Integrated structural optimisation of offshore wind turbine support structures based on finite element analysis and genetic algorithm

By accounting for almost 25% of the capital cost of an OWT (offshore wind turbine), optimisation of support structures provides an efficient way to reduce the currently high cost of offshore wind energy. In this paper, a structural optimisation model for OWT support structures has been developed based on a coupled parametric FEA (Finite Element Analysis) and GA (Genetic Algorithm), minimising the mass of the support structure under multi-criteria constraints. Contrary to existing optimisation models for OWT support structures, the proposed model is an integrated structural optimisation model, which optimises the components of the support structure (i.e. tower, transition piece, grout and monopile) simultaneously. The outer diameters and section thicknesses along the support structure are chosen as design variables. A set of constraints based on multi-criteria design assessment is applied according to standard requirements, which includes vibration, stress, deformation, buckling, fatigue and design variable constraints. The model has been applied to the NREL (National Renewable Energy Laboratory) 5 MW OWT on an 00 (Offshore Code Comparison Collaboration) monopile. The results of the application of the integrated optimisation methodology show a 19.8% reduction in the global mass of the support structure while satisfying all the design constraints. It is demonstrated that the proposed structural optimisation model is capable of effectively and accurately determining the optimal design of OWT support structures, which significantly improves their design efficiency. (C) 2017 Elsevier Ltd. All rights reserved

Effect of annealing on the superconducting properties of a-Nb(x)Si(1-x) thin films

a-Nb(x)Si(1-x) thin films with thicknesses down to 25 {\AA} have been structurally characterized by TEM (Transmission Electron Microscopy) measurements. As-deposited or annealed films are shown to be continuous and homogeneous in composition and thickness, up to an annealing temperature of 500{\deg}C. We have carried out low temperature transport measurements on these films close to the superconductor-to-insulator transition (SIT), and shown a qualitative difference between the effect of annealing or composition, and a reduction of the film thickness on the superconducting properties of a-NbSi. These results question the pertinence of the sheet resistance R_square as the relevant parameter to describe the SIT.Comment: 9 pages, 12 figure

Tailoring strain in SrTiO3 compound by low energy He+ irradiation

The ability to generate a change of the lattice parameter in a near-surface layer of a controllable thickness by ion implantation of strontium titanate is reported here using low energy He+ ions. The induced strain follows a distribution within a typical near-surface layer of 200 nm as obtained from structural analysis. Due to clamping effect from the underlying layer, only perpendicular expansion is observed. Maximum distortions up to 5-7% are obtained with no evidence of amorphisation at fluences of 1E16 He+ ions/cm2 and ion energies in the range 10-30 keV.Comment: 11 pages, 4 figures, Accepted for publication in Europhysics Letter (http://iopscience.iop.org/0295-5075

Microstructural evolution in ODS-EUROFER steel caused by high-dose He ion implantations with systematic variation of implantation parameters

The paper presents a detailed analysis of helium (He) bubble development in ODS-EUROFER steel caused by helium ion implantation in different regimes, with a particular attention to the role of the oxide nanoparticles in promoting the growth of He bubbles, helium accumulation and gas-driven swelling. The Transmission Electron Microscopy (TEM) characterization of steel samples implanted applying systematic variation of experimental parameters has allowed clarifying the trends of the bubble microstructure evolution depending on the implantation dose, flux, and sample temperature. It was found that in all investigated implantation regimes He bubbles formed both in the grain bulk and on various structural defects (dislocations, grain boundaries, oxide particles and carbide precipitates), but the sizes and densities of bubbles in different bubble populations were sensitive to particular irradiation conditions. In the majority of cases the main traps for implanted helium and the main contributors to the estimated swelling were bubbles associated with grain boundaries, though in some cases (high implantation dose or lower temperature) the bubbles in the grain bulk were competitive with the grain boundary bubble population. Oxide particles in ODS-EUROFER were found to be excellent nucleation sites for He bubbles and practically each observed particle hosted a single relatively large bubble, sometimes as large as the particle itself. However, the contribution of oxide-associated bubbles to the estimated swelling and He inventory was found to be minor as compared to other bubble populations because of a relatively low number density of nano-oxides. Comparison of ODS-EUROFER and EUROFER 97 samples implanted with He ions in identical regimes has demonstrated lower efficiency of ODS-EUROFER for accumulating implanted helium in bubbles and noticeably higher share of helium atoms trapped in the vacancy defects invisible by TEM

Machine Learning Bio-molecular Interactions from Temporal Logic Properties

With the advent of formal languages for modeling bio-molecu\-lar interaction systems, the design of automated reasoning tools to assist the biologist becomes possible. The biochemical abstract machine BIOCHAM software environment offers a rule-based language to model bio-molecular interactions and an original temporal logic based language to formalize the biological properties of the system. Building on these two formal languages, machine learning techniques can be used to infer new molecular interaction rules from temporal properties. In this context, the aim is to semi-automatically correct or complete models from observed biological properties of the system. Machine learning from temporal logic formulae is quite new however, both from the machine learning perspective and from the Systems Biology perspective. In this paper we present an ad-hoc enumerative method for structural learning from temporal properties and report on the evaluation of this method on formal biological models of the literature

Point defect distribution in high-mobility conductive SrTiO3 crystals

We have carried out positron annihilation spectroscopy to characterize the spatial distribution and the nature of vacancy defects in insulating as-received as well as in reduced SrTiO3 substrates exhibiting high-mobility conduction. The substrates were reduced either by ion etching the substrate surfaces or by doping with vacancies during thin film deposition at low pressure and high temperature. We show that Ti-vacancies are native defects homogeneously distributed in as-received substrates. In contrast, the dominant vacancy defects are the same both in ion-etched and substrates reduced during the film growth, and they consist of non-homogeneous distributions of cation-oxygen vacancy complexes. Their spatial extension is tuned from a few microns in ion-etched samples to the whole substrate in specimens reduced during film deposition. Our results shed light on the transport mechanisms of conductive SrTiO3 crystals and on strategies for defect-engineered oxide quantum wells, wires and dots

Recent Trends in Development of High Voltage Circuit Breakers with SF6 Alternative Gases

The available knowledge of state-of-the-art of SF6 alternative gases in switching applications was collected and evaluated in an initiative of the Current Zero Club together with CIGRE. The present contribution summarizes the main results of this activity and will also include the latest trends. The main properties and switching performance of new gases are compared to SF6. The most promising new gases are at the moment perfluoroketones and perfluoronitriles. Due to the high boiling point of these gases, in HV applications mixtures with CO2 are used. For MV insulation perfluoroketones are mixed with air, but also other combinations might be possible. The dielectric and switching performance of the mixtures, with mixing ratios that allow sufficiently low operating temperatures, is reported to be only slightly below SF6. Minor design changes or de-rating of switchgear are therefore necessary. Differences between the gas mixtures are mainly in the boiling point and the GWP