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A numerical study of the dynamics of a nine-module floating aquaculture platform in irregular waves is proposed, to examine the effect of the connector type between net cages and incident wave direction on the hydrodynamic response. A numerical model based on the coupled boundary element method and lumped-mass model was used to simulate the dynamic behavior of the aquaculture platform. Time-domain statistical analysis, and time-frequency analysis based on Hilbert-Huang transform on the motion responses of net cages and the mooring force responses of the platform were then carried out. The results indicate that the mooring system has a decisive influence on the frequency-domain characteristics of surge motion, while the influence of connector can be ignored. The surge motion under flexible hawser connector is less sensitive to wave incident direction, while the wave direction has a greater impact on surge motion under spherical joint connector. The amplitudes of pitch motion under two different connectors decrease significantly under oblique incident waves, compared with perpendicular incident wave condition. The wave incident direction has little effect on the overall mooring force response of the platform. The mooring force responses at different positions show completely different frequency characteristics when the cages are connected by spherical joints. The larger the pitch response of the cage, the smaller the mooring force response of the mooring chain connected to the net cage. There is a positive correlation between the gravity frequency of the mooring force response and the gravity frequency of the pitch response of the net cage. • A numerical model that couples the BEM and lumped-mass model was used to simulate the dynamic behavior of a nine-module aquaculture platform. • The effect of two kinds of connectors between net cages on motion and mooring force responses of the aquaculture platform are analyzed. • The mooring system has a decisive influence on the frequency-domain characteristics of surge motion. • The wave incident direction has a greater impact on the surge response under spherical joint connector. • There is a positive correlation between gravity frequencies of mooring force response and pitch response of net cage connected to the mooring chain. [ABSTRACT FROM AUTHOR]

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]

Computer simulations were conducted to understand the nonlinear dynamics of the cage array to establish an offshore fish farm capable of surviving the severe conditions. To that end, a large fish farm containing 16 net cages in a 2 × 8 configuration was modeled based on the lumped mass model. This numerical model was verified against the physical model tests regarding a single net cage and a net cage array. In particular, three different equivalent mesh groups were compared to each other to balance the numerical accuracy and the computational efficiency. Then, the candidate equivalent mesh group was used to separately model the rigid and the flexible cage arrays subjected to severe conditions. The results show that most trajectory patterns of mooring lines are not as elliptical as the water particle trajectories. This provides evidence to justify the perturbations about the equilibrium of the mooring grid for the full-scale aquaculture cage array system. Alongside this, flexible cages with lower bending stiffness have greater tension forces on the weather side. The bending stiffness has a predominant effect on the surge motion and is also the leading contributor to the nonlinearity of cage motion. The flexible cage with lower bending stiffness is appropriate for more exposed, open ocean fish farming applications, but the increased mooring tension should be taken into account for future design consideration. • Nonlinear dynamics of an aquaculture cage array were examined under severe conditions. • The nonlinear wave was considered by introducing the new Stoke wave solutions. • Flexible cages with lower bending stiffness exhibited greater tension forces on the weather side. • The bending stiffness contributed to the nonlinearity of cage motion had a predominant effect on the surge motion. [ABSTRACT FROM AUTHOR]

Floating aquaculture cages deployed in the nearshore affect the wave field and contribute to the coastal defense by damping incoming waves. Most pioneering works concerning aquaculture cages have concentrated on the hydrodynamics of the structures instead of their influence on the wave field. In order to bridge the gap, this paper examines the wave performance with the interference of floating aquaculture cages via physical model tests. The results show that the existence of cages increases wave height on the weather side. The wave-dissipation performance of the net cage is closely related to the ratio of the wavelength to the structural span, and the minimum transmission coefficients appear in the conditions with the maximum wave number. Moreover, the crests of the free surface elevation inside the floating frames are almost flat, which is particularly obvious in the long-period wave conditions. The surface elevations show nonlinearity in small-wavelength conditions, which is dominantly caused by the pitch motion of the cages. Nevertheless, the presence of the cage does not affect the phase differences in the wave elevation at different positions. The nets have an opposite effect on wave response inside the cage under the conditions of long-period and short-period waves. • The wave performance with the interference of floating aquaculture cages are examined via physical experiments. • The wave transmission coefficients were closely related to the ratio of the wavelength to the structural span. • The wave surface elevations inside the floating frames showed nonlinearity under small wavelengths. • The nets had an opposite effect on the wave response inside the floating frame in long- and short-period waves. [ABSTRACT FROM AUTHOR]

The rapid development of the marine industry offers more opportunities to combine aquaculture with other marine uses. This study reports a trestle-netting enclosure aquaculture facility that combines an offshore steel trestle with a marine aquaculture facility in which the trestle acts as a supporting substructure. In this study, the numerical models include one configuration without netting and three configurations with netting in different regular waves, which are generated based on stream function theory owing to nonlinear wave problems. The time series of the horizontal wave forces were obtained and analyzed in the four models. Numerical results showed that netting can significantly increase the positive amplitudes of horizontal wave forces, and the wave forces of trestle with the lee-side netting were almost smaller than those of the wave-side netting. Moreover, we investigated the nonlinear features of the wave forces and profiles. The horizontal asymmetry factors of the wave forces are affected by those of the wave profiles, while the vertical asymmetry factors of the wave forces are affected by those of the wave slope profiles. The effects of the netting on the force-positive amplitudes agree with the horizontal asymmetry factors of the wave forces but not with the vertical asymmetry factors. • Finite element models of trestle-netting enclosure aquaculture facility are established. • Hydrodynamic analysis of the complex models is conducted under nonlinear waves. • Effects of netting on wave loads and the nonlinear features of wave loads is discussed. [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]

Abstract: A three-dimensional (3D) numerical model is established to simulate the flow field around fishing plane nets in a current. The realizable k–ε turbulence model was chosen to describe the flow, and the governing equations are solved by using the finite volume method. In this model, the net is modeled using the porous media model. The unknown porous coefficients are determined from the hydrodynamic forces on the net and from the flow velocities and the attack angles using the least squares method. In order to validate the numerical model, the numerical results were compared with the data obtained from two physical model tests. The comparisons show that the numerical results are in good agreement with the experimental data. This numerical model is applicable for the simulation of the flow field around a fishing net. Using the proposed method, this paper presents the flow field around a plane net with different plane net inclination angles, plane net heights, spacing distances between two plane nets and plane net numbers. This study provides information about the flow field around the fishing net cage. [Copyright &y& Elsevier]

Abstract: Recent work in the area of open-ocean aquaculture-system dynamics has focused either on the response of fish cages in waves or the steady drag response from ocean currents, not on them combined. In reality, however, the forces bearing on these open-ocean structures are a nonlinear, multidirectional combination of both waves and current profiles. In this paper, a numerical model has been developed to simulate the dynamic response of the gravity cage to waves combined with currents. When current flows are combined with regular waves, gravity-cage motion response (including heave, surge, and pitch) and mooring-line forces have been calculated. To examine the validity of simulated results, a series of physical model tests have been carried out. The results of our numerical simulation are all in close agreement with the experimental data. [Copyright &y& Elsevier]

Abstract: The aim of this paper is to investigate the shape and tension distribution of fishing nets in current. A numerical model is developed, based on lumped mass method to simplify the net. The motion equation is set up for each lumped mass. The Runge–Kutta–Verner fifth-order and sixth-order method is used to solve these simultaneous equations, and then the displacement and tension of each lumped mass are obtained. In order to verify the validity of the numerical method, model tests have been carried out. The results by the numerical simulation agree well with the experimental data. [Copyright &y& Elsevier]

Extreme ocean waves are typically strongly nonlinear, with extreme wave energy concentrated above the static water surface, which has a complex impact on the hydrodynamics of structures extending above the mean sea level. In this study, we designed netting with three different heights above the water surface and two different solidities, and tested the hydrodynamics of these netting under a series of focused waves through physical model tests. The three heights (h) were designed to account for possible nearshore tidal and wave variations. The results indicate that the wave forces of the netting having sharper and steeper crest than those of the wave surface in the time domain, while it is opposite in frequency domain. Moreover, the wave forces changed significantly with increasing height of the netting above the water surface. Wave forces on netting above water were up to 0.8 and 2.0 times greater than those below water for h = 7.25 cm and h = 14.5 cm, respectively. Regardless of solidity, the rate of increase in netting wave forces gradually decreased with growing wave amplitude when h = 0 cm or h = 7.25 cm, but gradually increased when h = 14.5 cm. The force ratios of the two netting solidities were relatively stable and did not change with wave amplitude. The force ratios were always greater than the solidity ratio, mainly because of the drag coefficient in Morison's equation. Furthermore, steep waves acting on netting wound cause obvious vibration of the wave force because of water jet phenomenon, while the jet have little effect on wave surface elevation in 0.5 m behind the netting. Therefore, for aquaculture facilities such as fixed marine aquaculture cages, the netting design is not only limited by the solidity, but should also consider the hydrodynamic influence of the height that the netting extends above the water. • Netting design for aquaculture should consider both solidity and height above water. • The netting force ratio with different solidities is almost only related to the difference in drag coefficient. • Steep waves acting on netting wound cause obvious force vibration because of water jet. [ABSTRACT FROM AUTHOR]

Offshore net cages are aquaculture facilities that can provide satisfactory volumes of stocked fish. The safety of these structures is of great importance to aquaculture companies. Typhoons are considered to be the main cause of damage to offshore net cages. In this study, an artificial neural network (ANN) model was developed to predict the structural failure of high-density polyethylene offshore net cages in typhoon waves. A case study was conducted where the ANN model was used to predict the structural failure of the offshore net cages around Nanji Island, Wenzhou, China, during Typhoon Maria. Field survey was performed to study the hydrodynamics of the offshore net cages in different wave conditions and the results were used as the training data for the ANN model. By classifying the structural failure, the damage levels of offshore net cages can be predicted and used with wave forecasting before typhoon landing. Field survey was carried out immediately after the typhoon. The prediction and field survey results showed that the proposed ANN model can accurately predict the damage levels of offshore net cages under the influence of typhoon waves. • A model is proposed to predict the structural failure of fish cages in typhoon waves. • The damage levels of fish cages can be predicted rapidly and accurately. • The prediction model is validated against field survey results after Typhoon Maria. [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]

A series of physical model experiments were performed to investigate the characteristics of the motion responses of a multi-module aquaculture platform. A decay test in calm water and regular wave experiments were performed for the platform in a wave basin. The natural period, damping coefficients of the platform, horizontal stiffness of the mooring system in calm water, and motion responses of the platform modules in regular waves were obtained. Owing to the central enclosed cabin and greater mass, the living module of the platform has a larger natural period and damping coefficient than the aquaculture module. Furthermore, the existence of the nets has a significant effect on the motion characteristics of the modules, and the influence of the nets on the damping of the heave motion is larger than that of the pitch motion. The motion responses of the entire platform system in the surge (sway) and yaw directions exhibit obvious low-frequency characteristics. Under regular waves with two incident angles (45° and 180°), the three-degree-of-freedom motion responses of the two types of modules exhibit the same trend as the wave frequency increases. The surge and heave responses have low-frequency characteristics, whereas the pitch response exhibits wave–frequency characteristics. • An innovative offshore multi-module aquaculture platform was proposed. • Hydrodynamic responses of both the single module and platform were conducted. • Transfer functions of motion responses for various modules in waves were analyzed. [ABSTRACT FROM AUTHOR]

Abstract: Based on the lumped-mass method and rigid-body kinematics theory, a mathematical model of a gravity cage system attacked by irregular waves is developed to simulate the hydrodynamic response of cage system, including the maximum tension of mooring lines and the motion of float collar. The normalized response amplitudes (response amplitude operators) are calculated for the cage motion response in heave and surge, and the mooring line tension response, in regular waves. In addition, a statistical approach is taken to determine the motion and tension transfer functions in irregular waves. In order to validate the numerical model of a gravity cage attacked by irregular waves, numerical predictions have been compared with the experimental observations in the time and frequency domain. The effect of wave incident angle on the float collar motion, mooring line tension and net volume reduction of the gravity cage system in irregular waves is also investigated. The results show that at high frequencies, the cage system has no significant heave motion. It tends to contour itself to longer waves. The variation amplitude of mooring line forces decreases as the wave frequency increases. With the increasing of wave incident angle, the horizontal displacement of the float collar increases. [Copyright &y& Elsevier]

Extreme wind and waves can easily destroy aquaculture facilities in the open sea. Therefore, it is essential to analyze the hydrodynamic responses of aquaculture facilities based on a numerical method. To ensure the accuracy of calculation and avoid the huge computational resources required by computational fluid dynamics-CFD, this study adopts a new method that combines the boundary element method based on the potential flow theory with the Morison equation to simulate the hydrodynamic response of a semisubmersible aquaculture facility in pure waves. The hydrodynamic response, including mooring line tension and motion response, is simulated in pure waves and compared with experimental values. The results show that the numerical data agree well with the experimental data. Based on the above work, the numerical model presented here can be used to analyze the hydrodynamic response of a semisubmersible aquaculture facility. The effects of wavelength and wave steepness on the mooring line tension and motion response are studied. Additionally, with increasing draught, both the force on the mooring line and the motion response decrease, and thus, an effective way for an aquaculture facility to avoid damage due to severe waves is through properly increasing draught. • A new method combines the boundary element method with the Morison equation is applied. • Hydrodynamic responses of a semi-submersible aquaculture facility are analyzed. • Influence factors including wave steepness, wavelength and draught are analyzed. [ABSTRACT FROM AUTHOR]

Biofouling of netting adversely impacts aquaculture operations and the structural safety of fish cages. In this study, the effects of the hydroids on the hydrodynamic performance of a plane net in waves were determined experimentally. A series of plane nets with various levels of biofouling was obtained via field sampling from a fish farm. The hydrodynamic force and motion response of both clean and biofouled nettings in waves were measured in a wave-current tank. The corresponding drag and inertia coefficients of the nettings were then calculated. In the studied waves, the wave force acting on the biofouled netting was as high as 3.88 times that acting on the clean netting. The maximum amplitude of the horizontal motion for the most severely biofouled netting was 3.84 times that for the clean netting. For various wave conditions, the biofouled netting drag coefficients and inertia coefficients were 3.30–7.72 and 5.04–10.83, respectively. The results indicated that netting biofouling by hydroids increases the drag force more substantially than it increases the inertial force. • Force and motion responses of hydroid-fouled nets in waves is experimentally studied. • The drag and inertia coefficients of the hydroid-fouled nets are analyzed. • Ratio of inertia force to drag force of both clean and biofouled nets are discussed. [ABSTRACT FROM AUTHOR]

Abstract This paper investigates the short-term extreme value distribution of the tension on mooring lines and the reliability of grid mooring system for fish cage under ultimate limit state. The generalized probability density evolution method (GPDEM) is employed to determine the evolution of the probability information of mooring tension. The short-term extreme tension distribution of mooring lines is evaluated through the combination of the GPDEM and the virtual stochastic process model. And the reliability analysis under ultimate limit state is conducted based on the extreme tension distribution of mooring components in grid mooring system. In addition, the equivalent extreme-value event method is adopted to perform the reliability analysis of grid mooring system for fish cage. The results indicate that the equivalent extreme-value event method has a significant advantage over the narrow bound approach in accurately predicting the system reliability and a large uncertainty of the random allowable strength largely affects the system reliability of grid mooring system. Therefore, it is of vital importance to perform the uncertainty quantification of the allowable strength for accurately conducting the system reliability analysis in order to ensure the safety of offshore net cage structures. Highlights • The short-term extreme tension distribution of mooring line for net cage structure from the stochastic view without any assumptions is predicted. • Comparison of the extreme value distribution between the GPDEM and the distribution-fitting method is conducted. • The reliability analysis for the integrity of mooring system without dealing with the correlation information among different components failure is performed. [ABSTRACT FROM AUTHOR]

Biofouling on netting is an important problem, which can increase hydrodynamics and reduce water exchange across the netting. In this study, drag effect of netting panels with artificial hard and flexible fouling was investigated by physical model tests. The results showed that fouling can cause a rapid increase in netting drag, and that the drag amplification factor of a netting caused by severe hard fouling can be up to 30 times higher than that of a clean netting. With increasing fouling, the drag coefficients for artificial hard fouling can up to 54% higher than those flexible fouling. The formulae proposed to predict the drag coefficients of netting panels with severe hard fouling, can provide a conservative drag coefficient for netting cage design to evaluate the cage safety. • The hydrodynamic effect of netting with different types of biofouling is studied. • The blocking effect of netting with different levels of biofouling is analyzed. • The prediction formulae for drag coefficient of netting compensates for the inadequacy of the existing empirical formulae. [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]

Fluid flow around and drag of two cylindrical cruciform patterns, conventional (T0) and rotated 45º in its own plane (T45), were numerically investigated by solving three-dimensional Reynolds-averaged Navier-Stokes equations within the subcritical flow regime over angles of attack (AOA) from 90º to 0º. Firstly, the drag for a one-cruciform element was assessed, followed by analysis of a four-cruciform assembly (‘square mesh’) to take into account the wake effect of tandem elements. For the one-cruciform element, T45 experienced a less prominent streamline separation and consequently lower drag between 90° and 45° AOA, while T0 experienced progressively lower drag below 45° AOA owing to re-establishment of smoother streamlines caused by the gradually reduced circulation momentum from the adjacent vortex that rotates in the off-side direction. For the four-cruciform assemblies, T0 and T45 drag was essentially equal above 45º AOA; while below 45º, T45 had greater drag attributed to more prominent spanwise vortex downstream development. Overall, while the largest relative difference between the two orientations was 26.2% and 33.8% for the one- and four-cruciform configurations respectively at 0° AOA, for 30º and above AOA there were limited drag differences (generally below 10%). [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]

A novel sheet-pile groin structure consisting of row piles and a tied sheet has been introduced to resist the impact of tidal bores in recent years. However, the dynamic responses of the structure under tidal bore loads have not been carefully studied before. This paper proposed an analytical solution for the dynamic responses of a sheet-pile groin subjected to transient lateral excitation. To take the flexural and longitudinal vibrations into consideration, the piles and the sheet are modeled by Timoshenko beam (TB) theory and a one-dimensional rod, respectively. The soil around the piles is simulated by the dynamic Winkler foundation model. The excitation is considered by a lateral concentrated point load acting on the front pile. On this basis, the governing equations are constructed in the time domain and solved in the frequency domain, while the time-domain responses are obtained using the inverse Fourier transform. The accuracy of the presented analytical solution is validated by comparison with the results obtained from finite element method (FEM) simulation. The effects of the properties of the sheet, piles and soil on the dynamic responses are investigated through a comprehensive parametric study. • Dynamic responses of the sheet-pile groin subjected to a transient lateral excitation are developed. • The mathematical model takes the flexural and longitudinal vibrations into consideration to simulate the sheet-pile groin. • Velocity responses of the sheet-pile groin in time and frequency domain depend on the stiffness of the sheet-pile. • The higher shear wave velocity of the soil corresponds to a greater resonance frequency. [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]

This paper numerically studies the dynamic behaviors of a hinged multi-body floating aquaculture platform under regular waves. A coupled scheme that integrates the boundary element method (BEM) and the lumped-mass model is used to model the frames and the moorings/netting simultaneously. The effect of the hinge-joint rotational stiffness on the motion responses, mooring and hinge-joint forces at different wave steepnesses are examined. The results show that both the wave period and the hinge-joint rotational stiffness affect the pitch response of the multi-body aquaculture platform. However, the hinge-joint rotational stiffness has a predominant influence on the maximum pitch response. Unlike the pitch response, the stiffness has little effect on the heave response. Moreover, with the increase of stiffness, these two individual cages also show distinctive dynamic behaviors. The mooring force decreases with the stiffness and a 14.5% reduction has been obtained at the maximum stiffness. Under the same wave period, the y-direction rotation moment increases alongside the stiffness. When the wavelength is less than 0.9 times the structural span, the increased wave period decreases the y-direction rotation moment. In contrast, the stiffness rarely affects the z-direction hinge-joint force. • An innovative hinged multi-body aquaculture platform is investigated numerically. • A coupled scheme that integrates the boundary element method (BEM) and the lumped-mass model is applied. • The effect of the rotational stiffness on the dynamic responses at different wave steepnesses are examined. • Rotational stiffness has a predominant influence on the pitch response but it rarely affects the z-direction hinge-joint force. [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]