Final report for WP4.3: Enhancement of design methods ... - Upwind

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Rainflow evaluation The load cases shall be evaluated in rainflow counts according to two different assumptions for the availability of the turbine (100% and 85% or equivalent conservative value based on failure statistics). Combined with the two support orientations, that means four rainflow counts and weighting analyses have to be performed. The setups are as follows: 1. 100 % availability: rainflow count assuming DLC 1.2 and DLC 6.4 for the complete lifetime, Jacket orientation 0° 2. 100 % availability: rainflow count assuming DLC 1.2 and DLC 6.4 for the complete lifetime, Jacket orientation 45° 3. 85% availability: rainflow count assuming 85 % of lifetime DLC 1.2 and DLC 6.4, 15 % of lifetime DLC 7.2, Jacket orientation 0° 4. 85% availability: rainflow count assuming 85 % of lifetime DLC 1.2 and DLC 6.4,15 % of lifetime DLC 7.2, Jacket orientation 45° The highest resulting loads shall be used for jacket predesign. Step 2: Wind and waves misaligned The load case definitions of step two are, but for the wind-wave misalignment, equal to the load case definitions given in step one. As step two considers site specific directional distribution with a defined orientation of the support structure regarding north, the support structure orientation must not be varied. For DLC 7.2 no further load cases have to be set up, as assuming wind aligned with waves is conservative with regards to missing aerodynamic damping. Besides that, the IEC standard does not request consideration of wind-wave misalignment for DLC 7.2. The rainflow evaluation of step 2 includes both the dimensioning step 1 rainflow extended by the directional distributions of step 2 simulations. Wind-wave misalignment can be considered via several approaches of different complexity, the wind bin based wind-wave rose combination (exact method) or methods of reduced complexity. The exact method assumes that a wind direction – wave direction scatter diagram exists. This section additionally addresses an approach based on the assumption that wind-wave misalignment is independent of wind speed and wind direction (wind independent method). As wind and wave data for the present site are sufficient to include wind-wave misalignment via the exact method, a comparison to the results of the less complex wind independent method may be useful. Exact method The exact method assumes wind-wave misalignment to vary with three parameters: wind speed bin, wind direction and wave direction. Thus, one misalignment has to be computed for each wind bin, wind direction and wave direction combination, resulting in 4032 simulations (2 support structure orientations · 14 bins · 12 wind sectors · 12 wave sectors = 4032) for DLC 1.2 and DLC 6.4 if wind and wave seeds and wind misalignment are varied within. It is assumed that one seed for every single case is statistically sufficient due to the high number of load cases. Wind independent method To reduce the sheer amount of simulations and the effort of simulation setup, the wind independent method is based on the assumption that wind-wave misalignment is independent of wind speed and wind direction. First, wind and wave roses are tabulated as probability distributions and the misalignments with according probabilities of misalignments are derived. This is illustrated in the following table: 54
Wind dir. Wind direction probability [% wind rose] Table 5.26: Wind/wave misalignment, wind independent method Wave dir. Wave direction probability [% wave rose│winddir.] 0° P(0° wind) 0° P(0° wave│0° wind) 0° 0° P(0° wind) 30° P(30° wave│0° wind) 30° … P(0° wind) … … … 0° P(0° wind) 330° P(330° wave│0° wind) 330° 30° … 330° P(30° wind) P(330° wind) 55 Misalignment … … … … Next, the probabilities are summed up for each misalignment: P (φmiss = i) = ∑ P (φmiss = i) i = 0°; 30° …330° Probability of misalignment P (φmiss) P(0° wind) · P(0° wave) P(0° wind) · P(30° wave) P(0° wind) · P(330° wave) As the structural orientation is axi-symmetric to the wind direction (assuming active yaw and representation of wind misalignment via 8 deg rotor misalignment), the probabilities of misalignment can be taken as average of the sum of misalignments axi-symmetric to the wind direction, for instance: P (φmiss = 30°) = P (φmiss = 330°) = 0.5 · ( P (φmiss = 30°) + P (φmiss = 330°) ) This would result in half of the simulations of the exact method (2 support structure orientations · 14 bins · 12 wind sectors · 6 misalignments = 2016 simulations) for DLC 1.2 and DLC 6.4 if wind and wave seeds and wind misalignment are varied within. Furthermore, the setup of load cases would be significantly less time consuming compared to the exact method. Following example is used to illustrate the further load case setup: P (φmiss = 0°) = 30 % P (φmiss = 30°) = 25 % P (φmiss = -30°) = 25 % P (φmiss = 60°) = 10 % P (φmiss = 90°) = 10 % The exemplary misalignments would result in the following load case setup regarding wind and wave directions: Table 5.27: Example load case setup with wind/wave misalignment Global wind direction Global wave direction 0° 0°; 30°; -30°; 60°; 90° 30° 30°; 60°; 0°; 90; 120° … 330° 330°; 0°; 300°; 30°; 60°
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Project UpWind Contract No.: 019945
Page 3 and 4: Acknowledgement The presented work
Page 5 and 6: Summary The overall aim of the UpWi
Page 7: Table of Contents Acknowledgement..
Page 10 and 11: Task 4.1 Integration of support str
Page 12 and 13: Sequential coupling The sequential
Page 14 and 15: analysis. In the new multibody code
Page 16 and 17: Figure 2.4: 2nd global bending mode
Page 18 and 19: 3.2 Comparison of deterministic loa
Page 20 and 21: Figure 3.5: Time series of axial fo
Page 22 and 23: • Time domain simulation in ADCoS
Page 24 and 25: • A supplementary load vector for
Page 26 and 27: The following results are found: Fi
Page 28 and 29: Figure 4.5: Output positions in the
Page 30 and 31: It is directly visible that there i
Page 32 and 33: ated eigenfrequency is shifted into
Page 34 and 35: Water levels For the calculation of
Page 36 and 37: guidelines for the inclusion of cli
Page 38 and 39: damaging if the frequency of the ex
Page 40 and 41: uncertain parameters carefully. Thr
Page 42 and 43: Table 5.3 shows annual reliability
Page 44 and 45: Steel substructure for offshore win
Page 46 and 47: Table 5.16 shows the required FDF v
Page 48 and 49: A Fracture Mechanical (FM) modellin
Page 50 and 51: Figure 5.4: Annual reliability indi
Page 52 and 53: Further, the effect of possible ins
Page 56 and 57: For DLC 7.2 it has to be considered
Page 58 and 59: Guideline, DLC 1.5). Furthermore, t
Page 60 and 61: Table 5.28: Output locations for da
Page 62 and 63: From these results it can be clearl
Page 64 and 65: Figure 5.11: Normalised DELs with v
Page 66 and 67: Figure 5.14 presents normalized DEL
Page 68 and 69: Figure 5.16: Output locations for e
Page 70 and 71: UPWIND WP4: Offshore Support Struct
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UPWIND WP4: Offshore Support Struct
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Final report for WP4.3: Enhancement of design methods ... - Upwind

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