A Study on Added Resistance of a Restrained Body with Forward Speed in Waves

Abstract

Added resistance can be usually calculated by a method of the pressure integral on the wetted surface of a body or the momentum relation of the control volume. In a previous study, the values of Maruo's formula based on the latter for a surface-piercing body with linearised condition (so-called Neumann-Kelvin problem) was not in good agreement with the results of the former. In this study, the inconsistency of the Neumann-Kelvin problem is considered as a reason for its disagreement. For the validation of added resistance by these two methods, new terms in Maruo's formula need to be considered which are caused by the inconsistency in the rate of change of momentum and energy flux arising from the intersection in the surface-piercing body with forward velocity. The diffraction problem of a vertical circular cylinder which is a column of ocean structure is taken as an example, and first order fluid force and added resistance in regular waves are calculated. With respect to the added resistance, the result of modified formula based on Maruo's momentum theory in Neumann-Kelvin problem agrees well with that of the pressure integral method. The calculated result is compared with the measured result. First order fluid forces agree well. The results of added resistance generally show good agreement, but the accuracy of results needs to be improved as Froude number increases.