Learning Forum

[Jason Sum]

Hi, I am simulating the wind flowing across a Y-shape building to evaulate the wake effect behind. 

Mesh was done in Fluent Meshing, with minimum orthogonality of 0.2, and 5 inflation laters added to ground and building surface.

with BOI refinement in volume near the building

To be more accurate towards reality, I want to take the atmospheroc boundry layer for the wind flow inlet condition.

However, divergence and float points popped up on console when initiaizing. (while just using constant input to inlet velocity did not cause such issues), it is earnestly hoped for some guidance on this and some additional tips on using UDF, thanks!!!!

Error codes:

Divergence detected in AMG solver: ads-0

Divergence detected in AMG solver: ads-0

Divergence detected in AMG solver: ads-0

Divergence detected in AMG solver: ads-0

Divergence detected in AMG solver: ads-0

Divergence detected in AMG solver: ads-0

Divergence detected in AMG solver: ads-0

Divergence detected in AMG solver: ads-0

Divergence detected in AMG solver: ads-0

Divergence detected in AMG solver: ads-0

Divergence detected in AMG solver: ads-0

Divergence detected in AMG solver: ads-0

Divergence detected in AMG solver: ads-0

Divergence detected in AMG solver: ads-0

Divergence detected in AMG solver: ads-0

Divergence detected in AMG solver: ads-0

Divergence detected in AMG solver: ads-0

Divergence detected in AMG solver: ads-0

Divergence detected in AMG solver: ads-0

Divergence detected in AMG solver: ads-0 10 0.000000e+00

Hybrid initialization is done.

Error at host: floating point exception

Error at Node 4: floating point exception

Error at Node 0: floating point exception

Error at Node 1: floating point exception

Error at Node 2: floating point exception

Error at Node 3: floating point exception

Error at Node 5: floating point exception

Error at Node 6: floating point exception

Error at Node 7: floating point exception

Error at Node 8: floating point exception

Error at Node 9: floating point exception

Error at Node 10: floating point exception

Error at Node 11: floating point exception

Error at Node 12: floating point exception

Error at Node 13: floating point exception

Error at Node 14: floating point exception

Error at Node 15: floating point exception

Error at Node 16: floating point exception

Error at Node 17: floating point exception

Error at Node 18: floating point exception

Error at Node 19: floating point exception

===============Message from the Cortex Process================================

Compute processes interrupted. Processing can be resumed.

==============================================================================

Error: floating point exception

Error Object: #f

---------------------------------------------------------------------------------------------------------------------------------------------------------

Below is the UDF I taken reference from

&t=2395s:

#include "udf.h"
#define UREF 4.491 // reference wind speed at ZREF
#define ZREF 0.16 // height of the building, 2b
#define LREF 0.08 // characteristic length, b
#define CMU 0.09 // 

DEFINE_PROFILE(velocity_profile, thread, position)
{
	float x[ND_ND];
	float y;
	float u;
	face_t f;

	begin_f_loop(f, thread)
	{
		F_CENTROID(x,f,thread);
		y=x[1];
		u = UREF*pow(y/ZREF,0.27);
		F_PROFILE(f,thread,position) = u;
	}
	end_f_loop(f, thread)
}

/*  profile for kinetic energy, k  */


DEFINE_PROFILE(k_profile, thread, position)
{
	float x[ND_ND];
  	face_t f;

  	float A1 = 0.0042 ;
	float A2 = -0.0719 ;
	float A3 = 0.2692 ; 
	float A4 = 0.3671 ;
	float k, y, yb;
  	begin_f_loop(f, thread)
    	{
      		F_CENTROID(x,f,thread);
		y = x[1];
      		yb = y/LREF;
		k = A1*pow(yb,3)+A2*pow(yb,2)+A3*yb+A4 ;
      		F_PROFILE(f,thread,position)=k;
      		
    	}
  	end_f_loop(f, thread)
}

/* profile for dissipation rate, epsilon */


DEFINE_PROFILE(dissip_profile, thread, position)
{
  	float x[ND_ND];
  	face_t f;
	float A1 = 0.0042 ;
	float A2 = -0.0719 ;
	float A3 = 0.2692 ; 
	float A4 = 0.3671 ;
	float k, y, yb;
  	begin_f_loop(f, thread)
    	{
      		F_CENTROID(x,f,thread);
		y=x[1];
		yb = y/LREF;
		k = A1*pow(yb,3)+A2*pow(yb,2)+A3*yb+A4 ;
      		F_PROFILE(f,thread,position)=pow(CMU,0.75)*pow(k,1.5)/LREF;
    	}
  	end_f_loop(f,thread)
}

/* 
References:
[1] Yan MENG and Kazuki HIBI. Turbulent measurements of the flow field around a high-rise building. Journal of wind engineering. No 76, July 1998.
*/

[Rob]

You may want to check your direction vector for "up". If z is up it's not [1] in the vector definition! 

[Jason Sum]

Hi Rob, thank you for the guide.

I have rotated my geometry so that y is pointing upwards to meet the UDF.

Still same errors occur during initialisation. Everything works when I just insert constant velocity for inlet without udf

Sincerely hoped for further advice, Thanks!

[Rob]

I'd have changed the UDF! What is the minimum y value in the domain? Use the Scale tool in Fluent to find out. 

[Jason Sum]

 

 

Yes I have altered the ZREF and LREF according to my building geometry with height (z-axis): 150m and cross-sectional width: 64.4m. For the rest of the UDF, I think they describing the general solving for atmospheric boundary layer in velocity, k and epsilon, so I didnt modify it. 

 

 

#include "udf.h"
#define UREF 4.491 // reference wind speed at ZREF
#define ZREF 150.0 // height of the building, 2b
#define LREF 64.4 // characteristic length, b
#define CMU 0.09 // 

 

Or are you referring to the mini. y+ of my mesh domain?

Thank you for help.

 

 

[Rob]

No, what is the minimum y coordinate on the inlet? 

Before going too much into y+ how confident are you about the ground position and detail? I see far too many thinking y+ is the only mesh metric, and if you have bushes, trees, curbs etc did you also resolve all of those?