Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Simulations of Ship Harmonic Forced Roll Damping by Using Overset Grid
Ke Zeng, Min Gu, Lu Huang and Jiang Lu
China Ship Scientific Research Center; Key Laboratory on Hydrodynamics
Wuxi, Jiangsu, China

harmonic forced roll motion. Roll decay and harmonic excited roll basedon roll angle measurements make the comparison of the roll damping
coefficient between experiment and simulation difficult. Roll decay is afully non-stationary harmonic process, the initial state and higher Froudenumber have a strong influence on the test results. Considering therudder is used to hold the model on course in harmonic excited rollmotion, the propeller-rudder interaction adds the complexities for themodel test. The fixed roll axis of harmonic forced roll motion and thedirect determination of the moment make it easier to measure roll period
and amplitude. In this paper, we focus on the harmonic forced roll motion
to validate the established numerical methods. Besides model tests, thedevelopment of high-performance computers promotes the work for
estimating roll damping numerically. Finite volume methods seem to beappropriate to simulate the roll damping coefficients and flow
characteristics visually.

ABSTRACT
Roll damping is an input parameter for the second-generation intact
stability criteria and is also a key factor for predicting large roll motions
and capsizing in waves, accurately estimating roll damping is still achallenging task with large roll motion. In order to provide a reliable
method for predicting roll damping, this paper uses the unsteady RANS
equations combined with the VOF method. A numerical method for
simulating harmonic forced roll motion with different forward speeds isestablished by using overset grid approach. The accuracy of the method
is verified by existing experimental data, and the influences of rudder
and bilge keels are studied by varied forward speeds, roll amplitudes androll periods. The results show that the rudder and bilge keels contributenoticeably to roll damping with higher speed and larger roll amplitude,
and the bilge keel interacts with free surface leads to the error increasing
between the simulation and experiment.

Considering the forced roll technique, some studies have been dedicatedto experimental research and numerical simulation. Fullerton et al. (2006,2008) performed a range of forced roll experiments for a tumblehome
hull form, where motions, forces, and moments were measured. A motordriven mechanism was used to drive the model through roll amplitudes
of up to 50°with varying roll frequency. Bassler, et al. (2010, 2011)
executed a series of forced roll motion experiments at zero forward speed.
Force and moment measurements on both the hull and bilge keels wereobtained for a model of the midship section of the ONR configurations.
PIV was also used to measure the generated vortex field. Based on themodel experiments, the authors also proposed a piecewise model topredict the total ship roll damping with large amplitude motion. Wilson
et al. (2006) used a URANS solver called CFD-IOWA to simulate theforced roll motion of a naval combatant, the periodic response of theboundary layer to the rolling motion was described and quantified byusing a Fourier analysis. Miller et al. (2008) used CFD-IOWA tocompare forced roll moments for the DTMB Model 5613-1 at various
roll amplitudes, roll frequencies, and forward speeds. Handschel et al.
(2012, 2014) used RANS simulations to calculate roll damping
coefficients of a Post-Panamax container ship Duisburg Test Case with
two forward speeds and three roll amplitudes by forced roll motion
technique. The authors reported good agreements in all tested cases byusing the sliding interface method, concluded that the simulation of theforced roll case is more stable and results in less computational time thanroll decay, especially for large roll amplitudes.

KEY WORDS: Forced roll; Roll damping; RANS simulation; CFD.
INTRODUCTION
A ship may occur extreme roll motion in severe waves and winds
condition, thus leading to large amplitude roll motion. Large roll angles
and accelerations can cause significant crew inefficiency and reduce thestability of the hull, or leading to capsizing. A sufficient roll damping
moment prevents the dynamic loss of stability, and roll damping is also
fundamental in case of the majority of failure modes addressed bySecond Generation Intact Stability Criteria, thus the accurate predictionof roll damping of ships is particularly important.
At present, the estimation of roll damping is both challenging as well as
an extensively studied problem. Usually, there are three methods toevaluate the roll damping: semi-empirical approach, model test andnumerical simulation. The most popular semi-empirical method is acomponent-based method, which considers the physical processes of rollmotion damping with various means of energy dissipation, including
friction, lift, wave-making, and vortex generation from the hull, as wellas the influence of appendages (Ikeda, et al., 1978; Himeno, 1981).
Unfortunately, the range of application is limited in most extreme rollmotions. Different techniques of model test exist to estimate roll
damping, which are roll decay motion, harmonic excited roll motion and2506