Hello sgopal1,

I've struggled with the same issue many times with the Modelica.Fluid pump models.

The problem is — as the warning tells you — that the pump curve is not monotonically decreasing, meaning that the maximum of the curve is not at V_flow = 0 but to the right of it. The result is that there are two values of the volume flow giving the same pump head which is, numerically, a problem.

The reason for the non-monotonically decreasing curve is that, although you specify nominal points of V_flow and head that are monotonically decreasing, Modelica.Fluid.Machines.BaseClasses.PumpCharacteristics.PolynomialFlow will make a fit to the points without guaranteeing that the "leftmost" point has the maximum head. The figure in this spreadsheet https://docs.google.com/spreadsheets/d/ … sp=sharing shows you the nature of the problem.

I also share a small Modelica model that can plot the pump curve (polynomial) from the nominal values. Please see this link: https://drive.google.com/file/d/1kJVp3- … sp=sharing

In conclusion, I would say that your model (parameterization) is not to blame. Instead, the implementation of PolynomialFlow should make a greater effort to ensure a monotonical decrease.

Best regards,
Rene Just Nielsen

Thanks Rene. The polynomial fit makes total sense now. However, I do have initialization problems with the pump curves. I get the following warnings for all the pumps.

"The following assertion has been violated at time 0.000000"
pumps5149.delta_head_init >= 0.0
Variable violating min constraint: 0.0 <= pumps5149.delta_head_init, has value: -30.9507"

When I try to debug I see the following equation being violated
"
    final parameter SI.Height delta_head_init = flowCharacteristic(V_flow_single_init)-flowCharacteristic(0)
        "Used for simplified initialization model";
"
How do I resolve this.

crude-train-w-5pumps.mo