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1、2001 UGM Gambit: Tips & Tricks,June 4, 2001 Shyam Kishor,Outline,Data exchange with other CAD/CAE systems Clean-up and Construction strategies Useful Tips New Features of Gambit 2.0,Data exchange with other CAD/CAE systems,Direct options Standard-based options Importing meshes and faceted geometry C
2、AD-to-Gambit flowchart summaries,Direct Options - 1,ACIS-based CAD programs: e.g., AutoCAD, Cadkey, TurboCad Can export ACIS files (.sat or .sab) which can be imported into Gambit. ACIS version compatibility Gambit typically employs recent ACIS rev. (ACIS 6.3 for Gambit 2.0) Gambit can import and ex
3、port older versions of ACIS. Parasolid -based CAD programs: e.g., Unigraphics, SolidWorks, Solid Edge, PATRAN, ANSYS Can export Parasolid files (.x_t & .xmt_txt) which can be imported into Gambit Parasolid version compatibility Gambit can import and export most versions up through 11.1,Direct Option
4、s - 2,Direct (single-stage) translators for native CAD systems e.g., Pro-E/ACIS, Catia/ACIS Available from various vendors (see http:/ for full listing),Standard - based Options,Use of neutral file format to exchange data STEP IGES,Data exchange via STEP,STEP (STandard for the Exchange of Product mo
5、del data) : International standard that defines a neutral file format for the exchange of geometric, topologic, and annotation data. Most CAD programs include STEP export Pro/ENGINEER at no additional cost Most others as an add on Both STEP AP203 and STEP AP214 are supported by Gambit Better than IG
6、ES STEP supports solid models Creates real Gambit (ACIS) volumes after import. Topology/connectivity-related information is maintained STEP export Exports real geometry, including solid volumes,Data exchange via IGES,IGES (Initial Graphics Exchange Specification) Files: Most CAD programs can export
7、IGES files. Topology/connectivity information is lost when CAD programs export IGES surface data only. Some CAD packages export IGES-solids as well as IGES-surfaces. I-DEAS and CADDS Topology/connectivity information maintained. Gambit provides two options for IGES import Spatial Creates real geomet
8、ry Supports IGES-solids (MSBO) Native Creates virtual geometry for trimmed surfaces Supports surfaces only Use only as a fallback when Spatial translator fails IGES export Exports real geometry Supports IGES solids (MSBO),STEP/Parasolid-to-Gambit Flowchart,Real Geometry,Geometry Import,Check Geometr
9、y,Okay?,Connected?,Heal,No,Yes,No,Yes,Check Geometry,Heal,Connected?,Use Virtual Geometry,Better?,Yes,No,No (undo),Yes,STEP/ Parasolid,IGES-to-Gambit Flowchart,Real Geometry,Spatial Translator,IGES,Native Translator,Okay?,Check Geometry,Okay?,Connected?,Heal,No,Yes,No,Yes,Check Geometry,Heal,Connect
10、ed?,Use Virtual Geometry,Better?,Yes,No,No (undo),Yes,No,Yes,Data exchange via Mesh/Faceted Geometry-1,Import of mesh or faceted geometry files results in faceted geometry Supported Mesh Formats Faceted Geometry Formats FLUENT4 I-DEAS FTL FLUENT5 Optegra Visualizer TGRID STL FIDAP GAMBIT I-DEAS UNV
11、(Universal format) ANSYS PLOT3D (Formatted) NASTRAN PATRAN HYPERMESH,Data exchange via Mesh/Faceted Geometry-2,PLOT3D files with Iblanking and/or of binary type Use tfilter fe2ram from an operating system command prompt to first convert it to a Fluent/Fidap mesh file Import the resulting mesh in Gam
12、bit. Import of Mesh with hanging nodes is not supported Mesh Files Boundary types are not preserved during import. Generates faceted geometry from surface or volume mesh import. Use Virtual Geometry operations to work with entities. Convert virtual geometry to real if needed. Faceted Geometry Files
13、Similar to mesh but defining triangles unsuitable for meshing STL lacks zone grouping Use Feature Angle to separate faces Works well for well-defined edges; otherwise use as last resort.,CAD-to-Gambit Flowchart Summaries,In general, translation options listed in order of decreasing preference (left
14、to right). Some options require third party translator software. Best translation path depends on quality of CAD data (model).,Pro/E-to-Gambit Flowchart,Pro/Engineer,Gambit,Direct (STEP),Direct Translator,STEP,Optegra Visualizer,Mesh,STL,(real geometry),(faceted geometry),IGES*,*IGES native may prod
15、uce virtual geometry,ACIS,Direct Integration of Pro/E with Gambit 2.0,Catia-to-Gambit Flowchart,Catia,Gambit,IGES Solids (AIX only),Catia-ACIS Translator,STEP,IGES Surfaces*,Mesh,STL,ACIS,(real geometry),(faceted geometry),*IGES native may produce virtual geometry,I-DEAS-to-Gambit Flowchart,I-DEAS,G
16、ambit,IGES* MSBO,STEP,Faceted Part File (FTL),Mesh,STL,(real geometry),(faceted geometry),*IGES native may produce virtual geometry,Unigraphics-to-Gambit Flowchart,Unigraphics,Gambit,STEP,Unigraphics-ACIS Trans.,Parasolid,IGES*,Mesh,STL,ACIS,(real geometry),(faceted geometry),*IGES native may produc
17、e virtual geometry,SolidWorks-to-Gambit Flowchart,SolidWorks,Gambit,STEP,IGES*,Mesh,STL,ACIS,(real geometry),(faceted geometry),Direct ACIS Export,Parasolid,*IGES native may produce virtual geometry,CADDS-to-Gambit Flowchart,CADDS,Gambit,IGES*,CADDS-ACIS Translator,STEP,Mesh,STL,ACIS,(real geometry)
18、,(faceted geometry),*IGES native may produce virtual geometry,Outline,Data exchange with other CAD/CAE systems Clean-up and Construction strategies Useful Tips New Features of Gambit 2.0,Typical Cleanup Procedure for Imported Data,Delete unnecessary geometry Check validity of the geometry (visual +
19、check commands) Correct invalid geometry (Healing and/or reconstruction) Check connectivity by color coding Eliminate short edges Check connectivity Create additional geometry and form volume Simplify/edit edges, faces, volumes Decompose volume, if necessary Mesh the geometry Plan ahead Some operati
20、ons will not work with virtual geometry (booleans, sweeps except edges, revolves, certain splits) Postpone operations that create virtual entities.,Check Real Geometry,Checks for geometrical and topological inconsistencies. Topology problems must be fixed before meshing Geometry not C1, C2, G1or G2
21、Indicates lack of parametric/geometric continuity Operations like real booleans, splits and sweeps may fail Use virtual splits as fallback Do not prevent meshing Fix real geometry problems by healing and/or by regenerating entities Fix topology and virtual/faceted geometry problems by deleting (hidi
22、ng) and reconstructing entities,Typical Cleanup Procedure for Imported Data,Delete unnecessary geometry Check validity of the geometry (visual + check commands) Correct invalid geometry (Healing and/or reconstruction) Check connectivity by color coding Eliminate short edges Check connectivity Create
23、 additional geometry and form volume Simplify/edit edges, faces, volumes Decompose volume, if necessary Mesh the geometry Plan ahead Some operations will not work with virtual geometry (booleans, sweeps except edges, revolves, certain splits) Postpone operations that create virtual entities.,Healing
24、 Real Geometry-1,Healing is designed to detect and correct accuracy problems in ACIS models ACIS (geometry kernel of Gambit), a high precision modeler, needs all entities to satisfy stringent data integrity checks Geometry imported from other CAD systems often lacks the required accuracy & precision
25、 due to: Inherent numerical limitations in the original CAD system Limitations of data transfer through neutral file formats Differences in tolerance settings between the original CAD system and Gambit Three phases of Healing process: Geometry simplification Stitching Geometry building,Healing Real
26、Geometry-2,Geometry simplification Converts spline surfaces to corresponding analytic forms (e.g., planes, cylinders, circular cones etc.) wherever possible Results in a reduction of data size & speed improvements in geometric operations. Geometry simplification tolerance With tighter tolerance, onl
27、y spline surfaces which are exact analytic surfaces get simplified With relaxed tolerance, approximate analytic fits to spline surfaces are obtained. It may increase the gap between surfaces and healing in subsequent operations would be more difficult The default tolerance of 0.0001 should provide v
28、ery good approximation in most cases For some cases, overall results may be better if simplification is disabled,Healing Real Geometry-3,Stitching Stitch together the loose faces. Similar to volume stitch but can handle the gaps and does some geometry cleaning on the stitched data to handle small ed
29、ges occurring in the body. Main Characteristics : Handles varying gaps Resolves multiple vertices Handles small edges Split edges appropriately Ensure consistent face normals Stitching tolerances: Incremental stitching. Starts with minimum tolerance and increases in steps towards maximum tolerance M
30、inimum tolerance must always be smaller than the length of the smallest edge in the model Maximum tolerance denotes the largest gap in the model. The result of stitching could give one or more acis volumes.,Healing Real Geometry-4,Stitching,Healing Real Geometry-5,Geometry Building Builds the geomet
31、ry as necessary to correct the gaps & inaccuracies in the model. Improve precision of face, edge, and vertex data Recalculate the bad curves and points by recomputing intersections.,Transversal Intersections : Gaps are filled by extending the adjoining surfaces and recomputing the intersection,Heali
32、ng Real Geometry-6,Geometry Building,Tangential Intersection of Analytic Surfaces : Surfaces are snapped to each other using linear transformations,Tangential Intersection of Spline Surfaces: Correction via control points modification,Typical Cleanup Procedure for Imported Data,Delete unnecessary ge
33、ometry Check validity of the geometry (visual + check commands) Correct invalid geometry (Healing and/or reconstruction) Check connectivity by color coding Eliminate short edges Check connectivity Create additional geometry and form volume Simplify/edit edges, faces, volumes Decompose volume, if nec
34、essary Mesh the geometry Plan ahead Some operations will not work with virtual geometry (booleans, sweeps except edges, revolves, certain splits) Postpone operations that create virtual entities.,Connecting edges provides connectivity between faces. This enables faces to be stitched together to form
35、 volume.,Connect Edges,New option to preserve first edge shape during virtual edge connect Typical Procedure: Specify Real and Virtual Connect Real connects attempted first. Specify initial Tolerance or Shortest Edge % Connect on all edges. Repeat above step with successively larger tolerances. Incl
36、ude T-junction option as final step. Invoking too early may result in very small edges. Force Connect remaining disconnected edges. Failure to stitch together volume will result in error message identifying problem edges.,Connect Edges: Tolerances,Tolerances used for connect should be much less than
37、 mesh size. Mesh within the tolerance region gets pushed back to edge. For faces separated by a large gap, create new face to fill the gap. For faces that overlap by large amount, split each face with the intruding edge and form new face in center.,Connect Edges: T-Connect Option,Using T-Connect Opt
38、ion with relatively low tolerance can generate unwanted small edges. Use Highlight Shortest Edge to check length before and after operation. Can pick which vertices are to be involved in edge splits in Vertex list box (default is all).,Typical Cleanup Procedure for Imported Data,Delete unnecessary g
39、eometry Check validity of the geometry (visual + check commands) Correct invalid geometry (Healing and/or reconstruction) Check connectivity by color coding Eliminate short edges Check connectivity Create additional geometry and form volume Simplify/edit edges, faces, volumes Decompose volume, if ne
40、cessary Mesh the geometry Plan ahead Some operations will not work with virtual geometry (booleans, sweeps except edges, revolves, certain splits) Postpone operations that create virtual entities.,Simplify/Edit faces,Eliminate sliver faces Merge face with neighbor Avoid merging together connected fa
41、ces that form a sharp angle ( 90). Merge remaining edges Eliminate sharp corners and angles Split the face to isolate the bad angle Merge the new face to an adjacent face Merge the edges Collapse versus merge Merge for similar faces and sliver faces Collapse for symmetry, blends, fillets, etc. (coll
42、apse adds extra layer of topological information) If tolerance is larger than element size, or if element size is smaller than faces that were merged/collapsed, meshing may fail on merged surfaces,Virtual Cleanup During IGES Import,Attempts virtual cleanup through automated sequence of Connects/Merg
43、es. Merges edges based on length. Using merge tolerance. Merges edges based on angle. geometry.edge.VIRTUAL_MERGE_MIN_ANGLE Real connects of vertices, edges, faces. Virtual connects of vertices, edges, faces. Using connect tolerance. Edge connects with T-Option. If any changes are made, repeats Virt
44、ual connect of edges, faces. Attempts volume-stitch-virtual. Can also be used after import Open the IGES Import form Clear the File Name field Click Virtual Cleanup checkbox Click Accept,Outline,Data exchange with other CAD/CAE systems Clean-up and Construction strategies Useful Tips New Features of
45、 Gambit 2.0,Geometry Tips-1,If a particular boolean/split operation fails to work Could be due to complexity/quality of the model or due to difficulty in finding imprints of connected entities Disconnect the face/volume with adjacent entities by copying it Delete the original face/volume Perform the
46、 boolean/split on the copied entity Connect them back before meshing Use alternative operations e.g., an alternative to a split is: Get intersection of tool and the target while retaining the target Subtract the result (intersection) from the target while retaining the tool Do a connect If the tool
47、is enclosed by the target, intersection of the two is not needed.,Geometry Tips-2,Gambit 1.2.0 & higher support booleans of multiple entities (faces/volumes) in one step Use intersection/subtraction option to split one entity with multiple entities Occasionally, real volume stitch may produce unwant
48、ed edge splits ACIS-specific problem (incorrect topology being generated) Use Heal Faces in place of volume stitch command to create the volume May need to disconnect the faces if connected to other entities Reconnect them before meshing Virtual volume stitch can also be used,Geometry Tips-3,To crea
49、te real face by wireframe on noncoplanar surface, use a set of 3 or 4 edges per face Use alternative methods of face creation (e.g., net surface) wherever applicable New face creation methods and face primitives are available with Gambit 1.2.0 and higher Combine primitives, booleans and bottom-up tools for faster model building,Meshing Tips - 1,Vertex types may be changed for Boundary Layers only Allows desired BL creation in regions near vertices while maintain