Ride Control Systems - Reduced Motions on the Cost of Increased Sectional Forces ?

Implementation of passive and active ride control systems into both linear frequency and non-linear time domain strip theories is described. The ride control systems considered can consist of T-foils, fins or a combination of these. These appendages are taken into account by considering the lift forces induced by the flow around them.

In the frequency domain the appendages are included simply by modifying the equations of motion. This is done without introducing any non-linearities and hence the application of linear statistics is still valid. In the time domain the appendages are included by adding the lift forces to the exciting forces in the equations of motion.

One of the advantages in the time domain is that the angle of attack can be limited easily, as is often the case in real full scale ride control systems. This way cavitation and finally stalling can be avoided. In the frequency domain limits on the angle of attack cannot be set. Since the lift coefficient is treated linearly the calculated lift force is severely overestimated in rough sea.

Secondly the effect of including ride control systems in the calculations is demonstrated through comparisons of RMS values and of response operators for the ships main responses, e.g. motions, accelerations and sectional forces. Especially emphasis is given to the effect on the sectional forces, as preliminary results indicate that these in some cases are increased considerable by the T-foil ride control systems.

Finally, the effect of the ride control systems on the hydro-elastic behaviour of the hull girder is investigated with the non-linear time domain strip theory code.