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how to use dimensionless argument?

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Old   April 8, 2013, 00:19
Default how to use dimensionless argument?
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DongGunKo
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i made UDF with argument as mass fraction
but i don't know how to use that.
i have to type the argument unit but mass fraction does not have unit
plz help me
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Old   April 8, 2013, 02:08
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Lance
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Do you mean in a CEL expression? You can always make your CEL expression dimensionless by dividing by the proper unit, e.g. 10 [kg]/1[kg] would result in 10 (unitless).
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Old   April 8, 2013, 02:44
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i mean that in a user function tab, there are spaces for argument unit and result unit, but my User defined Function has a argument as a mass fraction so it is dimensionless.

typing like a m*m^-1 or something else show error in applying UDF in SOURCE TERM like below

The variable 'Mass Fraction' referenced in parameter 'Source' in object '/FLOW:Flow Analysis 1/DOMAIN:R1/SUBDOMAIN:Subdomain 1/FLUID:h2ol/SOURCES/EQUATION SOURCE:continuity' does not have one of the required prefixes: component or particle component.
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Old   April 8, 2013, 07:51
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If you have defined the variable, using an expression that contains the main variables in CFX, you don't need to specify unit. But if you are using actual values, you need to specify units -say 1 [m s-1] etc.

In case if the variable doesn't have units, don't give it even when you use it as a value. CFX will shout only when there is a discrepancy with dimensions of both sides of the expression.

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