Absorber Wave Energy Research Articles

SPH-based numerical modelling and performance analysis of a heaving point absorber type wave energy converter with a novel buoy geometry

Heaving point absorber (HPA) is one of the most promising technologies to absorb wave energy. Accordingly in this work, performance of a HPA in terms of capture-width-ratio (CWR) under the effect of hydrodynamics forces were analysed using the SPH-based open-source package: DualSPHysics. 395 cases of simulations, which include five different geometries with different densities of the buoy, different buoy height to wave height ratios, and damping coefficients of the WEC over a range of wave frequencies were studied and optimum operational parameters were found for the novel buoy geometry named: “Super cuboid”. Compared to other geometries, it produced up to 23 % of efficiency increment over a wide range of operational conditions. Furthermore, the flow patterns and pressure variation around different buoy geometries were studied and found that an increase in the projected area of the buoy in vertical direction tends to increase the pressure force which results in increase of CWR. The CWR is also slightly enhanced by the bottom shape of the buoy. Hence it is expected that the use of this novel buoy shape, will contribute to the design of more sustainable and reliable WECs in the future.

Physical Modelling Of A Centralized Controlled Array Of Five Wecfarm Wave Energy Converters

Point absorber wave energy converters (WECs) closely placed in array hydrodynamically interact through wave radiation and diffraction. The power absorption by these WECs is optimised by altering the WEC dynamics through the control of the Power Take-Off (PTO). As the WEC dynamics are changed, the hydrodynamic interactions change as well. Therefore, the PTO control should be optimized taking all these interactions into account, referred to as centralized control. The ‘WECfarm’ project has been initiated to study WEC arrays, and to address the research gap on available realistic and reliable data on WEC array tests to validate numerical models (Vervaet et al., 2022). This work discusses the experimental design, implementation and testing of a centralized controlled array of five ‘WECfarm’ heaving point absorber WECs, tested at the Coastal and Ocean Basin Ostend.

Environmental-Sensing and adaptive optimization of wave energy converter based on deep reinforcement learning and computational fluid dynamics

This paper introduces a novel coupled model for real-time control of the point absorber wave energy converter (WEC) using parallelized deep reinforcement learning (DRL), where the WEC is situated within a numerical wave tank (NWT) built with the method of computational fluid dynamics (CFD). An in-house solver is developed to couple with the DRL and CFD to solve the interaction between WEC and the fluid environment. Validations on wave generation, wave-floater interaction, and power take-off (PTO) unit are carried out. Then, neglecting the detailed model for the PTO technologies, the DRL-based strategy dynamically adjusts the PTO force as a function of the wave features and floater motion. Based on the interaction data, the model-free DRL is outstanding in adaptability and robustness. Simulation results reveal that DRL control improves the wave energy absorption in irregular wave environments, resulting in improvement of 107.5 % compared to the resistive control, with better device protection performance than the model predictive control (MPC). An additional analysis of model-free characteristics of DRL demonstrates the optimization ability independent of floater modeling. This work is the first in-depth study of DRL control of WECs in CFD simulation, providing a more accurate simulation and an optimization process closer to the reality.

Hydrodynamic performance of vertical cylindrical wave energy absorbers in front of a vertical wall

This paper studies the hydrodynamic performance of vertical cylindrical absorbers in front of a vertical wall. All the absorbers are independent of each other and restricted to only the heave motion. Based on a linear potential flow theory, an analytical solution is developed for the problems of wave diffraction and radiation by absorbers. In the solving procedure, the hydrodynamic problem is first transformed into an equivalent problem in an open water domain using the image principle. The number of absorbers in the equivalent problem is twice that in the real problem, and the plane layout is symmetric about the original vertical wall. The velocity potential of the fluid domain is obtained using the method of variable separation, and the unknown expansion coefficients in the velocity potential are determined by the matched boundary conditions. The heave excitation force, added mass, radiation damping, motion response, and energy capture width of the absorbers are calculated. Case studies are presented to show the effects of the wall reflection and hydrodynamic interaction on the energy extraction performance of the wave energy converter (WEC) system. Subsequently, the WEC performance under the action of irregular waves is analyzed by considering an incident wave spectrum, and the mean annual absorbed power of the device is estimated by considering the wave data statistics at the actual sites. The results indicate that when the wave motion resonates with the absorber motion, the energy extraction performance of the absorbers is significantly improved. The performance of the absorbers can be effectively improved when the structures are close to the antinodes of a standing wave field. By designing a reasonable plane layout, the hydrodynamic interaction can play a constructive role in the performance of the WEC system.

Regulating the Electronic Structure of MAX Phases Based on Rare Earth Element Sc to Enhance Electromagnetic Wave Absorption.

MAX phases are highly promising materials for electromagnetic (EM) wave absorption because of their specific combination of metal and ceramic properties, making them particularly suitable for harsh environments. However, their higher matching thickness and impedance mismatching can limit their ability to attenuate EM waves. To address this issue, researchers have focused on regulating the electronic structure of MAX phases through structural engineering. In this study, we successfully synthesized a ternary MAX phase known as Sc2GaC MAX with the rare earth element Sc incorporated into the M-site sublayer, resulting in exceptional conductivity and impressive stability at high temperatures. The Sc2GaC demonstrates a strong reflection loss (RL) of -47.7 dB (1.3 mm) and an effective absorption bandwidth (EAB) of 5.28 GHz. It also achieves effective absorption of EM wave energy across a wide frequency range, encompassing the X and Ku bands. This exceptional performance is observed within a thickness range of 1.3 to 2.1 mm, making it significantly superior to other Ga-MAX phases. Furthermore, Sc2GaC exhibited excellent absorption performance even at elevated temperatures. After undergoing oxidation at 800 °C, it achieves a minimum RL of -28.3 dB. Conversely, when treated at 1400 °C under an argon atmosphere, Sc2GaC demonstrates even higher performance, with a minimum RL of -46.1 dB. This study highlights the potential of structural engineering to modify the EM wave absorption performance of the MAX phase by controlling its intrinsic electronic structure.

Hydrodynamic Responses of Heaving Motion on One Body and Two Body Point Absorber Devices with Different Wave Condition in Malaysia

Wave energy harvesters are still not as mature as other types of renewable energy harvesting devices, particularly when it comes to commercialization, mass production, and grid integration, even though ocean waves around the world are known to contain high and dense quantities of energy. However, recent studies and optimizations suggested that the point absorber wave energy harvester may be a viable option. This paper provides a comprehensive comparison hydrodynamic damping analysis of the heaving motion on one body and two body point absorber wave energy harvesters by using Computational Fluid Dynamic (CFD) software. A simulation run was proposed for the analysis performance of damping of the point absorber devices to low wave height (0.7m-2.5m) and period (0.9s-2.2s). There are two types of point absorbers: one-body point absorber and two body point absorber. Both point absorber body are examined by simulation in terms of its heaving dynamic motion frequency in calm, medium and strong wave condition. This analysis highlights the extensive research being done to bring point absorbers closer to technical maturity, paving the way for commercialization and mass production for low wave characteristics. The results showed two body point absorber Response Amplitude Operator (RAO) is improved to absorbed low wave height compared to one body by RAO efficiency 17% and device efficiency 25%. The two-body point absorber performed better in all wave condition.

Hydrodynamic response analysis of a hybrid TLP and heaving-buoy wave energy converter with PTO damping

In the present study, the numerical investigation is performed to analyse the hydrodynamic performance of circular and concentric arrangements of cone-cylinder-type heaving point absorber wave energy converter (WEC) around a Frustum Tension-Leg Platform (FTLP) based on potential flow theory. The responses of the single FTLP and the FTLP-WEC hybrid system are analysed for the rated wind speed of a 5 MW wind turbine to observe the influence of the WECs on wind power absorption of wind turbines supported on FTLP. The presence of the FTLP floating wind turbine platform and other WECs affects the hydrodynamic coefficients of the WEC. The influence of the hybrid system on the hydrodynamic coefficients is analysed on determining the ratio of the hydrodynamic coefficients for a single WEC system to those for a hybrid system. Further, the study analyses the instantaneous wave power absorption for the WECs arranged around the FTLP in a circular and concentric pattern. The hydraulic power take-off for the hybrid system with two different control strategies is then discussed to improve the wave power absorption of the WECs. The study observed higher wave power absorption of the WECs with the influence of the PTO system. The mean interaction factor and the capture width ratio of the hybrid system are further studied to understand the influence of array arrangement for the WECs. The hybrid system is noted to have favourable dynamic responses for different environmental factors and contributes positively in increasing power output.

A new method for analysis of marine sustainable energy systems

This paper proposes to utilise a new adaptive kernel density estimation (KDE) methodology based on linear diffusion processes for predicting the probability distribution tails of sea-state parameters. A key conclusion was reached that the proposed new methodology can lead to more accurate prediction results than traditional methods based on fittings to a measured significant wave height data set at National Data Buoy Center station 46014. This proposed methodology was subsequently utilised for deriving an accurate 50-year environmental contour line that was used in the dynamic analysis of a two-body point absorber wave energy converter. After systematically analysing the calculation results, another key conclusion was drawn that it is advantageous to use a more reliable contour line derived using the proposed new methodology for long-term dynamic analysis of wave energy converters. In summary, the proposed new adaptive KDE methodology is recommended to be utilised and to be refined continuously in future research work in the field of long-term reliability analysis of marine sustainable energy systems.

Capture mechanism of a multi-dimensional wave energy converter with a strong coupling parallel drive

Wave energy is a promising renewable energy source. How to improve wave energy capture efficiency is a key challenge of wave energy generation. A multi-dimensional wave energy converter (MDWEC) with a strong coupling parallel drive is proposed. The MDWEC can efficiently absorb wave energy through a multi-dimensional moving body driven by six parallel hydraulic cylinders. Based on the Lagrangian approach, high nonlinear strong coupling dynamic models of the MDWEC are established. The hydraulic cylinder force acting on the converter is deduced according to the principle of virtual work. The nonlinear hydrostatic restoring force for different submerged body geometry shapes is derived. The vertical restoring force caused by pitch and roll, the pitch and roll restoring torque caused by deviating from the equilibrium position, the coupled radiation force, and the coupled inertial force between pitch and surge are considered. The hydrodynamic performance, the motion response, and the transient power behavior are investigated. The upper and lower platform hinge point radius, the hinge point center angle, and conversion parameters are optimized based on a genetic algorithm. Wave power capture ability comparison with different design parameters, shapes, and wave states is presented. As the significant wave height decreases from 3 m to 1 m, the capture efficiency increases from 68.3% to 79.1%. The capture ability of MDWEC with semiellipsolid is the highest. Compared with a heaving cone converter, the MDWEC improves the capture efficiency by 47.5% with a significant wave height of 1 m and an energy period of 4 s.

A novel 3D topological metamaterial for controllability of polarization-dependent multilayer elastic waves

The achievement of high-quality wave manipulation and energy concentration has always been considered as state-of-the-art technologies, especially for integrated photonics, acoustics, and mechanics. The exploration of the topological phase of matter provides abundant design tools for robust waveguiding that is immune to backscattering at small defects and sharp bends. Recent research has extended the elastic wave manipulation from 2D edge waveguiding to 3D planar waveguiding. However, most of them are limited to single-mode and single-frequency wave propagation along the designed plane. This paper introduces a novel 3D topological metamaterial structure whose geometrical parameters are specifically configured to obtain dual-mode topological states at distinct frequencies. Parametric studies are presented to demonstrate the controllability of bandgaps and to provide a design principle for preventing the effects of unwanted modes. Topological interface modes with either high group velocity or near-zero group velocity along the z direction are found. Full-scale finite element simulations are presented to uncover the elastic wave propagation behavior. The interesting layer-locked and layer-unlocked waveguiding based on excitation polarization and frequency for both straight path and zig-zag path are demonstrated. The outcomes of this work suggest abundant potential applications related to elastic wave control such as wave filters, energy harvesters, mechanical computers, and the like. This work may also help inspire future research on more complex and sophisticated multi-mode waveguiding in 3D spaces.

Two-Way Coupling Simulation of Fluid-Multibody Dynamics for Estimating Power Generation Performance of Point Absorber Wave Energy Converters

The objective of the present study is to develop and validate a two-way coupling simulation method between viscous fluid and multibody dynamics to estimate the power generation performance of point absorber wave energy converters. For numerical analysis of fluid dynamics, an enhanced density correction model was proposed to improve the accuracy and stability of the pressure calculation in DualSPHysics, an open-source code based on smoothed particle hydrodynamics (SPH). Through 2D hydrostatic and wave generation simulations, it was seen that the relative error in the average pressure was reduced from 11.81% to 1.64%. In addition, an interaction interface was developed to enable coupling simulation with RecurDyn, a commercial software for the simulation of multibody dynamics. Simulations were performed for a 3D single-body cylinder with a simple shape and a two-body floating wave energy converter (WEC) in regular waves, varying the linear damping coefficient of the power take-off (PTO) system to verify the proposed coupling simulation method for fluid-multibody dynamics. The results were benchmarked against experimental data, revealing a relative error of 1.05% with the experimental results when employing a high damping coefficient for the PTO system. Furthermore, to improve the efficiency of the two-body WEC, two design modifications were suggested; their impact on power generation performance improvement was examined. The developed method is anticipated to contribute to research aiming to enhance the power generation efficiency of various wave power devices with multiple elements and joints, pending further validation and refinement of the simulation approach.

Performance analysis of two generations of heaving point absorber WECs in farms of hexagon-shaped array layouts

ABSTRACT Numerical analyses are presented for two generations of a floating heaving point absorber wave energy converter (WEC) installed with different farm array layouts. The wave farm configurations are based on WECs developed by Waves4Power. The numerical models are developed in the DNV software package, Sesam. Parametric studies of the isolated WEC configurations and farm array layouts are conducted under typical environmental conditions and various incident wave directions to understand the hydrodynamic power performance and the levelised cost of energy (LCoE). Hexagonal layouts are proposed for deploying the WEC units and compared with a 10-unit layout termed StarBuoy, which has been reported in previous work. The results of the present study confirm that the interactions between arrayed units in a farm can have either positive or negative effects on the LCoE, which is dependent on the array layout and environmental conditions. The hexagonal array layouts lead to lower LCoE owing to constructive interaction effects.

Sizing and Control of the Electric Power Take Off for a Buoy Type Point Absorber Wave Energy Converter

This paper presents the study of power extraction and control of the electric power take off of a buoy type point absorber wave energy converter in heave. Two fundamental linear control strategies (the passive loading and optimum control) have been studied and their impacts on the sizing of generator were investigated. For the designed incident wave, a gearbox is needed to reach the rated speed of the generator. The generator is connected to the grid through a back-to-back converter which controls the electrical torque. Vector control technique is implemented to control the electric torque of the generator, by setting the direct axis current to zero. The results show that the current needed to control the electrical torque is too high for optimum control strategy. A method has been presented to reduce the power ratio significantly, but also with a decrease in average extracted power.

Optothermal shaping of lamb waves with square and spiral phase fronts

We introduce a Lamb-wave medium with tunable propagation velocities, which are controlled by a two-dimensional heating pattern produced by a laser beam. We utilized it to demonstrate that waves in an appropriately designed medium can propagate in the form of concentric squares, in contrast to the circular patterns typically emitted by a point source in a homogeneous two-dimensional medium. In order to avoid the concentration of wave energy in the middle of the sides of the squares, we propose two alternatives: a square wave that either rotates or exponentially decelerates as it expands. Additionally, we present how circular waves can be transformed into spiral waves utilizing the same tunable medium. The described experimental platform offers a new tool to generate shaped pulses for ultrasonic applications, which has the potential to improve the efficiency of energy and information transport.

Análise numérica de barreiras físicas para mitigar os efeitos da explosão de tanques de gás usando fluidodinâmica computacional

Abstract In many urban buildings, there is the presence of gas central storage, which contain pressurized tanks. One of the main risks in these places is an explosion, which may or may not is followed by fire. In general, the shock wave formed by this phenomenon is disastrous and can cause material damage and even fatalities. Recent research has contributed to understanding protective systems against this phenomenon; however, it is necessary to advance in developing protection devices for gas central storage. From this perspective, the implementation plan of these devices in order to mitigate the harmful effects of explosions are essential to raise the safety level in construction. Physical protection barriers are appropriate solutions for the protection of buildings, especially in places where it is impossible to bury gas reservoirs. In addition to the potential to reduce back pressure levels, protective walls, when properly designed, can also prevent the spread of debris from the explosion. Another kind of barrier that influences the propagation of the shock wave close to the ground is the ditches, whose function is related to the absorption and redirection of wave energy. Understanding the positioning, geometry, and overpressure attenuation potential of physical barriers are essential in developing safer and more reliable projects. This article aims to study protective barriers in buildings with pressurized gas tanks. The study was developed numerically using the Autodyn software. This program is a tool based on computational fluid dynamics (CFD). The protective capacity of the proposed types of protection regarding the mitigation of incident overpressures was evaluated qualitatively and quantitatively.

Real-Time Model Predictive Control Framework for a Point Absorber Wave Energy Converter With Excitation Force Estimation and Prediction

Real-Time Model Predictive Control Framework for a Point Absorber Wave Energy Converter With Excitation Force Estimation and Prediction

Numerical Investigation of a Point Absorber Wave Energy Converter Integrated with Vertical Wall and Latching Control for Enhanced Power Extraction

Numerical Investigation of a Point Absorber Wave Energy Converter Integrated with Vertical Wall and Latching Control for Enhanced Power Extraction

NUMERICAL ANALYSIS OF WAVE ENERGY POINT ABSORBERS BUOY SHAPE

ABSTRACT: Energy demands have increased dramatically nowadays giving rise to the growing consumption of electricity, most of which is provided by fossil fuels, which has increased energy costs as well as the harmful emissions resulting from fuel combustion. This has resulted in advancements in the use of renewable energy sources to satisfy the current energy demands. These sources include the use of solar, wind, and wave power to generate energy in a green manner. This paper presents the use of wave energy point absorbers with various shapes to assess their performance when exposed to waves. Four buoy shapes are modelled and analyzed using Ansys Aqwa to observe their motion as well as their responsiveness to the out of balance forces subjected on them. The results show that the cylindrically shaped buoy can achieve around 52.8% more motion in the vertical direction when compared to the average motion of the different buoy designs. This shows that a cylinder buoy is the economic option for optimized wave energy absorption.

Flexural wave rainbow trapping effect in the periodic non-uniform Euler-Bernoulli beams and its application in energy harvesting

The rainbow trapping of elastic wave enables spatial frequency shunting and energy concentration phenomenon, which implies that the broadband vibration will forbid propagating forward and occur energy concentration at different positions of metamaterial structure. This paper proposes a novel metamaterial consisting of the periodic non-uniform Euler-Bernoulli beams with an arbitrary profile section to achieve the rainbow trapping effect of flexural wave and application in piezoelectric energy harvester. Firstly, the differential quadrature method is introduced to solve a partial differential equation with variable coefficients. The convergence of this method is systematically demonstrated, and the correctness of band structures is validated by comparing theoretical results calculated by the differential quadrature method with those from the finite element method for different profiles. Based on band structures analysis, the working mechanism of the flexural wave rainbow trapping effect is attributed to the group velocity modulation; thereby, the constructed periodic array of non-uniform beams achieves integration of specific-band vibration reduction and energy enhancement at specific positions. Secondly, simulations indicate that the resonance rainbow trapping frequencies demonstrate more intense concentration of flexural wave energy compared to the counterpart with initial frequencies. Finally, the resonance rainbow trapping phenomenon demonstrates superiority in vibration energy harvesting. Specifically, when piezoelectric films are pasted on specific-position with enhanced energy density, the maximum output voltage in the independent circuit connection reaches up to 2.30V for the resonance rainbow trapping frequency of 8752Hz and the PVDF film position of x = 670 mm. Furthermore, simulations illustrate that the maximum output voltage and power are up to 4.52V and 1894.12 nW for the Series-A circuit connection, respectively, which is approximately the sum of the individual maximum output electrical energy generated by independent circuit connection at positions A and B. The proposed metamaterial beams can offer new selection guidelines for high-performance vibration energy harvesters.

Energy capture performance enhancement of point absorber wave energy converter using magnetic tristable and quadstable mechanisms

This paper proposes two magnetic multistable (tristable and quadstable) mechanisms to enhance the energy capture performance of point absorber wave energy converters (PAWECs) for low-amplitude waves. Accordingly, two mechanisms consisting of several coaxial magnetic rings are designed based on the superposition effect of magnetic fields. Compared with conventional magnetic bistable mechanisms, the proposed tristable and quadstable mechanisms feature lower potential barriers and greater distances between two outermost potential wells, facilitating the occurrence of large-amplitude interwell motions in low-amplitude waves. A mathematical model is established using the Cummins equation and equivalent magnetic charge approach to depict the dynamic behavior and performance of PAWECs. The energy capture performance and average annual output power of PAWECs with tristable and quadstable mechanisms are evaluated for regular and irregular waves. The findings demonstrate that the two mechanisms significantly improve the energy conversion efficiency, enhancing their robustness against low-amplitude waves and damping detuning. The design concept of nonlinear multistable PAWECs using the superposition effect of magnetic fields provides a promising alternative for exploiting wave energy resources with low energy densities.