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maximum (or minimum) value in a time domain
Posted 25.04.2012, 06:48 GMT-4 8 Replies
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I have a problem I cannot solve and you might help me.
In my time-dependent analysis I would like to know the maximum of value of a variable, which has been reached at previous time steps. But I can't figure it out how to that.
If my variable is v(t), then I would like to know max(v(t=t0), (t=t1), ..., v(t=ti)) at each time step.
Do you think it is possible to do that?
Thanks,
Daniel
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Once you define the expression, you should get the maximum or minimum value. Hope it helps.
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I think it is possible, try using Results ----> Derived values ----> maximum (or minimum) ---> line, surface or volume depending upon your domain dimension.
Once you define the expression, you should get the maximum or minimum value. Hope it helps.
Hej,
Thanks, but the problem is that I'm looking for the maximum (or minimum) for each point of the domain until the current time. And I want to use that value during the calculation.
Daniel
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You need this value for postprocessing or to change variable/model setting for next time step? If it is postprocessing, you may still be able to use what i wrote in the last post.
Good luck with your problem. Did you try contacting Comsol support on this?
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You can do this by creating a ODE and assigning the co-efficient to 0 and using the command "ODE variable - ((variable>=ODE variable)*variable +(variable<ODE variable)*ODE variable) for f. This will assign the maximum field value of the variable to the ODE variable which you can access in the end. Use segregated solver to solve for the variable first and then solve for the ODE.
Hope this helps.
Best
Lakshmi.
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@Mranal: I need this for next time step, not only for post-processing. I have tried with Comsol support, but it didn't help.
@Lakshmi: good idea, I tried but didn't work. It says that the matrix is singular.
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actually it works thanks, Lakshmi! The coefficient should be close to 0, but not exactly. Then it works. My only problem is that now the solver takes more time steps and it slows down the computation.
Daniel
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Another user was suggested by COMSOL support to use this global equation
d(Tmax)/dt = dT/dt*(dT/dt>0)*(T>Tmax)
to find the max of T over time.
Hope this reduces the time.
Best regards
Lakshmi.
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is there any chance to see the mph-file implementation of either one of these ODEs?
I think I am stuck in my evaluation ...
Regards
Markus