Oscillating Water Column Chamber Research Articles

Experimental Investigation of Wave Pressure on Breakwater-Integrated Oscillating Water Column Devices with a Perforated Wall

This study investigates the wave pressure on an Oscillating Water Column (OWC) device, which features a perforated wall positioned in front of the OWC chamber and is integrated with a caisson breakwater. The perforated wall is designed to mitigate wave impacts on the OWC device under storm wave conditions. To achieve this, a series of laboratory experiments were conducted using a 1:25 scale model, considering both regular and irregular waves. Wave pressure measurements and analyses were performed on various configurations to assess the effects of the perforated wall on the wave pressure exerted against the front wall of the OWC chamber and the caisson breakwater. The results indicate that the perforated wall effectively reduces the amplitude of water column oscillations within the OWC chamber during storm conditions, thereby significantly reducing wave pressure on the OWC chamber wall by approximately 14% and on the breakwater by about 20.3%.

Maximizing oscillating water column efficiency: The impact of vertical plate and guide vane

This study is centered on improving the hydrodynamic efficiency of a conventional Oscillating Water Column (OWC) that has a rectangular cross-section. The OWC chamber is modified by introducing a centrally installed vertical plate, dividing it into two sub-chambers, and further incorporating a quarter-circle guide vane beneath the vertical plate. Physical experiments are conducted under three scenarios: the conventional single-chamber OWC, the OWC with double sub-chambers separated by a vertical plate, and the OWC with both a vertical plate and a guide vane. Hydrodynamic efficiency is examined across varying Power Take-Off (PTO) dampings, incident wave frequencies, and wave heights. Results demonstrate substantial efficiency improvements with the vertical plate, particularly at lower dimensionless wave frequencies. The guide vane also boosts these benefits by preventing vortex formation due to flow separation, resulting in a total average efficiency increase of 42 %. Visual observations highlight the transition from sloshing to piston-like motion induced by the vertical plate, contributing to increased kinetic energy and improved efficiency. The study highlights that basic but effective modifications can substantially enhance OWC efficiency, suggesting promising directions for the development of wave energy conversion technology.

Non-linear turbine selection for an OWC wave energy converter

Turbine-induced damping is a critical parameter affecting the performance of oscillating water column (OWC) wave energy converters. Therefore, selecting the appropriate turbine-chamber combination is an essential step in their design. In this work, a methodology is developed to determine the optimum turbine diameter for a given chamber, i.e., the diameter which maximizes the pneumatic energy capture of the chamber under an extensive set of wave conditions—covering virtually the entire range of wave conditions relevant for wave energy exploitation. This novel approach combines physical and numerical modelling with dimensional analysis. Importantly, it results in a turbine diameter that enables the turbine to operate at maximum efficiency. Through the different modelling techniques applied, the methodology accounts for air compressibility effects and other non-linear effects. It is applicable to non-linear turbines, with the study focusing on the promising biradial turbine. The results indicate that using the proposed methodology to select the turbine diameter significantly improves the capture-width ratio of the OWC, with increases of up to 100% for individual sea states. Two turbine diameters were identified as appropriate for the proposed OWC chamber design, 1.1 m for low-energy sites, and 1.4 m for mid- and high-energy sites.

Three-dimensional numerical simulation of a cylindrical oscillating water column (OWC) device placed in a wave flume

A three-dimensional computational fluid dynamic (CFD) model is developed for simulating a cylindrical Oscillating Water Column (OWC) device for harvesting wave energy. The single-phase CFD model solves the Reynolds-Averaged Navier-Stokes (RANS) equations using the finite element method for simulating the wave motion and uses an aerodynamic model to simulate the flow through the air turbine. The model is implemented to simulate wave energy harvesting of a cylindrical OWC device. Through harmonic decomposition, it is found that the first harmonic wave surface elevation oscillates like a piston in the OWC chamber. However, both the amplitude and phase of the second harmonic wave surface elevation vary significantly along the wave direction in the OWC chamber, demonstrating a sloshing mode of the second harmonic. This study further proved the reduction of the capture width ratio caused by the transverse sloshing mode when the wavelength is the same as the wave flume width. The effect of the width of the wave flume on the peak CWR is found to be negligibly small when the wave flume width is three times the OWC diameter.

Oscillating water column wave energy converter arrays coupled with a parabolic-wall energy concentrator in regular and irregular wave conditions

Based upon previous research on a single, high-efficiency Oscillating Water Column (OWC) wave energy capture system (Mayon et al., 2021), this work further extends the numerical investigation to the layout design and performance of the wave energy convertor (WEC) array coupled with a parabolic, energy concentrating wall in both regular and irregular incident wave conditions. A heuristic method to identify the optimal siting of the component, cylindrical OWC WECs in the array, installed in the concave opening of the wall is presented. The most advantageous location of the chambers is found to lie on a parabolic curvature line which is inset from the wall. Two separate arrays composed of three and five component OWCs are investigated in a range of regular wave conditions. The hydrodynamic power and efficiency of each chamber in each of the arrays is determined, and subsequently the aggregated array performance is established. It is found that the primary OWC chamber in the array configuration can attain approximately the same hydrodynamic power output as a single, isolated OWC chamber located the parabolic wall focus, albeit with a narrower energy capture bandwidth. The secondary and tertiary component chambers in the arrays contribute a lesser, yet still considerable quantity of hydrodynamic power to the consolidated system. The cumulative hydrodynamic efficiency of the collective arrays is less than the hydrodynamic efficiency of a single OWC chamber at the wall focus, but more efficient than an isolated OWC chamber positioned in open-sea conditions. Moreover, the hydrodynamic efficiency of the arrays exhibits better stability across the range of incident wave periods investigated, denoting that the individual component chambers in the array are efficacious at different incident wave conditions. The five chamber array is comprehensively analysed in irregular incident wave conditions. The array system is demonstrated to maintain a high power output and efficient behaviour in irregular incident wave conditions-an effect attributable to the reflecting wall influence. In summary, the five-chamber array configuration yields a higher power output and improved stability in terms of efficiency performance when compared with the three-chamber array configuration in regular waves. The array maintains this exceptional performance in irregular incident wave conditions.

Numerical Study on the Performance of an OWC under Breaking and Non-Breaking Waves

A numerical model for the simulation of the performance of an oscillating water column (OWC) subjected to non-breaking and breaking waves is proposed in this paper. The numerical model consists of a hydrodynamic model specifically designed to simulate breaking waves and a pneumatic model that takes into account the air compressibility. The proposed numerical model was applied to evaluate the potential mean annual energy production from the waves of two coastal sites characterized by different hydrodynamic conditions: a deep-water condition, where the OWC interacts with non-breaking waves, and a shallow-water condition, where the OWC is subjected to breaking waves. The numerical results show that the effects of the air compressibility can be considered negligible only in numerical simulations of the performances of reduced-scale OWC devices, such as those used in laboratory experiments. We demonstrated that in real-scale simulations, the effect of the air compressibility within the OWC chamber significantly reduces its ability to extract energy from waves. The numerical results show that the effect of the air compressibility is even more significant in the case of a real-scale OWC located in the surf zone, where it interacts with breaking waves.

Experimental Validation of Power Output and Efficiency for an Oscillating Water Column (OWC)

With the global energy demand escalating and concerns over the environmental impact of fossil fuels, there's a pressing need for cleaner, sustainable alternatives. This study highlights the potential contribution of wave energy to the power needs of coastal structures in the context of renewable energy. The research evaluates the power output and efficiency for an Oscillating Water Column (OWC) system that can be integrated into coastal structures to meet part of their power needs. Findings from both theoretical calculations and a 1:10 scale model experiment are presented. The mechanical power output and efficiency of the system for a full-scale prototype were calculated for deep water conditions with a wave height of 3m. The water surface oscillation inside the chamber is assumed to reflect the oscillation occurring outside the chamber. The maximum average mechanical power output for the full-scale prototype, corresponding to a wavelength of 22.5 m, was determined to be 64.8 kW, achieving a mechanical efficiency of 64.4%. The overall efficiency of the system is calculated as 55% by assuming the generator efficiency to be 85%, resulting in an average power output of approximately 55 kW. A 1:10 scale model of the OWC system with a Wells turbine was constructed and tested in a tank for deep water conditions. Froude similarity and Keulegan-Carpenter similarity were used, ensuring a seamless transition from the model to the prototype. The OWC model was subjected to controlled heaving motion with a period of T=1.2 s. The power generated by the OWC model illuminated four integrated 3.4V LEDs on the Wells turbine, which were used to measure the power output produced. The power output of the model was measured to be a minimum of 0.12 W for a rotational speed of 107 rpm, which corresponds to a power output of 12 kW for the scaled-up prototype. This system has the potential for further enhancement by incorporating multiple OWCs into coastal structures exposed to wave action. Such development could facilitate meeting the power requirements of coastal structures, thereby contributing to the promotion of both renewable energy generation and a sustainable environment. Future research will focus on optimizing OWC chamber sizes for specific sites and refining the model to better capture water surface oscillation dynamics. l

Hydrodynamic performance of a land-based multi-chamber OWC wave energy capture system: An experimental study

Improving ocean wave energy capture in a cost-effective manner is a challenging task. Multi-chamber oscillating water column (OWC) devices are gaining favor due to their potentially efficient characteristics. This research experimentally investigated the hydrodynamic performance of a land-based OWC wave energy capture system with multiple chambers (ranging from 1 to 5). The free surface elevation, air pressure fluctuations, hydrodynamic efficiency, and reflection coefficient are considered. The hydrodynamic efficiencies of the overall, and sub-chambers in the OWC system with varying numbers of chambers are graphically presented. The influence of geometrical design parameters and wave conditions are also considered in evaluating the performance of the multi-chamber OWC system. It is found that the multi-chamber arrangement improves the hydrodynamic energy extraction characteristics compared to the traditional single-chamber setup. The sloshing mode of the chamber water column is utilized to effectively capture wave energy. As the number of chambers increases, the wave attenuation capability of the system improves for long waves. Yet, the overall efficiency declines when the number of OWC chambers exceeds 3. The chamber draft has the most substantial impact on the wave energy capturing capability, while the effects of opening ratio and wave height are attenuated due to multiple water-column interactions inside the chambers. The isometric sub-chamber structure demonstrates overall efficiency and wave attenuation advantages for short waves. The paper aims to guide the design and optimization of a multi-chamber OWC system.

Numerical analysis of 3D hydrodynamics and performance of an array of oscillating water column wave energy converters integrated into a vertical breakwater

Performance and hydrodynamics of an array of Oscillating Water Column (OWC) Wave Energy Converter (WEC) integrated into a vertical breakwater is studied. The FLUENT® software, in which the numerical model is based on the Reynolds-Averaged Navier-Stokes equations and the Volume of Fluid method for free surface flow modeling, is used in a 3D numerical wave tank. Three vertical breakwater configurations subject to the action of incident regular waves with periods from 6 to 12 s are studied: normal breakwater, with vertical walls parallel to the direction along the breakwater length; and two novel breakwater geometries, partially and fully convergent breakwaters, whose converging vertical walls are inclined θ in relation to this direction. Different spacing S from 0 to 20 m between the array of OWC devices and two converging wall angles θ, 30 and 45°, are investigated. Firstly, analysis of the influence of S for the normal breakwater shows that the vertical wall concentrates naturally a higher quantity of the incident wave energy inside OWC chamber devices and, consequently, increases their efficiencies. This effect is intensified as the spacing S increases. Secondly, analyses of the partially and fully convergent breakwaters allow concluding that these novel geometries, which direct an amount of incident wave energy into the OWC chamber, increase significantly the efficiency of the array of the OWC devices at the range of the wave periods. The highest performance of OWC device is obtained by the fully convergent breakwater with S = 20 m and θ = 45°, once 10 OWC devices inserted in a breakwater 300 m long have the same efficiency of 20 OWC devices inserted into the normal breakwater.

Characteristics of vortex evolution around a cylindrical oscillating water column device: An experimental study

The utilization of oscillating water column (OWC) converters with existing hydraulic/coastal structures has emerged as a crucial approach for the development of economically viable and environmentally sustainable green power generation devices. Integrating OWC converters into offshore wind turbine (OWT) monopiles is a promising solution in wind power industrialization. This paper presents an experimental investigation of the flow characteristics of an OWT-OWC system under regular wave conditions, focusing on the evolution of vortex structures. Particle image velocimetry (PIV) is employed to measure the flow field surrounding the OWC converter under different wave heights and wave period conditions. Based on the measured velocity field data, the evolution of vortices is examined using the Q-criterion. The results indicate that the wave period significantly affects the flow patterns. Specifically, an increase in wave period enhances the three-dimensional nature of the flow field. The vortices outside the OWC chamber are observed to connect and form a three-dimensional vortex ring, hindering efficient wave energy conversion. Conversely, the variation in wave height exhibits limited impact on the flow field evolution. However, as the wave height increases, the vortex strength and asymmetry experience a significant rise, making it difficult to form a stable three-dimensional vortex ring. Moreover, based on optimal geometric design considerations, it is recommended to increase the lateral angle and height of the sidewall openings to prevent vortex ring formation and minimize obstructions, while ensuring the structural safety of the OWT.

Experimental and numerical investigation on hydrodynamic performance of a 3D land-fixed OWC wave energy converter

The hydrodynamic performance of a land-fixed oscillating water column (OWC) wave energy device was thoroughly investigated under various wave conditions and geometric parameters through both experimental and numerical studies in a three-dimensional (3D) wave tank. The study involved the measurement and comparison of water surface elevation, air pressure in the OWC chamber, and hydrodynamic efficiency with the results obtained from the 3D Higher-Order Boundary Element Method (HOBEM). The influences of 3D effects, incident wave amplitude, front wall draught, and incident wave angle on the hydrodynamic performance of the OWC device were analyzed. The results demonstrate that, under actual sea conditions, the 3D effects significantly affect the hydrodynamic efficiency of the OWC, making it exceed unity near the resonance frequency. On the other hand, the incident wave angle was found to have minimal effect on the resonant frequency and varied trend of efficiency. However, the hydrodynamic efficiency decreases with increasing incident wave angle. These results highlight the importance of the consideration of the 3D effects and incident wave angles in optimizing the design and performance of fixed OWC wave energy devices.

Numerical Solution of Hydrodynamic Efficiency Equations for an Oscillating Water Column Wave Energy Converter Using the Method of Fundamental Solutions

The oscillating water column (OWC) converter, a prominent and widely adopted device for capturing wave energy, has yet to attain commercialization due to its intricate hydrodynamic behavior. Consequently, numerous laboratory and numerical studies have been carried out on OWC converters. One of the significant parameters in the study and comparison of different converters is their hydrodynamic efficiency parameter. Hence, the primary objective of this study is to examine the efficiency of an oscillating water column converter using the meshless method of fundamental solutions (MFS) to solve the governing equations. To address the challenges posed by the low wave steepness and to optimize computational efficiency, a complete linearization of two nonlinear sources at the boundary conditions inside and outside the OWC chamber was undertaken. Next, the boundary conditions were temporally discretized using three distinct methods: the Newmark, the forward differentiation formula, and the Runge-Kutta method of the fourth order. Subsequently, a comparison was made among these methods, revealing that the Newmark method exhibited a higher convergence rate to the solution. Using the developed numerical model, a more precise examination of the converter's efficiency, under various sloped bottom geometries, was conducted, surpassing the level of accuracy achieved in prior studies. Two key parameters, namely the opening, and slope, were identified as critical factors influencing the efficiency of converters considering sloped bottoms. The results indicated that the efficiency of the converter decreases with an increase in the slope and a decrease in the opening. Furthermore, to effectively interpret the efficiency of the converter, a suitable parameter was introduced the disparity in the free surface elevation inside and outside the chamber. This parameter proved valuable in providing insights into the converter's performance.

A 3D numerical investigation of the influence of the geometrical parameters of an I-beam attenuator OWC on its performance at the resonance period

The oscillating water column (OWC) is the oldest and most reliable concept for wave energy conversion. This paper investigates the hydrodynamic performance of one chamber of an I-Beam attenuator OWC at its natural frequency using fully nonlinear CFD. The effects of chamber geometry on the hydrodynamic performance are investigated by solving the unsteady Reynolds averaged Navier-Stokes equations using ANSYS-Fluent. Comparisons are made with experimental results in both a terminator and an attenuator orientation. The effects of PTO damping, chamber length, and chamber height on the hydrodynamic efficiency are investigated. Increasing the length of the chamber with constant PTO ratio improves the quality of the wave entering the chamber, while decreased length leads to stronger vortices. The optimum PTO coefficient is found to be close to that chosen for the experiments. Reducing the inner skirt height of the chamber significantly reduces all hydrodynamic parameters while a 20 % increase in the chamber's inner skirt height improves the efficiency of the OWC by about 15 %. Observations of the flow field make it clear that reducing the chamber's length can create vortices at the inlet of the OWC. The calculations highlight important nonlinear and viscous effects on the performance of an OWC chamber.

Study on Wave Energy Conversion Problem of Turbine-Integrated OWC Chamber

An oscillating water column (OWC) device is a promising wave energy converter (WEC) to utilize ocean wave energy resources. The OWC chamber absorbs the kinetic energy of ocean waves and converts the water column motion to reciprocating airflow. A power take-off system (PTO-system) of the OWC-WEC consists of an air turbine, generator, and power control system. An airflow drives an air turbine, which rotates a generator to produce electricity. The air turbine induces a pressure fluctuation due to its aerodynamic characteristics, which directly affects the fluid motion inside the chamber. In this study, the wave energy conversion problem of the OWC-WEC was discussed based on the experimental and numerical simulation results, considering the turbine-chamber interaction. The wave energy conversion problem from wave to power was solved using the finite element method (FEM)-based numerical wave tank in the time domain. The air turbine was numerically modeled based on aerodynamic coefficients and inertia properties. The validity of the present numerical method was examined by comparing it with the experimental results conducted in a two-dimensional wave flume at the Korea Research Institute of Ships and Ocean Engineering (KRISO). The effect of the turbine-chamber interaction on the energy conversion performance was investigated regarding the various rotational speeds of the air turbine based on experimental and numerical analysis. It was observed that the rotational speed conditions of the turbine, where the hydrodynamic performance of the OWC chamber and the aerodynamic performance of the turbine could be maximized, were different from each other. Therefore, it can be seen that a control technology considering the combined performance of the chamber and air turbine is required to maximize the energy conversion performance of the OWC-WEC.

Experimental investigation on the hydrodynamic performance of a pile-supported OWC-type breakwater

The present study considers the design optimisation of an Oscillating Water Column (OWC) incorporated into a pile-supported breakwater structure. This has been achieved by performing a substantial number of scaled physical model tests and a methodical variation of key device parameters within multiple configurations. The key aspects that have been investigated include: (a) the geometric characteristics of the breakwater structure, (b) the pneumatic efficiency of the OWC, (c) the geometry of the OWC chamber and (d) the relative position of the OWC chamber within the breakwater. The present work considers (monochromatic) regular waves of varying steepness and effective water depth as incident wave conditions. The efficiency of the designed structure in terms of shore protection capacity and wave energy extraction was assessed by quantifying relevant transmission coefficients and the power output metrics. This has been achieved by using a combination of collocated and complementary measuring devices, such as arrays of wave gauges, pressure transducers and a high-definition video camera. The study concluded that systematic refinement of the geometrical parameters can substantially enhance the overall hydrodynamic efficiency of a pile-supported OWC breakwater. Additionally, it was found that a configuration featuring a chamber positioned in front of the breakwater, with a relative chamber breadth of 0.67, outperforms wider breadth configurations in terms of both energy extraction efficiency and reduction of the transmission coefficient. Taken together, the present study provides an in-depth analysis of the effects of key design parameters of a breakwater-integrated OWC, its efficiency and shore protection potential.

The Effect of Hydrodynamics on the Power Efficiency of a Toroidal Oscillating Water Column Device

This study tries to identify the effect of hydrodynamics on the absorbed wave power using a toroidal Oscillating Water Column (OWC) device. To this end, the fundamental hydrodynamic boundary value problem for an arbitrary shaped toroidal OWC device of revolution with vertical axis is solved. The described method is based on the discretization of the flow field around the device by means of ring-shaped macro-elements, in each of which axisymmetric eigenfunction expansions for the velocity potential is made. The solution sought for the corresponding diffraction and radiation velocity potentials is achieved using Galerkin’s method. The applied formulation is generic and can be employed for arbitrary configurations of toroidal OWCs. Therefore, the numerical results shown and discussed in the present paper, in terms of the hydrodynamic loads and the air volume flows inside the OWC chamber, concern different types of OWCs. From the present analysis, it is demonstrated that the absorbed wave power by the examined toroidal devices is strongly affected by the geometrical parameters of the device; thus, these should be properly considered towards the maximization of the device’s wave power efficiency.

Experimental Study of a Fixed OWC-Type Wave Energy Converter with a Heave Plate and V-Shaped Channels for Intermediate-Water-Depth Applications

The study of oscillating water column (OWC)-type wave energy converters (WEC) has primarily focused on applications in the nearshore environment with an end use in residential power grids. This study examines the power performance of a new OWC geometry relative to blue economy energy objectives that focus on providing power in the intermediate-water-depth environment. The method examines power performance through the performance indicators of extraction efficiency, coefficient of amplification, and coefficient of pressure. The study discusses the implications of these coefficients relative to a new end use and examines if an analytical relationship between each indicator exists. The power performance is evaluated through experimental testing on a fixed-geometry OWC that consists of a cylindrical OWC chamber affixed above a heave plate with V-shaped channels. In evaluating power performance, the impact of different representative power take-off (PTO) damping values and directional dependence is investigated. It was found that incident wave angle has a minimal impact on extraction efficiency for this geometry and that a relationship exists between extraction efficiency, wave frequency, and PTO damping. It can be concluded that extraction efficiency can be expressed as a function of each coefficient, that an emphasis on extraction efficiency may be misguided for at-sea power applications, and that performance indicators have functionality in OWC design outside of power performance.

Experimental and numerical investigations on the solitary wave actions on a land-fixed OWC wave energy converter

The dynamic performance of a typical land-fixed oscillating water column (OWC) wave energy converter (WEC) under solitary waves (SW) is experimentally and numerically investigated. Both two-dimensional (2-D) and three-dimensional (3-D) numerical models are considered in the present study. The air orifices of the OWC chamber in 2-D and 3-D models are represented by a narrow rectangular opening and a circular opening, respectively, with the same opening ratio (i.e., the cross sectional area ratio between opening and the air chamber). It is found that the overflow of the orifice occurs when the wave height exceeds a threshold, which results in a larger wave force on the structure compared with that induced by the SW crest. The 2-D numerical model fails to predict the overflow phenomena due to the full submergence of the orifice. The overtopping and roof impacting phenomena are induced when the wave run-up exceeds the front wall height. A portion of the SW energy is released during this process. Hence, total wave forces are reduced. The effect of wave heights on force components exhibits different behaviors due to the coupling of air and water inside the chamber. Both the impacting force and overtopping discharge increase with incident wave heights.

Experimental study on hydrodynamic behavior and energy conversion of multiple oscillating-water-column chamber in regular waves

An oscillating water column (OWC) device is a promising wave energy converter that uses ocean wave energy resources. The OWC chamber absorbs the energy of ocean waves and significantly affects energy conversion performance. In this study, the hydrodynamic performance of a multiple OWC chamber was investigated experimentally, emphasizing its hydrodynamic behavior and energy conversion characteristics. A series of regular wave tests were conducted for single-, triple-, and asymmetric triple OWC chambers in a two-dimensional wave tank. The same orifice ratio was applied to the single and triple chambers to induce an equivalent turbine-chamber interaction owing to the pressure drop. It was found that the triple OWC chamber contributes to an increase in the converted pneumatic power compared to the single OWC chamber due to reducing the sloshing motion of the internal fluid. Moreover, the temporal fluctuation of the overall output power was reduced because of the water column motion of each triple OWC chamber with a phase difference. The rear chamber of the asymmetric triple chamber traps the wave energy and contributes to not only increasing the output power but also the variability. Therefore, it can be observed that multiple OWC chambers improve energy conversion performance by increasing the mean power output and reducing temporal fluctuation.

Role of dual breakwaters and trenches on efficiency of an oscillating water column

In this paper, the effects of double-submerged breakwaters and trenches on the hydrodynamic performance of an oscillating water column (OWC) are investigated. The multi-domain boundary element method is used to tackle the physical problem of wave scattering and radiation from the device. The role of the height of the breakwaters, depth of the trenches, width of the breakwaters and trenches, spacing between the structures, length of the OWC chamber, and other wave and structural parameters is investigated on the efficiency of OWC. The study reveals that there is an oscillating pattern of the efficiency curve in the presence of single or double breakwater/trenches; this pattern is absent when the bottom is flat. Moreover, compared to single or no breakwaters/trenches, the occurrence of full OWC efficiency is higher in the presence of double breakwaters/trenches. Furthermore, the amplitude of the oscillating pattern in the efficiency curve increases with an increase in the height and depth of the breakwaters and trenches, respectively. For some particular wave and structural parameters, zero OWC efficiency occurs nearly k0h=3.4 within 0<k0h<5 (k0 wave number and h water depth). This zero efficiency moves toward small wave numbers as the spacing between OWC and rigid breakwater/trench increases. The radiation conductance of OWC decreases with an increase in the barrier height. The findings outline the structural criteria that can be employed to build and deploy an effective OWC device.