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

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UPWIND WP4: Offshore Support Structures and Foundations is related to the size of the service vessel that should be considered for load case definitions. It is expected that the vessels are larger than the ones used for fixed offshore wind farms. Load Cases and Design Conditions The load cases and design conditions can follow the structure of the GL Guidelines for Offshore Wind Turbines (shown below) or the IEC 61400-3 standard. Additional considerations from particular aspects of floating and moored structures, as listed on the previous paragraph, shall be considered in the specification of the design and operative conditions. • Normal operation (DLC 1.x) • Operation plus occurrence of faults (DLC 2.x) • Start-Up, Stop (DLC 3.x, 4.x, 5.x) • Parked / Standstill / Ready for operation (DLC 6.x) • Parked / Standstill after occurrence of fault (DLC 7.x) • Maintenance / Transportation / Repair (DLC 8.x) Limit States: Examples Possible resulting limit states for FOWTs from the above Guidelines are listed below and in Table 9.1. Especially the accidental and the serviceability limit states with requirements for the stability of the motions and cares about floatability and leakage shall be considered. Ultimate limit state: • Normal operation plus occurrence of fault • Emergency stop procedures • Extreme environmental conditions (current, wind, wave, sea ice, temperatures) • Parked / standstill after occurrence of fault • Line tension limit Fatigue limit state: • Normal operation • Start / Normal stop procedures • Parked / standstill due to non-availability reasons Accidental limit state: • Loss of station keeping e.g. anchor or mooring line (free drifting) • Collision, ship impact Serviceability limit state: • Floating structure offset • Hydrodynamic stability • Motions • Floatability • Leakage • Clearance requirements for mooring of different structures Limit State ULS FLS Table 9.1: Possible Resulting Limit States Design Condition DLC Normal operation, operation plus occurrence of fault DLC 1.x, 2.x. 3.x Normal and emergency stop procedures DLC 4.x , 5.x Extreme environmental conditions (current, wind, wave, sea ice, temperatures) DLC 1.5, 1.6, 1.8, 6.x Parked / standstill DLC 6.x Hydrodynamic stability all DLCs Transport, erection, maintenance and repair DLC 8.x Normal operation DLC 1.2 Start / normal stop procedures DLC 2.3, 3.1, 4.1 136
UPWIND WP4: Offshore Support Structures and Foundations SLS ALS Parked / standstill due to availability reasons DLC 6.4, 7.2 Hydrodynamic stability all DLCs Motions all DLCs Floatability all DLCs Leakage, water on deck, openings Limitation of the movement (blade deflection) Loss of station keeping (free drifting) Ship impact Safety Factors Table 9.2 gives a comparison of the current safety factors adopted in the existing standards GL Guidelines for Offshore Wind Turbines [31] and IEC 61400-3 [69]. Table 9.3 summarises the limit states and safety factors of different standards, together with the associated return periods. Table 9.4 gives assumptions for environmental conditions (return periods) associated with different design conditions. Table 9.2: Safety Factors: Guidelines GL Offshore Wind Turbines 2005 and IEC 61400-3 Limit State Design Condition 137 GL 2005 Offshore Wind Turbines Normal operation plus occurrence of fault 1,10 / 1,20 1,10 / 1,35 ULS Emergency stop procedures Extreme environmental con- 1,20 1,35 ditions (wind, wave, sea ice, temperatures) 1,35 1,35 Parked / standstill 1,35 1,35 Parked / standstill after occurrence of fault 1,10 1,10 Normal operation 1,00 1,00 FLS Start / Normal stop procedures 1,00 1,00 Parked / standstill due to availability reasons 1,00 1,00 SLS Elastic deflections 1,00 n/a ALS n/a n/a n/a IEC 61400-3 Offshore Wind Turbines, Edition 1 It should be emphasized that safety factors for floating wind turbines should be assessed based on existing experience from various offshore standards, combined with consideration of: • Reliability level required • Uncertainties in loads, resistances and models used to calculate characteristic load effects and load bearing capacities • Computational models required / recommended for calculation of loads and load bearing capacities
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Project UpWind Contract No.: 019945
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Acknowledgement The presented work
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Summary The overall aim of the UpWi
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Table of Contents Acknowledgement..
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Task 4.1 Integration of support str
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Sequential coupling The sequential
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analysis. In the new multibody code
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Figure 2.4: 2nd global bending mode
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3.2 Comparison of deterministic loa
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Figure 3.5: Time series of axial fo
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• Time domain simulation in ADCoS
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• A supplementary load vector for
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The following results are found: Fi
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Figure 4.5: Output positions in the
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It is directly visible that there i
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ated eigenfrequency is shifted into
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Water levels For the calculation of
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guidelines for the inclusion of cli
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damaging if the frequency of the ex
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uncertain parameters carefully. Thr
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Table 5.3 shows annual reliability
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Steel substructure for offshore win
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Table 5.16 shows the required FDF v
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A Fracture Mechanical (FM) modellin
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Figure 5.4: Annual reliability indi
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Further, the effect of possible ins
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Rainflow evaluation The load cases
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For DLC 7.2 it has to be considered
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Guideline, DLC 1.5). Furthermore, t
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Table 5.28: Output locations for da
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From these results it can be clearl
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Figure 5.11: Normalised DELs with v
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Figure 5.14 presents normalized DEL
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Figure 5.16: Output locations for e
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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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