"mixed system involving complex equation"

[fixed-term.Sven.Baetzing@…]

Hello,

I am using OMEdit and I wrote a component which should simulate a 1-D mass with friction on a moveable ground.
The friction is included by the mean of stribeck-friction.

Depending on the frictionstate (slip, stick) the friction force and the accerlation of both masses are calculated in the equation part as follows:

if frictionMode == Stick then
    Ffric = flange_a.f - (flange_a.f + flange_b.f) / (mA + mB) * mA;
    aA = (flange_a.f + flange_b.f + g * (mA + mB)) / (mA + mB);
    aB = (flange_a.f + flange_b.f + g * (mA + mB)) / (mA + mB);
  elseif frictionMode == StartSlip then
    Ffric = Fc * sign(deltav) + vis * deltav + sticktionForce * exp(-stribeckFactor * abs(deltav)) * sign(deltav);
    aA = (flange_a.f - Ffric + g * mA) / mA;
    aB = (flange_b.f + Ffric + g * mB) / mB;

When I simulate the model I get the message that my model contains a mixed system involving algorithms or other complex-equations.

I think it's a rather easy component and not very complex algorithm included.
I'm rather sure that this lines make im stop simulate because I tested the model without them and it worked.

I hope you can help me to solve my problem.
Thank you for your help.

Complete model:

model TwoMassFriction
  import SI = Modelica.SIunits;
  extends Modelica.Mechanics.Translational.Interfaces.PartialTwoFlanges;
  // FUNCTION FOR STRIBECKFACTOR
  function stribeckFunction
    // INPUTS
    input Real sticktionForce;
    input Real vis;
    input Real vh;
    // OUTPUTS
    output Real stribeckFactor;
  algorithm
    if not sticktionForce == 0 then 
      if not vis == 0 then 
        stribeckFactor:=-log(vis * vh / sticktionForce) / vh;
        for i in 0:10 loop
                  stribeckFactor:=stribeckFactor - (-stribeckFactor * sticktionForce * exp(-stribeckFactor * vh) + vis) / (sticktionForce * exp(-stribeckFactor * vh) * (stribeckFactor * vh - 1));
        end for;
      else
        stribeckFactor:=-log(0.000001 / sticktionForce) / vh;
      end if;
    else

    end if;
  end stribeckFunction;
  parameter SI.Mass mA = 1 "mass body A";
  parameter SI.Mass mB = 1 "mass body 1";
  parameter SI.Force Fh = 10 "static friction";
  parameter SI.Force Fc = 5 "sliding friction";
  parameter Real vis(unit = "N.s/m") = 0 "viscous friction value";
  parameter SI.Velocity vh = 0.000001 "static velocity limit";
  parameter SI.Acceleration g = -9.81 "gravity";
  parameter Boolean initialize_sA = false;
  parameter Boolean initialize_sB = false;
  parameter Boolean initialize_vA = false;
  parameter Boolean initialize_vB = false;
  parameter SI.Position sA_init = 0;
  parameter SI.Position sB_init = 0;
  parameter SI.Velocity vA_init = 0;
  parameter SI.Velocity vB_init = 0;
  SI.Position sA;
  SI.Position sB;
  SI.Velocity vA;
  SI.Velocity vB;
  SI.Acceleration aA;
  SI.Acceleration aB;
  SI.Force Ffric "total friction";
  SI.Force deltaf "difference of forces";
  SI.Velocity deltav "difference of velocities";
  Integer frictionMode(start = Stick);
protected
  parameter Real stribeckFactor = stribeckFunction(sticktionForce, vis, vh);
  parameter SI.Force sticktionForce = Fh - Fc;
  constant SI.Velocity velLimit = 0.000005;
  constant Integer None = 0;
  constant Integer Stick = 1;
  constant Integer StartSlip = 2;
  constant Integer Slip = 3;
initial equation
  if initialize_sA then
    sA = sA_init;
  end if;
  if initialize_vA then
    vA = vA_init;
  end if;
  if initialize_sB then
    sB = sB_init;
  end if;
  if initialize_vB then
    vB = vB_init;
  end if;
  if Fh == 0 and Fc == 0 then
    frictionMode = None;
  end if;
algorithm
  when frictionMode == StartSlip and abs(deltav) > velLimit then
      frictionMode:=Slip;  elsewhen frictionMode == Stick and abs(Ffric) > Fh then
    frictionMode:=StartSlip;
elsewhen frictionMode == Slip and abs(deltav) < velLimit / 5 then
    frictionMode:=Stick;
  end when;
equation
  assert(mA > 0, "Negative mass is not allowed!");
  assert(mB > 0, "Negative mass is not allowed!");
  assert(Fh > Fc, "The Static friction should be larger than the Running friction!");
  sA = flange_a.s;
  sB = flange_b.s;
  vA = der(flange_a.s);
  vB = der(flange_b.s);
  aA = der(vA);
  aB = der(vB);
  deltav = vA - vB;
  deltaf = flange_a.f - flange_b.f;
  if frictionMode == None then
    Ffric = 0;
    aA = (flange_a.f - deltav * vis + mA * g) / mA;
    aB = (flange_b.f - deltav * vis + mB * g) / mB;
  elseif frictionMode == Stick then
    Ffric = flange_a.f - (flange_a.f + flange_b.f) / (mA + mB) * mA;
    aA = (flange_a.f + flange_b.f + g * (mA + mB)) / (mA + mB);
    aB = (flange_a.f + flange_b.f + g * (mA + mB)) / (mA + mB);
  elseif frictionMode == StartSlip then
    Ffric = Fc * sign(deltav) + vis * deltav + sticktionForce * exp(-stribeckFactor * abs(deltav)) * sign(deltav);
    aA = (flange_a.f - Ffric + g * mA) / mA;
    aB = (flange_b.f + Ffric + g * mB) / mB;
  elseif frictionMode == Slip then
    Ffric = Fc * sign(deltav) + vis * deltav + sticktionForce * exp(-stribeckFactor * abs(deltav)) * sign(deltav);
    aA = (flange_a.f - Ffric + g * mA) / mA;
    aB = (flange_b.f + Ffric + g * mB) / mB;
  else
    Ffric = 0;
    aA = 0;
    aB = 0;
  end if;

[Lennart Ochel]

There is no support for mixed systems at all - yet. See #2432.

[Lennart Ochel]

I couldn’t check this model, because it is not attached completely. Please, check if this is fixed due to r22641.

[Lennart Ochel]

I close this ticket, because mixed system handling is fixed and I cannot reproduce the example from the description. If there are still issues, please check #1478 and reopen this ticket.