Adding a term that includes time

ozgur · August 27, 2010, 10:05

Hi,

A very simple question: In OpenFOAM, how can I add a term that includes time into my equations?

My first attempt which doesn't work is as follows:

solve
(
fvm::ddt(T)==-exp(-time())
);

Thanks for any comments,

Ozgur

ngj · August 27, 2010, 10:23

Hi Ozgur

time() is not a known object, so use runTime.time().value() instead. The "value()" request is given as it strips off the dimensionality of the given time and merely returns a scalar. This is needed as exp() does not know how to handle dimensionedScalar.

Further you need to do "A * Foam::exp(- runTime.time().value())", where A is a dimensionedScalar A("null", dims , 1), where dims is the dimensions of ddt(T). If this is not added you will get an error while running the program due to the dimensional checking functionality, however the program will compile.

Instead of dims you could e.g. do "dimensionSet( 0, 1, -1, 0, 0, 0, 0)" which sets the dimensions to those of velocity.

Have a nice weekend,

Niels

ozgur · August 27, 2010, 13:59

Hi Niels,

Thank you very much. It worked fine

cheers,

Ozgur

August 27, 2010, 10:05	Adding a term that includes time	#1
ozgur New Member Ozgur Kirlangic Join Date: May 2009 Location: Istanbul Posts: 16 Rep Power: 16	Hi, A very simple question: In OpenFOAM, how can I add a term that includes time into my equations? My first attempt which doesn't work is as follows: solve ( fvm::ddt(T)==-exp(-time()) ); Thanks for any comments, Ozgur

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August 27, 2010, 10:23		#2
ngj Senior Member Niels Gjoel Jacobsen Join Date: Mar 2009 Location: Copenhagen, Denmark Posts: 1,900 Rep Power: 37	Hi Ozgur time() is not a known object, so use runTime.time().value() instead. The "value()" request is given as it strips off the dimensionality of the given time and merely returns a scalar. This is needed as exp() does not know how to handle dimensionedScalar. Further you need to do "A * Foam::exp(- runTime.time().value())", where A is a dimensionedScalar A("null", dims , 1), where dims is the dimensions of ddt(T). If this is not added you will get an error while running the program due to the dimensional checking functionality, however the program will compile. Instead of dims you could e.g. do "dimensionSet( 0, 1, -1, 0, 0, 0, 0)" which sets the dimensions to those of velocity. Have a nice weekend, Niels

August 27, 2010, 13:59		#3
ozgur New Member Ozgur Kirlangic Join Date: May 2009 Location: Istanbul Posts: 16 Rep Power: 16	Hi Niels, Thank you very much. It worked fine cheers, Ozgur