fluid structure interaction with *mat_soft_tissue and efg elements rudolf bötticher
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Fluid Structure Interaction with *MAT_SOFT_TISSUE and
EFG elements
Rudolf Bötticher
www.rudolf-boetticher.de
Birmingham, 25.05.2005www.rudolf-boetticher.de
Motivation• Assess whether EFG with FSI and MMALE
is possible for *MAT_SOFT_TISSUE.• Compare the results with standard elements.• Assess whether EFG is more robust.
Result will be:
EFG is a luxury hourglass control !
Birmingham, 25.05.2005www.rudolf-boetticher.de
EFG is easy!*CONTROL_EFG$ in 970 EFG and (dormant) IMPLICIT cards are not tolerated $ in the same deck$ implicit and axisymmetric EFG not implemented!
*SECTION_SOLID_EFG5,41$ the non-default bigger support helps to have consistent $ EFG simulations for *MAT_SOFT_TISSUE
1.4,1.4,1.4
Birmingham, 25.05.2005www.rudolf-boetticher.de
MM-ALE is easy,if you got a working deck to refine!
*ALE_MULTI-MATERIAL_GROUP
Proceedings
Birmingham, 25.05.2005www.rudolf-boetticher.de
FSI: tweaking of *CONSTRAINED_LAGRANGE_IN_SOLID
TSSFACNADV
METHCTYPE
DIRECPFACILEAK
5434a: always use the newest version for consistency and efficiency!
Birmingham, 25.05.2005www.rudolf-boetticher.de
*MAT_SOFT_TISSUE
*EOS_IDEAL_GAS
AET=4
ELFORM=11
*EOS_GRUENEISENbulk modulus*MAT_NULL
outflow
Birmingham, 25.05.2005www.rudolf-boetticher.de
*MAT_SOFT_TISSUE
• reinforced Mooney-Rivlin rubber
C1=C2= 5 MPa
K= 5 GPa (PR=0.4998)
reinforcement in tensionC5=500 MPa B-direction
Birmingham, 25.05.2005www.rudolf-boetticher.de
Why LS-DYNA for this problem?
• Curiosity
• Code is at your disposal
• Expect the same efficiency as for parallel crash simulation
• Rely on the advanced material modeling
other codes may be better
Birmingham, 25.05.2005www.rudolf-boetticher.de
Initial shortening of time step prevents intrusion
*CONTROL_TIMESTEP,,,,,222*DEFINE_CURVE222
Birmingham, 25.05.2005www.rudolf-boetticher.de
default*HOURGLASS 1,1,.00001
DIREC=3
PFAC=0.1
Birmingham, 25.05.2005www.rudolf-boetticher.de
no implicit, no time step split between tissue/ALE domain, no mass scaling!
RI HG6 EFG
K=5 GPa
near incompressibility and mm dimensions require tiny time step
Birmingham, 25.05.2005www.rudolf-boetticher.de
FSI, MMALE dependent on time step!
RI HG6 EFG
TSSFAC=0.25
Birmingham, 25.05.2005www.rudolf-boetticher.de
Robustness
• It proves difficult generating an extreme situation where EFG works but standard elements do not!
• EFG is superior in preventing hourglass modes.
Birmingham, 25.05.2005www.rudolf-boetticher.de
EFGELFORM=1
*HOURGLASS,6 EFG performance lack: 10% elements switched, CPU time +15%
971:*SECTION_SOLID_EFG1,411.4,1.4,1.4,,,3,2
Birmingham, 25.05.2005www.rudolf-boetticher.de
Conclusions
• FSI simulations with MMALE and *MAT_SOFT_TISSUE EFG solids are possible in LS-DYNA.
• EFG is superior in hourglass prevention for tricky cases.
• Time step dependence of FSI needs further investigation!