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time step algorithm
Posted Aug 11, 2016, 6:02 p.m. EDT Porous Media Flow Version 5.2a 1 Reply
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Hello,
As I know, Comsol can changes the time stepping in a model , for example when we select "Free" "BDF" in solvers. My question is what criteria does Comsol follow to do this change? How does Comsol know how much it should decrease or increase the time step for next iteration? What is the mathematical formula?
It would be great if anyone who knows related information, shares it here please.
Thanks,
Mehrdad
As I know, Comsol can changes the time stepping in a model , for example when we select "Free" "BDF" in solvers. My question is what criteria does Comsol follow to do this change? How does Comsol know how much it should decrease or increase the time step for next iteration? What is the mathematical formula?
It would be great if anyone who knows related information, shares it here please.
Thanks,
Mehrdad
1 Reply Last Post Aug 11, 2016, 7:11 p.m. EDT
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Posted:
8 years ago
I can see from internet and other foroum posts that :
" ... COMSOL reduces the time step size when it does not converge in the time or spatial domain ... "
or
" ...The Minimum step size is respected as long as the solver converges well. The automatic step-size algorithm detects poor convergence speed and other "problems" and reduces the step size ..."
But how does Comsol reduces the time step? If we use Runge-Kutta or Generalized alpha, then we have option "manual". I guess we can define something like Courant number by an expression in that option (maybe !). But how about "BDF" ?
" ... COMSOL reduces the time step size when it does not converge in the time or spatial domain ... "
or
" ...The Minimum step size is respected as long as the solver converges well. The automatic step-size algorithm detects poor convergence speed and other "problems" and reduces the step size ..."
But how does Comsol reduces the time step? If we use Runge-Kutta or Generalized alpha, then we have option "manual". I guess we can define something like Courant number by an expression in that option (maybe !). But how about "BDF" ?