94 publications from this institution
A new type of large torque air-cored cryogenic ac machine has been presented earlier. The experimental results obtained with the first prototype Supersat 001 are discussed. The experimental results are compared with the theorical ones deduced from a three-dimensional analytical model. The main results concern the static and dynamic behavior and the analysis of the losses which have led to the consideration of a new design of the first prototype.
Within the frame of the NECER program the scaling of capillary phenomena in a centrifuge has been investigated by cross-testing at several laboratories, using similar sample sizes and the same Congleton Sand. Drainage tests were carried out in Manchester, Lyngby and Bordeaux. The moisture retention profile was measured after the test and in-flight measurement of water content was also attempted, using radiotracers and tensiometers (Manchester) as well as dielectric FD and TDR probes (Lyngby and Bordeaux). Infiltration tests were conducted in Bochum, Manchester and Nantes. The movement of the water front was observed visually, and in some cases pore pressure transducers and tensiometers were also used. The test results indicate that the different laboratories get comparable results and that it appears to be possible to model the entire capillary zone in a centrifuge with the vertical dimension reduced by the g-factor N. Time dependant phenomena appear to be accelerated by the factor N squared.
The major drawback of usual dual-stator ac machines, when supplied by a voltage-source inverter (VSI), is the occurrence of extra harmonic currents. These extra currents circulate only in the stator windings and cause additional losses. This paper deals with the modeling and design of dual-stator winding ac machines for safe operation with a VSI. A new reference frame model for a dual-stator induction machine (DSIM), including mutual leakage coupling, is proposed. This model allows us to highlight the previously mentioned circulating harmonic currents. The leakage inductance associated with these harmonics is shown to have quite a small value, highly depending on the coil pitch. It is also shown that full pitch is required, and that special slot shape designs should be investigated, to limit the magnitude of circulating currents. Experimental results on a prototype of a DSIM are presented and they show a very good correlation with theoretical curves.
The major drawback of usual dual-stator AC machines supplied by a voltage source inverter (VSI) is the occurrence of large circulating harmonic currents, causing extra losses. This paper deals with the design of dual-stator winding AC machines for safe operation with VSI. A new reference frame model of a dual-stator induction machine (DSIM), including mutual leakage coupling, is proposed. The leakage inductance associated with the inaccurate harmonics is shown to have a quite small value, highly depending on the coil pitch. It is also shown that full pitch is required, and that special designs of slot shape should be investigated to limit the negative impact of circulating currents. Experimental results on a prototype of DSIM are presented and they show very good correlation with the theoretical curves.
This paper deals with a new kind of superconducting limiter which is not based on the transition from the superconducting state to the normal one by overtaking the critical current. This new superconducting current limiter has no current transport in the superconductor. Indeed, in our structure, the current limitation is based on the saturation of a high temperature bulk superconductor by the magnetic flux. The principle of this new type of limiter has been explained in a previous paper. Now we present the design of this kind of limiter and we show the influence of the temperature on its functioning.
Induction motor plays a very important role in industry applications. Early fault detection is one of the main problems. So, in order to detect an incipient defect, we must pay a special attention to the spectral analysis of instantaneous power. The effectiveness of this method is based on the reliability of the signals. The study of the product of voltage and current allows the detection of a rotor fault in induction motor. Several experiments were made on a test bed of 3 kW. A spectral analysis of instantaneous power for the detection of a half broken rotor bar is used to provide an accurate diagnosis. Comparisons between spectrums database when the motor is healthy and under rotor faults are presented and commented. The results obtained show the possibility to detect a half broken rotor bar in induction motor.
This paper is intended to show how to replace a fuzzy controller by a neural network one in a rotor field oriented control for induction motors. The output surface of the fuzzy controller is approached by a neural network. The neural network structure used for this controller is presented as well as the learning process necessary to prepare the neural network controller to act like a fuzzy one.Experimental results on position control and speed control under load are presented and commented as well as a discussion and comparison with classical Pl controllers.
ABSTRACT In this paper we propose a model of the synchronous machine for fast digital computation of its transient behaviour. This modelling avoids numerical inversion of the inductance matrix even when some stator phases are open-circuited and allows then a large saving in the computation time. The obtained models are tested in the simulation of some sudden short circuits of an alternator. Simulation and experimental results are compared as well as the computation time using this modelling and the usual one.
Machine learning (ML) models in material science and construction engineering have significantly improved predictive accuracy and decision making. However, the practical implementation of these models often requires technical expertise, limiting their accessibility for engineers and practitioners. A user-friendly graphical user interface (GUI) can be an essential tool to bridge this gap. In this study, a sustainable approach to improve the compressive strength (C.S) of plastic-based mortar mixes (PMMs) by replacing cement with industrial waste materials was investigated using ML models such as support vector machine, AdaBoost regressor, and extreme gradient boosting. The significance of key mix parameters was further analyzed using SHapley Additive exPlanations (SHAPs) to interpret the influence of input variables on model predictions. To enhance the usability and real-world application of these ML models, a GUI was developed to provide an accessible platform for predicting the C.S of PMMs based on input material proportions. The ML models demonstrated strong correlations with experimental results, and the insights from SHAP analysis further support data-driven mix design strategies. The developed GUI serves as a practical and scalable decision support system, encouraging the adoption of ML-based approaches in sustainable construction engineering.
We analyze analytically and numerically the stress distribution along the plug-rock interface and within an axially loaded plug emplaced in a borehole in rock. Experiments show that the interface strength increases with decreasing plug radius and with increasing plug length. Axial strength decreases as a power law of plug radius. An increase in the modulus ratio (ratio of plug modulus to rock modulus) increases the interface strength, until it levels off at a ratio of about 5.0. For short plugs, the tensile stresses may reach a magnitude significant to be of concern for long-term stability of the plug and of the host rock. Out studies suggest designing friction plugs with a length to radius ratio of at least 8.0. In practice, especially for short-term performance, e.g., emergency flood control or temporary diversions, a ratio of 8.0 may not be necessary or justified. For permanent abandonment plugs, it is essential to reduce the tensile stresses in the plug and in the host rock to a level that will minimize the risk of long-term deterioration. We recommend in situ experiments on larger diameter plugs to assess the validity of the proposed size effect extrapolation obtained in this study. Key words: borehole plugging (sealing), shaft seal design, plug-rock interface strength, axial strength, bond strength, cement grout.
This paper deals with an implementation of a stator flux oriented method on a DSP board to drive an induction motor. This method is based on the integration of EMF directly provided by two extra coils located on the equivalent /spl alpha/, /spl beta/ reference axes of the stator. The open-loop integration problem is solved thanks to an online offset compensation algorithm which offers robustness especially at low speed. Experimental results of speed control are presented and commented to show the effectiveness of this method.
Determining the elements of the equivalent scheme of an induction machine is not trivial. Knowing that the values of the parameters change with the operating point, we can only find an optimal set which is suitable to describe the dynamic behaviour of the machine. The calculations of the vector elements of the parameters are made using optimization methods. Some of these slowly converge while others diverge if the initial vector is far from the solution. Marquardt's method does not present these disadvantages. Taking into account some realistic constraints, we apply this method here in order to find electrical and mechanical parameters during the starting phase of an induction machine. Results of experiments and simulations are favourably compared.
