Absorber Wave Energy Research Articles

An Experimental Study of a Conventional Cylindrical Oscillating Water Column Wave Energy Converter: Fixed and Floating Devices

Oscillating water column (OWC) wave energy converters (WECs) are very popular types of wave energy converters due to their practical implementations, their versatility in deployment in different marine environments, and their high reliability in wave energy conversion. In development, different forms of OWCs have been proposed and advanced, such as fixed OWCs (on the shoreline, on breakwaters, or bottom standing) and floating OWCs (the spar and the backward-bent duct buoy, BBDB). In reality, a special type of OWC, the cylindrical OWC, is the simplest OWC in terms of its structural design and possible analytical/numerical solutions. However, such a simple OWC has not seen any practical applications because a cylindrical OWC is inefficient in wave energy absorption when compared to other types of OWC WECs. To study the simplest cylindric OWC, an experiment was carried out in a wave tank, and the relevant results are presented in this paper, with the aims of (i) analyzing the experimental data and exploring why such an OWC is inefficient in terms of wave energy absorption; (ii) providing experimental data for those who want experimental data to validate their numerical models; and (iii) establishing a baseline model so that comparisons can be made for improvements to the simple cylindrical OWC. As an example, an innovative solution was applied to the simple OWC such that its hydrodynamics and energy extraction performance can be significantly improved (the corresponding results will be presented in a separate paper).

An ultrasonic transducer for vibration mode conversion of wedge-shaped structure of acoustic black hole

Acoustic black hole (ABH) structure has been extensively used in vibration mitigation, noise reduction, energy harvesting and so on, owing to its unique sound wave trapping and energy concentration effects. Besides, ABH structure holds emerging potential in improving the performance of ultrasonic device and constructing multifunctional acoustic field. Hence, an ultrasonic mode-conversion transducer consisting of a longitudinal sandwich transducer and an ABH wedge radiant plate is proposed in this work, in order to explore the potential applications of ABH in ultrasonic levitation and multifunctional particle manipulation. The theoretical model of flexural vibration of the radiant plate is established by utilizing Timoshenko beam theory and transfer matrix method, and the calculated vibration frequencies are in good agreement with those obtained by finite element method (FEM). The electrical impedance frequency response characteristics, vibration modes and the near-field sound pressure distribution of the transducer in air are also simulated. The results indicate that the amplitude of the ABH wedge radiant plate increases stepwise, and the sound pressure exhibits a gradient distribution. A prototype of the transducer is fabricated and experimentally tested, confirming the accuracy of FEM simulations and the feasibility of the design approach. Finally, the result of the ultrasonic levitation experiment indicates that the ABH design can give rise to gradient distribution of sound pressure in standing wave sound field for achieving precise particle sorting.

Dynamic response of a semi-submersible floating wind turbine-point absorption wave energy hybrid energy system under rated and extreme conditions

In this paper, the response of a semi-submersible offshore wind turbine, combined with an absorbing wave energy converter (WEC), is analyzed within the FAST to AQWA coupling framework after single mooring line (ML) failure, under rated and extreme (1 in 10 years wind and wave) conditions. Comparisons are made among the six-degree of motions of the platform, power output, and tensions of the unbroken MLs. With upwind mooring line, the hybrid system suffers the most: surge up to 3.3 times the rotor diameter (D) due to the large hub forces and turbine power reduction by 80%, owing to the pitch response of the platform in both rated and extreme conditions; more likelihood of fatigue in unbroken ML under extreme conditions. Regardless of the failure line condition, the mean tension of the unbroken MLs reduces at the expense of larger motions, compared to a non-faulty line condition. The shutdown measures can reduce significantly the tensions in the MLs at rated conditions, owing to turbine larger influence on the platform than WEC, higher motion response and damping processes. The effect of the WEC on the platform is mainly reflected in heave and roll, providing more stability than in a stand-alone floating turbine case. During extreme conditions, the turbine shuts down, and thus, the response is more attributed to the drift of the platform rather than turbine or WEC operation. On a wider level, research is also needed to determine the response in simultaneously ML failures and misaligned operating flows.

WEC-Sim and NEMOH applications for the assessment of wave energy generation in the western coast of Italy located in the Mediterranean Sea through the 2-body point absorber (2BPA) wave energy converter

WEC-Sim and NEMOH applications for the assessment of wave energy generation in the western coast of Italy located in the Mediterranean Sea through the 2-body point absorber (2BPA) wave energy converter

Experimental investigation on L-Oscillating Water Column wave energy converter integrated with floating cylindrical breakwater

One promising renewable energy source for the future is wave energy, harnessed through L-Oscillating Water Column (L-OWC) Wave Energy Converters (WECs). Combining this device with lightweight floating breakwaters can have several advantages, including absorbing wave energy and attenuating waves. L-OWC and two cylindrical floating breakwaters, one in front of the structure and one at the back are coupled in the current study. Previous research indicates that the L-shaped OWC configuration is highly effective due to its increased added mass and enhanced structural stability. The 1:30 scale model, combining a floating breakwater with an Oscillating Water Column (OWC) system, was experimentally investigated in the wave flume at the NITK, Department of Water Resources and Ocean Engineering. This setup included L-shaped OWCs integrated with cylindrical breakwater configurations (2C, 3C, and 4C). OWCs integrate with lightweight floating breakwaters, offering both wave attenuation and energy extraction. The OWC achieved maximum efficiency of 30% under optimal conditions, with a wave period of approximately 1.8s and a wave height of 0.06 m for the model with three floating breakwaters. The work aligns with the United Nations' Sustainable Development Goals (SDG), specifically addressing clean and affordable energy (SDG 7), industry, innovation, and infrastructure (SDG 9), life below water (SDG 14), and life on land (SDG 15), highlighting its significant impact.

Optimal Control of Nonlinear, Nonautonomous, Energy Harvesting Systems Applied to Point Absorber Wave Energy Converters

Pursuing sustainable energy solutions has prompted researchers to focus on optimizing energy extraction from renewable sources. Control laws that optimize energy extraction require accurate modeling, often resulting in time-varying, nonlinear differential equations. An energy-maximizing optimal control law is derived for time-varying, nonlinear, second-order, energy harvesting systems. We demonstrate that sustaining periodic motion under this control law when subjected to periodic disturbances necessitates identifying appropriate initial conditions, inducing the system to follow a limit cycle. The general optimal solution is applied to two point absorber wave energy converter models: a linear model where the analytical derivation of initial conditions suffices and a nonlinear model demanding a numerical approach. A stable limit cycle is obtained for the latter when the initial conditions lie within an ellipse centered at the origin of the phase plane. This work advances energy-maximizing optimal control solutions for nonautonomous nonlinear systems with application to point absorbers. The results also shed light on the significance of initial conditions in achieving physically realizable periodic motion for periodic energy harvesting systems.

Dynamic response and power performance of a combined semi-submersible floating wind turbine and point absorber wave energy converter array

With the global demand for renewable energy rising, offshore renewable energy development has gained more attention. The combination of wind and wave energy is a new trend. Ensuring stability in combined systems is crucial for efficiency of absorbing energy. A novel combined wind and wave energy system with a semi-submersible floating wind turbine (FWT) and an array of six torus-shaped point absorber wave energy converters (WECs) is proposed. The dynamic response of combined system is investigated using 3D potential flow theory by comparing to the original system. The effects of power take-off (PTO) damping, WEC float shape and seasonal variation on the dynamic response and power performance of combined system are studied. The results show that the addition of WEC array improves the stability and power production of combined system. Meanwhile, the total power of combined system is approximately 2.5%–6.5 % higher than that of original system. PTO damping mainly affects the heave motion of combined system. As PTO damping increases, the first peak of mean power of WEC array shifts towards the long period, while the second peak of that shifts towards the short period. The conical-bottom WEC generates the most power compared to the flat-bottom WEC, hemispherical-bottom WEC and concave-bottom WEC. The combined system generates the most power in winter, and the total annual electricity output can be up to 2.99 × 104 MWh.

Wave-to-wire modelling and hydraulic PTO optimization of a dense point absorber WEC array

We investigate the hydrodynamic interactions and power extraction efficiency of a dense array of Point Absorber (PA) Wave Energy Converters (WECs) clustered around the fixed pillar of a wind turbine –the Ocean Grazer device– with a standard hydraulic Power Take-Off (PTO) system. Using potential flow theory, a detailed wave-to-wire model is developed in WEC-Sim with four distinct hydraulic PTO designs: i) Multi PTO-with individual hydraulic PTO systems for each buoy, ii) Shared PTO V1-with a unified PTO system for the entire array, iii) Shared PTO V2-with the accumulator volume split into two segments, and iv) Shared PTO V3-with four strategically distributed segments. Key parameters such as the diameter of the hydraulic pistons, volume and pre-charged pressure of the high-pressure accumulators, hydraulic motor displacement and the speed of the electric generator are optimized with a genetic algorithm and a parametric analysis across various sea states. The results highlight that strategically allocating the accumulators across the floaters of a dense WEC array can yield significantly higher power production and should be considered at the early design stages.

Ground-penetrating radar subsurface attenuation analysis based on a sparsity-promoting time-frequency transform

The attenuation characteristics of a medium involve the absorption of electromagnetic wave energy during its propagation and represent a crucial parameter for describing the properties of subsurface media. Due to the complex nature of signal attenuation, demanding consideration of numerous parameters, quantitative analysis is challenging. Time-frequency (TF) analysis is a promising technique that simultaneously analyzes nonstationary signals in the time and frequency domains. Although the quantitative characterization of attenuation factors using TF tools can be challenging, TF analysis retains substantial potential for qualitatively estimating attenuation from ground-penetrating radar (GPR) data. The sparsity-promoting TF (SPTF) transform method with [Formula: see text] and [Formula: see text] norms joint constraints has a significantly higher TF resolution than the linear TF transform in the time and frequency domains. We develop a method for high-resolution qualitative estimation of GPR attenuation based on the SPTF method. Synthetic experiments indicate that SPTF surpasses other methods regarding TF resolution, noise robustness, and fidelity to dominant frequencies. Subsequent qualitative attenuation results using synthetic and field data agree with synthetic model outcomes and actual leakage ranges. This alignment substantiates the superior resolution and accuracy of our approach compared with alternative methods, affirming its efficacy and superiority in GPR attenuation depiction.

Analysis of the fluid–structure coupling dynamic characteristics of flexible webbed wings under passive deformation

A wave glider with webbed wings (WGWWs) is a new type of unmanned surface robot that combines wave energy and solar energy as its energy supply, driven by flexible webbed wings (FWWs). Wave gliders with webbed wings are already playing an important role in marine science research. Flexible webbed wings are significant components of wave gliders with webbed wings that achieve the absorption and conversion of wave energy through bidirectional fluid–structure coupling with water flow. To address the issues of large deformations and nonconvergence under the strong coupling action of flexible webbed wings, a dynamic model of flexible webbed wings is first established on the basis of an analysis of the motion principle of a wave glider with webbed wings. The Mooney–Rivlin model was subsequently applied to describe the stress–strain relationship of a rubber hyperelastic material for flexible webbed wings. By adopting the overset method and dynamic mesh technology, employing the system coupling interface based on the data interaction platform of the ANSYS Workbench, as well as mechanical and fluid solvers, the transient dynamic characteristics of fluid–structure coupling of flexible webbed wings under different working conditions are obtained. Finally, by setting different sea conditions, the influences of wave height and period on the dynamic characteristics of flexible webbed wings are analyzed. The results indicate that the greater the wave height and the smaller the wave period are, the greater the power output of the flexible webbed wings is. Additionally, the influence of the wave height ratio period on the dynamic characteristics of flexible webbed wings is more pronounced.

Shape Optimization of a Point Absorber Wave Energy Converter for Reduced Current Drag and Improved Wave Energy Capture Using Neural Networks and Genetic Algorithms

Shape Optimization of a Point Absorber Wave Energy Converter for Reduced Current Drag and Improved Wave Energy Capture Using Neural Networks and Genetic Algorithms

Parametric study of traveling wave motion in energy absorption mode

There are two modes of traveling wave motion, traveling wave propulsion and traveling wave energy absorption. In this paper, a two-dimensional flexible traveling wave plate is taken as the research object. The characteristic length and characteristic parameter of traveling wave motion are determined by numerical simulation, and the parametric study of the traveling wave motion in energy absorption mode is conducted. The effects of dimensionless amplitude and dimensionless wave velocity on the energy absorption characteristics of flexible traveling wave plate are analyzed, and the mechanism of traveling wave energy absorption is revealed. The results show that the larger the dimensionless amplitude is, the stronger the work capacity of the traveling wave plate becomes, while the absolute amplitude or absolute wavelength has little effect on the work capacity of the traveling wave plate. Under different waveforms, the work capacity of the traveling wave plate increases first and then decreases as the dimensionless wave velocity increases. Within the parameter range studied in this article, when the dimensionless amplitude is 0.2 and the dimensionless wave velocity is 0.5, the traveling wave plate can achieve an energy absorption efficiency of about 40 %.

Unprecedented mechanical wave energy absorption observed in multifunctional bioinspired architected metamaterials

In practical engineering, noise and impact hazards are pervasive, indicating the pressing demand for materials that can absorb both sound and stress wave energy simultaneously. However, the rational design of such multifunctional materials remains a challenge. Herein, inspired by cuttlebone, we present bioinspired architected metamaterials with unprecedented sound-absorbing and mechanical properties engineered via a weakly-coupled design. The acoustic elements feature heterogeneous multilayered resonators, whereas the mechanical responses are based on asymmetric cambered cell walls. These metamaterials experimentally demonstrated an average absorption coefficient of 0.80 from 1.0 to 6.0 kHz, with 77% of the data points exceeding the desired 0.75 threshold, all with a compact 21 mm thickness. An absorptance-thickness map is devised for assessing the sound-absorption efficiency. The high-fidelity microstructure-based model reveals the air friction damping mechanism, with broadband behavior attributed to multimodal hybrid resonance. Empowered by the cambered design of cell walls, metamaterials shift catastrophic failure toward a progressive deformation mode characterized by stable stress plateaus and ultrahigh specific energy absorption of 50.7 J/g—a 558.4% increase over the straight-wall design. After the deformation mechanisms are elucidated, a comprehensive research framework for burgeoning acousto-mechanical metamaterials is proposed. Overall, our study broadens the horizon for multifunctional material design.

Scale parameters of soft structures for surrounding rock erosion prevention in rockburst-prone roadways

Practical experience in coal mines has suggested that establishing a loose and soft structure in the surrounding rock of roadways can play a role in wave attenuation, energy absorption and erosion prevention, which is conducive to the prevention of and reduction in the severity of rockburst disasters in coal mines. The scale parameters of soft structures includes two aspects: the size and the fracture degree of soft structures. The FLAC3D numerical simulation software was used to study the failure characteristics of roadways with different impact positions (roof impact, side impact) and different impact energies (104, 105, 106, and 107 J). The stress reduction rates of soft structures with different sizes and fracture degrees were calculated. Based on the stress reduction rate of the soft structure, the energy absorption effect of the soft structure around the roadway was obtained as a logarithmic function of the soft structure size, which is a power function related to its fracture degree, and the intersection range of the two curves was fitted. The stress reduction rate was 30% when the soft structure size of the surrounding rock of the roadway was 10–15 m and the fracture degree was represented by 30–40% of the coal strength, which was the most reasonable range of scale parameters. The research conclusions provide a parametric basis for improving the theory and practice of rockburst prevention and support in coal mine roadways.

A Novel Approach to Wave Energy Conversion Using CFD Technique

Abstract This article details the development and evaluation of a novel wave energy converter (WEC) aimed at efficiently capturing wave energy for electricity production. The study employs Computational Fluid Dynamics (CFD) techniques, specifically the URANS method and the k-ω SST turbulence model, to solve the Navier-Stokes equations and capture the free surface using the Volume of Fluid (VOF) model. The CFD results are validated against experimental data to ensure accuracy. Various design parameters of the proposed device were tested, revealing that the arms and bottom angle significantly affect its performance. Unlike the floating Wave Dragon (WD) device, which utilises potential energy and is set in deep water, the new fixed-seabed device is positioned in the transitional wave region near the shore, where waves retain 80% of their energy. It can be constructed from environmentally friendly cement, making it resistant to hurricanes and suitable for any wave turbine in the open sea. The MP687 turbine was used to capture the wave energy in the proposed device, testing its performance in three positions: in the open sea, in the middle of the device, and at the device’s outlet. The results show that the device significantly enhances wave energy concentration, especially when the turbine is placed at the outlet. The proposed device offers numerous advantages, including its fixed position in a high-energy wave zone, the efficient use of turbulent kinetic energy, and robust construction that can withstand storms.

Comparative Study on the Performances of a Hinged Flap-Type Wave Energy Converter Considering Both Fixed and Floating Bases

The dynamical modeling and power optimization of floating wind–wave platforms, especially in regard to configurations based on constrained floating multi-body systems, lack in-depth systematic investigation. In this study, a floating wind-flap platform consisting of a flap-type wave energy converter and a floating offshore wind turbine is solved in the frequency domain considering the mechanical and hydrodynamic couplings of floating multi-body geometries and a model that suits the constraints of the hinge connection, which can accurately calculate the frequency domain dynamic response of the flap-type WEC. The results are compared with bottom-fixed flap-type wave energy converters in the absence of coupling with a floating wind platform. Moreover, combined with traditional optimization methods of power take-off systems for wave energy conversion, an optimization method is developed to suit the requirements of floating wind-flap platform configurations. The results are drawn for a specific operation site in the South China Sea, whereas a sensitivity analysis of the parameters is performed. It is found that the floating wind-flap platform has better wave energy absorption performance in the low-frequency range than the bottom-fixed flap-type wave energy converter; the average power generation in the low-frequency range can increase by up to 150 kW, mainly due to constructive hydrodynamic interactions, though it significantly fluctuates from the sea waves’ frequency range to the high-frequency range. Based on spectral analysis, operational results are drawn for irregular sea states, and the expected power for both types of flap-type WECs is around 30 kW, which points to a similar wave energy absorption performance when comparing the bottom-fixed flap with the flap within the hybrid configuration.

Structural Quality Factor of Flo-TENG under Stochastic Wave Excitation.

Triboelectric nanogenerators (TENGs) have recently emerged as a promising technology for efficient water wave energy harvesting. However, there is a paucity of clear guidance regarding the optimal designs of TENGs and their shells to achieve efficient absorption and conversion of water wave energy in real random waves. Herein, from the perspective of wave-body interaction and energy transfer, this paper proposes a structural quality factor (Qunit) for the quantitative evaluation of both the motion of floating triboelectric nanogenerator (Flo-TENG) shells and their capability to absorb and convert water wave energy efficiently. The factor is further subdivided into the amplitude structural quality factor (Qacc), which characterizes shell motion amplitude, and the frequency structural quality factor (Qf), which describes shell motion frequency. This paper systematically investigates the impact of various shell parameters such as bow shapes, curvatures, inclinations, and immersion ratios on Qacc and Qf. The findings indicate that variations in shell shape result in distinct Qunit values along different axial directions of wave propagation. These variations directly influence energy absorption efficiency in these directions. These results provide fundamental guidance for the design of high-performance Flo-TENG shells and the selection of internal energy harvesting directions to enable more efficient energy conversion.

Comparative evaluation of floating OWC and BBDB wave energy converters by regular and irregular waves using numerical approach

ABSTRACT Point absorber wave energy converters (WECs) need to be predicted in order to estimate their durability in high sea states. Although little is known about hydrodynamics and there are few data available. Models of the wave conditions have been developed at the laboratory size using smooth particle hydrodynamics. To investigate how focused waves interact with a point absorber WEC, fixed OWC and BBDB type WEC are coupled. A validation research is evaluated by taking into account the wave amplitude and frequency. The hydrodynamic force and the motion response of the point absorber WEC have been measured throughout time. According to the numerical results, the hybrid configuration with the fixed OWC and BBDB has a significant impact on the motion response and hydrodynamic force. It is demonstrated that the position of hybrid OWCs affects the hydrodynamic force and intense motion response significantly.

On exploration of directional extreme mechanical attributes and energy absorption of bending-dominated and buckling-induced negative Poisson’s ratio metamaterials

This work numerically explores the directional mechanical characteristics, including the effective anisotropy, multiaxial yield surface, long-frequency stress phase wave propagation, buckling resistance, and energy absorption of bending-dominated (BE) and buckling-induced (BU) auxetic metamaterials, considering the influence of the relative density and negative Poisson’s ratio, for the first time. The accuracy of numerical homogenization in determining the effective Young’s modulus and wave analytical model calculating the wave velocity is confirmed by compared with experimental and numerical data, respectively, with a maximum percent difference of 14.6% for all comparisons found. The results show that BU auxetic structures possess unique mechanical properties, displaying their potential use for fabrication of metamaterials of zero-Poisson’s ratio and tunable strength allowing high strength-to-weight ratios. The anisotropy of BE structures is found to be more extreme compared to their BU counterparts. Interestingly, alignment of multiaxial yield surface of auxetic metamaterials is observed to be opposite to that of nonauxetic metamaterials, resulting in poor fitting against extended Hill’s criterion. The BU auxetic structure demonstrates a better impact wave resistance, but lower buckling resistance in y-direction compared with BE auxetic structure, and more. This work provides in-depth useful mechanical information on the structures before employing them in practical applications.

Experimental investigation on the anti-detonation performance of composite structure containing foam geopolymer backfill material

The compression and energy absorption properties of foam geopolymers increase stress wave attenuation under explosion impacts, reducing the vibration effect on the structure. Explosion tests were conducted using several composite structure models, including a concrete lining structure (CLS) without foam geopolymer and six foam geopolymer composite structures (FGCS) with different backfill parameters, to study the dynamic response and wave dissipation mechanisms of FGCS under explosive loading. Pressure, strain, and vibration responses at different locations were synchronously tested. The damage modes and dynamic responses of different models were compared, and how wave elimination and energy absorption efficiencies were affected by foam geopolymer backfill parameters was analyzed. The results showed that the foam geopolymer absorbed and dissipated the impact energy through continuous compressive deformation under high strain rates and dynamic loading, reducing the strain in the liner structure by 52% and increasing the pressure attenuation rate by 28%. Additionally, the foam geopolymer backfill reduced structural vibration and liner deformation, with the FGCS structure showing 35% less displacement and 70% less acceleration compared to the CLS. The FGCS model with thicker, less dense foam geopolymer backfill, having more pores and higher porosity, demonstrated better compression and energy absorption under dynamic impact, increasing stress wave attenuation efficiency. By analyzing the stress wave propagation and the compression characteristics of the porous medium, it was concluded that the stress transfer ratio of FGCS-ρ-579 was 77% lower than that of CLS, and the transmitted wave energy was 90% lower. The results of this study provide a scientific basis for optimizing underground composite structure interlayer parameters.