Technical note Studies on the feasibilities of control of ship roll using fins
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.
Roll performance of a small fishing vessel with live fish tank
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.
Handling and launching of heavy concrete caissons in a marine environment
Handling of heavy structures demand unusual crane capacity. Availability of such cranes may be limited in developing countries. An innovative way to construct and launch heavy concrete structures in a developing country, where crane availability is rare, to lift, transport and handle heavy structures, is discussed in this paper. Heavy caissons are used in the marine environment as breakwaters, as berthing facilities for vessels, as gravity structures to absorb energy from waves, etc. The methodology for constructing multi-caissons on-board a barge and then on-board a floating dock is the subject of this paper. The respective feasibilities are discussed. The free floating condition of the caisson and its righting arm stability are described. At first the caisson was considered as its lip wall opened to the sea. The case of lip wall closed for more bouyancy is also considered. The stability of the barge and floating docks is shown for various stages of completion of construction. After investigating many factors, a safe procedure for construction and launching thereafter is described in this paper. The problem of handling a heavy concrete structure from the view point of a naval architect is highlighted.