Fukushima Floating offshore Wind Farm Demonstration Project

Fukushima Floating Offshore met mast data

Schematic of substation

Outline of the floating offshore met mast

Category Fukushima floating offshore met mast
Meteorology/ Oceanography Wind speed, Wind direction, Wave height, Wave period, Current speed
Water depth 120m
Distance from shore 20km
Tower height 60m
Draft for floater 50m
Installation date 2013.11
Commencement date 2014.9

Observation parameters

Category Description Measurement device Measurement item Measurement location
Metrological Wind 9 Cup anemometers Wind speed
Wind direction
Wind speed, Wind direction
40,50,60m
60m~310m(12 layer)
10 Wind vanes
1 Doppler rider
Oceanography Wave 1 * Wave Buoy Wave height, Wave period** Offshore distance 20km,
near Fukushima Mirai
1 Wave meter Wave height, Wave period** Sea surface
Current 1 Wave meter Current speed,
Current direction
Water depth 6.5m, 8.5m,
11.0m
1 ADCP Water depth 5.5m, 7.6m,
11.8m

* Regarding installation of measurement device, wave buoy is located adjacent to “Fuikushima Mirai” about 20Km offshore from the Fukushima coast and 
other equipment is installed on the substation. 
					** Statistical significant wave height (H1/3) and significant wave period (T1/3) are calculated from the wave meter. Spectral significant wave height (Hs) and spectral significant wave period (Ts), which is equal to energy period Tm-1,0 , are calculated from wave spectral measured by the wave buoy.

1. Wind Data (January ~ December 2015)

1 : Wind speed (one year)

Constant 2015
1 2 3 4 5 6 7 8 9 10 11 12 year
Weibull distribution
Shape parameter (k)
1.85 1.67 1.9 2.05 2.1 2.46 1.47 2.02 1.93 1.55 2.29 2.07 1.88
Weibull distribution
Scale parameter (c)
9.07 8.71 8.55 9.15 8.54 7.95 6.24 7.25 6.92 8.08 8.29 8.38 8.12

Comment

If wind speed frequency distribution at 60m height is approximated by Weibull distribution, the shape parameter (k) is 1.88 and the scale parameter(c) is 8.12.

2:Wind rose (one year)

Comment

The dominant wind direction at 60m height is north-south. Wind blow from SSW direction is 12.9% of the time and from NNW direction is 12.6% of the time.

3:Vertical profile of Mean wind speed (one year)

Commentary

Mean wind speed profile normalized by mean wind at 40m height has the shear exponent of 0.1. The profile shows good agreement with the past observations data.

4:Turbulence intensity distribution for each wind speed

Comment

The turbulence intensity (90 percentile value) at 60m height is within C class of IEC category.

5:Mean wind speed and data availability

Description Measurement
height[m]
2015 Annualmean
wind speed
Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sept. Oct. Nov. Dec.
Mean wind
speed[m/s]
60m 8.1 8.0 7.5 8.1 7.4 6.8 5.9 6.3 6.2 7.5 7.2 7.4 7.2
Data acquisition
rate[%]
85.7 84.4 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 97.5

Comment

Monthly mean wind speed at 60m height is between 5.9m/s and 8.1m/s and annual mean wind speed is 7.2m/s. Mean wind speed from Jun. to Sept. is low and that from October to May is high. The mean wind speed of January, February and April exceeds 8m/s.

6:Monthly averaged turbulence intensity

Description Measurement
height
2015 Annualmean
value
Jan. Feb. Mar. Apr. May. Jun. Jul. Aug. Sept. Oct. Nov. Dec.
Mean turbulence
intensity[%]
60m
[All direction]
10.9 9.9 9.6 5.7 7.3 7.1 8.7 8.2 8.4 9.4 9.4 11.4 8.8

Comment

The monthly averaged turbulence intensity at 60m height is between 5.7% and 11.4% and the annual average turbulence intensity is 8.8%. Monthly average turbulence intensity in April is lowest at 5.7% and those from October to March exceeds 9%

2. Wave Data (January ~ December 2015)

1:Significant wave height frequency distribution (one year)

Significant wave height for each wave force scale

Comment

The maximum significant wave height frequency is 18.2% for the interval between 1.00m and 1.25m and 17.1% for the interval between 1.25m and 1.50m. The cases below 0.50m is negligible.

2:Wave rose (one year)

Comment

The dominant wave direction are SE & E direction and wave generally comes from the Pacific Ocean.

3:The significant wave period frequency distribution (one year)

Comment

The maximum significant wave period occurrence frequency is 27.0% for the interval between 8 sec and 9 sec and the significant wave period occurrence frequency for the interval between 7 sec and 10 sec is 70% of the total. The significant wave period frequency distribution below 5 sec is very low in order of 0.4%.

4:Frequency distribution table of wave height and wave period

0.0~ 1.0~ 2.0~ 3.0~ 4.0~ 5.0~ 6.0~ 7.0~ 8.0~ 9.0~ 10.0~ 11.0~ 12.0~ 13.0~ 14.0~ 15.0~ 16.0~ Frequency
occurrence
Frequency
rate[%]
7.00~                                   0 0.0
6.50~7.00                           2 5     7 0.1
6.00~6.50                       1   2 1 1   5 0.1
5.50~6.00                       1 1 5 2 1   10 0.1
5.00~5.50                   2 3 1 4 4 4     18 0.2
4.50~5.00                   3 6 1 1 15 2 1   29 0.3
4.00~4.50               1 4 21 10 5 8 12 1     62 0.7
3.50~4.00               4 22 46 43 25 25 18 2 1   186 2.1
3.00~3.50               7 30 66 76 30 17 13       239 2.7
2.50~3.00             23 55 115 154 76 16 16 5       460 5.3
2.00~2.50           7 94 180 317 131 81 63 23         896 10.2
1.75~2.00           14 76 208 238 169 69 21 3         798 9.1
1.50~1.75           41 140 338 338 187 138 28 10         1220 13.9
1.25~1.50         4 72 210 423 360 297 89 36 6         1497 17.1
1.00~1.25         8 119 223 526 450 230 27 8           1591 18.2
0.75~1.00         17 110 247 419 418 153 9 2           1375 15.7
0.50~0.75         2 36 98 149 73 7 1             366 4.2
0.25~0.50                 1                 1 0.0
~0.25                                   0 0.0
Frequency
occurrence
0 0 0 0 31 399 1111 2310 2366 1466 628 238 114 76 17 4 0 8760 100.0
Frequency
rate[%]
0.0 0.0 0.0 0.0 0.4 4.6 12.7 26.4 27.0 16.7 7.2 2.7 1.3 0.9 0.2 0.0 0.0 100.0  

Comment

Regarding relationship between wave height and wave period, significant wave height between 1.00m and 1.50m and significant wave period between 8 sec and 9 sec have maximum occurrence frequency.

5:Mean significant wave height and data availability (monthly)

Description 2015 Annual meana
significant
wave height
Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sept. Oct. Nov. Dec.
Mean significant
wave height[m]
1.6 2.0 1.5 1.5 1.3 1.3 1.5 1.9 1.8 1.8 1.8 1.5 1.6
Data acquisition
rate[%]
100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

Comment

Monthly mean significant wave height is between 1.3m and 2.0m and annual mean significant wave height is 1.6m.

6:Mean significant wave period and data availability

Description 2015 Annual meana
significant
wave period
Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sept. Oct. Nov. Dec.
Annual meana
significant
wave period[s]
8.2 9.0 8.3 7.6 7.9 7.7 9.1 9.1 9.3 8.5 7.8 7.4 8.3
Data acquisition
rate[%]
100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

Commentary

Monthly mean significant wave period is between 7.4 sec and 9.3 sec and annual mean significant wave period is 8.3 sec. Wave period on this site is long throughout the year due to influence of strong swell from Pacific Ocean.

3. Current Data (January ~December 2015)

1:Frequency distribution classified by current speed (one year)

Comment

At 11m below the sea level, the current speed in the range 0.0 and 0.3m/s accounts for about 81.6% of the total occurrence frequency.

2:The current direction frequency distribution (one year)

Commentary

At 11m below the sea level, the current direction from south is dominant and the current direction between SSW and S account for 35.8%

3:Mean current speed profile (one year)

Commentary

Mean Current speed between 6.5m and 11m below the sea level is within 0.17m/s and 0.18m/s. Significant difference in the current speed at different depth was not observed.

4:Mean current speed and data availability

Description Current
speed
[m]
2015 Annual mean
current speed
Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sept. Oct. Nov. Dec.
Current speed
[m/s]
6.5 0.10 0.08   0.13 0.14 0.17 0.14 0.31 0.33 0.27 0.15 0.11 0.18
8.5 0.11 0.09   0.14 0.15 0.18 0.13 0.26 0.30 0.26 0.14 0.10 0.17
11.0 0.11 0.09   0.14 0.17 0.20 0.15 0.31 0.31 0.26 0.14 0.09 0.18
Data acquisition
[%]
6.5 83.1 70.2 0.0 48.6 100.0 95.6 100.0 100.0 100.0 100.0 99.3 100.0 83.1
8.5 83.1 70.2 0.0 48.6 100.0 95.6 100.0 100.0 100.0 100.0 99.3 100.0 83.1
11.0 83.1 70.2 0.0 48.6 100.0 95.6 100.0 100.0 100.0 100.0 99.3 100.0 83.1

Comment

Monthly mean current speed at 11m below the sea level is between 0.08m/s and 0.33m/s and annual mean current speed is 0.18 m/s.

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Fukushima Offshore Wind Consortium

  • Marubeni Corporation
  • The University of Tokyo
  • Mitsubishi Heavy industries, Ltd.
  • Japan Marine United Corporation
  • Mitsui Engineering & Shipbuilding Co., Ltd.
  • Nippon Steel & Sumitomo Metal
  • Hitachi Ltd.
  • Furukawa Electric Co., Ltd.
  • Shimizu Corporation
  • Mizuho Information & Research institute, Inc