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

Numerical study on the flow field inside and around a semi-submersible mariculture ship with hybrid
structure
Neng ZHANG1,2, Li-lan ZHOU1,2,Shao-min WANG3
1. Key Laboratory of High Performance Ship Technology (Wuhan University of Technology), Ministry of Education, P. R. China.
2. School of Naval Architecture, Ocean and Energy Power Engineering, Wuhan University of Technology, P. R. China.
Wuhan, Hubei Province, P.R. China
3. South China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Guangzhou, Guangdong province, P. R. China.

led to the frequent occurrence of inshore biological diseases and a decline
in quality, causing serious impacts on soil and water resources and theecological environment. In addition, shallow mariculture face thechallenges of water depth, load effect, fish living environment and so on,which gradually shifted to the deep sea (Chu et al., 2020). Deep-seamariculture is a kind of aquaculture method that can fully utilize marine
resources, which promotes development of mariculture andenvironmental together, and will become the main development
mariculture method in the future. At present, net cage, mariculture ship
and floating mariculture platform are the current equipment. In the actual
mariculture process, the equipment will be affected by the environment,
especially in the deep sea or harsh and complex sea conditions, the living
environment of the organisms will be disturbed. In serious cases, theequipment will be damaged and the safety of the organisms will bethreatened. At the same time, unreasonable mariculture arrangement andserious wobbling will lead to direct death of organisms, so the researchon the hydrodynamic characteristics of aquaculture equipment has
become the focus.

ABSTRACTIn marine aquaculture, the fish is closely related to the flow field aroundthem. High flowing rate will cause the deformation of the net and reduce
the aquaculture volume, which is bad for the growth of fish. The low
flowing rate will lead to insufficient water exchange, which is also not
conducive to fish. Therefore, it is necessary to study the flow field aroundthe living place of fish. In this paper, the RANS (Reynolds-AveragedNavier-Stokes) equation based CFD (Computational Fluid Dynamics)
method was introduced to simulate the hydrodynamic characteristics ofa semi-submersible mariculture ship with truss and plate frame hybridstructure. In the calculation, a porous medium model is adopted tosimplify the net of the mariculture cage and ship. The flow field aroundthe mariculture ship is focused. Firstly, the method is validated bycomparing the plane net numerical results with experimental results.
Secondly, numerical simulation of the flow field inside and around theside nets and mariculture ship under three kinds of net solidities. Finally,mariculture ship without nets, with side nets and with both side andbottom nets are simulated to find the effects of nets on the flow field thatthe fish living. The results show that the numerical simulation is in good
agreement with the experimental values. With the increase of the net
solidity, the flow field inside the mariculture ship is attenuating. The
existence of the net has a great impact on the flow field around themariculture ship.

Various experimental and theoretical calculations have been carried out
to explore the hydrodynamic properties of net cages. Fredriksson et al.
(2001) devised a method to correct the projected area of a net cage by
considering the variation of the water resistance coefficient through theMorrison formula. Lader et al. (2005) measured the forces anddeformations of a flexible circular cage model at constant flow velocity
and summarised the relationship that the magnitude of the force on aflexible cage depends on the Reynolds number. Li et al. (2005) deriveda gravity similarity criterion which, combined with the variable scale
method and the field similarity criterion, is widely used to calculate theforce and deformation of cages under pure flow conditions. Tsukrov etal. (2011) conducted experiments on nylon nets and several copper alloy
nets with different solids, materials and mesh structures, and gave
Theoretical equations for the drag coefficients of nets with different
solids and knots

KEY WORDS: Porous media; Mariculture ship; Hydrodynamics;

Flow field

INTRODUCTION
In recent years, as the global population increases, the protein intake ofpeople will also increase, leading to a rapid growth in mariculture, which
not only meets the needs of people's lives, but also contributes to thedevelopment of national economies and the improvement of nationalpower. At present, Land-based and shallow mariculture are the main
forms of mariculture, with water depths of up to 20m（Mai et al., 2016）.
High aquaculture densities, poor water quality and serious pollution haveWith the development and efficiency of computer technology, numericalsimulation technology is gradually maturing, which is faster and cheaper
than experiments. Patursson et al. (2010) simplify the plane net to porous

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