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-   -   problem with oscillating cylinder (http://www.cfd-online.com/Forums/fluent/42300-problem-oscillating-cylinder.html)

 zonexo September 13, 2006 10:44

problem with oscillating cylinder

hi,

i'm trying to simulate a cylinder oscillating in a transverse fashion. i've met with some problems which i hope someone can help...

these are the steps i took:

2. prepare the plung.c udf file given as

#include "udf.h" /* this function defines velocity of center of gravity for pure plunging motion*/ /* Plunging motion equation is z(t)=h*sin(2*pi*f*t) */ DEFINE_CG_MOTION(plung, dt, vel, omega, time, dtime) { Thread *t; face_t *f; /*reset velocities */ NV_S(vel,=,0.0); NV_S(omega,=,0.0); if (!Data_Valid_P()) return; /* Get the thread pointer for which this motion is defined */ /* t=DT_THREAD(dt); */ /* vel[1] is the vertical plunging velocity */ /* These velocity below is for h=0.4c and f=0.993Hz */ vel[1] = 2.495*cos(6.2392*time); }

3. compile the source file

4. go to dynamic mesh - zones. i've selected cylinder with rigid body motion with the udf profile just compiled

5. set the BC of the cylinder with moving wall and use the library just compiled.

i wanted to start iteration but the "iterate" button is not highlighted.

so what have i missed out? tks in advance!

 philip September 13, 2006 11:57

Re: problem with oscillating cylinder

You need to initialize your solution. An initial guess is essential for any iterative solver.

 zonexo September 13, 2006 20:04

Re: problem with oscillating cylinder

hi,

tks. initialization worked. however when i tried to preview the mesh, i've got negative volume. from the preview, it's shown that the cylinder at the center's moving, but the other parts are not moving.

what other things must i do? i simply want the whole mesh to move up/down. no mesh deformation is required.

 philip September 14, 2006 10:13

Re: problem with oscillating cylinder

have you gone to Dynamic Mesh...Parameters... and turned remeshing on? You might want to play with the smoothing parameters too if you don't want to remesh.

Make sure you run Fluent from a dos-prompt.

-Philip-

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