ABSTRACT

To solve the problem of large roll motion of mono-hull ship of 1000-ton class under high sea conditions, three kinds of ship types are designed including Angle, Round Bilge and Mixed hull types. Roll damping of these ship types are calculated by CFD method, meanwhile, model tests are carried out to verify the numerical results. The results showed that, the numerical method is in good agreement with the model tests. The angle hull type has the faster roll decay speed and larger roll damping than other two ship types. Through the analysis of roll damping components, the proportion of damping components of three types of ship is obtained. This research provides a reference for the development of mono-hull ship type.

INTRODUCTION

About 1000 tons of mono-hull ship is widely applied in practical ship and offshore engineering, including patrol ships, deep sea fishing boats, small and medium-sized rescue ships, small transport ships and so on. Compared to the ship of large displacement, because of the limitation of tonnage measurement of this kind of ship, the seakeeping especially rolling performance under the high sea condition is bad. Anti-rolling devices such as bilge keels and fin are often used, but the space of the ship is reduced. Good ship shape design optimization can improve the roll performance from the inherent characteristics of the hull on the basis of adding anti-roll measures.

Referring to the influence of different hull types of mono-hull ship on roll damping (Zhang and Liu, 2001) and ship design experience, three ship types of widely varying in transverse section for the design of an ocean rescue ship of about 1000 tons are proposed in this paper, namely Round bilge, Angle and Mixed ship type. The study of roll damping has always been a hot and complicated research field of ship hydrodynamics. The study of roll damping characteristics of three hull types with large variations is the premise to study their roll motion performance, which is of great significance. Model test and empirical formula are the conventional methods of roll damping prediction. In the past two decades, CFD technology has been applied to calculate roll damping (Korpus and Falzarano, 1997), which can better reflect roll damping nonlinearity caused by viscosity of water. Yu et al. (2008) simulated forced roll motion of four different hull sections with 2D solution by CFD, and gave the time history of roll moment and roll damping coefficient under different roll Angles. The same method was used to simulate the rolling motion of a mono-hull ship by Zhu (2009). Zhang et al. (2017) studied the property of nonlinear roll damping of a trimaran ship. Metin (2018) and Simone et al. (2018) used dynamic mesh and overlapping mesh technology to simulate roll attenuation of DTMB5415 ship, and uncertainty analysis was carried out.

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