Distant radio buttons constitute mutually exclusive selectors that allow you to specify whether a specific light source is located close to (Ambient) or distant from (Distant) the model.

Orientation Globe

The Modify Lights orientation globe consists of a wireframe sphere upon which are located eight colored circles-each of which is displayed as either solid or hollow. Each circle represents one of the eight light sources. Solid circles represent light sources that are currently specified as On; hollow circles represent light sources that are currently specified as Off.

To reposition any of the eight light sources relative to the model (center of globe) left-click its corresponding circle on the orientation globe and left-drag the circle to the new location. To drag the light source to the side of the globe farthest from the viewer, drag it to the edge of the globe, then back toward the middle. The light source is located on the far side of the globe when it is located on the dashed portion of a circumferential line.

NOTE: If you reposition lights that are Ambient or Off, GAMBIT does not change model shading.

Annotate

When you click the Annotate command button, GAMBIT opens the Annotate form. The Annotate form allows you to add annotation objects such as arrows, lines, or text to any individual graphics window quadrant and to modify or delete such objects.

GAMBIT allows you to perform the following operations with respect to annotation objects.

Adding an Annotation Object

GAMBIT allows you to add the following types of annotation objects:

• Arrow—a straight line or series of connected line segments with a single arrowhead at one end
• Line—a straight line or series of connected line segments without an arrowhead at either end
• Text—alphanumeric text that can be placed anywhere in the graphics window

When you Add an annotation object to a graphics window quadrant, GAMBIT creates the object and fixes its position and orientation at an anchor point relative to the quadrant itself. Annotation objects do not move when you translate, rotate, or zoom in or out on the model. To specify the anchor point, left-click the graphics window at the anchor point.

If you resize a quadrant that contains annotation objects, GAMBIT maintains the positions of the object anchor points relative to the original proportions of the quadrant. However, GAMBIT does not alter Text or Title characters when you resize a quadrant, therefore, the characters retain their original size.

Arrow Object

To add an Arrow annotation object, perform the following steps:

NOTE: To create an arrow consisting of more than one line segment, repeat Step 5 for each endpoint of each intermediate segment. When you Shift-right-click to Apply the arrow annotation object, GAMBIT creates an arrow defined by the series of line segments and possessing a single arrowhead located at the last point selection point.

Line Object

To add a Line annotation object, follow the general directions outlined above with respect to adding an Arrow object but select the Object:Line in lieu of the Object:Arrow option in Step 2. The Line and Arrow annotation objects differ only in that the Line object does not include an arrowhead.

Text Object

To add a Text annotation object, perform the following steps:

NOTE: When you select the Object:Text option, GAMBIT displays a pushbutton labeled "Title" to the right of the Object option button. If you click the Title pushbutton, GAMBIT automatically fills the Text input field with the title of the current GAMBIT session.

Modifying an Annotation Object

To modify an annotation object, perform the following steps:

Deleting an Annotation Object

To delete an annotation object, perform the following steps:

Deleting All Existing Annotation Objects

To delete all existing annotation objects, perform the following steps:

Using the Annotate Form

The Annotate form (see below) allows you to add, modify, or delete annotations to the graphics display. To open the Annotate form, click the Annotate command button on the Global Control toolpad.

The Annotate form includes the following options and specifications.

Using the Set Color Form

The Set Color form allows you to specify the color of an annotation object. To open the Set Color form (see below), click the Color bar on the Annotate form.

The Set Color form includes the following specifications.

NOTE: You must click Apply to apply the color specification and close the form.

Specify Label Type

When you click the Specify Label Type command button, GAMBIT opens the Specify Label Type form. The Specify Label Type form allows you to specify the kinds of labels that are displayed when you display labels by means of the Specify Display Attributes form (see "Specify Display Attributes," below).

GAMBIT allows you to specify the display of any or all of the following types of labels.

To display a label, you must specify the label type, by means of the Specify Label Type form, and activate labels for the entity (or entities) of interest, by means of the Specify Display Attributes form. For example, to display the numbers of mesh intervals for all edges in the model, you must select the Interval options on the Specify Label Type form, then activate labels for all edges by means of the Specify Display Attributes form.

NOTE (1): If the Label option on the Specify Display Attributes form is On, changes made on the Specify Label Type form affect the model display as soon as they are specified.

NOTE (2): The Specify Label Type form specifications do not affect coordinate system labels.

Using the Specify Label Type Form

The Specify Label Type form (see below) allows you to specify the types of labels that are displayed by means of the Specify Display Attributes form. To open the Specify Label Type form, click the Label Type command button on the Global Control toolpad.

The Specify Label Type form consists of a field of check boxes that allow you to specify the display of the following label types (see above):

• Regular
• Scheme
• Interval
• Boundary Layer
• Size Function
• Boundary Type
• Continuum Type

Undo

The Undo command undoes GAMBIT operations in reverse order relative to their sequence of execution.

Overview

When you click the Undo command button, GAMBIT reverses the most recently executed operation. For example, if you create a vertex and click Undo, GAMBIT deletes the vertex.

Multiple Undo Operations

As you create and/or mesh a model, GAMBIT maintains and updates an "undo" list-that is, a first-in/last-out sequential list of Geometry, Mesh, Zones, Tools and Global Control commands performed during the modeling session. When you execute the Undo command, GAMBIT reverses the most recently executed operation and removes it from the undo list. If you execute the Undo command a second time, GAMBIT reverses and removes from the undo list the operation that you performed immediately prior to the most recently executed operation-and so on. For example, if you create and mesh a cylindrical volume, then click Undo, GAMBIT removes the mesh from the volume. If you click Undo a second time, GAMBIT deletes the volume.

By default, GAMBIT maintains 10 undo levels--that is, the undo list contains the 10 most recently executed operations. To increase or decrease the number of operations retained in the undo list, modify the GAMBIT UNDO default variable by means of the Edit Defaults form (see Section 4.2.4).

NOTE: Increasing the number of undo levels necessarily increases the amount of disk space required by the GAMBIT program.

Redo

The Redo command reverses the most recently executed GAMBIT Undo operation.

Overview

When you click the Redo command button, GAMBIT reverses the most recently executed Undo operation. For example, if you create a vertex and click Undo, GAMBIT deletes the vertex. If you then click Redo, GAMBIT restores the vertex to the model.

Multiple Redo Operations

GAMBIT allows you to Redo multiple-operation sequences that are undone by means of the Undo operation. For example, if you create and mesh a cylindrical volume, then click Undo, GAMBIT removes the mesh from the volume. If you click Undo a second time, GAMBIT deletes the volume. If you then click Redo, GAMBIT restores the volume, and if you click Redo a second time, GAMBIT restores the mesh.

By default, GAMBIT allows you to undo the 10 most recently executed operations and to Redo the 10 most recently executed Undo operations. To increase or decrease the number of operations that can be undone and/or redone, modify the GAMBIT UNDO default variable by means of the Edit Defaults form (see Section 4.2.4).

NOTE: Increasing the number of undo levels necessarily increases the amount of disk space required by the GAMBIT program.

Orient Model

The Orient Model command button allows you to apply a preset model orientation to all currently enabled quadrants, to orient the model with respect to a specified face or vector, and to store commands related to the current orientation in a journal file.

To open the menu of Orient Model options, right-click the Orient Model command button. The Orient Model menu includes the following options.

Using the View Face/Vector Form

The View Face/Vector option allows you to view the model from a direction normal to any one of the model faces or in relation to a specified vector. When you select the View Face/Vector on the Orient Model menu, GAMBIT opens the View Face/Vector form (see below). The View Face/Vector form allows you to specify the face toward which or vector along which the model is to be viewed.

The View Face/Vector form includes the following options:

Normal to Face Option

The Normal to Face option allows you to orient the model in the direction normal to a specified face. For instructions in specifying the face that defines the view direction, see "List Boxes," above. (NOTE: When you specify the Normal to Face option, GAMBIT scales the model to fit in the enabled quadrants when it reorients the model.)

Along Vector Option

The Along Vector option allows you to view the model in the direction of a specified vector. GAMBIT orients the model so that the specified vector is normal to the plane of the screen.

When you select the Along Vector option, GAMBIT displays a Define command button immediately below the Along Vector button. To specify the vector in the direction of which the model is to be viewed, click the Define command button to open the Vector Definition form. (See "Using the Vector Definition Form," below.)

Using the Vector Definition Form The Vector Definition form (see below) allows you to define a vector for use in GAMBIT operations such as model orientation or the specification of axes of rotation (for example, see Section 2.1.4 of the GAMBIT Modeling Guide). To define a vector, you must specify information regarding its magnitude and direction, as well as the location of its origin. GAMBIT provides several options for specifying such information).

The Vector Definition form includes the following specifications.

Active Coordinate System Vector	displays the coordinates of the origin (Start) and tip (End) for the current vector definition. (NOTE: The Start and End locations are always defined in terms of the active coordinate system.)
Magnitude	specifies the magnitude of the vector. (NOTE: If you input a negative value for the Magnitude parameter, GAMBIT reverses the direction of the vector relative to its Method-option definition but does not change the location of the vector origin.)
Method:	---------------------------------------------
Coord. Sys. Axis Edge 2 Points 2 Vertices Screen View	specifies the method to be used for specifying the vector endpoints. The available options are as follows: Coord. Sys. Axis—defines the vector with respect to one of the coordinate axes Edge—defines the vector by means of the endpoints of an existing edge 2 Vertices—defines the vector by means of two existing vertices 2 Points—defines the vector by means of two specified locations (points) in space Screen View—defines the vector relative to the model orientation currently displayed in the graphics window

The specifications available in the lower section of the Vector Definition form vary according to Method option. The following subsections describe specifications associated with each of the options listed above.

Specifying a Vector Defined by a Coordinate System Axis

When you select the Coord. Sys. Axis option, GAMBIT defines the vector with respect to a coordinate axis. To define the vector, you must specify the following information:

• The coordinate system to be used in defining the vector
• The axis and direction that defines the vector

For this option, the lower portion of the Vector Definition form appears as shown above and includes the following specifications.

Coordinate Sys.

specifies the reference coordinate system for the vector.

Direction:

contains radio buttons that allow you to specify the axis and direction to be used in the vector definition. The available options are as follows: X—Positive or Negative Y—Positive or Negative Z—Positive or Negative For example, if you specify c_sys.1 in the Coordinate Sys. list box and select the Z Negative orientation option, GAMBIT defines a vector that points in the negative direction along the z axis of c_sys.1 with an origin at the origin of c_sys.1.

Specifying a Vector Defined by a Model Edge

When you select the Edge option, GAMBIT defines the vector by means of the endpoint vertices of an existing edge. For this option, the lower portion of the Vector Definition form appears as shown below and includes the following specification.

Vector Definition form—Edge option specification

Edge

specifies an edge the endpoints of which define the origin, magnitude, and direction of the vector. The origin of the vector is located at the edge start endpoint vertex, and its tip is located at its end endpoint vertex. To reverse the direction of the vector, either middle-click the edge to reverse its sense or input a negative value for the Magnitude specification. (For a description of edge start and end vertices and the meaning of edge sense, see Section 2.3.1 of the GAMBIT Modeling Guide.)

Specifying a Vector Defined by Two Vertices

When you select the 2 Vertices option, GAMBIT defines the vector by means of the locations of two existing vertices. For this option, the lower portion of the Vector Definition form appears as shown below and includes the following specifications.

Vector Definition form—2 Vertices option specifications

Vertices:

contains two list boxes that specify vertices defining the origin (Start) and tip (End) of the vector. (NOTE: To reverse the direction of the vector, either switch the Start and End vertex specifications or input a negative value for the Magnitude specification.)

Specifying a Vector Defined by Two Points

When you select the 2 Points option, GAMBIT defines the vector by means of two point locations. For this option, the lower portion of the Vector Definition form appears as shown below and includes the following specifications.

Vector Definition form—2 Points option specifications

Coordinate Values:	contains two radio buttons that specify the point associated with the values currently displayed in the lower part of the form. The options, Point 1 and Point 2, specify the positions of the vector origin and tip, respectively. (NOTE: To reverse the direction of the vector, either switch the specifications for the two points or input a negative value for the Magnitude specification.)
Coordinate Sys	specifies the coordinate system of reference for the points that define the vector.
Type	------------------------------------------------------
Cartesian Cylindrical Spherical	specifies the type of coordinate system to be used in the current point specification.
Global | Local	specifies the location of the point with respect to either the Global or Local system.

Specifying a Vector Defined by the Current Screen View

When you select the Screen View option, GAMBIT defines the vector relative to the current orientation of the model in the graphics window. For this option, the lower portion of the Vector Definition form appears as shown below and includes the following specifications.

Vector Definition form—Screen View option specifications

Direction:

contains a group of paired radio buttons that allow you to specify the vector definition relative to the currently displayed orientation of the model in the graphics window. The six Direction options are as follows: Piercing—Out or In Horizontal—Right or Left Vertical—Up or Down For example, if you select the Piercing--In option and left-click on a graphics window quadrant, GAMBIT defines a vector pointing directly into the screen with an origin located in the center of the quadrant.

Specify Display Attributes

When you click the Specify Display Attributes command button, GAMBIT opens the Specify Display Attributes form (see below). The Specify Display Attributes form allows you to customize the appearance of the model in any currently enabled quadrant.

Using the Specify Display Attributes Form

The Specify Display Attributes form allows you to customize the appearance of the model in any or all of the graphics windows quadrants. It includes the following options.

The middle section of the Specify Display Attributes form allows you to select individual model entities or entire entity types for display specification. The available entity-type options include groups (Groups), volumes (Volumes), faces (Faces), edges (Edges), vertices (Vertices), boundary layers (B. Layers), and coordinate systems (C. Sys).

Specifying Display Attributes--Groups Example

The options available for each entity type are identical to those for model groups—which are as follows.

Render Model

The Render Model command allows you to render the model as either shaded, wireframe, or hidden. The symbol displayed on the Render Model command button indicates its current function. To change the function of the button, right-click it to open the menu of available functions, then select the desired function from the menu. When you select a function from the menu, GAMBIT automatically renders the model according to the selected function.

Specify Color Mode

The Specify Color Mode command button allows you to toggle between two modes of defining color for the lines, curves, and points as displayed in the active graphics-window quadrants. The two color modes are as follows:

• Topology—specifies that the colors displayed for vertices, edges, faces, and volumes correspond to the hierarchy of model entities.
• Connectivity—specifies that model colors are based on connectivity between entities.

Topology Mode

In the topology color mode, GAMBIT displays entity colors according to the GAMBIT geometry color conventions. The default topology color conventions are as follows.

You can change the default topology color conventions by means of the Edit Defaults form (see "Using the Edit Defaults Form" in Section 4.2.4).

The colors listed in the table above correspond to only those entities that do not constitute parts of higher-topology entities. For example, if an edge exists on its own, it is displayed as yellow, but if it constitutes part of a face, it is displayed as cyan.

Connectivity Mode

In the connectivity color mode, GAMBIT displays colors based on the connectivity between entities. The default connectivity color conventions are as follows.

For example, in the connectivity color mode, lone vertices are white but any vertex that constitutes an endpoint for two separate edges is colored orange. Similarly, lone edges are white, but an edge that an edge that is shared by three separate faces is colored deepskyblue.

If two coincident entities differ in the degree of their connectivity to other entities in the model, GAMBIT displays the color corresponding to the least-connected entity. For example, if a lone vertex is coincident with the corner vertex of a four-sided face, GAMBIT displays a white vertex at the location of coincidence.

NOTE (1): GAMBIT determines connectivity coloration for any entity on the basis of the number of sides of the entity that are connected to higher entities. If you create a face that includes a dangling edge, GAMBIT assigns the dangling edge a connectivity color of deepskyblue, because the face itself exists on two separate sides of the edge.

NOTE (2): You can change the default connectivity color conventions by means of the Edit Defaults form (see "Using the Edit Defaults Form" in Section 4.2.4).

Examine Mesh

When you click the Examine Mesh command button, GAMBIT opens the Examine Mesh form (see below). The Examine Mesh form allows you to display an existing mesh and to customize the characteristics of the mesh display.

To display a mesh by means of the Examine Mesh form, you must specify two major sets of parameters:

• Display Type
• Display Mode

The Display Type parameters determine which mesh elements are visible when the mesh is displayed. The Display Mode parameters determine the visual appearance of elements that are displayed.

Specifying the Display Type

There are three general Display Type specifications on the Examine Mesh form:

• Domain
• Element type
• Quality type

The domain specification allows you to define which region of the mesh is displayed. The element-type specification determines which element shapes are included in the group of displayed elements. The quality-type specification determines the quality criterion that is used to color displayed elements and/or to define which elements are displayed.

The following sections describe each of the specifications listed above.

Specifying the Domain

The domain specification consists of the following options:

• Plane
• Sphere
• Range

The Plane and Sphere options allow you to display mesh elements located relative to a planar or spherical cut through the mesh. The Range option allows you to display only those mesh elements the quality of which falls within specified limits with respect to a designated quality criterion.

The following sections describe the each of the options listed above and illustrate their relative effects on the mesh display for the elliptical cylinder shown in Figure 3-14. (NOTE: In this example, the cross section of the cylinder is elongated with respect to the x axis, and the cylinder is aligned with the z axis.)

Figure 3-14: Meshed elliptical cylinder

Plane Option

When you select the Plane option, GAMBIT displays a plane cut through the mesh. To customize the plane cut, you must specify two parameters:

• Cut Type
• Cut Orientation

The Cut Type specification determines whether GAMBIT displays a zero-thickness plane cut through the mesh or an array of mesh elements defined by their position with respect to the cutting plane. The Cut Orientation specification allows you to align the cutting plane with one of the three planes of the active coordinate system and to specify the position of the cutting plane.

Specifying the Cut Type

To specify the Cut Type, you must select one of the following options:

• Display cut
• Display elements

Display cut Option

Figure 3-15: Plane cut—Cut Type: Display cut option, y-z plane

You can align the cutting plane with any of the three Cartesian coordinate planes by means of the Cut Orientation slider bars (see "Specifying the Cut Orientation," below).

Display elements Option

A set of radio buttons corresponding to the Display elements suboptions is located above the Cut Orientation slider bars in the lower section of the Examine Mesh form. To select a Display elements suboption, click its corresponding radio button.

Figure 3-16 and Figure 3-17 show the effect of the 0 and - suboptions, respectively, on the mesh display for the elliptical cylinder shown in Figure 3-14. In both figures, the cutting plane is centered in the cylinder and aligned with the y-z plane.

Figure 3-16: Plane cut—Cut Type: Display elements, y-z plane, Suboption (0)

Figure 3-17: Plane cut—Cut Type: Display elements, y-z plane, Suboption (-)

NOTE: When you select the Display elements option, GAMBIT displays only those elements that meet both the domain and element type specifications currently specified in the Display Type field on the Examine Mesh form. For example, if you select the Plane option and specify the display of pyramidal elements only, GAMBIT displays only those mesh elements that are pyramidal in shape and are intersected by the specified cutting plane. (See "Specifying the Element Type," below.)

Specifying the Cut Orientation

To specify the Cut Orientation, you must specify the alignment and position of the cutting plane. The alignment and position specifications determine the following characteristics of the cutting plane:

• Alignment relative to the planes of the active coordinate system
• Location in the model domain

The alignment and position of the cutting plane are specified by means of the Cut Orientation slider bars located in the lower section of the Examine Mesh form (see above). There are three Cut Orientation slider bars, labeled X, Y, and Z.

GAMBIT allows you to align the cutting plane such that it is parallel to any one of the three coordinate planes of the active coordinate system. To orient the cutting plane, click the slider box corresponding to the axis that is normal to the desired coordinate plane. For example, to orient the reference plane such that it is parallel to the x-y coordinate plane (Figure 3-18), click the slider box labeled Z.

Figure 3-18: Plane cut—Cut Type: Display elements, x-y plane

To reposition the cutting plane in the model domain, left-drag the slider box to the left or right. When you left-drag the slider box, GAMBIT automatically updates the graphics window mesh display to reflect the current position of the box. To change the position of the cutting plane in increments, left-click the slider bar on either side of the slider box.

NOTE: If you activate a coordinate system other than the currently active system, GAMBIT automatically updates the orientation of the cutting plane with reference to the newly active system.

Sphere Option

• Cut Type
• Cut Orientation

The Cut Type specification determines whether GAMBIT displays a zero-thickness spherical shell or an array of mesh elements defined by their position with respect to the shell. The Cut Orientation specification allows you to position the center of the sphere and to specify the radius of the sphere.

Specifying the Cut Type

• Display cut
• Display elements

The spherical-cut Display cut and Display elements options produce effects similar to those of the corresponding plane-cut options but differ as outlined below.

Display cut Option

Figure 3-19: Sphere cut—Cut Type: Display cut option

The lines shown on the surface of the spherical cut represent lines of intersection between the sphere and either the mesh-element faces or the geometrical boundaries of the model components. You can position the sphere within the model domain and specify its radius by means of the Cut Orientation slider bars (see "Specifying the Cut Orientation," below).

Display elements Option

A set of radio buttons corresponding to the Display Elements suboptions is located above the Cut Orientation slider bars in the lower section of the Examine Mesh form. To select a Display elements suboption, click its corresponding radio button.

Figure 3-20, Figure 3-21, and Figure 3-22 show the effect of the -, 0, and + suboptions, respectively, on the mesh display for the elliptical cylinder shown in Figure 3-14. In each figure, the cutting sphere is located in the center of the cylinder, and its radius is that shown in Figure 3-19, above.

Figure 3-20: Sphere cut—Cut Type: Display elements, Suboption (-)

Figure 3-21: Sphere cut—Cut Type: Display elements, Suboption (0)

Figure 3-22: Sphere cut—Cut Type: Display elements, Suboption (+)

NOTE: When you select the Display elements option, GAMBIT displays only those elements that meet both the domain and element type specifications currently specified in the Display Type field on the Examine Mesh form. For example, if you select the Sphere option and specify the display of pyramidal elements only, GAMBIT displays only those mesh elements that are pyramidal in shape and are intersected by the specified cutting sphere. (See "Specifying the Element Type," below.)

Specifying the Cut Orientation

When you specify a Sphere cut, GAMBIT displays four Cut Orientation slider bars, labeled X, Y, Z, and R. The X, Y, and Z slider bars allow you to specify the position of the center of the sphere relative to the axes of the active coordinate system. The R slider bar allows you to specify the radius of the sphere.

Range Option

Figure 3-23: Elliptical cylinder mesh—Range option

To display mesh elements by means of the Range option, you must specify the following parameters:

• Quality criterion
• Range

To specify the quality criterion, you must use the Quality Type option button located at the bottom of the Display Type field (see "Specifying the Quality Type," below). To define the range, you must specify its lower and upper limits by means of the range components located in the lower section of the Examine Mesh form (see below).

When you select the Range option, GAMBIT displays two types of range components on the Examine Mesh form:

• Histogram
• Lower and Upper limit slider bars

Histogram

The range histogram consists of a bar chart representing the statistical distribution of mesh elements with respect to the specified quality criterion. Each vertical bar on the histogram corresponds to a unique set of lower and upper quality limits. To display those elements the quality of which falls within the limits represented by any vertical bar on the histogram, left-click the corresponding bar.

Lower and Upper Limit Slider Bars

The Lower and Upper limit slider bars allow you to specify the lower and upper limits of the quality range that determines which elements are displayed in the graphics window. To specify the Lower or Upper limit of the range, left-drag the appropriate slider box to the desired location. To change the Lower or Upper limit of the range incrementally, left-click the appropriate slider bar on either side of the corresponding slider box.

NOTE: If the Lower value is greater than the Upper value, GAMBIT simultaneously displays those elements with quality values less than the Upper value and greater than the Lower value.

Specifying the Element Type

• Class
• Shape

The class specification determines whether GAMBIT displays face elements or volume elements. The shape specification determines which element shapes are included in the set of displayed elements.

Class

• 2D Element
• 3D Element

Each class is associated with its own set of available element shapes (see below). To specify a class, left-click the class option button in the Display Type field and select either the 2D Element or 3D Element option.

Shape

The following table shows the element shapes corresponding to each element class.

When you display mesh elements by means of the Examine Mesh form, GAMBIT displays only those elements the shapes of which match the current element-type specifications. For example, if you specify a plane cut according to the following parameters:

GAMBIT displays only those volume elements that meet both of the following criteria:

• Intersected by the specified plane
• In the shape of either a brick or a wedge

Similarly, if you specify a plane cut according to the following parameters:

GAMBIT displays only those face elements that are intersected by the specified plane and possess a quadrilateral shape (see Figure 3-24).

Figure 3-24: Plane cut, y—z plane-2D Element, Quad

Specifying the Quality Type

• Which elements are displayed by means of the domain Range option (see "Range Option," above)
• The coloration of elements for faceted mesh displays (see "Faceted Option," below.)

The following sections describe the quality types available in GAMBIT and the correspondence between quality types and the mesh element types described in the previous section.

Quality Type Definitions

• Area
• Aspect Ratio
• Diagonal Ratio
• Edge Ratio
• EquiAngle Skew
• EquiSize Skew
• MidAngle Skew
• Stretch
• Taper
• Volume
• Warpage

The following sections summarize the definitions and characteristics of each of the specifications listed above.

Area

Aspect Ratio

Triangular and Tetrahedral Elements

where f is a scaling factor, and r and R represent the radii of the circles (for triangular elements) or spheres (for tetrahedral elements) that inscribe and circumscribe, respectively, the mesh element. For triangular elements, ; for tetrahedral elements, .

By definition,

where describes an equilateral element.

Quadrilateral and Hexahedral Elements

where is the average length of the edges in a coordinate direction (i) local to the element (see Figure 3-25) and n is the total number of coordinate directions associated with the element. For quadrilateral elements, n = 2; for hexahedral elements, n = 3.

Figure 3-25: Aspect Ratio ()—quadrilateral element

Again, by definition,

.

where describes an equilateral element.

Diagonal Ratio

where the are the lengths of the element diagonals. For quadrilateral elements, ; for hexahedral elements, .

By definition,

.

The higher the value of , the less regularly shaped is its associated element. For square quadrilateral elements and cubic hexahedral elements, .

Edge Ratio

where represents the length of the element edge i, and n is the total number of edges associated with the element.

By definition,

.

The higher the value of , the less regularly shaped is its associated element. For equilateral element shapes, .

EquiAngle Skew

where and are the maximum and minimum angles (in degrees) between the edges of the element, and is the characteristic angle corresponding to an equilateral cell of similar form. For triangular and tetrahedral elements, . For quadrilateral and hexahedral elements, .

By definition,

where describes an equilateral element, and describes a completely degenerate (poorly shaped) element.

NOTE: For pyramidal mesh elements, is equal to its maximum value for any of the five faces of the mesh element. In an ideal pyramidal mesh element, all four triangular faces are equilateral and the base of the pyramid is a square.

Table 3-1 outlines the overall relationship between and element quality.