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Gilles L.,Thirty Meter Telescope Observatory Corporation | Massioni P.,CNRS Ampere Laboratory | Kulcsar C.,University Paris - Sud | Raynaud H.-F.,University Paris - Sud | Ellerbroek B.,Thirty Meter Telescope Observatory Corporation
Journal of the Optical Society of America A: Optics and Image Science, and Vision | Year: 2013

This paper discusses the performance and cost of two computationally efficient Fourier-based tomographic wavefront reconstruction algorithms for wide-field laser guide star (LGS) adaptive optics (AO). The first algorithm is the iterative Fourier domain preconditioned conjugate gradient (FDPCG) algorithm developed by Yang et al. [Appl. Opt. 45, 5281 (2006)], combined with pseudo-open-loop control (POLC). FDPCG's computational cost is proportional to N log(N), where N denotes the dimensionality of the tomography problem. The second algorithm is the distributed Kalman filter (DKF) developed by Massioni et al. [J. Opt. Soc. Am. A 28, 2298 (2011)], which is a noniterative spatially invariant controller. When implemented in the Fourier domain, DKF's cost is also proportional to N log(N). Both algorithms are capable of estimating spatial frequency components of the residual phase beyond the wavefront sensor (WFS) cutoff frequency thanks to regularization, thereby reducing WFS spatial aliasing at the expense of more computations. We present performance and cost analyses for the LGS multiconjugate AO system under design for the Thirty Meter Telescope, as well as DKF's sensitivity to uncertainties in wind profile prior information. We found that, provided the wind profile is known to better than 10% wind speed accuracy and 20 deg wind direction accuracy, DKF, despite its spatial invariance assumptions, delivers a significantly reduced wavefront error compared to the static FDPCG minimum variance estimator combined with POLC. Due to its nonsequential nature and high degree of parallelism, DKF is particularly well suited for real-time implementation on inexpensive off-the-shelf graphics processing units. © 2013 Optical Society of America.

Feki N.,INSA Lyon | Clerc G.,CNRS Ampere Laboratory | Velex Ph.,INSA Lyon
Electric Power Systems Research | Year: 2013

This paper deals with the simulation of the dynamic behavior of induction motor/gear systems. The corresponding model combines: (i) a permeance network aimed at representing squirrel-cage induction motors and (ii) a 3D dynamic model of spur and helical gears including the shafts and bearings. Some classic motor defects (rotor eccentricity) and gear faults (tooth spalls) are considered and an iterative solution technique is presented which makes it possible to solve the coupled electro-mechanical problem. Based on a number of simulations, it is shown that the frequencies associated with defects can be identified and that distant detection and monitoring of tooth faults using stator currents seem promising alternatives to the classic techniques based on mechanical vibration analysis. © 2012 Elsevier B.V. All rights reserved.

Okubo H.,Nagoya University | Beroual A.,CNRS Ampere Laboratory
IEEE Electrical Insulation Magazine | Year: 2011

The recent technical trend of sulfur hexafluoride (SF6) substitutes and future perspectives in the development of electrical insulation techniques for electric power equipment are reviewed and discussed. © 2006 IEEE.

Imano A.M.,University of Douala | Beroual A.,CNRS Ampere Laboratory
IEEE Transactions on Dielectrics and Electrical Insulation | Year: 2010

This paper presents the results of a study carried out on the deformation of a water surface and the effect water drops have on both conducting and dielectric solid surfaces subjected to a 50-Hz-volage stress. Also, contained in it are fundamental observations of current discharges characterizing water drops and metal electrode configurations as well as those configurations resulting from a flat water surface and a metal electrode. The measurements taken with both rod and point electrodes also came under investigation. The inception field strength of partial discharges between water surface and metal electrodes is analyzed. The discharge activities between water drops and between a conducting water drop and a small rod electrode on a flat hydrophobic insulator are also investigated. The results obtained characteristics of show typical discharge current during the discharge inception and development with and without water filaments, with regard to drop-drop and drop-rod configurations on the dielectric solid surface. This experimental study provides a better understanding of the processes leading up to flashover of hydrophobic insulators through discharges between water drops resulting of the distortion of these drops. © 2010 IEEE.

Feki N.,CNRS Contacts and Structural Mechanics Laboratory | Clerc G.,CNRS Ampere Laboratory | Velex Ph.,CNRS Contacts and Structural Mechanics Laboratory
Mechanical Systems and Signal Processing | Year: 2012

Fault diagnosis in geared transmissions is traditionally based on vibration monitoring but, in a number of cases, sensor implementation and signal transfer from rotary to stationary parts can cause problems. This paper presents an original integrated electro-mechanical model aimed at testing the possibility and the interest of tooth fault detection based on electric measurements on the motor stator. The motor is simulated using Kron's transformation while the mechanical transmission is accounted for by a lumped parameter model. Tooth defects are assimilated to distributions of initial separations between the mating flanks whose positions and shapes are controlled. A unique non-linear parametrically excited differential system is obtained, which provides direct access to both the electrical and mechanical variables. A number of results are presented, which illustrate the possibility of tooth fault detection by stator current measurements with regard to the position and dimensions of the defect. © 2011 Elsevier Ltd. All rights reserved.

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