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#1 |
New Member
Jiaui Zhang
Join Date: Aug 2018
Location: Changsha, China
Posts: 17
Rep Power: 8 ![]() |
hi Foamers:
I am running a self-developed solver with combustion using seulex as OED solver. The case is running with a time step of [deltaT 5e-07]; Then, I will get such warning: FOAM Warning : From function seulex::solve(scalar& x, scalarField& y, stepState& in file ODESolvers/seulex/seulex.C at line 255 step size underflow :8.470329473e-22 So does anyone know why this warning appears? Will this warning affect the calculation result? Here is the link for seulex.c https://github.com/OpenFOAM/OpenFOAM...eulex/seulex.C |
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#2 |
Senior Member
Herpes Free Engineer
Join Date: Sep 2019
Location: The Home Under The Ground with the Lost Boys
Posts: 931
Rep Power: 12 ![]() |
It looks like the step size is very small to the extent that it cannot be represented in floating-point computation. Is varying time-step size setting on, so that your input for the time-step (i.e. deltaT 5e-07) has been changed during the simulation?
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#3 |
New Member
Jiaui Zhang
Join Date: Aug 2018
Location: Changsha, China
Posts: 17
Rep Power: 8 ![]() |
Yes, it seems to be the case, and there is no such warning when I reduce the time step from 5E-6 to 5E-7, but the case will cost a much longer time.
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#4 |
Senior Member
Herpes Free Engineer
Join Date: Sep 2019
Location: The Home Under The Ground with the Lost Boys
Posts: 931
Rep Power: 12 ![]() |
Use fixed time step, and fix the time-step 1e-7 or lower instead of using variable time step.
__________________
The OpenFOAM community is the biggest contributor to OpenFOAM: User guide/Wiki-1/Wiki-2/Code guide/Code Wiki/Journal Nilsson/Guerrero/Holzinger/Holzmann/Nagy/Santos/Nozaki/Jasak/Primer Governance Bugs/Features: OpenFOAM (ESI-OpenCFD-Trademark) Bugs/Features: FOAM-Extend (Wikki-FSB) Bugs: OpenFOAM.org How to create a MWE New: Forkable OpenFOAM mirror |
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#5 | |
Member
bany
Join Date: Nov 2019
Posts: 50
Rep Power: 7 ![]() |
Quote:
Sorry for recalling this Thread. When i use chemFoam to calculate the ignition delay time for PRF80 with seulex_KLU, the infinite warnings "step size underflow :0" occur, as shown in the attachment. The mechanism creates a Jacobian with a sparsity of 98%. The calculation is performed by chemFoam with fixed time step 1E-7. In fact, small time steps like 1E-8, 1E-9 are also attempted but with the same warnings. seulex_KLU is the solver seulex with KLU sparse matrix library, provided in the article https://doi.org/10.1016/j.combustflame.2016.09.018. |
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#6 | |
Member
bany
Join Date: Nov 2019
Posts: 50
Rep Power: 7 ![]() |
Quote:
The problem has been solved. We changed another computer and cluster and the warning disappeared. |
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