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CTRANS and DTRANS in 6DOF in fluent

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Old   June 28, 2010, 09:42
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  #21
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Hi

DEFINE_SDOF_PROPERTIES with sub macro SDOF_IYY you need to input your rigid body YY Moment of Inertia.
With SDOF_LOAD_M_Y you define a external moment applied to it.

If you want to calculate angular velocity just use DT_OMEGA_CG macro in your UDF and write it to a file.

Check FLUENT udf manual for more details.
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Old   April 9, 2011, 12:54
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Hello shehzad and...
I have a problem about the
SDOF_ZERO_TRANS e SDOF_ZERO_ROT properties.

i want to solve flow in a radial turbine wheel(with high RPM).
Because the flow work is done on the blades to make the blades rotating,I decided to use dynamics mesh with 6dof.
When I try to compile the UDF,FLUENT shows me:

..\..\src\stage.c(6) : error C2065: 'SDOF_ZERO_TRANS_X' : undeclared identifier
..\..\src\stage.c(7) : error C2065: 'SDOF_ZERO_TRANS_Y' : undeclared identifier
..\..\src\stage.c(8) : error C2065: 'SDOF_ZERO_TRANS_Z' : undeclared identifier
..\..\src\stage.c(9) : error C2065: 'SDOF_ZERO_ROT_X' : undeclared identifier
..\..\src\stage.c(10) : error C2065: 'SDOF_ZERO_ROT_Y' : undeclared identifier

Here there is my UDF
Quote:

#include"udf.h"

DEFINE_SDOF_PROPERTIES(stage, prop, dt, time, dtime)
{

/* Define the mass matrix */

prop[SDOF_MASS] = 0.02;
prop[SDOF_IXX] = 0.000067;
prop[SDOF_IYY] = 0.000067;
prop[SDOF_IZZ] = 0.000288;

/* Define the Degrees of Freedom allowed - Only z rotation is allowed */

prop[SDOF_ZERO_TRANS_X] = TRUE;
prop[SDOF_ZERO_TRANS_Y] = TRUE;
prop[SDOF_ZERO_TRANS_Z] = TRUE;
prop[SDOF_ZERO_ROT_X] = TRUE;
prop[SDOF_ZERO_ROT_Y] = TRUE;
printf (
"\nstage: updated 6DOF properties");
}


Could you help me please?
Thank you. Kind regards, mamadreza

Last edited by mamyjooooon; April 11, 2011 at 04:26.
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Old   April 10, 2011, 15:14
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please read my posts written above, actually fluent does not have facility to constrain the motion of a body in one or two or more dimensions with put writing udf. if u need to constrain the motion of ur turbine in all directions except in z direction, u need to write complete UDF. Compute_force_and_moment is the name of a macro that calculates teh forces and moments around a body due to the action of air or water. with the help of these moments and forces u can get of the motion of the body in the required direction. the movment of body can b calculated from these forces by using euler's forrmula. as i hav mentioned earlier in above posts.
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Old   April 11, 2011, 14:47
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hi shehzad
tanks for your reply
1-I find no data about Compute_force_and_moment via udf and internet,
so i don't know how to us this macro,
I'll thank you if give me some information on how to use this macro.
2-I can't find any information about forrmula in pervioyus posts
please guid me to certain post.
3-I want to constrain its translation,but I dont know how should do to get rotation only(the rotation axis is z)!
may you help me in giving constrained to the motion of blades?

Thank you for your attention

Last edited by mamyjooooon; April 11, 2011 at 15:40.
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Old   January 23, 2013, 07:48
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Dear shehzad and everyone,

I am new and doing the work which is similar to your case. If I ask some stupid questions here, please don't mind.

My first work is that I analyze the velocity and pressure of the wind turbine with fixed velocity of wind and fixed angular velocity of the wind turbine. My geometry is one wind turbine with three blades in a big cylinder. In this case, I used sliding mesh and didn't use dynamic mesh, and the wind turbine blades could rotate well.

And now, my second case is to do the wind-driven wind turbine case. I am wondering whether I need to use dynamic mesh with 6dof instead of sliding mesh. Could I use the the same settings in the first case and apply a UDF file which calculates the angular velocity to the boundary conditions of the blades instead of fixed angular velocity used in the first case. The formula I will use in the UDF file is:

angular velocity = the previous angular velocity + (torque * time step)/ moment of inertia

Can I get the calculated torque by fluent, and then I could use that in my UDF file?

After reading this thread, I am really confused how to do my second case. If someone can kindly give me some advice or guide, I will be thankful and appreciate your help very much.

Best Regards,
Michelle
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