An electromagnetic damper with rotating inertial mass to control the vibrations of structures

What is it about?

This paper presents a new type of electromagnetic damper with rotating inertial mass that has been developed to control the vibrations of structures subjected to earthquakes. The electromagnetic inertial mass damper (EIMD) consists of a ball screw that converts axial oscillation of the rod end into rotational motion of the internal flywheel, and an electric generator that is turned by the rotation of the inner rod. The EIMD is able to generate a large inertial force created by the rotating flywheel and a variable damping force developed by the electric generator. Device performance tests of reduced-scale and full-scale EIMDs were undertaken to verify the basic characteristics of the damper and the validity of the derived theoretical formulae. Shaking table tests of a 3-story structure with EIMDs and earthquake response analyses of a building with EIMDs were conducted to demonstrate the seismic response control performance of the EIMD. The EIMD is able to reduce story drifts as well as accelerations, and surpasses conventional types of dampers in reducing acceleration responses.

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Why is it important?

The electromagnetic inertial mass damper (EIMD) is able to generate a large inertial mass by the rotating flywheel and variable damping by the built-in electric generator. The EIMD achieves the following effects on structural dynamic properties: the generated inertial mass reduces the apparent input excitation to the structure, and elongates the natural period of the structure, and the induced damping increases the damping factor of the structure, while the generated inertial mass decreases the structure damping. The reduction of the input excitation and the elongation of the natural period are characteristics that cannot be achieved by conventional types of dampers. The induced variable damping can compensate for the decrease of the damping factor owing to the inertial mass.

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