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-   -   Time integral of the variable in POST (http://www.cfd-online.com/Forums/cfx/79422-time-integral-variable-post.html)

Luk_Fiz August 23, 2010 12:44

Time integral of the variable in POST
 
Hi all,
I have suprisingly simple question and cannot find an answer in the archiwe.

I have simple time-dependant simulation. In the transient results files I can visualize any quantity (velocity, density etc) on any given surface over the time - thats obvious. But how to visualise the time-integral of this quantity from the entire simulation on this surface? For example: integration of velocity*density gives something like "flow rate density" of units [kg/m2/s]. If I integrate this in time I have [kg/m2] what gives me "flow density" (not flow rate) in various regions of the plane during the entire simulation.

I am not going to discuss the physical sence of such integrated quantity, just want to know.

Luk

ghorrocks August 23, 2010 18:23

In post-processing you can calculate these values for any timestep you have saved a results file for. But the best way is to set up a monitor point with the CEL to evaluate the expression and do it as the solver progresses. Then you get the thingn evaluated at all time steps (or even all coefficient loops if that is of interest).

Luk_Fiz August 24, 2010 08:24

Can You please describe how to calculate these time integrals? I really cannot find anything in documentation.

Maybe I can make myself more clear. Lets take for example velocity for given node or element, lets take 2 timesteps each of 1 [s].Than:
Timestep 1) Velocity=1[m/s]
Timestep 2) Velocity=2[m/s]

And the quantity in witch I am interested into is:
1[m/s]*1[s]+2[m/s]*1[s]=3[m]

using simplest integration possible.

Can anyone help how to inisist such a integration in POST? I would be very gratefull.

Luk

ghorrocks August 24, 2010 18:52

You cannot do time integrals in CEL in Post or the solver for that matter. You will have to export the results of the time and value and integrate them using another package.


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