Kazuyoshi Kihara

Utilization of Wave Dissipating Caissons as an OWC Type Wave Energy Convertor

Wave energy convertors (WEC) of oscillating water column (OWC) types make compressed air due to vertical movement of a part of water column, which are surrounded by some walls in water. As a result, the compressed air works to rotate an air turbine which also works for an electrical generator. If a structural system can make to move water such like a water column, a shape of a structure would not matter.Wave dissipating caissons installed in or on the existing production line can make to transfer a water wave to a flow and to reduce wave energy by making to overflow them. The caissons which can be overflowed by the water would actuate a water region vertically such like an oscillating water column system.This study investigated if we can utilize wave dissipating caissons as a WEC. Wave dissipating caissons also decrease wave energy due to passing through themselves. Even so, when an air turbine can be installed onto the caisson in order to harvest wave energy, it would be possible to produce electricity at low cost. The study conducted model experiments using the model assumed that wave dissipating double-caissons were remodelled to OWC type WECs with side walls and evaluated performance of the primary conversion of them. In addition, effects of how to arrange the number of the WECs on the primary conversion efficiency were investigated with theoretical calculations based on the linear potential theory and the possibility of utilization of wave dissipating caissons as a WEC was examined in the study.Copyright

A study on Wave Energy Absorption of Breakwater with OWC type Wave Energy Convertors

東日本大震災において原子力発電所が被災したことに より,自然エネルギーの利用が見直されている.振動水 柱型空気タービン方式(OWC型)波力発電装置は30数 年にわたる研究開発と実証試験が行われた実績があるも のの,発電コストが高いことから,開発が停滞していた. OWC型波力発電装置は,小島ら(1983)の波力発電ケ ーソンと同様,ケーソン前面に没水部が開口した空気室 を設けており,入射波によって空気室内に水塊が上下動 し,同時に空気室に設けられたノズルを通して空気流が 生じ,この空気流によって空気タービン発電機を駆動す る.この課題は,エネルギーの1次変換効率(入射した 波エネルギーと空気室内の圧力と水位変動から計算され るエネルギーの比)が,波の周期が共振周期を外れると 急減する点であった.そのため共振する周期帯を広げ, 発電出力向上を目的として,図-1に示すような法線直角 方向に突出したプロジェクティングウォール(以下, PW)と呼ぶ壁構造を空気室の前面に設置した.本研究 では,PW-OWC型の波力発電装置を取り付けたケーソン の発電効率について,中規模と大規模の水理模型実験に より検討した.

Large Scale Tests on Buoyancy-Driven Vertical Piling Breakwater with Buoyancy-Driven Piles

This report describes the results of the large scale model tests on the buoyancy-driven vertical piling breakwater by using the buoyancy-driven piles. This breakwater consists of rows of steel pip. piles and each pile consists of upper and lower steel pipes. The overall performance of this breakwater has been verified, but the relation between stress and wave power is not cleared at the part of lap joint between upper pipes and lower pipes, at which large stress may be occurred. So, the large scale model tests by using the buoyancy-driven piles were conducted. Main results of this paper are that movement of the upper pile under waves is confirmed and the relationship between the strain at the lap part and the wave power is clarified qualitatively.

Protection Performance against Tsunamis due to Buoyancy-Driven Vertical Piling Breakwater

This research investigates the protection performance against tsunami with the buoyancy- driven vertical breakwater by using the numerical simulations. Macro-Micro scale interlocked tsunami simulator named STOC (Storm surge and Tsunami simulator in Oceans and Coastal areas) has been applied to the series of simulations. Results of comparison of tsunami height in the Wakayama-shimotsu port and Fukura port due to Tokai, Tonankai and Nankai earthquakes indicates that this new breakwater decreases tsunami height and inundation area. Although the dissipating rate is depending on the position of this breakwater, the breakwater with 10% opening brings a 33% decrease in the maximum tsunami height.

A COUNTERMEASURE AGAINST LOW FREQUENCY MOTIONS OF A MOORED SHIP USING SHIELDING STRUCTURE

This paper shows a countermeasure against low frequency motions of a moored ship. It is difficult to decrease the low frequency surge motions of the ship moored by fiber ropes, because breakwater cannot prevent the entrance of low frequency components of ocean waves. Furthermore the very small damping force of surge motion interferes reducing resonance motions in the low frequency range. The shielding structure, which is close to the weather side of the ship, is prevent the flow due to the low frequency waves so it decreases the wave exciting force. Then the effect of the shielding structure is confirmed by the tank tests. Moreover, the effect of the structure, which consists of flame structure and membrane, is also confirmed. This shielding structure effectively decreases the low frequency surge motions of a moored ship.