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Research Papers: Ocean Renewable Energy

Improvement of Performance of Wave Power Conversion Due to the Projecting Walls for Oscillating Water Column Type Wave Energy Converter

[+] Author and Article Information
Tomoki Ikoma

Department of Oceanic Architecture
and Engineering,
College of Science and Technology,
Nihon University,
7-24-1 Narashinodai,
Funabashi, Chiba 274-8501, Japan
e-mail: ikoma.tomoki@nihon-u.ac.jp

Koichi Masuda, Hisaaki Maeda

Department of Oceanic Architecture
and Engineering,
College of Science and Technology,
Nihon University,
7-24-1 Narashinodai,
Funabashi, Chiba 274-8501, Japan

Hikaru Omori

IHI Scube Co., Ltd.,
3-1-1 Toyosu, Koto-ku,
Tokyo 135-0061, Japan

Hiroyuki Osawa

Japan Agency for Marine-Earth Science
and Technology (JAMSTEC),
2-15 Natsushima-cho,
Yokosuka, Kanagawa 237-0061, Japan

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received November 6, 2013; final manuscript received December 2, 2015; published online February 24, 2016. Assoc. Editor: Hideyuki Suzuki.

J. Offshore Mech. Arct. Eng 138(2), 021902 (Feb 24, 2016) (10 pages) Paper No: OMAE-13-1105; doi: 10.1115/1.4032603 History: Received November 06, 2013; Revised December 02, 2015

This paper describes a method to improve the performance of primary conversion of wave power takeoff. The wave energy converter (WEC) used here was of oscillating water column (OWC) type. This method for improvement has been already proposed in past research and its usefulness has been confirmed. It involves projecting walls (PWs) being attached to the front of the inlet–outlet of the OWC. The prediction method of hydrodynamic behaviors for the OWC type WEC with PWs installed is explained in this paper. The boundary element method with the Green's function is applied, and influence of air pressure and free surface within every air-chamber was directly taken into consideration in the prediction method based on linear potential theory. Validity of the prediction method was proved by comparing the results with the 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 were investigated. From the calculations, length of the PWs was shown to affect the efficiency of primary conversion. It was possible to equip the PWs so as to enable improvements in oblique waves to beam sea conditions as well as in the head sea conditions. This paper examined not only the PWs but also the application and effects of the end walls (EWs) with the slit. The EWs were very useful to improve the efficiency.

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References

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Ikoma, T. , Osawa, H. , Masuda, K. , and Maeda, H. , 2012, “ A Prediction Method and Efficiency of Primary Conversion of OWC Type WEC With Projecting Walls,” OCENS2012 IEEE YEOSU Conference and Exhibition, Paper No. 120113-034.
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Ikoma, T. , Masuda, K. , Rheem, C. K. , Maeda, H. , and Watanabe, Y. , 2012, “ Primary Conversion Efficiency of OWC Type WECs Installed on a Large Floating Structure,” ASME Paper No. OMAE2012-83337.

Figures

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Fig. 1

Conceptual illustration of an OWC type WEC with PWs

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Fig. 2

Coordinate system: SH—hull surface, SF—free water surface, SFA—free surface of OWC, and SB—sea bottom

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Fig. 3

Experimental model plan and setup system: (a) horizontal plan and (b) section plan (unit: mm)

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Fig. 4

Comparison of mean water levels

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Fig. 5

Comparison of air pressure

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Fig. 6

Comparison of efficiency of primary conversion

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Fig. 7

Comparison of primary efficiency of OWC models in head seas with or without PWs attached (0 deg)

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Fig. 8

Comparison of primary efficiency of OWC models in oblique waves of 45 deg with or without PWs attached

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Fig. 9

Comparison of primary efficiency of OWC models in beam seas (90 deg) with or without PWs attached

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Fig. 10

Model setup for calculations in shallower water: (a) horizontal plan and (b) section plan (unit: mm)

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Fig. 11

Variation of primary conversion efficiency due to length of PWs

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Fig. 12

Effect of damping coefficient αs on efficiency with LP = 7 m

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Fig. 13

Variation of efficiency due to incident wave angle with LP = 7 m

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Fig. 14

Model setup for calculations of model in shallow water with EWs attached

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Fig. 21

Comparison of water elevations at P1 and P2 to time of t seconds in case of PW length of 4.0 m with EW of 3.0 m slit at λ/La = 5

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Fig. 20

Comparison of water elevations at P1 and P2 in case of PW length of 4.0 m with EW of 3.0 m slit at λ/La = 5

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Fig. 19

Variation of water elevation to time of t seconds in case of PW length 7.0 m without EW at λ/La = 5

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Fig. 18

Comparison of water elevations at P1 and P2 in case of PW length of 7.0 m without EW at λ/La = 5

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Fig. 17

Variation of efficiency due to difference of incident wave angle with BS = 3 m

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Fig. 16

Variation of efficiency due to difference of slit width

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Fig. 15

Comparison of efficiency of EWs attached type and not attached type

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