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Weird simulation at Basic hydraulic cylinder - Derivative[solved]
Weird simulation at Basic hydraulic cylinder - Derivative[solved]
Hi!
This is my setup:
It's only the cylinder I have some problems with. The cylinder's code lines are those:
Code:
model Double_acting_cylinder "Hydraulic cylinder"
// Mass of piston and rod
parameter Modelica.SIunits.Mass M "Mass of piston and rod";
// Area of piston cap area
parameter EasyHydraulics.Setup.AreaUnit A1 "Area cap side";
// Area of piston rod area
parameter EasyHydraulics.Setup.AreaUnit A2 "Area rod side";
// Rod lenght
parameter Modelica.SIunits.Length L "Length of rod";
// Volymetric efficiency of cylinder
parameter EasyHydraulics.Setup.EfficiencyUnit ve(start = 0) "Volymetric efficiency";
// Mechanic efficiency of cylinder
parameter EasyHydraulics.Setup.EfficiencyUnit me(start = 0) "Mechanic efficiency";
// Position of cylinder
Modelica.SIunits.Position s(start = 0) "Position rod";
// Velocity of cylinder
Modelica.SIunits.Position v(start = 0) "Velocity rod";
// Input of cylinder
EasyHydraulics.Setup.Connecter C1 annotation(...);
// Output of cylinder
EasyHydraulics.Setup.Connecter C2 annotation(...);
// Connection rod
Modelica.Mechanics.Translational.Interfaces.Flange_b rod annotation(...);
equation
// Compute the flow out and in
C2.Q = C1.Q*A2/A1;
// Compute the position
rod.s = s;
// Compute the derivative of position
v = der(s);
// ODE equation of the cylinder
10 * A1 * C1.P * me = M * der(v) + rod.f + 10 * A2 * C2.P * me;
annotation(...)
end Double_acting_cylinder;
Below the "equation". I first compute the output flow at the cylinder. Then I sett the rod's position equal to the rod position s. Then I take the derivative of position s to find the velocity v.
After I have found the velocity v, I simulate the ordinary differential equation:
10*Cap Area * Pressure at Cap side * mechanical efficiency = Mass of (rod + piston)*accleration + force at the rod + 10*Area rod side * pressure at rod side * mechanical efficiency.
Notice that I multiply the areas with 10, because the area's is in cm^2 and not m^2. Hydraulic units.
My question is: Why does this not working? I think it has something to do with the values I sett the position of the rod because the results of position and velocity of the rod look like this:
Is this right thing to do? Set the position of rod
Code:
rod.s = s;
Then get the force from the spring.
Code:
rod.f
Edit:
The code says:
Code:
// Velocity of cylinder
Modelica.SIunits.Position v(start = 0) "Velocity rod"
But it should be
Code:
// Velocity of cylinder
Modelica.SIunits.Velocity v(start = 0) "Velocity rod"
The results are the same anyway.
Thank you
Re: Weird simulation at Basic hydraulic cylinder - Derivative[solved]
Found the solution!
Insted of this:
Code:
// ODE equation of the cylinder
10 * A1 * C1.P * me = M * der(v) + rod.f + 10 * A2 * C2.P * me;
use this:
Code:
// ODE equation of the cylinder
M * der(v) = 10 * A1 * C1.P * me + rod.f + 10 * A2 * C2.P * me;
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