Frequency Domain Analysis on Primary Conversion Efficiency of a Floating OWC-type Wave Energy Converter

Nagata, Shinji; Toyota, Kazutaka; Imai, Yasutaka; Setoguchi, Toshiaki; Nakagawa, Hiroyuki

doi:10.2534/jjasnaoe.14.123

Cited by 9 publications

(6 citation statements)

References 8 publications

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“…Frequency-domain analysis is a widely used method for wave-structure interactions and, in the method, the dynamic system is assumed to be fully linear: the governing equation is the linear Laplace equation (based on the incompressible potential flows); the body and seabed boundary conditions are linear; and the free-surface condition can be linearized for practical applications. Although the assumptions are strict, the frequencydomain analysis could provide reliable and accurate assessments for the hydrodynamic parameters and responses, such as the added mass, the radiation-damping coefficients, the wave-excitation forces, and the response amplitude operators (RAOs) [1][2][3][4][5], and, in some cases, it can be even extended to hydro-elastic analysis [6] and the elastic wave-energy converters (WECs) [7,8]. For its applications in wave-energy converters, the conventional frequency-domain analysis may provide an accurate calculation for the resonance frequency/period of the device, which is generally regarded as the most important parameter for wave-energy converters, since most wave-energy converters would be ideally optimized to have resonance with the wave for efficient energy extraction from the waves [9,10].…”

Section: Introductionmentioning

confidence: 99%

Time-Domain Implementation and Analyses of Multi-Motion Modes of Floating Structures

Sheng

Tapoglou

et al. 2022

JMSE

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The study of wave-structure interactions involving nonlinear forces would often make use of the popular hybrid frequency–time domain method. In the hybrid method, the frequency-domain analysis could firstly provide the reliable and accurate dynamic parameters and responses; then these parameters and responses are transformed to the parameters to establishing the basic time-domain equation. Additionally, with the addition of the required linear and nonlinear forces, the time-domain analysis can be used to solve for the practical problems. However, the transformation from the frequency domain to the time domain is not straightforward, and the implementation of the time-domain equation could become increasingly complicated when different modes of motion are coupled. This research presents a systematic introduction on how to implement the time-domain analysis for floating structures, including the parameter transformations from the frequency domain to the time domain, and the methods for calculating and approximating the impulse functions and the fluid-memory effects, with special attention being paid to the coupling terms among the different motion modes, and the correctness of the time-domain-equation implementation. The main purpose of this article is to provide relevant information for those who wish to build their own time-domain analyses with the open-source hydrodynamic analysis packages, although commercial packages are available for time-domain analyses.

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Section: Introductionmentioning

confidence: 99%

Time-Domain Implementation and Analyses of Multi-Motion Modes of Floating Structures

Sheng

Tapoglou

et al. 2022

JMSE

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“…The numerical results are compared with those of a single-chamber OWC (Fig.1). This paper presents the results of 2D numerical analysis in frequency domain for the OWCs by Nagata et al's 5) method. The major physical quantities examined are the primary conversion efficiency, EFF; the reflection coefficient, K R ; and the air pressure in the air-chambers, p/w 0 H; where the pressure p is nondimensionalized using the specific weight of water, w 0 , and the incident wave height, H. The numerical model is validated by comparing with the experimental data of one-chamber OWC by Ojima et al 6),7)…”

Section: Introductionmentioning

confidence: 99%

A Numerical Study on Multi-Chamber Oscillating Water Columns

et al. 2015

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A two-dimensional frequency-domain numerical analysis on the primary conversion efficiency of multi-chamber Oscillating Water Columns (OWCs) is presented. The numerical model is developed by combining the hydrodynamics of the interaction between the wave and the OWC and the thermodynamics of the air chambers. The wave-induced force is calculated using the boundary element method based on the velocity potential theory. The air flow is studied using mass and energy conservation equations and an equation of state. The air pressure in the air chambers, the reflection coefficient, and the primary conversion efficiency of each of the chambers, as well as the combined efficiency, are evaluated using the boundary integral equations. In addition, the behavior of these physical quantities, along with the variations in the nozzle ratio, the relative water depth, the depth of the curtain wall, and the width of the front-chamber are investigated using the calculated results.

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“…In all these studies, incompressible air is assumed. More recently, FIG Nagata et al 10 divided the whole flow region into two coupled regions: one region represents the external flow field, and the other the flow field in the OWC water column. These two regions are coupled via their sharing surface to form a full dynamic system.…”

Section: Introductionmentioning

confidence: 99%

On thermodynamics in the primary power conversion of oscillating water column wave energy converters

Sheng¹,

Alcorn²,

Lewis³

2013

Journal of Renewable and Sustainable Energy

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Type of publicationArticle (peer-reviewed) The paper presents an investigation to the thermodynamics of the air flow in the air chamber for the oscillating water column wave energy converters, in which the oscillating water surface in the water column pressurizes or de-pressurises the air in the chamber. To study the thermodynamics and the compressibility of the air in the chamber, a method is developed in this research: the power take-off is replaced with an accepted semi-empirical relationship between the air flow rate and the oscillating water column chamber pressure, and the thermodynamic process is simplified as an isentropic process. This facilitates the use of a direct expression for the work done on the power take-off by the flowing air and the generation of a single differential equation that defines the thermodynamic process occurring inside the air chamber. Solving the differential equation, the chamber pressure can be obtained if the interior water surface motion is known or the chamber volume (thus the interior water surface motion) if the chamber pressure is known. As a result, the effects of the air compressibility can be studied. Examples given in the paper have shown the compressibility, and its effects on the power losses for large oscillating water column devices. V C 2013 American Institute of Physics.

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Frequency Domain Analysis on Primary Conversion Efficiency of a Floating OWC-type Wave Energy Converter

Cited by 9 publications

References 8 publications

Time-Domain Implementation and Analyses of Multi-Motion Modes of Floating Structures

Time-Domain Implementation and Analyses of Multi-Motion Modes of Floating Structures

A Numerical Study on Multi-Chamber Oscillating Water Columns

On thermodynamics in the primary power conversion of oscillating water column wave energy converters

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