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

Research on added resistance of improved configuration based on moonpool with recess
Jia-Yu Sun1, Shi-Li Sun1,*, Jin-Hui He 2, Shu-Zheng Sun1
1 College of Shipbuilding Engineering, Harbin Engineering University

Harbin, Heilongjiang, China
2 Marine Design and Research Institute of China.
Shanghai, China

areas, the moonpool is generally let open during drillship transit. Due tothe presence of ship motions and navigation speeds, violent fluid
motions occur in the moonpool, which increases the fuel consumption
and endangered operation safety. Several attempts have been made to
improve the hydrodynamic performance of drillship moonpool. Do
Vale Machado et al. (2016) investigated the influence of shape and sizeof the moonpool on the resistance of a drillship and proposed a fKN3J
configuration with the best resistance performance. Son et al. (2008),
Hammargren and Törnblom (2012) discussed the effect of recess heighton flow pattern in the moonpool and moonpool resistance performancebased on Fluent and OpenFOAM, respectively. Through RANS
simulations based on Shipflow, Sivabalan predicted the total resistanceof a drillship with moonpool at low forward speed and investigated theeffect of varying cross-section on resistance of a drillship (Sivabalan,Surendran and Balakrishnan, 2016; Sivabalan and Surendran, 2017).
Through the comprehensive CFD parametric study, Ma et al.(2016)
studied the effects of moonpool dimensions on added resistance ofrectangular moonpool. CFD results suggested that moonpool induced
added resistance is mainly attributed to the vortices shed from the front
wall of moonpool, which enter into the moonpool and impinge on themoonpool rear wall. To study the modified moonpool forms on
resistance performance of a drillship, Mao et al. (2019) performed
numerical calculations on a drillship at different transit speeds.
Meanwhile, the rules and causes of moonpool forms on ship resistanceand flow pattern characteristics were analyzed.
However, much of the research up to now has been conducted on theresistance optimization of rectangular moonpool. In addition, the effectof moonpool on ship motions has rarely been discussed before. In
present work, the resistance performance and influence on ship motionsof two moonpool configurations is compared at three typical ship
speeds. Drillship without moonpool is also considered for comparison.
Mesh convergence test is carried out for drillship without moonpool at
Fn = 0.164 in three mesh resolutions. In order to investigate the reasonsfor variation of resistance, the free surface elevation in the moonpool isalso considered.

ABSTRACT
Moonpools are the vertical openings on drillships and offshore
structures applied to lower or lift equipment for operation. Open
moonpools have an adverse impact on ship’s resistance performance. In
this paper, added resistance of two moonpool configurations isinvestigated by numerical method using OpenFOAM. Numericalresults suggest that the notch on recess in the moonpool can effectively
reduce moonpool added resistance, especially for higher navigation
speed. Meanwhile, compared with the configuration without notch,
pitch and heave amplitudes of drillship decrease significantly, which isadvantageous for seakeeping performance of a drillship.

KEY WORDS: Moonpool; resistance; ship motions; OpenFOAM.
NOMENCLATURE
INTRODUCTION
Moonpools are vertical openings employed on drillship and offshore
structures through the decks and the hull bottom structures. Due to thepresence of free surface in the moonpool, open moonpool has anadverse impact on drillship resistance performance. The fluid periodic
movement in the moonpool brings a significant increase in total
resistance of drillship, which leads to extra fuel consumption during
ship’s navigation.
During the last two decades, researches on moonpool resonancefrequencies have drawn high interest. Many studies have focused on theprediction of moonpool resonance frequencies. Molin derived pistonand sloshing modes of moonpools in infinite and finite depth in theframework of potential theory (Molin, 2001, 2017; Molin et al., 2018).
Newman (2018) investigated the resonant frequencies of moonpool
with a recess using numerical simulations based on WAMIT andtheoretical solution analyses. Zeyu Shi proposed a method to analyze
the natural oscillation characteristics of fluid in the moonpool based on
modified Fourier series method (Shi et al., 2019; Shi, 2020).
On account of long distances form operation sea regions to coastal

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