International Shipbuilding Progress - Volume 47, issue 451

Authors: Myrhaug, Dag | Dahle, Emil Aall | Rue, Håvard | Slaattelid, Olav H.

Article Type: Research Article

Abstract: This paper applies the distributions of Myrhaug and Rue (1993a, 1998) and Myrhaug and Slaattelid (1999) to rolling of smaller vessels in beam seas in a simplified manner. The emphasis here is on how the statistical properties of successive wave periods can be used to identify dangerous (synchronous) wave situations at sea and for comparison of ships with different damping and roll periods.

Citation: International Shipbuilding Progress, vol. 47, no. 451, pp. 253-266, 2000

Authors: Kar, A.R.

Article Type: Research Article

Abstract: The well-known and widely used method of Floodable Length Calculation proposed by Dipl. Ing. F. Shirokauer is undoubtedly easy to comprehend and suitable for manual calculation. But the method is often found to be tedious for manual calculation owing to the involvement of assumption and 'trial & error' approach and not very simple to write Computer Programs. The method proposed in this paper is a direct analytical method not having requirement for any assumption …and/or 'trial and error' for determination of the desired parameters, hence found to be more efficient, accurate and very simple for computer programming. Show more

Citation: International Shipbuilding Progress, vol. 47, no. 451, pp. 267-274, 2000

Authors: Millward, A. | Weynberg, P.A.

Article Type: Research Article

Abstract: A new method of improving the roll stability of a fishing vessel has been developed which makes use of a fin/wing attached to the bottom of a central fin under the vessel where it will not interfere with fishing activities. Model tests have been carried out to investigate the feasibility of this concept and have shown that, with the flaps operating under active control, considerable reductions in roll motion can be achieved.

Citation: International Shipbuilding Progress, vol. 47, no. 451, pp. 275-286, 2000

Authors: Edgar, D.R. | Horwood, J.M.K. | Thurley, R. | Belmont, M.R.

Article Type: Research Article

Abstract: It has recently been recognised that it is realistic to make predictions of the detailed sea surface shape typically up to 30 seconds ahead. This offers the prospect of substantially increasing the operating envelope in a wide range of marine operations. This article examines, from the point of view of a potential user of this technology, how the various parameters involved in such a Deterministic Sea Wave Prediction System affect the prediction time and also how …prediction time can be traded versus precision. Show more

Citation: International Shipbuilding Progress, vol. 47, no. 451, pp. 287-301, 2000

Authors: Centeno, R. | Fonseca, N. | Soares, C. Guedes

Article Type: Research Article

Abstract: An approach is presented to calculate catamaran motions in regular waves. The method is mainly based on two-dimensional potential flow theory in which some viscous forces are considered through a cross flow drag approach. When the viscous effects are not considered the response amplitude at the resonance frequencies is largely over predicted. This work presents the basic theoretical formulation for the hydrodynamic forces and induced motions. To check the validity of the implemented model, calculations are …performed on twin-cylinders and simple catamaran hull forms and the results are compared with other published experimental results. The influence of the variation of the viscous coefficients in the ship motion responses is analysed on one of the catamaran models. Show more

Citation: International Shipbuilding Progress, vol. 47, no. 451, pp. 303-323, 2000

Authors: Suneja, B.P. | Datta, T.K.

Article Type: Research Article

Abstract: Efficiency of linear and nonlinear feedback control strategies for the response reduction of the Articulated Leg form (ALP) under random waves is investigated. The linear and nonlinear control laws are derived by minimizing a quadratic and a higher order performance function respectively. The degree of nonlinearity in the latter is regulated by incorporating a 'nonlinearity-weighting-factor' in the control law. The controlled equation of motion (in both control strategies) is solved by an iterative frequency domain …technique in which the linear terms are retained on the left hand side, while all nonlinear terms are taken to the right hand side of the equation of motion and treated as loading terms. The solution is essentially obtained by the Newton-Raphson technique. Using the proposed control strategies, the response of a single hinge articulated tower is obtained under a few related parametric variations in order to investigate the performance of both control strategies. Show more

Citation: International Shipbuilding Progress, vol. 47, no. 451, pp. 325-347, 2000