
[Sponsors] 
June 26, 2006, 12:21 
UDF divergence of a vector

#1 
Guest
Posts: n/a

i am working with the eulerian model and I would like to add a new term in the dispersed phase momentum equation. I can add easy terms using the macro DEFINE_SOURCE but i need the divergence of a vector. I made some easy probes to calculate the divergence of vector but i didn't suceed. Is there any macro to calculate the divergence of a vector? Is there anyone who has made a udf to calculate the divergence? I created some udf that use the divergence theorema to calculate the volume of a cell and the result is good, but when i tried to probe the udf in the steady state continuity equation the udf failed. If theres is someone interested i would send him my udfs. Sorry I am a spanish girl and i explain the best i could.


April 15, 2010, 15:32 

#2 
Member
Casey
Join Date: Jun 2009
Posts: 98
Rep Power: 17 
Did you ever get this? I am working on the same thing. I just submitted a support question to FLUENT, I will post the result.
Casey 

June 8, 2010, 11:55 

#3 
Member
Casey
Join Date: Jun 2009
Posts: 98
Rep Power: 17 
Yeah, I did. I cant get the simulation to converge at first. I opened up a service request with fluent, but they said the UDF is running fine and that the problem must be somewhere else. I am not happy with the fact that the simulation does not converge for the first few time steps, so I am going to keep looking into it, but below is the divergence part of the UDF I wrote.
Casey /* Include statements */ #include "udf.h" /************************************************** ********************* UDF for specifying frictional pressure ************************************************** **********************/ DEFINE_PROPERTY(pf_cfifteen, cp, tp) { real np = 5.; real nn = 2.; real esmax = 0.63; real esmin = 0.5; real bp = 0.6237; real sm_val = 1.0e12; real P[ND_ND]; real delt, pfr, nc, fric, Smag, vfrac, dudx, dudy, dvdx, dvdy, r, radv, DIV; /* Retrieve volume fraction and magnitude of the deviatoric Smag tensor */ /*x direction is axial direction, y direction is radial so dvdy = d(radialvelocity)/dradial */ vfrac = C_VOF(cp,tp); dudx = C_U_G(cp,tp)[0]; dudy = C_U_G(cp,tp)[1]; dvdx = C_V_G(cp,tp)[0]; dvdy = C_V_G(cp,tp)[1]; radv = C_V(cp,tp); C_CENTROID(P,cp,tp); r = P[1]; DIV = dvdy + radv/r + dudx; Smag = sqrt(pow((dvdy(1./3.)*DIV),2.)+2.*pow((0.5*(dudydvdx)),2.)+pow((dudx(1./3.)*DIV),2.)); __________________________________________________ ____ I had to leave out the rest of the UDF because it pertains to my research and I have not published yet. Below here it just uses the DIV in "if" statements, so any user that wants to use the above DIV part of the code you just need the folowing: __________________________________________________ __________ dudx = C_U_G(cp,tp)[0]; dudy = C_U_G(cp,tp)[1]; dvdx = C_V_G(cp,tp)[0]; dvdy = C_V_G(cp,tp)[1]; radv = C_V(cp,tp); C_CENTROID(P,cp,tp); r = P[1]; DIV = dvdy + radv/r + dudx; Smag = sqrt(pow((dvdy(1./3.)*DIV),2.)+2.*pow((0.5*(dudydvdx)),2.)+pow((dudx(1./3.)*DIV),2.)); __________________________________________________ _________ Hope this helps everyone! Casey 

September 4, 2014, 18:06 

#4  
Senior Member
Join Date: May 2011
Posts: 231
Rep Power: 16 
Hi Casey,
if the case is 2D than we should divide the DIV by 2 right? thanks in advance! Quote:


Thread Tools  Search this Thread 
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
how to set periodic boundary conditions  Ganesh  FLUENT  15  November 18, 2020 06:09 
UDF for wall slipping  HFLUENT  Fluent UDF and Scheme Programming  0  April 27, 2011 12:03 
64bit error compiling UDF : divergence detected  UtoS_99  FLUENT  7  March 29, 2011 03:19 
UDF: Density Cell Gradient Vector Macros  matteo  FLUENT  0  December 1, 2007 12:14 
changing gravity vector direction using UDF  Nico  FLUENT  0  September 7, 2006 12:00 