Acoustics, Dynamics, and Controls Commons^™

Helmholtz Equation Least Squares Based Near-Field Acoustic Holography With Laser, Wu Zhu

Wayne State University Dissertations

This dissertation presents the HELS based NAH with laser and use normal surface velocity as input in near-field acoustic holography. The conventional HELS based NAH uses acoustic pressure as input to reconstruct sound field quantities, while this modified HELS based NAH with laser utilizes the normal surface velocities measured by LDV to reconstruct the acoustic quantities at interested positions. Theoretical principles of the HELS based NAH with laser have been fully developed and the method has been verified in theoretical perspective. Two theoretical examples verify that HELS based NAH with laser can obtain exactly the same results as analytic solution. …

Vibration Of Steel-Framed Floors Supporting Sensitive Equipment In Hospitals, Research Facilities, And Manufacturing Facilities, Di Liu

Theses and Dissertations--Civil Engineering

Floors have traditionally been designed only for strength and deflection serviceability. As technological advances have been made in medical, scientific and micro-electronics manufacturing, many types of equipment have become sensitive to vibration of the supporting floor. Thus, vibration serviceability has become a routinely evaluated limit state for floors supporting sensitive equipment. Equipment vibration tolerance limits are sometimes expressed as waveform peak acceleration, and are more often expressed as narrowband spectral acceleration, or one-third octave spectral velocity.

Current floor vibration prediction methods, such as those found in the American Institute of Steel Construction Design Guide 11, Floor Vibrations Due to Human …

Networked Heterogeneous Systems In A Ros-Enabled Cloud Environment, Christopher Reid

College of Graduate Studies: Theses & Dissertations

It is important in the development of cloud robotics that the challenges presented by transferring computational loads to networked resources are properly addressed. The challenges include network latency, data integrity, security, and privacy. The objective of the present work is to investigate the issues of latency and data integrity in a representative cloud robotics environment. The present work involves setting up a cloud robotics network in an open-source Robot Operating System (ROS) framework and carrying out investigations on the levels of latency and reduction in data integrity as utilization of the network increases. In this study, a virtual datacenter has …

Eigenvector Pruning Method For High Resolution Beamforming, Jorge E. Quijano, Lisa M. Zurk

Electrical and Computer Engineering Faculty Publications and Presentations

This paper introduces an eigenvector pruning algorithm for the estimation of the signal-plus-interference eigenspace, required as a preliminary step to subspace beamforming. The proposed method considers large-aperture passive array configurations operating in environments with multiple maneuvering targets in background noise, in which the available data for estimation of sample covariances and eigenvectors are limited. Based on statistical properties of scalar products between deterministic and complex random vectors, this work defines a statistically justified threshold to identify target-related features embedded in the sample eigenvectors, leading to an estimator for the signal-bearing eigenspace. It is shown that data projection into this signal …

Temperature Dependence Of Shear Speed In Micellar Fluid, E.G. Sunethra Kumari Dayavansha

Electronic Theses and Dissertations

Wormlike micellar (WM) fluids are viscoelastic and can support shear waves. Phase transitions of the micellar aggregates are temperature dependent and can manifest as sharp changes in the shear wave speed as a function of temperature. Thus, shear waves provide a good tool for detecting the existence of phase transitions. In this work, the variation of shear speed with temperature of 200mM CTAB/NaSal micellar fluid in a 5:3 ratio was studied. The dependence of shear wave speed on time between fluid synthesis and measurement was also investigated. Shear wave propagation through the fluid was observed as a time varying birefringence …

Airborne Path Frequency Based Substructuring Method And Its Applications, Rui He

Theses and Dissertations--Mechanical and Aerospace Engineering

Frequency based substructuring (FBS) is routinely used to model structural dynamics. It provides a framework for connecting structural subsystems together, assessing path contributions, determining the effect of mount modification, and identifying inverse forces. In this work, FBS methods are extended to include acoustic subsystems and connecting pipes and ducts. Connecting pipes or ducts are modeled using the transfer matrix approach which is commonly used for modeling mufflers and silencers below the plane wave cutoff frequency. The suggested approach is validated using boundary element method (BEM) simulation. Applications of the procedure include determining airborne path contributions, the effect of treating ducts …

Development And Validation Of Finite Element Approaches To Determine The Insertion Loss Of Louvered Terminations Including Parametric Investigations, Huangxing Chen

Theses and Dissertations--Mechanical and Aerospace Engineering

Louvers are employed at the ends of HVAC ducts to direct airflow, provide weather protection, and attenuate noise. This details two finite element approaches that can be used to assess the acoustic attenuation from a louvered termination. In the first approach, plane wave propagation is assumed inside of a duct with a non-reflective source. On the receiver side, a baffled termination is assumed and the radiation condition is simulated using a non-reflective boundary condition called an automatically matched layer. In the second approach, a short aperture is placed between two infinite acoustic spaces. On the source side, a diffuse acoustic …

Determination Of Isolator Transfer Matrix And Insertion Loss With Application To Spring Mounts, Shishuo Sun

Theses and Dissertations--Mechanical and Aerospace Engineering

Transmissibility is the most common metric used for isolator characterization. However, engineers are becoming increasingly concerned about energy transmission through an isolator at high frequencies and how the compliance of the machine and foundation factor into the performance. In this study, the transfer matrix approach for isolator characterization is first reviewed. Two methods are detailed for determining the transfer matrix of an isolator using finite element simulation. This is accomplished by determining either the mobility or impedance matrix for the isolator and then converting to a transfer matrix. One of the more useful metrics to characterize the high frequency performance …

A Subsystem Identification Approach To Modeling Human Control Behavior And Studying Human Learning, Xingye Zhang

Theses and Dissertations--Mechanical and Aerospace Engineering

Humans learn to interact with many complex dynamic systems such as helicopters, bicycles, and automobiles. This dissertation develops a subsystem identification method to model the control strategies that human subjects use in experiments where they interact with dynamic systems. This work provides new results on the control strategies that humans learn.

We present a novel subsystem identification algorithm, which can identify unknown linear time-invariant feedback and feedforward subsystems interconnected with a known linear time-invariant subsystem. These subsystem identification algorithms are analyzed in the cases of noiseless and noisy data.

We present results from human-in-the-loop experiments, where human subjects in- teract …

The University Of Akron 2015 Sae Zips Baja Off-Road Racing Team 2015 Suspension System Design, Ryan W. Timura

Williams Honors College, Honors Research Projects

Baja SAE has been an important part of the University of Akron for the last 20 years. In the early stages, Zips Baja won many races and was one of the best Baja teams around. In more recent years, the teams have not been able to keep up the high place finishes. The 2015 Baja team aims to start a new trend of high place finishes for the years to come. With many design leaders returning from the previous year, passed down knowledge, and experience from last year, it should be an attainable goal.

An Axisymmetric Finite Element Model To Study The Earplug Contribution To The Bone Conduction Occlusion Effect, Martin K. Brummund, Franck Sgard, Yvan Petit, Frédéric Laville, Hugues Nélisse

Études primaires

An axisymmetric linear elasto-acoustic finite element (FE) model of an occluded human external ear is proposed to simulate the bone conduction occlusion effect (OE). The model consists of a cylindrical ear canal cavity surrounded by layers of biological tissues (skin, cartilage and bone) in which an earplug is inserted. Geometrical and material properties are taken from the literature. OEs are predicted for foam and silicone earplug FE-models using COMSOL Multiphysics (COMSOL®, Sweden). The FE-model is shown to predict the experimental OE measured in two healthy human reference groups wearing foam or silicone earplugs, satisfactorily. Deviations between model and experiment are …

High-Resolution Bottom-Loss Estimation Using The Ambient-Noise Vertical Coherence Function, Lanfranco Muzi, Martin Siderius, Jorge E. Quijano, Stan E. Dosso

Electrical and Computer Engineering Faculty Publications and Presentations

The seabed reflection loss (shortly "bottom loss") is an important quantity for predicting transmission loss in the ocean. A recent passive technique for estimating the bottom loss as a function of frequency and grazing angle exploits marine ambient noise (originating at the surface from breaking waves, wind, and rain) as an acoustic source. Conventional beamforming of the noise field at a vertical line array of hydrophones is a fundamental step in this technique, and the beamformer resolution in grazing angle affects the quality of the estimated bottom loss. Implementation of this technique with short arrays can be hindered by their …

Control Of Responses Of Smart Plate Structures Under Non-Stationary Random Excitations, Xiaojian Yang

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

This thesis is concerned with an investigation of the control of responses of plate structures with piezoelectric layers and under complicated excitations modeled as a non-stationary random process. The plate structures and piezoelectric layers are both discretized by the mixed formulation finite element method (FEM).

The investigation consists of three parts. The first part is a literature survey and theoretical development. The second part is the eigenvalue solution and computation of uncontrolled response statistics of laminated plate structures under nonstationary random excitations. The final part is the introduction and application of the stochastic central difference (SCD) method that was presented …

Wingtip Dynamics Simulator, Eugene Fox, Nick Rodriguez, Steven Rieber

Mechanical Engineering

Raytheon is a defense contracting company with an electronic warfare division that is developing a radio frequency signal triangulation system. Part of the focus in improving this technology is the need for accurate and real time locational knowledge of the signal receivers, which are located at the tips of aircraft wings. Due to turbulence during flight, the fluttering motion of the wings alter the distance and angle relationships of the two receivers and add noise to the received signal data, which negatively affect the triangulation estimates. To mitigate this error caused by the wing flutter, Raytheon is developing a software …

Experiment And Simulation Of The Acoustic Signature Of Fatigued-Cracked Gears In A Two-Stage Gearbox, Matthew James Ostiguy

Master's Theses

This thesis focuses on the development of a health monitoring system for gearbox transmissions. This was accomplished by developing and understanding a two-stage gearbox computer model that emulates an actual gearbox test rig. The computer model contains actual gearbox geometry, flexible shafts, bearings, gear contact forces, input motor torque, output brake torque, and realistic gearbox imbalance. The gear contact force of each gear stage and the input bearing translational acceleration were the main outputs compared between a healthy gearbox and damaged gearbox computer model. The damage of focus was a fatigue crack on the input pinion gear. A sideband energy …

The Icon Horn Loudspeaker, Vincent Phan

Mechanical Engineering

A horn loudspeaker in layperson terms is essentially taking a megaphone and integrating it into a standard speaker. Similar to a cheerleader yelling into a megaphone, the horn loudspeaker will amplify the sound from the speaker with no additional power needed. Using standard speaker horn theory, the geometry of the “megaphone” can be engineered to tune the acoustic performance tailored to loudness and/or specific acoustics frequencies. The horn contours are similar to traditional orchestra instruments such as the French horn, trumpet, and tuba. The iconic beauty of a horn married with the quantitative engineering theory creates an aesthetic yet functional …

Assessment Of Noise-Induced Annoyance By Tones In Noise From Building Mechanical Systems, Joonhee Lee, Lily M. Wang

Durham School of Architectural Engineering and Construction: Faculty Publications

Prominent tones in noise generated by mechanical equipment in buildings can cause complaints from occupants in buildings. The ISO 1996-2 and ANSI S1.13 standards describe methodologies and metrics to quantify tonality perception, but the influence of tones in noise on human annoyance and performance is not fully understood yet. This paper investigates annoyance responses of humans while exposed to background noise with tonal components. Twenty participants completed digit span tasks while exposed to noise signals with differing levels of tones and overall loudness. Subjects were also asked to rate their annoyance after completing tasks under each noise signal. The subjective …

The Impact Of Building Acoustics On Speech Comprehension And Student Achievement, Lily M. Wang

Durham School of Architectural Engineering and Construction: Faculty Publications

The movement for improved classroom acoustics has primarily been grounded on studies that show how building acoustics (i.e. background noise levels and room reverberation) affect speech intelligibility, as determined by speech recognition tests. What about actual student learning, though? If students do not understand each spoken word in the classroom perfectly, can they still manage to achieve high scholastic success? This presentation will review two recent studies conducted at the University of Nebraska – Lincoln, linking classroom acoustic conditions to student learning outcomes and speech comprehension (rather than simply recognition). In the first, acoustic measurements in two public school districts …

Effects Of Room Acoustics On Comprehension Of Foreign-Accented Speech By Native And Non-Native English-Speaking Listeners, Zhao Peng, Kristin E. Hanna, Brenna N. Boyd, Lily M. Wang

Durham School of Architectural Engineering and Construction: Faculty Publications

In a previous study by the authors, reverberation time (RT) and background noise level (BNL) were both found to have negative effects on native and non-native English-speaking listeners in comprehending English speech produced by native American-English-speaking talkers. Comprehension scores were adjusted for listeners’ baseline English proficiency levels. In the present study, instead of native English-speaking talkers, two native Mandarin Chinese talkers (one male, one female) with similar English spoken proficiency were recruited to produce the same speech materials used in the previous study. A similar methodology was adopted to conduct speech comprehension tests on three groups of listeners: 1) native …

Development Of Sound Quality Metrics For Gear Rattle In Diesel Engines, Brandon Sobecki

Open Access Theses

Sound quality is an important factor in the design of competitive diesel engines. The noise produced by specific components and mechanisms in the engine can play a significant role in determining the perceived quality of the overall noise and in turn the perceived quality of the engine. The goal of the present research is to characterize the sounds produced by the phenomenon known as gear rattle and to develop a model that can be used to assess gear rattle levels in a way that connects directly with human perception of rattle. Most previous work in this area has been focused …