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Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

Model Test and Numerical Simulation
for Floating Oscillating Water Column Type Wave Energy Converter with Backward Bend Duct
Shunka C. Hirao, Kentaroh Kokubun, Toshifumi Fujiwara
Offshore Advanced Technology Department, National Maritime Research InstituteNational Institute of Marine, Port and Aviation Technology

Mitaka, Tokyo, Japan

ABSTRACTF-OWC-WEC MODEL

In this paper, the kinematic dynamics of an oscillating water column
wave energy converter with backward bend duct buoy were studied. A
scaled model test and numerical simulation were conducted. The uniquepoint of the oscillating water column in the model test is that it has an
air reservoir for force similarity in the column, Moreover, the Maxwell
model that air spring effect in the column and power generation turbine
model are connected in series was applied to the numerical simulation
as a more reasonable measure. The results of the model test and thenumerical simulation showed a good agreement.

A floating oscillating water column type wave energy converter (FOWC-WEC) is one of the wave energy converter types that have beenstudied (Miyazaki, 1980 and Osawa, 2002), and the back bending ductbuoy type (BBDB) (Nagata, 2008), placed as a promising F-OWCWEC, is discussed in this paper. An F-OWC-WEC consists of an airchamber that converts wave power into air flow, a turbine that converts
the air flowing in and out of the air chamber into rotational energy, agenerator and a floater. In the BBDB, the air chamber is located on theupper side of waves and the duct for passing waves to the air chamberis connected to the lower side of waves.

KEY WORDS: oscillating water column type wave energy converter;back bend duct buoy; air reservoir; orifice; Maxwell model.

OWC physical modeling
The OWC section could be modelled as shown in Fig. 1. The
compressibility of air was treated as an air spring. The air resistance due
to an actual turbine could be simulated by an orifice in model test, by adamper in numerical simulation. The OWC section can be treated as
Maxwell model with a series of a spring and a damper in numericalsimulation.

INTRODUCTION
National Maritime Research Institute, NMRI, had been studying theanalytical method on safety assessment of floating power generation
facilities for ten years more. As a part of these studies, a backward bend
duct buoy oscillating water column type wave energy convertor (OWCWEC) was also studied in our institute. The purpose of this study is toconfirm the feasibility of model tests and numerical calculations,
including phenomena specific to an OWC-WEC. One of the uniqueparts of the OWC that has an air chamber is which is not found in otherWECs. In this study, a scale model test and numerical simulation, with
Maxwell model are carried out for a floating oscillating water column
wave energy converter, taking into account the characteristics of the airchamber (Hirao, 2016 and Kokubun, 2017). In the model test, an air
reservoir was used, giving priority to the similarity of the air force. In
the numerical simulation, the air chamber was modeled using a
Maxwell model with a spring and a damper connected in series. The
effectiveness of the model test and the numerical simulations isexamined and reported in this paper. The novelty of this paper is thatthe spring and damper coefficients of Maxwell's model were obtained
from experiments, and numerical simulations were performed using
these values.

空気
抵 Air
抗resistanceTurbineタービン

減
衰 DamperMaxwellモデル
Maxwellmodel

Orifice
オリフィス(Air hole)
（空気穴）

空Air
気
springばば
Springねね

Water
水柱
columnFig. 1 Air chamber model
The pressure change of the actual machine isand that of the modelis. The Froude's law was selected to match the ratio of inertia andgravity between the actual and the scale size. When the scale was , itmust be Eq. (1).

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