Influence of advanced load simulation models on fatigue design of jackets for offshore wind turbines.

Constant developments in the field of offshore wind energy have increased the range of water depths at which wind farms are planned to be installed. Therefore, in addition to monopile support structures suitable in shallow waters (up to 30 m), different types of support structures, able to withstand severe sea conditions at the greater water depths, have been developed. For water depths above 30 m, the jacket is one of the preferred support types. Jacket represents a lightweight support structure, which, in combination with complex nature of environmental loads, is prone to highly dynamic behavior. As a consequence, high stresses with great variability in time can be observed in all structural members. The highest concentration of stresses occurs in joints due to their nature (structural discontinuities) and due to the existence of notches along the welds present in the joints. This makes them the weakest elements of the jacket in terms of fatigue. In the numerical modeling of jackets for offshore wind turbines, a reduction of local stresses at the chord-brace joints, and consequently an optimization of the model, can be achieved by implementing joint flexibility in the chord-brace joints. Therefore, in this work, the influence of joint flexibility on the fatigue damage in chord-brace joints of a numerical jacket model, subjected to advanced load simulations, is studied.

Evaluation of Th and U contamination in the CUORE experiment using a delayed coincidence analysis

The discovery of the neutrino mass is a direct evidence of new physics. Several questions arise from this observation, regarding the mechanism originating the neutrino masses and their hierarchy, the violation of lepton number conservation and the generation of the baryon asymmetry. These questions can be addressed by the experimental search for neutrinoless double beta (0\nu\beta\beta) decay, a nuclear decay consisting of two simultaneous beta emissions without the emission of two antineutrinos. 0\nu\beta\beta decay is possible only if neutrinos are identical to antineutrinos, namely if they are Majorana particles. Several experiments are searching for 0\nu\beta\beta decay. Among these, CUORE is employing 130Te embedded in TeO_2 bolometric crystals. It needs to have an accurate understanding of the background contribution in the energy region around the Q-value of 130Te. One of the main contributions is given by particles from the decay chains of contaminating nuclei (232Th, 235-238U) present in the active crystals or in the support structure. This thesis uses the 1 ton yr CUORE data to study these contamination by looking for events belonging to sub-chains of the Th and U decay chains and reconstructing their energy and time difference distributions in a delayed coincidence analysis. These results in combination with studies on the simulated data are then used to evaluate the contaminations. This is the first time this analysis is applied to the CUORE data and this thesis highlights the feasibility of it while providing a starting point for further studies. A part of the obtained results agrees with ones from previous analysis, demonstrating that delayed coincidence searches might improve the understanding of the CUORE experiment background. This kind of delayed coincidence analysis can also be reused in the future once the, CUORE upgrade, CUPID data will be ready to be analyzed, with the aim of improving the sensitivity to the 0\nu\beta\beta decay of 100Mo.

Prokaryotic community structure in ultra-slow spreading Southwest Indian Ridge.

The Southwest Indian Ridge segment that extends between 10° and 16° E has the slowest spreading rate of any other oceanic ridge (about 8.4 mm/year). In 2013 during the expedition ANTXXIX/8 seismology, geology, microbiology, heat flow analyses were carried out. Here, no hydrothermal plumes or black smoker systems were found but the results of the survey allowed to identify areas with peculiar characteristics: Area 1 with higher heat flux bsf; Area 2 where in 2002 the presence of hydrothermal emissions was hypothesized (Bach et al., 2002); Area 3 with anomalies of methane, ammonium, sulphide and dissolved inorganic carbon in pore water sediment profiles, and recovery of fauna vents. All these aspects suggest the presence of a hydrothermal circulation. Using Illumina 16S gene tag, statistical tools and phylogenetic trees, I provided a biological proof of the presence of hydrothermal circulation in this ridge segment. At Area 3, alpha and beta diversity indexes showed similarities with those described for venting microbial communities and about 40-70% of the dominant microbial community was found phylogenetically related to clones isolated hydrothermal-driven environments. Although the majority of chemosynthetic environment related taxa were not classified like autotrophic prokaryotes, some of them are key taxa in support of the presence of hydrothermal circulation, since they are partners of consortia or mediate specific reaction typically described for hydrothermal and seep environments, or are specialized organisms in exploiting labile organic substrates. Concluding, these results are remarkable because support the importance of ultra slow spreading ridge systems in contributing to global geochemical cycles and larval dispersion of vent fauna.