Solver speed
Solver speed
(OP)
Mirror, mirror on the wall, who has the fastest solver of them all? What about the slowest?
I recently started using STAAD.Pro (I know, most of folks in this forum use the more high end, general purpose FEA programs) and I'm amazed how slow the solver is. I've got a 6000 node model composed entirely of plate elements and its taking about 10 minutes to solve. This is nothing fancy, no nonlinear, no gaps, no nothing, just linear static analysis.
I've used SAP2000, COSMOS/M and DesignStar (I think the last two have the same solver) and they all would just laugh at a model this size. OK, maybe just snicker. I would like to be able to go to my boss and show him that there are faster solvers out there. Besides people's personal experience that you can share here, are there any resources that compare solver run times?
I recently started using STAAD.Pro (I know, most of folks in this forum use the more high end, general purpose FEA programs) and I'm amazed how slow the solver is. I've got a 6000 node model composed entirely of plate elements and its taking about 10 minutes to solve. This is nothing fancy, no nonlinear, no gaps, no nothing, just linear static analysis.
I've used SAP2000, COSMOS/M and DesignStar (I think the last two have the same solver) and they all would just laugh at a model this size. OK, maybe just snicker. I would like to be able to go to my boss and show him that there are faster solvers out there. Besides people's personal experience that you can share here, are there any resources that compare solver run times?





RE: Solver speed
For comparison to your numbers I ran our FEA solver (NE Nastran) for a similar shell model (7524 nodes). The model was a fuel tank so there was some complexity, not just a flat plate. It took 10 seconds for the entire run on my Intel P4 PC. I then ran a large model (1.1 million degrees of freedom, over 340,000 nodes). The model was of a bracket modeled using parabolic (tet10) elements. That run took 250 seconds. For both models I requested stress output. I think the reason NE Nastran is so fast is it using the same basic equation solvers as COSMOS but with different element formulations.
Older FEA programs may still use the slower skyline versus a fully sparse storage format which means more operations on zeros. For large solid models an iterative versus direct solver seems to work a lot better. Other types of analysis like eigenvalue extraction or nonlinear may take a lot more time since they involve multiple solves.
For small models and people on a budget these older, less efficient programs may be acceptable regardless of the solver times.
RE: Solver speed
Having a lot of experience with "high-end" as you say,I suppose that Natran falls into that category (?), and also having colleges working today with STAAD.Pro.
STAAD.Pro works ok with beams by is extremely slow with plates for som reason. It is not a factor 2 or 5 or even 10, it's worse. That is my experience but I haven't done any serious testing.
I usually advice people that need to stay away from STAAD.Pro for a number of reasons.
Regards
Thomas
RE: Solver speed
Hey, thanks for the comparison. That'll give me some ammo if I want to broach the subject of switching software.
Thomas, care to elaborate on why to stay away from STAAD.Pro? As you can see from my post, I'm having the same speed issues that you mentioned. I'm not emotionally invested in STAAD so you won't hurt my feelings.
RE: Solver speed
I just say in my own post that I missed something.
What I meant to say is that if you need plates, stay away from STAAD.Pro.
Reasons?
Like you said, slow solver but also not at very flexible mesher and limited postprocessing capabilities.
STAAD.Pro works ok with beams and the numerous codes available makes it interresting. But like I said, I don't use it myself much today. So my primary experience is with the older versions.
My primary tool today is Nastran/Femap and that is an altogether different story. We did some tests a few years ago when we had real speed issues with STAAD.Pro. Plates and beams about 25000 nodes I think. For Nastran seconds, for STAAD.Pro hours, a bit exaggerated but the difference was huge.
Just my $0.02
Thomas
RE: Solver speed
I put some compression only springs in the 6000 node model I mentioned but pared it down to one load case. It took 42 minutes to solve! Unbelievable!
I agree about the postprocessor. It's not very good at all. For instance, the X and Y stresses are only reported in the local system and only the membrane stresses at that. The moments are just that, not the stress in the extreme fiber caused by bending in plate, but a moment per unit length value. What the heck is that? I wanted the stress at the extreme fiber in the local x direction so I had to import the data into a spreadsheet, calc the stress due to bending, then add it to the membrane stress. At least it does maximum principle and von Mises stresses.
Sounds like you've got the same issues with it that I have. I just don't see how they are able to foist this crap on the public. There must not be too many people who actually use plate elements in STAAD.
RE: Solver speed
I am in the middle of modeling a curved continuous steel box girder bridge(lots of plates), and am having quite a bit of difficulty pulling off stresses. Reading through staad's manual I have figured out what stresses are output by staad, but like you said "what the heck is a moment per unit length". can you give me any advise on how to calculated stresses from what is output from staad. thanks.
RE: Solver speed
RE: Solver speed
Now, on to your question, kwrohde. To get the stress due to bending divide the moment per unit length by the section modulus per unit length. In other words, divide by (thk^2/6). Don't forget, this is the stress at the extreme fiber due to bending. You still have to add in the membrane stress to get the total stress at the face. Good luck with the signs.
Now, I've got to get back on my high horse. Why should you have to do this? The data is all there so the program could easily give you the bending stress and total stress in the local coordinates. Other programs I've used do.
Oh, you could also look at von Mises stresses, at least these are reported for the top and bottom faces. So are principle stresses.
RE: Solver speed
In the software I normally use there is no such thing as membrane stress given. Only Top/Bot Normal stress and I think that is much better.
Regards
Thomas
RE: Solver speed
I feel your pain.
RE: Solver speed
RE: Solver speed
Maybe after I build up a little credibility here, I'll suggest that they switch software also.
RE: Solver speed
Because up to this conversation, I thought all other programs had the same speed problem. Definitely a compelling reason to change now that I have this info.
RE: Solver speed
Number of nodes: 72103
Number of elements: 65536
Number of degrees of freedom: 216284
Number of non-zero stiffness terms: 8331680
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Solver speed
What software are you using?
RE: Solver speed
NEiNASTRAN VERSION 8.4.4.328
OPERATING SYSTEM = WINDOWS XP
CPU SPEED = 2806 MHZ
INSTALLED MEMORY = 1024 MEGABYTES
GRID POINTS = 141656
ELEMENTS = 81657
MODEL SIZE = 424968 DEGREES OF FREEDOM
MATRIX SIZE = 15973149 WORDS 182.8 MEGABYTES
SEMIBANDWIDTH = 353 WORDS
TOTAL CPU TIME = 220.9 SECONDS
WALLCLOCK TIME = 238.6 SECONDS
I would recommend a different program unless you like to wait hours for results.
RE: Solver speed
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Solver speed
RE: Solver speed
Personally I use MSC.Nastran and it has better performance than STAAD but no built-in codecheck. I prefer Nastran but for the occasional user who works a lot with structural codes and typically frame (beam) structures with up to say 5000 gridpoints i would say STAAD works just fine.
RE: Solver speed
RE: Solver speed
RE: Solver speed
My question to you is that we have been looking into Cosmos and I want to be sure it can still handle these simple models the same as Staad would. Having a true FEA software would be a big benift for connections etc. but if at the expense of our frame analysis it is not worth it.
Any comments are appreciated.
Thanks.
RE: Solver speed
RE: Solver speed
few days ago a friend here modeled a bridge.
Nothing unusual.
one load case.
And what a surprise!!
the total vertical loads were not equal to the sum of reactions!!!!!!!
So................
Otherwise i would consider SAP.
Good interface, corect outputs, and a verry good"bag" of elements.
For something more complex..
Nastran, Lusas or in my opinon ANSYS
At least you my be sure you are not geting the wrong result from a corect inputs.(ike from Staad)
At the end the speed is not everything. I prefer to not to have nightmares
my $0.02
y
(to get it right assume you are wrong)