Surendran Sankunny

Consequences of roll motions can degrade the effective performance of a ship in a seaway. Roll motion stability becomes more critical when the moving ship encounters beam seas. Such stability is ensured using the actions of extra fins fitted to hull. Roll motion is controlled if the accelerations are high enough to cause any panicky situations for the passengers in the case of a passenger ship. Mission requirements, vessel types, loading conditions, and environmental loads cause the extent of roll and roll accelerations for a ship. In this article, the feasibility of control of roll motion using active fins is discussed. Such fins are better suited for certain types of naval ships. The stability of such vessels becomes critical during fast maneuverings and more critical in the presence of unfavorable weather conditions. Roll motion analysis on the basis of a frigate ship is performed, and proposal to reduce the roll motion using fins is also presented. Lift coefficients corresponding to various angles of attack were obtained using Fluent. Turbulence was modeled using k – ε (two-equation) model and Reynolds stress model. A number of simulations were performed for various sea conditions, and effect of ship speed on the angle of attack required for the fin to stabilize the ship was determined. Case studies were taken up with various sea states and with varying forward speeds of the ship in the beam sea. © 2006 Copyright Taylor and Francis Group, LLC.

Fuzzy logic controller to reduce the roll motions of a ship using active fins is discussed in this article. Roll minimization is a requisite for various operations in the sea. Fin action provides enhanced state of stabilization especially when the vessel is performing a fast manoeuvring amidst rough environmental disturbances. The fins, in turn, are activated by electro-hydraulic mechanism based on the in-built intelligence as per suitable control theories. In this article, the fin pairs are activated using fuzzy logic control algorithm. The design of fuzzy controller is simple and need not require complicated mathematical procedures. A frigate-type warship is considered for the demonstration purpose. The control output is the fin angle. Non-linear roll motions are controlled using active fins. Fins lift characteristics in hydrodynamic flow were studied using CFD package Fluent. Input variable fuzzification, fuzzy membership functions and output set de-fuzzification are discussed in the article. A fairly good amount of reduction in roll amplitude is achieved through various simulations in random sea. The approach can be used for irregular sea conditions. © Woodhead Publishing Ltd.