# UDF for Oscillations

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 February 10, 2004, 17:00 UDF for Oscillations #1 Cfdtoy Guest   Posts: n/a Hi In case i want to oscillate a wall with a frequency f, does anyone know how to create a UDF for the same ? . There is a spring analogy in the website however, i want the oscillation to be somethin like a sine wave kinda. thanks for ur time and help Cfdtoy

 February 16, 2004, 03:21 Re: UDF for Oscillations #2 FJ Guest   Posts: n/a Hi, DEFINE_CG_MOTION is very suitable for your issue. If the wall velocity is a function of time, It's very easy to coding . You just define the following in the UDF macro. vel[0] = sin(2*3.14*f) Thanks FJ

 February 18, 2004, 17:50 "Non Positive Volumes" ..Re: UDF for Oscillations #3 Cfdtoy Guest   Posts: n/a Hi there Thanks for the response. I used the sinusoidal variation, I kinda tend to get "non-positive volume Exist" Message during my simulation using Dynamic Meshes. Although, I use min and max volumes as the same as given by the Grid Check Function Does anyone know how to treat the message ? Thanks CFDtoy

 February 23, 2004, 01:42 Re: "Non Positive Volumes" ..Re: UDF for Oscillati #4 FJ Guest   Posts: n/a Hi, It must be that the time step size is too large to re-mesh. To use small time step size, it will be no problem. FJ

 February 26, 2004, 18:11 Re: UDF for Oscillations #5 Cfdtoy Guest   Posts: n/a Hello FJ... Thanks for the response. I would like to explain my situation a little better. I have an object ( say Diameter 'd') placed in a liquid. This rod ( solid wall around) is protuding inside the domain. Now, the rod is made to move back and forth with an frequency 'f' ..so..if i take a rod placed in the domain and mesh it around, the movement of the wall (rod) would be considered as a case of dynamic meshing isnt it ? Hence, I request help for writing a UDF for the wall movement ..I did look around Fluent and came to know about the Define_CG_Motion but how about Define_Grid_motion ? If you can ..can you help me with a sample code ? Thanks CFDtoy

 February 27, 2004, 02:20 Re: UDF for Oscillations #6 FJ Guest   Posts: n/a Hi, I'll send you cas file and UDF directly. FJ

 March 12, 2004, 08:21 Re: UDF for Oscillations #7 Qureshi Guest   Posts: n/a Can I also have the file and UDF?

 March 15, 2004, 05:36 Re: UDF for Oscillations #8 FJ Guest   Posts: n/a Hi, The UDF is very simple , see the followings. --- #include "udf.h" real freq = 1.; DEFINE_CG_MOTION(osc, dt, vel, omega, time, dtime) { vel[0] = sin(2*M_PI*freq*time); } --- This is my personal opinion that UDF for FLUENT MDM function is not so difficult compared with its settings. I mean, I think , most difficult settings is "Define-Dynamic Mesh-Zones". Sometimes this function makes me unhappy!. FJ

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