Applications of multiple resonators for noise reduction and mechanical vibration damping

Abstract

Low frequency noise absorption and vibration damping has been a challenge in everyday life, compromising the quality of life and health especially for urban dwellers. A small, reliable, effective passive noise absorption and damping system that is easy to install and maintain at low-cost is needed. In this research, two kinds of acoustic metamaterials were researched to see if they have the properties necessary to develop such a system. Acoustics metamaterials were well-proved effective low-frequency noise absorbers. Two types of acoustics metamaterials, split tube resonators and membrane-type acoustic metamaterial (MAMM), were investigated here. A split tube resonators is a box consists of two narrow splits, two narrow channels and an air cavity. Friction is generated when air passes the resonators. This feature leads to absorption of sound. Two split tube resonators can form a unit of ventilated metamaterial absorber (VMA). Using two layers of VMA could reach almost perfect absorption at < 500 Hz in experiments and simulations. MAMM consists of an elastic membrane with a locally decorated pattern mounted on a rigid frame. Perfect absorption at multiple frequencies could be demonstrated in experiments and simulations in 200 ‒ 1000 Hz using an asymmetric resonator. Next, MAMM could be used as a tuned mass damper in the damping system. The damping parameters, frequency and quality factor can be tuned easily and studied by the effective mass method. Multiple frequency dampers and multiple dampers with different frequencies were studied. The damping effect on primary resonance on a beam and plate with free boundaries could be lowered by 20dB using MAMM as tuned mass dampers. The coherent super decay phenomenon was discovered when multiple dampers were applied to a structure. It is a linear sum of the displacement of several damped oscillators that can collectively decay much faster than the individual ones. The concept of coherent super decay was introduced and applied in a simulation of a 10-storey building. This simulation was done easily by using the effective mass methodology. The maximum displacement of the building was lowered by 39.9% with 100 dampers whose total mass was only 1.8% of the whole building.

Date of Award	2021
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Zhi Yu YANG (Supervisor)