FEA om multiple computers
FEA om multiple computers
(OP)
Hi all
I little something I've been thinking about.
I have a friend who works with 3d Studio Max. When he does rendering work he runs over the company network and uses several computers working together.
Has anybody tried running FEA in the same manner? I routinely use more than one processor to solve a problem but all the processors are in the same computer, is that necessary?
Just a question
Thomas
I little something I've been thinking about.
I have a friend who works with 3d Studio Max. When he does rendering work he runs over the company network and uses several computers working together.
Has anybody tried running FEA in the same manner? I routinely use more than one processor to solve a problem but all the processors are in the same computer, is that necessary?
Just a question
Thomas





RE: FEA om multiple computers
For example, ABAQUS can use MPI.
RE: FEA om multiple computers
Just one man's thoughts anyway...
RE: FEA om multiple computers
Cheers
Greg Locock
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: FEA om multiple computers
For the "how much processing power do you really need". Well you can never get to much can you? (A joke, although doesn't work that well in writing.)
I agree with you that a 2P quad core system will go a long way. But the reason for my question was a discussion we had at the office.
It seems like the days when we get higher and higher clockspeeds are if not over at least slowing down. Now it's parallel processing and I'm not sure that the softwares are running twice as fast on 2 cores instead of one. Some are good at it, others not that good. And then you have the licensing part. One processor one license, two processors two licences in some cases.
But like I said, It was just a thought I sent out to se what response I would get.
Thanks
Thomas
RE: FEA om multiple computers
RE: FEA om multiple computers
Pja explained well the reasons why FEA don't scale parallelly very well. To return to your question, the answer is definitely NO, the same solver scaled on 10 processors will not be as fast as if it was running on a SINGLE processor having 10x the power.
Some algorithms which are used to optimize the processes in a non-parallel architecture are even non-scalable: in fact, in ANSYS Parallel some features are not available, though you would expect the parallel solvers to be identical to their "mono-core" parents... On their turn, the "mono-cores" run well on a single physical processor but begin to get confused (i.e., not so efficient) if ran in MPI on more than one machine. I don't have any info, but I suspect any solver which "parallelizes" via shared-memory architecture (MPI and others) to be fairly unefficient. With Ansys, don't even know if you still can do that with v.11...
It is still a matter of fact, in my opinion (but there are some numerical reasons to comfort me), that in FEA you'd better use the most powerful processor (SINGLE-processor) you can afford, with the largest amount of RAM allowed by your system (for example, if you use XP-32 or even Vista, it's no use having more than 3 GB of RAM: the OS won't even "see" it and the really available memory will be even far less, around 2 GB if you are very lucky...).
Regards
RE: FEA om multiple computers
I agree that there are reasons why FEA don't scale parallelly very well. The assembly procedure does but the timeconsuming solving of the equations don't.
I have seen benchmarks where certain softwares are supposed to scale well up to approximately 10 processors. By no means a 10x speed increase but still significant. One problem as I understand it is that the processors doesn't seem to increase their speed as they used to. We can't run the same code on a new computer and things automaticly go faster. Now they get more cores instead so things need to run parallell. The solution might be things like huge RAM-memorys and domain decomposition etc. There are numerical "tricks" but they only do so much.
It will be interesting to see what happens in the future.
Regards
Thomas
RE: FEA om multiple computers
Thomas, you're right, although some solvers of the newest generations do parallelize the solution process, not only the assembly procedure. However, they are not able to do this at the same speed "as if" they could do it in "mono-thread" on a single processor.
Things get a bit confused nowadays, in my opinion, because the "multi-core" architecture is somewhere between a "multi-thread mono-processor" and a real "multi-processor". As a result, on the Pentium 4 platform even telling if, say, Ansys will behave better by disabling hyperthreading or by keeping it and asking for 2 "processors" in the program, was nearly impossible. I made this test and two different machines behaved in opposite ways!
Of course, building ultra-powerful single-processors is technically impossible, so the discussion about the "10x - the - power" processor is completely theoretical: you will have to do with 10 processors because you will never get the "10x" single-processor. With a little time, the algorythms will progress on this base.
From this point of view, things are much easier in the 3D animation / rendering field (for example, afaik, radiosity algorithms scale very well).
Regards
RE: FEA om multiple computers
The only thing to do is to put a true model (ie one of yours) on a suitable set of machines and run the tests. I was lucky in that I got this done for free with support from both software and hardware vendors.
In terms of using 'spare' capacity in an office environment this is often not very fruitfulas PC usually get used more than you think.
RE: FEA om multiple computers
My gut feeling is that the bottlenecks on larger models are now the limitation of 32 bit Windows OS to access memory, and the speed of access to swap files on the hard drive, rather than the amount of RAM, or number or speed of processors. However I need to do some more trials with different operating systems and drives, when I have spare time to investigate this.
RE: FEA om multiple computers
Cheers
Greg Locock
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: FEA om multiple computers
http
According to them:
Both the element computations and linear equation solution
can be executed in parallel. Parallelization tends to be
more effective with increasing problem size. Problems under
100,000 degrees of freedom (DOF) will typically not show a
decrease in execution time when more than 2 cores are used
a problem. Problems under 2 million DOF will typically
not show significant speedup beyond 16 cores. Problems with
a small number of iterations will also not show good
overall speedup with added cores as only the actual
iterations are executed in parallel. The input
file preprocessor and initialization code execute on a
single core.
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