7.4 Export
7.4.1 Exporting the Finite Element Model
Export {Abaqus [Explicit]* [Partial]* | Nastran | Ideas | Patran | LSDyna | Fluent} <’filename’> [Block <id_list>] [Sideset <id_list>] [Nodeset <id_list>] [BCSet <id_list>] [dimension {2|3}***] [Overwrite] [Everything] [NX]**
Export VRML <’filename’> [Overwrite]
** NX keyword only available with I-DEAS Exporter
***The dimension argument is also optional. Most element types have an inherent dimensionality associated with them. For example, a truss or beam element is inherently 2D while a hex or tetra element is 3D. Without this argument, only the x-y location of the nodal coordinates of 2D elements are written to the Exodus II file. Using the argument dimension 3, in this example, permits the full 3D coordinates to be written.
Export Abaqus <’filename’> [Block <id_list>] [Sideset <id_list>] [Nodeset <id_list>] [BCSet <id_list>] [dimension {2|3}] [nodefile <’filename’>] [elementfile <’filename’>] [flatfile] [overwrite] [everything]
By default, Cubit will reassign node and element IDs based on which block they are in. If the everything keyword is present, Cubit will export all nodes and elements in the model, whether they are in a block or not.
The I-DEAS Universal file can be read into Siemen’s NX application if the file is generated using the NX keyword. This is because extra information must be written to an I-DEAS Universal file in order for NX to be able to read it.
There are a few keywords specifically for the Abaqus exporter. flatfile can be used if the user desires Cubit to write out the model as a "flat file." Abaqus refers to files a "flat files" when they do not use the *PART/*INSTANCE structure. All nodes and elements will be defined at the global level. The keywords elementfile and nodefile can be used to instruct Cubit to export the nodes and/or elements to a separate file.
If the explicit keyword is used with Abaqus, Cubit will write an Abaqus Explicit deck. The one Explicit-only feature that Cubit supports is fixed mass scaling.
If the partial keyword is used with Abaqus, Cubit will write a partial Abaqus deck. Cubit will output the mesh as defined by the Abaqus keywords PART, NODE, ELEMENT, NSET, ELSET, and SURFACE. Everything else is ignored. Use the Abaqus keyword INCLUDE to include this file in a master Abaqus deck for analysis.
Specific Exporter Commands:
Export Abaqus [explicit] ’<filename>’ [Block <id_list>] [Sideset <id_list>] [Nodeset <id_list>] [BCSet <id_list>] [group <id_list>] [instance block <id_list> [source_csys <id_list>] target_csys <id_list> [preview]][dimension {2|3}] [overwrite] [everything] [partial]
Set Abaqus Precision <n=6>
Note: This command can be used to control the number of decimal places written to the Abaqus file.
Export Nastran ’<filename>’ [Block <id_list>] [Sideset <id_list>] [Nodeset <id_list>] [BCSet <id_list>] [dimension {2|3}] [overwrite] [everything]]
Export Ideas ’<filename>’ [NX] [Block <id_list>] [Sideset <id_list>] [Nodeset <id_list>] [BCSet <id_list>] [dimension {2|3}] [overwrite] [everything]
Export Patran ’<filename>’ [Block <id_list>] [Sideset <id_list>] [Nodeset <id_list>] [BCSet <id_list>] [overwrite] [everything][dimension {2|3}]
Export Lsdyna ’<filename>’ [Block <id_list>] [Sideset <id_list>] [Nodeset <id_list>] [BCSet <id_list>] [overwrite]
Export VRML <’filename’> [Overwrite]
Export Fluent ’<filename>’ [Block <id_list>] [Sideset <id_list>] [Nodeset <id_list>] [BCSet <id_list>] [dimension {2|3}] [overwrite] [everything]
Note: The following command is for exporting mesh geometry:
Export Fluent ’<filename>’ [Surface <id_list>|Volume <id_list>] [Overwrite]
7.4.1.1 Supported element types
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*Thermal element
**Check to make sure the element’s properties are correct after exporting
***Also exports lofting factor for shell elements (IDEAS)
^ The element type will be HEX but the number of nodes will be the number of nodes in the pyramid
7.4.1.2 Supported boundary conditions types
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*** Does not allow separate temperatures for top and bottom of shell elements. Values will be averaged.
7.4.2 Defining PARAMS for NASTRAN
List Nastran Exporter Params
Set Nastran Exporter Params Add ’<param_string>’
Set Nastran Exporter Params Remove ’<param_string>’
Set Nastran Exporter Params Clear
7.4.3 Instancing Parts with ABAQUS
The ABAQUS file format allows users to instance a mesh multiple times. An example of this would be to create a mesh of a single bolt, but instance the bolt mesh several times in the ABAQUS model file to generate multiple bolts.
To export an ABAQUS file with instanced parts
Click file and then export.
Select the desired location to save the file.
Enter the file name.
Select abaqus from the save as type drop-down menu.
Click save. A new window will appear.
Enter the appropriate settings.
Click finish.
export abaqus <’filename’> [block <id_list>] [sideset <id_list>] [nodeset <id_list>] [bcset <id_list>] [group <id_list>] [instance block <id_list> [source_csys <id>] [target_csys <id_list>] [mesh_only] [overwrite] [everything]
Note: By default, the Abaqus exporter writes 6 decimal places. The command set abaqus precision <n> can be used to change the number of decimal places written.
The mesh_only option can be used to export only the mesh, which includes the nodes, elements, nodesets, and sidesets. The mesh only file can then be included in an abaqus input deck.
7.4.4 Exporting ANSYS CDB files
Coreform Cubit can export *.cdb files to be used in ANSYS Mechanical simulations via the APDL command cdread,all,filename,cdb. All exported entities must be part of a block. By default, this is a mesh only export. Optionally, the surface geometry may also be exported in a parallel IGES file. The mesh and the geometry are not associated in ANSYS.
Export Ansys CDB <’filename’> [Block <id_list>] [Geometry] [Overwrite]
7.4.5 Exporting an Exodus II File
To export an Exodus II file
Click file and then export.
Select the desired location to save the file.
Enter the file name.
Select exodus from the save as type drop-down menu.
Click save. A new window will appear.
Enter the appropriate settings.
Click finish.
Export [Genesis|Mesh] ’<filename>’ [dimension {2|3}] [Block <id_list>] [XML ’<filename>’]
The dimension argument is also optional. Most element types have an inherent dimensionality associated with them. For example, a truss or beam element is inherently 2D while a hex or tetra element is 3D. Without this argument, only the x-y location of the nodal coordinates of 2D elements are written to the Exodus II file. Using the argument dimension 3, in this example, permits the full 3D coordinates to be written.
The optional block argument may also be added to the export command. Without this argument, all blocks defined in the current model will be exported to the Exodus II file. This argument permits the user to specify only a portion of the blocks in the model. The <id_list> may be any valid set of integers corresponding to the Blocks in the current model.
The XML optional argument may also be added to the export command. When this argument is included and assembly data exists in the model, an XML file is written which describes the relationship between block IDs in the Exodus II file and parts in the assembly. See the Parts, Assemblies and Metadata section for details.
7.4.5.1 Element and Node ID Maps
Element ID map and node ID map are always written to the Exodus II file. The IDs written to the node ID map are the node IDs used to refer to nodes at the Cubit command line. The IDs written to the element ID map are the Global Element IDs which are assigned to the hex, tet, quad, etc. when they are added to an element block. The node and element ID maps can be used when a particular element or node is referred to in a downstream application and the corresponding node or element in Cubit must be found. Some analysis and post-processing applications consider these maps to be optional, while others ignore the maps even if they are present. See the https://github.com/gsjaardema/seacas#exodus for more information on element and node ID maps.
7.4.5.2 Exporting a Parallel Mesh for pCAMAL
Export Parallel "<filename>" [Block <id_list>] [Overwrite] [Processor <number>]
The processor option allows the user to specify the number of processors that will be used to mesh the volume with the pCAMAL option. This same option exists in the pCAMAL application and is more often used there since the number of available processors is known then rather than when the output file is created in Cubit.
If the processor option is given, Cubit attempts to balance the number of sweepable volumes to run on n processors by converting many-to-one sweeps to one-to-one sweeps, subdividing the sweep volume along its sweep direction, or partitioning the source surface of a one-to-one sweep if the number of source quads is much larger than the number of layers.
7.4.5.3 Converting an Exodus II file to ASCII
The Exodus II file format is binary. It is frequently necessary to view the contents of the Exodus II file as plain text. A publicly available tool known as ncdump can be used to view the contents of an Exodus II file. ncdump is part of the netCDF library and is currently available from Unidata at the following URL:
ncdump filename.e > filename.txt
Another option for converting between binary and ASCII formats of Exodus II files is a utility known as exotxt. Exotxt is part of the https://github.com/gsjaardema/seacas tool suite. Contact the Sandia Cubit development team for a copy of this utility.
Note that the ’stock’ ncdump utility should work for most meshes; however, Sandia increases some of the dimensions in order to handle larger meshes (more element blocks, boundary conditions, variables). The dimensions we increase in netcdf.h are:
NC_MAX_DIMS (max dimensions per file) from 100 to 65536
NC_MAX_VARS (max variables per file) from 2000 to 524288
7.4.5.4 Controlling Exodus II Output Precision
Set Exodus Single Precision [On|Off]
7.4.5.5 Large Exodus Format
Set Large Exodus [On|OFF]
7.4.6 Exporting Fluent Grid Files
Geometry can be exported from Cubit to the Fluent .msh format. This format can be used to exchange grid information between .msh compatible programs including Fluent, GAMBIT, and TGrid.
To export a fluent grid file
Click file and then export.
Select the desired location to save the file.
Enter the file name.
Select fluent from the save as type drop-down menu.
Click save. A new window will appear.
Enter the appropriate settings.
Click finish.
Export Fluent ’<filename>’ [Block <id_list>] [Sideset <id_list>] [Nodeset <id_list>] [BCSet <id_list>] [Dimension{2|3}] [Overwrite] [Consolidate]
In order to guarantee that the grid file will be compatible with Fluent, all bodies must be merged (See Geometry Merging). Several types of Fluent boundary condition zones are now implemented in Cubit. They are:
axis
exhaust fan
fan
inlet vent
intake fan
interface
interior
mass flow inlet
outflow
outlet vent
periodic
periodic shadow
porous jump
pressure far field
pressure inlet
pressure outlet
radiator
symmetry
velocity inlet
wall
If consolidate is used, all user defined blocks will be combined into a single block.
Boundary condition zones created in two different ways. The first way involves user-defined mesh groups consisting only of quads (3D), triangles (3D), or element edges (2D) (See Geometry Groups). The second way involves sidesets. Specifying a boundary condition consists of selecting a user-defined mesh group or a sideset, or a surface. Selecting a surface automatically assigns the boundary condition to the sideset associated with that surface. The boundary condition type is specified and is either given a name or an id (See Using CFD Boundary Conditions). Groups or sidesets of mixed type (e.g. hexes and faces) will not be exported. All surfaces not set to one of the first seven boundary condition types are automatically set to type ’wall’. The various parameters for each of the boundary condition types must be set within either Fluent or GAMBIT.
Cell zones are automatically created for 3D meshes containing blocks. Blocks must contain entire and continuous volumes in order to create a valid grid. In 2D models, the cell zones are created from sidesets containing only quads or tris. In order to create a valid grid, these sidesets must contain whole, continuous surfaces. All cell zones are by default set to type ’fluid.’
If no entities are specified, the entire model is exported. In order to export selected entities, the types ’volume’ and ’surface’ can be specified. In 2D cases, use ’surface’ while in the 3D case use ’volume.’
The exporter can handle higher-order elements, although Fluent will convert the elements to first-order upon import.
7.4.7 Exporting Sierra Files
Sierra input decks can be exported from Cubit.This capability was added in response to a need to translate Abaqus input decks to Sierra input decks by importing the Abaqus deck into Cubit and then immediately exporting the Sierra deck.Therefore, it is assumed that most of the input deck information has been created outside of Cubit and that the user will not interact with it in Cubit .
The Sierra input deck writer is simply another export format and as a result it can be used for any currently defined mesh and input deck info defined in Cubit.
The Sierra input deck exporter relies on some of the mesh-specific information that is generated when exporting the Genesis mesh.Therefore, you should export the Genesis mesh before exporting the Sierra input deck.