On the Three-dimensional Correction Factors for the Added Mass and the Added Mass Moment of Inertia Related to Manoeuvrability in Shallow Water

Abstract

When we want to estimate the added mass and the added mass moment of inertia of a ship, the strip method which has proved to be very useful for the calculation of ship motion in waves, seems to be suitable, because it is possible to take the hull form of a ship into consideration in detail. However, since the strip method is based on two-dimensional consideration of the flow field around a three-dimensional body, both the added mass and the added mass moment of inertia obtained by the strip method are always excessively large compared with their exact values.Therefore in this paper, the correction factors are introduced separately for the added mass as to the swaying motion, and for the added mass moment of inertia as to the yawing motion in an analogous way to the correction factor for the added mass of the vertical ship hull vibration.Especially, the effect of finite water depth on these correction factors is investigated from the viewpoint of ship's manoeuvrability in restricted waters. As a result, it is found that the correction factors decrease with decrement of the water depth, and that the correction factor for the added mass moment of inertia is smaller than that for the added mass.