Cel expressions Time dependent
 

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

Re: Cel expressions Time dependent
 

Hi You've fixed or variable timestep

Re: Cel expressions Time dependent
 

I have fixed timestep

Re: Cel expressions Time dependent
 

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

Re: Cel expressions Time dependent
 

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.

Re: Cel expressions Time dependent
 

Hello Rogerio to do these operation you've to use fortran subroutine best regards

Re: Cel expressions Time dependent
 

How?

Re: Cel expressions Time dependent
 

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.

Re: Cel expressions Time dependent
 

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.