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May 7, 2014, 07:54 
UDF for VortexInduced Vibrations debug

#1  
New Member
AFM
Join Date: Nov 2013
Posts: 14
Rep Power: 5 
Hello to everybody;
Now I am investigating about VIV using tappered cylinders (3D); I am using 2way FSI but the calculations are so slow (LESWALE model in CFD and nonlinear calculation in Transient Structural). I really need to do these calculations faster, so I think in use an UDF for VIV. Searching in the web, I found the next code, originally for a 2D problem: Quote:
The second issue is a simple question: Is it possible to use this code in my 3D problem, or I will have to adapt the code? Thank you very much. Bests regards. 

February 22, 2016, 06:50 

#2  
Member
N B Khan
Join Date: Jan 2014
Posts: 38
Rep Power: 5 
Quote:
I am also looking for UDF for 2D and 3D case... If you found the solution please share... n_bkhan@yahoo.com Thanks Regards Niaz 

March 15, 2016, 19:07 

#3 
New Member
esho
Join Date: Mar 2016
Posts: 1
Rep Power: 0 
Hi, I know this is an old problem, but the problem you may have had is trying to interpret the udf. Some macros such as those for dynamic meshes do not interpret, but rather are compiled.
On that note, if you got it to work, could you please share your UDF with me? I am attempting this problem as well to get familiar with dynamic meshing. Thank you in advance. 

March 16, 2016, 00:02 

#4  
Member
N B Khan
Join Date: Jan 2014
Posts: 38
Rep Power: 5 
Quote:
I used the UDF #include "udf.h" static real v_prev = 0.0; DEFINE_CG_MOTION(osc,dt,vel,omega,time,dtime) { Thread *t; Domain *d = Get_Domain(1); real x_cg[3], force[3], moment[3]; real accl, dv; real mass = 0.2; real wn = 12.0; real k= mass * wn*wn; real c = 2*mass*wn*0.00; int i; NV_S(vel, =, 0.0); NV_S(omega, =, 0.0); t = DT_THREAD(dt); for(i=0;i<3;i++) x_cg[i]=DT_CG(dt)[i]; Compute_Force_And_Moment(d, t, x_cg, force, moment, TRUE); force[1] += k*x_cg[1]  c*vel[1]; accl = force[1]/mass; dv = accl*dtime; v_prev+=dv; vel[1] = v_prev; printf("Computed force: %g \n", force[1]); printf("Velocity: %g\n", vel[1]); } DEFINE_CG_MOTION(osc_inert,dt,vel,omega,time,dtime ) { vel[0] = 0.0; vel[1] = v_prev; } Yes you are right the issue is with the intrepret. I successfully run the udf using compiler for 2D problem but i dont know whether it will run on 3D or not. I have 2 more questions 1. how to change the above UDF to forced oscillation to find VIV forces 2. How to measure amplitude and forces... I know the above mentioned UDF calculate the forces(printf("Computed force: %g \n", force[1]; printf("Velocity: %g \n", vel[1]) but I dont know where it will be available in FLUENT ... I am also very beginner to the dynamic mesh study. My problem is exactly same like your problem. We can share study with each other if you agree. My name is niaz and email n_bkhan@yahoo.com Thanks in advance. Best Regards Niaz 

May 19, 2016, 02:49 

#5 
New Member
Rahil
Join Date: Mar 2016
Posts: 5
Rep Power: 3 
Hi esho_adelaide, were you able to get this working? I am trying this udf for VIV of a 2D cylinder but the cylinder is not moving?


Tags 
3d problem, fsi, udf, viv 
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