International Shipbuilding Progress - Volume 32, issue 373

Authors: Ferdinande, V.

Article Type: Research Article

Abstract: In a straightforward theoretical way, a general formula of the power absorption in waves by a floating body with two degrees of freedom, viz. a vertical and a horizontal mode, is derived. The vertical and horizontal motions apparently can be treated as uncoupled, provided asymmetry of the body with respect to the vertical axis is not very pronounced. Because of the multiterm character of these expressions of power extraction, the individual influence of each factor involved is more easily recognizable. Subsequently, general directions regarding optimum design of a wave energy device are deduced.

DOI: 10.3233/ISP-1985-3237301

Citation: International Shipbuilding Progress, vol. 32, no. 373, pp. 204-209, 1985

Authors: Cardo, A. | Francescutto, A. | Nabergoj, R.

Article Type: Research Article

Abstract: The characteristic features of subharmonic oscillations in the nonlinear rolling of a ship are investigated. The mathematical model used for this purpose is given by a second order differential equation taking into account both the righting moment and the damping nonlinearities. The righting moment is expressed by a cubic polynomial, whereas the damping effects are nonlinear both in angle and angular velocity. Particular attention is devoted to subharmonics for the case of a ship in upright equilibrium position. It has been proved that a subharmonic oscillation with tuning factor 3 can be present only after the excitation intensity has …exceeded a threshold level. The phenomenon can be particularly dangerous for ships whose righting moment shows a strong departure from the linearity. This occurs in particular for modern container ships. Show more

DOI: 10.3233/ISP-1985-3237302

Citation: International Shipbuilding Progress, vol. 32, no. 373, pp. 210-214, 1985

Authors: Flower, J.O.

Article Type: Research Article

Abstract: The Beecham-Titchener (B-T) method is a technique for obtaining approximate analytical solutions of nonlinear differential equations representing the oscillatory behaviour of underdamped dynamical systems. The method closely parallels the better-known method of Kryloff and Bogoliuboff (K-B) but appears less restrictive in its application and is generally superior in its prediction of the frequency behaviour of nonlinear systems. Simpson has extended the B-T method to cope with nonlinearities that are even functions of, for example, position and velocity. These types of nonlinearities are common in the marine dynamics area (it is shown, in the appendix, how to deal with such nonlinearities …using the K-B method). In this paper the B-T method is applied to some simple nonlinear mooring and ship-rolling problems and, where appropriate, a comparison is made of its efficacy with that of the K-B technique. So far as the author is aware the applications described here are the first outside of the flight-dynamics area. Show more

DOI: 10.3233/ISP-1985-3237303

Citation: International Shipbuilding Progress, vol. 32, no. 373, pp. 215-224, 1985