On the roll damping of surfaced submarines

Abstract

This thesis investigates the roll damping of surfaced submarines. Modern diesel-electric submarines can spend a significant time sailing in surfaced condition. When sailing in this condition, the submarine will roll due to the excitation by waves. The (very) large rolling angles that occur are bothersome to the crew and possibly dangerous to the submarine and its systems. The large angles occur, because the roll damping of a submarine is low when compared to ordinary surface ships. The rudders contribute the most to the roll damping of a submarine. Hardly any research into the roll damping of submarines is found in the open literature. For these reasons, the following research question is formulated: Which rudder configuration provides the most roll damping for a surfaced submarine at speed? Six different rudder configurations are compared over a range of roll amplitudes, roll frequencies and forward speeds. The comparison is made using a newly developed mathematical model. The mathematical model calculates the lift and drag forces generated by the rudders using thin airfoil theory, whilst taking the effects of very high angles of attack and the vicinity of the free surface into account. The model is validated against an extensive series of experiments on a model submarine. The model submarine had a scale of 1:24. Forced oscillation tests were performed at the towing tank of Delft University of Technology. Forces normal to the rudders and the torque acting on the hull were measured. The results of the experiments showed that the mathematical model could be used to predict the qualitative trends in the roll damping of surfaced submarines. For every combination of roll amplitude, roll frequency and forward speed that was studied, the trend was similar: the large X-rudders with bowplanes generate the most roll damping. Adding bowplanes to a given aft rudder configuration always increases the roll damping.