5. USING THE MODELING TOOLS

NOTE: The Turbo Functions commands represent a specialized command set that can be licensed from Fluent. They are not included in the standard set of GAMBIT functions.

5.1 Coordinate Systems

5.1.1 Overview

Coordinate systems provide reference points and directions for GAMBIT operations such as the construction of volume primitives and geometry Move and Copy operations. GAMBIT performs all such operations with respect to a specified coordinate system. For example, if you create a rectangular brick volume according to the specifications shown in Figure 5-1, GAMBIT creates a unit cube one corner of which is located at the center of coordinate system c_sys.1.

Figure 5-1: Example Create Real Brick form specifications

There are two types of coordinate systems:

• Global (c_sys.1)
• Local

The global coordinate system, c_sys.1, is a permanent system that serves as the default coordinate system for all GAMBIT geometry operations. Local coordinate systems allow you to perform GAMBIT geometry operations at localized regions in the model domain. They are particularly useful for the creation of geometry in regions that are distant from the center of the model.

NOTE: GAMBIT does not allow you to delete the global coordinate system.

5.1.2 Coordinate System Commands

The following commands are available on the Tools/Coordinate System subpad.

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

The Create Coordinate System command allows you to create a local coordinate system for use in creating and manipulating model geometry.

To create a coordinate system, you must specify the following parameters.

• System type
• Location and orientation

Specifying the System Type

There are three types of coordinate systems: Cartesian, cylindrical, and spherical. They differ from each other only with respect to the manner in which the coordinates for any given location are expressed. The coordinate specifications for each type of system are as follows.

When you perform modeling operations such as creating vertices or moving volumes, GAMBIT allows you to specify the relevant coordinates or offset parameters with respect to either the global coordinate system (c_sys.1) or the currently active local coordinate system. The default coordinate parameters for the local system are those defined for the system when it is created or modified (see "Modify Coordinate System," below).

For example, if you create a local coordinate system labeled c_sys.2 and specify the system type as spherical, then activate the system and open the Create Real Vertex form, the default coordinate parameters shown in the Local text boxes on the Create Real Vertex form are r (r), t () and p () rather than x (x), y (y), and z (z). To change the Local text box coordinate parameters on any form, specify the coordinate system type using the Type option button located on the form.

Specifying the Location and Orientation

You can specify the location and orientation of the new system by means of two options available on the Create Coordinate System form. The two options are as follows:

• Offset/Angle
• Vertices

The Offset/Angle option allows you to specify the following parameters for the new system:

• The coordinates of its origin
• The angle (in degrees) by which each of its coordinate axes are rotated relative to a reference system.

The Vertices option allows you to specify existing vertices that define the origin, x axis, and x-y plane for the new system. The specifications associated with each option are described below.

Using the Create Coordinate System Form

To open the Create Coordinate System form (see below), click the Create Coordinate System command button on the Tools/Coordinate System subpad.

The Create Coordinate System form contains the following options and specifications.

Specifying Coordinate System Offset and Angle

When you select the Offset/Angle option, the middle section of the Create Coordinate System form appears as shown above. The corresponding options and specifications are as follows.

Specifying Vertices That Define the New System

To specify the location and orientation of the new system by means of vertices, you must specify three vertices (see Figure 5-2):

• Origin
• X axis
• XY plane

Figure 5-2: Defining a new coordinate system using vertices

The location of the origin of the system is defined by the Origin vertex. The direction of the x axis is defined by a vector that points from the Origin vertex toward the X axis vertex. The orientation of the x-y plane is defined such that it contains both the x-axis vector and a vector that points from the Origin vertex to the XY plane vertex.

When you select the Vertices option, the middle section of the Create Coordinate System form appears as shown below.

The options and specifications available for the Vertices option are as follows.

Specifying the System Label

The Modify Coordinate System command allows you to change the coordinate system label and the default system parameter type.

Using the Modify Coordinate System Form

To open the Modify Coordinate System form (see below), click the Modify command button on the Tools/Coordinate System subpad.

The Modify Coordinate System form contains the following options and specifications.

The Activate Coordinate System command allows you to activate an existing coordinate system.

When you activate a coordinate system, GAMBIT uses the system as the default reference system for operations such as creating, moving, and copying topological entities.

Using the Activate Coordinate System Form

To open the Activate Coordinate System form (see below), click the Activate Coordinate System command button on the Tools/Coordinate System subpad.

The Activate Coordinate System form contains the following specification.

The Display Grid command allows you to activate and display a grid associated with any existing coordinate system.

Overview

When you activate and display a grid, GAMBIT displays a rectangular planar grid in the graphics window. The dimensions of the grid are defined relative to the coordinate system with which it is associated. The grid is always parallel to one of the Cartesian coordinate planes but may be offset from the origin of the coordinate system.

Using the Mouse to Create Vertices

When the grid is displayed in any graphics window quadrant, GAMBIT allows you to create vertices by means of the mouse-regardless of whether the Create Vertex form is open. To create a vertex by means of the mouse, Ctrl-right-click at the desired vertex location. GAMBIT creates the vertex at the selection point-which is defined as the point of intersection between the grid plane and a line normal to the screen that passes through the cursor location.

Specifying the Grid Parameters

To define and display a grid, you must specify the following parameters.

• Coordinate system
• Visibility
• Grid definition
• Snap option
• Grid type

The following sections describe each of the specifications listed above.

Specifying the Coordinate System

GAMBIT allows you to define and display a grid for any existing coordinate system. When you define and display a grid, GAMBIT activates the coordinate system associated with the grid.

Specifying Visibility

When you define and display a grid, GAMBIT allows you to specify the graphics window quadrants in which the grid is displayed. You can specify that the grid is displayed in any or all quadrants, but each specified quadrant displays only the currently active grid. For example, you cannot simultaneously display an x-z grid in one quadrant and a y-z grid in a separate quadrant.

Defining the Grid

To define the grid, you must specify its orientation, location, dimensions, and characteristics by means of the Plane, Axis, Offset, Minimum, Maximum, and Increment specifications on the Display Grid form. The specifications are defined as follows.

Specifying the Snap Option

When you create a grid, GAMBIT allows you to specify that any vertices created by means of the mouse are "snapped" to the grid. When a vertex is snapped to the grid, it is created at the grid point nearest to the selection point rather than at the selection point itself. To activate the snap option for any grid, select the Snap checkbox at the bottom of the Display Grid form.

Specifying the Grid Type

The grid type determines the manner in which the grid is displayed. There are two grid-type options: Points and Lines. When you select the Points option, GAMBIT displays the grid as a matrix of parallel rows of points. When you select the Lines option, GAMBIT displays the grid as a series of intersecting perpendicular lines.

Using the Display Grid Form

To open the Display Grid form (see below), click the Grid command button on the Tools/Coordinate System subpad.

The Display Grid form contains the following specifications.

The Display Ruler command allows you to display rulers along any or all of the axes in the currently active coordinate system.

To display a ruler along any of the coordinate axes, you must specify the following parameters.

• Display status (On or Off)
• Range status (On or Off)
• Number of intervals and subintervals

If the range status is on, you must also specify the lower and upper limits of the ruler range.

Specifying the Display Status

The display status determines whether or not the ruler is displayed in the graphics window. To display or erase the ruler for any particular axis in the active coordinate system, select On or Off, respectively, in the Ruler field corresponding to the axis.

Specifying the Range Status

The range status determines whether the lower and upper limits of the ruler are user-specified or automatically set by GAMBIT for any particular axis. To specify the range status for any axis, select On or Off in the Range field corresponding to the axis. The range status specification operates in the following manner.

• If you specify the range status as On for any axis, GAMBIT allows you to specify the lower and upper limits for the ruler in the Min and Max text boxes corresponding to the axis.
• If you specify the range status as Off for any axis, GAMBIT automatically determines the lower and upper limits of the axis ruler.

When GAMBIT automatically determines the lower and upper limits for an axis ruler, it constructs a theoretical "bounding box" that encompasses all components of the model domain, including topological entities, coordinate systems, and rulers themselves. The bounding box represents a rectangular brick volume the edges of which are aligned with the axes of the global coordinate system, c_sys.1.

When GAMBIT displays a ruler with an automatically determined range, it sets the range so that the ruler is exactly contained by the sides of the bounding box. If you increase the length of a user-specified ruler beyond the current limits of the bounding box, GAMBIT increases the size of the bounding box to accommodate the new ruler dimensions. GAMBIT also adjusts all currently displayed, automatically determined rulers so that, again, they are exactly contained by the sides of the bounding box.

Specifying the Intervals and Subintervals

The number of intervals for any axis determines the locations along the ruler at which GAMBIT displays tic marks and corresponding numbers. The number of subintervals determines the spacing of tic marks between numbered marks. For example, if you specify a ruler range of -5 to +5 with 10 intervals and 2 subintervals, GAMBIT displays a ruler that contains numbered tic marks at -5, -4, -3, -2, -1, 0, 1, 2, 3, 4, and 5 and tic marks without numbers at -4.5, -3.5, -2.5, -1.5, -0.5, 0.5, 1.5, 2.5, 3.5, and 4.5.

Using the Display Ruler Form

To open the Display Ruler form (see below), click the Display Ruler command button on the Tools/Coordinate System subpad.

The Display Ruler form contains the following options and specifications.

The Summarize Coordinate Systems command allows you to display (in the Transcript window) summary information for one or more coordinate systems.

When you summarize a coordinate system, GAMBIT displays four sets of global x, y, and z coordinates corresponding to the system. One set defines the origin of the system. The other three define the endpoints of unit vectors that point from the origin in the directions of the x, y, and z axes.

Using the Summarize Coordinate Systems Form

To open the Summarize Coordinate Systems form (see below), click the Summarize command button on the Tools/Coordinate System subpad.

The Summarize Coordinate Systems form contains the following specification.

The Delete Coordinate Systems command allows you to delete one or more existing local coordinate systems. (NOTE: You cannot delete the global coordinate system, c_sys.1.)

Using the Delete Coordinate Systems Form

To open the Delete Coordinate Systems form (see below), click the Delete command button on the Tools/Coordinate System subpad.

The Delete Coordinate Systems form contains the following specification.

© Fluent, Inc. 10/29/01