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Gridgen Version 14.01 R1

April 2002

New Features

Gridgen Version 14 introduces several features the most powerful of which is a Tcl-based scripting language called Glyph. Glyph addresses analysts' requirements for methods that decrease the time required for meshing, make meshing more repeatable, and integrate meshing into the CFD process. Glyph consists of over 200 commands that provide procedural access to the complete range of Gridgen's functionality, from setting preferences and working with CAD models, to applying mesh techniques and exporting boundary conditions and mesh data formatted for a CFD solver. When combined with Tcl's open and portable programming environment you can:

  • build a customized meshing application specifically for configurations of interest to you and your organization
  • develop convenience features that augment your day to day meshing process
  • link Gridgen to CFD solver, post-processor, and optimization applications to fully integrate CFD into your design process

Gridgen's implementation of Glyph includes the ability to journal (write to file) the commands executed during an interactive session to provide a starting point for parametric regeneration of meshes.

Gridgen Version 14 also features a significant enhancement to the On DB Ents command for creating unstructured domains (i.e. triangular surface grids) on CAD models. While Version 13.3 was able to automatically generate meshes on sloppy CAD models using its Merge command for fault-tolerant meshing, you asked for additional capability to remove the grid's relation to the underlying CAD topology. This was accomplished through the addition of optional post-processing steps for On DB Ents that will

  1. join adjacent domains if their relative turning angles are less than an user-specified limit followed by
  2. a decimation (grid point removal) sweep in the unstructured grid solver that removes artifacts from sliver surfaces and other small features in the CAD model.

Gridgen Version 14 also features two new techniques for working with CAD geometry. It is often the case that users choose to bypass the topological and mathematical complexity of NURB models by using triangular faceted data for a geometry representation. Triangular faceted data, most often transferred in the de facto standard STL format, may also be the only manner in which a geometry is represented (3D scanner, legacy FEA models, etc.). Therefore, Gridgen Version 14 may import triangular faceted data from STL, VRML, and NASTRAN file formats for use as geometry in the database. These database entities, known as shells, may be automatically (or manually) split into components that are more amenable to meshing using a tool called Feature Extraction that splits shells along lines of angular discontinuity.

Last but not least, CAD data may now be acquired in its native format (e.g. a CATIA model file) instead of a neutral format such as IGES. This optional capability allows you to eliminate a step from your analysis process (generation of the neutral file) and improve the quality of data transfer from CAD to CFD. In addition to native CAD formats this feature also supports STEP and ACIS .sat files. Native CAD Import (with the exception of ACIS files) requires additional licenses beyond those for Gridgen itself.

Please be aware that the IGES reader has been improved and, therefore, may import entities differently into Version 14 than it did in Version 13.3. Therefore, it is possible that a Gridgen file (.gg) generated on an IGES file in Version 13.3 won't map correctly to the same IGES file in Version 14. In order to continue your work in Version 14 we recommend that you save a composite database (.dba) file from Version 13.3 and carry that forward into Version 14.

The Gridgen Version 14 User Manual is delivered to you on the CD in PDF format which may be viewed and printed using Adobe Acrobat Reader. This gives you the freedom to print individual manual chapters as necessary in the volume required for your internal use. Please see the Right To Use License for details.

Also, Gridgen Version 14 does not require environment variables to operate the on-line help or tutorials correctly. Therefore, we recommend that you remove all Gridgen-related environment variables prior to running Gridgen Version 14.

Gridgen Version 14's new features are described in the following sections.

Setting Defaults and Tolerances

Changing tolerances has been moved to its own menu within the Defaults menu (see the Tolerances command). This change was made to emphasize the delicate nature of meshing tolerances - and the effects they can have on your grid.

A default setting was added for the new unstructured domain meshing attribute: cell to cell normal angle deviation. Pressing the Uns Dom MaxAng button allows you to set a limit on the maximum change in normal vector allowed between neighboring cells.

You may now use the DB Coord IJ or UV radio buttons to set your preferred means of seeing the numerical values of a parametric database entity's coordinates. The UV form is the traditional way of seeing coordinates while IJ refers to indexing based on numbering of the surface's or curve's intervals.

New default settings for Split Angle and Join Angle have been added for other new features that split and join entities, respectively, based on the relative turning angle.

The unstructured block (tetrahedra) solver's attributes have been changed to MaxMem and SizeFac. MaxMem sets an upper bound on the RAM to be used by the tet solver. SizeFac is a scaling factor that allows larger cells to be built on the interior of a block.

Graphical User Interface

The environment variable GRIDGEN_TEMPDIR is used to specify a directory (Unix) or folder (Windows) into which the tetrahedral solver will write temporary files. The current working directory will be used if GRIDGEN_TEMPDIR is not set.

The environment variable GRIDGEN_BINDIR is used to specify the path to the directory (Unix) or folder (Windows) in which the executable program for the tetrahedral solver (called gridgen_tet (Unix) or gridgen_tet.exe (Windows)) can be found. You must set this environment variable if you performed a non-standard installation. Otherwise, Gridgen will be able to automatically find the tetrahedral solver.

The Quick Keys have been expanded. There are now three rows of four Quick Keys each:

ConDomBlkDB
DefI/OASWGlyph
QuitSaveDispHelp

The new Quick Keys are in the second row. Def takes you to the Defaults menu. Glyph takes you to the Scripting menu.

The r and R hot keys are no longer used to abort from text input. The Esc (escape) hot key has taken over that function.

In the Display menu's Photo feature, commands have been added to export raster screen dumps of the Display window in bitmap (.bmp) and Portable Network Graphics (.png) formats. The bitmap format is replaced by RGB (.rgb) format on SGI systems.

The Browser list for picking domains may now be sorted by A/SW boundary condition type.

Importing and Exporting Files

The format of the Gridgen (.gg) and composite database (.dba) files was changed to accommodate new features. Keeping with Gridgen history, Gridgen (.gg) files exported from Version 14 may not be imported into any previous Gridgen version. The same is true for composite database (.dba) files.

On-going improvements to the CAD data import will result in Version 14's CAD import differing from previous versions. Therefore, we recommend that you continue to use Version 13.3 to complete work on any grids that require CAD databases. One alternative to this approach is to export a composite database (.dba) file from Version 13.3 and import that followed by the Gridgen (.gg) file in to Version 14. New grids requiring CAD or existing grids not requiring IGES files should be worked in Version 14.

Due to the replacement of GCL with Glyph, the GCL File Import and Export commands have been replaced with the Export Glyph Init Data command and Glyph Journaling (in the Scripting menu), respectively.

Unstructured (triangular) domains may now be imported from NASTRAN bulk data files.

Shells (triangular faceted surfaces in the database) may be imported from STL, VRML, NASTRAN, and NASTRAN-L file formats.

CAD data may be imported into the database from ACIS' .sat files.

CAD data may be imported into the database from CATIA v4, Pro/E v17-20, and STEP AP203 files (optional capabilities - additional licensing required).

Creating Database Entities

No changes.

Creating Connectors

Connectors created using the On DB Ents command on shell entities may be automatically split by setting the Split Ang default.

Creating Domains

The Domains, Create, On DB Ents command has been enhanced through the addition of the following capabilities.

  1. Auto Merge. Connectors and nodes along the boundaries of adjacent domains are merged according to tolerances. This results in a "water tight" mesh topology.
  2. Con Split. Connectors are split at feature angles.
  3. Auto Join. Adjacent domains are automatically joined into a single domain if their relative turning angles are less than a specified limit.
  4. Decimation: After the previous two steps are complete, Gridgen runs the resulting domain(s) through smoothing and decimation (grid point removal) sweeps in the unstructured solver.

Expanded connector merging options are available during Domains, Create, Assemble Edges.

Creating Blocks

Block topology has been extended to allow baffles: faces on a block's interior. Baffles allow the modeling of thin surfaces (e.g. turning vanes) inside a volumetric region. They also provide a means of specifying grid cell sizes on the interior of a block. The baffles capability required the addition of the following commands to block face assembly.

  1. Face Filter
  2. NonManifold
  3. AutoJoin
  4. Save as Baffle
  5. AutoSave Off , Face , or Faces
  6. Mesh Both Sides

Grid Methods for Connectors

No changes.

Grid Methods for Structured Domains and Blocks

The Examine command is now available from within the Run Solver Structured command for both domains and blocks.

Grid Methods for Unstructured Domains and Blocks

Decimation (grid point removal) has been added to the unstructured (triangular) solver for domains.

Grid attributes for the block unstructured (tetrahedral) solver have been changed to include Tetra Memory Size (limit on memory to be allocated) and Tetra Size Factor (blending factor between boundary cell size and interior cell size).

Grid Extrusion Methods

No changes.

Modify

Database shells (triangular faceted surfaces) have the following restrictions with respect to the Modify commands.

  • Shells cannot be split.
  • Shells cannot be joined.
  • Shells cannot be intersected with any other database entity.

A Mirror transformation was added for all entity types.

Miscellaneous

The addition of shells (triangular faceted surfaces) into Gridgen's supported database entities included the addition of the Feature Extraction command in the Database menu. Feature extraction allows you to split shells into smaller shells based on geometric features. Database curves may also be created as the result of feature extraction. Feature extraction is based on a maximum turning angle allowed between the normal vectors of adjacent triangles in the shell.

The Merge command for connectors has been significantly improved including addition of the ability to Pick the entities to be merged.

Diagnostic Functions

A new function was added for structured grids that measures the smoothness of the i-, j-, and k-directed grid lines. New functions were added for determining viscous resolution: height of the first cell into a block and relative angle of grid lines into a block. These viscous resolution functions are available when Examine is invoked from the ANALYSIS SOFTWARE menu.

The Examine command's computational coordinate plane hiliter for structured grids may now may be extended into blocks connected to the focus block - see the Extend toggle button.

Diagnostic functions that measure the variation of a quantity from one cell to the next now take into account cells from connecting structured blocks.

The Examine command's functionality is now available from within the Elliptic Solver menu.

Analysis Software Interfaces

Export filters for CFD++, CRUNCH, NCC, and TACOMA were added.

Zone merging was added to Fluent v5 export.

The ability to Create, Modify, and Delete custom BCs was added.

Mirroring of blocks may be done implicitly during export.

Scripting

Version 13.3's Gridgen Command Language (GCL) was replaced in its entirety by Glyph, a Tcl-based programming environment.

Software Performance Reports

Because this is the first release, there are no defects to correct.