# Dynamic mesh : Oscillating cylinder

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 June 4, 2015, 03:09 Dynamic mesh : Oscillating cylinder #1 New Member   Paul Join Date: Jun 2015 Posts: 3 Rep Power: 4 Sponsored Links Hi, I am a beginner in Fluent 15.0 and I am trying to realize the modelisation of a flow through an oscillating cylinder. I don't have any problem loading the UDF describing the movement of the cylinder but I can't see anthing with "Preview Mesh Motion" or even "Display Zone Motion" in the Dynamic Task page. I am using Smoothing and Remeshing as Mesh Methods. Maybe the problem comes from the UDF I am using : #include "udf.h" DEFINE_CG_MOTION(pis,dt,vel,omega,time,dtime) { Thread*t; face_t*f; real A=1; real freq=1; real pi=3.14159265; real w=2*pi*freq; real v=A*w*sin(w*time); /*reset velocities */ NV_S(vel,=,0.0); NV_S(omega,=,0.0); if (!Data_Valid_P()) return; t=DT_THREAD(dt); vel[1] = v; } I don't know if it is related but i am also not able to edit the Function Hooks. This problem may have been already explained in this forum but I couldn't find any explanations. Does someone have an answer ? Thanks ! FarooqRasheed likes this.
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 June 4, 2015, 07:22 #2 Member   alireza Join Date: Jul 2009 Posts: 32 Rep Power: 9 Hi 1- Did you use complied or interpreted? you should use compiled. 2- Did you set solver to unsteady condition? you UDF is right but you can comment this lines (its not necessary). /*reset velocities */ NV_S(vel,=,0.0); NV_S(omega,=,0.0); if (!Data_Valid_P()) return; t=DT_THREAD(dt); -------------------------------------- if you did (do) these steps, you have to see mesh motion.

 June 8, 2015, 03:23 #3 New Member   Paul Join Date: Jun 2015 Posts: 3 Rep Power: 4 Hi alireza_b, Thanks for your answer. Unfortunately, I already used compiled UDF and the solver was in unsteady conditions. Therefore, I still do not know how to see the mesh motion. When I use "Preview Mesh Motion", the same calcul is done all over again without changes in the meshing. Isn't there other options that have to be activated to display the mesh motion ? Thanks.

 June 8, 2015, 14:00 #4 Member   alireza Join Date: Jul 2009 Posts: 32 Rep Power: 9 Hi what is your time step? Could you increases it and see what happens? maybe your time step is too low, so it takes time a lot to change in cylinder position. I suggest you calculate the frequency and then calculate period and use this time step. Dt=Period/2000 I saw it a lot in many paper by Fluent.

 June 9, 2015, 15:18 #5 New Member   Paul Join Date: Jun 2015 Posts: 3 Rep Power: 4 Thanks for your advices. It turns out I just had to launch the simulation without the moving cylinder before adding the dynamic mesh and the movement based on the UDF (maybe this was evident for anyone else). I can finally see the cylinder moving. Now, I am having trouble with the position of the cylinder during the simulation. Even when I set his gravity center at the coordinates (0,0) in the Dynamic Mesh options, it oscillates with another origin during the simulation. But maybe it is just a small problem to solve. Anyway, thank you for your answers.

 May 12, 2017, 08:01 oscillating cylinder dynamic mesh #6 New Member   rihen full Join Date: May 2012 Posts: 10 Rep Power: 7 I try to solve a flow past a oscillating cylinder between paralel wall. I would like to make cylinder goes up and down. But I cannot prepare udf file for cylinder motion. Can you help me?

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