Measurement of Added mass of Ships with Unconventional Dimensions

Abstract

For the numerical simulations of manoeuvring slip motions or the slow oscillations of single moored ships, it is necessary to specify the hydrodynamic coefficients in the equation of motion at low frequency. Recently, computer analysis has become to be practical to obtain added mass and other coefficients. However, so-called Motora's chart, which was presented by Motora about twenty years ago, is still available to estimate added mass coefficients because of the simple and practical use of it. Meanwhile, as Motora's chart was produced based on the experiments with conventional type ships of those days, added mass of ships with unconventional dimensions such as recent ultra wide beam ships can not be obtained from the chart. In this report, added mass of several such particular ships are measured by a new model test so-called CAT (Constant Accelerating Test), and the chart is extended to those ships confirming by both model tests and the computer calculations based on three dimensional sourse distribution method. Throught our study, it is found that Motora's chart is still available for such particular ships by means of extrapolating the chart. Also, measured added mass from CAT shows that the added mass at decelerating condition is smaller than that of accelerating condition, which suggests that the different values of added mass have to be used when ship motion is simulated.