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CFX-PRE monitor point... multi-variable arguments for locator based functions

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Old   November 17, 2011, 09:37
Default CFX-PRE monitor point... multi-variable arguments for locator based functions
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Is it somehow possible to do as the title of the thread reads, and define a multi-variable argument, locator based function?

A little more info:
My simulation involves a jet of fluid, pointing in the X positive direction. Using CFX_PRE V13
I want to find the spread angle of the jet, i.e angle between the majority of the vectors and the vector (1,0,0) (x-positive direction)

So I start with the equation for an angle between 2 vectors:
\alpha = \text{acos} \left( \frac{\vec{u} \bullet \vec{v}}{\left| \vec{u}\right| \left| \vec{v} \right|} \right)

where u is the vector (1,0,0) and v is the velocity vector at the mesh locator OUTLET.

since the u vector is fully dercribed in only one direction and is the unity vector, the formula can be simplified to:
\alpha = \text{acos} \left( \frac{v_{1} }{ \left| \vec{v} \right|} \right)
*Note; here alpha is actually defining the half spread angle.

This could be set as an expression as follows:
alpha=acos(Velocity u*1 [m s^-1]/(Velocity u^2+Velocity v^2+Velocity w^2))
*Note I multiply with 1 [m s^-1] to keep dimensions consistent.

Now if I set a monitor point as:
massFlowAve(alpha)@OUTLET
I get a error message along the lines of:

"The function 'massFlowAve' referenced in parameter 'Expression Value' in object '/FLOW:Flow Analysis 1/OUTPUT CONTROL/MONITOR OBJECTS/MONITOR POINT:ALPHA_MONITOR' has an invalid argument, 'alpha'. Only arguments that consist of a single recognised variable name are supported by the solver."

As far as I can tell, the problem above basically means that I can only define one variable (e.g Velocity u) and not 2 or 3 variables in the locator based function; massFlowAve().
Note that the exact same method DOES work for me in CFX-POST. Thas is defining the same expression, and using the function calculator.
So does anyone have an idea how to circumvent this problem in CFX-PRE??

Thanks in advance!
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Old   November 17, 2011, 16:52
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There's an easy way to do this... create an algebraic Additional Variable equal to alpha and then use the AV as the argument to the locator based function.
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Old   November 17, 2011, 17:22
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You're right! works perfect. Thanks for the help.
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Old   November 18, 2011, 00:16
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Hi,
I tried to do the same, but I am not getting how to define algebric additional variable. I was able to define AV but the problem is I am not getting an option of writing an expression for it or giveing its type as algebric, i searched CFX help but to no avail.
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Old   November 18, 2011, 11:42
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After you create the AV, you need to edit your domain to enable the AV in that domain. It's in the domain settings that you say it's algebraic.
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Old   November 19, 2011, 01:15
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Thanks,
Now I am getting it.
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Old   February 8, 2015, 21:51
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Hi, I really tried to do the same that you posted. I am trying to set a boundary condition in a multi-phase simulation dependent of (Fluid1. Volume Fraction*Velocity v)=VC= my AV, but when I tried to define the boundary condition I got this messaje

"The Additional Variable 'VC' referenced in parameter 'Normal Speed' in object '/FLOW:Flow Analysis 1/DOMAINefault Domain/BOUNDARY:top/BOUNDARY CONDITIONS/MASS AND MOMENTUM' is fluid-dependent and therefore requires a fluid prefix."

How can I set a prefix on my AV?

Thank you for your help

Last edited by jaimesdiegop; February 9, 2015 at 12:18.
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