<p> An experimental study will be carried out to determine the suitability of Green Natural Fiber Reinforced Polymer plates (GNFRP) manufactured with hemp fibers, with the purpose of using them as structural materials for the flexural strengthening of reinforced concrete (RC) beams. Four identical RC beams, 96 inches long, are tested for the investigation, three control beams and one test beam. The first three beams are used as references; one unreinforced, one with one layer of Carbon Fiber Reinforced Polymer (CFRP), one with two layers of CFRP, and one with n layers of the proposed, environmental-friendly, GNFRP plates. The goal is to determine the number of GNFRP layers needed to match the strength reached with one layer of CFRP and once matched, assess if the system is less expensive than CFRP strengthening, if this is the case, this strengthening system could be an alternative to the currently used, expensive CFRP systems.</p>

<p> Aero-optical distortions are detrimental to airborne optical systems. To study distortion mechanisms, compressible large-eddy simulations are performed for a Mach 0.5 turbulent boundary layer and a separated shear layer over a cylindrical turret with and without passive control in the upstream boundary layer. Optical analysis is carried out using ray tracing based on the computed density field and Gladstone-Dale relation.</p><p> In the flat-plate boundary layer, the effects of aperture size, Reynolds number, small-scale turbulence, different flow regions and beam elevation angle are examined, and the underlying flow physics is analyzed. Three momemtum-thickness Reynolds numbers, <i>Re</i>_&thetas; = 875, 1770 and 3550, are considered. It is found that the level of optical distortions decreases with increasing Reynolds number within the Reynolds number range considered. The contributions from the viscous sublayer and buffer layer are small, while the wake region plays a dominant role followed by the logarithmic layer. By low-pass filtering the fluctuating density field, it is shown that small-scale turbulence is optically inactive. Consistent with previous experimental findings, the distortion magnitude is dependent on the propagation direction due to anisotropy of the boundary-layer vortical structures. Density correlations and length scales are analyzed to understand the elevation-angle dependence and its relation to turbulence structures. The applicability of Sutton's linking equation to boundary-layer flows is examined, and excellent agreement between linking equation predictions and directly integrated distortions is obtained when the density length scale is appropriately defined.</p><p> The second case studied involves a separated shear layer over a cylindrical turret with a flat window, with inflow from a flat-plate boundary layer with and without passive control devices. The flow and optical results show reasonable agreement with experimental data for the baseline case without control. Aperture size effect, frequency spectra of OPD and two-point spatial correlations of OPD are investigated. The similarities and differences of distortion characteristics compared to those induced by turbulent boundary layers are discussed. The distortions by a separated shear layer are much larger in magnitude and spatially less homogeneous than those induced by an attached boundary layer. It is found that pressure fluctuations are significant and play a dominant role in inducing density fluctuations and associated optical distortions in a separated shear layer, in contrast to the dominant role of temperature fluctuations in a turbulent boundary layer. When passive control is applied using a row of thin and tall pins in the upstream boundary layer, the numerical results confirm key experimental findings. The flow above the optical window is characterized by two distinct shear layers, whose combined effect leads to a significant reduction of density fluctuation magnitude in the main shear layer and associated optical distortions compared to the uncontrolled flow with a single strong shear layer.</p>

<p> Noise generated by flow over rough surfaces is an important issue in naval applications and in aeronautical engineering. This work numerically investigates roughness-induced noise from low-Mach-number turbulent boundary layers. The computational approach is based on Lighthill's acoustic analogy with acoustic sources obtained from large-eddy simulation. An acoustic formulation is derived, which shows that each roughness element acts as an individual in-plane dipole source strengthened by its image in the wall. Flow configurations investigated include boundary-layer flows over a single hemispherical roughness element, a pair of streamwisely aligned hemispherical elements and three roughness fetches consisting of 10 &times; 4 hemispherical, cuboidal and cylindrical roughness elements, respectively.</p><p> Results for a single hemispherical roughness element and a pair of hemispherical elements show that the spanwise dipole, which has been overlooked before, is of larger or similar strength compared to the streamwise dipole. The viscous contribution to the dipoles is negligible compared to the pressure contribution. The main sound sources arise from the impingement of incoming turbulence and the unsteady horse-shoe vortices generated around the element. The roughness-induced unsteady wake motions are unimportant as a source of self noise. However, they significantly enhance sound radiation from a downstream hemisphere.</p><p> The effects of multi-element interactions and the roughness shape are investigated with arrays of 10 &times; 4 sparsely distributed hemispheres, cuboids and short cylinders. The dipole strength, orientation and spatial distribution show strong dependence on the roughness shape. Correlations between dipole sources associated with neighboring elements are found to be small for these sparsely distributed roughness arrays. Correlations and coherence between roughness dipoles and surface pressure fluctuations are analyzed, which reveals the importance of the impingement of upstream turbulence and surrounding vortical structures to dipole sound radiation, especially in the streamwise direction. For roughness shapes with sharp frontal edges, the edge-induced unsteady separation and reattachment also play important roles in sound generation. Large-scale turbulent structures in the boundary layer have a relatively low influence on roughness dipoles, except for the first row of elements.</p>

<p> New onboard technologies will be required for future cockpits to support the altered responsibilities of pilots under the NextGen program. Effective Cockpit Displays of Information (CD Tis) should provide more flexibility to pilots en route and reduce the probability of conflicts. However, precise input from pilots can be difficult due to the unstable environment in the cockpit. The present study used a non-traditional input device (Novint Falcon) to examine the effect of force feedback on operator performance during point-and-click movements in a CDTI environment when distractors are present. Twelve participants performed point-and-click tasks with varying amounts of force feedback, distractor locations, target sizes, distances, and movement directions. Overall movement times (OMTs) were recorded. Results demonstrated that force feedback did not reduce or match OMTs relative to the computer mouse. However, significant interactions with other target variables highlighted conditional differences between the force levels, as well as distractor effects.</p>

<p> This work proposes a new method for using reduced order models in lieu of high fidelity analysis during the sensitivity analysis step of gradient based design optimization. The method offers a reduction in the computational cost of finite difference based sensitivity analysis in that context. </p><p> The method relies on interpolating reduced order models which are based on proper orthogonal decomposition. The interpolation process is performed using radial basis functions and Grassmann manifold projection. It does not require additional high fidelity analyses to interpolate a reduced order model for new points in the design space. The interpolated models are used specifically for points in the finite difference stencil during sensitivity analysis. </p><p> The proposed method is applied to an airfoil shape optimization (ASO) problem and a transport wing optimization (TWO) problem. The errors associated with the reduced order models themselves as well as the gradients calculated from them are evaluated. The effects of the method on the overall optimization path, computation times, and function counts are also examined. </p><p> The ASO results indicate that the proposed scheme is a viable method for reducing the computational cost of these optimizations. They also indicate that the adaptive step is an effective method of improving interpolated gradient accuracy. The TWO results indicate that the interpolation accuracy can have a strong impact on optimization search direction.</p>

<p> We present the background and motivation for ground vehicle autonomy, and focus on uses for space-exploration. Using a simple design example of an autonomous ground vehicle we derive the equations of motion. After providing the mathematical background for nonlinear systems and control we present two common methods for exactly linearizing nonlinear systems, feedback linearization and backstepping. We use these in combination with three adaptive control methods: model reference adaptive control, adaptive sliding mode control, and extremum-seeking model reference adaptive control. We show the performances of each combination through several simulation results. We then consider disturbances in the system, and design nonlinear disturbance observers for both single-input-single-output and multi-input-multi-output systems. Finally, we show the performance of these observers with simulation results.</p>

<p>Due to growing environmental concern over the continued use of fossil fuels, methods to limit emissions and partially replace fossil fuel use with renewable biofuels are of considerable interest. Developing chemical kinetic models for the chemistry that affects combustion properties is important to understanding how new fuels affect combustion energy conversion processes in transportation devices. This thesis reports the experimental study of several important reactions (the H + O₂ branching reaction, the key decomposition reactions of <i>tertiary</i>-butanol, the dehydration reaction of isopropanol, and the retro Diels-Alder reaction of cyclohexene) and develops robust analysis methods to estimate the absolute uncertainties of specific elementary rate constants derived from the experimental data. In the study of the above reactions, both a direct and indirect rate constant determination technique with associated uncertainty estimation methodologies are developed. </p><p> In the study of the decomposition reactions, a direct determination technique is applied to experimental data gathered in preparation of this thesis. In the case of the dehydration reaction of <i>tertiary</i>-butanol and the retro Diels-Alder reaction of cyclohexene, both of which are used as internal standards for relative rate studies (Herzler <i>et al</i>. 1997) and chemical thermometry (Rosado-Reyes <i>et al</i>. 2013) , analysis showed an &sim;20 K difference in the reaction rate between the reported results and the previous recommendations. In light of these discrepancies, an uncertainty estimation of previous recommendations illuminated an uncertainty of at least 20 K for the dehydration reaction of <i>tertiary</i>-butanol and the retro Diels-Alder reaction of cyclohexene, thus resolving the discrepancies. </p><p> The determination of the H + O₂ branching reaction and decomposition reactions of isopropanol used an indirect determination technique. The uncertainty of the H + O₂ branching reaction rate is shown to be underestimated by previous analysis (Hong <i>et al</i>. 2011, Tur&aacute;nyi, <i> et al</i>. 2012), and the dehydration reaction of isopropanol is shown to be four times faster than theoretical predictions. Analyses of uncertainties for these reactions show that a linearized local sensitivity analysis does not completely capture uncertainties. </p><p> Appendix B in this thesis includes additional work conducted during the preparation of this thesis, namely the measurement of derived cetane numbers for jet fuel surrogates. </p>

<p> Numerical investigations of flow past a partially rotating, circular cross-section, stepped cylinder in uniform flow at varying velocity ratios, diameter ratios and Reynolds Numbers are performed. The resulting flow fields are analyzed visually for the effect of rotation on the wake and numerically for the effect on lift/drag forces as well as vortex shedding rates. Simulations are run where either the large or small-diameter cylinder was rotating while the other cylinder was held stationary. Simulations were performed with end plates to minimize end effects. Results show with increasing the velocity ratio when the large cylinder rotates, vortex shedding is suppressed across the entire wake span. Comparatively, an increase in velocity ratio for the small-diameter cylinder during rotation results in increased wake activity and a larger drag force.</p>

<p> Over the last two decades, a large number of exoplanets have been confirmed with the rate of discovery increasing in recent years primarily as new instruments with improved sensitivities have become available. Direct imaging of an Earth-like planet is now an important goal of the science community. This is a challenging problem for two primary reasons. First, the intensity ratio between the bright star and its dim Earth-like companion is expected to be approximately ten orders of magnitude and, second, the angular separation to the star is very small. </p><p> An external occulter is a specially-shaped spacecraft that is flown in formation with a telescope in order to block most of the starlight before it reaches the entrance pupil thereby allowing planetary light outside of the occulter's inner working angle to become visible. Designing a shape for the occulter spacecraft to enable suppression over a wavelength band of interest requires modeling through scalar diffraction theory. Typical designs feature occulters that are tens of meters across at a separation of tens of thousands of kilometers from the space telescope. </p><p> In this dissertation, we focus on occulter design and scaling to enable experimental optical verification of occulters in the laboratory. We provide experimental results that establish a 10^-5 suppression level in the pupil and 10^-10 contrast in the focal plane, which are both approximately two orders of magnitude below the ideal performance of the testbed. We use numerical simulation to study the sensitivity of the occulter design in the laboratory and determine that performance is feature-size limited. We provide the design of a longer and flight-like occulter experiment, and study its sensitivity to determine the expected performance.</p>

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2008. / Source: Dissertation Abstracts International, Volume: 69-05, Section: B, page: 3230. Adviser: Henrique Reis. Includes bibliographical references (leaves 165-171) Available on microfilm from Pro Quest Information and Learning.