Oscillating Water Column Research Articles

Numerical Study on the Dynamic Characteristics of a Coupled Wind–Wave Energy Device

A wind–wave coupled device integrating an offshore fixed wind turbine and an OWC (oscillating water column) wave energy device is proposed in this study. Its dynamic characteristics under extreme environmental conditions are analyzed for practical design and development using a numerical model established based on the commercial finite element method platform ANSYS-Workbench, which is then validated using experimental data for an offshore fixed wind turbine model. The modal analysis results indicate that installing the OWC system does not modify the basic dynamic characteristics of the original wind turbine. Under different extreme environmental conditions at different design water levels, stress concentration can be observed at different locations on the structures. Although the gap between the sub-chambers of the OWC system can be increased to reduce stress on the chamber and piles, an excessively large gap will enhance structural complexity and increase construction costs. An appropriate relative size for the gap between the sub-chambers is recommended for practical design.

Slamming Loads Induced by Dam-Break Flow on Land-Based Oscillating Water Columns: Numerical and Experimental Study

Slamming Loads Induced by Dam-Break Flow on Land-Based Oscillating Water Columns: Numerical and Experimental Study

Enhancing wave energy harvesting through integration of IEA 15 MW wind turbine on oscillating water columns equipped platform

Enhancing wave energy harvesting through integration of IEA 15 MW wind turbine on oscillating water columns equipped platform

Enhancing wave power focus with periodic wave-guiding walls in a three-unit oscillating water column array integrated with a vertical breakwater

Enhancing wave power focus with periodic wave-guiding walls in a three-unit oscillating water column array integrated with a vertical breakwater

Study on Efficient and Stable Energy Conversion Method of Oscillating Water Column Device Based on Energy Storage Valve Control

Study on Efficient and Stable Energy Conversion Method of Oscillating Water Column Device Based on Energy Storage Valve Control

An Experimental Study of a Conventional Cylindrical Oscillating Water Column Wave Energy Converter: Fixed and Floating Devices

Oscillating water column (OWC) wave energy converters (WECs) are very popular types of wave energy converters due to their practical implementations, their versatility in deployment in different marine environments, and their high reliability in wave energy conversion. In development, different forms of OWCs have been proposed and advanced, such as fixed OWCs (on the shoreline, on breakwaters, or bottom standing) and floating OWCs (the spar and the backward-bent duct buoy, BBDB). In reality, a special type of OWC, the cylindrical OWC, is the simplest OWC in terms of its structural design and possible analytical/numerical solutions. However, such a simple OWC has not seen any practical applications because a cylindrical OWC is inefficient in wave energy absorption when compared to other types of OWC WECs. To study the simplest cylindric OWC, an experiment was carried out in a wave tank, and the relevant results are presented in this paper, with the aims of (i) analyzing the experimental data and exploring why such an OWC is inefficient in terms of wave energy absorption; (ii) providing experimental data for those who want experimental data to validate their numerical models; and (iii) establishing a baseline model so that comparisons can be made for improvements to the simple cylindrical OWC. As an example, an innovative solution was applied to the simple OWC such that its hydrodynamics and energy extraction performance can be significantly improved (the corresponding results will be presented in a separate paper).

Investigating air compressibility effects in numerical modeling of oscillating water column wave energy converters: a case study on performance and accuracy

ABSTRACT Wave energy, as a clean and abundant resource, offers significant potential for sustainable power. Oscillating Water Column (OWC) is a key technology in this domain. In studies related to OWC, air compressibility can be a significant parameter. This research examines the error caused by neglecting the effects of air compressibility in numerical modeling. To this end, a numerical solution for a 1:10 scaled OWC model was developed based on RANS equations and the Volume of Fluid (VoF) method for free surface water. The wave conditions studied correspond to those in the Caspian Sea. For validation, the pressure within the chamber was compared with experimental results. The results indicated that the error for the incompressible model is 9.89% and for the compressible model is 8.43%. To account for air compressibility effects, a User-Defined Function (UDF) was added to the numerical solution, which adjusts the air density according to isentropic pressure equations. The results showed that considering air compressibility can lead to up to a 5.71% overestimation of the converter’s output power at certain incident wave frequencies. Additionally, at resonance conditions where the incident wave frequency matches the natural frequency of the converter, the effect of air compressibility is minimized.

Hydrodynamic Performance of an Oscillating Water Column Device Installed in an Offshore Wind Turbine

Hybrid wind–wave energy devices have attracted significant attention for their potential to efficiently harness marine energy while reducing construction costs. In this work, the hydrodynamic performance of an oscillating water column (OWC) device installed in an offshore wind turbine was investigated. A three-dimensional numerical model was developed based on computational fluid dynamics. The numerical predictions demonstrate good agreement with the corresponding experimental results. The effects of key factors, such as chamber diameter, chamber draft, and pneumatic damping, on the energy capture performance were analyzed. The variation patterns of the free surface elevation, the air pressure, and the capture width ratio were analyzed. Additionally, flow characteristics and vortex dynamics around the device were presented for better understanding the energy capture process of the hybrid device. The results reveal that a larger chamber diameter is beneficial for energy conversion, and the optimal chamber draft and pneumatic damping were identified. Furthermore, the operating performance of the optimized device under irregular wave conditions was predicted.

Ocean Wave Energy Converter

This research paper presents a comparative analysis of power extraction from an Oscillating Water Column (OWC) and a Point Absorber using mathematical modeling. Both systems are modeled under the same wave input conditions, with the OWC utilizing airflow dynamics to drive a turbine, and the Point Absorber modeled through heave motion equations. Linear wave theory and hydrodynamic interactions are applied to calculate power output. Results indicate that the OWC performs optimally in nearshore environments with consistent waves, while the Point Absorber is more efficient in offshore conditions. The comparison highlights how different wave characteristics influence energy capture efficiency.

The influence of parameters on the hydrodynamic characteristics of oscillating water column devices: A numerical study

The influence of parameters on the hydrodynamic characteristics of OWC (oscillating water column) devices exhibits a coupling phenomenon, which is frequently neglected. To elucidate the comprehensive influence and its mechanism of structure parameters on the hydrodynamic characteristics of offshore OWC devices, a structure with a bottom plate was selected in this study. Through numerical simulation, the hydrodynamic characteristics of the chamber with variations in PTO (power take off) coefficient α, chamber length Bs, internal depth Jn, and under water length of front wall Je with different wave conditions are investigated. The following conclusions are primarily drawn: The research method of using the relative wavelength L/Bs as a non-dimensional parameter and solely varying the wavelength L has its drawbacks. In cases that L/Bs is held constant, the efficiency of chambers differing only in Bs can vary by more than 70%. The influence of each parameter on the effectiveness is interrelated. Chambers with a lower α exhibit a more pronounced impact of Bs. The efficiency of device with a smaller relative wavelength L/Bs is more significantly affected by the Jn. The mechanism by which the parameters affect efficiency is primarily since chambers with shorter Bs or greater Jn exhibit smaller deformations during internal liquid surface oscillation, resembling a more uniform oscillating water column. This allows more energy to be utilized for pushing air in and out of the chamber above, thereby enhancing the energy conversion capability. The results of this research can provide valuable insights for the design of OWC devices.

NUMERICAL INVESTIGATION AND NEW INTELLIGENT SYSTEM FOR PERFORMANCE IMPROVEMENT OF A RADIAL IMPULSE TURBINE FOR WAVE ENERGY CONVERSION

This study presents a numerical investigation into the influence of rotor blade geometry on the performance of oscillating water column (OWC) impulse turbines for wave energy conversion. A numerical model was developed and validated using experimental data for both circular and elliptical rotor profiles. Simulations were conducted for inhalation and exhalation modes of turbine operation, focusing on flow angles, flow coefficients, and losses coefficients in various turbine components. Results reveal significant differences in performance and flow behavior between turbines with circular and elliptical blade profiles, particularly in the inhalation mode. Circular blade profiles demonstrated superior performance and favorable flow characteristics, whereas elliptical profiles exhibited more pronounced flow separation attributed to higher curvature variation. The findings underscore the critical role of blade profile in determining turbine performance, highlighting the importance of optimizing blade design for enhanced efficiency. Building upon these results, an integration of an intelligent control system for guide vane geometric angles is proposed to ensure optimal alignment with downstream flow angles throughout the cycle. This study contributes to the understanding of turbine performance in OWC systems and provides insights for future design optimization efforts aimed at maximizing energy conversion efficiency.

Redial basis function-finite difference method to investigate the wave energy extraction by a land-fixed oscillating water column device

Redial basis function-finite difference method to investigate the wave energy extraction by a land-fixed oscillating water column device

Performance Optimization Techniques on Point Absorber and Oscillating Water Column Wave Energy Converter: A Comprehensive Review

Performance Optimization Techniques on Point Absorber and Oscillating Water Column Wave Energy Converter: A Comprehensive Review

Numerical Analysis of the Influence of Rectangular Deflectors and Geometry of L-Shaped Channel over the Performance of a Savonius Turbine

The present work investigates the influence of rectangular deflectors on the performance of a Savonius turbine mounted in an L-shaped channel, which represents a geometry like that found in one oscillating water column (OWC) device. It also performs a geometric investigation of the entrance region of the channel. More precisely, it investigates the effect of the height/length ratio (H1/L1) of the entering region of the channel on the system performance for three different configurations: (1) without the use of deflectors, (2) with just one deflector upstream the turbine, and (3) with one deflector upstream and another downstream the turbine. The geometric investigation is performed based on the constructal design method, and the entering channel area (A1) is the problem constraint. The performance indicators are the mechanical power in the Savonius turbine and the available power in the device. For all cases, it is considered turbulent airflow in the domain, being solved by the unsteady Reynolds Averaged Navier–Stokes mass and momentum equations. The numerical solution was obtained with the finite-volume method using the Ansys FLUENT software (version 2021 R1). The k-ω shear stress transport turbulence closure model is used. The results demonstrated that the mechanical and available powers depend on the H1/L1 ratio, regardless of the usage of deflectors. For instance, differences of up to 16.35% in mechanical power and 7.25% in available power were observed between the best and worst performance configurations in the case without deflectors. The use of deflectors resulted in increases of two and three times in available and mechanical powers, respectively, when the cases with one and two deflectors are compared with those without deflectors. This demonstrates that the enclosed domain and the insertion of the deflectors can enhance the performance of the Savonius turbine.

Machine learning for predicting flow and pressure in an oscillating water column wave energy converter

The use of wave energy presents itself as a renewable alternative, diversifying the energy matrix and reducing the consumption of fossil fuels. One of the prominent devices for ocean wave harvesting is the Oscillating Water Column (OWC), which consists of a hydropneumatic chamber where the oscillation of the water surface compresses the confined air, driving a turbine. This work combines numerical simulation and machine learning algorithms, aiming to develop predictive models for mass flow rate and pressure through the OWC chamber. The database for the models was created using Design of Experiments (DOE) techniques, where different combinations of wave height and wavelength were simulated via Computational Fluid Dynamics (CFD) using the Finite Volume Method (FVM). Subsequently, the wave elevation height data is fed into a fully connected deep neural network, which uses the simulated data for learning and returns predictions based on the provided information. The model's performance is evaluated in terms of a cost function (Mean Squared Error). The employed model allows for the identification of flow rate and pressure peaks for the wave period provided at the input, and the results show differences of up to 5% in RMS (Root Mean Square) between the predictions and the CFD data. The main contribution of this work lies in the use of machine learning in predicting traditional operating conditions of an OWC device, introducing a concept that can be applied in the early stages of the design of such devices.

Hydrodynamic Analysis of an Oscillating Water Column Wave Energy Converter

Hydrodynamic Analysis of an Oscillating Water Column Wave Energy Converter

Numerical and Experimental Study on the Hydrodynamic Performance of a Sloping OWC Wave Energy Converter Device Integrated into Breakwater

This study presents numerical and experimental investigations on an oscillating water column (OWC) wave energy device integrated into a sloping breakwater. Regular waves were generated in a physical wave tank to investigate the hydrodynamic performance and extraction efficiency of the small-scale nested OWC device. Simultaneously, to complement various scenarios, numerical simulations were conducted using the open-source computational fluid dynamics platform OpenFOAM. The volume of fluid (VOF) method was employed to capture the complex evolution of the air–water interface, and an artificial source term (Forchheimer flow region) was introduced into the Navier–Stokes equations to replace the power take-off (PTO) system. By analyzing wave reflection properties, energy absorption efficiency, and wave run-up, the hydrodynamic characteristics of the inclined OWC device were explored. The comparison between the numerical and experimental results indicate a good consistence. A smaller front wall draft broadens the high-efficiency frequency bandwidth. For relatively long waves, increasing the air chamber width enhances energy conversion efficiency and reduces wave run-up. The optimal configuration was achieved with the following dimensionless parameters: front wall draft a/h=1/3, air chamber width d1/h=2/9, and slope i=2. Due to the sloped structure, when compared with a vertical OWC, long waves can more easily enter the chamber. This causes the efficient frequency bandwidth to shift towards the low frequency range, allowing more wave energy to be converted into pneumatic energy. As a result, wave run-up is reduced, enhancing the protective function of the breakwater.

Numerical Simulation of Hydrodynamic Performance of an Offshore Oscillating Water Column Wave Energy Converter Device

Wave energy, as a renewable energy source, plays a significant role in sustainable energy development. This study focuses on a dual-chamber offshore oscillating water column (OWC) wave energy device and performs numerical simulations to analyze the influence of chamber geometry on hydrodynamic characteristics and wave energy conversion efficiency. Unlike existing studies primarily focused on single-chamber configurations, the hydrodynamic characteristics of dual-chamber OWCs are relatively underexplored, especially regarding the impact of critical design parameters on performance. In this study, STAR-CCM+ V2302 software (Version 2410, Siemens Digital Industrial Software, Plano, TX, USA) is utilized to systematically evaluate the effects of key design parameters (including turbine configuration, mid-wall draught depth, and wall angles) on the hydrodynamic performance, wave energy capture efficiency, and wave reflection and loading characteristics of the device. The findings aim to provide a reference framework for the optimal design of dual-chamber OWC systems. The results show that the dual-chamber, dual-turbine (2C2T) configuration offers a 31.32% improvement in efficiency compared to the single-chamber, single-turbine (1C1T) configuration at low wave frequencies. In terms of reducing wave reflection and transmission, the 2C2T configuration outperforms the dual-chamber, single-turbine configuration. When the wall angle increases from 0° to 40°, the total efficiency increases by 166.37%, and the horizontal load decreases by 20.05%. Additionally, optimizing the mid-wall draught depth results in a 9.6% improvement in efficiency and a reduction of vertical load by 11.69%.

Performance improvement of a full-scale oscillating water column device by employing a novel double oscillating water column

The energy present in the ocean surface waves can be extracted using an oscillating water column (OWC) device. In the present work, the performance characteristics of a normal OWC, an opposite OWC and a novel double OWC employing Savonius rotors are investigated at different sea states in a numerical wave tank (NWT) using the computational fluid dynamics (CFD) code ANSYS-CFX. The Savonius rotor is known to be an inexpensive energy harvesting device. The waves in the NWT were generated using a piston type wave-maker. The results from the computational work were compared with experimental work. For the normal OWC, a maximum power output of 18.85 kW, which corresponds to an efficiency of 22.44% was recorded at 60 rpm for the mean wave condition. On the other hand, for the opposite OWC, the peak power and efficiency were 10.4 kW and 12.38% respectively for the mean sea state. For the novel double OWC, the flow in the front OWC has more energy compared to the flow in the rear OWC for both advancing flow and retreating flow, resulting in a combined peak power of 19.5 kW at the mean sea state. This represented an increase of 3.45% in the power production.

Hydrodynamic Performance Investigations of OWC and Hybrid System: Geometry of OWC and Rectangular Submerged Breakwater

Due to its simplicity and high reliability, the Oscillating Water Column (OWC) has been a prominent focus of research. This study investigates the impact of OWC geometry on hydrodynamic performance by analyzing the effects of draft, chamber width, and Power Take Off (PTO) damping on energy conversion efficiency, reflection coefficient, transmission coefficient, and dissipation coefficient. The motion of the water column under different PTO damping conditions is analyzed. In addition, the hydrodynamic performance of the submerged breakwater-OWC hybrid system is studied and compared with that of a standalone OWC. The results show that a higher opening height improves the energy conversion efficiency of the OWC under medium-to-long waves. There is an optimal draft for the OWC to maximize the energy conversion efficiency for different wave periods. Meanwhile, the optimal draft increases with the wave period. Increasing PTO damping does not change the resonance period of the OWC, while the free surface elevation inside the chamber reduces. Within a range of periods around the maximum inclination, multi-point measurements of the wave elevation in the chamber are necessary to reduce measurement errors caused by the spatial non-uniformity of the water column. The submerged breakwater-OWC hybrid system exhibits a higher energy conversion efficiency under medium-to-long waves compared to a standalone OWC, and there is an optimal breakwater length.