Wave Tank Research Articles

Effect of wind conditions on the performance of an Oscillating Water Column energy converter

Local atmospheric conditions surrounding an off-shore Oscillating Water Column device — OWC hereinafter —, in particular wind action, may affect OWC performance and efficiency, specially over long harvesting intervals, i.e. yearly energy production. This work proposes an experimental study of a simple off-shore OWC where different ambient conditions are compared. More specifically, it proposes a set of experimental tests in laboratory wave flume, under both calm and external wind conditions, which represent a more realistic situation in full-scale prototypes. The results show that the external wind modifies the ambient conditions by changing the temperature, humidity and pressure values of the air surrounding the OWC device, affecting the density and the thermodynamic balance. This affects negatively the OWC performance, reducing the maximum pneumatic power by up to 15%, which can be extrapolated to a reduction of 3% in the total amount of annual energy produced.

Non-Equilibrium Scour Evolution around an Emerged Structure Exposed to a Transient Wave

The present study evaluates the performance of two numerical approaches in estimating non-equilibrium scour patterns around a non-slender square structure subjected to a transient wave, by comparing numerical findings with experimental data. This study also investigates the impact of the structure’s positioning on bed evolution, analyzing configurations where the structure is either attached to the sidewall or positioned at the centerline of the wave flume. The first numerical method treats sediment particles as a distinct continuum phase, directly solving the continuity and momentum equations for both sediment and fluid phases. The second method estimates sediment transport using the quadratic law of bottom shear stress, yielding robust predictions of bed evolution through meticulous calibration and validation. The findings reveal that both methods underestimate vortex-induced near-bed vertical velocities. Deposits formed along vortex trajectories are overestimated by the first method, while the second method satisfactorily predicts the bed evolution beneath these paths. Scour holes caused by wave impingement tend to backfill as the flow intensity diminishes. The second method cannot sufficiently capture this backfilling, whereas the first method adequately reflects the phenomenon. Overall, this study highlights significant variations in the predictive capabilities of both methods in regard to the evolution of non-equilibrium scour at low Keulegan–Carpenter numbers.

Millimeter Wave Multi-mode OAM-MIMO Channel Capacity Study

This study examines the theoretical aspects of channel capacity for millimeter wave multi-mode Orbital Angular Momentum (OAM) Multiple Input Multiple Output (MIMO) systems. It begins with a theoretical analysis of these channels, highlighting their importance and potential applications in wireless communications. A Sparse Bayesian Learning (SBL) based Joint Uplink and Downlink Channel Estimation (JUDCE) approach is then employed to estimate the downlink channel using uplink training signals, while accounting for inactive receiving antennas. Exploiting the sparsity of millimeter wave channels, the downlink channel estimation is modeled as a compressed sensing problem using a binary mask matrix. An SBL framework is developed to efficiently tackle this problem. Theoretical and simulation results indicate the proposed method significantly improves channel estimation accuracy and spectral efficiency of downlink transmissions, underscoring its importance for the advancement of future communication technologies.

Influence of wakes interaction and upstream turbulence on three tidal turbines behaviour

The current study presents numerical results on three tidal turbine models (two in front, one downstream) interacting in a turbulent upstream flow. The numerical results come from a lifting-line (LL) embedded in a Lagrangian vortex particle (VP) solver: Dorothy LL-VP. The objective is to assess the extent to which this numerical tool is suited to reproduce accurately wakes interaction as well as fluctuating loads perceived by the downstream turbine. To this aim, the numerical set-up reproduces an experimental campaign led at IFREMER’s wave and current flume tank. The downstream turbine is placed at different positions to change the wakes interaction. Two upstream turbulence intensities (TI) experimentally tested are reproduced numerically using the synthetic eddy method (SEM). Favourable comparisons are obtained between numerical and experimental wakes, including velocity profiles. Preliminary results suggest that the downstream turbine performance decrease is numerically well captured. More investigations are needed on the loads fluctuations with longer computation time, and adding an angular velocity controller as well as hub modelling to Dorothy LL-VP.

Numerical study on the cavity dynamics of water entry and exit for a high-speed projectile crossing a wave

The high-speed projectile moving near the sea level will significantly suffer from the effects of waves. The water entry and exit of a high-speed projectile crossing a wave are investigated by detached-eddy simulation. Three simulations with different altitudes through the wave are conducted to analyze the altitude's influence on the cavity dynamics. To validate the numerical model, a water-entry experiment is carried out in a wave tank for comparison. The projectile crossing the wave forms a cavity channel from water entry to exit. Because the water below the cavity is more difficult to displace than the atmosphere with the water surface under the cavitation effects, the downward expansion of vapor is blocked, and the wave surface is lifted. Consequently, the cavity above the projectile expands more strongly until breaking through the water surface, while the cavity below the projectile keeps closed, and the projectile is wetted. Thus, a nose-up pitching moment is generated at water entry, while the drag force is gradually enhanced during the water exit, and a lift force acts toward the atmosphere. As the altitude increases, the upper cavity becomes more open, but the lower cavity shrinks, leading to the augmentation of the lift force.

Experimental Study on Spacing Effect in Arrays of Draft-Varying Floating WEC-Dikes

This study examines the impact of the spacing parameter on the efficacy of an array of hybrid modules functioning as both floating breakwaters and wave energy converters. The dual functionality is ensured by the ability of the device to autoadjust its submergence. The behavior of multiple 1:40 scaled modules was tested in the wave tank of the University of Campania “Luigi Vanvitelli”. The objective was to assess the hydraulic performance of the array by analyzing transmission, reflection, and dissipation coefficients under different wave conditions. Specifically, the transmission coefficient ranges between 0.85 and 0.51, depending on the relative wavelength and wave steepness, while the reflection and dissipation coefficients vary, respectively, between 0.70–0.20 and 0.55–0.3. In any case, the results underscore the critical importance of the spacing parameter.

Generalized extended (2+1)-dimensional Kadomtsev-Petviashvili equation in fluid dynamics: analytical solutions, sensitivity and stability analysis

This study discusses a new version of the (2+1)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(2+1)$$\\end{document}-dimensional Kadomtsev-Petviashvili equation. This equation is used to model the behavior of nonlinear waves in various fields like ferromagnetic media, ion-acoustic waves in plasma physics, and fluid dynamics. It is instrumental in modeling surface and internal waves in straits or channels. The main goal of the research is to determine the exact solutions for this equation and analyze their physical characteristics. We obtain exact solutions using two improved techniques, namely the modified extended tanh-function and the modified generalized Kudryashov methods. These techniques investigate various exact solutions, such as exponential, rational, hyperbolic, and trigonometric. Besides, the sensitivity and the stability analysis of the model are presented. Additionally, three- and two-dimensional contour plots are created to present the physical behavior of the exact solutions.

Impact of focused wave groups on pier structures: a case study of severe breaking waves at Pont del Petroli during storm Gloria

In January 2020, the footbridge connecting the seaward platform of the Pont del Petroli pier to Badalona beach collapsed due to the severe sea storm named Gloria. Approximately 15 m of the footbridge fell into the sea as a result of prolonged wave action and strong impacts. To understand the complex interaction between waves and structures that led to the pier’s collapse during the storm, a composite modelling approach was developed. The loads on each pier element were initially evaluated using the meshless DualSPHysics code, which employs the Smoothed Particle Hydrodynamics (SPH) method. This evaluation was conducted under severe wave conditions analogous to those experienced during the storm. Numerical models informed the design of an experimental campaign carried out at the Maritime Engineering Laboratory of Universitat Politècnica de Catalunya—BarcelonaTech, using the CIEM large-scale wave flume facility in Barcelona, Spain. Post-storm bathymetric surveys revealed significant alterations in the seabed profile near the affected infrastructure, including sediment deposition and a reduction in water depth from 10 m to 8 m. Consequently, it was anticipated that wave transformation and breaking in the vicinity of the structure would be substantially affected. To explore this phenomenon, various extreme wave impacts were experimentally simulated using focused wave groups. The physical model findings unveiled the forces that the pier endured during the storm Gloria. The results indicate that wave phases influence individual waves, with waves that are biased and asymmetric experiencing higher peaks than those focused on the crest. This insight helps to explain the structural failure of the footbridge during the storm and underscores the importance of considering wave phase impacts in the design and assessment of coastal infrastructure. The combined numerical and experimental approach provides a comprehensive understanding of the forces at play, contributing valuable knowledge to the field of coastal engineering and infrastructure resilience.

Experimental and Numerical Investigations for Impact Loading on Platform Decks

Experimental measurement and numerical simulations were carried out for investigating the impact loading behavior of platform decks under regular and irregular wave actions. In the numerical simulation section, a full-scale numerical wave tank was established using STAR-CCM+ software. A decreased tendency can be observed for an increased relative length of platform when the incident wave length is double the deck length. The increased deck height can also decrease impact loading on the platform, which is due to the platform being far away from the incident wave. Impact loading on the deck decreases with the increase in inclination angle, which can be explained by the deck bottom being directly exposed to the incident wave at negative inclination angles. Finally, the variation tendency of impact loading on platform decks under irregular wave actions is similar to that under regular wave actions, including the averaged values and significant values.

Bathymetry reconstruction from experimental data using PDE-constrained optimisation

Knowledge of the bottom topography, also called bathymetry, of rivers, seas or the ocean is important for many areas of maritime science and civil engineering. While direct measurements are possible, they are time consuming, expensive and inaccurate. Therefore, many approaches have been proposed how to infer the bathymetry from measurements of surface waves. Mathematically, this is an inverse problem where an unknown system state needs to be reconstructed from observations with a suitable model for the flow as constraint. In many cases, the shallow water equations can be used to describe the flow. While theoretical studies of the efficacy of such a PDE-constrained optimisation approach for bathymetry reconstruction exist, there seem to be few publications that study its application to data obtained from real-world measurements. This paper shows that the approach can, at least qualitatively, reconstruct a Gaussian-shaped bathymetry in a wave flume from measurements of the free surface level at up to three points. Achieved normalised root mean square errors (NRMSE) are in line with other approaches.

Finding the best shape of floating wave energy converters for different primary geometries: Experimental and numerical investigations

This research aimed to identify the optimal geometry for maximizing wave energy extraction from wave energy converters (WECs) by employing different primary geometries of floating bodies (specifically, cube, cylinder, and sphere). Laboratory experiments were conducted using a wave tank to generate waves with varying characteristics. The floats were subjected to waves of different wave conditions, including height (4 cm, 6 cm, and 9 cm) and frequency (0.9 Hz and 0.83 Hz). Multiple probes and sensors were used to collect experimental data. The results revealed that when hit by a wave with a height of 9 cm and a frequency of 0.9 Hz, the rectangular cube experienced an average displacement of 12 cm and 14 cm along its length, with the same weight and draft, respectively. Furthermore, comparisons of the experimental data across different scenarios indicated that the rectangular cube, elongated perpendicular to the incident waves, performed well in most of the test cases. The efficiency of primary wave energy conversion was evaluated for all floated bodies and wave conditions, encompassing a range of values from 0.02 to 0.34. Additionally, numerical simulations of wave and float displacement demonstrated good agreement with the experimental observations.

Impact of wave action on the entrainment rate and droplet size of oil

Oil dispersed on the water surface undergoes fragmentation into droplets, subsequently entering the water column under wave action. The oil entrainment rate and the droplet size distribution (DSD) significantly influence the subsequent migration and transformation of oil in the water column. A wave tank system was employed to investigate the impact of wave action on oil entrainment rate and DSD. The experimental results revealed that increased wave height and wave frequency facilitated the entry of oil into the water column and fragmented it into dispersed droplets. Relationships between oil entrainment rate and energy dissipation, as well as DSD, were established and supported by mathematical regression analyses. Non-linear regression analysis indicated that the cumulative frequency distribution of DSD adhered to the Log-Normal and Rosin-Rammler distributions. These findings contribute to a comprehensive understanding of natural oil dispersion and subsea transport, valuable for estimating the origin of oil spills.

Numerical investigation of the response of the hybrid wave energy converter including oscillating water column and horizontal floating cylinder to irregular waves

The main goal of this research is to investigate the effect of some geometrical parameters on an onshore Hybrid Wave Energy Converter (HWEC) including an onshore Oscillating Water Column (OWC) and a Horizontal Floating Cylinder (HFC) under regular and irregular waves. The TMA spectrum is the basis of this study. The wave spectrum is used to generate irregular waves in a numerical wave tank using Ansys-fluent software based on URANS equations. Active wave absorption is used to avoid the effect of reflected waves. Also, the SST k−ω turbulence model and the VOF scheme are used for turbulence modeling and interface tracking, respectively. The results confirm that the efficiency of the HWEC is higher than the efficiency of an OWC and the efficiency of an HFC in both regular and irregular waves. Besides, the efficiency of the HWEC in irregular waves is lower than its efficiency in regular waves. A comparison of the TMA and JONSWAP spectrum on HWEC performance shows that HWEC performance is lower on the JOANSWAP spectrum. This study shows that the use of irregular waves is essential to obtain more realistic results from analyses of the onshore HWEC performance, despite their need for high computational cost.

Modelling the far-field effect of drag-induced dissipation in wave–structure interaction: a numerical and experimental study

In the interaction of water waves with marine structures, the interplay between wave diffraction and drag-induced dissipation is seldom, if ever, considered. In particular, linear hydrodynamic models, and extensions thereof through the addition of a quadratic force term, do not represent the change in amplitude of the waves diffracted and radiated to the far field, which should result from local energy dissipation in the vicinity of the structure. In this work, a series of wave flume experiments is carried out, whereby waves of increasing amplitude impinge upon a vertical barrier, extending partway through the flume width. As the wave amplitude increases, the effect of drag – which is known to increase quadratically with the flow velocity – is enhanced, thus allowing the examination of the far-field effect of drag-induced dissipation, in terms of wave reflection and transmission. A potential flow model is proposed, with a simple quadratic pressure drop condition through a virtual porous surface, located on the sides of the barrier (where dissipation occurs). Experimental results confirm that drag-induced dissipation has a marked effect on the diffracted flow, i.e. on wave reflection and transmission, which is appropriately captured in the proposed model. Conversely, when diffraction becomes dominant as the barrier width becomes comparable to the incoming wavelength, the diffracted flow must be accounted for in predicting drag-induced forces and dissipation.

A physical model study on the hydraulic performances of vertical breakwaters with retreated wave walls

This paper describes a 2D physical model study on the hydraulic performances of composite vertical breakwaters with retreated wave walls. The research is an expansion of a previous experimental study by the same Authors: a very large number of experiments, in the order of 2,000, have been carried out by exploring and varying a wide range of wave and geometrical parameters of the structure, to investigate their effect and importance. In order to make feasible the execution of this large number of tests, a small-scale wave flume was used and regular wave conditions were reproduced. The influence of the wave wall retreat has been investigated in terms of wave-induced forces, reflection coefficients and wave overtopping discharges, comparing the hydraulic performances of structures with retreated walls with those of a flushed wall configuration under the same wave conditions. The large number of experiments allowed to formulate a detailed description of the complex phenomena at hand, providing statistical indicators that can be used as guidelines for preliminary design purposes of such structures, quantifying the relevant sources of uncertainty. The analysis confirmed and extended the previous findings and indicates that, on average, the hydraulic performances of structures with retreated crown wall vary significantly from those of flushed wall configurations. Specifically: (I) the forces acting on the wave wall increase of a factor up to 1.5, due to the occurrence of impulsive loads; (II) the forces acting on the caisson trunk decrease of a factor up to 0.91; (III) the global forces can decrease reaching a minimum reduction factor of 0.87, although some dangerous exceptions, in which equal or larger loads, than those occurring for standard flushed wall configuration, have been registered; (IV) the reflection coefficients decrease of a factor up to 0.83; (V) the wave overtopping discharges increase up to 2.55 times those with flushed walls.

A Numerical Study of the Performance of Point Absorber Wave Energy Converters

Free-floating and submerged wave energy converters (SWECs) are regarded as promising technologies for renewable energy production. These converters rely on a heave-motion buoy to capture the kinetic energy of ocean waves and convert it into electrical energy through power conversion systems. To better understand the impact of various factors on power generation and efficiency, the effects of different buoy shapes (rectangular, circular cylinder, and trapezoidal fin), submergence depths (0, 0.1, and 0.2 m), wave heights (0.04, 0.06, and 0.1 m), and spring stiffness (50 and 100 N/m) were investigated. A 2D numerical wave tank with a buoy was simulated, and the results were validated against experimental data. Information on vorticity, vertical displacement, power absorption, and efficiency are provided. The findings indicate that the buoy shape and wave height significantly affect power absorption and efficiency. Additionally, this study reveals that increasing submergence leads to higher power absorption and lower conversion efficiency.

Physical Model Study Of Standing Wave Impact Loads On Gates And Decks Of The Existing Discharge Sluices In The Afsluitdijk The Netherlands

To anticipate the rising sea level and to meet the increased flood safety standards the Afsluitdijk in the northwest of The Netherlands is currently being reconstructed. The Afsluitdijk is the dam, with a length of 30 km, that closes the IJsselmeer basin, the former Zuiderzee. Outside the dam lie the Waddenzee and the North Sea. The reconstruction of the dam includes the reinforcement of the dam and the raising of the crest level, the renovation of the existing discharge sluices and the building of new pumping stations, discharge sluices and flood gates. Higher design waves and water levels, including the effects of sea level rise, present determining loads for drawing up the strength and stability of these hydraulic structures. One of these loads is the wave impact load on the gates, supporting beams and bridge decks of the discharge sluices. At first, these loads have been calculated using a design approach which has been based on analytical models, only partially validated (Almeida and Hofland, 2020). It showed that these loads due to vertical wave impacts can be higher than the strength of the gates and the existing bridge decks. Therefore, load reduction measures are required. To better predict the wave impact loads, which strongly depend on the configuration of the gates and decks, a physical model study in a wave flume has been carried out at Deltares (Capel and van der Werf, 2023). This abstract is about the results of this model study, focusing on the wave impacts on the existing discharge sluices near Kornwerderzand, because at this location these loads are the highest.

2D And 3D Physical Model Testing For The Rehabilitation On The Frioul Port Breakwater (France)

A white archipelago anchored in the Mediterranean Sea 2 km off the coast of Marseille (France), the port of Frioul is made up of the Pomègues islands (to the south) and Ratonneau (to the north). It is protected on the west side by the Berry breakwater (renovated in 1984), and on the east side by the Condorcet breakwater (figure 1.a). The port was built in the early 1820s (Berry breakwater) to take care of the quarantine of ships coming from areas infected by yellow fever, then developed in the 1850s (Condorcet breakwater in the East) to make it a military port. The current findings highlight that the eastern breakwater is seriously damaged and must be rehabilitated (figure 1.b). Accordingly, the rehabilitation solution, which consists to replace the actual rock armour unit, was physically modelled, and tested for its hydraulic stability and the overtopping performance as well as the forces and pressures acting on the crown wall. The process includes recreation of breakwater cross sections in a 2D wave flume at a scale of 1:35 (figure 2.a), and a optimized breakwater configuration proposed in a 3D wave basin at a scale of 1:50 (figure 2.b). These two campaigns made it possible to compare and optimize the design, first with the state of the art (Van Gent, M., et van der Werf, I., 2019) (Mares-Nasarre and van Gent, M., 2020), then with the observations and measurements collected from the modeling.

Considerations for designing a new wave generator system in an existing flume

Van Halteren Technologies Boxtel B.V. (formerly known as Bosch Rexroth B.V.) has designed, manufactured, installed, and commissioned the new electrical driven wave generator system in the existing Large Wave Flume (GWK) at FZK in Hannover. The aim of the replacement was designing a new wave generator system, with optimized performance in the given space in the existing flume, and replace the hydraulics for an electrically driven system. The width and depth of the flume are five and seven meters respectively. The water depth is variable up to five meters. In order to get the most out of the finite length of the flume the space for the wave maker is limited. Given the limited space for the wave maker we had to apply a dry back wave generator system which has the advantage of a rather compact design compared to a wet back wave generator. This also introduced challenges such as a seal system around the moving wave segment at the side walls and floor as well as a compensator for compensating the static force of the variable water depth. The hydrodynamic forces are provided by the electrically driven system. The wave generator has been provided with an Active Reflection Compensation system (ARC) for compensating the reflected waves traveling to the wave segment. This ARC must be capable to handle variable water depths, even when the water depth is changed in order to simulate high and low water conditions.

Effectiveness Of Stilling Wave Basins In Reducing Wave Overtopping On Dikes And Rubble Mound Breakwaters

Motivated by the impacts of Climate Change (CC), such as rising sea levels and the increased intensity and frequency of storms, the importance of adapting our coastal defense structures has never been more important (Toimil, 2020). With CC causing coastal structures to be exposed to more extreme hydraulic conditions than originally designed for, there is an increased risk of these structures failing in terms of stability and hydraulic performance, such as wave overtopping. To reduce wave overtopping, structural modifications of existing coastal structures are often adopted and in this work the analysis of wave overtopping discharge at slope structures equipped with Stilling Wave Basins (SWB) at their crest (Figure 1) is investigated.