If Statement

Zaktatir · June 17, 2010, 11:03

hello,
i want to know why my If statement doesn't work if write:
if(Water.Volume Fraction==0.5,Velocity1,Velocity2) although, Water.Volume Fraction can be 0.5 in my domain (my interphase)...
I want to write a special expression estimating the wave length on an interphase
(for >0.5 it works)

ghorrocks · June 17, 2010, 20:54

Forget C. Try if(Water.Volume Fraction=0.5,Velocity1,Velocity2)

Zaktatir · June 18, 2010, 03:26

what shall i forget, and = is not a logical operator

ghorrocks · June 18, 2010, 07:04

== is a logical operator in C. That's why I said forget C as CFX does not use C for expressions. = is a logical operator in CEL.

Zaktatir · June 18, 2010, 10:43

WARNING
Syntax error detected in the expression assigned to 'mfrac'.
Successfully read 24 characters:
if(Water.Volume Fraction
then error detected at:
=0.5,1,2)
Details - Unexpected character.

ERROR
Syntax error detected in the expression assigned to 'mfrac'.
Successfully read 24 characters:
if(Water.Volume Fraction
then error detected at:
=0.5,1,2)
Details - Unexpected character.

----------------------- i i should use "==" and this statement delivers wrong results ( as if Water.Volume Fraction never takes the value 0.5)

ghorrocks · June 19, 2010, 07:09

I see - in that case you may well be right about the ==. And as you say, VF is never exactly 0.5 so it will never be true anywhere. You will have to specify a range - and I don't think CEL supports AND/OR statements. You may have to construct this logic the hard way with step() functions eg step(VF-0.4)*step(0.6-VF) to find nodes where VF is between 0.4 and 0.6.

June 17, 2010, 11:03	If Statement	#1
Zaktatir Senior Member Join Date: Jan 2010 Location: Germany Posts: 268 Rep Power: 17	hello, i want to know why my If statement doesn't work if write: if(Water.Volume Fraction==0.5,Velocity1,Velocity2) although, Water.Volume Fraction can be 0.5 in my domain (my interphase)... I want to write a special expression estimating the wave length on an interphase (for >0.5 it works)

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June 17, 2010, 20:54		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	Forget C. Try if(Water.Volume Fraction=0.5,Velocity1,Velocity2)

June 18, 2010, 03:26		#3
Zaktatir Senior Member Join Date: Jan 2010 Location: Germany Posts: 268 Rep Power: 17	what shall i forget, and = is not a logical operator

June 18, 2010, 07:04		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	== is a logical operator in C. That's why I said forget C as CFX does not use C for expressions. = is a logical operator in CEL.

June 18, 2010, 10:43		#5
Zaktatir Senior Member Join Date: Jan 2010 Location: Germany Posts: 268 Rep Power: 17	WARNING Syntax error detected in the expression assigned to 'mfrac'. Successfully read 24 characters: if(Water.Volume Fraction then error detected at: =0.5,1,2) Details - Unexpected character. ERROR Syntax error detected in the expression assigned to 'mfrac'. Successfully read 24 characters: if(Water.Volume Fraction then error detected at: =0.5,1,2) Details - Unexpected character. ----------------------- i i should use "==" and this statement delivers wrong results ( as if Water.Volume Fraction never takes the value 0.5)

June 19, 2010, 07:09		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	I see - in that case you may well be right about the ==. And as you say, VF is never exactly 0.5 so it will never be true anywhere. You will have to specify a range - and I don't think CEL supports AND/OR statements. You may have to construct this logic the hard way with step() functions eg step(VF-0.4)*step(0.6-VF) to find nodes where VF is between 0.4 and 0.6.