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 francesco_capuano May 12, 2010 17:11

CX_Find_Cell_With_Point: problem

Hi everyone,
I've got a problem with the function CX_Find_Cell_With_Point, which I've found right in this forum (it is not mentioned in the UDF manual): you give it the coordinates of the point, it gives you back the cell index in which the point is. The example given by the user Gearboy was:

#include "udf.h"
DEFINE_ON_DEMAND(find_cell)
{
cell_t c;
CX_Cell_Id cx_cell;
real NV_VEC(pt);
real c_centroid[ND_ND];
NV_D(pt, =, 0.5, 0.3, 0.2); //coordinate of your specified location,it must be in the domain coordinate range
CX_Start_ND_Point_Search();
cx_cell=*CX_Find_Cell_With_Point(pt);
CX_End_ND_Point_Search();
c=RP_CELL(&cx_cell); //the right cell number
C_CENTROID(c_centroid,c,t);
Message0("coordinate of the specified point: x=%g,y=%g,z=%g\n",pt[0],pt[1],pt[2]);
Message0("coordinate of the cell found: x=%g,y=%g,z=%g\n",c_centroid[0],c_centroid[1],c_centroid[2]);
}

The problem is: if I use this function for a single point, or for a loop of points in a flat-plate mesh, it works perfectly; if I use this function inside a loop of points for any other case, even very simple (like an airfoil), Fluent simply goes off after a while (during the elaboration), despite all the points in the loop are in the domain coordinate range and, apparently, there are no other problems with the case and the rest of the function. It seems like a memory limit is reached, or something like that. I'm quite new to Fluent and UDFs world, so I really don't know what to do, I really appreciate any suggestion.

 francesco_capuano May 13, 2010 14:36

I precise that after some seconds of elaboration Fluent gives ACCESS VIOLATION error... help me please!

 psc3 May 15, 2010 08:28

try to replace real NV_VEC(pt);

with

float NV_VEC(pt);

I had a problem with this UDF and that change solved it...

Pedro

 francesco_capuano May 16, 2010 15:51

Thank you Pedro for your suggestion, that's a good idea, but it doesn't work for my case.
Anyway, I've fixed the bug: I realized that the problem for the function was to analyze the points belonging to the boundary face (probably it is unable to judge whether they belong to the computational domain or not), so excluding that points from the loop the UDF works fine.

 dmoroian May 17, 2010 07:30

Are you sure it works ok?
This instruction:
Code:

`cx_cell=*CX_Find_Cell_With_Point(pt);`
doesn't look right. It should give you a syntax error. At first glance I would write it as:
Code:

`cx_cell = CX_Find_Cell_With_Point(pt);`

 francesco_capuano May 17, 2010 09:55

Thanks for helping, dmoroian, but the function CX_Find_Cell_With_Point(pt) requires the asterisk. As I said, the problem does not regard the syntax, but the point you ask the function to analyze. It seems not to work fine for the boundary points...

 deluge August 26, 2013 15:08

Hi,

This line
Code:

`cx_cell = CX_Find_Cell_With_Point(pt);`
or this one, it doesn't matter which one
Code:

`cx_cell=*CX_Find_Cell_With_Point(pt);`
always gives me the error:
error C2440: '=' : cannot convert from 'int' to 'CX_Cell_Id'
Does anybody know how to avoid it?

You do not provide the full warning/error message, do you? It could be misleading. There should be some warning messages tell 'implicit declaration of function CX_Find_Cell_With_Point'. Please include the right header file,
Code:

`#include "cxiface.h"`
for fluent version 6.x

The interface for this function changed in version 14 so I do not discuss the header file in this version because the above code does not work any way.

 deluge August 27, 2013 03:37

I'm using the latest version, that's 14.5.7. There is no more cxiface.h and a grep search revealed there is no more CX_Find_Cell_With_Point either.

Has anybody an idea how the corresponding commands are called in 14.x.x?

 dmoroian August 27, 2013 05:11

Yes it is in
Code:

`fluent/fluent14.5.7/cortex/src/cxndsearch.h`

 deluge August 28, 2013 04:21

Thanks a lot for that!

But the syntax seems to be a bit more complex than before.

Code:

```FLUENT_EXPORT ND_Search *CX_Start_ND_Point_Search(ND_Search *, cxboolean do_domain, int t_id); FLUENT_EXPORT CX_Cell_Id *CX_Find_Cell_With_Point(ND_Search *, double v[3], double time); FLUENT_EXPORT ND_Search *CX_End_ND_Point_Search(ND_Search *);```
The functions require more inputs.
Code:

```CX_Start_ND_Point_Search(); cx_cell=*CX_Find_Cell_With_Point(pt); CX_End_ND_Point_Search()```
doesn't work because of a lack of inputs. Does anybody have an example for that? I find these input datatypes very confusing.

 KingSt April 5, 2014 21:35

Quote:
 Originally Posted by deluge (Post 448467) Thanks a lot for that! But the syntax seems to be a bit more complex than before. Code: ```FLUENT_EXPORT ND_Search *CX_Start_ND_Point_Search(ND_Search *, cxboolean do_domain, int t_id); FLUENT_EXPORT CX_Cell_Id *CX_Find_Cell_With_Point(ND_Search *, double v[3], double time); FLUENT_EXPORT ND_Search *CX_End_ND_Point_Search(ND_Search *);``` The functions require more inputs. Code: ```CX_Start_ND_Point_Search(); cx_cell=*CX_Find_Cell_With_Point(pt); CX_End_ND_Point_Search()``` doesn't work because of a lack of inputs. Does anybody have an example for that? I find these input datatypes very confusing.
Hi deluge,

Did you figure out this problem??? I am suffering the exactly same problem as yours. Could you guys give any suggestion? Appreciate!

 garvitgoel June 24, 2014 13:14

Quote:
 Originally Posted by deluge (Post 448467) Thanks a lot for that! But the syntax seems to be a bit more complex than before. Code: ```FLUENT_EXPORT ND_Search *CX_Start_ND_Point_Search(ND_Search *, cxboolean do_domain, int t_id); FLUENT_EXPORT CX_Cell_Id *CX_Find_Cell_With_Point(ND_Search *, double v[3], double time); FLUENT_EXPORT ND_Search *CX_End_ND_Point_Search(ND_Search *);``` The functions require more inputs. Code: ```CX_Start_ND_Point_Search(); cx_cell=*CX_Find_Cell_With_Point(pt); CX_End_ND_Point_Search()``` doesn't work because of a lack of inputs. Does anybody have an example for that? I find these input datatypes very confusing.
can somebody please explain how to use these search functions.
I cant under stand what t_id and v[3] and time are.

 marialhm January 18, 2016 04:57

Quote:
 Originally Posted by garvitgoel (Post 498480) can somebody please explain how to use these search functions. I cant under stand what t_id and v[3] and time are.
Dear Garvit,

Have you figured it out? I need to use it now, but I have no idea what those mean.

Thanks.

 marialhm January 18, 2016 05:01

Quote:
 Originally Posted by KingSt (Post 484093) Hi deluge, Did you figure out this problem??? I am suffering the exactly same problem as yours. Could you guys give any suggestion? Appreciate!

 ASimonsen July 19, 2016 03:09

Solution for v. 17.1

Hi

I tool a look at it and figured out how to do it. Ansys has posted a note on their website (required user access):
Macro CX_Find_Cell_With_Point form has
changed from R11 to R14.5/R15.
Problem/Description:
Macro CX_Find_Cell_With_Point form has changed from R11 to R14.5/R15.
Solution:
Code:

```#include <udf.h> #include "cxndsearch.h" static ND_Search *domain_table=NULL; DEFINE_ON_DEMAND(locate_cell) { CX_Cell_Id *cx_cell; real tmpp[ND_ND]; . . . domain_table = CX_Start_ND_Point_Search( domain_table,TRUE,-1); cx_cell = CX_Find_Cell_With_Point(domain_table,tmpp,0.0); domain_table=CX_End_ND_Point_Search(domain_table); . . /* Can save domain table as a static pointer so that you can check if it's been created yet and not recreate it every time. */ .}```
After messing around with it I found a way to locate the cell:

Code:

```#include <udf.h> #include "cxndsearch.h" static ND_Search *domain_table = NULL; DEFINE_ON_DEMAND(locate_cell) {         cell_t c;         Thread *t;         CX_Cell_Id *cx_cell;                 real P[3];         real P_Cell[3];                 domain_table = CX_Start_ND_Point_Search(domain_table,TRUE,-1);         for (int i = 0; i < 100; i++) {                 P[0] = 0.0;                 P[1] = 0.0;                 P[2] = (real)i / 100.0 * 5.0;                                 cx_cell = CX_Find_Cell_With_Point(domain_table,P,0.0);                 if (cx_cell) {                         c = RP_CELL(cx_cell);                         t = RP_THREAD(cx_cell);                         C_CENTROID(P_Cell,c,t);                         Message("Found cell at [%g,%g,%g] with centroid [%g,%g,%g].\n",P[0],P[1],P[2],P_Cell[0],P_Cell[1],P_Cell[2]);                 } else {                         Message("Could not find cell at [%g,%g,%g]!\n",P[0],P[1],P[2]);                 }         }         domain_table = CX_End_ND_Point_Search(domain_table); }```

 wond October 19, 2016 01:15

so good job!!

 youjfwhu December 25, 2016 22:24

Problems running in PARALLEL

Quote:
 Originally Posted by ASimonsen (Post 610172) Hi I tool a look at it and figured out how to do it. Ansys has posted a note on their website (required user access): Macro CX_Find_Cell_With_Point form has changed from R11 to R14.5/R15. Problem/Description: Macro CX_Find_Cell_With_Point form has changed from R11 to R14.5/R15. Solution: Please use the following header files and format for new releases Code: ```#include #include "cxndsearch.h" static ND_Search *domain_table=NULL; DEFINE_ON_DEMAND(locate_cell) { CX_Cell_Id *cx_cell; real tmpp[ND_ND]; . . . domain_table = CX_Start_ND_Point_Search( domain_table,TRUE,-1); cx_cell = CX_Find_Cell_With_Point(domain_table,tmpp,0.0); domain_table=CX_End_ND_Point_Search(domain_table); . . /* Can save domain table as a static pointer so that you can check if it's been created yet and not recreate it every time. */ .}``` After messing around with it I found a way to locate the cell: Code: ```#include #include "cxndsearch.h" static ND_Search *domain_table = NULL; DEFINE_ON_DEMAND(locate_cell) {     cell_t c;     Thread *t;     CX_Cell_Id *cx_cell;         real P[3];     real P_Cell[3];         domain_table = CX_Start_ND_Point_Search(domain_table,TRUE,-1);     for (int i = 0; i < 100; i++) {         P[0] = 0.0;         P[1] = 0.0;         P[2] = (real)i / 100.0 * 5.0;                 cx_cell = CX_Find_Cell_With_Point(domain_table,P,0.0);         if (cx_cell) {             c = RP_CELL(cx_cell);             t = RP_THREAD(cx_cell);             C_CENTROID(P_Cell,c,t);             Message("Found cell at [%g,%g,%g] with centroid [%g,%g,%g].\n",P[0],P[1],P[2],P_Cell[0],P_Cell[1],P_Cell[2]);         } else {             Message("Could not find cell at [%g,%g,%g]!\n",P[0],P[1],P[2]);         }     }     domain_table = CX_End_ND_Point_Search(domain_table); }```
It's a good job and thank for your sharing.

But I've got a problem in parallel running. When I use this UDF in parallel processing, it returns me the error notice like this:

0 (..\src\mpsystem.c@1173): mpt_read: failed: errno = 10054
MPI Application rank 0 exited before MPI_Finalize() with status -1

The Parallel FLUENT process could not be started.

My benchmark is a 2D rotor problem, a rectangular water channel with a cross blender in it. I used the "Mesh motion" for the rotating zone surrounding the blender and the "interface" boundary condition. What I want to do is MONITORING THE PRESSURE ON A DYNAMIC POINT. This point is initially located in the rotating zone and it will rotate with the zone
synchronously.

Now I have tried many methods, such as the different MPI methods and I have check the RAM and I have made sure the firewall is closed ......by the way, my workstation can run other udfs using the parallel processing, this UDF is the only one that cannot be used in parallel running.

At last I found that the problem result form the macro "RP_CELL" and "RP_THREAD", when I made these two codes as notes , it can run well in parallel.

My udf is here:

************************************************** ******
#include "udf.h"
#include "surf.h"
#include"cxndsearch.h"
static ND_Search *domain_table=NULL;
real R=0.05;
static float xTheory=0.20535;/*The initial x coordiate of the dynamic monitoring point*/
static float yTheory=0.13535;/*The initial y coordiate */
static float theta=0.785398;/*The initial phase angle */
static float p01=0.0;/*The initial pressure */
static float tim=0.0;
float c_centroid[2];

DEFINE_EXECUTE_AT_END(execute)
{

#if !RP_NODE
FILE *fp_p01;
#endif

double pt[2];
cell_t c;
CX_Cell_Id *cx_cell;

#if !RP_NODE
tim=RP_Get_Real("flow-time");
theta=theta+0.001*10;/*The angular velocity is 10 rad/s and the timestep is 0.001s */
xTheory=0.17+R*cos(theta);
yTheory=0.1+R*sin(theta);
pt[0]=xTheory;
pt[1]=yTheory;

domain_table = CX_Start_ND_Point_Search(domain_table,TRUE,-1);
cx_cell=CX_Find_Cell_With_Point(domain_table,pt,0. 0);
c=RP_CELL(cx_cell);/*The error should RESULT FROM this macro */
t=RP_THREAD(cx_cell);/*The error should RESULT FROM this macro */
C_CENTROID(c_centroid,c,t);
p01=C_P(c,t);
domain_table = CX_End_ND_Point_Search(domain_table);
#endif

#if !RP_NODE
fp_p01=fopen("p01.txt","a+");
fprintf(fp_p01,"%15.4f\t%d\t%d\t%d\t%15.6f\t%15.6f \t%15.6f\t%15.6f\t%15.6f\t%15.6f\t\n",tim,cx_cell, c,t,theta,xTheory,yTheory,c_centroid[0],c_centroid[1],p01);
fclose(fp_p01);
#endif
}

 ASimonsen December 26, 2016 05:42

Hi youjfwhu

I haven't tried anything in Fluent, but I'm pretty sure the problem is that you're using (#if !RP_NODE) instead of (#if !RP_HOST). Remember that when you're running Fluent in parallel, the cells are located on the computer nodes. The host is only there to do some communication stuff etc. So when you're trying to locate cells using CX_Find_Cell_With_Point in a section of your code, which is only running on the host (!RP_NODE), you'll get an error.

I've used my own piece of code on a parallel process as well, where it works just fine. But in my code, the CX_Find_Cell_With_Point is located within a (!RP_HOST)-section.

 youjfwhu December 26, 2016 10:47

Problem still exists

Quote:
 Originally Posted by ASimonsen (Post 631249) Hi youjfwhu I haven't tried anything in Fluent, but I'm pretty sure the problem is that you're using (#if !RP_NODE) instead of (#if !RP_HOST). Remember that when you're running Fluent in parallel, the cells are located on the computer nodes. The host is only there to do some communication stuff etc. So when you're trying to locate cells using CX_Find_Cell_With_Point in a section of your code, which is only running on the host (!RP_NODE), you'll get an error. I've used my own piece of code on a parallel process as well, where it works just fine. But in my code, the CX_Find_Cell_With_Point is located within a (!RP_HOST)-section.
Thank you for your advice and I've changed (RP_NODE) into （RP_HOST）,but the new problem is that it can ONLY RUN ONE TIMESTEP and the same error notice appears on the window.

MPI Application rank 0 exited before MPI_Finalize() with status -1073741819

999999 (..\src\mpsystem.c@1173): mpt_read: failed: errno = 10054

The Parallel FLUENT process could not be started.

Actually I think your suggestion is very important and useful. The first timestep is finished and the whole udf is processed(since the last 3 sentences of the udf is about printing some messages on a *.txt file and the results shows that it is correct).

**************************************************
#include "udf.h"
#include"cxndsearch.h"
static ND_Search *domain_table;
real R=0.05;
static float xTheory=0.20535;
static float yTheory=0.13535;
static float theta=0.785398;
static float p01=0.0;
static float tim=0.0;
static float c_centroid[2];
static cell_t c;
static CX_Cell_Id *cx_cell;
static double pt[2];

DEFINE_EXECUTE_AT_END(execute)
{
#if !RP_HOST
FILE *fp_p01;
#endif

#if !RP_HOST
tim=RP_Get_Real("flow-time");
#endif

#if !RP_HOST
theta=theta+0.001*10;
xTheory=0.17+R*cos(theta);
yTheory=0.1+R*sin(theta);
pt[0]=xTheory;
pt[1]=yTheory;
#endif

#if !RP_HOST
domain_table = CX_Start_ND_Point_Search(domain_table,TRUE,-1);
cx_cell=CX_Find_Cell_With_Point(domain_table,pt,0. 0);
c=RP_CELL(cx_cell);
C_CENTROID(c_centroid,c,t);
p01=C_P(c,t);
domain_table = CX_End_ND_Point_Search(domain_table);
#endif

#if !RP_HOST
fp_p01=fopen("p01.txt","a+");
fprintf(fp_p01,"%15.4f\t%15.6f\t%15.6f\t%15.6f\t%1 5.6f\t%15.6f\t%15.6f\t\n",tim,theta,xTheory,yTheor y,c_centroid[0],c_centroid[1],p01);
fclose(fp_p01);
#endif
}

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