Comparative investigation of diagnosis media for induction machine mechanical unbalance fault

For an induction machine, we suggest a theoretical development of the mechanical unbalance effect on the analytical expressions of radial vibration and stator current. Related spectra are described and characteristic defect frequencies are determined. Moreover, the stray flux expressions are developed for both axial and radial sensor coil positions and a substitute diagnosis technique is proposed. In addition, the load torque effect on the detection efficiency of these diagnosis media is discussed and a comparative investigation is performed. The decisive factor of comparison is the fault sensitivity. Experimental results show that spectral analysis of the axial stray flux can be an alternative solution to cover effectiveness limitation of the traditional stator current technique and to substitute the classical vibration practice.     

On the evaluation of wind loads for wind turbines' foundation design: Experimental and numerical investigations

In the past two decades, wind farms have been enjoying renewed interest as means for clean and renewable energy production. Larger and taller wind turbines are used for harvesting wind energy. In this paper, a boundary‐layer wind tunnel experiment was carried out on a model of the 5‐MW National Renewable Energy Laboratory (NREL) wind turbine, to evaluate overall wind‐induced base loadings in a parked condition. While mean and background base loadings were measured experimentally, a posttest dynamic analysis framework is developed to assess inertial loads analytically. The analytical analysis is carried out under both rigid and flexible tower‐foundation assumptions. Whenever applicable, the wind tunnel measurements are compared with NREL results, which were obtained by using the Fatigue, Aerodynamics, Structures, and Turbulence (FAST) software. The comparison shows a good agreement between the proposed approach and the available FAST results. In addition, the study indicates that the flexibility of the foundation may result in a reduced overall wind loads, due to base isolation effects. However, the assumption of a rigid foundation results in a slightly conservative base loads. This said, depending on the available foundation system, the methodology followed in the current paper remains in force and the base stiffness can be updated to permit the estimation of actual foundation loadings.     

Support vector machine based decision for mechanical fault condition monitoring in induction motor using an advanced Hilbert-Park transform

In this work we suggest an original fault signature based on an improved combination of Hilbert and Park transforms. Starting from this combination we can create two fault signatures: Hilbert modulus current space vector (HMCSV) and Hilbert phase current space vector (HPCSV). These two fault signatures are subsequently analysed using the classical fast Fourier transform (FFT). The effects of mechanical faults on the HMCSV and HPCSV spectrums are described, and the related frequencies are determined. The magnitudes of spectral components, relative to the studied faults (air-gap eccentricity and outer raceway ball bearing defect), are extracted in order to develop the input vector necessary for learning and testing the support vector machine with an aim of classifying automatically the various states of the induction motor.     

Thermomechanical material parameters characterization of the superalloy PN 3601669-7 under low-velocity impacts

This work concerns the characterization of the thermodynamic behavior of the superalloy Airsist 215 (PN 3601669-7) containing cobalt. Such superalloys are used in aeronautical construction, in the hot parts of the turbine. They are frequently used for the production of the paddles. The parts in service are subjected to dynamic solicitations and thermal fluctuations over the course of time. They are responsible for modification and degradation of material properties. This can lead to the appearance of cracks and, in the long term, to the rupture of these parts. In this paper, a preliminary physical study is made on the appearance of the cracks, followed by experiments using shocks at ambient temperature and under a heating situation which simulates combustion. It is found that these dynamic loads have a significant impact on the development of the cracks that appear on the segments of the turbine nozzle. The study is devoted to the elastic shock of Hertz-Boussinesq extended to viscoelastic bodies by direct convolution of Riemann-Stielges. The interest resides in the local convolution and the distribution of stresses in the contact zone. The shock excitation method includes a deduced force in the load and disload phases. This force is an impulse which approaches a Dirac function. The sample can be modeled approximately by a system of one degree of freedom for natural frequency, damping and transfer function. The spectral response of the specified shock allows calculation of the damping. Every point of this spectrum gives the response for the linear system of the transfer function. Then, viscoelastic shock parameters are deduced.     

An improved spectral analysis of the stray flux component for the detection of air-gap irregularities in squirrel cage motors

For machines? monitoring purpose, the classical motor current signature analysis has shown its weakness in distinguishing the eccentricity occurrence in presence of others mechanical faults. Although Park?s vector approach can cover this drawback, the high cost due to the requirement to use three current sensors associated with an advanced processing technique, makes it less desired by industrialists. In this paper, we suggest an alternative diagnosis method based on a suitable processing of the stray flux data. The experimental results have revealed the potential of a simple search coil for the detection and the distinction of the accurate eccentricity nature even in presence of similar mechanical faults.     

Experimental analysis of the influence of the voltage waveform on ozone generation efficiency

Although the dielectric barrier discharge (DBD) has been widely considered and studied for ozone generation, only a few studies have examined the influence of the alternating voltage waveform on the ozone rate production. This paper analyses the influence of the voltage shape on the ozone concentration and the energy efficiency of a DBD cylindrical ozone generator. Three voltage signals were studied using a high-voltage amplifier: sinusoidal, triangular and rectangular signals with voltage values up to 8 kV and frequencies up to 1.1 kHz. The obtained results showed that the efficiency of the ozone generator depends strongly on the type of the voltage waveform. The maximum values of the energy efficiency and the ozone concentration were obtained with the triangular voltage signal. This wave shape configuration has been successfully used for discolouration of water contaminated by textile dye.     

Investigation of load transfer mechanisms in granular platforms reinforced by geosynthetics above cavities

Geosynthetic-reinforced soils constitute an interesting solution for bridging cavities. Many methods have been developed to analyze the stability of soil-geosynthetic-cavity systems, but none of them is able to take into account all the complexities of these mechanisms. Many researchers have assumed mechanisms developed in the reinforced granular platform when cavities appear, such as load transfer and expansion of materials. However, they are not fully understood because many factors can influence the design, such as the cavity opening processes, the type, and the density of the soil.In this study, a new laboratory apparatus is developed to simulate two different cavity opening procedures (trapdoor and progressive opening) for different geometric configurations. A series of tests is conducted for three granular soils with two different geosynthetic sheets. By measuring the shape of the surface soil settlement and the geosynthetic deflection, the expansion coefficient is calculated. A novel tactile pressure sensor is used to observe the load transfer during the cavity opening. The experimental data are analyzed and the influence of the experimental conditions (geometric and soil properties and the opening procedure) are also discussed. Correspondingly, elicited findings can be used to propose recommendations to improve the existing design methods.     

New separation method of metal/plastic micronized particles using travelling wave conveyors

The paper reports an experimental investigation for studying the movement dynamics and the separation of micronized particles on a poly-phase travelling wave conveyor (TWC). A digital balance and a sensitive electrometer controlled by Labview software were used to analyse the velocity and the material flow rate on a three-phase conveyor with respect to the variation of both the amplitude and the frequency of the applied voltage. It was found that about 80% of the particles mass move together in one single wave and that the electric charge gained by the particles increases with the intensity of the electric field. Moreover, preliminary experiments showed that it is possible to separate a granular mixture of plastic and copper micronized particles using a TWC. Successful experiments were carried out on micronized samples of both electric cable and electronic card wastes. High purity metal was recovered.