An original method to compute a superconducting screen is considered. It is shown that this problem is equivalent to a magnetostatic inverse problem, which is solved using a genetic algorithm. This method is appropriate to superconducting films of any shape hecause only surface currents are to be considered for superconducting materials. To illustrate the method two examples are presented.
A superconducting magnet energy storage (SMES) can be used as a pulsed power supply. A superconducting coil stores energy without electrical losses and this energy can be recovered through a second wire on which the charge (electromagnetic launcher, for example) is linked. The design of such an apparatus needs to solve simultaneously thermal, magnetic, and electric equations. We proposed a three-dimensional finite difference method to solve these coupled problems. This tool enables us to describe resistive zones of expansion in thick coils during a quench and to predict the duration and the efficiency of the discharge. Moreover, it indicates if the coil is prevented from an excessive temperature increase. Then, a probative device is described and experimental results are compared with theoretical ones.
Dans les zones littorales soumises à defortes marées, sont apparues de nombreuses perturbations ou ruines d'ouvrages induites par des contraintes océaniques.Si les conséquences nuisibles de l'agitation de la houle ne tardent pas à apparaître sur la carapace des ouvrages, la marée a un impact différé et peut engendrer des désordres majeurs aussi bien au niveau du noyau de l'ouvrage qu'au niveau de la carapace.Des affouillements locaux ont ainsi été observés au pieds des talus d'estran, mais aussi des ruptures en grand glissement causées par la marée.Depuis plusieurs années, l'étude de stabilité de pentes n'a pas cessé d'être affinée par différents développements, par contre l'influence du niveau piézométrique dû à la marée dans les calculs de stabilité de talus d'estran n'a jamais été abordée.A partir d'un code numérique de stabilité de pentes (PETAL du L.C.P.C.) on utilise la méthode des perturbations pour caractériser les lignes de glissement et pour définir le coefficient de sécurité associé.Dans le but de nous permettre de prendre en compte l'influence d'un cycle de marée sur la stabilité d'une pente, nous évaluons l'augmentation du risque engendré par l'action hydraulique cyclique de la marée.Différents cas, avec un sol de référence, ont été étudiés en faisant varier d'une part la pente du talus et d'autre part le niveau d'eau établi dans le massif.L'utilisation de l'outil numérique a permis de quantifier l'influence de la marée, à différents instants du cycle, sur le coefficient de sécurité au grand glissement d'un talus estuarien semiimmergé.Les résultats obtenus montrent une réduction significative du coefficient de sécurité et mettent en évidence l'importance de la prise -en compte de la marée dans les calculs de stabilité des talus d'estran.
This paper deals with instrument fault detection within a reconfigurable vector control scheme of induction motor. Current sensors failures are detected and reconfiguration of current measurement is achieved in order to allow continuous operation of the vector control. Simulation and experiments using a 5.5 kW machine are used to verify the theory.
<title>Abstract</title> Bridge abutment is the most critical civil engineering infrastructure directly exposed to floodwater. Previous research focused on the bridge abutment scouring under diverse flow conditions with different types of countermeasures. To date, no study has been conducted to observe energy reduction and flow dynamics around bridge abutment. Therefore, the current research investigates energy reduction and flow dynamics around bridge abutments with eco-friendly materials (brick waste (BW) and marble waste (MW)) under subcritical flow conditions. Experiments were performed in a controlled laboratory setting to investigate different parameters such as water surface profile, energy reduction, reduction of fluid force index (RFI%), moment index (RMI%), and delay in floodwater arrival time. These parameters were investigated under different conditions including without waste (WW) and with eco-friendly materials. The result demonstrates that energy reduction increases by increasing the Froude number (Fr) from 0.13 to 0.22. Energy reduction increases up to 5.95%, 6.5%, and 6.27% in the case of WW, MW, and BW respectively. The use of MW resulted in maximum energy reduction where the average energy reduction reached 4.38%. The highest RFI% of 8.86% and RMI% of 12.44% were recorded with the use of MW during the experiments. The findings also show that a significant reduction in floodwater arrival occurred in the case of MW up to 68% compared to without abutment case in the channel. These findings provide valuable insights into flow characteristics and energy dissipation around bridge abutments, contributing to sustainable and resilient hydraulic infrastructure design.
International audience
Superconducting Magnetic Energy Storage can be used to produce very high pulsed power peak. A superconducting coil is magnetically coupled with another coil linked to the load. During the storage phase, the current is constant. In order to transfer the energy to the load, we cause the quench of the superconducting coil. It is very important to know the efficiency of the transfer and how much energy is discharged in the Helium vessel. In this paper, we propose an analytical method which enables us to calculate very quickly the electrical parameters of such a device.
In electrical engineering, static converters generate harmonics; consequently the losses in the conductors increase. To use High-Tc superconductors for current transportation, it is important to evaluate and to measure their losses. Under the assumption that the superconductor is only exposed to its self-field, Bean's model is used to compute these losses. This work deals with the losses in a cylindrical High-Tc superconductor current-lead. It is made of compacted composite of Bi-Pb-Sr-Ca-Cu-O-2223, the value of its critical current is about 100 A (measured with I /spl mu/V/cm criteria). Two types of measuring methods are used. The first of them uses a differential amplifier associated with a computer, which calculate the instantaneous power by numerical integration. The second series of experiments, valid only with sinusoidal current, are made using a lock-in amplifier measuring the R.M.S. voltage. The value of transport current is high enough to be compatible with applications. Both methods give nearly the same results for sinusoidal signal. Measurements are made with non-sinusoidal current, to do that the superconductor sample is fed by a dimmer switch. The experiments show that the losses are essentially a function of the maximum value of the current, not of the firing angle. We conclude that the shape of the current is not important compared to its peak value.
The present paper focuses by means of an experimental study, on the effect of a bearing fault on the stator current signatures in induction motors. The variation in the amplitude of the characteristic components is not so significant. For that and in order to depict the presence of the fault harmonic signatures, the authors used the phase analysis of Hilbert transform applied on the spectrum modulus of the line current.
