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Instert new variable witch depent on time step

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Old   February 6, 2008, 10:54
Default Instert new variable witch depent on time step
  #1
Ordoumpozanis
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Hi I want to insert an equation witch gets the temperature of each cell from one specific area of the domain at the time t and recalculate a variable so at the time stem t+1 to read this new variable. I believe that I must insert an expresion but I don't know how to specify an area and how to give a function of time values in transient .

if anyone help me

thanks

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Old   February 6, 2008, 13:38
Default Re: Instert new variable witch depent on time step
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Rogerio Fernandes Brito
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On Solver Control, u will alble to use "Monitor Points".
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Old   February 7, 2008, 15:05
Default Re: Instert new variable witch depent on time step
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CycLone
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You can use the probe() function to get values from a monitor point, or use one of the other available expressions to return values from a 2D or 3D region. It's not clear from your description what you're trying to do. Can you describe it differently?

-CycLone
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Old   February 7, 2008, 17:51
Default Re: Instert new variable witch depent on time step
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Ordoumpozanis
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I have a surface that gets solar radiation Qsun. this surface gets warm because of this radiation. I want to import the radiation from the surface to the sky because the temperature gets to hi. So I need the Temperature of the surface. I run in transient and I want to import an expression of calculate the new Q which is Qsun-Qsky. So I want to calculate the new Q from the time step "t" and to import in to the time step "t+1". To do this I need to have the Temperature of this surface and a way to import a value from the previous time step to the current time step.

thank you
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Old   February 8, 2008, 12:34
Default Re: Instert new variable witch depent on time step
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CycLone
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If you write an expression as a function of T, the solver will actually do exactly what you need. Since the boundary condition is assembled before the timestep is solved, the value of T which the CEL expression accesses is actually the old T. Your expression is then used to apply a new T for the timestep.

Instead of using an expression as above, you might instead define your black body temperature as the sky temperature and add an energy source to the boundary equal to Qsun (on the boundary condition, go to the "Sources" tab). This should do what you want.

-CycLone
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Old   February 12, 2008, 06:06
Default Re: Instert new variable witch depent on time step
  #6
Ordoumpozanis
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Cyclone thank you Could you give me an example of an expretion with time, because i am trying to find any emaple and I can't.

thank you

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Old   February 12, 2008, 16:30
Default Re: Instert new variable witch depent on time step
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CycLone
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Hi Ordoumpozanis,

Since you have an equation in mind, write it out as you would on paper and post it. Explain what the variables mean and I can show you how to do it with CEL.

CEL is really quite straightforward. You write expressions as you normally would. Include the dimensions of constants and refer to solver variables (Temperature, Pressure, 't' for time) by name. If you keep this in mind and remember the the available variables all come from the existing solution (i.e. the last timestep) it's really quite straightforward.

The hard part is actually believing it's that easy!

-CycLone
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Old   February 12, 2008, 17:18
Default Re: Instert new variable witch depent on time step
  #8
PKN
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I dont have an answer to your question but i was wondering if "ordoumpozanis" is your real name. If yes, then can you pronounce it and how many people have been able to pronounce it correctly so far. Thank you
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