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IMPROVEMENT OF WAVE POWER ECONOMY BY TERMINATOR BACKWARD BENT DUCT BUOY WITH CYLINDER DUCT
Y. Masuda1, A. Thakker2, T. Lewis3 and Xi. Liang4
1The Pacific Society
JAPAN
2Wave Energy Research Team, University of Limerick, IRELAND
3University of Cork, IRELAND
4Guangzhou Institute of Energy Conversion
Chinese Science Academy, CHINA
ABSTRACT
It is commonly established that wave power has a higher power density than wind power. The wave energy power generation device which makes use of air turbine was developed from navigational buoy and from test of Kaimei.
A new device "Backward Bent Duct Buoy" developed and was found that conversion efficiency was ten times greater that found from Kaimei. Also, the mooring force was significantly reduced. It was found from the water tank test, based on single float, that terminator BBDB can absorb wave power in wide width of wave front. Test on two and three floats terminator were conducted. Based on the results, wave power generator cost in open sea was estimated to be 10 Euro Cent in high power wave density wave sites, such as Ireland (60 KW/m) by 1:36 scale three floats terminator BBDB model. Also, it was estimated the cost to be 15 Cent Euro in low power wave density, such as Japan (10 KW/m) by 1:25 scale model.
CHARACTERISTIC OF WAVE POWER
Solar power (150 watts/square meter) is highly concentrated to wave power through wind blow on wide sea surface, and it is transmitted as swell from far distant area. Table 1 shows wind and wave conditions with fully developed sea state.
Table 1. Comparison of wind power and wave power by wind speed
| (Wind speed U m/s) |
(Wave height Hs m) |
(Wave period Second) |
(Wave Power KW/m) |
(Wind Power KW/square meter) |
| 5.1 |
0.55 |
3.3 |
5 |
0.08 |
| 10.3 |
2.3 |
6.6 |
16 |
0.67 |
| 15.4 |
5.0 |
9.9 |
120.2 |
2.3 |
| 20.6 |
9.0 |
13.2 |
520 |
5.4 |
| 25.7 |
14.0 |
16.5 |
1600 |
10.0 |
|
In the case of 15 m/s wind speed, wave power through 1 m width is equal to solar power of 500 square meters, and wind power of 50 square meters. Wind power is proportional to wind speed cubed. While fully developed wave power is to wind speed raised to the fifth Power. It is evident that wave power concentrates wind power in dramatic proportions. Therefore use of wave power will be a much better way than solar or wind usage.
Wave power density in the world is shown in Figure 1. High wave power such as 60 KW/m is reported in Ireland, low wave power such as 10 KW/m is reported in Japan and middle wave power such as 20 KW/m is reported in many islands including Hawaii. It is desired to generate electric power economically in not only high wave power areas (60 KW/m. Ireland), but also in low wave power area (10 KW/m such as Japan).
Figure 1. Wave power power distribution in the world
(produced by USA National Climate Center)
VARIOUS WAVEPOWER GENERATOR
There have been various wave power devices studied: the Oscillating Water Column (OWC) with floating buoy (Fig.2), Center pipe Buoy (Fig.3) Kaimei Buoy (80m long, 12m wide.)
Figure 2. Center pipe Buoy
Figure 3. Ship shape Kaimei Buoy
Figure 4. Original Single Float BBDB Model
Kaimei sea test was conducted at Yura Japan Sea from 1976 to 1984. Safety and long life of wave power device were confirmed, but conversion efficiency from wave power to air output was not good enough. In order to improve the efficiency, Backward Bent Duct Buoy (BBDB) was proposed. As shown in Figure 4, BBDB has an air chamber in the bow, and the duct is bent to backward, it opens to the stern. Air output per the same area of air chamber improved power ten times higher than Kaimei. The Buoy length was decreased to 30%, and mooring force was decreased significantly by function of oscillating water in the bent duct.
Mighty Whale (Fig.5) is another type that has Frontward Bent Duct. It was tested by JAMSTEC for the past four years on the Pacific side of Japan. This buoy is 50 m long and 30 m wide. The test by JAMSTEC will finish soon
At this time a 200 KW project named B2D2 (same as BBDB) started in Ireland by Dr Tony Lewis of Cork University. We wish to support this Ireland's test. After this single BBDB study, Terminator BBDB will be studied to use wider width of wave front.
Figure 5. Mighty Whale
CHARACTERISTIC OF OPEN SEA WAVE
Open sea waves are irregular waves. Let's call 1/3 of the average highest significant waves Hs. We observe that Hs and wavelengths L have characteristics constant Hs/L. Wave scatter diagram from the Japan Sea and North Atlantic is shown in Figures 6 and 7. Highest wave is distributed in line of Hs/L=1/20 by dotted line. Average power wave is distributed in line of Hs/L=1/40 by solid line. It is a very important wave characteristic that average power wave in Figures 6 and 7 are same. These are the basic wave characteristics in most of open seas.
Figure 6. Wave Scatter diagram of Japan Sea (Yura)
Figure 7. Wave Scatter diagram of North Atlantic
MODEL TEST
BBDB model tests were conducted in Japan, China, Ireland and India. Chinese model tests were two years ago.
Figure 8. The floating body model 3-3
Figure 9. Twin connection Floating body model
Figure 10. Trinity connection floating body model
Figure 11. Middle model 3-3
Figure 12. Small model 3-3
Table 2. Performance of Chinese model's optimal response point to peak periods
only
| Model plan |
Code |
Ho(m) |
Tpeak(S) |
Hi(m) |
?P
mmAq |
NWatts |
Q
cm3/s |
Hi/Ho |
?P/H0 |
Eff(%) |
Effave(%) |
| Model 3-3 |
1-1 |
0.1 |
1.25 |
0.136 |
38.4 |
6.342 |
16.2 |
1.36 |
0.384 |
108.9 |
|
| Middle Model 3-3 |
M1-1 |
0.1 |
1.1 |
0.113 |
37.2 |
4.787 |
10.01 |
1.13 |
0.372 |
106 |
|
| Small Model 3-3 |
S1-1 |
0.1 |
0.96 |
0.1192 |
37.7 |
3,247 |
7,477 |
1.192 |
0.377 |
102 |
| Twin Connection Model 3-3 |
2-1-1 |
0.1 |
1.25 |
0.1196 |
36.1 |
5.895 |
14.180 |
1.196 |
0.361 |
92.5 |
93.85 |
| 2-1-2 |
0.1186 |
41.1 |
6.066 |
14.065 |
1.185 |
0.411 |
95.2 |
| Twin Connection Model 3-3 |
2-3-1 |
0.1 |
1.25 |
0.1234 |
37.6 |
6.515 |
14.695 |
1.234 |
0.376 |
101 |
103 |
| 2-3-2 |
7 |
0.1019 |
42.2 |
6.741 |
14.364 |
1.019 |
0.422 |
105 |
| Twin Connection Model 3-3 |
2-4-1 |
0.1 |
1.25 |
0.1329 |
35.5 |
6.239 |
15.575 |
1.329 |
0.355 |
97.9 |
|
| 2-4-2 |
0.1167 |
39.6 |
7.575 |
16.662 |
1.167 |
0.396 |
118.8 |
| Three Connection Model 3-3 |
3-1-1 |
0.1 |
1.25
|
0.1134 |
38.9 |
6.151 |
13.708 |
1.134 |
0.389 |
95.9 |
89.4 |
| 3-1-2 |
7 |
0.0939 |
38.2 |
5.836 |
13.462 |
0.939 |
0.382 |
91 |
| 3-1-3 |
|
0.0981 |
32.9 |
5.213 |
13.571 |
0.981 |
0.329 |
81.3 |
| Three Connection Model 3-3 |
3-3-1 |
0.1 |
1.24
|
0.1174 |
35.9 |
5.905 |
14.341 |
1.174 |
0.359 |
93.2 |
95.17 |
| 3-3-2 |
3 |
0.1028 |
36.8 |
6.564 |
17.165 |
1.028 |
0,368 |
103.6 |
| 3-3-3 |
|
0.1032 |
33.5 |
5.623 |
14.349 |
1.032 |
0.335 |
88.7 |
| Three Connection Model 3-3 |
3-4-1 |
0.1 |
1.25 |
0.1296 |
39 |
6.998 |
15.289 |
1.296 |
0.39 |
109.8 |
104.5 |
| 3-4-2 |
0.1954 |
38.8 |
7.069 |
14.944 |
1.054 |
0.388 |
110.9 |
| 3-4-3 |
0.1093 |
31.8 |
5.915 |
15.333 |
1.093 |
0.318 |
92.8 |
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