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Geometry to Mesh Glyph Scripts
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README.rst

GeomToMesh Glyph Scripts

Introduction

These scripts are provided as-is to Pointwise users for performing automated mesh generation from an attributed geometry database and a set of user-defined parameters. The scripts can be used with Pointwise versions 18.1 and higher. Note that the scripts can use some features that were introduced in 18.2, such as Elevate on Export to generate mesh files that support High Order elements. The scripts will ignore meshing parameters and geometry attributes that are not applicable to the version of Pointwise being used.

These scripts were developed under a subcontract from MIT as part of their U.S. Air Force Contract FA8650-14-C-2472.

The objective of this project was to create a set of scripts to be executed within the Pointwise mesh generation program that automatically make a single block unstructured mesh given geometry created using Engineering Sketch Pad (ESP). No foreknowledge of the elements contained in the geometry file is required. If the geometry forms a closed model, then a completed unstructured mesh is the expected result. The scripts create surface meshes that adhere to the geometry and are sized to respect all length scales. A set of default meshing parameters is provided, but can be optionally and selectively superseded by means of a user-defined parameter file. These parameters control the operation of Pointwise during execution. The default parameters were developed to incorporate many best practices that produce a quality unstructured mesh with smoothly varying mesh characteristics.

Note

Even though attribution is not possible with IGES and STEP geometry files, the scripts will attempt to generate a completed unstructured volume mesh for the input geometry. The final mesh will exhibit all the quality characteristics afforded by the processes and best practices, but will not have any characteristics provided through geometry attribution. If the geometry is both closed and of high quality, the likelihood of a completed mesh is high. Once generated, the mesh can be modified using Pointwise to apply problem-specific attributes to meet additional quality criteria.

Usage

The main script is GeomToMesh.glf. It can be used either in batch mode from the command line, or in the Pointwise GUI. All of the support scripts must reside in the same directory as GeomToMesh.glf, including:

  • GeomToMeshDefaults.glf -- Default parameter values that control the meshing process.
  • GMDatabaseUtility.glf -- Functions used for accessing geometry and retrieving attributes.
  • GMUtility.glf -- Functions for performing various meshing operations.
  • GMSafeUtility.glf -- Functions for isolating loading of user-defined parameter files to prevent malicious commands from being executed by the master script.
  • GMMeshParamCoords.glf -- Functions for creating and writing Geometry to Mesh Associativity (GMA) files.

Additionally, the script QuiltToSurfMesh.glf can be used to perform quilt-based surface meshing only.

GUI

https://raw.github.com/pointwise/GeomToMesh/master/GeomToMeshGUI.png

From the Script menu, click Execute... and browse to the directory containing the GeomToMesh.glf and support scripts. Type in or select the geometry file and optional user-defined attributes file, then click Start. A variety of informational messages about the geometry assembly and meshing process are emitted to the message window.

For ease of repeated usage, it is recommended to add GeomToMesh.glf to the Script Toolbar using the Script Toolbar Manager... under the Script menu.

Batch

In the directory containing the desired geometry and optional user-defined attributes file, run a command similar to the following:

Windows:

% <path-to-pointwise-install>\win64\bin\tclsh.exe <path-to-scripts>\GeomToMesh.glf geometry-file user-defaults.glf

Non-Windows (Linux and Mac OS/X):

% <path-to-pointwise_install>/pointwise -b <path-to-scripts>/GeomToMesh.glf geometry-file user-defaults.glf

Where:

  • <path-to-pointwise-install> is the full path to your licensed Pointwise installation directory
  • <path-to-scripts> is the full or relative path to the directory containing GeomToMesh.glf and its support scripts

Results

In either batch or GUI mode, GeomToMesh will write the final mesh file in Pointwise format with a name consisting of the geometry file name with ".GeomToMesh" appended to it. Optionally, a CAE file can be exported for CGNS, Gmsh and UGRID formats, including high order elements if specified and supported by the format.

Usage Notes

Mesh Parameters

The meshing process is controlled through either global meshing parameters (which can be customized for each project), or by attributes attached to geometry elements. The global parameters are set via a combination of the provided GeomToMeshDefaults.glf and a customization script that overrides the defaults as needed.

It is highly recommended that the provided GeomToMeshDefaults.glf file remain unaltered. These parameters represent the "best practice" values that generally produce quality unstructured volume grids under normal circumstances. To define a custom set of parameters:

  • copy GeomToMeshDefaults.glf to the directory where the geometry (CAD) file is located
  • rename the copy to indicate the objective of the customization, e.g. "CoarseSettings.glf"
  • edit the values in that file as desired

The custom settings file is specified as input, and is sourced into the main script after the provided default settings (GeomToMeshDefaults.glf) file. So, only the settings that need to be superseded need to be present.

Geometry Attributes

Geometry attributes allow fine-grained control over mesh generation, and supersede the global settings where applicable.

Supported geometry formats for GeomToMesh include EGADS, IGES, STEP and NMB (Pointwise proprietary geometry format) files. GeomToMesh will attempt to create a single unstructured block volume mesh. IGES and STEP files will not contain GeomToMesh attributes, so the resulting volume mesh will be of the isotropic variety with no viscous boundaries or layers.

NMB or EGADS files may contain GeomToMesh attributes, and thus may include directives that will customize the resulting volume mesh, and may include viscous boundaries and layers. ESP writes EGADS files, and has the ability to assign GeomToMesh attributes to entities in the model. As shown in the table below, GeomToMesh looks for attributes in the form of key-values pairs on faces, curves and nodes in the model that have the prefix "PW:", such as "PW:Name Body" or "PW:WallSpacing 0.001". A list of the possible Pointwise specific attributes is provided below, and also in the provided Excel spreadsheet AttributeVocabulary.xlsx.

When these attributes are found they guide Pointwise to alter the default behavior to produce a mesh that has features of interest to the user, such as boundary conditions and viscous layers.

Note: Preceding $ indicates it is a literal character string

Key Value Geometry Location Description
PW:Name   Face Boundary name for domain or collection of domains.
PW:QuiltName   Face Name to give one or more quilts that are assembled into a single quilt. No angle test is performed.
PW:Baffle $Baffle or $Intersect Face Either a true baffle surface or a surface intersected by a baffle.
PW:DomainAlgorithm $Delaunay, $AdvancingFront, $AdvancingFrontOrtho Face Surface meshing algorithm.
PW:DomainIsoType $Triangle, $TriangleQuad Face Surface cell type. Global default is Triangle.
PW:DomainMinEdge $Boundary or > 0.0 Face Cell Minimum Equilateral Edge Length in domain.
PW:DomainMaxEdge $Boundary or > 0.0 Face Cell Maximum Equilateral Edge Length in domain.
PW:DomainMaxAngle [ 0, 180 ) Face Cell Maximum Angle in domain (0.0 = NOT APPLIED)
PW:DomainMaxDeviation [ 0, infinity ) Face Cell Maximum Deviation in domain (0.0 = NOT APPLIED)
PW:DomainSwapCells $true or $false Face Swap cells with no interior points.
PW:DomainQuadMaxAngle ( 90, 180 ) Face Quad Maximum Included Angle in domain.
PW:DomainQuadMaxWarp ( 0, 90 ) Face Cell Maximum Warp Angle in domain.
PW:DomainDecay [ 0, 1 ] Face Boundary decay applied on domain.
PW:DomainMaxLayers [ 0, infinity ) Face Maximum T-Rex layers in domain.
PW:DomainFullLayers [ 0, infinity ) Face Number of full T-Rex layers in domain. (0 allows multi-normals)
PW:DomainTRexGrowthRate [ 1, infinity ) Face T-Rex growth rate in domain.
PW:DomainTRexType $Triangle, $TriangleQuad Face Cell types in T-Rex layers in domain.
PW:DomainTRexIsoHeight > 0.0 Face Isotropic height for T-Rex cells in domain. Default is 1.0.
PW:PeriodicTranslate "tx; ty; tz" Face Periodic domain with given translation vector.
PW:PeriodicRotate "px; py; pz; nx; ny; nz; ang" Face Periodic domain with given point, normal and rotation angle.
PW:PeriodicTarget $true or $false Face Target domain of a translate or rotate periodic domain. This domain will be deleted before the creation of the periodic domain.
PW:WallSpacing > 0.0 Face Viscous normal spacing for T-Rex extrusion.
PW:TRexIsoHeight > 0.0 Model Isotropic height for volume T-Rex cells. Default is 1.0.
PW:TRexCollisionBuffer > 0.0 Model T-Rex collision buffer. Default is 0.5.
PW:TRexMaxSkewAngle [ 0, 180 ] Model T-Rex maximum skew angle. Default 180 (Off).
PW:TRexGrowthRate [ 1, infinity ) Model T-Rex growth rate.
PW:TRexType $TetPyramid, $TetPyramidPrismHex, or $AllAndConvertWallDoms Model T-Rex cell type.
PW:BoundaryDecay [ 0, 1 ] Model Volumetric boundary decay. Default is 0.5.
PW:EdgeMaxGrowthRate [ 1, infinity ) Model Volumetric edge maximum growth rate. Default is 1.8.
PW:MinEdge $Boundary or > 0.0 Model Tetrahedral Minimum Equilateral Edge Length in block.
PW:MaxEdge $Boundary or > 0.0 Model Tetrahedral Maximum Equilateral Edge Length in block.
PW:ConnectorMaxEdge > 0.0 Edge Maximum Edge Length in connector.
PW:ConnectorEndSpacing > 0.0 Edge Specified connector endpoint spacing.
PW:ConnectorDimension > 0 Edge Specify connector dimension.
PW:ConnectorAverageDS > 0.0 Edge Specified average delta spacing for connector dimension.
PW:ConnectorMaxAngle [ 0, 180 ) Edge Connector Maximum Angle. (0.0 = NOT APPLIED)
PW:ConnectorMaxDeviation [ 0, infinity ) Edge Connector Maximum Deviation. (0.0 = NOT APPLIED)
PW:NodeSpacing > 0.0 Node Specified connector endpoint spacing for a node.

Future Enhancements

Pointwise versions 18.3 and higher will provide tools to allow users to edit/add attributes to geometry within the GUI. The geometry can then be exported as an NMB file (Pointwise native geometry) and then processed by the GeomToMesh scripts.

GeomToMesh attributes can exist in EGADS files written by newer versions of ESP. Pointwise V18.3 and higher will be able to import EGADS files which are the native geometry files for ESP. For versions prior to V18.3, geometry attributes can be stored in Pointwise file (.nmb) using a conversion tool called egads2nmb (provided by ESP) that transforms a standard ESP (.egads) file to a Pointwise proprietary geometry format file (.nmb). At this time, there are no plans to support other types of attributed geometry file formats.

Examples

The example directory includes several small cases that demonstrate the operation of the scripts.

Special Usage Notes

Baffle Surfaces

Baffles are domains that "float" in the interior of a block, and are used to control grid clustering and other aspects of the interior. The surface elements (triangles and quads) in a baffle domain are guaranteed to exist in the isotropic portion of the final volume mesh. Geometric face elements may be attributed with PW:Baffle with a value of "Baffle" or "Intersect". The generated domain for a geometric face element attributed as "Baffle" will be added to the resulting volume grid as a true baffle. If the baffle domain will intersect with another domain, such as an outflow boundary, then boundary geometry element should be attributed as "Intersect".

Periodic Domains

Periodic domains are created in pairs where one is the "source" and the other (its periodic partner) is an exact copy that has been transformed from the source, typically through either translation or rotation. Only pure translation or rotation periodic domains may be generated by GeomToMesh. The geometric face that represents the source domain should be attributed with PW:PeriodicTranslate or PW:PeriodicRotate with a value component comprised of a translation vector, "tx; ty; tz" or a rotation transform, "px; py; pz; nx; ny; nz; angle", respectively. The translation form includes the three components of the translation from the source domain to the target domain. The rotation transform includes the origin point, normal (rotation axis) and angle used to define the pure rotation from the source domain to the target domain. If there is a geometric face that represents the intended periodic partner domain, it must be attributed with PW:PeriodicTarget and a value of "true". The domain automatically created for this geometric face will be replaced with the periodic domain copy through the designated transformation.

Reference

The scripts are the subject of an AIAA paper "Automatic Unstructured Mesh Generation with Geometry Attribution", AIAA-2019-1721 presented at AIAA Science and Technology Forum and Exposition 2019 in San Diego, CA. Please refer to that reference for details about the processes followed for automated mesh generation.

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