An Abstraction and Meshing Technique for Industry Problems Michael Hancock, Debashis Basu, Ashish Das, Nilanjan Mukherjee ( )

SDRC Confidential – Do Not Copy Need for Abstraction Interoperability through STEP, IGES and Vendor to Vendor translator compatibility -- a must !! - CAD Data quality becomes a major issue. Sliver surfaces Unstitched geometry Industry Approach for FE Analysis - FIX the CAD and mesh Fix the CAD ( geometry ) with another CAD tool Make additional changes considering Analysis Intent - Create and mesh an Abstraction of the geometry using virtual topology that only refers to the geometry Geometry is never modified Analysis Intent built-in to some degree Good mesh quality achievable Define Boundary Conditions on the abstraction

SDRC Confidential – Do Not Copy Abstraction Process STL data Legacy FE data Create abstraction Group to criteria De-feature Re-feature Re-mesh to Analysis cycle(s) requirement Synthesized geometry Native geometry Geometry abstraction Group to criteria De-feature Re-feature Mesh to meet requirement Analysis cycle(s) Imported Geometry

SDRC Confidential – Do Not Copy Analysis Intent What is Analysis Intent ? - Feature Removal, Simplification Suppression - Features (thru hole, blind hole, etc) - Edges - Vertex Small feature removal (auto-merge) Bead Abstraction Boundary Smoothing Isthmus removal - Design Alternatives (need New features) Bead Creation Replace existing curve to a new boundary

SDRC Confidential – Do Not Copy Virtual Topology from Surfaces Virtual Topology - The area entity of the virtual topology is called a Section - Section can reference one or more surfaces - Section ->Loops ->Curves->connectors - Section-surface relation is tracked - If curve is on edge(s), curve-edge relation is tracked Characteristics - Loops are always closed - There could be multiple loops, but at least one - A loop cannot self-intersect - Section must be meshable - Adjacent sections share a common boundary

SDRC Confidential – Do Not Copy Shell of Sections forms a Water-Tight Virtual Volume Sections can be made water-tight even if there are unstitched surfaces with gaps and overlaps Free edges of unstitched surfaces Sections define a water-tight volume Volume is not water-tight

SDRC Confidential – Do Not Copy Section Creation Options Basic option - Hole suppression - Curve Merging - Surface Grouping - Tolerance Advanced option - Total Curvature - Pre-process fillets - Combine cylinders - Surface merge based on target element size

SDRC Confidential – Do Not Copy Section Creation Abstraction on forward creation of sections Auto create -- std.Auto create -- adv. Mesh on counter-bore

SDRC Confidential – Do Not Copy Manual Modification Tools Manipulating the virtual topology entities - changes section definition - meshing reacts to the change - boundary conditions react to the change - Any removal operation can be undone by an add operation Some capabilities - Add, Remove, Replace connectors Split, Merge, Stretch curves - Add, Remove, Replace curves Split, Merge, Stitch sections ( sometimes loops ) - Add, Remove loops Un-suppress, suppress features attached to loop(s)

SDRC Confidential – Do Not Copy De-featuring: Remove Loop De-featuring --- entity suppression ( remove hole ) At times it is helpful to be able to create hard points for mesh to snap to.

SDRC Confidential – Do Not Copy De-featuring: Isthmus Removal De-featuring --- Isthmus removal ( replace curve ) 3 sections created over 72 surfaces 30 mm mesh Still 3 sections !! The 2 isthmus sections contain 2 outer loops each. 30 mm mesh ( free mapped, allow tri ) An isthmus section Replace curve operation removes the isthmus. Still one section with two outer loops.

SDRC Confidential – Do Not Copy De-featuring --- Auto-merge (small feature removal) - Higher order operator built De-featuring: Auto-merge Section 518 surfaces410 sections Using auto-merge with 13 mm to suit analysis intent

SDRC Confidential – Do Not Copy De-featuring: Bead Abstraction De-featuring --- Bead Abstraction Two sections on surfaces defining beads Extract median line defining bead Ensure mesh to capture stiffness Mesh may go across the entire section May remove the rail curves of the beads Create median line on fillets Final representation for bead and fillet

SDRC Confidential – Do Not Copy De-featuring: Boundary Smoothing De-featuring --- Boundary smoothing Laplacian smoothing for nodes that has no projection space

SDRC Confidential – Do Not Copy Re-featuring: Bead Creation Re-featuring --- Bead Creation

SDRC Confidential – Do Not Copy Re-featuring: Replace Curve Re-featuring --- Replace curve to a new boundary - Mesh will get projected to underlying surfaces - Additional options Ignore surface for projection Add surface for projection (surface is not a part of the solid )

SDRC Confidential – Do Not Copy Example: A Shell Part Completely unstitched geometry 393 surfaces ->112 sections -> 5481 elements created Automated Abstraction: <5 minutes Manual Editing of Abstraction <15 minutes Mesh Generation < 5 minutes

SDRC Confidential – Do Not Copy Example: A Solid Part 1481 surfaces, 1062 sections, par.tri, par.tet

SDRC Confidential – Do Not Copy CAD neutral ? The Abstraction works on a CAD NEUTRAL level while providing flexibility for analysis and design modifications. Future direction – Abstraction on Mesh Industry reaction - Ford Power-train says “time to mesh large power-train model was reduced by 75% in last one year” - ZF Friedrichshafen AG says “section meshing is a key in the process chain”

SDRC Confidential – Do Not Copy Abstract AN ABSTRACTION AND MESHING TECHNIQUE FOR INDUSTRY PROBLEMS. - Michael Hancock, Debashis Basu, Ashish Das and Nilanjan Mukherjee The most commonly used data exchange methods between the CAD and CAE application are (a) Direct translators, which are vendor-to-vendor data exchange, (b) Indirect translators, like IGES, STEP, STL and the like and (c) Consistent kernel, like ACIS, Parasolid and the like. Although there has been many thoughts on creating a CAD neutral framework, in reality the design data containing surface information is handed over to the analysis land through one of the above data exchange channels. Any surface data from an industry model, coming through one of the above data exchange channels, brings imperfect geometry with gaps, overlaps and surface degeneracy. Meshing such surfaces is highly unlikely to produce quality mesh with a desired density. This paper proposes an abstraction technique that creates an auxiliary simplified topology referencing the underlying imperfect (sometimes perfect) geometry. A meshing strategy is presented that works directly on the abstraction layer. The synergy between the abstraction and meshing techniques provides one way of achieving “CAD neutrality”, trying to embed the concept in the process. The idea here is to accept any surface data from any data exchange channel, be it stitched or unstitched, and create a watertight topology layer (the abstraction) spanning multiple surfaces which is then used for meshing. An application based on this abstraction technique provides the flexibility to remove topological details irrelevant for finite element analysis while providing the facility to perform design modification (for example elimination of holes) without altering the geometry. The technique eliminates the need to repair any underlying imperfect geometry. The meshing technique smoothes out effects from geometry deficiencies and works on any unspecified (void) region within the abstraction to produce a quality mesh of the desired density.

Get There Faster ™ Solutions to...