Noise from fluid flow over rough surfaces is an important consideration in the design and performance of certain vehicles with high surface-area-to-perimeter ratios. A new method of noise control based on the anatomy of owls is developed and consists of fabric or fibrous canopies suspended above the surface. The method is tested experimentally and is found to reduce the total far-field noise emitted by the surface. The treatment also is found to reduce the magnitude of pressure fluctuations felt by the underlying surface by up to three orders of magnitude. Experimental investigations into the effects of geometric parameters of the canopies lead to an optimized design which maximizes noise reduction. The results obtained during the canopy experiment inspired a separate new device for the reduction of trailing edge noise. This type of noise is generated by flow past the wing of an aircraft or the blades of a wind turbine, and is a source of annoyance for those in surrounding communities. The newly developed treatment consists of small fins, or "finlets," placed near the trailing edge of an airfoil. The treatment is tested experimentally at near-full-scale conditions and is found to reduce the magnitude of far-field noise by up to 10 dB. Geometric parameters of the finlets are tested to determine the optimal size and spacing of the finlets to maximize noise reduction. Follow-up computational and experimental studies reveal the fluid mechanics behind the noise reduction by showing that the finlets produce a velocity deficit in the flow near the trailing edge and limit the magnitude and spanwise correlation lengthscale of turbulence near the trailing edge, factors which determine the magnitude of far-field noise. In a final experiment, the finlets are applied to a marine propeller and are found to reduce not only trailing edge noise, but also noise caused by the bluntness of the trailing edge. The results of this experiment show the potential usefulness of finlets to reduce noise from rotating systems, such as fans or propellers, as well as from structures which feature blunt trailing edges. / Ph. D.

Yes / Manning’s roughness coefficient (n) has been widely used to estimate flood discharges and flow depths in natural channels. Therefore, although extensive guidelines are available, the selection of the appropriate n value is of great importance to hydraulic engineers and hydrologists. Generally, the largest source of error in post-flood estimates is caused by the estimation of n values, particularly when there has been minimal field verification of flow resistance. This emphasizes the need to improve methods for evaluating the roughness coefficients. Trinidad and Tobago currently does not have any set method or standardised procedure that they use to determine the n value. Therefore, the objective of this study was to develop a soft computing model in the calculation of the roughness coefficient values using low flow discharge measurements for a stream. This study presents Gene-Expression Programming (GEP), as an improved approach to compute Manning’s Roughness Coefficient. The GEP model was found to be accurate, producing a coefficient of determination (R2) of 0.94 and Root Mean Square Error (RSME) of 0.0024.

Abrasive blasting is a common process for cleaning or roughening the surface of a material prior to the application of a coating. Although the process has been in practice for over 100 years, the lack of a comprehensive understanding of the complex interactions that exist with the process can still yield an inferior surface quality. Subsequently, parts can be rejected at one of many stages of the manufacturing process and/or fail unexpectedly upon deployment. The objective of this work is to evaluate the effect of selected input parameters on the characteristics of the blasted surface characteristics so that a more useful control strategy can be implemented. To characterize surface roughness, mechanical profilometry was used to collect average roughness parameter, Ra. Decreasing blast distance from 6” to 4” gave ΔRa = +0.22 µm and from 8” to 6” gave ΔRa = +0.22 µm. Increasing blast pressure from 42 psi to 60 psi decreased the Ra by 0.33 µm. Media pulsation reduced Ra by 0.56 µm and the use of new media reduced Ra by 0.47 µm. Although blasting under the same conditions and operator on different days led to ΔRa due to shorter blast times, there was no statistically significant variance in Ra attributed to blasting on different days. Conversely, a ΔRa = +0.46 µm was observed upon blasting samples with different cabinets. No significant ΔRa was found when switching between straight and Venturi nozzles or when using different operators. Furthermore, the feasibility of fiber optic sensing technologies was investigated as potential tools to provide real time feedback to the blast machine operator in terms of substrate temperature. Decreasing the blast distance from 6” to 4” led to ΔT = +9.2 °C, while decreasing the blast angle to 45° gave ΔT= -11.6 °C for 304 stainless steel substrates. Furthermore, increasing the blast pressure from 40 psi to 50 psi gave ΔT= +15.3 °C and changing from 50 psi to 60 psi gave ΔT= +9.9 °C. The blast distance change from 8” to 6” resulted in ΔT = +9.8 °C in thin stainless steel substrate temperature. The effects of substrate thickness or shape were evaluated, giving ΔT= +7.4 °C at 8” distance, ΔT= +20.2 °C at 60 psi pressure, and ΔT= -15.2 °C at 45° blasting when comparing thin stainless steel against 304 stainless steel (thick) temperatures. No significant ΔT in means was found when going from 6” to 8” distance on 304 stainless steel, 40 psi and 60 psi blasting of thin SS, as well as angled and perpendicular blasting of thin SS. Comparing thick 304 and thin stainless steel substrates at a 6” blast distance gave no significant ΔT. / Master of Science

The wings of most species of owl have been shown to possess three unique physical attributes which allow them to hunt in effective silence: a comb of evenly-spaced bristles along the wing leading-edge; a compliant and porous fringe of feathers at the trailing-edge; and a velvety down material distributed over the upper wing surface. This investigation focuses on the last of the mechanisms as a means to reduce noise from flow over surface roughness. A microscopic study of several owl feathers revealed the structure of the velvety down to be very similar to that of a forest or a field of crops. Analogous surface treatments (suspended canopies) were designed which simulated the most essential geometric features of the velvety down material. The Virginia Tech Anechoic Wall-Jet Facility was used to perform far-field noise and surface pressure fluctuation measurements in the presence of various combinations of rough surfaces and suspended canopies. All canopies were demonstrated to have a strong influence on the surface pressure spectra, and attenuations of up to 30 dB were observed. In addition, all canopies were shown to have some positive effects on far-field noise, and optimized canopies yielded far-field noise reductions of up to 8 dB across all frequencies at which roughness noise was observed. This development represents a new passive method for roughness noise control with possibility for future optimization and application to engineering structures. / Master of Science

The Federal Aviation Administration proposed a new concept for measuring airport pavement condition that consolidates measures of Foreign Object Damage (FOD), skid resistance, and smoothness into a single number. This research verified that FOD, skid resistance, and smoothness are necessary and sufficient to completely describe airport pavement serviceability and proposed a mathematical framework to reduce these properties to a single number describing the serviceability of the pavement. Serviceability was defined as “meeting the expectations of the user.” An extensive review of standards, regulations, and research indicated these components are each an expectation of the various types of airport pavement user. This review did not identify any other user expectations, indicating that these are the only components to airport pavement serviceability and thus are both necessary and sufficient. The research developed a framework called Serviceability Level (SL) to combine the components into a single index based on the probability of the pavement being FOD-free, skid resistant, and smooth. The framework allows measuring and forecasting each component separately, which should improve the accuracy of pavement management models and result in more efficient use of limited infrastructure resources. The probabilistic nature of SL gives it a real-world meaning and allows integration of pavement condition into risk management systems and general airport asset management systems.

O problema da previsão da resistência ao escoamento em canais tem atraído a atenção dos engenheiros há longo tempo. Durante os últimos decênios a resistência ao escoamento em canais abertos de fundo fixo tem sido amplamente investigada, usando rugosidade artificial nas superfícies de canais experimentais. A adoção do coeficiente de rugosidade para um canal natural significa estimar a resistência de este ao escoamento. A utilização de um valor incorreto deste coeficiente pode ter grandes impactos na estimação da vazão e em conseqüência no dimensionamento dos projetos de obras hidráulicas. Apresenta-se, mediante pesquisa bibliográfica, os métodos de cálculo para avaliação do coeficiente de rugosidade ou coeficiente de resistência, dando ênfase a aqueles desenvolvidos para canais naturais com rugosidade de grande escala, sem os efeitos do transporte de sedimentos. Em modelo físico avaliam-se os efeitos da distribuição, tamanho e forma dos elementos geométricos na resistência ao escoamento. Espera-se que os resultados da pesquisa proporcionem ao engenheiro os critérios necessários para a avaliação do coeficiente de rugosidade. Os métodos diretos de medição de vazões nos rios nem sempre podem ser levados a cabo em rios de montanha , especialmente na época de cheia, devido às grandes declividades (i>1%), material de grandes dimensões no leito (pedras, seixos, matacões), submersão relativa menor do que 1, condições estas de escoamento que podem ser perigosas para os equipamentos de medição. Em tais circunstâncias é necessário o uso de métodos indiretos. A aplicação das relações de resistência ao escoamento em rios de montanha torna-se difícil pelos escassos conhecimentos na avaliação do coeficiente de resistência. Faz-se uma comparação das diferentes formulações existentes da resistência ao escoamento com dados de um rio dos Andes peruanos, determinando-se uma equação de ajuste. / The flow resistance estimation problem in channels has attracted the engineer's attention for a long time. During the last decades the flow resistance in open channels with rigid bed has been research with the use of artificial roughness in bed flumes. Adapting a natural channel roughness coefficient means the estimation of the corresponding resistance to flow. The use of an incorrect value in this coefficient might produce a big impact in the discharge estimation, as well as in the hydraulic work project. The calculation methods to estimate the roughness coefficient or resistance coefficient are showed through this bibliographic research, attaching importance to those developed for channels with large scale roughness; this without the sediment transport effects into account. The distribution, size and shape effects of the geometric elements in the flow resistance are evaluated in a physical model. It is expected that the research results provide the engineer with the required criteria to estimate the roughness coefficient. The direct methods of the discharge measurement in rivers can not always take place in mountain rivers, owing to the following reasons: high gradients (i>1%), big dimension material (cobbles and boulders), relative submergence lower than unit; flow conditions that might be dangerous for the measuring equipment. Under these circumstances it is necessary the use of indirect methods. The application of flow resistance relations in mountain rivers turns very difficult, due to the limited knowledge in resistance coefficient evaluation. In the following research has been made a comparison of the different existing flow resistance equations in mountain rivers, for a river in the Peruvian Andes by establishing a fitting curve.

O problema da previsão da resistência ao escoamento em canais tem atraído a atenção dos engenheiros há longo tempo. Durante os últimos decênios a resistência ao escoamento em canais abertos de fundo fixo tem sido amplamente investigada, usando rugosidade artificial nas superfícies de canais experimentais. A adoção do coeficiente de rugosidade para um canal natural significa estimar a resistência de este ao escoamento. A utilização de um valor incorreto deste coeficiente pode ter grandes impactos na estimação da vazão e em conseqüência no dimensionamento dos projetos de obras hidráulicas. Apresenta-se, mediante pesquisa bibliográfica, os métodos de cálculo para avaliação do coeficiente de rugosidade ou coeficiente de resistência, dando ênfase a aqueles desenvolvidos para canais naturais com rugosidade de grande escala, sem os efeitos do transporte de sedimentos. Em modelo físico avaliam-se os efeitos da distribuição, tamanho e forma dos elementos geométricos na resistência ao escoamento. Espera-se que os resultados da pesquisa proporcionem ao engenheiro os critérios necessários para a avaliação do coeficiente de rugosidade. Os métodos diretos de medição de vazões nos rios nem sempre podem ser levados a cabo em rios de montanha , especialmente na época de cheia, devido às grandes declividades (i>1%), material de grandes dimensões no leito (pedras, seixos, matacões), submersão relativa menor do que 1, condições estas de escoamento que podem ser perigosas para os equipamentos de medição. Em tais circunstâncias é necessário o uso de métodos indiretos. A aplicação das relações de resistência ao escoamento em rios de montanha torna-se difícil pelos escassos conhecimentos na avaliação do coeficiente de resistência. Faz-se uma comparação das diferentes formulações existentes da resistência ao escoamento com dados de um rio dos Andes peruanos, determinando-se uma equação de ajuste. / The flow resistance estimation problem in channels has attracted the engineer's attention for a long time. During the last decades the flow resistance in open channels with rigid bed has been research with the use of artificial roughness in bed flumes. Adapting a natural channel roughness coefficient means the estimation of the corresponding resistance to flow. The use of an incorrect value in this coefficient might produce a big impact in the discharge estimation, as well as in the hydraulic work project. The calculation methods to estimate the roughness coefficient or resistance coefficient are showed through this bibliographic research, attaching importance to those developed for channels with large scale roughness; this without the sediment transport effects into account. The distribution, size and shape effects of the geometric elements in the flow resistance are evaluated in a physical model. It is expected that the research results provide the engineer with the required criteria to estimate the roughness coefficient. The direct methods of the discharge measurement in rivers can not always take place in mountain rivers, owing to the following reasons: high gradients (i>1%), big dimension material (cobbles and boulders), relative submergence lower than unit; flow conditions that might be dangerous for the measuring equipment. Under these circumstances it is necessary the use of indirect methods. The application of flow resistance relations in mountain rivers turns very difficult, due to the limited knowledge in resistance coefficient evaluation. In the following research has been made a comparison of the different existing flow resistance equations in mountain rivers, for a river in the Peruvian Andes by establishing a fitting curve.

A comprehensive understanding of the interactions between orthopaedic and dental implant surfaces with the surrounding host tissue is essential in the design of advanced biomaterials that better promote bone growth and osseointegration of implants. Dental implants with roughened surfaces and high surface energy are well known to promote osteoblast differentiation in vitro and promote increased bone-to-implant contact in vivo. In addition, increased surface roughness increases osteoblasts response to the vitamin D metabolite 1α,25(OH)2D3. However, the exact mechanisms mediating cell response to surface properties and 1α,25(OH)2D3 are still being elucidated. The central aim of the thesis is to investigate whether integrin signaling in response to rough surface microtopography enhances osteoblast differentiation and responsiveness to 1α,25(OH)2D3. The hypothesis is that the integrin α5β1 plays a role in osteoblast response to surface microtopography and that 1α,25(OH)2D3 acts through VDR-independent pathways involving caveolae to synergistically enhance osteoblast response to surface roughness and 1α,25(OH)2D3. To test this hypothesis the objectives of the studies performed in this thesis were: 1) to determine if α5β1 signaling is required for osteoblast response to surface microstructure; 2) to determine if increased responsiveness to 1α,25(OH)2D3 requires the vitamin D receptor, 3) to determine if rough titanium surfaces functionalized with the peptides targeting integrins (RGD) and transmembrane proteoglycans (KRSR) will enhance both osteoblast proliferation and differentiation, and 4) to determine whether caveolae, which are associated with integrin and 1α,25(OH)2D3 signaling, are required for enhance osteogenic response to surface microstructure and 1α,25(OH)2D3. The results demonstrate that integrins, VDR, and caveolae play important roles in mediating osteoblast response to surface properties and 1α,25(OH)2D3. Silencing of the β1 integrin in osteoblast-like MG63 cells significantly reduced osteogenic response to surface topography and 1α,25(OH)2D3. Silencing of the α5 subunit did not alter the response of MG63 cells to changing surface roughness or chemistry, although future work must confirm these results given similar cell surface α5 integrin expression observed in control and α5-silenced cells. Multifunctional RGD, KRSR, and KSSR coated surfaces show that RGD increased osteoblast proliferation and reduced differentiation, KRSR had no affect on osteoblast phenotype, and KSSR increased osteoblast differentiation. These results suggest that titanium surfaces can be modified to manipulate proliferation and differentiation and that RGD/KSSR functionalized surfaces could be further investigated for use as osteointegrative surfaces. The results using VDR deficient osteoblasts demonstrate that 1α,25(OH)2D3 acts via VDR-dependent mechanisms in cells cultured on titanium surfaces that support terminal differentiation. In caveolae deficient osteoblasts, 1α,25(OH)2D3 affected cell number, alkaline phosphatase activity, and TGF-β1 levels, although levels of osteocalcin and PGE2 were not affected. These results are consistent with the hypothesis that VDR is required for the actions of 1α,25(OH)2D3, but that caveolae-dependent membrane 1α,25(OH)2D3 signaling modulates traditional VDR signaling. The exact mechanisms for this interaction remain to be shown. Overall, these results are important in better understanding the role of β1 integrin partners in mediating osteoblast response to implant surfaces and in understanding how integrin signaling can alter osteoblast differentiation and responsiveness to 1α,25(OH)2D3 via genomic and non-genomic pathways.

Road damage identification is still largely based on visual inspection methods and profilometer data. Visual inspection methods heavily rely on expert knowledge which is often very subjective. They also result in traffic flow interference due to the need for redirection of traffic to alternative routes during inspection. In addition to this, accurate high-speed profilometers, such as scanning vehicles, are extremely expensive often requiring strong economic justifications for their acquisition. The low-cost profilometers are very slow, typically operating at or less than walking speeds, causing their use to be labour-intensive if applied to large networks.This study aims at developing a road damage identification methodology for both paved and unpaved roads based on modelling the road-vehicle interaction system with an artificial neural network. The artificial neural network is created and trained with vehicle acceleration data as inputs and road profiles as targets. Then the trained neural network is consequently used for reconstruction of road profiles upon simulating it with vertical vehicle accelerations. The simulation process is very fast and can often be completed in a very short time thus making it possible to implement the methodology in real-time. Three case studies were used to demonstrate the feasibility of the methodology and the results on field tests carried out on mine vehicles with crudely measured road profiles showed a majority of the tested roads were reconstructed to within a fitting accuracy of less than 40% at a correlation level of greater than 55% which in this study was found to be practically acceptable considering the limitations imposed by the sizes of the haul trucks and their tyres as well as the quality of the road profiles and lack of control in the vehicle operation. / Thesis (PhD)--University of Pretoria, 2015. / Mechanical and Aeronautical Engineering / Unrestricted

This diploma thesis deals with the final quality of the surface under variable working conditions during milling. The first part deals with the definition of qualitative parameters describing surface properties. This is followed by a brief description of the cutting resistance measurements. The thesis is complemented by experimental verification using front milling and its evaluation. The aim of the experiment is to determine the dependence of the surface quality and the size of cutting resistors under the variable working conditions of the machine that do not make a common part of the manufacturing processes.