[lex]

Hi all,

Can anyone explain how do i add a condition if i want to avoid zero division error (Esp expressions)?

Below is the expression i have enter.

EXPRESSIONS:
Esp = (Uf^3)/(0.41*z)
Uf = sqrt(k*sqrt(0.09))
Ug = 13 [m s^-1]
Uz = Ug*((z/Zg)^0.25)
Zg = 400 [m]
k = 1.5*(Uz*0.12)^2

Need to set a condition that z must be greater than zero and not more than 400 m.

Thanks in advance.

Lex

[ghorrocks]

You can do conditional stuff either using the step() function, or if you use V12 you can use the new "if" statement. Look in the CEL reference guide for details.

[ckleanth]

if you have a number that is divided by zero

A = x/y where y -1<y<1

the follwing is numericaly similar and you dont have divide by zero

A = x/ (y + 1e-15[m])

[lex]

Hi,

Thanks for the advice. Problem resolved.

Lex

[Timon]

Originally Posted by ckleanth

if you have a number that is divided by zero

A = x/y where y -1<y<1

the follwing is numericaly similar and you dont have divide by zero

A = x/ (y + 1e-15[m])

Except for y=1-1e-15[m]. So use:
A = sign(y)*x/ max(abs(y),1e-15[m])

[jalarron]

in CFDPOST-ANSYS v12, the function sign() is not found? do I need to do something different?
Cheers,
Javier

[kingjewel1]

Originally Posted by jalarron

in CFDPOST-ANSYS v12, the function sign() is not found? do I need to do something different?
Cheers,
Javier

I found that by adding 1e-15 or so didn't work for me. Is there a difference between Version11 (which I'm running) and V12?