Tesis sobre el tema "Hydrodynamic efficiency"

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering; and, (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.
Includes bibliographical references (p. 69-70).
Investigations into unsteady flapping foil propulsion have shown that it is an efficient and high thrust means of propulsion. Extensive work has been done to optimize the efficiency of two-dimensional flapping foils, varying both the kinematics of the motion and the flexibility of the foil. However, no thorough investigation into the hydrodynamic efficiency of three-dimensional flapping foils has been made. In this thesis, experimental hydrodynamic efficiency measurements and force measurements of a three-dimensional flapping foil are presented. These measurements were made by mounting a small, six-axis dynamometer directly onto the foil shaft of a flapping foil module. The module uses two computer controlled servo motors to actuate a foil in a sinusoidal pitch and roll motion, similar to the motion of a penguin's wing. The measured thrust coefficients compared well to previous experimental results, and the on-shaft dynamometer proved to be a valuable sensor. However, the experimental apparatus must be modified before reliable efficiency results can be made for the entire range of kinematics.
(cont.) Once these improvements are made, a thorough investigation into the effects of foil geometry and flexibility can be done to find the optimum efficiency parameters of a three-dimensional flapping foil. These optimum efficiency parameters will be valuable for the development of flapping foil vehicles.
by Karl-Magnus Weidmann McLetchie.
S.M.

An anguilliform swimming robot replicating an idealized motion is a complex marine vehicle necessitating both a theoretical and experimental analysis to completely understand its propulsion characteristics. The ideal anguilliform motion within is theorized to produce ``wakeless'' swimming (Vorus, 2011), a reactive swimming technique that produces thrust by accelerations of the added mass in the vicinity of the body. The net circulation for the unsteady motion is theorized to be eliminated. The robot was designed to replicate the desired, theoretical motion by applying control theory methods. Independent joint control was used due to hardware limitations. The fluid velocity vectors in the propulsive wake downstream of the tethered, swimming robot were measured using Particle Image Velocimetry (PIV). Simultaneously, a load cell measured the thrust (or drag) forces of the robot via a hydrodynamic tether. The measured field velocities and thrust forces were compared to the theoretical predictions for each. The desired, ideal motion was not replicated consistently during PIV testing, producing off-design scenarios. The thrust-computing method for the ideal motion was applied to the actual, recorded motion and compared to the load cell results. The theoretical field velocities were computed differently by accounting for shed vortices due to a different shape than ideal. The theoretical thrust shows trends similar to the measured thrust over time. Similarly promising comparisons are found between the theoretical and measured flow-field velocities with respect to qualitative trends and velocity magnitudes. The initial thrust coefficient prediction was deemed insufficient, and a new one was determined from an iterative process. The off-design cases shed flow structures into the downstream wake of the robot. The first is a residual disturbance of the shed boundary layer, which is to be expected for the ideal case, and dissipates within one motion cycle. The second are larger-order vortices that are being shed at two distinct times during a half-cycle. These qualitative and quantitative comparisons were used to confirm the possibility of the original hypothesis of ``wakeless'' swimming. While the ideal motion could not be tested consistently, the results of the off-design cases agree significantly with the adjusted theoretical computations. This shows that the boundary conditions derived from slender-body constraints and the assumptions of ideal flow theory are sufficient enough to predict the propulsion characteristics of an anguilliform robot undergoing this specific motion.

The ability of fish to deform their bodies in steady swimming action is gaining from robotic designers. While bound by the same physical laws, fish have evolved to move in ways that often outperform artificial systems in critical measures such as efficiency, agility, and stealth through thousands of years of natural selection. As we expand our presence in the ocean with deep-sea exploration or offshore drilling for petroleum and natural gas, the demand for prolonging underwater operations is growing significantly. Therefore, it is critical for robotic designers to understand the physics of pisciform (fish-like) locomotion and learn how to effectively implement the propulsive mechanisms into their designs to create the next generation of aquatic robots. Aiming to assist this process, this thesis presents an experimental apparatus called Towed Biolocomotion Emulator (TBE), which is capable of imitating the undulating action of different fish species in steady swimming and can be quickly adapted to different configurations with modular modules. Using the TBE device, an experiment is performed to test its hydrodynamic performance and evaluate the effectiveness of the bio-inspired locomotion implemented on such a mechanical system. The analysis of hydrodynamic data collected from the experiment shows that there exists a small range of kinematic parameters where the undulating motion of the device produces the optimal performance. This result confirms the benefits of utilizing pisciform locomotion for small-scale underwater vehicles. In addition, this thesis also proposes a reduced-order flow model using the unsteady vortex lattice method (UVLM) to predict the hydrodynamic performance of such a system. The proposed model is then validated with the experimental data collected earlier. The tool developed can be employed to quickly explore the possible design space early in the conceptual design stage for such a bio-mimetic vehicle.
Master of Science
It is no surprise that through thousands of years of natural evolution, marine species possess incredible ability to navigate through water. As we expand our presence in the sea, more and more tasks require underwater operations such as ocean exploration, oil-rig maintenance, etc. Yet, most of the underwater robotic vehicles still utilize propellers as the primary propulsive mechanism. In many cases, the bio-inspired propulsion system that mimics the swimming action of fish offers many advantages in agility, maneuverability, and stealth. With the rising interest in the field, the works presented in this thesis aim to expand our understanding of how to implement the bio-inspired propulsive mechanism to robotic design. To achieve this, a mechanical device is designed to mimic the swimming action of different fish species. Then, an experiment is performed to subject the device to different fish-like motions and test their effectiveness. In addition, a reduced-ordered model is also introduced as an alternative method to predict the hydrodynamic performance of this propulsive mechanism. The works presented in this thesis help to expand the toolbox available for the engineer to design the next generation of the underwater robotic vehicle.

Denna studie handlar om den fartförlust och därmed den ökade energiförbrukningen som drabbar fartyg på grunt vatten. Syftet var att ta reda på hur mycket kortare en grund passage behöver vara för att den ska vara ett bättre alternativ än en lång och djup rutt med hänsyn till bränsleförbrukning och tidsåtgång. Resultatet av detta blev att det inte går att dra några generella slutsatser som gäller för alla fartygstyper men att det går att se tydliga tendenser. Studien hade även som målsättning att skapa ett underlag som skulle kunna användas av nautiker vid planering av resor, detta presenterades i form av en sammanställning av de resultat som erhållits vid beräkning av fartförlust i öppet vatten. Någon sammanställning gjordes inte för begränsat vatten eftersom exempelfartygen där fick likadana resultat vilket skulle ha gjort en sådan överflödig. Syftet uppnåddes genom användande av kvantitativa studier i form av matematiska beräkningsmetoder för att beräkna fartförlust, bränsleförbrukning och tidsåtgång för ett antal exempelfartyg.
This study concerns the speed loss and thereby the increased energy consumption which affects ships in shallow water. The aim of the study was to gain knowledge of how much shorter a shallow passage is required to be in order to be the better alternative compared to a long and deep route with regard to fuel and time consumption. The result was that it is not possible to draw any definitive conclusions which are applicable to all ship types, however, there are clear patterns. Moreover, the goal of the study was to aid mariners facing a choice between a long and deep route and a short and shallow route, this was done by creating a compilation of the results for speed loss in open water. Due to the results for confined waters being the same for all the ships in the study, no compilation was done for confined waters as it was deemed excessive. The aim of the study was achieved by quantitative research in the form of mathematical models to calculate speed loss, fuel consumption and time consumption for a number of fictitious ships.

Although oscillating water column type wave energy devices are nearing the stage of commercial exploitation, there is still much to be learnt about many facets of their hydrodynamic performance. This research uses the commercially available FLUENT computational fluid dynamics flow solver to model a complete OWC system in a two dimensional numerical wave tank. A key feature of the numerical modelling is the focus on the influence of the front wall geometry and in particular the effect of the front wall aperture shape on the hydrodynamic conversion efficiency. In order to validate the numerical modelling, a 1:12.5 scale experimental model has been tested in a wave tank under regular wave conditions. The effects of the front lip shape on the hydrodynamic efficiency are investigated both numerically and experimentally and the results compared. The results obtained show that with careful consideration of key modelling parameters as well as ensuring sufficient data resolution, there is good agreement between the two methods. The results of the testing have also illustrated that simple changes to the front wall aperture shape can provide marked improvements in the efficiency of energy capture for OWC type devices.

Corrosion within the oil and gas sector is an ongoing concern for operators. The challenging nature of extraction and processing fluids is an unavoidable cause of severe metallic corrosion. With modern emphasis on health, safety and the environment, the case for managing corrosion has become an imperative agenda. Whilst new and more effective methods of mitigation are key, an interim solution is improving the value of current methods. A literature survey carried out within this project has revealed CO2 corrosion as contributing to most corrosion related failures within the industry. The corrosion behaviour in CO2 containing environments is complex partly due to the wide range of prevailing conditions such as temperature, CO2 concentration and flow conditions. For oil and gas transportation pipelines, internal corrosion mitigation can be achieved by the use of chemical inhibitors. Inhibitors have been established to be effective but are by no means a complete solution. Issues such as their effectiveness in high velocity and high shear flow are a main consideration for their function. The hydrodynamic nature of the flowing fluids can affect inhibitor efficiency by either slowing the rate of formation of the inhibitive layer or causing degradation of well-formed inhibitive layers. A combined effect may also be active. The corrosion behaviour of carbon steel in simulated oilfield conditions is investigated in this project with emphasis on conditions of varying velocity, impinging flow and consequently shear stress. Since inhibition is the main mitigation technique for fluid related corrosion, the efficiency of a commercially used inhibitor is, in this case assessed in the abovementioned conditions. To simulate both impingement and flow, a jet impingement apparatus is used in conjunction with a segmented-electrode specimen set up to separately study the erosion-corrosion behaviour of different hydrodynamic zones under the jet. Corrosion rates are measured by gravimetric analysis and results are also evaluated with electrochemistry. Additionally, galvanic interactions between the different hydrodynamic zones have been investigated. Visual and light-optical microscopic examinations are also used to assess variable effects within the zones. Under such conditions, the corrosion rates have been found to be significantly higher in impingement zones. Aerated conditions have shown a significant variation in corrosion behaviour between impingement and non-impingement zones. The results in CO2 saturated brines are consistent but with evidence of different relations between hydrodynamics and the corrosion rate. The inhibitor has been shown to be effective in CO2 saturated brines and significantly influenced by both inhibitor concentration and hydrodynamic conditions. Inhibitor efficiency has also shown a complex dependence on concentration and establishes a need to evaluate optimum inhibitor concentrations before field application. Evaluation of the mass loss results against electrochemistry has shown a large discrepancy between the two methods. This rather surprising result suggests solid-free flow is not entirely free of erosion and synergistic effects. This comprehensive study has not only improved current knowledge on the relation between hydrodynamics and inhibitor efficiency but also indicates a critical need to evaluate suitability of current monitoring methods. Electrochemical methods are increasingly used as a method of choice and while they contribute significant monitoring data, they are observed to be unable, alone, to monitor erosion and synergy. An industry review on their suitability to monitor solid-free flow corrosion is recommended.

Numerous studies have shown that cardiac diastolic dysfunction and diastolic filling play a critical role in dictating overall cardiac health and demonstrated that the filling wave propagation speed is a significant index of the severity of diastolic dysfunction. However, the governing flow physics underlying the relationship between propagation speed and diastolic dysfunction are poorly understood. More importantly, currently there is no reliable metric to allow clinicians the ability to diagnose cardiac dysfunction. There is a greater need than ever for more accurate and robust diagnostic tools with the increasing number of deaths caused by this disease. Color M-mode (CMM) echocardiography is a technique that is commonly used in the diagnosis of Left Ventricular Diastolic Dysfunction (LVDD) and is used as the image modality in this work. The motivation for the current work is a hypothesized change in the mechanism driving early diastolic filling. The early filling wave of a healthy patient is driven by a rapid early diastolic relaxation creating a pressure difference within the left ventricle despite the fact the left ventricular volume is increasing. As diastolic dysfunction progresses, the left ventricular relaxation declines and it is hypothesized that the left atrial pressure rises to create the favorable pressure difference needed to drive early diastole. This changes the mechanism driving early diastolic filling from a pulling mechanism primary driven by left ventricular relaxation to a pushing mechanism primarily driven by high left atrial pressure. Within this study, CMM echocardiography images from 125 patients spanning healthy and the three stages of LVDD are analyzed using a newly developed automated algorithm. For the first time, a series of isovelocity contours is utilized to estimate the conventional propagation velocity. A critical point within the early filling wave is quantified as the point of early filling velocity deceleration. The clinically used propagation velocity is compared to a novel critical point propagation velocity calculated as a weighted average of the propagation velocities before and after the critical point showing an increase in the correlation between decreasing diastolic dysfunction stage and decreasing propagation velocity. For the first time the spatial pressure distributions calculated as the pressure relative to the mitral valve pressure at each location from the mitral valve to the ventricular apex, are quantified and analyzed at the instant of peak mitral to apical pressure difference for patients with varying stages of LVDD. The analysis of the spatial pressure distribution revealed three filling regions present in all patients. The pressure filling regions were used to calculate a useful filling efficiency with healthy patients having a useful filling efficiency of 64.8 ± 12.7% and severely diseased filling patients having an efficiency of 37.1 ± 12.1%. The newly introduced parameters and analysis of the CMM echocardiography data supports the hypothesis of a change in the mechanism driving early diastolic efficiency by displaying a decline in the early diastolic propagation velocity earlier into the left ventricle for severely diseased patients than for healthy filling patients and a premature breakup of the progressive pressure gradient fueling early diastolic filling in severely diseased patients.
Master of Science

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2010.
ENGLISH ABSTRACT: Immersed membrane systems hold many operational and environmental advantages in biological treatment of wastewater. However, immersed membrane filtration have only found application in niche markets to date because of higher capital and operating costs associated with membrane fouling. But with capital costs on the decline as membranes become less expensive, immersed membrane systems are increasingly considered as an attractive alternative to conventional treatment processes. Operating costs remain high however, since energy intensive techniques such as air-sparging are required to limit membrane fouling. Improving the air-scouring efficiency of air-sparged immersed membranes can significantly reduce operating costs and unlock the immersed membrane system technology to wider application. The aim of this study was to identify factors that will improve air-scouring efficiency in order to produce guidelines that will help in the development of an immersed microfiltration membrane system with a resulting lower operating cost. Although, the research was done on a flat-sheet microfiltration membrane, the guidelines obtained can be used for the development of any immersed microfiltration membrane arrangement. An airlift reactor set-up was chosen for this study. Six system hydrodynamic factors were evaluated in a factorial design to determine their effects on the cross-flow velocity profile. They were the downcomer area to riser area ratio, top clearance distance, bottom clearance distance, aeration intensity, water depth and air sparger location. It was found that the air-scouring efficiency was increased by generating a cross-flow velocity profile with increased magnitude and uniformity, but absolute uniformity of the cross-flow velocity profile was found to be a prerequisite for optimisation of air-scouring efficiency. Downcomer area to riser area ratio was found to be 99.9% significant in determining the magnitude of the cross-flow velocity profile. Two models were developed to respectively predict the relative magnitude and uniformity of the cross-flow velocity profile. By using these two models, a methodology was developed to design an airlift reactor set-up that would produce system hydrodynamics with an improved air-scouring efficiency.
AFRIKAANSE OPSOMMING: Gesonke membraanstelsels beskik oor talle bedryfs- en omgewingsvoordele in biologiese behandeling van afvalwater. Maar weens die hoër kapitaal- en bedryfskostes wat gepaardgaan met membraanbevuiling, kon gesonke membraanstelsels tot op hede nog net toepassing in nismarkte vind. Maar soos kapitaalkoste daal met al hoe goedkoper membrane beskikbaar, word gesonke membraanstelsels al hoe aanlokliker as ‘n alternatief vir konvensionele behandelingsprosesse. Bedryfskostes bly egter hoog aangesien energie-intensiewe tegnieke soos lugborreling benodig word om membraanbevuiling te vertraag. Deur die effektiwiteit van die skropaksie wat lugborreling aan gesonke membrane bied te verbeter, kan ‘n beduidende besparing in bedryfskostes teweeggebring word om sodoende die uitgebreide toepassing van gesonke membraanstelsel tegnologie moontlik te maak. Hierdie studie het ten doel gehad die identifisering van faktore wat lugskropaksie effektiwiteit kan verbeter en om riglyne op te stel vir die ontwikkeling van ‘n gesonke mikrofiltrasie membraanstelsel met gevolglik laer bedryfskostes. Alhoewel hierdie navorsing ‘n plat-blad mikrofiltrasie membraan gebruik het, kan die riglyne steeds vir enige gesonke mikrofiltrasie membraanuitleg gebruik word. Daar is besluit op ‘n lugligter-reaktor opstelling vir hierdie studie. Ses stelselhidrodinamika faktore is geëvalueer in ‘n faktoriale ontwerp om hul effekte op die kruisvloei snelheidsprofiel te bepaal. Hulle was die afvloei-area tot opvloei-area verhouding, topruimte-afstand, bodemruimte-afstand, belugtingsintensiteit, waterdiepte en belugterligging. Daar is bevind dat die lugskropaksie effektiwiteit verhoog word wanneer ‘n kruisvloei snelheidsprofiel geskep word met ‘n verhoogde grootte en gelykvormigheid, maar die absolute gelykvormigheid van die kruisvloei snelheidsprofiel is gevind om ‘n voorvereiste te wees vir optimale effektiwiteit. Afvloei-area tot opvloei-area verhouding is gevind om 99.9% beduidend te wees in die bepaling van die snelheidsprofiel se grootte. Twee modelle is ontwikkel om afsonderlik die relatiewe grootte en gelykvormigheid van die kruisvloei snelheidsprofiel te voorspel. Die modelle is in ‘n metodologie vervat vir die ontwerp van ‘n lugligter opstelling met stelselhidrodinamika wat verbeterde lugskropaksie effektiwiteit sal skep.

Energy efficiency and propulsive characteristics of a 10 cm undulatory rainbow trout (oncorhynchus mykiss) swimming in a stationary position are considered. Two CFD simulations are performed utilizing dynamic grid meshing (FLUENT 6.3). The first simulation uses a laminar flow model with an added hydrofoil shape in order to test if thrust and drag can be brought to unity. The second simulation uses a Large-Eddy Simulation (LES) turbulence model to determine if transition to turbulence along the fish's surface leads to boundary layer separation. The expected results caused by adding these two features to earlier simulations do not occur. Thrust and drag are not found to be equal with usage of the thicker fish shape; instead both thrust and drag increase by 40-80% while diverging in value. Evidence of boundary layer separation is not present with usage of the LES turbulence model. Swimming energy efficiency is calculated to be 70% in both simulations. A brief analyses of boundary layer and downstream wake are included, showing general agreement with earlier studies. Limitations of the simulation are discussed. Future work regarding the author's preparation for an additional simulation of a rainbow trout utilizing a swimming method known as the Karman Gait is also considered. This preparation includes the creation of a 2-D grid domain and programs to define the kinematics of the fish and produce a specified vortex inlet condition.

Several types of reactors are encountered in industry where reagents in a gas and a liquid phase need to be catalysed by a solid catalyst. Common reactors that are used to this end, are trickle-bed reactors, where gas and liquid flow cocurrently down a packed bed of catalyst. Apart from the catalytic process itself, several mass transfer steps can influence the rate and/or selectivity of a solid catalysed gas-liquid reaction. In trickle-bed reactors, flow morphology can have a major effect on these mass transfer steps. This study investigates the interaction between liquid flow morphology and mass transfer in trickle-bed reactors from three different angles. The primary focus is on liquid-solid mass transfer and internal diffusion as affected by the contacting between the liquid and the catalyst. First, the contacting between the liquid and the solid in trickleflow, or wetting efficiency, is characterised using colorimetry. Though this investigation is limited to the flow of nitrogen and water over a packed bed at ambient conditions, it provides useful information regarding liquid flow multiplicity behaviour and its influence on the distribution of fractional wetting on a particle scale. The colorimetric study also provides descriptions of the geometry of the liquid-solid contacting on partially wetted particles. These are used in a second investigation, for the numerical simulation of reaction and diffusion in partially wetted catalysts. This second investigation uses numerical simulations to evaluate and develop simple theoretical descriptions of liquid-solid contacting effects on catalyst particle efficiency. Special attention is given to the case where external and intraparticle mass transfer rates of both a volatile and non-volatile reagent affect the overall rate of reaction. Also, since these are not often considered in theoretical studies, some suggestions are made for the evaluation of the particle efficiency of eggshell catalyst. Finally, liquid-solid contacting is investigated in a high-pressure pilot reactor. Wetting efficiency is measured with a useful technique that does not rely on descriptions of particle kinetics or liquid-solid mass transfer rates. Liquid-solid mass transfer coefficients are also measured and results agree well with the colorimetric investigation, suggesting the existence of different types of flow within in the hydrodynamic multiplicity envelope of trickle-flow. Since it consists of different investigations of liquid-solid contacting from different angles, the study highlights several aspects of liquid-solid contacting and how it can be expected to influence trickle-bed reactor performance.
Thesis (PhD)--University of Pretoria, 2009.
Chemical Engineering
unrestricted

This master thesis deals with qualifications of the catalytic materials for positive electrode low-temperature fuel cells. The teoretical part focuses on the physical and chemical properties of low-temperature fuel cells. There are described methods of hydrodynamic RDE and RRDE. RRDE study utilizes methods linear and cyclic voltammetry for qualifying performance of catalytic materials and presentation of results. The practical part describes the preparation various types of carbon materials. There are monitored the oxygen reduction using RRDE. Catalytic materials are evaluated: CV, stability, kinetic parameters, creation of intermediate H2O2 and kinetics of electrode reactions.

La connectivité est supposée influencer fortement la dynamique et la pérennité des populations d’organismes marins. Ainsi, étudier l’évolution et le maintien des patrons de connectivité au sein des populations marines semble essentiel pour la planification spatiale, la création et la gestion des Aires Marines Protégées (AMP). Cependant, comprendre la complexité des processus régissant la connectivité entre les populations marines nécessite l’utilisation d’outils, qui associent des modèles biophysiques et des informations caractérisant les relations entre démographie et génétique, résultant des échanges larvaires entre les populations. L’objectif de cette thèse de doctorat est donc, d’évaluer les patrons de connectivité génétique au sein des populations de gorgones à une échelle régionale et d'explorer les processus induisant la connectivité observée, grâce à des simulations de modèles prenant en compte les connectivités hydrologique, démographique et génétique. Le premier chapitre présente un modèle de métapopulation spatialement explicite qui, grâce à l’utilisation de matrices de connectivité stochastique, permet d’évaluer l’effet de la démographie sur la fréquence des allèles dans une métapopulation d’espèces marines benthiques sessiles. Le modèle est alors utilisé pour déterminer l’effet des traits démographiques et de la structure de connectivité sur la diversité génétique de la métapopulation. Le deuxième chapitre présente une analyse des patrons de connectivité génétique de deux espèces communes et largement répandues de gorgones, à une échelle régionale : Paramuricea clavata en mer de Ligure et Eunicella singularis dans le Golfe du Lion. Les deux espèces présentent de forts patrons de structure génétique à l’échelle régionale, bien que leur capacité de dispersion ne semble pas limitante (>100m). Le troisième chapitre vise à tester si la dispersion larvaire seule permet d'expliquer la connectivité réalisée d’E. singularis dans le Golfe du Lion, en appliquant le modèle présenté dans le Chapitre 1, et en comparant les patrons de structure génétique modélisés, aux résultats obtenus dans le Chapitre 2, par les méthodes empiriques d’analyse de données génétiques. Les patrons de structure génétique modélisés en ne prenant en compte que la structure spatiale de dispersion sont similaires à ceux observés entre les populations d’E. singularis dans cette région, suggérant le rôle prépondérant de la connectivité hydrologique dans la distribution régionale de l'espèce, tant au niveau démographique que génétique. La capacité d’évaluer le développement des structures génétiques entre populations, sous différents scénarios démographiques et hydrologiques, avec le modèle de paysage sous-marin présenté dans le Chapitre 1 s'avère donc un outil efficace pour la planification spatiale et la pérennité des populations marine
Connectivity is expected to strongly influence the dynamics and persistence of marine populations. Studying the development and maintenance of connectivity patterns among marine populations is, thus, essential for spatial planning and the proper design and management of Marine Protected Areas (MPAs). However, understanding the complex processes driving marine population connectivity requires the use of tools that integrate bio-physical models with information regarding the demographic and genetic linkages resulting from the larval exchange among populations. Therefore, the aim of this PhD dissertation is to evaluate the patterns of genetic connectivity among gorgonian populations at a regional scale, and disentangle the processes that shape the observed connectivity by using model simulations accounting for hydrological, demographic and genetic connectivity. The first chapter presents a spatially explicit metapopulation model that, using stochastic connectivity matrices, assesses the effect of demography on allele frequencies in a marine metapopulation of sessile benthic species. The model is then used to evaluate the effect of demographic traits and connectivity structure on the genetic diversity of a marine metapopulation. The second chapter examines the patterns of genetic connectivity of two common and widely distributed gorgonian species at a regional scale: Paramuricea clavata in the Ligurian Sea, and Eunicella singularis in the Gulf of Lions. Both species exhibit strong patterns of genetic structure at a regional scale, although the dispersal capacity of each species does not seem limited (>100 m). The third chapter discerns among the potential processes shaping the realized connectivity of E. singularis in the Gulf of Lions by applying the model presented in Chapter 1, and comparing the modeled patterns of genetic structure to the results obtained from empirical genetic data in Chapter 2. Modeled and empirical results show similar patterns of genetic structure among populations of E. singularis in the region. Genetic and demographic differentiation among populations is demonstrated to result from the spatial structure of dispersal alone. The ability to evaluate the expected development of genetic structure among populations under different demographic and hydrological scenarios using the seascape model presented in Chapter 1 provides a useful tool with relevance for marine spatial planning and the persistence of marine populations

This document contains a proposal for the creation of a simulator that can accurately model the interaction of electromagnetic (EM) and semiconductor effects for modern wireless devices including nonlinear and/or active devices. The proposed simulator couples the balanced semiconductor equations (charge, momentum, kinetic energy) with a FDTD full-wave Yee-based electromagnetic (EM) simulator. The resultant CAD tool is able to model the response of one semiconductor device to both small signal and DC bias based on the process parameters (material, charge distribution and doping) without any a-priori knowledge of the device performance characteristics, thus making it extremely useful in modeling and integrating novel devices in RF and Wireless topologies. As a proof of concept an n+--i--n+ diode will be simulated. In the future, more complicated structures, such as MODFETs, will be modeled as well.

Дисертація присвячена питанням теоретичних та експериментальних досліджень процесу сушіння у робочому просторі багатоступеневих гравітаційних поличних сушарок із вертикальним секціонуванням робочого простору. Запропоновано аналітичні рівняння, що описують: закономірності сушіння одиночної частинки та їх сукупності; гідродинаміку руху газового потоку, одиночної частинки та дисперсного матеріалу в режимі стисненого потоку; ефективність ступеневого сушіння дисперсного матеріалу на кожній полиці каскаду і в апараті в цілому. Експериментально визначено режими роботи сушарки, досліджено вплив конструкції полиці та організації руху сушильного агента на гідродинамічні показники руху потоків у робочому просторі гравітаційної поличної сушарки та інтенсивність зневоднення дисперсного матеріалу, одержано критеріальну залежність, що дозволяє прогнозувати значення коефіцієнта масовіддачі під час сушіння в гравітаційних поличних сушарках. На базі створених фізичної та математичної моделей і проведених експериментальних досліджень розроблено методику інженерного розрахунку багатоступеневих сушарок поличного типу з визначенням основних геометричних характеристик апарата і температурно-вологісних параметрів потоків дисперсного матеріалу та сушильного агента. Запропонована методика оцінювання енергоефективності процесу сушіння дисперсних матеріалів за критерієм питомих енерговитрат на інтенсифікацію. Запропоновані та захищені патентами України нові високоефективні пристрої для здійснення процесу сушіння. Проведено дослідно-промислове впровадження поличних сушарок із порівняльним аналізом товарної продукції, результати якого показали високу ефективність розробленого обладнання.
Диссертация посвящена вопросам теоретических и экспериментальных исследований процесса сушки в рабочем пространстве многоступенчатых гравитационных полочных сушилок с вертикальным секционированием рабочего пространства. Предложена физическая модель движения взаимодействующих потоков, что позволяет определить периоды сушки дисперсного материала касательно особенностей проведения данного процесса в гравитационной полочной сушилке. Создана математическая модель, описывающая: 1) закономерности сушки одиночной частицы и частиц во взвешенном слое в режиме стеснённого движения с определением времени прогрева и обезвоживания дисперсного материала; 2) гидродинамику движения газового потока, одиночной частицы и частицы в режиме стеснённого движения с определением времени пребывания дисперсной фазы в рабочем пространстве сушилки; 3) температурно-влажностные характеристики взаимодействующих потоков и эффективность каждой ступени сушилки с учетом гидродинамики рабочего пространства аппарата, конструкции полок, свойств сушильного агента и способа организации его движения. Экспериментально установлено влияние конструкции полки и организации движения сушильного агента на гидродинамические характеристики работы гравитационной полочной сушилки и время пребывания дисперсного материала в объеме аппарата. Определены основные гидродинамические режимы работы гравитационной полочной сушилки в зависимости от нагрузки по потокам, а также время пребывания дисперсной фазы в каждом из режимов. Получена критериальная зависимость, позволяющая прогнозировать значение коэффициента массоотдачи при сушке в гравитационных полочных сушилках. Получены данные о температурно-влажностных характеристиках взаимодействующих потоков и эффективности ступеней сушилки в зависимости от конструкции полки и организации движения сушильного агента. Показано, что за счет изменения конструкции полки и организации движения сушильного агента возможно управление временем пребывания обезвоживаемого материала и значением эффективности каждой ступени сушилки. На основе созданных физической и математической моделей и проведенных экспериментальных исследований разработана методика инженерного расчета многоступенчатых сушилок полочного типа с определением основных геометрических характеристик аппарата и температурно-влажностных параметров потоков дисперсного материала и сушильного агента. Предложена методика оценки энергоэффективности процесса сушки дисперсных материалов по критерию удельных энергозатрат на интенсификацию. Предложены и защищены патентами Украины новые высокоэффективные устройства для осуществления процесса сушки. Проведено опытно-промышленное внедрение полочных сушилок со сравнительным анализом товарной продукции, результаты которого показали высокую эффективность разработанного оборудования.
Thesis is devoted to theoretical and experimental researches of the drying process in the workspace of multistage shelf gravitational dryers with vertical sectioning of the workspace. In thesis it is proposed the analytical equations describing: regularities of a single particles drying and their aggregates; hydrodynamics movement of the gas flow, single particles and disperse material in the compressed flow regime; efficiency of stage drying of disperse material on each cascade shelf and totally in the device. The regimes of dryers were determined experimentally, it was studied the influence of shelf design and the organization of the drying agent movement on hydrodynamic indicators of flows movement in the working space of gravitational shelf dryer and intensity of disperse material dehydration, it is received the criteria dependence that allows to predict the value of the mass-transfer coefficient while drying in the gravitational shelf dryers. The methodology of engineering calculation of multistage shelf-type dryers with the determination of the basic geometric characteristics of the device and temperaturemoisture parameters of dispersed material and drying agent flows was developed based on the established physical and mathematical models and conducted experimental researches. It is proposed the methodology of energy efficiency evaluation of the drying of dispersed materials due the criterion of the specific energy consumption for intensification. New high-effective devices for the drying process are proposed and patented in Ukraine. Experimental and industrial adoption of shelf dryers was made alongside with the comparative analysis of commodity output, the results of which demonstrated the high efficiency of the devices.

The standard approach to modelling fluid flow through a porous medium was developed decades ago, when computational resources were insufficient to feasibly simulate the flow directly. In this thesis, the feasibility of such flow simulation with modern computing power is demonstrated via the development of three accurate and efficient dual-scale models of porous media flow. An important outcome of the research is that the new dual-scale modelling framework accurately and efficiently simulates flows with a range of Reynolds numbers through a variety of heterogeneous porous media.

Les procédés électrochimiques d'oxydation avancée constituent une technologie efficace pour traiter les produits pharmaceutiques car ils permettent la formation d'oxydants puissants tels que les radicaux hydroxyles capables d'éliminer presque tout type de contaminants organiques grâce à leur très haut pouvoir oxydant. Parmi eux, l’électro-Fenton et l’oxydation anodique sont des méthodes respectueuses de l'environnement car ils n'utilisent aucun réactif chimique (oxydation anodique) ou uniquement l'oxygène de l'air et des ions fer en tant que catalyseur (électro-Fenton).Dans cette thèse, quatre produits pharmaceutiques appartenant à des familles différentes ont été sélectionnés en fonction de leur toxicité et de leur présence dans les eaux de l'environnement. Leur élimination de l'eau a été effectuée par électro-Fenton. Les objectifs de ce travail étaient de déterminer (i) les meilleures conditions opératoires à l’échelle du laboratoire (courant et concentration du catalyseur), (ii) la cinétique de dégradation et de minéralisation et enfin (iii) de proposer une voie de minéralisation basée sur des intermédiaires aromatiques, des acides carboxyliques et des ions libérés dans la solution.Comme ces traitements ont été appliqués avec succès, un réacteur pilote composé alternativement d'anodes en BDD et de cathodes en feutre de carbone, doté d’un système d'aération et fonctionnant en mode continu a été construit pour évaluer la faisabilité d’un changement d’échelle et se diriger vers une pré-industrialisation du procédé. Différentes configurations d'électrodes ont été testées. Le débit et le courant se sont avérés être plus influents sur le taux de minéralisation et sur la consommation d'énergie, respectivement. Pour mieux comprendre le rôle du débit et des configurations, une étude hydrodynamique a été réalisée. Le modèle hydrodynamique a été associé à un modèle cinétique de minéralisation afin d'obtenir un modèle permettant de prédire le pourcentage de minéralisation à différentes positions à l'intérieur du réacteur en régime permanent. Ainsi, ce modèle peut aider à optimiser les conditions opératoires et à dimensionner les futurs réacteurs en fonction de l’objectif de minéralisation du traitement (taux de minéralisation élevé, traitement combiné, flux élevé,…).Afin de réduire les coûts opératoires, la combinaison d’un procédé électrochimique et d’un traitement biologique a ensuite été étudiée. Afin d’obtenir un traitement combiné efficace, il a été constaté que le traitement électrochimique devait (i) dégrader l'hydrochlorothiazide (ii) réduire de manière significative la concentration de ses intermédiaires aromatiques car ils inhibent de manière significative l'activité bactérienne, (iii) favoriser la formation de molécules biodégradables telles que les acides carboxyliques. La biodégradation de quatre acides carboxyliques formés lors du traitement par électro-Fenton de l'hydrochlorothiazide a également été étudiée. Il a été démontré qu'ils étaient dégradés de manière séquentielle avec différentes phases de latence et cinétiques de dégradation. Ainsi, pour les minéraliser, un réacteur de type «piston» est recommandé. La combinaison de traitement a ensuite été appliquée à un traitement électrochimique effectué à faible courant avec une anode en BDD et une anode en Platine. Un degré de minéralisation de 38 et 50% a été obtenu par le traitement biologique permettant d'atteindre un taux de minéralisation global de 66 et 85% avec les anodes en BDD et Platine respectivement. Ainsi, cette combinaison de traitement a été un succès, un changement d’échelle du procédé peut alors être envisagé
Electrochemical advanced oxidation processes (EAOPs) constitute an efficient technology to treat the pharmaceuticals as they allow the formation of strong oxidants such as hydroxyl radicals able to remove nearly any type of organic contaminants thanks to their very high oxidation power. Among them the electro-Fenton and anodic oxidation processes are environmentally friendly methods as they use no chemical reagent (anodic oxidation) or only oxygen of air and iron ions as a catalyst (electro-Fenton).In this thesis, four pharmaceuticals from different families and structures were selected based on their toxicity and their occurrence in environmental waters and their removal from water was performed by EAOPs. The objectives of this work were to determine the best operating conditions at lab scale (current and catalyst concentration), investigate the kinetic of degradation and mineralization and finally propose a mineralization pathway based on aromatic intermediates, carboxylic acids and ions released to the solution.As these treatments were successfully applied, a lab scale pilot reactor composed alternately of BDD anodes and carbon felt cathodes with a bottom aeration system and working in the continuous mode was built to scale-up these processes in order to pre-industrialize them. Different configurations of electrodes were tested. The flow rate and the current were found to be more influent on the mineralization rate and on the energy consumption, respectively. To deeper understand the role of the flow rate and the configurations a hydrodynamic study was performed. The hydrodynamic results were gathered with a kinetic model for the mineralization to obtain a model predicting the percentage of mineralization at different position inside the reactor during the steady state. Thus, this model can help to optimize the operating conditions and to size future reactors depending on the mineralization objective of the treatment (high mineralization rate, combined treatment, high flow, …).To reduce operating cost, the combination of an electrochemical process and a biological treatment was then investigated. In this frame, it was found that electrochemical treatment can (i) degrade the hydrochlorothiazide (ii) reduce significantly the concentration of its aromatic intermediates as they were shown to significantly inhibit the bacterial activity, (iii) promote the formation of biodegradable molecules such as carboxylic acids. The biodegradation of four carboxylic acids formed during the electro-Fenton treatment of the hydrochlorothiazide at lab scale was also studied. It was demonstrated that they were sequentially degraded with different lag phases and kinetics of degradation. Thus to mineralize them, a “plug flow” type reactor is recommended. The combination of treatment was then applied with an electrochemical treatment performed at low current with a BDD anode and a Platine anode. A mineralization degree of 38% and 50% were obtained by the biological treatment enabling to globally reach a mineralization rate of 66% and 85% with the BDD and the Platine anodes respectively. Thus this combined treatment was successful and open the way for the scale-up of these processes

碩士
國立成功大學
航空太空工程學系
105
Nowadays, renewable energy plays a crucial role in building a more sustainable life for the world by cutting back the energy consumption from traditional fossil fuel sources-the main cause of global warming. Beside the conventional kinds of renewable energy such as wind and solar, marine current energy has yet been significantly deployed although it has the greatest potential of energy. One of the recent technology for marine tidal current energy conversion is the utilization and adaptation of the conventional horizontal-axis turbine with the implementation of diffuser-augmented duct. This duct enables the turbine performance be raised a significant percentage. The main purpose of this research is to study the possibility and physics that can further enhance the hydrodynamic performance of the diffuser-augmented tidal turbine with a nozzle add-on device. Hydrodynamic performance assessment and model design is based on computational fluid dynamics (CFD) simulations. A comparison of the potential performance of the original ducted turbine and the modified models with nozzle add-on was also carried out. The add-on nozzle is designed to create a converged channel surrounding the duct outlet in order to accelerate the outbound flow and create a pressure drop surrounding the duct outlet. Hence, it creates a larger pressure difference between the inlet and outlet flow of the system. Wider pressure difference will result in a greater mass flow entering the system leading to the improvement in power output. Moreover, the pressure difference also is bigger across the blade surface and generates bigger torque and power output. Parametric study of the design in various configurations, mainly the nozzle length and the nozzle inlet/outlet area ratios, have been conducted to understand the influence of the geometric parameters on the turbine performance. The results confirmed that the overall hydrodynamic efficiency of the diffuser-augmented turbine has been significantly improved. The maximum hydrodynamic efficiency improvement was found to be equal to 28.2% with the nozzle add-on device implemented.

碩士
國立中山大學
機械工程學系研究所
88
Abstract The removing efficiency of surface roughness for the hydrodynamic polishing process under semi-contact lubricating condition was investigated in this thesis. The experimental relationships between surface roughness and polishing were first examined. From the relationships, the potential influential factors of the removing efficiency and the magnitude of surface roughness were identified. Finally, a mathematical model that was related to the removing efficiency and the magnitude of surface roughness was proposed. Based on the experimental study, it was shown that the surface roughness would be rapidly reduced at the beginning by polishing process and then hardly improved afterward. This trend implied that surface roughness would not be completely removed during the polishing process. It was proposed that the amplitude and wavelength of surface roughness would affect the removing efficiency of surface roughness. Further, the removing efficiency was not sensitive to the tool velocity. From the mathematical model, several points were concluded. First, the removing efficiency was positively proportional to the amplitude of surface roughness. Second, the removing efficiency was inversely to the amplitude of surface roughness. Third, the removing efficiency was inverse proportional to a waviness of tool surface. Fourth, the removing efficiency was not sensitive to tool velocity. Finally, there existed an achievable minimum surface roughness for a surface with specific wavelength. The magnitude of a minimum surface roughness was shown to be proportional to the wavelength of work surface.

碩士
國立中興大學
水土保持學系所
104
This research aims to evaluate the efficiency of dredging scenarios in Malun stream by using CCHE-2D hydrodynamic model. The dredging scenarios were: do-nothing, dredge at the main stream with compound cross-section, and dredge at the confluence of the Malun stream and Lanyang river. Considering different depths of dredge at the confluence, there were six dredging scenarios investigated in the present study. Through the simulation of the bed changes in a flood event, the aggradation of the dredging areas were used to evaluate the efficiency of dredging scenarios. The verification of CCHE-2D model showed the Modified Engelund & Hansen formula with the adaptation length equal to 1000 meters successfully rep resented the bed changes in the study areas. The simulation results showed the averaged height of aggradation was about 1.5 meters near the Malun bridge in the do-nothing scenario. The corresponding value of dredge at the main stream increased to 1.7 meters, because the sediment was trapped in the dredging areas. Near the Malun bridge, it resulted in a decrease of the areas of the crosssection and a corresponding decrease of ability to pass flood. However, dredge at the confluence showed an increase of flow velocity and ability of sediment transport. Moreover, the height of aggradation decreased with the increase of dredging depth. As the dredging depth ranging at 1.5~2.0 meters, the height of aggradation was less than 1.0 meters. Dredge at the confluence of the Malun stream and Lanyang river was found to the most effective dredging scenarios among the others.

碩士
國立屏東科技大學
環境工程與科學系所
106
While industries developed in Taiwan, some factories did not adequate dispose sewage that made some fields contaminated seriously by heavy metal. Heavy metals in soil can be absorbed differently by different particle size. Soil washing that separate the particles by hydrodynamic or sieve, and/or chemical extract heavy metals on soil particles, is one of the feasible technology for heavy metal contaminated soils. However, it still has some limitations. In this study, six contaminated soil samples were collected for soil washing to find out the limitations of this technology. Six sites ( N, C, T, L, D and J ) of soil samples were collected from factories and agricultural fields. Cu is the contaminant of soil T and Cr are others’. Soils N, C, T and L came from a soil treatment plant. We collected samples from each washing unit and evaluate the extraction efficiency of the process. We also do laboratory scale test, using sequential sedimentary technology to separate soils into four particle sizes (sand, coarse silt, fine silt, clay), to compare the result. Soil liquid ratio 1:2 or 1:10 of 0.1 N HCl chemical extractions were applied on silt and clay. For high Cr soil L and soil D, 0.1 N HCl and EDTA consecutive extraction were applied for better extraction efficiency. In this study, 20% of Cu in soil T was the three easy extracted fractions (water-soluble fraction, exchangeable fraction and carbonate fraction). Cr in soils N, C, L, D and J were distributed in the most stable three fractions (Fe-Mn Oxide fraction, organic fraction and residual fraction) which had less environmental impact. Soil particles separated in laboratory showed that the concentration of heavy metals varied with the soil particles size. Most sands were uncontaminated except those from high Cr soil L and soil D. Simulates real plant chemical extraction using 0.1 N HCl showed that extraction efficiency of six soils were less than 30%. Soil T has the highest extraction efficiency (28%). Raising the soil liquid ratio can improve the heavy metals extraction efficiency. The consecutive extraction of 0.1 N HCl and EDTA has better extraction efficiency than 0.1 N HCl. 0.1 N HCl can extract part of Cr of Fe-Mn oxide fraction and consecutive extraction can extract almost all the Cr of Fe-Mn oxide fraction. After soils N, C and T were treated by chemical extraction in real plant, both coarse particles and fine particles were clean. However, the recovery rates of heavy metal were still unbalanced. According to the results, soil washing technology is not proved to be suitable for high contaminated and low sand content soil.

碩士
國立中興大學
水土保持學系所
104
According to the Soil and Water Conservation technology norms of the Soil and Water Conservation Bureau of the Council of Agriculture of Executive Yuan, people should dredging at least one time each year when setting up the trapping efficiency of detention and deposit ponds inside the development base on the slope land, in order to maintain enough volume of detention and deposit ponds. Moreover, people should consider the convenience of dredging when designing, and maintaining adequate air ventilationlest for producing biogas which may cause danger This research uses the real example as the object of research, using the flow model CCHE2D to investigate the iji3mpacts of the sedimentation area of different positions of outlet and inlet of detention and deposit ponds, and different detentions and deposit ponds aspect ratio. By the velocity of flow inside the detention and deposit ponds and the position of the sand drops and deposits, and the quantity of the sand drop as basis to judge the benefits of the detention and deposit ponds to achieve the goal of designing the controlling Settlement location to improve the efficiency of detention and deposit ponds. According to the research, there would be the deposit of the mud in the place where there is a vortex, the speed of the circulation and on the corner inside the pound. Furthermore, when the distance of the inlet is far away from the outlet , it meets the Soil and Water Conservation technology standard better.by contrast, if the distance is closer, it can cause the jet stream and can’t defer the flood to meet the time effect Keyword: detention and deposit ponds, silting basin efficiency, CCHE2D

碩士
淡江大學
化學工程與材料工程學系碩士班
100
The separations of sugars from hydrolysis suspension using hollow fiber and flat plate membranes are studied. The effects of operating conditions and hydrodynamic methods on the sugar separation performance are discussed. The hollow fibers used in the experiments are made of polysulfone, and their mean pore size is 10 kD. In the filtration of pure glucose, the main resistance source is the membrane because of trivial membrane fouling, and the sugar transmission decreases slightly under high pressures. When enzyme exists in the suspension, the filtration rate decreases about 85 - 90% compared to those in the filtration of pure glucose. The major resistances are due to the enzyme blocking in the membrane pores and the cake formation on the membrane surface. Increasing the transmembrane pressure results in higher glucose yield. However, this effect becomes trivial when the pressure exceeds 80 kPa. An increase in cross-flow velocity under fixed transmembrane pressure leads to higher filtration rate. The filtration rate increases three times when cross-flow velocity increases from 0.3 to 1.5 m/s. Some empirical equations are established to correlate the filtration resistances with operating conditions. The filtration rate can be estimated accurately by substituting the calculated resistances into modified Darcys’ law. In addition, several hydrodynamic methods are tested to increase the filtration rate. A pulse feeding way may increase the filtration rate by 24.7%, while the way of step-increasing pressure can increase the filtration rate as high as 34.6%.

Residence time distributions have become an important analytical tool in the analysis of many types of flow systems. Residence time distributions have proven to be effective for analysing trickle bed reactors, as it allows determination of parameters under operating conditions allowing no interference of these conditions. By studying the residence time distribution a great amount of information can be obtained and therefore used to determine a number of hydrodynamic parameters. Due to recent findings that prewetting has a tremendous effect on a number of hydrodynamic parameters such as holdup, wetting efficiency and pressure drop, it is therefore the aim of this study to investigate the effect of trickle flow morphology or prewetting on a trickle bed reactor. The residence time distribution is obtained whereby hydrodynamic parameters are determined and therefore the effect the flow morphology has on various hydrodynamic parameters is highlighted. A number of methods were used to determine these parameters, namely that of the best-fit method, whereby the PDE model was used, and the method of moments. Operating conditions included varying gas and liquid flow rates for porous and non-porous catalyst particles at atmospheric pressure. The different prewetting procedures used during this work included the following:

• Non-wetted
• Levec-wetted
• Super-wetted

From this investigation the following conclusions were made:

Prewetting has a great effect on the hydrodynamic parameters of trickle bed reactors

The differences in prewetting can be attributed to differing flow morphologies for the different prewetted beds i.e. the dominant flow morphology for a non-wetted bed is that of rivulets and for prewetted beds that of film flow

It was also found that at low liquid flow rates the flow morphology in prewetted beds changes from film flow to a combination of rivulet and film flow

The different flow morphologies for prewetted and non prewetted beds was confirmed by the residence time distributions and various parameters obtained there from

At low liquid flow rates the flow morphology becomes a more predominant factor in creating the tailing effect present in residence time distribution for prewetted beds

The tailing effect in residence time distributions is a result of both internal diffusion and liquid flow morphology, where the liquid flow morphology is the more dominant factor

The use of residence time distributions to determine a number of hydrodynamic parameters proved to be very useful and accurate by means of different methods, i.e. method of moments and best-fit method

Differences in the liquid holdup determined from the method of moments and the weighing method confirmed that different flow morphologies exist for different prewetted beds

An increase in the dispersion coefficient with prewetting was observed indicating that the amount of micro mixing is different for the different prewetted beds

Differences in residence times and high values for the dynamic holdup, for the porous packing, confirmed that the PDE model does not model well the porous packing response curves due to the lack of internal diffusion and internal holdup in this model

The dynamic-static mass transfer showed that film flow, as in prewetted beds, results in slower mass transfer as opposed to rivulet flow and therefore it is concluded that prewetting results in different flow morphologies.

Following this study it is recommended that a residence time distribution model be used or developed that incorporates the effects of internal diffusion and internal holdup as present in porous catalyst particles. In addition, it was found that very few correlations could accurately predict hydrodynamic parameters due to the absence of the effect of prewetting and therefore it is recommended that correlations be developed that incorporate the effect of prewetting.
Dissertation (MEng)--University of Pretoria, 2008.
Chemical Engineering
unrestricted

This research was performed with a focus on two key aspects of energy cost–reduction for offshore OWC devices; improving the power extraction efficiency and reducing the excess margin in structural safety factors by a better understanding of wave–induced loads on these devices. This study utilised information from three different resources. First, 2D and 3D numerical results from fully nonlinear Computational Fluid Dynamics (CFD) simulations performed using the commercial code STAR–CCM+ that was validated in good agreement with physical scale model measurements at each stage of increasing complexity during this research. Second, published experiments in the literature for 2D OWC devices subjected to unidirectional regular waves to validate the 2D CFD models of this study. Third, experiments conducted in the towing tank of the Australian Maritime College (AMC) for 3D offshore stationary and floating–moored OWC devices (at a model–scale of 1:50) subjected to unidirectional regular and irregular waves. These experiments were designed to (1) compare the hydrodynamic performance of both devices, (2) estimate wave–induced loads on the fixed device during operating conditions, (3) investigate the survivability of the floating–moored device with intact and damaged mooring systems and (4) validate the 3D CFD models of this study. Using the combined CFD and experimental approach, it was found that optimizing the underwater geometry of an offshore stationary OWC device could significantly improve the power extraction efficiency up to 0.97. However, this efficiency could be reduced due to air compressibility effects at full–scale. The surge motion of the floating–moored device improved device efficiency in regular and irregular waves. Furthermore, the effectiveness of deploying offshore OWC devices in deep–water where waves are more energetic was proven by increasing the extracted pneumatic energy by a maximum of about 7.7 times when wave height was doubled (incident wave energy increased four times). The instantaneous position of the floating–moored OWC device and its interactions with a certain wave train was more important than the maximum wave height in an irregular sea state when assessing device survivability. Survivability with a damaged mooring system was the key analysis for mooring design. For this analysis, using an equivalent design regular wave condition along with the current safety factors recommended for offshore oil and gas platforms was found to over–design the mooring system of the floating OWC device. The good agreement between CFD experiments for survivability analysis with intact and damaged mooring systems in regular waves highlighted that CFD is a very promising tool a designer can employ to investigate and assess device survivability under different conditions upon further validations in irregular waves.

Indiana University-Purdue University Indianapolis (IUPUI)
A gearless hydraulic wind energy transfer system utilizes the hydraulic power transmission principles to integrate the energy of multiple wind turbines in a central power generation location. The gearless wind power transfer technology may replace the current energy harvesting system to reduce the cost of operation and increase the reliability of wind power generation. It also allows for the integration of multiple wind turbines to one central generation unit, unlike the traditional wind power generation with dedicated generator and gearbox. A Hydraulic Transmission (HT) can transmit high power and can operate over a wide range of torque-to-speed ratios, allowing efficient transmission of intermittent wind power. The torque to speed ratios illustrates the relationship between the torque and speed of a motor (or pump) from the moment of start to when full-load torque is reached at the manufacturer recommended rated speed. In this thesis, a gearless hydraulic wind energy harvesting and transfer system is mathematically modeled and verified by experimental results. The mathematical model is therefore required to consider the system dynamics and be used in control system development. Mathematical modeling also provided a method to determine the losses of the system as well as overall efficiency. The energy is harvested by a low speed-high torque wind turbine connected to a high fixed-displacement hydraulic pump, which is connected to hydraulic motors. Through mathematical modeling of the system, an enhanced understanding of the HTS through analysis was gained that lead to a highly efficient hydraulic energy transmission system. It was determined which factors significantly influenced the system operation and its efficiency more. It was also established how the overall system operated in a multiple wind turbine configuration. The quality of transferred power from the wind turbine to the generator is important to maintaining the systems power balance, frequency droop control in grid-connected applications, and to ensure that the maximum output power is obtained. A hydraulic transmission system can transfer large amounts of power and has more flexibility than a mechanical and electrical system. However high-pressure hydraulic systems have shown low efficiency in wind power transfer when interfaced with a single turbine to a ground-level generator. HT’s generally have acceptable efficiency at full load and drop efficiency as the loading changes, typically having a peak around 60%. The efficiency of a HT is dependent on several parameters including volumetric flow rate, rotational speed and torque at the pump shaft, and the pressure difference across the inlet and outlet of the hydraulic pump and motor. It has been demonstrated that using a central generation unit for a group of wind turbines and transferring the power of each turbine through hydraulic system increases the efficiency of the overall system versus one turbine to one central generation unit. The efficiency enhancement depends on the rotational speed of the hydraulic pumps. Therefore, it is proven that the multiple-turbine hydraulic power transfer system reaches higher efficiencies at lower rotational speeds. This suggests that the gearbox can be eliminated from the wind powertrains if multiple turbines are connected to the central generation unit. Computer simulations and experimental results are provided to quantify the efficiency enhancements obtained by adding the second wind turbine hydraulic pump to the system.

Η Πακλιταξέλη (PTX) αποτελεί ένα ευρέως διαδεδομένο αντινεοπλασματικό φάρμακο και ενδείκνυται σε μεταστατικό καρκίνο του μαστού, καρκίνο ωοθηκών, μη μικροκυτταρικό καρκίνο του πνεύμονα και σε σάρκωμα Kaposi ασθενών με AIDS. Παρ’ όλα αυτά, η σημαντική τοξικότητα που εμφανίζει (μυελοκαταστολή, νευροτοξικότητα, αντιδράσεις υπερευαισθησίας), υπογραμμίζει την αναγκαιότητα για μορφοποίησή της σε Συστήματα Ελεγχόμενης Χορήγησης Φαρμάκων (DDS), με σκοπό τη μείωση των ανεπιθύμητων ενεργειών και την αύξηση της βιοδιαθεσιμότητας του φαρμάκου. Τα πολυμερικά μικκύλια έχουν μελετεθεί εκτενώς τα τελευταία χρόνια ως Συστήματα Ελεγχόμενης Χορήγησης Φαρμάκων. Η ενσωμάτωση υπερπαραμαγνητικών νανοκρυσταλλιτών οξειδίου του σιδήρου (SPIONs) στον πυρήνα των PTX-μικκυλίων, παρέχει τη δυνατότητα μαγνητικής στόχευσης του φαρμάκου στην επιθυμητή περιοχή δράσης, καθώς και τη θεραπεία του καρκίνου μέσω επαγωγής μαγνητικής υπερθερμίας, με την εφαρμογή εναλλασσόμενου μαγνητικού πεδίου. Επιπλεόν, η χρήση των SPIONs ως σκιαγραφικά μέσα (Τ2-contrast enhancement) στη μαγνητική τομογραφία πυρηνικού συντονισμού (MRI), εξασφαλίζει το πλεονέκτημα ταυτόχρονης διάγνωσης και θεραπείας (Theranostics), αποκαλύπτοντας την πολυλειτουργικότητα των συστημάτων αυτών. Οι συγκεκριμένοι νανοφορείς, έχοντας μικρό μέγεθος (100-200nm), θεωρούνται κατάλληλοι για να αποφύγουν την οψωνινοποίηση απο τις λιποπρωτεϊνες του αίματος, την επίθεση απο τα φαγοκύτταρα του Δικτυοενδοθηλιακού συστήματος (RES) καθώς και την ταχεία νεφρική κάθαρση, με αποτέλεσμα την παρατεταμένη κυκλοφορία τους στο αίμα (stealth systems) και την εκλεκτική πρόσληψη τους απο τους συμπαγείς καρκινικούς όγκους, μέσω του φαινομένου της ενισχυμένης διαπερατότητας και κατακράτησης (EPR effect). Οι ιδιότητες αυτές, καθιστούν τα συγκεκριμένα συστήματα πολύτιμα εργαλεία στον τομέα της νανοϊατρικής. Η παρούσα μεταπτυχιακή διατριβή πραγματεύεται τη σύνθεση υδρόφοβων SPIONs μέσω της τεχνικής της θερμικής αποικοδόμησης. Μελετήθηκαν οι συνθετικές παράμετροι (πρόδρομη ένωση, ποσότητα ελαϊκού οξέος, θερμοκρασία και διάρκεια αντίδρασης, ρυθμός αύξησης της θερμοκρασίας κ.α) που επηρεάζουν το μέγεθος, το σχήμα και τη διασπορά του μεγέθους των σχηματιζομένων νανοκρυσταλλιτών (5-13nm, σ: 10-20%), καθώς διαδραματίζουν σημαντικό ρόλο στη μαγνητική συμπεριφορά των υβριδικών νανονοφορέων. Στη συνέχεια, πραγματοποιήθηκε σύνθεση υβριδικών νανοφορέων με εγκλωβισμό των SPIONs σε πολυμερικά μικκύλια. Η παρασκευή των υπερπαραμαγνητικών μικκυλίων επιτελέστηκε με την τεχνικη solvent diffusion and evaporation (nanoprecipitation), με χρήση του αμφίφιλου συμπολυμερούς πολυ(γαλακτικό οξύ)-πολυ(αιθυλενογλυκόλη) (PLA-PEG). Στον υδρόφοβο πυρήνα των μικκυλίων (PLA) δεσμεύονται υδρόφοβες ενώσεις (PTX, SPIONs), ενώ το υδρόφιλο κέλυφος (PEG) προσδίδει κολλοειδή σταθερότητα σε υδατικά μέσα (δομή πυρήνα-κελύφους). Διερευνήθηκαν διάφορες συνθετικές παράμετροι (μοριακό βάρος συμπολυμερούς, ποσότητα SPIONs, ρυθμός προσθήκης οργανικής φάσης κ.α) και προσδιορίστηκαν οι βέλτιστες συνθήκες για την παρασκευή υπερπαραμαγνητικών μικκυλίων μεγέθους <200nm, με αξιοσημείωτη κολλοειδή σταθερότητα (μέχρι και έξι μήνες), σε συνθήκες παρόμοιες με αυτές του ανθρώπινου πλάσματος (pH: 7.4, ιοντική ισχύς: 0.15Μ). Στο επόμενο στάδιο της παρούσας εργασίας, μελετήθηκαν οι παράγοντες που επηρεάζουν τη φόρτωση-ενκαψυλίωση της PTX και των SPIONs στα πολυμερικά μικκύλια (ποσότητα PTX, ποσότητα και μέγεθος SPIONs, μοριακό βάρος PLA-PEG, ρυθμός προσθήκης οργανικής φάσης κ.α), σε φυσιολογικές συνθήκες (pH:7.4, ιοντική ισχύς: 0.15Μ). Αναπτύχθηκε πρωτόκολλο μέσω του οποίου έγινε κατορθωτός ο διαχωρισμός των μαγνητικών νανοφορέων απο τους μη μαγνητικούς, καθώς και ο υπολογισμός της φόρτωσης-ενκαψυλίωσης PTX και SPIONs ξεχωριστά, τόσο στους μαγνητικούς και μη μαγνητικούς νανοφορείς, όσο και στο μέιγμα αυτών. Οι συγκεκριμένοι νανοφορείς χαρακτηρίζονται απο εξαιρετικά υψηλή απόδοση ενκαψυλίωσης φαρμάκου (93 %wt.) και φόρτωση φαρμάκου που ανέρχεται στο 4.8 %wt. Oι αμιγώς μαγνητικοί νανοφορείς επιδεικνύουν υψηλή απόδοση ενκαψυλίωσης νανοκρυσταλλιτών (70 %wt.), ενώ η φόρτωση σε φάρμακο και SPIONs ανέρχεται σε 5.2 και 20 %wt. αντίστοιχα. Σε αμφότερες τις περιπτώσεις οι νανοφορείς, μεγέθους (υδροδυναμική διάμετρος) 170nm, χαρακτηρίζονται απο ικανοποιητική μαγνητική συμπεριφορά. Εξετάστηκε η επίδραση του μεγέθους των νανοκρυσταλλιτών στη μαγνητική συμπεριφορά των νανοφορέων. Οι αμιγώς μαγνητικοί νανοφορείς με μεγαλύτερο μέγεθος SPIONs παρουσιάζουν καλύτερη μαγνητική συμπεριφορά. Τέλος, πραγματοποιήθηκαν μελέτες αποδέσμευσης του φαρμάκου σε PBS (0.14Μ, pH:7.4) στους 37oC και διερευνήθηκε η επίδραση της εφαρμογής εναλλασσόμενου μαγνητικού πεδίου στην αποδέσμευση της PTX απο τους μαγνητικούς νανοφορείς (Triggered Drug Release). Σε κάθε περίπτωση, παρατηρήθηκε ελεγχόμενη αποδέσμευση του φαρμάκου για 24 ώρες, σε συνθήκες που προσομοιάζουν με αυτές του πλάσματος. Ο φυσικοχημικός χαρακτηρισμός των νανοφορέων πραγματοποιήθηκε με HPLC, DLS, TGA, TEM και μαγνητοφόρηση.
Paclitaxel (PTX) is one of the most successful anticancer drugs against a broad range of solid tumors, such as metastatic breast cancer, ovarian cancer, non-small-cell lung cancer and AIDS-related Kaposi sarcoma. However, the serious systematic side effects of PTX (myelosuppression, neurotoxicity, hypersensitivity) underline the need for formulation of PTX in Drug Delivery Systems (DDS), in order to reduce the side effects and increase the bioavailability of the drug. Among DDS, polymeric micelles have drawn much attention due to their great flexibility in tuning drug solubility, micelle size, targeted drug delivery and stability. Incorporation of Superparamagnetic Iron Oxide Nanocrystals (SPIONs) inside the core of drug-loaded polymeric micelles, imparts to the final Drug Delivery System the prospect of physical (magnetic) targeting, intrinsic therapeutic function (hyperthermia-based cancer therapy under alternating external magnetic field), T2-based contrast enhancement in magnetic resonance imaging (MRI) and remotely triggered drug release. These core-shell polymeric micelles having small size (100-200nm), are considered appropriate for avoiding both opsonization, macrophages attack by ReticuloEndothelial System (RES) and rapid renal clearance, thus allowing micelles to be taken up preferably by solid tumors through Enhanced Permeability and Retention (EPR) effect. Therefore, such nanoassemblies encode high potential in nanomedicine, due to their dual nature (Therapeutic+Diagnostic = Theranostics). In particular, we have studied the synthesis of organophilic SPIONs through thermal decomposition. The synthetic parameters (precursor, precursor:oleic acid ratio, reaction temperature and duration, heat rate, etc.) affecting the size, shape and size distribution of the nanocrystals have also been examined thoroughly, since they play a key-role concerning the magnetic behavior of the final hybrid. Nanosized SPIONs with narrow size distribution were synthesized (5-13nm, σ: 10-20%). The preparation of poly(lactic acid)-block-poly(ethyleneglycol) (PLA-PEG) micelles encapsulating hydrophobic SPIONs, by varying the molecular weight of the polymers, the amount of SPIONs and the addition rate during micelle assembly, has also been investigated. The core-shell superparamagnetic micelles were prepared through solvent diffusion and evaporation technique (nanoprecipitation). PTX and SPIONs are being incorporated into the micelle’s hydrophobic core (PLA) through hydrophobic interactions, whereas the hydrophilic shell (PEG) stabilizes the micelles in aqueous dispersions, optimizing their colloidal stability and providing prolonged circulating time. The optimum parameters were determined, conferring to the micelles (Hydrodynamic Diameter < 200nm) high colloidal stability (up to six months) at biorelevant conditions (pH:7.4, ionic strenght: 0.15M). The next phase of the present master thesis focused on studying the factors (amount of PTX and SPIONs, molecular weight of PLA-PEG, addition rate, etc.) affecting the Loading of PTX and SPIONs into the polymeric micelles and how they can be fine-tuned towards high drug loading, while retaining their size at a scale where long circulation would not be precluded. Through protocol establishment, we have managed to separate the magnetic and non magnetic micelles, and to determine individually the loading of PTX and SPIONs for magnetic, non magnetic micelles, as well as for the mixture of them. The micelles’ mixture exhibits very high Drug Encapsulation Efficiency (93 %wt.) and 4.8 %wt. Drug Loading (D.L). Magnetic nanocarriers display high Magnetic Encapsulation Efficiency (70 %wt.), with D.L and Magnetic Loading of 5.2 and 20 %wt. respectively, In both cases, micelles demonstrate adequate magnetic behavior and small sizes (hydrodynamic diameter: 170nm), under conditions which simulate with human plasma (pH:7.4, ionic strenght: 0.15M). The effect of SPIONs’ size on the magnetic behavior of hybrid colloids, was also examined. Magnetic nanocarriers encapsulating SPIONs of greater size exhibit better magnetic behavior. Finally, we have conducted Drug release studies in PBS (0.14M, pH:7.4) at 37oC. The effect of SPIONs presence on the release profile of PTX, including triggered drug-release by application of AC magnetic field, has also been investigated. PTX-magnetic micelles exhibit Controlled Drug release for 24 hours. Several techniques have been used for the characterization of such nanoassemblies, like: HPLC, DLS, TGA, TEM, XRD, Magnetophoresis and Triggered Drug release by application of AC magnetic field.