Oscillating Water Column Wave Power Research Articles

Experimental Validation of the Capture Chamber Model in Mutriku MOWC Wave Power Plant

Wave energy holds the potential to fulfill 15% of the EU's energy demand by 2050, thereby reducing CO2 emissions by 136 million metric tons per megawatt-hour, as outlined in the EU Energy Road Map. Similarly, the Spanish Renewable Energies Plan underscores the significant marine energy potential in Spain, particularly emphasizing wave energy. Within this framework, Oscillating Water Column (OWC) converters currently stand as among the most promising wave energy conversion technologies, offering the capability to harness ocean energy from various on-shore and floating structures. This paper introduces an analytical model of the wave capture chamber parameterized for a specific on-shore OWC wave power plant. The model is specifically adapted and parameterized for the Mutriku Marine Offshore Wave Power Plant located on the coast of the Spanish Basque Country. Subsequently, validation is conducted using both real wave entry data measured on-site and experimental output power data generated in the plant.

Development of a Simulation Model for Digital Twin of an Oscillating Water Column Wave Power Generator Structure with Ocean Environmental Effect

This research article focuses on developing a baseline digital twin model for a wave power generator structure located in Yongsu-ri, Jeju-do, South Korea. First, this study performs a cause analysis on the discrepancy of the dynamic properties from the real structure and an existing simulation model and finds the necessity of modeling the non-structural masses and the environmental factors. The large amounts of the ballast are modeled in the finite element model to enhance the accuracy of the digital twin. Considering the influence of environmental factors such as tide level and wave direction, the added mass effect of structural members, one of the hydrodynamic effects, depending on the change of the ocean environments is calculated based on the rule of Det Norske Veritas and applied. The results indicate that non-structural mass components significantly impact the dynamic characteristics of the structure. Additionally, environmental factors have a greater effect on the dynamic behavior of the box-type structure compared to lightweight offshore structures.

Model predictive control based on air pressure forecasting of OWC wave power plants

Ocean waves hold a promising potential as a sustainable source of clean energy. However, in order to make wave energy converters financially viable, particularly in the case of the oscillating water column (OWC), it is crucial to optimize the power take-off system to maximize performance. Most control strategies focus solely on turbine performance, often at the expense of overlooking the overall wave-to-wire system performance. Therefore, a model predictive control (MPC) strategy using short-term air pressure prediction was proposed to enhance electrical energy delivered to the grid. The Mutriku wave power plant (Spain) was case-studied for evaluating the control approaches, which focused on maximizing average power (turbine or generator) from an OWC equipped with the innovative biradial turbine. In comparison to the reference baseline strategy, the implementation of MPC (with a 16-second forecast) resulted in a minor 2%-increase in the average turbine power. However, when it comes to the generator power accumulated over a year, the MPC strategy produced an improvement of more than 8%. Since generator power is the ultimate product, this improvement is significant. Nonetheless, the MPC strategy exhibited a non-smooth control response compared to other strategies. Improving control action quality should be a primary focus of future research.

Numerical modelling of a box-type and bottom-detached oscillating water column wave energy conversion device: a comparison with experimental data and between BEM and CFD numerical modelling

Utilization of Boundary Element Method (BEM) based on linear potential flow for modelling Oscillating Water Column (OWC) devices has gained popularity in the last two decades. The commercial BEM solver WAMIT has been used widely for modelling OWCs and validated using experimental modelling (Delauré et. al. 2003, Bingham et. al. 2015, Faÿ 2020). The open-source BEM solver NEMOH has however been mostly ineffective in modelling OWCs since the main approach adopted previously modelled the imaginary piston as a thin disk. In this research, the multi-body interaction problem has been adopted in modelling a box-type and bottom-detached OWC device in NEMOH, where the imaginary piston has been modelled to the length of the internal water column (Penalba et.al. 2017) and compared with experimental data. A further comparison is drawn with the numerical method of Computational Fluid Dynamics (CFD) , which has shown to be accurate for modelling OWC devices (Simonetti et. al. 2015), yet requires significantly higher computational resources than BEM. A two-dimensional CFD numerical wave tank, developed generating and absorbing waves with the waves2Foam toolbox (Jacobsen et al., 2012) of the open-source package OpenFOAM, is used for comparative purposes.
 REFERENCES:
 Delauré, Y. & Lewis, A. (2003). “3D hydrodynamic modelling of fixed oscillating water column wave power plant by a boundary element methods.” Ocean Engineering. 30. 309-330. 10.1016/S0029-8018(02)00032-X.
 Bingham, H.B.; Ducasse, D.; Nielsen, K. et al (2015). “Hydrodynamic analysis of oscillating water column wave energy devices.” J. Ocean Eng. Mar. Energy 1, 405–419 (2015). https://doi.org/10.1007/s40722-015-0032-4
 Faÿ F.-X. (2020). “Modelling and Control for the Oscillating Water Column in Wave Energy Conversion.” PhD Thesis, Universidad del País Vasco.
 Jacobsen, N.G., Fuhrman, D.R. & Fredsøe, J., (2012). “A wave generation toolbox for the open-source CFD library : OpenFoam”. International Journal for numerical methods in fluids, 70, pp.1073–1088.
 Simonetti, Irene & Cappietti, Lorenzo & Elsafti, Hisham & Oumeraci, Hocine. (2015). “Numerical Modelling of Fixed Oscillating Water Column Wave Energy Conversion Devices: Toward Geometry Hydraulic Optimization.” 10.1115/OMAE2015-42056.
 Penalba, M., Kelly, T., Ringwood, J. 2017, NEMOH for Modelling Wave Energy Converters: A Comparative Study with WAMIT. 12th European Wave and Tidal Energy Conference , Cork, Ireland. https://www.researchgate.net/publication/319160625.

Study on an Oscillating Water Column Wave Power Converter Installed in an Offshore Jacket Foundation for Wind-Turbine System Part II: Experimental Test on the Converting Efficiency

This study is an experimental study corresponding to an analytical study presented previously, where a scaled-down model was built and tested in a water tank by following the size and shape of the structure applied in the analytical study. In this study, a wave energy converter of an oscillating water column (OWC) system is integrated with the infrastructure of a jacket-type offshore platform applied to an offshore wind turbine system. The purpose is to conduct a combination system through the simultaneous utilization of both wind power and wave power so that sustainable energy can be maximized. During the analytical study’s analysis, the airflow response and the converting efficiency of wave energy from an OWC system integrated with an offshore template structural system were evaluated. By following the analytical study’s analysis, the performance of all the systems is tested, including the airflow velocity, pneumatic power, and the converting efficiency of the power from waves. The experimental data are analyzed and discussed in terms of the variations of the OWC system’s geometrical parameters. The parameters under consideration include the exhale orifice-area of airflow, gate-openings of inflow water, and the submerged chamber depth. It is found from the experimental results that, through the comparison between the experimental data and the analytical results, the results of the analytical study’s analysis are countable, and an open sea OWC system can be successfully applied to the template structure of offshore wind power infrastructure as a secondary generating system for the multi-purpose utilization of the structure.

Study on an Oscillating Water Column Wave Power Converter Installed in an Offshore Jacket Foundation for Wind-Turbine System Part I: Open Sea Wave Energy Converting Efficiency

This study is focused on the wave energy converter of an oscillating water column (OWC) system that is integrated with a jacket type infrastructure applied for an offshore wind turbine system. In this way, electricity generation by both wind power and wave power can be conducted simultaneously to maximize the utilization of sustainable energy. A numerical analysis was performed in this research to model and simulate the airflow response and evaluate the converting efficiency of wave energy from an OWC system integrated with an offshore template structural system. The performance of the system including the generating airflow velocity, air-pressure in the chamber, generating power and then the converting efficiency of power from waves are all analyzed and discussed in terms of the variations of the OWC system’s geometrical parameters. The parameters under consideration include the exhale orifice-area of airflow, gate-openings of inflow water and the submerged chamber depth. It is found that from the analytical results the performance of the OWC wave energy converter is influenced by the dimensional parameters along with the design conditions of the local environment. After a careful design based on the in-situ conditions including water depth and wave parameters, an open OWC system can be successfully applied to the template structure of offshore wind power infrastructure as a secondary generating system for the multi-purpose utilization of the structure.

Structural Safety Analysis for an Oscillating Water Column Wave Power Conversion System Installed in Caisson Structure

In this study, an alternative way, a so called caisson based type of oscillating water column (OWC) wave energy converting system was proposed to capture and convert wave energy. Since the caisson structure is constructed to protect the coastal line or ports, it is important to know if a built-in associated OWC system will be a burden to affect the safety of the structure or it is safe enough to work appropriately. In this study, three steps of structural analysis were performed: firstly, the analysis for the structural safety of the whole caisson structure; secondly, performing the mechanic analysis for the chamber of the associated OWC system; and finally, performing the analysis for the wave induced air-pressure in the chamber under the design conditions of a local location during the wave-converting operation. For the structural safety analysis, a typical structural model associated with caisson breakwater was built and analyzed while the shape of the structure, material applied to the construction, and associated boundary conditions were all set-up according to the wave and structures. The motion and the strain distribution of the caisson structure subjected to designated waves of 50-year return period were evaluated and compared to the safety requirement by the code. For the analysis of the energy converting performance, a numerical method by using a theorem of unsteady Navier–Stokes equations in conservation form was used to analyze the proposed OWC model when the structure subjected to an incident wave of a 10-year return period.

Maximizing Output Power in Oscillating Water Column Wave Power Plants: An Optimization Based MPPT Algorithm

This paper proposes an optimization based maximum power point tracking (MPPT) algorithm for selection of appropriate external rotor resistances of wound rotor induction generator (WRIG). The generator coupled with a Wells turbine is used in oscillating water column (OWC) wave power plants. The Wells turbine suffers with stalling behaviour that reduces the average output power significantly. Hence, the objective is to prevent aerodynamic stalling of the Wells turbine and hence maximizing the output power simultaneously. But inappropriate selection of rotor resistance leads to excessive power loss. Therefore, two approaches have been applied: (i) the rotor resistance values are selected manually by trial and error method or non-optimized approach (ii) a performance index has been derived and minimized using particle swarm optimization technique to obtain the optimized values of rotor resistance. Simulation results have been performed for turbine efficiency, output power and power loss in external rotor resistance. Finally, the proposed control approach is illustrated for two particular cases of regular and irregular waves.

Rotational Speed Optimization in Oscillating Water Column Wave Power Plants Based on Maximum Power Point Tracking

After the 2015 United Nations Climate Change Conference (COP21) the interest for clean and renewable energy is high priority in global energy policy. In this sense, the ocean offers a great potential for energy harnessing. However, in the path to commercialization, conversion systems still lack maturity. Oscillating water column (OWC) power plants are among the most promising cost-effective and ecologically compatible technologies. The NEREIDA MOWC wave power plant, located on the Basque coast of Mutriku, is a clear example of this principle. In addition, the maximum power point tracking (MPPT) strategy, which has already been used successfully in other renewable energy systems, stands out as one of the most useful schemes. In this context, this paper focuses on the implementation of a novel MPPT control approach for the OWC systems in order to optimize the power delivered to the grid. For this purpose, a full wave-to-wire plant model is introduced, and a new MPPT-based control scheme is presented. The controller continuously adjusts the energy conversion of the doubly fed induction generator according to an established MPPT curve so as to optimize the power generated. In order to demonstrate the goodness and feasibility of the proposed control scheme, its behavior is tested and compared in two representative case studies of both uncontrolled and controlled plants. In the first case, an air valve control is employed, and in the second case, an MPPT-based control strategy has been implemented. Results show that the proposed MPPT-based control successfully matches the optimum rotational speed, allowing maximum active power generation.

Characteristics of Hydrodynamics and Generating Output of the Offshore Floating Wave Energy Device “Mighty Whale”

In this paper, a new numerical calculation method is presented; it was developed for the analysis of the hydrodynamic characteristics of a floating, oscillating water column (OWC) type wave power device. The method is examined by comparing results calculated with the method with results of water tank experiments. The examination was concerned with the determination of hydrodynamic coefficients, characteristics of air pressure and water level in an air chamber, and characteristics of hull motion and wave energy absorption. The calculated results agreed with the results of water tank tests; the method presented adequately estimated the hydrodynamic characteristics of the floating OWC type wave power device, including the wave energy absorption effects. An estimation method is presented for the output power of a turbine-generator system. The method was developed for the design of the “Mighty Whale” turbine-generator system. Moreover, the method was assessed by comparing predictions with open sea test results. The mean value of the output power was estimated reasonably well. In conclusion, the estimation methods presented are useful for the design of floating OWC wave power devices. Such tools are useful for the designer interested in developing optimal wave power devices.

Performance Prediction of an OWC Wave Power Plant with 3-D Characteristics in Regular Waves

The primary wave energy conversion by a three-dimensional bottom-mounted oscillating water column (OWC) wave power device in regular waves has been studied. The linear potential boundary value problem has been solved following the boundary matching method. The optimum shape parameters such as the chamber length and the depth of the front skirt of the OWC chamber obtained through two-dimensional numerical tests in the frequency domain have been applied in the design of the present OWC chamber. Time-mean wave power converted by the OWC device and the time-mean second-order wave forces on the OWC chamber structure have been presented for different wave incidence angles in the frequency-domain. It has been shown that the peak period of <TEX>$P_m$</TEX> for the optimum damping parameter coincides with the peak period of the time.mean wave drift force when <TEX>${\gamma}=0$</TEX>.

A time-domain numerical simulator for oscillating water column wave power plants

This paper presents a time-domain numerical simulator of oscillating water column (OWC) wave power plants. The whole problem (the simulation of the movements of the inner free surface due to the excitation of the outer sea-waves) is split into two subproblems: an outer one, dealing with the incident, diffracted and radiated waves, solved once for all, and an inner one, concerning the inner water volume behavior. The kernel of this simulator is a hybrid numerical method [Josset C, Clément AH, Duclos G. A hybrid method for time-domain simulation of oscillating water column wave power plants. Ocean Engineering, to appear.] which allows for the coupling of these two problems. After the validation of each part of this simulator, it was applied to the European wave energy power plant seated on Pico Island, Azores, first to estimate the annual performance of the plant, then to simulate different alternative configurations, in a way to improve the productivity.

Nonbreaking Wave Forces on Multiresonant Oscillating Water Column Wave Power Caisson Breakwater

Experimental measurements of in-line wave forces on a 1:50 scale model of an array of multiresonant oscillating water columns (MOWCs), a free-standing wave energy caisson, are reported. Wave forces on a vertical wall were measured and compared with Sainflou's and Goda's formulas, which serve as base for studying wave forces on an MOWC array. A range of hydrodynamic parameters with different damping of the OWC chamber and center-to-center (c/c) spacing were used. In general, the force on the MOWC caisson array is twice that of the vertical wall for maximum damping of the OWC chamber. Reduction of damping of the OWC air chamber reduces the force on the array of caissons by 35-60% of the force on a vertical wall. It is found that shoreward force magnitude is greater than seaward. For spacing of 2-3 times the harbor width, the OWC array acts like a perforated breakwater, experiencing 60% of wave forces on the vertical wall, while for a c/c spacing range of 4-5, it behaves like a vertical wall. Incorporation of an air pressure release by pass system for the OWC chamber is recommended, as this will reduce in-line wave forces on a caisson array to a range of about 35-40%. The nonlinear response of the OWC on wave forces warrants the use of a numerical model and further investigation.

3D hydrodynamic modelling of fixed oscillating water column wave power plant by a boundary element methods

A three-dimensional (3D) numerical model of fixed Oscillating Water Column system (OWC) is presented and validated. The steady-state potential flow boundary value problem due to regular wave interaction with the OWC is solved by a first order mixed distribution panel method. Ocean response predictions are derived using a deterministic statistical model based on a spectral analysis method. The model validation focusses on diffraction predictions and involves convergence tests and numerical comparisons with independent potential flow computations. Predictions of both regular and irregular wave responses are also compared against experimental results. Sample results including the yearly-averaged power conversion efficiency are presented in the final section to illustrate the method’s suitability to a 3D hydrodynamic design optimisation.

THE ISLAY WAVE POWER PROJECT: AN ENGINEERING PERSPECTIVE.

Keywords QUEENS UNIVERSITY BELFAST, CHARLES BRAND, KIRK MCCLURE MORTON CAMBRIDGE ENGINEERING DESIGN POWER, WAVES, PROJECTS, ENGINEERING, ENERGY, HOSTILE, ENVIRONMENT, SEA, WATER, DESIGN, CONSTRUCTION, OSCILLATING, COLUMNS, STORMS, MOTION, ELECTRICITY, CONVERSION, TECHNOLOGY, COSTS, ECONOMICS, MODULAR, SYSTEMS, DEVELOPMENT, SHORELINE, CONVERTERS, CAPTURE, CHAMBERS, RESOURCES, OPERATION, TURBINES, GENERATORS, MECHANICAL, ELECTRICAL ISLAY, ISLE OF ISLAY, SCOTLAND UK... Show All

The Q.U.B. Axisymmetric and Multi-Resonant Wave Energy Convertors

This paper describes the optimization of the power conversion chain and the engineering design considerations of an oscillating water column wave power device which would form part of a 2-GW power station. Novel features of the principal device described include the multi-resonant concept, which considerably widens the frequency bandwidth response, and the use of the simple highly efficient Wells self-rectifying air turbine in the secondary power conversion stage. It is concluded that using established technology wave power stations comprising sea bed mounted reinforced concrete structures could produce power for as little as 1.3p per kW-hr after the initial capital repayment period and thus the economics are similar to that of hydro-electric power.