# FSI analysis-Turn a straight tube to constricted tube

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 March 11, 2014, 19:08 FSI analysis-Turn a straight tube to constricted tube #1 Senior Member   Ashkan Javadzadegan Join Date: Sep 2010 Posts: 255 Rep Power: 15 Hello everyone, I am trying to perform a FSI analysis to turn a straight tube (image (a)) to a constricted tube (image (b)). http://tinypic.com/r/25s4rhs/8[/IMG] I have done FSI modelling before in stenosed arteries in which artery wall expands as the results of fluid pressure. However, this problem is different and I am confused with the boundary conditions which could turn a straight tube to a constricted one. I would be happy if anyone could help me with this. Regards, ashtonJ

 March 12, 2014, 09:58 #2 Senior Member   Join Date: Apr 2009 Posts: 531 Rep Power: 19 I would guess this is due to the Bernoulli effect. The flow accelerates through a constriction, which drops the static pressure and pulls in the walls. It might not be possible to solve this case. If the structure is in compression and wants to buckle, but is prevented from doing so due to the fluid, then you may not be able to get a stable solution unless you use a single-matrix FSI solver. You can test this by applying a reasonable negative pressure to the structure without doing FSI. If you can get a stable solution in a Static Structural analysis then you are OK, if not then you could try Transient Structural with a very small time step, but that may not be enough.

 March 12, 2014, 16:44 #3 Senior Member   Ashkan Javadzadegan Join Date: Sep 2010 Posts: 255 Rep Power: 15 Dear Stumpy, Thank you. The real problem is related to an artery which is blocked in heart muscle, the artery partially contracts as the result of heart contraction. I mean, physically, the image (b) (normal tube) should be converted to image (a) (constricted tube). Is there a way to do two-way FSI in normal tube by applying an external pressure on the structure, which gradually turn the normal tube to the constricted one! Regards, AshtonJ

 March 13, 2014, 10:48 #4 Senior Member   Join Date: Apr 2009 Posts: 531 Rep Power: 19 You can certainly apply an external pressure to the structure causing it to deform inwards. But what's preventing the tube completely collapsing?

 March 14, 2014, 03:17 #5 Senior Member   Ashkan Javadzadegan Join Date: Sep 2010 Posts: 255 Rep Power: 15 I tried exerting a pressure on the structure, but pressure applies on the whole surface and creates a uniform narrowing. What I need is to create a deep narrowing in the middle of the artery and becomes gradually unimpeded toward distal and proximal of the artery, like a sinusoidal signal.

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