Body

Currently, CUBIT can create volumes:

1. from surfaces by sweeping a single surface into a 3D solid,
2. by offsetting an existing volume,
3. by sweeping a curve around an axis.
4. by stitching together surface that can form a closed volume.
5. by lofting from one surface to another surface.
6. by thickening a surface body.

Sweeping of planar surfaces, belonging either to two- or three-dimensional bodies, is allowed, and some non-planar faces can be swept successfully, although not all are supported at this time. The following methods for generating volumes are described:

• Sweep Surface Along Vector
• Sweep Surface About Axis
• Sweep Surface Along Curve
• Offset
• Sweep Curve About Axis
• Stitch Surfaces Together
• Loft Surfaces Together
• Thicken Surfaces

Command Line

There are four forms of the sweep command; the syntax and details for each are given below. In each form, the optional draft_angle parameter specifies the angle at which the lateral faces of the swept solid will be inclined to the sweep direction. It can also be described as the angle at which the profile expands or contracts as it is swept. The default value is 0.0. The optional draft_type parameter is an ACIS-related parameter and specifies what should be done to the corners of the swept solid when a non-zero draft angle is specified. A value of 0 is the default value and implies an extended treatment of the corners. A value of 1 is also valid and implies a rounded (blended) treatment of the corners.

1. Sweep Surface Along Vector: Sweeps a surface a specified distance along a specified vector. Specifying the distance of the sweep is optional; if this parameter is not provided, the face is swept a distance equal to the length of the specified vector.

2. Sweep Surface About Axis: Sweeps a surface about a specified vector or axis through a specified angle. The axis of revolution is specified using either a starting point and a vector, or by a coordinate axis. This axis must lie in the plane of the surfaces being swept. The steps parameter defaults to a value of 0 which creates a circular sweep path. If a positive, non-zero value (say, n) is specified, then the sweep path consists of a series of n linear segments, each subtending an angle of [( sweep_angle ) / ( steps-1 )] at the axis of revolution.

Specifying multiple surfaces that belong to the same body will not work as expected, as ACIS performs the sweep operation in place. Hence, if a range of surfaces is provided, they ought to each belong to different bodies.

3. Sweep Surface Along Curve: This command allows the user to sweep a planar surface along a curve:

One of the ends of the curve must fall in the plane of the surface and the curve cannot be tangential to the surface. Sweep along curve also supports an additional draft type "2" which implies a "natural" extension of the corners from their curves.

The sweep operations have been designed to produce valid solids of positive volume, even though the underlying solid modeling kernel library that actually executes the operation, ACIS, allows the generation of solids of negative volume (i.e., voids) using a sweep.

4. Offset: The following command creates a body offset from another body at the specified distance. The new surfaces are extended or trimmed appropriately. A positive distance results in a larger body; a negative distance in a smaller body.

5.Sweep Curve About Axis: Sweeps a curve or set of curves about a given axis through a specified angle. The axis is specified the same as in the Sweep Surface About Axis command. The steps, draft_angle, and draft_type options are the same as are described above. To create the solid, the make_solid option must be specified, otherwise a surface will be created, rather than a solid. If the rigid option is specified, then the curve or set of curves will remain oriented as originally oriented, rather than rotating about the axis.

Sweep Curve <curve_id_range> { axis <xpoint ypoint zpoint xvector yvector zvector> | xaxis | yaxis | zaxis } angle <degrees> [steps <Number_of_sweep_steps>] [draft_angle <degrees>] [draft_type <integer>] [make_solid] [rigid]

6. Stitch Surfaces Together: A body can be created from various surfaces that form a closed volume with command below. The geometry must be ACIS-type geometry (ie. can be imported from IGES, STEP or fastq files)

Create Body Surface <surface_id_range>

This option is also available for limited cases for facet-based surfaces.

7. Loft Surfaces Together: A body can be "lofted" between two surfaces to form a new body. Surfaces from solid bodies and sheet bodies may be used to create a loft body. In order to create the loft body, two surfaces coincident to the input surfaces are created. The loft body is extruded along the shortest path between the corresponding vertices that define the shapes of the two copied surfaces. This new body is solid. The surfaces used to create the loft body are unchanged.

Create Body Loft Surface <surface1_id> <surface2_id>

It is recommended that lofting only be attempted between similar surfaces. For example, lofting from a trapezoidal surface (whose shape is defined by four end vertices) to a triangular surface (whose shape is defined by three end vertices) will force the lofting function to transform the cross-section of the loft body in mid-extrusion, often with poor results (e.g., a skewed or self-intersecting loft body). Attempting to loft between nearly perpendicular surfaces generally produces poor results as well.

Lofting can be used to split a body in order to create a more structured mesh. Figure 1 below shows a single volume swept from a large paved surface. Figure 2 shows this same volume after surfaces defined on the source and target surfaces have been used to create a loft body. This original body was chopped with the loft body. The resulting two bodies were merged. The yellow volume was swept as the volume in Figure 1 was but the purple volume was submapped, producing a much more structured mesh overall.

Figure 1. Single swept volume with a large paved face.

Mesh After the Loft

Figure 2. Two merged volumes.The yellow volume is paved and the purple volume is submapped.

8. Thicken Surfaces: A surface body can be thickened to create a volume body. The surface can be thickened in both directions using the "both" keyword, thickened in the direction of surface normal using a positive depth, or thickened in the opposite direction using a negative depth. To thicken multiple surfaces, all surface normals must be consistent.

Thicken [body] <body_list> depth <depth> [both]

GUI

Selecting the Body button in the Create window will provide six options for generating volumes in CUBIT. You can create a volume...

by extruding a surface

by sweeping a surface along a curve

as an offset from another volume

by sweeping a surface about a curve

by lofting between two surfaces

by thickening surfaces