[H.H]

please can any help me for solving following polynomial function of local heat flux on Cylindrical pipe. having issues in applying Cartesian to polar logic (arctan theta) .


DEFINE_PROFILE(heatflux,thread,position)
{
real x[ND_ND],xcoord,ycoord,Degree;
face_t f;
begin_f_loop(f,thread)
{
F_CENTROID(x,f,thread);
Degree=x[2];
Degree=atan(ycoord/xcoord)*(180/3.14159265);

if (0<=Degree&&Degree<=88) F_PROFILE(f,thread,position) = 1005-3.0*Degree+0.689*pow(Degree,2)-0.0005*pow(Degree,3);
else F_PROFILE(f,thread,position) = -19.90+1.9*Degree-1049.0*pow(Degree,2)+0.005*pow(Degree,3);
}

end_f_loop(f,thread)
}

[`e`]

Use the Message(); function to check your code (debugging); print the angles and heat fluxes and compare them to what you expect. Read about the atan2 function; this function returns the angle in the correct quadrant.

[H.H]

Sir, thanks for the suggestion. but what will be the position of message(); line??
Can you do me a favor? to rephrase the program according to you suggestion of message(); line as well as by using atan2 (tetha) suggestion. please if u donot mind. it might take precious time of yours. but im trying to some for ouple of days, but im unable to program and having limited time left for my project defend.

i will be thankful to you always.
Regards,
H.H

[`e`]

You're using the variables ycoord and xcoord without initialising (garbage numbers from memory); evaluate these values for each face (and include the Message(); function):

#include "udf.h"

DEFINE_PROFILE(heatflux,thread,position)
{
	real x[ND_ND],xcoord,ycoord,Degree; 
	face_t f;
	
	begin_f_loop(f,thread)
	{
		F_CENTROID(x,f,thread);
		xcoord = x[0];
		ycoord = x[1];
		Degree=atan(ycoord/xcoord)*(180/3.14159265);
		Message("Degree = %e at [x,y,z] = [%e,%e,%e]\n",Degree,x[0],x[1],x[2]);

		if (0<=Degree&&Degree<=88) F_PROFILE(f,thread,position) = 1005-3.0*Degree+0.689*pow(Degree,2)-0.0005*pow(Degree,3);
		else F_PROFILE(f,thread,position) = -19.90+1.9*Degree-1049.0*pow(Degree,2)+0.005*pow(Degree,3);
	} 
	end_f_loop(f,thread)
}

If you're not getting the correct degree for the corresponding Cartesian coordinates then have a read of this reference page for the atan2 function.