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Structural probabilistic assessment of Offshore Wind Turbine
operation fatigue based on Kriging interpolation
Rui Teixeira...
Outline
• Introduction
• Offshore wind turbine fatigue design methodology
• Structural probabilistic assessment of Offshor...
Why is Offshore Wind Turbines development important?
• Global warming is a scientific fact.
• Renewable energy needs to be...
Introduction
• Probabilistic analysis of the design of Offshore Wind Turbine (OWT)
towers
• OWT Towers fatigue life
• OWT ...
Offshore wind turbine fatigue design methodology
• Computationally demanding task.
• Current methodology involves the
extr...
• Using Kriging surrogate models to design towers to fatigue
• Short term damage follows a Lognormal
distribution.
• Krigi...
Probabilistic optimization of the design of OWT towers
Loads tower
sections.
NREL FAST
Monopile OWT
Rainflow
counting,
dam...
Results - Structural probabilistic assessment of Offshore WindTurbine operation
fatigue based on Kriging interpolation
• 1...
Conclusions
• A new approach was implemented to design OWT to fatigue design. It is a “non-
intrusive” methodology.
• The ...
Further Developments:
• Stochastic sensitivity of the Design of Experiments (DoE).
• No additional complexity should be co...
Thank you!
Rui Teixeira rteixeir@tcd.ie
This project has received funding from the European Union’s Horizon 2020 research ...
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"Structural probabilistic assessment of offshore wind turbine operation fatigue based on Kriging interpolation" presented at ESREL2017 by Rui Teixeira

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Abstract: The probabilistic analysis of Offshore Wind Turbines (OWT) is not a new practice. The standards for designing OWT (IEC 61400 class) emphasizes that assessing uncertainty is of major importance inside the design chain. Still, major challenges related to the uncertainty and the probabilistic assessment pose to the sector and its development. The analysis of operational loads is one them. The problem of analyzing extreme responses or cumulated damage in operation during the design phase is significantly related to its high computational cost. As we progressively add complexity to the system to account for its uncertainties, the computational effort increases and a perceptive design becomes a heavy task. If an optimization process is then sought, the designing effort grows even further. In the particular case of fatigue analysis, it is frequent to not be able to cover a full lifetime of simulations due to computational cost restrictions. The mentioned difficulties fomented the utilization of surrogate models in the reliability analysis of OWT. From these surrogate approximations the ones based on Kriging models gained a special emphasis recently for structural reliability. It was shown that, for several applications, these models can be efficient and accurate to approximate the response of the system or the limit state surfaces. The presented paper tackles some of the issues related to their applicability to OWT, in a case specific scenario of the tower component subjected to operational fatigue loads. A methodology to assess the reliability of the tower component to fatigue damage is presented. This methodology combines a Kriging model with the theory of extreme values. A one-dimensional Kriging case using the state of art NREL’s monopile turbine is presented. The reliability of the OWT tower is calculated for 20 years. The results show that the usage of a Kriging model to calculate the long term damage variation shows a high potential to assess the reliability of OWT towers to fatigue failure.

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"Structural probabilistic assessment of offshore wind turbine operation fatigue based on Kriging interpolation" presented at ESREL2017 by Rui Teixeira

  1. 1. Structural probabilistic assessment of Offshore Wind Turbine operation fatigue based on Kriging interpolation Rui Teixeira, Alan O’Connor and Maria Nogal Department of Civil, Structural and Environmental Engineering, Trinity College Dublin, Dublin James Nichols and Mark Spring Lloyd’s Register, United Kingdom ESREL2017, 21st June 2017 This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 642453
  2. 2. Outline • Introduction • Offshore wind turbine fatigue design methodology • Structural probabilistic assessment of Offshore Wind Turbine operation fatigue based on Kriging interpolation • Conclusions • Further developments
  3. 3. Why is Offshore Wind Turbines development important? • Global warming is a scientific fact. • Renewable energy needs to be “pulled” forward. • EU targets of 20% of Renewable Energy in total energy consumption by 2020 and 27% by 2030 (EU Commission). • Projections of >2°C increase in global temperature by 2100 compared with pre- industrial levels (Paris Agreement). Source: Siemens 2014 report
  4. 4. Introduction • Probabilistic analysis of the design of Offshore Wind Turbine (OWT) towers • OWT Towers fatigue life • OWT are highly complex systems that are affected by multiple sources of uncertainty. Demand a strong reliability design basis. Why?
  5. 5. Offshore wind turbine fatigue design methodology • Computationally demanding task. • Current methodology involves the extrapolation of load cycles using a Peak-Over-threshold approach. Below the threshold level loads are accounted deterministically (IEC 61400-3). • Still they may account for substantial damage for low SN slope (m) materials. High damage generated by small amplitude loads. • Ok for e.g. blades. • Not ok for e.g. tower.
  6. 6. • Using Kriging surrogate models to design towers to fatigue • Short term damage follows a Lognormal distribution. • Kriging is an interpolation model that considers Gaussian uncertainty in the interpolation. Probabilistic optimization of the design of OWT towers • Applied to decrease computational cost. • Potential of application for reliability is very high.
  7. 7. Probabilistic optimization of the design of OWT towers Loads tower sections. NREL FAST Monopile OWT Rainflow counting, damage summation and statistical characterization of short-term damage. Kriging surrogate model. Long term fatigue damage distribution. Statistically accurate? No Yes
  8. 8. Results - Structural probabilistic assessment of Offshore WindTurbine operation fatigue based on Kriging interpolation • 100 evaluations of 20 years damage (time demanding). • Very low probability of failure NREL 5MW monopile OWT. • Variations of short term damage with the wind are very high. • 72 evaluations to create the model + 60 evaluations to correct it. Validated with m- life.
  9. 9. Conclusions • A new approach was implemented to design OWT to fatigue design. It is a “non- intrusive” methodology. • The Gaussian properties of the Kriging surface are adequate for simulating short term damage on the OWT tower. • Using the Kriging to approximate the damage surface of the model can cut computational time from the design analysis. • OWT fatigue design is a very computer resource consuming task. • Using the estimation of error in some points of the DoE to correct the prediction is valid option but that needs more research. • It demands many additional simulations to converge the statistical distributions.
  10. 10. Further Developments: • Stochastic sensitivity of the Design of Experiments (DoE). • No additional complexity should be considered in the model if the variable does not account for important information in regard of OWT tower damage. • Adaptive Design of Experiments when creating the surrogate model. • Allows to optimize the ratio cost/accuracy when creating the surrogate model. • Study the influence of deterministic prediction in DoE when creating the surrogate model. • Nevertheless, interesting potential to design and optimize the design of OWT towers to operational fatigue.
  11. 11. Thank you! Rui Teixeira rteixeir@tcd.ie This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 642453

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