2.4 Face Commands

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

2.4.1 Form Face

The Form Face command button allows you to perform the following operations.

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

Create Face From Wireframe

The Create Face From Wireframe command allows you to create a face from three or more existing edges.

To create a face by means of the Create Face From Wireframe option, you must specify the following parameters:

• The edges that define the wireframe
• The face type—real or virtual

Specifying Edges of the Wireframe

GAMBIT employs the following rules for specifying edges used to create a face by means of the Create Face From Wireframe option.

• The sequence in which you specify the wireframe edges does not affect the final form of the face.
• The edges do not have to be connected to each other, but each edge must possess endpoint vertices that are coincident with the endpoint vertex of one other specified edge (see Figure 2-53).

Figure 2-53: Wireframe endpoint vertex requirements

Specifying the Face Type

GAMBIT allows you to create both real and virtual faces using the Create Face From Wireframe command. To create a real face, you must specify only real edges for the wireframe. To create a virtual face, you can specify any combination of real and/or virtual edges for the wireframe.

Creating a Real Face

The following rules apply to the creation of a real face.

• To construct a real face, you must specify only real edges for the wireframe.
• If the specified edges are not coplanar, GAMBIT applies the following rules with respect to the creation of the face.
• If you specify only two edges, GAMBIT attempts to construct a skin-surface face. (See "Create Real Skin Surface Face," below.)
• If you specify three or four edges, GAMBIT checks the orientation of the edges to determine whether the edges meet with tangent continuity at their endpoints. If the edges don't meet with tangent continuity, GAMBIT does not create the face.

Creating a Virtual Face

If you specify the creation of a virtual face, you can also specify a host face or volume.

• If you do not specify a host face or volume, GAMBIT creates an orphan face—the shape of which is defined only by means of its boundary edges.
• If you specify a host face or volume, GAMBIT creates a parasite face and employs the existing geometry (shape) of the host entity to define the shape of the virtual face.

Specifying the Tolerance Value

If you specify a host face for the creation of a virtual face, GAMBIT allows you to specify a Tolerance value. The tolerance value consitutes the maximum allowable distance between the wireframe edges and the surface of the host face.

Using the Create Face From Wireframe Form

To open the Create Face From Wireframe form (see below), click the Create Face From Wireframe command button on the Geometry/Face subpad.

The Create Face From Wireframe form includes the following specifications.

Create Real Parallelogram Face

The Create Real Parallelogram Face command allows you to create a real, four-sided face in the shape of a parallelogram.

To create a face by means of the Create Real Parallelogram Face option, you must specify three existing real vertices that define the face. The vertices are designated as Origin, Base, and Inclineand are defined as shown in Figure 2-54.

Figure 2-54: Parallelogram—face vertex definitions

The edges formed in the creation of the face are defined such that their senses are from the Origin vertex to the Base vertex and from the Incline vertex to the Origin vertex. If you reverse the specifications regarding which vertices constitute the Base and Incline vertices, respectively, the shape of the resulting face does not change, but GAMBIT reverses the sense of each of its edges.

Using the Create Real Parallelogram Face Form

To open the Create Real Parallelogram Face form (see below), click the Create Real Parallelogram Face command button on the Geometry/Face subpad.

The Create Real Parallelogram Face form includes the following specifications.

The Create Real Polygon Face command allows you to create a planar, polygonal face defined by a set of existing real vertices. (NOTE: If you specify a set of five or more vertices, all vertices in the set must be coplanar.)

To execute the Create Real Polygon Face command, you must specify a set of at least three vertices. To create the polygonal face, GAMBIT first creates a closed loop of edges that join the specified vertices then creates a face bounded by the closed loop.

The order in which the vertices are specified on the Create Real Polygon Face form determines the order in which the bounding edges are created— which, in turn, affects the shape of the created face. As an example of this effect, consider the set of six vertices shown in Figure 2-55(a).

Figure 2-55: Effect of vertex specification sequence

Figure 2-55(b) and Figure 2-55(c) show two example faces created using the vertex specification sequences listed in the following table.

To open the Create Real Polygon Face form (see below), click the Create Real Polygon Face command button on the Geometry/ Face subpad.

The Create Real Polygon Face form includes the following specifications.

The Create Real Circular Face From Vertices command allows you to create a planar face in the shape of a full circle.

GAMBIT provides two methods for creating a face in the shape of a full circle. Both methods require you to specify three existing vertices to define the size and location of the circle. The methods are defined as follows:

• Method 1—specifies one vertex that constitutes the center of the circle and two vertices that lie on the circular edge that bounds the face
• Method 2—specifies three vertices that lie on the circular edge that bounds the face

Method 1 (Figure 2-56(a)) requires that the two vertices that lie on the circular bounding edge are equidistant from the vertex at the center of the circle. Method 2 (Figure 2-56(b)) requires only that the three specified vertices are not collinear.

Figure 2-56: Circular face specifications

To open the Create Real Circular Face From Vertices form (see below), click the Create Real Circular Face From Vertices command button on the Geometry/ Face subpad.

The Create Real Circular Face From Vertices form includes the following specifications.

The center section of the Create Real Circular Face From Vertices form varies according to the method selected to construct the bounding circle. The specifications available on the center section of the form are as follows.

When you specify Method 2 for the creation of a circular face, the middle section of the Create Real Circular Face From Vertices form appears as shown below.

The Create Real Elliptical Face From Vertices command allows you to create a face that represents a section of a full ellipse.

To create an elliptical face, you must specify the following parameters (see Figure 2-57):

• Center vertex—located at the center of the full ellipse
• Major vertex—defines the length of the major axis
• On Edge vertex—defines the dimensions of the full ellipse
• Start Angle and Stop Angle— define the size and location of the elliptical section that bounds the face

Figure 2-57: Elliptical face specifications

The Center, Major, and On Edge vertices define the shape and size of the full ellipse of which the face constitutes a section. The Start Angle and Stop Angle define the size and position of the face relative to the Center vertex and major axis. (NOTE: The three vertices that define the ellipse must not be collinear.)

To open the Create Real Elliptical Face From Vertices form (see below), click the Create Real Elliptical Face From Vertices command button on the Geometry/ Face subpad.

The Create Real Elliptical Face From Vertices form includes the following specifications.

Create Real Skin Surface Face

The Create Real Skin Surface Face command allows you to create a real, four-sided face by specifying a series of edges that define its surface.

Specifying Edges for a Skin-Surface Face

To create a face by means of the Create Real Skin Surface Face option, you must specify two or more existing edges that define the face. The first and last edges that you specify comprise two of the four sides of the face. The other two sides consist of continuous curves fit through the start and end endpoint vertices of all specified edges. The surface of the created face constitutes an interpolation through all of the edges specified for the face.

As an example of edge specification for the Create Real Skin Surface Face operation, consider the four edges shown in Figure 2-58(a). If you use all four edges to create a face by means of the Create Real Skin Surface Face operation, GAMBIT creates a face such as that shown in Figure 2-58(b).

Figure 2-58: Create Skin Surface Face edge specifications

The first and last edges specified (1 and 4, respectively) comprise two of the four boundary edges of the skin-surface face. The other two boundary edges (5 and 6) consist of continuous curves constructed through the endpoint vertices of the original four edges.

NOTE (1): The order in which you specify edges determines the shape of the resulting face. For example, to create the face shown in Figure 2-58(b), you must specify the edges in the order (1, 2, 3, 4) or (4, 3, 2, 1), rather than (1, 4, 2, 3) or (3, 2, 1, 4).

NOTE (2): GAMBIT ignores edge sense when creating a face by means of the Create Skin Surface Face operation. For example, the final shape of the face shown in Figure 2-58(b) is independent of the senses of the edges that define its surface.

Using the Create Real Skin Surface Face Form

To open the Create Real Skin Surface Face form (see below), click the Create Real Skin Surface Face command button on the Geometry/Face subpad.

The Create Real Skin Surface Face form includes the following specifications.

Create Real Net Surface Face

The Create Real Net Surface Face command allows you to create a real, four-sided face by specifying two sets of logically parallel edges that define the boundaries and shape of its surface.

Specifying Edges for a Net-Surface Face

To create a face by means of the Create Real Net Surface Face option, you must specify two or more sets of existing edges that define the shape of the face. Each set must include at least two edges. The surface of the created face constitutes an interpolation through all of the edges specified for the face.

As an example of edge specification for the Create Real Net Surface Face operation, consider the edges shown in Figure 2-59(a). The figure consists of nine edges, four of which (designated by the letter u) are logically perpendicular to the other five (designated by the letter v).

Figure 2-59: Create Net Surface Face edge specifications

If you use all four edges in the u direction and all five edges in the v direction to create a net-surface face, GAMBIT creates a face such as that shown in Figure 2-59(b). If you specify edges in either direction the lengths of which exceed the boundary defined by the first or last edges specified in the other direction, GAMBIT truncates the created face. As an example of such truncation, consider the edges shown in Figure 2-59(a), above. If you specify edges 2, 3, and 4 in the u direction and edges 2, 3, 4, and 5 in the v direction, GAMBIT creates the net-surface face shown in Figure 2-59(c). Note that the final form of the net-surface face approximates the intersection of skin-surface faces created by means of edges 2, 3, and 4 in the u direction and edges 2, 3, 4, and 5 in the v direction.

NOTE (1): To create a face by means of the Create Net Surface Face operation, you must specify the edges monotonically in each direction with respect to their relative positions in defining the face. For example, to create the face shown in Figure 2-59(b), you must specify the u-direction edges in the order (1, 2, 3, 4) or (4, 3, 2, 1) and the v-direction edges in the order (1, 2, 3, 4, 5) or (5, 4, 3, 2, 1).

NOTE (2): GAMBIT ignores edge sense when creating a face by means of the Create Net Surface Face operation. For example, the final shape of the face shown in Figure 2-59(b) is independent of the senses of the edges that define its surface.

Specifying the Tolerance Option

If the edges in the u direction do not exactly intersect the edges in the v direction (or vice versa), you must select the Tolerance option and specify a tolerance value. The tolerance value is the maximum allowable distance between any of the edges and the resulting face.

Using the Create Real Net Surface Face Form

To open the Create Real Net Surface Face form (see below), click the Create Real Net Surface Face command button on the Geometry/Face subpad.

The Create Real Net Surface Face form includes the following specifications.

Create Real Face From Vertex Rows

The Create Real Face From Vertex Rows command allows you to create a four-sided face by specifying a series of vertex rows that define the surface of the face.

To create a face by means of the Create Real Face From Vertex Rows option, you must specify the following parameters:

• A sequence of vertices that define the face
• The number of rows of vertices to be used in defining the face
• The method used to fit curves through the vertices that define the face

The vertex locations define the overall shape of the face. The number of rows determines the shape and numbering of the edges created in the creation of the face.

Specifying the Vertex Sequence

When you specify vertices for the Create Real Face From Vertex Rows operation, you must select the vertices in an ordered sequence that represents the position of each vertex in a sequential series of rows. That is, you must specify all the vertices that constitute the first row, then all the vertices that constitute the second row, and so on.

The first and last rows of vertices specified define edges that comprise two of the four sides of the face. The other two sides of the face consist of continuous curves fit through two sets of vertices defined as follows:

• The first vertex specified in each row
• The last vertex specified in each row

As an example of vertex specification for the Create Real Face From Vertex Rows operation, consider the face shown in Figure 2-60. The face is defined by four rows of three vertices each. The numbers associated with the vertices in the figure indicate the sequence in which the vertices are specified when creating the face.

Figure 2-60: Create Real Face From Vertex Rows specifications—4 rows

Specifying the Number of Vertex Rows

When you create a face by means of the Create Real Face From Vertex Rows operation, you must specify the number of rows represented by the specified vertices. The total number of vertices must represent an integer multiple of the number of vertex rows. For example, if you specify a total of 12 vertices, you must specify either 2, 3, 4, or 6 vertex rows. The number of vertices in each row is equal to the total number of vertices divided by the number of rows.

It is possible to create a face of a given shape using two different specifications for the number of rows. For example, the face shown in Figure 2-61 represents a face created from the same set of vertices employed to create the face in Figure 2-60. The face differs from the face in Figure 2-60 in that it is created by specifying three rows of four vertices each rather than four rows of three vertices each.

Figure 2-61: Create Real Face From Vertex Rows specifications—3 rows

Although the shapes of the two faces are identical to each other, they differ in two respects:

• The sequence in which the vertices are specified
• The numbering of the edges created in the creation of the face

Specifying the Curve Fit Method

GAMBIT allows you to specify one of two methods by which curves are fit through the vertex rows to define the face. The two methods are as follows.

• Interpolate
• Approximate

If you select the Approximate method, you must also specify a Tolerance value. (For a description of the Interpolate and Approximate methods and the Tolerance value, see "Specifying the Curve Construction Method" in Section 2.3.1, above.)

Using the Create Real Face From Vertex Rows Form

To open the Create Real Face From Vertex Rows form (see below), click the Create Real Face From Vertex Rows command button on the Geometry/ Face subpad.

The Create Real Face From Vertex Rows form includes the following specifications.

Revolve Edges

The Revolve Edges command allows you to create real, two-, three-, or four-sided faces by revolving existing edges about a specified axis.

To create a face by means of the Revolve Edges option, you must specify the following parameters:

• One or more real or non-real edges to be revolved
• The axis of rotation
• The angle through which the edges are revolved about the axis

When you create a face by revolving an edge, GAMBIT sweeps the edge through the specified angle of rotation (see Figure 2-62). One of the edges that GAMBIT creates in the process of creating the face is a duplicate of the edge to be revolved. The other two edges are circular arc edges centered at the axis of rotation. If the axis of rotation passes through either endpoint of an edge to be swept, GAMBIT does not execute the Revolve Edges operation.

Figure 2-62: Revolve Edge operation

Specifying Edges to Be Revolved

To create faces by means of the Revolve Edges form, you must specify one or more real or non-real edges to be revolved about the axis of rotation. GAMBIT creates a separate face corresponding to each specified edge. The specified edges can be straight or curved, and they do not have to be coplanar with the axis of rotation.

NOTE: If you revolve a non-real edge to create a face, GAMBIT first creates a real copy of the non-real edge, then revolves the real copy to create the face.

Specifying the Axis and Angle of Rotation

To specify the axis of rotation, you must define the axis by means of the Vector Definition form. For a description of the Vector Definition form and its operation, see "Using the Vector Definition Form" in Section 2.1.4. The conventions regarding the angle of rotation for the Revolve Edges operation are identical to those described in "Rotating an Entity" in Section 2.1.4.

Using the Revolve Edges Form

To open the Revolve Edges form (see below), click the Revolve Edges command button on the Geometry/Face subpad.

The Revolve Edges form includes the following specifications.

Sweep Edges

The Sweep Edges command creates real faces by sweeping one or more edges along a specified path. If you sweep a non-real edge to create a face, GAMBIT first creates a real copy of the non-real edge, then sweeps the real copy to create the face.

To create a face by means of the Sweep Edges command , you must spec­ify the following parameters.

• Profile
• Path
• Type

Specifying the Sweep Profile

Specifying the Sweep Path

• Edge
• Vector

When you define the sweep path by specifying a vector, GAMBIT defines the path as a straight line possessing the magnitude and direction of the vector. You must define the vector by means of the Vector Definition form (see "Using the Vector Definition Form" in Section 2.1.4).

Specifying the Sweep Type

GAMBIT provides two general types of sweep operations:

• Rigid
• Perpendicular

Performing a Rigid Sweep

When you perform a rigid sweep operation, GAMBIT projects the profile along the entire length of the specified path without altering the orienta­tion of the profile. The shape and orientation of a face created by means of a rigid sweep operation depend on two factors:

• The shape of the profile and its orientation relative to the path
• The shape and direction of the path

The following examples demonstrate the effects of the shapes and orienta­tions of the profile and path on the final form of a face created by means of a simple rigid sweep operation.

Rigid Sweep—Profile Perpendicular to the Path

Figure 2-63 illustrates a rigid sweep operation in which the path and profile consist of straight edges oriented perpendicular to each other. In this case, the profile is aligned with the x coordinate axis, and the path lies in the y-z coordinate plane.

Figure 2-63: Rigid sweep—straight, perpendicular profile and path

To create a face by means of the rigid sweep operation, GAMBIT performs the following two-step procedure (see Figure 2-63(b)):

1. Project copies of the path onto the profile endpoints.
2. Project a copy of the profile, itself, to connect the upper endpoints of the projected paths.

Rigid Sweep—Profile Not Perpendicular to the Path

The profile edges for a rigid sweep operation can be located anywhere in the model domain as long as they are not parallel to the path. For example, Figure 2-64 shows a rigid sweep operation similar to that shown in Figure 2-63 but in which the profile consists of a curved, circular arc edge that lies in the x-z plane. As in the previous example, the boundary edges of the created face consist of the original profile edge, a projected copy of the profile edge, and two edges that represent projected copies of the path.

Figure 2-64: Rigid sweep—profile not perpendicular to the path

Rigid Sweep—Curved Path

The path used for a rigid sweep opera­tion can be straight or curved. To employ a straight path, you can define the path by means of either a straight edge or a vector. To employ a curved path, you must define the path by means of a curved edge.

Figure 2-65 shows a rigid sweep operation similar to that shown in Figure 2-64 but for which the path consists of a circular arc edge that lies in the y-z plane. As in the two previous examples, the boundary edges of the created face consist of the original profile edge, a projected copy of the profile edge, and two edges that represent projected copies of the path.

Figure 2-65: Rigid sweep—curved profile, curved path

Performing a Perpendicular Sweep

 Overview

Perpendicular sweep operations differ from rigid sweep opera­tions in that, for perpendicular sweeps, the initial orientation between the profile and path is main­tained along the entire length of the sweep path. Rigid sweeps, by contrast, maintain the orientation of the profile with respect to the global coordinate system along the sweep path.

As an example of the difference between rigid and perpendicular sweep operations, consider the profile and path shown in Figure 2-66(a). In this case, the profile consists of a straight edge aligned with the y coordinate axis, and the path is defined by a circular arc edge that lies in the y-z plane.

Figure 2-66: Example Rigid and Perpendicular sweep operations—curved path

The differences between the created faces can be summarized as follows.

• If you perform a rigid sweep using the path and profile shown in Figure 2-66(a), GAMBIT maintains the angle of the profile with respect to the global coordinate system, thereby creating the horn-shaped face shown in Figure 2-66(b).
• If you perform a perpendicular sweep with a zero draft angle (see below), GAMBIT maintains the angle between the path and profile and creates the face shown in Figure 2-66(c).

Perpendicular sweep operations can be modified such that the boundary edges of the created face deviate from the projected sweep path by a specified angle. Such modifications are specified by means of the following options on the Sweep Edges form:

• Draft
• Twist

Draft Option

To sweep a single profile edge-such as that shown in Figure 2-66, above-by means of the perpendicular draft operation, GAMBIT performs the following procedure (see Figure 2-67):

1. Project a copy of the path onto the start endpoint of the profile edge (Figure 2-67(a)).
2. Trace the end endpoint of the profile edge along the projected path, maintaining the original angle between the profile and projected path (Figure 2-67(b)).
3. Project a copy of the profile, itself, to connect the endpoints of the projected profile and traced end endpoint (Figure 2-67(c)).

NOTE: The procedure described above applies strictly only to sweep operations that involve a zero draft angle. For a description of the effect of draft angle on faces resulting from perpendicular draft sweep operations, see "Effect of Draft Angle," below.

Figure 2-67: Perpendicular draft method—procedure

The characteristics of the face created from a perpendicular draft sweep operation depend, in part, on the following factors:

• Profile edge sense
• Draft angle

Effect of Profile Edge Sense

As noted above, when you sweep an edge by means of the perpendicular draft method and specify a zero draft angle, GAMBIT copies and projects the profile onto the start endpoint of the profile edge and maintains the angle between the profile and path along the entire length of the path. Consequently, the start and end endpoint designations (which determine the edge sense) influence the shape of the created face.

As an example of the dependence on edge sense described above, consider the path and profile shown in Figure 2-68(a). The path consists of a circular arc edge that lies in the y-z plane, and the profile consists of a single edge aligned with the y coordinate axis.

Figure 2-68: Effect of profile sense on swept face

The characteristics of the face created by means of a perpendicular draft sweep of the profile shown in Figure 2-68(a) depend on the sense of the profile edge in the following manner.

• If the profile edge is defined such that vertex A constitutes its start endpoint, the sweep operation results in the face shown in Figure 2-68(b). To create the face shown in Figure 2-68(b), GAMBIT copies the path edge and projects it onto vertex A of the initial profile. In this case, the outer curved boundary edge of the face represents the copied projection of the sweep path.
• If the profile edge is defined such that vertex B constitutes its start endpoint, the sweep operation results in the face shown in Figure 2-68(c). To create the face shown in Figure 2-68(c), GAMBIT copies the path edge and projects it onto vertex B of the initial profile. In this case, the inner curved boundary edge of the face represents the copied projection of the sweep path.

Effect of Draft Angle

When you perform a sweep operation by means of the draft method, GAMBIT allows you to specify a draft angle for the created face. The draft angle specifies the angle by which the boundary edges of the created face deviate from the projected path.

The effect of the draft angle specification depends strongly on the shapes and orientations of the profile and path relative to each other. Figure 2-69 shows the effect of draft angle for two simple profiles and paths similar to those shown above.

Figure 2-69: Effect of draft angle on swept face

In Figure 2-69(a), the path and profile consist, respectively, of a circular arc edge aligned with the y-z plane and a straight edge aligned with the y coordinate axis. In this case, the draft angle determines the angle by which the plane that contains the created face deviates from the y-z plane.

NOTE (1): For the path and profile configuration shown in Figure 2-69(a), the perpendicular draft sweep operation always creates a planar face aligned with the y coordinate axis, regardless of draft angle. NOTE (2): The projections of the three faces shown in Figure 2-69(a) onto the y-z coordinate plane are identical to each other in shape, size, and orientation.

In Figure 2-69(b), the path consists of a circular arc edge aligned with the y-z plane the profile edge is aligned with the x coordinate axis. In this case, the draft angle specification serves to increase or decrease the size of the swept arc represented by the created face.

Twist Option

When you perform a perpendicular sweep operation by means of the twist option, GAMBIT revolves the profile through a specified angle as it sweeps the profile along the length of the path. The profile and path can be either straight or curved, but curved paths require an additional restriction with respect to the orientation between the profile and path (see below).

Using a Straight Path

Figure 2-70 illustrates the effect of the perpendicular twist sweep operation for a configuration that involves a straight sweep path. In this case, the profile is defined by a circular arc edge that lies in the x-z plane, the path is defined by a straight edge that is similar in orientation to that shown in Figure 2-63, above, and the twist angle is specified as 360^o.

Figure 2-70: Effect of perpendicular twist sweep operation—straight path

Using a Curved Path

Under certain circumstances, GAMBIT allows you to perform twist sweep operations using a curved path. Figure 2-71 illustrates the effect of the twist sweep operation for a configuration that involves a curved path. In this case, the path is defined by a circular arc edge similar in orientation to that shown in Figure 2-65. The profile consists of a single, straight edge one endpoint of which is connected to the start point of the path, and the twist angle is specified as 180^o.

Figure 2-71: Effect of perpendicular twist sweep operation—curved path

Using the Sweep Edges Form

To open the Sweep Edges form (see below), click the Sweep Edges command button on the Geometry/Face subpad.

The Sweep Edges form includes the following specifications.

2.4.2 Create Face

The Create Face command button allows you to perform the following operations.

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

The Create Real Rectangular Face command creates a real planar face in the shape of a rectangle.

When you execute the Create Real Rectangular Face command, GAMBIT creates a real rectangular, planar face. GAMBIT orients and locates the face such that it is aligned with one of the coordinate planes of a specified reference coordinate system. The Create Real Rectangular Face command includes the following input parameters:

• Width
• Height
• Coordinate Sys.
• Direction

The Width and Height parameters determine the dimensions of the rectangular face. (NOTE: If you do not specify the Height parameter, GAMBIT creates a square face with sides of the length specified by the Width parameter (and vice versa)). The Coordinate Sys. parameter specifies the reference coordinate system for the face creation operation. The Direction parameter specifies the orientation and location of the face relative to the reference coordinate system.

To open the Create Real Rectangular Face form (see below), click the Create Real Rectangular Face command button on the Geometry/Face subpad.

The Create Real Rectangular Face form includes the following specifications.

The Create Real Circular Face command creates a real planar face in the shape of a circle.

When you execute the Create Real Circular Face command, GAMBIT creates a real circular, planar face. GAMBIT orients and locates the face such that it is aligned with one of the coordinate planes of a specified reference coordinate system. The Create Real Circular Face command includes the following input parameters:

• Radius
• Coordinate Sys.
• Plane

The Radius parameter determines the size of the circular face. The Coordinate Sys. parameter specifies the reference coordinate system for the face creation operation. The Plane parameter specifies the orientation of the face relative to the reference coordinate system. (NOTE: The created face is always centered at the origin of the reference coordinate system.)

To open the Create Real Circular Face form (see below), click the Create Real Circular Face command button on the Geometry/Face subpad.

The Create Real Circular Face form includes the following specifications.

The Create Real Elliptical Face command creates a real planar face in the shape of an ellipse.

When you execute the Create Real Elliptical Face command, GAMBIT creates a real elliptical, planar face. GAMBIT orients and locates the face such that it is aligned with one of the coordinate planes of a specified reference coordinate system. The Create Real Elliptical Face command includes the following input parameters:

• Radius 1
• Radius 2
• Coordinate Sys.
• Plane

Radius 1 and Radius 2 represent the lengths of the major and minor axes of the ellipse. For the purposes of this command, the major and minor axes are always aligned with the coordinate axes of the plane in which the elliptical face is created. Either parameter, Radius 1 or Radius 2, can serve as the major or minor axis of the ellipse. (NOTE: If you do not specify Radius 2, GAMBIT creates a circular face of radius Radius 1.)

The Coordinate Sys. parameter specifies the reference coordinate system for the face creation operation. The Plane parameter specifies the orientation of the face relative to the reference coordinate system. (NOTE: The created face is always centered at the origin of the reference coordinate system.)

To open the Create Real Elliptical Face form (see below), click the Create Real Elliptical Face command button on the Geometry/Face subpad.

The Create Real Elliptical Face form includes the following specifications.

2.4.3 Boolean Operations

The Boolean Operations command button allows you to perform the following operations.

Each of the commands listed above allows you to perform a Boolean operation involving two or more faces. The specified faces do not have to be planar, but they must be coincident in the intersecting region between them. (NOTE: For the lone exception to this rule, see "Unite Real Faces," below.)

Figure 2-74: Boolean face operations

Each Boolean operation form includes at least one Retain option. When you perform a Boolean operation involving a set of specified faces, GAMBIT replaces the specified faces with a single face that constitutes the result of the operation. If you select the Retain option, GAMBIT retains the original faces when it performs the Boolean operation.

The Unite Real Faces command allows you to unite two or more overlapping faces into one or more real faces.

When you unite overlapping faces by means of the Unite Real Faces command, GAMBIT creates one real face that represents the union of the overlapping faces. If you specify a set of faces on the Unite Real Faces form such that the set consists of two or more subsets of faces that overlap each other but do not overlap the faces of any other subset, GAMBIT creates a separate real face for each subset.

Using the Unite Real Faces Form

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

The Unite Real Faces form includes the following specifications.

The Subtract Real Faces command allows you to perform a Boolean subtraction involving two or more real faces.

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

The Subtract Real Faces form includes the following specifications.

Intersect Real Faces

The Intersect Real Faces command allows you to perform a Boolean intersection of two or more real faces.

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

The Intersect Real Faces form includes the following specifications.

2.4.4 Connect/Disconnect Faces

The Connect/Disconnect Faces command button allows you to perform two operations.

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

NOTE: The Specify Color Mode command button on the Graphics/Windows Control toolpad allows you to display model colors based on entity connectivity rather than topology. For a description of the use of the Specify Color Mode command button, see the GAMBIT User's Guide, Section 3.4.2.

Connect Faces

The Connect Faces command allows you to connect two or more faces. (NOTE: If you connect two or more meshed faces, and the meshes on each face are topologically identical to each other, GAMBIT preserves the meshes when connecting the faces.)

To connect faces, you must specify the following parameters:

• Two or more faces to be connected
• The connection type

Specifying the Faces to Be Connected

The faces to be connected can be real or virtual, but they are subject to certain restrictions imposed by the connection type (see below).

Specifying the Connection Type

There are four types of face connection operations:

• Real
• Virtual (Forced)
• Virtual (Tolerance)
• Real and Virtual (Tolerance)

The following sections describe the basic features of each connection type.

Specifying a Real Connection

The Real option allows you to connect coincident real faces--that is, two or more real faces the edges of which are coincident. When you connect real faces and specify the Real option, GAMBIT deletes all but one of the specified faces and connects the remaining real face to any and all volumes of which the deleted faces were a part.

Specifying a Virtual (Forced) Connection

The Virtual (Forced) option allows you to connect real and/or virtual faces, regardless of their proximity to each other. When you connect faces and specify the Virtual (Forced) option, GAMBIT replaces the specified faces with a virtual face. If a specified face constitutes part of a volume, GAMBIT overlays the volume with a virtual volume and forms the virtual volume according to the shape and position of the new virtual face.

Specifying a Virtual (Tolerance) Connection

The Virtual (Tolerance) option allows you to specify that only those real and/or virtual faces the edges of which are near to each other to within a specified tolerance are connected. There are two ways to express the tolerance value:

• Tolerance
• Shortest Edge%

The Tolerance specification represents the tolerance value as expressed in absolute distance units. The Shortest Edge% specification represents the tolerance value expressed as a percentage of the length of the shortest edge.

Specifying a Real and Virtual (Tolerance) Connection

When you specify the Real and Virtual (Tolerance) option, GAMBIT performs the following two operations in sequence:

1. Real connect operations for faces that are coincident to within the global tolerance value
2. Virtual (Tolerance) connect operations for unconnected, specified faces that are near to each other to within the user-specified tolerance

Using the Connect Faces Form

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

The Connect Faces form includes the following specifications.

Disconnect About Real Face

The Disconnect About Real Face command allows you to disconnect individual real faces and/or volumes that share a common face.

When you disconnect faces, GAMBIT creates a new face for all but one of the entities to which the specified face is connected. For example, if the specified face is shared by three volumes, GAMBIT creates two new faces that are coincident with the specified face and connects them to two of the three volumes. The original face is connected to the remaining volume.

Specifying the Edge and Vertex Options

GAMBIT provides the following three options with respect to the treatment of endpoint vertices for the disconnected edges:

• Face + Edges/Vertices
• Face Only
• Face + Selected Edges

The following table describes the effects associated with each option.

Using the Disconnect About Real Face Form

To open the Disconnect About Real Face form (see below), click the Disconnect command button on the Geometry/Face subpad.

The Disconnect About Real Face form includes the following specifications.

2.4.5 Modify Face Color/Label

The Modify Face Color/Label command button allows you to perform two operations.

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

Modify Face Color

The Modify Face Color command allows you to change the displayed color of the geometry and/or mesh and/or shading associated with one or more faces.

Using the Modify Face Color Form

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

The Modify Face Color form includes the following specifications.