rigid body rotation through an axis not passing through centre of gravity

ranjith · November 21, 2012, 10:50

I am trying to simulate the dynamics of an artificial heart valve. I have a rotating disc which I model as a rigid body. problem is my rotation axis does not pass through the cg. is it possible to do such a simulation in CFX...if not is it possible to do it in fluent..

ghorrocks · November 21, 2012, 17:29

Can you post an image of what you want to model? There are many possible approaches to model rotating gizmos.

ranjith · November 21, 2012, 22:24

Thankyou Glenn for your reply. Please find the pics in the below two links

http://en.wikipedia.org/wiki/File:Chitra_Valve.jpg

http://www.google.co.in/imgres?hl=en...9,r:0,s:0,i:87

The valve consists of a suture ring in the periphery, a metallic cage with 3 struts- two major struts(the two in the bottom in the first pic link) and a minor strut(the one on the top) and a disc( the white disc in the pic). The disc opens and closes depending on the pressure difference across it allowing blood to flow through it. In my simulation I am modeling the disc as a rigid body. The disc is seated on the major struts and it opens and closed about an axis which is passing through the tip of the two major struts. The problem is that this axis does not pass through the centre of gravity of the disc

ghorrocks · November 22, 2012, 04:23

You might also be able to model this with a rotating frame of reference, linked to the torque of the valve. Including inertia will be difficult in this approach - I do not know whether that is important or not.

ranjith · November 22, 2012, 07:02

Could you explain in a bit more detail. The valve disc rotates through an angle of around 75 degrees. So I suppose I define the disc as an immersed solid as well as a rotational frame and link its rotation to the torque on the valve...am I right?

ghorrocks · November 22, 2012, 16:08

No, not correct. This approach does not use rigid bodies, instead it uses rotating frames of reference. Put the disc as a cut-out in the mesh in a circular region linked to the rest of the domain with a GGI. Work out the torque on the disc and rotate it to a new position based ont he torque, and you can include limits on the motion to allow it to lock shut.

Have a look at the turbomachinery examples for how to set up the rotating frames of reference. Obviously these rotating frames of reference go around with constant angular velocity, what I am saying here is you change the angular velocity to model your flap rotating open and shut.

November 21, 2012, 10:50	rigid body rotation through an axis not passing through centre of gravity	#1
ranjith New Member ranjith Join Date: Dec 2009 Posts: 19 Rep Power: 16	I am trying to simulate the dynamics of an artificial heart valve. I have a rotating disc which I model as a rigid body. problem is my rotation axis does not pass through the cg. is it possible to do such a simulation in CFX...if not is it possible to do it in fluent..

November 21, 2012, 22:24		#3
ranjith New Member ranjith Join Date: Dec 2009 Posts: 19 Rep Power: 16	Thankyou Glenn for your reply. Please find the pics in the below two links http://en.wikipedia.org/wiki/File:Chitra_Valve.jpg http://www.google.co.in/imgres?hl=en...9,r:0,s:0,i:87 The valve consists of a suture ring in the periphery, a metallic cage with 3 struts- two major struts(the two in the bottom in the first pic link) and a minor strut(the one on the top) and a disc( the white disc in the pic). The disc opens and closes depending on the pressure difference across it allowing blood to flow through it. In my simulation I am modeling the disc as a rigid body. The disc is seated on the major struts and it opens and closed about an axis which is passing through the tip of the two major struts. The problem is that this axis does not pass through the centre of gravity of the disc Last edited by ranjith; November 21, 2012 at 22:41.

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November 21, 2012, 17:29		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Can you post an image of what you want to model? There are many possible approaches to model rotating gizmos.

November 22, 2012, 04:23		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	You might also be able to model this with a rotating frame of reference, linked to the torque of the valve. Including inertia will be difficult in this approach - I do not know whether that is important or not.

November 22, 2012, 07:02		#5
ranjith New Member ranjith Join Date: Dec 2009 Posts: 19 Rep Power: 16	Could you explain in a bit more detail. The valve disc rotates through an angle of around 75 degrees. So I suppose I define the disc as an immersed solid as well as a rotational frame and link its rotation to the torque on the valve...am I right?

November 22, 2012, 16:08		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	No, not correct. This approach does not use rigid bodies, instead it uses rotating frames of reference. Put the disc as a cut-out in the mesh in a circular region linked to the rest of the domain with a GGI. Work out the torque on the disc and rotate it to a new position based ont he torque, and you can include limits on the motion to allow it to lock shut. Have a look at the turbomachinery examples for how to set up the rotating frames of reference. Obviously these rotating frames of reference go around with constant angular velocity, what I am saying here is you change the angular velocity to model your flap rotating open and shut.