# CG Motion UDF Problem

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 May 18, 2012, 11:30 CG Motion UDF Problem #1 New Member   Leonardo Armas Join Date: Apr 2012 Posts: 2 Rep Power: 0 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? Looking forward to your answer. Thanks!

 June 1, 2012, 11:42 #2 New Member   Leonardo Armas Join Date: Apr 2012 Posts: 2 Rep Power: 0 Just to say that I have solved the problem: CG motion macro only works when compiled!!

 June 2, 2012, 01:21 #3 New Member   Jessica Simberg Join Date: Mar 2012 Posts: 17 Rep Power: 6 Hi, your missing a math header, try using these: #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... leoarmas likes this.

August 1, 2012, 06:58
#4
New Member

Hossein
Join Date: Jul 2012
Posts: 1
Rep Power: 0
Quote:
 Originally Posted by leoarmas 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?

 April 10, 2015, 02:59 udf for flapping motion in hover #5 New Member   roham lavimi Join Date: Apr 2015 Posts: 1 Rep Power: 0 I cant write udf code for flapping motion in hover, help me, im so confused

 April 10, 2015, 03:22 #6 New Member   Jessica Simberg Join Date: Mar 2012 Posts: 17 Rep Power: 6 do it with solidworks flow simulation. J

October 9, 2015, 01:55
#7
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Manahara Manatunga
Join Date: Mar 2014
Posts: 10
Rep Power: 4
Quote:
 Originally Posted by hossein66 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

April 4, 2016, 02:13
#8
New Member

mortezasekaloo
Join Date: Apr 2016
Posts: 4
Rep Power: 2
Quote:
 Originally Posted by manahara 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

May 14, 2016, 03:04
Dynamic mesh flapping wing - Interface problem
#9
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Arun raj.S
Join Date: Jul 2011
Posts: 72
Rep Power: 7
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

Attached Files
 second.c (1.1 KB, 14 views)

 Tags udf cg motion

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