combined wave and wind fatigue damage for offshore structures€¦ · front end engineering design...

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


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


S.M.I.L.E.-FEM GmbH

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.


S.M.I.L.E.-FEM GmbH

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


S.M.I.L.E.-FEM GmbH

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


S.M.I.L.E.-FEM GmbH

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


S.M.I.L.E.-FEM GmbH

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


S.M.I.L.E.-FEM GmbH

Wind conditions


S.M.I.L.E.-FEM GmbH

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


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Fatigue analysis locations


S.M.I.L.E.-FEM GmbH

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.


S.M.I.L.E.-FEM GmbH

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


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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


S.M.I.L.E.-FEM GmbH

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


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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]


S.M.I.L.E.-FEM GmbH

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


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


S.M.I.L.E.-FEM GmbH

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


S.M.I.L.E.-FEM GmbH

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)


S.M.I.L.E.-FEM GmbH

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


S.M.I.L.E.-FEM GmbH

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


S.M.I.L.E.-FEM GmbH

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)


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


S.M.I.L.E.-FEM GmbH

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


S.M.I.L.E.-FEM GmbH

Thank you for your attention! Please ask questions!

combined wave and wind fatigue damage for offshore structures€¦ · front end engineering design...

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