Wind/Wave Misalignment in the Loads Analysis of a Floating Offshore Wind Turbine

Barj, Lucie; Jonkman, Jason; Robertson, Amy; Stewart, Gordon M.; Lackner, Matthew A.; Haid, Lorenz; Matha, Denis; Stewart, Susan W.

doi:10.2514/6.2014-0363

Cited by 28 publications

(20 citation statements)

References 10 publications

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“…These are variables used to represent environmental conditions in the IEC and other standards. From these site data, we model these variables with the following distributions, chosen based on goodness of fit and previous experience: wind speed ( V h u b ): Weibull; wave direction ( θ w or WaveDir): von Mises conditioned on wind speed; wave height ( H s ): gamma conditioned on wind speed and wave direction; wave period ( T p ): gamma conditioned on wind speed and wave height; and wind‐platform direction ( θ p or PlatformDir): von Mises conditioned on wind speed. …”

Section: Model Backgroundmentioning

confidence: 99%

High‐throughput computation and the applicability of Monte Carlo integration in fatigue load estimation of floating offshore wind turbines

et al. 2015

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Long-term fatigue loads for floating offshore wind turbines are hard to estimate because they require the evaluation of the integral of a highly nonlinear function over a wide variety of wind and wave conditions. Current design standards involve scanning over a uniform rectangular grid of metocean inputs (e.g., wind speed and direction and wave height and period), which becomes intractable in high dimensions as the number of required evaluations grows exponentially with dimension. Monte Carlo integration offers a potentially efficient alternative because it has theoretical convergence proportional to the inverse of the square root of the number of samples, which is independent of dimension. In this paper, we first report on the integration of the aeroelastic code FAST into NREL's systems engineering tool, WISDEM, and the development of a high-throughput pipeline capable of sampling from arbitrary distributions, running FAST on a large scale, and postprocessing the results into estimates of fatigue loads. Second, we use this tool to run a variety of studies aimed at comparing grid-based and Monte Carlo-based approaches with calculating long-term fatigue loads. We observe that for more than a few dimensions, the Monte Carlo approach can represent a large improvement in computational efficiency, but that as nonlinearity increases, the effectiveness of Monte Carlo is correspondingly reduced. The present work sets the stage for future research focusing on using advanced statistical methods for analysis of wind turbine fatigue as well as extreme loads.

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Section: Model Backgroundmentioning

confidence: 99%

High‐throughput computation and the applicability of Monte Carlo integration in fatigue load estimation of floating offshore wind turbines

et al. 2015

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“…This has been documented through analyses for offshore turbines with monopile foundations [32], and is also expected to be a problem for floating wind turbines [33]. In the current study, some of the base cases were run with misaligned wind and waves (0-90 • ), both with head wind and wind from the side with the rotor yawed 90…”

Section: Phase 2 -Environmental Conditions For Wind-wave Misalignmentmentioning

confidence: 92%

“…14). The reason for the different conclusion in [33] and [32] will be further discussed in another paper with misalignment as the main focus [19]. In short, the bending moments from wind and waves act around different axes, and thus the contribution to fatigue damage comes in different cross section locations.…”

Section: Misaligned Wind and Wave Conditionsmentioning

confidence: 94%

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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“…Based on observations in the North Sea, it is common to reach 30° of misalignment, but misalignments greater than 60° occur less than 5% of the time . Therefore, misalignment effects on four different FHAWTs were investigated in conditions of up to 90° of misalignment between the wind and wave directions by Bachynski et al, whereas Barj et al conducted a study on wind‐wave misalignment in the loads analysis of a spar floating wind turbine for all angles between wind and wave directions.…”

Section: Introductionmentioning

confidence: 99%

Stochastic dynamic response analysis of a floating vertical-axis wind turbine with a semi-submersible floater

2016

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Floating vertical-axis wind turbines (FVAWTs) provide the potential for utilizing offshore wind resources in moderate and deep water because of their economical installation and maintenance. Therefore, it is important to assess the performance of the FVAWT concept. This paper presents a stochastic dynamic response analysis of a 5 MW FVAWT based on fully coupled nonlinear time domain simulations. The studied FVAWT, which is composed of a Darrieus rotor and a semisubmersible floater, is subjected to various wind and wave conditions. The global motion, structural response and mooring line tension of the FVAWT are calculated using time domain simulations and studied based on statistical analysis and frequency-domain analysis. The response of the FVAWT is compared under steady and turbulent wind conditions to investigate the effects of turbulent wind. The advantage of the FVAWT in reducing the 2P effect on the response is demonstrated by comparing the floating wind turbine with the equivalent land-based wind turbine. Additionally, by comparing the behaviour of FVAWTs with flexible and rigid rotors, the effect of rotor flexibility is evaluated. Furthermore, the FVAWT is also investigated in the parked condition. The global motions and structural responses as a function of the azimuthal angle are studied. Finally, the dynamic response of the FVAWT in selected misaligned wind and wave conditions is analysed to determine the effects of wind-wave misalignment on the dynamic response.

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Wind/Wave Misalignment in the Loads Analysis of a Floating Offshore Wind Turbine

Cited by 28 publications

References 10 publications

High‐throughput computation and the applicability of Monte Carlo integration in fatigue load estimation of floating offshore wind turbines

High‐throughput computation and the applicability of Monte Carlo integration in fatigue load estimation of floating offshore wind turbines

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

Stochastic dynamic response analysis of a floating vertical-axis wind turbine with a semi-submersible floater

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