Maximum Wave Energy Research Articles

Comparative Study of Oscillating Surge Wave Energy Converter Performance: A Case Study for Southern Coasts of the Caspian Sea

The search for renewable energy supplies for today’s global energy demand, particularly ocean wave energy for coastal areas, has become undeniably widespread in the last two decades. The Caspian Sea represents an immense opportunity for using ocean renewable energy, especially considering its long shoreline. In this study, the locations with maximum potential wave energy were chosen in the central, eastern, and western zones of the Caspian Sea’s southern coasts. Accordingly, the wave and bathymetric data were used as the input to calculate the oscillating surge wave energy converter’s flap geometric dimensions based on previous studies. Then, the geometric model was designed, and then the wave energy converters were modeled in the Wave Energy Converter Simulator (WEC-Sim) module in the MATLAB software. Furthermore, eight models in each sea state were simulated to find the best value of the PTO damping coefficient, which led to the highest capture factor. Finally, all the external forces on the WEC’s flap and the converter’s power output results were compared, taking into account the effects of the flap height on the total power output. It was found that Nowshahr port has more potential than the Anzali and Amirabad ports, as the converter’s absorbed power proved to be 16.7 kW/m (Capture factor = 63%) at this site. Consequently, by conducting a comparative analysis between the selected sites, the excitation, radiation damping, and power take-off forces were scrutinized. The results show that the highest applied forces to the converter’s flap occurred at Nowshahr port, followed by the Anzali and Amirabad ports, due to the directional characteristics of the waves at the central coasts of the Caspian Sea.

Numerical study on wave attenuation of extreme waves by emergent rigid vegetation patch

Attributed to the processes of wave focusing, extreme waves often occur unexpectedly with huge wave height in both deep and shallow water regions, which can cause serious damages to the coastal infrastructures, and threaten the intactness of coastal communities. Field observations after extreme weather events have revealed that as a type of natural barrier, coastal vegetations can effectively attenuate the intensity of extreme surges and waves and thus play a good role in naturally protecting the coast. Usually, focused wave is used as a typical extreme wave model to study the great impact of extreme waves on the coast. To numerically evaluate the wave attenuation of extreme waves by the emergent rigid vegetation patch, a high-resolution numerical wave tank has been established by applying the nonhydrostatic numerical wave model (NHWAVE), where both 2nd-order crest and trough focused waves can be generated by considering wave-wave interactions. The efficiencies of the rigid emergent vegetation patch in mitigating the maximum wave amplitude and total wave energy of both crest and trough focused waves as function significant wave height, peak wave period, water depth, vegetation density and width have been well analyzed and discussed. The results indicate that the emergent rigid vegetation patch can effectively reduce the maximum wave amplitude of focused wave by averagely 31% and the total wave energy by averagely 45%, thus, showing that coastal vegetation can effectively protect the coast from extreme waves. It is hoped that the research findings drawn from this study can further broaden our understanding on the wave attenuation of extreme waves by coastal vegetations.

Numerical Analysis of Wave Energy Extraction Performance According to the Body Shape and Scale of the Breakwater-integrated Sloped OWC

Research on the development of marine renewable energy is actively in progress. Various studies are being conducted on the development of wave energy converters. In this study, a numerical analysis of wave-energy extraction performance was performed according to the body shape and scale of the sloped oscillating water column (OWC) wave energy converter (WEC), which can be connected with the breakwater. The sloped OWC WEC was modeled in the time domain using a two-dimensional fully nonlinear numerical wave tank. The nonlinear free surface condition in the chamber was derived to represent the pneumatic pressure owing to the wave column motion and viscous energy loss at the chamber entrance. The free surface elevations in the sloped chamber were calculated at various incident wave periods. For verification, the results were compared with the 1:20 scaled model test. The maximum wave energy extraction was estimated with a pneumatic damping coefficient. To calculate the energy extraction of the actual size WEC, OWC models approximately 20 times larger than the scale model were calculated, and the viscous damping coefficient according to each size was predicted and applied. It was verified that the energy, owing to the airflow in the chamber, increased as the incident wave period increased, and the maximum efficiency of energy extraction was approximately 40% of the incident wave energy. Under the given incident wave conditions, the maximum extractable wave power at a chamber length of 5 m and a skirt draft of 2 m was approximately 4.59 kW/m.

Research on buoy–chain–sprocket wave energy capture technology

A high-reliability, low-cost buoy–chain–sprocket wave energy capture device is proposed. Resonance theory is used to improve its wave energy capture efficiency and reduce its cost. The testing principle of the buoy–chain–sprocket model is proposed, and comparable resonant and nonresonant experimental floating body models were constructed based on finite depth linear wave theory and the resonance principle. Then the methods and results of the model experiments are described. Based on using Morison equation to calculate wave load, simulation and verification of the model experiment were conducted by using AQWA and OrcaFlex software. Finally, to eliminate the size effect and the impact of one-way wave energy collection, based on the simulation technology described above, sea-state prototype models of resonant and nonresonant buoy–chain–sprocket wave energy capture devices with one-way and two-way acquisition characteristics were constructed. Simulations were then conducted to get the maximum wave energy gathering efficiency. The research result indicates that the nonresonant buoy–chain–sprocket wave energy capture device with one-way acquisition has higher wave energy capture efficiency than the resonant buoy–chain–sprocket wave energy capture device.

Coastal erosion in NW Spain: Recent patterns under extreme storm wave events

Coastal dunes are sensitive to both anthropic and natural processes of erosion. In this study, we analyse the geomorphic changes in 15 dune-fringed coastlines of Asturias (NW Spain) for the period 1992 to 2014 to determine specific drivers of erosion. Coastline migration patterns were obtained using geospatial analysis of vertical aerial images and field surveys. The annual and maximum wave energy, maximum significant wave height, duration and number of storm events were determined for each climatic year by using available wave data from both recorded buoy data (1997–2014) and the WAM numerical model (1956–2015). The study shows that since 2006, coastline retreat has significantly accelerated along the Asturias coast. In particular, severe erosion of sandy beaches and dunes occurred in 2013/14, reaching up to 40 m of coastline retreat and destroying numerous ports and seafront promenades. Increased frequency of unusually strong storm waves, with significant wave height (Hs) exceeding 9 m, together with an unusual 5° westward variation from the mode in offshore wave approach direction during these storms, appear to be the main catalysts in heightened erosion capacity of storm waves in the 2013/14 period. This resulted in the removal of small dune areas and a severe recession in the easternmost part of the largest (natural) dune fields in the region. Under these stormy periods, foredunes and climbing dunes developed notably pronounced escarpments and blowouts, with sand subsequently relocated into the foreshore and backshore zones. This study demonstrated that increased frequency in powerful storm events (Hs > 9 m) and an alteration in storm approach direction, can lead to significantly enhanced erosion of dune coastlines, even along those that are modally-attuned to high energy events.

The Use of News Information Published in Newspapers to Estimate the Impact of Coastal Storms at a Regional Scale

The evaluation of coastal damage caused by storms is not straightforward and different approaches can be applied. In this study, damage caused by extreme storms is evaluated at a regional scale based on news information published in regional newspapers. The data derived from the news are compared with hydrodynamic parameters to check the reliability of this methodology as a preliminary” fast approach” to evaluate storm damage and to identify hotspots along the coast. This methodology was applied to the two most extreme storms ever recorded along the Spanish Mediterranean coast, which occurred in January 2017 and January 2020, severely impacting the coast and causing significant community concerns. The news information from different media sources was processed and weighted to describe the resulting erosion, inundation, sand accumulation, and destruction of infrastructures. Moreover, an accuracy index for scoring the quality of the information was proposed. In spite of some limitations of the method, the resulting regional coastal hazard landscape of damage provides a rapid overview of the intensity and distribution of the damage and enables one to identify the location of potential hotspots for the analyzed extreme storm events. The results show that estimated damage intensity is better related to maximum wave energy than cumulative wave energy during a storm, and that beach characteristics should also be included for understanding the distribution of coastal damage.

Surface gravity wave scattering by multiple slatted screens placed near a caisson porous breakwater in the presence of seabed undulations

In the present study, the effectiveness of using multiple slatted screens placed in front of a caisson porous breakwater to dissipate the incident wave energy is analyzed. To model the water flow through the slatted screens, a quadratic (nonlinear) pressure drop condition which involves both the inertial and drag effects is considered. Further, for thick porous structure, the well known Sollitt and Cross (1972) model is used. To handle the nonlinear boundary conditions, an iterative multi-domain boundary element method (BEM) is used. The numerical convergence of the multi-domain BEM based solutions is presented. Energy identities for flow past a single slatted screen, multiple slatted screens and for the present problem are derived. The study shows that the minimum reflection coefficient (<1%) and maximum wave energy dissipation (>98%) can be obtained by using four slatted screens. Further, for moderate values of perforation-effect Keulegan-Carpenter number (KC), the reflection coefficient attains maximum for b1λ≈n2,n=1,2,3,⋯ (b1 is the distance between the rigid caisson and the front slatted screen, λ is the incident wavelength) irrespective of the variations in the number of slatted screens. Further, the transmission coefficient, horizontal and vertical wave forces acting on the rigid caisson attain maximum for b1/λ≈0.55n, and minimum occurs for 2n+14<b1λ<3n+26,n=0,1,2,3,⋯. The Bragg resonance in the reflection coefficient occurs at Bragg value ≈1.6 irrespective of the variations of KC number. Moreover, the reflection coefficient increases around the Bragg value for higher values of KC number without altering the peak value in the reflection coefficient.

Water Oscillation Modelling Inside OWC Chamber for Wave Energy Conversion

Among wave energy converters (WECs), the Oscillating Water Column (OWC) system is considered as one of the most promising converters; this system works on the principle of water oscillations in an enclosed air chamber due to incident sea waves. The amount of pneumatic power that can be harvested depends on the elevation level, the water oscillations' frequency inside the chamber, and the chamber's global damping. A one-dimensional (1-D) unsteady model has been elaborated to analyze the water elevation's dynamic behavior. Great attention has been paid to determining the natural frequency and the global damping for maximum wave energy capture. The model is based on a water mass block moving periodically upward and downward as a piston inside the chamber, inducing the enclosed air to flow alternately through a turbine. The Lagrangian formalism has been adopted to derive the governing differential equation for the piston water motion. Then the poincare-Lindstedt method has been used to deal with the non-linearity of the problem. The elaborated model has been adapted to an OWC system in the case of monochromatic waves. Results have been compared to another referenced paper for validation and pertinence. Fair agreements have been noted.

Enhancement of Wave Energy Dissipation in Two-Dimensional Acoustic Black Hole by Simultaneous Optimization of Profile and Damping Layer

Acoustic black hole (ABH) effect in thin-walled structures provides drastic wave focalization. In a practical ABH structure with a tapering thickness profile, the concentrated wave energy can be efficiently dissipated by introducing a damping layer to the local high energy density area. In this paper, simultaneous optimization of the geometric parameters of the ABH profile and the topology of the damping layer covering the ABH area is investigated based on the former study of wave focalization. To optimize the ABH structure for achieving maximum energy dissipation, parametric modelling is implemented, and the dissipated energy is computed by the commercial finite element software Abaqus. The optimal geometric parameters of the ABH thickness profile are obtained by the method of moving asymptotes (MMA). The topological optimization problem of the damping layer is solved by using optimality criteria (OC). These two algorithms are nested alternatively in the main optimization procedure. The influence of mesh size and direction of wave incidence on the optimization is discussed. Numerical results show that the proposed approach is efficient in finding the optimal design for the ABH structure to achieve maximum wave energy dissipation. In addition, the influence of coupling between the host ABH plate and the layer on the optimization is investigated. Superior performance of energy dissipation is achieved by the proposed method comparing to the results before the optimization.

Optimal wave energy extraction for oscillating water columns using second‐order sliding mode control

Ocean waves are an important renewable energy resource and several fields of are concurrently working to improve technologies for harnessing their power. In that context, this study presents a control to optimise the performance of oscillating water column systems. As a first contribution, a novel criterion to attain maximum wave energy extraction is developed, resulting in an enhancement of the global power efficiency of the system. Then, taking advantage of the proposed criterion, a second-order sliding mode control set-up is designed, with power extraction maximisation the primary objective and reactive power regulation a secondary one. Simulation results confirm the highly satisfactory performance of the proposed controller and its robustness in the presence of the inherent uncertainties and disturbances in the non-linear system.

Effect of Wave Power Device Arrangement in Double-Water-Chamber Type Seawall towards Wave Power Extraction Rate and Wave Dissipation

Utilization of the ocean energy to meet the electricity need is important to realization. The increasing need for electricity and environmental issues are the reasons. In last several decades a number of studies on wave energy device have been carried to find the effective one. In this paper, the double-water-chamber type seawall is basically adopted that has a similar structure to the OWC was examine to extract wave power. In the experiment various arrangement of wave power device inside the double water-chamber was tested to obtain optimum of wave extraction rate. Another function of the double water-chamber as wave dissipation is also clarified in the experiment. Based on experimental result the maximum wave energy conversion efficiency is about 30% and the reflection coefficient of the double-water-chamber seawall is about 0.3 on average.

Characterization of Wind-Sea- and Swell-Induced Wave Energy along the Norwegian Coast

The necessity to reduce C O 2 emissions in combination with the rising energy demand worldwide makes the extensive use of renewable energy sources increasingly important. To that end, countries with long coastlines, such as Norway, can exploit ocean wave energy to produce large amounts of power. In order to facilitate these efforts as well as to provide quantitative data on the wave energy potential of a specific area, it is essential to analyze the weather and climatic conditions detecting any variabilities. The complex physical processes and the atmosphere-wave synergetic effects make the investigation of temporal variability of wave energy a challenging issue. This work aims to shed new light on potential wave energy mapping, presenting a spatio-temporal assessment of swell- and wind-sea-induced energy flux in the Nordic Seas with a focus on the Norwegian coastline using the NORA10 hindcast for the period 1958–2017 (59 years). The results indicate high spatial and seasonal variability of the wave energy flux along the coast. The maximum wave energy flux is observed during winter, while the minimum is observed during summer. The highest coastal wave energy flux is observed in the Norwegian Sea. The majority of areas with dominant swell conditions (i.e., in the Norwegian Sea) are characterized by the highest coastal wave energy flux. The maximum values of wave energy flux in the North Sea are denoted in its northern parts in the intersection with the Norwegian Sea. In contrast to the Norwegian Sea, areas located in the North Sea and the Barents Sea show that wind sea is contributing more than swell to the total wave energy flux.

Long-term assessment of wave energy in the China Sea using 30-year hindcast data

In this study, a long-term assessment of the wave energy in the China Sea was performed for a 30-year time interval (1988–2017), using the model WAVEWATCH-III. The reliability of the wave simulation results was increased by means of longer time horizon data compared to other relevant studies in the China Sea. This analysis provided information on the regional distribution as well as on the monthly and seasonal variability. The exploitation and stability of wave energy were taken into consideration, so as to find the advantage of resource exploitation. Results indicated that values of significant wave height and wave power density had obviously differences compared with different months, especially in December with a maximum significant wave height of 2.7 m and 35 kW/m of wave power density. The minimum value of them appeared in May, was 1.0 m and 4.5 kW/m, respectively. The distribution of wave energy was abundant in winter and the poorest in summer. In winter, the significant wave height in most areas was above 1.8 m, while the maximum wave energy density in summer was only 1.2 m. As for the wave power density, in winter values in most areas were above 18 kW/m, while the maximum value in summer was only 12 kW/m. In sight of regional distribution, the highest wave energy potential was located in the Northern South China Sea, the East China Sea, the Ryukyu Islands waters, east of the Taiwan Island and the Luzon Strait, with coefficient of variation was within 2.0 and occurrence of exploitation was above 80%, whereas the Bohai Sea, the northern part of the Yellow sea, the Gulf of Thailand, and the Northern Bay were in poor contribution, with occurrence of exploitation was within 50%.

Effect of the PTO Damping Force on the 2D Oscillating Buoy Wave Energy Converter Integrated into a Pile-Restrained Floating Breakwater

The aim of the study is to evaluate the parametric effect of a power take-off (PTO) system on an integration system of an oscillating buoy wave energy device with a pile-restrained floating breakwater. To consider the viscous effect, the study is carried out with three conditions using OpenFOAM, i.e., the linear optimal PTO system, the fixed PTO damping coefficient, and the Coulomb PTO system. The results show that the maximum wave energy capture ratio (CWR) of the device can merely reach 0.35 in the present work, when considering the viscous effect. This result is smaller than that obtained from potential flow. In addition, the linear optimal PTO coefficient under viscous flow should be larger than the theoretical optimal coefficient in terms of the potential flow. A comparison of the Coulomb damping model and the linear damping model also shows that the Coulomb damping model has a good performance in terms of both wave energy capture efficiency and coastal protection. Hence, the effect of the PTO system on such an integration system can be an essential factor to achieve an optimal design.

Wave Energy Assessment around the Aegadian Islands (Sicily)

This paper presents the estimation of the wave energy potential around the Aegadian islands (Italy), carried out on the basis of high resolution wave hindcast. This reanalysis was developed employing Weather Research and Forecast (WRF) and WAVEWATCH III ® models for the modelling of the atmosphere and the waves, respectively. Wave climate has been determined using the above-mentioned 32-year dataset covering the years from 1979 to 2010. To improve the information about wave characteristics regarding spatial details, i.e., increasing wave model resolution, especially in the nearshore region around the islands, a SWAN (Simulating WAves Nearshore) wave propagation model was used. Results obtained through the development of the nearshore analysis detected four energetic hotspots close to the coast of the islands. Near Marettimo island, only one hotspot was detected with a maximum wave energy flux of 9 kW/m, whereas, around Favignana, three hotspots were identified with a maximum wave energy flux of 6.5 kW/m. Such values of available wave energy resource are promising to develop different projects for wave energy converters in specific areas along the coast, in order to improve the energetic independence of Aegadian islands.

EKF Based Fuzzy PI Controlled Speed Sensorless Power Optimal Control of a Direct Drive Power System

Faced with wave irregularity, the corrosion of the mechanical sensor in wave power generation systems, hazardous working conditions, and the inaccuracy of conventional control methods in the shifting system, a new type of irregular wave maximum wave energy capture strategy are proposed. The motivation behind the strategy is speed sensorless power optimal control of a direct drive wave power system by an extended Kalman filter (EKF) and self-tuning fuzzy proportional integral (PI) control. In our strategy, a fast Fourier transform (FFT) is utilized to analyze the spectrum of the irregular wave excitation force, and the maximum superposition control condition of the wave energy extraction is constructed by the vector superposition principle. Taking the voltage and current parameters of the generator as the input, based on two stages of prediction and update, an EKF observer system is established to estimate the speed and position of the power generation system. The fuzzy parameters are used to dynamically adjust the PI parameters so as to achieve optimal power state tracking control. The simulation results show that the FFT can meet the power optimal tracking requirements of unknown irregular waves. The proposed speed sensorless control scheme has good dynamic characteristics, small degree and position observation errors, and strong robustness, and allows the system to follow a given value.

Feasibility study of wave energy harvesting along the southern coast and islands of Iran

Due to the distance of remote coastal areas and multiple islands in the south of Iran from the national grid, establishing wave power plants is highly beneficial. Therefore, in this study, the wave energy potential at these regions is investigated. For this purpose, wave characteristics are provided using European Centre for Medium-Range Weather Forecasts (ECMWF) for ten years, and validated against buoy measurements in two different intervals. The annual, seasonal and monthly variations of wave characteristics and seasonal wave energy flux roses along with the annual occurrence probability of different sea states are also assessed. According to the results, the wave energy in the Oman Sea reaches to its maximum, 17 kW/m at Chabahar port, in summer, and the maximum wave energy in Persian Gulf and Strait of Hormuz, which reaches to 10 kW/m in Kish Island, occurs in winter. In fact, wave parameters in the central regions of Persian Gulf have the higher values than Oman Sea in this season. Finally, Chabahar port in Oman Sea, Kangan port, Kish Island and Kharg Island in the Persian Gulf are considered as the wave energy hotspots, and the most suitable wave energy converter (WEC) systems are suggested for the selected hotspots.

Numerical investigation of front-wall inclination effects on the hydrodynamic performance of a fixed oscillation water column wave energy converter

One of the main geometrical parameters of the fixed oscillating water column wave energy converters is the inclination angle of front wall. In this study, the effects of this parameter on the hydrodynamic performance of an oscillating water column is investigated using a fully nonlinear two-dimensional numerical wave tank, which is developed using the Ansys Fluent 15.0 commercial software. The accuracy of the developed wave tank is first examined by simulating an oscillating water column, having a front wall normal to the water-free surface, subjected to linear, small amplitude incident waves. The resultant absorption efficiencies are compared with available analytical data in the literature, where a good agreement was observed. Next, the simulations are performed for strongly nonlinear waves, up to the wave steepness of 0.069 ( H/L = 0.069), where H is the wave height and L is the wave length. Results show that the absorption efficiency of the oscillating water column decreases considerably as the wave height increases. Moreover, the maximum wave energy absorption efficiency for the highly nonlinear waves occurs at a pneumatic damping coefficient lower than that of the linear theory. Then, the absorption efficiency of the oscillating water column is determined for eight various front wall configurations at various incident wave periods. Results show that, the front walls that are slightly bent towards the inner region of the oscillating water column chamber are more efficient at some wave periods in comparison with the cases studied in this paper.

Long-Term Macro-Scale Assessment of Wave Power of Black Sea by an Optimized Numerical Model

Sea wave power is one of the cleanest renewable energy resources with the potential to mitigate the challenges of global warming and climate change while contributing to the ever-increasing energy demand. Studies show that wave energy production is closely related to wave height and wave period. Accordingly, the potential assessment and characterization of wave energy is vital for planning, production and utilization of wave energy. This study investigated the monthly, seasonal and annual wave energy characteristics of the Black Sea using the third-generation, state-of-the-art numerical model, MIKE 21 SW, based on 37 years of wind data obtained from the European Centre for Medium-Range Weather Forecasts. To set up the model and represent actual field conditions, computational mesh of the study domain was optimized and then the model was calibrated using data observed at nine points. According to the results of the study, the maximum mean monthly wave energy was obtained in the months of January and February. In terms of seasons, the maximum mean seasonal wave energy was observed in the winter. The analysis of the results at annual scale showed that the western part of the sea has more wave energy potential than the eastern part.

The maximum wave energy conversion by two interconnected floaters: Effects of structural flexibility

The effect of structural flexibility on the maximum wave energy conversion by two interconnected floaters is investigated. For the wave energy converter (WEC), the relative pitch motion of two floaters is converted into electricity by a power take off (PTO) system, which is simplified as a linear damper. The hydrodynamic coefficients of the WEC are calculated based on linear potential flow theory. The coupled effects of structural deformation and hydrodynamic interaction are considered using an approximate approach based on discrete-modules and Euler-Bernoulli beam bending. Then equations of motion of the hinged two-floater WEC with structural deformation considered are established in frequency domain. Based on the motion equations, a mathematical model is proposed for evaluating the maximum wave energy conversion of a hinged two-floater WEC in waves. This mathematical model can be used to calculate the maximum power capture and the corresponding optimum PTO damping for both rigid and flexible two-floater WEC with or without motion constraints. Results show that the structural flexibility has a negative effect on the power capture performance for relatively large wave length but a positive influence for relatively small wave length. The motion constraints lead to a reduction of the captured power for both rigid and flexible WEC.