The present thesis, carried out at Aventa, aims at the extrapolation and evaluation of structural loads acting on an offshore wind turbine with a floating platform under nominal power production conditions. The study focuses on the IEA 15 MW Reference Wind Turbine, coupled with the UMaine VolturnUS-S Reference Platform, a semi-submersible floating structure developed by the University of Maine. The design of this system falls within the framework of the international IEA Wind TCP Task 37, which is part of the IEA Wind Technology Collaboration Programme (TCP). The choice of this system is consistent with global trends in the wind energy sector, characterized by an increasing demand for wind power and the development of ever-larger turbines. To maximize energy production, installations are progressively being moved to offshore areas farther from the coast, where wind conditions are stronger and more stable. However, this relocation leads to an increment in seabed depth, making the use of fixed-bottom foundations impractical and requiring floating platforms capable of ensuring turbine stability and safety. For the analysis of the integrated floating offshore wind turbine system - comprising the tower, rotor, nacelle, floating platform and mooring system - a location situated south of Japan was selected. For this site, a comprehensive collection of metocean data (wind, waves and currents) was carried out to characterize the environmental conditions and to define the mathematical models used in the numerical simulations. The adopted methodology was developed in accordance with the main international DNV and IEC standards. In particular, DNV-ST-0437 and IEC 61400-3 were applied for the definition of the Design Load Cases (DLC) relevant to offshore wind turbines, while DNV-RP-C205 provided the guidelines for developing the environmental models representing wind, wave and current fields. Subsequently, the fatigue analysis was performed following the recommendations of DNV-RP-C203, which defines the criteria and methodologies for assessing the fatigue life of structures subjected to cyclic loading in marine environments. This approach ensures full consistency with best engineering practices and guarantees that the structural load simulations are realistic, reliable and fully compliant with recognized industry standards. The main results obtained from the study indicate that the present work can be regarded as an initial guideline for the fatigue-life assessment of offshore wind turbines, providing a structured starting point for future investigations. Some aspects of the analysis, due to time and computational constraints, were simplified through approximations; further investigation of these aspects represents the natural continuation of the overall project. More detailed analyses and the development of targeted methodologies will increase the reliability of the numerical models and, consequently, broaden their potential applications.
Il presente lavoro di tesi, svolto presso l’azienda Aventa, ha come obiettivo l’estrapolazione e la valutazione dei carichi strutturali agenti su una turbina eolica offshore con struttura galleggiante, in condizioni operative di produzione nominale di energia. Lo studio prende in esame la IEA 15 MW Reference Wind Turbine, accoppiata alla piattaforma galleggiante semi-sommergibile UMaine VolturnUS-S Reference Platform, sviluppata dall’Università del Maine. La progettazione di questo sistema rientra nell’ambito del progetto internazionale IEA Wind TCP Task 37, parte del programma IEA Wind Technology Collaboration Programme (TCP). La scelta del sistema considerato è coerente con le tendenze globali nel settore eolico, caratterizzate da una crescente richiesta di energia eolica e dallo sviluppo di turbine di taglia sempre maggiore. Per massimizzare la produzione, le installazioni sono progressivamente spostate verso aree offshore più distanti dalla costa, dove il vento è più intenso e costante. Questo allontanamento comporta però un aumento della profondità del fondale, rendendo impraticabile l’uso di fondazioni fisse e rendendo necessarie piattaforme galleggianti, in grado di garantire stabilità e sicurezza anche in acque profonde. Per l’analisi del sistema integrato della turbina eolica offshore galleggiante - comprendente torre, rotore, navicella, piattaforma galleggiante e sistema di ormeggio - è stata individuata una località situata a sud del Giappone. Per tale sito è stata condotta una raccolta completa dei dati meteo-marini (vento, onde e correnti), necessari per caratterizzare le condizioni ambientali e definire i modelli matematici impiegati nelle simulazioni numeriche. La metodologia adottata è stata sviluppata in conformità con i principali standard internazionali DNV e IEC. In particolare, le norme DNV-ST-0437 e IEC 61400-3 sono state utilizzate per la definizione dei Design Load Case (DLC) applicabili alle turbine eoliche offshore, mentre la DNV-RP-C205 ha fornito le linee guida per la costruzione dei modelli ambientali rappresentativi dei campi di vento, onda e corrente. Successivamente, l’analisi a fatica è stata condotta in accordo con le linee guida riportate nella DNV-RP-C203, che definisce i criteri e le metodologie per la valutazione della vita a fatica delle strutture soggette a carichi ciclici in ambiente marino. Tale approccio assicura coerenza con le migliori pratiche ingegneristiche e garantisce che le simulazioni dei carichi strutturali risultino realistiche, affidabili e pienamente aderenti agli standard di settore. I risultati principali emersi dallo studio indicano che il presente lavoro può essere considerato una prima linea guida per l’analisi della vita a fatica delle turbine offshore, fornendo un punto di partenza strutturato per studi futuri. Alcuni aspetti dell’analisi, per motivi legati a vincoli temporali e computazionali, sono stati semplificati tramite approssimazioni; lo studio di tali aspetti rappresenta la naturale evoluzione dell’intero progetto. Analisi dettagliate e sviluppi di metodologie mirate, accresceranno l’affidabilità dei modelli numerici e con esso le potenziali applicazioni.
Simulazione Dinamica Integrata di una Turbina Eolica Offshore Galleggiante e Valutazione della Vita a Fatica della Torre
PULZELLA, PIERLUIGI
2024/2025
Abstract
The present thesis, carried out at Aventa, aims at the extrapolation and evaluation of structural loads acting on an offshore wind turbine with a floating platform under nominal power production conditions. The study focuses on the IEA 15 MW Reference Wind Turbine, coupled with the UMaine VolturnUS-S Reference Platform, a semi-submersible floating structure developed by the University of Maine. The design of this system falls within the framework of the international IEA Wind TCP Task 37, which is part of the IEA Wind Technology Collaboration Programme (TCP). The choice of this system is consistent with global trends in the wind energy sector, characterized by an increasing demand for wind power and the development of ever-larger turbines. To maximize energy production, installations are progressively being moved to offshore areas farther from the coast, where wind conditions are stronger and more stable. However, this relocation leads to an increment in seabed depth, making the use of fixed-bottom foundations impractical and requiring floating platforms capable of ensuring turbine stability and safety. For the analysis of the integrated floating offshore wind turbine system - comprising the tower, rotor, nacelle, floating platform and mooring system - a location situated south of Japan was selected. For this site, a comprehensive collection of metocean data (wind, waves and currents) was carried out to characterize the environmental conditions and to define the mathematical models used in the numerical simulations. The adopted methodology was developed in accordance with the main international DNV and IEC standards. In particular, DNV-ST-0437 and IEC 61400-3 were applied for the definition of the Design Load Cases (DLC) relevant to offshore wind turbines, while DNV-RP-C205 provided the guidelines for developing the environmental models representing wind, wave and current fields. Subsequently, the fatigue analysis was performed following the recommendations of DNV-RP-C203, which defines the criteria and methodologies for assessing the fatigue life of structures subjected to cyclic loading in marine environments. This approach ensures full consistency with best engineering practices and guarantees that the structural load simulations are realistic, reliable and fully compliant with recognized industry standards. The main results obtained from the study indicate that the present work can be regarded as an initial guideline for the fatigue-life assessment of offshore wind turbines, providing a structured starting point for future investigations. Some aspects of the analysis, due to time and computational constraints, were simplified through approximations; further investigation of these aspects represents the natural continuation of the overall project. More detailed analyses and the development of targeted methodologies will increase the reliability of the numerical models and, consequently, broaden their potential applications.| File | Dimensione | Formato | |
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https://hdl.handle.net/20.500.12075/25587