Selective Mass Scaling (SMS)

Transcription

1 Slctiv Mass Scaling (SMS) Thory and Practic Thomas Borrvall Dynamor Nordic AB Octobr 20 LS DYNA information

2 Contnt Background Is SMS nwsworthy? Thory and Implmntation Diffrnc btwn CMS and SMS Undr th hood Whn and how to us SMS Rcnt tdvlopmnts Rotational SMS Supportd dfaturs Exampls

3 SMS origins Lars Olovsson t.al., Slctiv Mass Scaling for Explicit Finit Elmnt Analyss, Int. J. Num. Mthods Eng. (2005) Implmntd in LS DYNA for SMP in May 2006 Supportd for MPP in Sptmbr 2006 Supportd trivial boundary constraints and adaptivity Initially intndd for mtal forming Sinc thn things hav volvd

4 Explicit Finit Elmnts Gomtry updat a v u n M i ( fn fn v n/ 2 n/ 2 n un v n/ 2 ) a n t t Mass matrix diagonal M m m m n I Stability t 2 min E max l min m El

5 Convntional Mass Scaling Augmnt mass matrix maintaining diagonal structur M m m m m I n m m t tnw m tnw min El t m t CPU ~ t N ( t tothr ) CMS t nw Shortr simulation tims so far so good

6 Problms with CMS Adding diagonal mass affcts all ignmods qually much ω/ ω 0 ω/ ω 0 i i In particular rigid body and low frquncy mods ar affctd Structur tnds to dform in low frquncy mods Inrtia ffcts put a practical limit to th tim stp

7 SMS ida High frquncy mods rlativly unimportant for structural rspons, only limits tim stp Supprss high frquncy contnt and lav low frqncy mods unaffctd ω/ ω 0 ω/ ω 0 i i Modify th structur of th addd mass matrix to slct affctd mods

8 Slctiv Mass Scaling Augmnt mass matrix projcting out rigid body mods i M m m T m m m I ii n i For rigid body mod, no inrtia is addd T i j ij m i 0 Timstp incras th sam as with CMS

9 Exampl p 3D mmbran Projcting out translational rigid body mods only T T T T T T m m m m m m Gnralization to othr lmnts straightforward Thi i th df ltsms h This is th dfault SMS schm

10 Usag *CONTROL_ TIMESTEP DT2MS IMSCL RMSCL SMS can b applid to ntir modl (IMSCL=) or a part st ( IMSCL is part st ID) Rotational mass scaling activatd by RMSCL

11 Tip loadd cantilvr

12 (A)No mass scaling, (B) Convntional mass scaling (C) Slctiv mass scaling

13 Dp draw

14 No mass scaling Slctiv mass scaling 22 min 6 sc min 50 sc

15 Enrgy balanc no mass scaling Enrgy balanc slctiv mass scaling

16 Problm # with SMS Mass matrix not diagonal, rquirs solution of linar systm of quations Ma f Solvd using a Prconditiond Conjugat Gradint (PCG) with Jacobi prconditionr Linar convrgnc, numbr of itrations dpnds on condition numbr of systm matrix M n tnw ~ ( M) ~ t ~ t tcpu N tsms tothr t t itr N itr ~ Saturation in CPU tim, manifstd in larg problms nw

17 SMS on Adaptiv Fndr Tim stp Spdup

18 Modlling rcommndations Apply SMS to critical parts that rquir fin msh Spotwlds Bolts String whl Adhsiv bondings Choos tim stp with car Byond som valu nothing is gaind, only inrtia is addd d Problm dpndnt, trial and rror

19 Problm #2 with SMS a a D ai ad ~ T ~ ~ T C MCa I C f MaC Ca I ac M I f I Each constraint imposd dirctly on acclrations must b individually tratd Boundary prscribd motion Boundary SPC Adaptivity Rigid bodis (including nodal rigid bodis) Rigid walls Tid contact

20 Planar rigid walls Implmntd March 2009

21 Tid contacts Implmntd Octobr 200

22 Pak buckling forc

23 NCAC Non modl quad shlls 30 bams 2852 solids contact for th ntir modl Trmination tim scs Timstp scs Ascii and binary outputs disabld. Pr-dcomposd with cpu 23

24 NCAC Non modl 24

25 NCAC Non modl 28x2x4 Dt= minuts 8 scs 8% mass incras Convntional mass scaling 28x2x42 5 minuts Dt= Slctiv mass scaling Ongoing dvlopmnt to support mor faturs for slctiv mass scaling 25

26 Gomtric rigid walls Implmntd Jun 20

27 Rotational SMS Includ rotational rigid body mods in projction of addd mass matrix Furthr rduc inrtia for problms involving rotations Coupld dimnsions maks th schm CPU intnsiv Practical us rmains to b sn

28 Rotational SMS No mass scaling Slctiv mass scaling Rotational slctiv mass scaling Convntional mass scaling

29 Summary SMS incrass th stabl tim stp in xplicit simulations without significantly affcting inrtial proprtis It has volvd to b an important ingrdint in automotiv industry It rquirs som xprinc for maximal fficincy It is not a final product but continuously dvlopd to support nw faturs addd and/or rquird in th front nd of simulations