Comparative Analysis of Mechanical and Magnetic Amplitude Stoppers in an Energy Harvesting Absorber 111 Fig. 2 Primary structure amplitude: (a) soft mechanical stoppers, (b) hard mechanical stoppers, and (c) magnetic stoppers Fig. 3 Average harvested power: (a) soft mechanical stoppers, (b) hard mechanical stoppers, and (c) magnetic stoppers absorber contacts the stoppers with zero velocity. Magnetic stoppers’ effects seem to be between the soft and hard mechanical stiffnesses, where medium-size gaps show an adequate control of the structure, but small gaps show a loss of control and aperiodic regions. Figure 3 shows the three cases effects on the average power generated. While investigating the energy harvested, peak power and the bandwidth are considered. Mechanical stoppers with a soft stiffness show great results. As the gap gets smaller, the peak power increases. The first peak shifts to the right increasing the power over the operable range of harvesting energy. Mechanical stoppers with hard stiffness show a decrease in power when there is any contact. Small gaps show the generation of a broadband region. This is desirable to generate more energy, but the extreme decrease in amplitude nullifies any benefit the broadband region would provide. A gap of 50 millimeters for magnetic stoppers shows a slight increase in power, but smaller gaps show a decrease in power. Again, a broadband region is present but is outweighed by the extremely small amplitudes. 4 Conclusions The results showed that mechanical stoppers with a soft stiffness are the most promising. The primary structure’s amplitude remains controlled while increasing the amount of energy harvested. Mechanical stoppers with a hard stiffness are not desirable. This case loses all control of the primary structure regardless of gap size if there is contact and has a great decrease of energy harvested. Magnetic stoppers with a medium gap are beneficial with regard to control of the primary structure and energy harvested, but smaller gaps show similar results to the hard stiffness case. Acknowledgments T. Alvis and A. Abdelkefi acknowledge the funding support from Sandia National Laboratories which is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the US Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. SAND202013824A.
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