A Comparative Analysis of Self-Rectifying Turbines for the Mutriku Oscillating Water Column Energy Plant

Oscillating Water Column (OWC) based devices are arising as one of the most promising technologies for wave energy harnessing. However, the most widely used turbine comprising its power take-off (PTO) module, the Wells turbine, presents some drawbacks that require special attention. Notwithstanding different control strategies are being followed to overcome these issues; the use of other self-rectifying turbines could directly achieve this goal at the expense of some extra construction, maintenance, and operation costs. However, these newly developed turbines in turn show diverse behaviours that should be compared for each case. This paper aims to analyse this comparison for the Mutriku wave energy power plant.This work was supported by the MINECO through the Research Project DPI2015-70075-R (MINECO/FEDER, UE) and in part by the University of the Basque Country (UPV/EHU) through PPG17/33. The authors would like to thank the collaboration of the Basque Energy Agency (EVE) through Agreement UPV/EHUEVE23/6/2011, the Spanish National Fusion Laboratory (EURATOM-CIEMAT) through Agreement UPV/EHUCIEMAT08/190, and EUSKAMPUSCampus of International Excellence

Variable Speed Control In Wells Turbine-Based Oscillating Water Column Devices: Optimum Rotational Speed

The effects of climate change and global warming reveal the need to find alternative sources of clean energy. In this sense, wave energy power plants, and in particular Oscillating Water Column (OWC) devices, offer a huge potential of energy harnessing. Nevertheless, the conversion systems have not reached a commercially mature stage yet so as to compete with conventional power plants. At this point, the use of new control methods over the existing technology arises as a doable way to improve the efficiency of the system. Due to the nonuniform response that the turbine shows to the rotational speed variation, the speed control of the turbo-generator may offer a feasible solution for efficiency improvement during the energy conversion. In this context, a novel speed control approach for OWC systems is presented in this paper, demonstrating its goodness and affording promising results when particularized to the Mutriku's wave power plant.This work was supported in part by the University of the Basque Country (Universidad del Pais Vasco UPV/Euskal Herriko Unibertsitatea EHU) through Project PPG17/33 and by the MINECO through the Research Project DPI2015-70075-R (MINECO/FEDER, EU), as well as to the Basque Government through Ph.D. Grant PIF PRE_2016_2_0193. The authors would like to thank the collaboration of the Basque Energy Agency (EVE) through Agreement UPV/EHUEVE23/6/2011, the Spanish National Fusion Laboratory (EURATOM-CIEMAT) through Agreement UPV/EHUCIEMAT08/190 and EUSKAMPUS - Campus of International Excellence. They would also like to thank Yago Torre-Enciso and Olatz Ajuria from EVE for their collaboration and help

Centralized Airflow Control to Reduce Output Power Variation in a Complex OWC Ocean Energy Network

A centralized airflow control scheme for a complex ocean energy network (OEN) is proposed in this paper to reduce the output power variation (OPV). The OEN is an integrated network of multiple oscillating water columns (OWCs) that are located at different geographical sites connected to a common electrical grid. The complexity of the OWC-OEN increases manifolds due to the integration of several OWCs and design of controllers become very challenging task. So, the centralized airflow control scheme is designed in two stages. In control stage-1, a proportional-integral- (PI-) type controller is designed to provide a common reference command to control stage-2. In control stage-2, the antiwindup PID controllers are implemented for the airflow control of all the OWCs simultaneously. In order to tune the large number of control parameters of this complex system, a fitness function based on integral squared error (ISE) is minimized using the widely adopted particle swarm optimization (PSO) technique. Next, the simulation results were obtained with random wave profiles created using the Joint North Sea Wave Project (JONSWAP) irregular wave model. The OPV of the proposed OWC-OEN was reduced significantly as compared to the individual OWC. It was further observed that the OPV of the proposed scheme was lower than that achieved with uncontrolled and MPPT controlled OWC-OEN. The effect of communication delay on the OPV of the proposed OWC-OEN scheme was also investigated with the proposed controller, which was found to be robust for a delay up to 100 ms.This work was supported in part by the Basque Government through project IT1207-19 and MCIU/MINECO through RTI2018-094902-B-C21/RTI2018-094902-B-C22 (MCIU/AEI/FEDER, UE)

Self-Adaptive Global-Best Harmony Search Algorithm-Based Airflow Control of a Wells-Turbine-Based Oscillating-Water Column

The Harmony Search algorithm has attracted a lot of interest in the past years because of its simplicity and efficiency. This led many scientists to develop various variants for many applications. In this paper, four variants of the Harmony search algorithm were implemented and tested to optimize the control design of the Proportional-Integral-derivative (PID) controller in a proposed airflow control scheme. The airflow control strategy has been proposed to deal with the undesired stalling phenomenon of the Wells turbine in an Oscillating Water Column (OWC). To showcase the effectiveness of the Self-Adaptive Global Harmony Search (SGHS) algorithm over traditional tuning methods, a comparative study has been carried out between the optimized PID, the traditionally tuned PID and the uncontrolled OWC system. The results of optimization showed that the Self-Adaptive Global Harmony Search (SGHS) algorithm adapted the best to the problem of the airflow control within the wave energy converter. Moreover, the OWC performance is superior when using the SGHS-tuned PID.This work was supported in part by the Basque Government, through project IT1207-19 and by the MCIU/MINECO through RTI2018-094902-B-C21 / RTI2018-094902-B-C22 (MCIU/AEI/FEDER, UE)

Development of Multi-Oscillating Water Columns as Wave Energy Converters

Wave energy development continues to advance in order to capture the immense ocean energy available globally. A large number of wave energy conversion concepts have been developed and researched to date but we are still not able to see a convergence of technologies. This provides the requirement and additional opportunity for further research. This paper provides a review and discusses the development of the OWC concept of wave energy converters in general and the evolved variation of the M-OWC more specifically. The review outlines the increased potential of the M-OWC concept and its current state through its advancement in recent years. Although still under development the M-OWCs have the potential to provide promising results, through the various innovative concepts under consideration, and support the progression and further development of wave energy as another serious contender in the renewables energy mix

Efficient response of an onshore Oscillating Water Column Wave Energy Converter using a one-phase SPH model coupled with a multiphysics library

In this paper the numerical modelling of an Oscillating Water Column (OWC) Wave Energy Converter (WEC) is studied using DualSPHysics, a software that applies the Smoothed Particle Hydrodynamics (SPH) method. SPH is a Lagrangian meshless method used in a growing range of applications within the field of Computational Fluid Dynamics (CFD). The power take-off (PTO) system of the OWC WEC is numerically modelled by adding a force on a plate floating on top of the free surface inside the OWC chamber. That force is implemented in the multiphysics library Project Chrono, which avoids the need of simulating the air phase that is computationally expensive in the SPH methods. Validation is carried out with experimental data received from the Korea Research Institute of Ship and Ocean Engineering (KRISO) and Ocean Energy Systems (OES) of the International Energy Agency (IEA) Task 10. The numerical and experimental water surface elevation at the centre of the OWC WEC chamber and the airflow speed through the orifice are compared for different wave conditions and different PTO systems (different orifice diameters at the top part of the chamber of the OWC WEC). Results show that DualSPHysics is a valid tool to model an OWC WEC with and without PTO system, even though no air phase is included.Research Foundation - Flanders | Ref. 1SC5421NXunta de Galicia | Ref. ED431C 2021/44Agencia Estatal de Investigación | Ref. IJCI-2017-3259

Experimental and Numerical Modelling of a Multiple Oscillating Water Column Structure

The potential exists for ocean energy from waves to meet a large fraction of future global energy needs. Furthermore, synergies between the existing offshore wind industry, and the future offshore wave energy industry, can be exploited. This thesis is concerned with the physical and numerical modelling of an offshore floating platform, as proposed by a commercial developer. It is envisaged that the platform will capture both wave and wind energy, using an array of oscillating water columns (OWC) and conventional wind energy technology. The focus of this thesis is on the wave energy-capturing aspects of the proposed platform. A 1:50, physical scale model of the proposed platform is described, and a tank testing programme for the model, in a variety of configurations, is outlined. A frequency domain, numerical model of the physical scale model is developed. Predictions from the numerical model are compared to the tank testing results. Based on the results of tank testing, and predictions from the numerical model, a number of useful tools for future design work have been created, and some fundamental changes to the design of the platform are proposed. On completion of the tank testing, the platform progressed to Technical Readiness Level 3. Due to the complexities of studying and numerically modelling the hydrodynamic and thermodynamic interactions within the array of OWCs in the model platform, a nonlinear, time domain, numerical model, at a scale of 1:50, of a single OWC from the proposed platform, with control components, is developed. Predictions from the numerical model are compared to the results of testing on a physical model of the single OWC. An investigation to quantify the effect of air compression in the single-OWC model, not captured using Froude scaling, is conducted. The investigation leads to a proposed novel method for measuring the hydrodynamic parameters of a water column. The key conclusions from this thesis are: • A non-linear, time-domain numerical model has been developed for a single-OWC with novel cross section and control components. The numerical model has been extensively validated using the rests obtained from narrow tank testing. • A new method for determining hydrodynamic parameters has been developed and demonstrated numerically. The method has been implemented for an OWC, but requires further validation. • It has been demonstrated through the analysis of data obtained from tank testing that the airflow from the chambers of a V-shaped, 32-OWC wave energy converter (WEC) can absorb power from the wave front with an efficiency of up to 37 % at a wave period of 1.13 s. • A frequency domain model of the multiple degree-of-freedom WEC, predictions from which compare well with results obtained from tank testing, has been developed

Complementary Airflow Control of Oscillating Water Columns for Floating Offshore Wind Turbine Stabilization

The implementation and integration of new methods and control techniques to floating offshore wind turbines (FOWTs) have the potential to significantly improve its structural response. This paper discusses the idea of integrating oscillating water columns (OWCs) into the barge platform of the FOWT to transform it into a multi-purpose platform for harnessing both wind and wave energies. Moreover, the OWCs will be operated in order to help stabilize the FOWT platform by means of an airflow control strategy used to reduce the platform pitch and tower top fore-aft displacement. This objective is achieved by a proposed complementary airflow control strategy to control the valves within the OWCs. The comparative study between a standard FOWT and the proposed OWC-based FOWT shows an improvement in the platform’s stability.This work was supported in part by the Basque Government, through project IT1207-19 and by the MCIU/MINECO through the projects RTI2018-094902-B-C21 and RTI2018-094902-B-C22 (MCIU/AEI/FEDER, UE)

Wells turbine for wave energy conversion : a review

In the past twenty years, the use of wave energy systems has significantly increased, generally depending on the oscillating water column (OWC) concept. Wells turbine is one of the most efficient OWC technologies. This article provides an updated and a comprehensive account of the state of the art research on Wells turbine. Hence, it draws a roadmap for the contemporary challenges which may hinder future reliance on such systems in the renewable energy sector. In particular, the article is concerned with the research directions and methodologies which aim at enhancing the performance and efficiency of Wells turbine. The article also provides a thorough discussion of the use of computational fluid dynamics (CFD) for performance modeling and design optimization of Wells turbine. It is found that a numerical model using the CFD code can be employed successfully to calculate the performance characteristics of W-T as well as other experimental and analytical methods. The increase of research papers about CFD, especially in the last five years, indicates that there is a trend that considerably depends on the CFD method