Discussion Forum

Hi everyone,

I am trying to model a fluid power intensifier manufactured by Parker. It is a hydraulic piston cylinder assembly. I am using the ALE FSI model (Navier Stokes+Moving mesh+ plain strain) as a base to build mine. I have changed both the inlet and outlet boundaries according to my application, but where I am still having trouble with is the boundary condition for the piston. In the geometry I have it as a rectangle inside a bigger rectangle (the cylinder). I have set the top and bottom edges of the piston rectangle to "roller" condition in the Plain Strain mode boundary conditions. The other edges of the piston rectangle have been set to both to "structural velocity" and "structural displacement". I increased the Young's modulus so the rectangle will not bend under fluid load.
When trying to solve, I keep getting errors regarding various issues of the same nature: " Failed to evaluate variable Jacobian". All variables referenced are with respect to the top and bottom edges of the piston cylinder (which are in contact with the edges of the wider cylinder rectangle).
Here is an example of the error I get:

=============================

Exception:
com.femlab.jni.FlNativeException: Failed to evaluate variable jacobian
Messages:
Failed to evaluate variable jacobian
- Variable: T_x_mmglf
- Geometry: 1
- Boundary: 6

Stack trace:
at xevalutil.cpp, row 2850, ()
at com.femlab.solver.FlSolver.femTime(Native Method)
at com.femlab.solver.FemTime.run(Unknown Source)
at com.femlab.server.FlRunner.run(Unknown Source)
at com.femlab.util.i.run(Unknown Source)
at com.femlab.util.aa.run(Unknown Source)

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Any ideas, comments, corrections are very appreciated.