Integrating electrical and aerodynamic characteristics for DFIG wind energy extraction and control study

A doubly fed induction generator (DFIG) wind turbine depends on the control of the system at both generator and turbine levels, and the operation of the turbine is affected by the electrical characteristics of the generator and the aerodynamic characteristics of the turbine blades. This paper presents a DFIG energy extraction and control study by combining the two characteristics together in one integrative environment to examine various factors that are critical for an optimal DFIG system design. The generator characteristics are examined for different d‐q control conditions, and the extracted power characteristics of the turbine blades versus generator slip are presented. Then, the two characteristics are analyzed in a joint environment. An integrative study is conducted to examine a variety of parametric data simultaneously for DFIG maximum wind power extraction evaluation. A close‐loop transient simulation using SimPowerSystem is developed to validate the effectiveness of steady‐state results and to further investigate the wind energy extraction and speed control in a feedback control environment. Copyright © 2009 John Wiley & Sons, Ltd.     

Peptidic Ligands to Control the Three‐Dimensional Self‐Assembly of Quantum Rods in Aqueous Media

The use of peptidic ligands is validated as a generic chemical platform allowing one to finely control the organization in solid phase of semiconductor nanorods originally dispersed in an aqueous media. An original method to generate, on a macroscopic scale and with the desired geometry, three‐dimensional supracrystals composed of quantum rods is introduced. In a first step, nanorods are transferred in an aqueous phase thanks to the substitution of the original capping layer by peptidic ligands. Infrared and nuclear magnetic resonance spectroscopy data prove that the exchange is complete; fluorescence spectroscopy demonstrates that the emitter optical properties are not significantly altered; electrophoresis and dynamic light scattering experiments assess the good colloidal stability of the resulting aqueous suspension. In a second step, water evaporation in a microstructured environment yields superstructures with a chosen geometry and in which nanorods obey a smectic B arrangement, as shown by electron microscopy. Incidentally, bulk drying in a capillary tube generates a similar local order, as evidenced by small angle X‐ray scattering.     

Further option for solar concentrators: Aluminum first surface mirrors

The research and development of aluminum first surface solar mirrors is presented. Two protection films for the aluminum layer are discussed: Si₂O₃ and SiO₂. Two electron guns (e-gun) are used to manufacture aluminum first surface solar mirrors. One, for aluminum evaporation, eliminates or minimizes pinholes observed when aluminum is evaporated with tungsten filaments. The other e-gun allows the evaporation of SiO and SiO₂ without the mirror contamination previously seen due to the air when the chamber was opened. Better adherence between the aluminum film and the Si₂O₃ or SiO₂ is obtained due the use of two electron guns that does not permit the chamber to open. Si₂O₃ is a material obtained by oxidation of SiO by admitting some oxygen into the evaporation chamber (10⁻⁴ Torr). The optimum thickness of the aluminum layer was 1000 Å or higher, about 2500 Å for the Si₂O₃, and 3200 Å for the SiO₂. The specular reflectance of these mirrors is about 0.89. These mirrors were tested in the environmental chamber for accelerated weathering without any important degradation, making them another option for solar concentrators in solar energy applications.     

Characterization of electromagnetic fields close to microwave devices using electric dipole probes

A methodology to thoroughly characterize an electric near‐field probe based on small dipole antenna is presented. Both theoretical investigations and experimental direct measurements determine the various characteristics of the probe such as selectivity, sensitivity and spatial resolution. Results show the efficiency of the probe for diagnosing electromagnetic phenomena. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2008.     

Characterisation of elastomers fracture behavior by energetic parameters

The knowledge of fracture behavior of elastomers necessitates the comprehension of crack initiation and propagation phenomena which pose difficulties related to the deformation of elastomers. The reliability of elastomer materials is linked to their resistance to rupture. This resistance can be evaluated using the global approach of fracture mechanics. The objective of this work is to numerically analyze by finite element method the characterization of rupture behavior of these materials on the basis of energetic parameters. Consideration is given to the evolution of the deformation energy density to quantify the energy of tear of a real material identified by hyper-elastic material models.     

Plane wave spectrum theory applied to nearfield measurements for electromagnetic compatibility investigations

Electromagnetic near-field measurement is commonly used to characterise radiated emissions of electronic devices and to study interferences between components and systems. To reduce the number of measurements that usually take a long time, the authors apply a post-processing technique based on the plane wave spectrum (PWS) theory. This post-processing enables the computation of the magnetic field at various distances above the device from two planar measurements only. The authors first present the theory of the PWS approach and in a second step, it is applied to a passive circuit to validate the process. Finally, post-processing is applied to an active circuit.     

Stress Intensity Factor <Emphasis Type="Italic">K</Emphasis><Subscript>I</Subscript> and <Emphasis Type="Italic">T</Emphasis>-Stress Determination in HDPE Material

For the characterization of high-density polyethylene (HDPE) pipes according to the operating conditions, the Nol ring test is an adequate method to rapidly and inexpensively determine the mechanical properties with good effectiveness. In this work, Nol ring tests will be carried out on HDPE material with different crack depth ratios. Based on these results, the brittle fracture of HDPE will be studied and a new experimental technique for measuring stress intensity factor (SIF) and T-stress under mode I conditions is developed. The formulation of the normal strains, close to the crack tip, is given using the first five terms of the generalized Westergaard formulation. Then, in a second step, these formulations are applied to analytically determine the optimum locations for the rectangular rosette to eliminate the errors due to higher order terms of the asymptotic expansion.