1. A Study on the Multi-Material ALE Scheme with FSI in LS-DYNA
Rudolf Bötticher TMB GmbH
Introduction
Thank You.
Hello. Good Morning.
I will talk about multi-material ALE – ELFORM 11.
I want to compare the influence of the two advection schemes.
And I will do this in situations, where these advection schemes interact with Fluid-Structure Interfaces.

2. Motivation
Assess time step dependence of multi-material ALE (ELFORM=11) results for the two advections schemes with a FSI interface present .
1. Airbag - Random Error
2. Water Jet – Troubles & Monitoring
3. Duct – Leakage
4. Conclusions
The motivation of the talk is to track down the time stepe dependence of FSI results in former works. I want to clear, whether the energy dissipation of the advection schemes and the count of advection cycles are the source for this problem.
I start off with an illustrative example about the random error you might expect in LS-DYNA runs with FSI. I will use an airbag deployment example for that.
Then I will use the example of a fluid jet impacting a surface to show some of the troubles you might get in simulations with three and more fluids. And I will talk about ways of monitoring the solution.
After that, I will treat the biomedical prototype duct from former work again. I will explain the measures to sooth time stepe dependence, and put a spotlight on extreme leakage.
Some concluding remarks will end the the talk. .
Bonn,

3. Tested this on 9th May 2007 with ls971_s_11220_winx64_p on the same machine:
the effect has vanished!!!
Caution: random error!
Rerun input deck with *AIRBAG_ALE five times each for no-switching (UP), switching and ALE METH=1, and switching and ALE METH=2 and for two settings of the time step (TSSFAC)
32 bit single precision 5434a SMP (s_5424a_p) on dual Opteron with Windows x64
Is a LS-DYNA solver run always a deterministic function evaluation?
Multi-Material ALE is important for out of position airbag simulations
Bonn,

4. Airbag pressure
Bonn,

5. - TSSFAC=0.5 - TSSFAC def. METH=1 - Donor Cell Scheme Bonn, 10.11.2005

6. - TSSFAC=0.5 - TSSFAC def. METH=2 - v. Leer Scheme Bonn, 10.11.2005
.....
Bonn,

7. Troubles: Inter-ALE-material interfaces
Interface tracking near FSI with three fluids
Re-appearance of ALE-materials
LS-PrePost
SelPar
tick Fluid box
Bonn,

8. FSI: tweaking of *CONSTRAINED_LAGRANGE_IN_SOLID (CLIS)
Ongoing development 5434a and beyond: always use the newest version for consistency and efficiency!
TSSFAC
NADV
METH
CTYPE
DIREC
PFAC
ILEAK
Bonn,

9. Monitoring of interface advancing
FSI-interface energy dependent on time step, which is more important than advection method
Monitoring of interface advancing
Bonn,

10. User-specified penalty stiffness and leakage control important
Bonn,

11. Modeling
Intelligent grouping of inter-ALE-material and ALE-material to Lagrangian interfaces.
Individual penalty stiffness. New treatment of initial FSI-penetration on CLIS.
Water
Soft tissue
EFG
No hourglass energy!
Air
Bonn,

12. No time step dependence anymore as compared to investigation in 2004
EFG
Bonn,

13. TSSFAC=0.6 TSSFAC=0.3 Water Air Bonn, 10.11.2005

14. DIREC=6
sp dp
Bonn,

15. Conclusions
The strong influence of the parameters on CLIS in conjunction with the time step on the creation of non-physical interface energy may yield low quality results.
Random error with multiple CPUs!
Advection scheme less important.
I want to conclude my talk.
Well, the difference of the advection schemes is not the natural suspect, if time step dependence of the solutions have to be tracked down.
The influence of the time step in interplay with the parameters of the CLIS card are of greater importance. The impulse of non-physical contact energy has to be monitored.
Do not forget the ALE-material interfaces.
Keep in mind the possible random error of a LS-DYNA solver run.
Som that‘s all.
I hope that some of the experiences I gathered may be helpful in your work in finding work arounds in LS-DYNA.
Thanks for listening. .
Bonn,