Discussion Forum

Hi,

I have some problems in coupling the lubrication shell interface with a global equation.

I'm using the lubrication shell to model a tilting pad: I impose the pressure on the borders of the pad (two different values for inlet and outlet) and I calculate the inlet and outlet flow rates.

Before and after the pad there are other oil flows (not dependent from the modelled pad) so the pressure on the borders would vary with time searching balance between these oil flows: by adding a global equation I would like to model this pressure variation. The ODE is the following:

dp/dt-(constant)*(sum of flow rates)=0 (one equation for the inlet of the pad and another for the outlet).

The flow rates are calculated in the lubrication shell and solving the ODE I would like to find new pressure values and impose them on the borders of the pad, until convergence is reached.

The lubrication shell model works fine and so the ODE, but the complete model (time dependent) seems to by-pass the global equation: the pressure values don't follow the flow rate balance and the ODE never reach convergence.

In effect it seems that I can't use the state variable p from the ODE as a boundary condition for the lubrication shell. Am I right?

Best regards,
Daniele