Hi together,

I am quite new here in the community and just face my first serious problem.

Let me explain the background at first:
I want to create a small library for special fluid applications (lubrication).
For this library, I also need basic components such as pipes. To calculate the pressure drop in a pipe, I need the friction factor. Up to now, I used approximated equations that could be solved easily, since the wanted variable was already separated on the left side. But now, I'd like to use those equations that can be found in literature, e.g. the Prandtl-Karman-equation:

1/sqrt(lambda) = 2 * log10(Re * sqrt(lambda) / 2.51)
lambda: friction factor
Re: Reynoldsnumber

Obviously, this equation has to be solved iteratively. I managed to do so by using the Modelica Standard library: Modelica.Math.Nonlinear.solveOneNonlinearEquation. I get the correct result.

And here's my problem: I now want to use this component (e.g. a pipe) in another model (a network consisting of several pipes and so on), but I get the error message:
Failed to instantiate equation
lambda = Modelica.Math.Nonlinear.solveOneNonlinearEquation(function OilCircuit.Functions.FrictionFactor.Smooth.PrandtlKarman(Re = 27000), 0.0001, 0.1, 0.001);.

Well, it seems that one can't instatiate an equation. But I can't find any other solution to solve this.
Can anyone help?

Thank you very much! Regards, Jan