Fatal error during Normal Mode simulation

rex.he over 5 years ago

When I did Normal Modes simulation using MFLUID, VMOPT=2, I get below fatal error:

*** USER FATAL MESSAGE 6136 (UDSFA)

INSUFFICIENT CORE FOR NUMERIC PHASE OF SPARSE DECOMPOSITION.

USER ACTION: INCREASE CORE BY ********** WORDS

0FATAL ERROR

1 * * * END OF JOB * * *

How can I fix this?

0 Hrishikesh Phadke over 5 years ago

Memory settings look good and the error message looks misleading. Use the same memory settings in following runs.

Can you run without the virtual mass to ensure modeling is alright? Also just to ensure this is not version specific try running in lower version like 2014.1 , or 2017.1...

If nothing works then you might have to send us the file to try further debugging.
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0 rex.he over 5 years ago

OK, i will try to run it by removing the MFLUID, then run, but do you noticed that the dry mode frequency seems found by the simulation, so only the second step of calculating the wet mode is stopped....

Meanwhile, I will try to install a old version in my sever, thanks!
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0 Hrishikesh Phadke over 5 years ago

Yes. That is true... But we have used almost all the memory on your server, so there is not much more you can do there....

Could be the newer version is more memory intensive ? So just give a try with older versions..
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0 rex.he over 5 years ago

Today I tried to use Nastran 2017.1, 2016&2020, but the same error is still here.... May be the elements included in the MFLUID is too many, I do not know whether there is a limit number for it.

Anyway, thanks for your suggestion!
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0 Hrishikesh Phadke over 5 years ago

MFLUID is very memory intensive. You can try using METHOD(COUPLED)=XX in case control. This will give you comparable answer, not exactly same as MFLUID. This is there from Nastran 2020 QRG.

4. METHOD(COUPLED) is only used when STRUCTURE and FLUID COUPLED problem. The

corresponding EIGRL or EIGR requires either the frequency range of interest or ND (number of

roots desired) entry. The real coupled modes computation is done with combination of Lanczos

method and Subspace iteration method.

METHOD(COUPLED) is recommended for heavy fluid (like liquids) model. When it is applied to

the light fluid model, it might require more coupled modes to get the correct result.

Just require to model the complete structure and the fluid cavity and use the METHOD(COUPLED)=XX..

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0 rex.he over 5 years ago

OK, thank you for all your help. So the Virtual Fluid Mass Method is not feasible in Nastran if the wet element is too many, am I right? if I am right, which is the feasible wet element number to run the simulation?

Thanks again.

Meanwhile, I will try to set up another model by using your above suggestion.
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0 Hrishikesh Phadke over 5 years ago

There is no limit to the feasible wet element number, but is limited by the hardware resources...
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