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Difference between Time dependent and Time discrete
Posted 23.09.2013, 12:24 GMT-4 Fluid & Heat, Heat Transfer & Phase Change, Studies & Solvers 2 Replies
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Hi,
I am working on a conjugate heat transfer problem. By t=20s, the system reaches steady state. Then I would like to see the system response after t=20s, using step function to switch off a source after t=20s.
The time step, I use is 0.5s.
However, whenever I use time dependent solver, I could see the step function switches off somewhere around 19.0 s itself, which actually should not be the case (This is noticed this through the change in solution after 19s).
But, this issue is not there in the case of time-discrete solver, where the source is perfectly switched off only after 20s. (solution remains same upto 20s)
I would like to know what precisely is the difference between time-dependent and time-discrete models?
I am working on a conjugate heat transfer problem. By t=20s, the system reaches steady state. Then I would like to see the system response after t=20s, using step function to switch off a source after t=20s.
The time step, I use is 0.5s.
However, whenever I use time dependent solver, I could see the step function switches off somewhere around 19.0 s itself, which actually should not be the case (This is noticed this through the change in solution after 19s).
But, this issue is not there in the case of time-discrete solver, where the source is perfectly switched off only after 20s. (solution remains same upto 20s)
I would like to know what precisely is the difference between time-dependent and time-discrete models?
2 Replies Last Post 25.09.2013, 11:33 GMT-4
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Posted:
1 decade ago
Sathish,
What do you mean when you say, "The time step, I use is 0.5s"?
If this is the time step you enter under Study Settings>Times, by default this will only govern the requested times for output (not the solver steps themselves). If you switch Time Stepping under the Time Dependent solver to Intermediate or Strict or Manual then you are adding control over the actual time steps that the solver takes.
Also, check the "smoothing" of the step function. The transition zone could be causing this behavior where the load is switching off "early."
Best regards,
Josh Thomas
AltaSim Technologies
What do you mean when you say, "The time step, I use is 0.5s"?
If this is the time step you enter under Study Settings>Times, by default this will only govern the requested times for output (not the solver steps themselves). If you switch Time Stepping under the Time Dependent solver to Intermediate or Strict or Manual then you are adding control over the actual time steps that the solver takes.
Also, check the "smoothing" of the step function. The transition zone could be causing this behavior where the load is switching off "early."
Best regards,
Josh Thomas
AltaSim Technologies
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Posted:
1 decade ago
Thanks Josh,
I already solved the issue. I mistook the Study Settings>Times as solver stepping times, which is actually not the case. I controlled the exact timesteps within time dependent solver with strict option.
This was genuinely confusing for a starter using time dependent solver in COMSOL.
Sathish
I already solved the issue. I mistook the Study Settings>Times as solver stepping times, which is actually not the case. I controlled the exact timesteps within time dependent solver with strict option.
This was genuinely confusing for a starter using time dependent solver in COMSOL.
Sathish