The interactions of trailing vortex pairs shed from the tips of two rectangular wings have been studied through helium bubble flow visualizations and extensive hot wire velocity measurements made between 10 and 30 chord lengths downstream. The wings were placed tip to tip at equal and opposite angles of attack, generating pairs of co-rotating and counter rotating vortices. Meaningful hot wire measurements could be made because the vortices were found to be insensitive to probe interference and experienced very small wandering motions. The co-rotating pairs were observed to rotate around each other and merge. Upstream of the merging location, the vortices have approximately elliptical cores. These are surrounded by the two wing wakes which join together around the two cores. Flow in the vicinity of the cores appears fully developed. During the merging process, the cores rotate rapidly about each other, winding the wing wakes into a fine spiral structure. Merger roughly doubles the core size and appears to produce turbulence over abroad range of frequencies. The counter rotating pairs move sideways under their mutual induction and slightly apart; their flow structure changing little with downstream location. These cores remain fairly circular and do not become fully developed within 30 chord lengths of the measurements. / Master of Science

In a gas turbine, a small portion of air is bled from the compressor to provide cooling to keep the turbine at a safe operating temperature. The air flows through several passages in between where the components of the turbine are assembled. In this study, the heat transfer and pressure loss characteristics of two of these passages are investigated experimentally. The first of the two passages investigated is the passage in between the turbine blade root and disc. This passage has a unique geometry resembling an S-shape. The heat transfer and pressure loss characteristic of this passages in not well documented. For this study, a model of the realistic S-shaped passage has been made. In addition, a simplified rectangular duct with hydraulic diameter similar to that of the realistic S-shaped passage was constructed along with three other rectangular passages at aspect ratios, 17.33, 8.81, 3.93, and 2.02. This study aims to determine if rectangular duct correlations are valid for the realistic S-shaped model. Specifically, flow in low Reynolds number ranges of less than 3000 are of interest. With the effect or rotation and aspect ratio being of primary concern in the study, an experimental rig was constructed to measure the heat transfer and pressure loss in these models. The experiments were conducted with both clockwise and counterclockwise rotation to account for the passage on the pressure side and suction side of the passage. The centerline Nusselt number distribution measured to check if the flow was fully developed. The effect of rotation caused swirling, increasing the entrance length in the duct and also enhanced heat transfer. The rotation also enhanced the heat transfer in the fully developed region. The fully developed experimental data for the simplified rectangular ducts showed good correlation with that of literature. However, the realistic S-shaped duct showed lower heat transfer values than the simplified rectangular ducts. Still, the effect of rotation is seen enhancing the rotation inf the realistic S-shaped duct. Additionally, the friction factor which was measured using the cross-sectional average static pressure showed similar results for the realistic S-shaped duct and the simplified rectangular duct. The passage between turbine disc bore and shaft is modeled as an annular duct with inner surface rotation. Flow in the turbulent region is studied and the test sections are made to have short length to hydraulic dimeter ratios. Along the centerline, the onset of Taylor vortices can be seen enhancing the Nusselt number in regions where the flow should be fully developed. This effect can also be seen enhancing the heat transfer in the fully developed region. The presence of Taylor vortices also adds resistance increasing the pressure loss across the duct. / Master of Science / Industrial gas turbines are designed to have an optimum overall pressure ratio for target temperatures rise. The demand for higher efficiency and power continues to push the operating pressure and temperature. Air systems is the flow network to provide necessary cooling to keep the machinery at a safe operating temperature. In this study, two passages of the air system in the turbine are of interest. The passage between turbine blade root and disc, and the passage between the turbine disc and shaft. The effect of rotation on the flow through the two passages are of primary interest with focus on heat transfer and pressure loss characteristics. This experimental study presents unique results as a realistic model of the passage which resembles an S-shape was constructed and tested. The passage in between the turbine disc and shaft forms a rotating annular passage. There is limited data available representing the realistic geometrical shape of the annular passage under rotation. Therefore, the present study aims to present data for more realistic geometry and operating conditions. In addition, simplified rectangular ducts and annular ducts are also tested for comparison purpose. The results of the study showed that the rotation does provide a significant increase in heat transfer and pressure loss in experiment modeling the passage between the turbine blade root and disc. Comparing the realistic S-shape passage and the rectangular passage with similar aspect ratio, the realistic S-shape passage showed less heat transfer and less sensitivity to the effect of rotation. The pressure loss characteristics on the other hand proved to be very similar. For the experiments modeling the passage between turbine disc and shaft, the effect of rotation once again showed to increase the heat transfer and pressure loss. The effect is more prominent when there is less axial flow.

Numerical techniques for designing planar arrays with low side lobe level often require memory intensive optimization algorithms and also initialization in the form of some known values of radiation pattern parameters beforehand - information that may not be available when designing arrays. A few analytical methods exist in the literature that can be used to design rectangular lattices of isotropic elements for desired half-power beamwidth and side lobe level, but the number of elements of the array often should be known before the design process. Some array designs based on analytical techniques may suffer from severe performance limitations, an example is the uniformly excited array which cannot produce side lobe levels below ̶13.3 dB. The goal of this study is to present an analytical technique for synthesis of planar arrays that, for specified radiation pattern requirements, not only provides quick solutions for the required number of elements and its distribution along the length and width of the array rectangular lattice, but also produces low side lobes without any limitation. A new class of non-uniformly excited equally spaced planar arrays is introduced and investigated in this study. The new array uses the patterns of uniformly excited linear arrays as its building blocks and has a separable element current distribution, hence making it mathematically convenient to analyze its radiation properties in terms of those of its constituent linear arrays. The proposed planar array does not suffer from the side lobe level limitation of uniformly excited planar arrays, and its synthesis, due to the analytical nature of description of its radiation properties, does not require iterative procedures that are inherent to numerical techniques. Radiation characteristics of the proposed planar array, including directivity, side lobe level, half-power beamwidths, far-field three dimensional radiation patterns, and element excitation currents, are examined and simulation results for several example cases are presented. The analysis culminates with successfully mapping a continuous radiation pattern to discrete element currents in a rectangular lattice geometry. The synthesis procedure is validated by successfully designing various planar arrays with desired requirements in terms of side lobe level and half-power beamwidths in the principal planes. Several design examples are presented. Radiation characteristics of the synthesized arrays are compared with the desired design requirements which were used as input information in the synthesis process. For the cases studied, the achieved performance characteristics are close to the desired ones. / MS / A group of similar antennas that radiate with equal intensity in all directions and each fed with a certain current amplitude is called an isotropic antenna array. When the distance between the adjacent antenna elements in an array is constant, it is called an equidistant array. Furthermore, when the array elements take up the geometry of a rectangular lattice, they are referred to as rectangular planar array. In antenna array design, it is always desirable that the isotropic array is set up in a manner that it establishes a stronger communication link in the desired direction while minimizing any communication in other directions. This can be achieved by changing the spatial footprint of the array’s radiation also known as its array factor. The array factor can be altered by either adjusting the inter-element spacing or changing the current amplitude of each element. A great number of techniques have been proposed over the years that aim to minimize communication in undesired directions. Most of these techniques achieve the objective by employing computationally complex algorithms that require a lot of time and memory. For other synthesis techniques, some design information is required to be known beforehand which may not be possible. The aim of this study is to present an easier analytical approach that designs rectangular planar array for specified radiation pattern requirements. The radiation requirements entail the direction in which the communication link is required to be established and the extent to which radiation in other directions is permissible – characterized by side lobe level of the array factor. The strength of the communication link is measured by directivity and half power beam width of the array factor. It is found that the proposed array in the study minimizes communication in unwanted directions in a much more effective manner than a rectangular array with each element fed with an equal current amplitude – also known as uniformly excited planar array. The performance of the proposed planar array in terms of directivity, half power beam width and side lobe level is first simulated and presented. The design procedure is then validated by designing various planar arrays with desired radiation requirements. Several design examples are presented. Radiation characteristics of the synthesized arrays are compared with the desired design requirements which were used as input information in the synthesis process. For the cases studied, the achieved performance characteristics are close to the desired ones.

Yes / A sudden dam failure is usually simulated by the rapid removal of a gate in laboratory tests and numerical simulations. The gate-opening time is often determined according to the Lauber and Hager instantaneous collapse criterion (referred to as Lauber-Hager criterion) established for a rectangular open channel with a dry bed. However, this criterion is not suitable for non-rectangular channels or initial wet-bed conditions. In this study, the effect of the gate-opening time on the wave evolution is investigated by using the large eddy simulation (LES) model. The instantaneous dam break, namely the dam break without a gate, is simulated for comparison. A gate-opening criterion for generating dam-break flow in non-rectangular wet bed channel is proposed in this study, which can be used as an extension of the Lauber-Hager criterion and provides a more comprehensive and reasonable estimate of the gate opening time. / National Natural Science Foundation of China (Grant No: 51879179), the Open Fund from the State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University (SKHL1809) and Sichuan Science and Technology Program (No. 2019JDTD0007).

Thesis (MEng) -- Stellenbosch University, 2014. / ENGLISH ABSTRACT: Solar energy is a time dependent, high-temperature radiant energy resource. The utility of a solar thermal energy system increases if the hot temperature source is available when it is needed most. This is realized by the thermal storage of the solar energy. Thermal storage gives greater versatility to a solar energy system by decoupling the heat source from the heat sink. A large quantity of energy may be stored during the melting process in a phase change material (PCM) within a small temperature range. This molten PCM can then deliver its absorbed heat at a constant temperature in a heating application. In this study a phase change storage system (PCS) is developed and proposed for a solar water heating application. This PCS system stores more heat per unit mass than would be possible with water across the same temperature range. The heat transfer rate in and out of many PCMs is slow because of the low thermal conductivity of the PCM. However, heat transfer enhancers (HTE), such as heat pipes and fins may be added to enhance heat absorption and heat removal rates. Heat pipes have the inherent capability to transfer heat at high rates across large distances, even where the temperature difference is small. In this thesis a description is given of a PCS system consisting of paraffin wax as the PCM and which uses rectangular heat pipes in conjunction with aluminium fins to enhance heat transfer. The storage design is modular and each module has the characteristic that enhanced heat transfer in and out of the PCM is possible when the module is heated or cooled. It also has the capability to quickly absorb or alternatively to supply heat at a nearly constant temperature during the phase change of the module. A rectangular module was designed and built. The module was then analysed under controlled heat absorption and heat removal cycles. The heat up experiment involved an electrical kettle as the hot temperature source. The heat sink was a mains water heat exchanger. The experimental results were compared to those of a transient numerical model, which calculates theoretically how the module will perform thermally under the given test conditions. The numerical model of the experimental set-up was validated when it was found that the numerical model results resemble the experimental results. The numerical model was then adapted to simulate a novel solar water heater (SWH) with an additional PCS container. The improvement over previous designs is that the additional storage container can be heated to a higher temperature than the allowable geyser temperature. The system also heats up and cools down at a faster rate than would be possible without the HTEs. From the numerical simulation the size and performance of such a system is determined. This numerical analysis indicated that a phase change storage system in a SWH application will increase the hot water delivered by a given solar collector and geyser by increasing the storage capacity and by heating up the geyser overnight for early morning hot water use. / AFRIKKANSE OPSOMMING: Son energie is ‘n tyd afhanklike, hoë temperatuur radiasie energiebron. Die bruikbaarheid van ‘n sontermiese energie sisteem verhoog indien die hoë temperatuur bron beskikbaar is wanneer dit die meeste benodig word. Dit kan verwesenlik word deur die sonenergie termies te stoor. Termiese storing bied groter veelsydigheid aan ‘n sontermiese stelsel deur effektief die hittebron te ontkoppel van die hitte sink. ‘n Groot hoeveelheid energie kan, gedurende die smeltingsproses in ‘n faseveranderingsmateriaal binne ‘n nou temperatuurband gestoor word. Hierdie gesmelte materiaal kan weer op sy beurt in die waterverhittingstoepassing, die geabsorbeerde hitte teen ‘n konstante temperatuur oordra. In hierdie studie word ‘n sonwaterverwarmer stelsel wat aangepas is deur ‘n addisionele latente hittestoor daaraan te heg, voorgestel. Hierdie faseverandering hittestoor kan meer hitte stoor as wat water in dieselfde temperatuur band sou kon. Die hitteoordrag tempo na en van baie van die faseveranderingsmateriale (FVM) is egter as gevolg van die lae termiese geleidingskoëfisient, stadig. Hierdie eienskap kan gelukkig verbeter word deur hittepype en hitteoordrag verhogings materiaal soos vinne by te voeg. Hittepype het die inherente eienskap om hitte teen ‘n hoë tempo oor groot afstande, oor te dra, selfs oor ‘n klein temperatuurverskil. In hierdie tesis word ‘n ondersoek rakende ‘n faseverandering storingsisteem wat bestaan uit paraffien was as die FVM en reghoekige hittepype wat te same met met aluminium finne gebruik word om die hitteoordragtempo te verhoog, beskryf. Die stoorontwerp is modulêr en elke module het die kenmerk van hoë hitteoordrag na en van die FVM. Die module het verder ook die eienskap om vining hitte te absorbeer of hitte af te gee. Dit gebeur teen ‘n konstante temperatuur gedurende die faseverandering van die FVM. Presies so ‘n reghoekige module is ontwerp en gebou en onder beheerde hitte absorbering- en hitte verwyderingsiklusse analiseer. Tydens die verhittings eksperiment is ‘n elektriese ketel van gebruik gemaak wat gedien het as die hoë temperatuur bron. Die hitte sink was ‘n hitteruiler wat kraanwater van ‘n konstante hoogte tenk ontvang het. Die resultate van die volledige toets is met die resultate van tydafhanklike numeriese model vergelyk. Hierdie numeriese model bereken teoreties wat die module se storing verrigting onder gegewe toets omstandighede sal wees. Die numeriese model se resultate het goed vergelyk met die resultate van die eksperimente. Die numeriese model van die module is toe aangepas om ‘n sonwaterverwarmer met addisionele stoortenk wat fase verandering materiaal gebruik, te simuleer. Hierdie ontwerp is anders as vorige ontwerpe in die sin dat hoër temperature as wat die warmwatertoestel kan hanteer, in die faseverandering storingstenk, bereik kan word. Die sisteem kan ook as gevolg van die hitteoordrag verhoging materiaal, vinniger verhit of afkoel en teen ‘n vinniger tempo. Die simulasie van die sonwaterverwarmer met FVM word gebruik om die grootte en verrigting van die sisteem te bepaal. Hierdie numeriese model toon aan dat wanneer ‘n addisionele faseverandering storingstelsel in ‘n sonwaterverwarmer toepassing gebruik word, die warm water wat die verbruiker uit die sisteem kan verkry, kan verhoog. Die rede hiervoor is dat meer hitte gestoor kan word, wat beskikbaar gemaak word aan die warm water tenk.

The telescoping cantilever beam structure is applied in many different engineering sectors to achieve weight/space optimisation for structural integrity. There has been limited theory and analysis in the public domain of the stresses and deflections involved when applying a load to such a structure. This thesis proposes (a) The Tip Reaction Model, which adapts classical mechanics to predict deflection of a two and a three section steel telescoping cantilever beam; (b) An equation to determine the Critical buckling loads for a given configuration of the two section steel telescoping cantilever beam assembly derived from first principles, in particular the energy methods; and finally (c) the derivation of a design optimization methodology, to tackle localised buckling induced by shear, torsion and a combination of both, in the individual, constituent, hollow rectangular beam sections of the telescopic assembly. Bending stress and shear stress is numerically calculated for the same structure whilst subjected to inline and offset loading. An FEA model of the structure is solved to verify the previous deflection, stress and buckling predictions made numerically. Finally an experimental setup is conducted where deflections and stresses are measured whilst a two section assembly is subjected to various loading and boundary conditions. The results between the predicted theory, FEA and experimental setup are compared and discussed. The overall conclusion is that there is good correlation between the three sets of data.

Dans cette thèse, nous étudions des problèmes algorithmiques dans les complexes CAT(0) planaires et rectangulaires munis d'une m ́etrique intrinsèque l_2. Nous proposons des algorithmes de calcul du plus court chemin dans les complexes CAT(0) planaires et rectangulaires et de construction de l'enveloppe convexe d'un ensemble fini de points dans les complexes CAT(0) planaires. E ́tant donné un complexe CAT(0) rectangulaire 2-dimensionnel K à n sommets, nous proposons un algorithme qui, pour toute paire de points calcule la distance et le plus court chemin en temps sous-lin ́eaire en nombre de sommets de K, en utilisant une structure de données de taille O(n^2). Le deuxième problème étudié est celui du plus court chemin entre un point-source donné et tout autre point dans un complexe CAT(0) planaire K a n sommets. Pour cela, nous proposons un algorithme qui, pour tout point y de K, étant donnée le point source x et la carte géodésique SPM(x), construit le plus court chemin γ(x,y) en temps O(n), en utilisant une structure de données de taille O(n^2). Enfin, nous nous intéressons au calcul de l'enveloppe convexe d'un ensemble de k points dans un complexe CAT(0) planaire à n sommets. Nous proposons un algorithme qui construit l'enveloppe convexe en temps O(n^2 + nk log k) en utilisant une structure de données de taille O(n^2 + k). / In this thesis, we study algorithmic problems in CAT(0) planar and rectangular complexes with an intrinsic l_2−metric. We present algorithms for some algorithmic problems, such as computing the shortest path and the convex hull of a finite set of points in CAT(0) planar and rectangular complexes. We present an efficient algorithm for answering two-point distance queries in a given CAT(0) rectangular complex K with n vertices. Namely, we show that for a CAT(0) rectangular complex K with n vertices, one can construct a data structure of size O(n^2) so that, given any two points in K, the shortest path can be computed in subliniar time of n. The second problem presented is computing shortest path from a single-source to the query point in a CAT(0) planar complex. We propose an algorithm which computes in O(n) time the shortest path between a given point and the query point in a CAT(0) planar complex with n vertices, using a given shortest path map and data structure of size O(n^2). Finally, we study the problem of computing the convex hull of a set of k points in a CAT(0) planar complex with n vertices. We describe an algorithm which computes the convex hull in O(n^2 + nk log k) time, using a data structure of size O(n^2 + k).

Os Polímeros Reforçados com Fibras (PRF) são materiais compósitos constituídos por fibras unidas por uma matriz polimérica. São leves, não corrosivos, possuem alta resistência à tração e são de simples execução. O PRF em forma de tecido é utilizado para envolver o pilar de concreto armado promovendo a restrição das deformações laterais pelo efeito de membrana. Nos pilares com seção transversal circular, esse efeito de membrana é desenvolvido ao longo de todo o seu perímetro. Já para seções quadradas ou retangulares, esse efeito de membrana se desenvolve apenas nos cantos arredondados, reduzindo, assim, a eficiência do confinamento. Por conta dessa limitação, esta pesquisa propõe a utilização de um mecanismo auxiliar constituído por tirantes transversais de aço ancorados por perfis longitudinais, que juntamente com o PRF vão promover o confinamento nos maiores lados de seções de pilares retangulares. Foram realizados ensaios experimentais de dez pilares de concreto, cujos resultados confirmaram o maior incremento de força e ductilidade nos pilares devido à presença dos tirantes, verificando também que os perfis longitudinais contribuem diretamente com a força axial no pilar. Por meio da análise numérica em elementos finitos foi possível observar o acréscimo de regiões de concreto efetivamente confinado devido à presença dos tirantes. Com a análise paramétrica realizada foram identificados os parâmetros e como eles influenciam no comportamento dos pilares reforçados com a técnica: a relação entre os lados da seção transversal, a taxa de PRF; a taxa de tirantes de aço e a rigidez do perfil de ancoragem. Por fim, foi desenvolvido um modelo analítico que possibilita calcular a parcela de força resistida pelo concreto confinado e pelos perfis de ancoragem de modo independente, indicando boas correlações com os resultados experimentais e numéricos. / Fiber Reinforced Polymers (FRP) are composite materials consisting of fibers bonded by a polymer matrix. They are lightweight, non-corrosive, have high tensile strength and simple to apply. The FRP jacket is used to wrap the concrete column and restrict the lateral expansion by the membrane effect. In columns with circular cross section, the membrane effect is developed along its entire perimeter. However, in square or rectangular sections this effect is only developed at the rounded corners, resulting in a decrease of the confinement efficiency. Due this limitation, this research proposes the use of an auxiliary mechanism made up of transverse steel ties anchored by longitudinal bars, which together with the FRP, promote confinement on the biggest sides of rectangular sections of columns. Experimental tests were carried out on ten concrete columns, whose results confirmed the greatest force increase and ductility due to the presence of the steel ties and that the anchor bars contribute directly with the axial force. Through the numerical analysis in finite elements methods it was possible to observe the effective confined concrete regions due to the presence of the ties. With the parametric analysis performed some parameters were identified and how they influence in behavior of columns reinforced with this technique: the relationship between the sides of the cross section; the PRF rate; the steel ties rate and the stiffness of the anchor bar. Finally, an analytical model was developed allowing calculate the force resisted by the confined concrete and the anchor bars forces independently, indicating good correlations with the experimental and numerical results.

O escoamento hidrodinâmico é descrito por meio das equações da continuidade e da quantidade de movimento em conjunto com as condições iniciais e de contorno. Neste trabalho de pesquisa, o escoamento não permanente na saída de um canal retangular curto de declividade nula, resultante da abertura rápida de uma comporta foi experimentalmente investigado. Para determinar o coeficiente de pressão e o comprimento do trecho a montante da comporta com distribuição de pressão não hidrostática, usou-se um modelo unidimensional, descrito pelas equações de Saint Venant, para representar o fenômeno. Utilizou-se o método de Lax-Wendroff para obter as curvas características do fenômeno e compará-las com os resultados obtidos experimentalmente. Várias comparações foram feitas possibilitando a avaliação de valores para os parâmetros que definem a região com distribuição de pressão não hidrostática. Os resultados calculados para os valores de parâmetros constantes, estão de acordo com os resultados experimentais. Os resultados experimentais ajustam-se melhor quando os valores dos parâmetros variam no decorrer do tempo. / The hydrodynamic flow is described by means of the equations of the continuity and momentum together with the initial conditions, the boundary conditions. In this research work, the unsteady flow at the exit of a short rectangular channel of zero slope, resulting from the fast opening of a floodgate was investigated experimentally. For determining the pressure coefficient and the length of the upstream reach of the floodgate with non-hydrostatic pressure distribution, a one-dimensional model described by Saint Venant equations is used to represent the phenomenon. The Lax-Wendroff method was used to obtain the curves characteristics of the phenomenon and to compare them with the results obtained experimentally. Several comparisons were made to facilitate the evaluation of values for the parameters that define the region with non-hydrostatic pressure distribution. The results calculated for the values of constant parameters are in agreement with the experimental results. The experimental results are better adjusted when the values of the parameters vary in elapsing of the time.

The performance of reinforced concrete (RC) columns during recent earthquakes has clearly demonstrated the possible failures associated with inadequate confining reinforcement. The confinement reinforcement requirements of older codes were less stringent than present standards. Many studies were conducted by applying different retrofitting techniques for RC columns that have inadequate confinement reinforcement. A new retrofitting technique by means of Carbon Fiber Reinforced Polymer (CFRP) was developed and tested in many countries in the last decade. This technique is performed by CFRP wrapping the critical region of columns. The effectiveness of CFRP retrofitting technique was shown in many studies conducted worldwide. In Turkey, the frame members are considerably deficient from the seismic detailing point of view. Therefore, in order to use the CFRP retrofitting technique effectively in Turkey, experimental evidence is needed. This study investigates the performance of CFRP retrofitted RC columns with deficient confining steel and low concrete strength. It was concluded by experimental and analytical results that the CFRP retrofitting method can be implemented to seismically deficient columns. Moreover, two design approaches were proposed for CFRP retrofit design of columns considering safe design regulations.