External media failed with Modelica.Fluid.Pipes.DynamicPipe

[anushkaperera]

I am trying to simulate the following model, which failed (I am using Dymola):

Here is the error message:

I could simulate the following model, here I am using Modelica.Fluid.Pipes.StaticPipe segment:

I am using CoolProp via ExternalMedia 4.0.0.

The following is the full code:

Testing.zip

[justnielsen]

The error is not necessarily due to the use of ExternalMedia but rather to the setup of the dynamic model:

In the top figure, it looks as if you have chosen the default modelStructure=av_vb for the pipe. This means that the downstream pressure boundary (boundary1)is directly connected to a 'volume element' in the pipe at port_b. This binding, in turn, forces the pressure derivative in the volume element to be zero, resulting in the failure to differentiate the equation system.

Solution: set modelStructure=av_b to decouple the pressure in the (most downstream) volume from the fixed pressure in boundary1 through a flow model.

[anushkaperera]

Thanks!

Could you run successfully with suggested solution? I could not. Did you use Dymola? If I had used package Medium_ph = Modelica.Media.Water.StandardWaterOnePhase; instead, for example, still the same code would have worked without touching modelStructure.

[thorade]

It seems like the tool wants to differentiate for index reduction, but the function it tries to differentiate is setState_pTx, a function that uses records as output. Functions with records as input or output cannot be differentiated.
There are two options:

• Avoid the high index problem and the need to reduce the index. High index problem typically occurs by connecting two volumes together (and therefore forcing pressure state to be identical). This is what was suggested above, change structure to av_b.
• Use a scalar function like density_pTx and similar instead of setState_pTx, these can in theory be differentiated.

In both cases, I think this is an issue in the model you are trying to build, and not in the ExternalMedia library

[plevisse-naarea]

Hello,
I've been encountering the same issues.
Dymola 2023, with VS 2022.
ExternalMedia 4.1.1

model Test "Crash-proof standalone model" extends Modelica.Icons.Package; // 1. Mandatory global fluid system manager inner Modelica.Fluid.System system(allowFlowReversal = true); // 2. THE CRITICAL FIX: Declare a static package (REMOVED 'replaceable') package LocalSCO2 = ExternalMedia.Media.CoolPropMedium(mediumName = "CO2", substanceNames = {"CO2"}, ThermoStates = Modelica.Media.Interfaces.Choices.IndependentVariables.pT, singleState = false, onePhase = true, Temperature(min = 285, max = 2000, start = 315, nominal = 315), AbsolutePressure(min = 6.5e6, max = 1.0e8, start = 8e6, nominal = 8e6), SpecificEnthalpy(start = 5.0e5, nominal = 5.0e5)); // 3. Components instantiated with the stable static package reference Modelica.Fluid.Sources.Boundary_pT boundary(nPorts = 1, redeclare package Medium = LocalSCO2, p = 9.0e6, T = 273.15 + 400.0) annotation ( Placement(transformation(origin = {-66, 24}, extent = {{-10, -10}, {10, 10}}))); // Upstream high pressure: 9.0 MPa // Upstream temperature: 400 °C Modelica.Fluid.Valves.ValveCompressible valveCompressible(redeclare package Medium = LocalSCO2, CvData = Modelica.Fluid.Types.CvTypes.Av, Av = 1.0e-4, p_nominal = 9.0e6, dp_nominal = 1.5e6, m_flow_nominal(fixed = false), m_flow(start = 1.0), dp(start = 1.5e6)) annotation ( Placement(transformation(origin = {-18, 24}, extent = {{-10, -10}, {10, 10}}))); // 1. PROVIDE THE MANDATORY VALUES FOR THE COMPILER // 2. THE ULTIMATE TRICK: Provide a value but un-fix it so it doesn't fight the loop Modelica.Fluid.Sources.Boundary_pT boundary1(nPorts = 1, redeclare package Medium = LocalSCO2, p = 7.5e6, T = 273.15 + 35.0) annotation ( Placement(transformation(origin = {60, 24}, extent = {{10, -10}, {-10, 10}}))); // Downstream low pressure: 7.5 MPa Modelica.Blocks.Sources.Ramp ramp(height = -0.5, duration = 10, offset = 1, startTime = 5) annotation ( Placement(transformation(origin = {-42, 68}, extent = {{-10, -10}, {10, 10}}))); Modelica.Fluid.Pipes.DynamicPipe pipe(redeclare package Medium = LocalSCO2, length = 10, diameter = 0.1, m_flows(each start = 1)) annotation ( Placement(transformation(origin = {20, 22}, extent = {{-10, -10}, {10, 10}}))); equation connect(boundary.ports[1], valveCompressible.port_a) annotation ( Line(points = {{-56, 24}, {-28, 24}}, color = {0, 127, 255})); connect(ramp.y, valveCompressible.opening) annotation ( Line(points={{-31,68},{-18,68},{-18,32}}, color = {0, 0, 127})); connect(valveCompressible.port_b, pipe.port_a) annotation ( Line(points = {{-8, 24}, {10, 24}, {10, 22}}, color = {0, 127, 255})); connect(pipe.port_b, boundary1.ports[1]) annotation ( Line(points = {{30, 22}, {50, 22}, {50, 24}}, color = {0, 127, 255})); end Test;

I keep getting this error : "Must translate function pipe.getCriticalPressure_Unique178.

Internal error: trying to compile function but did not find it."

This does not occur in OMC, only in Dymola... Can't quite understand why.

It's linked to the pipe, I've managed to run other state computations with ExternalMedia in other standalone components.

[plevisse-naarea]

As an addition on this topic : I've done the most MWE possible with just the pipe :

model test_pipe
  import Modelica.Fluid.Types.ModelStructure;

  // --- . Composants ---
  Modelica.Fluid.Pipes.DynamicPipe pipe_hot(
    redeclare package Medium =ExternalMedia.Examples.CO2CoolProp,
    nNodes=2,
    length=2,
    isCircular=true,
    diameter=0.05,
    use_HeatTransfer=true,
    redeclare model HeatTransfer =
        Modelica.Fluid.Pipes.BaseClasses.HeatTransfer.IdealFlowHeatTransfer);

end test_pipe;

This fails directly with :

[plevisse-naarea]

Update (solved) : after a lot of tweaking in the variable editor I've found the culprit.
Advanced.RelyOnCompiledFunctions = 1 did it for me !