ANSYS Nonlinear Convergence Best Practices PDF
Preview ANSYS Nonlinear Convergence Best Practices
ANSYS Nonlinear Converggence Best Practices Peter R. Barrett, P.E. September 27, 2012 RReevv.. 22//33//22001166 © 2016 CAE Associates ANSYS Nonlinear Convergence Best Practices Nonlinearities Overview: Large Deflection — Material Nonlinearities — Contact — Characterize Convergence Difficulty with Examples Relatively Straight Forward (easy) Problems — Challenging (i.e. really hard) Problems — Stepp-byy-Stepp Converggence Procedure Rigid body motion 1. Force balance not obtained 2. MMaatteerriiaall IInnssttaabbiilliittiieess aanndd//oorr EElleemmeenntt ffoorrmmuullaattiioonn eerrrroorr 33.. Q&A www.caeai.com 2 All Products Exhibit Nonlinearities AAllwwaayyss ssttaarrtt wwiitthh tthhee ssiimmpplleesstt lliinneeaarr aannaallyyssiiss iiff ppoossssiibbllee!! www.caeai.com 3 Large deflection Affects Stiffness wwwwww..ccaaeeaaii..ccoomm 4 Material properties cannot always be assumed to be linear wwwwww..ccaaeeaaii..ccoomm 5 Contact is the most common source of nonlinearity and often the most difficult to ssoollvvee!! SStatus changes, friction, pprreessssuurree WWhheenn, wwhheerree?? What is the pressure? wwwwww..ccaaeeaaii..ccoomm 6 Characterize Convergence Difficulty Easier Problems DDefformattiions are rellattiivelly smallll — Nonlinear strains (plasticity, creep, swelling) are small — Contact status does not oscillate — MModdells are smallll andd siimplliiffiiedd ((22DD, AAxiisymmettriic)) — Symmetric boundary conditions are utilized — Displacement based loads — LLoadds resulltt iin ttensiille membber sttresses — Nonlinear buckling to the point of instability (Post buckling not needed) — 444000999 PPPaaarrrtttsss 999666777 CCCooonnntttaaacccttt PPPaaaiiirrrsss www.caeai.com 7 Characterize Convergence Difficulty Harder Problems VVery llarge ddefformattiion — Large strains with large distortion — Contact chatter and/or loose fitting assemblies — CConttactt slliiddiing wiitthh hhiighh ffriicttiion coeffffiiciientt — Post buckling response — Large 3D models with complex geometry — NNo symmettry bbounddariies — Force based loads — www.caeai.com 8 Pin Insert Model Hard Solution Model the entire Pin / socket assembly — Mesh fine enough to capture local — stress concentrations Use a force based analysis to model — pin insertion and removal Determine critical locations / load — sstteeppss Easier Solution Model a single axi-symmetric — PPiinn//SSoocckkeett aasssseemmbbllyy Create mapped mesh with refinement — on contact surfaces and areas of high stress Use a displacement controlled solution — Use auto time stepping and smart — output controls since max stress might not occur at the final solution step www.caeai.com 9 Gasket Assembly HHaarrdd PPrroobblleemm Large model — Complex loading sequence — MMuullttiippllee bboolltt llooaaddss — Frictional Contact — Nonlinear material response — www.caeai.com 10
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