4.2 Geometry Creation
There are three primary ways of creating geometry for meshing in Cubit. First, Cubit provides many geometry primitives for creating common shapes (spheres, bricks, etc.) which can then be modified and combined to build complex models. Secondly, geometry can be imported into Cubit. Finally, geometry can be defined by building it from the "bottom up", creating vertices, then curves from those vertices, etc. Two of these three methods for creating geometry in Cubit will be described in detail in this section.
All of these geometry creation commands have been expressed in the GUI’s command panels. To navigate to the volume creation command panels, for example, select "Mode-Geometry", then "Operation - Create Geometry", then "Entity-Create Volumes", as shown below. Other geometry creation command panels are available for each geometry type.
4.2.1 Bottom-Up Geometry Creation
Cubit supports the ability to create geometry from a collection of lower order entities. This is accomplished by first creating vertices, connecting vertices with curves and connecting curves into surfaces. Currently only ACIS bodies or volumes may not be constructed by stitching a set of surfaces together, and only in a certain number of cases; however surfaces may also be swept or rotated to create bodies or volumes. Existing geometry may be combined with new geometry to create higher order entities. For example, a new surface can be created using a combination of new curves and curves already extant in the model. Commands and details for creating each type of geometry entity are given below.
4.2.1.1 Creating Volumes
Currently, Cubit can create volumes:
from surfaces by sweeping a single surface into a 3D solid,
by offsetting an existing volume,
by extending one or more surfaces or sheet bodies
by sweeping a curve around an axis,
by stitching together surfaces that can form a closed volume,
by lofting from one surface to another surface, or
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.
There are five forms of the sweep command; the syntax and details for each are given below. Common options for first four forms are:
draft_angle: This 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.
draft_type: This 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.
anchor_entity: The default behavior for the sweep command is to move the source surface along a path to create a new 3D solid. The anchor_entity option instructs the sweep to leave the source surface in its original location.
include_mesh: This option will sweep the source surface and existing mesh into a meshed 3D solid. The mesh size is automatically computed using the Default auto interval specification.
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.
4.2.1.1.1 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. The include_mesh option will create a volumetric mesh if the surface is already meshed as shown below. The keep option will keep the original surface while creating the volume.
To sweep a Surface
On the Command Panel, click on Geometry and then Volume.
Click on the Create action button.
Select Sweep from the drop-down menu.
Enter the value for theSurface ID(s). This can also be done using the Pick Widget function.
Click on Along Vector.
Enter in the appropriate values for X, Y and Z.
Enter in any other desired options from this menu.
Click Apply.
Sweep Surface {<surface_id_range>} Vector <x_vector y_vector z_vector> [Distance <distance_value>] [switchside] [Draft_angle <degrees>] [Draft_type <0|1>][rigid][anchor_entity][include_mesh] [keep] [merge]
4.2.1.1.2 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. The include_mesh option will create a volumetric mesh if the surface is already meshed as shown below. The keep option will keep the original surface while creating the volume.
To sweep a Surface About an Axis
On the Command Panel, click on Geometry and then Volume.
Click on the Create action button.
Select Sweep from the drop-down menu.
Enter the value for the Surface ID(s). This can also be done using the Pick Widget function.
Click on About Axis.
Select the appropriate Axis of Rotation.
Enter in any other desired options from this menu.
Click Apply.
Sweep Surface {<surface_id_range>} Axis {<xpoint ypoint zpoint xvector yvector zvector>|Xaxis|Yaxis|Zaxis} Angle <degrees> [switchside] [Steps <number_of_sweep_steps>] [Draft_angle <degrees>] [Draft_type <0|1>][rigid][anchor_entity][include_mesh] [keep] [merge]
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.
4.2.1.1.3 Sweep Surface Along Curve
This command allows the user to sweep a planar surface along a curve:
To sweep a Surface Along a Curve
On the Command Panel, click on Geometry and then Volume.
Click on the Create action button.
Select Sweep from the drop-down menu.
Enter the value for the Surface ID(s). This can also be done using the Pick Widget function.
Click on Along Curve.
Enter in the Curve ID.
Select any other appropriate settings from this menu.
Click Apply.
Sweep Surface <surface_id_range> Along Curve <curve_id> [Draft_angle <degrees>] [Draft_type <0 | 1 | 2>][rigid][anchor_entity][include_mesh] [keep] [individual] [merge]
The include_mesh option will create a volumetric mesh if the surface is already meshed. The keep option will keep the original surface while creating the volume.
Figure 99: Volume generated by sweeping a surface along a reference curve
4.2.1.1.4 Sweep Surface Perpendicular
This command allows the user to sweep a planar surface perpendicular to the surface:
To sweep a Surface Perpendicular
On the Command Panel, click on Geometry and then Volume.
Click on the Create action button.
Select Sweep from the drop-down menu.
Enter the value for the Surface ID(s). This can also be done using the Pick Widget function.
Click on Perpendicular.
Enter in the desired Distance.
Enter in any other appropriate settings from this menu.
Click Apply.
Sweep Surface <surface_id_range> Perpendicular Distance <distance> [Switchside] [Draft_angle <degrees>] [Draft_type <integer>][anchor_entity][include_mesh] [keep] [merge]
The sweeping plane must be planar in order to determine the sweep direction. The switchside option will reverse the direction of the sweep.
Figure 100: The original surface is retained with the 'keep' option. A new volume is created by sweeping the surface along the surface normal.
The include_mesh option will create a volumetric mesh if the surface is already meshed. The keep option will keep the original surface while creating the volume.
4.2.1.1.5 Sweep Surface to a Volume
This command allows users to sweep a surface to a volume.
To sweep a Surface to a Volume
On the Command Panel, click on Geometry and then Volume.
Click on the Create action button.
Select Sweep from the drop-down menu.
Enter the value for the Surface ID(s). This can also be done using the Pick Widget function.
Click on Target Volume.
Enter in the appropriate values for Volume ID, Direction and Plane.
Click Apply.
Sweep Surface <surface_id_range> Target {Volume|Body} <id> [Direction {options}] [Plane {options}]
The direction keyword can be used to control the direction of sweep. Without it, Cubit will determine the sweep direction (usually normal to the sweeping surface). The plane option can be used to define a stopping plane.
4.2.1.1.6 Offset
The following command creates a body offset from another body or set of surfaces 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.
To create a Sheet Offset from a Surface
On the Command Panel, click on Geometry and then Surface.
Click the Create action button.
Select Offset from the drop-down menu.
Enter in the appropriate values for From Surface ID(s) and Offset Value.
Enter in any other desired settings from this menu.
Click Apply.
Create Body Offset [From] Body <id_range> Distance <value>
Create Sheet Offset From Surface <id_list> Offset <val> [Surface <id_list> Offset <val>] [Surface <id_list> Offset <val> ...] [Preview]
This option is also available for limited cases for facet-based surfaces.
4.2.1.1.7 Sheet Extended from Surface
The following command creates a body offset from another body or set of surfaces 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.
To create a Sheet Extended from a Surface.
On the Command Panel, click on Geometry and then Surface.
Click on the Create action button.
Select Extended Surface from the drop-down menu.
Enter in the desired value for Surface ID(s).
Enter in any other appropriate settings from this menu.
Click Apply.
Create Sheet Extended From Surface <id_list> [Intersecting <entity_list>] [Extended {Percentage|Absolute} <val>] [Preview]
This command allows multiple surfaces to be extended at the same time. Optionally, you can give a list of bodies to intersect for this calculation. You can also extend the size of the surface by either a percentage distance or an absolute distance of the minimum area size. The plane can be previewed with the preview option. Figure 1 shows a set of surfaces being created using the extended absolute option.
4.2.1.1.8 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.
To sweep a Curve about an Axis
On the Command Panel, click on Geometry and then Surface.
Click on the Create action button.
Select Sweep from the drop-down menu.
Enter in the value for the Curve ID(s). This can also be done using the Pick Widget function.
Select Axis/Angle from the Sweep Method Menu.
Enter in the appropriate Axis of Rotation.
Enter in any other desired settings from this menu.
Click Apply.
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]
4.2.1.1.9 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 (i.e. imported from IGES, STEP or fastq files) This option is also available for limited cases for facet-based surfaces.
The heal option will attempt to close small gaps in the surface; the noheal option disables this behavior. The keep option preserves the original surfaces.
All of the surfaces must form a closed water-tight volume for this command to succeed unless the sheet option is specified. The sheet option allows for the creation of an open body.
To create a body with the Heal Option
On the Command Panel, click on Geometry and then Volume.
Click on the Create action button.
Select From Bounding Surfaces from the drop-down menu.
Enter the value for the Surface ID(s). This can also be done using the Pick Widget function.
Select any other appropriate setting from this menu.
Click Apply.
Create {Body|Volume} Surface <surface_id_range> [HEAL|Noheal] [Keep] [Sheet]
4.2.1.1.10 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.
To loft Surfaces to create a Volume
On the Command Panel, click on Geometry and then Volume.
Click on the Create action button.
Select Lofted Volume from the drop-down menu.
Enter the value for Surface ID(s). This can also be done using the Pick Widget function.
Select an other appropriate settings from this menu.
Click Apply.
Create {Body|Volume} Loft Surface <ids> [guide curve <id_list> [global_guides]] [Takeoff_factors <one value per surface in order>=.001] [Takeoff_vector Surface <id> {direction options}] [match vertex <ids>] [closed] [preview] [show_matching_curves]
Source surface ids must be specified in lofting order
Go to Location, Direction, and Axis Specification to see the direction command description.
The following options are available for lofting:
Guide curve: Multiple curves may be specified to guide the loft. The curves must touch each source surface. If the global_guides option is specified the guides curves are applied in a global nature.
Takeoff_factors: Takeoff factors control how strongly the loft follows the takeoff vectors. When specifying takeoff factors one value must be specified for each source surface.
Takeoff_vector: The takeoff vector controls the direction of the loft for each surface. The default takeoff vector for each surface is the normal at the surface centroid. One takeoff vector may be specified for each surface.
Match vertex: This option guides the loft in how to match the vertices of the source surfaces. Multiple match vertex sets may be specified. When specifying match vertices, one vertex id from each source surface must be specified. The match vertices must be specified in loft order.
Closed: This option attempts to create a toroidal solid. The last source surface is lofted to the first source surface.
Preview: This option will preview the linking curves of the final solid.
Show_matching_curves: This option will preview how the vertices of the source surfaces will be matched.
Lofting can be used to split a body in order to create a more structured mesh. Figure 2 below shows a single volume swept from a large paved surface. Figure 3 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 2 was but the purple volume was submapped, producing a much more structured mesh overall.
4.2.1.1.11 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.
To thicken a Surface
On the Command Panel, click on Geometry and then Volume.
Click on the Modify Volumes action button.
Select Thicken from the drop-down menu.
Enter the appropriate values for Volumes ID(s) and Depth.
To Thicken the volume in both direction, check the Thicken in both directions box.
Click Apply.
Thicken [Volume|BODY] <id> Depth <depth> [Both]
4.2.1.1.12 Sweeping a Surface to a Plane
Sweeps a surface normal to a plane and towards the plane until the swept surface reaches the plane. See plane options for ways to describe a plane.
To sweep a Surface to a Plane
On the Command Panel, click on Geometry and then Volume.
Click on the Create action button.
Select Sweep from the drop-down menu.
Enter in the desired values for Surface ID(s) and Volume ID. This can also be done by using the Pick Widget function.
Click on Target Volume.
Click on Plane.... Another menu will appear.
Enter in the appropriate settings.
Click Apply. The menu will disapear leaving the selected settings in the Plane field.
Enter in any other desired settings from this menu.
Click on Apply.
Sweep surface <id> target plane <options>
4.2.1.1.13 Sweep Surface along a Direction
Sweep a surface along a direction to create a volume. See direction options for ways to specify a direction.
To sweep a Surface along a Direction
On the Command Panel, click on Geometry and then Volume.
Click on the Create action button.
Select Sweep from the drop-down menu.
Enter in the desired values for Surface ID(s). This can also be done using the Pick Widget function.
Click on Direction from the Sweep Method menu.
Click on the Direction... button. Another menu will appear.
Enter in the appropriate settings.
Click Apply. The menu will disapear leaving the selected settings in the Direction field.
Enter in any other desired settings from this menu.
Click Apply.
Sweep Surface <surface_id_range> Direction (options) [switchside] [draft_angle <degrees>] [draft_type <integer>] [rigid] [anchor_entity] [include_mesh] [keep] [merge]
Figure 104: Surface extruded along -X direction without 'include_mesh' option.
4.2.1.1.14 Sweep Surface along Helix
Sweep a surface along a helix, where the helix is defined by an axis, thread_distance (distance between turns in axis direction), axis, and handedness (right_handed or left_handed.
To sweep a Surface or Curve along a Helix
On the Command Panel, click Geometry.
To sweep a surface, click on Volume. To sweep a curve, click on Surface.
Click on the Create action button.
Select Sweep from the drop-down menu.
Enter in the desired Surface or Curve ID(s). This can also be done using the Pick Widget function.
Select Helix from the Sweep Method menu.
Click the appriapte Axis from the Axis of Rotation menu.
Enter in the appropriate values for Helix Height and Rotation Angle.
Enter in any other desired settings
Click Apply.
Sweep {Surface|Curve} <id_range> Helix {axis <xpoint ypoint zpoint xvector yvector zvector> | xaxis | yaxis | zaxis} thread_distance <val> angle <val> [RIGHT_HANDED|left_handed] [anchor_entity] [include_mesh] [keep] [merge]
Specifying multiple Surfaces that belong to the same Body can cause the creation of invalid Bodies and is discouraged.
axis = axis about which to create the sweep
thread_distance = distance between each 360 degree segment of the helix
angle = number of degrees in rotation of the helix
4.2.1.1.15 Volume Copy
Create a new volume by copying an existing volume. There are a number of commands to support this function. Below is the command panel which is accessed via Geometry/Volume/Create/Copy. Notice the opportunity to copy with various transforms, include the mesh from the source volume, and include boundary conditions from the source volume.
4.2.1.2 Creating Curves
Curves are created by specifying the bounding lower-order topology (i.e. the vertices) and the geometry (shape) of the curve (along with any parameters necessary for that geometry).
4.2.1.2.1 Straight
Create Curve [Vertex] <vertex_id> [Vertex] <vertex_id> [On Surface <surface_id>]
Create Curve Axis {options}
The length of the axis must be specified. Go to Location, Direction, and Axis Specification to see the axis command description.
Create Curve Polyline Location {options} Location {options} ...
Notice that two or more locations are used to define a polyline. See Location, Direction, and Axis Specification for the location command description.
4.2.1.2.2 Parabolic, Circular, Ellipse
Create Curve [Vertex <vertex_id> [Vertex] <vertex_id> [[Vertex] <vertex_id> [Parabolic|Circular|ELLIPSE [first angle <val=0> last angle <val=90>]]]
The angle options will specify what portion of the ellipse to create. If none are specified, first angle will default to 0 and last angle to 90 and the ellipse will go from vertex 1 to vertex 2; if the vertices are free vertices they will be consumed in the ellipse creation. First angle tells Cubit where to start the ellipse – the angle from the first axis (v1 - v3) specified. Last angle tells Cubit where to end the ellipse – the angle from the first axis. The angle follows the right-hand rule about the normal defined by (v1 - v3) X (v2 - v3).
4.2.1.2.3 Spline
Create Curve Spline {List of locations} [delete]
See Location, Direction, and Axis Specification to view the location specification syntax.
4.2.1.2.4 Example
create curve spline vertex 1 to 10
An alternate form of the command can be used with only vertex ids using the syntax below and is retained for backwards compatibility.
Create Curve [Vertex] <start_vertex> <end_vertex> <interior_vertex_ids> [Spline] [Delete]
4.2.1.2.5 Copy
Create Curve From Curve <curve_id>
4.2.1.2.6 Combine Existing Curves
Create Curve combine curve <id_list> [delete]
4.2.1.2.7 Arc Three
Create Curve Arc Three {Vertex|Curve} <id_list> [Full]
4.2.1.2.8 Arc End Vertices and Radius
Create Curve Arc Vertex <id_list>
Radius <value> Normal {<x> <y> <z>} | {direction options} [Full]
Go to Location, Direction, and Axis Specification to see the direction command description.
4.2.1.2.9 Arc Center Vertex
Create Curve Arc Center Vertex <center_id> <end1_id> <end2_id>
[Radius <value>] [Full]
[Normal {<x> <y> <z>} | {direction options}]
Go to Location, Direction, and Axis Specification to see the direction command description.
Requires 3 Vertices - first is the center, the other two are the end points of the arc. A normal direction is required when the three points are colinear. Otherwise a normal direction is optional.
4.2.1.2.10 Arc Center Angle
Create Curve Arc Center {<x=0> <y=0> <z=0>} | {location options}
Radius <value>
Normal {<x> <y> <z>} | {direction options}
Start Angle <value=0> Stop Angle <value=360>
Go to Location, Direction, and Axis Specification to see the location and direction command descriptions.
4.2.1.2.11 From Vertex Onto Curve
Create Curve From Vertex <vertex_id> Onto Curve <curve_id> [Fraction <f> | Distance <d> | Position <xval><yval><zval> | Close_To Vertex <vertex_id> [[From] Vertex <vertex_id> (optional for ’Fraction’ & ’Distance’)]] [On Surface <surface_id>]
Default = Normal to the Curve
4.2.1.2.12 Offset
Create Curve Offset Curve <id_list> Distance <val> [Direction <x> <y> <z>] [Rounded|EXTENDED|Natural]
Direction is optional for offsets of individual straight curves only
In all cases, the specified vertices are not used directly but rather their positions are used to create new vertices.
4.2.1.2.13 From Mesh Edge
Create Curve From Mesh Node <id> Edge <id> [Length <val>]
The adjacent edge indicates which direction to propagate the curve.
The curve will be composed of mesh edges up to the specified length.
If no length is specified the curve will propagate as far as the boundary of the mesh. Figure 107 shows a example of a curve generated from the mesh.
The underlying geometry kernel used for this command is Mesh-Based geometry. The new curve will also be meshed with the edges it was propagated through. A related command for assigning mesh edges directly to a mesh block is the Rebar command. See Element Block Specification for more details.
Full hexes or full tets must be used to propagate the curves through the interior of volume.
4.2.1.2.14 Close To
Create Curve Close_To {Vertex|Curve|Surface|Volume|Body} <id_1> {Vertex|Curve|Surface|Volume|Body} <id_2>
4.2.1.2.15 Surface Intersection
Create Curve Intersecting Surface <id_list>
4.2.1.2.16 By Projection
The project command projects curves, or the curves of a surface another a single surface or multiple surfaces of a volume or body. The command syntax is as follows:}
Project {Curve <id_list> | Surface <id_list } Onto Surface <surface_id> [Imprint [Keepcurve] [Keepbody]] [Trim]
Project { Curve <id_list> | Surface <id_list> Onto {Body <id> | Volume <id>} [Target_surface <id_list>] [Imprint [Keepcurve] [Keepbody]]}
The first form of the command takes a list of curves or surfaces, and a projection surface. If a list of curves is given, the result will be the creation of a set of free curves on top of the projection surface. If a list of surfaces is given, the result will be the same as selecting the curves of the surface (i.e. a group of free curves on the projecting surface).
4.2.1.2.17 Creating a Helix
Create Curve Helix { axis <xpoint ypoint zpoint xvector yvector zvector> | xaxis | yaxis | zaxis } location (options) thread_distance <value> angle <value> [RIGHT_HANDED | left_handed]
axis = axis about which to create the helix
location (options) = starting point of the helix
thread_distance = distance between each 360 degree segment of the helix
angle = number of degrees in rotation of the helix
handedness = right-handed or left- handed threads
4.2.1.2.18 Tangents
This command will create a spline curve by specifying the end points and the tangents at those points. The command syntax is as follows:
create curve tangent vertex <id> [direction (options)] vertex <id> [direction (options)]
create curve tangent location (options) direction (options) location (options) direction (options)
The first form of the command takes an existing vertex and an optional tangent direction. If the direction is not specified, it will be taken from the tangent at the endpoint of the connected curve. If the vertex is not connected to a curve, or it is connected to multiple curves, the direction must be specified. If the vertex is not connected to a curve, it will be incorporated into the new curve. Otherwise, a new vertex will be created for the new curve.
The second form of the command takes a location and a tangent direction. The directions must be specified and vertices will be created for the locations.
The two command forms can also be mixed. A curve can be created from an existing vertex and a specified location.
4.2.1.2.19 Examples
create curve tangent location 0 0 0 direction 1 0 0 location 1 1 0 direction 1 0 0
create curve tangent vertex 1 vertex 3
merge vertex all
Figure 110: Create tangent curve by specifying vertices on curves. Tangents are extracted from the curve at the vertex location.
Go to Location, Direction, and Axis Specification to see the location and direction command description.
4.2.1.3 Creating Surfaces
There are two major ways to create surfaces in Cubit. First, surfaces can be created in Cubit by fitting an analytic or spline surface over a set of bounding curves. In this case, the curves must form a closed loop, and only one loop of curves may be supplied. The second method, is by sweeping a curve about an axis, along a vector, or along another curve. The result of these surface creation commands is a "sheet body" or a body that has zero measurable volume (it does however have a volume entity). This body may be decomposed with booleans and special webcutting commands or it may be used as a tool to decompose other bodies. Booleans can be used to cut holes out of these surfaces.
4.2.1.3.1 Bounding Curves
The first form of this command produces an analytic or spline surface fit to cover the bounding curves.
To create a Surface by Bounding Curves
On the Command Panel, click on Geometry and then Surface.
Click on the Create action button.
Select Bounding Curves from the drop-down menu.
Enter in the appropriate values in the Curve ID(s) field. This can also be done using the Pick Widget function.
Click Apply.
Create Surface Curve <curve_id_1> <curve_id_2> <curve_id_3>...
Bound Curves with On Surface option
On the Command Panel, click on Geometry and then Surface.
Click on the Create action button.
Select Bounding Curves from the drop-down menu.
Click on the On Surface button.
Enter in the appropriate values for Curve ID(s) and On Surface. This can also be done using the Pick Widget function.
Click Apply.
Create Surface Curve <id_list> On Surface <surface_id>
4.2.1.3.2 Bounding Vertices or Nodes
The second form of this command uses vertices to fit an analytic spline surface. The On Surface option creates the surface from a set of nodes and vertices that all lie on one surface and restrains the surface to match the geometry of the underlying surface. The project option will project the nodes or vertices to the specified surface.
To create a Surface by bounding Vertices or Nodes
On the Command Panel, click on Geometry and then Surface.
Click on the Create action button.
Select Vertex List from the drop-down menu.
Select Vertex or Node from the Select menu.
Enter in the appropriate value for Vertex ID(s) or Node ID(s). This can also be done using the Pick Widget function.
Click on the On Surface button and enter the appropriate value in for Surface ID.
Click Apply.
Create Surface [Node|Vertex| <id_list>] [On Surface <surface_id> {Project} ]
4.2.1.3.3 Copy
The next form creates a surface using the same geometric description of the specified surface. The new surface will be a stand-alone sheet body that is geometrically identical to the user supplied surface.
To create a Surface by making a Copy
On the Command Panel, click on Geometry and then Surface.
Click on the Create action button.
Select Copy from the drop-down menu.
Enter in the appropriate value for Surface ID(s). This can also be done using the Pick Widget function.
Click on Transform Copied Surfaces and select Move, Rotate, Reflect or Scale.
Enter in the appropriate settings.
Click Apply.
Create Surface From Surface <surface_id>
4.2.1.3.4 Extended Surface
The fourth form of the command creates a surface that is extended from a given surface or list of surfaces. The specified surface’s geometry is examined and extended out "infinitely" relative to the current model in Cubit (i.e. extended to just beyond the bounding box of the entire model). The given surfaces are extended as shown in the table.
To create a Surface by Extending a Surface
On the Command Panel, click on Geometry and then Surface.
Click on the Create action button.
Select Extended Surface from the drop-down menu.
Enter in the appropriate value for Surface ID(s). This can also be done using the Pick Widget function.
Enter in any other appropriate settings.
Click Apply.
Create Surface Extended From Surface <surface_id>
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Multiple surfaces can be offset at the same time to form a sheet body, by using the Create Sheet Extended from Surface command.
4.2.1.3.5 Planar Surface
The following commands create planar surfaces. The first passes a plane through 3 vertices, the second uses an existing plane, the third creates a plane normal to one of the global axes, and the fourth creates a plane normal to the tangent of a curve at a location along the curve. By default, the commands create the surface just large enough to intersect the bounding box of the entire model with minimum surface area. Optionally, you can give a list of bodies to intersect for this calculation. You can also extend the size of the surface by either a percentage distance or an absolute distance of the minimum area size. The plane can be previewed with the command Draw Plane [with]... (where the rest of the command is the same as that to create the surface).
To create a Planar Surface through 3 vertices
On the Command Panel, click on Geometry and then Surface.
Click on the Create action button.
Select Planar Surface from the drop-down menu.
Select Vertex from the Create Planar Surface With Plane menu.
Enter in the appropriate values for Vertex ID 1, 2 and 3. This can also be done using the Pick Widget function.
Enter in any other appropriate settings from this menu.
Click Apply.
Create Planar Surface [With] Plane Vertex <v1_id> [Vertex] <v2_id> [Vertex] <v3_id> [Intersecting] Body <id_range>] [Extended Percentage|Absolute <val>]
On the Command Panel, click on Geometry and then Surface.
Click on the Create action button.
Select Planar Surface from the drop-down menu.
Select Surface from the Create Planar Surface With Plane menu.
Enter in the appropriate value for Surface ID. This can also be done using the Pick Widget function.
Enter in any other appropriate settings from this menu.
Click Apply.
Create Planar Surface [With] Plane Surface <surface_id> [Intersecting] Body <id_range>] [Extended Percentage|Absolute <val>]
On the Command Panel, click on Geometry and then Surface.
Click on the Create action button.
Select Planar Surface from the drop-down menu.
Select XYZ from the Create Planar Surface With Plane menu.
Select XY Plane, ZX Plane or YZ Plane from the select menu.
Enter in the desired Offset Value.
Enter in any other appropriate settings from this menu.
Click Apply.
Create Planar Surface [With] Plane {Xplane|Yplane|Zplane} [Offset <val>] [Intersecting] Body <id_range>] [Extended Percentage|Absolute <val>]
On the Command Panel, click on Geometry and then Surface.
Click on the Create action button.
Select Planar Surface from the drop-down menu.
Select Normal To Curve from the Create Planar Surface With Plane menu.
Enter in the appropriate Curve ID value. This can also be done using the Pick Widget function.
Select Fraction, Distance, Position or Near Vertex from the Select menu.
Enter in any other appropriate settings from this menu.
Click Apply.
Create Planar Surface [With] Plane Normal To Curve <curve_id>{Fraction <f>| Distance <d> | Position <xval><yval><zval> | Close_to vertex <vertex_id>} [[From] Vertex <vertex_id> (optional for ’fraction’ & ’distance’)] [Intersecting] Body <id_range>] [Extended Percentage|Absolute <val>]
4.2.1.3.6 Net Surface
Net surfaces can be created with two different commands. A net surface passes through a set of curves in the u-direction and a set of curves in the v-direction (these u and v curves would looked like a mapped mesh). The first form of the command uses curves to create the net surface. The curves must pass within tolerance of each other to work. The second form uses a mapped mesh to create the surface. The mapped mesh can be of a single surface or a collection of mapped or submapped surfaces that form a logical rectangle. By default net surfaces are healed to take advantage of any possible internal simplification.
To create a Net Surface from UV curves
On the Command Panel, click on Geometry and then Surface.
Click on the Create action button.
Select Net Surface from the drop-down menu.
Select From UV Curve from the select menu.
Enter in the appropriate values for U Curve ID(s) and V Curve ID(s). This can also be done using the Pick Widget function.
Enter in any other appropriate settings from this menu.
Click Apply.
Create Surface Net U Curve <id_list> V Curve <id_list> [Tolerance <value>] [HEAL|Noheal]
On the Command Panel, click on Geometry and then Surface.
Click on the Create action button.
Select Net Surface from the drop-down menu.
Select Mapped Surface from the select menu.
Enter in the appropriate value for Surface ID(s). This can also be done using the Pick Widget function. The surface must be meshed.
Enter in any other appropriate settings from this menu.
Click Apply.
Create Surface Net [From] [Mapped] Surface <id_list> [Tolerance <value>] [HEAL|Noheal]
4.2.1.3.7 Offset
The following command creates surfaces offset from existing surfaces at the specified distances.
To create a Surface offset from an Existing Surface
On the Command Panel, click on Geometry and then Surface.
Click on the Create action button.
Select Offset from the drop-down menu.
Enter in the appropriate value for From Surface ID(s). This can also be done using the Pick Widget function.
Enter in the appropriate value for Offset Value.
Enter in any other approrpriate settings from this menu.
Click Apply.
Create Surface Offset [From] Surface <id_list> Distance <val>
Figure 111: Offsetting surfaces to form individual surfaces or sheet bodies
4.2.1.3.8 Skinning
The following command creates a skin surface from a list of curves. An example of a skin surface is to create a surface through a set of parallel lines.
To create a Surface by Skinning
On the Command Panel, click on Geometry and then Surface.
Click on the Create action button.
Select Skin Curve from the drop-down menu.
Enter in the appropriate values for Curve ID(s). This can also be done using the Pick Widget function.
Click Apply.
Create Surface Skin Curve <id_list>
4.2.1.3.9 Sweeping of Curves
A curve or a set of curves can be swept along a path to create new surfaces. The path may be specified as an axis and angle, a vector and distance, by indicating another curve or set of contiguous curves, or by specifying a target plane. The following commands show the options available:
To sweep a Curve along an Axis
On the Command Panel, click on Geometry and then Surface.
Click on the Create action button.
Select Sweep from the drop-down menu.
Select Axis/Angle from the Sweep Method menu.
Enter in the appropriate value for Curve ID(s). This can also be done using the Pick Widget function.
Select the appropriate Axis from the Axis of Rotation menu.
Enter in the appropriate values for Angle and Steps.
Enter in any other appropriate settings from this menu.
Click Apply.
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] [Include_mesh] [Keep][Rigid]
On the Command Panel, click on Geometry and then Surface.
Click on the Create action button.
Select Sweep from the drop-down menu.
Select Vector and Distance from the Sweep Method menu.
Enter in the appropriate value for Curve ID(s). This can also be done using the Pick Widget function.
Enter in the appropriate values in the Vector X,Y,Z field.
Enter in any other appropriate settings from this menu.
Click Apply.
Sweep Curve <curve_id_range> Vector <xvector yvector zvector> [Distance <distance>] [Draft_angle <degrees>] [Draft_type <integer>] [Include_mesh] [Keep] [Rigid]
On the Command Panel, click on Geometry and then Surface.
Click on the Create action button.
Select Sweep from the drop-down menu.
Select Along Curve from the Sweep Method menu.
Enter in the appropriate value for Curve ID(s). This can also be done using the Pick Widget function.
Enter in any other appropriate settings from this menu.
Click Apply.
Sweep Curve <curve_id_range> Along Curve <refcurve_id_range> [Draft_angle <degrees>] [Draft_type <integer>] [Include_mesh] [Keep] [Rigid]
On the Command Panel, click on Geometry and then Surface.
Click on the Create action button.
Select Sweep from the drop-down menu.
Select Target Volume from the Sweep Method menu.
Enter in the appropriate values for Volume ID and Curve ID(s). This can also be done using the Pick Widget function.
Enter in the appropriate settings for Direction. Click on the Direction... button to open a separate window to specify settings.
Enter in the appropriate settings for Plane. Click on the Plane... button to open a separate window to specify settings.
Click Apply.
Sweep Curve <curve_id_range> Target Plane <options>
Sweep Curve <curve_id_range> Target {Volume|Body} <id> Direction {options} [Plane <options>] [Unite]
In the above commands, the include_mesh option will create a surface mesh if the curve is already meshed (see figure below). The keep option will keep the original curve while creating the surface.
The sweep curve target plane command sweeps a curve until it hits a target plane. The options for the target plane are described under Specifying a Plane.
The last command sweeps a curve to a target volume or body and can only be used on sheet bodies. Use the direction keyword to specify the sweep direction and the plane keyword to specify a stopping plane. The unite keyword will unite the sheet bodies after sweeping
The other options are as follows:
draft_angle: determines how much drafting in of the surface is desired
draft_type:
0 => extended (draws two straight tangent lines from the ends of each segment until they intersect)
1 => rounded (create rounded corner between segments)
2 => natural (extends the shapes along their natural curve)
rigid: normally the curve will rotate to maintain its original orientation to the sweep path. The rigid option disallows this rotation.
4.2.1.3.10 Midsurface
Multisurfaces may be created midway between pairs of surfaces using the following command:
To create a Surface midway between pairs
On the Command Panel, click on Geometry and then Surface.
Click on the Create action button.
Select Midsurface from the drop-down menu.
Enter the appropriate values for Volume ID and Surface ID Pairs. This can also be done using the Pick Widget function.
Click Apply.
Create Midsurface {Body|Volume} <id> Surface <id11> <id12> ... <idN1> <idN2>
Figure 113: Multisurface created with the Create Midsurface command
Figure 114: Midsurface created from 2 pairs of cylindrical surfaces
Midsufaces can also be extracted without surface pair specification if the resulting surface is a single sheet of surfaces (no T intersections).
For automatic midsurface extraction
On the Command Panel, click on Geometry and then Surface.
Click on the Create action button.
Select Auto Midsurface from the drop-down menu.
Enter the appropriate values for Volume ID(s). This can also be done using the Pick Widget function.
Enter the appropriate values for Lower Bounds and Upper Bounds.
Enter in any other appropriate settings from this menu.
Create Midsurface {Body|Volume} <id_range> Auto [Delete] [Transparent] [Thickness] [Limit <lower_bound> <upper_bound>] [Preview]
create midsurface volume 1 auto delete
The command option descriptions are listed below.
auto enables the automatic mid-surface algorithm. Turning Auto off requires the user to specify a single surface pair to create a mid-surface.
transparent shows the successfully midsurfaced volumes as transparent in the graphics display
thickness applies a 2D property to the created mid-surface geometry.
limit search range gives the algorithm a range to find surface pairs within.
4.2.1.3.11 Weld Profile
Create Surface Weld [Root] Location {options} Weld Surface <id_list> Length <val> [<val2>]
create surface weld root location vertex 25 weld surface 13 14 length 2
4.2.1.3.12 Creating A Surface From Mesh Entities
Surfaces may be created from the boundaries of meshed volumes, surfaces, and/or from individual quadrilateral mesh elements. The individual option makes it so you can enter multiple surfaces at once, and not have them merged together into a larger surface, but instead retain their own original boundaries. The optional tolerance value allows the user to specify a tolerance to which the resulting surface should be fit. The default value is 0.001. If surface creation fails, increasing the tolerance value can help.
Create Acis [From] {Surface <id_range> | Volume <id_range> | Face < id_range> [Individual]} [Tolerance <value>]
4.2.1.3.13 Creating a Circular Surface
This command creates a 2D circular surface. The surface will be centered at the origin and on the z-plane if a plane option is not specified.
To create a Cirular Surface using a radius
On the Command Panel, click on Geometry and then Surface.
Click on the Create action button.
Select Circle from the drop-down menu.
Select Radius from the Specify Circle Using menu.
Enter in the appropriate Radius value.
Select XPlane, YPlane or ZPlane.
Click Apply.
create surface circle radius <value> {xplane|yplane|ZPLANE}
To create a 2D circular surface by specifying three vertices
On the Command Panel, click on Geometry and then Surface.
Click on the Create action button.
Select Circle from the drop-down menu.
Select Center Vertex from the Specify Circle Using menu.
Enter in the appropriate values for Center, Vertex 1 and Vertex 2. This can also be done using the Pick Widget function.
Click Apply.
create surface circle center vertex <v1_id> <v2_id> <v3_id>
To create a 2D circular surface by forming a circular curve through three points.
On the Command Panel, click on Geometry and then Surface.
Click on the Create action button.
Select Circle from the drop-down menu.
Select Vertex List from the Specify Circle Using menu.
Enter in the appropriate values for Vertex 1, Vertex 2 and Vertex 3. This can also be done using the Pick Widget function.
Click Apply.
create surface circle vertex <v1_id> <v2_id> <v3_id>
4.2.1.3.14 Creating a Parallelogram
This command creates a 2D parallelogram surface, centered at the origin, by specifying three corner vertices.These vertices will form three consecutive corners of the parallelogram surface.
To create a 2D parallelogram surface
On the Command Panel, click on Geometry and then Surface.
Click on the Create action button.
Select Parallelogram from the drop-down menu.
Enter in the appropriate values for Vertex 1, Vertex 2 and Vertex 3. This can also be done using the Pick Widget function.
Click Apply.
create surface parallelogram vertex <v1_id> v2_<id> <v3_id>
4.2.1.3.15 Creating an Ellipse
This command creates a 2D elliptical surface, centered at the origin, by specifying at least a major radius.On an x-y plane this radius will be the radius along the x-direction.The minor radius will be the radius along the y-direction.By default, the surface will lie in the z-plane.
To create a 2D elliptical surface
On the Command Panel, click on Geometry and then Surface.
Click on the Create action button.
Select Ellipse from the drop-down menu.
Select Radius from the Specify Ellipse Using menu.
Enter in the appropriate values for Major Radius and Minor Radius.
Select XPlane, YPlane or ZPlane.
Click Apply.
Create Surface Ellipse major radius <value> [minor radius <value>] [xplane|yplane|ZPLANE]
To create a 2D elliptical surface using three vertices
On the Command Panel, click on Geometry and then Surface.
Click on the Create action button.
Select Ellipse from the drop-down menu.
Select Vertex List from the Specify Ellipse Using menu.
Enter in the appropriate values for Axis 1 Vertex ID, Axis 2 Vertex ID and Origin Vertex ID. This can also be done using the Pick Widget function.
Click Apply.
Create Surface Ellipse vertex <v1_id> <v2_id> <v3_id>
4.2.1.3.16 Creating a Rectangle
This command creates a rectangular surface centered at the origin.If only a width value is specified, the surface will be a square.On an x-y plane, the width value is the x-direction and the height is the y-direction.By default, the surface will lie in the z-plane.
To create a rectangular surface centered at the origin
On the Command Panel, click on Geometry and then Surface.
Click on the Create action button.
Select Rectangle from the drop-down menu.
Enter in the appropriate values for Width and Height (Optional).
Select XPlane, YPlane or ZPlane.
Click Apply.
Create Surface rectangle width <value> [height <value>] [xplane|yplane|ZPLANE]
4.2.1.4 Creating Vertices
The basic commands available for creating new vertices directly in Cubit are detailed in this section.
4.2.1.4.1 XYZ location
The simplest form of this command is to specify the XYZ location of the vertex. It can also be created lying on a curve or surface in the geometric model by specifying the curve or surface id; the position of the vertex will be the point on the specified entity which is closest to the position specified on the command. With all of these commands, the user is able to specify the color of the vertex.
To create a Vertex by specifying the XYZ location
On the Command Panel, click on Geometry and then Vertex.
Click on the Create action button.
Select Coordinates from the drop-down menu.
Enter in the appropriate values for X Coordinate, Y Coordinate and Z Coordinate.
Select Curve or Surface from the Create On menu.
Enter in the appropriate values for Curve ID or Surface ID. This can also be done using the Pick Widget function.
Optionally, specify the color.
Click Apply.
Create Vertex <x><y><z> [On [Curve | Surface] <id>] [Color <color_name>]
4.2.1.4.2 On Curve - Fraction
A vertex can be positioned a certain fraction of the arc length along a curve using the second form of the command.
To create a Vertex from the On Curve options
On the Command Panel, click on Geometry and then Vertex.
Click on the Create action button.
Select On Curve from the drop-down menu.
Enter in the appropriate value for Curve ID(s). This can also be done using the Pick Widget function.
Select Fraction, Distance, Position, Close to Vertex, Segments or Midpoint from the Specify Location menu.
Enter in the remaining appropriate information for this menu.
Optionally, specify the color.
Click Apply.
Fraction: Divides the selected curve into segments based on the fraction value entered and creates a vertex at the end of the first segment. Specify from which direction by seleting Start, End or Vertex. For example, create a vertex at .25 (1/4) the length of a curve.
Distance: Creates a vertex on the selected curve the specified number of units away from the starting point (start, end, vertex, curve and surface). For example, create a vertex a distance of 2 along a curve with length 5.
Position: Creates a vertex at the location entered into the X,Y and Z coordinates.
Close to Vertex: Creates a vertex on the selected curve at the closest point to a specified vertex.
Segments: Divides the selected curve into a specified number of segments and creates a vertex at each endpoint.
Midpoint: Creates a vertex at the Midpoint of the selected curve.
Vertex 3 in the following example was created with this command:
create vertex on curve 1 fraction 0.25 from vertex 1
4.2.1.4.3 On Curve - General
Create Vertex On Curve <id_list> { MIDPOINT | Start | End | Fraction <val 0.0 to 1.0> [From Vertex <id> | Start|End] | Distance <val> [From {Vertex|Curve|Surface} <id> | Start|End] | {{Close_To|At} Location {options} | Position <xval><yval><zval>|{Node|Vertex} <id>} | Extrema [Direction] {options} [Direction {options}] [Direction {options}] | Segment <num_segs> | Crossing {Curve|Surface} <id_list> [Bounded|Near] } [Color <color_name>]
4.2.1.4.4 From Vertex
Create Vertex from Vertex <id_list> [ On {Curve|Surface} <id> ] [Color <color_name>]
4.2.1.4.5 At Arc
Another form simply creates vertices at arc or circle centers.
To create a Vertex in the Center of an Arc
On the Command Panel, click on Geometry and then Vertex.
Click on the Create action button.
Select Arc Center from the drop-down menu.
Enter in the appropriate value for Curve ID(s). This can also be done using the Pick Widget function.
Optionally, specify the color.
Click Apply.
Create Vertex Center Curve <id_list> [Color <color_name>]
4.2.1.4.6 At Intersection
The last form creates vertices at the intersection of two curves. If the bounded qualifier is used, the vertices are limited to lie on the curves, otherwise the extensions of the curves are also used to calculate the intersections. The near option is only valid for straight lines, where the closest point on each curve is created if they do not actually intersect (resulting in two new vertices).
To create a Vertex at an Intersection
On the Command Panel, click on Geometry and then Vertex.
Click on the Create action button.
Select At Intersection from the drop-down menu.
Enter in the appropriate values for Curve ID 1 and Curve ID 2. This can also be done using the Pick Widget function.
Enter in any other appropriate settings from this menu.
Optionally, specify the color.
Click Apply.
Create Vertex AtIntersection Curve <id1> <id2> [Bounded] [Near] [Color <color_name>]
4.2.2 Geometric Primitives
The geometric primitives supported within Cubit are pre-defined templates of three-dimensional geometric shapes. Users can create specific instances of these shapes by providing values to the parameters associated with the chosen primitive. Primitives available in Cubit include the brick, cylinder, torus, prism, frustum, pyramid, and sphere. Each primitive, along with the command used to generate it and the parameters associated with it, are described next. For some primitives, several options can be used to generate them, and are described as well.
4.2.2.1 General Notes
Primitives are created and given an ID equal to one plus the current highest body ID in the model.
Primitive solids are created with their centroid at the origin or the world coordinate system.
For primitives with a Height or Z parameter, the axis going through these primitives will be aligned with the Z axis.
For primitives with a Major Radius and a Minor Radius, the Major Radius will be along the X axis, the Minor Radius along the Y axis.
For primitives with a Top Radius, this radius will be that along the X axis; the Y axis radius will be computed using the Major, Minor and Top Radii given.