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TECHNICAL PAPERS

# Improved Concept and Model of Eddy Current Damper

[+] Author and Article Information
Henry A. Sodano

Mechanical Engineering Department,  Michigan Technological University, 1400 Townsend Dr., Hdoughton, MI 49931hsodano@mtu.edu

Jae-Sung Bae

Wind Power/Fluid Machinery Research Center, Department of New & Renewable Energy Research,Korea Institute of Energy Researchjsbae@kier.re.kr

Daniel J. Inman

Center for Intelligent Material Systems and Structures, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0261dinman@vt.edu

W. Keith Belvin

Structural Dynamics Branch, NASA Langley Research Center, Hampton, VA 23681-0001w.k.belvin@larc.gov

J. Vib. Acoust 128(3), 294-302 (Nov 03, 2005) (9 pages) doi:10.1115/1.2172256 History: Received August 24, 2004; Revised November 03, 2005

## Abstract

When a conductive material experiences a time-varying magnetic field, eddy currents are generated in the conductor. These eddy currents circulate such that they generate a magnetic field of their own, however the field generated is of opposite polarity, causing a repulsive force. The time-varying magnetic field needed to produce such currents can be induced either by movement of the conductor in the field or by changing the strength or position of the source of the magnetic field. In the case of a dynamic system the conductor is moving relative to the magnetic source, thus generating eddy currents that will dissipate into heat due to the resistivity of the conductor. This process of the generation and dissipation of eddy current causes the system to function as a viscous damper. In a previous study, the concept and theoretical model was developed for one eddy current damping system that was shown to be effective in the suppression of transverse beam vibrations. The mathematical model developed to predict the amount of damping induced on the structure was shown to be accurate when the magnet was far from the beam but was less accurate for the case that the gap between the magnet and beam was small. In the present study, an improved theoretical model of the previously developed system will be formulated using the image method, thus allowing the eddy current density to be more accurately computed. In addition to the development of an improved model, an improved concept of the eddy current damper configuration is developed, modeled, and tested. The new damper configuration adds significantly more damping to the structure than the previously implemented design and has the capability to critically damp the beam’s first bending mode. The eddy current damper is a noncontacting system, thus allowing it to be easily applied and able to add significant damping to the structure without changing dynamic response. Furthermore, the previous model and the improved model will be applied to the new damper design and the enhanced accuracy of this new theoretical model will be proven.

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## Figures

Figure 1

Schematic of conductive material passing through a magnetic field and the generation of eddy currents

Figure 2

Schematic showing the magnetic flux of one and two magnets

Figure 3

Cantilever beam in magnetic field generated by permanent magnet

Figure 4

Magnetic field and the eddy currents induced in the cantilever beam

Figure 5

Schematic of the circular magnetized strip depicting the variable used in the analysis

Figure 6

Schematic demonstrating the effect of the imaginary eddy currents

Figure 7

Schematic showing the variables associated with the conducting plate

Figure 8

Schematic showing the dimensions of the beam

Figure 9

Experimental setup showing position of magnets and conducting plates

Figure 10

Magnetic flux lines with contours of the radial flux By for two magnets

Figure 11

Magnetic flux density By for a case of lg∕b=0.2

Figure 12

Eddy current density before and after the image method is applied

Figure 13

Experimental and predicted damping ratio of the beam’s first mode for the system used in Sodano (21) and the damping ratio predicted by the improved model developed in this paper

Figure 14

Experimentally obtained frequency response of the system before and after placement of the magnets

Figure 15

Time response of the beam to an initial displacement when one and two magnets are present

Figure 16

Measured and predicted frequency response of the beam for the case that the magnet is located 4mm from the beam

Figure 17

Experimental and predicted damping ratio of the beam’s first mode as a function of the gap between the magnet and beam

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