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-   -   creating a field function (http://www.cfd-online.com/Forums/star-ccm/65922-creating-field-function.html)

can_yas June 30, 2009 19:21

creating a field function
 
Hello,

I am working on a project where I have to simulate the flow of air through a pipeline.

I want to create the velocity inlet profile on star ccm+.

How do I implement this function into the program.

funktion :
-2E-08z^4 + 2E-05z^3 - 0,007z^2 + 1,03z- 4,578


Thanks in advance.
Can

SKK July 1, 2009 05:37

(-2*pow(10,8)*(pow($$Centroid[2],4))) + (2*pow(10,5)*(pow($$Centroid[2],3))) - (0.007*(pow($$Centroid[2],2))) + (1.03*($$Centroid[2])) - 4.578

In the above formulation you can also use $$Position[2] instead of $$Centroid[2] is thats what you need.

To implement the field function on the boundary
Region > Boundaries> Physics Values > Velocity Magnitude (Method > field function)

can_yas July 1, 2009 06:59

(-2 * Pow (10.8) * (pow ($ $ Centroid [2], 4))) + (2 * pow (10.5) * (pow ($ $ Centroid [2], 3))) - (0.007 * (pow ($ $ Centroid [2], 2))) + (1.03 * (pow ($ $ Centroid [2], 1))) - 4.578

I have the equation changed(red color), ist dies correct?
and if I have this equation enter into the program, I get error message "Compiled field function type is not vector "

Thanks in advance.
Can

SKK July 1, 2009 07:06

Quote:

Originally Posted by can_yas (Post 221058)
(-2 * Pow (10.8) * (pow ($ $ Centroid [2], 4))) + (2 * pow (10.5) * (pow ($ $ Centroid [2], 3))) - (0.007 * (pow ($ $ Centroid [2], 2))) + (1.03 * (pow ($ $ Centroid [2], 1))) - 4.578

I have the equation changed(red color), ist dies correct?
and if I have this equation enter into the program, I get error message "Compiled field function type is not vector "

Thanks in advance.
Can

Try this, just copy and paste...

(-2 * pow (10,8) * (pow ($$ Centroid [2], 4))) + (2 * pow (10,5) * (pow ($$ Centroid [2], 3))) - (0.007 * (pow ($$ Centroid [2], 2))) + (1.03 * ($$ Centroid [2])) - 4.578

In the pow command variables are separated with commas. Also, no space between the two $$ signs.

can_yas July 1, 2009 07:41

Thank you for your effort, unfortunately, does not again.diese equation is a velocity distribution in a Pipe.
I have descriped cylindrical coordinatesystem in the Inlet .it must be the Origin in the middle? Part(Pipe) has a symmetry Plane :)

Maddin July 1, 2009 08:30

Sure that he need to write the E8 as a pow?
Normally it works without this fine?!

can_yas July 1, 2009 08:53

Hi,

I have changed the equation again.

-0.00000002 * (pow ($$ Centroid [2], 4)) + 0.00002 * (pow ($$ Centroid [2], 3)) -
0.007 *(pow($$ Centroid [2], 2)) + 1.03 * ($$ Centroid [2]) - 4.578


Unfortunately, I get the same error message again,"Compiled field function type is not vector "

Thanks

SKK July 1, 2009 09:01

Have you changed the field function 'Type' to vector?

I don't get this error message. I am using an older version of STAR CCM+. I will check it with the new version later and let you know.

Maddin July 1, 2009 09:02

Hmm is the function set a scalar?

can_yas July 1, 2009 09:18

No, I have field function 'Type' Scalar. I am using version 4.2 of STAR CCM+. how did they coordinate system defined?

SKK July 1, 2009 09:23

for vector definition, the three velocity components are described [x,y,z]. I guess in your case it would be

[0,0,-0.00000002 * (pow ($$ Centroid [2], 4)) + 0.00002 * (pow ($$ Centroid [2], 3)) -
0.007 *(pow($$ Centroid [2], 2)) + 1.03 * ($$ Centroid [2]) - 4.578]

Maddin July 1, 2009 09:27

4.2? You mean 4.02? ;)
In the properties you have the function type.
Make a screenshot.

SKK July 1, 2009 09:32

Quote:

Originally Posted by Maddin (Post 221067)
Sure that he need to write the E8 as a pow?
Normally it works without this fine?!

You're right, it works fine. I like to use pow so that I dont miss a zero...

can_yas July 1, 2009 09:39

Quote:

Originally Posted by SKK (Post 221078)
for vector definition, the three velocity components are described [x,y,z]. I guess in your case it would be

[0,0,-0.00000002 * (pow ($$ Centroid [2], 4)) + 0.00002 * (pow ($$ Centroid [2], 3)) -
0.007 *(pow($$ Centroid [2], 2)) + 1.03 * ($$ Centroid [2]) - 4.578]


That is really unbelievable. This works. I am very grateful for their help:D

can_yas July 1, 2009 09:41

Quote:

Originally Posted by Maddin (Post 221079)
4.2? You mean 4.02? ;)


course V4.02:(

Maddin July 1, 2009 10:11

@SKK: Maybe you should make a benchmark for this extra pow function :D :D :D

A other way would be to use $Centroid_i (maybe a "cleaner" way).
Of cource you need the vector "style" for the velocity :D I make too much 2D :D


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