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Fluid library to complicated for OMC?

#10428  Permalink Top

Fluid library to complicated for OMC?

Jan-07-21 13:32:38

I’m still struggling with getting the fluid library to work consistently. I’ve created a pretty simple model which uses a PID to control a pump that pumps against a valve that creates some back pressure.

This model works perfectly in Dymola but in OMC I get all kinds of errors both with this and if I do changes. Could any one help with what I’m doing wrong? Or is the fluid library just to “complicated” for OMC at this stage?

Model:

Code:


model test

replaceable package Medium =

      Modelica.Media.Water.ConstantPropertyLiquidWater                           constrainedby

    Modelica.Media.Interfaces.PartialMedium "Medium in the component"

      annotation (choicesAllMatching = true);

  Modelica.Fluid.Sources.FixedBoundary boundary(redeclare package Medium = Medium, nPorts = 1, p = 160000, use_p = true)  annotation(

    Placement(visible = true, transformation(origin = {-86, -36}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));

  Modelica.Fluid.Sources.FixedBoundary boundary1(redeclare package Medium = Medium, nPorts = 1, p = system.p_ambient, use_p = true)  annotation(

    Placement(visible = true, transformation(origin = {64, -36}, extent = {{-10, -10}, {10, 10}}, rotation = 180)));

  inner Modelica.Fluid.System system(p_start(displayUnit = "Pa") = 160000)  annotation(

    Placement(visible = true, transformation(origin = {-84, 78}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));

  Modelica.Fluid.Valves.ValveIncompressible valveIncompressible(redeclare package Medium = Medium, CvData = Modelica.Fluid.Types.CvTypes.OpPoint, dp_nominal(displayUnit = "Pa") = 50000, m_flow(fixed = false), m_flow_nominal = 250, opening_nominal = 1)  annotation(

    Placement(visible = true, transformation(origin = {24, -36}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));

  Modelica.Fluid.Machines.PrescribedPump pump(redeclare package Medium = Medium, redeclare function flowCharacteristic =

        Modelica.Fluid.Machines.BaseClasses.PumpCharacteristics.quadraticFlow (

          V_flow_nominal={0,0.25,0.5}, head_nominal={100,60,0}), N(fixed = false), N_nominal = 1200, V = 1, checkValve = true, energyDynamics = Modelica.Fluid.Types.Dynamics.FixedInitial, massDynamics = Modelica.Fluid.Types.Dynamics.FixedInitial, use_N_in = true) annotation(

    Placement(visible = true, transformation(origin = {-58, -36}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));

  Modelica.Blocks.Sources.Constant setpoint(k = 0.2) annotation(

    Placement(visible = true, transformation(origin = {-83, 57}, extent = {{-5, -5}, {5, 5}}, rotation = 0)));

  Modelica.Fluid.Sensors.VolumeFlowRate volumeFlowRate(redeclare package Medium = Medium) annotation(

    Placement(visible = true, transformation(origin = {-26, -36}, extent = {{-6, -6}, {6, 6}}, rotation = 0)));

  Modelica.Blocks.Continuous.LimPID pid(Ti = 0.1, controllerType = Modelica.Blocks.Types.SimpleController.PI, k = 125, yMax = 1200, yMin = 300, y_start = 300) annotation(

    Placement(visible = true, transformation(origin = {-54, 60}, extent = {{-6, -6}, {6, 6}}, rotation = 0)));

  Modelica.Blocks.Sources.Constant constant1(k = 0.7) annotation(

    Placement(visible = true, transformation(origin = {1, 13}, extent = {{-5, -5}, {5, 5}}, rotation = 0)));

equation

  connect(valveIncompressible.port_b, boundary1.ports[1]) annotation(

    Line(points = {{34, -36}, {54, -36}}, color = {0, 127, 255}));

  connect(boundary.ports[1], pump.port_a) annotation(

    Line(points = {{-76, -36}, {-68, -36}}, color = {0, 127, 255}));

  connect(pump.port_b, volumeFlowRate.port_a) annotation(

    Line(points = {{-48, -36}, {-32, -36}}, color = {0, 127, 255}));

  connect(setpoint.y, pid.u_s) annotation(

    Line(points = {{-78, 58}, {-61, 58}, {-61, 60}}, color = {0, 0, 127}));

  connect(volumeFlowRate.V_flow, pid.u_m) annotation(

    Line(points = {{-26, -29}, {-34, -29}, {-34, 50}, {-54, 50}, {-54, 53}}, color = {0, 0, 127}));

  connect(pid.y, pump.N_in) annotation(

    Line(points = {{-47, 60}, {-24, 60}, {-24, 38}, {-58, 38}, {-58, -26}}, color = {0, 0, 127}));

  connect(volumeFlowRate.port_b, valveIncompressible.port_a) annotation(

    Line(points = {{-20, -36}, {14, -36}}, color = {0, 127, 255}));

  connect(constant1.y, valveIncompressible.opening) annotation(

    Line(points = {{6.5, 13}, {24.5, 13}, {24.5, -29}}, color = {0, 0, 127}));

  annotation(

    uses(Modelica(version = "3.2.3")));

end test;

#10621  Permalink Top

Re: Fluid library to complicated for OMC?

Mar-08-21 11:06:23

Tested in v1.17.0-dev.beta3 (64-bit) (windows) still loads of errors

#10622  Permalink Top

Re: Fluid library to complicated for OMC?

Mar-08-21 14:35:13

This seems like a bug. Compiling this with the new front-end gets you:

Code:


[1] 14:52:43 Symbolic Warning

The model contains alias variables with redundant start and/or conflicting nominal values. It is recommended to resolve the conflicts, because otherwise the system could be hard to solve. To print the conflicting alias sets and the chosen candidates please use -d=aliasConflicts.



[2] 14:52:43 Translation Error

Jacobian StateSetJac0 contains non-linear components. This indicates a singular system or internal generation errors.

This is the errors you're getting when compiling? Also there are some errors during simulation:

Code:


C:/temp/FluidTest/FluidTest.exe -port=56775 -logFormat=xmltcp -override=startTime=0,stopTime=1,stepSize=0.002,tolerance=1e-6,solver=dassl,outputFormat=mat,variableFilter=.* -r=C:/temp/FluidTest/FluidTest_res.mat -w -lv=LOG_STATS -inputPath=C:/temp/FluidTest -outputPath=C:/temp/FluidTest

Matrix singular!

The initialization finished successfully with 3 homotopy steps.

Error solving nonlinear system 260 at time 0.366001

Error solving nonlinear system 260 at time 0.366001

nonlinear system 260 fails: at t=0.366001

[1] Real pid.limiter.u(start=0, nominal=1)

[2] Real pump.medium.p(start=160000, nominal=100000)

[3] Real pump.s(start=0, nominal=1)

Simulation process failed. Exited with code -1.

The old frontend seems to simulate this fine. I will make a bug report with this.

#10623  Permalink Top

Re: Fluid library to complicated for OMC?

Mar-08-21 14:41:13

Bug report opened: https://trac.openmodelica.org/OpenModelica/ticket/6410

#10625  Permalink Top

Re: Fluid library to complicated for OMC?

Mar-09-21 05:44:32

Thanks, I seem to end up in something like this every time my fluid models start getting complex

#11071  Permalink Top

Re: Fluid library to complicated for OMC?

Jul-26-21 07:28:36

Tested again on v1.18.0-dev.beta1. Still getting same errors. I see there is no issue for this on github, trac issue here https://trac.openmodelica.org/OpenModelica/ticket/6410. Should I open a new one on github?

#11097  Permalink Top

Re: Fluid library to complicated for OMC?

Sep-06-21 07:58:38

Same issue with latest v1.18.0. I've opened a new issue on github https://github.com/OpenModelica/OpenMod … ssues/7868

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