Numerical Studies of a Floating Cylindrical OWC WEC

2012 ◽  
Author(s):  
Wanan Sheng ◽  
Anthony Lewis ◽  
Raymond Alcorn
Keyword(s):  
Numerical Simulation ◽  
Water Column ◽  
Wave Energy ◽  
Water Surface ◽  
Mechanical Energy ◽  
Hydrodynamic Performance ◽  
Coupling Effects ◽  
Energy Devices ◽  
Power Extraction ◽  
Device Development

Oscillating water column (OWC) wave energy converters (WECs) are a popular type of wave energy devices. Generally, the OWC WECs have a simple structure and working principle, but with a high conversion efficiency, and a high reliability in power take-off due to a small torque and a high rotation speed for a certain power extraction. The OWC devices convert wave energy into pneumatic energy primarily by producing the pressured and de-pressured air (pneumatic energy) in the air chamber through the motions of the interior water surface in the water column. Conventionally, the pneumatic energy is converted into mechanical energy through an air turbine (in small scaled model, an orifice or porous membrane material is used for non-linear or linear power take-off modelling). However, these processes are very limitedly understood due to the complexities of the hydrodynamics, aerodynamics, and thermodynamics and their coupling effects. Theoretical and numerical attempts are very limited, especially when the coupling effects are included. As a result of the difficulties, in the device development, the most popular and acceptable approach may be the model tests, with different scaling factors in their corresponding development stages, as recommended by the relevant wave energy development protocols. To reduce the dependencies on the physical modelling in the OWC device development, numerical methods are very desirable to accommodate the simulation and assessment of the hydrodynamic and aerodynamic/thermodynamic performances of the OWC WECs. This is the main target of this investigation. In this numerical simulation, the hydrodynamic performances (including the motions of the structure and the interior water surface in waves) are carried out by employing a conventional boundary element method (i.e., WAMIT in this case) in frequency domain. To include the effects of the airflow passing through an orifice, its aerodynamic performance is much simplified by assuming its effects on the hydrodynamic performance through some extra damping coefficients to the motions of the floating structure and to the motion of the interior water surface. In this way, the interior water surface response can be obtained for the coupling effects of the hydrodynamics and aerodynamics of the OWC WEC. In this regard, an important issue in the numerical simulation is to seek an appropriate representation of the damping levels.

Scale and Configuration Effects of an Airchamber on PTO of Oscillating Water Column Type Wave Energy Converters

2021 ◽  
Author(s):  
Tomoki Ikoma ◽  
Shota Hirai ◽  
Yasuhiro Aida ◽  
Koichi Masuda
Keyword(s):  
Water Column ◽  
Wave Energy ◽  
Water Surface ◽  
Air Pressure ◽  
Scale Model ◽  
Linear Potential ◽  
Oscillating Water Column ◽  
Wave Energy Converters ◽  
Air Chamber ◽  
Energy Converters

Abstract Wave energy converters (WECs) have been extensively researched. The behaviour of the oscillating water column (OWC) in OWC WECs is extremely complex due to the interaction of waves, air, and turbines. Several problems must be overcome before such WECs can be put to practical use. One problem is that the effect of the difference in scale between a small-scale experimental model and a full-scale model is unclear. In this study, several OWC models with different scales and geometries were used in forced oscillation tests. The wave tank was 7.0 m wide, 24.0 m long, and 1.0 m deep. In the static water experiment, we measured the air pressure and water surface fluctuations in an air chamber. For the experiments, models with a box shape with an open bottom, a manifold shape with an open bottom, and a box shape with a front opening, respectively, were fabricated. Furthermore, 1/1, 1/2, and 1/4 scale models were fabricated for each shape to investigate the effects of scale and shape on the air chamber characteristics. Numerical calculations were carried out by applying linear potential theory and the results were compared with the experimental values. The results confirmed that the air chamber shape and scale affect the air pressure fluctuation and water surface fluctuation inside the OWC system.

Evaluation of 3-D Computational Model of Oscillating Water Column Converter with Constructal Design with Three Degrees of Freedom and Limited Chimney Height

2021 ◽  
Vol 407 ◽  
pp. 128-137
Author(s):  
Vinícius Bloss ◽  
Camila Fernandes Cardozo ◽  
Flávia Schwarz Franceschini Zinani ◽  
Luiz Alberto Oliveira Rocha
Keyword(s):  
Water Column ◽  
Wave Energy ◽  
Degrees Of Freedom ◽  
Numerical Study ◽  
Mechanical Energy ◽  
Ocean Waves ◽  
Response Surfaces ◽  
Oscillating Water Column ◽  
Promising Source ◽  
Three Degrees Of Freedom

Theoretically, ocean waves contain enough mechanical energy to supply the entire world’s demand and, as of late, are seen as a promising source of renewable energy. To this end, several different technologies of Wave Energy Converters (WEC) have been developed such as Oscillating Water Column (OWC) devices. OWCs are characterized by a chamber in which water oscillates inside and out in a movement similar to that of a piston. This movement directs air to a chimney where a turbine is attached to convert mechanical energy. The analysis conducted was based on the Constructive Design Method, in which a numerical study was carried out to obtain the geometric configuration that maximized the conversion of wave energy into mechanical energy. Three degrees of freedom were used: the ratio of height to length of the hydropneumatic chamber (H1/L), the ratio of the height of the chimney to its diameter (H2/d) and the ratio of the width of the hydropneumatic chamber to the width of the wave tank (W/Z). A Design of Experiments (DoE) technique coupled with Central Composite Design (CCD) allowed the simulation of different combinations of degrees of freedom. This allowed the construction of Response Surfaces and correlations for the efficiency of the system depending on the degrees of freedom (width and height of the chamber), as well as the optimization of the system based on the Response Surfaces.

scholarly journals Wave power extraction from a bottom-mounted oscillating water column converter with a V-shaped channel

2014 ◽  
Vol 470 (2167) ◽  
pp. 20140074 ◽  
Author(s):  
Zhengzhi Deng ◽  
Zhenhua Huang ◽  
Adrian W. K. Law
Keyword(s):  
Water Column ◽  
Water Depth ◽  
Wave Energy ◽  
High Efficiency ◽  
Expansion Method ◽  
Opening Angle ◽  
Energy Extraction ◽  
Oscillating Water Column ◽  
Wave Direction ◽  
Power Extraction

An analytical theory is developed for an oscillating water column (OWC) with a V-shaped channel to improve the pneumatic efficiency of wave energy extraction. An eigenfunction expansion method is used in a cylindrical coordinate system to investigate wave interaction with the OWC converter system. Auxiliary functions are introduced to capture the singular behaviours in the velocity field near the salient corners and cusped edges. Effects of the OWC dimensions, the opening angle and length of the V-shaped channel, as well as the incident wave direction, on the pneumatic efficiency of wave energy extraction are examined. Compared with a system without the V-shaped channel, our results show that the V-shaped channel can significantly increase the conversion efficiency and widen the range of wave frequency over which the OWC system can operate at a high efficiency. For typical coastal water depths, the OWC converter system can perform efficiently when the diameter of the OWC chamber is in the range of 1 5 – 1 2 times the water depth, the opening angle of the V-shaped channel is in the range of [ π /2, 3 π /4] and the length of the V-shaped channel is in the range of 1–1.5 times the water depth.

scholarly journals Experimental Study of a Moored Floating Oscillating Water Column Wave-Energy Converter and of a Moored Cubic Box

Energies ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 1834 ◽  
Author(s):  
Minghao Wu ◽  
Vasiliki Stratigaki ◽  
Peter Troch ◽  
Corrado Altomare ◽  
Tim Verbrugghe ◽  
...  
Keyword(s):  
Water Column ◽  
Wave Energy ◽  
Water Surface ◽  
Wave Energy Converter ◽  
Surface Elevation ◽  
Mooring Line ◽  
Oscillating Water Column ◽  
Energy Converter ◽  
Large Wave ◽  
Water Surface Elevation

This paper describes experimental research on a floating moored Oscillating Water Column (OWC)-type Wave-Energy Converter (WEC) carried out in the wave flume of the Coastal Engineering Research Group of Ghent University. This research has been introduced to cover the existing data scarcity and knowledge gaps regarding response of moored floating OWC WECs. The obtained data will be available in the future for the validation of nonlinear numerical models. The experiment focuses on the assessment of the nonlinear motion and mooring-line response of a 1:25 floating moored OWC WEC model to regular waves. The OWC WEC model motion has 6 degrees of freedom and is limited by a symmetrical 4-point mooring system. The model is composed of a chamber with an orifice on top of it to simulate the power-take-off (PTO) system and the associated damping of the motion of the OWC WEC model. In the first place, the motion response in waves of the moored floating OWC WEC model is investigated and the water surface elevation in the OWC WEC chamber is measured. Secondly, two different mooring-line materials (iron chains and nylon ropes) are tested and the corresponding OWC WEC model motions and mooring-line tensions are measured. The performance of these two materials is similar in small-amplitude waves but different in large wave-amplitude conditions. Thirdly, the influence of different PTO conditions is investigated by varying the diameter of the top orifice of the OWC WEC model. The results show that the PTO damping does not affect the OWC WEC motion but has an impact on the water surface elevation inside the OWC chamber. In addition, an unbalanced mooring configuration is discussed. Finally, the obtained data for a moored cubic model in waves are presented, which is a benchmarking case for future validation purposes.

Performance of a Shore Fixed Oscillating Water Column Device for Different Bottom Slopes and Front Wall Drafts: A Study Based on Computational Fluid Dynamics and BIEM

2020 ◽  
Vol 143 (3) ◽  
Author(s):  
Piyush Mohapatra ◽  
K. G. Vijay ◽  
Anirban Bhattacharyya ◽  
Trilochan Sahoo
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Water Column ◽  
Wave Energy ◽  
High Efficiency ◽  
Boundary Integral ◽  
Hydrodynamic Performance ◽  
Chamber Pressure ◽  
Front Wall ◽  
Oscillating Water Column

Abstract Oscillating water column (OWC) wave energy converters are one of the most widely researched devices for ocean wave energy harvesting. This study investigates the hydrodynamic performance of a shore-fixed OWC device for different bottom slopes using two numerical approaches, namely, computational fluid dynamics (CFD) and boundary integral equation method (BIEM). In the BIEM method, the boundary value problem is solved in two-dimensional Cartesian coordinates using the linear water wave theory. The CFD model uses a numerical wave tank (NWT) built using the volume of fluid (VOF) method. Numerical computations are carried out for different sloped bottom geometries and front wall drafts to analyze the hydrodynamic efficiency. There is a general agreement between CFD and BIEM results in terms of resonating behavior of the device. It is observed that the front wall draft has a more significant effect, a lower draft leading to a wider frequency band for optimum conversion at high efficiency. While the BIEM-based analysis resulted in improved performance curve for few of the steeper slopes, the CFD study predicted a lower peak efficiency for the same slopes due to the consideration of real fluid characteristics. Detailed performance comparisons are presented using the time histories of free surface elevation, chamber pressure, and streamlines at different time instants within the OWC chamber.

scholarly journals Hydrodynamic Performance of a Hybrid System Combining a Fixed Breakwater and a Wave Energy Converter: An Experimental Study

Energies ◽  
2020 ◽  
Vol 13 (21) ◽  
pp. 5740
Author(s):  
Wei Peng ◽  
Yingnan Zhang ◽  
Xueer Yang ◽  
Jisheng Zhang ◽  
Rui He ◽  
...  
Keyword(s):  
Experimental Study ◽  
Hybrid System ◽  
Wave Energy ◽  
Wave Energy Converter ◽  
Hydrodynamic Performance ◽  
Scale Model ◽  
Wave Power ◽  
Energy Converter ◽  
Power Extraction ◽  
Wave Induced

In this paper, a hybrid system integrating a fixed breakwater and an oscillating buoy type wave energy converter (WEC) is introduced. The energy converter is designed to extract the wave power by making use of the wave-induced heave motions of the three floating pontoons in front of the fixed breakwater. A preliminary experimental study is carried out to discuss the hydrodynamic performance of the hybrid system under the action of regular waves. A scale model was built in the laboratory at Hohai University, and the dissipative force from racks and gearboxes and the Ampere force from dynamos were employed as the power take-off (PTO) damping source. During the experiments, variations in numbers of key parameters, including the wave elevation, free response or damped motion of the floating pontoons, and the voltage output of the dynamos were simultaneously measured. Results indicate that the wave overtopping and breaking occurring on the upper surfaces of floating pontoons have a significant influence on the hydrodynamic performance of the system. For moderate and longer waves, the developed system proves to be effective in attenuating the incident energy, with less than 30% of the energy reflected back to the paddle. More importantly, the hydrodynamic efficiency of energy conversion for the present device can achieve approximately 19.6% at the lowest wave steepness in the model tests, implying that although the WEC model harnesses more energy in more energetic seas, the device may be more efficient for wave power extraction in a less energetic sea-state.

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