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 leoarmas May 18, 2012 11:30

CG Motion UDF Problem

Hello World!

I have been working in the past few days trying to understand UDFs but i think i've reached a dead end...

This is what i'm trying to do:

I'm just trying to simulate the flow around a body wich is moving up and down with a sinusoidal law of motion. To do this i have written my UDF just as is shown below:

#include "udf.h"

DEFINE_CG_MOTION(object_mov, dt, vel, omega, time, dtime)
{
real a, w, pi;

pi = 3.1415;

/* define motion variables */
a = 0.05; /* 0.05m movement amplitude */
w = 2 * pi * 2; /* 2Hz frequency */

/* define object movement law */
vel[0] = 0;
vel[1] = -a * w * sin(w*time);
vel[2] = 0;
}

I have no problem interpreting this UDF into Fluent. However, when defining the dynamic zone the following warning appears:

"Warning: incorrect cg motion UDF wing on zone 4 (assuming no motion)"

Do you have any clue why could this be? is my UDF correctly written?
Thanks!

 leoarmas June 1, 2012 11:42

Just to say that I have solved the problem: CG motion macro only works when compiled!!

 Jessica.S June 2, 2012 01:21

Hi,

#include "udf.h"
#include "stdio.h"
#include "stdlib.h"
#include "math.h"
#include "dynamesh_tools.h"
#include "storage.h"

In addition, define an intermediate (i.e. "real v = 0") variable for the motion:

v = -a * w * sin(w*time);
vel[1] = v;

hopefully it will solve your problem...

 hossein66 August 1, 2012 06:58

Quote:
 Originally Posted by leoarmas (Post 364313) Just to say that I have solved the problem: CG motion macro only works when compiled!!
How do you fix it? I have this problem but I can't fix it! Can you help me?

 roham4peace April 10, 2015 02:59

udf for flapping motion in hover

I cant write udf code for flapping motion in hover, help me, im so confused

 Jessica.S April 10, 2015 03:22

do it with solidworks flow simulation.

J

 manahara October 9, 2015 01:55

Quote:
 Originally Posted by hossein66 (Post 374796) How do you fix it? I have this problem but I can't fix it! Can you help me?
Hi, Define CG Motion can only be compiled not interpreted. Please try compiling the UDF rather :)

 morteza 1374 April 4, 2016 02:13

Quote:
 Originally Posted by manahara (Post 567252) Hi, Define CG Motion can only be compiled not interpreted. Please try compiling the UDF rather :)
hi
I am the student of fluid mechanics and now I am studying on fluid project. The subject of my project is about blade turbine that Oil radially impacts to the turbine blades by a nozzle, causing the turbine to spin. I have a problem in modeling of turbine that I don’t know how to obtain moment of inertia of blade and fluid and how to relate this challenge to the Cg motion until I can model this turbine in fluent software. Please help me

 arunraj May 14, 2016 03:04

Dynamic mesh flapping wing - Interface problem

1 Attachment(s)
Hi everyone,

I am simulating flapping wing of aerofoil. I have created three zones, zone 1, 2 and 3. Zone 1 has aerofoil with structured mesh around the aerofoil. Zone 2 and 3 has unstructured gird. My problem is I have properly followed all the steps. But I am not able to achieve what I want. Because the shadow of the interface is taking as wall and is not moving along with the domain. Kindly someone help in sorting out this issue. I have attached my UDF alos. Please have a look. Thank you so much