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Biofouling is an inevitable problem in marine aquaculture and it is prone to cause many negative effects on the hydrodynamic behavior of the aquaculture facility. In this study, the dominant biofouling on the netting of fish farms in the Yellow Sea of China was determined by field sampling. Plane nets with various levels of biofouling were obtained by submerging nets at different depths and for different durations. Drag acting on the biofouled nets in currents were investigated using laboratory experiment. The results indicate that drag acting on the net increases with increasing level of biofouling. Compared to the clean net, the accumulation of biofouling can lead to over 10 times more hydrodynamic load on nets. Flow fields around the biofouled nets were simulated using a porous-media fluid model which was validated by corresponding laboratory experiment. As the level of biofouling increases, the flow velocity downstream from the net decreases continuously. The net with the greatest level of biofouling produces the most serious shielding effect with 21.4% reduction in flow velocity. Using the proposed empirical equations, both the drag on and flow velocity downstream from a hydroid-fouled net can be predicted. [ABSTRACT FROM AUTHOR]

In this study, waves propagating through a square array of 16 net cages with different levels of biofouling are numerically studied using a three-dimensional computational fluid dynamics (CFD) model. A porous-media fluid model is adopted to simulate both clean and biofouled netting of a cage array in waves. A numerical wave tank is built, and the oscillating-boundary method is adopted to generate waves. The flow motion is solved by the Navier-Stokes equations, and the free water surface is captured using the volume of fluid (VOF) method. The numerical model is validated by comparing the numerical data with corresponding experimental measurements of a net-cage model with clean netting. To analyze wave attenuation, a numerical analysis of wave elevation both inside and around the cage arrays is presented, which considers the effect of biofouling. Based on the results of the present study, the effect of biofouling on wave elevation is noticeable; the damping effect of the cage array increases with increasing level of biofouling. Furthermore, the incident angle of waves has a noticeable effect on the wave field inside and around the cage array. [ABSTRACT FROM AUTHOR]

In this study, waves propagating through a square array of 16 net cages with different levels of biofouling are numerically studied using a three-dimensional computational fluid dynamics (CFD) model. A porous-media fluid model is adopted to simulate both clean and biofouled netting of a cage array in waves. A numerical wave tank is built, and the oscillating-boundary method is adopted to generate waves. The flow motion is solved by the Navier-Stokes equations, and the free water surface is captured using the volume of fluid (VOF) method. The numerical model is validated by comparing the numerical data with corresponding experimental measurements of a net-cage model with clean netting. To analyze wave attenuation, a numerical analysis of wave elevation both inside and around the cage arrays is presented, which considers the effect of biofouling. Based on the results of the present study, the effect of biofouling on wave elevation is noticeable; the damping effect of the cage array increases with increasing level of biofouling. Furthermore, the incident angle of waves has a noticeable effect on the wave field inside and around the cage array. [ABSTRACT FROM AUTHOR]

With the growth of global population, the demand for seafood has been increasing. Aquaculture as a sustainable industry provides a new direction to satisfy the rising demand for seafood. However, typhoons, a common disaster in coastal areas, can cause massive waves that can threaten the safety of aquaculture facilities. Therefore, studying the facilities' failure probability under typhoon waves with different return periods is crucial. The example of offshore high-density polyethylene net cages in the seas near Guishan Island, Zhuhai, China, was examined in this study. The wave conditions for different return periods for these seas were predicted using the SWAN+ADCIRC model and the local wave statistics for the last 30 years. Based on the prediction results, the hydrodynamic loads and stresses of the primary cage structure (floating collar, nets, and mooring lines) in typhoon waves at different return periods were calculated using the lumped-mass and finite element methods. Meanwhile, the failure probability of the cage components was analyzed based on the Monte Carlo method. According to the failure probability and cost of different components, the suitable size of the each of the cage components in the representative seas was studied. This study affords a reference for the design of the cage and improve the aquaculture insurance. • Relation between typhoon waves and failure probability of HDPE net cage components. • SWAN+ADICRC model combined with local hydrographic data to predict typhoon waves. • Lumped-mass and finite element methods for hydrodynamic loads on components. • Quantitative response relationship established using Monte Carlo method. [ABSTRACT FROM AUTHOR]

Gravity-type fish cages are playing an increasingly important role in fishery aquaculture. As the main load-bearing component of gravity-type fish cages, the floating collar supports the whole cage and undergoes large deformations. In this paper, a numerical method is developed to study the motions and elastic deformations of an HDPE floating collar in waves. The governing equations of motions are established by Newton׳s second law, and those governing the deformations are obtained according to the curved beam theory and the modal superposition method. Damping of the elastic deformations is introduced and analysed in detail to improve the numerical model. To validate the numerical model, a series of physical model tests are conducted. Good agreement between the numerical and experimental data is obtained. The numerical results indicate that the in-plane and out-of-plane deformations calculated using the first four modes yield satisfactory precision. The positions of the maximum deformations in different wave propagation directions and the effect of the forms of the mooring line arrangement have also been investigated. The numerical results show that the four-point-mooring cage is more reliable than the single-point-mooring cage. The endpoints of the diameters that are parallel or perpendicular to the wave direction have the largest deformation. [ABSTRACT FROM AUTHOR]

A vessel-shaped floating aquaculture platform has numerous advantages over traditional high-density polyethylene gravity cages. Combined with a single-point mooring system, the unique structural form of the vessel shape can significantly reduce the environmental loads transmitted from the bow. This study used potential flow theory and dynamic composite cable theory to simulate the hydrodynamic responses of a single-point moored vessel-shaped floating aquaculture platform in waves. The motion response, mooring force response, and reaction force of the nets were simulated in regular waves and compared with experimental values. The numerical and experimental results agree well. After the validation, the response amplitude operators of the floating frames of the platform were calculated and analyzed in the frequency domain. Then, time-domain calculations were carried out to investigate the hydrodynamic characteristics of the platform. The results show that the heave and pitch responses of the front frame are significantly higher than those of the rear frames of the same platform. The increase in the number of floating frames decreases the motion responses and increases the mooring force response of the platform. The X and Z components of the hinge joint force between the floating front frames are significantly higher than those between the rear frames. Similarly, the reaction force of the nets of the floating front frame is higher than that of the rear frames under the same wave conditions. [ABSTRACT FROM AUTHOR]

In the present work, the hydrodynamic characteristics of full-scale rectangular otter board were studied by numerical simulation, including the effects of aspect ratios (AR), flow distribution around the otter board, induced velocity, induced angle of attack (AOA), effective AOA and induced drag coefficient. It was demonstrated that the otter board had a critical AOA of 40° (when the stall appeared) and induced AOA of 3~10°. The maximum induced drag coefficient was 0.185, which is a great contribution to the total drag coefficient. The otter board exhibited better performance when the AR was set to 0.5, and higher AR had a smaller critical AOA (the stall happened earlier). The maximum lift coefficient decreased with an increasing AR, while the maximum lift-to-drag ratio increased. The induced drag coefficients showed similar trends across ARs, initially rising with an increase of the AOA, and then dropping. The flow distribution around the otter board showed that the wing-tip vortex was fully developed at the AOA of 40°, and the AR can affect the development of the wing-tip vortex. [ABSTRACT FROM AUTHOR]