On the Stability Derivatives of High Speed Ships Oscillating in Low Frequency

Abstract

This paper presents a theoretical method of calculating the hydrodynamic derivatives for sway and yaw of high speed ships oscillating in low frequency. A commonly known, practical procedure to deal with this problem is: (l) to evaluate the added mass and the radiation force by the strip theory and (2) to add the dynamic lift force without consideration on the free-surface effect. It is well recognized, however, that the strip theory can not evaluate correctly the free-surface effect in the low frequency or high speed range. On the other hand, Chapman has established a numerical method which may account for the advance speed effect on the hydrodynamic coefficients, but it is not certain yet whether Chapman's method is valid also for the case of sway and yaw oscillation. In this paper a new method is provided from the point of view of the generalized lifting-surface problem, assuming high Froude number and low frequency in addition to the thin-ship approximation. A series of sway and yaw oscillation experiments for a flat plate and a Wigley ship model are carried out at the Osaka University Ship Experiment Tank. Comparison of the test result with the existing and present theories are also discussed.