International Shipbuilding Progress - Volume 42, issue 432

Authors: Bose, N.

Article Type: Research Article

Abstract: A two-dimensional time-domain constant potential panel method was used for analysis of chordwise flexible oscillating hydrofoils as oscillating propulsors. The oscillatory motions as well as the chordwise deflections were of large amplitude. Results are presented of propulsive thrust coefficient and efficiency over ranges of motion parameters including varied reduced frequency, pitch amplitude and feathering parameter; heave amplitude/chord ratio; pitching axis position; phase between pitching and heaving motions; and deflected shape. The ranges were taken about a favourable operating point for a flexible oscillating NACA 0012 foil. A peak in propulsive efficiency was found for each motion parameter variation studied. Propulsive …efficiency varied strongly with changes in heave amplitude/chord ratio, pitch amplitude and phase between heaving and pitching motions, but less strongly for variations in pitching axis position and flexibility. Show more

DOI: 10.3233/ISP-1995-4243201

Citation: International Shipbuilding Progress, vol. 42, no. 432, pp. 281-294, 1995

Authors: Nayfeh, A.H. | Oh, I.G.

Article Type: Research Article

Abstract: The dynamic stability and complicated motions of a vessel in following or head regular waves are investigated when the frequency in pitch is nearly twice the frequency in roll. The damping in the pitch mode is modeled by a linear viscoins damping term, whereas that of the roll mode is modeled by the sum of a linear viscous part and a quadratic viscous part. The method of multiple scales is used to determine a system of four nonlinear first-order equations governing the modulation of the amplitudes and phases of the pitch and roll. Force-response and frequency-response curves are generated. Coexistence …of multiple solutions is found. The jump phenomenon continues to exist, whereas the saturation phenomenon ceases in the presence of quadratic damping. Hopf bifurcations are found. Near these bifurcations, the modulation equations possess limit-cycle solutions and hence the steady-state motion is a periodically modulated pitch and roll motion. Numerical simulations are used to investigate the bifurcations of these limit cycles and how they lead to chaos and hence chaotically modulated pitch and roll motions. Show more

DOI: 10.3233/ISP-1995-4243202

Citation: International Shipbuilding Progress, vol. 42, no. 432, pp. 295-324, 1995

Authors: Xu, Changwen | Yu, Minghua

Article Type: Research Article

Abstract: In order to solve the multi-objective fuzzy optimization problems of ship structures, two approaches, known as the Maximum Level Method and the Linear Weighted Sum Method, based on the different forms of fuzzy decision-making are presented. In these methods, the membership functions are constructed for the subsets of the fuzzy goals subject to the fuzzy constraints, and then the multi-objective fuzzy optimization problem is transformed into the single-objective ordinary optimization problem, which can be solved by using nonlinear programming techniques. The proposed approaches are illustrated by two numerical examples in the application of ship structural design.

DOI: 10.3233/ISP-1995-4243203

Citation: International Shipbuilding Progress, vol. 42, no. 432, pp. 325-341, 1995

Authors: Guha, S. | Sayer, P.G.

Article Type: Research Article

Abstract: Precise station keeping of deeper offshore platform is of vital importance both for drilling and production operations. With the gradual expansion of offshore activities towards deeper water and more severe seastates, loads on conventional motion and drift control mechanisms are increasing, resulting in a corresponding increase in operation costs. An oscillating hydrofoil has proved itself to be an efficient converter of wave energy to useful thrust. This simple device has great potential for offshore applications, particularly in controlling wave induced mean horizontal drift forces.

DOI: 10.3233/ISP-1995-4243204

Citation: International Shipbuilding Progress, vol. 42, no. 432, pp. 343-356, 1995

Authors: Krishnankutty, P. | Vendhan, C.P.

Article Type: Research Article

Abstract: Ocean wave is an important marine environmental phenomena which influences the performance of a marine structure. This necessitates a detailed hydrodynamic study of the wave-structure interaction problem. In the present work the finite element method has been demonstrated as an effective tool to solve the complex linearised three-dimensional hydrodynamic problem. The developed software has been validated for regular bodies and applied to a multi-body (twin-barge) system.

DOI: 10.3233/ISP-1995-4243205

Citation: International Shipbuilding Progress, vol. 42, no. 432, pp. 357-379, 1995

Article Type: Other

DOI: 10.3233/ISP-1995-4243206

Citation: International Shipbuilding Progress, vol. 42, no. 432, pp. 381-382, 1995