This paper investigates the feasibility of an electromagnetism energy harvester (EMEH) for scavenging electric energy from transportation infrastructures and powering of conventional sensors used for their structural health monitoring. The proposed EMEH consists of two stationary layers of three cuboidal permanent magnets (PMs), a rectangular thick aircore copper coil (COIL) attached to the free end of a flexible cantilever beam whose fixed end is firmly attached to the highway bridge oscillating in the vertical motion due to passing traffic. The proposed EMEH utilizes the concept of creating an alternating array of permanent magnets to achieve strong and focused magnetic field in a particular orientation. When the COIL is attached to the cantilever beam and is placed close to the PMs, ambient and traffic induced vibration of the cantilever beam induces eddy current in the COIL. The tip mass and stiffness of the cantilever beam are adjusted such that a low-frequency vibration due to the passing traffic can effectively induce the vibration of the cantilever beam. This vibration is further amplified by tuning the frequency of the cantilever beam and its tip mass to resonance frequency of the highway bridge. The numerical results show that the proposed EMEH is capable of producing an average electrical power more than 1 W at the resonance frequency 4 Hz over a time period of 1 second that alone is more than enough to power conventional wireless sensors.
This paper is focused on the analytical model, design, and simulation of a variable coil-based friction damper (VCBFD)
for vibration control of structures. The proposed VCBFD is composed of a soft ferromagnetic plate, made of a linear
magnetic material, and two identical thick rectangular air-core coils connected in parallel, each one attached to the plate
through a friction pad. The friction force is provided by a normal force produced through an attractive electromagnetic
interaction between the air-core coils (ACs) and the soft ferromagnetic plate when sliding relative to each other. The
magnitude of the normal force in the damper is varied by a semi-active controller that controls the command current
passing through the ACs. To demonstrate the efficiency of the proposed VCBFD and its semi-active controller, it has
been implemented on a two-degree-of-freedom (2DOF) base-isolated model subjected to the acceleration components of
three records of strong earthquakes. The results show that the performance of the proposed VCBFD in its passive-on
mode is overshadowed by the undesirable effects of stick-slip motion. However, the damper in its semi-active mode is
more successful in not only reducing the displacement of the base-floor but also avoiding stick-slip motion, due to acting
completely in its sliding phase.
This paper presents analytical modeling of a novel type of passive friction damper for seismic hazard mitigation of structural systems. This seismic protective device, which is termed as Passive Electromagnetic Eddy Current Friction Damper (PEMECFD), utilizes a solid-friction mechanism in parallel with an eddy current damping system to dissipate a larger amount of input seismic energy than that by a device with based on solid friction only. In this passive damper, friction force is produced through a magnetic repulsive action between two permanent magnets (PMs) magnetized in the direction normal to the friction surface. The eddy current damping force in the damper is generated because of the motion of the PMS in the vicinity of a conductor. Friction and eddy current damping parts of the damper are able to produce ideal rectangular and elliptical hysteresis loops individually. Seismic hazard mitigation effectiveness of the proposed damper has been demonstrated through an implementation on a two-degree-of-freedom frame building structure. Numerical results show that the proposed damper is more efficient in dissipating input seismic energy than a Passive Linear Viscous Damper (PLVD) with same force capacity.
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