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Geometric optimization of dielectric elastomer electrodes for dynamic applications
No full textInternational audienc
Predicting the Type of Nonlinearity of Shallow Spherical Shells: Comparison of Direct Normal Form with Modal Derivatives
No full textInternational audienceNonlinear vibrations of free-edge shallow spherical shells with large amplitudes are investigated, with the aim of predicting the type of nonlinearity (hardening/softening behaviour) for each mode of the shell, as a function of the radius R of curvature of the shell, from the plate case (R → ∞) to the limit of non-shallow shell. Two different models (based on von Kármán's assumptions or on full numerical finite element approach), and two different methods (normal form and modal derivatives) are contrasted
Predictions of thermodynamic properties and phase equilibria of refrigerant systems with COSMO approaches
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Fishing behaviours and fisher effect in decision-making processes when facing depredation by marine predators
No full textInternational audienceFishers aim to optimise cost– benefit ratios of their behaviour when exploiting resources. Avoidance of interactions with marine predators (i.e. their feeding on catches in fishing gear, known as depredation) has recently become an important component of their decisions. How fishers minimise these interactions whilst maximising fishing success is poorly understood. This issue is addressed in a sub- Antarctic, long- line fishery confronted with extensive depredation by sperm whales Physeter macrocephalus and killer whales Orcinus orca by examining a 15- year data set. Whereas a broad range of behaviours was identified from spatio- temporal and operational descriptors, none combined high fishing success with low frequency of interactions. With experience, fishers favoured exploitation of productive patches with high frequencies of interactions over avoidance behaviours. Such decisions, although potentially optimal in the short term, are likely to intensify pressures on fish stocks and impact depredating whales. Therefore, the present study provides additional evidence to inform management decisions pertaining to the coexistence between fisheries and marine predators
Adaptation of the nuclear safety code CATHARE3 to supercritical helium flow
No full textSeveral international projects on nuclear fusion are in progress and comprise cryogenic systems for cooling components such as superconducting magnets. Different thermal-hydraulic codes already exist for sizing and validating these cryogenic devices. However, there is still no qualified scientific calculation tool to perform safety thermal hydraulic analyses encountered in fusion reactors. For this purpose, we have started the adaptation of the CATHARE system code, the reference thermal-hydraulic tool for safety studies of French Pressurised Water Reactors developed by CEA, EDF, Framatome, and IRSN, to model supercritical helium flows. Properties of supercritical helium were already available in CATHARE with the fluid library REFPROP. We implemented suitable correlations for friction factors and heat transfer coefficients to account for specific hydraulic parameters of helium flow in Cable In Conduit Conductors (CICC) that are used in superconducting magnets. Then, we performed first evaluations of the CATHARE code abilities to model thermal-hydraulic transient in cryogenic devices of a tokamak. Two cases of helium flow in a CICC of a JT-60SA toroidal field coil have been studied, and comparisons were performed with experimental data and the THEA code developed by CryoSoft. Simulations focusing on the behaviour of a device protected by a safety valve against incidental pressure increase were also performed. CATHARE results were compared with available experimental data on supercritical helium discharge through the safety valve of a tank in case of failure of the insulating vacuum
Effective Model for Elastic Waves in a Substrate Supporting an Array of Plates/Beams with Flexural and Longitudinal Resonances
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Effective Model for Elastic Waves in a Substrate Supporting an Array of Plates/Beams with Flexural and Longitudinal Resonances
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Undulator design for a laser-plasma-based free-electron-laser
No full textInternational audienceThe fourth generation of synchrotron radiation sources, commonly referred to as the Free Electron Laser (FEL), provides an intense source of brilliant X-ray beams enabling the investigation of matter at the atomic scale with unprecedented time resolution. These sources require the use of conventional linear accelerators providing high electron beam performance. The achievement of chirped pulse amplification allowing lasers to be operated at the Terawatt range, opened the way for the Laser Plasma Acceleration (LPA) technique where high energy electron bunches with high current can be produced within a very short centimeter-scale distance. Such an advanced acceleration concept is of great interest to be qualified by an FEL application for compact X-ray light sources. We explore in this paper what the LPA specificities imply on the design of the undulator, part of the gain medium. First, the LPA concept and state-of-art are presented showing the different operation regimes and what electron beam parameters are likely to be achieved. The LPA scaling laws are discussed afterwards to better understand what laser or plasma parameters have to be adjusted in order to improve electron beam quality. The FEL is secondly discussed starting with the spontaneous emission, followed by the different FEL configurations, the electron beam transport to the undulator and finally the scaling laws and correction terms in the high gain case. Then, the different types of compact undulators that can be implemented for an LPA based FEL application are analyzed. Finally, examples of relevant experiments are reported by describing the transport beamline, presenting the spontaneous emission characteristics achieved so far and the future prospects