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Prev in Time Dependent Study

Posted 26 set 2012, 15:15 GMT-4 Fluid & Heat, Heat Transfer & Phase Change, Studies & Solvers Version 4.2a 5 Replies

George Carlin
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Hello,

I am solving a time dependent Non-Isothermal Flow problem. I need a way to generate a delta T value during processing. In other words, I need a way to access the value of T from the previous time step and use it to calculate a variable, while the problem is being solved..

Is there any sort of prev(T,1) ability for a time-dependent study?

Thank you for your help!
5 Replies Last Post 28 set 2012, 08:21 GMT-4
George Carlin
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Posted: 1 decade ago 27 set 2012, 08:25 GMT-4
If anybody has any tips for running a time discrete solver model that may help as well.

But there has to be a way to access a previous time step value of a dependent variable during processing. The values are saved because I can view them in post processing.
If anybody has any tips for running a time discrete solver model that may help as well. But there has to be a way to access a previous time step value of a dependent variable during processing. The values are saved because I can view them in post processing.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 27 set 2012, 09:43 GMT-4
Hi

you have this reference, old but still valid www.comsol.eu/support/knowledgebase/1042/

but also check "Help " Operators - Special Operators prev() (or BDF if applicable)

You can also search on the FORUM, it has been discussed several times ;)

--
Good luck
Ivar
Hi you have this reference, old but still valid http://www.comsol.eu/support/knowledgebase/1042/ but also check "Help " Operators - Special Operators prev() (or BDF if applicable) You can also search on the FORUM, it has been discussed several times ;) -- Good luck Ivar
George Carlin
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Posted: 1 decade ago 27 set 2012, 10:25 GMT-4

Hi

you have this reference, old but still valid www.comsol.eu/support/knowledgebase/1042/

but also check "Help " Operators - Special Operators prev() (or BDF if applicable)

You can also search on the FORUM, it has been discussed several times ;)

--
Good luck
Ivar


Hi Ivar,

Thank you for the reply. I searched the forum but could not find anything useful for a time-dependent solver. I may have found a work around, however.

I set the time step to be strictly 0.01s (this may change if I find it is not accurate enough) and use the Tt value (slope of Temperature at that time step). By multiplying 0.01 [s] by Tt, this should give delta T for the last time step.

Does this make sense to you? At first glance it seems to be returning correct delta T values, but more investigation is needed before I can say definitively.
[QUOTE] Hi you have this reference, old but still valid http://www.comsol.eu/support/knowledgebase/1042/ but also check "Help " Operators - Special Operators prev() (or BDF if applicable) You can also search on the FORUM, it has been discussed several times ;) -- Good luck Ivar [/QUOTE] Hi Ivar, Thank you for the reply. I searched the forum but could not find anything useful for a time-dependent solver. I may have found a work around, however. I set the time step to be strictly 0.01s (this may change if I find it is not accurate enough) and use the Tt value (slope of Temperature at that time step). By multiplying 0.01 [s] by Tt, this should give delta T for the last time step. Does this make sense to you? At first glance it seems to be returning correct delta T values, but more investigation is needed before I can say definitively.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 27 set 2012, 11:17 GMT-4
Hi

I cannot really say which is best, as what you are doing is not something I have done so far (prev() operators),
To date, I have always managed with only the old "3.5 way" that works also in v4 ;)

--
Good luck
Ivar
Hi I cannot really say which is best, as what you are doing is not something I have done so far (prev() operators), To date, I have always managed with only the old "3.5 way" that works also in v4 ;) -- Good luck Ivar
George Carlin
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Posted: 1 decade ago 28 set 2012, 08:21 GMT-4
An update to my solution: I found in the documentation that you can use the variable "timestep" which holds the value of the current timestep the solver is taking.

So to find my delta Temperature, I multiplied the slope of Temperature at the current timestep, Tt, by the variable "timestep" which should provide a delta value.
An update to my solution: I found in the documentation that you can use the variable "timestep" which holds the value of the current timestep the solver is taking. So to find my delta Temperature, I multiplied the slope of Temperature at the current timestep, Tt, by the variable "timestep" which should provide a delta value.

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