Wall Deformation and swelling of an artery
 

Hi all,

I am trying to incorporate a mechanism in Ansys CFX which can predict arteriosclerotic formation in an artery.
My idea is the following:
I have got a cylindrical shaped artery with a bifurcation. As the blood flows through this bifurcation artery several regions of the wall (which are imposed to a threshold value of Wall Shear Stress)become inflamed and start to swell. This results in a formation of a bump (solid material) which reduces the cross sectional area of the flow.

You can see the explanation in the picture below.

I already tried to increase the viscosity of the blood to extreme high values (from 3.6e-3 Pa s to 1000 Pa s), but this leads to very high pressures of the high viscous parts of my fluid. I want this parts to "rest". I looked through the multi phase tutorials but couldn't find anything which really fits my problem. Maybe it is possible to some kind deform the surface mesh of the artery...

In general it should be a solidification process, I've read that this is possible to implement in FLUENT.
Do you have some ideas how to do this in Ansys CFX? Or maybe some keywords to look at.

Thank you very much!
Michael

You can probably do this in CFX either with a moving mesh or an immersed solid approach. Either should work. You could probably also use a momentum source to drive the flow in the restricted region to zero (which is effectively what the immersed solid approach does).

Generating massive variations in viscosity over short distances is bound to lead to convergence problems. From the little I know of this flow I do not think viscosity is equivalent to what is physically happening - so of course the solver has problems making it converge.

Dear all,
I have the same problem, I have a pipe that fluid is passing through unimpeded, the pipe then narrows to form the constriction shown in the attached image http://tinypic.com/r/25s4rhs/8.
Is it possible to model this using moving mesh approach? If yes, please let me know how it is doable.

Thank you.
AshtonJ

This is the image link
http://tinypic.com/r/25s4rhs/8

You can define expressions in CFX on how far to move the mesh during a simulation by either applying a total deformation or the deformation per TimeStep/Iteration.
Create an expression where you feed in x,y,z-coordinates and then simply "return" the desired end position/total mesh deformation in [m].

Check the above expression with the ploting feature in CFX-Pre. Make sure to get the desired behavior for the mesh movement (e.g. MeshMovement for Y ramped wrt. x-coord).

Just an idea: If you have a tube - you can also convert the movement to radius/theta/z by referencing the whole simulation on a new coordinate system.

Dear mvoss,

Thank you. I tried but the following error was given;
At least one highly skewed element has been detected on a wall
boundary, leading to an unreliable near-wall distance calculation
for the turbulent wall functions. The solver will continue
to execute, but convergence and/or accuracy may be affected.
Please consider improving the mesh quality.

Actually, I do not understand the expression you defined, I need to create a narrowing only in the middle section of the pipe. Where in your expression, this is included. I would be too pleased if you explain a bit more moving mesh modelling, especially for my case.

I've done FSI analysis before, but this is first time I do moving mesh stuff. More details about moving mesh settings in CFX will help me a lot.

Thank you.
Regards,
ashtonJ

Did you check the expression in the plot window? There you can see pretty good what the expression is doing. (It is a smooth cubic curve changing from 0 to 1 over the desired RampLength) - the shape of the rampe is what the tube will look like. You really need to understand whats going on there.
The expression from above is moving the elements outwards and is just an example - you need to define what fits your task the best.
How come you did FSI without dealing with moving meshes - One-Way-FSI?
Did you do the tutorials on the moving mesh feature? If not, then i would highly recommend it.
What ANSYS version are you on?

Yes, I did check the expression shape. Now I guess I understand what the expression is doing, the x in the expression should represent the longitudinal axis, in my case, it should be changed to z.
I've done two-way FSI in elastic arteries, which were deformed due to the pressure wave. In the FSI modellings, I had no control on the mesh displacement.
As suggested, it's better to go through the moving mesh tutorials.
Thank you very much for your help.

Sorry, one more question. In two-dimensional case, the x in your expression shows the longitudinal axis and rampe represents the radius of the tube. Am I correct? If yes, how come the rampe start from zero? Does this mean that the radius at that point is zero?