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Old   December 4, 2007, 12:28
Default Cel expressions Time dependent
  #1
Juan Maria Campos
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Hi everybody,

I want to create a variable through a CEL Expression dependent of the value of this variable at the former timestep.

How can I make it?

thanks in advance
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Old   December 6, 2007, 10:30
Default Re: Cel expressions Time dependent
  #2
mac
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Hi You've fixed or variable timestep
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Old   December 7, 2007, 04:24
Default Re: Cel expressions Time dependent
  #3
Juan Maria Campos
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I have fixed timestep

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Old   December 7, 2007, 10:12
Default Re: Cel expressions Time dependent
  #4
mac
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It's seem to be simple but I don't know what do you want to do with this variable. Can u explain more thx
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Old   December 10, 2007, 09:20
Default Re: Cel expressions Time dependent
  #5
Rogerio Fernandes Brito
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I have the same problem. I wanna put a heat flux, in [W/m^2] as a boundary condition (BC) that varying with the time "t", in [s], using the CEL expressions. At the CFX v5.6, the BC of heat flux must have the same unity, as [W/m^2].

If my heat flux varies with the time as, for example:

q(t)=t^2+3*t-4 with q in [W/m^2] and t (time, not T of temperature) in [s].

My doubt: How to transform the expression 't^2+3*t-4' from [s] to [W/m^2]?

I can´t use a heat flux as a BC in [s]. Only in [W/m^2].

Rogerio.

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Old   December 12, 2007, 03:16
Default Re: Cel expressions Time dependent
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mac
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Hello Rogerio to do these operation you've to use fortran subroutine best regards
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Old   December 12, 2007, 09:13
Default Re: Cel expressions Time dependent
  #7
Rogerio Fernandes Brito
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How?
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Old   December 27, 2007, 06:54
Default Re: Cel expressions Time dependent
  #8
Rafael Brandao
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Rogerio, I think you may try to divide t by the unit (1 [s]) and turn it into an adimensional expression. Then you multiply the result by the new unit.

Your expression then becomes

q(t)=((t/1 [s])^2+3*(t/1 [s])-4)*1 [W/m^-2]

Hope it helped.
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Old   December 27, 2007, 19:16
Default Re: Cel expressions Time dependent
  #9
Rogerio Fernandes Brito
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This way, I think it´s better (on CFX-v5.6 version):

Expression Editor

Expressions

Name Definition

AA 1.0 s

BB 1.0 W m^-2

HeatFlu BB*(t/AA)^2+3*(t/AA)^4

Please, see page 123 from CFX-5 Tutorials.

I´d like to thank for helping me.

Rogério Fernandes Brito.

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