Guest Editorial: Advances in Wave Energy Conversion Systems

Ocean waves are a largely untapped energy resource, and the global wave potential is estimated at about 32,000 TWh/year. Due to its great provide renewable sustainable electricity without carbon dioxide emission, conversion technology has attracted extensive attention from multi-disciplinary communities. Compared with wind solar power, power ocean characterised by high density spatio-temporal availability. However, levelised cost of (LCoE) higher than that radiation. The LCoE can be reduced technical innovations, especially in novel concepts, key components, real-time control systems so forth. In addition, integrated into offshore structures cost-effective form multifunction platforms. This Special Issue aims update recent advances related all over world. There are, total, 32 papers accepted for publication after careful peer review revisions. authors based 13 different countries/regions, including United Kingdom, Ireland, China, Australia, America, Brazil forth, covering five continents, is, Europe, Asia, North America South America. These selected broadly categorised six topics: (A) analysis prediction, (B) modelling converters (WECs) farms, (C) system design implementation, (D) model validation case studies, (E) concepts (F) WEC optimisation grid connection. All these topics greater or lesser extent, referred paper, entitled ‘A research commercial perspective’ Guo Ringwood, in-depth discussion their influence on commercialisation. paper also summaries historical ongoing commercialisation efforts devoted technology. Significant variability resource plays fundamental role diversifying successful development need collective approach common issues, example, modelling, take-off (PTO) design, control, survivability, performance metrics Historical indicates investor risk must providing more certainty national international supporting programmes policies, focussing technological challenges reduce LCoE, uncertainty examine limitations supply chains marine licensing arrangements, while maximising industry-academy-government collaboration. other 31 aforementioned 6 topics, summary each topic given below. Readers highly recommended read full if interested. Lemessy et al., ‘Analysis Caribbean climate harvesting’, analyse ten-year data region. Characteristic parameters, average height, period, flux, represent Sea, obtained. Extreme sea states determined using peak threshold method. statistical identifies requirements WECs targeted Sea. Bento ‘Ocean forecasting convolutional neural networks’, propose new short-term horizon, network (CNN) models. study validates capability CNN architectures work as prediction engine, even horizons up h. Numerical results imply input dependencies feature extraction conducted models useful improve accuracy. CNN-based shows management, it accurate horizon Shahroozi ‘Considerations dissipative losses converters’, investigate dependency length level chain. sensitivity noise, amplitude constraints, effects encountered realistic discussed considered reveal length. Intensive numerical simulations conclude length, required achieve maximum output systems, shorter generally been assumed date, ranging few seconds half period. Faedo ‘LMI-based passivation LTI application structures’, an optimisation-based technique linear time-invariant (LTI) which applied dynamics waves, ensuring passivity. Based state-space model, properly designed perturbation introduced computed solving set matrix inequalities (LMIs) minimise objective. An platform device exemplified demonstrate effectiveness importance proposed dynamic structures. Tan ‘Power absorption multi-axis converter’, numerically operating 3 degrees freedom (DoFs). single DoF device, capable absorb harmonic waves. this study, real states, seven Zhejiang nearshore sites East China used simulation, indicating absorbed 5 kW. efficiency 29% reported most energetic site Shengshan. Kurniawan ‘Numerical simulation parametric resonance simplified models’, present computation-efficient method simulate non-linear WECs. Different Froude-Krylov method, considers time-varying body's centres gravity buoyancy rather evaluating forces according instantaneous wetted surface. Although no included, hydrostatic only accounted approximately, predict pitch reasonable offers computationally efficient way time domain. Song ‘The anti-impact oscillating buoy various air cushions’, cushions variety shapes mitigate impact force enhance survivability environments. Qualitative cylindrical cushion performs well mechanism. Both experimental improvement resistance slowed down increase volume, there exists upper limit positively correlated velocity buoy. Dizon ‘Modular horizontal pendulum converter: Exploring feasibility observation applications U.S. Pacific Northwest’, applying Self-Contained Observations Payload (SCOOP) National Data Buoy Center, deployed off coast Washington State, pendulum's radius arm, mass, PTO damping parametrically studied effect subjected seasonal variation climate. It concluded 20 kg mass satisfy SCOOP base requirement W throughout year. clearly proves utilising applications. Wei ‘Modelling converter array nonlinear mixed time-domain/frequency-domain method’, dense arrays systems. balance describe response frequency domain evaluated solved Grazer array, equipped adaptable piston pumping demonstrates some parameters accuracy computational cost. effectively costs, remaining acceptable arrays. serve predictive farms measurements. Haider ‘Application conversion’, mathematical framework implement controller (NMPC) production, when function non-quadratic, piecewise discontinuous. NMPC pseudo-quadratisation weight scheduling, confirmed experimentally target machine emulator. Gu heaving point absorber causal feedback controller, combination PID quadratic damper maximising. A fully submerged spherical heave, considering viscous drag force, evaluate framework. regular irregular compute easy implement. conventional PI strategy better terms bandwidth capture. Yang inertia self-tuning phase floating multi-body maximise capture width ratio (CWR) (FMB) automatically tuning total hull. validate meeting optimal condition. Therefore, significant CWR achieved FMB WEC. Xu ‘Maximum tracking mechanical rectification mechanism, transfer reciprocating motion rotary through ball screw. drives permanent magnet synchronous generator produce electricity. algorithm efficiency. confirm under conditions. Hillis ‘Wave stabilisation mooring load reduction control’, modifying f loads. approximate significantly loading system, capturing same amount mean passive controller. Thus, highlights reducing mitigating cyclic failure one major cost-driver factors design. ‘Energy-maximising moment-based constrained farms’, arrays, practical constraints state variables input. To burden developed map objective tractable program finite dimension. farm consisting CorPower-like devices strategy. show effective production physical limitations. Machado ‘Hierarchical emulation hyperbaric develop hierarchical strategies laboratory facility. floats hydro-pneumatic storage (HSS), scheme implemented facility doubly fed induction generator, HSS pressure Conventional controllers adopted scheme, advanced methods will future. Li tank verification configurations’, four configurations WECs, body WEC, two-body plate (Reference Model 3), cylindrically shaped secondary body. For derived then verified tests. revealed captured streamlined shape, two times (up 66.5%) Reference Coupling relative stroke, turn improves Wu ‘Experimental analyses hydraulic waves’, performance, CWR, coefficient both identified achieving value CWR. Davidson ‘Opening air-chamber water column spar avoid resonance’, theoretical background regarding occurrence oscillating-water-column (OWC) spar-buoy report flume behaviour configurations, (1) closed (2) open-air chamber, OWC scale 1:100. observed coupling between within weakened opening chamber. Moreover, damped natural heave shifted comparison chamber configuration. Correspondingly, characteristics altered due roll/pitch modes. findings relief valve installed top possible avenue depress detection occurrence. Silva ‘Air Mutriku plant: Review study’, summarise overview data, obtained Basque Country, Spain, least squares support vector (LS-SVM) developed, chambers. LS-SVM errors found vary 9% 25%, 1 s. Regressive models, AR ARMA slightly (8% 22%) much lower thus, preferred MPC-like strategies. Ermakov ‘Rotors conversion—Practice possibilities’, existing ideas create fundamentally direction development, particularly those harnessing elliptical fluid particles employment rotor. Three main aspects rotor-based reviewed: studies prototypes, derivation (3) philosophies devices. large rotors, convergence geometry not reached yet. Some problems, torque fluctuation, addressed may bringing rotors operational reality. Huang calculation experiment external type navigation lighted buoys’, ‘Sharp Eagle’ pontoon vertical plates. flow theory generalized mode Additionally, tests carried out tank. device's improved proper coefficient. expected continuous buoys small middle size. Zheng ‘Performance plate-wave breakwater’, (pWEC), moored front stationary breakwater. pWEC composed flexible piezoelectric layers bonded faces it. As propagate elastic transformed effect. Eigen matching method-based hydroelastic electromechanical hydrodynamic problems coupled together. width, submergence edge types plate, draft breakwater, attenuation investigated. dramatically influenced pWEC. Ning ‘Theoretical investigation WEC-floating breakwater system’, cost-sharing concept. variable separation-based two-dimensional system. surging front-pontoon perform pitching absorption, high-frequency peaks associated motion, induced ‘hydrodynamic constructive effect’, gap resonance. Peng triple hybrid three pontoons, modules, extract and, meanwhile, attenuate coastal protection. subject literature, pontoons close another, benefits sharing foundation. Two setups, equal drafts step-change drafts, tested Tank testing integration multi-pontoon robust stabilising output. advantageous whereas attenuating energy. Further should harvesting wave. Garcia-Teruel Clark, ‘Reliability-based hull point-absorber structural reliability objectives’, geometric compromise Damage Equivalent Loading (DEL), order structure Optimised indicate larger convex leads DEL, smaller concave DEL. highlight conducting early stage optimise reliability. Bao ‘Parametric optimization backpropagation predicting nine parameters. Taguchi comprehensive 1:20 wave-current verify conversion. applicable targeting specific site. Sergiienko ‘Importance drivetrain electrical optimising quality power. drive. wav-to-wire derived, incident generator. Drivetrain performed gear or/and flywheel inertia. Simulation optimised change allowing operate efficiencies. peak-to-average quality. Said ‘Grid energy—Overview perspectives’, informative classification integration, imposed codes, technologies integration. After analysing seldom urgent wave-to-grid takes account train Murad ‘Control hysteresis-SVPWM current bidirectional buck/boost storage’, two-level electric mode, three-phase AC/DC rectifier controlled proportional DC/DC consists super-capacitors batteries buffer fluctuation modelled storage, Blavette ‘Upgrading test overplanting: techno-economic analysis’, compare several electrothermal export cable determine profitability upgrading sites. investigated numerically, first precise second techno-economical farms. that, worse-case conditions profitable upgrade further detailed needed general case. Issue, ‘Advances systems’, have shown improvements across fields Recent clarified pathway advance enhancing industry-academia-government collaboration bridge valley death R&D high-TRL activities. With increasing emphasis provision carbon-free energy, diversify mix sources, poised supplement, complement, mature technologies. next decade crucial deciding make breakthrough become mainstream Guest Editors appreciate authors’ contributions systems’. They would like extend appreciation anonymous reviewers who provided insightful inspiring comments suggestions. Without reviewers, cannot reach such is. thanks go Editor-in-Chief IET Renewable Power Generation, Prof. David Infield, giving opportunity, Managing Editor Dr. Jessica Jones, her considerable Editors. Bingyong John Ringwood thank Marie Skłodowska-Curie Action (Grant No. 841388) Science Foundation Ireland SFI/13/IA/1886, 12/RC/2302-P2 Marine Energy Centre). declare conflict interest. Guo, Northwestern Polytechnical University, (Lead Editor). graduated B.Eng. M.Sc. Information Countermeasure Technology Underwater Acoustics, 2010 2013, respectively. He received Ph.D. degree Electronic Engineering University Hull, UK, 2017. worked post-doctoral researcher Nonlinear Dynamics Control Lab, Exeter, 2019–2021, Curie Postdoctoral Research Fellow Centre Research, Maynooth 2019–2021. His interests lie Siming Zheng, Plymouth, UK Hydraulic Tsinghua 2016. From April 2020 now, he works fellow. Before was postdoctoral fellow completing his Ph.D., prior College Cork, 12 months visiting student. revolves around hydroelasticity plates, scattering metamaterial focus converters. V. Maynooth, (Guest B.Sc. (Eng.) Electrical TU Dublin Strathclyde University. spent number years City member academic staff School Engineering, concurrent Massey Auckland. joined 2000, founding head department built greenfield site, serving Dean 2001 2006. currently professor Director Associate IEEE Transactions Sustainable Journal Energy, Subject Energies, Deputy RPG. biomedical engineering João C. Henriques, Lisbon, Portugal Henriques assistant Department Mechanical Instituto Superior Técnico (IST), Portugal. Technical Lisbon 1993 2007, simulating high-speed compressible flows. Since 2008, areas (WECs), aerodynamic turbines published 57 peer-refereed journals. holds patents, field another participated eight European projects Dahai Zhang, Zhang born 1981. Mechatronic (ZJU), Hangzhou, 2010. 2011 ZJU Lancaster since 2018. dealing intelligent condition monitoring fault diagnosis machines turbine, tidal converter, distributed generation smart grids.