Hi,

I'm trying to model a train, but it seems that the current model is not solvable. I'm baffled how to initialise the system to obtain a solution. 

In the model there are 5 main components: train, motor, driver, track and signalling system. Train movement is governed by Newton's second law
m*a=f-r,
where:
f - tractive force from the motor, depends on train velocity;
r - running resistance, depends on train position;
Signalling system provides the driver with information regarding speed limits, which is a function of the train position as well.
So, both inputs f and r depend on the train position, which seems to be the main cause of the problem.

A simplified model is listed below. I would greatly appreciate it if you could give me any advise regarding this issue.

model testmodel
  vehicle train;
  controller driver;
  propulsion motor;
  signalling signallingSystem;
  track mainline;
equation
  connect(train.v, driver.speedometer);
  connect(driver.poweringSignal, motor.poweringSignal);
  connect(motor.f, train.f);
  connect(train.s, signallingSystem.s);
  connect(signallingSystem.PSR, driver.PSR);
  connect(train.s,mainline.s);
  connect(mainline.r,train.r);
end testmodel;

class vehicle
  parameter Real m=170000; //mass of the vehicle
  Real a; //acceleraion
  input Real f; //tractive force derived from the propulsion system
  input Real r; //running resistance due track gradient
  output Real v; //speed
  output Real s; //displacement
equation
  // equation of motion, Newton's second law
  v=der(s);
  a=der(v);
  m*a=f-r;
end vehicle;


class controller
  input Real speedometer; //speed information from the vehicle
  input Real PSR; //permament speed restriction from signalling system
  output Boolean poweringSignal; //control signal to the propulsion system
equation
  poweringSignal = if speedometer>PSR then false else true;
end controller;


class propulsion
  input Boolean poweringSignal; //powering signal from the controller
  output Real f; //tractive force to the vehicle
equation
  //f = 120000;
  f = if poweringSignal==true then 120000 else 0; //tractive force
end propulsion;


class signalling
  output Real PSR (start=100); //permament speed restriction
  input Real s; //current position
equation
  PSR = if s<1 then 0.3 else 10;
end signalling;


class track
  input Real s;//position of the vehicle
  output Real r (start=0, fixed=false);//running resistance depends on position
equation
  r=if s<5 then 10000 else 50000;
end track;


System run on:
Open Modelica 1.5.0 RC2
Win XP Pro 64-bit