EXPECTED VALUES OF WAVE POWER ABSORPTION AROUND THE JAPANESE ISLANDS USING OWC TYPES WITH PROJECTING WALLS

PRESENTED BY SHAKKIR T (12NA30019)

Department of Ocean Engineering & Naval ArchitectureIIT Kharagpur

Tomoki IkomaDept. of Oceanic Architecture and EngineeringCollege of Science and Technology (CST),Nihon UniversityFunabashi, Chiba, Japan

Hiroyuki OsawaDept. of Oceanic Architecture and EngineeringCST, Nihon UniversityYokosuka, Kanagawa, Japan

Koichi MasudaDept. of Oceanic Architecture and EngineeringCST, Nihon UniversityFunabashi, Chiba, Japan

Hisaaki MaedaDept. of Oceanic Architecture and EngineeringCST, Nihon UniversityFunabashi, Chiba, Japan

INTRODUCTION OWC types are the most common WEC in Japan Application of projecting walls attached OWC types has been

investigated to have multiple resonance by an OWC and an artificial harbour

Previous studies confirmed that the primary efficiency increased due to effects of the walls, however, this research was under a 2D problem

This paper considers it as a 3D problem so that the model test is carried out in a wave tank.

Expected value of acquirable wave power in a year is estimated using the frequency data of ocean waves around Japan Islands

Performance improvement of the primary efficiency is quantitatively examined regarding the present devices with the artificial harbour

Oscillating Water Column (OWC)

Carried out in test basin of a Funabashi campus of Nihon University.

Basin : L = 24 m, B = 7 m, D = 1 m Regular waves with period 0.7 to 1.65 s Total 15 wave periods 2 Variation of wave height (2 cm and 4 cm) Water elevations at inlet and the interior of the harbour

are measured with wave meters in order to confirm resonance.

Pectinate wave meter within the air chamber above OWC to check volume variation

Pressure sensor to measure the pressure inside the air chamber

Load cell to measure heave force and pitch moment Current meter at the inlet to measure the water flow

MODEL EXPERIMENT - SETUP

5 Models conventional OWC type without the harbour :

1. OWC-A 2. OWC-B Projecting wall type or OWC with harbour:

3. PW-OWC A 4. PW-OWC B 5. PW-OWC AB

EXPERIMENT - MODELS

440 mm300 mm

Power of air compression due to OWC motion (averaged over a time period)

Power of Incident wave

Primary efficiency

Aw : Area of water plane of OWC T : Wave period ν(t) : Mean vertical motion of OWC P(t) : Air pressure inside OWCρ : Density of fluid g : Acceleration of gravity a : Amplitude of the incident wave, Cg : Group velocityB : Overall width of the models which is 0.44 m

PRIMARY EFFICIENCY CALCULATION

PW-OWC A PW-OWC B PW-OWC AB

OWC A OWC B

RESULTS OF EFFICIENCY OF PRIMARY CONVERSION

Primary efficiency of the harbour attached models is clearly higher

For harbour attached models efficiency doesn’t decrease in long wavelength range

The nozzle ratio values (1/200 and 1/300) were decided from the results of Ikoma et al

In case of the harbour attached models, the efficiency of a low nozzle ratio case is higher than that of a large nozzle ratio one.

Whereas in case of non harbour models, the tendency is reverse.

RESULTS OF EFFICIENCY OF PRIMARY CONVERSION

The efficiency of OWC-A is relatively good, however the efficiency decreases in long wavelength range

The decrease is inhibited by the effect of the harbour in long wavelength range.

The efficiency of the OWC-B type is not good in all of wavelength range, which is under 0.5

However, by attaching the harbour, the efficiency in wide wavelength range increases but not so much as PW-OWC A

IMPROVEMENT BY ATTACHING HARBOUR - I

The efficiency of a bad model of OWC B becomes near to a good efficiency model of OWC A when the harbour is attached.

In short wavelength range which is under λ/La<4.0, the efficiency of PW-OWC A is better than that of PW-OWC AB

In long wavelength range, the efficiency of PW-OWC AB seems better than that of PW-OWC A

IMPROVEMENT BY ATTACHING HARBOUR - II

Observation points of waves (14)

Probability of random waves at Kiyan-misaki(Okinawa)

Probability of significant wave periods

EVALUATION OF PRIMARY EFFICIENCY USING ACTUAL OCEAN WAVE DATA

The wave power W ( per unit width )can be approximately obtained as

The appearance frequency of ocean waves is now assumed as ψ(H1/3, T1/3) using the significant wave height H1/3 and the significant wave period T1/3.

The year expected value E[Wa], which is in kW/m (kilo watt per unit width), of the wave power can be expressed as follows:

Expected values of wave power in every season in an year at observation points (unit: kilo watt per unit width)

The year expected value of the acquirable wave power of the wave generation system is expressed as

Probability density function ϕ(H1/3, T1/3) can be defined as

On discretization

ESTIMATION OF YEAR EXPECTED VALUE OF POTENTIAL CAPACITY OF GENERATION POWER

EVALUATION OF HARBOUR ATTACHED OWC IN ACTUAL SEAS If experimental model assumed as 1/50 scale T=1s in

model scale corresponds to T=7s in full scale

Length of OWC = 15 m and total length = 25-30m in full scale

The performance of the harbour attached models is very good comparing with non-harbour models which are conventional OWC

Its dominance is 1.5 to 1.7 times the performance of conventional OWC types.

In both the results of 1/50 and 1/80 set, the acquirable power in case of 1/80 is larger than that in case of 1/50.

nozzle ratio: 1/300, Scale: 1/50

nozzle ratio: 1/300, Scale: 1/80

WINTER SEASONSPRING SEASON

SUMMER SEASONAUTUMN SEASON

Variation of the expectations during the four seasons is quite large

The acquirable power of the spring season is very low.

The acquirable wave power of Sakata and Wajima, in the winter season is very high but not throughout the year

In the summer the expectations of Kiyan-misaki and other areas on a pacific ocean side increase because effects of the typhoon.

The expected values on the Japanese sea side are very low in the summer.

CONCLUSIONS Effects of the artificial harbour attaching to the conventional OWC type system in order to

improve the primary efficiency was investigated.

Model experiments were carried out and the evaluation of the performance using the year expected value of the acquirable wave power were performed

Installation of the artificial harbour is very much effective in order to improve the primary efficiency of wave power absorption.

Using the fixed OWC system proposed, we can get a few kilo watts per unit width around the Japanese islands.

Whereas in case of floating systems, it is important to keep a good primary efficiency in wide wave period range for utilization of wave power on seas around the Japanese islands.

REFERENCES Hiroyuki Osawa, Yukihisa Washio, Tsuyoshi Miyazaki,Taira Hotta and Takeaki Miyazaki, “R&D

ofTechnologies of Wave Energy Application - Developmentof Offshore Floating Wave Power Device named Mighty- Whale-,” JAMSTEC, 2004.

Kazutaka Toyoda, Shuichi Nagata, and other 4 persons,“Experimental Study on Primary Energy ConversionCharacteristics of Backward Bent Duct Buoy,” J. ofJASNAOE, Vol. 6, pp.247-255, 2007.

Hisaaki Maeda, Yasufumi Onishi, Chang-Kyu Rheem,Tomoki Ikoma and other 3 persons, “Flexible Response Reduction on a Very Large Floating Structure due toOWC Wave Power Devices,” J. of the Society of Naval Architects of Japan, Vol. 188, pp.279-285, 2000.

Tomoki Ikoma, Hiroyuki Osawa and other 3 persons,“Improvement of the Primary Conversion of the OWC system by Attaching the Artificial Harbor for WavePower Absorption,” Procs. of the 21st Ocean Engineering Symposium, OES21-156, CD-ROM, 2009.

JAMSTEC, “Technical Manual for OWC Type Wave Power Devices,” 2004.

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