<p> Wind turbine noise at low frequencies less than 300Hz is not only annoying to humans but has been proven to cause serious health issues. Additionally, animals are severely affected by wind turbines because a small increase in ambient noise (as is produced by wind turbines) significantly reduces their listening ability. In an attempt to better understand and characterize the aerodynamic noise of wind turbine blades, experimental testing was completed on PowerWorks 100kW and GudCraft WG700 blade specimens in the University of California, Davis Transportation Noise Control Center's anechoic chamber. Experimental testing and data analysis proved approximately 4.0dB to 6.0dB was produced due to the blades' geometric design for both blade specimens at low frequencies. This noise was maximized at the blades' leading edge along the central portion of the blades' radius. Theoretical prediction models have been used to determine that, for typical wind speeds and low frequencies, noise generated due to the tip passing frequency is clearly predominant.</p>

<p> There is an interest in producing accurate and reliable computer simulations to predict the dynamic behavior of heterogeneous materials and to use these simulations to gain further insight into experimental results. In so doing, a more complete understanding of the multiple-length scales involved in heterogeneous material compaction can be obtained. Mesoscale computer simulations of dynamically shocked materials have proven to be a beneficial resource in unraveling data not observed in planar shock impact experiments, such as stress and temperature interactions between grains. </p><p> The modeled mono-dispersed geometry of particles, the densities of each material, equations of state, material properties and many other factors affect the simulated outcomes. By studying and analyzing these variables, many of which highlight the difference between experimental and simulated results, there manifests additional insight into the shock dynamics of the different heterogeneous granular materials. The heterogeneous materials in this study were created both by a "shake and pack" method, where individual grains were randomly seeded into the computational domain and grown until the grains matched the experimental volume fraction and average diameter. </p><p> Three planar shock experiments were utilized to validate simulation models and parameters: 1. Brake pad powder compaction at Marquette University, 2. Dry sand experiments at Georgia Tech, and 3. Release of dry sand at Cambridge University. Planar shock impact experiments were simulated using two different hydrocode packages: CTH and iSALE. Validated models are then used to setup future dry, water, and possible ice saturated sand release experiments. Particle velocity and stress traces obtained from the computer simulations were compared to VISAR, PDV, and Manganin gage measurements obtained from experiments. The results from simulations are compared to experiments and discussed in this document.</p>

<p> The field of shock physics as a whole has only recently begun to pay particular attention to modeling heterogeneous materials under shock loading. These materials are important because of their practicality in terms of creating stronger, more shock resistant materials. To understand why they absorb shock impact energy better than homogeneous materials means that the small-scale processes that occur during the shock loading of these heterogeneous materials needs to be understood. Recent computational experiments, called mesoscale simulations, have shown that explicitly incorporating small-scale heterogeneous features into hydrocode simulations allows the bulk shock response of the heterogeneous material to be observed while not requiring the use of empirically determined constitutive equations. Including these features in simulations can offer insights into the irreversible mechanisms that dominate the propagation of shock waves in heterogeneous materials. </p><p> Three cases where the mesoscale approach for modeling the dynamic shock loading of heterogeneous materials are presented. These materials fall into three categories: granular - dry sand, granular with binder - concrete, and granular contained in a metal foam with a binder - granular explosive contained in an aluminum foam. The processes in which shock waves propagate through each material are addressed and relationships between the three materials are discussed. Particle velocity profiles for dry sand and concrete was obtained from Harvard University and Eglin Air Force Base, respectively. Mesoscale simulations using CTH are conducted for each type of heterogeneous material and the results are compared to the experimental data.</p>

<p> Particles in turbulence flows, either natural or artificial, can be charged. According to the previous research, electrical charge on particles has an influence on both rain enhancement and particle clustering in turbulent flow. Due to the Lorenz effect of unipolar or bipolar charged particles, particles tend to attract or repel to each other. Moreover, it is well known that electrical field exists in the atmosphere that has an effect on charged particles, especially droplets. As a result, the dynamic behaviors of charged particles can be rather different from uncharged particles, which, to date, are not systematically studied yet.</p><p> In order to systematically investigate the charged particles, we developed a method involving holographic particle tracking velocimetry (HPTV) technique to study the kinetic behavior of charged particles in flow. Theoretical analysis was also carried out to correlate kinetic behavior of particles and charge amount on them. This thesis also validated the feasibility of this method. The results of the validation experiment show that this method is capable to measure the velocity and acceleration of particles. By means of the second-order polynomial regression of particles' motion, the average acceleration, initial position and initial velocity of particles were obtained. With the mathematical model of a product of two normally distributed variables, the error bounds in measurement of particle kinetics can be acquired. Therefore, combining with the electrical field and diameter range of particles, we can quantitatively study the dynamic behavior of charged particles in flow.</p><p> In order to verify this, some experiments were designed and performed. We applied this method to quantitatively measure the behavior of particles to acquire the charge amount on particles from an enclosed chamber used in turbulence experiments. The result showed that although the charge amount was very low, most particles were charged with positive charge in the enclosed chamber. This result agreed with the triboelectric effect theory that in the friction with PVC tube, glass bubble particles prefer to lose electron and show positive charge. We also studied the effect of fan speed and material on charge amount on particles. Our results show that, by means of changing the material of tube, particle charge level is reduced, although more theoretical and experimental research should be carried out to confirm this conclusion.</p>

<p> It is important to characterize surface and transmitted wavefront errors in terms of the spatial content. The errors are typically analyzed in three spatial domains: figure, ripple (or mid-spatial frequency) and roughness. These errors can affect optical system performance. For example, mid-spatial frequency errors can lead to self-focusing and power loss in a high-power laser system. Currently, power spectral density (PSD) is used for the spatial content characterization in high-end optics, although there are potential pitfalls. For example, the low spatial content is removed before calculation, only a small fraction of surface data are used, and the results are sensitive to details like the windowing.</p><p> As an alternative, the structure function (SF) does not have such problems. It is the expectation of the squared height difference as a function of separation. The linear SF has been used in astronomy and captures data of all spatial frequencies. However, it does not capture anisotropy on the surface. The two-quadrant area SF introduced in this dissertation obviates this problem. It is computationally correct for any arbitrary aperture over all spatial content with anisotropic information. </p><p> This dissertation discusses some computational issues of the SF, which includes the calculation of the linear / area SF, sliding sampling method for large numbers of points within the aperture, analysis of periodic errors, and connection between the linear SF and area SF. </p><p> Moreover, the relationships between the SF and other surface characterization techniques (Zernike polynomials, autocorrelation function (ACF), PSD, and RMS gradient) have been investigated. It turns out that the linear SF of the sum of the Zernike terms only equals to the sum of the linear SF of each of the Zernike polynomials with different azimuthal frequencies. However, this theorem does not apply to the area SF. </p><p> For stationary surfaces, the SF contains similar information as ACF, but it provides better visualization. The SF is computationally correct for any arbitrary aperture shape without extra processing, while the PSD always needs additional mathematical processing. After connecting the SF to the RMS gradient, the SF slope at the origin has been evaluated. </p><p> Use of a SF to specify optical surfaces over the full range of spatial frequencies of interest implies the combination of data from instruments with substantially different lateral resolutions. This research shows the combination of data from a Fizeau and a coherence scanning interferometer (CSI) for various precision surfaces. The investigation includes the connection method of the coordinate systems between the Fizeau data and the CSI sub-aperture data, the convergence of the averaged SF of sub-aperture samples, the uncertainty analysis, and the effect of the instrument transfer function (ITF). </p><p> In addition, the SF was used to explore two typical noise contributions (electronic noise and air turbulence) in phase shifting interferometry. Based on dynamic measurements, the SF was used to analyze the spatial components of a diamond turned surface after the compensation machining. </p><p> In summary, the SF is a useful tool to specify and characterize the spatial content of optical surfaces and wavefronts.</p>

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2008. / Source: Dissertation Abstracts International, Volume: 69-05, Section: B, page: 3237. Adviser: Narayana R. Aluru. Includes bibliographical references (leaves 123-131) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007. / Source: Dissertation Abstracts International, Volume: 69-02, Section: B, page: 1281. Adviser: Gregory Elliott. Includes bibliographical references (leaves 339-350) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007. / Source: Dissertation Abstracts International, Volume: 68-07, Section: B, page: 4560. Adviser: Robert D. Moser. Includes bibliographical references (leaves 119-122) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007. / Source: Dissertation Abstracts International, Volume: 68-11, Section: B, page: 7393. Adviser: Duane D. Johnson. Includes bibliographical references (leaves 124-133) Available on microfilm from Pro Quest Information and Learning.

Thèse (Ph.D.)--Université de Sherbrooke (Canada), 2008. / Titre de l'écran-titre (visionné le 1 février 2007). In ProQuest dissertations and theses. Publié aussi en version papier.