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Parallel simulation on STAR-CCM+ 11.06.010-R8

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Old   June 8, 2017, 04:29
Default Parallel simulation on STAR-CCM+ 11.06.010-R8
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Hossein M.Ghasemi
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Dear colleagues and friends;
I want to simulate 90,000 particles with 10mm and 15 mm diameter in a container.
I decide to run this simulation on a PC with 64 core i7 Intel Xeon 1.6 Ghz. on windows server 2016 in parallel mode. I set the simulation "parallel on localhost". But when I adjust the simulation on parallel mode, it is too slow
to run relative to the series mode.
However, I tested this simulation on a quad Core i7 3.4 Ghz. cores in parallel mode and the simulation became much faster than previous one.

- Could any one help me to make the simulation faster on the 64 cores PC ?

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Old   August 28, 2017, 05:54
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Danilo Ciliberti
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Hello! Probably you can't get a faster simulation, and here I explain why. Usually it is a matter of mesh size: the STAR-CCM+ manual advices to use a CPU every 250000 cells. Further increase in CPUs number may lead to bottlenecks and the simulation will slow down, because the time needed to exchange information among CPUs or cores is longer than the time used to solve the equations.

Second: recently, Siemens has issued on the Steve Portal an article where it is stated that hyper threading technology may increase the computational time, since mesh generation and flow solving almost use the 100% of a CPU thread, so that the task switching on a physical core due to hyper threading could slow down the simulation, although hyper threading may speed up other phases like post-processing. Are these 64 cores physical? Or are you on a machine with 2 CPUs with 16 physical core each and 32 logical cores each?

Third and perhaps most important: the Intel Xeon you are using is just 1.6 GHz per core, a computational power far below the laptop where I am writing... To solve your issue try to use less cores according to your mesh size. However, since the CPU clock frequency is slow, do not expect much improvement, because the parallelization will help you on big size. You also did not mention about the RAM of the workstation.
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Old   August 30, 2017, 08:21
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lagrangian solving is very different to eulerian flow solving with one of the main issues being the partitioning required by the particle solver changes with time so you might find that dynamic partitioning helps which is far more important for unstready cases
i would also search on the steve support portal for other speed up tips
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