Immersed solid: prescribing translation and separately solving for rotation?

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July 27, 2020, 11:51
Immersed solid: prescribing translation and separately solving for rotation?
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Maria C
Join Date: Jul 2020
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Hi all,

I am trying to simulate the flow in a cylindrical tube containing a mechanical heart valve with the immersed solid method. The valve is made of two leaflets, the rotation of which is controlled by the flow field around them. The valve is pushed by an external actuator, resulting in translation along the tube axis. During the translation, the leaflets also rotate (see image for simplified cross-section).
Ideally, I would like to prescribe the translation exactly (distance against time), while keeping the rotation flow-driven.

I understand I can model the leaflet as a rigid body with one rotational degree of freedom. This seems to work fine if solving for rotation only.
However, the only way of prescribing translational motion to a rigid body seems to be to define the forces acting on it, which are unknown since they would depend on the flow. I have tried a few force inputs to achieve the desired motion but it seems very unstable.

Is there a way to "de-couple" the rotation from the translation, so to prescribe the required translation, while the rigid body solver only solves for rotation? Or is there a simpler workaround?

Many thanks
Attached Images
 Valve movement.jpg (77.0 KB, 7 views)

 July 27, 2020, 21:13 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,480 Rep Power: 140 If the motion is known in advance then you do not use rigid bodies to model this. You use moving mesh. Then you can define any motion you like, including translation, rotation and any combination. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

 July 28, 2020, 05:56 #3 New Member   Maria C Join Date: Jul 2020 Posts: 2 Rep Power: 0 I will look into the moving mesh method more, but as far as I understand, you can only use a moving mesh if you know exactly how the solid moves. To clarify: I don't know the solid motion completely, apologies for the confusion! I only know the translation of the leaflets, but I do not know how and when the leaflets rotate. The rotation of each leaflet depends on the flow velocity, pressures, etc., so I would like to find out how it rotates under different flow conditions, while still applying the (known) translation. Is that possible using either the moving mesh or immersed solid method?

 July 28, 2020, 06:09 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,480 Rep Power: 140 Can you do this using FSI? Where ANSYS Mechanical has a rigid body solver which prescribes the oscillating motion and the pin joint for the leaflets, and is coupled to CFX over the leaflet surfaces for the fluid flow. So the FEA model is rigid body model, not a flexible body model. Then the rigid body motions are constrained and defined in ANSYS rather than CFX. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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