Rudder Roll Stabilization – Graphical User Interface

This is a short tutorial that is meant to get you started with using the graphical user interface for the design of rudder roll stabilization controllers.

Running the script rrsdemo opens the Simulink model ship.mdl and the graphical controller design tool (the GUI can be also opened independently by typing rrstool). Follow the steps below to get familiar with the interface.

1.      The Design GUI. Used to design PID, MPC, GMV and LQG controllers for the rudder roll stabilization problem. The initial screen looks like this:

2.      Menu File can be used to load any saved models and settings or to save the current session. For example, load the rrsdata file by selecting File -> Load Session…

3.      Change the controller to LQG. When switching the controller, the plots are updated automatically and the front panel should now look like this:

It is possible to add and remove poles and zeros of the weightings (all transfers are in continuous time). Pressing the UPDATE button updates the plots accordingly. Also, the calculated controller parameters are copied to MATLAB workspace for use in Simulink model. 

4.      Menu Ship invokes an editor for viewing and modifying ship components:   

5.      After designing the controller, you can simulate the system using the Simulink model. In the model, double-click the LQG button to connect the LQG controller. The ‘none’ button corresponds to no rudder-roll feedback but with the fin controller in the local loop. After the simulation is finished, you can plot the results by pressing TIME button, as shown below. The open-loop and closed-loop variance of roll angle is printed in the command window, together with the controller roll reduction ratio.
 

6.      Wave model. It can be seen and plotted in the GUI -> Ship menu by pressing the Diagram/Responses toggle button (yellow plot):

The actual disturbance model used for the controller design is obtained by filtering this model through the roll closed-loop transfer (incl. the fin controller). That corresponds to the ‘output disturbance’.  

7.  Fin stabilization. The roll reduction achieved by using fins can be seen by pressing the PLOT button under the fin controller transfer function (needed another pole to make the system proper – otherwise Simulink won’t run).
The black plot shows the sensitivity from the waves to e_phi. The ‘true’ sensitivity to roll is different and shown in red (higher frequencies attenuated)

9.       GMV design. The design procedure is more or less as follows:

• design the weights by adding/removing poles and zeroes to the error and control weightings

• Press UPDATE button to update the plots. The ‘Stable?’ textbox is also updated

• When satisfied, run the Simulink model and watch the Roll angle scope – any problems will be apparent there

• You can stop the simulation at any time and plot the results by pressing TIME button on the Simulink model. The roll reduction ratio will be displayed in the figure, as well as in the command window 

10. Continuous-time ship models are used to simulate the ship in Simulink, while the controllers are discrete with sample time Ts = 0.1s. The design (weightings) is done in continuous-time domain, and then discretized. The LQG controller is actually continuous but its discretized version is used in the simulation.