# creating a field function

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 June 30, 2009, 19:21 creating a field function #1 New Member   Join Date: Jun 2009 Posts: 7 Rep Power: 10 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 Last edited by can_yas; July 1, 2009 at 03:26.

 July 1, 2009, 05:37 #2 Member   Join Date: Mar 2009 Posts: 55 Rep Power: 10 (-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) Last edited by SKK; July 1, 2009 at 06:58.

 July 1, 2009, 06:59 #3 New Member   Join Date: Jun 2009 Posts: 7 Rep Power: 10 (-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

July 1, 2009, 07:06
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Quote:
 Originally Posted by can_yas (-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.

 July 1, 2009, 07:41 #5 New Member   Join Date: Jun 2009 Posts: 7 Rep Power: 10 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 Last edited by can_yas; July 1, 2009 at 09:03.

 July 1, 2009, 08:30 #6 Senior Member   Join Date: Mar 2009 Posts: 203 Rep Power: 11 Sure that he need to write the E8 as a pow? Normally it works without this fine?!

 July 1, 2009, 08:53 #7 New Member   Join Date: Jun 2009 Posts: 7 Rep Power: 10 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

 July 1, 2009, 09:01 #8 Member   Join Date: Mar 2009 Posts: 55 Rep Power: 10 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.

 July 1, 2009, 09:02 #9 Senior Member   Join Date: Mar 2009 Posts: 203 Rep Power: 11 Hmm is the function set a scalar?

 July 1, 2009, 09:18 #10 New Member   Join Date: Jun 2009 Posts: 7 Rep Power: 10 No, I have field function 'Type' Scalar. I am using version 4.2 of STAR CCM+. how did they coordinate system defined?

 July 1, 2009, 09:23 #11 Member   Join Date: Mar 2009 Posts: 55 Rep Power: 10 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]

 July 1, 2009, 09:27 #12 Senior Member   Join Date: Mar 2009 Posts: 203 Rep Power: 11 4.2? You mean 4.02? In the properties you have the function type. Make a screenshot.

July 1, 2009, 09:32
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Quote:
 Originally Posted by Maddin 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...

July 1, 2009, 09:39
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 Originally Posted by SKK 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

July 1, 2009, 09:41
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Quote:
 Originally Posted by Maddin 4.2? You mean 4.02?

course V4.02

 July 1, 2009, 10:11 #16 Senior Member   Join Date: Mar 2009 Posts: 203 Rep Power: 11 @SKK: Maybe you should make a benchmark for this extra pow function A other way would be to use \$Centroid_i (maybe a "cleaner" way). Of cource you need the vector "style" for the velocity I make too much 2D

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