Surendran Sankunny

Container ships move at a higher speed compared to other merchant ship types. A fin attached to the ship hull proves to be more efficient in controlling the moving ship. However, such attachments on the naked hull attract additional problems such as slamming, requirement of continuous maintenance, etc. The main objective of this study is to find the influence of fin action at various angles of attack with the incoming flow and recommend the best possible fin position for the least resistance. While experiments were performed for different angles of attacks of the fin with respect to the flow, a reduction in resistance was observed for an Fn range of 0.13–0.26. The fin was fitted at the lowest possible location of the hull surface at the bow part of the ship. Experimental investigation was done using model tests in a towing tank to determine the resistance of a scaled down model and it was compared with computer simulation. The interaction of a bow fin fitted to a container ship with its own generated and encountering waves are discussed in this paper. It was observed that at certain angles of attack of the fins favourable resistance characteristics were observed. Modifications from the expected resistance due to fin effect are paid attention in this study. Various resistance values for different angles of attack of the fin were compared and an angle of attack of 5° is found to be the best.

The very purpose of attaching fins to the hull is to reduce the roll motions of a ship. Roll minimization is a requisite for various operations in the seas. The presence of fin system provides enhanced state of stabilization especially when the vessel is performing a fast maneuvering amidst rough environmental disturbance. The fins in turn are activated by electro-hydraulic mechanism based on the in-built intelligence as per control theory like proportional-integral-derivative (PID) or fuzzy logic. As per this paper, fin system is activated using PID control algorithm. A frigate-type warship is considered for the demonstration purpose. Nonlinear roll motions are controlled using active fins. Lift characteristics of the fins in hydrodynamic flow were studied using CFD package fluent. Good amount of reduction in roll amplitude is achieved from various simulations in random sea. The approach can be used for any irregular sea conditions. © 2006 Elsevier Ltd. All rights reserved.

The world container fleet shows the fastest growth of any ship type. The infrastructure for loading and unloading container ships are also growing in many ports around the world. Such a trend is due to the fact that the containerized transportation is becoming more and more attractive due to many factors. The increasing demand in container transportation is met by use of more number of container ships including Post-Panamax and Malacca-max containers. Loss of containers in seas and accidents of container vessels are reported from many parts of seas. New generation containers are severely hit by parametric rolling. Pure loss of stability, due to exponential increase of roll in either broaching-to or head sea conditions, is called parametric rolling, is subjected to rigorous investigation by many researchers. Algebraic expression based on well known Duffing's method is proposed for solutions in parametric rolling. The variation in GM and damping values from trough to crest conditions associated with bow flare immersion and emergence in head sea conditions with pitch resonance with the heading waves are said to be the prime reason for parametric rolling. A simple model to predict the beginning of parametric rolling is described in this paper. © 2006 Elsevier Ltd. All rights reserved.

The concept of live fish tanks in trawlers is to use the catch in a better condition and to reduce marine pollution. It also reduces the infrastructure meant to freeze the catch to preserve it for longer period. But the presence of additional free surface in the vessel challenges the stability of the vessel. This is besides the sloshing effect due to the moving liquid mass in the tank. Roll motions are initiated due to various factors related to the hull characteristics of the vessel, loading and operating conditions and its interaction with the environment. Location of fish tank, its orientation, arrangement of baffles inside the tank to reduce the free surface affects and careful design of tank opening are to be given priority during the design, manufacturing and tank testing. The results obtained from tank test of model are compared with that of analytical method. The non-linear roll performance become further complicated due to the free surface and sloshing effects of the mass in the live fish tank. Wave makers are used for generating waves under laboratory conditions compatible with the scaled down model of the trawler model. The tests are conducted in the towing tank of Pusan National University. © 2005 Elsevier Ltd. All rights reserved.

Control devices are selected in the preliminary design stage of any large platforms. This is true for deciding fin area for roll/pitch control of moving platform and thruster sizes and numbers for maneuvering assistance in the case of very low speed conditions. For moored platform the excursions are to be determined to activate the thruster system to reduce the line tension. In the case of a drill ship with moonpool there are some additional parameters of interaction. To some extent the parameters can be contained by optimizing the size and shapes of moon pools on board ships. The dynamics of a moored platform fitted with moon pool are determined here. Such responses are necessary to arrive at the actual sizes and numbers of thrusters to keep the vessel within the tolerances of excursion for ease and accurate operations. © IFAC.

This paper is a continuation of a technical note published in Ocean Engineering in Vol. 30 (2003). Stability of Ro-Ro ships was subjected to rigorous investigation by many researchers recent past. Stability of a ship is to be ensured during design stage for various loading conditions. Two typical conditions of departure and arrival are usually chosen by naval architects. Out of all types of motions of a ship, the critical motion leading to capsize is the roll. Ship roll motions are very complicated and difficult to analyze, as there are various parameters involved in the motion. Large angle roll motions are nonlinear in many aspects. For larger angles of roll many nonlinearties become significant. Various representations of damping and restoring terms found in the literature are investigated and their solutions are analyzed. Data of a Ro-Ro vessel is used to demonstrate the applicability of the proposed procedure. In the present study, the problem of ship safety has been considered with regard to the rolling motion of a ship in beam waves. A parametric investigation is undertaken to identify and quantify the effect of a number of key parameters viz., wave slope, wave frequency etc. on the capsizing conditions of a ship. Nonlinear response of ship is determined in the frequency domain. © 2005 Elsevier Ltd. All rights reserved.

The effects of free-surface waves on the floating structures are of great importance in the offshore industry. Among the six degrees of motions of a surface ship the absence of restoring forces in surge, sway and yaw led to critical situations for moored ships in the recent times. The order of forces in horizontal plane and their exciting frequencies are matters of interest. The resonance with the presence of moored chains led to many accidents in the recent past. The lines in dry conditions may not give good damping and in wet condition they may trigger the system to chaotic motions and jumps. Two different loading conditions of a container ship model are tested with waves in laboratory conditions in two different drafts. The mooring lines are chosen as per scale law and the energy under the response spectrum is determined from the plots. The results give new insights into the movement of a berthed ships subjected to waves. Response of the moored ship to different loading conditions in different water depths are discussed in this paper. The paper gives the order of energy due to first-order and slowly varying movement of a berthed container model in a towing tank. © 2006 Elsevier Ltd. All rights reserved.