Eddy Current Flows Around Cracks in Thin Plates for Nondestructive Testing

1982 ◽  
Vol 49 (2) ◽  
pp. 389-395 ◽  
Author(s):  
S. Mukherjee ◽  
M. A. Morjaria ◽  
F. C. Moon
Keyword(s):  
Current Density ◽  
Eddy Current ◽  
Eddy Currents ◽  
Low Frequency ◽  
Numerical Results ◽  
Thin Plates ◽  
Line Integral ◽  
Faraday’S Law ◽  
Induced Currents ◽  
Current Flows

The boundary element method is used to calculate the induced electric current flow around cracks in thin conducting plates. A low frequency approximation leads to a Poisson equation for the current density potential or stream function. A kernel is used which produces the correct singularity at the crack tip. The boundary condition on the crack, derived from Faraday’s law, requires the line integral of the current density around the crack to be zero. Numerical results for induced currents due to a circular induction coil ore given. These results show that hot spots, due to Joule heating, can occur at the tips of the crack. Comparison of numerical results with infrared scanning experiments of eddy currents in a cracked plate are given. It is hoped that the numerical method presented here will provide a tool to simulate both new and conventional nondestructive eddy current testing techniques.

Interaction of induced currents with cracks in thin plates

1988 ◽  
Vol 418 (1854) ◽  
pp. 229-246 ◽  
Keyword(s):  
Current Density ◽  
Eddy Currents ◽  
Plate Theory ◽  
Plate Thickness ◽  
Infinite Plate ◽  
Skin Depth ◽  
Simple Expression ◽  
Thin Plates ◽  
Faraday’S Law ◽  
Induced Currents

The induction of eddy currents in a conducting, non-magnetic plate containing a through-the-thickness crack is considered in the limit where the plate thickness ( h ) is small compared with the electromagnetic skin depth ( δ ). The plate is represented by a current sheet and the crack by a distribution of generalized current vortices. The current density for these vortices must differ from that of conventional hydrodynamic vortices so as to be consistent with Faraday’s law for self-induction. The vortex density, and hence the induced current in the cracked plate, can be obtained by solving a one-dimensional singular integral equation involving the current density for the uncracked plate which is assumed to be known. The case where the induced currents are produced by a probe coil, as in eddy-current non destructive inspection, is investigated in detail and a simple expression is derived for ∆ Z , the change in coil impedance due to the crack. The formalism is applied to the specific problem of an infinite plate containing a straight crack. Analytical results are presented for the limiting cases of long and short cracks, and a numerical method based on Gauss-Chebyshev quadrature is used for intermediate crack length. These theoretical results are compared with experimental measurements of ∆ Z and the thin-plate theory is found to be in excellent agreement with experiment (to within 5% or better) for values of h / δ up to 0.4.

Eddy Current Measurement for Characterizing Soft Tissues

2012 ◽  
Author(s):  
Emily K. Sequin ◽  
Joseph West ◽  
Vish V. Subramaniam
Keyword(s):  
Eddy Current ◽  
Eddy Currents ◽  
Soft Tissues ◽  
Low Frequency ◽  
Morphological Structure ◽  
Current Measurement ◽  
Phase Changes ◽  
Induced Voltage ◽  
Porcine Muscle ◽  
Lock In

Real-time and non-invasive imaging of tissues and detection of diseases on millimeter to centimeter scales can be useful in some clinical applications such as determination of margins during cancer surgery and image-guided pathology. In this paper, we describe an eddy current measurement method for characterizing soft tissues. The device consists of a pair of concentrically wound coils, a primary coil excited by a low frequency (<100 kHz) sinusoidal voltage, inducing a voltage and current in the secondary detecting coil. When a conducting sample is present, eddy currents develop in the sample and alter the induced voltage and phase on the detecting coil. The output voltage and phase of the detecting coil are then monitored using lock-in amplification. Experimental measurements on porcine muscle tissue examine the effects of varying tissue macrostructure and conductivity on the eddy current detector. Three sets of experiments are presented. First, muscle samples cut into different sized grids simulating the restriction of eddy current domains show that morphological structure has a strong influence on the detector signal. Second, eddy current measurements made on porcine muscle samples at varying degrees of dehydration show that as conductivity decreases, eddy current signals also decrease. Finally, measurements on porcine muscle samples soaked overnight in deionized water complement the dehydration experiments and confirm detector voltage and phase changes decrease with decreasing conductivity.

scholarly journals Eddy current density asymmetric distribution of damper bars in bulb tubular turbine generator

2017 ◽  
Vol 66 (3) ◽  
pp. 571-581
Author(s):  
Hongbo Qiu ◽  
Xiaobin Fan ◽  
Ran Yi ◽  
Jianqin Feng ◽  
Jie Wu ◽  
...  
Keyword(s):  
Current Density ◽  
Eddy Current ◽  
Optimization Design ◽  
Eddy Currents ◽  
Leeward Side ◽  
Asymmetric Distribution ◽  
Turbine Generator ◽  
Density Distributions ◽  
Transient Electromagnetic ◽  
Eddy Current Density

AbstractThe major reasons that cause the damage of damper bars in the leeward side are found in this paper. It provides a route for the structure optimization design of a hydro generator. Firstly, capacity of a 24 MW bulb tubular turbine generator is taken as an example in this paper. The transient electromagnetic field model is established, and the correctness of the model is verified by the comparison of experimental results and simulation data. Secondly, when the generator is operated at rated condition, the eddy current density distributions of damper bars are studied. And the asymmetric phenomenon of the eddy current density on damper bars is discovered. The change laws of the eddy currents in damper bars are determined through further analysis. Thirdly, through the study of eddy current distributions under different conditions, it is confirmed that the stator slots and armature reaction are the main factors to affect the asymmetric distribution of the eddy current in damper bars. Finally, the studies of the magnetic density distribution and theoretical analysis revealed the asymmetric distribution mechanism of eddy current density.

scholarly journals Analytical Analysis of a Novel Brushless Hybrid Excited Adjustable Speed Eddy Current Coupling

Energies ◽  
2019 ◽  
Vol 12 (2) ◽  
pp. 308 ◽  
Author(s):  
Yibo Li ◽  
Heyun Lin ◽  
Hai Huang ◽  
Hui Yang ◽  
Qiancheng Tao ◽  
...  
Keyword(s):  
Eddy Current ◽  
Eddy Currents ◽  
Core Loss ◽  
Element Analysis ◽  
Copper Loss ◽  
Faraday’S Law ◽  
Speed Regulation ◽  
Adjustable Speed ◽  
Current Coupling ◽  
Drive Systems

A novel brushless hybrid excited adjustable speed eddy current coupling is proposed for saving energy in the drive systems of pumps and fans. The topology and operation principle of the coupling are presented. Based on the real flux paths, the fluxes excited by permanent magnet (PM) and field current are analyzed separately. A magnetic circuit equivalent (MEC) model is established to efficiently compute the no-load magnetic field of the coupling. The eddy current and torque are calculated based on the proposed MEC model, Faraday’s law, and Ampere’s law. The resultant magnetic fields, eddy currents, and torques versus slip speeds under different field currents are studied by the MEC-based analytical method and verified by finite element analysis (FEA). The copper loss, core loss, and efficiency were investigated by FEA. The analytically predicted results agree well with the FEA, and the analysis results illustrate that a good speed regulation performance can be achieved by the proposed hybrid excited control.

Determination of eddy current losses and hysteresis losses in magnetic circuits of electrical machines

2020 ◽  
pp. 54-58
Author(s):  
S. M. Plotnikov
Keyword(s):  
Eddy Current ◽  
Magnetization Reversal ◽  
Eddy Currents ◽  
Technical Problem ◽  
Electrical Machines ◽  
Eddy Current Losses ◽  
Hysteresis Losses ◽  
Magnetic Circuits ◽  
Core Losses ◽  
Reversal Frequency

The division of the total core losses in the electrical steel of the magnetic circuit into two components – losses dueto hysteresis and eddy currents – is a serious technical problem, the solution of which will effectively design and construct electrical machines with magnetic circuits having low magnetic losses. In this regard, an important parameter is the exponent α, with which the frequency of magnetization reversal is included in the total losses in steel. Theoretically, this indicator can take values from 1 to 2. Most authors take α equal to 1.3, which corresponds to the special case when the eddy current losses are three times higher than the hysteresis losses. In fact, for modern electrical steels, the opposite is true. To refine the index α, an attempt was made to separate the total core losses on the basis that the hysteresis component is proportional to the first degree of the magnetization reversal frequency, and the eddy current component is proportional to the second degree. In the article, the calculation formulas of these components are obtained, containing the values of the total losses measured in idling experiments at two different frequencies, and the ratio of these frequencies. It is shown that the rational frequency ratio is within 1.2. Presented the graphs and expressions to determine the exponent α depending on the measured no-load losses and the frequency of magnetization reversal.

Contact Current Density Analysis Inside Human Body in Low-Frequency Band Using Geometric Multi-Grid Solver

2020 ◽  
Vol E103.C (11) ◽  
pp. 588-596
Author(s):  
Masamune NOMURA ◽  
Yuki NAKAMURA ◽  
Hiroo TARAO ◽  
Amane TAKEI
Keyword(s):  
Frequency Band ◽  
Current Density ◽  
Human Body ◽  
Low Frequency ◽  
Density Analysis

scholarly journals An Alternative Method for Calculating the Eddy Current Loss in the Sleeve of a Sealless Pump

Actuators ◽  
2021 ◽  
Vol 10 (4) ◽  
pp. 78
Author(s):  
Tomislav Strinić ◽  
Bianca Wex ◽  
Gerald Jungmayr ◽  
Thomas Stallinger ◽  
Jörg Frevert ◽  
...  
Keyword(s):  
Eddy Current ◽  
Three Dimensional ◽  
Eddy Current Loss ◽  
Theoretical Background ◽  
Air Gap ◽  
Magnetic Flux Density ◽  
Pump Impeller ◽  
Current Loss ◽  
Faraday’S Law ◽  
Transient Simulations

A sealless pump, also known as a wet rotor pump or a canned pump, requires a stationary sleeve in the air gap to protect the stator from a medium that flows around the rotor and the pump impeller. Since the sleeve is typically made from a non-magnetic electrically conductive material, the time-varying magnetic flux density in the air gap creates an eddy current loss in the sleeve. Precise assessment of this loss is crucial for the design of the pump. This paper presents a method for calculating the eddy current loss in such sleeves by using only a two-dimensional (2D) finite element method (FEM) solver. The basic idea is to use the similar structure of Ampère’s circuital law and Faraday’s law of induction to solve eddy current problems with a magnetostatic solver. The theoretical background behind the proposed method is explained and applied to the sleeve of a sealless pump. Finally, the results obtained by a 2D FEM approach are verified by three-dimensional FEM transient simulations.

scholarly journals Low-frequency sinusoids for enhanced shear buckling performance of thin plates

2021 ◽  
Vol 177 ◽  
pp. 106475
Author(s):  
Peter Y. Wang ◽  
Maria E.M. Garlock ◽  
Ted P. Zoli ◽  
Spencer E. Quiel
Keyword(s):  
Low Frequency ◽  
Thin Plates ◽  
Shear Buckling
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