Inertial-Amplified Mechanical Resonators for the Mitigation of Ultralow-Frequency Vibrations

Significance 

Vibration energy or acoustic waves are common phenomena in most mechanical systems. Several strategies have been employed to mitigate vibration in these systems. Among them, vibration absorbers are widely used to reduce or eliminate vibrations in harmonically excited systems. While conventional absorbers generally work well at higher frequencies, they exhibit poor performance at lower frequency ranges due to the presence of large wavelengths. Despite the limitations of the narrow frequency bandwidth, the subwavelength characteristic of resonance-based metamaterials can result in a compact absorber design. However, ultralow frequency absorption still faces constraints and challenges for noise requiring huge attenuation ratios. Addressing such inevitable problems requires effective strategies.

Dampers are widely used structures to suppress general mechanical vibrations and seismic waves. They consist of damped spring-mass-resonators comprising an embedded energy dissipation mechanism. However, since these dissipative components are usually heavy and bulky, a large mass is needed to make the device responsive at low frequencies. This explains the reason why most dampers with operating frequencies less than 10Hz are usually large structures. Nevertheless, more effective design approaches for vibrational energy-absorption devices are still necessary to improve their functionality in practical applications, especially in those instances where only limited space is available.

Herein, Dr. Zhen Dong and Professor Ping Sheng from Hong Kong University of Science and Technology developed a new design for vibrational energy-absorption device based on the inertial amplification concept. This approach utilized the coupling between rotational and translational motions. It also adopted a rather simple mechanical interconnection involving ball-screw structures. A series of experiments were conducted to verify the ultralow frequency responses of the prototype compared to those of analytical models. Their research work is currently published in the peer-reviewed journal, Physical Review Applied.

The research team showed that lightweight and compact resonator devices, with weights below 1kg and dimensions of 10 – 20 cm, can also achieve ultralow-frequency resonance responses at a seismic frequency range from 0.5 to 5 Hz. This was mainly attributed to the effects of the resulting inertial amplification. The fabricated functional prototypes achieved very large inertial-amplification factors (IAF), as high as 137. The meaning of IAF is that the actual resonance frequency corresponds with a resonator with a mass that is IAF-times larger. Moreover, the experimental results agreed well with the analytical modeling of the inertial-amplification mechanism, suggesting the feasibility of the proposed design approach.

Dr. Dong and Professor Sheng proposed a structurally refined device configuration, and they demonstrated its capability to achieve total vibrational absorption through simulations. Upon excitation, it achieved total vibrational energy absorption with a comparable broadband working range in the ultralow frequency range. Such kind of designs proved advantageous for mitigating ultralow frequency vibrations in situations with limited space. Furthermore, it was noted that diverse practical needs could be met by tuning the operational frequency range of these devices. For example, the proposed design could be adapted easily for resonance frequencies up to 100 Hz by miniaturizing its dimensions and reducing the inertial-amplification factor. It is envisioned that strong, low vibrations can be effectively mitigated by attaching multiple number of such miniature resonant-dampers.

In summary, the study revealed the salient features of inertial-amplified mechanical resonators in terms of ultralow frequency response, compactness and comparative broadband total-vibrational-absorption. Generally, resonators capable of responding to ultra-frequency range are usually bulky structures. The inertial-amplified resonator is an unconventional solution to the inherent problem associated with ultralow frequency vibration mitigation, as compact and lightweight devices can fit in limited spaces. In a statement to Advances in Engineering, Professor Ping Sheng explained that the compact design has adequate flexibility and options for different practical applications. Moreover, it also offers energy harvesting possibilities when coupled with piezoelectric elements.

Inertial-Amplified Mechanical Resonators for the Mitigation of Ultralow-Frequency Vibrations - Advances in Engineering

About the author

Dr. Zhen Dong
Postdoctoral Researcher, Hong Kong Automotive Platforms and Application Systems R&D Centre, Hong Kong Productivity Council
Email: [email protected]
Tel: +852 2788 5560
Address: 4/F, HKPC Building, 78 Tat Chee Avenue, Kowloon, Hong Kong
ResearchGate: https://www.researchgate.net/profile/Zhen-Dong-13

Dr. Zhen Dong is currently a post-doctoral researcher at the Hong Kong Automotive Platforms and Application Systems (APAS) R&D Centre, undertaken by the Hong Kong Productivity Council (HKPC). He earned his Batchelor degree in Science from the School of Physics, Shandong University in Mainland China, and Ph.D. degree in physics from the Hong Kong University of Science and Technology, supervised by Prof. Ping Sheng. During his Ph.D. studies, his research covered electronic transport properties of low-dimensional nano carbon materials at cryogenic temperatures, and developing new acoustic and mechanical metamaterials for tackling the low-frequency absorption problem beyond the causality limit, aiming to design new absorption devices with compact size and cheap cost to mitigate noises and vibrations in scenarios related to large machinery, transformers, vehicle engines, etc. After joining the APAS Centre, Dr. Dong is now working on R&D projects related to autonomous driving technology and new battery and charging solutions for electric & new energy vehicles.

About the author

Ping Sheng is a senior member of the Institute for Advanced Study and Professor Emeritus at HKUST. He obtained his BSc in Physics from the California Institute of Technology, and PhD in Physics from Princeton University in 1971. After a stay at the Institute for Advanced Study, Ping joined RCA David Sarnoff Research Center in 1973. In 1979 he joined the Exxon Corporate Research Lab, where he served as the head of the theory group during 1982-86. In 1994 Ping joined the HKUST as a professor of physics and served as the head of the physics department from 1999 to 2008.

Prof. Sheng is a Fellow of the American Physical Society and a Member of the Asia Pacific Academy of Materials. He served as the Executive Editor of Solid State Communications, a Division Associate Editor of Physical Review Letters and a member of the editorial board of New Journal of Physics. He was awarded Technology Leader of the Year by the Sing Tao Group in 2002, the Brillouin Medal by the International Phononics Society in 2013, the National Natural Science Award (second class) by the State Council of the People’s Republic of China in 2014, and the Rolf Landauer Medal by the ETOPIM Society in 2018.

Prof. Sheng has published more than 480 papers with a total of over 44,500 citations, with an h-index of 97 (by Google Scholar). He has presented over 350 keynote, plenary or invited talks at international meetings and conferences. His research interests include acoustic metamaterials, superconductivity in carbon nanotubes, nanostructured graphene, giant electrorheological fluids, fluid-solid interfacial phenomena, and effective medium theory of composites.

Reference

Dong, Z., & Sheng, P. (2022). Inertial-amplified mechanical resonators for the mitigation of ultralow-frequency vibrations. Physical Review Applied, 18(1).

Go To Physical Review Applied

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