UDF for defining CG_Motion of a rigid ball

Sufyan Abushaala · November 17, 2014, 06:50

Dear all

I am simulating a a rigid ball moving along a horizontal pipe, and I was wondering if any body can help writing a UDF for CG motion of that ball.

The problem is all about controlling the ball motion and keep it away from the pipe wall in order to prevent the collision between them.

I would be grateful if someone could provide a help on that.

Regards,

vasava · November 18, 2014, 04:22

Are you prescribing the motion of the ball or is it moving along the some fluid?

Sufyan Abushaala · November 18, 2014, 05:43

Dear Vasava

I am not prescribing the ball motion, it is flown by the fluid. I am using a UDF to define the ball mass and its moments of inertia.
I have an error once the ball hits the pipe wall, and I need to keep it away from that wall. It is likely controlling the motion range in both Y and Z directions.

Any help please?
Regards,

pakk · November 18, 2014, 07:25

Quote:

I have an error once the ball hits the pipe wall, and I need to keep it away from that wall.

It would make more sense to me to fix the error. If there is no physical mechanism that prevents the ball from hitting the pipe wall, it does not make sense to put such a mechanism in your simulation.

Sufyan Abushaala · November 18, 2014, 07:29

Dear Pakk

You are right Pakk. Although that can be fixed using the contact detection feature added recently to fluent, but it is still new and not easy to apply.
So, having some restriction to the ball motion in order to prevent the collision is something can help despite the inaccuracy that might be achieved.

Regards,

pakk · November 18, 2014, 07:32

But be aware that if you add an unphysical restriction to the ball motion, you will get an unphysicial solution.

Before you can start writing a udf, you should think about what kind of restriction you want to add. What should happen to the ball when it gets close to the wall? What is "close" in your case?

Sufyan Abushaala · November 18, 2014, 07:39

Yes right. That should be taken into account.

November 17, 2014, 06:50	UDF for defining CG_Motion of a rigid ball	#1
Sufyan Abushaala New Member Sufyan Abushaala Join Date: Feb 2014 Location: Huddersfield, UK Posts: 18 Rep Power: 12	Dear all I am simulating a a rigid ball moving along a horizontal pipe, and I was wondering if any body can help writing a UDF for CG motion of that ball. The problem is all about controlling the ball motion and keep it away from the pipe wall in order to prevent the collision between them. I would be grateful if someone could provide a help on that. Regards,

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
UDF parallel error: chip-exec: function not found?????	shankara.2	Fluent UDF and Scheme Programming	1	January 16, 2012 23:14
simple rigid body motion UDF	Dan	FLUENT	0	January 11, 2006 06:48
Dynamic meshing: UDF for rigid body Motion	Manoj Kumar	FLUENT	0	June 20, 2005 02:02
how to write a udf about roatation of rigid.	ccgwin	FLUENT	3	December 11, 2002 09:14
UDF, UDF, UDF, UDF	Luc SEMINEL	Main CFD Forum	0	November 25, 2002 05:01

November 18, 2014, 04:22		#2
vasava Senior Member Paritosh Vasava Join Date: Oct 2012 Location: Lappeenranta, Finland Posts: 732 Rep Power: 23	Are you prescribing the motion of the ball or is it moving along the some fluid?

November 18, 2014, 05:43		#3
Sufyan Abushaala New Member Sufyan Abushaala Join Date: Feb 2014 Location: Huddersfield, UK Posts: 18 Rep Power: 12	Dear Vasava I am not prescribing the ball motion, it is flown by the fluid. I am using a UDF to define the ball mass and its moments of inertia. I have an error once the ball hits the pipe wall, and I need to keep it away from that wall. It is likely controlling the motion range in both Y and Z directions. Any help please? Regards,

November 18, 2014, 07:29		#5
Sufyan Abushaala New Member Sufyan Abushaala Join Date: Feb 2014 Location: Huddersfield, UK Posts: 18 Rep Power: 12	Dear Pakk You are right Pakk. Although that can be fixed using the contact detection feature added recently to fluent, but it is still new and not easy to apply. So, having some restriction to the ball motion in order to prevent the collision is something can help despite the inaccuracy that might be achieved. Regards,

November 18, 2014, 07:32		#6
pakk Senior Member Join Date: Nov 2013 Posts: 1,965 Rep Power: 27	But be aware that if you add an unphysical restriction to the ball motion, you will get an unphysicial solution. Before you can start writing a udf, you should think about what kind of restriction you want to add. What should happen to the ball when it gets close to the wall? What is "close" in your case?

November 18, 2014, 07:39		#7
Sufyan Abushaala New Member Sufyan Abushaala Join Date: Feb 2014 Location: Huddersfield, UK Posts: 18 Rep Power: 12	Yes right. That should be taken into account.