Current Displacement Research Articles

MODELLING OF DYNAMIC MODES OF AN INDUCTION ELECTRIC DRIVE AT PERIODIC LOAD

Goal. Development of methods and mathematical models, based on them, for the calculation of transients and steady-state modes of induction electric drives operating in periodic load mode. Methodology. The developed algorithms are based on a mathematical model of an induction motor, which takes into account the saturation of the magnetic core and the displacement of current in the rotor bars. The processes are described by a system of nonlinear differential equations in the orthogonal axes x, y, which enables the results to be obtained with the smallest amount of calculations. The magnetization characteristics by the main magnetic flux and the leakage fluxes are used to calculate the electromagnetic parameters of the motor. To account for the current displacement in the rotor bars, the short-circuited winding is considered as a multilayer structure formed by dividing the bars in height by several elements. Results. Due to the variable load on the motor shaft, electromagnetic processes in both transient and steady state modes of the electric drive in any coordinate system are described by a system of nonlinear differential equations. The result of the calculation of the transients is obtained as a result of their integration time dependencies of coordinates (currents, electromagnetic torque, etc.) at a given law of change of the moment of loading. The proposed method of calculating steady-state mode is based on algebraization of differential equations on the mesh of nodes of the process cyclicity period and allows to obtain periodic dependencies in the time domain. Originality. The problem of calculating a steady-state periodic mode is solved as a boundary problem for a system of first-order differential equations with periodic boundary conditions, which allows to obtain instantaneous dependences during the period of currents, electromagnetic torque, capacities and other coordinates. Practical significance. Using the developed algorithm, it is possible to calculate the static characteristics of periodic processes as dependencies on different parameters of the cycle of periodic load or other coordinates, which is the basis for the choice of the motor for overload, power, heating, etc., as well as to detect the possibility of resonance.

Modelling of Dynamic Modes of An Induction Electric Drive at Periodic Load

Goal: Development of methods and mathematical models, based on them, for the calculation of transients and steady-state modes of induction electric drives operating in periodic load mode. Methodology: The developed algorithms are based on a mathematical model of an induction motor, which takes into account the saturation of the magnetic core and the displacement of current in the rotor bars. The processes are described by a system of nonlinear differential equations in the orthogonal axes x, y, which enables the results to be obtained with the smallest amount of calculations. The magnetization characteristics by the main magnetic flux and the leakage fluxes are used to calculate the electromagnetic parameters of the motor. To account for the current displacement in the rotor bars, the short-circuited winding is considered as a multilayer structure formed by dividing the bars in height by several elements. Results: Due to the variable load on the motor shaft, electromagnetic processes in both transient and steady state modes of the electric drive in any coordinate system are described by a system of nonlinear differential equations. The result of the calculation of the transients is obtained as a result of their integration time dependencies of coordinates (currents, electromagnetic torque, etc.) at a given law of change of the moment of loading. The proposed method of calculating steady-state mode is based on algebraization of differential equations on the mesh of nodes of the process cyclicity period and allows to obtain periodic dependencies in the time domain. Originality: The problem of calculating a steady-state periodic mode is solved as a boundary problem for a system of first-order differential equations with periodic boundary conditions, which allows to obtain instantaneous dependences during the period of currents, electromagnetic torque, capacities and other coordinates. Practical significance: Using the developed algorithm, it is possible to calculate the static characteristics of periodic processes as dependencies on different parameters of the cycle of periodic load or other coordinates, which is the basis for the choice of the motor for overload, power, heating, etc., as well as to detect the possibility of resonance.

A cost-effective voice coil motor-based portable micro-indentation device for in situ testing

Abstract To evaluate the mechanical properties of structures in service, a portable micro-indentation device was developed and built. The basic design principle of the indentation device, i.e. measurement of the indentation depth and the indentation force with sufficient accuracy, was discussed. To avoid using load cell to decrease the machine compliance, a new method that using the current through voice coil motor to calculate the indentation force was proposed. After analyzing the equivalent mechanical model of the developed device, an eddy current displacement sensor was installed on the device to improve the measurement accuracy of indentation depth. Indentation tests were performed on polymethylmethacrylate (PMMA) and unplasticized polyvinyl chloride (UPVC) with the developed device and the commercial indentation device ZHU2.5 to demonstrate the validity and accuracy of the developed micro-indentation device.

Effect of noise on quantum transport of a charged particle in a tight-binding lattice

We investigate diffusion of a quantum charged particle in a tight-binding lattice (TBL) under fluctuating noisy electric fields. Several closed-form expressions such as that of probability propagator, average current, and mean-squared displacement are derived. The particular effect of Gaussian noise in a 1D TBL is studied in detail and a comparison is made with the case of a telegraph noise. The Gaussian white noise and telegraph noise show up in different manifestations in the underdamped regime. On the contrary, when relaxation is rapid the noisy field averages out to zero yielding delocalization for both Gaussian and telegraphic noisy electric fields. Depending on the strength of noise and the external field one can observe different current characteristics.

Stable control of magnetically suspended motor with heavy self-weight and great moment of inertia

In this article, for the translation and radial rotation of the magnetically suspended motor (MSM) with heavy self-weight and great moment of inertia, robust control functions are designed to improve the disturbance attenuation by minimizing model uncertainties introduced by variations of current stiffness and displacement stiffness. On the one hand, the H∞ control function with the mixed sensitivity is designed to the translational control of the MSM. On the other hand, for the rotation control of the MSM around radial axes, μ-synthesis is utilized to attenuate disturbances caused by the gyroscopic coupling with variable rotational speed. Simulation is developed to testify the disturbance attenuation of control functions when pulse-type, sinusoidal-type and random-type disturbances are imposed on the MSM respectively. Furthermore, experiments about axial translation and radial rotation are conducted to validate the robust stability of designed control functions. Both simulation and experimental results indicate that the robust control scheme has better ability on disturbance attenuation of the MSM with great inertia of moment and heavy self-weight.

(Invited) Dynamic Electrochemical Control of Oxide Thin Film Oxygen Stoichiometry with Application to Electrochemical Mechanical Actuation

Dynamic chemical expansion (DCX) provides a direct method for probing defect induced dilation (chemical expansion) of thin films during voltage induced changes in defect concentration. The voltages, applied across electrochemical cells, pump oxygen in or out of the film leading, in turn, to measurable expansions on the nano-scale. In this work, both the current and mechanical displacement response to an electrochemical driving force are modeled in the time domain using previously derived defect equilibria and kinetics relationships previously established for the studied thin film Pr0.1Ce0.9O2-δ system. The response is also modeled in the frequency domain, by approximating the mechanical response as linear, resulting in an electrochemomechanical admittance spectroscopy interpretation of the system. The relationship between equivalent circuit parameters used to fit the admittance spectra and constants in the equation of motion are discussed. Figure 1

Counterurbanisation: why settled families move out of the city again

After decades of massive family suburbanisation, we have observed a steady increase in family households in various European capitals, including Amsterdam. Currently, the number of Amsterdam families is still increasing, however the number of families leaving the city is also growing and again on the rise. How can we explain this change, particularly for settled families that used to avoid outmigration? Empirical results are obtained from a qualitative study of urban middle class parents with children of primary school age who have recently moved out of Amsterdam. The results reveal that the shortage in the supply of family housing at a reasonable price for all families is the prime incentive to move. Underneath shared financial argumentations, however, we can distinguish three types of families that have specific motivations to move: pragmatic movers, displaced families and happy movers. The motivations to move are strongly related to different parental narratives of a ‘good childhood environment’. The results reveal further that the current displacement patterns are not only class-driven but include highly educated double-income family households. This paper ends with a short discussion of how to prevent cities from becoming homogeneous, rich non-family places.

Measurement Method for Quality Control of Cylinders in Roll-to-Roll Printing Machines

This paper describes a measurement method for the quality control of cylinders for printing machines based on roll-to-roll presses. If the surface finishing of the cylinders is not adequate, the printing is unacceptable, and the defective cylinders must be reworked. The performed quality check of the cylinder surface roughness by means of contact methods was unable to identify the cylinder defects, and acceptance of the manufactured cylinders before integration was demanded to the visual inspection performed by trained operators. In this work a contactless measurement method based on the eddy current displacement sensor was proposed and validated as a tool for quality check as an alternative to optical roughness measurements. A test bench for the characterization of printer cylinders was designed and manufactured, allowing for the validation of the proposed method on different batches of cylinders and the identification of a threshold to guide the acceptance of tested cylinders prior to mounting on the roll-to-roll press.

Agency and mobility in the context of development-induced migration: the case of Three Gorges out-migrants

ABSTRACT Recently, scholarship on migration has shifted to address people’s agency and reflexivity, particularly those of marginal groups such as refugees, older migrants and rural-urban migrants. These individuals are not passively suffering victims, but able to develop strategies to overcome the ‘frictions’ of mobility. Empirically based in data on the world’s largest-scale forced migration, resulting from the Three Gorges Dam project in China, this paper interrogates the lived experiences of those suffering as a result of development-induced migration from the perspectives of the new mobility paradigm and human agency. It examines the association between migrants’ agency and mobility, and how both are intertwined with the migrants’ resettlement experiences and life chances. The results shed light on the study of mobility and migration by addressing heterogeneity in age; we argue that engagement with both younger and older migrants offers rich potential to bridge the gap between the concepts of mobility and mooring. In practice, the paper exposes the shortcomings of current displacement and resettlement policies, which tend to overlook the well-being of older migrants, and suggests more nuanced ways of devising policies and practices in the future.

Linear modeling of alternative active magnetic bearings with four interconnected poles and distributed windings

Magnetic bearing applications have been going through continuous evolution. Several researchers, in cooperation with specialized companies, have proposed numerous new applications. Among them, not only those related to transportation system but also to the energy conversion area. Nevertheless, due to its particular characteristics, the magnetic bearings still face certain difficulties to be widely utilized by the industry. One of them is related to the high cost of the mechanical parts manufacturing. Although the materials can be easily found in the market, the customized production is highly expensive. In order to overcome this difficulty, the authors have been studying the possibilities of using the stators of commercial induction motors as the stators of active magnetic bearings (AMB). In this paper, two four poles motor types were considered; the first one has a two-phase stator and the second one a three-phase stator. Through finite elements analysis, the net magnetic forces were evaluated and compared with the produced by a conventional eight poles AMB. For both stators, two conditions were simulated: first, one of the windings was kept unconnected or opened and, second, all the windings were supplied. From the results, both coefficients of its force linearized models, control current and rotor displacement were obtained. Furthermore, the three-phase stator, with all of its windings being supplied, is shown to be more appropriated to be used as the stator of an AMB, given that its linearized model shows less influence of the shaft misalignment in the resultant magnetic forces.

Displacement measurement of a concrete bridge under traffic loads with fibre-reinforced polymer-packaged optical fibre sensors

Current displacement measurement methods cannot cope with the demands of the long-term measurement of small- or medium-span concrete bridges because of some technology or economic challenges. In this article, a displacement measurement method is proposed for concrete bridges based on fibre-reinforced polymer-packaged optical fibre sensors. The sensing principle and manufacture process of the proposed sensor are introduced as well as the strain sensing property. Then, a relationship is established between the strain and the displacement based on the distributed strain monitoring. Finally, some field tests are implemented using a simply supported concrete bridge. The tests include static loading test, dynamic loading test with specific speeds and dynamic random traffic loading test. The field test results show that the proposed method can measure the displacement of concrete bridges under traffic loads with reasonable accuracy. Moreover, different types of sensor distributions are proposed to investigate the displacement measurement effects to optimise the sensor installation. Although the sensors cover only some key parts of the girder, the results also verify the accuracy of the proposed method. Therefore, the proposed method can be implemented in concrete bridges in future.

Study of the Parameters of the Substitution Scheme and Calculation of Mechanical Characteristics of Asynchronous Motors of the AIR Series Taking into Account the Skin Effect in the Rotor Winding

Studies of catalog data and parameters of substitution schemes for asynchronous motors of the air series with a short-circuited rotor have been performed in order to obtain general laws and analytical expressions depending on the engine power. In the Mathcad computer-aided design system, 32 engines were studied, and machines with a synchronous speed of 1500 rpm were taken as the main ones. Catalog data in the reference literature, according to manufacturers and other sources, differ significantly from each other, and so analytical expressions that reflect their average values are needed. General regularities and analytical expressions for determining the necessary parameters are obtained. An approximate method for calculating mechanical characteristics is proposed that takes into account the skin effect and current displacement in the rotor winding, which allows obtaining mechanical characteristics with an increased starting torque.

Dynamic Stiffness Analysis and Measurement of Radial Active Magnetic Bearing in Magnetically Suspended Molecular Pump

Current stiffness and displacement stiffness are two important parameters of radial active magnetic bearing (RAMB) that are generally considered as constants in a control system. However, such presumption may lead to the probable degradation of the control performance of the RAMB system when the perspective that the current and displacement stiffness should be variable due to variations in the speed. On this regard, a structure analysis and stiffness measurement method based on non-variable stiffness would not be feasible for RAMB under high-speed conditions. This paper presented an analysis of the dynamic stiffness characteristics of RAMB by means of a dynamic equivalent magnetic circuit method and laid out a comparison between the results of the theoretical analysis and the simulation results of finite element method. In particular, a novel dynamic stiffness measurement method of RAMB under high-rotation frequency was introduced. Results of experiments on the dynamic stiffness of RAMB demonstrated an excellent agreement with the theoretical research and the finite element analysis results, thereby verifying the rationality of the discussed dynamic stiffness characteristics. Practically, the proposed measurement method of RAMB dynamic stiffness provides an accurate analysis for the dynamic stiffness and contributes inspiring research significance for the dynamic properties of RAMB.

A Hindcast Approach to Diagnosing the Equatorial Pacific Cold Tongue SST Bias in CESM1

AbstractAn ensemble seasonal hindcast approach is used to investigate the development of the equatorial Pacific Ocean cold sea surface temperature (SST) bias and its characteristic annual cycle in the Community Earth System Model, version 1 (CESM1). In observations, eastern equatorial Pacific SSTs exhibit a warm phase during boreal spring and a cold phase during late boreal summer–autumn. The CESM1 climatology shows a cold bias during both warm and cold phases. In our hindcasts, the cold bias during the cold phase develops in less than 6 months, whereas the cold bias during the warm phase takes longer to emerge. The fast-developing cold-phase cold bias is associated with too-strong vertical advection and easterly wind stress over the eastern equatorial region. The antecedent boreal summer easterly wind anomalies also appear in atmosphere-only simulations, indicating that the errors are intrinsic to the atmosphere component. For the slower-developing warm-phase cold bias, we find that the too-cold SSTs over the equatorial region are associated with a slowly evolving upward displacement of subsurface ocean zonal currents and isotherms that can be traced to the ocean component.

Deformation in a nonlocal magneto-thermoelastic solid with hall current due to normal force

The present article is concerned about the study of disturbances in a homogeneous nonlocal magneto-thermoelastic medium under the combined effects of hall current, rotation and two temperatures. The model under assumption has been subjected to normal force. Laplace and Fourier transform have been used for finding the solution to the field equations. The analytical expressions for conductive temperature, stress components, normal current density, transverse current density and displacement components have been obtained in the physical domain using a numerical inversion technique. The effects of hall current and nonlocal parameter on resulting quantities have been depicted graphically. Some particular cases have also been figured out from the current work. The results can be very important for the researchers working in the field of magneto-thermoelastic materials, nonlocal thermoelasticity, geophysics etc.

WHAT’S GOING ON?

AbstractOnce nearly eighty percent Black, South LA is now two-thirds Latino. The demographic change was due to many factors, including a Black exodus driven by economic precarity, fear of crime, and experiences of over-policing and a Latino influx initially spurred by an immigration surge that could not be accommodated in traditional entry neighborhoods. While earlier research often focused on the conflicts between groups, time has passed and our new work points to contemporary quotidian accommodations between residents. We also document an emerging style of Black-Brown community organizing that seeks to both acknowledge the nuance of difference and create a shared sense of place identity. This article lifts up the Black experience in that transition of space and politics and notes how a sense of loss can result from such a dramatic change in a place that was once an iconic and literal home for much of Black Los Angeles. We suggest that that sense of loss is exacerbated by a legacy of racist asset-stripping and a deep worry about Black erasure due to current displacement pressures from gentrification. We close by discussing how organizers and political leaders need to take these dynamics into account when both building coalitions and ensuring Black futures in what is now a Black-Brown political and social space.

Mathematical Model of a Solid Rotor Asyncronous Electric Machine

The article deals with solid rotor asynchronous electric machine mathematical model. It is substantiated that the use of generalized electrical machine theory for building the mathematical model is rational at the design stage to analyze the electromagnetic and electromechanical processes in an electric machine and a power converter. The mathematical model with some circuits on the rotor was considered to account for the effect of current displacement in a solid rotor. We used the field theory to determine the number of circuits. For this purpose, the calculations series of the magnetic field distribution in the active part of the electric machine when the rotor is stationary (in short circuit mode) and the stator winding are powered by different frequencies currents were carried out. The modeling of a high-speed electric generator with a solid asynchronous rotor was carried out. Its power is 100kW and its rotational speed is 100 000 rpm. The analysis of the high-speed generator parameter approximation showed that the use of three circuits in the equivalent circuit is rational to account for the effect of current displacement in a solid rotor. The mathematical model results when connecting a rotating high-speed electric generator to a voltage source are showed. The assessment of the current displacement effect in a solid rotor was examined twice: with one circuit in a rotor chain and with three circuits in it. Comparison of the electromagnetic processes modeling results showed that the use of three circuits model provides the more accurate representation of electromagnetic processes in the solid rotor asynchronous electric machine. The modeling results significantly differs during transients when using the one-circuit model. In the steady state, the stator current fundamental harmonics and the average value of electromagnetic moment are the same for both models.

Determination of Equivalent Circuit Parameters of a Solid Rotor Asynchronous Electric Machine

The article deal with the determining the equivalent circuit parameters of a solid rotor asynchronous electric machine. To solve the problem, we determined the structure and parameters of a mathematical model using known geometric relationships and parameters of used materials. The least square method is used to determine the equivalent circuit parameters of an unlaminated-rotor asynchronous electric machine. The magnetic field distribution is calculated when the stator winding is supplying with a sinusoidal current and under short-circuit conditions. The imaginary part of the stator phase inductance versus stator current frequency when the rotor is fixed is calculated using the field theory. This dependence is approximated. The system of algebraic equations determining the approximation parameters is non-linear. The Levenberg-Marquardt method provides solution convergence of the equation system when using two or more loops on the rotor. The selection of the initial approximation largely determines the convergence of the solution made by the iterative method. The preliminary studies showed that the use of simplified scheme of the substitution of an asynchronous electric machine with one contour on the rotor is suitable as an initial approximation of parameters. The numerical solution of the equations determined the approximation parameters. The equivalent circuit parameters of high-speed electric generator with solid asynchronous rotor was made as an example of using of the approach under consideration. We need to use three loops on the rotor in the mathematical model of the asynchronous electric machine to take into account the effect of current displacement in solid rotor.

Analysis of sliding electric contact characteristics in augmented railgun based on the combination of contact resistance and sliding friction coefficient

The contact resistance between the armature and rails is an important indicator of the contact characteristics in electromagnetic launches. As the contact resistance depends not only on the contact state but also on the contact stress and temperature, there are some limitations in analyzing the contact characteristics using only the contact resistance. In this paper, the contact characteristics of the augmented railgun are analyzed by the combination of contact resistance and sliding friction coefficient. Firstly, the theoretical calculation model of the contact resistance and friction coefficient of the augmented electromagnetic railgun is established. Then the contact resistance and friction coefficient are calculated by the measured values of the muzzle voltage, rail current and armature displacement. Finally, the contact characteristics are analyzed according to the features of the waveforms of the contact resistance and the friction coefficient, and the analysis conclusions are verified by experimental rail images. The results showed that: the aluminum melt film gradually formed on the contact surface reduces the contact resistance and the friction coefficient; the wear and erosion of the armature cause deterioration of the contact state; after the transition, the reliability of the sliding contact between the armature and rails decreases, resulting in an increase in contact resistance.

Multiple data-driven approach for predicting landslide deformation

Currently, mathematical models such as the regression model, grey prediction model, and neural networks are commonly used to predict landslide displacement. In this study, we develop multi-data-driven models for prediction of landslide displacement. Multi-kernel learning and weighted learning methods are integrated with the grey prediction theory and three models are constructed to predict landslide displacement: the kernel-based grey model, multi-kernel grey model, and weighted multi-kernel grey model. All three models are simple to calculate and easy to program. The models were applied to a case study of the Baishuihe landslide in the Three Gorges reservoir, China. The influence of rainfall, reservoir water level, landslide rate, and historical displacement on the current displacement of the landslide were investigated, and multi-data-driven prediction models with input parameters (rainfall, reservoir water level, landslide rate, and historical displacement) and an output parameter (current displacement) were developed. The results show that the weighted multi-kernel grey model has better prediction accuracy than the kernel-based grey model and the multi-kernel grey model. These findings can be widely applied in practical landslide prediction.