The development of aerodynamic boundary layers on wind turbine blades is an important consideration in their performance. It can be quite challenging to replicate full scale conditions in laboratory experiments, and advanced diagnostics become valuable in providing data not available from traditional means. A new variant of Doppler global velocimetry (DGV) known as cross-correlation DGV is developed to measure boundary layer profiles on a wind turbine blade airfoil in the large scale Virginia Tech Stability Wind Tunnel. The instrument provides mean velocity vectors with reduced sensitivity to external conditions, a velocity measurement range from 0ms^-1 to over 3000ms^-1, and an absolute uncertainty. Monte Carlo simulations with synthetic signals reveal that the processing routine approaches the Cramér-Rao lower bound in optimized conditions. A custom probe-beam technique is implanted to eliminate laser flare for measuring boundary layer profiles on a DU96-W-180 wind turbine airfoil model. Agreement is seen with laser Doppler velocimetry data within the uncertainty estimated for the DGV profile. Lessons learned from the near-wall flow diagnostics development were applied to a novel benchmark model problem incorporating the relevant physical mechanisms of the high amplitude periodic turbulent flow experienced by turbine blades in the field. The model problem is developed for experimentally motivated computational model development. A circular cylinder generates a periodic turbulent wake, in which a NACA 63215b airfoil with a chord Reynolds number Re_c = 170, 000 is embedded for a reduced frequency k = (pi)fc/V = 1.53. Measurements are performed with particle image velocimetry on the airfoil suction side and in highly magnified planes within the boundary layer. Outside of the viscous region, the Reynolds stress profile is consistent with the prediction of Rapid Distortion Theory (RDT), confirming that the redistribution of normal stresses is an inviscid effect. The fluctuating component of the phase- averaged turbulent boundary layer profiles is described using the exact solution to laminar Stokes flow. A phase lag similar to that in laminar flow is observed with an additional constant phase layer in the buffer region. The phase lag is relevant for modeling the intermittent transition and separation expected at full scale. / Ph. D.

It is demonstrated that the method for locating a velocity profile origin, or plane of zero velocity, by fitting log profiles to streamwise velocity measurements is applicable to a larger range of roughness scales than previously expected. Five different sets of detailed, experimental velocity measurements were analyzed encompassing sediment-scale roughness elements, roughness caused by rigid vegetation, and large-scale roughness elements comprised of mobile bedforms. The method resulted in similar values of normalized zero-plane displacement for all roughness types considered. The ratios of zero-plane displacement, dh, to roughness height, ks, were 0.20 and 0.26 for the sediment- and vegetation-scale experiments, respectively. The results for the two experiments with bedform dominated roughness were 0.34 and 0.41. An estimate of dh/ks ranging from 0.2 to 0.4 is therefore recommended for a range of roughness types with the higher end of the range being more appropriate for the larger, bedform-scale roughness elements, and the lower end for the sediment-scale roughness elements. In addition, it is demonstrated that the location of the plane of zero velocity is temporally constant even when the bed height is not. The effects of roughness element packing density were also examined with the identification of a possible threshold at 4%, above which zero-plane displacement is independent of packing density. The findings can be applied to field velocity measurements under mobile bed conditions, facilitating the calculation of turbulence parameters such as shear velocity, by using point measurements and providing guidelines for the estimation of an appropriate value for zero-plane displacement. / Master of Science

Supersonic hot jet noise causes significant hearing impairment to the military workforce and results in substantial cost for medical care and treatment. Detailed insight into the turbulence structure of high-speed jets is central to understanding and controlling jet noise. For this purpose a new instrument based on the Doppler global velocimetry technique has been developed. This instrument is capable of measuring three-component velocity vectors over ex-tended periods of time at mean data-rates of 100 kHz. As a demonstration of the applicability of the time-resolved Doppler global velocimetry (TR-DGV) measurement technique, statistics of three-component velocity measurements, full Reynolds stress tensors and spectra along the stream-wise direction in a cold, supersonic jet at exit Mach number Mj = 1.4 (design Mach number Md = 1.65) are presented. In pursuance of extending the instrument to planar op- eration, a rapid response photomultiplier tube, 64-channel camera is developed. Integrating field programmable gate array-based data acquisition with two-stage amplifiers enables high-speed flow velocimetry at up to 10 MHz. Incor- porating this camera technology into the TR-DGV instrument, an investigation of the perfectly expanded supersonic jet at two total temperature ratios (TTR = 1.6 and TTR = 2.0) was conducted. Fourth-order correlations which have direct impact on the intensity of the acoustic far-field noise as well as convective velocities on the lip line at several stream-wise locations were obtained. Comprehensive maps of the convective velocity and the acoustic Mach number were determined. The spatial and frequency scaling of the eddy convective velocities within the developing shear layer were also investigated. It was found that differences in the radial diffusion of the mean velocity field and the integral eddy convective velocity creates regions of locally high convective Mach numbers after the potential core. This, according to acoustic analogies, leads to high noise radiation efficiency. The spectral scaling of the eddy convec- tive velocity indicates intermittent presence of large-scale turbulence structures, which, coupled with the emergence of Mach wave radiation, may be one of the main driving factors of noise emission observed in heated supersonic jets. / Ph. D.

In-situ geotechnical testing of surficial sediment layers in areas of active sediment dynamics can provide essential information about physical and geotechnical variations of sediment properties with regards to active sediment remobilization processes. For example, portable free fall penetrometers (PFFPs) can assist with the detection of mobile sediment layers. They are easy to deploy, and can provide a large spatial coverage in a time- and cost-effective manner. However, they often struggle to provide more detailed information about the properties of mobile sediment layers due to a lack of calibration and validation in existing data sets. Currently, existing sediment samplers often disturb, or ignore the uppermost sediment layers. Simultaneous sediment sampling and geotechnical profiling is needed to fill this gap, and to drive data interpretation forward. A field investigation of surficial sediments was conducted in the wetland waterways of coastal Louisiana in 2014. In-situ tests were conducted using PFFP, and disturbed sediment samples were collected in selected locations. The results allowed us to map changes in sediment strength and stratification, and correlate the geotechnical results to local site characteristics. However, the need for high quality sediment samples for calibration and validation was emphasized by the results. Three different sediment sampler add-on units targeting mobile layers were designed and manufactured based on lessons-learned from the literature. The designs were tested in the laboratory and in the field (Yakutat, Alaska and York River, Virginia) in 2017. The samples were analyzed to understand the influence of different sampler characteristics on collected sample quality, and, to define mobile layer sampler characteristics that enable simultaneous geotechnical testing and the collection of high quality samples. Following field survey campaigns in the York River, Virginia in 2016 allowed to assess surficial sediment layer characteristics and behavior based on a coupled analysis of geotechnical data from in-situ PFFP tests and the sedimentological data collected using box cores and the novel sediment sampler. In summary, novel strategies and instrumentation to carry out simultaneous sediment sampling and geotechnical profiling of seabed surface layers were tested, and new pathways for geotechnical data analysis for the investigation of mobile seabed layers were presented. / PHD / Coastal erosion and evolution, marine slope stability, river bank stability, maintenance of navigable water depth, or the stability of offshore structures are some of the modern challenges impacted by subaqueous sediment dynamics. Although, numerous researchers have investigated this issue for decades, some gaps in knowledge still prevail due to its interdisciplinary and complex nature. One of the most intriguing questions related to seabed soil behavior is the characterization of the sediment layers and textures at the seafloor surface being directly involved in sediment transport processes and local geomorphodynamics. These layers are often characterized by a most recent sediment deposition history, and a loose particle arrangements. Accordingly, these sediment layers show almost no resistance to accommodate loads (the sediment strength), and are highly erodible. The strength of surficial layers can be evaluated using portable free fall penetrometers (PFFPs) which are rapid and economic geotechnical site investigation tools designed to geomechanically test seabed surface layers. Nevertheless, there is a lack of data from areas of active sediment dynamics leading to gaps in understanding regarding sediment strength variations affected by active sediment transport processes. This research widens the use of PFFPs into wetland waterways (e.g. channels, lakes, and strait). Moreover, first attempts to quantify the influence of wave forces on sediment beds were also made and promising results were obtained which can open paths to new interdisciplinary. However, the PFFPs are challenged by a lack of physical sediment samples to groundtruth and verify the collected data. Thus, the sampling of such sediment layers is a currently missing part in the framework of in-situ investigations. This dissertation aimed to develop a novel field sampling technology in terms of an add-on unit that can be attached to portable dynamic penetrometers for deployment in areas of active sediment dynamics. Thus, the data to measure sediment strength can be collected simultaneously with physical seabed samples. Different sampler designs were tested and evaluated, and new pathways for joint geotechnical and sedimentological data analysis demonstrated. The results of this research can therefore contribute to the current understanding of seabed sediment behavior.

The examination of the application and accuracy of optical sensors for the purpose of determining rail lubricity of top-of-rail friction modifier is investigated in this research. A literature review of optical sensors as they relate to detecting thin layers is presented, as well as a literature review of the significant aspect of surface roughness on optical signature. Both commercially available optical sensors and optical devices, such as independent lasers and detectors, are examined in a comprehensive parametric study to determine the most suitable configuration for a prototype with adequate third-body detection. A prototype is constructed considering parameters such as sunlight contamination, vibrations, and angle of detection. The prototype is evaluated in a series of laboratory tests with known lubricity conditions for its accuracy of measurements and susceptibility to environmental conditions, in preparation for field testing. Upon field testing the prototype, the data indicates that it is capable of providing subjective measurements that can help with determining whether a rail is highly lubricated or unlubricated, or it is moderately lubricated. It is anticipated that the device could be used to provide a rail lubricity index. The investigation of the optical response of a rail in various conditions, including top-of-rail friction modifier presence and underlying surface roughness, reveals the behavior of friction modifying material on rail/wheel interactions. It is determined that surface roughness is imperative for distinguishing between scattering due to surface condition and scattering due to third-body layers. Additionally it is revealed that friction modifying materials become entrapped within the surface roughness of the rail, effectively causing a "seasoning" effect instead of a simple third body layer. This provides some explanation on the inadequacy of determining lubricity conditions using contacting methods since they cannot detect the entrapped material that are revealed only when the top of rail undergoes a micro deformation due to a passing wheel. Furthermore, the fluorescent signature of flange grease can be utilized to detect any flange grease contamination on top of rail. The results of the study indicate that it is possible to have practical optical sensors for top-of-rail third body layer detection and any contamination that may exist, initially through spot checking the rail and eventually through in-motion surveying. / Master of Science / Top-of-rail friction modifiers are used in the railway industry for a variety of reasons, including, but not limited to, reduction in wear and fuel savings; although their use has been widely accepted, methods of detection of such materials have not been adequately developed. Presently, methods of measurement of physical aspects of a rail are used in order to deduce the presence or lack of friction modifier on top-of-rail. However, no direct method of measurement exists in the published literature today. This study examines the use of optical sensors for the purpose of determining rail lubricity conditions. The literature is reviewed in this study for all applicable topics pertaining to the optical detection of top-of-rail friction modifier, including the optical theory used and the importance of surface roughness on an optical signature. Different characteristics of optical sensors are examined and a configuration is determined for the construction of a prototype device. This device utilizes laser reflective detectors and a fluorescence sensor in order to distinguish friction modifier presence or other third-body layers. This prototype was tested and evaluated in a series of laboratory tests with known lubricity conditions in preparation for field testing. Additionally, metrics were developed using optical theory in order to quantify the differences between different lubricity conditions. It was seen that this prototype was able to determine the presence of friction modifier by its laser reflective properties, and the presence of flange grease contamination through its fluorescence signature. Field testing with this prototype confirmed the prototype’s ability to distinguish adequate lubricity conditions using these metrics. It is anticipated that the device could be used to provide a rail lubricity index that is able to aid railway professionals in maintenance practices regarding rail lubricity.

Experimental investigations were conducted with and without the presence of the surface-mounted obstacle to quantify its effects on the far wake. The obstacle chosen for this study was a 3:2 elliptical nose NACA 0020 tail wing-body (Rood body), approximately of height equal to the boundary layer thickness at one of the measurement locations of the flow. The experiments were performed by varying the Reynolds number of the flow and manipulating the pressure gradient distributions using a NACA 0012 airfoil placed within the wind tunnel test section. The measurements were acquired utilizing a spanwise traversing boundary layer rake and a point pressure sensing microphone array. The findings reveal that the presence of the obstacle introduces disruptions in the flow, such as vortex and jet regions in the wake. However, the overall flow behavior remains consistent with that of an undisturbed turbulent boundary layer, for varying Reynolds numbers and pressure gradients. Notably, an adverse pressure gradient and lower Reynolds number both accentuate the prominence of the jet and vortex region within the wake, with the trend reversing towards the other end of the spectrum. This behavior is akin to the larger turbulent boundary layer under adverse pressure gradients and lower Reynolds numbers. Furthermore, the presence of obstacles induces an increase in the overall level of the wall pressure spectrum by approximately 2 dB, regardless of the flow condition. Additionally, it leads to a deviation in the slope of the mid-frequency range of the autospectra compared to the smooth wall case. Specifically, the mid-slope frequency of an undisturbed turbulent boundary layer is steeper than that observed in the disturbed wake flow caused by the obstacle. / Master of Science / The interaction between turbulence and aerodynamic surfaces gives rise to wall-pressure fluctuations, which in turn induce structural vibrations and acoustic noise. On surfaces turbulent flows meet, antennae, flaps, and other frequently mounted measuring devices. The flow in their wake is impacted by the coherence of a turbulent boundary layer being disrupted by these impediments mounted on aerodynamic surfaces. They also alter the nature of the pressure fluctuations that are generated on the surface of interest. The far wake of a Rood Body obstacle was studied using a point pressure sensing microphone array and a spanwise traversing boundary layer rake. Experimental measurements were taken for a range of Reynolds numbers and pressure gradient environments at the Virginia Tech Stability Wind Tunnel. Results show that the boundary layer rake measurements resolve the presence of the obstacle wake successfully, by characterizing the wake structures and confirming the presence of jet and vortex regions in the wake of the obstacle. Surface pressure measurements reveal that the presence of the obstacle causes the low-frequency content of the wall pressure to be less dominant than the no obstacle case, while the high-frequency content becomes more dominant in the presence of the obstacle. The presence of obstacles also increases the overall levels of the wall pressure spectrum by approximately 2 dB.

The principle notion of this thesis has been to propel ideas derived through architecture, experience, intuition, and program in order to transform idea into form. The attempts to understand gallery as a place where people can show their work for a short amount of time, allowing for a continual engagement between works and viewers. / Master of Architecture

The articulation of frame and skin forms the space concertedly. The project, stemming from this assertion, searches, explores and articulates the intricate relationship between structure, skin and space as prominent elements of architecture. / Master of Architecture

what is architecture? what defines space? how do you define separation and integration of spaces? what is the relationship of human scale to space elements? how can architecture be studied? Architecture is an combination of science and art to make spaces for human needs and activities. What can an architect do to make a project, a building, not only serve its purpose but to go beyond that? A space supports human desire and imagination. Architecture provides the means and methods to make the spaces. The elements of the structure, column, wall, beam, and floor, play a very important role in defining and/or dividing a space. A room can be defined by four walls, columns or even beams. The material of the floor also outlines space. Walls, a series of columns, or ceiling beams can define an edge or enclose space and differentiate its meaning and function. The understanding of these elements and their relationship with each other and with people is the purpose of this study. In an urban situation often there is a need to design buildings with spaces for multiple activities. Separation of spaces and functions, as well as integration of different parts, is vital in such a design. Columns and walls enclose the space and characterize privacy. Their material and its characteristics make the edges of space opaque, transparent or semitransparent. The dimensions of columns and beams show the scale of the space, constraining the relationship of the people to the structural elements. / Master of Architecture

Recent developments in functional magnetic resonance imaging (fMRI) methods at high magnetic field strengths (≥7 T) promise the non-invasive indirect measurement of neural activation at the spatial scale of cortical columns and layers. However, the achievable spatial specificity of fMRI, which is ultimately limited by the spatio-temporal properties of the hemodynamic response, is still waiting to be fully characterized. To examine the spatial specificity of the blood oxygenation level dependent (BOLD) contrast exploited by fMRI, the spatial point spread function (PSF) of the gradient echo (GE) and the spin echo (SE) BOLD signal tangential to the cortical surface was determined at different cortical depths. Both GE- and SE-BOLD showed a loss in spatial specificity toward the pial surface, demonstrating the impact of unspecific macrovascular contributions to both contrasts and only a minor advantage of the SE-BOLD signal for high-resolution fMRI applications. However, unidirectional draining of deoxygenated blood mainly limits spatial specificity in the radial direction. To examine the discriminability of laminar information, ocular dominance columns (ODCs) in the primary visual cortex (V1) were mapped using fMRI sensitive to either the BOLD contrast or cerebral blood volume (CBV) changes, and the stimulated eye was decoded using a machine learning classifier at different cortical depths. Only CBV-fMRI showed increased prediction accuracies at the cortical depth that matched neurophysiological expectations, showing its improved spatial specificity and potential for layer-specific fMRI in humans. Furthermore, the thin-thick-pale stripe pattern in the secondary visual cortex (V2) was targeted, exploiting the sensitivity to color and binocular disparity of thin and thick stripes, respectively. The structure-function relationship of the stripe architecture to cortical myelin was studied, which so far has shown inconsistent findings in multiple histological experiments. High-resolution quantitative MRI (qMRI) parameter maps of the longitudinal relaxation rate (R1) were used as a proxy for cortical myelin content. The comparison of fMRI and qMRI maps showed that both thin and thick stripes have lower R1 than surrounding cortical tissue, pointing toward higher myelin content of pale stripes. While macrovascular contributions in fMRI must be considered cautiously, the thesis demonstrates the capabilities to study structure-function relationships and retrieval of laminar information at the spatial scale of cortical columns with high-resolution fMRI at 7 T.:List of figures List of tables List of acronyms 1 Introduction 1.1 Imaging the human brain 1.2 The visual cortex 1.3 Vascular supply of the cerebral cortex 1.4 Thesis outline 2 Background 2.1 Nuclear magnetic resonance 2.1.1 Nuclear magnetic moment 2.1.2 Zeeman effect 2.1.3 Bulk magnetization 2.1.4 Excitation 2.1.5 Relaxation 2.1.6 Refocusing 2.1.7 Detection 2.2 Magnetic resonance imaging 2.2.1 Gradients 2.2.2 Spatial encoding 2.2.3 Echo-planar imaging 2.3 Functional magnetic resonance imaging 2.3.1 Blood 2.3.2 Hemodynamic response 2.3.3 BOLD-fMRI 2.3.4 CBV-fMRI 2.4 Spatial specificity 2.4.1 Point spread function 2.4.2 Imaging PSF 2.4.3 Physiological PSF 3 Cortical depth-dependent spatial specificity of GE- and SE-BOLD 3.1 Introduction 3.2 Theory 3.3 Materials and methods 3.3.1 Participants 3.3.2 General procedure 3.3.3 Visual stimulation 3.3.4 Imaging 3.3.5 Data preprocessing 3.3.6 MTF model fitting using MCMC 3.4 Results 3.4.1 GE- and SE-BOLD maps 3.4.2 Percent signal changes across cortical depth 3.4.3 Cortical distances along iso-eccentricity lines 3.4.4 MCMC diagnostics 3.4.5 Estimated MTF parameters 3.4.6 MTF within veins 3.5 Discussion 4 Laminar profile of human ocular dominance columns 4.1 Introduction 4.2 Materials and methods 4.2.1 Participants 4.2.2 General procedure 4.2.3 Visual stimulation 4.2.4 Imaging 4.2.5 Data preprocessing 4.2.6 Pattern classification 4.3 Results 4.3.1 Topography of ocular dominance columns 4.3.2 Reproducibility of ocular dominance maps 4.3.3 Univariate contrasts across cortical depth 4.3.4 Decoding accuracies across cortical depth 4.4 Discussion 5 Cortical myelination of the secondary visual cortex (V2) 5.1 Introduction 5.2 Materials and methods 5.2.1 Participants 5.2.2 General procedure 5.2.3 Visual stimulation 5.2.4 Imaging 5.2.5 Data analysis 5.3 Results 5.3.1 Functional mapping of color-selective and disparity-selective stripes 5.3.2 Consistent qMRI maps across cortical regions and cortical depth 5.3.3 Higher myelination of pale stripes 5.4 Discussion 6 General discussion A Gradient-based boundary registration B Construction of anaglyph spectacles C Supplementary data for chapter 3 D Supplementary data for chapter 4 E Supplementary data for chapter 5 F Analysis of registration accuracy Acknowledgements Bibliography Curriculum vitae Declaration of authorship