[Tran Quang]

Hi everybody, Previous I used ANSYS Fluent to simulate but now, I'm using Star CCM+ software to simulate for the HVAC project. because I just used this software in a few weeks. So I have a problem. I hope that everybody helps me.

I want to hook C language code (similar ANSYS Fluent) into STAR CCM+ to wind speed calculate. I don't know how to do. This is my code. Please help me.

Can you help me how to create field function according to this formula

My formula V2=3.7*log(z/0.6)/log(10.0/0.6)

Thank you so much

This my codel from fluent

#include "udf.h"


DEFINE_PROFILE(log_velocity,thread,index)
{
real y[ND_ND];
real z;
face_t f;


begin_f_loop(f,thread)
{
F_CENTROID(y,f,thread);
z = y[1];
F_PROFILE(f,thread,index) = 3.7*log(z/0.6)/log(10.0/0.6);
}
end_f_loop(f,thread)
}

[cwl]

[fluid23]

This should be easy. I haven't worked with Fluent much so forgive me if I miss something, but you should not need to do a loop to define this field function.

Simply go to tools and right click 'field functions' and select 'create new'. Rename it whatever you want and then set the definition as follows. Also, note that I am assuming this is a log 10 and not log e function you have defined. (For log e just use log() instead of log10().

3.7*log10($$Position[2]/0.6)/log10(10/0.6)

That should define that function at the centriod of each cell based on the z coordinate ($$Position[2]).

[Tran Quang]

Thank you so much for your help. I was sending messenge on Skype to you

[Tran Quang]

Originally Posted by fluid23

This should be easy. I haven't worked with Fluent much so forgive me if I miss something, but you should not need to do a loop to define this field function.

Simply go to tools and right click 'field functions' and select 'create new'. Rename it whatever you want and then set the definition as follows. Also, note that I am assuming this is a log 10 and not log e function you have defined. (For log e just use log() instead of log10().

3.7*log10($$Position[2]/0.6)/log10(10/0.6)

That should define that function at the centriod of each cell based on the z coordinate ($$Position[2]).

Hello Sir.
Thank you so much for your help. But when I have imported your formula into STAR CCM+ I have met a problem " A Floating point exception has occurred: floating point exception {Invalid operation}.

Thank you so much

[JBeilke]

Just think a moment about the logarithmus of zero.

[fluid23]

Originally Posted by Tran Quang

Hello Sir.
Thank you so much for your help. But when I have imported your formula into STAR CCM+ I have met a problem " A Floating point exception has occurred: floating point exception {Invalid operation}.

Thank you so much

Wait... are you trying to assign boundary conditions or a value in every cell of your domain?

Also, as Joern pointed out. The equation you defined blows up (goes to negative infinity) when z=0. That is probably the source of your floating point error.

If you are simply trying to apply a velocity profile to your boundary there are better ways to go about it.

[Tran Quang]

Originally Posted by fluid23

This should be easy. I haven't worked with Fluent much so forgive me if I miss something, but you should not need to do a loop to define this field function.

Simply go to tools and right click 'field functions' and select 'create new'. Rename it whatever you want and then set the definition as follows. Also, note that I am assuming this is a log 10 and not log e function you have defined. (For log e just use log() instead of log10().

3.7*log10($$Position[2]/0.6)/log10(10/0.6)

That should define that function at the centriod of each cell based on the z coordinate ($$Position[2]).

.

Hello sir.

If I can calculate my model based on the y coordinate. How to changed [2]?

[fluid23]

The Cartesian coordinates are specified by the $$Position vector, where $$ denotes a vector quantity. X is $$Position[0], Y is $$Position[1] and Z is $$Position[2].

[Tran Quang]

Originally Posted by fluid23

The Cartesian coordinates are specified by the $$Position vector, where $$ denotes a vector quantity. X is $$Position[0], Y is $$Position[1] and Z is $$Position[2].

I very much appreciate your help