The prediction of ship stability during the early stages of design is very important from the point of vessel's safety. Out of the six motions of a ship, the critical motion leading to capsize of a vessel is the rolling motion. In the present study, particular attention is paid to the performance of a ship in beam sea. The linear ship response in waves is evaluated using strip theory. Critical condition in the rolling motion of a ship is when it is subjected to synchronous beam waves. In this paper, a nonlinear approach has been tried to predict the roll response of a vessel. Various representations of damping and restoring terms found in the literature are investigated. A parametric investigation is undertaken to identify the effect of a number of key parameters like wave amplitude, wave frequency, metacentric height, etc. © 2002 Elsevier Science Ltd. All rights reserved.

S. Surendran

Department of Ocean Engineering

J. Venkata Ramana Reddy

Accident prevention

Computer simulation

Rolling

SYNCHRONOUS BEAM WAVES

Ships

Hydrodynamics

SHIP DESIGN

stability

Stability analysis

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Numerical simulation of ship stability for dynamic environment

Ocean Engineering

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.

Studies on an algorithm to control the roll motion using active fins

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.

Ships and Offshore Structures

Control of ship roll motion by active fins using fuzzy logic

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.

Simplified model for predicting the onset of parametric rolling

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.

Technical note Studies on the feasibilities of control of ship roll using fins

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.

Roll performance of a small fishing vessel with live fish tank

Empirical calculation of roll damping for ships and barges

The effect of nonlinear damping and restoring in ship rolling

1989 Annual environmental report for the Strategic Petroleum Reserve

Applied Ocean Research

Roll response of semisubmersibles with non-linear restoring moment characteristics

International Shipbuilding Progress

Roll response of a ship under the action of a sudden excitation

Journal	Data powered by TypesetOcean Engineering
Publisher	Data powered by TypesetElsevier BV
Open Access	No