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Comparison of Experimental and Numerical Model Results of Oscillating Water Column System Under Regular Wave Conditions

  • Farrokh MahnamfarEmail author
  • Abdüsselam Altunkaynak
  • Yasin Abdollahzadehmoradi
Research Paper
  • 30 Downloads

Abstract

Wave energy has attracted significant attention because of its non-polluting nature, environment friendliness, low operational cost and simple maintenance procedures compared to other clean energy sources. In this study, it was attempted to optimize an oscillating water column (OWC) wave energy converter, which is constructed on a shoreline. This study proposed numerical and physical models for the optimization of the OWC-type wave energy converters. Sixty-four experimental sets were carried out by a piston-type wave maker in order to investigate the influence of wave parameters, water depth and geometry of coastal structures on the efficiency of the system. A numerical model of the experimental model sets of the OWC system was performed by a software called Flow 3D. Intersection with a water–air in the software for the determination of the free surface of a volume of fluid method is used. Kε turbulence model was used for turbulent model. The drag coefficient, surface roughness, pipe roughness and surface tension were used for calibration. It is observed that the numerical model results follow the experimental model results. The numerical and the experimental model results were compared with each other by taking into consideration the mean squared error, coefficient of determination (R2) and Nash–Sutcliffe efficiency (NSE) as performance evaluation criteria. According to the test results, the NSE value was obtained to be 0.97 and this value also shows very good agreement between numerical results and experimental results. The experimental results showed that wave parameters are strongly related to the outflow of air from the chamber, whereas the slope angle of the chamber is inversely related. Considering different water depths, the various wave series and angle of the chamber, maximum efficiency of OWC was obtained at 50 cm, wave series No. 1 and an angle of 40°, respectively.

Keywords

Wave energy Wave energy converters Experimental testing Numerical modeling Performance evaluation criteria OWC 

Abbreviations

CFD

Computational fluid dynamics

FAVOR

Fractional area/volume obstacle representation

LIMPET

Land installed marine powered energy transformer

NS

Navier–Stokes

MSE

Mean square error

NSE

Nash–Sutcliffe coefficient

OWC

Oscillating water column

RANS

Reynolds-averaged Navier–Stokes

REWEC

Resonant wave energy converter

VOF

Volume of fluid

List of Symbols

A

The cross-sectional area of the outflow air tube

Ax

Fractional area at the centers of cell faces normal to the x-direction

Ay

Fractional area at the centers of cell faces normal to the y-direction

Az

Fractional area at the centers of cell faces normal to the z-direction

C1ε, C2ε, C3ε

Constant values

D

Diameter of air outflow tube

Diff

Diffusion term

d

Water depth

E

Mean air velocity from the results of experimental model

\(\bar{E}\)

Mean of E values

e

Height of opening of the OWC front wall

F

Fraction of fluid in each cell

fx

Viscous acceleration in x-direction

fy

Viscous acceleration in y-direction

fz

Viscous acceleration in z-direction

Gk

Buoyancy production term

Gx

Body accelerations in the x-direction

Gy

Body accelerations in the y-direction

Gz

Body accelerations in the z-direction

H

Incident wave height

k

Kinetic energy of turbulent

L

Wavelength

N

Mean air velocity from the results of numerical model

\(\mathop N\limits^{ - }\)

Mean of N values

P

Pressure

Pk

Turbulent kinetic energy production

Powc

Power of output air

Q

Air discharge

R2

Coefficient of determination

Re

Reynolds number

RSOR

Mass source

T

Wave period

t

Time

u

Velocity component in x-direction

V

Velocity of air flow

v

Velocity component in y-direction

Vf

Volumetric fluid fraction in each cell

w

Velocity component in z-direction

X

Front wall length of oscillating water column system

x

Coordinate in x-direction

xmax

Downstream boundary condition

xmin

Upstream boundary condition

y

Coordinate in y-direction

Z

Elevation head

z

Coordinate in z-direction (m)

zmax

Upper limit of the solution

zmin

Base wall

α

Front wall angle of oscillating water column system

γ

Specific weight

ΔP

Differential pressure

ε

Dissipation rate of turbulent kinetic energy (kε model)

µa

Dynamic viscosity of air

ρ

Density

ρa

Density of air

ρw

Density of water

ω

Specific dissipation rate of turbulent kinetic energy (k − ω model)

Notes

Acknowledgements

This research was funded by TUBITAK (The Turkish National Science and Technology Foundation) under the Grant Number 112M413. The authors are grateful to TUBITAK for supporting our study.

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Copyright information

© Shiraz University 2019

Authors and Affiliations

  1. 1.Faculty of Engineering, Department of Civil EngineeringSakarya UniversityAdapazarıTurkey
  2. 2.Faculty of Civil Engineering, Hydraulics DivisionIstanbul Technical UniversityMaslak, IstanbulTurkey
  3. 3.Faculty of Engineering and ArchitectureIstanbul Gelisim UniversityAvcilar, IstanbulTurkey

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