Problems with zero flow through Modelica.Fluid.Fittings.GenericResistances.VolumeFlowRate

[julfrei-hystar]

Running the model with the code below on OpenModelica v1.20.0 (64-bit) on Windows 11 Pro, I get the following timer values:

127.642s [ 60.1%] simulation
212.397s [100.0%] total

Setting the constant openingA to 0 and openingB to 1, the following timer values are achieved:

0.339589s [ 31.5%] simulation
1.07687s [100.0%] total

The only difference between the two lines is the element Modelica.Fluid.Fittings.GenericResistances.VolumeFlowRate.
Does anyone know the reason for this significant difference?

model fluidCircuit

  inner Modelica.Fluid.System system(T_start = 308, energyDynamics = Modelica.Fluid.Types.Dynamics.FixedInitial, m_flow_start = 16.5, massDynamics = Modelica.Fluid.Types.Dynamics.FixedInitial) annotation(
    Placement(visible = true, transformation(origin = {-90, 90}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));
  replaceable package Medium = Modelica.Media.CompressibleLiquids.LinearWater_pT_Ambient constrainedby Modelica.Media.Interfaces.PartialMedium;

  Modelica.Fluid.Vessels.OpenTank tank(redeclare package Medium = Medium, crossArea = 0.3, height = 0.8, nPorts = 3, portsData = {Modelica.Fluid.Vessels.BaseClasses.VesselPortsData(diameter = 0.065), Modelica.Fluid.Vessels.BaseClasses.VesselPortsData(diameter = 0.065, height = 0.3), Modelica.Fluid.Vessels.BaseClasses.VesselPortsData(diameter = 0.065, height = 0.3)}) annotation(
    Placement(visible = true, transformation(origin = {110, 70}, extent = {{-20, -20}, {20, 20}}, rotation = 0)));

  Modelica.Blocks.Sources.Constant const(k = 1500) annotation(
    Placement(visible = true, transformation(origin = {-10, 0}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));
  Modelica.Fluid.Machines.PrescribedPump pump(redeclare package Medium = Medium, redeclare function flowCharacteristic = Modelica.Fluid.Machines.BaseClasses.PumpCharacteristics.polynomialFlow(V_flow_nominal = {0, 0.01, 0.02, 0.026, 0.034}, head_nominal = {25.5, 25, 24, 22, 17.5}), redeclare function powerCharacteristic = Modelica.Fluid.Machines.BaseClasses.PumpCharacteristics.quadraticPower(V_flow_nominal = {0.01, 0.02, 0.03}, W_nominal = {4000, 6000, 7800}), N(start = 1500), N_nominal = 1500, V = 0.005, use_powerCharacteristic = true) annotation(
    Placement(visible = true, transformation(origin = {80, -20}, extent = {{10, -10}, {-10, 10}}, rotation = 0)));

  Modelica.Blocks.Sources.Constant openingA(k = 1) annotation(
    Placement(visible = true, transformation(origin = {50, 90}, extent = {{-10, 10}, {10, -10}}, rotation = -180)));
  Modelica.Fluid.Valves.ValveLinear valveA(redeclare package Medium = Medium, dp_nominal(displayUnit = "Pa") = 100000, m_flow_nominal = 10) annotation(
    Placement(visible = true, transformation(origin = {20, 30}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));
  Modelica.Blocks.Sources.Constant openingB(k = 0) annotation(
    Placement(visible = true, transformation(origin = {-40, 90}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));
  Modelica.Fluid.Valves.ValveLinear valveB(redeclare package Medium = Medium, dp_nominal(displayUnit = "Pa") = 100000, m_flow_nominal = 10) annotation(
    Placement(visible = true, transformation(origin = {-10, 60}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));

  Modelica.Fluid.Fittings.GenericResistances.VolumeFlowRate resistance2(redeclare package Medium = Medium, a = 30000000, b = 0) annotation(
    Placement(visible = true, transformation(origin = {-70, 60}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));
  Modelica.Fluid.Fittings.GenericResistances.VolumeFlowRate resistance1(redeclare package Medium = Medium, a = 30000000, b = 0) annotation(
    Placement(visible = true, transformation(origin = {20, -20}, extent = {{-10, 10}, {10, -10}}, rotation = -180)));

  Modelica.Fluid.Pipes.StaticPipe pipe1(redeclare package Medium = Medium, diameter = 0.1, length = 5) annotation(
    Placement(visible = true, transformation(origin = {110, 10}, extent = {{-10, -10}, {10, 10}}, rotation = -90)));
  Modelica.Fluid.Pipes.StaticPipe pipe2(redeclare package Medium = Medium, diameter = 0.1, length = 5) annotation(
    Placement(visible = true, transformation(origin = {50, -20}, extent = {{-10, 10}, {10, -10}}, rotation = -180)));
  Modelica.Fluid.Pipes.StaticPipe pipe3a(redeclare package Medium = Medium, diameter = 0.1, length = 5) annotation(
    Placement(visible = true, transformation(origin = {-40, 30}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));
  Modelica.Fluid.Pipes.StaticPipe pipe3b(redeclare package Medium = Medium, diameter = 0.1, length = 5) annotation(
    Placement(visible = true, transformation(origin = {-40, 60}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));
  Modelica.Fluid.Pipes.StaticPipe pipe4a(redeclare package Medium = Medium, diameter = 0.1, length = 5) annotation(
    Placement(visible = true, transformation(origin = {50, 30}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));
  Modelica.Fluid.Pipes.StaticPipe pipe4b(redeclare package Medium = Medium, diameter = 0.1, length = 5) annotation(
    Placement(visible = true, transformation(origin = {50, 60}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));
  
equation
  connect(pipe3b.port_b, valveB.port_a) annotation(
    Line(points = {{-30, 60}, {-20, 60}}, color = {0, 127, 255}));
  connect(pipe3a.port_b, valveA.port_a) annotation(
    Line(points = {{-30, 30}, {10, 30}}, color = {0, 127, 255}));
  connect(resistance1.port_a, pipe2.port_b) annotation(
    Line(points = {{30, -20}, {40, -20}}, color = {0, 127, 255}));
  connect(valveB.port_b, pipe4b.port_a) annotation(
    Line(points = {{0, 60}, {40, 60}}, color = {0, 127, 255}));
  connect(valveA.port_b, pipe4a.port_a) annotation(
    Line(points = {{30, 30}, {40, 30}}, color = {0, 127, 255}));
  connect(resistance2.port_a, resistance1.port_b) annotation(
    Line(points = {{-80, 60}, {-90, 60}, {-90, -20}, {10, -20}}, color = {0, 127, 255}));
  connect(pipe1.port_a, tank.ports[1]) annotation(
    Line(points = {{110, 20}, {110, 50}}, color = {0, 127, 255}));
  connect(pipe4a.port_b, tank.ports[2]) annotation(
    Line(points = {{60, 30}, {70, 30}, {70, 50}, {110, 50}}, color = {0, 127, 255}));
  connect(pipe4b.port_b, tank.ports[3]) annotation(
    Line(points = {{60, 60}, {70, 60}, {70, 50}, {110, 50}}, color = {0, 127, 255}));
  connect(pipe2.port_a, pump.port_b) annotation(
    Line(points = {{60, -20}, {70, -20}}, color = {0, 127, 255}));
  connect(pump.port_a, pipe1.port_b) annotation(
    Line(points = {{90, -20}, {110, -20}, {110, 0}}, color = {0, 127, 255}));
  connect(const.y, pump.N_in) annotation(
    Line(points = {{1, 0}, {80, 0}, {80, -10}}, color = {0, 0, 127}));
  connect(pipe3a.port_a, resistance1.port_b) annotation(
    Line(points = {{-50, 30}, {-70, 30}, {-70, -20}, {10, -20}}, color = {0, 127, 255}));
  connect(resistance2.port_b, pipe3b.port_a) annotation(
    Line(points = {{-60, 60}, {-50, 60}}, color = {0, 127, 255}));
  connect(openingB.y, valveB.opening) annotation(
    Line(points = {{-28, 90}, {-10, 90}, {-10, 68}}, color = {0, 0, 127}));
  connect(openingA.y, valveA.opening) annotation(
    Line(points = {{39, 90}, {20, 90}, {20, 38}}, color = {0, 0, 127}));
  annotation(
    Diagram(coordinateSystem(extent = {{-100, 100}, {140, -40}})),
    uses(Modelica(version = "4.0.0")),
    version = "");
end fluidCircuit;