International Shipbuilding Progress - Volume 22, issue 250

Authors: Alvestad, R. | Brown, S.H.

Article Type: Research Article

Abstract: This paper describes the second phase of a hybrid computer simulation of two ships maneuvering during underway replenishment operations. Two identical Mariner class merchant ships are used in this study. However, the simulation program is easily adapted to any class of surface ship. The ships’ dynamics are simulated on an EAI 680 analog computer, while the nonlinear interaction forces are generated on a PDP 15 (DEC) digital computer. The first phase of the project considered only the interaction effects on the leading ship due to the close proximity of the tracking ship. This second phase considers the interaction …effects on both the leading and tracking ships in calm water and in two different regular seas. Computer runs are made to study the control variables necessary for manual control of the leading and tracking ships. A third phase will be directed to establishing the essential variables needed for ship control during underway replenishment and their required accuracy. Selection and display of these manual control parameters for monitoring by the conning officer and/or helmsmen may extend the operating conditions under which underway replenishment can be carried out. Show more

DOI: 10.3233/ISP-1975-2225001

Citation: International Shipbuilding Progress, vol. 22, no. 250, pp. 187-203, 1975

Authors: Hoekstra, M.

Article Type: Research Article

Abstract: This paper deals with the problem of the prediction of the effective wake distribution in the propeller plane of a ship, using the measured nominal wake of a model as a starting point. The chosen prediction method consists of two successive steps, viz. a scale effect correction to obtain the nominal wake field of the actual ship and the prediction of the difference between nominal and effective wake. With regard to the scale effect, a method is introduced based on a threefold contraction of the model nominal wake field in dependency of its harmonic content. An empirical approach is used …to account for the scale effect on the diffusion of the wake peak in the centerplane which starts as soon as the flow has left the stern. Further, the scale effect on bilge vortices, assuming that they are generated near the same point on ship and model, is calculated. Application of the method shows promising results. It is felt, however, that our knowledge of the scale effect on generation of bilge vortices is unsufficient at present. The need for more correlation data is emphasized. Concerning the transition from nominal to effective wake, a rough estimate is made of the influence of the propeller-hull interaction on the flow by a. an approximation of the influence of the image of the propeller in the hull. b. a concentric contraction of the wake field to account for changes in the boundary layer profile and c. the calculation of the effect of screw race contraction on the axial velocity distribution in the bilge vortex, if present. an approximation of the influence of the image of the propeller in the hull. a concentric contraction of the wake field to account for changes in the boundary layer profile and the calculation of the effect of screw race contraction on the axial velocity distribution in the bilge vortex, if present. Show more

DOI: 10.3233/ISP-1975-2225002

Citation: International Shipbuilding Progress, vol. 22, no. 250, pp. 204-219, 1975

Authors: van den Pol, E.

Article Type: Research Article

Abstract: This paper relates some of the encountered difficulties during an investigation to apply the ‘classic’ Von Kármán line source technique to a given ‘tear drop’ body of revolution. Finally it is shown how reasonable results were achieved together with some pressure-distributions.

DOI: 10.3233/ISP-1975-2225003

Citation: International Shipbuilding Progress, vol. 22, no. 250, pp. 220-224, 1975