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-   -   CFX Oscillating Cylinder FSI Problem (http://www.cfd-online.com/Forums/cfx/120851-cfx-oscillating-cylinder-fsi-problem.html)

vplpaul July 16, 2013 06:48

CFX Oscillating Cylinder FSI Problem
 
Hello everyone,

I am trying to do a FSI simulation in CFX using CEL expressions, the problem is of a cylinder mounted on a spring damper system. The expressions used are similar to the ones used in the tutorial with the addition of a damping coefficient term. But unfortunately the amplitude of oscillation predicted by CFX is much higher than the reference values. My CEL expressions are as follows,

m = 1.1e-4 [Kg]
K = 12.012 [N m^-1]
C = 5e-5 [Kg s^-1]
FFlow = force_y@INTERFACE (INTERFACE is the interface between the cylinder and fluid)
MeshVel = areaAve(Mesh Velocity Y)@INTERFACE
YOld = areaAve(Total Mesh Displacement Y)@INTERFACE
tstep = 5e-4 [s]
Numer = (m*YOld)/tstep^2) + (m*MeshVel/tstep) + (C*YOld/tstep) + FFlow
Denom = (m/tstep^2) + (C/tstep) + K
YNew = Numer/Denom

I then use this YNew value to specify the displacement of the mesh at the next time step.

I don't know why this set up doesn't work. If somebody can tell me anything about it, it would be very helpful.

Thanks!

Also can anyone tell me how the Mesh Velocity Y function calculates the mesh velocity? Is it the velocity change from the previous mesh or from the initial mesh?

stumpy July 23, 2013 16:43

Check Mesh Velocity Y is giving you something sensible. I saw monitor points for this giving strange values recently.


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