New Features in Cubit 13.1

Meshing

Adjust Boundaries Orthogonal Command

Adjust Boundaries Orthogonal is a new mesh operation that applies smoothing to the nodes of both the curves and surface simultaneously to achieve approximate perpendicular mesh edges at the boundaries.



These images illustrate the effect of the adjust boundaries orthogonal command. Left is the initial mesh and right is the mesh after applying the command.

New Sweep Meshing Options

Sweeping continues to be the workhorse algorithm for Cubit, where a large portion of volume meshing tasks utilize this important capability. A number of new options have been added for this release, allowing the user greater control over the resulting hex mesh. The following outlines the main new features:

1. Propagate Bias: The new propagate_bias option attempts to preserve the source bias by propagating bias mesh schemes from the curves of the source surface to the curves of the target surface.
2. Sweep Smoothing: To ensure adequate mesh quality, optional smoothing schemes are available to reposition the interior nodes. The sweep tool permits five types of smoothing: linear, smart_affine, residual, winslow and auto. These smoothing schemes are described in more detail in the documentation.
3. Sweep Transform: Swept meshes are created by projecting points between the source and target surfaces using affine transformations and then connecting them to form hexahedra. The method used to calculate the affine transformations is set using the sweep_transform option. In previous versions of Cubit, a generalized least_squares approximation was used for computing node locations, which could sometimes perform poorly for simple translation sweeps. In Cubit 13.1 we introduce an explicit translate option that will perform a simple interpolation between source and target surfaces. Although least_squares remains the default sweep transform method and is the most general, consider using translate if you get poor result on simple linear translation swept volumes.
4. Autosmooth target: With this option turned on the target surface mesh is smoothed before the volume is swept rather than relying on the sweep transformation to place the nodes.

Coincident quad check improvement

The topology check coincident quad command now checks for nodes at the same location whether they are part of the same quad, or a different mesh block. In other words, instead of comparing only the actual nodes used to define the two quads, coincident nodes on neighboring meshes are also checked. The previous behavior would detect no coincident quads in two adjoining unmerged blocks.

Directional Refinement

Often there are cases where the model dictates a very thin region such as a gasket or membrane, adjacent to a large blocky region. To achieve a good element aspect ratio in the thin part, the element size in the thick region would may need to be too small. Directional refinement addresses this problem, by allowing the user to limit the directions in which refinement will take place using a reference surface or plane. These figures show how the green membrane was refined only in the plane of the membrane without adding additional elements through its thickness. Using Cubit's standard refinement operation, the elements through the thickness would also be refined.

Improved preview for curve meshing

The command panel for curve meshing (Meshing > Curve > Mesh) currently provides options for previewing the mesh prior to mesh generation. This feature has been improved and made more consistent with this release of Cubit.

New Options in Curve Bias for Multiple Start Positions

To mesh a set of curves with a bias, often a start vertex is required. Previously the command syntax would only permit a single start vertex, which would not allow specification of bias on multiple curves. This enhancement changes the syntax for the curve bias command to accept multiple start vertices to allowing meshing of multiple curves simultaneously.

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Geometry

New Helix Curve and Volume Creation

New commands to generate free curves and volumes defined as helix have been added.



This image on the left shows two helix curves generated with the commands

create curve helix zaxis location 1 0 0 thread_distance 1 angle 5000 left_handed
create curve helix zaxis location 1 0 0 thread_distance 1 angle 5000 right_handed

The image on the right was created by sweeping a circle along a helix path using the following commands

create surface circle radius 0.5 yplane
body 1 mov x 2
sweep surface 1 helix zaxis thread_distance 3 angle 1000 right_handed

GUI for Auto Midsurface Command

The ability to automatically create midsurfaces from volumes is a relatively new feature in Cubit. In version 13.1, we introduce a command panel in the GUI to control its options. It can be accessed from the command panel Geometry > Surface > Create > Auto Midsurface

Manage Gaps and Overlaps Tool

Cubit 13.1 has a new tool for quickly identifying and fixing gaps and overlaps in assembly models. The Gaps and Overlaps Tool is part of Cubit's Wizard Power Tool (or ITEM). This tool provides diagnostic information on gaps and overlaps. Cubit 13.1 introduces a smart solution interface that provides options for resolving the issues that were identified. When the user selects an issue identified by Cubit, the tool displays possible solutions for fixing it. The user simply clicks execute to perform the selected solution. Solutions usually consist of typical intersection/subtraction or tweak operations that are currently manually done in cubit. The packaged solutions allows the user to quickly step through each problem and fix it.

Curve Orient Sense Command

The tangent direction or orientation sense of one or more curves can now be modified using the new command curve orient sense. Orientation can be defined using location and direction options. This is especially useful when defining the bias characteristics for multiple curves simultaneously.

Sweep Sheet with Multiple Surfaces

The ability to sweep or extrude a surface to generate a volume has been an important capability in Cubit, however it has been limited to sweeping single surfaces. Cubit 13.1 adds the capbility to sweep multiple surfaces that belong to the same sheet body in the same command. The following figure at left shows a single sheet body containing 4 separate surfaces. The result is shown at right where all 4 surfaces have been extruded siultaneously.

Sweep Meshed Surfaces

Cubit currently provides the capability to create a volume by sweeping a surface through a specified path. With this release, we provide the feature to sweep a meshed surface. This means that a swept solid mesh will also be generated in the new volume based on the 2D mesh defined on the source surface. To use this capability, use the new include_mesh option on most of the sweep surface commands.



The image at left shows a surface (sheet body) that has been meshed with quads. Applying the sweep surface command with the include_mesh option resulted in the mesh at right. The result is a volume meshed with hexahedra where the mesh intervals in the sweep direction are automatically computed.

Sweep Meshed Curves

Similar to sweeping a meshed surface to create a meshed volume, Cubit 13.1 also introduces the feature to sweep a meshed curve into a meshed surface. The resulting mesh generated on the new surface will be a mapped mesh using the intervals defined on the source curve with automatic intervals in the sweeping direction. To use this capability, use the new include_mesh option on the sweep curve command.

New Merge Option in Split Curve Command

Previously the split curve command would split a curve at a specified location but leave the two (or more) resulting curves unconnected. The new merge option allows the user to automatically connect the two curves where the new vertex is created.

New Create Curve Arc Command Options

Two new options for creating Arcs in Cubit have been added. These include:

1. Create an arc by selecting two end vertices and specifying a radius and normal direction.
2. Create an arc using the center position of the arc, the radius, the normal direction and the sweep angle.

New Options in Loft Volume Command

The Create Volume Loft command in Cubit provides the ability to create a volume between two or more reference surfaces. The resulting volume can be controlled in a variety of ways. Cubit 13.1 introduces several new keywordsto the create volume loft command to extend the control of how the resulting volume is defined. These include: Guide curve, Takeoff_factors, Takeoff_vector, Match vertex, Closed, Preview and Show_matching_curves. See the documentation for a complete description of each option. These new options can be controlled through an extensive new GUI command panel shown at left. It can be accessed through the command panels at Geometry > Volume > Create > Lofted Volume The images below illustrate some of the new capability. The first image shows three independent surfaces that will be used as reference surfaces for the loft. The second image shows a resulting lofted volume where the takeoff_factors have been adjusted. The third image shows the use of a guide curve, where curve 49 was used to guide the loft through the three surfaces.

New Options in Sweep Surface Command

The ability to extrude a surface to create a volume has been available in Cubit for some time now. In Cubit 13.1 we introduce several new options for defining the direction of sweep. These include Cartesian axes, curve tangent, surface normal and various methods for defining a vector.

New "include_merged" option in Move and Rotate Commands

To apply a transformation such as a translation or rotation to a set of merged bodies, Cubit previously required that each of the volumes to be moved be transformed separately. Cubit 13.1 introduces the new include_merged option for both the rotate and move commands which will automatically apply the same transformation to any entities that are merged with the specified entity.

Move Group Command

The syntax for the command Move {Vertex|Curve|Surface|Volume|Body|Group} <id_range> has now been updated to include Groups. This makes the command Move <entity> syntax consistent with the <entity> Move form of the command.

Scale About Reference Point Command

The scale transformation in Cubit has now been enhanced to permit scaling about an arbitrary reference point rather than the previous capability of scaling about the origin.

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Materials and Boundary Conditions

New Initial Condition Options

Users may now create and modify initial conditions of temperature, displacement, velocity, acceleration, and field variable. Initial conditions are applied to nodesets. Presently, an initial condition may apply to a single nodeset. Commands to list and delete initial conditions are also available.

New Material Creation Options

Users may specify user constants as part of a material definition. User constants are stored as field properties. The user may also specify a value for DepVar, which is an Abaqus-specific variable.

New Copy Boundary Conditions Options

When creating new geometric entities using Cubit's Copy command, Nodesets, Sidesets and Blocks defined on the original entity can now also be copied. The following commands can be used to turn this feature on and off for nodesets, sidesets and blocks respectively:

set copy_nodeset_on_geometry_copy [on | OFF| use_original]
set copy_sideset_on_geometry_copy [on | OFF| use_original]
set copy_block_on_geometry_copy [on | OFF| use_original]

Boundary Conditions propagated through Webcut Operations

New geometric entities will also be created when using Cubit's webcut operations. Nodeset, Sideset and Block information contained on the original entities can now also be transferred to the resulting webcut entities.

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Import/Export

Partial ABAQUS Export

Cubit can now export an Abaqus deck that contains only the mesh described by the *NODE, *ELEMENT, *NSET, *ELSET, and *SURFACE keywords. Use the partial option to get only the mesh portion of the Abaqus file. A complete file also includes the Abaqus keywords and data used to define parts, assemblies, instances, materials, initial conditions, and analysis parameters.

Enhanced ABAQUS Export Command

Node-file/element-file output: Use the nodefile and elementfile options to export separate files of nodes and elements. Cubit writes a different element file for each part.

Flat-file: Use the flatfile option to export a Abaqus file with all nodes and elements in the global space, i.e., no *PART or *INSTANCE keywords.

New "Solid" Option when exporting IGES

The new solid option on the export iges command allows solid volumes to be exported as Manifold Solid B-Rep Objects (MSBO). Without this option, the iges file is simply a collection of stand-alone surfaces.

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Graphics, Utilities, etc.

New Delete APREPRO variable function

Users may now delete APREPRO variables after one is defined. For example, the following snippet defines a variable, uses it in a Cubit command, and then deletes it.

# {var1=2*PI/5}
create brick x {var1} y {var1/2} z {var1*1.5}
# {delete(‘var1’)}

The delete functionality has also been incorporated in to the Graphical APREPRO Editor, where the ability to delete a variable after it has been defined in the table, can now be performed.

New Color Global Command

Normally, Cubit will display surfaces and curves in a rotating set of default colors. The ability to assign a single designated color to all surfaces, curves and vertices has been added for Cubit 13.1

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Beta Features

Cubit remains an active development platform for cutting-edge methods in geometry preparation and mesh generation. Some features that are still under development may not be quite ready for release, but may be valuable in some settings. The following is a list of new beta features that have been made available in Cubit version 13.1. Their functionality is not yet complete, has not been fully tested, however in many settings the new capability may be very valuable. Your help in reporting defects and offering suggestions on these features is appreciated. To turn on or off any of the features listed below, issue the following command from the command line:

Set developer [on|off]

Remesh Tets Free Option

The remesh tet <range> free command is a beta feature and requires the user to enter the command “set developer on” to enable it. The free option enables the new capability to re-mesh merged and unmerged surfaces that may bound the specified range of tets. A new triangle mesh replaces the old one, which may improve element quality if the old mesh is distorted. (This option does not yet remesh curves that are within the range defined by the tets).



The left image shows the initial deformed tetrahedral mesh. The right image shows the mesh after re-meshing with the free option and an analysis-based sizing function.

Parallel Refinement

For those who have access to the Sierra stk_adapt module, Cubit 13.1 supports parallel refinement. Parallel mesh refinement allows refinement to go beyond the memory limits of a single processor. The resulting mesh size is only limited by the number of processors you have available to perform the refinement. To use this feature, first create a course mesh for your model.  Then using the command below, two files will be created that can be used in an external stk_adapt process.

Refine Parallel [Fileroot <'root filename'>] [Overwrite] [No_geom] [No_execute] [Processors <int>] [Numsplit <int>] [Version <'Sierra version'>]

Stk_adapt can also be run directly from Cubit if the executable is in the correct path. When running stk_adapt, a series of mesh files, one for each processor, will be generated on disk that have been refined or subdivided based on the numsplit option. The ability to refine to the precise smooth geometry definition is also available in this beta release.



The left image shows an initial hex mesh generated in Cubit with 2365 hexes. The right image displays a uniformly refined mesh using stk_adapt with 20 processors. The result is about 1.35 million hexes where the colors represent the different processors used in the refinement.

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Limitations in Cubit 13.1

As of Cubit 13.0, the Granite Geometry Kernel is no longer supported.

The Mac OS X port does not support the changing mouse cursors on pre-selection. It is recommended that a 3-button mouse be used for the Mac OS X version since interactive transformation utilizes all three buttons.

Fixed Problems from Pevious Versions

The following items are the user-reported bugs fixed since last release of Cubit (March 2011).

*The defects listed above are only those user-reported issues deemed "critical" or "blocker".

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