A Boundary Element Model of Perturbed Magnetic Flux Density Component in Eddy Current NDT of Flaws

Concentrated stresses and residual ones are critical for the metal structures’ health, because they can cause microcracks that require emergency maintenance or can result in potential accidents. Therefore, an accurate approach to the measurement of stresses is key for ensuring the health of metal structures. The eddy current technique is an effective approach to detect the stress according to the piezoresistive effect. However, it is limited to detect the surface stress due to the skin effect. In engineering, the stress distribution is inhomogeneous; therefore, to predict the inhomogeneous stress distribution, this paper proposes a nondestructive approach which combines the eddy current technique and finite element (FE) method. The experimental data achieved through the eddy current technique determines the relationship between the applied force and the magnetic flux density, while numerical simulations through the FE method bridge the relationship between the magnetic flux density and the stress distribution in different directions. Therefore, we can predict the inhomogeneous stress nondestructively. As a case study, the applied stress in a three-point-bending simply supported beam was evaluated, and the relative error is less than 8% in the whole beam. This approach can be expected to predict the residual stress in metal structures, such as rail and vehicle structures, if the stress distribution pattern is known.

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Rotor Power Losses in Planar Radial Magnetic Bearings — Effects of Number of Stator Poles, Air Gap Thickness, and Magnetic Flux Density

Volume 5: Manufacturing Materials and Metallurgy; Ceramics; Structures and Dynamics; Controls, Diagnostics and Instrumentation; Education ◽

10.1115/98-gt-316 ◽

1998 ◽

Cited By ~ 7

Author(s):

P. E. Allaire ◽

M. E. F. Kasarda ◽

L. K. Fujita

Keyword(s):

Magnetic Flux ◽

Flux Density ◽

Eddy Current ◽

Power Loss ◽

Magnetic Bearing ◽

Air Gap ◽

Magnetic Bearings ◽

Magnetic Flux Density ◽

Power Losses ◽

Loss Mechanism

Rotor power losses in magnetic bearings cannot be accurately calculated at this time because of the complexity of the magnetic field distribution and several other effects. The losses are due to eddy currents, hysteresis, and windage. This paper presents measured results in radial magnetic bearing configurations with 8 pole and 16 pole stators and two laminated rotors. Two different air gaps were tested. The rotor power losses were determined by measuring the rundown speed of the rotor after the rotor was spun up to speeds of approximately 30,000 rpm, DN = 2,670,000 mm-rpm, in atmospheric air. The kinetic energy of the rotor is converted to heat by magnetic and air drag power loss mechanisms during the run down. Given past publications and the opinions of researchers in the field, the results were quite unexpected. The measured power losses were found to be nearly independent of the number of poles in the bearing. Also, the overall measured rotor power loss increased significantly as the magnetic flux density increased and also increased significantly as the air gap thickness decreased. A method of separating the hysteresis, eddy current and windage losses is presented. Eddy current effects were found to be the most important loss mechanism in the data analysis, for large clearance bearings. Hysteresis and windage effects did not change much from one configuration to the other.

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Radial Planar Magnetic Bearing Analysis With Finite Elements Including Rotor Motion and Power Losses

Volume 4: Manufacturing Materials and Metallurgy; Ceramics; Structures and Dynamics; Controls, Diagnostics and Instrumentation; Education; IGTI Scholar Award ◽

10.1115/97-gt-503 ◽

1997 ◽

Cited By ~ 5

Author(s):

R. D. Rockwell ◽

P. E. Allaire ◽

M. E. F. Kasarda

Keyword(s):

Finite Element ◽

Magnetic Flux ◽

Flux Density ◽

Electric Fields ◽

Eddy Current ◽

Magnetic Bearing ◽

Magnetic Bearings ◽

Magnetic Flux Density ◽

Magnetic Vector Potential ◽

Power Losses

No literature is currently available which has evaluated finite element power loss models for magnetic bearings and compared the results to experimental results. In this paper a finite element model of the magnetic and electric fields in magnetic bearings, including the motion of the magnetic material in the rotor, is developed. It evaluates the two dimensional magnetic vector potential, magnetic flux density, electric field, eddy current, and power losses in an example magnetic bearing configuration. Results were obtained for both a solid rotor and a laminated rotor. For a solid rotor, both the magnetic flux density and eddy current plots at high rotational speeds are concentrated at the outer edge of the rotor. The ratio of calculated solid to laminated losses is found to be in the range of measured results by other authors. An effective axial conductivity was employed to model a laminated rotor and compared to experimental loss measurements. The correlation between measured and calculated results is quite good for a range of rotor speeds, magnetic flux density, and air gap thickness.

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Simultaneous measurement of thickness and lift-off using the tangential component of magnetic flux density in pulsed eddy current testing

Insight - Non-Destructive Testing and Condition Monitoring ◽

10.1784/insi.2021.63.6.341 ◽

2021 ◽

Vol 63 (6) ◽

pp. 341-347

Author(s):

Hang Xu ◽

Donglin Li ◽

Tao Chen ◽

Xiaochun Song

Keyword(s):

Magnetic Flux ◽

Flux Density ◽

Eddy Current ◽

Tangential Component ◽

Magnetic Flux Density ◽

Logarithmic Scale ◽

Time To Peak ◽

Pulsed Eddy Current ◽

Lift Off ◽

Two Parameters

The pulsed eddy current (PEC) technique is commonly used in the petrochemical and power generation industries to measure two parameters: the degree of pipe wall corrosion and the thickness of the insulation shield. These two parameters can be evaluated by examining the thickness of conductive materials and the lift-off distance, respectively. To explore a possible technique for simultaneously measuring the thickness and the lift-off, the present study envisaged the development of a PEC testing method based on detecting the tangential component of the magnetic flux density. The tangential component of the magnetic flux density was excited by two racetrack-type coils injecting currents in opposite directions that were picked up by a magnetic sensor. The slope in logarithmic scale and the time-to-peak of the magnetic signal were verified to characterise the features of the thickness and the lift-off, respectively. By analysing the simulation and experimental results, the feasibility of simultaneously measuring the thickness and the lift-off was demonstrated.

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Rotor Power Losses in Planar Radial Magnetic Bearings—Effects of Number of Stator Poles, Air Gap Thickness, and Magnetic Flux Density

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.2818528 ◽

1999 ◽

Vol 121 (4) ◽

pp. 691-696 ◽

Cited By ~ 8

Author(s):

P. E. Allaire ◽

M. E. F. Kasarda ◽

L. K. Fujita

Keyword(s):

Magnetic Flux ◽

Flux Density ◽

Eddy Current ◽

Power Loss ◽

Magnetic Bearing ◽

Air Gap ◽

Magnetic Bearings ◽

Magnetic Flux Density ◽

Power Losses ◽

Loss Mechanism

Rotor Power losses in magnetic bearings cannot be accurately calculated at this time because of the complexity of the magnetic field distribution and several other effects. The losses are due to eddy currents, hysteresis, and windage. This paper presents measured results in radial magnetic bearing configurations with eight pole and 16 pole stators and two laminated rotors. Two different air gaps were tested. The rotor power losses were determined by measuring the rundown speed of the rotor after the rotor was spun up to speeds of approximately 30,000 rpm, DN = 2,670,000 mm-rpm, in atmospheric air. The kinetic energy of the rotor is converted to heat by magnetic and air drag power loss mechanisms during the run down. Given past publications and the opinions of researchers in the field, the results were quite unexpected. The measured power losses were found to be nearly independent of the number of poles in the bearing. Also, the overall measured rotor power loss increased significantly as the magnetic flux density increased and also increased significantly as the air gap thickness decreased. A method of separating the hysteresis, eddy current and windage losses is presented. Eddy current effects were found to be the most important loss mechanism in the data analysis, for large clearance bearings. Hysteresis and windage effects did not change much from one configuration to the other.

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Flux Density and Air Gap Effects on Rotor Power Loss Measurements in Planar Radial Magnetic Bearings

Volume 4: Manufacturing Materials and Metallurgy; Ceramics; Structures and Dynamics; Controls, Diagnostics and Instrumentation; Education; IGTI Scholar Award ◽

10.1115/97-gt-017 ◽

1997 ◽

Cited By ~ 2

Author(s):

P. E. Allaire ◽

M. E. F. Kasarda ◽

E. H. Maslen ◽

G. T. Gillies ◽

L. K. Fujita

Keyword(s):

Magnetic Flux ◽

Flux Density ◽

Eddy Current ◽

Power Loss ◽

Magnetic Bearing ◽

Air Gap ◽

Magnetic Bearings ◽

Magnetic Flux Density ◽

Power Losses ◽

Loss Mechanism

The rotor power losses in magnetic bearings are due to eddy currents, hysteresis, and windage. The influence of air gap magnetic flux density and air gap thickness is not well understood at this time. This paper presents measured results in two magnetic bearing radial configurations with a laminated rotor. The rotor power losses were evaluated by measuring the rundown speed of the rotor, in air, after the rotor was spun up to speeds of approximately 30,000 rpm in atmospheric air. The kinetic energy of the rotor is converted to heat by magnetic and air drag power loss mechanisms during the run down. A method of separating the hysteresis, eddy current and windage losses is presented. Eddy current effects were found to be the most important loss mechanism in the data analysis. Hysteresis and windage effects did not change much from one configuration to the other. The measured rotor power loss increased significantly as the magnetic flux density increased and also increased significantly as the air gap thickness decreased.

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Magnetic Shielding for Coreless Linear Permanent Magnet Motors

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.416-417.45 ◽

2013 ◽

Vol 416-417 ◽

pp. 45-52 ◽

Cited By ~ 4

Author(s):

K.J.W. Pluk ◽

J.W. Jansen ◽

E.A. Lomonova

Keyword(s):

Magnetic Flux ◽

Permanent Magnet ◽

Flux Density ◽

Element Model ◽

Magnetic Flux Density ◽

Magnetic Shielding ◽

Permanent Magnet Motors ◽

Local Reduction ◽

Periodic Model ◽

Modeling Assumption

This paper concerns the local reduction of the magnetic flux density by means of magnetic shielding. Using a spatial frequency description, a 2-D semi-analytical periodic model is obtained for a coreless single-sided linear permanent magnet motor. The magnetic shield is included in the modeling using mode-matching. The obtained magnetic flux density is compared to a finite element model and is verified with measurements. The results show a reasonable agreement between the semi-analytical model and the measurements. Some large deviations occur due to the modeling assumption that the shield has a linear permeability, while the used shields are saturated. However, the semi-analytical modeling method is accurate enough for design purposes and initial calculations, especially when being aware of the possible saturation of the shield.

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Analysis Of Eddy Current Loss Of IPMSM According To The Material Of Permanent Magnet

Turkish Journal of Computer and Mathematics Education (TURCOMAT) ◽

10.17762/turcomat.v12i6.1959 ◽

2021 ◽

Vol 12 (6) ◽

pp. 508-513

Author(s):

Byeong-Chul Lee Et.al

Keyword(s):

Finite Element Analysis ◽

Magnetic Flux ◽

Permanent Magnet ◽

Flux Density ◽

Eddy Current ◽

Eddy Current Loss ◽

Magnetic Flux Density ◽

Element Analysis ◽

Eddy Current Losses ◽

Current Loss

In order to reach the performance of the permanent magnet embedded rotor, the choice of magnet is very important. It must be thermally stabilized, and at this point, discussion of eddy current losses is necessary.To proceed with this study, a permanent magnet embedded synchronous motor used in the compressor currently being designed was selected. To derive the eddy current losses in the neodymium-magnets, current density was calculated through the equation. The eddy current loss was mathematically derived using the magnetic conductivity and residual magnetic flux density. Finally, comparative verification was performed through finite element analysis simulation. In this paper, eddy current losses in a N series magnet are mathematically analyzed and we perform comparative verification through simulation using finite element analysis. The Br value indicating the residual magnetic flux density is the lowest in N30 series and the largestin the N48 series. In the case of using the N30 series, the amount of magnetic flux that can be generated is low, so in order to increase the same output, the electric field must be increased by drawing more current from the stator winding. That is, the torque can be further increased. However, since the magnetic flux density experienced by the permanent magnet also increases, eddy current loss that may occur in the magnet eventually increases. There are also a method of using a split magnet to reduce eddy current losses. Inthe case of a permanent magnet holding a large residual magnetic flux density, the magnets loss is reduced, but there is a disadvantage that the price may be expensive. The losses in the permanent magnet are dissipated as heat. If the eddy current loss increases, the magnet demagnetizes, which in turn leads to a decrease in performance. In the selection of magnets, analysis of losses is essential.

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