Wave Energy Applications Research Articles

Experimental study of a WEC array-floating breakwater hybrid system in multiple-degree-of-freedom motion

Installing an array of wave energy converters (WECs) on an existing breakwater is viable to reduce the high cost and improve the reliability of wave energy applications. The interaction between WECs and floating breakwater under multi-degree-of-freedom motion is crucial but not well investigated, especially the impact of WECs on the mooring system of the breakwater. This article fills this gap by experimentally studying a hybrid system consisting of a rectangle floating breakwater and an array of oscillating body WECs. The interactions between the WEC and the breakwater, the effect of the WEC bottom shape on the hybrid system, and the performance of the hybrid system in waves with different nonlinearities are investigated. Results indicate that the wave amplification effect of the breakwater improves the wave energy conversion performance of the WEC by up to 324.6%. As the WEC absorbs wave energy, the mooring forces of the breakwater in the pitch and surge directions decrease by up to 19.8% and 47.4%, respectively. When the incident wave height increases, the energy extraction performance of the hybrid system improves while the wave attenuation performance decreases. This study provides a reference for the practical application of WEC-breakwater hybrid systems and test data for the validation of numerical methods.

A piezoelectric-electromagnetic hybrid energy harvester for low-frequency wave motion and self-sensing wave environment monitoring

Techniques for harvesting energy and environmental monitoring are crucial for the development and application of wave energy. Here, we propose a piezoelectric-electromagnetic hybrid energy harvester (PEHEH) for low-frequency wave motion and self-sensing wave environment monitoring. The PEHEH consists of an electromagnetic energy harvester (EMH) and two distinct types of piezoelectric energy harvesters (PEH-1 and PEH-2). The combination of piezoelectric power generation and electromagnetic power generation can effectively harvest low-frequency wave energy. Using the L-shaped piezoelectric cantilever can make it produce large deformation under low-frequency excitation to obtain better power output. The movement of the spherical magnet in the channel tube changes the magnetic flux in the coil to generate electricity. The PEHEH is designed to float on the surface of the water to harvest wave energy in multiple directions. According to the experimental findings, the PEHEH can obtain a power output of 32.58 mW with the optimal combination of parameters. The PEHEH can supply power to the LEDs and enable them to emit light properly. Meanwhile, using the PEH-1 and PEH-2 as the power supply part and the EMH as the self-sensing part, the PEHEH can realize the monitoring of wave amplitude in the actual wave environment. The above results verified that PEHEH has the functions of self-powering and self-sensing. This research provides a novel technical solution for the development and utilization of wave energy.

Optimal gear ratio selection of linear primary permanent magnet vernier machines for wave energy applications

AbstractLinear permanent magnet vernier generators offer a high capability of force density, making them appealing configurations for wave energy harvesting systems. In absolute terms, the performance of these machines is significantly influenced by the selection of slot/pole combinations based on the magnetic gearing effect. For the first time, this paper aims to investigate the impact of different gear ratios on a wide array of linear primary permanent magnet vernier machines (LPPMVMs) with different slot/pole combinations based on fair criteria to offer a more comprehensive understanding of gear ratio selection. To find the optimal number of slots and poles, the response surface methodology is adopted to obtain a robust design and make a fair comparison among LPPMVMs with optimum design characteristics using a cost‐effective approach for the fast and reliable optimisation process. The higher gear ratios result in higher thrust force capability. This will help establishing a new route toward faster develpment of advanced LPPMVMs. The power loss models of LPPMVMs are studied to predict their steady‐state and transient thermal behaviours, verifying their stability and safety, while a simple external forced convection method can be utilised. To verify the model, finite element analysis is exploited to confirm the electromagnetic and thermal analysis results and provide a more exhaustive investigation.

High efficiency and wideband wave energy capture of a bistable wave energy converter with a displacement amplifier

Ocean wave energy is a kind of renewable energy with huge reserves, which can play an important role in the future construction of smart oceans. The low capture efficiency and narrow bandwidth of traditional wave energy capture devices seriously restrict the large-scale application of wave energy. To address these issues, a rack-pinion-lever-spring (RPLS) adaptive bistable Power Take-Off (PTO) mechanism with a time-varying potential barrier is proposed and applied to a point absorber wave energy converter (WEC). In the proposed nonlinear PTO system, a rack-pinion-lever (RPL) mechanism, as a displacement amplifier, has an effect on enhancing the poor amplitude sensitivity issue of the negative stiffness mechanism. Based on linear wave theory, a special nonlinear one-and-half-degree of freedom dynamic model is developed to describe the adaptive bistable wave energy converter (AB WEC). In comparison with the traditional bistable WEC (TB WEC) and equivalent linear WEC, the numerical results show that the AB WEC can greatly enhance the capture efficiency of lower frequency energy, especially at small wave excitations. The energy capture efficiency of the AB WEC is close to that of the TB WEC even at large wave amplitudes and is higher than that of the equivalent linear WEC. Finally, the wave energy capture characteristics of the three kinds of systems are studied based on the wave distribution diagram of a certain sea area in the South China Sea. The results show that the AB WEC has a large wave height adaptability in the low frequency region. The AB PTO mechanism with a displacement amplifier proposed in this paper can provide a technical reserve for the highly efficient and wide bandwidth capture of low frequency ocean wave energy.

Observer-Based Fault Estimation Applied to a Point Absorber Wave Energy Converter

The economic viability of wave energy conversion systems is one of the open points among the research community. To lower the energy cost, the devices in charge of extracting the wave power, called wave energy converters (WEC), are often controlled by means of optimal control (OC) strategies. Such OC systems, which have proven their effectiveness in wave energy applications, often rely on a mathematical model of the device (and, in some cases, on the wave excitation force) to optimize the control action provided to the system. Nevertheless, the marine environment results hostile for general device safe operations, potentially triggering a variety of faults in the WEC system. Such condition (for example, a sensor failure or additional friction inside a gearing) directly affects the system dynamics. If this deviation is not considered by the control algorithm, the energy production performance can degrade considerably, or the control action itself can cause a more serious fault. A possible solution is that of designing an algorithm capable of compensating for eventual faults in the system, while still respecting the initial design performance or, when not possible, preserving the main device functionalities. Such a control strategies belong to the family of Fault Tolerant Control (FTC) techniques, which can be divided into two macro-categories: Passive (PFTC) and active (AFTC) algorithms. While PFTC systems are designed offline and can account only for a predefined set of system faults, AFTC algorithms are more suitable to tackle significant system deviations from the nominal model. For this purpose, such algorithms may require some routine to detect, isolate and eventually estimate the specific fault. This task is accomplished by Fault Detection and Identification (FDI) routines. According to the AFTC algorithm, the FDI module must accomplish different tasks. Furthermore, the FDI module accuracy plays a crucial role in some AFTC strategies, since the poor estimation of a faulty signal can induce the controller to behave incorrectly. This paper presents an FDI algorithm applied to a point-absorber wave energy converter (WEC). The proposed structure consists of an observer-based strategy in charge of detecting, isolating, and tracking effectively faulty signals occurring in numerical simulations. The results demonstrate the proposed observer effectiveness for a predefined set of actuator and sensor faults, both in the case of independent, and simultaneous fault occurrence.

A Non-Stationary and Directional Probabilistic Analysis of Coastal Storms in the Greek Seas

The variability of coastal storms over the years and direction is considered in a unified, innovative approach, providing crucial information for a wide variety of coastal engineering studies and wave energy applications under the impact of climatic change. Specifically, an alternative easy-to-apply technique is presented and applied to consider the storms’ direction as a covariate. This technique enables the probabilistic representation of coastal storms in every direction over the directional domain and is efficiently incorporated into a non-stationary directional extreme value analysis. The developed methodology is applied to six locations in the Greek Seas. Based on the derived results, the most likely and most extreme significant wave height estimates present, in general, a bimodal behavior with pronounced maxima. In particular, the first peak is observed before the twenty-first century, while the second peak is likely to occur around the middle of the twenty-first century. Furthermore, coastal storms coming from directions of large fetches are the most severe storms, presenting though a drop in their intensity at the end of the twenty-first century. On the contrary, coastal storms of fetch-limited directions may present minor variations in their probability distributions over the years.

Application and Prospect of Wave Energy in Marine Robots

Marine robots are an important tool for developing and exploring the ocean, which can adapt and work in the harsh marine environment. However, energy supply is one of the important factors that limit the operational capabilities of marine robots, and obtaining energy from the marine environment is an important way to improve the operating time and scope of marine robots. Wave energy is the most widely distributed in the ocean, with high energy flow density and easy to develop renewable clean energy. Therefore, wave energy can be used to provide energy for marine robots. Wave energy provides the possibility to solve the problem between the basic endurance and limited energy of marine robots. This paper introduces wave energy, summarizes the application of wave energy in marine robots, and analyzes its development trend, so as to provide reference for energy research of marine robots.

Wave energy potential analysis in the Kenitra-Atlantic coastal area (Morocco): First results

Waves generated by winds can transport a large amount of energy across the oceans with little loss. This paper explores the satellite-based data to assess the wave energy potential of Kenitra-Atlantic coastal area (Morocco), with an overall purpose of supporting the plans for developing and using wave energy, and provide guidance about the appropriate applications of wave energy of the Kenitra coastal area. Kenitra is important harbour and industrial city in Morocco. Various indexes, including the temporal distributions of wave parameters and wave energy fluxes, the occurrence of the effective significant wave height and wave energy flux, the variability and frequency of the wave status, were calculated from satellite measured weekly wave data, covering about 3 years (June 2019-November 2022) period. Results indicated that the area is characterized by moderate energy compared to South Africa, the most energetic site in the continent, with average wave significant wave of 1.6 ± 0.7, average wave period of 8.4 ± 2.4 s, average wave energy flux of 11.7 ± 14.0 kW m−1 and with the rate of variability of 28–45%. High energy above the threshold (> 10 kW m−1) for viable electricity production, applying turbines directly powered by waves, occurs only during the northern hemisphere winter (December–March). Hence, for off shore Kenitra, the study recommends other applications for wave energy other than electricity production through wave powered turbines, such as, reverse osmosis membrane-based electricity production technology, desalination, irrigation and water pumping for marine culture, mini-hydro and recreational. Subsequently, future studies may focus on the socio-economic viability of these wave energy applications and on developing other low energy demanding applications.

Mechanical Analysis and Optimal Design of Wave Energy Device

At present, the global energy problem is serious. Wave energy is the kinetic energy and potential energy of waves on the ocean surface. Because of its high energy density, wide distribution, and long continuous operation of the device, it has become the focus of academic research. The key problem to be solved urgently for the large-scale application of wave energy is how to optimize the energy conversion efficiency of wave energy devices. This paper starts from the Newtonian dynamic equation, analyzes the motion state of the wave energy device in different wave environments, and studies the optimization and control of its power output. This paper first adopts the analysis method of first whole and then isolation, and establishes a one-dimensional coordinate system with the zero point of sea level. Then, the force analysis of the system is carried out, the dynamic differential equation is established, and the initial draft of the system is solved through the initial balance equation. Since the dynamic equation is a second-order linear ordinary differential inhomogeneous linear equation, the fourth-order Runge is used. The Kutta method is used to solve the problem, and the numerical solution for the position and velocity of the float is obtained. Secondly, the movable coordinate system is established with the float as the reference system, and the force analysis of the oscillator is carried out to obtain its relative dynamic equation. Then, the initial relative position of the oscillator is solved through the initial balance equation, and the relative dynamic differential equation is obtained by using the fourth-order Runge-Kutta method to obtain the numerical solution of the relative position and relative velocity of the oscillator with respect to time. Finally, the numerical solution of the absolute position and absolute velocity of the oscillator with respect to time is obtained through coordinate transformation.

Control of Cascaded Multilevel Converter for Wave Energy Applications

This paper proposes a control scheme for a wave energy conversion system based on a linear generator and a cascaded multilevel converter. The mechanical conversion system is composed of a buoy connected directly to a linear generator. The windings of the generator are individually controlled by a cascaded multilevel power converter using independent maximum power point tracking to improve energy harvesting. The output of the cascaded converter is controlled to keep the DC capacitors balanced and generate a multilevel voltage at the output terminals which reduces the losses in the underwater transmission line. Experimental results show the performance of the proposed control scheme maximizing the power generation by imposing a current with the same waveform of the induced voltage and balancing the DC capacitors.

A novel carbon nanotubes doped natural rubber nanocomposite with balanced dynamic shear properties and energy dissipation for wave energy applications

Mechanical characterizations of natural rubber filled with carbon-based nanomaterials were extensively studied in tensile and tear modes whereas fewer attempts have been conducted on a dynamic shear condition using a double-bonded shear test piece. This is of importance since natural rubbers are widely used as flexible membranes for wave energy harvesting devices. Therefore, this study was aimed to explore the microstructural, rheological, and dynamic viscoelastic characteristics of natural rubbers filled with different Multi-Walled Carbon Nanotubes (MWCNTs) contents. A combined compounding approach was employed to ensure a homogenous CNT dispersion was achieved. Transmission electron microscopy (TEM) was performed for the materials characterization while the processability and curing parameters of the compounds were investigated using the Mooney viscosity and rheometry test. Dynamic shear properties were compared using a cyclic test performed on a double-bonded shear test piece. TEM images showed that an optimum CNTs dispersion was reached at 3 phr MWCNTs loading whereas increasing CNT content resulted in further inhomogeneity. The addition of CNTs into the natural rubber not only improved the curing properties of the compound, i.e., low scorch and curing times, but it also increased the Mooney viscosity, the rheological properties, and the dynamic shear properties of the nanocomposite compared to the pristine rubber. The Payne and Mullins effects were also observed for all compounds manifesting dependency on the CNTs content and applied strain amplitude. Finally, MWCNT enhanced the dissipated energy of the nanocomposites with respect to the neat rubber in which an increase of 1040 % in energy dissipation for 10 phr MWCNTs compared to the control at a strain amplitude of 200 % was achieved.

Research and Prospect of Wave maker Design and Wave making Application

Wave energy is clean energy with huge development potential. At present, structural energy reform is an important issue in my country’s development. Therefore, the research on the application of wave energy can promote the structural reform of my country’s energy to a certain extent. This paper summarizes the history of wave simulation development and the current status of wave applications, and compares and analyzes wave-making by pushing plate-type wave machines, rocking plat-type wave machines, box-type wave machines, and combined wave-making according to different wave-making methods. Machine building characteristics. Combined with the application status of wave energy, the wave energy power generation is summarized, and the economic and technical status of wave energy power generation is described in detail. Finally, the development trend and application prospect of wave application are summarized.

Comparison of Offline, Real-Time Models and Hardware-in-the-Loop Test Results of a Power Take-Off for Wave Energy Applications

The power take-off (PTO) of a wave energy converter (WEC) converts mechanical power extracted from the waves into electrical power. Increasing PTO performance under several operational conditions is therefore essential to reduce the levelized cost of energy of a given wave energy concept and to achieve higher levels of technology readiness. A key task in the WEC design will then be the holistic assessment of the PTO performance in combination with other subsystems. It is hence important that WEC designers are aware of the different modeling options. This paper addresses this need and presents two alternative wave-to-wire modeling approaches based on a 250 kW modular electromechanical PTO coupled to an oscillating wave surge converter (OWSC) device. The first is a detailed and accurate offline model. The second model is a simplified and faster version of the first, being adequate for rapid analyses and real-time (RT) simulation. The paper presents the benchmarking of the offline model against the RT model and the hardware-in-the-loop (HIL) tests of the PTO. The normalized root-mean-square error (NRMSE) is considered as a quantitative indicator for the measurement of real-time and HIL test results against the offline simulation. Results show that the dynamics of the offline model are well represented by the RT model with execution times up to 10 times faster. The offline model also depicts well the behavior observed in the HIL tests with the NRMSE values for the PTO position, velocity, and force above 0.90, which shows the HIL test results replicates with fidelity the dynamic behavior of the complete model. Meaningful differences are however present and highlighted in this paper. An understanding of the advantages and drawbacks of these three approaches is fundamental to properly design a WEC during its project cycle and validate PTO concepts with a certain level of simplification.

Development and deployment of a credible unstructured, six-DOF, implicit low-Mach overset simulation tool for wave energy applications

An unstructured, low-Mach, balanced-force, volume of fluid methodology is coupled to an implicit, six-DOF overset formulation for the simulation of wave-based renewable energy devices. We propose an overlapping unstructured mesh construct that affords a wave energy converter (WEC) geometry to move freely about a background domain. A control volume finite element (CVFEM) numerical discretization, which includes novel residual-based stabilization, is developed. Credibility of this simulation tool is established by code verification, which demonstrate design-order numerics on linear and quadratic conformal and overset meshes, and model validation. A CVFEM balanced-force method is applied to a static bubble configuration using conformal and mixed topology overset meshes, while an obstructed dam break case is used to establish the viability of the proposed numerical construct. A validation hierarchy that focuses on falling and rising spheres in quiescent flow showcases the stability of the overset and six-DOF coupling approach. Finally, a buoy validation case is presented that demonstrates the efficacy of the parallel, implicit overset approach for this challenging multiphase flow regime by including both low- and high-displacement configurations along with a large wave displacement numerical benchmark with and without mooring.

Linear Permanent Magnet Vernier Generators for Wave Energy Applications: Analysis, Challenges, and Opportunities

Harvesting energy from waves as a substantial resource of renewable energy has attracted much attention in recent years. Linear permanent magnet vernier generators (LPMVGs) have been widely adopted in wave energy applications to extract clean energy from oceans. Linear PM vernier machines perform based on the magnetic gearing effect, allowing them to offer high power/force density at low speeds. The outstanding feature of providing high power capability makes linear vernier generators more advantageous compared to linear PM synchronous counterparts used in wave energy conversion systems. Nevertheless, they inherently suffer from a poor power factor arising from their considerable leakage flux. Various structures and methods have been introduced to enhance their performance and improve their low power factor. In this work, a comparative study of different structures, distinguishable concepts, and operation principles of linear PM vernier machines is presented. Furthermore, recent advancements and innovative improvements have been investigated. They are categorized and evaluated to provide a comprehensive insight into the exploitation of linear vernier generators in wave energy extracting systems. Finally, some significant structures of linear PM vernier generators are modeled using two-dimensional finite element analysis (2D-FEA) to compare their electromagnetic characteristics and survey their performance.

High gain DC-DC voltage lift switched-inductor multilevel boost converter for supporting grid connection of wave energy conversion

This paper presents a transformerless high gain DC-DC voltage lift switched multilevel boost converter for wave energy application. The proposed converter is designed for unidirectional power transfer and provides a high voltage gain supporting the wave energy high peak, low average power levels, required for pro systems. The output voltage acquired from generators in wave energy applications will be generally low and must be stepped up by using a DC-DC converter to enable power grid integration. The significant features of the proposed multilevel converter are; transformer-less topology using a single, low side switch, low voltage stress across switch, continuous input current, and modularity. The performance of the proposed converter is compared with transformer-less single inductor multilevel boost converter in term of the voltage gain, number of components and devices stress. The proposed converter has been designed with a rated power of 10 kW, input voltage is 600 V, output voltage is 10 kV and switching frequency is 100 kHz. The performance of the converter is verified through simulation results.

Indonesia-Finland Renewable Energy Development Cooperation

As the largest archipelagic country globally, Indonesia requires much energy to develop and preserve development and its natural wealth. As a biologically rich country, Indonesia has eight (8) renewable energy sources that must be processed and then utilised for maximum energy fulfilment throughout the archipelago and must be adjusted to its geographical specifications. The declaration of cooperation between Indonesia and Finland was signed by diversifying renewable energy sources from solar energy, bioenergy, and ocean wave energy. The implementation based on the MoU is the first to develop practical and environmentally sound technology using wind energy and ocean wave energy. The application of ocean wave energy as an alternative source of electrical energy by using technology. Second, the development of natural resources and technology in the electricity sector. This condition is done by building a micro hydropower plant. This research shows that cooperation between the two countries is quite effective. Both countries depend on each other to fulfil their respective interests. Because of that, there has been an effect between countries to re-enhance cooperation in the energy sector for a relatively long period, starting again from 2011–to 2014.

Nature inspired design modification of fluidic diode for wave energy harvesting device

Abstract A fluidic diode (FD) coupled with the unidirectional turbine (UT) can improve its flow rectification operating in a bi-directional airflow. However, the shape of the FD is not standardized like other fluidic components, and they are usually problem-specific. The performance of the FD is given by diodicity, which is the ratio of pressure drop for the reverse to forward direction. This article aims to improve the performance of the FD proposed for wave energy application by modifying its shape, which is inspired by the bud of the lotus flower. The modified model is numerically studied by solving three-dimensional steady-state Reynolds Averaged Navier Stokes equations using the commercial computational fluid dynamics software ANSYS FLUENT 16.2. The proposed modification had a lesser pressure drop in both directions compared to the base model. The detailed flow physics and performance analysis of the modified FD are presented.

Wave energy assessment for the nearshore region of the northern South China Sea based on in situ observations

The northern coastal region of the South China Sea (SCS) is the key area for wave energy research and application. Planning for wave energy resources and equipment development depends on the accurate assessment of energy distribution and variation characteristics. Based on in situ observation data for 19 months, this paper systematically assesses the wave energy resources of three typical coastal sites in the northern SCS. The results show that wave energy resources have significant temporal and spatial variabilities. The eastern part of the SCS’s northern shore has the most energy, followed by the western part and the center part. The mean energy densities during the observation period are 2.1, 0.75, and 0.33 kW/m, respectively. The energy density is relatively high in summer, followed by winter and autumn, and relatively low in spring. For example, the mean energy densities on the northeast coast of the SCS in the four seasons are 3.1, 1.8, 1.7, and 1.2 kW/m, respectively. Based on statistics for three in situ sites, the considerable energy is mostly contributed by the sea state with a wave height between 0.5 m and 1.5 m and a period between 5 s and 9 s. This study emphasizes the importance of in situ observations for wave energy measurement in nearshore locations, and the results may provide support for the planning and utilization of wave energy in the northern SCS.

A layout optimization method based on wave wake preprocessing concept for wave-wind hybrid energy farms

Major investment of renewable energy currently focuses on wind and solar, which are commercially mature. However, there is no large commercial application of wave energy, despite more than four decades of continuous development. Previous research has indicated that wave energy could supply a significant portion of world electricity consumption. Therefore, it is critical to incentivize the utilization of wave energy. The hybrid energy farms, combining wave energy with wind energy, have been considered as one of the most viable solutions to promote mature grid integration of wave energy. However, combining wind and wave requires the identification of adequate locations for both resources and development of layout optimization algorithms capable of handling the complexity of wave wakes. Wave wake analysis has been one of the biggest hurdles for the development of recursive wave farm layout optimization algorithms due to the required extremely time consuming computation processes for each wave wake iteration. This research proposes a new approach by preprocessing the wave wakes beforehand the actual execution of the recursive layout optimization algorithm. This proposed preprocessed wave wake model can be integrated with the different optimization algorithms to identify optimal layouts for hybrid wave-wind farms. The new approach was tested in two selected locations in the Gulf of Mexico with over 36 years (1979–2015) of historical meteorological data. It identifies locations capable of sustaining commercially viable levels of wind and wave energy while simultaneously avoiding risk from extreme oceanic conditions that in the past have damaged or destroyed wave energy converters. Although the two locations have different meteorological conditions, the new approach was able to identify layouts with promising results in both locations. Results indicated that the selected locations could produce very good power output with a wave-wind hybrid energy farm, and most wave and wind energy devices generated capacity factor with values higher than commercial threshold limits.