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modelicadymola

How to find the variables selected by the tearing algorithm in Dymola

I'd like to find the set of variables selected by the tearing algorithm in Dymola. so that I could know which variables link different parts of the system together. But I am not sure how to show these variables in Dymola. I checked the help document of Dymola but didn't find anything related to how to show these variables. enter image description here

Solution

  • You should be able to see it in dsmodel.mof, which is created after setting Advanced.OutputModelicaCode = true; or activating it in the UI using "Simulation Setup -> Translation -> Generate listing of translated Modelica code in dsmodel.mof".

    Dymola will generate the relevant code in the // Torn part. Searching for this in dsmodel.mof is a good option as the file can get pretty big.

    The exact code will depend on the type of problem. Two examples:

    (1) A rather simple electrical like this RLC-circuit with algebraic loop will be solved symbolically, with the resulting code:

    ...
// Linear system of equations
// Tag: simulation.linear[1]
  // Symbolic solution
    /*  Original equation
    resistor1.v = constantVoltage.V-resistor.v-capacitor.v;
    */
    resistor1.p.i :=  -(capacitor.v-constantVoltage.V+resistor.R_actual*
      inductor.i)/(resistor.R_actual+resistor1.R_actual);
  // Torn part
    resistor.p.i := inductor.i+resistor1.p.i;
    resistor.v := resistor.R_actual*resistor.p.i;
    resistor1.v := resistor1.R_actual*resistor1.p.i;
// End of linear system of equations
...

    In this case the tearing variable is resistor1.p.i, with the equation to compute it stated directly there.

    (2) Translating Modelica.Thermal.FluidHeatFlow.Examples.TwoMass will give you a non-nonlinear case, i.e. when an iteration is needed to solve the system of equations. You should find something like:

    ...
  // Start values for iteration variables of non-linear system of 1 equations: 
  //   pipe2.V_flow(start = 0)
algorithm // Torn part
  pipe2.flowPort_a.m_flow := pipe2.V_flow*pipe2.medium.rho;
  pipe1.flowPort_a.m_flow :=  -(pipe2.flowPort_a.m_flow+ambient1.flowPort.m_flow);
...

    The tearing variable is pipe2.V_flow in this case, with the start value for the iteration.