scholarly journals Performance of an Array of Oscillating Water Column Devices in Front of a Fixed Vertical Breakwater

2020 ◽  
Vol 8 (11) ◽  
pp. 912
Author(s):  
Dimitrios N. Konispoliatis
Keyword(s):  
Water Column ◽  
Power Efficiency ◽  
Wave Train ◽  
Linear Potential ◽  
Angle Of Incidence ◽  
Oscillating Water Column ◽  
Incoming Wave ◽  
Reflected Waves ◽  
Vertical Breakwater ◽  
Linear Potential Theory

The present study explores the performance of an array of cylindrical oscillating water column (OWC) devices, having a vertical symmetry axis, placed in front of a bottom seated, surface piercing, vertical breakwater. The main goal of this study is the investigation of a possible increase in the power efficiency of an OWC array by applying, in the vicinity of the array, a barrier to the wave propagation, aiming at amplifying the scattered and reflected waves originating from the presence of the devices and the wall. To cope with the set goal, a theoretical analysis is presented in the framework of linear potential theory, based on the solution of the proper diffraction, and pressure-radiation problems in the frequency domain, using the image theory, the matched axisymmetric eigenfunction expansion formulation, and the multiple scattering approach. Numerical results are presented and discussed in terms of the expected power absorption by the OWCs comparing different array’s characteristics i.e.,: (a) angle of incidence of the incoming wave train; (b) distances from the breakwater; and (c) geometric characteristics of the different arrangements. The results show that compared to the isolated OWC array (i.e., no presence of the wall), the power efficiency of the OWCs in front of a breakwater is amplified at specific frequency ranges.

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.

Improvement of Wave Power Take-Off Performance due to the Projecting Walls for OWC Type WEC

2013 ◽  
Author(s):  
Tomoki Ikoma ◽  
Koichi Masuda ◽  
Hikaru Omori ◽  
Hiroyuki Osawa ◽  
Hisaaki Maeda
Keyword(s):  
Prediction Method ◽  
Air Pressure ◽  
Wave Power ◽  
Linear Potential ◽  
Oscillating Water Column ◽  
Air Chamber ◽  
Pressure Water ◽  
Linear Potential Theory ◽  
Hydrodynamic Behaviors ◽  
Water Elevation

This paper describes a method in order to improve the performance of the primary conversion of wave power take-off. A corresponding wave energy convertor (WEC) is an oscillating water column (OWC) type. The method of the improvement has been proposed and its usefulness has been confirmed in past researches. In the method, projecting walls were attached onto front of inlet-outlet of OWC. The prediction method of hydrodynamic behaviors for the projecting walls installed OWC type WEC is explained in the paper. The boundary element method with the Green’s function is applied and influence of air pressure and free surface within every an air-chamber was directly taken into consideration in the prediction method based on a linear potential theory. Validity of the prediction method was proved comparing with results of model experiments. Series calculations are performed with the prediction method. Behaviors of air pressure, water elevation and the efficiency of primary conversion of wave power are investigated. From the calculations, length of the projecting walls was shown to affect the efficiency of primary conversion. It was available to equip the projecting walls for the improvement in oblique waves to beam sea condition as well as head sea condition. As well as only the projecting walls, application and effects of the end walls with the slit were investigated in the paper. The end walls were very useful to improve the efficiency.

Interaction of Waves With Steady Intake/Discharge Flow Emanating From a 3-D Body

2007 ◽  
Author(s):  
Bala Padmanabhan ◽  
R. Cengiz Ertekin
Keyword(s):  
Steady Flow ◽  
Surface Condition ◽  
Linear Potential ◽  
Intake Rate ◽  
Mooring Lines ◽  
Incoming Wave ◽  
Total Potential ◽  
Warm Surface Water ◽  
Linear Potential Theory ◽  
Steady Potential

It has been proposed that the warm surface-water intake pipes distributed around an OTEC plant can generate adequate momentum to globally position a platform to overcome the second-order drift forces, thereby eliminating the need for additional power for thrusters or for mooring lines. It is evident that if the intake rate of the flow is high, there will be interaction among the locally created steady flow due to the intake, the incoming wave and the ensuing platform motions. In this work, we address such concerns by developing a linear theory for obtaining the motions (in the presence of incoming waves) of arbitrary 3-D bodies from which there is a steady intake/discharge. The boundary-value problem is formulated within the assumption of linear potential theory by decomposing the total potential into oscillatory and steady components. The steady potential is further decomposed into double-model and perturbation potentials. The time harmonic potential is coupled with the steady potential through the free-surface condition. The potentials are obtained using the quadratic boundary-element method. The effect of the steady flow on hydrodynamic force coefficients and RAOs are studied.

Wave power extraction from an oscillating water column at the tip of a breakwater

2009 ◽  
Vol 626 ◽  
pp. 395-414 ◽  
Author(s):  
HERVÉ MARTINS-RIVAS ◽  
CHIANG C. MEI
Keyword(s):  
Water Column ◽  
Angle Of Incidence ◽  
Oscillating Water Column ◽  
Sea Waves ◽  
Power Extraction ◽  
Grid Connection ◽  
Simple Geometry ◽  
Construction Operation ◽  
The Waves ◽  
Extracted Power

To reduce the costs of construction, operation, maintenance, energy storage and grid connection, some devices for extracting energy from sea waves are likely to be installed on the coast. We study theoretically a single oscillating water column (OWC) installed at the tip of a long and thin breakwater. The linearized problems of radiation and scattering for a hollow cylinder with an open bottom are then solved by the usual method of eigenfunction expansions and integral equations. Since a thin breakwater is the limit of a wedge, an exact solution for the diffraction by a solid cylinder at the tip of a wedge is derived to facilitate the analysis. Following Sarmento & Falcão (J. Fluid Mech., vol. 150, 1985, pp. 467–485), power takeoff by Wells turbines is modelled by including air compressibility in the chamber above the water surface. The effects of air compressibility on the extraction efficiency is studied. It is shown that for this simple geometry the angle of incidence affects the waves outside the structure but not the extracted power.

scholarly journals Performance of an U-Shaped Oscillating Water Column Wave Energy Converter Device under Oblique Incident Waves

Fluids ◽  
2021 ◽  
Vol 6 (4) ◽  
pp. 137
Author(s):  
Kshma Trivedi ◽  
Santanu Koley ◽  
Kottala Panduranga
Keyword(s):  
Water Column ◽  
Structural Parameters ◽  
Physical Parameters ◽  
Front Wall ◽  
Angle Of Incidence ◽  
Oscillating Water Column ◽  
Energy Converter ◽  
Chamber Length ◽  
Wide Range ◽  
Incident Waves

The present study deals with the performance of an U-shaped oscillating water column device under the action of oblique incident waves. To solve the associated boundary value problem, the dual boundary element method (DBEM) is used. Various physical parameters associated with the U-shaped OWC device, such as the radiation susceptance and conductance coefficients, and the hydrodynamic efficiency, are analyzed for a wide range of wave and structural parameters. The study reveals that the resonance in the efficiency curve occurs for smaller values of wavenumber with an increase in chamber length, submergence depth of the front wall and opening duct, and width of the opening duct. It is observed that with appropriate combinations of the angle of incidence and incident wavenumber, more than 90% efficiency in the U-shaped OWC device can be achieved.

scholarly journals Elastic oscillations of water column in the 2003 Tokachi-oki tsunami source: in-situ measurements and 3-D numerical modelling

2007 ◽  
Vol 7 (2) ◽  
pp. 243-249 ◽  
Author(s):  
M. A. Nosov ◽  
S. V. Kolesov
Keyword(s):  
Water Column ◽  
Low Frequency ◽  
Tsunami Source ◽  
Compressible Medium ◽  
Linear Potential ◽  
Essential Difference ◽  
Bottom Pressure ◽  
Spectral Maximum ◽  
Linear Potential Theory

Abstract. During the 2003 Tokachi-Oki tsunamigenic earthquake the real-time JAMSTEC observatory obtained records which provided a unique opportunity to have a look deep inside the tsunami source. Considering water column as a compressible medium we processed the bottom pressure records in order to estimate amplitude, duration and velocity of bottom displacement. Spectral analysis of the records revealed a clear manifestation of the low-frequency elastic oscillations of water column. We also presented 3-D finite-difference numerical model developed in the framework of linear potential theory of ideal compressible fluid to better understand dynamical processes in the tsunami source. The model reproduces position of the main spectral maximum rather correctly. However, due to neglecting of crust elasticity and to lack of exact knowledge of spatiotemporal laws of bottom motion, there is an essential difference between in-situ observed and computed spectra.

Interaction of Waves With a Steady Intake/Discharge Flow Emanating From a 3D Body

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Bala Padmanabhan ◽  
R. Cengiz Ertekin
Keyword(s):  
Steady Flow ◽  
Surface Condition ◽  
Linear Potential ◽  
Intake Rate ◽  
Mooring Lines ◽  
Incoming Wave ◽  
Total Potential ◽  
Warm Surface Water ◽  
Linear Potential Theory ◽  
Steady Potential

It has been proposed that the warm surface-water intake pipes distributed around an OTEC plant can generate adequate momentum to globally position a platform to overcome the second-order drift forces, thereby eliminating the need for additional power for thrusters or for mooring lines. It is evident that if the intake rate of the flow is high, there will be interaction among the locally created steady flow due to the intake, the incoming wave, and the ensuing platform motions. In this work, we address such concerns by developing a linear theory for obtaining the motions (in the presence of incoming waves) of arbitrary 3D bodies from which there is a steady intake/discharge. The boundary-value problem is formulated within the assumption of the linear potential theory by decomposing the total potential into oscillatory and steady components. The steady potential is further decomposed into double-model and perturbation potentials. The time harmonic potential is coupled with the steady potential through the free-surface condition. The potentials are obtained using the quadratic boundary-element method. The effect of the steady flow on hydrodynamic force coefficients and response amplitude operators is studied.

Water waves in shallow channels of rapidly varying depth

1992 ◽  
Vol 241 ◽  
pp. 311-332 ◽  
Author(s):  
A. Nachbin ◽  
G. C. Papanicolaou
Keyword(s):  
Shallow Water Equations ◽  
Water Waves ◽  
Water Wave ◽  
Wave Equations ◽  
Linear Potential ◽  
Reflected Waves ◽  
Time Harmonic ◽  
Linear Potential Theory ◽  
Vertical Scales ◽  
Good Agreement

We analyse the linear water-wave equations for shallow channels with arbitrary rapidly varying bottoms. We develop a theory for reflected waves based on an asymptotic analysis for stochastic differential equations when both the horizontal and vertical scales of the bottom variations are comparable to the depth but small compared to a typical wavelength so the shallow water equations cannot be used. We use the full, linear potential theory and study the reflection–transmission problem for time-harmonic (monochromatic) and pulse-shaped disturbances. For the monochromatic waves we give a formula for the expected value of the transmission coefficient which depends on depth and on the spectral density of the O(1) random depth perturbations. For the pulse problem we give an explicit formula for the correlation function of the reflection process. We compare our theory with numerical results produced using the boundary-element method. We consider several realizations of the bottom profile, let a Gaussian-shaped disturbance propagate over each topography sampled and record the reflected signal for each realization. Our numerical experiments produced reflected waves whose statistics are in good agreement with the theory.

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