Abstract :

Wind energy has received a vast attention in recent years. Multi-megawatt offshore wind turbines (OWTs) mounted on large diameter monopiles are being widely used nowadays in practice. There is a general acceptance that the overall weight of OWTs must be kept to a minimum to reduce their cost. This eventually resulted in a highly flexible slender structure that is dynamically sensitive. The high sensitivity to the highly variable external loads demands special design consideration regarding the natural frequency of the OWT system which must be outside the excitations frequencies to avoid resonance. In addition to the resonance avoidance criterion, OWTs must verify stringent serviceability design requirements during their lifetime, which demand the consideration of a reliable numerical tool with an advanced soil constitutive model for the computation of the OWT dynamic responses. Modal and dynamic analyses of such complicated structures have been well-covered in literature using different aeroelastic simulation tools based on a limited number of degrees of freedom and/or make use of simplified assumptions related to the OWT superstructure, the soil-foundation interaction and the soil behavior. In response to these challenges, this thesis presents a three-dimensional finite element (FE) model that reflects the OWT behavior to a high degree of accuracy and that is used for the computation of the OWT modal and dynamic responses. Another aim of this thesis is to study the excessive vibration mitigation of OWTs. In this regard, this thesis presents a novel technique in which FE analysis is combined with a control system to study the real-time performance of an active tuned mass damper in reducing the OWT vibrations.

JURY

Rapporteurs :
Monsieur Salah Laghrouche, Maître de Conférences HDR à l’Université de Technologie de Belfort-Montbéliard
Monsieur Hussein Mroueh, Professeur à l’Université de Lille Sciences et Technologies

 Examinateurs :
Madame Anne Pantet, Professeur à l’Université du Havre
Monsieur Isam Shahrour, Professeur à l’Université de Lille Sciences et Technologies

Directeurs de thèse :
Monsieur Abdul-Hamid Soubra, Professeur à l’Université de Nantes
Monsieur Mourad Aït-Ahmed, Professeur à l’Université de Nantes

Encadrante :
Madame Valentine Rey, Maître de Conférences à l’Université de Nantes

Invité :
Monsieur Yves Marin, Senior Project Manager – Expert Structural Engineer