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Research Papers: Energy Systems Analysis

# Maximum Wave Energy Conversion by Two Interconnected Floaters

[+] Author and Article Information
Siming Zheng

State Key Laboratory of
Hydroscience and Engineering,
Tsinghua University,
Beijing 100084, China
e-mail: zhengsm11@mails.tsinghua.edu.cn

Yongliang Zhang

State Key Laboratory of
Hydroscience and Engineering,
Tsinghua University,
Beijing 100084, China
e-mail: yongliangzhang@tsinghua.edu.cn

Wanan Sheng

Marine Renewable Energy Ireland,
University College Cork,
Cork P43 C573, Ireland
e-mail: w.sheng@ucc.ie

1Corresponding author.

Contributed by the Advanced Energy Systems Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received August 24, 2015; final manuscript received January 10, 2016; published online March 11, 2016. Assoc. Editor: Abel Hernandez-Guerrero.

J. Energy Resour. Technol 138(3), 032004 (Mar 11, 2016) (11 pages) Paper No: JERT-15-1318; doi: 10.1115/1.4032793 History: Received August 24, 2015; Revised January 10, 2016

## Abstract

Interconnected floaters could use relative rotations around connection joints to drive a power take-off (PTO) system, such that the ocean wave energy can be converted into a useful energy. In this paper, our attention is on the PTO optimization for the interconnected floaters. A fully linear dynamic system, including the linear hydrodynamics of the interconnected floaters and a linear PTO system, is considered. Under assumptions of linear theory, we present a mathematical model for evaluating the maximum wave energy conversion of two interconnected floaters based on the three-dimensional wave radiation–diffraction theory. The model is validated by comparison of the present results with the published data, and there is a good agreement. The model can be employed to calculate the maximum power absorbed by the interconnected floaters under motion constraints due to the restraints of pump stroke or/and collision problem between the floaters. The influence of wave frequency, PTO system, floater rotary inertia radius, and motion constraints on the power capture capability of the two interconnected floaters is also examined. It can be concluded that enlarging the rotary inertia of each floater by using mass nonuniform distribution can be seen as an alternative way of adding PTO inertia. The maximum relative power capture width of the two interconnected floaters with optimized PTO system under constraints is much smaller than that without any motion constraints for long waves.

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## References

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## Figures

Fig. 1

Schematic of two hinged floaters on the sea: (a) top view and (b) side view

Fig. 2

Variation of ηmax and c¯opt with r¯ for d¯  = 1.0, T¯  = 3.5, and k¯  =  I¯  = 0

Fig. 3

Variation of ηmax and c¯opt with kL for different k¯ and I¯ : (a) ηmax and (b) c¯opt

Fig. 4

Variation of pitch velocity phase with kL for different k¯ and I¯ (broken lines) and variation of pitch excitation moment phase with kL (solid line): (a) fore floater and (b) aft floater

Fig. 5

Variation of ηmax, c¯opt, and x¯opt with kL for different I¯ (marks) and different r¯ (lines), k¯  = 0: (a) ηmax, (b) c¯opt, and (c) x¯opt

Fig. 6

Variation of pitch velocity phase with kL for different I¯ (marks) and different r¯ (broke lines) and variation of pitch excitation moment phase with kL (solid line), k¯  = 0: (a) fore floater and (b) aft floater

Fig. 7

Variation of ηmax and c¯opt with r¯ for T¯=2.8,  3.5,  and 4.2, d¯  = 1.0, and k¯  =  I¯  = 0

Fig. 8

Variation of ηmax,c, c¯opt,c, and x¯opt,c with kL for A/L = 1/20, k¯  = 0, I¯  = 0, and r¯  = 1.4 with different upper limits δ

Fig. 9

Variation of ηMAX, c¯OPT, k¯OPT, I¯OPT, and x¯OPT with kL for the floaters with different floater rotary inertia r¯  = 0.58, 1.1, and 1.4

Fig. 10

Variation of ηMAX,c, c¯OPT,c, and x¯OPT,c with kL for A/L = 1/20, k¯  = 0, I¯  = 0, and r¯  = 1.4 and five upper limits δ

Fig. 11

Comparison of optimized power capture widths using different principles

Fig. 12

Comparison of ηmax with optimized cPTO and η with specified cPTO for k¯  =  I¯  = 0

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