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Small time step & slow solving process

Posted 12 mars 2017, 06:29 UTC−4 Studies & Solvers, Structural Mechanics Version 5.2 6 Replies

Donovan Wang
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Hi
I'm building a 2D, time dependent model relating to Solid Mechanics/Heat Transfer in Solids/Coefficient Form PDE. They are coupled by the thermal expansion and swelling of the solid. The creep deformation of the solid is also included. I've generated a mesh of ~4000 elements and of 450 000 DOF. The default solver is used and is running on a computer of 64 cores and 96G RAM.
However, the time step taken by the solver is about 1/1 000 of the total time range and the time cost is huge on the solving. I've tried ways of :
1, BDF method while setting the steps taken by the solver as STRICT, and the initial step is given manually.
2, Segregated instead of Fully coupled
3, refining the mesh to about 8000 element and 850 000 DOF
And still running very slow.

Is there anyone have any idea about accelerating the solving process?

Thank you!
XiaoKang
6 Replies Last Post 30 mai 2017, 05:07 UTC−4
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Hello Donovan Wang

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Antoni Artinov
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Posted: 7 years ago 29 mai 2017, 03:12 UTC−4
Hi,

it will be better to "uncouple" the problem, in the sense to solve firstly for the heat transfer and after that to put the temperature field as a load for the structural analysis using "variables not solved for" in the solver sequence. There is mostly no need of bidirectional coupling, as the deformation is usually small and geometrical nonlinearities are neglected, so that the structure does not influence the heat transfer. If it doesn't help I could give you also some advices for the solver settings and the mesh.

Best regards,

Antoni Artinov
Hi, it will be better to "uncouple" the problem, in the sense to solve firstly for the heat transfer and after that to put the temperature field as a load for the structural analysis using "variables not solved for" in the solver sequence. There is mostly no need of bidirectional coupling, as the deformation is usually small and geometrical nonlinearities are neglected, so that the structure does not influence the heat transfer. If it doesn't help I could give you also some advices for the solver settings and the mesh. Best regards, Antoni Artinov
Mohammad Amin Kazemi
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Posted: 7 years ago 30 mai 2017, 00:04 UTC−4
Updated: 7 years ago 30 mai 2017, 00:09 UTC−4
Xiaokang ,

In addition to doing what Antoni suggested, loose the absolute and relative errors if you have tightened them to a very small value.

My results, for example, wouldn't change if I increased the error from 1e-6 to 1e-4 while a significant improvement in the simulation time was achieved by doing so.

Amin,
Xiaokang , In addition to doing what Antoni suggested, loose the absolute and relative errors if you have tightened them to a very small value. My results, for example, wouldn't change if I increased the error from 1e-6 to 1e-4 while a significant improvement in the simulation time was achieved by doing so. Amin,
Donovan Wang
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Posted: 7 years ago 30 mai 2017, 02:31 UTC−4
Dear Artinov:
Thank you for your suggestion. I'll try to use unidirectional coupling in future works.
The problem seems to be relating to the Coefficient Form PDE. And I've used a Weak Form PDE instead which works well.

Sincerely
Xiaokang
Dear Artinov: Thank you for your suggestion. I'll try to use unidirectional coupling in future works. The problem seems to be relating to the Coefficient Form PDE. And I've used a Weak Form PDE instead which works well. Sincerely Xiaokang
Donovan Wang
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Posted: 7 years ago 30 mai 2017, 02:37 UTC−4
Dear Amin:

Thanks for the advice. I found it really useful to change the relative tolerance when it comes to convergence problems. I've changed the relative tolerance to the default setting (1e-3) and it works well.

Sincerely
Xiaokang
Dear Amin: Thanks for the advice. I found it really useful to change the relative tolerance when it comes to convergence problems. I've changed the relative tolerance to the default setting (1e-3) and it works well. Sincerely Xiaokang
Mohammad Amin Kazemi
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Posted: 7 years ago 30 mai 2017, 04:19 UTC−4
Don't forget to make sure how much the results change when you decrease the tolerence, lets say from 1e-3 to 5e-4. If a significant change was observed, then you need to make the error smaller until a minor change is observed.
Amin,
Don't forget to make sure how much the results change when you decrease the tolerence, lets say from 1e-3 to 5e-4. If a significant change was observed, then you need to make the error smaller until a minor change is observed. Amin,
Donovan Wang
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Posted: 7 years ago 30 mai 2017, 05:07 UTC−4
Hi, Amin

Thanks for the notice. I'll pay attention to that.

Xiaokang
Hi, Amin Thanks for the notice. I'll pay attention to that. Xiaokang

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