Details
| Original language | English |
|---|---|
| Qualification | Doctor of Engineering |
| Awarding Institution | |
| Supervised by |
|
| Date of Award | 11 Aug 2023 |
| Publication status | Published - 2024 |
Abstract
to produce climate-neutral energy. Therefore, an accelerated installation of offshore
wind turbines is required. The design is to be achieved with respect to standards and
guidelines. Especially probabilistic design methods allow an accurate and economic
structural design.
Not only the environmental conditions vary during the lifetime, but the short-term
loads are also subject of random scattering. For the design of offshore wind turbines,
the required load simulations are usually carried out in time domain. In comparison, it is less time-consuming to obtain loads by means of frequency-domain analysis. This is very beneficial for the probabilistic design which requires significantly more load simulations in time domain. However, non-linearities and time-variant behaviour of offshore wind turbines cannot be represented well during the load simulation in frequency domain.
Extreme loads and fatigue loads can be calculated by means of frequency-domain analysis. The determination of the distribution functions of extreme values is well established on a theoretical background. As for the fatigue design, different empirical models exist which describe the distribution function of fatigue loads on the basis of frequency-domain analysis. In this thesis, a new model is introduced which leads to more accurate results.
Since frequency-domain analysis is not always suitable, the transformation of signals
given in frequency domain is required to generate respective random time series. As for the design of offshore wind turbines, only limited recommendations are stated in standards on how to carry out this transformation. Detailed analysis shows that accurate results with respect to wave-induced loads are also obtained for coarser discretisation of spectra. The resulting loads and their statistical properties are still accurate, while the numerical effort can be reduced in comparison to the stated recommendations.
On the basis of theoretical findings, time series from load simulations of offshore wind turbines are analysed regarding their spectral properties. Investigations are carried out to evaluate the agreement between the extreme load and fatigue loads which are either simulated or calculated on the basis of the spectral properties. It is also shown that currents within sea states lead to increased fatigue loads.
Keywords
- Offshore wind energy, Load simulation, Frequency-domain analysis, Fatigue, Probabilistic design, contains research data
Sustainable Development Goals
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2024. 199 p.
Research output: Thesis › Doctoral thesis
}
TY - BOOK
T1 - Probabilistic design of support structures for offshore wind turbines by means of non-Gaussian spectral analysis
AU - Kelma, Sebastian
N1 - This thesis results from my occupation as research associate at the Institute for Steel Construction of the Gottfried Wilhelm Leibniz Universität Hannover. The basic ideas arose during my research activities within the joint research projects “Probabilistische Sicherheitsbewertung von Offshore-Windenergieanlagen” and “GIGAWIND life”, which were financially supported by the Lower Saxony Ministry of Science and Culture and the Federal Ministry for Economic Affairs and Energy, respectively. First of all, I express my gratitude to Prof. Dr.-Ing. Peter Schaumann for the possibility to learn and carry out research at the Institute for Steel Construction as well as for his guidance, patience, and constant motivation through the many years. The trust in my professional skills and the freedom to work on the topics of my thesis contributed significantly to the finalisation of my dissertation. I like to thank Prof. Dr.-Ing. Michael Beer for being the second examiner, for his interest, as well as for the valuable comments and discussions. Furthermore, I acknowledge Prof. Dr.-Ing. Andreas Reuter for chairing the doctoral committee and supporting the examination procedure. I like to thank the colleagues at the Institute for Steel Construction for the pleasant and productive working atmosphere. I always enjoyed the fruitful and enjoyable discussions and talks, may they have been of work-related, scientific, or non-scientific nature. Special thanks go to Dr. rer. nat. Florian Kelma, Jan Kulikowski, and Joshua Possekel, who proofread parts of the thesis and provided many helpful comments and proposals for improvements. Last but not least, I thank my friends and especially my family. Thank you for all the support and encouragements which you gave to me in all the years and in so many various ways. Danke für Euren Beitrag zu dieser Arbeit.
PY - 2024
Y1 - 2024
N2 - Offshore wind energy is of special importance in order to meet the ambitious goalsto produce climate-neutral energy. Therefore, an accelerated installation of offshorewind turbines is required. The design is to be achieved with respect to standards andguidelines. Especially probabilistic design methods allow an accurate and economicstructural design.Not only the environmental conditions vary during the lifetime, but the short-termloads are also subject of random scattering. For the design of offshore wind turbines,the required load simulations are usually carried out in time domain. In comparison, it is less time-consuming to obtain loads by means of frequency-domain analysis. This is very beneficial for the probabilistic design which requires significantly more load simulations in time domain. However, non-linearities and time-variant behaviour of offshore wind turbines cannot be represented well during the load simulation in frequency domain.Extreme loads and fatigue loads can be calculated by means of frequency-domain analysis. The determination of the distribution functions of extreme values is well established on a theoretical background. As for the fatigue design, different empirical models exist which describe the distribution function of fatigue loads on the basis of frequency-domain analysis. In this thesis, a new model is introduced which leads to more accurate results.Since frequency-domain analysis is not always suitable, the transformation of signalsgiven in frequency domain is required to generate respective random time series. As for the design of offshore wind turbines, only limited recommendations are stated in standards on how to carry out this transformation. Detailed analysis shows that accurate results with respect to wave-induced loads are also obtained for coarser discretisation of spectra. The resulting loads and their statistical properties are still accurate, while the numerical effort can be reduced in comparison to the stated recommendations.On the basis of theoretical findings, time series from load simulations of offshore wind turbines are analysed regarding their spectral properties. Investigations are carried out to evaluate the agreement between the extreme load and fatigue loads which are either simulated or calculated on the basis of the spectral properties. It is also shown that currents within sea states lead to increased fatigue loads.
AB - Offshore wind energy is of special importance in order to meet the ambitious goalsto produce climate-neutral energy. Therefore, an accelerated installation of offshorewind turbines is required. The design is to be achieved with respect to standards andguidelines. Especially probabilistic design methods allow an accurate and economicstructural design.Not only the environmental conditions vary during the lifetime, but the short-termloads are also subject of random scattering. For the design of offshore wind turbines,the required load simulations are usually carried out in time domain. In comparison, it is less time-consuming to obtain loads by means of frequency-domain analysis. This is very beneficial for the probabilistic design which requires significantly more load simulations in time domain. However, non-linearities and time-variant behaviour of offshore wind turbines cannot be represented well during the load simulation in frequency domain.Extreme loads and fatigue loads can be calculated by means of frequency-domain analysis. The determination of the distribution functions of extreme values is well established on a theoretical background. As for the fatigue design, different empirical models exist which describe the distribution function of fatigue loads on the basis of frequency-domain analysis. In this thesis, a new model is introduced which leads to more accurate results.Since frequency-domain analysis is not always suitable, the transformation of signalsgiven in frequency domain is required to generate respective random time series. As for the design of offshore wind turbines, only limited recommendations are stated in standards on how to carry out this transformation. Detailed analysis shows that accurate results with respect to wave-induced loads are also obtained for coarser discretisation of spectra. The resulting loads and their statistical properties are still accurate, while the numerical effort can be reduced in comparison to the stated recommendations.On the basis of theoretical findings, time series from load simulations of offshore wind turbines are analysed regarding their spectral properties. Investigations are carried out to evaluate the agreement between the extreme load and fatigue loads which are either simulated or calculated on the basis of the spectral properties. It is also shown that currents within sea states lead to increased fatigue loads.
KW - Offshore-Windenergie
KW - Lastsimulation
KW - Frequenzbereichanalyse
KW - Ermüdung
KW - Probabilistische Strukturauslegung
KW - enthält Forschungsdaten
KW - Offshore wind energy
KW - Load simulation
KW - Frequency-domain analysis
KW - Fatigue
KW - Probabilistic design
KW - contains research data
U2 - 10.15488/15784
DO - 10.15488/15784
M3 - Doctoral thesis
ER -