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save time history of spanwise force distribution on Windows OS

Method

use UDF to strip the interest surface(where force is applied)

Steps 

 - open case file, check the *ID* of  solid sourface ( cylinder/blade surface)
- check the spanwise direction(such as z direction), and force direction( such lift, y axis, drag, x axis)
 - Make the appropriate changes in the UDF
   +(Axis direction, Force direction, no. of strips and ID of the wall zone)
- lauch Fluent from command line
  + Open the Start screen (press Windows button on your keyboard, Type 'VS2013 x86 x64 Cross Tools Command Prompt'
  + Navigate to your working folder, i.e. the folder where your case and data files are (.cas & .dat).
  + Type “fluent” in the command window to launch Fluent  or  “C:\Program Files\ANSYS Inc\v161\fluent\ntbin\win64\fluent.exe” (quotation signs included, in case of standard installation; fluent version: 16.1).
  + Make sure that on the *Environment tab* 'Setup Compilation Environment for UDF' is ticked. The default address is fine.

- *Compile the UDF* using Define->User-Defined->Functions->Compiled...
- Read in the case file
- Increase no. of User-Defined Memory(UDM) to 1
   + Define->User-Defined->Memory...
- Initialize the solution so that UDM is initialized
- Read in the data file
- Execute the demand function "force"
   +Define->User-Define->Execute On Demand...
- Plot contours of UDM-0 and check if the strips are marked correctly
- Fluent will report the spanwise distribution on the Fluent terminal
- A file called spanwise-force-report.txt will also be created
 

code

/*******************************************************/
/* Used to obtain a time history of spanwise force report on 3D blade/cylinder/wing */
/*******************************************************/
#include "udf.h"
#include "para.h"
/* Spanwise direction */
#define AXIS_X 0
#define AXIS_Y 0
#define AXIS_Z 1
/* The direction along which the force is to be reported */
#define F_X 1
#define F_Y 0
#define F_Z 0
/* Number of strips into which the wing is to be divided */
/* Increasing this number increases the resolution of reporting */
/* It is however limited by the number of cells present along the spanwise direction
*/
/* Recommended value: */
/* For unstructured cells: no of cells along spanwise dir. divided by 3 */
/* For structured cells: no. of cells along spanwise dir. divided by 3 */
#define N_STRIPS 20
/* ID of the wing boundary zone */
/* You can get this from the Boundary Conditions Panel */
#define TID 5

/* Make sure you increase no. of User Defined Memory to 1 */
/* The UDM stores the strip number for each cell */
/* You can see contour plots of cell values of UDM-1 to check */
/* if the strips are marked correctly */
DEFINE_EXECUTE_AT_END(force) /* execute at every iteration (steady), or time step( unsteady)*/
{
  #if !RP_HOST
    Domain *d=Get_Domain(1);
    int i;
    real A[ND_ND];
    real axis[3], force_dir[3];
    face_t f;
    Thread *t=Lookup_Thread(d,TID);
    cell_t c;
    Thread *tc;
    real x[ND_ND];
    real NV_VEC(presforce),NV_VEC(viscforce);
    real NV_VEC(dforce_pres),NV_VEC(dforce_visc);
    real pforce[N_STRIPS+1],vforce[N_STRIPS+1];
    real press=0.0;
    real pressure=0.0;
    real visc=0.0;
    real min_dist=1000000000;
    real max_dist=-1000000000;
    real dist=0;
    real strip_length;
    FILE *fp;
    NV_S(A,=,0.0);
    NV_S(dforce_pres,=,0.0);
    NV_S(dforce_visc,=,0.0);
    NV_S(presforce,=,0.0);
    NV_S(viscforce,=,0.0);
    axis[0]=AXIS_X;
    axis[1]=AXIS_Y;
    axis[2]=AXIS_Z;
    force_dir[0]=F_X;
    force_dir[1]=F_Y;
    force_dir[2]=F_Z;
   
  #if PARALLEL
  if (I_AM_NODE_ZERO_P)
    fp=fopen("spanwise-force-report.txt", "a+");  /* open file and write data; "a+": append and update*/
  #else
    fp=fopen("spanwise-force-report.txt", "a+");
  #endif
    begin_f_loop(f, t)
    if (PRINCIPAL_FACE_P(f,t))
    {
        F_CENTROID(x, f, t);
        dist=NV_DOT(x, axis);
        if(dist<min_dist) min_dist=dist;
        if(dist>max_dist) max_dist=dist;
    }
    end_f_loop(f, t)
   
  #if PARALLEL
  /* get global min and max on node 0*/
    min_dist=PRF_GRLOW1(min_dist);
    max_dist=PRF_GRHIGH1(max_dist);
  #endif   
    strip_length=(max_dist-min_dist)/N_STRIPS;
    Message0("Marking strips...");
   
    begin_f_loop(f,t)
    {
        F_CENTROID(x,f,t);
        c=F_C0(f, t);
        tc=THREAD_T0(t);
        dist=NV_DOT(x, axis);
        /* assign strip number to UDM-0 */
        C_UDMI(c,tc,0)=(int)((dist-min_dist)/strip_length);
    }
    end_f_loop(f,t)
    Message0("Done\n");
   
    for(i=0;i<=N_STRIPS;i++)
    {
        pforce[i]=0;
        vforce[i]=0;
    }

    begin_f_loop(f,t)
    if (PRINCIPAL_FACE_P(f,t))
    {
        F_AREA(A,f,t);
        c=F_C0(f, t);
        tc=THREAD_T0(t);
        i=(int)(MIN(N_STRIPS,C_UDMI(c, tc, 0)));
        /* report force if thread id TID corresponds to a wall */
     if (THREAD_TYPE(t)==THREAD_F_WALL)
     {
  /* pressure force of the strip i along vector (F_X,F_Y,F_Z) */       
        pforce[i]+=F_P(f, t) * NV_DOT(A, force_dir);
  /* viscous force of the strip i along vector (F_X,F_Y,F_Z) */               
        vforce[i]+=(-1*(NV_DOT(F_STORAGE_R_N3V(f,t,SV_WALL_SHEAR),force_dir)));   
        /*Message("CHECK: %d\n",sizeof(vforce) / sizeof(vforce[0]));*/   
     }
     else
     {
     if (f==0) Message0("No forces will be reported since, zone of ID %d is not a wall",TID);
     }
    }
    end_f_loop(f,t)
    Message0("\n\nPressure force\t Viscous force");
   
  #if PARALLEL
/* Get forces of each partition on node 0 */
       for(i=0;i<=N_STRIPS;i++)
    {
        pforce[i]=PRF_GRSUM1(pforce[i]);
        vforce[i]=PRF_GRSUM1(vforce[i]);
    }
  /* report force on node 0 in parallel- Node0 should have a disk system otherwise UDF has to be rewritten to exchange data through the host */   
  if (I_AM_NODE_ZERO_P)
  {
    for(i=0;i<=N_STRIPS;i++)
    {
        press+=pforce[i];
        visc+=vforce[i];
        Message0("\n %g \t %g",pforce[i],vforce[i]);
        fprintf(fp, "%d \t %f \t %f \n", i, pforce[i], vforce[i]);
    }
    Message0("\n---------- -----------");
    Message0("\n %g\t%g",press,visc);

    fclose(fp);
  }
  #else
    for(i=0;i<=N_STRIPS;i++)
    {
        press+=pforce[i];
        visc+=vforce[i];
        Message("\n %g \t %g",pforce[i],vforce[i]);
        fprintf(fp, "%d \t %f \t %f \n", i, pforce[i], vforce[i]);
    }
    Message("\n---------- -----------");
    Message("\n %g\t%g",press,visc);

    fclose(fp);
  #endif
    Message0("\nUDF DONE\n");
  #endif    /* !RP_HOST */
}



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