THESIS
2021
1 online resource (xix, 118 pages) : illustrations (some color)
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 t...[
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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.
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