Enhanced vibration suppression using linear and nonlinear locally resonant acoustic metamaterials, inerters and friction dampers

Abstract

Vibration suppression and noise control of mechanical equipment are critical aspects of engineering and design, aiming to mitigate the adverse effects of unwanted but inevitable vibrations and noise on human comfort, structural integrity, and overall system performance. This study focused on passive control methods that utilised isolators and absorbers to isolate or dissipate vibrations. Vibration control faces several challenges, including the need to address space constraints, low-frequency control, nonlinear dynamic characteristics, and complex coupled system dynamics. Advances in control techniques, manufacturing, and computational tools have facilitated significant progress in these fields. However, further research and development about novel structural design and analysis methods are needed to overcome challenges and achieve optimal control strategies for diverse applications. This thesis has dedicated considerable efforts and endeavors to address the aforementioned challenges.

The study began by proposing the application of linear and geometrically nonlinear inerter-based resonator in locally resonant acoustic metamaterials (LRAM) and their performance on the low-frequency wave attenuation was evaluated. The LRAM was modeled as 1-D chain system composed of mass-in-mass unit cells connected by springs, and the geometrical nonlinearity was achieved by two lateral inerters linking the resonator and lumped mass symmetrically with respect to the horizontal springs. Compared with linear inerter-based LRAM, the proposed nonlinear inerter-based structure had the property of a low-frequency bandgap with sufficient width. The nonlinearity could extend the original material parameter restrictions, leading to lower-frequency bandgap.

Furthermore, a diatomic-chain LRAM structure with a negative-stiffness mechanism was presented for enhanced suppression of vibration transmission. The bandgap properties were studied and shown to enhance performance benefits by introducing two extra bandgaps that exploit Bragg scattering. With the application of negative-stiffness mechanism, the bandgap shifted toward the lower frequency range, effective from zero frequency, thus achieving ultralow frequency vibration control. The proposed implementation was shown to yield desirable bandgap properties, providing potential benefits for vibration suppression.

A novel Flexnertia metastructure concept was subsequently proposed to perform vibration suppression through coupling rotational inerter to structural flexural motion. Theoretical analysis and experimental test of the proposed structure with emphasis on dissipating structural flexural motion was exhibited. The results were in good agreement, confirming that the average overall response of the metastructure was significantly reduced. The attenuation became most pronounced in the low-frequency range where structures tend to suffer most due to high response around the regime of the first flexural modes.

The study further explored a coupled structure based on a nonlinear hysteresis friction damper subjected to harmonic forces for vibration suppression. The forced response was well controlled by the normal force applied to the friction damper, and the amplitude and frequency of the resonance peaks could be varied within a certain range by changing force magnitude. The results indicated that the friction damper participates in the energy dissipation in the frequency band around the resonance frequency, thereby enabling high-amplitude vibration filtering. It confirmed that such friction dampers have the potential to be designed to be adjustable and meet different vibration control objectives.

Overall, the research results presented herein make a significant contribution to the development of linear and nonlinear advanced mechanisms for vibration control. Several novel configurations were demonstrated with obvious dynamic advantages from the perspective of power flow and vibration transfer. Further research endeavors were warranted to concentrate on the nonlinear systems based on the excellent properties of acoustic metamaterials, inerters and friction dampers.

Date of Award	Oct 2024
Original language	English
Awarding Institution	University of Nottingham
Supervisor	Jian Yang (Supervisor) & Xiaosu Yi (Supervisor)