[1988]

Hi

I found this UDF online (I am not very familiar with UDF coding) and I used it to calculate OSI. I am using ANSYS-Fluent 2021.
I used 5 memories for the UDM and run the simulation. All the values out of these UDMs are zero. Any suggestions?

/******************************************************
	Oscillatory shear index
******************************************************/

#include "udf.h"
#include "math.h"
#include "storage.h"
#include "sg_udms.h"

#define domain_ID 1
#define zone_ID 1


/* Initialize the UDM value to zero in complete domain */
DEFINE_INIT(meminit,domain)
{
	Thread *c_thread;
	cell_t c;

	thread_loop_c(c_thread,domain)
	{
		begin_c_loop(c, c_thread)
		{
			C_UDMI(c,c_thread,0)= 0;
			C_UDMI(c,c_thread,1)= 0;
			C_UDMI(c,c_thread,2)= 0;
			C_UDMI(c,c_thread,3)= 0;
			C_UDMI(c,c_thread,4)= 0;
		}
		end_c_loop(c, c_thread)
	}
}

/* Calculate wall shear stress and store them in UDM */
DEFINE_EXECUTE_AT_END(OSI)
{
	Domain *domain;
	real area;
	face_t f;
	real A[ND_ND];
	cell_t c, c0;
	Thread *t,*t0, *c_thread;
	real wallshear [ND_ND];

	domain = Get_Domain(domain_ID);
	t = Lookup_Thread(domain,zone_ID);

	begin_f_loop(f, t)
	{
		F_AREA(A,f,t);
		area = NV_MAG(A);
		NV_V(wallshear,=,F_STORAGE_R_N3V(f,t, SV_WALL_SHEAR));
		c0 = F_C0(f,t);
		t0 = THREAD_T0(t);
		C_UDMI(c0,t0,0) = NV_MAG(wallshear)/area;
		C_UDMI(c0,t0,1) = -wallshear[0]/area;
		C_UDMI(c0,t0,2) = -wallshear[1]/area;
		C_UDMI(c0,t0,3) = -wallshear[2]/area;
		C_UDMI(c0,t0,4) = (1.-sqrt(C_UDMI(c0,t0,1)*C_UDMI(c0,t0,1) + C_UDMI(c0,t0,2)*C_UDMI(c0,t0,2) + C_UDMI(c0,t0,3)*C_UDMI(c0,t0,3))/C_UDMI(c0,t0,0))/2;
	}
	end_f_loop(f,t)
}

[pakk]

Maybe you did not hook the execute_at_end?

[1988]

Thank you for the response. Is it a line or something that I am missing in the code or you mean running the CFD and having the UDF compiled? I compiled it with no error and ran the CFD simulation with no problem.

[pakk]

After compiling the UDF, you have to tell Fluent to use it. This is called hooking. Look in the manual, it is explained below every example of a UDF.

[AlexanderZ]

compile UDF
load compiled library (in console you will see the list of available functions, you've loaded)
in interface:
user defined-> function hooks ->
initialization -> choose you function -> ok
execute at end -> choose you function -> ok
->ok

[mep20108@tezu.ac.in]

After compilation of UDF, one warning is generated on console screen.

'unsigned long' [-Wint-to-void-pointer-cast]
return ( (void * POINTER_32) (unsigned long) (UNLONG_PTR) P);

I want to know where is the problem. If anyone help it must be appreciated.
Thanks in advance.

[AlexanderZ]

in case you need help you should provide the whole information:
full log output
warnings usually don't lead to problems with running the code

[mep20108@tezu.ac.in]

Dear AlexanderZ,
After compilation and hooking the UDF when I start the simulation the fluent exits without showing any error. Try so many times but not succeeded. I am using Ansys 2022R1. Can anyone help what is the actual problem. Here is the screenshot of the Fluent.

[sara9310]

Originally Posted by mep20108@tezu.ac.in

Dear AlexanderZ,
After compilation and hooking the UDF when I start the simulation the fluent exits without showing any error. Try so many times but not succeeded. I am using Ansys 2022R1. Can anyone help what is the actual problem. Here is the screenshot of the Fluent.

Did you find the solution to the problem? I have similar problem.

[mep20108@tezu.ac.in]

Dear shima,
First you set user defined memory (UDM).
In this case it is 5. Make sure you have also changed zone Id as per your boundary where you want apply OSI.
After that you can go for hooking.
I did in similar way it solved my problem.
Hope it works for you too.

[sara9310]

Originally Posted by mep20108@tezu.ac.in

Dear shima,
First you set user defined memory (UDM).
In this case it is 5. Make sure you have also changed zone Id as per your boundary where you want apply OSI.
After that you can go for hooking.
I did in similar way it solved my problem.
Hope it works for you too.

Thank you!
I set the number of memories
But Where is the "Zone id" in fluent?
And exactly what should i do?

[aerosuraj1]

zone id for each component, you can see it in the boundary condition

[sara9310]

Originally Posted by aerosuraj1

zone id for each component, you can see it in the boundary condition

How can i enter "zone id" in osi code?

[aerosuraj1]

Originally Posted by sara9310

How can i enter "zone id" in osi code?

you need to edit the UDF file.
you can use a platform like ''visual studio'' or ''geany''

[sara9310]

Originally Posted by aerosuraj1

you need to edit the UDF file.
you can use a platform like ''visual studio'' or ''geany''

Thank you
I wrote
real zone_ID = 21;
But when i complie udf; 2 error is showing:
1) missing ';' before constant
2) 'real' : illegal use of this type as an expression

How can i solve these problems?!

[aerosuraj1]

Originally Posted by sara9310

Thank you
I wrote
real zone_ID = 21;
But when i complie udf; 2 error is showing:
1) missing ';' before constant
2) 'real' : illegal use of this type as an expression

How can i solve these problems?!

can you post your UDF code here, so that the expert members take a look and suggest any changes.

[sara9310]

Originally Posted by aerosuraj1

can you post your UDF code here, so that the expert members take a look and suggest any changes.

Thank you
I upload udf file. When I compile this udf, for two line:
real domain_ID=1;
real zone_ID=21;
These errors appear:
1) missing ';' before constant
2) 'real' : illegal use of this type as an expression

[aerosuraj1]

Originally Posted by sara9310

Thank you
I upload udf file. When I compile this udf, for two line:
real domain_ID=1;
real zone_ID=21;
These errors appear:
1) missing ';' before constant
2) 'real' : illegal use of this type as an expression

Dear Shima,
delete line numbers 54 (real domain_ID = 1 and 55 (real zone_ID = ? from your UDF code and try to run it.
I am quite sure this time you will run it successfully.
All the best

[sara9310]

Originally Posted by aerosuraj1

Dear Shima,
delete line numbers 54 (real domain_ID = 1 and 55 (real zone_ID = ? from your UDF code and try to run it.
I am quite sure this time you will run it successfully.
All the best

I complied code without these two lines and run it; when I select "osi" in contours of cfd-post, anything is showing!
Some body tell me zone id should specify in code; how can I solve this problem?

[aerosuraj1]

Originally Posted by sara9310

I complied code without these two lines and run it; when I select "osi" in contours of cfd-post, anything is showing!
Some body tell me zone id should specify in code; how can I solve this problem?

I am glad that you have successfully compiled and run the simulation.
Yes, the zone ID should be specified in the code for the component on which you would like to see the OSI contours in CFD post. (mostly, people use to see the OSI contours on the "wall", so the zone ID of the wall should be specified within the code).