Offshore Code Comparison Collaboration Continuation Within IEA Wind Task 30: Phase II Results Regarding a Floating Semisubmersible Wind System

This paper deals with the feasibility of using a 5 MW drivetrain which is designed for a land-based turbine, on floating wind turbines. Four types of floating support structures are investigated: spar, TLP and two semi-submersibles. The fatigue damage of mechanical components inside the gearbox and main bearings is compared for different environmental conditions, ranging from cut-in to cutout wind speeds. For floating wind turbines, representative wave conditions are also considered.All wind turbines are ensured to follow similar power curves, but differences in the control system (integral to different concepts) are allowed. A de-coupled analysis approach is employed for the drivetrain response analysis. First, an aero-hydro-servo-elastic code is employed for the global analysis. Next, motions, moments and forces from the global analysis are applied on the gearbox multi body model and the loads on gears and bearings are obtained. The results suggest that the main bearings sustain more damage in floating wind turbines than on land-based. The highest main bearing damage is observed for the spar floating wind turbine. The large wave induced axial load on the main shaft is found to be the primary reason of this high damage in the spar wind turbine. Apart from the main bearings -which are located on the main shaft outside the gearbox -other bearings and gears inside the gearbox hold damages in floating wind turbines equal or even less than in the land-based turbine. It is emphasized that the results presented in this study are based on a drivetrain with two main bearings, which considerably reduces the non-torque loads on

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“…In this study, the orientation of 92 the platform with respect to the wind is opposite that described by Robertson et al [26,27]. …”

supporting

confidence: 53%

Stochastic dynamic load effect and fatigue damage analysis of drivetrains in land-based and TLP, spar and semi-submersible floating wind turbines

et al. 2015

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“…The semi-submersible design is based on that used in the OC4 Phase II project [11] and also tested in the DeepCwind project [10]. To maintain the same draft specified for the floating HAWT, the ballast was rearranged to accommodate the VAWT, as described by Wang et al [12].…”

Section: Semi-submersiblementioning

confidence: 99%

A Comparison on the Dynamics of a Floating Vertical Axis Wind Turbine on Three Different Floating Support Structures

Borg

Collu

2014

Energy Procedia

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To increase the competitiveness of offshore wind energy in the global energy market, it is necessary to identify optimal offshore wind turbine configurations to deliver the lowest cost of energy. For deep waters where floating wind turbines are the feasible support structure option, the vertical axis wind turbine concept might prove to be one of these optimal configurations. This paper carries out a preliminary investigation into the dynamics of a vertical axis wind turbine coupled with three generic floating support structures originally intended for horizontal axis wind turbines. The modifications to the original characteristics of the support structures were kept to a minimum to illustrate the use of floating horizontal axis wind turbine platforms for floating vertical axis wind turbines Issues regarding the adequacy of the mooring systems are outlined and an overview of platform responses in a number of varying met-ocean conditions is presented and discussed.

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“…In Ref. [19], the resonance effect was seen also for a TLP and the semi-submersible used in the OC4 study [20]. Thus, instead of optimising the design, it seems relevant to keep this standard design and highlight the issue.…”

Section: Eigenperiodsmentioning

confidence: 99%

Time domain analysis procedures for fatigue assessment of a semi-submersible wind turbine

Kvittem

Moan

2015

Marine Structures

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Long term time domain analysis of the nominal stress for fatigue assessment of the tower and platform members of a three-column semisubmersible was performed by fully coupled time domain analyses in SimoRiflex-AeroDyn. By combining the nominal stress ranges with stress concentration factors, hot spot stresses for fatigue damage calculation can be obtained. The aim of the study was to investigate the necessary simulation duration, number of random realisations and bin sizes for the discretisation of the joint wind and wave distribution. A total of 2316 3-hour time domain simulations, were performed.In mild sea states with wind speeds between 7 and 9 m/s, the tower and pontoon experienced high fatigue damage due to resonance in the first bending frequency of the tower from the tower wake blade passing frequency (3P).Important fatigue effects seemed to be captured by 1 hour simulations, and the sensitivity to number of random realisations was low when running simulations of more than one hour. Fatigue damage for the tower base converged faster with simulation duration and number of random realisations than it did for the platform members.Bin sizes of 2 m/s for wind, 1 s for wave periods and 1 m for wave heights seemed to give acceptable estimates of total fatigue damage. It is, however, important that wind speeds that give coinciding 3P and tower resonance are included and that wave periods that give the largest pitch motion are included in the analysis.

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Offshore Code Comparison Collaboration Continuation Within IEA Wind Task 30: Phase II Results Regarding a Floating Semisubmersible Wind System

Cited by 125 publications

References 3 publications

Stochastic dynamic load effect and fatigue damage analysis of drivetrains in land-based and TLP, spar and semi-submersible floating wind turbines

Stochastic dynamic load effect and fatigue damage analysis of drivetrains in land-based and TLP, spar and semi-submersible floating wind turbines

A Comparison on the Dynamics of a Floating Vertical Axis Wind Turbine on Three Different Floating Support Structures

Time domain analysis procedures for fatigue assessment of a semi-submersible wind turbine

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