Dissertations / Theses on the topic 'Capillarity on rough surfaces'
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1
Fedeli, Livio. "Numerical techniques for the study of wetting on rough surfaces and contact angle hysteresis." Doctoral thesis, SISSA, 2011. http://hdl.handle.net/20.500.11767/4256.
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LIU, WEN. "TRANSPORT PHENOMENA ASSOCIATED WITH LIQUID METAL FLOW OVER TOPOGRAPHICALLY MODIFIED SURFACES." UKnowledge, 2012. http://uknowledge.uky.edu/me_etds/16.
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Brazing and soldering, as advanced manufacturing processes, are of significant importance to industrial applications. It is widely accepted that joining by brazing or soldering is possible if a liquid metal wets the solids to be joined. Wetting, hence spreading and capillary action of liquid metal (often called filler) is of significant importance. Good wetting is required to distribute liquid metal over/between the substrate materials for a successful bonding.
Topographically altered surfaces have been used to exploit novel wetting phenomena and associated capillary actions, such as imbibitions (a penetration of a liquid front over/through a rough, patterned surface). Modification of surface roughness may be considered as a venue to tune and control the spreading behavior of the liquids. Modeling of spreading of liquids on rough surface, in particular liquid metals is to a large extent unexplored and constitutes a cutting edge research topic.
In this dissertation the imbibitions of liquid metal has been considered as pertained to the metal bonding processes involving brazing and soldering fillers. First, a detailed review of fundamentals and the recent progress in studies of non-reactive and reactive wetting/capillary phenomena has been provided. An imbibition phenomenon has been experimentally achieved for organic liquids and molten metals during spreading over topographically modified intermetallic surfaces. It is demonstrated that the kinetics of such an imbibition over rough surfaces follows the Washburn-type law during the main spreading stage. The Washburn-type theoretical modeling framework has been established for both isotropic and anisotropic non-reactive imbibition of liquid systems over rough surfaces. The rough surface domain is considered as a porous-like medium and the associated surface topographical features have been characterized either theoretically or experimentally through corresponding permeability, porosity and tortuosity. Phenomenological records and empirical data have been utilized to verify the constructed model. The agreement between predictions and empirical evidence appears to be good. Moreover, a reactive wetting in a high temperature brazing process has been studied for both polished and rough surfaces. A linear relation between the propagating triple line and the time has been established, with spreading dominated by a strong chemical reaction.
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Sahlin, Fredrik. "Hydrodynamic lubrication of rough surfaces." Licentiate thesis, Luleå : Luleå University of Technology, 2005. http://epubl.luth.se/1402-1757/2005/83.
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Lines, Claire Deborah. "Inverse scattering by unbounded rough surfaces." Thesis, Brunel University, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.408886.
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Qi, Lin. "Measuring perceived gloss of rough surfaces." Thesis, Heriot-Watt University, 2012. http://hdl.handle.net/10399/2579.
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This thesis is concerned with the visual perception of glossy rough surfaces, specifically those characterised by 1/fB noise. Computer graphics were used to model these natural looking surfaces, which were generated and animated to provide realistic stimuli for observers. Different methods were employed to investigate the effects of varying surface roughness and reflection model parameters on perceived gloss. We first investigated how the perceived gloss of a matte Lambertian surface varies with RMS roughness. Then we estimated the perceived gloss of moderate RMS height surfaces rendered using a gloss reflection model. We found that adjusting parameters of the gloss reflection model on the moderate RMS height surfaces produces similar levels of gloss to the high RMS height Lambertian surfaces. More realistic stimuli were modelled using improvements in the reflection model, rendering technique, illumination and viewing conditions. In contrast with previous research, a non-monotonic relationship was found between perceived gloss and mesoscale roughness when microscale parameters were held constant. Finally, the joint effect of variations in mesoscale roughness (surface geometry) and microscale roughness (reflection model) on perceived gloss was investigated and tested against conjoint measurement models. It was concluded that perceived gloss of rough surfaces is significantly affected by surface roughness in both mesoscale and microscale and can be described by a full conjoint measurement model.
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Turbil, Colette. "Light Scattering from Complex Rough Surfaces." Electronic Thesis or Diss., Sorbonne université, 2018. http://www.theses.fr/2018SORUS205.
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Lorsque la lumière interagit avec un objet, deux phénomènes peuvent avoir lieu : la lumière peut être absorbée ou déviée par l’objet, ce dernier phénomène étant généralement qualifié de diffusion de la lumière. Malgré l’intérêt de la communauté scientifique au cours des dernières décennies, la diffusion de la lumière induite par des surfaces rugueuses reste un problème complexe à traiter, ceci étant principalement dû à la grande multidisciplinarité requise pour l’étude du phénomène. Ce travail multidisciplinaire est basé sur l’étude de quatre différents domaines scientifiques qui doivent être considérés en parallèle pour traiter le phénomène de diffusion de la lumière de manière globale. Une vingtaine d’échantillons, fabriqués au laboratoire ou par des procédés industriels, sont sélectionnés pour leurs différentes apparences visuelles. Leur morphologie est caractérisée grâce à trois dispositifs expérimentaux, qui permettent ainsi de décrire la rugosité sur quatre décades de fréquences spatiales. Ensuite, la distribution angulaire de l’intensité lumineuse diffusée par les échantillons est mesurée, et confirme la grande variété des propriétés optiques des surfaces examinées. Finalement, ces données expérimentales sont utilisées et comparées aux résultats de deux types de modèles de diffusion de la lumière, l’un basé sur l’optique géométrique et l’autre sur l’optique physique. L’étude montre que les propriétés optiques des échantillons étudiés peuvent être assez fidèlement reproduites par le modèle de diffusion de la lumière basé sur l’optique physique. En revanche, le modèle basé sur les lois de l’optique géométrique ne parvient pas à produire des résultats satisfaisantsWhen light interacts with an object, two types of phenomena can occur: light can be either absorbed or redirected by the object. The latter phenomenon is generally referred to as light scattering. Despite the significant efforts over the past decades of the scientific community, light scattering from rough surfaces remains a complex problem. This is partly due to the high degree of multidisciplinary that is required for its study. The present multidisciplinary study is related to four scientific domains that must be examined to consider the full light scattering phenomenon. First, a large panel of a rough surface, elaborated by ourselves in the laboratory or manufactured industrially, is selected for its wide range of visual aspect. The morphology of the samples are characterized using three experimental tools which allow us to describe their surface morphologies over four decades of spatial frequencies. Then the angular intensity distributions of the light scattered from the samples are measured which confirm the wide variety of optical properties of the samples. Finally, these reliable and representative experimental data are compared to the results of different light scattering models, based on both the physical and the geometrical optics approaches. The main conclusion we drew from this work is that for the examined surfaces, the light scattering can be approximated fairly well by a model based on the physical optics approach, while at the same time, geometrical optics models are not able to give an adequate description of the same scattering data
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Schwarzer, Norbert. "Modelling of Contact Problems of Rough Surfaces." Universitätsbibliothek Chemnitz, 2006. http://nbn-resolving.de/urn:nbn:de:swb:ch1-200600165.
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In this paper it is shown that a completely analytical theory based on the extended Hertzian approach together with additional considerations taking into account the geometrical conditions of a curved surface provide an appropriate model for the theoretical “simulation” of a variety of asperity contact problems. This model yields relatively fast and easy to use tools for the analysing of contact problems arising in connection with rough surfaces.
In this study the results are shown on the example of a 3µm-DLC-coating on a steel substrate with asperities of about 100µm in diameter and 15µm height. It is found, that – under a general average pressure of 1GPa – the ideal asperity tip contact situation would lead to severe damage due to plastic flow within the steel substrate. On the other hand a rather conforming contact situation appears to be completely non critical.
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Andersson, Robin. "Flow Over Large-Scale Naturally Rough Surfaces." Licentiate thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-136.
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The fluid mechanical field of rough surface flows has been developed ever since the first experiments by Haagen (1854) and Darcy (1857). Although old, the area still holds merit and a surprising amount of information have to this day yet to be fully understood, which surely is a proof of its complexity. Many equations and CFD tools still rely on old, albeit reliable, concepts for simplifying the flow to be able to handle the effects of surface roughness. This notion is, however, likely to change within a not so unforeseeable future. The advancement of computer power has opened the door for more advanced CFD tools such as Direct Numerical Simulation (DNS) and Large Eddy Simulation (LES). It can be argued that once a given flow situation has been fully accessible by numerical simulations, it is likely to be fully understood within a few years 1 . However, DNS is still limited to small scales of roughness and relatively low Reynolds number which is in contrast with given hydropower conditions today. The hydropower industry annually supplies Sweden with about 45% of its electricity production, and tunnels of various types are regularly used for conveying water to or from turbines within hydropower stations. The tunnels are a vital part of the system and their survival is of the essence. Depending on the manner of excavation, the walls of the tunnels regularly exhibit a roughness, this roughness may range from a few mm to m, which is true especially if the tunnel have been subjected to damage. For natural roughness e.g. hydropower tunnels, there is no clear way to distinguish between rough surface flows and flow past obstacles. Yet, to be able to distinguish between the two cases has proven to be important. This work is aimed to increase the understanding of how the wall roughness affects the flow, and how to treat it numerically. Paper A employs the use of pressure sensors to evaluate local deviations in pressure as well as head loss due to the surface roughness. Paper B is aimed at using PIV to evaluate the flow using averaging techniques and characteristic length scales. Paper C Further investigates the data from the PIV and pressure measurements and Evaluates the possibility to use basic but versatile turbulence models to evaluate the flow in such tunnels.
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Morales, Espejel Guillermo Enrique. "Elastohydrodynamic lubrication of smooth and rough surfaces." Thesis, University of Cambridge, 1993. https://www.repository.cam.ac.uk/handle/1810/260244.
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Different aspects of Elastohydrodynamic Lubrication (EHL) are studied. For smooth surfaces, a novel approach which solves separately the inlet and outlet regions by using the fracture mechanics equations, is proposed to solve EHL line contacts for shape and pressure. For rough surfaces, the full EHL geometry is reduced to an infinitely long contact with known mean film thickness and pressure; so real-roughness steady state analyses are carried out by considering the separate Fourier components of roughness and pressures, transient analysis by applying general finite difference methods. The subsurface stresses under micro-EHL are also calculated and given in form of a probability rather than a specific value and location. Initially, full-geometry EHL line contacts of smooth surfaces are studied. The spike of pressures is assumed to be singular and the idea is to start with an original Hertzian pressure distribution, then the edges of this pressure are truncated and the effects calculated via linear fracture mechanics; after this, the removed pressures are replaced by the converged inlet and outlet pressures, previously obtained by iterating the Reynolds and fracture mechanics equations. It is found that the outlet pressures follow a modified logarithmic function and therefore the exit bump in the shape joins the parallel film zone with a finite value of slope, unlike the Greenwood extension of Grubin's theory. From a set of solutions, the behaviour of the pressure spike as a function of two dimensionless numbers is followed. Comparisons with results from full numerical solutions are shown, giving good agreement. The scheme is later extended to consider compressibility and the Roelands viscosity law. After reducing full EHL geometry, the effects of real and wavy roughness in microEHL of Newtonian and Eyring fluids with or without compressibility are studied. Steady state analyses of real roughness show that only the high frequency components remain after deformation. By linearizing the Reynolds- Eyring equation an analytical solution is obtained and a criterion for the deformation of the roughness in EHL is given; from this, it is shown that the deformation is very much dependent on the ratio λ/ħ, obtaining little deformation for low values of it. Transient analyses of roughness in lubrication are also carried out considering the infinitely long contact. It is found that the transient pressure and film distributions are made of two parts: a) the well known steady state solution, plus b) a complementary function depending only on the modulation of film and pressures from the inlet. It is shown that the conclusions outlined for some authors (e.g. Venner and Lubrecht) about pressures travelling with the velocity of the roughness but shape with the average velocity of the lubricant, are only a particular case of a more general understanding. It is now believed that there is no a real physical damping in the transient shape.
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Ross, Christopher Roger. "Direct and inverse scattering by rough surfaces." Thesis, Brunel University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318675.
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Kutlar, Ahmet Ihsan. "Turbulant boundary layers on rough painted surfaces." Thesis, University of Liverpool, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359178.
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Shi, Fan. "Elastic wave scattering from randomly rough surfaces." Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/44383.
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Elastic wave scattering from randomly rough surfaces and a smooth surface are essentially different. For ultrasonic nondestructive evaluation (NDE) the scattering from defects with smooth surfaces has been extensively studied, providing fundamental building blocks for the current inspection techniques. However, all realistic surfaces are rough and the roughness exists in two dimensions. It is thus very important to understand the rough surface scattering mechanism, which would give insight for practical inspections. Knowledge of the stochastics of scattering for different rough surfaces would also allow the detectability of candidate rough defects to be anticipated. Hence the main motivation of this thesis is to model and study the effect of surface roughness on the scattering field, with focus on elastic waves. The main content of this thesis can be divided into three contributions. First of all, an accurate numerical method with high efficiency is developed in the time domain, for computing the scattered waves from obstacles with arbitrary shapes. It offers an exact solution which covers scenarios where approximation-based algorithms fail. The method is based on the hybrid idea to combine the finite element (FE) and boundary integral (BI) methods. The new method efficiently couples the FE equations and the boundary integral formulae for solving the transient scattering problems in both near and far fields, which is implemented completely in the time domain. Several numerical examples are demonstrated and sufficiently high accuracy is achieved with different defects. It enables the possibility for Monte Carlo simulations of the elastic wave scattering from randomly rough surfaces in both 2D and 3D. The second contribution relates to applying the developed numerical method to evaluate the widely used Kirchhoff approximation (KA) for rough surface scattering. KA is a high-frequency approximation which limits the use of the theory for certain ranges of roughness and incidence/scattering angles. The region of validity for elastic KA is carefully examined for both 1D and 2D random surfaces with Gaussian spectra. Monte Carlo simulations are run and the expected scattering intensity is compared with that calculated by the accurate numerical method. An empirical rule regarding surface parameters and angles is summarized to establish the valid region of both 2D and 3D KA. In addition, it is found that for 3D scattering problems, the rule of validity becomes stricter than that in 2D. After knowing the region of validity, KA is applied to investigate how the surface roughness affects the statistical properties of scattered waves. An elastodynamic Kirchhoff theory particularly for the statistics of the diffused field is developed with slope approximations for the first time. It provides an analytical expression to rapidly predict the expected angular distribution of the scattering intensity, or the scattering pattern, for different combinations of the incidence/scattering wave modes. The developed theory is verified by comparison with numerical Monte Carlo simulations, and further validated by the experiment with phased arrays. In particular the derived formulae are utilized to study the effects of the surface roughness on the mode conversion and the 2D roughness caused depolarization, which lead to unique scattering patterns for different wave modes.
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Kim, Min-Joong. "Light scattering from characterised random rough surfaces." Thesis, Imperial College London, 1989. http://hdl.handle.net/10044/1/47513.
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Lechleiter, Armin. "Factorization methods for photonics and rough surfaces." Karlsruhe Univ.-Verl. Karlsruhe, 2008. http://d-nb.info/989642755/04.
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Liu, Kuang-Yu. "Equilibrium of wetting layers on rough surfaces /." free to MU campus, to others for purchase, 1997. http://wwwlib.umi.com/cr/mo/fullcit?p9842594.
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Porter, Matthew Stanton. "Soft x-ray speckle from rough surfaces /." view abstract or download file of text, 2000. http://wwwlib.umi.com/cr/uoregon/fullcit?p9957568.
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Thesis (Ph. D.)--University of Oregon, 2000.Typescript. Includes vita and abstract. Includes bibliographical references (leaves 100-104). Also available for download via the World Wide Web; free to University of Oregon users. Address: http://wwwlib.umi.com/cr/uoregon/fullcit?p9957568.
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Semprebon, Ciro. "Wetting on Anisotropically Patterned and Rough Surfaces." Doctoral thesis, Università degli studi di Padova, 2009. http://hdl.handle.net/11577/3426025.
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Since Young in 1805 described in words the trigonometric relations between the contact
angle and the forces acting on a droplet in mechanical equilibrium on a sulid surface, many advances
in the description of several aspects of wetting behavior have been done. Besides the
recent years developements in the field of micropatterning allowed the production surfaces with
chemical and geometrical regular patterns, which make possible a direct test of theoretical models.
Beyond the patterns characterized by a global isotropic disposition if the surface asperities
and heterogeneities, patterns constituted of series of parallel stripes or reliefs have been produced,
introducing an anisotropic element in the substrate. Recently many works focused on the characterization
of the anisotropic behavior of droplets on those surfaces. However there is not a
complete theory describing the anisotropy of droplets in these conditions. Furthermore most part
of previous works study the anisotropy on regular patterns made by micrometric channels.
To give a general description of those aspects of the anisotropic behavior which are independent
by the nature of the micrometric regular pattern, and to focus on the influence of different
wettabilities, in this thesis we studied the anisotropic wetting of droplets sitting on the top of single
posts, characterized by flat surfaces and sharp corners, and made with different materials. The
anisotropy was quantified by measuring the contact angles and base elongations in the two principal
symmetry axis. Measurements were obtained by a homemade apparatus, and the analysis
software has been entirely developed in this thesis. The main finding is that the contact angle
difference and the base eccentricity show the same relation within the experimental errors
regardless of surface wettability. These measurements were complemented by numerical simulations
with the Lattice Boltzmann method, which showed a good agreement with experimental
results. We also developed a simple geometrical model, valid for small eccentricities which reproduces qualitatively
experimental and numerical data.
In addition, during this thesis I characterized the wetting properties of thin (isotropic) films of
nanostructured titania, and related them to the morphological parameters of the substrates.Da quando Young nel 1805 descrisse a parole le relazioni trigonometriche tra l’angolo di contatto e le forze agenti su una goccia in equilibrio meccanico su una superficie solida sono stati ottenuti molti progressi nella descrizione di vari aspetti del wetting. Inoltre i progressi degli ultimi anni nel campo della microlavorazione hanno permesso di ottenere in modo semplice superfici con pattern chimici e geometrici assai regolari, su cui è stato possibile testare sperimentalmente le ipotesi dei vari modelli teorici. Oltre a tutti i pattern caratterizzati da una disposizione globalmente isotropa delle asperità, sono stati prodotti pattern costituiti da una serie di strisce e rilievi paralleli gli uni agli altri, introducendo così un elemento anisotropo nel substrato. Negli ultimi anni molti lavori sono stati rivolti alla caratterizzazione del comportamento anisotropo delle gocce su tali substrati. Tuttavia ad oggi non esiste una teoria completa che descriva l’anisotropia di gocce in queste condizioni. Inoltre la maggior parte dei lavori precedenti riguarda lo studio dell’anisotropia su pattern regolari costituiti da canali micrometrici. Per fornire una descrizione generale di quegli aspetti del comportamento anisotropo che sono indipendenti dai dettagli del pattern regolare su scala micrometrica, e per evidenziare l’influenza di diverse bagnabilità della superficie, in questa tesi abbiamo studiato il wetting anisotropo di gocce depositate su singoli rilievi, caratterizzati da una supervicie piana e spigoli vivi, e costruiti con diversi materiali. L’anisotropia è stata quantificata misurando gli angoli di contatto e le dimensioni della base delle gocce nei due principali assi di simetria. Le misure sono state ottenute con un apparato fatto in casa, e il software di analisi è stato interamente sviluppato durante questa tesi. Il risultato principale consiste nel fatto che la differenza tra gli angoli di contatto nelle due direzioni e l’eccentricità di base mostrano la stessa relazione all’interno degli errori sperimentali, indipendentemente dalla bagnabilità del substrato. Queste misure sono state completate tramite simulazioni numeriche per mezzo del metodo Lattice Boltzmann, e che hanno mostrato un buon accordo con i risultati sperimentali. Inoltre abbiamo formulato un semplice modello geometrico, valido per piccoli, che riproduce qualitativamente sia i risultati sperimentali che quelli numerici. Inoltre in questa tesi ho caratterizzato la bagnabilità di sottili film (isotropici) di titania nanostrutturata, mettendola in relazione con le proprietà morfologiche dei substrati stessi.
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Zhou, Yanmin. "Insect adhesion on rough surfaces and properties of insect repellent surfaces." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709055.
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Letnes, Paul Anton. "Optical Polarization Effects of Rough and Structured Surfaces." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for fysikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-20132.
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The reflection and scattering of light from surfaces is a topic that has been much discussed in the scientific literature. The application of optical methods for the characterization of surfaces and the understanding of natural phenomena is dependent on good models for the optical properties of surfaces and interfaces. In this work, we will examine three different aspects of the optical properties of surfaces and interfaces. The measurement of polarization effects of surfaces is dependent on wellperforming Mueller matrix ellipsometers. While designing Mueller matrix ellipsometers for a single wavelength is trivial, the design of broad-band imaging ellipsometers is a much more challenging problem. We discuss the use of genetic algorithms to optimize such ellipsometers in a very general fashion, and apply them to ellipsometers based on various liquid crystal technologies. The results include an ellipsometer design which was patented, and which outperforms previous designs both in terms of spectral bandwidth and noise propagation. Recent progress in the ability to manipulate matter on the nanoscale has led to great interest in the biological, chemical, and physical properties of nanoparticles and nano-sized structures. Depositing nanoparticles on top of a surface modifies the optical properties of both the particles as well as the substrate: any optical resonances that the particle(s) possess are modified by the substrate, and the reflectivity of the substrate is changed due to the presence of the particles. The electromagnetic interactions between nanoparticles and substrate are here investigated in the quasistatic regime, with discussion of both small clusters of nanoparticles as well as (infinite) periodic lattices of nanoparticles deposited on a substrate. The results include analysis of the interactions and resonances found in nanoparticle clusters deposited on a substrate. When light is incident on surfaces possessing random roughness or structure, the light is scattered according to the statistical properties of the surface. While there has been significant progress on surface scattering from surfaces with one-dimensional surface profile functions, less attention has been devoted to numerical models of surfaces possessing two-dimensional surface profiles. The main reason for this is that the solution of these models requires a large amount of computational power, even by today’s standards. We attempt to shed some light on optical effects observed in scattering from two-dimensional rough surfaces, with some focus on polarization effects, which are absent in scattering from one-dimensional surfaces. The Mueller matrix for a rough surface is also calculated, and describes the full polarization effects of rough surface scattering.
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Knotts, Michael E. "Experimental studies of multiple scattering by rough surfaces." Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/30269.
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Arens, Tilo. "The scattering of elastic waves by rough surfaces." Thesis, Brunel University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311560.
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Basra, Narinder Singh. "Wave scattering by rough surfaces with varying impedances." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615863.
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Gullon, Cristina. "Height recovery of rough surfaces from intensity images." Thesis, Heriot-Watt University, 2003. http://hdl.handle.net/10399/401.
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Hatziioannou, John. "The scattering of electromagnetic waves by rough surfaces." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627099.
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Stanek, Clay James. "The scattering of waves from randomly rough surfaces." Thesis, University of Cambridge, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.619627.
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Ang, K. C. "Assessment of complex electron beam textured rough surfaces." Thesis, University of Southampton, 2009. https://eprints.soton.ac.uk/195957/.
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Peng, Wei. "Contact Mechanics of Multilayered Rough Surfaces in Tribology." The Ohio State University, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=osu1002737061.
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Dalvi, Siddhesh Narayan. "UNDERSTANDING CONTACT MECHANICS AND FRICTION ON ROUGH SURFACES." University of Akron / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=akron158957808488289.
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Neyland, Ryan P. "Colloid Detachment from Rough Surfaces in the Environment." Link to electronic thesis, 2005. http://www.wpi.edu/Pubs/ETD/Available/etd-050505-114151/.
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Awadallah, Ra'id S. M. S. "Rough Surface Scattering and Propagation over Rough Terrain in Ducting Environments." Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/30549.
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The problem of rough surface scattering and propagation over rough terrain in
ducting environments has been receiving considerable attention in the literature. One
popular method of modeling this problem is the parabolic wave equation (PWE) method.
In this method, the Helmholtz wave equation is replaced by a PWE under the assumption
of predominant forward propagation and scattering. The resulting PWE subjected to the
appropriate boundary condition(s) is then solved, given an initial field distribution, using
marching techniques such as the split-step Fourier algorithm. As is obvious from the
assumption on which it is based, the accuracy of the PWE approximation deteriorates in
situations involving appreciable scattering away from the near-forward direction, i.e.
when the terrain under consideration is considerably rough. The backscattered field is
neglected in all PWE-based models.
An alternative and more rigorous method for modeling the problem under
consideration is the boundary integral equation (BIE) method, which is formulated in two
steps. The first step involves setting up an integral equation (the magnetic field integral
equation, MFIE, or the electric field integral equation EFIE) governing currents induced
on the rough surface by the incident field and solving for these currents numerically. The
resulting currents are then used in the appropriate radiation integrals to calculate the field
scattered by the surface everywhere in space. The BIE method accounts for all orders of
multiple scattering on the rough surface and predicts the scattered field in all directions in
space (including the backscattering direction) in an exact manner.
In homogeneous media, the implementation of the BIE approach is
straightforward since the kernel (Green's function or its normal derivative) which appears
in the integral equation and the radiation integrals is well known. This is not the case,
however, in inhomogeneous media (ducting environments) where the Green's function is
not readily known. Due to this fact, there has been no attempt, up to our knowledge, at
using the BIE (except under the parabolic approximation) to model the problem under
consideration prior to the work presented in this thesis.
In this thesis, a closed-form approximation of the Green's function for a two-
dimensional ducting environment formed by the presence of a linear-square refractivity
profile is derived
using the asymptotic methods of stationary phase and steepest descents. This Green's
function is then modified to more closely model the one associated with a physical
ducting medium, in which the refractivity profile decreases up to a certain height,
beyond which it becomes constant. This modified Green's function is then used in the
BIE approach to study low grazing angle (LGA) propagation over rough surfaces in the
aforementioned ducting environment. The numerical method used to solve the MFIE
governing the surface currents is MOMI, which is a very robust and efficient method that
does not require matrix storage or inversion.
The proposed method is meant as a benchmark for people studying forward
propagation over rough surfaces using the parabolic wave equation (PWE). Rough
surface scattering results obtained via the PWE/split-step approach are compared to those
obtained via the BIE/MOMI approach in ducting environments. These comparisons
clearly show the shortcomings of the PWE/split-step approach.Ph. D.
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Hegge, Torstein Storflor. "Scalar wave scattering from two-dimensional, randomly rough surfaces." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for fysikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-13847.
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We study scalar waves scattered from self-affine and Gaussian correlated surfaces. The simulations are performed using rigorous simulation of the integral equations derived from the Helmholtz equation, describing a scalar wave above a non-penetrable surface with a hard wall or free surface boundary condition.An incident, Gaussian shaped beam is scattered from the surface, and the full angular distribution of the scattered intensity is obtained. Self-affine and Gaussian correlated random surfaces are generated, and the resulting scattered intensity is averaged over a large number of surfaces (in the order $N_s=3000$), using the ergodicity of the surface.Compared with analytical calculation of the scattered intensity in the Kirchhoff approximation, our approach gives similar results for less rough surfaces. Compared with simulations of electromagnetic waves scattered from a perfect conductor, without recording the polarisation of the scattered light, our simulations give similar results when using a hard wall boundary condition.We observe phenomena such as specular scattering for less rough surfaces, diffuse forward scattering for more rough surfaces and enhanced backscattering for surfaces where waves scattered multiple times by the surface roughness gives a large contribution to the scattered intensity.
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West, Martin Alan. "Methods of contact analysis of non-conforming rough surfaces." Thesis, Imperial College London, 1991. http://hdl.handle.net/10044/1/8907.
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Rapetto, Marco. "Rough surfaces in contact : artificial intelligence and boundary lubrication." Licentiate thesis, Luleå tekniska universitet, Maskinelement, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-25874.
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Interacting surfaces are found in mechanical systems and components. Since engineered surfaces are not perfectly smooth, only a fraction of the nominal surface area is actually in contact. This fraction is denoted as the real area of contact, Ar, and is formed by the sum of the contact spots between the two touching surfaces. If these contacting surfaces are sliding, then friction and wear occur in these actual contacts. Friction and wear may be controlled by lubrication: depending on the operating conditions different types of lubrication regime exist. When the surfaces are completely separated by the fluid film and load is carried by hydrodynamic action, contacts operate in hydrodynamic regime. When the load is carried by the lubricating fluid and asperity contact, the regime becomes mixed lubrication. In boundary lubrication, surfaces are in contact and the load is carried by surface asperities. In many cases this is the critical lubrication regime that governs the life of the components. Due to the complexity of thin film boundary lubrication, design of lubricated interfaces is still a trial-and-error process. The mechanism of formation and rupture of oxide layers and boundary layers is not completely known and a reliable model for rough surfaces in boundary lubrication is currently lacking. This study focuses on boundary lubrication regime: the effect of surface roughness on the real area of contact is investigated and a numerical model for the sliding interaction between two asperities in sliding contact is developed. Numerical simulations of normal, dry, friction free, linear elastic contact of rough surfaces are performed. A variational approach is followed and the FFT-technique is used to speed up the numerical solution process. Five different steel surfaces are measured using a Wyko optical profilometer and several 2-D profiles are taken. The real area of contact and the pressure distribution over the contact length are calculated for all the 2-D profiles. A new slope parameter is defined. An artificial neural network is applied to determine the relationship between the roughness parameters and the real area of contact. Boundary lubrication mechanism is usually controlled by the additives present in the oil that form low friction, protective layers on the wearing surfaces. Chemical reactions between the lubricant molecules and the asperity surface may take place. These reactions are activated by certain values of pressure and temperature. Fundamental research on the influence of surface roughness on contact conditions is hence required and is a key factor in understanding the wear mechanism in boundary lubrication condition since pressure distribution, shear stresses, frictional heating, mechanical wear highly depends on surface topography. Modelling boundary lubrication requires knowledge in many fields: contact mechanics, thermodynamics, surface chemistry etc, thus different sub-models interacting each other must be created. It is complicated and may be not feasible within a foreseeable time period to take into account all the different parameters and evaluate them. Artificial intelligence is a way to overcome the problem and determine the relationship between input parameters and desired outputs. An elasto-plastic analytical model is used to determine the variation of pressure distribution and shear stress during the collision process of two asperities in sliding contact. The outputs of the elasto-plastic model are inputs of the thermal model that calculates the temperature rise during the collision process. The desorption of the adsorbed layer is determined by using existing adsorption theories and finally the probability of wear is computed at each time step of the collision process. Different results obtained using different adsorption theories and different input parameters are compared.Godkänd; 2008; 20080512 (ysko)
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Bergström, David. "The absorption of laser light by rough metal surfaces /." Luleå : Division of Manufacturing Systems Engineering, Department of Applied Physics and Machanical Engineering, Luleå University of Technology, 2008. http://epubl.luth.se/1402-1544/2008/08.
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Rapetto, Marco Pietro. "Rough surfaces in contact : artificial intelligence and boundary lubrication /." Luleå : Luleå University of Technology, 2008. http://epubl.ltu.se/1402-1757/2008/16/.
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West, Charles Stanley. "Backscattering enhancement from plasmon polaritons on rough metal surfaces." Thesis, Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/29914.
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Conrad, Jeffrey G. "Propagation of vertically polarized waves over rough ocean surfaces." Thesis, Monterey, California. Naval Postgraduate School, 1997. http://hdl.handle.net/10945/8867.
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Approved for public release; distribution is unlimitedThe problem of propagation of vertically polarized radiowaves in an inhomogeneous atmosphere and over rough ocean surfaces is solved using the parabolic equation method. The solution of the parabolic equation is accomplished through the use of the Fourier split-step algorithm. Formulation of the equations is based upon (1) recognizing that the Fourier kernels of the transform equations in the split step algorithm represent planes waves and (2) compensating for the effects of rough ocean surfaces by using a rough surface reduction factor directly in the spectral domain. To accomplish this a redefinition of the Fourier transform pair is done to ensure mathematical consistency. The formulation also incorporates the first and second derivatives of the refractivity index to accommodate steep gradients in the refractivity profile. Hanning windows are used in both the spatial and wavenumber domains to contain computational requirements. The effects on propagation by varying parameters such as wave heights, computational domain ceilings, frequency and step size are investigated
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Harley, Alan Stewart. "Correlation scale effects in light scattering from rough surfaces." Thesis, Imperial College London, 1989. http://hdl.handle.net/10044/1/47463.
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Pruin, Bernard. "Wave propagation over one- and two-dimensional rough surfaces." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624138.
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Kim, Hyunjun. "Radar image studies of scattering from random rough surfaces /." The Ohio State University, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=osu1486402288263568.
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Pärssinen, Mikael. "Studies on dynamic response caused by contact between rough surfaces." Doctoral thesis, KTH, Vehicle Engineering, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3196.
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Berry, Elizabeth. "Fabrication of multiscale random rough surfaces with prescribed surface statistics." Thesis, Imperial College London, 1986. http://hdl.handle.net/10044/1/37944.
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Harp, Susan R. "A computational method for evaluating cavitating flow between rough surfaces." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/16838.
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Ogilvy, J. A. "On the theory of ultrasonic wave scattering from rough surfaces." Thesis, University of Bath, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.378884.
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Thomassier, Vincent 1971. "Electromagnetic backscattering from penetrable rough surfaces based on moment method." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/42776.
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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1997.Includes bibliographical references (leaves 91-95).
by Vincent Thomassier.
M.S.
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Zhang, Yuanyuan. "Friction prediction for rough surfaces in an elastohydrodynamically lubricated contact." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSEI063.
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Le frottement à l’interface des surfaces influence les performances des éléments mécaniques. Le frottement a été étudié expérimentalement dans la plupart des études. Dans ce travail, le frottement est prédit à l'aide d'une simulation numérique dans des conditions de contact rugueux avec une lubrification élastohydrodynamique (EHL). La technique classique Multigrille fonctionne bien pour limiter le temps de calcul et les besoins en mémoire. Cependant, le choix de la grille grossière a une influence importante sur la robustesse du code et son efficacité pour résoudre le problème brut. Dans la première partie de ce travail, une méthode de construction de grille grossière proposée par Alcouffe et al. est implémenté dans le code EHL Multigrille indépendamment du temps. Ensuite ce solveur modifié est étendu aux cas transitoires pour résoudre le problème de contact avec rugosité. La courbe de frottement est généralement représentée en fonction du « ratio », le rapport entre l'épaisseur du film d'huile et la valeur moyenne quadratique de la rugosité de la surface. Cependant, ce paramètre est moins approprié pour tracer les variations de frottement dans des conditions de haute pression (régime élasto piézo-visqueux). Dans la deuxième partie de ce travail, le coefficient de frottement est calculé à l'aide du code EHL modifié pour de nombreuses conditions de fonctionnement ainsi que pour les paramètres d'ondulation de surface. Les résultats de la simulation montrent qu'il n'y a pas de courbe de frottement unique lorsque l'ancien paramètre « ratio »est utilisé. En se basant sur la théorie de la réduction d'amplitude, un nouveau paramètre de dimensionnement qui dépend des conditions de fonctionnement et des paramètres d'ondulation est trouvé, ce qui peut donner une courbe de frottement unique pour les situations de haute pression. Pour les surfaces rugueuses plus complexes, une méthode basée sur la densité spectrale de puissance (PSD) est proposée pour prédire les variations de frottement dans la troisième partie de ce travail. La rugosité artificielle de la surface est utilisée pour tester d’abord la méthode de prédiction rapide. Un bon accord est trouvé entre la simulation numérique complète et cette prédiction rapide. La méthode de prédiction rapide est ensuite appliquée pour analyser la variation de frottement de la rugosité de surface mesurée. Le nouveau paramètre d’échelle et l’augmentation du frottement prédite par la méthode PSD montrent une bonne précision technique pour une utilisation pratiqueThe friction of interfacial surfaces greatly influences the performance of mechanical elements. Friction has been investigated experimentally inmost studies. In this work, the friction is predicted by means of numerical simulation under an elastohydrodynamic lubrication (EHL) rough contact condition. The classical Multigrid technique performs well in limiting computing time and memory requirements. However, the coarse grid choice has an important influence on code robustness and code efficiency to solve the rough problem. In the first part of this work, a coarse grid construction method proposed by Alcouffe et al. is implemented in the current time-independent EHL Multi-Grid code. Then this modified solver is extended to transient cases to solve the rough contact problem. The friction curve is usually depicted as a function of “lambda ratio”, the ratio of oil film thickness to root-mean-square of the surface roughness. However this parameter is less suitable to plot friction variations under high pressure conditions (piezoviscous elastic regime). In the second part of this work, the friction coefficient is computed using themodified EHL code for many operating conditions as well as surface waviness parameters. Simulation results show that there is no single friction curve when the old parameter "lambda ratio" used. Based on the Amplitude Reduction Theory, a new scaling parameter depends on operating condition and waviness parameters is found, which can give a unified friction curve for high pressure situation. For more complex rough surfaces, a power spectral density (PSD) based method is proposed to predict friction variations in the third part of this work. The artificial surface roughness is employed to test the rapid prediction method firstly. Good agreement is found between the full numerical simulation and this rapid prediction. Then the rapid prediction method is applied to analyze the friction variation of measured surface roughness. Both the new scaling parameter and the friction increase predicted by the PSD method show good engineering accuracy for practical use
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Smith, Benjamin Scott. "Wall Jet Boundary Layer Flows Over Smooth and Rough Surfaces." Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/27597.
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The aerodynamic flow and fluctuating surface pressure of a plane, turbulent, two-dimensional wall jet flow into still air over smooth and rough surfaces has been investigated in a recently constructed wall jet wind tunnel testing facility. The facility has been shown to produce a wall jet flow with Reynolds numbers based on the momentum thickness, Re&delta = &deltaUm/&nu, of between 395 and 1100 and nozzle exit Reynolds numbers, Rej = Umb/&nu, of between 16000 and 45000. The wall jet flow properties (&delta, &delta*, &theta, y1/2, Um, u*, etc.) were measured and characterized over a wide range of initial flow conditions and measurement locations relative to the wall jet source. These flow properties were measured for flow over a smooth flow surface and for flow over roughness patches of finite extent. The patches used in the current study varied in length from 305 mm to 914 mm (between 24 and 72 times the nozzle height, b) and were placed so that the leading edge of the patch was fixed at 1257 mm (x/b = 99) downstream of the wall jet source. These roughness patches were of a random sand grain roughness type and the roughness grain size was varied throughout this experiment. The tests covered roughness Reynolds numbers (k+) ranging from less than 2 to over 158 (covering the entire range of rough wall flow regimes from hydrodynamically smooth to fully rough). For the wall jet flows over 305 mm long patches of roughness, the displacement and momentum thicknesses were found to vary noticeably with the roughness grain size, but the maximum velocity, mixing layer length scale, y1/2, and the boundary layer thickness were not seen to vary in a consistent, determinable way. Velocity spectra taken at a range of initial flow conditions and at several distinct heights above the flow surface showed a limited scaling dependency on the skin friction velocity near the flow surface.
The spectral density of the surface pressure of the wall jet flow, which is not believed to have been previously investigated for smooth or rough surfaces, showed distinct differences with that seen in a conventional boundary layer flow, especially at low frequencies. This difference is believed to be due to the presence of a mixing layer in the wall jet flow. Both the spectral shape and level were heavily affected by the variation in roughness grain size. This effect was most notable in overlap region of the spectrum. Attempts to scale the wall jet surface pressure spectra using outer and inner variables were successful for the smooth wall flows. The scaling of the rough wall jet flow surface pressure proved to be much more difficult, and conventional scaling techniques used for ordinary turbulent boundary layer surface pressure spectra were not able to account for the changes in roughness present during the current study. An empirical scaling scheme was proposed, but was only marginally effective at scaling the rough wall surface pressure.Ph. D.
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Venkatakrishnan, Abishek. "Molecular Simulations Study of Adsorption of Polymers on Rough Surfaces." University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1427812323.
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Bashir, Imran. "Acoustical exploitation of rough, mixed impedance on porous surfaces outdoors." Thesis, Open University, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.606960.
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This thesis is a contribution towards developing cost-effective ways for reducing outdoor traffic noise in outdoor environments by exploiting the interaction between sound travelling directly to a listener from the source and sound reflected by the intervening ground . Sound propagation over different kinds of porous, rough and mixed impedance ground surfaces have been studied experimentally and numerically. Measurements of short-range acoustic level difference spectra over outdoor ground surfaces and artificially-created surfaces outdoors and in the laboratory have been compared with predictions to establish suitable impedance models. Sound propagation over mixed impedance ground having single or multiple impedance discontinuities has also been studied . Acoustic transmission loss through vegetation, crops and hedges has been investigated. • The phenomenon of sound diffraction and periodicity due to rough periodic ground surfaces has been explored through artificially created rough surfaces in the laboratory and outdoors. The phenomenon of surface wave propagation over rough hard surfaces and porous surfaces has been explored through laboratory experiments. Measured data indoors and outdoors have been used to validate numerical (BEM and FEM), empirical and analytical (MST) prediction techniques. The validated numerical methods have been used to make predictions at scales suitable for attenuating traffic noise by means of carefully designed ground treatments. The work has also been extended to railway and tramway noise. It has been found that replacing hard ground with porous ground, introducing single or multiple impedance discontinuities, growing vegetation and introducing low height roughness can all contribute between 3 and 15 dB additional attenuation of traffic noise. In respect of replacing hard ground by porous ground, it is concluded that the ground with lowest flow resistivity i.e. grassland left untouched and allowed to grow wild gives the best attenuation performance. However, dividing a single width of soft ground into alternating strips of hard and soft surfaces does not improve the insertion loss. The overall width of the soft surface is the main factor. Cultivating crops over porous ground can enhance the attenuation but the effect is not very significant for A-weighted levels as most of additional attenuation occurs at higher frequencies above 3 kHz. A 0.3 m high and at least 3 m wide lattice structure design is found to be very useful for traffic noise attenuation since it offers greater insertion loss than the same width and height of parallel low walls and the resulting attenuation is azimuthal angle independent. It has been shown also that the potentially negative effect on insertion loss due to propagation of roughness-induced surface waves over rough surfaces can be reduced by introducing sound absorbing material in between the walls.
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Letherman, Sophie Bella. "Turbulence modelling of oscillatory flows over smooth and rough surfaces." Thesis, University of Manchester, 2000. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.488128.
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This study investigates turbulence models for application to boundary layer flows. Firstly, steady channel flow and transient pipe flows are considered. Calculations of a low-Reynolds-number k-epsilon model, a k-epsilon-S model (a strain parameter model which has not been applied to unsteady flows previously) and a Reynolds Stress Transport model are compared with experimental and DNS data. The eddy viscosity turbulence models (k-epsilon, k-epsilon-S) satisfactorily predict the mean flow parameters of steady channel flow. However the k-epsilon-S model proves superior in comparison with turbulence quantities. Near to the pipe wall, the k-epsilon-S model best captures the details of periodic pipe flow detail, whereas in the outer flow region the RSTM gives closest agreement with the experimental data. The high-Reynolds-number k-epsilon and k-l eddy viscosity turbulence models are examined in a separate study of oscillatory flows over smooth and rough beds. The computations are considered over a wider range of experimental parameters than previously investigated. The turbulence models are assessed by comparison with field measurements and laboratory data sets including a new set of experimental measurements. Both models predict the bed shear stress and velocity adequately, but the k-epsilon model emerges as the superior scheme when considering turbulence quantities. An attempt is made to quantify the uncertainty in the Reynolds shear stress and eddy viscosity experimental data. The k-epsilon model calculations more frequently lie within the experimental uncertainty bands. However this uncertainty range is wide; any improvement would require a corresponding improvement in the experimental resolution of rough bed flows.