International Shipbuilding Progress - Volume 14, issue 153

Authors: Pollak, E.G. | Frankel, E.G.

Article Type: Research Article

Abstract: It has recently become increasingly important to evaluate the relative performance of complete systems so as to arrive at an optimum allocation of resources to attain a certain mission with a maximum probability of success. Ships are complex systems subject to a multitude of effects which may cause component, subsystem, or system failures. These, in turn may require a diverse range of corrective actions resulting in loss of availability, reduced mission capability, costs, etc. In this paper mathematical models are derived which may be of use in estimating the probability of success in attaing the required level of performance …and completing the design mission. Show more

DOI: 10.3233/ISP-1967-1415301

Citation: International Shipbuilding Progress, vol. 14, no. 153, pp. 179-190, 1967

Authors: Vugts, J.H.

Article Type: Research Article

Abstract: A method of calculating the effect of bow antipitching fins on the motions of a model is presented and compared in detail to the results of measurements. The agreement is quite satisfactory, both for the case of fixed and for controlled fins. Next this method is applied to a general cargo ship of the Sixty Series equipped with fixed and with activated fins, respectively. The activated fins are controlled by a nonlinear feedback signal of the pitch velocity. The absolute and relative ship motions in regular and irregular long-crested waves are computed and compared to the motions without fins. …The results show a pitch reduction of about one third, while the heaving is not significantly changed. The additional advantage of activated over fixed fins is only slight. Also some particulars of the flow pattern about the fins are established by underwater photographs. Show more

DOI: 10.3233/ISP-1967-1415302

Citation: International Shipbuilding Progress, vol. 14, no. 153, pp. 191-215, 1967

Authors: Tasai, Fukuzo

Article Type: Research Article

Abstract: In this paper an approximate method is introduced to calculate the swaying force, yawing and rolling moments acting upon a ship navigating in oblique waves. It next treats of linear coupled equations of swaying, yawing and rolling, where the ship has a finite velocity, in order to derive an approximate method for solving the problems of forced oscillation. As the first step for studing such coupled motions in three degrees of freedom in lateral plane, the author investigated mutual coupling actions among swaying, yawing and rolling when the ship has zero velocity. That is to say, the author …worked out a numerical calculation for three kinds of hull forms by means of the linear coupled equations of swaying, yawing and rolling which he derived in 1965 for the case of zero ship velocity. The results can be epitomized as follows:- a. In case of a hull form with cut up stern, there is a remarkable coupling action between yawing and rolling. Also in this case, if yawing is restrained, rolling will find its maximum value in quartering seas. b. Depending on hull shapes, it may be possible that we may find rolling at its maximum in quartering seas because of the coupling actions of swaying and yawing. c. When a ship has a cross section of large beam/draft ratio, the coefficient of effective wave slope γ sometimes becomes much larger than that of Dr. Watanabe’s theoretical calculation. In case of a hull form with cut up stern, there is a remarkable coupling action between yawing and rolling. Also in this case, if yawing is restrained, rolling will find its maximum value in quartering seas. Depending on hull shapes, it may be possible that we may find rolling at its maximum in quartering seas because of the coupling actions of swaying and yawing. When a ship has a cross section of large beam/draft ratio, the coefficient of effective wave slope γ sometimes becomes much larger than that of Dr. Watanabe’s theoretical calculation. Show more

DOI: 10.3233/ISP-1967-1415303

Citation: International Shipbuilding Progress, vol. 14, no. 153, pp. 216-228, 1967