Mechanical Engineering Commons^™

Development And Application Of Novel Sound Absorbers, Weiyun Liu

Theses and Dissertations--Mechanical Engineering

The sound absorbers in most common use today are porous materials like fibers and foams. This work examines three alternatives to porous absorbers: microperforated panels, acoustic fabrics, and additively manufactured absorbers. The research is a combination of design, measurement and characterization of their properties, and analysis.

Microperforated panels are thin metallic or plastic panels with sub-millimeter size holes or perforations. Sound absorption can be tuned by adjusting the spacing between the panel and a cavity behind the panel. Several different configurations were considered where the geometry behind the panel was divided up into channels of varying length and cross-sectional area. …

Impedance-To-Scattering Matrix Method For Large Silencer Analysis, Peng Wang

Theses and Dissertations--Mechanical Engineering

Large silencers used in the power generation industry usually have a very large cross section at the inlet and outlet. Higher-order modes will populate the inlet and outlet even at very low frequencies. Although the silencer itself is often modeled by a three-dimensional analysis tool such as the boundary element method (BEM) or finite element method (FEM), a direct computation of the transmission loss (TL) from the BEM or FEM model can be challenging without incorporating certain forms of modal expansion.

A so-called “impedance-to-scattering matrix method” is proposed to extract the modes at the inlet and outlet from the BEM …

The Effect Of Honeycomb Cavity: Acoustic Performance Of A Double-Leaf Micro Perforated Panel, Yuxian Huang, Kai Ming Li

The Summer Undergraduate Research Fellowship (SURF) Symposium

A micro perforated panel (MPP) is a device consisting of a thin plate and submillimeter perforations for reducing low frequency noise. MPPs have many advantages compared to traditional sound absorption materials, such as durability and designability, and they can be used in a variety of places such as room interior designs, passenger and crew compartments of aircrafts and combustion engines. The models in this study were designed and fabricated with the latest 3-D printing technology. The transmission loss and sound absorption coefficient of the 3-D printed double-leaf MPPs with honeycomb cavities were studied. According to the established theory, MPPs work …

Studies To Improve Exhaust System Acoustic Performance By Determination And Assessment Of The Source Characteristics And Impedance Optimization, Yitian Zhang

Theses and Dissertations--Mechanical Engineering

It is shown that the relationship between an impedance change and the dynamic response of a linear system is in the form of the Moebius transformation. The Moebius transformation is a conformal complex transformation that maps straight lines and circles in one complex plane into straight lines and circles in another complex plane. The center and radius of the mapped circle can be predicted provided that all the complex coefficients are known. This feature enables rapid determination of the optimal impedance change to achieve desired performance.

This dissertation is primarily focused on the application of the Moebius transformation to enhance …

Effect Of Compression On The Transmission Loss Of Porous Material, Yingchao Yang, J Stuart Bolton

The Summer Undergraduate Research Fellowship (SURF) Symposium

Porous materials are commonly applied in sound absorption in different places. Transmission loss, one of the vital parameters determining the performance of the material, will change when the material is compressed. Usually the compression that might affect the properties to the greatest extent are normal compression and the deformation can be simplified as 1D compression model. In order to verify the prediction, some formulas taking several parameters (porosity, tortuosity, flow resistivity and characteristic lengths) into account are applied and also the Johnson et al’s model of limp structure. Dynamic density of limp model and bulk modulus are thus obtained and …

Design Of A Catenoidal Shaped Anechoic Termination, Kyle Myers

Masters Theses

An analytical model is developed in this thesis to predict the reflection coefficient of an anechoic termination consisting of a catenoidal horn connected to a tube lined with absorbing material. The theoretical predictions are compared to experimental measurements on a prototype. Comparisons are made for a variety of arrangements, including, an open horn, and a horn connected to absorbing terminations of two different lengths. The absorbing terminations are either open or closed to the environment and the analytical model can account for both these scenarios. The results indicate that the new model can accurately predict the reflection coefficient for each …

Analog Feedback Control Of An Active Sound Transmission Control Module, Jason Derek Sagers

Theses and Dissertations

This thesis provides analytical and experimental proof-of-concept for a new feedback-controlled sound transmission control module for use in an active segmented partition (ASP) array. The objective of such a module is to provide high transmission loss down to low audible frequencies while minimizing the overall mass of the module. This objective is accomplished in the new module by using actively controlled panels in conjunction with analog feedback controllers. The new module also overcomes two limitations that exist in current ASP modules: the inability to control broadband random-noise and the lack of bidirectional control through the module. Overcoming these limitations represents …