A new mathematical model for resonant-column measurements including eddy-current effects

2005 ◽  
Vol 42 (1) ◽  
pp. 121-135 ◽  
Author(s):  
Giovanni Cascante ◽  
John Vanderkooy ◽  
Wilson Chung
Keyword(s):  
Mathematical Model ◽  
Wave Velocity ◽  
Eddy Current ◽  
Eddy Currents ◽  
Damping Ratio ◽  
Resonant Column ◽  
Induced Voltage ◽  
Eddy Current Damping ◽  
Dry Sand ◽  
Resonant Column Device

Wave velocity and attenuation are commonly studied in the laboratory with the resonant-column device (American Society for Testing and Materials standard), which is driven by a set of coils and magnets. This paper presents a new and robust mathematical model of the electromechanical resonant-column system. The model is used to compute various transfer functions. Eddy currents, a new source of damping identified in the resonant-column device, introduce damping proportional to the velocity of the magnets. Eddy-current damping is considered in the mathematical model. A testing program is devised to calibrate the resonant column with three aluminum probes. Experimental and theoretical results show an excellent agreement (4% maximum error). Exploratory results are presented for a dry-sand specimen. A resonant-column device is modified to demonstrate the significant effect of the induced voltage (electromotive force (EMF)) on damping ratio if tests are not based on current measurements. Free-vibration tests on aluminum specimens and a dry-sand specimen show a significant effect of the induced EMF (up to 400% increase in damping for the sand specimen). The induced voltage depends on the resonant frequency and damping of the specimen. In the case of aluminum probes, eddy-current damping represents 20–150 times the material damping of the specimen. Preliminary results on dry sand show that eddy-current damping represents up to a 15% increase in damping ratio. However, the magnitude of eddy-current damping depends on the configuration and materials used in the resonant-column device. The smaller the damping ratio of the specimen is, the more important the eddy-current damping becomes.Key words: damping, eddy currents, mechanical waves, resonant-column device, shear modulus, wave velocity.

Modeling of a New Active Eddy Current Vibration Control System

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
Henry A. Sodano ◽  
Daniel J. Inman
Keyword(s):  
Magnetic Field ◽  
Vibration Control ◽  
Electric Fields ◽  
Eddy Current ◽  
Eddy Currents ◽  
Vibration Suppression ◽  
Frequency Doubling ◽  
Damping Force ◽  
Theoretical Derivation ◽  
Eddy Current Damping

There exist many methods of adding damping to a vibrating structure; however, eddy current damping is one of few that can function without ever coming into contact with that structure. This magnetic damping scheme functions due to the eddy currents that are generated in a conductive material when it is subjected to a time changing magnetic field. Due to the circulation of these currents, a magnetic field is generated, which interacts with the applied field resulting in a force. In this manuscript, an active damper will be theoretically developed that functions by dynamically modifying the current flowing through a coil, thus generating a time-varying magnetic field. By actively controlling the strength of the field around the conductor, the induced eddy currents and the resulting damping force can be controlled. This actuation method is easy to apply and allows significant magnitudes of forces to be applied without ever coming into contact with the structure. Therefore, vibration control can be applied without inducing mass loading or added stiffness, which are downfalls of other methods. This manuscript will provide a theoretical derivation of the equations defining the electric fields generated and the dynamic forces induced in the structure. This derivation will show that when eddy currents are generated due to a variation in the strength of the magnetic source, the resulting force occurs at twice the frequency of the applied current. This frequency doubling effect will be experimentally verified. Furthermore, a feedback controller will be designed to account for the frequency doubling effect and a simulation performed to show that significant vibration suppression can be achieved with this technique.

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.

Model of Eddy Current Damping Mechanism for the Suppression of Beam Vibrations

Aerospace ◽  
2004 ◽  
Author(s):  
Henry A. Sodano ◽  
Jae-Sung Bae ◽  
Daniel J. Inman ◽  
W. Keith Belvin
Keyword(s):  
Magnetic Field ◽  
Theoretical Model ◽  
Eddy Current ◽  
Damping Ratio ◽  
Power Supplies ◽  
Damping Force ◽  
Electromagnetic Damping ◽  
Eddy Current Damping ◽  
Eddy Current Damper ◽  
External Power

The movement of a conductor through a stationary magnetic field or a time varying magnetic field through a stationary conductor generates electromagnetic forces that can be used to suppress the vibrations of a flexible structure. In the present study, a new electromagnetic damping mechanism is introduced. This mechanism differs from previously developed electromagnetic braking systems and eddy current dampers because the system investigated in the following manuscript uses the radial magnetic flux of a permanent magnet to generate the electromagnetic damping force rather than the flux perpendicular to the magnet’s face as done in other studies. One important advantage of the proposed mechanism is that it is simple and easy to be applied. Additionally, a single magnet can be used to damp the transverse vibrations that are present in many structures. Furthermore, it doesn’t require any electronic devices or external power supplies, therefore functioning as a non-contacting passive damper. A theoretical model of the system is derived using electromagnetic theory, enabling us to estimate the electromagnetic damping force induced on the structure. The proposed eddy current damper was constructed and experiments were performed to verify the precision of the theoretical model. It is found that the proposed eddy current damping mechanism increases the damping ratio by up to 150 times and provides sufficient damping force to quickly suppress the beam’s vibration.

Modeling Eddy-Current Damping Force in Magnetic Levitation Systems With Conductors

2017 ◽  
Author(s):  
Mohammad Khodabakhsh ◽  
Mehran Ebrahimian ◽  
Bogdan Epureanu
Keyword(s):  
Permanent Magnet ◽  
Eddy Current ◽  
Eddy Currents ◽  
Magnetic Levitation ◽  
Analytical Models ◽  
Damping Force ◽  
Element Analysis ◽  
Wide Range ◽  
Eddy Current Damping ◽  
Damping Effects

An analytical method is used to develop a model to calculate steady-state eddy-current damping effects in two configurations of magnetic levitation (maglev) systems. The eddy-current based force (eddy-current force) is used for high precision positioning of a levitated permanent magnet in maglev systems. In these systems, the motion of the levitated permanent magnet and changes of the coil’s currents, generate eddy current in the conductors. The proposed analytical model is used to calculate both effects. A conductive cylindrical shell around the levitated object is implemented as a new technique to generate eddy currents in maglev systems. The model is also employed to obtain eddy-current damping effects in a system with a conductive plate beneath the levitated object. The analytical models match results from high fidelity finite element analysis (FEA) with acceptable accuracy in a wide range of operations. Advantages of the two configurations are discussed.

Analysis and Modeling of Eddy Current Damping for Short-Stroke DC Linear Motor

2013 ◽  
Vol 416-417 ◽  
pp. 300-304
Author(s):  
Dong Hua Pan ◽  
Jia Xi Liu ◽  
Feng Jing Shen ◽  
Li Yi Li ◽  
Ming Na Ma
Keyword(s):  
Magnetic Field ◽  
Eddy Current ◽  
Eddy Currents ◽  
Linear Motor ◽  
Force Model ◽  
Equivalent Resistance ◽  
Damping Force ◽  
Conductive Material ◽  
Charge Model ◽  
Eddy Current Damping

Eddy currents induced in a conductor in a changing magnetic field produce a damping force proportional to the heat generated in the conductive material. In this paper, the damping force of short-stroke DC Linear Motor (DCLM) is researched, and then model of damping force is established. In the preliminary work, the analytical expression of magnetic field distribution is obtained by the charge model, so the eddy current inducted in the conductor is calculated. Then the damping force is obtained after the equivalent resistance and inductance of conductors are calculated. The formula of damping force is obtained to optimize damping structure of short-stroke DCLM. The accuracy of damping force model is proved by the experiment.

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.

scholarly journals Evaluation of Dynamic Properties of Sodium-Alginate-Reinforced Soil Using A Resonant-Column Test

Materials ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 2743
Author(s):  
Seongnoh Ahn ◽  
Jae-Eun Ryou ◽  
Kwangkuk Ahn ◽  
Changho Lee ◽  
Jun-Dae Lee ◽  
...  
Keyword(s):  
Shear Modulus ◽  
Sodium Alginate ◽  
Shear Failure ◽  
Dynamic Properties ◽  
Damping Ratio ◽  
Reinforced Soil ◽  
Resonant Column ◽  
Column Test ◽  
Alginate Solution ◽  
Resonant Column Test

Ground reinforcement is a method used to reduce the damage caused by earthquakes. Usually, cement-based reinforcement methods are used because they are inexpensive and show excellent performance. Recently, however, reinforcement methods using eco-friendly materials have been proposed due to environmental issues. In this study, the cement reinforcement method and the biopolymer reinforcement method using sodium alginate were compared. The dynamic properties of the reinforced ground, including shear modulus and damping ratio, were measured through a resonant-column test. Also, the viscosity of sodium alginate solution, which is a non-Newtonian fluid, was also explored and found to increase with concentration. The maximum shear modulus and minimum damping ratio increased, and the linear range of the shear modulus curve decreased, when cement and sodium alginate solution were mixed. Addition of biopolymer showed similar reinforcing effect in a lesser amount of additive compared to the cement-reinforced ground, but the effect decreased above a certain viscosity because the biopolymer solution was not homogeneously distributed. This was examined through a shear-failure-mode test.

Analysis and Experiments of Eddy Current Brakes with Moving Magnets

2008 ◽  
Vol 575-578 ◽  
pp. 1299-1304 ◽  
Author(s):  
Jaw Kuen Shiau ◽  
Der Ming Ma ◽  
Min Jou
Keyword(s):  
Drag Force ◽  
Relative Motion ◽  
Eddy Current ◽  
Eddy Currents ◽  
Test System ◽  
Image Method ◽  
Electromagnetic Interactions ◽  
Finite Dimensional ◽  
Conducting Plate ◽  
Lorentz Force Law

This paper discusses the magnetic drag force resulting from the relative motion of a permanent magnet moving along a finite dimensional conducting plate. The image method with imaginary eddy currents is investigated. Boundary conditions are established to ensure that the eddy currents vanished at the boundaries of the conducting plate. Magnetic drag force is computed based on the eddy current distributions using Lorentz force law. A test system is built to demonstrate the magnetic brakes arose from the electromagnetic interactions.

Preliminary Investigations of Machine Frame Vibration Damping Using Eddy Current Principle

2016 ◽  
Vol 821 ◽  
pp. 288-294 ◽  
Author(s):  
George Juraj Stein ◽  
Peter Tobolka ◽  
Rudolf Chmúrny
Keyword(s):  
Mathematical Model ◽  
Natural Frequency ◽  
Eddy Current ◽  
Asynchronous Motor ◽  
Oscillatory System ◽  
Vibration Damping ◽  
Combined Effects ◽  
Magnetic Forces ◽  
Novel Approach ◽  
Vibration Attenuation

A novel approach to vibration attenuation, based on the eddy current principle, is described. The combined effects of all magnetic forces acting in the oscillatory system attenuate frame vibrations and, concurrently, decrease the damped natural frequency. A mathematical model of the forces balance in the oscillatory system was derived before. Some experimental results from a mock-up machine frame excited by an asynchronous motor are presented.

Geometric Effects on Eddy Current Bearing Performance

1989 ◽  
Vol 111 (2) ◽  
pp. 209-214 ◽  
Author(s):  
J. A. Tichy ◽  
K. A. Connor
Keyword(s):  
Eddy Current ◽  
Eddy Currents ◽  
Load Capacity ◽  
Complex Mixture ◽  
Journal Bearings ◽  
Magnetic Bearings ◽  
Repulsive Forces ◽  
The Magnetic Field ◽  
Geometric Effects ◽  
Current Journal

The properties of magnetic bearings, particularly those based on repulsive forces due to eddy currents, are determined by a complex mixture of electrical and mechanical length and time scales. A perturbation solution for the magnetic field structure based on careful ordering of these parameters has permitted the effects of realistic gap geometries to be analyzed. The load capacity of eddy current journal bearings is found to be somewhat larger than previously predicted in an earlier paper which used magnetic fields based on constant gap size. The present results may be of interest to those concerned with calculating eddy currents in conventional attractive magnetic bearings.

Sign in / Sign up

Export Citation Format

Share Document