offshore windfarm design: waves currents
TRANSCRIPT
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Waves & Current
by David Cerda Salzmann
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Environmental Loads: Onshore
air
sea
soil
wind
waves ¤t
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Environmental Loads: Offshore
air
sea
soil
wind
waves ¤t
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Waves
Consider waves for:
• Extremes
• Fatigue
• Installation & Maintenance
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Current
Consider current for:
• Extremes
• Fatigue
• Installation & Maintenance
• Scour
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In this lecture...
• What data do you need
• What do you use it for
• Next hour: where to get data from
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Ocean Surface Waves
Definition:
“Perturbations that propagate through water”
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Regular Waves
crest
trough
wave length λ [m]
wave heightH [m]
mean sea level (MSL)
snap shot: t = fixed
x
zero-crossing
ζ(x)
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Regular Waves
crest
trough
wave period T [s]
wave heightH
mean sea level (MSL)
time history: x=fixed
t
zero-crossing
ζ(t)
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Irregular Waves
crest
trough
wave period T
wave heightH
mean sea level (MSL)
time history: x=fixed
t
ζ(t)
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Irregular Waves
Tz = Mean zero (up/down)-crossing period [s]
Hs = Significant wave height [m]
"Average of highest 1/3 of the waves in the record."
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Wind Waves
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Wind Waves
Wave generation influenced by:
• Wind speed
• Fetch: distance over which the waves have travelledunder that wind field
• Duration of the wind speed
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Wind Waves
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Wind Waves
Wave characteristics influenced by:
• Refraction
• Diffraction
• Breaking WavesH ≤ 0.78 * d
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Wind Waves
SO:
Look at the map and use common sense!
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Wind Waves
Trinidad
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Wind Waves Resuming
The development of wind waves requires:
• Wind speed
• Fetch
• Time
• Water Depth
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Wave Statistics
Required for Simulations & Calculations
• Short term 3 hours
• Long term year(s)
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Short term statistics
Series of regular waves
Wave Spectrum:Statistical representation of
3-hour sea state
Wave Time Series:Irregular!
0 10 20 30 40 50 60 70 80 90 100-2
0
2
t (s)
x(m
)JONSWAP
PM
f
S
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Short term statistics
JONSWAP
PM
f
S
JONSWAP: Fetch limitedPierson-Moskowitz: Fully developed sea
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Short term statistics
JONSWAP
PM
f
S
HS = Significant Wave Height [m]TZ = Mean Zero Crossing Period [s]
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Short term statistics
Hs, Tz
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Short term statistics
Hs, Tz
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Long term statistics
Hs
[m]Tz
[s]0 - 1 1 - 2 2 – 3 3 – 4 4 – 5 5 - 6 6 - 7 7 - 8 Sum:
6.5 - 7.0 06.0 - 6.5 0.1 0.15.5 - 6.0 0.1 0.1 0.25.0 - 5.5 0.1 0.1 0.24.5 - 5.0 1 14.0 - 4.5 4 43.5 - 4.0 4 5 93.0 - 3.5 19 0.1 19.12.5 - 3.0 0.1 38 38.12.0 - 2.5 27 43 701.5 - 2.0 0.1 115 5 120.11.0 - 1.5 6 220 1 2270.5 - 1.0 236 145 1 3820.0 - 0.5 1 1 113 14 0.1 0.1 129.2sum: 1 0 1 355.1 521.1 111.1 10.4 0.3 1000
So: Wave scatter diagram is the long-term statistical representation
of sea states
0 10 20 30 40 50 60 70 80 90 100-2
0
2
t (s)
x(m
)
0 10 20 30 40 50 60 70 80 90 100-2
0
2
t (s)
x(m
)
0 10 20 30 40 50 60 70 80 90 100-2
0
2
t (s)
x(m
)
0 10 20 30 40 50 60 70 80 90 100-2
0
2
t (s)
x(m
)
0 10 20 30 40 50 60 70 80 90 100-2
0
2
t (s)
x(m
)
0 10 20 30 40 50 60 70 80 90 100-2
0
2
t (s)
x(m
)
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Environmental Data
Scatter diagram gives the wave data:
• Over a certain period
• For a certain location
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Long term statistics
H s
[m]T z
[s]0 - 1 1 - 2 2 – 3 3 – 4 4 – 5 5 - 6 6 - 7 7 - 8 Sum:
6.5 - 7.0 06.0 - 6.5 0.1 0.15.5 - 6.0 0.1 0.1 0.25.0 - 5.5 0.1 0.1 0.24.5 - 5.0 1 14.0 - 4.5 4 43.5 - 4.0 4 5 93.0 - 3.5 19 0.1 19.12.5 - 3.0 0.1 38 38.12.0 - 2.5 27 43 701.5 - 2.0 0.1 115 5 120.11.0 - 1.5 6 220 1 2270.5 - 1.0 236 145 1 3820.0 - 0.5 1 1 113 14 0.1 0.1 129.2sum: 1 0 1 355.1 521.1 111.1 10.4 0.3 1000
Wave scatter diagram
f
S
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Extreme wave height
H s
[m]T z
[s]0 - 1 1 - 2 2 – 3 3 – 4 4 – 5 5 - 6 6 - 7 7 - 8 Sum:
6.5 - 7.0 06.0 - 6.5 0.1 0.15.5 - 6.0 0.1 0.1 0.25.0 - 5.5 0.1 0.1 0.24.5 - 5.0 1 14.0 - 4.5 4 43.5 - 4.0 4 5 93.0 - 3.5 19 0.1 19.12.5 - 3.0 0.1 38 38.12.0 - 2.5 27 43 701.5 - 2.0 0.1 115 5 120.11.0 - 1.5 6 220 1 2270.5 - 1.0 236 145 1 3820.0 - 0.5 1 1 113 14 0.1 0.1 129.2sum: 1 0 1 355.1 521.1 111.1 10.4 0.3 1000
Wave scatter diagram
Chance of occurrence
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Extreme wave height
Highest expected value for Hs
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Extreme wave height
Largest wave during lifetime:
From Rayleigh probability density function
or
Hmax ≈ 1.86* Hsor
Hmax = 0.78* d
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Extreme wave height
Extreme wave height knownadd period to wave height:
maxmin 46.2 HT =
maxmax 70.3 HT =
(1:9.5)
(1:21)
steepness
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Extreme wave height
Wave form:
Wave theory
Water particle velocities and accelerations
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Extreme wave height
For Example:
Linear/Airy Wave theory:
)sin(sinh
)(cosh),( , nn
n
nnnan t
dk
dzktzu εωωζ +⋅+⋅⋅=
)cos(sinh
)(cosh),( 2
, nnn
nnnan t
dk
dzktzu εωωζ +⋅+⋅⋅=&
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Extreme wave height
Finally determine loads:
the Morison Equation
21 14 2( , ) m df t z C D u C D u uρπ ρ= ⋅ ⋅ + ⋅ ⋅&
velocityacceleration
• Unit: [N/m]
• Vertically distributed load along pile
f (t,z)
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Resuming
• Extreme Wave Load
• From Extreme Maximum Wave Height Hmax
• From Extreme Significant Wave Height Hs
• From Scatter Diagram
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Fatigue
All stress variations during entire lifetime
All loads during entire lifetime
Environmental conditions during entire lifetime
Scatter diagrams: waves and wind
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Fatigue
Hs-Tz
Hs-Vw
lower 00 04 05 06 07 08 09 10 11 12 13 14 15
lower upper 04 05 06 07 08 09 10 11 12 13 14 15 total
00 01 0 0.2 0 0.5 0 0 0 0 0 0 0 0 0 0.7
01 02 0 2.0 6.0 6.4 1.8 0.7 0 0 0 0 0 0 0 16.9
02 03 0 0 9.1 9.1 3.6 3.1 0.7 0.2 0 0 0 0 0 25.8
03 04 0 0 0.5 12.2 8.6 1.8 1.1 0.2 0.2 0 0 0 0 24.6
04 05 0 0 0 1.1 6.6 2.0 0.9 0.2 0 0 0 0.2 0 11.0
05 06 0 0 0 0 4.2 3.1 1.3 0.4 0 0.2 0 0 0 9.2
06 07 0 0 0 0 0.2 3.5 2.2 0 0 0 0 0 0 5.9
07 08 0 0 0 0 0 1.8 1.3 0.2 0 0 0 0 0 3.3
08 09 0 0 0 0 0 0 1.6 0 0 0 0 0 0 1.6
09 10 0 0 0 0 0 0 0.2 0.2 0 0 0 0 0 0.4
10 11 0 0 0 0 0 0 0 0 0.4 0 0 0 0 0.4
11 12 0 0 0 0 0 0 0 0 0 0 0 0 0 0.0
12 13 0 0 0 0 0 0 0 0 0.2 0 0 0 0 0.2
13 0 0 0 0 0 0 0 0 0 0 0 0 0 0.0
total 0.0 2.2 15.6 29.3 25.0 16.0 9.3 1.4 0.8 0.2 0.0 0.2 0.0
lower 00 04 05 06 07 08 09 10 11 12 13 14 15
lower upper 04 05 06 07 08 09 10 11 12 13 14 15 total
00 01 0 0.2 0 0.5 0 0 0 0 0 0 0 0 0 0.7
01 02 0 2.0 6.0 6.4 1.8 0.7 0 0 0 0 0 0 0 16.9
02 03 0 0 9.1 9.1 3.6 3.1 0.7 0.2 0 0 0 0 0 25.8
03 04 0 0 0.5 12.2 8.6 1.8 1.1 0.2 0.2 0 0 0 0 24.6
04 05 0 0 0 1.1 6.6 2.0 0.9 0.2 0 0 0 0.2 0 11.0
05 06 0 0 0 0 4.2 3.1 1.3 0.4 0 0.2 0 0 0 9.2
06 07 0 0 0 0 0.2 3.5 2.2 0 0 0 0 0 0 5.9
07 08 0 0 0 0 0 1.8 1.3 0.2 0 0 0 0 0 3.3
08 09 0 0 0 0 0 0 1.6 0 0 0 0 0 0 1.6
09 10 0 0 0 0 0 0 0.2 0.2 0 0 0 0 0 0.4
10 11 0 0 0 0 0 0 0 0 0.4 0 0 0 0 0.4
11 12 0 0 0 0 0 0 0 0 0 0 0 0 0 0.0
12 13 0 0 0 0 0 0 0 0 0.2 0 0 0 0 0.2
13 0 0 0 0 0 0 0 0 0 0 0 0 0 0.0
total 0.0 2.2 15.6 29.3 25.0 16.0 9.3 1.4 0.8 0.2 0.0 0.2 0.0
lower 00 04 05 06 07 08 09 10 11 12 13 14 15
lower upper 04 05 06 07 08 09 10 11 12 13 14 15 total
00 01 0 0.2 0 0.5 0 0 0 0 0 0 0 0 0 0.7
01 02 0 2.0 6.0 6.4 1.8 0.7 0 0 0 0 0 0 0 16.9
02 03 0 0 9.1 9.1 3.6 3.1 0.7 0.2 0 0 0 0 0 25.8
03 04 0 0 0.5 12.2 8.6 1.8 1.1 0.2 0.2 0 0 0 0 24.6
04 05 0 0 0 1.1 6.6 2.0 0.9 0.2 0 0 0 0.2 0 11.0
05 06 0 0 0 0 4.2 3.1 1.3 0.4 0 0.2 0 0 0 9.2
06 07 0 0 0 0 0.2 3.5 2.2 0 0 0 0 0 0 5.9
07 08 0 0 0 0 0 1.8 1.3 0.2 0 0 0 0 0 3.3
08 09 0 0 0 0 0 0 1.6 0 0 0 0 0 0 1.6
09 10 0 0 0 0 0 0 0.2 0.2 0 0 0 0 0 0.4
10 11 0 0 0 0 0 0 0 0 0.4 0 0 0 0 0.4
11 12 0 0 0 0 0 0 0 0 0 0 0 0 0 0.0
12 13 0 0 0 0 0 0 0 0 0.2 0 0 0 0 0.2
13 0 0 0 0 0 0 0 0 0 0 0 0 0 0.0
total 0.0 2.2 15.6 29.3 25.0 16.0 9.3 1.4 0.8 0.2 0.0 0.2 0.0
lowerlower 0000 0404 0505 0606 0707 0808 0909 1010 1111 1212 1313 1414 1515
lowerlower upperupper 0404 0505 0606 0707 0808 0909 1010 1111 1212 1313 1414 1515 totaltotal
0000 0101 000 0.20.20.2 000 0.50.50.5 000 000 000 000 000 000 000 000 000 0.70.7
0101 0202 000 2.02.02.0 6.06.06.0 6.46.46.4 1.81.81.8 0.70.70.7 000 000 000 000 000 000 000 16.916.9
0202 0303 000 000 9.19.19.1 9.19.19.1 3.63.63.6 3.13.13.1 0.70.70.7 0.20.20.2 000 000 000 000 000 25.825.8
0303 0404 000 000 0.50.50.5 12.212.212.2 8.68.68.6 1.81.81.8 1.11.11.1 0.20.20.2 0.20.20.2 000 000 000 000 24.624.6
0404 0505 000 000 000 1.11.11.1 6.66.66.6 2.02.02.0 0.90.90.9 0.20.20.2 000 000 000 0.20.20.2 000 11.011.0
0505 0606 000 000 000 000 4.24.24.2 3.13.13.1 1.31.31.3 0.40.40.4 000 0.20.20.2 000 000 000 9.29.2
0606 0707 000 000 000 000 0.20.20.2 3.53.53.5 2.22.22.2 000 000 000 000 000 000 5.95.9
0707 0808 000 000 000 000 000 1.81.81.8 1.31.31.3 0.20.20.2 000 000 000 000 000 3.33.3
0808 0909 000 000 000 000 000 000 1.61.61.6 000 000 000 000 000 000 1.61.6
0909 1010 000 000 000 000 000 000 0.20.20.2 0.20.20.2 000 000 000 000 000 0.40.4
1010 1111 000 000 000 000 000 000 000 000 0.40.40.4 000 000 000 000 0.40.4
1111 1212 000 000 000 000 000 000 000 000 000 000 000 000 000 0.00.0
1212 1313 000 000 000 000 000 000 000 000 0.20.20.2 000 000 000 000 0.20.2
1313 000 000 000 000 000 000 000 000 000 000 000 000 000 0.00.0
totaltotal 0.00.0 2.22.2 15.615.6 29.329.3 25.025.0 16.016.0 9.39.3 1.41.4 0.80.8 0.20.2 0.00.0 0.20.2 0.00.0
lower 00 02 04 06 08 10 12 14 16 18 20 22 24
lower upper 02 04 06 08 10 12 14 16 18 20 22 24 total
00 01 0.1 0.1 0.3 0.1 0.0 0 0 0 0 0 0 0 0 0.6
01 02 1.0 2.0 4.6 4.5 2.0 0.3 0.0 0 0 0 0 0 0 14.4
02 03 0.6 1.5 3.7 7.1 8.7 4.7 1.3 0.1 0.0 0.0 0 0 0 27.7
03 04 0.1 0.4 1.2 3.2 5.1 6.2 4.1 1.0 0.3 0.0 0 0 0 21.6
04 05 0.0 0.1 0.4 1.0 2.9 3.7 4.1 2.3 0.7 0.1 0.0 0.0 0 15.3
05 06 0 0.0 0.0 0.2 0.9 1.6 2.5 2.7 1.4 0.2 0.0 0 0 9.5
06 07 0 0 0.0 0.0 0.2 0.4 0.8 1.3 1.2 0.4 0.0 0 0 4.3
07 08 0 0 0 0.0 0.0 0.2 0.3 0.6 1.1 0.6 0.1 0 0 2.9
08 09 0 0 0 0 0.0 0.0 0.1 0.2 0.8 0.6 0.1 0 0 1.8
09 10 0 0 0 0 0 0.0 0.0 0.1 0.3 0.3 0.1 0 0 0.8
10 11 0 0 0 0 0 0 0.0 0.0 0.1 0.1 0.0 0 0 0.2
11 12 0 0 0 0 0 0 0.0 0.0 0.0 0.1 0.1 0.0 0 0.2
12 13 0 0 0 0 0 0 0.0 0.0 0.0 0.1 0.0 0.0 0 0.1
13 14 0 0 0 0 0 0 0 0 0 0.0 0.0 0.0 0 0.0
14 15 0 0 0 0 0 0 0 0 0 0.0 0.0 0 0 0.0
15 16 0 0 0 0 0 0 0 0 0 0 0.0 0 0 0.0
16 0 0 0 0 0 0 0 0 0 0 0 0 0 0.0
total 1.8 4.1 10.2 16.1 19.8 17.1 13.2 8.3 5.9 2.5 0.4 0.0 0.0
lower 00 02 04 06 08 10 12 14 16 18 20 22 24
lower upper 02 04 06 08 10 12 14 16 18 20 22 24 total
00 01 0.1 0.1 0.3 0.1 0.0 0 0 0 0 0 0 0 0 0.6
01 02 1.0 2.0 4.6 4.5 2.0 0.3 0.0 0 0 0 0 0 0 14.4
02 03 0.6 1.5 3.7 7.1 8.7 4.7 1.3 0.1 0.0 0.0 0 0 0 27.7
03 04 0.1 0.4 1.2 3.2 5.1 6.2 4.1 1.0 0.3 0.0 0 0 0 21.6
04 05 0.0 0.1 0.4 1.0 2.9 3.7 4.1 2.3 0.7 0.1 0.0 0.0 0 15.3
05 06 0 0.0 0.0 0.2 0.9 1.6 2.5 2.7 1.4 0.2 0.0 0 0 9.5
06 07 0 0 0.0 0.0 0.2 0.4 0.8 1.3 1.2 0.4 0.0 0 0 4.3
07 08 0 0 0 0.0 0.0 0.2 0.3 0.6 1.1 0.6 0.1 0 0 2.9
08 09 0 0 0 0 0.0 0.0 0.1 0.2 0.8 0.6 0.1 0 0 1.8
09 10 0 0 0 0 0 0.0 0.0 0.1 0.3 0.3 0.1 0 0 0.8
10 11 0 0 0 0 0 0 0.0 0.0 0.1 0.1 0.0 0 0 0.2
11 12 0 0 0 0 0 0 0.0 0.0 0.0 0.1 0.1 0.0 0 0.2
12 13 0 0 0 0 0 0 0.0 0.0 0.0 0.1 0.0 0.0 0 0.1
13 14 0 0 0 0 0 0 0 0 0 0.0 0.0 0.0 0 0.0
14 15 0 0 0 0 0 0 0 0 0 0.0 0.0 0 0 0.0
15 16 0 0 0 0 0 0 0 0 0 0 0.0 0 0 0.0
16 0 0 0 0 0 0 0 0 0 0 0 0 0 0.0
total 1.8 4.1 10.2 16.1 19.8 17.1 13.2 8.3 5.9 2.5 0.4 0.0 0.0
lower 00 02 04 06 08 10 12 14 16 18 20 22 24
lower upper 02 04 06 08 10 12 14 16 18 20 22 24 total
00 01 0.1 0.1 0.3 0.1 0.0 0 0 0 0 0 0 0 0 0.6
01 02 1.0 2.0 4.6 4.5 2.0 0.3 0.0 0 0 0 0 0 0 14.4
02 03 0.6 1.5 3.7 7.1 8.7 4.7 1.3 0.1 0.0 0.0 0 0 0 27.7
03 04 0.1 0.4 1.2 3.2 5.1 6.2 4.1 1.0 0.3 0.0 0 0 0 21.6
04 05 0.0 0.1 0.4 1.0 2.9 3.7 4.1 2.3 0.7 0.1 0.0 0.0 0 15.3
05 06 0 0.0 0.0 0.2 0.9 1.6 2.5 2.7 1.4 0.2 0.0 0 0 9.5
06 07 0 0 0.0 0.0 0.2 0.4 0.8 1.3 1.2 0.4 0.0 0 0 4.3
07 08 0 0 0 0.0 0.0 0.2 0.3 0.6 1.1 0.6 0.1 0 0 2.9
08 09 0 0 0 0 0.0 0.0 0.1 0.2 0.8 0.6 0.1 0 0 1.8
09 10 0 0 0 0 0 0.0 0.0 0.1 0.3 0.3 0.1 0 0 0.8
10 11 0 0 0 0 0 0 0.0 0.0 0.1 0.1 0.0 0 0 0.2
11 12 0 0 0 0 0 0 0.0 0.0 0.0 0.1 0.1 0.0 0 0.2
12 13 0 0 0 0 0 0 0.0 0.0 0.0 0.1 0.0 0.0 0 0.1
13 14 0 0 0 0 0 0 0 0 0 0.0 0.0 0.0 0 0.0
14 15 0 0 0 0 0 0 0 0 0 0.0 0.0 0 0 0.0
15 16 0 0 0 0 0 0 0 0 0 0 0.0 0 0 0.0
16 0 0 0 0 0 0 0 0 0 0 0 0 0 0.0
total 1.8 4.1 10.2 16.1 19.8 17.1 13.2 8.3 5.9 2.5 0.4 0.0 0.0
lowerlower 0000 0202 0404 0606 0808 1010 1212 1414 1616 1818 2020 2222 2424
lowerlower upperupper 0202 0404 0606 0808 1010 1212 1414 1616 1818 2020 2222 2424 totaltotal
0000 0101 0.10.10.1 0.10.10.1 0.30.30.3 0.10.10.1 0.00.00.0 000 000 000 000 000 000 000 000 0.60.6
0101 0202 1.01.01.0 2.02.02.0 4.64.64.6 4.54.54.5 2.02.02.0 0.30.30.3 0.00.00.0 000 000 000 000 000 000 14.414.4
0202 0303 0.60.60.6 1.51.51.5 3.73.73.7 7.17.17.1 8.78.78.7 4.74.74.7 1.31.31.3 0.10.10.1 0.00.00.0 0.00.00.0 000 000 000 27.727.7
0303 0404 0.10.10.1 0.40.40.4 1.21.21.2 3.23.23.2 5.15.15.1 6.26.26.2 4.14.14.1 1.01.01.0 0.30.30.3 0.00.00.0 000 000 000 21.621.6
0404 0505 0.00.00.0 0.10.10.1 0.40.40.4 1.01.01.0 2.92.92.9 3.73.73.7 4.14.14.1 2.32.32.3 0.70.70.7 0.10.10.1 0.00.00.0 0.00.00.0 000 15.315.3
0505 0606 000 0.00.00.0 0.00.00.0 0.20.20.2 0.90.90.9 1.61.61.6 2.52.52.5 2.72.72.7 1.41.41.4 0.20.20.2 0.00.00.0 000 000 9.59.5
0606 0707 000 000 0.00.00.0 0.00.00.0 0.20.20.2 0.40.40.4 0.80.80.8 1.31.31.3 1.21.21.2 0.40.40.4 0.00.00.0 000 000 4.34.3
0707 0808 000 000 000 0.00.00.0 0.00.00.0 0.20.20.2 0.30.30.3 0.60.60.6 1.11.11.1 0.60.60.6 0.10.10.1 000 000 2.92.9
0808 0909 000 000 000 000 0.00.00.0 0.00.00.0 0.10.10.1 0.20.20.2 0.80.80.8 0.60.60.6 0.10.10.1 000 000 1.81.8
0909 1010 000 000 000 000 000 0.00.00.0 0.00.00.0 0.10.10.1 0.30.30.3 0.30.30.3 0.10.10.1 000 000 0.80.8
1010 1111 000 000 000 000 000 000 0.00.00.0 0.00.00.0 0.10.10.1 0.10.10.1 0.00.00.0 000 000 0.20.2
1111 1212 000 000 000 000 000 000 0.00.00.0 0.00.00.0 0.00.00.0 0.10.10.1 0.10.10.1 0.00.00.0 000 0.20.2
1212 1313 000 000 000 000 000 000 0.00.00.0 0.00.00.0 0.00.00.0 0.10.10.1 0.00.00.0 0.00.00.0 000 0.10.1
1313 1414 000 000 000 000 000 000 000 000 000 0.00.00.0 0.00.00.0 0.00.00.0 000 0.00.0
1414 1515 000 000 000 000 000 000 000 000 000 0.00.00.0 0.00.00.0 000 000 0.00.0
1515 1616 000 000 000 000 000 000 000 000 000 000 0.00.00.0 000 000 0.00.0
1616 000 000 000 000 000 000 000 000 000 000 000 000 000 0.00.0
totaltotal 1.81.8 4.14.1 10.210.2 16.116.1 19.819.8 17.117.1 13.213.2 8.38.3 5.95.9 2.52.5 0.40.4 0.00.0 0.00.0
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Fatigue
Hs-Tz-Vw
Hs Tz < 3.0 3.0 - 4.0 4.0 - 5.0 5.0 - 6.0 6.0 - 7.0 7.0 - 8.0 8.0 - 9.0 9.0 - 10.0 10.0-11.017.5 0.2 0.7 0.4 1.3
15 0.3 0.6 0.9>4.0 12.5 0.4 0.4 0.8
17.5 0.7 0.4 1.115 0.9 0.9
3.5 - 4.0 12.5 1.0 1.017.5 0.2 1.4 1.6
15 0.3 1.2 1.53.0 - 3.5 12.5 0.4 0.9 1.3
17.5 1.1 0.9 2.015 2.0 0.2 2.2
12.5 3.0 3.02.5 - 3.0 10 0.3 0.3
17.5 2.5 0.5 3.015 3.0 0.4 3.4
12.5 4.0 0.2 4.210 1.1 1.1
7.5 0.2 0.22.0 - 2.5 2.5 0.2 0.2
17.5 0.1 0.3 0.4 0.5 1.315 1.4 1.4 0.2 0.4 0.3 0.3 0.2 4.2
12.5 3.0 2.8 0.2 0.1 6.110 3.9 0.6 4.5
7.5 1.6 1.65 0.5 0.5
1.5 - 2.0 2.5 0.4 0.415 0.1 0.1 0.3 0.2 0.4 0.5 1.6
12.5 0.6 0.2 0.7 0.4 0.2 0.1 2.210 4.4 1.8 0.5 6.7
7.5 4.5 4.55 1.9 1.9
1.0 - 1.5 2.5 0.4 1.0 1.412.5 0.2 0.2 0.4
10 3.0 3.07.5 2.4 3.0 1.7 7.1
5 2.8 2.0 0.1 4.90.5 - 1.0 2.5 4.3 4.3
10 0.2 0.1 0.37.5 2.2 0.3 2.5
5 0.7 2.2 1.6 0.1 4.60.0 - 0.5 2.5 0.8 3.6 1.4 0.2 6.0
0.8 14.2 31.2 34.4 10.3 4.6 1.2 1.7 1.6 100.0
93 states
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Fatigue
Hs-Tz-Vw
Reduce to
16 states
Hs Tz Vw %1 0.25 3.82 3.30 8.72 0.25 5.63 6.47 4.63 0.75 3.84 5.19 14.54 0.75 5.54 9.15 5.05 0.58 10.5 11.67 0.36 1.25 4.44 6.00 7.87 1.25 4.86 10.29 6.98 1.25 8.28 13.19 3.69 1.75 4.59 8.64 7.0
10 1.75 4.99 13.31 8.611 1.75 8.73 15.83 3.012 2.25 5.59 13.97 12.113 2.75 5.77 14.47 7.514 3.25 6.3 15.17 4.415 3.75 6.63 15.08 3.016 4.25 7.47 15.42 3.0
100.0
![Page 40: Offshore Windfarm Design: waves currents](https://reader034.vdocuments.us/reader034/viewer/2022042512/5583a371d8b42a5b318b5243/html5/thumbnails/40.jpg)
Fatigue
Now lifetime loads can be simulated:
• Aerodynamic loads: BEM
• Hydrodynamic loads: Morison
Then stresses can be determined along structure
![Page 41: Offshore Windfarm Design: waves currents](https://reader034.vdocuments.us/reader034/viewer/2022042512/5583a371d8b42a5b318b5243/html5/thumbnails/41.jpg)
Fatigue
Stress Time Series
σamp
log N
Stress Histogram
σ
Time
![Page 42: Offshore Windfarm Design: waves currents](https://reader034.vdocuments.us/reader034/viewer/2022042512/5583a371d8b42a5b318b5243/html5/thumbnails/42.jpg)
Fatigue
σamp
log N
n1
n2
n3
n4n5
N1
N2
N3N3
N4
N5
Miner’s Damage Rule:
5
5
4
4
3
3
2
2
1
1
N
n
N
n
N
n
N
n
N
n
N
n
i
i ++++=∑
Damage < 1.0
S-N curve
![Page 43: Offshore Windfarm Design: waves currents](https://reader034.vdocuments.us/reader034/viewer/2022042512/5583a371d8b42a5b318b5243/html5/thumbnails/43.jpg)
Installation & Maintenance
Workability:
Different activities have different workability limits
Sailing
Transfer
Jacking up
Jack-up working
Hs = 4m
Hs = 2m
Hs = 1m
Hs = 3m
![Page 44: Offshore Windfarm Design: waves currents](https://reader034.vdocuments.us/reader034/viewer/2022042512/5583a371d8b42a5b318b5243/html5/thumbnails/44.jpg)
Current
Horizontal movement of water, due to tidal waves
![Page 45: Offshore Windfarm Design: waves currents](https://reader034.vdocuments.us/reader034/viewer/2022042512/5583a371d8b42a5b318b5243/html5/thumbnails/45.jpg)
Current
Flow pattern North Sea
![Page 46: Offshore Windfarm Design: waves currents](https://reader034.vdocuments.us/reader034/viewer/2022042512/5583a371d8b42a5b318b5243/html5/thumbnails/46.jpg)
Current
Determine flow patterns and tidal differences
BIG DIFFERENCE
=
BIG CURRENT
![Page 47: Offshore Windfarm Design: waves currents](https://reader034.vdocuments.us/reader034/viewer/2022042512/5583a371d8b42a5b318b5243/html5/thumbnails/47.jpg)
Current
• Length and time scale of tidal waves much larger than of wind waves
• Currents considered as flow of constant velocity
• Vertical variation: Current profile over depth
![Page 48: Offshore Windfarm Design: waves currents](https://reader034.vdocuments.us/reader034/viewer/2022042512/5583a371d8b42a5b318b5243/html5/thumbnails/48.jpg)
Current profiles
z z z
d
Power profile Linear profile Bilinear profile
0( )current c
z dU z U
d
α+ =
0c
zU
d =
Uc0 Uc0 Uc0
![Page 49: Offshore Windfarm Design: waves currents](https://reader034.vdocuments.us/reader034/viewer/2022042512/5583a371d8b42a5b318b5243/html5/thumbnails/49.jpg)
Current effects
• Hydrodynamic loads on monopile
uuDCuDCtf dm ⋅⋅+⋅⋅= ρρπ 212
41 )( &
velocity
Morison Equation:
![Page 50: Offshore Windfarm Design: waves currents](https://reader034.vdocuments.us/reader034/viewer/2022042512/5583a371d8b42a5b318b5243/html5/thumbnails/50.jpg)
Current effects
• Hydrodynamic loads on monopile
• Scour
• Caused by current
• Between 1.3*D and 2.5*D
• Consider when designing
![Page 51: Offshore Windfarm Design: waves currents](https://reader034.vdocuments.us/reader034/viewer/2022042512/5583a371d8b42a5b318b5243/html5/thumbnails/51.jpg)
Current effects
• Hydrodynamic loads on monopile
• Scour
• Installation & Maintenance: vessel manoeuvring
![Page 52: Offshore Windfarm Design: waves currents](https://reader034.vdocuments.us/reader034/viewer/2022042512/5583a371d8b42a5b318b5243/html5/thumbnails/52.jpg)
So.... Resuming:
• Long term: scatter diagrams
• Short term: wave spectra
• Hs and Tz
• Current velocity & profile
• Extremes
• Fatigue
• Installation & Maintenance
• Scour