Search Results (20)

Fish protection and guidance are critical factors in the design and operation of water intakes at hydropower plants. In this study, the hydraulic performance of the angled Oppermann fine screen has been investigated in a hybrid model with and without a guidance wall. The experiments were conducted under two different angles of 30° and 45°, and a bar spacing of 10 mm at a large-scale flume with a width of 2 m. Just up- and downstream of the screen, three-dimensional velocities were measured with Acoustic Doppler Velocimetry (ADV). In the computational fluid dynamics (CFD) model, the Large Eddy Simulation (LES) coupled with the Darcy–Forchheimer law, in which screens were modeled as homogeneous porous media, was employed. The experimental results revealed that velocities less than 0.5 m/s just upstream of the Oppermann fine screen and tangential velocity gradients over the entire cross-section of the screen were found to be 0.04–0.338 m/s/m and 0.04–0.856 m/s/m for α = 30° and α = 45°, respectively, creating favorable hydraulic conditions for effective downstream fish guidance. The CFD model was validated against the experimental data within an acceptable error range, both for the velocity and the turbulent kinetic energy. Numerical simulations showed that implementing a curved guidance wall creates a symmetrical and homogeneous downstream flow field without the formation of recirculation zones behind the angled screen. Full article

To enhance the hydrodynamic stability of offshore floating photovoltaic (OFPV) platforms under complex sea conditions, this study proposes a novel arc-plate dual-pontoon floating breakwater. A combined methodology of experimental investigation and numerical simulation was integrated to systematically study its hydrodynamic responses and attenuation performance. A two-dimensional numerical wave flume was established in FLOW-3D, and the results were validated against experimental data. The results reveal that the wave energy reduction is primarily achieved through the wave reflection in front of the pontoons and turbulence-induced dissipation guided by the arc plate. The effects of key structural parameters (pontoon draft depth, arc plate span, and the relative freeboard height) were studied to optimize its performance. The results show that both the increasing draft depth and arc plate span can significantly improve the attenuation under long-period waves. Additionally, higher relative freeboard heights help to reduce both the transmission coefficient and horizontal wave force, with the optimal value identified as 0.7. The findings suggest theoretical insights and possible indications for the design of the floating breakwater system in offshore renewable energy applications. Full article

The generation and propagation of water waves in a numerical wave flume with Ursell numbers (Ur) ranging from 0.67 to 43.81 were investigated using the wave generation theory of Goring and Raichlen and a two-dimensional numerical viscous wave flume model. The unsteady Navier–Stokes equations, along with nonlinear free surface boundary conditions and upstream boundary conditions at the wavemaker, were solved to build the numerical wave flume. The generated waves included small-amplitude, finite-amplitude, cnoidal, and solitary waves. For computational efficiency, the Jacobi elliptic function representing the surface elevation of a cnoidal wave was expressed as a Fourier series expansion. The accuracy of the generated waveforms and associated flow fields was validated through comparison with theoretical solutions. For $Ur<26.32$, small-amplitude waves generated using Goring and Raichlen’s wave generation theory matched those obtained from linear wave theory, while finite-amplitude waves matched those obtained using Madsen’s wave generation theory. For $Ur>26.32$, nonlinear wave generated using Goring and Raichlen’s theory remained permanent, whereas that generated using Madsen’s theory did not. The evolution of a cnoidal wave train with $Ur=43.81$ was examined, and it was found that, after an extended propagation period, the leading waves in the wave train evolved into a series of solitary waves, with the tallest wave positioned at the front. Full article

This study seeks to optimize the shape of a wave absorber with an inclined porous plate using an artificial neural network (ANN) model to improve the operating efficiency and experimental accuracy of a square wave basin. As our numerical tool, we employed the dual boundary element method (DBEM) to avoid the rank deficiency problem occurring at the degenerate plate boundary with zero thickness. A quadratic velocity model incorporating a CFD-based drag coefficient was employed to account for energy dissipation across the porous plate. The developed DBEM tool was validated through comparisons with self-conducted experiments in a two-dimensional wave flume. The input features such as the inclined angle and plate length affect the performance of the wave absorber. These features have been optimized to minimize the averaged reflection coefficient and the installation space (spatial footprint) with the application of a trained ANN model. The dataset used for training the ANN model was created using the DBEM model. The trained model was subsequently utilized to predict the averaged reflection coefficient using a larger dataset, aiding in the determination of the optimal wave absorber design. In the optimization process of minimizing both reflected waves and spatial footprint, the weighting factors are assigned according to their relative importance to each other, using the weighted sum model (WSM) within the multi-criteria decision-making framework. It was found that the optimal design parameters of the non-dimensional plate length ($l/h$) and inclined angle ($\theta$) are $1.46$ and $5.34°$ when performing with a weighting factor ratio (80%: 20%) between reflection and spatial footprint. Full article

Floating breakwaters (FBs) play an important role in protecting coastlines, marine structures, and ports due to their simple construction, convenient movement, cost-effectiveness, and environmental friendliness. However, the traditional box-type FBs are flawed due to their requiring large sizes for wave attenuation and their overly high level of wave reflection. In this paper, a novel partial T special-type FB with wave attenuation on the surface and flow blocking below the water has been presented. First, the User-Defined Function (UDF) feature in ANSYS Fluent was employed to compile the six degrees of freedom (6-DOF) motion model. A two-dimensional viscous numerical wave flume was developed using the velocity boundary wave-generation method and damping dissipation wave-absorption method, with fully coupled models of the FBs developed. A VOF multiphase flow model and a RANS turbulence model were employed to capture the free flow of gas–liquid two-phase flow. Then, the performance of wave attenuation of the new FB was compared with that of the traditional box-type FB of the same specifications. The simulation results showed that the transmission coefficient of the new FB is significantly lower than that of the box-type FB, and the dissipation coefficient is notably higher, demonstrating excellent performance of wave attenuation, particularly for long-period waves. As wave height increases, the novel FB benefits from its wave attenuation mechanism, with a lower reflection coefficient compared to the box-type FB. Finally, through parametric analysis, some design recommendations of the novel FB suitable for practical engineering applications in deep-sea aquaculture are presented. Full article

In this paper, the Smoothed Particle Hydrodynamics (SPH) method is used in a C# environment to simulate the interaction between freak waves and bottom-fixed structures by establishing a fluid dynamics model. Paraview software 5.10.1 was used to analyze and visualize the simulation results. In order to simulate wave propagation accurately, the reliability of the model was verified by comparing experimental and simulated data. A two-dimensional numerical wave flume was established based on the SPH method, a conservative Riemann solver was introduced, a repulsive boundary condition was adopted, and a slope was used to eliminate wave reflection. Bottom-fixed structures of different heights and lengths, as well as different wave conditions, were selected to numerically simulate the interaction between freak waves and bottom-fixed structures. The results show that the height of bottom-fixed structures and wave conditions have a significant effect on hindering the propagation of rogue waves, while the length has little effect on the propagation of deformed waves. When the amplitude of the wave remains constant, both the period andthe duration of the deformed wave are longer. This research is of certain significance for the prediction of freak waves in marine engineering and the application and promotion of SPH methods. Full article

The aim of this study is to better understand cross-reef wave-driven current characteristics, which are crucial to biological, ecological, and geomorphological processes within coral reefs. This study reports a set of new wave flume measurements to assess flow along the water depth and across a fringing reef profile under the action of a plunging breaker. Laboratory results are presented in view of cross-reef variations in both the wave height and the mean water level (MWL); the vertical profiles of wave-averaged mean currents below the wave trough and along the reef are also presented. To resolve the two-dimensional vertical (2DV) flow characteristics across the reef, Reynolds-Averaged Navier–Stokes (RANS) equations were solved using k-ω SST closure, modified to improve stability, and a Volume of Fluid (VOF) approach was used to capture the water surface. This numerical model was first validated via experimental measurements in view of waves and flows. It was then used to analyze the cross-reef distributions of the mean flow field, turbulent kinetic energy (TKE), and Reynolds shear stress across the reef. Full article

To investigate the overtopping and slamming phenomena that occur in the interactions between waves and oscillating surge wave energy converters (OSWECs), a two-dimensional numerical wave flume was established using computational fluid dynamics (CFD) software Fluent by adding the momentum source terms into the original Navier–Stokes equation. Numerical convergence studies of the mesh sizes and time steps were firstly performed to ensure the sufficient accuracy of the numerical model. The variations in the wave heights along the wave propagation direction in the wave-generating area, working area, and wave-absorbing area were analyzed. The dynamics of the flap-type OSWEC were simulated using the overset mesh function embedded in Fluent. In addition, the numerical results were compared with the experimental data, and good agreements were achieved. External torque was applied to the hinge joint of the OSWEC to simulate the forces due to the power take-off (PTO) system, and the identified optimal PTO damping was compared with the numerical results based on the potential flow theory, which verified the correctness of the numerical PTO system. On this basis, nonlinear wave slamming by the sharp-eagle OSWEC was analyzed. The results show that under certain incident wave conditions, the sharp-eagle OSWEC can effectively reduce the maximum rotation angle and angular velocity compared with those of the flap-type OSWEC, and there is no overtopping that occurring for the sharp-eagle OSWEC. Furthermore, the sharp-eagle OSWEC performs better than the flap-type OSWEC. Full article

In coastal waters, wave propagation is often affected by rivers and tides. The wave current interaction increases the complexity of the wave propagation. In this study, we consider the Boussinesq type equation with an improved dispersion term as the governing equation and establish a numerical model of wave propagation in the coexistence of wave current environment. Firstly, we use the MIKE 21 BW model to simulate the propagation of dual-frequency waves. The Navier–Stokes equation wave model is used to verify the results and the Fourier transform is used to analyze and discuss the dual-frequency waves. Our findings show that the numerical model established by the Boussinesq equation can better describe the nonlinear interaction between waves more accurately at a much higher computational efficiency compared with the Navier–Stokes equation wave model. In addition, we set the constant current source point in the wave numerical model and conduct the numerical simulation of waves in the current environment, by improving the mass source wave generation method. The numerical simulation of wave-current interactions between uniform and variable water depths is performed, thus demonstrating its capability to describe accurately the influence of water flow on wave propagation. Full article

The boundary element method (BEM) with Lagrangian formulation is a conceptually simple and efficient method for the simulation of nonlinear wave shoaling, with or without impermeable coastal structures, up to the wave breaking. However, in post-breaking flows, the domain is no longer simply connected, and the BEM is not efficient for the generation of a new free surface. Volumes of fluid (VOF) methods are made to track the fluid-free surfaces after breaking, but they are more numerically complex and less efficient relative to the BEM before breaking. This study presents a numerical model, named BELWF—boundary elements Lagrangian wave flume—for the mathematical simulation of two-dimensional wave flumes. The BELWF can simulate the hydrodynamics of wave shoaling over a coast profile, with submerged impermeable coastal structures of any geometry. The developed model is applied to simulate and study Geotube structures. The BELWF is validated by comparisons with OpenFOAM simulations. Both the BELWF and OpenFOAM simulations show that the most critical state, regarding the sliding stability of the Geotube, occurs, typically just before breaking, where the BELWF reasonably assesses the wave loads and the sliding stability. Hence, the BELWF is a valid and efficient method for the preliminary design of impermeable coastal structures. Finally, the BELWF is applied to simulate a practical design example of a complete shoaling process along a sloped shore with a Geotube structure at the shallow water, which develops a plunging breaker. The simulation well captures the critical event considering the sliding stability of the structure. Full article

The presence of microplastics has been reported in most marine environments. Their accumulation can affect the marine ecosystem, and their consumption by small organisms of various sizes can indirectly affect human beings who consume them. Recent observations have reported the pathways and fates of microplastics surrounding man-made coastal structures, such as artificial reefs. However, basic research elucidating the physical behavior near the structure is scarce. We implemented a two-dimensional numerical wave flume simulating intermediate waves with a weak current in a coastal area to investigate the behaviors of microplastics corresponding to parameters such as particle size (0.2, 1, and 5 mm), particle density (900, 1000, and 1100 $\mathrm{kg}/{\mathrm{m}}^3$), and submerged artificial structure. The results showed that smaller particles had a stronger horizontal dispersion but a weaker horizontal advection. Installing a submerged structure increased the flow rate above the structure. It also increased particle accumulation upstream and downstream near the edge and corner of the structure. The accumulation was significantly affected by the installation of the structure when the resuspension of microplastics occurred intermittently. This work elucidates the mechanisms underlying the distribution, accumulation, and dispersion of microplastics that are important in predicting the fate of microplastics in the vicinity of artificial structures. Full article

In this paper, a two-dimensional time-domain numerical flume has been established to model and investigate nonlinear interactions between nonlinear surface waves and a submerged inclined thin plate. The model solves the Laplace equation and the fully nonlinear free surface boundary conditions within the framework of potential flow theory based on the high-order boundary element method. The mixed Euler–Lagrangian method is applied to update the water surface at each time step, and the fourth-order Runge–Kutta method for time stepping. A so-called four-point method was employed to separate the second-order harmonic free and bounded wave that has the same wave frequency but different wave celerity in front of and behind the submerged plate. It is found that the amplitude of the second-order harmonic free wave increases with the inclination angle of the submerged plate, and the level/amount of the increase is larger for a larger wave steepness. In addition, the amplitudes of both the second-order reflected and transmitted waves are found to increase with the wave steepness, and their empirical relationships are derived for potential use in practical engineering. Full article

The frequency of droughts and floods is increasing due to the extreme climate. Therefore, water resource planning, allocation, and disaster prevention have become increasingly important. One of the most important kinds of hydrological data in water resources planning and management is discharge. The general way to measure the water depth and discharge is to use the Acoustic Doppler Current Profiler (ADCP), a semi-intrusive instrument. This method would involve many human resources and pose severe hazards by floods and extreme events. In recent years, it has become mainstream to measure hydrological data with nonintrusive methods such as the Large-Scale Particle Image Velocimetry (LSPIV), which is used to measure the surface velocity of rivers and estimate the discharge. However, the unknown water depth is an obstacle for this technique. In this study, a method combined with LSPIV to estimate the bathymetry was proposed. The experiments combining the LSPIV technique and the continuity equation to obtain the bed elevation were conducted in a 27 m long and 1 m wide flume. The flow conditions in the experiments were ensured to be within uniform and subcritical flow, and thermoplastic rubber particles were used as the tracking particles for the velocity measurement. The two-dimensional bathymetry was estimated from the depth-averaged velocity and the continuity equation with the leapfrog scheme in a predefined grid under the constraints of Courant–Friedrichs–Lewy (CFL). The LSPIV results were verified using Acoustic Doppler Velocimetry (ADV) measurements, and the bed elevation data of this study were verified using conventional point gauge measurements. The results indicate that the proposed method effectively estimated the variation of the bed elevation, especially in the shallow water level, with an average accuracy of 90.8%. The experimental results also showed that it is feasible to combine the nonintrusive imaging technique with the numerical calculation in solving the water depth and bed elevation. Full article

The hydrodynamic response of a land-based oscillating water column (OWC) wave energy converter under various irregular wave conditions is investigated numerically. Based on the potential flow theory, a two-dimensional fully nonlinear numerical wave flume (NWF) is developed to model the hydrodynamic characteristics using the time-domain higher-order boundary element method (HOBEM). The inner-domain sources method and JONSWAP energy spectrum is used to generate the irregular incident waves, and a linear pneumatic model is used to determine the pneumatic pressure inside the chamber. The free surface elevations at the chamber centre and the oscillatory pneumatic pressures induced by the vertical motion of the water column are recorded. The influence of irregular waves on the hydrodynamic characteristics of the OWC device is carried out by comparison with the regular waves, and a number of significant wave heights and peak wave periods are considered. The hydrodynamic efficiency of the OWC device in irregular wave conditions is observed to be lower than that in regular waves for most wave frequencies, especially near the resonant frequency. Full article

Phosphorus is the main limiting factor in river eutrophication, whose distribution law is affected by sediment and hydrodynamics. Based on the sediment of Wujiadu Hydrological Station in the middle reaches of the Huaihe River, a physical experiment of phosphorus adsorption onto sediment in a dynamic environment was carried out in this paper to obtain two important parameters of the water quality model. By considering the effect of adsorption and desorption, diffusion, sedimentation and suspension, a numerical model of a three-dimensional periodic flume was established, verified and then applied to the generalized river according to the shape of the cross section in the Bengbu reach of the Huaihe River. The spatial-temporal distribution law of phosphorus was obtained with different single inflow factors. When DP or AP changed, the overall trend of downstream DP was consistent with that of incoming DP/AP; however, it became more complex when SS or Q changed, which aggravated the sedimentation and re-suspension process. When incoming DP changed, $D{P}_{\max }$ decreased with the distance, while when incoming AP or SS changed, $D{P}_{\max }$ increased at first and then decreased. The relationship between $\Delta D{P}_{\max }$ and $\Delta T{P}_{\mathrm{in}}$ was fitted into a straight line with a slope of 0.9951, while it was 0.2154 with the change of incoming SS. The effect of the not-constant time of the inflow on the peak concentration of phosphorus along the river was much weaker than that of the peak concentration. Full article