Impact of turbulence induced loads and wave kinematic models on fatigue reliability estimates of offshore wind turbine monopiles

Lorenzo Colone*, Anand Natarajan, Nikolay Krasimirov Dimitrov

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

The cost of offshore wind turbine substructures has a significant impact on competitiveness of the wind energy market and is affected by conservative safety margins adopted in the design phase. This implies that an accurate design load prediction, especially of those resulting in fatigue damage accumulation, may help achieve more cost-effective solutions. In this article, the impact of turbulence and wave loads on fatigue reliability of pile foundations is investigated for a 5-MW offshore wind turbine. Loads obtained by varying turbulence percentiles are compared with those obtained from the full joint probability distribution of wind speed and turbulence through Monte Carlo (MC) simulations, and from the equivalent turbulence level currently adopted by IEC standards. The analyses demonstrate that a lower equivalent turbulence percentile leads to a more realistic and less conservative estimation of fatigue loads. Subsequently, the research focuses on studying the effects of uncertain marine environments on the fatigue load distribution, showing that the latter is insensitive to the random variability of the hydrodynamic coefficients. With respect to the wave kinematic model, a comparison between nonlinear and linear waves clearly suggests that hydrodynamic forces depend significantly on the kinematic model adopted and the operational conditions of the turbine. Furthermore, a term is derived to correct the error introduced by Wheeler stretching at finite water depths. The respective model uncertainties that originate from the nonlinear irregular wave model and Wheeler correction are quantified and employed in a reliability analysis. In a case study, the results are finally compared in terms of estimated probability of failure, with the aim to quantify the influence of environmental models on monopile reliability.
Original languageEnglish
JournalOcean Engineering
Volume155
Pages (from-to)295-309
ISSN0029-8018
DOIs
Publication statusPublished - 2018

Keywords

  • Offshore wind turbine
  • Monopile foundation
  • Turbulence
  • Nonlinear waves
  • Model uncertainty
  • Fatigue reliability

Cite this

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title = "Impact of turbulence induced loads and wave kinematic models on fatigue reliability estimates of offshore wind turbine monopiles",
abstract = "The cost of offshore wind turbine substructures has a significant impact on competitiveness of the wind energy market and is affected by conservative safety margins adopted in the design phase. This implies that an accurate design load prediction, especially of those resulting in fatigue damage accumulation, may help achieve more cost-effective solutions. In this article, the impact of turbulence and wave loads on fatigue reliability of pile foundations is investigated for a 5-MW offshore wind turbine. Loads obtained by varying turbulence percentiles are compared with those obtained from the full joint probability distribution of wind speed and turbulence through Monte Carlo (MC) simulations, and from the equivalent turbulence level currently adopted by IEC standards. The analyses demonstrate that a lower equivalent turbulence percentile leads to a more realistic and less conservative estimation of fatigue loads. Subsequently, the research focuses on studying the effects of uncertain marine environments on the fatigue load distribution, showing that the latter is insensitive to the random variability of the hydrodynamic coefficients. With respect to the wave kinematic model, a comparison between nonlinear and linear waves clearly suggests that hydrodynamic forces depend significantly on the kinematic model adopted and the operational conditions of the turbine. Furthermore, a term is derived to correct the error introduced by Wheeler stretching at finite water depths. The respective model uncertainties that originate from the nonlinear irregular wave model and Wheeler correction are quantified and employed in a reliability analysis. In a case study, the results are finally compared in terms of estimated probability of failure, with the aim to quantify the influence of environmental models on monopile reliability.",
keywords = "Offshore wind turbine, Monopile foundation, Turbulence, Nonlinear waves, Model uncertainty, Fatigue reliability",
author = "Lorenzo Colone and Anand Natarajan and Dimitrov, {Nikolay Krasimirov}",
year = "2018",
doi = "10.1016/j.oceaneng.2018.02.045",
language = "English",
volume = "155",
pages = "295--309",
journal = "Ocean Engineering",
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publisher = "Pergamon Press",

}

Impact of turbulence induced loads and wave kinematic models on fatigue reliability estimates of offshore wind turbine monopiles. / Colone, Lorenzo; Natarajan, Anand; Dimitrov, Nikolay Krasimirov.

In: Ocean Engineering, Vol. 155, 2018, p. 295-309.

Research output: Contribution to journalJournal articleResearchpeer-review

TY - JOUR

T1 - Impact of turbulence induced loads and wave kinematic models on fatigue reliability estimates of offshore wind turbine monopiles

AU - Colone, Lorenzo

AU - Natarajan, Anand

AU - Dimitrov, Nikolay Krasimirov

PY - 2018

Y1 - 2018

N2 - The cost of offshore wind turbine substructures has a significant impact on competitiveness of the wind energy market and is affected by conservative safety margins adopted in the design phase. This implies that an accurate design load prediction, especially of those resulting in fatigue damage accumulation, may help achieve more cost-effective solutions. In this article, the impact of turbulence and wave loads on fatigue reliability of pile foundations is investigated for a 5-MW offshore wind turbine. Loads obtained by varying turbulence percentiles are compared with those obtained from the full joint probability distribution of wind speed and turbulence through Monte Carlo (MC) simulations, and from the equivalent turbulence level currently adopted by IEC standards. The analyses demonstrate that a lower equivalent turbulence percentile leads to a more realistic and less conservative estimation of fatigue loads. Subsequently, the research focuses on studying the effects of uncertain marine environments on the fatigue load distribution, showing that the latter is insensitive to the random variability of the hydrodynamic coefficients. With respect to the wave kinematic model, a comparison between nonlinear and linear waves clearly suggests that hydrodynamic forces depend significantly on the kinematic model adopted and the operational conditions of the turbine. Furthermore, a term is derived to correct the error introduced by Wheeler stretching at finite water depths. The respective model uncertainties that originate from the nonlinear irregular wave model and Wheeler correction are quantified and employed in a reliability analysis. In a case study, the results are finally compared in terms of estimated probability of failure, with the aim to quantify the influence of environmental models on monopile reliability.

AB - The cost of offshore wind turbine substructures has a significant impact on competitiveness of the wind energy market and is affected by conservative safety margins adopted in the design phase. This implies that an accurate design load prediction, especially of those resulting in fatigue damage accumulation, may help achieve more cost-effective solutions. In this article, the impact of turbulence and wave loads on fatigue reliability of pile foundations is investigated for a 5-MW offshore wind turbine. Loads obtained by varying turbulence percentiles are compared with those obtained from the full joint probability distribution of wind speed and turbulence through Monte Carlo (MC) simulations, and from the equivalent turbulence level currently adopted by IEC standards. The analyses demonstrate that a lower equivalent turbulence percentile leads to a more realistic and less conservative estimation of fatigue loads. Subsequently, the research focuses on studying the effects of uncertain marine environments on the fatigue load distribution, showing that the latter is insensitive to the random variability of the hydrodynamic coefficients. With respect to the wave kinematic model, a comparison between nonlinear and linear waves clearly suggests that hydrodynamic forces depend significantly on the kinematic model adopted and the operational conditions of the turbine. Furthermore, a term is derived to correct the error introduced by Wheeler stretching at finite water depths. The respective model uncertainties that originate from the nonlinear irregular wave model and Wheeler correction are quantified and employed in a reliability analysis. In a case study, the results are finally compared in terms of estimated probability of failure, with the aim to quantify the influence of environmental models on monopile reliability.

KW - Offshore wind turbine

KW - Monopile foundation

KW - Turbulence

KW - Nonlinear waves

KW - Model uncertainty

KW - Fatigue reliability

U2 - 10.1016/j.oceaneng.2018.02.045

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