Presence Of Skin Effect Research Articles

Boundary condition independence of non-Hermitian Hamiltonian dynamics

Non-Hermitian skin effect, namely that the eigenvalues and eigenstates of a non-Hermitian tight-binding Hamiltonian have significant differences under open or periodic boundary conditions, is a remarkable phenomenon of non-Hermitian systems. Inspired by the presence of the non-Hermitian skin effect, we study the evolution of wave-packets in non-Hermitian systems, which can be determined using the single-particle Green's function. Surprisingly, we find that in the thermodynamical limit, the Green's function does not depend on boundary conditions, despite the presence of skin effect. We proffer a general proof for this statement in arbitrary dimension with finite hopping range, with an explicit illustration in the non-Hermitian Su-Schrieffer-Heeger model. We also explore its applications in non-interacting open quantum systems described by the master equation, where we demonstrate that the evolution of the density matrix is independent of the boundary condition.

Optimization of the shape of an induction heating device in the presence of skin effect in the coils

Purpose The optimization of the cross section of an axisymmetric induction heating device is performed by means of genetic algorithms (GAs). Design/methodology/approach The hybrid finite element method–Dirichlet boundary condition iteration method is used to deal with the unbounded nature of the field. The formulation of the electromagnetic problems takes into account skin and proximity effects in the source currents. Findings The convergence of GAs towards the optimum is very fast, since less than a thousand analyses have been necessary. Originality/value A special derivation of the finite element global system is presented which allows us to save computing time.

New Approach for Accurate Prediction of Eddy Current Losses in Laminated Material in the Presence of Skin Effect With 2-D FEA

Two-dimensional finite element (FE) models normally assume the laminated core as a non-conductive material, and therefore, the damping effect of the eddy currents is ignored in the field solution. Besides, the use of integrated iron loss models in FE software could result in overestimated eddy current losses at high frequencies if the skin effect is ignored. This paper presents a simple way to accurately predict eddy current losses in laminations with FE analysis. An experimental setup along with the simulation models is used to demonstrate the validity of the method. The utility of this method in loss separation and identification of loss coefficients in the presence of skin effect is also illustrated. This method is also applied to a synchronous permanent magnet (PM) machine with sinusoidal current.

Skin effect in steel sheets under rotating induction

By means of a newly developed broadband measuring setup we have overcome the usual upper limit for the test frequency, around a few hundred Hz, which is encountered in the two-dimensional characterization of magnetic steel sheets at technical inductions and we have measured the rotational losses in low-carbon steels up to 1 kHz and peak induction 1.7 T. An important piece of information is thus retrieved upon a frequency range useful to predict the performance of high-speed electrical machines. Our experiments, performed on thick (0.640 mm) laminations, have brought to light the emergence of the skin effect under rotational fields. This is revealed by an abrupt deviation of the excess loss component, calculated under the conventional loss separation procedure, from its well-known linear dependence on the square root of the frequency. A simple magnetic constitutive law under rotating induction is proposed and introduced into the electromagnetic diffusion equation, which is solved by finite elements coupled to a non-linear algorithm. The classical rotational eddy current loss, largely prevalent with respect to the hysteresis and excess loss components on approaching the kHz frequencies in low-carbon steels, is then calculated in the presence of skin effect, permitting one to achieve full analysis of the rotational losses and good predicting capability upon a broad range of frequencies and peak inductions.

Conjugate heat transfer in a bimetallic conductor with variable electric resistivity

Abstract In this work, we analyze theoretically the conjugate heat conductive mechanism resulting from an alternating electrical current that flows continuously in an aluminum conductor steel reinforced (ACSR), taking into account that the electric resistivity is dependent on temperature. This last consideration conducts us to analyze simultaneously the electrical and thermal effects in both conductor materials. In this manner, we need to solve a double conjugate thermo-electric model. In addition, the presence of skin effect causes significant radial temperature differences, since for high frequencies the electric current tends to flow over the surface of the conductor and therefore, the heat generation produced by Joule effect, is no uniform. Based on an equation for predicting the alternating current density and described by a non-linear wave equation, numerical solutions for the above equation together with the heat conduction equation are possible to predict the current density and the temperature profiles. In particular, the influence of the environmental convective conditions, the skin effect and the influence of the variable resistivity on current density and temperature fields, are clarified. The above effects show that the electrical and thermal operation of the electrical networks can be subject to several factors that made, in general, more difficult the full utilization of the electrical transport.

GHz permeability of soft CoZr films: The role of exchange–conductivity coupling

The microwave permeability of CoZr films with different thicknesses is investigated. While Landau–Lifschitz model accounts for the response of the thinnest samples, several peaks are observed on the permeability of thicker layers. A simple model commonly used to account for the permeability of layers in the presence of skin effect is compared to a more sophisticate model taking into account the exchange–conduction coupling. Both models are found to be equivalent. They fail to account for the observed high frequency peaks. Introducing pinning conditions at the interface reproduces qualitatively observed behavior, suggesting the presence of standing spinwaves.

Modeling of borehole Stoneley waves in the presence of skin effects

An important aspect of oil production from a geological formation is the process of flow into a well penetrating the formation. Recent laboratory experiments indicate that well-inflow can be significantly reduced by a skin effect caused by the presence of a thin layer of low permeability around the wellbore. This impairment layer is drilling induced and differs from the mudcake that is usually encountered when logging a well. Whereas a mudcake may have built up on the borehole wall during drilling, the drawdown pressure often removes it when oil is produced from the well. In contrast with such a temporary mudcake, the impairment layer is believed to form a permanent flow impedance throughout the lifetime of a well unless extensive cleaning measures are taken. A simple poro-elastic model is constructed to investigate the propagation of Stoneley waves in a borehole with a thin impairment layer. If the impairment layer affects Stoneley wave propagation, it may be possible to acoustically detect this layer with sonic logging tools. Using realistic values for the impairment flow impedance, model calculations for a typical sandstone reservoir of 20% porosity indicate that the impairment layer changes the dispersion characteristics of borehole Stoneley waves. The magnitude of these changes increases with increasing mobility of the reservoir pore fluid.

Effective Medium Theory For Microwave Dielectric Constant and Magnetic Permeability of Conducting Stick Composites

In this paper we consider high frequency properties of composite materials. We use Monte Carlo simulations and Effective Medium Theory (EMT) to calculate the dielectric constant and the magnetic permeability. The EMT is a well-known approximation which is used for describing the conductivity, dielectric constant, and magnetic permeability of granular materials consisting of conducting and nonconducting components. Different modifications of this theory are considered when the skin layer depth is larger then the characteristic size of the conducting inclusions. In the microwave range it is necessary to take into account the internal inductance of the materials and presence of strong skin effect in conducting granules. In this paper we calculate the internal inductance of materials using a Monte Carlo simulation and then derive EMT equations in the presence of skin effects and the internal inductance. We obtain the dielectric constant for the materials with different shapes of conducting inclusions (spheres...

Effective Medium Theory of Dielectric Constant of Granular Materials in the Presence of Skin Effect

We consider the behavior of the dielectric constant of percolation composite systems. An example of such systems is a composite material consisting of a disordered mixture of metallic and insulating particles. A reduction in concentration P of the metallic (conducting) component reduces the static conductivity of the composite, so that it vanishes at some critical concentration PC known as the percolation threshold.

Simulation of induction logging by the finite-element method

The response of an electromagnetic induction logging tool passing through many invaded thin beds is simulated by the finite-element method. This simulation has achieved high accuracy by using a difference potential which enables the transmitter-receiver mutual coupling to be treated analytically. Consequently the removal of the mutual coupling from the induction tool response has no numerical ill effects. The finite-element model is truncated at a very large distance with a zero field outside the model. In order to achieve both accuracy and computational efficiency, the grid is projected to the truncation surface by gradually increasing its size according to an estimated error analysis of the finite-element method. The numerical results were verified against analytical solutions for limiting cases and excellent agreement was obtained. In the presence of skin effect, which is beyond Doll's analysis by geometrical factor theory, the finite-element solution conveniently provides a way to check and improve the interpretation of induction logs. It also lends itself to future applications in tool design, signal processing, and resistivity inversion schemes.

Simulation of induction logging by the finite‐element method

The response of an electromagnetic induction logging tool passing through many invaded thin beds is simulated by the finite‐element method. This simulation has achieved high accuracy by using a difference potential which enables the transmitter‐receiver mutual coupling to be treated analytically. Consequently the removal of the mutual coupling from the induction tool response has no numerical ill effects. The finite‐element model is truncated at a very large distance with a zero field outside the model. In order to achieve both accuracy and computational efficiency, the grid is projected to the truncation surface by gradually increasing its size according to an estimated error analysis of the finite‐element method. The numerical results were verified against analytical solutions for limiting cases and excellent agreement was obtained. In the presence of skin effect, which is beyond Doll’s analysis by geometrical factory theory, the finite‐element solution conveniently provides a way to check and improve the interpretation of induction logs. It also lends itself to future applications in tool design, signal processing, and resistivity inversion schemes.

Short-Time Well Test Data Interpretation in the Presence of Skin Effect and Wellbore Storage

The log-log type-curve described here shows clearly the presence and duration of wellbore storage as well as the presence and duration of wellbore storage as well as the presence of linear flow due to fracturing. It can be used to presence of linear flow due to fracturing. It can be used to obtain quantitatively the information normally obtained from pressure buildup analyses and to identify the proper straight pressure buildup analyses and to identify the proper straight line in pseudo-radial flow for a fractured well. Introduction Specifications for modem well testing (drawdown or buildup) are usually written in such a way that a well will be tested for a period of time long enough to reach and define a proper "straight line" when test data are plotted in conventional manners. Pressure data obtained before the straight line is reached are not often analyzed, despite the fact that a number of publications have advanced methods for doing so. publications have advanced methods for doing so. One reason for this situation is that many factors are known to affect the short-time data. "Short-time data" signify data obtained before a conventional straight line is reached. Some of the factors are the effects of wellbore storage, perforations, partial penetration, and well stimulation such as fracturing or acidizing. Although the effects of such factors are generally known, the duration and importance have not been clearly defined in all cases particularly when these effects are combined in a well test. However, recent studies have revealed a great deal of potentially useful information concerning the analysis of short-time well test data. Our purpose here is to illustrate the interpretation of short-time well test data through presentation of field examples. Factors to be considered presentation of field examples. Factors to be considered will include wellbore storage, well damage, and fractured wells. Wellbore Storage and Skin Effect The effect of wellbore storage or unloading was originally considered by van Everdingen and Hurst. These studies called attention to the fact that the storage or unloading of fluid contained within the wellbore could cause a significant difference between the surface production rate and the sand-face flow rate in a well immediately following sudden changes in production rate. Gladfelter et al. presented a method production rate. Gladfelter et al. presented a method for correcting pressure buildup data for the changing sand-face flow rate. In another publication a method was presented for estimating the duration of the storage effect, and the Gladfelter et al. correction was generalized to apply to drawdown data. Fundamentally, wellbore storage can occur in several ways. Fluid can be stored by compression of the fluid in a completely filled wellbore, or by movement of a gas-liquid interface. Russell presented a method for analysis of the latter case, pointing out that the virtue of the method was that it was not necessary to know the sand-face flow rate as was the case in the Gladfelter et al. method. One problem with Russell's method was that only a portion of the short-time data was used, yet no criterion for selection of the data was presented. presented. Recently, Agarwal et al. re-examined this problem and presented dimensionless pressure-dimensionless time plots for the case of a well in an infinitely large reservoir, producing at constant surface production rate, and having wellbore storage and a skin effect. Fig. 1 presents a portion of their results. The usual definitions of dimensionless groups were employed. JPT P. 97