Ocean Wave Energy Research Articles

Coupled Short-Ig Wave Dunamics Over A Shallow Barrier Reef

Reef barriers play a major role many coral islands, by sheltering the lagoon from the ocean wave energy and then creating a unique habitat for many species. This filtering action becomes increasingly crucial for ecosystems health and shoreline protection in the context of climate change and related sea level rise, degradation of coral systems and modification of wave conditions. A strong research effort has therefore been engaged by the coastal oceanographers community for the last two decades to improve our knowledge and prediction skills of wave dynamics over coral reef systems. A widely reported observation is the importance of infragravity waves (IG) over wave-driven reef systems, whether fringing or barrier reefs. IG are primarily forced by groups in the incoming short-wave (SW) field, either by the release of bound waves or the breakpoint oscillations (Bertin et al. 2018). IG period typically ranges between 30 and 200s, which makes them prone to excite or interact with natural seiching modes in reef-lagoon systems often ranging in the Very Low Frequency (VLF) band. Further research efforts are now necessary to better understand the interaction between long IG/VLF oscillations and SW field. In particular, long waves are expected to play a dynamic depth-filtering role on SW energy, acting as long carrier wave able to promote the propagation of larger SW groups by IG/VLF crests. More generally, the spectral energy transfers over the reef crest-flat system and their relative importance w.r.t. frictional and breaking dissipation are not fully understood over the complete range of surface waves. The aim of the present study is to analyse and to discuss a series of field observations performed on the barrier reef of Maupiti Island, French Polynesia. A particular focus is placed on the interaction between SW and IG wave fields across the reef crest-flat system.

Research on Maximum Power Control of Direct-Drive Wave Power Generation Device Based on BP Neural Network PID Method

Ocean wave energy is a new type of clean energy. To improve the power generation and wave energy conversion efficiency of the direct-drive wave power generation system, by addressing the issue of large output errors and poor system stability commonly associated with the currently used PID (proportional, integral, and derivative) control methods, this paper proposes a maximum power control method based on BP (back propagation) neural network PID control. Combined with Kalman filtering, this method not only achieves maximum power tracking but also reduces output ripple and tracking error, thereby enhancing the system’s control quality. This study uses a permanent magnet linear generator as the power generation device, establishes a system dynamics model, and predicts the main frequency of irregular waves through the Fast Fourier Transform method. It designs a desired current tracking curve that meets the maximum power strategy. On this basis, a comparative analysis of the control accuracy and stability of three control methods is conducted. The simulation results show that the BP neural network PID control method improves power generation and exhibits better accuracy and stability.

Enhanced triboelectric nanogenerators in saline environments and their applications in the ocean

Blue energy resources hold immense potential in alleviating global energy pressures, with the Triboelectric Nanogenerator (TENG) gaining attention for its unique ability to harvest ocean energy. However, applying TENG technology in the ocean still faces challenges due to its limited performance in hypersaline environments. In this work, a solid-liquid contact-based TENG is proposed for harvesting ocean wave energy. The TENG generates a significant charge output reaching up to 2.5 μC in saline water and excels in producing substantial instantaneous currents of up to 2 mA. This TENG ensures a relatively stable output in hypersaline environments. Furthermore, the TENG demonstrates the capability to degrade 98.83 % of organic dye Rhodamine B in 360 min by ionizing sodium chloride solution. Finally, a self-powered system for monitoring environmental parameters and detecting water levels is developed. This work showcases the high efficiency of TENG in harvesting energy from the ocean environment and demonstrates its immense potential for applications in marine environmental monitoring and seawater purification.

Multi-pillar piezoelectric stack harvests ocean wave energy with oscillating float buoy

Piezoelectric Energy Harvesting (PEH) has emerged as a promising alternative to traditional batteries for self-powered sensors. This paper proposed a multi-pillar piezoelectric stacks oscillating float wave energy harvesting device that utilizes a unique rack, pinion, and cam system to convert the heaving motion of the float into a unidirectional rotation. Subsequently, the cam actuates a linkage rod, driving multiple piezoelectric stack pillars to generate electrical energy. The innovative cam mechanism introduces frequency upconversion to improve the efficiency of power generation in conjunction with piezoelectricity. A theoretical methodology is also derived and validated with simulation and experimental model tests to characterize the output power. The results demonstrate that the system attains a peak output voltage of 32 V and a power output of 3.5 mW when utilizing 10 piezoelectric translation units connected in parallel. This achievement is facilitated by the oceanic force generated by wave motion, which exerts a force of 500 N over a wave period of 3 s. The sustainable energy solutions are developed for remote sensor applications in marine environments, offering potential advancements in the field of autonomous and self-powered sensing systems.

Modeling dynamic power generation from ocean waves in the Kingdom of Tonga: A comprehensive analysis using integrated mechanical and electrical framework

Globally, ocean wave energy can significantly reduce carbon dioxide emissions from the electricity generation sector. Wave energy converters (WECs) could be installed in the Kingdom of Tonga, which is surrounded by ocean, where the average wave energy flux is greater than 7 kW/m. There is a lack of feasibility studies in this area due to the unavailability of measured data on wave parameters and properties; hence, the potential of WEC is yet to be discovered or exploited. This study proposes an integrated mechanical and electrical modeling framework to analyze the impact of wave characteristics on dynamic power generation in three main islands of Tonga, including ‘Eua, Tongatapu, and Niuafo’ou. The mechanical simulation involves using a 2D Fourier wave model to identify the important factors that affect the power potential of ocean waves, such as wave height and period. The wave model is linked to a comprehensive electrical simulation model developed in Matlab Simulink, which includes a permanent magnet linear synchronous generator (PMLSG), rectifier, buck converter, inverter, and load to estimate the electrical power potential per 1 m2 of ocean area. According to the findings, in ‘Eua, the maximum annual generation intensity output is 90.45 kWh/m2, whereas in Niuafo'ou, the minimum is 48.5 kWh/m2. Applying this to a region (12.57 m2) where a WEC has been deployed in Australia, the highest yearly electricity generation in ‘Eua ranges between 926.41 and 1136.96 kWh/y, but in Tongatapu and Niuafo'ou, it ranges between around 610 and 899 kWh/y.

Ocean Wave Energy Potential in Southern Waters of Malang

Ocean or marine energy has immense renewable energy capability, able to provide more than double the world’s current electricity consumption. Ocean energy is considered a non-polluting, renewable source of energy. The research was conducted in the waters of South Malang, East Java Province. This research utilizes wave modeling data that has been picture confirmed and processed within one year, in 2022. This procedure will yield the monthly height, period, and direction of wave arrival. The data used to create a map of the location of wave energy in South Malang comes from previously created wave energy maps. This location map is the result of an overlay of multiple prior maps in order to create a site that can be developed for the usage of wave energy. According to the results, the southern locations of Donomulyo, Bantur, and Sumbermanjing have the most potential for using wave energy for buoy planting. Point 29 is the closest point following point 30 to point 34. However, point 29 is the area covered by the turtle migratory route. Point 34 is the farthest away from the other two places if the distance from the coastline to the potential point is calculated perpendicularly. Despite its distance from the coast, this site experiences the least disturbance when compared to others.

High-sensitivity blue-energy-shuttle and in-situ electrical behaviors in ocean

Although various triboelectric nanogenerators (TENGs) and hybrid ocean kinetic energy harvesters (OKEHs) have been devised for blue energy harvesting, the lack of studies in the real ocean has hindered their progress. Here, a high-sensitivity modular shuttle-like hybrid nanogenerator (MSHG) is prepared, comprising contact-separation TENG, piezoelectric nanogenerator (PENG), and electromagnetic generator (EMG) components. Its acceleration feature and electrical performance were systematically investigated under various conditions, from laboratory setups to real ocean waves. The MSHG responds sensitively to low-level excitations and exhibits robust energy harvesting capability in the ocean. Statistical analysis shows that its most probable output frequency reaches 0.83 Hz, which is about four times higher than the main frequency of the ocean wave (0.1–0.2 Hz). A 12-integrated MSHG system effectively harvests ocean wave energy to power a water-quality detector, while its most probable acceleration amplitude is approximately 24% of the maximum in a simulated linear motor motion and 57% of the mean value under simulated water wave. The findings provide valuable insights for advancing nanogenerator applications in real oceans.

Harvesting Ocean Wave Energy via Magnetoelastic Generators for Self-Powered Hydrogen Production

Harvesting Ocean Wave Energy via Magnetoelastic Generators for Self-Powered Hydrogen Production

Hydrodynamic performance of a land-based multi-chamber OWC wave energy capture system: An experimental study

Improving ocean wave energy capture in a cost-effective manner is a challenging task. Multi-chamber oscillating water column (OWC) devices are gaining favor due to their potentially efficient characteristics. This research experimentally investigated the hydrodynamic performance of a land-based OWC wave energy capture system with multiple chambers (ranging from 1 to 5). The free surface elevation, air pressure fluctuations, hydrodynamic efficiency, and reflection coefficient are considered. The hydrodynamic efficiencies of the overall, and sub-chambers in the OWC system with varying numbers of chambers are graphically presented. The influence of geometrical design parameters and wave conditions are also considered in evaluating the performance of the multi-chamber OWC system. It is found that the multi-chamber arrangement improves the hydrodynamic energy extraction characteristics compared to the traditional single-chamber setup. The sloshing mode of the chamber water column is utilized to effectively capture wave energy. As the number of chambers increases, the wave attenuation capability of the system improves for long waves. Yet, the overall efficiency declines when the number of OWC chambers exceeds 3. The chamber draft has the most substantial impact on the wave energy capturing capability, while the effects of opening ratio and wave height are attenuated due to multiple water-column interactions inside the chambers. The isometric sub-chamber structure demonstrates overall efficiency and wave attenuation advantages for short waves. The paper aims to guide the design and optimization of a multi-chamber OWC system.

Roly-poly inspired tribo-electromagnetic energy harvester toward sustainable ocean energy harvesting

With the increasing global population, the demand for energy has also risen significantly. However, the utilization of fossil fuels for the purpose of energy production has resulted in the release of carbon emissions, accelerating the global warming. Therefore, the demand for carbon-free and renewable energy sources, which can replace the fossil fuels, is growing. In this study, a roly-poly-structure-inspired hybridized energy generator (RPHG) is demonstrated by combining a roly-poly triboelectric nanogenerator with an electromagnetic generator. By utilizing the RPHG, multiple vibrations can be induced from an external force due to the recovering force originated by the roly-poly structure of the RPHG. Consequently, the RPHG is capable of harvesting multiple vibrations from a single input vibration. To optimize the electrical performance of the RPHG, the effects of the substrate shape and the number of polytetrafluoroethylene balls into the electrical output is investigated. Also, the effect of the center of gravity on the electrical output generated from the RPHG is theoretically and experimentally confirmed. As a result, the average vibration number is increased from 2.6 to 25.1 with the 20 polytetrafluoroethylene balls when the tilted substrate with a tilted angle of 170° is applied to the RPHG, compared to the electrical output is generated from the RPHG with a flat substrate. The synergistic effect of the hybridization is demonstrated by comparing the charging speeds of a capacitor and the RPHG shows the fastest speed for charging the capacitor. Furthermore, our RPHG generates 2.45 and 19.29 times higher electrical output than the roly-poly triboelectric nanogenerator (RP-TENG) and electromagnetic generator, respectively. The proposed RPHG demonstrates the 195% higher conversion efficiency in terms of energy compared to the power owing to its unique structure. Also, although the RP-TENG and TENG without roly-poly structure (NRP-TENG) generate similar electrical power, the RP-TENG generates 242% higher electrical energy than NRP-TENG, showing the great potential to harvest the mechanical energy due to the roly-poly structure. As an application, a self-powered ocean wave monitoring system is implemented using the RPHG and it successfully detects strong, calm, and gentle waves. These results show the great potential of the RPHG to harvest vibration and ocean wave energy. Hence, we expect our RPHG to be a promising energy-harvesting solution for generating carbon-free energy.

Optimization of power take-off system settings and regional site selection procedure for a wave energy converter

Ocean wave energy stands as a crucial component in the quest for sustainable and renewable energy sources, essential in the global effort to mitigate climate change. However, a significant challenge in this field is optimizing the efficiency of Wave Energy Converters (WECs) on a regional scale, particularly Oscillating Surge Wave Energy Converters (OSWECs). This challenge stems from the complex, nonlinear interactions between ocean waves and these devices, necessitating precise tuning of Power Take-Off (PTO) system settings and optimal placement for the highest possible performance and stability. To address this challenge, our study introduces the Hill Climb - Explorative Grey Wolf Optimizer (HC-EGWO), a novel algorithm combining local search and swarm-based global optimization strategies. This hybrid approach effectively balances exploration and exploitation in the solution space, leading to more optimal PTO settings for OSWECs. Alongside this algorithmic development, we conduct a thorough feasibility analysis based on the constraints of the flap’s maximum angular motion. This ensures the optimized OSWEC operates within safe and efficient limits. In a comparative analysis with the Genetic Algorithm (GA), the Particle Swarm Optimization (PSO), the artificial Gorilla Troops Optimizer (GTO), and different implementations of the GWO, our results show an improvement in power output, with the HC-EGWO method achieving up to a 3.31% increase over other variations of the GWO and 45% increase compared to all the methods. The findings of this study not only demonstrate the effectiveness of the HC-EGWO method but also provide strategic insights for the deployment of OSWECs in areas like the South Caspian Sea, where unique environmental factors imply careful consideration in the site selection process.

Bio-multisensory-inspired gate-attention coordination model for forecasting short-term significant wave height

Accurate forecasting of significant wave heights (SWH) plays an important role in the generation and conversion of ocean wave energy, being a promising clean energy source, while a challenging task since the SWH is produced by a complex natural process. Additionally, some deep forecasting models integrate parallel and recursive structures via unexplained ways to present intelligent fitting, leading to insufficient inheritance of hybrid advantages. Since biological multisensory systems automatically cope with complex time series, this paper explores a bio-multisensory-inspired gate-attention coordination network (BGC-Net) for forecasting SWH. Specifically, inspired by the multisensory cognitive process, the BGC-Net includes sensory capture, brain memory, and forecasting components, and their collaboration offers a clear multi-level handling process. In internal implementations, through mimicking that multiple senses independently capture external stimuli, the first component adopts several activation functions for suppressing data fluctuations and detecting the complex nonlinear and linear features. Through mimicking that the left and right hemispheres interact and collaborate electrical impulses, the second component integrates both gate-driven recursive and self-attention-driven parallel structures to extract multivariate and temporal dependencies at the feature level. Through mimicking that a higher cerebral cortex fuses extracted information for the final cognition, the third component proposes three feature fusion ways of concatenate, attention, and gated fusion, and takes the best one to generate SWH forecasts. In summary, the BGC-Net not only has interpretability at the biological level but also effectively integrates the advantages of parallel and recursive structures. Five experiments and six analyses all indicate that the BGC-Net exceeds 17 baselines, has root mean squared error (RMSE) average improvements with 22.30% and 19.22% for two datasets, and provides references to support SWH forecasting.

Assessment and prediction of significant wave height using hybrid CNN-BiLSTM deep learning model for sustainable wave energy in Australia

Wave energy is regarded as one of the powerful renewable energy sources and depends on the assessment of significant wave height (Hs) for feasibility. Hence, this study explores the potential of wave energy by assessing and predicting Hs for two study sites in Queensland (Emu Park and Townsville), Australia. Assessment and prediction of Hs is extremely important for reliable planning, cost management and implementation of wave energy projects. The study utilized oceanic datasets based on wave measurements obtained from buoys along coastal regions of Queensland that are transmitted to nearby receiver stations. The parameters of the datasets include maximum wave height, zero up crossing wave period, peak energy wave period and sea surface temperature to accurately predict Hs. A new hybrid Convolutional Neural Network (CNN) and Bidirectional Long Short Term (BiLSTM) deep learning model with Multivariate Variational Mode Decomposition (MVMD) is developed which is benchmarked by Multi-Layer Perceptron (MLP), Random Forest (RF) and Categorical Boosting (CatBoost) to compare the performance. All models attain relatively high-performance results. The MVMD-CNN-BiLSTM attains slightly better performance values for both study sites among all developed models with highest correlation values of 0.9957 and 0.9986 for Emu Park and Townsville, respectively. Other performance evaluation metrics were also higher for MVMD-CNN-BiLSTM with lowest error values in comparison to the benchmark models. The annual mean of Hs is also computed to compare and obtain an insight with a linear projection. There is a greater ocean wave energy potential for Emu Park for a 10-year period with a projected mean Hs of 0.865 m in comparison to Townsville where the projected mean was of 0.665 m.

Improving the OWC Wave Energy Converter Power Take-Off Efficiency throughout Experimental and Numerical Characterisation of an SCIG

The increasing interest in the use of renewable energy technologies is directing attention towards the potential contribution of marine energy technologies, especially ocean wave energy, to world energy demand. While open-sea demonstrations of full-scale devices have been carried out to validate several technologies, the focus now is shifting to optimising the components for efficiency and reliability. The efficiency of the electrical generator plays a crucial role in wave-to-wire numerical models for converting wave energy into usable electricity. It provides essential data that enables the industry to reduce technical risks and uncertainties. Wave-to-wire models typically simplify the generator’s efficiency through assuming a single curve based on the load. This curve is usually provided by the machine manufacturers for the nominal rotational speed. However, the rotational speed varies in the case of air turbines used in OWC devices. Therefore, to accurately estimate decision variables derived from these models, a comprehensive efficiency map is necessary. This map should demonstrate the performance at different rotational speeds and loads, as it directly influences the estimation of key parameters. The main objective of the present work is to improve the generator behaviour of an OWC for different generator operation regimes. For this purpose, a numerical model of the generator’s efficiency will be developed throughout the segregation of losses and validated experimentally. Finally, an optimal control law will be presented to maximise the electrical power output of the wave energy converter, considering the efficiency of both the generator and the turbine.

Fluid Oscillation‐Driven Bi‐Directional Air Turbine Triboelectric Nanogenerator for Ocean Wave Energy Harvesting

AbstractOcean wave energy is one of the important renewable energy sources. However, random, low‐frequency, and micro‐amplitude characteristics of ocean waves make it difficult for traditional electromagnetic generators to collect wave energy efficiently. The emergence of triboelectric nanogenerator (TENG) provides an extremely effective technical means for the collection of low‐frequency and micro‐amplitude wave energy. In this work, a non‐contact turntable‐structured oscillating water column TENG (OWC‐TENG) is designed by combining an OWC wave energy conversion mechanism with a TENG for the first time. The OWC is optimized through simulation experiments according to the principles of ship hydrostatics and wave theory. The output performances of the OWC‐TENGs with different structural parameters under different water wave excitation conditions are then tested. The TENG delivers a maximum output current of 55.45 µA and an output power of 5.28 mW, which corresponds to a power density of 114.8 W m−3, enabling a stable power supply for small sensors at sea. This work provides a new solution to the efficient collection of low‐frequency micro‐amplitude ocean wave energy for powering various offshore equipments, presenting broad application prospects in ocean blue energy development and offshore Internet of Things.

Repulsive magnetic levitation-based electromagnetic energy harvesting of a low-frequency ocean wave

In this study, an electromagnetic energy harvester for a low-frequency ocean wave was developed in a compact 3D-printed structure. Ocean wave energy conversion technologies exist, but maintaining them in the harsh marine environment is crucial for business. Friction increases maintenance costs. Therefore, magnetic levitation, being friction-free, is used for cost-effective, low-maintenance electromagnetic energy harvesting applications. Low-frequency oscillating energy is captured using repulsive magnetic levitation with a buoy and generating electricity using a permanent magnet and copper coil. A levitating magnet is repelled by a fixed one, inducing electricity as it passes through a coil. Experiments with a 0.1 Hz sine wave mimic the average frequency of ocean waves, showing successful voltage peaks at intervals. The output voltage and measured power from the harvester exhibit variations influenced by multiple parameters. The maximum output voltage observed was 3.4 V and an average of 99 mW of power was calculated. The experiment demonstrates the feasibility of using repulsive magnetic levitation for low-frequency wave energy harvesting and also encompasses various harvester configurations, including transfer magnet forces and top magnets.

Pengaruh Dimensi Saluran Buang dan Sudut Kipas Generator Terhadap Kinerja Perangkat Oscillating Water Column

This research aims to investigate the potential for optimizing ocean wave energy conversion using an Oscillating Water Column (OWC) device by focusing on the influence of variations in exhaust duct diameter and generator fan angle. Electrical energy, as a major need in Indonesia, demands exploration of renewable energy sources as an alternative to fossil fuels. Experiments were carried out by varying the exhaust duct diameter (5.5 cm, 4.5 cm, 3.5 cm) and generator fan angle (20°, 25°, 30°). The research results show that there is a significant influence of these two variables on OWC performance. The results of wind speed measurements show that with an exhaust channel dimension of 5 cm, the wind speed at an angle of 45° reaches 2.24 m/s, while at angles of 35° and 40° it is 0 m/s. In the same dimensions, increasing the exhaust duct dimensions increases the wind speed, with a dimension of 15 cm providing optimal results at all fan angles. Measuring the fan RPM in the exhaust duct dimensions (5 cm, 10 cm, 15 cm) shows that in the dimensions 5 cm and 15 cm, the fan RPM is 0 at an angle of 35°. Increasing exhaust duct dimensions, especially the 10 cm and 15 cm dimensions, provides a significant increase in RPM at 40° and 45° angles. The 15 cm dimension provides the best performance, especially at 45° angles. Voltage measurements at three angles (35°, 40°, 45°) with varying exhaust channel dimensions show that at dimensions of 5 cm and 15 cm, the voltage is 0 V at an angle of 35°. Increasing the fan angle, especially in the 10 cm and 15 cm dimensions, provides increased voltage. Dimensions 10 cm, at an angle of 45°, reaches the highest voltage of 24.68 V.

Ocean energy

This article presents the principles and technologies for converting the main renewable ocean energy resources (ocean thermal energy, wave energy and tidal energy) into electricity. Their energy production potential is put into perspective in terms of the challenges of the energy transition.

Pressure Pulsation Analysis of Oscillating Water Column Rotor Eccentricity Based on the Pulsation Tracking Network Method

An oscillating water column (OWC) is typical of axial rotor turbines, which are used to convert ocean wave energy into electrical energy. This device impacts downstream pressure pulsations when its rotor becomes eccentric. This study compared the details of pressure pulsations downstream of eccentric and non-eccentric rotors under three operating conditions: low flow A, high-efficiency flow B, and high flow C. Computational fluid dynamics (CFD) simulations based on the pulsation tracking network (PTN) method were used for the OWC device to compare the experimental results. The results indicate downstream pressure pulsations were mostly dominated by the blade frequency in non-eccentric low-flow cases. In the other eccentric operating conditions, downstream pressure pulsations were mainly dominated by the 2-, 3.6-, 6-, and 7-times rotation frequencies and the 0.5-times blade frequency. The phase change of downstream pressure pulsations in eccentric and non-eccentric conditions is consistent with the flow direction. The phase change is relatively uniform and steady before eccentricity and becomes turbulent after eccentricity, which affects its steadiness. In this study, the OWC device did not significantly change with or without rotor eccentricity at a 1-time blade frequency intensity; however, at a 1-time rotation frequency, the OWC device showed a significant increase in the pressure pulsation amplitude after rotor eccentricity. The study of the dominant frequency, amplitude, and phase of pressure pulsations in OWC devices with eccentric rotors can help prevent excessive pressure pulsations that can lead to incidents.

Comparative Numerical Study of Conventional and Hydraulic Wells Turbine for Ocean-Wave Energy Conversion

The Wells turbine is an ocean wave energy converter that has been implemented in several countries around the world. The hysteresis phenomenon, which causes a torque reduction when the rotor acquires air flow acceleration, is one of the Wells turbine's drawbacks. One enhancement strategy is converting the conventional Wells turbine, which operates in air, into a hydraulic Wells turbine, which operates in ocean water. This method aims to obtain a higher density of working fluid, which can increase the momentum acting on the Wells turbine blades. This research compared the performance and hysteresis phenomenon of conventional and hydraulic Wells turbines. A CFD method based on Reynolds Averaged Navier-Stokes (RANS) and k-ω SST turbulence model is used in this study. Under transient conditions, 3D modeling with periodic boundaries is applied to model the hysteresis phenomenon. This study demonstrated that the hydraulic Wells turbine outperforms the conventional Wells turbine. According to the simulation result, the hydraulic turbine achieves a significant improvement in maximum torque, approximately 124% of the conventional air turbine torque. The concept of immersing the Wells turbine in ocean water improves its efficiency as well. Furthermore, unlike the conventional one, the hydraulic Wells turbine does not exhibit hysteresis.