Design Of Wave Energy Converter Research Articles

Study review of the electrical power generation: Wave energy converting device system from the swell

This paper presents the design of an innovative wave energy converter, namely, Electrical Power Generation - WEC Device System from the Swell, abbreviated as WECFS. This WEC device has been registered for a patent in the Spanish Office of the Patents and Brands (OEPM) with the registration number of the innovative utility model-Patent Model: 202131440(5). The study reported in this paper endeavours to demonstrate the technical feasibility, functional mechanical-kinematic behaviour, and the performance of the proof-of-concept WEC device system, in order to determine their energy extraction capacities and functionalities. The overall energy extracted with eight electrical generators A/C is 0.185 MWatts calculated analytically. The levelized cost of energy is a very important metric in determining whether to move forward with the project, where the cost of energy target has been as cheap as $0.07kWh; this value of LCOE could be improved with optimisations on the practical design parameters. This preliminary study investigates the factors influencing standardized and industrialized for the new WEC device system and can be used to guide the optimization of this type of device technology.

Duct Attachment on Improving Breaking Wave Zone Energy Extractor Device Performance

A challenging wave energy converter design that utilized the denser energy part of the nearshore breaking wave zone to generate electricity was introduced in 2016 by Shintake. The Okinawa Institute of Science and Technology Graduate University’s project aims to take advantage of breaking wave energy to harness electricity. The 2016 version of the device consisted only of a bare turbine and power generator. Early exploration of the design recorded short periods and high impact wave pressures were experienced by the structure, with the turbine unable to harvest energy effectively. Additional structure to not only reduce incoming impact pressure but also increase the duration of water flow through the turbine was needed. These are the main reasons behind incorporating the duct attachment into the design. This paper show that the duct is capable of halving the impact pressure experienced by the turbine and can increase the energy exposure by up to 1.6 times the bare turbine configuration. Furthermore, it is also said that wave angle (β) = 40° is the critical angle, although the duct still increases wave energy exposure to the power take-off up to β = 60°.

Extension and improvement of synchronous linear generator based point absorber operation in high wave excitation scenarios

The exploitation of marine wave energy resource has led to the design of numerous Wave Energy Converter (WEC) configurations. The power absorption of a WEC is tightly related to its physical properties and the characteristics of the incoming wave front. Additionally, the operational range of a WEC is limited to certain characteristics of the incoming waves. These restrictions are usually related to limitations in the maximum force of the Power Take-off (PTO) system and the safety of the WEC. As a result, the power production of the WEC must be stopped during sea states of high wave elevation. With the objective of improving the operation of a WEC during these sea states, a Field Weakening (FW) control functionality is proposed to be implemented in the control system of a single-body linear in heave oscillating point absorber with a Permanent Magnet Synchronous Linear Generator (PMSLG) based electrical PTO system. The aim of the aforementioned functionality is to attenuate the magnetic flux in the PMSLG during sea states of high wave elevation. The influence of the size of a WEC on the benefits of the proposed FW functionality is also studied. To that end, two point absorbers with different size are analysed with NEMOH and a wave-to-wire (W2W) model of each WEC is developed. This W2W model enables analysis of the performance and power production of the WECs at different sea states of interest. The obtained results show a remarkable improvement of the operation of a WEC with the implementation of the FW strategy during sea states of high excitation, which leads to an extension of its operation and subsequent additional energy/hydrogen generation.

Geometric Analysis through the Constructal Design of a Sea Wave Energy Converter with Several Coupled Hydropneumatic Chambers Considering the Oscillating Water Column Operating Principle

The work presents a numerical study of a wave energy converter (WEC) device based on the oscillating water column (OWC) operating principle with a variation of one to five coupled chambers. The main objective is to evaluate the influence of the geometry and the number of coupled chambers to maximize the available hydropneumatic power converted in the energy extraction process. The results were analyzed using the data obtained for hydropneumatic power, pressure, mass flow rate, and the calculated performance indicator’s hydropneumatic power. The Constructal Design method associated with the Exhaustive Search optimization method was used to maximize the performance indicator and determine the optimized geometric configurations. The degrees of freedom analyzed were the ratios between the height and length of the hydropneumatic chambers. A wave tank represents the computational domain. The OWC device is positioned inside it, subject to the regular incident waves. Conservation equations of mass and momentum and one equation for the transport of the water volume fraction are solved with the finite volume method (FVM). The multiphase model volume of fluid (VOF) is used to tackle the water–air mixture. The analysis of the results took place by evaluating the performance indicator in each chamber separately and determining the accumulated power, which represents the sum of all the powers calculated in all chambers. The turbine was ignored, i.e., only the duct without it was analyzed. It was found that, among the cases examined, the device with five coupled chambers converts more energy than others and that there is an inflection point in the performance indicator, hydropneumatic power, as the value of the degree of freedom increases, characterizing a decrease in the value of the performance indicator. With the results of the hydropneumatic power, pressure, and mass flow rate, it was possible to determine a range of geometry values that maximizes the energy conversion, taking into account the cases of one to five coupled chambers and the individual influence of each one.

Energy Content Characterization of Water Waves Using Linear and Nonlinear Spectral Analysis

Abstract The survivability, safe operation, and design of marine vehicles and wave energy converters are highly dependent on accurate characterization and estimation of the energy content of the ocean wave field. In this study, analytical solutions of the nonlinear Schrödinger equation (NLS) using periodic inverse scattering transformation (IST) and its associated Riemann spectrum are used to obtain the nonlinear wave modes (eigen functions of the nonlinear equation consisting of multiple phase-locked harmonic components). These nonlinear wave modes are used in two approaches to develop a more accurate definition of the energy content. First, in an ad hoc approach, the amplitudes of the nonlinear wave modes are used with a linear energy calculation resulting in a semi-linear energy estimate. Next, a novel, mathematically exact definition of the energy content taking into account the nonlinear effects up to fifth order is introduced in combination with the nonlinear wave modes, the exact energy content of the wave field is computed. Experimental results and numerical simulations were used to compute and analyze the linear, ad hoc, and exact energy contents of the wave field, using both linear and nonlinear spectra. The ratio of the ad hoc and exact energy estimates to the linear energy content was computed to examine the effect of nonlinearity on the energy content. In general, an increasing energy ratio was observed for increasing nonlinearity of the wave field, with larger contributions from higher-order harmonic terms. It was confirmed that the significant increase in nonlinear energy content with respect to its linear counterpart is due to the increase in the number of nonlinear phase-locked (bound wave) modes.2

Fast nonlinear Froude\u2013Krylov force calculation for prismatic floating platforms: a wave energy conversion application case

Computationally fast and accurate mathematical models are essential for effective design, optimization, and control of wave energy converters. However, the energy-maximising control strategy, essential for reaching economic viability, inevitably leads to the violation of linearising assumptions, so the common linear models become unreliable and potentially unrealistic. Partially nonlinear models based on the computation of Froude–Krylov forces with respect to the instantaneous wetted surface are promising and popular alternatives, but they are still too slow when floaters of arbitrary complexity are considered; in fact, mesh-based spatial discretisation, required by such geometries, becomes the computational bottle-neck, leading to simulations 2 orders of magnitude slower than real-time, unaffordable for extensive iterative optimizations. This paper proposes an alternative analytical approach for the subset of prismatic floating platforms, common in the wave energy field, ensuring computations 2 orders of magnitude faster than real-time, hence 4 orders of magnitude faster than state-of-the-art mesh-based approaches. The nonlinear Froude–Krylov model is used to investigate the nonlinear hydrodynamics of the floater of a pitching wave energy converter, extracting energy either from pitch or from an inertially coupled internal degree of freedom, especially highlighting the impact of state constraints, controlled/uncontrolled conditions, and impact on control parameters’ optimization, sensitivity and effectiveness.

Reliability‐based hull geometry optimisation of a point‐absorber wave energy converter with power take‐off structural reliability objectives

Recent studies have focused on optimising wave energy converter (WEC) designs, maximising their power performance and techno-economic feasibility. Reliability has yet to be fully considered in these formulations, despite its impact on cost and performance. In this study, this gap is addressed by developing a reliability-based design optimisation framework for WEC hull geometries to explore the trade-off between power performance and power take-off (PTO) system damage equivalent loading (DEL). Optimised hull geometries for two sites are considered (from the centre of the North Sea and off the west coast of Norway), and two directions of motions (heave and surge). Results indicate that site characteristics affect the potential power production and DEL for an optimal WEC design. These are also affected by the direction of motion for power extraction, which also significantly changes optimal hull shape characteristics. Optimal surging WEC designs have edges facing oncoming wave directions, while heaving WECs have pointed bottoms, both to streamline movement. Larger, more convex WECs result in greater power production and DEL, while smaller, more concave WECs result in lesser power production and DEL. These findings underline the importance of considering WEC hull geometry in early design processes to optimise cost, power production, and reliability.

An efficient fully Lagrangian solver for modeling wave interaction with oscillating wave surge converter

In this paper, we present an efficient, accurate and fully Lagrangian numerical solver for modeling wave interaction with oscillating wave surge converter (OWSC). The key idea is to couple SPHinXsys, an open-source multi-physics library in unified smoothed particle hydrodynamic (SPH) framework, with Simbody which presents an object-oriented application programming interface for multi-body dynamics. More precisely, the wave dynamics and its interaction with OWSC is resolved by a Riemann-based weakly-compressible SPH method in SPHinXsys, and the solid-body kinematics is computed by Simbody library. Numerical experiments demonstrate that the proposed solver can accurately predict the wave elevations, flap rotation and wave loading on the flap in comparison with laboratory experiment and numerical investigation. In particularly, the new solver shows optimized computational performance through CPU cost analysis and comparison with commercial software package ANSYS FLUENT and other SPH-based solvers in literature. Furthermore, a linear damper is applied for imitating the power take-off system to study its effects on the hydrodynamics properties of OWSC and efficiency of energy harvesting. In addition, the present solver is used to model extreme wave condition using the focused wave approach to investigate the extreme loads and motions of OWSC under such extreme wave conditions. It is also worth noting that though the model validation used herein is a bottom hinged oscillating wave energy converter (WEC), the obtained numerical results show promising potential of the proposed solver to future applications in the design of high-performance WECs.

Parametric study and optimization of a two‐body wave energy converter

The parametric study and optimization of a two-body wave energy converter (WEC) for the wave and current conditions in the region of Zhaitang Island (China) is presented. Nine parameters are considered, and their influence on the power captured by the two-body WEC is investigated following both single-parameter and multi-parameter approaches. A backpropagation neural network model is developed and applied to predict the captured power for any given values of the nine parameters and the wave frequency. Then the robust design method, also known as the Taguchi method, is implemented to study the comprehensive effects of the parameters on the power output of the device. Moreover, scale model experiments are conducted to verify and confirm the influence of the principal parameters on the power output. Combining numerical simulations, a neural network model and experimental work, this study provides an optimization programme for the main parameters of the device in the target sea region and, at a more general level, references for two-body WEC designs based on specific sea states.

Расчет эффективности преобразования энергии морского волнения в электроэнергию

Object and purpose of research. The object of the study is the wave energy converters (WEC) into electric power. The purpose of the study is to draw up a differential equation describing the operation of the WEC, its solution and determination for the design parameters influence of the WEC on the efficiency of energy conversion. Materials and methods. The theoretical methods adopted in ship mechanics and theory are used to study the operation of complex mechanisms and dynamics of marine objects. The data on the characteristics of electric generators are used. Main results. The differential equation describing the operation of the WEC on regular wave is compiled. The equation relates the characteristics of waves to the design parameters of the WEC. Generalized characteristics of electric generators are obtained. Systematic calculations are carried out; they show the influence of the WEC design parameters on the efficiency of wave energy conversion into electric power. Conclusion. The results can be used in design of the WEC. The resulting differential equation makes it possible to investigate the operation of the WEC in various marine conditions and to evaluate the influence of design parameters on the efficiency of energy conversion. The generalized characteristics of electric generators can be used in design of wave power structures and wind power plants.

Cost-Benefit Analysis of a Hybrid Biophysical Approach to Wave Energy Extraction: Bio-Oscillator

A cost-benefit analysis (CBA) is described for a novel wave energy converters (WEC) design based on a marine hybrid bio-structure—a combination of macroalgae, shellfish or other species on a built frame. The Bio-Oscillator design utilises a hard “skeleton” (e.g., carbon fibre, wood) on which biological organisms (e.g., shellfish, large macroalgae) are grown. As waves pass by, the load generated by the oscillating drag and inertia is transferred through mooring lines to power takeoff technology. This novel approach essentially reverses the typical marine engineering view that “bio-fouling is bad” and instead leverages off the added-drag of biological growth on structures. The approach results in a structure that is largely biodegradable, naturally self-replicating and synergistic with the background environment, self-de-risking in terms of failure impact and can leverage off its own form to enhance energy capture beyond a conventional design. This reduces impact while connecting with conventional marine industries such as aquaculture. A CBA examines the economic pros and cons of this approach, focusing on installation and material costs, along with benefits from synergistic production. The analysis suggests that in addition to typical wave energy obstacles (e.g., cable length, capture width, and power take off) the benefits (biodegradability, harvestability, and carbon reduction) of replacing much of the mass of the structure with living biological material can be included.

Maybe less is more: Considering capacity factor, saturation, variability, and filtering effects of wave energy devices

While a great deal of research has been performed to quantify and characterize the wave energy resource, there are still open questions about how a wave energy developer should use this wave resource information to design a wave energy converter device to suit a specific environment or, alternatively, to assess potential deployment locations. It is natural to focus first on the impressive magnitudes of power available from ocean waves, and to be drawn to locations where mean power levels are highest. However, a number of additional factors such as intermittency and capacity factor may be influential in determining economic viability of a wave energy converter, and should therefore be considered at the resource level, so that these factors can influence device design decisions. This study examines a set of wave resource metrics aimed towards this end of bettering accounting for variability in wave energy converter design. The results show distinct regional trends that may factor into project siting and wave energy converter design. Although a definitive solution for the optimal size of a wave energy converter is beyond the reaches of this study, the evidence presented does support the idea that smaller devices with lower power ratings may merit closer consideration.

Physical Modelling of the Effect on the Wave Field of the WaveCat Wave Energy Converter

The WaveCat is a moored Wave Energy Converter design which uses wave overtopping discharge into a variable v-shaped hull, to generate electricity through low head turbines. Physical model tests of WaveCat WEC were carried out to determine the device reflection, transmission, absorption and capture coefficients based on selected wave conditions. The model scale was 1:30, with hulls of 3 m in length, 0.4 m in height and a freeboard of 0.2 m. Wave gauges monitored the surface elevation at discrete points around the experimental area, and level sensors and flowmeters recorded the amount of water captured and released by the model. Random waves of significant wave height between 0.03 m and 0.12 m and peak wave periods of 0.91 s to 2.37 s at model scale were tested. The wedge angle of the device was set to 60°. A reflection analysis was carried out using a revised three probe method and spectral analysis of the surface elevation to determine the incident, reflected and transmitted energy. The results show that the reflection coefficient is highest (0.79) at low significant wave height and low peak wave period, the transmission coefficient is highest (0.98) at low significant wave height and high peak wave period, and absorption coefficient is highest (0.78) when significant wave height is high and peak wave period is low. The model also shows the highest Capture Width Ratio (0.015) at wavelengths on the order of model length. The results have particular implications for wave energy conversion prediction potential using this design of device.

Modelling of Unidirectional Oscillating Buoy Wave Energy Converter Based on Direct Mechanical Drive System Under Irregular Wave

The development of wave energy converters (WEC) is increasing over time with various designs. The need for a WEC design that emphasizes the level of simplicity, portability, and closeness of its implementation to the nearshore is quite interesting to discuss. One of the WECs that can meet these criteria is oscillating buoy based on a direct mechanical drive system. This research proposes the concept of oscillating buoy WEC based on a direct mechanical drive system, which is designed with a unidirectional gear system to be able to generate energy both in the upward and downward wave phases. The WEC is also making to produce high rotation on the output side from the small motion of the buoy, especially in the heave direction. Predicting the power generated by this concept is very interesting because up to now, there has not been sufficient analytical model to estimate the power generated by oscillating buoys WEC based on a direct mechanical drive system, especially under irregular waves. In this work, an analytical method is conducting to describe the interaction between the model and irregular waves from the JONSWAP model. Model interaction is simulating numerically using the MATLAB program. The buoy translational motion of the model in the heave direction, which is converting to electric power by increasing the rotation of the gearbox and the energy stored in the flywheel, can produce significant output power. In the future, the proposed model can be used to develop more feasible and efficient models of wave energy converters.

Meta‐heuristic optimisation approach for wave energy converter design by means of a stochastic hydrodynamic model

A methodology to automate the sizing of a wave energy converter (WEC) is presented. The preliminary design of WEC geometry is addressed as a mathematical program by means of a meta-heuristic optimisation, which includes as key aspects the use of a multi-objective differential evolutionary (DE) algorithm and the implementation of a stochastic hydrodynamic model of the WEC. In this methodology, the WEC concept, the control strategy, the power take-off characteristics and the location have been taken into consideration due to their strong influence on the WEC design. As a case example, a real project has been selected, and the methodology has been applied to two test locations. Stochastic models are used to handle irregular sea states and to obtain statistical information while reducing the calculation effort when compared to time-domain models. The output derived from the proposed methodology is a set of feasible solutions so-called Pareto frontier. These solutions can be used as inputs for a detailed design process. Data from real projects could be used to further develop the sizing methodology by improving the algorithm convergence, refining the requirements, or including new restrictions.

Design and simulation of point absorber wave energy converter

The paper aims to design and simulation of a wave energy harvesting system commonly known as point absorber for Ennore port located in the coastal area of Chennai, India. The geographical condition of India, which is surrounded by the three sides with seas and ocean, has enormous opportunity for power production through wave energy harvesting system. The wave energy converter device is a two-body floating system and its both parts are connected by power take-off unit which acts as spring mass damper system. In this paper, the hydrodynamic diffraction, stability analysis, frequency, and time response analysis is carried out on ansys-aqwa. The numerical results are compared with the results obtained from the similar experiments for validation of CFD solver. Effects of the properties featuring wave characteristics including wave height and wave period of Ennore port on the energy conversion, Froude-Krylov and diffraction force, response amplitude operator (RAO) are studied. Based on the study, float diameter, draft, geometry, and varying damping coefficient for power generation are optimized. Finally, the optimally designed point absorber is simulated as per Indian ocean energy harvesting standard and mass of the system, heave dimension, diffraction forces, and pressure variations are computed.

Annual performance of the second-generation variable-geometry oscillating surge wave energy converter

Recent studies in wave energy have highlighted the need for a structured innovation approach in wave energy converter (WEC) design because cost-of-energy estimates have remained high. One such innovation being investigated by the National Renewable Energy Laboratory is WEC geometry control, which uses control surfaces in combination with an oscillating surge WEC (OSWEC) to increase device availability and power generation while limiting structural costs. This study performs the first analysis of annual performance for a novel OSWEC with geometry control to understand how the geometry control affects availability, annual power generation, and structural loadings like the power-take-off (PTO) torque or surge foundation force. Device hydrodynamic coefficients are calculated using linear potential theory for six geometry configurations. A nonideal PTO system is assumed and quadratic viscous damping losses are considered. Annual performance is evaluated and compared for three U.S. wave energy sites. The WEC geometry and PTO system are controlled on a sea-state basis to optimize for power capture while remaining under limits set on motion amplitude and structural loads. Results indicate that geometry control can increase availability up to 25 days in an average year depending on design limits, increase average power generation, and significantly reduce peak structural loads.

The Wave Energy Converter Design Process: Methods Applied in Industry and Shortcomings of Current Practices

Wave energy is among the many renewable energy technologies being researched and developed to address the increasing demand for low-emissions energy. The unique design challenges for wave energy converter design—integrating complex and uncertain technological, economic, and ecological systems, overcoming the structural challenges of ocean deployment, and dealing with complex system dynamics—have lead to a disjointed progression of research and development. There is no common design practice across the wave energy industry and there is no published synthesis of the practices that are used by developers. In this paper, we summarize the methods being employed in WEC design as well as promising methods that have yet to be applied. We contextualize these methods within an overarching design process. We present results from a survey of WEC developers to identify methods that are common in industry. From the review and survey results, we conclude that the most common methods of WEC design are iterative methods in which design parameters are defined, evaluated, and then changed based on evaluation results. This leaves a significant space for improvement of methods that help designers make better-informed decisions prior to sophisticated evaluation, and methods of using the evaluation results to make better design decisions during iteration. Despite the popularity of optimization methods in academic research, they are less common in industry development. We end this paper with a summary of the areas of WEC design in which the testing and development of new methods is necessary, and where more research is required to fully understand the influence of design decisions on WEC performance.

Effects of sea ice on wave energy flux distribution in the Bohai Sea

Abstract The wave energy flux distribution in the Bohai Sea during wintertime is re-evaluated based on SWAN with the added sea-ice effect, which is derived from an ice-ocean coupled model, FVCOM. Simulated wave parameters and ice cover agree well with the measured wave data and the MODIS images of sea-ice cover, respectively. The results indicate that the decrease of wave energy flux is mainly caused by the formed ice which leads to the reduction of the effective wind fetch and transferred momentum from air to the ocean surface. The numerical results in a typical winter from 2011 to 2012 show that, due to the presence of sea ice, the average wave energy fluxes can be decreased by up to 80% in Liaodong Bay, while up to 50% in Bohai Bay and Laizhou Bay. Under the extreme winter-weather conditions, more pronounced reduction of wave energy flux caused by ice is observed. The findings also imply that in the design of wave energy converters (WECs) and their deployed locations in the Bohai Sea, even the likely ice-free areas in winter time, the effect of other ice-covered regions on the decrease of wave energy flux as a result of decrease in wind fetch should be considered.

High-resolution hindcasts for U.S. wave energy resource characterization

The marine and hydrokinetic (MHK) industry is at an early stage of development and has the potential to play a significant role in diversifying the U.S. energy portfolio and reducing the U.S. carbon footprint. Wave energy is the largest among all the U.S. MHK energy resources, which include wave energy, ocean current, tidal-instream, ocean thermal energy conversion, and river-instream. Wave resource characterization is an essential step for regional wave energy assessments, Wave Energy Converter (WEC) project development, site selection and WEC design. The present paper provides an overview of a joint modelling effort by the Pacific Northwest National Laboratory and Sandia National Laboratories on high-resolution wave hindcasts to support the U.S. Department of Energy’s Water Power Technologies Office’s program of wave resource characterization, assessment and classifications in all US coastal regions. Topics covered include the modelling approach, model input requirements, model validation strategies, high performance computing resource requirements, model outputs and data management strategies. Examples of model setup and validation for different regions are provided along with application to development of classification systems, and analysis of regional wave climates. Lessons learned and technical challenges of the long-term, high-resolution regional wave hindcast are discussed.