The migration of aquaculture facilities to high-energy wave environments necessitates robust structural assurance against complex hydrodynamic loads. Addressing the limitations of current designs, this study introduces a novel vibration control strategy for truss net cages by replacing conventional solid ballast with tuned liquid dampers (TLDs) integrated within the hollow columns. A high-fidelity numerical framework was constructed employing both the volume of fluid (VOF) method and overset mesh techniques, which was validated through physical experiments. Results indicate that the TLD system offers superior dynamic stability compared to solid ballast, attenuating maximum pitch motion and mooring forces by 37.69% and 32.23%, respectively. The damping mechanism is attributed to the significant phase difference between the cage motion and internal liquid sloshing, particularly near the structure's natural period (phase difference of 87.4 deg). Additionally, the TLD provides a critical stabilizing mechanism at peak angular velocities, by converting accumulated gravitational potential energy into a restoring moment that opposes cage rotation. These findings validate the efficacy of TLD integration in truss cages and offer essential design insights for improving the survivability of offshore aquaculture systems.

The safety and generating efficiency of FPV platforms in harsh environments have received increased attention owing to the rapid development of offshore photovoltaic systems. In this study, the hydrodynamic response of an FPV array to regular waves was investigated using a physical model, and the output characteristics of the photovoltaic cell in dynamic operation scenarios are studied based on the illumination and series PV array power generation model. The effects of wave height, wavelength, wave direction, and multi-floating body connection on the motion response, mooring force, and generation efficiency of this type of FPV were analyzed. The results show that the longitudinal oscillatory motion response of the FPV array can be primarily categorized into wavefrequency modal components and other low-frequency components. The low-frequency modal components exhibited large-scale slow-drift motion, whereas the wave-frequency modal components exhibited smallamplitude oscillations based on the low-frequency modal components. The surge motion amplitude of the FPV module connected by a ball hinge was mainly affected by the waves and connector type, whereas that of the platform connected by a cable was mainly affected by waves. Ball hinged connections can enhance FPV motion stability and reduce mooring forces, in terms of wave length and direction sensitivity. The FPV array with ball hinge can reduce the inter-module maximum power point disparity to 2.5 %, effectively mitigating grid frequency/voltage fluctuations caused by power oscillations. Overall, the findings of this study offer valuable insights and practical guidance for maximum power tracking algorithm improvements of FPVs, contributing to the advancement of more efficient and reliable FPV technologies.

Optimizing feed utilization is a critical challenge in offshore aquaculture, where low efficiency and high costs persist due to difficulties in predicting feed dispersal. This study addresses this issue by employing a Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) framework, featuring a non-spherical drag model, to analyze the transport and dispersion of feed pellets in a truss net cage. One-way coupling was utilized to simulate the trajectories of dilute concentrations of both short cylindrical (H/D = 0.2, 0.4, 0.6) and slender cylindrical (H/D = 2.24, 2.47, 2.83) pellets. The results reveal that under cross-flow conditions, the particle Stokes number (St) is significantly less than unity (St << 1), indicating that trajectories are primarily governed by the local flow field. The pellet aspect ratio was identified as a key determinant of rotational dynamics, slender pellets exhibited more vigorous rotation, which enhanced their spatial dispersion. Particle shape significantly influenced residence time. While slender pellets settled faster in still water, short cylindrical pellets had shorter residence times in the presence of a current. By accurately modeling small-scale particle dynamics within a largescale environment, this research provides valuable insights for optimizing feed pellet geometry to enhance aquaculture efficiency.

Fish school motion can substantially influence the hydrodynamic characteristics and waste discharge performance of aquaculture tanks. Herein, a computational fluid dynamics (CFD)-based fluid-structure interaction model was coupled with a discrete phase model to investigate waste transport and discharge under the disturbance induced by bionic fish schools. The model was applied to three tank configurations, with the no-fish condition serving as the control case. In the circular tank, the presence of fish schools reduced the mean flow velocity by approximately 23%-32% and decrease the particle discharge rate at 60 s by approximately 37%-50% relative to the no-fish case. In the square arc angle tanks, fish schools caused a 2%-9% reduction in mean velocity, and the overall flow structure remained comparatively stable. However, in the square tank, fish-induced motion enhanced mixing with localized low-velocity regions, increasing the mean velocity by up to approximately 42% and increasing the particle discharge rate at 110 s from 3.6% to 20.9%. These findings indicate that, in tanks with relatively weak baseline flow patterns, turbulence generated by fish school motion can serve as an important driving mechanism for particle transport. Overall, this study elucid ates the role of fish school motion in shaping tank hydrodynamics and waste discharge efficiency and provides insights for aquaculture system design.

The effectiveness of waste collection and disposal in the recirculating aquaculture tank is essential for aqua-culture welfare. Optimizing tank geometry offers a viable method for improving the internal cleanliness of these systems. This study investigates the effect of the diameter-to-depth ratio (L/H, where L represents the tank's long side and H the water depth) on the collection and discharge performance of pollutants by utilizing computational fluid dynamics to analyze the flow field and settleable particle distribution through the solution of Reynolds-averaged Navier-Stokes equations and the discrete phase model. The accuracy of the numerical method is confirmed using experimental data from the literature. This study examined velocity distribution, eddy formation, and turbulent kinetic energy across various diameter-to-depth ratios in circular, square arc angle, and square tanks. The collection and discharge performance is evaluated by tracking 1000 uniform 2 mm settleable particles within a Lagrangian framework. Findings indicate that circular and square arc angle tanks offer superior hydrodynamic conditions and particle management, with suggested L/H ratios of 2:1-5:1. Conversely, square tanks perform less effectively, with optimal L/H ratios of 2:1-4:1. This study offers a theoretical foundation and guidance for the design of the tank.

Optimizing inlet angles in aquaculture tanks using computational fluid dynamics (CFD) requires time-consuming simulations across numerous operating conditions, while conventional physics-informed neural networks (PINNs) struggle to reconstruct high-shear and near-wall high-gradient flows from sparse data. This study proposes a Feature-Augmented parametric Physics-Informed Neural Network (FA-pPINN) for rapid flow-field prediction in circular aquaculture tanks. The framework integrates inlet-angle encoding, local flow features, incompressible Reynolds-averaged Navier–Stokes constraints, a non-negative turbulent eddy-viscosity mapping, progressive physics-informed training, and offline posterior fusion calibration. A dataset of 19 steady three-dimensional CFD cases spanning inlet angles from 0° to 90° was constructed. Predictive performance was assessed using three held-out cases at 15°, 45°, and 75°. FA-pPINN accurately reconstructed the complex nonlinear flow fields. Compared with a conventional PINN, it increased the coefficient of determination from 0.0656 to 0.9972 and reduced the root-mean-square error from 0.1044 to 0.0057 m/s (94.6%). The global relative L2 error was approximately 4.5%, and the maximum local absolute error remained below 0.008 m/s. Once trained, FA-pPINN predicted one case in 0.549 s, versus approximately 1 h for CFD. The framework therefore enables stable, accurate, and rapid flow-field prediction and inlet-angle screening under fixed geometry and boundary conditions within the prescribed angle range.

The hydrodynamics of aquaculture tanks are essential in recirculating aquaculture systems to enhance fish growth and development. However, existing studies on the hydrodynamics of these tanks frequently ignore the presence of fish, making it difficult to understand the complex and variable interactions between the flow field and cultured fish. The presence of fish and their swimming significantly affects the flow field dynamics of the tanks. This study used computational fluid dynamics (CFD) to examine the flow regime affected by fish swimming motion and its impact on the flow field. We found that (i) CFD can accurately simulate the impact of fish swimming motion on the flow field, as validated by physical modeling experiments. (ii) The presence and swimming of fish can negatively affect the flow conditions in the tank to varying degrees. (iii) Adjusting the inlet velocity is one of the most effective methods for optimizing the flow field conditions. The numerical model developed in this study, which couples fish population dynamics with the aquatic environment, enabling accurate simulation of hydrodynamic mechanisms influenced by fish and structural parameters. This model provides a valuable reference for enhancing aquaculture practices in recirculating aquaculture systems.

Fishery-photovoltaic complementary (FPC) structures have gained increasing attention due to their efficient space utilization and economic benefits. While extensive research has been conducted on the hydrodynamic characteristics of floating photovoltaic (FPV) systems, studies on FPC structures remain relatively limited. This study investigates the effects of net solidity, net depth, and bottom weight on the safety, aquaculture performance, and power generation performance of a novel FPC structure through model tests. The results indicate that higher net solidity and lighter bottom weights lead to greater mooring forces under wave action. Additionally, the effect of net depth on mooring forces is determined by wave forces and damping effects. An increase in bottom weight mass significantly amplifies mooring forces under current conditions. Moreover, higher net solidity, greater net depth, and lighter bottom weights significantly reduce the effective aquaculture volume when subjected to waves or currents. The total radiation received by the FPC structure remains largely unchanged compared to that of an FPV structure. However, irradiance fluctuations decrease significantly with increasing net solidity, net depth, and bottom weight mass. These findings provide valuable insights for the design of FPC structures that ensure a balance between aquaculture sustainability and power generation efficiency.

Accurately predicting the hydrodynamic response of nets subjected to irregular waves continues to be a significant issue because traditional methods do not adequately include the statistical characteristics of irregular waves and the effects of multi-hydrodynamic factors. This study systematically investigated the hydrodynamic interactions between irregular waves and net panels using integrated experimental and numerical approaches. Statistical regression analysis was conducted to assess the effects of the significant wave height H-1/3, significant wave period T-H(1/3), and net solidity S-n on the hydrodynamic responses. The results indicated that the significant wave height had a greater influence on the force magnitude than the significant wave period. Normalization using the product of Reynolds number (Re) and Keulegan-Carpenter number can enhance the linearity of force prediction compared to single-dimensionless parameters. Correlation and significance analyses identified five critical dimensionless parameters governing the hydrodynamic coefficients. Predictive hydrodynamic models of the nets were developed using an artificial neural network (ANN) and nonlinear regression, with the ANN demonstrating superior accuracy. A non-hydrostatic porous-media model was employed to simulate irregular wave-net interactions and was validated against physical experiments through a comparative analysis of the effective wave forces and force spectra. Out-of-sample testing confirmed the robustness of both the predictive models, although the ANN predictions exhibited enhanced reliability at longer effective wavelengths.

An offshore wind energy-aquaculture integrated platform, combining a floating vertical-axis wind turbine with a fish cage (VAWT-FC), is proposed in this study. To investigate its hydrodynamic response characteristics, laboratory experiments were conducted using a 1:100 scale physical model. Regular wave tests were performed to analyze the platform's behavior under various wave heights and periods. The results show that the heave, surge, pitch motions, and mooring line tension all increased with wave height. For instance, as the wave height increased from 3 cm to 12 cm, pitch motion increased from 3.17 degrees to 11.70 degrees, and mooring tension increased by 229 %. With increasing wave period, surge and heave initially decreased and then increased, while pitch showed the opposite trend. A critical inflection point was observed at a wave period of 0.8 s, where the pitch amplitude peaked and both surge and heave reached minimum values-corresponding to a wavelength approximately equal to the platform's 0.851 m span. Furthermore, wave overtopping was found to occur in two distinct stages as wave height increased and in three stages as wavelength increased. In contrast, wave breaking was observed to evolve through two phases under the influence of both increasing wave height and wavelength. The findings offer valuable insights for the development and optimization of multi-functional offshore platforms integrating renewable energy and aquaculture.

Existing studies on fish swimming have generally examined the effects of the surrounding flow field under stationary conditions using a uniform incoming flow. Moreover, most research has focused on flow phenomena around individual fish or specific regions of the fish body. However, an increasing number of studies have demonstrated that group locomotion not only reduces energy consumption but also provides sociological benefits, including predator avoidance and enhanced predation success. In this study, we employ an overset mesh technique—implemented through the secondary development of a user defined file in Fluent—to investigate the influence of passive hydrodynamics on the self-propelled swimming of fish under a uniform incoming flow. This study primarily focuses on elucidating the mechanisms underlying fish self-propelled swimming and the relationships among tail-beat frequency, incoming flow velocity, and swimming performance, while also examining the hydrodynamic variations in both juxtaposed and tandem fish pair configurations. The study demonstrated that passive hydrodynamics did not contribute to speed gain in side-by-side swimming fish. As the inter-fish spacing decreased, the negative effects became more pronounced, although phase variations enhanced propulsion. In contrast, tandem swimming fish benefited from hydrodynamic interactions, with the upstream fish experiencing greater advantages than the downstream fish; however, the influence of wake vortices occasionally disrupted these benefits. However, due to intermittent interference from the wake vortex, these hydrodynamic benefits are not consistently sustained. In this study, we examine the variations in key parameters during the swimming process of fish schools, which is essential for elucidating their underlying swimming mechanisms. Hydrodynamic interactions are crucial for the energy efficiency of fish schools. We studied these dynamics using a computational model of self-propelled fish, which offers a more realistic view than traditional stationary simulations where fish cannot move freely. Our results show that for fish swimming side-by-side, hydrodynamic forces are generally detrimental to propulsion. However, this disadvantage is overcome if they coordinate their tail beats in an anti-phase pattern. In contrast, for fish swimming in a line, passive fluid forces are beneficial, causing them to naturally settle into a stable, energy-efficient formation. These findings clarify the physical mechanisms that drive collective swimming behavior and can inform the design of more efficient underwater robotic swarms.

The hydrodynamic performance of aquaculture tanks is crucial for fish welfare and tank self-cleaning. To optimize tank geometry and improve the flow environment, this study employed computational fluid dynamics to investigate the effects of varying diameter-to-depth ratios (L/H) on four tank types: circular, square arc angle, octagonal, and square. The hydrodynamic performance was assessed by analyzing flow velocity, vortex generation, turbulence kinetic energy, turbulence dissipation rate, and effective energy utilization. The numerical model was validated through physical experiments. Results indicated that increasing the diameter-to-depth ratio within the same tank type led to a progressive decrease in turbulence intensity, an expansion of low-velocity areas, and a reduction in average velocity and energy utilization coefficient. Optimal diameter-to-depth ratios ranged from 2:1 to 5:1 for circular, square arc angle, and octagonal tanks, and 2:1 to 3:1 for square tanks. Tanks within these optimal ranges exhibited superior hydrodynamic performance. Overall, this study provides a theoretical basis for selecting aquaculture tanks with optimal diameter-to-depth ratios.

The wind and wave conditions in the near-island waters are milder than those in the open sea area due to the shielding effect of island terrain, which makes the near-island waters the main direction for the transformation and upgrading of the marine aquaculture industry. The installation of multi-body net cage platforms adjacent to islands will complicate wave propagation characteristics, consequently modifying the nearshore wave hydrodynamic environment. This study investigates the influence of multi-body floating aquaculture platforms on wave propagation characteristics near slope terrain through systematic physical model tests. The experimental analysis focuses on platform-induced modifications to wave parameters, wave height distributions, nonlinear wave properties, and time-frequency characteristics of surface elevation. Results indicate that platform presence significantly reduces wave heights on the slope, with the attenuation magnitude diminishes as wave recurrence periods increase. The Composite Weibull distribution analysis reveals an increased shape parameter and a reduced transition wave height under platform conditions. Nonlinear wave characteristics exhibit distinct spatial patterns: wave asymmetry and skewness decrease at cage positions, while slope-region nonlinearity remains predominantly governed by water depth variations. Spectral analysis demonstrates that platform installation suppresses higher-order spectral energy density peaks and increases dominant wave frequencies near the structure. These findings provide critical insights into hydrodynamic interactions between aquaculture infrastructure and nearshore wave dynamics, offering practical guidance for coastal aquaculture facility design in island-sheltered waters.

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.

This study presents an improved porous media model for simulating the interaction between the fixed aquaculture nets and flow. The fluid motion is computed based on the Reynolds time-averaged Navier–Stokes equations on the regular Eulerian mesh. The porous media model simulates the nets, where the interface between the complex shapes of the nets and the fluid is determined by the continuous forced immersed boundary (IB) method. The fluid volume fraction is defined and embedded in the porous media coefficients and porosity equations to set the porous media parameters at IB. Several cases validate the model, including the flow interactions with the single net panel, gravity net cage, and offshore aquaculture platform. Meanwhile, the effects of incoming velocity, attack angle, solidity, and the shape of the net on the simulation are investigated. The numerical model can reasonably predict the hydrodynamic of the nets with a relative error of less than 8%. Moreover, the computational efficiency of the hydrodynamic of complex shaped nets is significantly improved, with a maximum of about 11.54 times.

Large-scale pile-net enclosures are increasingly utilized in marine engineering. However, simulating their interactions with waves remains a significant challenge. This study presents a numerical model that coupled porous media model and direct-forcing immersed boundary method to simulate the interaction between the pile-net enclosure structure and waves. The damping effect of the netting was simulated by porous media, while the pile was simulated using the direct-forcing immersed boundary method. The numerical model was verified based on experimental results obtained from corresponding physical model tests. Using the proposed numerical approach, this paper investigates the effects of wave period, net solidity, spacings of piles and wave incident angles on the hydrodynamic of the pile-net enclosure structure, including wave field and pile group coefficients. The results show that the pile-net enclosure structure demonstrates a damping effect on wave propagation, particularly for high-frequency waves. An increase in net solidity significantly impacts the wave forces on downstream piles. Additionally, the angle of incidence of the wave affects the orientation of the reflected wave crest line. When the piles are symmetrically positioned in pairs along the wave propagation direction, the wave height inside the structure decreases.

This study analyzes the effect of nozzle geometry on the dynamic characteristics of water jets. The flow characteristics of Helmholtz oscillators with three different nozzle shapes (four, six, and eight petals) are investigated using large eddy simulations. The relationship between coherent structures and cavitation is illustrated using the vortex transport equation. The results show that the evolution of cavitation clouds in a Helmholtz cavity results in a periodic change in the jet pressure and the formation of pulsed water jets from petal-shaped nozzles. In addition, the cavitation bubbles inhibit the stretching and expansion of the vortex structure, and the convergence of the turbulent kinetic energy is conducive to maintaining its stability. The four-petal nozzle has the highest velocity at the central axis of the jet at 1.76% higher than that of the six-petal nozzle. When the number of petals in the nozzle is increased from six to eight, the velocity decreases by 7.96%. The streamwise vortex strength of the jet with six petals is enhanced by 61.31% compared to the four-petal case, while the eight-petal nozzle jet is only 11.75% higher than that of the six-petal nozzle. The six-petal nozzle significantly improves the mixing characteristics by slightly reducing the velocity. This study provides guidance for reducing the stagnation pressure loss when using nozzles with special shapes to enhance jet mixing.

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.

Nonlinear interactions of an oblique wave with an aquaculture cage array containing 16 net cages in a 2 x 8 configuration is studied in this paper. Our objective is to understand the nonlinear dynamics of the cage array induced by different hydrodynamic forcing mechanisms under oblique wave attack. To this end, we use an efficient numerical scheme with a robust implicit finite-element method for the nonlinear wave-structure interactions. The nonlinear and non-stationary data is decomposed by the empirical mode decomposition method, allowing for identification of different hydrodynamic forcing mechanisms. Then, physical model tests of a cage array in the 1 x 3 configuration under the low-frequency wave are conducted to verify the present numerical model. The harmonic responses of the surge and heave between numerical simulations and experimental tests are close to each other; indicating that the present numerical model is feasible to predict the dynamic response of the cage array in waves. The results highlight that the flexible cage with lower elastic modulus shows larger excursion in the weather side of the cage array, and the flexible cage has a better ability to absorb energy from incident waves. However, the elastic modulus of the floating collar has little effect on the surge and heave motions. Under the oblique wave attack, the nonlinear responses of a representative mooring are identified to be wave-frequency and low-frequency driven, and the nonlinear sway responses are found to be dominant by lowfrequency excitations.

This study aimed to examine the nonlinear dynamics of aquaculture platforms using the Hilbert–Huang transform (HHT). First, a numerical model that couples the boundary element method and lumped-mass model was used to simulate the dynamic behavior of a multi-body floating aquaculture platform in irregular waves. Second, a time–frequency analysis method based on the HHT was used to analyze the dynamic responses, including motion and mooring force responses. The results highlight that the surge motion of the net cage is dominated by the low-frequency components, whereas the heave and pitch motions are dominated by the wave-frequency components. The pitch response of the net cage has an obvious energy concentration near the peak frequency region of the incident wave. The surge motion of the net cage in the middle of the platform has a greater response to wave components with lower frequencies than that of the other two cages. The inherent characteristic vibration form of the mooring force response is affected by both the low-frequency characteristic of surge motion and the wave-frequency characteristic of motions in the vertical plane. The amplitudes of the wave-frequency components of the mooring force are much larger than those of the low-frequency components, which is like the characteristics of heave and pitch motions. The gravity periods of the wave-frequency mode components of the mooring force response were very close to the gravity period of the surge motion.