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Question on Time Step Dependent study

Posted Jan 20, 2012, 4:29 p.m. EST Fluid & Heat, Materials, Modeling Tools & Definitions, Parameters, Variables, & Functions, Results & Visualization, Studies & Solvers Version 4.1, Version 4.2, Version 4.2a 5 Replies

Tim Tan
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Hi ,

I wish to conduct a time step dependent study for a time dependent simulation. I.e to say, run the same simulations with different time step. As the time step is smaller , it should be able to get a more accurate result as compared to a larger time step.

I wish to compare the difference in performance for the different time step.

However according to what i read through for comsol , COMSOL pick its internal time step own time step when running.The time step that we enter are the time step we want to see for the solutions. The internal time step is controlled by changing the tolerances.

I wish to ask if the program can be forced to conduct the simulated at a define time step like t=1, t=0.1 without changing its tolerance?

i noticed that the time step can adjust under steps taken by solver , from the option of free to Intermediate and strict. Does this change the time step in which the program simulate or it just displaying the time step according to the solution needed?

i hope i have not confuse any of you. feel free to clarify with me

Thanks

Tim

5 Replies Last Post Feb 29, 2012, 1:17 p.m. EST
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Jan 20, 2012, 4:54 p.m. EST
Hi

use the contextual help most answers are therein.

Indeed "free" mode is for COMSOL decided time steps, excellent for diffusion problems, but unlucky for periodic BC conditions.

Intermediate, take the user defined ones, but still might add a few in-between if the results are poor

Strict is only solving for the values you define

--
Good luck
Ivar
Hi use the contextual help most answers are therein. Indeed "free" mode is for COMSOL decided time steps, excellent for diffusion problems, but unlucky for periodic BC conditions. Intermediate, take the user defined ones, but still might add a few in-between if the results are poor Strict is only solving for the values you define -- Good luck Ivar
Tim Tan
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Posted: 1 decade ago Jan 21, 2012, 12:06 a.m. EST

Hi

use the contextual help most answers are therein.

Indeed "free" mode is for COMSOL decided time steps, excellent for diffusion problems, but unlucky for periodic BC conditions.

Intermediate, take the user defined ones, but still might add a few in-between if the results are poor

Strict is only solving for the values you define

--
Good luck
Ivar


Thanks Ivar !! Great help. !
[QUOTE] Hi use the contextual help most answers are therein. Indeed "free" mode is for COMSOL decided time steps, excellent for diffusion problems, but unlucky for periodic BC conditions. Intermediate, take the user defined ones, but still might add a few in-between if the results are poor Strict is only solving for the values you define -- Good luck Ivar [/QUOTE] Thanks Ivar !! Great help. !
Osameh Ghazian
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Posted: 1 decade ago Feb 29, 2012, 11:05 a.m. EST
Hi Ivar,

I changed the time stepping to Strict, but the time steps in the LOG are still not matching with my defined time steps. I just want the solver to use the exactly my time steps. what should i do ?
Hi Ivar, I changed the time stepping to Strict, but the time steps in the LOG are still not matching with my defined time steps. I just want the solver to use the exactly my time steps. what should i do ?
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Feb 29, 2012, 1:11 p.m. EST
Hi

normally it tries to use only yours, but if it fails it still tries to take smaller steps to get on line again, probably you have too tough initial conditions compared to your BC.

And are you in BDF or Gen-alpha ?

--
Good luck
Ivar
Hi normally it tries to use only yours, but if it fails it still tries to take smaller steps to get on line again, probably you have too tough initial conditions compared to your BC. And are you in BDF or Gen-alpha ? -- Good luck Ivar
Osameh Ghazian
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Posted: 1 decade ago Feb 29, 2012, 1:17 p.m. EST
I am using BDF, I have a periodic BC ( time dependent) , so that is the reason I change free to strict in my solver.
I am using BDF, I have a periodic BC ( time dependent) , so that is the reason I change free to strict in my solver.

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