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Time range crashes simulation

Posted 28.01.2021, 14:00 GMT-5 Fluid & Heat, Computational Fluid Dynamics (CFD) Version 5.5 4 Replies

HB
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I am running a CFD timde-dependent simulation using the mixture model. When I run the simulation with a time range t=0-5s the simulation runs well. However, when I run the simulation with the exact same setup with a time range t=0-10s, the simulation crashes almost immediately (t=4.764e-7s).

I was wondering what could be causing this behavior and how I could fix it.

Thanks in advance for any help. Humberto

4 Replies Last Post 28.01.2021, 14:31 GMT-5
Robert Koslover Certified Consultant
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Posted: 3 years ago 28.01.2021, 14:17 GMT-5

I would guess (just a guess) this relates to the time stepping process. Are you setting the time step sizes or are you allowing the software to do it? I suggest you pay close attention to that. There are many other possible problems, however. If you can't find the cause of the problem, I suggest you post your model to the forum so others can see the details.

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Scientific Applications & Research Associates (SARA) Inc.
www.comsol.com/partners-consultants/certified-consultants/sara
I would guess (just a guess) this relates to the time stepping process. Are *you* setting the time step sizes or are you allowing the software to do it? I suggest you pay close attention to that. There are many other possible problems, however. If you can't find the cause of the problem, I suggest you post your model to the forum so others can see the details.
HB
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Posted: 3 years ago 28.01.2021, 14:22 GMT-5

Hi, Robert. Thanks for your reply.

I am using the "Free" option in the BDF method and an automatic maximum step constraint.

Hi, Robert. Thanks for your reply. I am using the "Free" option in the BDF method and an automatic maximum step constraint.
Robert Koslover Certified Consultant
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Posted: 3 years ago 28.01.2021, 14:29 GMT-5

I am using the "Free" option in the BDF method and an automatic maximum step constraint.

Yup. Consider something less free. Maybe even "strict." You can make it a bit more free later, maybe, once you get it to actually start executing.

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Scientific Applications & Research Associates (SARA) Inc.
www.comsol.com/partners-consultants/certified-consultants/sara
>I am using the "Free" option in the BDF method and an automatic maximum step constraint. Yup. Consider something less free. Maybe even "strict." You can make it a bit more free later, maybe, once you get it to actually start executing.
Jeff Hiller COMSOL Employee

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Posted: 3 years ago 28.01.2021, 14:31 GMT-5

Indeed, like Robert hints at above, the automatic time stepping algorithm is the very likely source of the change in behavior when you change the final time. See my colleague Henrik's post in this thread, and this Knowledge Base entry.

Best,

Jeff

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Jeff Hiller
Indeed, like Robert hints at above, the automatic time stepping algorithm is the very likely source of the change in behavior when you change the final time. See my colleague Henrik's post in [this thread](https://www.comsol.com/forum/thread/108101/time-dependent-temperature?last=2016-03-30T05:33:04Z), and this [Knowledge Base entry](https://www.comsol.com/support/knowledgebase/1254). Best, Jeff

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