Research Papers

Modeling of a New Active Eddy Current Vibration Control System

[+] Author and Article Information
Henry A. Sodano

Department of Mechanical and Aerospace Engineering, Arizona State University, Tempe, AZ 85287-6106henry.sodano@asu.edu

Daniel J. Inman

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

J. Dyn. Sys., Meas., Control 130(2), 021009 (Feb 29, 2008) (11 pages) doi:10.1115/1.2837436 History: Received August 25, 2005; Revised August 13, 2007; Published February 29, 2008

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.

Copyright © 2008 by American Society of Mechanical Engineers
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Figure 1

Schematic showing the configuration of the active eddy current damper

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Figure 2

Magnetic field and the eddy currents induced in the cantilever beam

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Figure 3

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

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Figure 4

Nondimensional eddy current density of the conductor

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Figure 5

Experimental setup used to verify the frequency doubling effect

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Figure 6

Experimental setup used to measure the magnetic field generated by the permanent magnet

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Figure 7

Schematic showing the dimensions of the beam

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Figure 8

Experimental setup of active eddy current damper

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Figure 9

Applied current and the resulting eddy current force, demonstrating the force occurs at twice the applied frequency

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Figure 10

Plot of the measured and simulated applied current and resulting eddy current force at 30Hz

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Figure 11

Experimentally measured frequency response of coil and frequency response of a transfer function with a single pole at 15Hz indicating their match

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Figure 12

Block diagram/flow chart of feedback control system

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Figure 13

Frequency response of the beam with active eddy current control

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Figure 14

Simulated time response before and after control is applied to the first and second mode of vibration.




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