Start value problem in der() function of medium - Modelica

alimuradpasha

I am modeling with Modelica in Ansys Twin builder. I encounter with an initialization error when I compile the code, although I give initialization values. Error is as follows;

Iteration variable "der(Hochdrucktank.medium.h)" is missing start value!

Iteration variable "der(Niederdrucktank.medium.h)" is missing start value!

Iteration variable "der(Swept1.medium.p)" is missing start value!

The code is as follows;

Iteration variable "der(Swept1.medium.p)" is missing start value!

model Hochdruckreiniger2
    Real dummyStart_V_hochdrucktank(start=0);
    Real dummyStart_V_niederdrucktank(start=0);
    Real dummyStart_h_sweptvolume(start=0);
    Real dummyStart2(start=0);
    Real dummyStart3(start=0);
    //Component(s)
    Modelica.Fluid.Machines.SweptVolume Swept1 (
        pistonCrossArea = 0.0001131,
        clearance = 0.000002,
        portsData = {Modelica.Fluid.Vessels.BaseClasses.VesselPortsData(diameter=
        0.1),Modelica.Fluid.Vessels.BaseClasses.VesselPortsData(diameter=
        0.1)},
        redeclare package Medium = Modelica.Media.Water.StandardWater,
        nPorts = 2,
        use_portsData = true,
        p_start = 100,
        use_T_start = true;
    inner Modelica.Fluid.System system;
    Modelica.Fluid.Vessels.OpenTank Niederdrucktank (
        redeclare package Medium = Modelica.Media.Water.StandardWater,
        nPorts = 1,
        height = 40.84,
        crossArea = 10,
        portsData = {Modelica.Fluid.Vessels.BaseClasses.VesselPortsData(diameter=
        0.1)},
        h_start = 100,
        V(start = 10));
    Modelica.Fluid.Vessels.OpenTank Hochdrucktank (
        redeclare package Medium = Modelica.Media.Water.StandardWater,
        nPorts = 1,
        height = 4997,
        crossArea = 10,
        portsData = {Modelica.Fluid.Vessels.BaseClasses.VesselPortsData(diameter=
        0.1)},
        h_start = 100,
        V(start = 100));
    Modelica.Mechanics.Translational.Sources.Position Posit1 (exact = true);
    Modelica.Fluid.Valves.ValveIncompressible Hochdruckventile (
        dp_nominal = 66.6175,
        m_flow_nominal = 0.04873,
        rho_nominal = 1019.921,
        opening = opening_HP,
        redeclare package Medium = Modelica.Media.Water.StandardWater);
    Modelica.Fluid.Valves.ValveIncompressible Niederdruckventile (
        dp_nominal = 65.21,
        m_flow_nominal = 0.04873,
        rho_nominal = 998.388,
        opening = opening_NP,
        redeclare package Medium = Modelica.Media.Water.StandardWater);
    Modelica.Blocks.Sources.Sine Sine1 (amplitude = 0.000000629669, freqHz = 46.6666, offset = 0.00000313588);


equation
    T_per=pi/(180*3600*N/60);//Radian  
        f=((V_max-V_tod)/2)*sin((2*pi*time*T_per)+(V_tod+(V_max-V_tod)/2));
          if der(f)>=0 then
            opening_NP=1;
            opening_HP=0;
           else
            opening_NP=0;
            opening_HP=1;
          end if;
    dummyStart_V_hochdrucktank=der(Hochdrucktank.V);
    dummyStart_V_niederdrucktank=der(Niederdrucktank.V);
    dummyStart2=der(Hochdrucktank.medium.h);
    dummyStart3=der(Niederdrucktank.medium.h);
    dummyStart_h_sweptvolume=der(Swept1.medium.p);
    //Connection(s)
    connect(Posit1.flange, Swept1.flange);
    connect(Hochdrucktank.ports[1], Hochdruckventile.port_a);
    connect(Hochdruckventile.port_b, Swept1.ports[2]);
    connect(Niederdrucktank.ports[1], Niederdruckventile.port_a);
    connect(Niederdruckventile.port_b, Swept1.ports[1]);
    connect(Sine1.y, Posit1.s_ref);
end  Hochdruckreiniger2;

Do you know how to solve this problem? Thanks for your helps in advance!

dheerajvemula

Hi, Is the message - "Iteration variable "der(Hochdrucktank.medium.h)" is missing start value!" generated as a warning or error ? If it is a warning, you don't have worry about it. The model should compile successfully.

JoseLuisGonzalez

Inside Twin Builder, you can access Modelica examples for the different libraries, you can view the diagram and Modelica text. Also, as a general rule, it is always a good practice to start building systems from simple to more complex in incremental steps, that can help in identifying problems.

Unfortunately, a full answer to this question is beyond the scope of Ansys employees. Hopefully another member can help you.