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CFX Oscillating Cylinder FSI Problem

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Old   July 16, 2013, 06:48
Smile CFX Oscillating Cylinder FSI Problem
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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.


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?
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Old   July 23, 2013, 16:43
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Check Mesh Velocity Y is giving you something sensible. I saw monitor points for this giving strange values recently.
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