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Integrating wave energy converters with marine structures such as breakwaters, piles, and offshore wind turbines offers benefits in terms of wave power extraction, construction costs, and survivability. In this paper, the integration of an oscillating water column(OWC) into a vertical tubular structure is considered. The OWC chamber is enclosed by the tubular-structure with its submerged side partially open to the sea. As ocean waves propagate through the device, an air turbine installed at the top of the chamber can be driven to extract wave power. An analytical model based on potential flow theory and the eigen-function matching method is developed to solve the wave scattering and radiation problems of the device in finite water depths. Wave excitation volume flux, hydrodynamic coefficients, optimal turbine damping and power capture factor are evaluated. Upon successful validation, the model is applied to investigate the effect of the radius and finite wall thickness of the tubular-structure, the size and position of the opening on wave power extraction. We find that a thinner chamber wall thickness offers benefits to wave power extraction in terms of a broader primary band of power capture factor response, and that a broader and higher capture factor band can be achieved by increasing the height of the vertical opening. • We develop an analytical model to study an OWC integrated into a tubular structure. • The OWC lateral opening can be applied at any position beneath the mean water level. • The new analytical model eliminates the need for the thin wall assumption. • The small wall thickness of the chamber offers benefits for wave power extraction. • Increasing height of the opening leads to a broader efficiency band. [ABSTRACT FROM AUTHOR]

Integrating wave energy converters into coastal structures such as breakwaters, seawalls or jetties not only offers benefits in terms of construction costs but also improves wave energy extraction. In this paper a novel theoretical model based on linear potential flow theory is developed to study the performance of an oscillating water column (OWC) integrated into a vertical structure in water of finite water depth. The model has three fundamental advantages relative to previous works: no thin-wall restriction (the thickness of the OWC chamber wall is considered), no singularities, and far fewer truncating terms in the eigen-function expansions. The OWC chamber is a vertical cylinder semi-embedded in the structure with a submerged, open bottom. As water waves impinge on the structure, the water column in the chamber oscillates and drives an air turbine installed at the chamber top to extract wave power. Using linear wave theory, the velocity potential in the water domain is decomposed into scattering and radiation potentials whose unknown coefficients are determined by the eigen-function matching method. Upon successful validation, the model is used to investigate the influence of the thickness of the chamber wall and the radius and submergence of the chamber on wave power absorption. • Analytical model of Oscillating Water Column mounted on coastal structure. • Developed without the simplifying assumption of a thin-walled OWC chamber. • Considers the three main design parameters: radius, submergence & wall thickness. • Upon successful validation using published data, model is applied. • Sensitivity analysis of OWC power performance vs. main design parameters. [ABSTRACT FROM AUTHOR]

A novel hybrid wave energy converter (WEC) consisting of a floating oscillating water column (OWC) and several oscillating floats hinged around is proposed. Both water oscillation of the OWC and the wave-induced relative rotation of each float around the OWC are employed to extract wave power. To carry out the hydrodynamic analysis of the hybrid WEC, a theoretical model based on potential flow theory, separation of variables method and eigen-function matching method is presented. Hydrodynamic interaction between the OWC and the floats oscillating independently in surge, sway, heave, roll, pitch and yaw modes is considered. To verify the correctness of the theoretical hydrodynamic model, a specific example is computed and a numerical code based on a boundary element method is also employed as a comparison. The theoretical results are found in good agreement with ones obtained by using different approaches. The theoretical hydrodynamic model is then adopted to evaluate the dynamic response and power absorption of the hybrid WEC in frequency domain. Additionally, the corresponding isolated OWC and hinged floats are computed, respectively, and compared to demonstrate how to interact beneficially between the OWC and the floats in terms of q -factor. Effect of the geometry of both the OWC and the floats, and the spacing distance between them on power exploration of the hybrid WEC is investigated. The results reveal that the hybrid WEC holds a wider bandwidth of frequency response with a higher maximum power capture factor compared with those of the isolated OWC and hinged floats. [ABSTRACT FROM AUTHOR]

Abstract Hybrid wave farms, consisting of different types of Wave Energy Converters (WECs), have rarely been investigated so far. In this work we propose a hybrid wave farm consisting of Oscillating Water Columns (OWCs) and point-absorbers (PAs), and develop a semi-analytical model of the interaction between this hybrid wave farm and the incident wave field. The OWCs and PAs are modelled as truncated cylinders with and without moonpools, respectively, each with its own outer radius, inner radius, draft and mass. The hydrodynamic model solves the wave diffraction and radiation problems using linear potential flow theory and the methods of separation of variables and eigen-function matching. The independent oscillations of each WEC in any degree of freedom, including both translating and rotating modes, together with the pressure fluctuations of the air inside each OWC chamber, are all accounted for. The model is successfully validated based on numerical data, and thereupon applied to two configurations of the hybrid wave farm. We find that the excitation volume flux/forces are strongly dependent on the incident wave direction, the spacing between the WECs and, more generally, the configuration of the farm. The hydrodynamic coefficients, especially those of the PAs, are sensitive to the spacing and configuration. Notwithstanding the interest of these results in relation to the selection of the optimum configuration and WEC spacing of the hybrid wave farm for specific locations (with specific prevailing wave directions), the interest of this work lies in the semi-analytical model itself, which is found to be efficient in modelling the interaction of the hybrid wave farm and the wave field, and can be used in future wave farm projects. Highlights • We propose a hybrid wave farm with two types of Wave Energy Converters (WECs). • The two types are: Oscillating Water Columns and Point Absorbers. • We develop an analytical model of wave field–wave farm interaction. • We validate the analytical model with numerical results, with excellent agreement. • We perform a sensitivity analysis of wave direction and WEC spacing for two layouts. [ABSTRACT FROM AUTHOR]

In this paper, a hybrid wave energy converter (WEC) is proposed, consisting of a fixed inverted flume with long length and a bottom hole, and a long floating cube hinged with the flume. The inverted flume and the long floating cube works as an oscillating water column (OWC) and a rotational float, respectively, to capture power from incident waves. To study the performance of this hybrid WEC, analytical solution of the wave diffraction/radiation problems, considering the hydrodynamic interaction between the OWC and the float, is derived based on linear potential flow theory and eigen-function expansion matching method in the two-dimensional Cartesian coordinate systems. The corresponding hydrodynamic coefficients, such as wave excitation forces, added mass and wave radiation damping, are also obtained, which can be further used in evaluation of the maximum theoretical power absorption of the hybrid WEC. Results are compared with a parallel study of an isolated OWC and an isolated float. Additionally, analytical study on power capture capability of the device for various geometrical parameters is then carried out. [ABSTRACT FROM AUTHOR]

Oscillating water column (OWC) devices and oscillating buoys (OBs) are two of the main types of wave energy converters (WECs). In this paper a hybrid oscillating water column-oscillating buoy wave energy converter is proposed, which we have named OWCOB. The oscillating buoy is hinged at the outer wall of the oscillating water column. As waves propagate through the OWCOB, the water column within the OWC chamber moves up and down, producing air flow to propel a turbine. Meanwhile, the oscillation of the OB drives a separate hydraulic system. To solve the wave diffraction and radiation problems of the OWCOB and investigate its energy capture performance, an analytical model is developed based on linear potential flow theory and the eigenfunction matching method. Assuming that the PTOs of the OWC and OB are both linear, the wave power extraction of the OWCOB is evaluated in the frequency domain. Of the two configurations considered, the OWCOB with the OWC opening waveward and the OB hinged leeward is found to have a broader primary frequency band of wave power capture compared to the OWCOB with the OWC opening and the OB on the same side. Further, a thorough sensitivity analysis of power capture is carried out considering the main design parameters (size and submergence of the OWC opening, distance between the OWC and the OB, OB hinge elevation, OB radius), which can form the basis of an optimization study for a particular wave climate. Importantly, we find that the OWCOB performs generally better than stand-alone OWCs and OBs, not least in terms of frequency bandwidth. • We propose a hybrid wave energy converter, OWCOB, combining two technologies. • Namely, an Oscillating Water Column (OWC) and an Oscillating Buoy (OB). • We develop a model to investigate its wave energy capture performance. • A multi-parameter sensitivity study is carried out with the main design parameters. • We find that the hybrid OWCOB performs better than stand-alone OWCs or OBs. [ABSTRACT FROM AUTHOR]

In this paper we consider hybrid wave farms, in which different types of WEC are combined, through a case study involving oscillating water columns (OWCs) and point-absorbers (PAs). A new parameter, called " H-factor ", is introduced to compare hybrid (multi-type) and conventional (single-type) wave farms in terms of wave power capture. We develop an ad hoc semi-analytical model to calculate the H-factor in a computationally efficient manner, and apply it to investigate how the H-factor and, consequently, the power capture, depend on: (i) the spacing and layout of the WECs, (ii) the type of WEC technology, and (iii) the wave conditions. We discuss the influence of these factors and, in the process, show that the H-factor is a valuable decision-aid tool. For specified wave conditions and layout limitations, a conventional wave farm may not be the most efficient option as a result of a destructive array effect, whereas a hybrid farm can be more efficient if a constructive hybrid effect occurs (if the H-factor value is above unity). This constructive hybrid effect can even overcome the destructive array effect for specified cases, demonstrating the potential advantage of hybrid wave farms relative to conventional wave farms. • Hybrid wave farm, with two types of Wave Energy Converters (WECs). • We propose the novel H-factor to compare performance with single-type farms. • We perform a sensitivity analysis: type of WECs, layout, and wave conditions. • The H-factor is proven to be a useful decision-aid tool. • Hybrid farm is advantageous relative to single-type farms in certain conditions. [ABSTRACT FROM AUTHOR]

The U-Oscillating Water Column (U-OWC) is a wave energy harvester exploiting the working principle of oscillating water columns for capturing and converting energy from sea waves. U-OWC devices can be integrated into a breakwater to enable wave energy extraction and provide shelter for port activities. In this work, a coupled Smoothed Particle Hydrodynamics (SPH) model was developed and applied to investigate the hydrodynamics of a U-OWC breakwater. The numerical model is validated against the experimental results over a range of regular wave conditions. An extensive campaign of computational tests is then carried out, studying the effects of geometrical parameters on the hydrodynamic performance and wave loading over the U-OWC breakwater. It shows that the geometrical parameters of the U-shape have a significant effect on the air pressure inside the chamber and the load phase difference between the two sides of the lip wall. The minimum load and maximum capture efficiency designs for U-OWC breakwaters cannot be satisfied geometrically at the same time. This demonstrates that it is necessary to consider comprehensively the structural reliability and hydrodynamic performance in the design and construction of a U-OWC breakwater. • We develop a coupled SPH model to investigate the performance of a U-OWC. • We carry out a series of physical tests of a U-OWC in a wave flume. • Numerical results of free surface and air pressure agree well with physical data. • An air pressure–volume flux function is employed to simulate the pneumatic PTO system. • Device geometry has different effects on hydrodynamic efficiency and wave loads. [ABSTRACT FROM AUTHOR]

The accurate evaluation of the wave energy conversion of oscillating water column (OWC) wave energy converter has consistently plagued scholars. In this paper, an original and well-validated test platform is proposed for exploring the flow characteristic of a nonlinear power take-off (PTO) damping, with which a more accurate and stable measurement of captured energy is obtained in the laboratory modelling. This study utilizes ten orifices to comprehensively investigate the impact of the PTO damping on an offshore stationary cylindrical OWC device. The joint effect of the PTO damping with wave height (H i) or draft of OWC (Dr) is examined. The damping coefficient C f = 10350 is found to be the optimal damping coefficient, in terms of both the peak wave energy conversion and the efficient bandwidth. It is revealed that the variations of the PTO damping can regulate the effect of Dr and H i on wave energy conversion. An appropriate reduction in PTO damping can alleviate the weak energy output caused by the increased Dr and H i. The effect of increased H i on wave energy conversion could be judged by the size relation of the maximum and minimum values of internal pressure data. • We propose a novel test platform to enhances OWC wave energy measurement. • Ten orifices are utilized to explore power take-off (PTO) damping impact on OWC device. • The optimal damping coefficient C f = 10350 boosts energy conversion. • PTO damping adjusts the effects of wave height and draft of OWC on power absorption. [ABSTRACT FROM AUTHOR]

Assorted novel low-reflection structures have been developed for the need of berthing safety in the harbor. The oscillating water column (OWC)-type wave absorbers offer significant benefits as they not only reduce reflected waves but also harness wave energy effectively. Based on the previous studies, a multi-factor comprehensive research on the reflection characteristics, energy extraction performance as well as the wave power dissipation of OWC-type wave absorbers is carried out. The influence of opening ratios is the key point, and the coupled effects of it with the incident wave height and the front wall draft on the hydrodynamic characteristics of the OWC are further investigated. The results indicate that though a larger opening ratio results in a smaller valley value of wave reflection coefficient within the experimental wave frequency range, an appropriate opening ratio can weaken the sensitivity of the reflection behavior of OWC to wave frequency and widens the low reflection frequency band. The existence of vortex-dissipated energy leads to a difference in the wave frequencies corresponding to the minimal wave reflection and maximum extraction efficiency. Besides, reducing the front wall draft is preferred in enhancing efficiency and reducing wave reflection, and meantime this will be accompanied by a shift in resonant frequency. A decrease in wave height has a similar effect, but the effect is not as significant as the change in the draft. The increase of wave height will cripple anti-reflection performance due to the enhancement of radiated wave energy. The OWC-type wave absorber is convincingly competitive in terms of low wave reflection, compared with other extensively studied breakwaters. [ABSTRACT FROM AUTHOR]

Oscillating water column (OWC) device is possibly the most studied among various wave energy converters and many different realizations of the technology have been investigated. To study the complex hydrodynamic behaviour of an OWC, a two-dimensional numerical wave tank based on the weakly compressible smoothed particle hydrodynamics (SPH) method is developed in this paper. A simplified pneumatic model is proposed here to simulate the effect induced by a pneumatic power take-off system within the framework of a single-phase SPH model, and implemented to determine the air pressure imposed on the free surface inside the OWC chamber. Additionally, a regional ghost particle approach, as boundary condition in SPH, is proposed to better simulate fluid dynamics near a thin wall. The overall computation cost is reduced dramatically due to the employment of the regional ghost particle boundary condition method. First, the numerical model is validated under regular waves using published physical and numerical data. An extensive campaign of computational tests is then carried out, studying the performance of the OWC for various wall thicknesses and damping coefficient under various wave conditions. The results demonstrate that the present SPH model can be used as a practical tool for the development of high-performance OWCs. • We establish a 2D SPH model to investigate the performance of an OWC. • An air pressure–volume flux function is employed to simulate the pneumatic PTO system. • We propose a regional ghost particle approach to simulate a thin front wall. • The OWC with thinner walls has a better performance in terms of power absorption. • The optimal damping coefficient is not sensitive to the dimensionless wave height. [ABSTRACT FROM AUTHOR]

• Hydrodynamics of pile-supported OWC breakwaters have been analytically modeled. • A local increase in back draft is adopted to improve performance. • Effects of chamber breadth and wall draft on hydrodynamic performance are studied. • Air compressibility on energy extraction and wave transmission are investigated. • A practical optimization strategy by setting PTO damping at two constants is tested. A pile-supported OWC breakwater is a novel marine structure in which an oscillating water column (OWC) is integrated into a pile-supported breakwater, with a dual function: generating carbon-free energy and providing shelter for port activities by limiting wave transmission. In this work we investigate the hydrodynamics of this novel structure by means of an analytical model based on linear wave theory and matched eigenfunction expansion method. A local increase in the back-wall draft is adopted as an effective strategy to enhance wave power extraction and reduce wave transmission. The effects of chamber breadth, wall draft and air chamber volume on the hydrodynamic performance are examined in detail. We find that optimizing power take-off (PTO) damping for maximum power leads to both satisfactory power extraction and wave transmission, whereas optimizing for minimum wave transmission penalizes power extraction excessively; the former is, therefore, preferable. An appropriate large enough air chamber volume can enhance the bandwidth of high extraction efficiency through the air compressibility effect, with minimum repercussions for wave transmission. Meanwhile, the air chamber volume is found to be not large enough for the air compressibility effect to be relevant at engineering scales. Finally, a two-level practical optimization strategy on PTO damping is adopted. We prove that this strategy yields similar wave power extraction and wave transmission as the ideal optimization approach. [ABSTRACT FROM AUTHOR]