super ! that was quick !
Thanks

fjld_forum@telenet.be

many thanks.
F.

I want to change the e-mail I used when I created the account but I can't seem to find where to do this in 'my profile'.
Help appreciated.

Kind regards,
F.

Ok. Thanks: it appears to be installed ... I'm just wondering if it is the right thing to use since it is not maintained any longer.

Is the openmodelica plugin for Eclipse still actively maintained ?

I tried to Install new software on Eclipse Oxygen.3 (Ubuntu 16.04) using the link http://www.ida.liu.se/labs/pelab/modeli … elica/MDT/ as found on http://www.ida.liu.se/labs/pelab/modeli … elica/MDT/ but that appears to be broken.

Hi,

Thanks for the answer. I had done it in this manner as the SweptVolumes need to move in opposite directions and their forces partially cancel each other (the difference is transferred through the external flange).

I have now produced a forceMotionInvertor as

model ForceMotionInvertor
  parameter Real L = 0.055;
  Modelica.Mechanics.Translational.Interfaces.Flange_b flange_b2 annotation(...);
  Modelica.Mechanics.Translational.Interfaces.Flange_b flange_bE annotation(...);
  Modelica.Mechanics.Translational.Interfaces.Flange_b flange_b1 annotation(...);

equation
  flange_b1.s + flange_b2.s = L;
  flange_b1.f + flange_b2.f + flange_bE.f = 0;
  flange_bE.s = flange_b2.s;

annotation(
    uses(Modelica(version = "3.2.2")));

end ForceMotionInvertor;


This appears to resolve the #equations/#variables but now I'm struggling with the signs of the various quantities (that should be another topic once I understand what I don't understand).

I'm trying to implement a double action piston using SweptVolumes but I obtain an over-constrained system with 2 equations too much. The code for the double action piston is as follows:

model DoubleActionPiston

  // mechanical connection
  Modelica.Mechanics.Translational.Interfaces.Flange_b flange annotation(
    Placement(visible = true, transformation(origin = {104, 0}, extent = {{-10, -10}, {10, 10}}, rotation = 0), iconTransformation(origin = {104, 0}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));

  //hydraulic connection to piston 1
  Modelica.Fluid.Interfaces.FluidPort_a port_1(redeclare package Medium = Modelica.Media.Incompressible.Examples.Glycol47) "feed piston 1" annotation(
    Placement(visible = true, transformation(origin = {-104, 40}, extent = {{-10, -10}, {10, 10}}, rotation = 0), iconTransformation(origin = {-104, 40}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));

  //hydralic connection to piston 2
  Modelica.Fluid.Interfaces.FluidPort_b port_2(redeclare package Medium = Modelica.Media.Incompressible.Examples.Glycol47) "feed piston 2" annotation(
    Placement(visible = true, transformation(origin = {-104, -40}, extent = {{-10, -10}, {10, 10}}, rotation = 0), iconTransformation(origin = {-104, -40}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));

  //piston parameters
  parameter Real L = 0.055 "piston stroke [m]";
  parameter Real D = 0.040 "piston diameter [m]";
  parameter Real d1 = 0.000 "piston 1 shaft diameter [m]"; // there is no shaft on that side
  parameter Real d2 = 0.010 "piston 2 shaft diameter [m]";
  parameter Real s0 = 0.0275 "piston (2) starting position [m]";
  parameter Real c1 = 0.01 "piston 1 clearance [m]";
  parameter Real c2 = 0.01 "piston 2 clearance [m]";

  //pistons modeled as Modelica.Fluid.Machines.SweptVolume
  Modelica.Fluid.Machines.SweptVolume p1(redeclare package Medium = Modelica.Media.Incompressible.Examples.Glycol47, clearance = p1.pistonCrossArea * c1, nPorts = 1, pistonCrossArea = Modelica.Constants.pi * (D ^ 2 - d1 ^ 2) / 4, s(each fixed = true, each start = L - s0)) annotation(
    Placement(visible = true, transformation(origin = {-40, 40}, extent = {{-10, -10}, {10, 10}}, rotation = -90)));

  Modelica.Fluid.Machines.SweptVolume p2(redeclare package Medium = Modelica.Media.Incompressible.Examples.Glycol47, clearance = p2.pistonCrossArea * c2, nPorts = 1, pistonCrossArea = Modelica.Constants.pi * (D ^ 2 - d2 ^ 2), s(each fixed = true, each start = s0)) annotation(
    Placement(visible = true, transformation(origin = {40, 40}, extent = {{-10, 10}, {10, -10}}, rotation = -90)));

  inner Modelica.Fluid.System system annotation(
    Placement(visible = true, transformation(origin = {-74, 70}, extent = {{-10, -10}, {10, 10}}, rotation = 0)));

equation
  //hydraulic connections to the pistons
  connect(port_2, p2.ports[1]) annotation( Line(points = {{-104, -40}, {80, -40}, {80, 38}, {50, 38}}));
  connect(port_1, p1.ports[1]) annotation(Line(points = {{-104, 40}, {-74, 40}, {-74, 42}, {-50, 42}}));


  //pistons do not move independently
  p1.flange.s = L - p2.flange.s;
 
  //piston mechanical output
  flange.s = p2.flange.s;
  flange.f = p1.flange.f - p2.flange.f;
 
  annotation(
    uses(Modelica(version = "3.2.2")));
end DoubleActionPiston;

As can be inferred from the code the double action piston is implemented as 2 SweptVolume pistons/cylinders, "p1" and "p2", with equations linking their position as well as the force and position at the piston shaft is  collected in "flange".

As mentioned I get an over constrained system with:

"""
Check of DoubleActionPiston completed successfully.
Class DoubleActionPiston has 116 equation(s) and 114 variable(s).
62 of these are trivial equation(s).
"""

What are the two variables that are missing or which 2 equations are too much ?