Questions for the experts!! 1

[qwicker]

Hi all you expert Ansys users,

I was hoping to get some feedback on one of my models that I am running. I have a working model, and I am confident in the results. However, I have many models to run and the run times are quite long (in my opinion). I was looking for some thoughts, comments, and advice.

I have a very Large Deformation, nonlinear analysis with about a dozen contact pairs. I have a high level model for rubber (Ogden 3rd order). There are metalic parts encased in a large rubber boot (as a cable bend stiffener). The model has about 200,000 elements. My model takes approximately 2 weeks to solve. This is my hardware configuration:
2x quad core Xeon 3.2Ghz
32GB RAM (fastest available)
15,000rpm SAS drives in RAID 10 (is that a problem?)

I have the full blown Ansys license. Available is the HPC license, VT accelerator, SMP, DANSYS, etc.

I currently am using shared memory parallel with 6 processors (I found that 6 is better than using all 8).

Even thought the model *should* fit incore, the pivoting option keeps activating which (I believe) is causing an out of core solution. For the shared memory Sparse Solver I use the BCSOPTION,,incore. For DANSYS and the distributed solver I issue the DSPOPTION,,incore command. However this always fails in solution because of the pivoting and exceeding the amount of predicted memory!

Does anyone have input, comments, suggestions, quetions?

Thanks!!!!!!!!!

 

[qwicker]

Thanks, I actually am having convergence difficulties. (I said I got convergence yesterday but I lied b/c I forgot to apply my load haha).. anyways, what keeps happening is the solution oscillates. My criterion and forced convergence value seem to move in unison. I will try the update at each equlibrium iteration. I have really simplified my model, and glued many volumes together (which i origonally had as bonded contact). I am using solid 186 elements (alot of memory requirments) so I am going to change to solid 185.

I also have a low level neo-hookean model for polyethelene. It is not very critical and I do not need a complex model. however I know neohookean can become unstable in certain situations. My data is just uniaxial tension.
Thanks guys!

 

[ifegermany]

Hi qwicker,

to get back to your initial question i.e.
'why did the Sparse solver not solve in-core'.

I did check your output1.jpg:

at least at that attempt to run the job
you got less RAM available then required for in-core
(excerpt reported in attachment).

Why your box started out at "only" 24 o/o 32GB RAM
at that instant is another matter. Appears as if other apps
occupied (32GB - 24GB avail - 2GB say_for_OS) say 6GB of
your RAM. 24GB were just low to fit the model in-core.

Free some additional RAM.

Hope that helps.

Frank Exius
IFE Deutschland

http://www.ife-ansys.de

Germany

 

[qwicker]

IfeGermany,
That was the issue I was getting with the pivoting option. The initial memory requirement was only 22GB but then it would change every step varying as much as 3GB so I could never properly predict the memory. It always went out of core.

However though, I have rebuilt my model and glued many volumes instead of using contact pairs. I also am now using the symmetric solver instead of unsymm. My issue is no longer incore as I have achieved that with the DSPARSE. I am now playing with the contact parameters (stiffness). I also have the update each iteration (PAIR based) as well as the augmented lagrange formulation. My model is much smaller now and more efficient. However the tradeoff seems to be that the contact parameters have to be properly adjusted. I always get the below warning. I have the stiffness factor set at 0.05

*** WARNING *** CP = 44.928 TIME= 12:06:22
The default contact stiffness used for contact pair identified by real
constant set 16 is affected by defined inelastic material properties,
even if the material properties are inactive. You shoud confirm that
the appropriate contact stiffness was used.

 

[ifegermany]

qwicker,

"..affected by defined inelastic material properties.."
ANSYS reduces the stiffness to a factor of 1/100 if
plasticity is present, if I recall ok.

Check with Contact Guide - if this applies only if plasticity is actually present,
or if the sole definition of the plasticity law is sufficient to trigger this.


P.S. wrt xSPARSE I'd leave BCSOPTION resp. DSPOPTION to default parameter values.
At times I used manual memory setup -m -db instead of automatic RAM allocation.

Frank Exius
IFE Deutschland

 

[qwicker]

Hi Stringmaker et al,

I have uploaded my database as you suggested. I have really troubleshooted this to death. I have removed components and gotten convergence, I just cannot get it when the entire model is assembled. I really appreciate you taking a look when you have a moment.
Unfortunately I was having issues uploading the file as 1 piece so I had to break it up into 4 RAR files. Please just save them all in the same location and unzip the first part to remake the .cdb file.

Thanks so much!

http://my.engineering.com/pg/file/Qwicker/read/173994/ansys1

http://my.engineering.com/pg/file/Qwicker/read/173995/ansys2

http://my.engineering.com/pg/file/Qwicker/read/173996/ansys3

http://my.engineering.com/pg/file/Qwicker/read/173997/ansys4

 

[qwicker]

Just to show my convergence issue, I attached the below picture of my solution progress.