Constant Frequency Value Research Articles

Fundamental Frequency Normalization for Reliable Detection of Rotor and Load Defects in VSD-Fed Induction Motors

Rotor fault is a condition that may occur in induction motors due to high forces and stresses on rotor bars or end rings. When this occurs, the machine may lead to a forced outage in production lines. Several methods have been proposed in the literature for the detection of rotor faults; however, they cannot work under variable frequency conditions, and they are very sensitive to mechanical load oscillations. This paper presents a novel frequency normalization methodology for reliable rotor defect diagnosis in variable-frequency drive-fed systems. The normalization is implemented by demodulating the stator current signal with a time-variant factor. As a result, the fundamental component of the stator current is normalized in a constant frequency value, whereas avoiding spectral leakage and frequency smearing. This enables the transient stator current signature analysis to accurately locate targeted fault signatures. The effectiveness of the proposed frequency normalization approach is demonstrated by analyzing the stator current of motors under non-stationary conditions. Experimental results show that the proposed methodology can detect and distinguish between load oscillations and rotor fault signatures for avoiding false rotor fault alarms.

Comprehensive prediction of coal seam thickness by using in-seam seismic surveys and Bayesian kriging

Quantitative determination of the coal seam thickness distribution within the longwall panel is one of the primary works before integrated mining. In-seam seismic (ISS) surveys and interpolations are essential methods for predicting thickness. In this study, a new quantitative method that combines ISS and Bayesian kriging (BK), called ISS–BK, is proposed to determine the thickness distribution. ISS–BK consists of the following six steps. (1) The group velocity of Love waves is plotted by using the simultaneous iterative reconstruction technique under a constant frequency value. (2) An approximate quantitative relationship between the thickness and the group velocity is fitted based on sampling points of the coal seam thickness, which are measured during the process of entry development. (3) The group velocity map is translated into a primary thickness map according to the above-mentioned fitted equation. (4) By subtracting the ISS prediction result from the actual thickness at a sampling point, the residual variable is created. (5) The residual distribution is interpolated within the whole longwall panel by applying BK. The residual map establishes the interconnection between the ISS survey and BK. (6) A refined thickness distribution map can be obtained by overlapping the primary thickness map and the residual map. The application of this method to the No. 2408 longwall panel of Yuhua Coal Mine using ISS–BK showed a considerable improvement in thickness prediction accuracy over ISS. The residuals of ISS and ISS–BK mainly lie in the intervals (− 3.0, 3.0 m) and (− 1.0, 3.0 m), respectively. The accurate prediction rates [where the residual lies in the interval (0, 0.1 m)] of ISS and ISS–BK are 9.39% and 50.28%, respectively, and the effective prediction rates (where the residual is less than 1.0 m) of ISS and ISS–BK are 61.88% and 77.90%, respectively. All the above statistics reflect a considerable improvement in the ISS–BK method over the ISS method.

Potential Induction Heating using MOSFET H-Bridge Circuit for Material Synthesis

Here we report our effort to integrate microcontroller to control AC current-generating MOSFET H-bridge circuit-based device. We have carried out the tests of the potential application of the induction heating generated by the device for material synthesis by controlling the variation of AC current at constant frequency value. The results showed that at the constant frequency value, the heating process depended on the amount of AC current. The different responses of different kind of materials to the different frequencies at constant AC current value have also been observed. The results provide the fundamental base for further development of induction heating furnace using microcontroller based AC current generation device.

Experimental investigation of frequency and amplitude of density wave oscillations in vertical upflow boiling

Historically, study of two-phase flow instabilities has been arguably one of the most challenging endeavors in heat transfer literature due to the wide range of instabilities systems can manifest depending on differences in operating conditions and flow geometry. This study utilizes experimental results for vertical upflow boiling of FC-72 in a rectangular channel with finite inlet quality to investigate Density Wave Oscillations (DWOs) and assess their potential impact on design of two-phase systems for future space missions. High-speed flow visualization image sequences are presented and used to directly relate the cyclical passage of High and Low Density Fronts (HDFs and LDFs) to dominant low-frequency oscillations present in transient pressure signals commonly attributed to DWOs. A methodology is presented to determine frequency and amplitude of DWO induced pressure oscillations, which are then plotted for a wide range of relevant operating conditions. Mass velocity (flow inertia) is seen to be the dominant parameter influencing frequency and amplitude of DWOs. Amplitude of pressure oscillations is at most 7% of the time-averaged pressure level for current operating conditions, meaning there is little risk to space missions. Reconstruction of experimental pressure signals using a waveform defined by frequency and amplitude of DWO induced pressure fluctuations is seen to have only moderate agreement with the original signal due to the oversimplifications of treating DWO induced fluctuations as perfectly sinusoidal in nature, assuming they occur at a constant frequency value, and neglecting other transient flow features. This approach is nonetheless determined to have potential value for use as a boundary condition to introduce DWOs in two-phase flow simulations should a model be capable of accurately predicting frequency and amplitude of oscillation.

Electrical Power Quality Analysis and Hydraulic Performance for Photo Voltaic Surface Water Pumping Unit

Photovoltaic now used in new irrigation system as a source of renewable energy to run the pumps. It’s can be used in remote areas, which it’s very difficult and more expensive to establish power stations or to install transmission lines to connect these areas with the electrical grid. Surface pump can be used in modern irrigations systems and connected to PV power supply to save energy and water. In this paper a system contains 10 hp surface pump and 15 kW PV system uses to drive the pump unit are studied. The paper investigates mathematical models for surface PV pumping system component. The performance of this system is studied by using this mathematical model during a long time, and the effect of solar radiations values on the system performance is estimated. The paper introduced a simulations and experimental results of the PV pumping in daily hourly average during one year. A good agreement between the simulations results and experimental results are found. The paper investigates the overall performance foxing on the water flow rate values obtained from the unit during one year. Also the electrical power quality analysis of the AC voltage feeds for the pump unit are measured and calculated. Due to solar radiations variation during day hours, and during different months the electrical performance such as; voltage current, power and also harmonic contents is changed depends on the values of solar radiations. The electrical signals and power quality are measured on the field by using power quality devices in different days and statues of operations. The results showed that; during low radiations periods the voltage and frequency are varied in a constant relation to reduce the pump speed and hence reduce the water flow rate to be proportional to input energy come from the PV panels. In case of high solar radiations the inverter runs the pump at constant frequency values depend on pump specifications. And during clouds occurred the system is stopped.

Can echolocation calls of Cuban mormopid bats visualized through a heterodyne system?

In this study, we evaluate the potential of the heterodyne system for the acoustic identification of bat species from Mormoopidae in Cuba. The heterodyne transformation of the echolocation calls of the three mormoopid species of Pteronotus (P. macleayii, P. quadridens and P. parnellii) was initially analyzed by setting the frequency of the heterodyne detector (f tuned) 5 kHz above and below the constant frequency value of the second harmonic, respectively. We then studied the feasibility for the identification of several Pteronotus species with single ftuned values. The heterodyne transformation of calls from the mormoopid Mormoops blainvillii and four Cuban phyllostomid bats was studied by selecting frequency values contained in the calls of each of the species under study. We showed that, by selecting the appropriate f tuned, the Pteronotus species could be accurately identified based on the spectral signatures of their heterodyned calls. Frequency modulated (FM) bats presented very similar heterodyne signatures and therefore could not be identified to species level. The study points to heterodyne detectors as appropriate to conduct acoustic surveys of mormoopids and other constant frequency (CF) and quasi CF bat species.

On the quantitative determination of coal seam thickness by means of in-seam seismic surveys

By means of in-seam seismic (ISS) surveys carried out at Karvina coal mine of OKD, Czech Republic, in two neighbouring panels it is shown how the distribution of coal seam thickness can be investigated if the coal seam consists of almost pure coal. The coal seam under investigation was considerably affected by erosion, which resulted in thickness changes amounting from ∼30 cm up to ∼4.40 m. First, by applying ISS-tomographic inversion to the group travel times for a constant frequency value, the distribution of the related group velocity was determined, which showed the extension of the erosions within the survey areas. By correlating the group velocity distribution with known values of the coal seam thickness along a gate, a relation in terms of a polynomial approximation between these quantities could be derived. This relation is specific for a chosen frequency value and resolves in general only some of the thickness range. For the application presented in this paper, a value of 200 Hz was chosen for the constant frequency value by which a range of coal seam thicknesses from about 100 cm to about 300 cm was resolved. This was the main objective of the surveys. For the investigation of a greater variation of coal seam thickness (or even the complete thickness distribution), the described procedure has to be repeated for different constant frequency values. The final thickness map then has to be combined from the individual results for the different constant frequency values. The thickness range that was investigated by the surveys was in good agreement with the thickness encountered by mining the panel.

Smooth muscle stiffness variation due to external longitudinal oscillations

This research focuses on an in vitro investigation of the stiffness changes of contracted airway smooth muscles (ASM) subjected to external longitudinal oscillations. ASM tissues were dissected from excised pig tracheas and stimulated by a chemical stimulus (acetylcholine, 10 −3 M) to produce maximum contractions. The tissues were then systematically excited with external oscillations. Various frequencies, amplitudes and durations were used in the experiments to determine stiffness changes in response to these variations. Force changes were recorded to reflect the muscle stiffness changes. Two stiffness definitions were used to quantify the results, dynamic stiffness to reflect variations during oscillation and static stiffness to reflect the net effect of oscillation. Under isometric contractions, these two stiffnesses were determined before, during and after oscillations. Incorporating an empirical stiffness equation, a two-dimensional finite element model (FEM) was developed to generalize the tissue responses to oscillation. The main outcomes from this work are: the dynamic stiffness has the tendency to decrease as the frequency and/or amplitude of external oscillation increases; the static stiffness has the tendency of decreasing with an increase in the frequency and/or amplitude of excitation until it reaches almost a constant value for frequencies at and above 25 Hz. The difference in the behavior of the dynamic and static stiffness changes may be attributed to the effect of elasticity and mass inertia that are involved in the dynamic motion. The findings of this research are in agreement with the hypothesis that oscillations exert a direct action on the contractile processes by causing an increased rate of actin–myosin detachments.

Geographical Variation in Echolocation Call and Body Size of the Okinawan Least Horseshoe Bat, Rhinolophus pumilus (Mammalia: Rhinolophidae), on Okinawa-jima Island, Ryukyu Archipelago, Japan

The Okinawan least horseshoe bat, Rhinolophus pumilus, is a cave-dwelling species endemic to the central and southern Ryukyus, Japan. We analyzed variation in the constant frequency (CF) of the echolocation call and in forearm length (FAL) of this species on Okinawa-jima Island on the basis of data for 479 individuals from 11 caves scattered over the island. CF values in samples from six caves, all located in the southwestern half of Okinawa-jima, were significantly higher than those in samples from five caves in the northeastern half of the island. Also, FAL was significantly greater in the latter group than in the former group, although the ranges of variation in this character substantially overlapped between the two groups. These results suggest substantial differentiation between R. pumilus populations on Okinawa-jima. The implications of our findings for the conservation of this endangered bat species are briefly discussed.

ACOUSTIC IDENTIFICATION OF MORMOOPID BATS: A SURVEY DURING THE EVENING EXODUS

Echolocation calls emitted by the 4 species of Cuban mormoopid bats were compared to determine vocal signatures that enable identification of each species in the field during their evening exodus. Echolocation calls produced by Mormoops blainvilli are downward frequency-modulated (FM) signals in the range of 68.4– 52.5 kHz. Echolocation calls emitted by Pteronotus macleayii and P. quadridens have a similar design consisting of a short constant-frequency (CF) segment followed by a downward FM segment. The CF segment was at 70.0 kHz in calls from P. macleayii, and at 83.3 kHz in calls from P. quadridens. Echolocation calls from P. parnellii consist of a long CF segment, which is preceded by a short initial upward sweep and followed by a downward FM terminal sweep. The CF value of the 2nd harmonic was a good parameter for species identification. The features of the echolocation calls of each of the species were used to identify them during the evening exodus from 2 Cuban caves.

Variation in the frequency of the echolocation calls of Hipposideros ruber in the Gulf of Guinea: an exploration of the adaptive meaning of the constant frequency value in rhinolophoid CF bats

Abstract This study describes variation patterns in the constant frequency (CF) segment of echolocation calls of the bat Hipposideros ruber within and among populations across the region of the Gulf of Guinea. Correlations of variation in CF with variation in body size, body condition, environmental humidity and presence of ecologically similar species are studied in an attempt to identify the forces driving the evolution of CF. We found that bats may adapt the frequency to humidity, and that CF may evolve under interspecific interactions, either of ecological or of social nature. The results support an adaptive value for the high values of CF, and challenge the ‘Allotonic Frequency Hypothesis’. We found correlation between frequency and a body condition index, which may trigger social selection processes in this species sexually dimorphic in CF. Combined social and environmental selection on CF could trigger diversification of bats along ecotones separating habitats with contrasting air humidity.

Echolocation calls of bats are influenced by maternal effects and change over a lifetime.

The greater horseshoe bat, Rhinolophus ferrumequinum, is a model species in echolocation studies, and emits calls containing long constant-frequency (CF) components. The bats have auditory systems tuned sharply to frequencies close to the resting CF (RF) values. Call frequency and neural processing are both flexible within individual bats which use this mode of echolocation. The simple structure of the calls makes them ideal for sonographic analysis. Here, in a large-scale and long-term analysis of changes in the vocalizations of bats we show that: (i) the calls of R. ferrumequinum aged 1-28 years vary seasonally and over a lifetime in a predictable manner; and (ii) an infant's RF is at least partly determined by the RF of its mother. We consider the relative importance of genetic and learning factors upon the correlation between RFS of mothers and offspring.

The plateaus in basilar membrane vibration data—explained

In recent measurements of basilar membrane tuning curves both the amplitude and the phase approach a constant value for frequencies above the transition frequency. To analyse the origin of these plateaus it is common to use the property that the basilar membrane‐stapes displacement ratio has the same form when plotted against x (=distance to stapes) or log f (=log frequency). An analysis of the situation beyond the characteristic place then shows that the phase plateau is caused by the mass‐controlled character of the membrane impedance there. The magnitude of the ratio decreases sharply in that region; the added mass effect of multi‐dimensional modelling leads to a change in slope, but not to a plateau. The x vs log f transformation however looses its validity for frequencies above the highest resonance frequency in the cochlea. For those frequencies the membrane response tends to become frequency independent, which yields the plateau. Hence amplitude plateaus measured in one animal at different places must begin at the same frequency, and must have a decreasing level with increasing x. This is in agreement with the experimental data.

Theory of the resonance Raman effect in crystals

The dependence of the Raman-scattered intensity on exciting frequency is investigated theoretically for the case where this frequency is close to an absorption line or absorption band of the scattering crystal. Both spontaneous and stimulated Raman scattering are discussed. For scattering by electronic levels of impurity atoms in crystals, it is found that the Raman intensity achieves a constant maximum value when the absorption coefficient at the exciting frequency is much larger than the inverse sample length. It is assumed that the absorption in this case is produced by allowed transitions of the impurity atoms themselves. For Raman scattering by lattice vibrations, the effects of proximity of the exciting frequency to the intrinsic electronic absorption edge are investigated. It is found that the Raman efficiency increases steeply as the exciting frequency approaches the absorption edge from below. The efficiency falls to a small constant value for frequencies above the edge, while the absorption coefficient increases rapidly in this region. The optimum exciting frequency to use is the frequency at which the absorption coefficient begins to rise significantly from its zero value below the edge.

A Theoretical Discussion of the Electrical Properties of the Soil

It has been shown by Ratcliffe and White that the effective specific inductive capacity (ε) and the effective conductivity (σ) of soil placed, as dielectric, in a simple condenser vary in a marked manner with frequency. The range of frequency used was from 0·1 × 106 cycles per second to 10 × 106 cycles per second. It was found that at 6·1 × 106 cycles per second the specific inductive capacity was very large (about 40 e.s.u.) and that it decreased to a value of about 12 e.s.u. at 10 × 106 cycles per second. This latter value agrees with the value found in experiments on the propagation of short radio waves over the surface of the earth. The effective conductivity of the soil had a low value at 0·1 × 106 cycles per second but increased rapidly to a constant value for frequencies above 3 × 106 cycles per second.