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

Study on Vibration Reduction Design of a Ro-Ro Ship with twin-skeg
Lu-feng Pan, Hua-wei Zhou, Li-wei Mou, Xian-qun Mao, Chen-fei Ma
Marine Design & Rearch Institute of China ,Shanghai, China

improve the uniformity of wake field in different positions of the hullby CFD method. Chen JP et al. (Chen JP, 2016) studied the lines
optimization of the 10,000 twin-skeg container vessel, which carriedout by parametric modeling and CFD simulations. In terms of thedatabase analysis, Yasuo Ichinose et al. (Yasuo Ichinose, 2019)improved the wake field with a wake field design system and enhanced
the performance of energy saving devices and propeller.

ABSTRACT .
It is easy to cause the unevenness of the wake field behind the tail forthe twin-skeg type ship due to the shielding of the skeg. Moreover, thevibration of the propeller induced by the propeller working in theuneven wake field is the main reason for the vibration of the ship whichis still a difficult problem in the ship design. Therefore, it is necessary
to study the influence of the skeg shape on the vibration of this typeship. In this paper, the tiwn-skeg ship with arge breadth and shallow
draught is studied. Due to the skeg shape is affected by the shallow
draught, there are too many limitations to reduce the hull vibration by
optimizing the propeller. Thus, the skeg shape of a RO-RO ship withtwin-skeg controlled by the water line at a height of 0.4D (D is thediameter of the propeller) away from the center line of the propeller
shaft is investigated, and the nominal wake field of the propeller disc issimulated by CFD method to observe the variation in the unevenness of
the wake field in the different exit angle as well as the tail thickness of
this water line. Additionally, adopting the CFD calculation of thenominal wake field at the propeller disc as the input of the modelexperiment, propeller-induced fluctuation pressure under the same
propeller and the same working condition is detected by the cavitationtunnel experiment. The results show that the variation of the skeg
parameters represented by exit angle and tail thickness has a significant
influence on the unevenness of the wake field and the propellerinduced fluctuation pressure. And it is realizable to reduce the vibrationof ship by modifying these parameters of skeg which provides anoptimum direction for the vibration reduction design of the RO-RO
ship with twin-skeg.

The studies are based on improving the line shape, so as to improve thewake field. In this paper, in order to more specifically study theinfluence of the change of the skeg shape on the propeller inducedvibration, a type of RO-RO ship with twin-skeg was studied. And theskeg characteristics represented by exit angle and tail thickness of thewater line with distance of 0.4D from centerline of shaft are employed.
Firstly, compared with the model experiment, a reliable CFD method isobtained to simulate the wake field under different skeg parameters.
And all results are obtained by a commercial program called STARCCM+. Then, based on the obtained wake field as the input of thecavitation tunnel experiment, the hull vibration represented bypropeller fluctuating pressure and cavitation pattern under different
skeg shapes are studied. It is essential provide a direction for thevibration reduction design of the RO-RO ship with twin-skeg.

NUMERICAL METHODS AND MODELLINGThe numerical simulation of wake field behind the skeg by CFD
method has been widely used. In this section, the CFD modeling for
wake field analysis is discussed.

KEY WORDS:

RO-RO ship; skeg shape; nominal wake field;
propeller fluctuation pressure; CFD; cavitation tunnel experiment;

Physics ModelingThe unsteady ship wake fields are supposed to be governed by theReynolds-averaged Navier-Stokes (RANS) equations. Besides, the k-ε
turbulence model is adopted which used widely for ship viscous flows(Sungeun Kim, 2011). And discretization method used in CFD method
is Finite Volume Methods (FVM) which greatly improved thecomputational efficiency.

INTRODUCTION
The twin-skeg is widely used in wide breadth and shallow draft vessels
such as ro-ro ships and landing ships. However, due to the shielding
effect of the tail skeg, there will be a huge peak and gradient of thewake field behind the tail. To make matters worse, it will cause a rapid
increase in propeller pulsating pressure, which induces vibrations of thehull. Saydam et al. (Saydam, 2018) designed a vortex generator toIn order to obtain the nominal wake field more accurately, considering3946