Simulation Task 3 – Load Dynamics in Hopsan
In this simulation task, load dynamics will be studied using Hopsan. The program has been developed
at the division Fluid and Mechatronic Systems at Linköping University since the late 1970s, and has
played an important role in research as well as in education. It has also been used widely in the
industry. In 2009 the development of a new simulation platform was initiated at the division. This
new version of Hopsan is an object-oriented C++ application with focus on multi-core support and
compatibility. The program is free and can be downloaded at http://www.iei.liu.se/flumes/systemsimulation/hopsan.
In this simulation task, we will use the latest version of the program to be able to demonstrate the
latest features. Go to http://www.iei.liu.se/flumes/system-simulation/hopsan and press “Download”
in the left menu. Open the folder “Hopsan-0.6.8” and download “Hopsan-0.6.8-win32-zip.zip”. Save it
on your account and unzip it. Go into the “bin” folder and open “HopsanGUI.exe”.
Exercise 1
Model a servo system using a C-type pressure source, a 4/3 Directional Valve, a C-type Tank, a C-type
Piston, a Translational Mass, a Force Source and a Pulse signal. Use the default parameters, except
for the supply pressure (200 bar), dead volume in the cylinder (3 litre), mass (1000 kg), pulse
amplitude (0,0001) and pulse stop time (3 s). Plot the velocity and analyse the result.
Exercise 2
Add another mass to the system and put a Translational Spring between the two masses. Both
masses should have a weight of 500 kg, the total mass is thus the same as in exercise 2. Calculate the
hydraulic spring stiffness. Set the mechanical Spring Coefficient to 100 x kh. Lower the mechanical
spring stiffness until you can discover the anti-resonance. Set the spring stiffness to 0,1 x kh. What
happens and why? Can you draw any conclusions?
Exercise 3
Set the mechanical spring coefficient to 100 x kh and change the dead volumes in the cylinder to 0,3
litre. Add a position feedback to the system with a PI-controller. The reference signal should be a
step from 0 to 0,5 m. Tune the controller to get a fast and stable system.
Exercise 4
The lesson assistant will demonstrate features like animation, frequency analysis and optimization.