Mitigation of Flanking Noise Transmission in Periodic Structures of Lightweight Elements

Parthkumar Gandalal Domadiya

    Research output: Book/ReportPh.D. thesis

    Abstract

    Lightweight structures becoming increasingly popular within the building industry and hence they requires immediate attention to address their vibro-acoustic behaviour. Flanking noise transmission is one of the main concerns while using lightweight panels in buildings, since sound can travel through structural junctions and radiates into neighbouring rooms. To diminish the flanking transmission of sound, frames are usually designed with single or double studs or constructed with layers of foam or another viscoelastic material. This thesis is investigating the behaviour of flanking noise transmission in periodic structures of lightweight elements by employing various numerical, analytical and experimental methods.

    At first, three dimensional finite-element (FE) models of a Z-shaped lightweight panel structure based on various frame designs, inclusion of air and structural coupling between elements are considered for describing flanking noise transmission through panels. It is assumed that the ribs are fully fixed to the plates in case of various frame designs, and a parametric study is carried out on the centre panel with regard to various spacing between the ribs. Solid finite elements are adopted for the structure and the computations are carried out in frequency domain. The effect of employing periodicity in panels is described by determining decibel levels at the receiver wall surface when source wall comes under diffuse field excitation. Furthermore, to understand wave propagation characteristics in periodic structures, the structure must be simplified; hence, one dimensional structures such as bars and beams are considered for further investigation. A periodic bar model comprised of systemically placed Plexiglas and steel elements is generated using two methods: an FE method and a Floquet theory. A parameter study is carried out regarding the influence of the number of periodic cells at various frequencies within a semi-infinite bar, and stop bands are illustrated at certain periodic intervals within the structure.

    Finite element models and Floquet theory for Euler-Bernoulli and Timoshenko beams is applied on beam structures with periodic material inhomogeneity. The FE approach is based on a standard FE formulation for which proper transmitting boundary conditions are introduced to evaluate the insertion loss in a semi-infinite beam. Representation of pass and stop-bands is given in terms of the insertion loss and dispersion curves, and the influence of the beam periodicity on vibration transmission is investigated by embedding a variable number of periodic cells in a semi-infinite beam. The computations are carried out in the frequency domain with the load acting as a concentrated harmonically varying lateral load at the end of the semi-infinite beam.

    In addition, a beam with periodically changing cross-section is considered for further evaluation of vibration transmission based on the FE method, dynamic stiffness matrix (DSM) method, wave finite element method (WFE) and experimental analysis. Experimental analysis is performed by suspending a beam in the laboratory to provide simple supported boundary conditions under two types of structural excitation: a suspended mini-shaker and instrumented hammers. The transmission loss coefficient is calculated to predict the noise and vibration insulation periodically embedded cells structure. Numerical and experimental results are compared and discussed thoroughly. Excellent agreement between the numerical and experimental models in terms of stop-bands is showed. Results shows that few repetitions of a cell are sufficient to drastically reduce disturbance transmission whose dominant frequencies fall within the stop-bands.
    Original languageEnglish
    Place of PublicationAalborg
    PublisherDepartment of Civil Engineering, Aalborg University
    Number of pages128
    Publication statusPublished - 2014
    SeriesDCE Thesis
    Number58
    ISSN1901-7294

    Bibliographical note

    The thesis will be defended at 13:00, 21/2 2014 in F-108 at Sohngaardsholmsvej 57, 9000 Aaborg

    Keywords

    • Building Industry
    • Lightweight Structures
    • Vibro-Acoustic Behaviour
    • Acoustic Noise
    • Flanking Noise Transmission
    • Vibrations
    • Numerical Models
    • Analytical Methods
    • Experimental Methods

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