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 Aquaculture Environment in Deep-sea Cage with Waves
Xiaonan Yuan1, Quanming Miao1*, Changfang Zou1, Chenyi Wang1
1

School of Ocean Engineering, Jiangsu Ocean University,Lianyungang, Jiangsu, China

ABSTRACTThe flow field inside the deep-sea cage is affected by many factors. In
recent years, many scholars have done a lot of research on the influenceof mesh on the velocity of flow field through different methods such asmodel test measurement and simulation. Bi et al. (2013) respectively
used Particle Image Velocimetry (PIV) and Acoustic Doppler
Velocimeter (ADV) to study the effects of different net solidity, netinclination, net spacing and net number of plane nets on downstream
velocity. The results showed that these parameters had different effects
on the flow field around the aquaculture cage. Tu et al. (2020) verified
the feasibility of using three-dimensional multi-slack time (MRT)
Lattice Boltzmann model to simulate the flow field of plane net underconstant flow conditions. The effects of net solidity and flow velocity onhydrodynamic characteristics and flow-velocity attenuation wereanalyzed by using this model. The results showed that velocity
attenuation was mainly related to the net solidity of the plane net.
Patursson et al. (2010) used Reynolds mean Navier-Stokes equations andκ-ε turbulence model to describe the flows. The mesh plates weresimulated as porous media, and the flow characteristics of the meshplates were studied through computational fluid dynamics (CFD) andmodel test measurement, and porous media resistance coefficients wereobtained. GUI et al. (2006) proposed a model that can be applied to theanalysis of velocity drop inside the cage, which can improve theaccuracy of numerical simulation of hydrodynamic characteristics of thecage. In the study of the effect of the net on waves, Pal et al. (2007)
studied the stress of three different screen plates in five different regularwaves by means of real sea measurement and numerical simulation.
Chan et al. (2001) studied the scattering of surface waves by elastic
fishing nets, The effects of fishnet rigidity and porosity on reflection
coefficient and hydrodynamic pressure are shown.

In this paper, the characteristics of the flow field inside the deep-sea
aquaculture cage in the sea and the effects of different oxygen supply
methods on the diffusion of micro-nano bubbles and the distribution offeed particles were studied by numerical simulation. The results showthat the cage net can reduce the influence of external waves and currentson the internal flow field of the cage. When the wavelength is large, theinfluence of waves on the internal flow field of the cage cannot beignored. When the total oxygen injected into the cage is the same, thediffusion of oxygen in the form of micro-nano bubbles inside the cage
will be affected by the method of oxygen supply, waves and currents.
The injection of oxygen can promote the diffusion of fish feed inside thecage, and also increases the residence time of fish feed inside the cage,so it can improve the breeding environment. The results of this paper can
provide technical support for the selection of oxygenation method andfeeding method in the deep-sea aquaculture cage.

KEY WORDS: Deep-sea farming; Aquaculture net cage; Wave; DPM.
INTRODUCTION
China has rich marine fishery resources, and its aquaculture production
accounts for about 70% of the total of the world. China is the world's
largest producer of fishery and trader of aquatic products. However, withthe increase in people's demand for aquatic products, resulting in overexploitation of fishery resources and less space for offshore aquaculture(Naylor R et al.,2005), moreover, a large amount of residual feeding andfish feces produced by cage culture are lost to the sea, which seriously
affects the offshore mariculture environment (R.S.S. Wu,1995). This
results in frequent occurrence of fish diseases, decline of major economic
fish resources, and almost extinction of some species in some waters.
Deep-sea cage culture can increase the output of aquatic products andrelieve the pressure of offshore aquaculture. Therefore, in order toachieve the effect of improving fish quality and reducing environmental
impact of deep-sea cage, it is very necessary to study the deep-sea cage
culture environment, and the research results will play a positive role inguiding the production practice of deep-sea cage culture (NaylorR.L.,2000).

The residual feed and feces produced in the process of the deep-sea cagefarming have a great impact on the environment. Studies on the diffusion
law of particulate matter are as follows: Corneret al. (2006) based on theModern Geographical Information System (GIS) model, developed afish waste particle diffusion module, which can predict the distributionof feed and excrement every year or the whole production cycle. Navaset al. (2011) studied the effects of average velocity, stationary water
cycle and bulk water cycle in Irish fjord (shallow sea fjord system) by
combining 3d hydrodynamic model and particle tracking model, which

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