Hello,

Can anyone give an advice on connections between nested and top classes? I am a bit confused how it works. I have two models for comparison:
1. vehicle and its motor as two separate classes
2. motor as a nested class of the vehicle class

I use the standard mechanical connectors, Flange_a and Flange_b for communication between these classes.
In the first case it works perfectly fine. However, the second one, it returns either an error of structural singularity or an error of overdetermined model. I tried to encapsulate the motor class, but it did not work either.

Can anyone help me with this, please?
Here are simplified models:

1. vehicle and its motor as two separate classes
model test_model
  vehicle test_vehicle;
  motor test_motor;
equation
  connect(test_vehicle.vehicle_connector, test_motor.motor_connector);
end test_model;

class vehicle
  Real velocity,displacement (start=0);
  parameter Real mass = 170;
  Flange_a vehicle_connector;
equation
  velocity = der(displacement);
  mass*der(velocity) = -vehicle_connector.f; // vehicle is powered by a motor
  vehicle_connector.s = displacement;
end vehicle;

class motor
  Real speed;
  Flange_b motor_connector;
equation
  speed = der (motor_connector.s);
  motor_connector.f = 100+0.2*speed; 
end motor;

connector Flange_a
  Real s;
  flow Real f;
end Flange_a;

connector Flange_b
  Real s;
  flow Real f;
end Flange_b;


2. motor as a nested class of the vehicle class
class vehicle
  Real velocity,displacement (start=0);
  parameter Real mass = 170;
  Flange_a vehicle_connector;
  motor testmotor;
equation
  connect(vehicle_connector, testmotor.motor_connector);
  velocity = der(displacement);
  mass*der(velocity) = -vehicle_connector.f; // vehicle is powered by a motor
  vehicle_connector.s = displacement;
end vehicle;

class motor
  Real speed;
  Flange_b motor_connector;
equation
  speed = der (motor_connector.s);
  motor_connector.f = 100+0.2*speed; 
end motor;

connector Flange_a
  Real s;
  flow Real f;
end Flange_a;

connector Flange_b
  Real s;
  flow Real f;
end Flange_b;

Any advice is highly appreciated.
Many thanks,
Ivan

PS: My system: WinXP Pro, OpenModelica 1.5 RC2