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.

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.

On the Efficiency and Transmission Characteristics of a 1:20 Model Fixed Wave Energy Device

2003 ◽  
Author(s):  
E. Vijayakrishna Rapaka ◽  
S. Neelamani ◽  
R. Natarajan
Keyword(s):  
Wave Propagation ◽  
Water Column ◽  
Water Depth ◽  
Wave Energy ◽  
Oscillating Water Column ◽  
Wave Energy Conversion ◽  
Transmission Characteristics ◽  
Energy Device ◽  
Average Value ◽  
Model Study

Wave transmission and pneumatic efficiency of an oscillating water column (OWC) type wave energy device resting on group of piles is investigated using physical model study. The caisson blocks 45% of the water depth. The co-efficient of transmission of the device varies from 0.1 to 0.4 for B/L range of 0.1 to 0.7, where ‘B’ is the width of the caisson in the direction of wave propagation and ‘L’ is the wavelength. The pneumatic efficiency varies from 20% to 50% with an average value of 0.35. The results of the present study can be used in the design of OWC caisson used for both wave energy conversion and breakwater in deeper water.

Air Turbine and Primary Converter Matching in Spar-Buoy Oscillating Water Column Wave Energy Device

2013 ◽  
Author(s):  
J. C. C. Henriques ◽  
A. F. O. Falcão ◽  
R. P. F. Gomes ◽  
L. M. C. Gato
Keyword(s):  
Water Column ◽  
Wave Energy ◽  
Rotational Speed ◽  
Time Domain Analysis ◽  
Wave Climate ◽  
Numerical Code ◽  
Oscillating Water Column ◽  
Wave Direction ◽  
Power Performance ◽  
Air Turbine

The oscillating water column (OWC) equipped with an air turbine is possibly the most reliable type of wave energy converter. The OWC spar-buoy is a simple concept for a floating OWC. It is an axisymmetric device (and so insensitive to wave direction) consisting basically of a (relatively long) submerged vertical tail tube open at both ends and fixed to a floater that moves essentially in heave. The air flow displaced by the motion of the OWC inner free-surface, relative to the buoy, drives an air turbine. The choice of air turbine type and size, the regulation of the turbine rotational speed and the rated power of the electrical equipment strongly affect the power performance of the device and also the equipment’s capital cost. Here, numerical procedures and results are presented for the power output from turbines of different sizes equipping a given OWC spar-buoy in a given offshore wave climate, the rotational speed being optimized for each of the sea states that, together with their frequency of occurrence, characterize the wave climate. The new biradial self-rectifying air turbine was chosen as appropriate to the relatively large amplitude of the pressure oscillations in the OWC air chamber. Since the turbine is strongly non-linear and a fully-nonlinear model of air compressibility was adopted, a time domain analysis was required. The boundary-element numerical code WAMIT was used to obtain the hydrodynamic coefficients of the buoy and OWC, whereas the non-dimensional performance curves of the turbine were obtained from model testing.

Fluidic Components for Oscillating Water Column Based Wave Energy Plants

2011 ◽  
Author(s):  
Prasad V. Dudhgaonkar ◽  
V. Jayashankar ◽  
Purnima Jalihal ◽  
S. Kedarnath ◽  
T. Setoguchi ◽  
...  
Keyword(s):  
Water Column ◽  
Wave Energy ◽  
High Efficiency ◽  
Reverse Flow ◽  
Forward Direction ◽  
Oscillating Water Column ◽  
High Impedance ◽  
Energy Plant ◽  
Wide Range ◽  
Fluidic Diode

A bidirectional (oscillating) air flow is central to energy conversion from wave to wire in an oscillating water column based wave energy plant. Several classes of bidirectional turbines, which operate with such an oscillating flow, have been designed and tested with limited efficiencies. A topology which uses fluidic diodes in conjunction with unidirectional turbines is shown to significantly improve the efficiency. The design and test results from several fluidic diodes for such an application are discussed. It is shown that a combination of a fluidic diode and the unidirectional turbine can achieve a very high impedance to reverse flow while having a high efficiency in the forward direction, over a wide range of flow coefficients.

scholarly journals Wave Power Extraction from a Dual Oscillating-Water- Column System Composed of Heave-Only and Onshore Units

Energies ◽  
2019 ◽  
Vol 12 (9) ◽  
pp. 1742 ◽  
Author(s):  
Chen Wang ◽  
Zhengzhi Deng ◽  
Pinjie Wang ◽  
Yu Yao
Keyword(s):  
Water Column ◽  
High Performance ◽  
High Efficiency ◽  
Hydrodynamic Characteristics ◽  
Width Ratio ◽  
Oscillating Water Column ◽  
Power Extraction ◽  
Column System ◽  
Vertical Restraint ◽  
Conversion Efficiencies

With the aim of broadening the wave-frequency bandwidth of high-efficiency, a small-scaled dual oscillating-water-column (OWC) system consisting of two heave-only and onshore units was numerically investigated by a well-validated computational fluid dynamics (CFD) model. Based on the popular open source package OpenFOAM, the volume of fluid (VOF) method was employed to track the transformation of the air–water interface under the excitation of regular waves. The six degree of freedom (6DOF) solver was applied to duplicate the heaving motion of the floating device. The effects of the two chamber widths b 1 and b 2 , the vertical restraint force (represented by the dimensionless stiffness coefficient K), the back-lip draught d 2 of the floating device, and the gap Δ L between the two OWCs on the hydrodynamic characteristics and the wave energy conversion efficiencies were examined. The numerical results show that a larger width ratio b 2 / b 1 with a relatively shallow back-lip draught is more conducive to the high-performance over a broader frequency range. The floating device with a stronger vertical restraint force is more satisfactory for the high-performance of the system. Moreover, a relatively small gap is more recommended in the stage of design and construction.

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