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• A new method combining the porous media and rigid wall is applied to analyze the flow field. • The blocking effect of the semi-submersible aquaculture platform on water flow is analyzed. • A phenomenon including low flow velocity region and vortex generation are studied. The study of flow velocity distribution inside and around a semi-submersible aquaculture platform is extremely important for the living environment of marine fish, especially in the open sea. Therefore, a method combining porous media and rigid walls is established to analyze the flow patterns inside and around a semi-submersible aquaculture platform. In the present study, the shear stress transport k–omega turbulence model is chosen to describe the flow, and the governing equations are solved by using the finite volume method. The fish nets and main frame, including pontoons, columns, and braces, are modeled by porous media and rigid wall conditions, respectively. The accuracy of the numerical model is verified, and the results show that the experimental values agree with the calculated values. By comparing the flow field of aquaculture platforms with and without fish nets, it can be concluded that fish nets play a vital role in the attenuation of flow velocity. In addition, vortices exist near the wall of the aquaculture platform. The risk of resonance will increase when the frequency of the vortex shedding is close to the natural frequency of the structure, which should be avoided in practical engineering. [ABSTRACT FROM AUTHOR]

Intensifying and expanding sustainable aquaculture is essential for achieving the United Nations' global goal of the Decade of Action. Cage culture is a typical aquaculture method in the world. As an essential part of cages, the nets maintain the breeding space, protect the cultured species and prevent them from escaping. In the cages, the nets have the most significant proportion and bear most of the hydrodynamic load. Meanwhile, the nets are small-scale, flexible structures prone to large displacement and deformation in wave and current, reducing cultural space and threatening cultured species' health. In addition, the wave and flow fields around the nets will determine the cages' water exchange, which affects the cultured species' welfare. Studying the netting hydrodynamic characteristics is crucial to ensure the culture facilities' security and promote cage culture development. This study reviews the research on netting hydrodynamics from hydrodynamic loads, dynamic response, and the flow-wave field around the nets. Summarizes the unsolved research problems and future explore directions, which provides a reference for designing and optimizing cages. Combining multiple parameters and focusing on the connection between them is the key to encouraging the sustainable development of aquaculture. • The cage nets' hydrodynamics are analyzed from hydrodynamic loads, dynamic response, and the flow-wave field. • The formulas for the no-fouling nets' hydrodynamic coefficient and their application scope are summarized. • The cages' structural parameters' effect on the netting dynamic response is explored. • The netting wake effect is analyzed based on the impact range and biological effects. • The fish school effects on the netting hydrodynamic characteristics are discussed. [ABSTRACT FROM AUTHOR]

The primary purpose of the aquaculture facility is to provide a comfortable living environment and achieve welfare aquaculture for cultured fish in the open sea. Nevertheless, it has been a challenge to accurately assess the suitable flow region of the cultured fish inside the aquaculture facility for the severe ocean environment, which is a pressing concern for aquaculture farmers. First, the maximum domed swimming speed (MDSS) is used as an indicator to assess the swimming ability of Sciaenops ocellatus in this study, which can be measured through a vertical circulation water channel. Subsequently, the porous media theory is adopted and applied to predict the flow field inside the shielding device of the submersible aquaculture facility based on the shear stress transport k-omega turbulence model using the computational fluid dynamics (CFD) approach. In addition, combining the swimming ability of Sciaenops ocellatus and current speed distribution inside the shielding device of a submersible aquaculture facility, the suitable flow region is quantitatively assessed. The results indicate that when middle height, the inclined angle and net solidity are 0.4 m, 3π/12 and 0.65, respectively, the current speed inside the shielding device attenuates below the maximum domed swimming speed of Sciaenops ocellatus - 0.76 m/s and meets the survival of Sciaenops ocellatus for the actual sea condition with an incident current speed of 1.5 m/s. In addition, a suitable flow region for Sciaenops ocellatus, which is 204.512 m3 and accounts for 17.76% of the total aquaculture volume, is formed and located inside the shielding device, close to the downstream sides, and gradually extends towards the middle of the shielding device. Based on the swimming ability of Sciaenops ocellatus, using numerical means to describe the suitable flow region in detail is to provide clear and macroscopic guidance for aquaculture farmers. • Quantitative evaluation on the suitable flow region inside the shielding device is carried out. • The swimming ability of Sciaenops ocellatus is assessed through a vertical circulation water channel test. • The flow field distribution inside the shielding dvice is predicted through CFD model based on porous media. [ABSTRACT FROM AUTHOR]

Increasing demand for seafood drives the aquaculture industry to new-generation offshore aquaculture systems with high production efficiency. As a healthy, sustainable and ecological aquaculture pattern, the pile-net enclosure has been widely applied in the aquaculture industry in China. The flow field distribution and hydrodynamic characteristics are of great importance for the welfare of farmed fish and the structure safety. This paper proposes a one-way fluid-structure coupling model to examine the flow interaction with the pile-net structures. A series of physical experiments are conducted to verify the accuracy of the numerical model. Then, different configurations, pile-net at different locations and distance between upstream and downstream pile-nets are selected to estimate their influence on the flow field and hydrodynamic characteristics of pile-net structures. Results show that the net intensifies the velocity attenuation and reduces the velocity in front of the structure. The variation of vortices is affected by the downstream pile-net and the distance between twines and piles. The wake width behind the pile is barely affected by intersection angles between pile-net and flow, but the wake width behind the net increases slightly with the increase of intersection angles between pile-net and flow. Increasing the intersection angles between pile-net and flow aggravates the attenuation of downstream velocity. The computed force decreases with decreasing intersection angles between pile-net and flow. Double rows of the pile-net intensify the upstream and downstream velocity attenuation. The distance between pile-nets has little influence on downstream flow velocity. The interaction between upstream and downstream pile-net structures weakens with the increase of the distance between upstream and downstream pile-nets. With this understanding, the proposed model can be further used to assess the hydrodynamic performance of the pile-net enclosure and the large offshore aquaculture platform under steady flows, oscillating flows and waves. • A one-way fluid-structure coupling model is proposed to examine the flow interaction with the pile-net structures. • The influence of different flow incident angles is analyzed. • Suggestions about the design and constructions of the pile-net structure are presented. [ABSTRACT FROM AUTHOR]

As aquaculture moves from inshore to the deep sea, developing a comfortable swimming environment for the farmed fish to cope with the strong current in the open sea becomes vitally imperative. This study designs a novel net cage with a shielding device to provide a sheltered area for the farmed fish at extreme ambient current speeds. Considering the time-consuming and substantial economic loss caused by the destruction of the net cage in situ measurements, a numerical method based on computational fluid dynamics (CFD) modeling is employed to evaluate the flow field of the net cage. Three characterized parameters, namely the height of the middle plane nets, the inclined angle of plane nets, and the net solidity, are used to estimate their influences on the flow field of a net cage and the drag force loaded on it. The results highlight that the height variation of the middle-plane nets has little effect on the flow field and the drag force. Nevertheless, the increased inclined angle of plane nets and net solidity leads to a dramatic fluctuation regarding the current velocity distribution and the drag force. In particular, the increase of the inclined angle for the plane nets causes a noticeable increase in the cage volume. With this understanding, further aquaculture net cages can potentially be designed to better withstand the ocean's rigors and maintain the aquaculture industry's sustainability. • A novel dependable habitat of farmed fish: a novel design of net cage with a shielding device is researched. • Hydrodynamic characteristics of a novel design of net cage with a shielding device based on CFD are studied. • The influences of the inclined angle of plane nets on the flow field, drag force and cage volume are discussed. • The effects of net solidity on the flow field and drag force are thoroughly analyzed. [ABSTRACT FROM AUTHOR]

Predicting the distribution of flow velocity inside a semi-submersible aquaculture platform and taking measures to optimize the flow field are critical to provide a dependable inhabit for farmed fish. This paper examines the hydrodynamics of a semi-submersible fish farm under current using the porous media method combined with a rigid wall based on the shear stress transport k-omega turbulence model. The results show that the presence of nets expands the low flow area and provides a better inhibit for farmed fish in the severe currents. The increase of net solidity enhances the damping effect on the flow, and it also simultaneously increases the current loads acting on the net. The attenuation caused by different net solidities produces a 66.10 % deficit of the flow velocity in maximum inside aquaculture platform. A maximum increase of 36.82 % for the drag force acting on the aquaculture platform is obtained. Furthermore, the distribution of drag force acting on the aquaculture platform in current is also assessed. Although the drag force of the frame-only is approximately twice compared to the net-only case, the improvement in the strength of the net structure under the action of flow should not be ignored. • A novel dependable habitat of farmed fish: a semi-submersible aquaculture platform is researched. • A new method combining the porous media and rigid wall is applied to analyze hydrodynamic characteristic. • The influence of the existence of the net and the net solidity on the flow field and drag force is studied. • The drag force acting on the net-only and frame-only for the aquaculture platform are discussed. [ABSTRACT FROM AUTHOR]