combined wave and wind fatigue damage for offshore structures€¦ · front end engineering design...
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ANSYS CONFERENCE & 29. CADFEM USER´S MEETING 1
S.M.I.L.E.-FEM GmbH
Combined Wave and Wind Fatigue Damage
for Offshore Structures Ronald Horn, S.M.I.L.E.-FEM GmbH, Heikendorf Hongxia Gu, IMPaC Offshore Engineering GmbH, Hamburg ANSYS CONFERENCE & 29. CADFEM USER´S MEETING October, 19-21th, 2011, Stuttgart
ANSYS CONFERENCE & 29. CADFEM USER´S MEETING 2
S.M.I.L.E.-FEM GmbH IMPaC's SERVICES
IMPaC Offshore Engineering GmbH Integrated Project/Field Development Engineering
Overall Consultancy Conceptual & Feasibility Studies Front End Engineering Design (FEED) Detailed Design
Procurement & Logistics
Construction Management
Contract Preparation & Management Planning & Monitoring Construction / Installation
Supervision & Management
EPCM / EPC
Project Management
Research & Development
ANSYS CONFERENCE & 29. CADFEM USER´S MEETING 3
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S.M.I.L.E.-FEM GmbH S Structural and thermal analysis M Multiphysics solutions I Interaction of fluid and structure L Life cycle and fatigue analysis E Explicit dynamics analysis Within the project, S.M.I.L.E.-FEM GmbH is subsidiary of IMPaC Offshore Engineering.
ANSYS CONFERENCE & 29. CADFEM USER´S MEETING 4
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Scope Ultimate strength analysis of met mast tower Ultimate strength analysis of working platform Ultimate strength analysis of foundation Ultimate strength analysis of overall structure
Fatigue strength analysis of overall structure Boat impact analysis Lifting analysis Installation analysis Driveability analysis of monopile Connection detail analysis
ANSYS CONFERENCE & 29. CADFEM USER´S MEETING 5
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Project meteorological station (met mast) of wind farm typical monopile / transition piece structure foundation 95 m height above LAT LAT 25 m above sea bed 33 m monopile penetration in soil length of monopile/transion piece/tower: 62.0 m / 24.0 m / 74.5 m 35 m/s wind velocity, return period 50 years,10 min., LAT +10m 15,13 m maximum wave height, return period 50 years 13 s max. design wave period, return period 50 years 1,34 m current velocity, return period 50 years
ANSYS CONFERENCE & 29. CADFEM USER´S MEETING 6
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Model No. Analysis
Model Type Element Type global local detail 1D 2D 3D
Lattice tower model Strength analysis Of tower X X
Simplified tower model Overall Structure Analysis X X
Working platform model Working Platform Stress Analysis X X
Foundation model Foundation Analysis X X
Overall structure model
Strength Analysis, Fatigue Analysis X X
Boat landing model Boat Impact Analysis X X
Lifting model WP & TP Lifting Analysis X X
Lifting model MP Lifting Analysis X X
Flange model Flange Analysis X X
Grout connection Grouted Connection Analysis X X
Landing point model Installation Analysis X X
ANSYS CONFERENCE & 29. CADFEM USER´S MEETING 7
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Fatigue analysis Fatigue strength analysis of overall structure • Fatigue estimation due to wind • Fatigue estimation due to wave • Fatigue estimation due to pile driving • Total fatigue life estimation
ANSYS CONFERENCE & 29. CADFEM USER´S MEETING 8
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Wind conditions
ANSYS CONFERENCE & 29. CADFEM USER´S MEETING 9
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Wave conditions
Marine Condition Case 1 Case 2 Case 3 Case 4
DLC No. DLC 6.1b DLC 6.1c DLC 6.5 DLC 8.5
Code required Wave Height Hred50 Hmax50 Hred1 HsT
Recurrence Period 50 years 50 years 1 year Limiting
Used Wave Height (m) 10.69 15.13 8.32 1.30
Significant Wave Height Hs (m) 8.1 8.1 6.3 1.3
Design Wave Period TD1 (s) 10.09 10.09 8.9 4.04
Design Wave Period TD2 (s) 12.99 12.99 11.46 5.21
Ice Formations No no yes no
Loads Factor 1.35 1.35 1.35 1.1
ANSYS CONFERENCE & 29. CADFEM USER´S MEETING 10
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Fatigue analysis locations
ANSYS CONFERENCE & 29. CADFEM USER´S MEETING 11
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Fatigue analysis method
where: l = total number of blocks of the stress range for summation, I = 28 ni = number of stress cycles in block i Ni = number of induced stress cycles determined from the S-N curve
The fatigue analysis has been carried out according to GL Wind, by using cumulative damage ratio method (Palmgreen und Miner) The cumulative damage ratio D should not exceed the limit damage ratio of 1.
ANSYS CONFERENCE & 29. CADFEM USER´S MEETING 12
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S-N curve
The S-N curve for welded joints has been used in the analysis Log N = 6.69897+ m*Q where: Q = log (∆σRc / (γM * ∆σi ) – 0.3994/ m0 m0 = 3 (for welded joints) m = 5 ∆σRc = corrected fatigue strength reference value γM = partial material safety factor, γM = 1.25 ∆σi = stress range of block i
ANSYS CONFERENCE & 29. CADFEM USER´S MEETING 13
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Stress range Considering the axial stress and bending stress, the following stress range has been computed in all fatigue load cases Δσ = max(σ1) – min(σ3) with σ1: maximum principal stress σ3: minimum principal stress
ANSYS CONFERENCE & 29. CADFEM USER´S MEETING 14
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Wave load cases
0
2
4
6
8
10
12
14
16
18
0
5000000
10000000
15000000
20000000
25000000
30000000
35000000
40000000
45000000
1 2 3 4 5 6 7 8 9 10111213141516171819202122232425262728
Significant Wave Height Hs and 20 years Occurance
ANSYS CONFERENCE & 29. CADFEM USER´S MEETING 15
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Wave load fatigue results
1,00E+00
1,00E+02
1,00E+04
1,00E+06
1,00E+08
1,00E+10
1,00E+12
1 3 5 7 9 11 13 15 17 19 21 23 25 27
Endured stress cycles
0
20000
40000
60000
80000
100000
120000
140000
1 3 5 7 9 11 13 15 17 19 21 23 25 27
Stress range Δσ [N/m²]
ANSYS CONFERENCE & 29. CADFEM USER´S MEETING 16
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Fatigue damage calculation procedure 1. Use wave scatter diagram to obtain load classes for
wave heights and occurances 2. Calculate wave fatigue damage 3. Use identical wind occurrences, gust is induced by
wave (most conservative assumption) 4. Calculate Weibull parameter for N(Hs) wave height
occurrences and N(v) wind speed occurrences from met data
5. Correlate Hs and v 6. Obtain significant wind speed per load class 7. Calculate wind fatigue damage 8. Combine fatigue results from wind / wave 9. Combine with pile driving fatigue damage
ANSYS CONFERENCE & 29. CADFEM USER´S MEETING 17
S.M.I.L.E.-FEM GmbH
Wind load cases • relationship between wave height and wind speed (Weibull distributions) • 28 identical fatigue classes and number of stress cycles per class • wave and wind conditions described by the Weibull distribution • Weibull function parameters A (scale parameter) and k (shape parameter) are specified to correlated wave height and wind speed • time-dependent gust is calculated for each class according to GL wind • gust prescribed as transient force depending on height (and class).
Wind Wave
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Weibull distribution
Wave: blue Wind: red
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Wind speed / wave height correlation
V10m,3h = 0.737*v80m,10min
The profile given by GL Wind is used to calculate the wind speed at hub height (57 m) from the transferred scatter data (10 m) height:
V(z) = vhub (z / zhub)0.14
Vertical wind profile
ANSYS CONFERENCE & 29. CADFEM USER´S MEETING 20
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Wind speed / gust
v(z,t) = v(z) – 0.37*vgustN * sin(3πt/T)*(1-cos(2πt/T) with vgustN as the maximum value of the wind speed for the extreme operating gust according to GL Wind, IV – Part 2, 4.2.2.4.2 vgustN = β*(σ1/(1+0.1*(D/Λ1))) with standard deviation σ1, GL Wind, equation 4.2.5, β =6.4 (N=50), Λ1 = 21 m and D= rotor diameter (corresponding to tower height)
ANSYS CONFERENCE & 29. CADFEM USER´S MEETING 21
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Wind load cases
0
5
10
15
20
25
30
35
40
0
5.000.000
10.000.000
15.000.000
20.000.000
25.000.000
30.000.000
35.000.000
40.000.000
45.000.000
1 2 3 4 5 6 7 8 9 10111213141516171819202122232425262728
Wind speed / 10y-occurance vs load case
ANSYS CONFERENCE & 29. CADFEM USER´S MEETING 22
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Wind load fatigue results
0,00E+00
1,00E-03
2,00E-03
3,00E-03
4,00E-03
5,00E-03
6,00E-03
7,00E-03
0
5000
10000
15000
20000
25000
30000
1 3 5 7 9 11 13 15 17 19 21 23 25 27
Stress range / damage ratio vs load case
ANSYS CONFERENCE & 29. CADFEM USER´S MEETING 23
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Combined wind and wave fatigue damage
with D = combined in-place damage ratio due to wave and wind D1 = calculated fatigue damage for the high frequency response D2 = calculated fatigue damage for the low frequency response ν1 = mean zero up crossing frequency for the high frequency response ν2 = mean zero up crossing frequency for the low frequency response m = inverse slope of the S-N curve (=5) (index 1 refers to wind and index 2 to wave)
ANSYS CONFERENCE & 29. CADFEM USER´S MEETING 24
S.M.I.L.E.-FEM GmbH
Results of combined wind and wave fatigue damage
1,00E-09
1,00E-08
1,00E-07
1,00E-06
1,00E-05
1,00E-04
1,00E-03
1,00E-02
1,00E-01
1,00E+001 2 3 4 5 6 7 8 9 10
Wave (green), wind (blue) and combined (white) fatigue damage
LifeFat = (1-DPD) * Lifein-place
ANSYS CONFERENCE & 29. CADFEM USER´S MEETING 25
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Summary 1. Less complex structures and suitable environmental
conditions require less complex methods 2. Influence of environmental conditions on the load
generation must be treated very carefully 3. If applicable, identical load cases and occurrences
can be chosen 4. Then, fatigue damage contributions can be calculated
separately for identical load cases 5. If applicable, individual results of wave, wind and pile
driving fatigue damage can be combined
ANSYS CONFERENCE & 29. CADFEM USER´S MEETING 26
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Thank you for your attention! Please ask questions!