# CFX Oscillating Cylinder FSI Problem

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 July 16, 2013, 06:48 CFX Oscillating Cylinder FSI Problem #1 New Member   Vipul Join Date: Jun 2013 Posts: 3 Rep Power: 6 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?

 July 23, 2013, 16:43 #2 Senior Member   Join Date: Apr 2009 Posts: 532 Rep Power: 14 Check Mesh Velocity Y is giving you something sensible. I saw monitor points for this giving strange values recently.

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