Rozprawy doktorskie na temat „TES SYSTEM”

With increasing awareness of environmental issues and worldwide requirements for sustainable development, renewable energy technologies with lower environmental impact, especially those having abundant resources like wind and solar energy, attract more attention. Concentrating Solar Power (CSP) is one of the most promising solar energy technologies. Indeed, thermal energy storage (TES) units could be integrated into CSP plants, enhancing their flexibility and capacity factor. However, tower based CSP plants still remain cost intensive. This study evaluates the performance of a 55MWe combined-cycle CSP plant with rock-bed TES located in Sevilla, Spain. Sensitivity analysis has been performed to assess the influence of critical parameters. Furthermore, in order to decrease the costs with increasing efficiency, improved CSP plant schemes have been proposed. In the study, EES, SAM and TRNSYS are used to design and simulate the model from technological perspective, then the capital and operational costs are calculated in MATLAB. For one-year simulation of the designed case, the performance of the plant is determined by the trade-off among several conflicting factors. The study focuses on three key indicators to measure the performance- levelized costs of electricity (LCoE), capital expenditure (CAPEX) and efficiency factor (UF). As long as CAPEX is within the acceptable range, LCoE would be the most concerned one-as low as possible, then followed by UF. Compared to conventional CCGT plant, the proposed combined-cycle tower-based CSP plant, with efficiency of 0.49 and LCoE of 196USD/MWe, enables efficiency improvements, while both CAPEX and LCoE are higher. On the other hand, it has to be noticed that CCGT relies on fuel (natural gas) price, which means higher risks and operational expenditure (OPEX). A sensitivity study is involved varying gas turbine expansion ratio (to vary its outlet temperature and therefore supply power for the bottoming Rankine cycle), size of TES and solar multiple (SM). It can be found that same LCoE and UF could be achieved with lower CAPEX by setting appropriate parameters. The study also introduces two improved CSP plant schemes with sensitivity study. To some extent, the LCoE decreases due to increasing power output and the efficiency of the system simultaneously increases.
Med ökad medvetenhet om miljöfrågor och globala krav på hållbar utveckling lockar förnybar energi teknologi med lägre miljöpåverkan, särskilt de som har stora resurser som vind och solenergi, mer uppmärksamhet. Concentrating Solar Power (CSP) är en av de mest lovande solenergi teknologierna. Faktiskt kan värmeenergi lagringsenheter integreras i CSP-anläggningar, vilket förbättrar deras flexibilitet och kapacitetsfaktor. Träbaserade CSP-anläggningar är dock fortfarande kostnads intensiva. Denna studie utvärderar prestandan för en 55MWe CSP-anläggning med kombinerad cykel med TESsandbädd i Sevilla, Spanien. Känslighetsanalys har utförts för att bedöma påverkan av kritiska parametrar. För att minska kostnaderna med ökad effektivitet har dessutom förbättrade CSP-anläggningsprogram föreslagits. I studien används EES, SAM och TRNSYS för att designa och simulera modellen ur teknologiskt perspektiv, sedan beräknas kapital och driftskostnader i MATLAB. För ett års simulering av det planerade fallet bestäms anläggningens prestanda av bytet mellan flera motstridiga faktorer. Studien fokuserar på tre nyckelindikatorer för att mäta prestandanivå kostnaderna för el (LCoE), investeringar (CAPEX) och effektivitetsfaktor (UF). Så länge CAPEX ligger inom det acceptabla intervallet, skulle LCoE vara den mest bekymrade en så låg som möjligt, följt av UF. Jämfört med konventionell CCGT-anläggning möjliggör den föreslagna träbaserade CSP-anläggningen med kombinerad cykel med effektivitet 0,49 och LCoE på 196USD / MWe effektivitetsförbättringar, medan både CAPEX och LCoE är högre. Å andra sidan måste man notera att CCGT förlitar sig på bränslepriset (naturgas), vilket innebär högre risker och driftsutgifter (OPEX). En känslighetsstudie är involverad med varierande utvidgning förhållande för gasturbin (för att variera dess utloppstemperatur och därmed leverera ström för botten Rankine-cykeln), storlek på TES och sol multipel (SM). Det kan konstateras att samma LCoE och UF skulle kunna uppnås med lägre CAPEX genom att ställa in lämpliga parametrar. Studien introducerar också två förbättrade CSP-anläggningar med känslighetsstudie. I viss utsträckning minskar LCoE på grund av ökad effekt och systemets effektivitet ökar samtidigt.

A Thermal conductivity probe fo rhigh temperature(HT-TCP) has been built and tested. Its design and construction procedure are adapted from the ambient temperature ther- mal conductivity probe(AT-TCP) due to the good performance softhislast.The construction procedure and the preliminary tests are accurately described.The probe contains a PtwireasheaterandatypeKthermocouple(K-TC)as temperature sensor, and its size are so small (diameter0.6mmandlength60mm) to guaranteea length to diameter ratioofabout100.Calibration tests with glycerolfor temperatures between 0C and 60C have shown a good Agreement with literature data,within3%.First tests on aternarysalt(18%inmassof NaNO3, 52% KNO3, and30% LiNO3) at120C and 150C , have given good results:an Agreement was found with the Thermal conduc- tivity of the standard solar salt(60% NaNO3, 40% KNO3), even if the data for this last have been extrapolated,being it solidat those temperatures. Unfortunately, at the higher temperaturetested(200C), the viscosityof the salt highly decreases,and free convection starts, making the measurements unreliable. A numerica linvestigation of the performance of the storage and evolution of the ther- mocline for theOPTSFull scaleconguration and for the OPTSsystem of theEnea Casaccia facility is carriedon.The full scale conguration has a tankheightinthe order of12m,because this choice allow stop operate the systeminnatural convection regime forlow charge fraction softh e storage.In order to obtainnumerical results in a time scalesuitable with computer resources and activities, the adoption of anaxisym- metric simplication of the geometriesis pursuit. The code OpenFOAMversion2.2.0 is used to perform the simulations. Code and model settings together with the adopted computational grids,initia land boundary conditionsare described in the following sec- tions. A summary of the simulation results is then given. A steady-state numerical investigation of the MSHeatExchanger prototype developed in ENEA Casaccia is presented.This component is realized to perform the heat exchange between moltensalts(aternarymixture ) and adiathermicoil and with a moderate tem- peraturegap(38C). In order to optimize the heate xchangereciency and toobtain the greatest contact are a between uids the pipe line series of diathermicoil is designed with anhelical geometry.The moltensaltsside is aconvectionalcy lindricalgeome- try with the Greater diameter in the region where pipe line series are located while the other portion of the heater has a diameter lower than the length of the cylinder.The codeOpenFOAMversion2.2.0 is use d to perform the simulations for the discharging phase. Code and model settings together with the adopted computational grids, initial and boundary conditions are described in the following sections and summary of the simulation results is then given.

This thesis used Computational Fluid Dynamic Software Ansys Fluent to evaluate the design of a Zeolite 13X based Thermochemical Energy Storage System. The system is designed to provide constant hot water supply during night-time for a solar Membrane Distillation (MD) system. It overcomes the intermittent nature of solar energy to provide a sustainable energy solution for mining water treatment in Australia. The utilization of CFD also proposed a method to predict the performance of a designed TES which estimated the critical configurations such as optimal charging/discharging flow rate, temperature, relative humidity, and pipe arrangement configuration, etc.

In this thesis, I have developed a range of theoretical and numerical techniques for modelling the behaviour of partially coherent optical systems and multi-mode detectors. The numerical simulations were carried out for the ultra-low-noise Transition Edge Sensors (TESs) being proposed for use on the SAFARI instrument on the cooled aperture infrared space telescope SPICA (34 - 210 μm). The optical behaviour of the SAFARI system is described in terms of the optical modes of the telescope, as distinct from the optical modes of the detector. The performance of the TESs were assessed in terms of signal power, background power and photon noise. To establish a method for precisely characterising and calibrating ultra-low-noise TESs, a cryogenic test system was designed and engineered to measure the optical efficiencies of the SAFARI TESs. The multi-mode, partially coherent illumination conditions of the measurement system were engineered to be precisely the same as those of the telescope. A major difference between the test system and the telescope’s optics is that the telescope will have focusing elements, but the test system was designed to avoid focusing elements in order to keep the optical path as clean as possible. The theoretical formalism and numerical models were adapted accordingly to address this difference. The numerical simulations show that the test system could provide near identical optical performance as that of the telescope system even though the focusing elements were absent. I also performed experimental measurements to investigate the optical efficiencies of the multi-mode TESs. The detectors worked exceedingly well in all respects with satisfactory optical efficiencies. In addition, it has been shown that the optical model provides a good description of the optical behaviour of the test system and detectors. Further modal analysis was developed to study losses in the multi-mode horns. The optical behaviour of the waveguide-mounted thin absorbing films in the far-infrared was modelled using a mode-matching method.

Ce travail porte sur l'étude de la propriété d'(A,B)-invariance de polyèdres convexes et son application à la commande sous contraintes et au problème l1. D'abord, nous proposons une caractérisation explicite de l'(A,B)-invariance de polyèdres convexes pour des systèmes en temps discret. Cette caractérisation se traduit par des conditions nécessaires et suffisantes sous la forme de relations matricielles linéaires, et présente deux avantages majeurs vis-à-vis de celles rencontrées dans la littérature : elle s'applique à tous les polyèdres convexes et elle ne nécessite pas le calcul de sommets. Ces avantages se font sentir notamment dans le calcul du domaine (a,b)-invariant supremal inclus dans un polyèdre donne, pour lequel nous proposons une méthode numérique. Le problème de calculer une loi de commande rendant positivement invariant en boucle fermée un polyèdre (a,b)-invariant est également traite. Les relations d'(A,B)-invariance sont alors généralisées à des systèmes soumis à des contraintes linéaires sur la commande et à des systèmes soumis à des perturbations additives bornées. Puis, les résultats obtenus en temps discret sont étendus aux systèmes en temps continu. Ensuite, le problème d'atténuation de perturbations additives persistantes, connu dans la littérature comme problème l1, est étudié. Les domaines (A,B)-invariants intérieurement stabilisables sont d'abord caractérises. Puis, nous proposons une approche décomposée pour le calcul du domaine intérieurement stabilisable supremal inclus dans le polyèdre défini par les contraintes de performance l1. Un niveau de performance donne est atteignable si et seulement si ce domaine supremal n'est pas vide. Cette approche géométrique permet notamment de déterminer directement la solution du problème l1 pour une classe importante de systèmes. Enfin, nous étendons l'étude de l'(A,B)-invariance de polyèdres à des systèmes dont le modèle est soumis à des incertitudes du type structure.

Thesis (M.S. in Contract Management)--Naval Postgraduate School, September 2003.
Thesis advisor(s): Jeffrey Cuskey, David Krueger. Includes bibliographical references (p. 89-91). Also available online.

Fjärrvärme i dagens Sverige är ett väletablerat sätt att leverera värme för både industriell och privat användning. Med nästa generations fjärrvärmesystem vid horisonten kan förändringar av existerande fjärrvärmenät komma att bli vanligt förekommande. Trots att det inte är fullt aktuellt med den typen av renoveringar ännu så måste fjärrvärmenät ibland byggas ut för att hantera nya situationer som kan uppstå. För att få en god uppskattning om vad de nya situationerna kommer kräva, och potentiellt kosta, så är simuleringsmodeller ett användbart verktyg. Den här studien har granskat en kommande ökning av effektbehovet och en konsekvent ökning av den producerade värmen angående fjärrvärmesystemet lokaliserat i Malå. Granskningen genomfördes via etablering av en simuleringsmodell som baserats på metoder från tillgänglig litteratur. Empiriska värden användes både som indata till modellen och för feluppskattning. Två hypotetiska scenarier undersöktes där effektbehovet hos en industrikund antas dubbleras, ett som systemet ser ut idag och det andra med ett termiskt energilager i form av en ackumulatortank inkluderat. Simuleringssvaren gav en uppskattning av hur mycket effekt en ny produktionsenhet behöver kunna producera för att nå ett eftersökt mål. Dessa visade på att en ny produktionsenhet med en effekt av minst 10.50 MW är nödvändigt. Vidare så indikerade resultaten att installation av ett sådant energilager med den valda styrningen inte reducerar effektmagnituden hos en ny produktionsenhet. De visade dock på att införande av energilagret kan medföra en reduktion i antalet effektsvängningar som förekommer i systemet. Beroende på övrig konfiguration så minskades förekomsten av antalet effektsvängningar mellan 0.2 till 25.5 procent med ett energilager av den minsta undersökta volymen infört.
District heating in Sweden is a well established way of delivering heat for both industrial and private applications. With the next generation of district heating on the doorstep, changes of existing district heating networks may become a regular occurrence. Despite the fact that these kinds of reconstructions are not quite applicable yet, refurbishments of existing district heating networks are still sometimes necessary in order to deal with new prerequisites that may appear. In order to achieve a good estimation of what these new prerequisites will require and possibly cost, the usage of tools such as models for simulation are valuable. This study has evaluated a future increase of power demand and the subsequent expansion of the produced heat concerning the district heating network located in the city of Malå. The evaluation was carried forth by establishment of a simulation model which was based on present literature. Empirical data was used both as input and for error estimation. Two hypothetical scenarios were examined in which the power demand of an industrial customer is assumed to be doubled. The first represented the system as it is defined presently, while the other introduced a tank thermal energy storage to the system. The results of the simulation yielded an estimate of how much heat a new plant needs to produce in order to attain a set goal. These suggested that the necessary heat production in the new plant needs to be at least 10.50 MW. Furthermore, the results indicated that the inclusion of a thermal energy storage of this kind and with the defined priorities will not reduce the required size of a new production plant. However, they did indicate that the defined thermal energy storage may contribute to a reduction in the number of power fluctuations occurring in the system. Depending on other configurations, the frequency of the power fluctuations were reduced between 0.2 to 25.5 percent with the inlcusion of the smallest examined thermal energy storage.

La technique de transmission multi-porteuse à étalement de spectre, MC-CDMA, est un candidat potentiel pour les interfaces radio des futurs systèmes radio mobiles. Cette technique bénéficie d'une part de la robustesse de la transmission multi-porteuse OFDM face à la propagation multi-trajets et d'autre part de la flexibilité de l'accès multiple à répartition par codes CDMA. Cette thèse s'intéresse à l'étude des performances systèmes de la technique MC-CDMA en voie descendante. L'objectif est de valider au niveau système les concepts et algorithmes de la couche physique MC-CDMA.
La thèse s'articule autour de deux thématiques qui sont liées. La première thématique concerne l'abstraction de la couche physique au niveau système. Cette thématique est aussi connue sous le nom d'interfaçage entre les niveaux lien physique et système. L'abstraction de la couche physique a pour principal objectif de définir une mesure adéquate pour prédire la qualité de transmission au niveau système. Dans cette thèse, nous étudions l'abstraction de la couche physique suivant deux échelles de temps. La première échelle est macroscopique et porte sur la transmission de plusieurs trames de données subissant des évanouissements de canal indépendants. La deuxième échelle est dite microscopique et porte sur la transmission d'une seule trame de données subissant un évanouissement particulier du canal. L'abstraction macroscopique est appropriée pour une évaluation des performances systèmes par des simulations systèmes statiques alors que l'abstraction microscopique est plus appropriée pour une évaluation plus précise des performances systèmes ainsi que pour étudier les algorithmes d'adaptation de lien par des simulations systèmes dynamiques. Dans notre étude, nous analysons les problèmes soulevés par les deux types d'abstraction et proposons des nouvelles solutions appropriées.
La deuxième thématique concerne l'évaluation de la capacité cellulaire des algorithmes et configurations de la couche physique MC-CDMA. En utilisant l'abstraction macroscopique, nous développons une méthodologie semi analytique d'évaluation de la capacité cellulaire. L'évaluation de la capacité est faite aussi bien au niveau lien à travers un nouvel indicateur de capacité qu'au niveau système à travers un simulateur statique de type Monte Carlo. La méthodologie développée ici est un outil simple et efficace pour identifier les algorithmes et configurations de couche physique les mieux adaptés pour un environnement donné.

Mots clefs - MC-CDMA, modélisation d'interférence, interfaçage lien système, capacité cellulaire, simulations systèmes.

This work is focused on the visualization and thus in the aid in finding explanations for the behavior of polymer structures as they exist in solution. For this aim, preparation and imaging techniques based on cryo-TEM protocols were developed for a large variety of polymeric specimens using new commercially available devices and the results were compared with the findings of other means of structural investigations. The systems used in this work were chosen, as their investigations can be adapted to other polymer systems by slight adaptation of the preparation procedures.

One of the most crucial issues nowadays is the protection of the environment and the replacement of fossil fuels, which are abundantly used around the world, with more efficient and renewable sources. The highest portion of global energy demands today is used in heating and cooling purposes. One way of alleviating the fossil-based thermal energy uses is to harvest excess thermal energy using thermochemical storage materials (TCMs) for use at heating/cooling demands at different times and locations. Along this, in this master’s thesis, a bench-scale thermochemical heat storage (TCS) system is numerically designed, as a part of a collaborative project: Neutrons for Heat Storage (NHS), funded by Nordforsk. The TCS system that is designed herein employs the reversible chemical reaction of ammonia with a metal halide (MeX) for a heat storage capacity of 0.5 kWh, respectively releasing and storing heat during absorption and desorption of ammonia into and from the MeX. This system is designed for low temperature heat applications, around 40-80 °C. SrCl2 is chosen as the metal halide to be used, based on the research outcomes in determining the most suitable materials conducted by NHS project partners. In the ammonia-SrCl2 system, only the absorption and desorption between SrCl2∙NH3 and SrCl2∙8NH3 are considered. The main reason is because absorption/desorption between the last ammine and SrCl2 undergoes at a significantly higher/lower reaction pressure (for a given temperature), with a significant volume change compared to the rest of the ammines, and therefore is practically less cost effective. This thesis also includes a detailed discussion of four different thermochemical storage designs from literature, found as the most relevant to the present TCS system study, which use the reaction between ammonia and metal halides. The first system that was examined is a TCS system built by the NHS project partners at Technical University of Denmark (DTU), owing to its similarities with the desired project, regarding the design and parameters the system uses. This system works in batch mode, only allowing either absorption (i.e. heat release) or desorption (i.e. heat storage) at a given cycle. Thus, upgrading the design of this TCS system at DTU is considered as a most-likely solution to the research objectives of this current thesis project. Moreover, the TCS system at DTU uses storage conditions and desorption temperature similar to the current project’s desired low temperature range of 40-80 °C. The second system discussed herein from literature uses two reactors for cold and heat generation, which means that both charging and discharging processes occur simultaneously. This simultaneous operability is the main reason that this particular system was examined in this thesis. The next discussed system from literature also uses two reactors, for absorption and desorption processes, which work reversibly when each process is completed, like in the desired concept of this project. These two systems (i.e., the secondly and the thirdly discussed systems) use the reversible solid-gas reaction for absorption and desorption between SrCl2∙NH3 and SrCl2∙8NH3, however, the conditions of pressure and temperature between them differ. The second system from literature operates at desorption and absorption at respective conditions of 96 °C, 15 bar and 87 °C, 11 bar while the third system discussed operates at 103 °C, 16 bar and 59 °C, 3 bar during desorption and absorption respectively. The last system from literature that is discussed herein provides the same desorption temperature of 80 °C. Inaddition this particular study suggests that the reaction of solid with gaseous NH3 is better (than the solid with liquid NH3 reaction) based on results derived from several different low-pressure experiments of the reactions. The main differences between all these discussed systems from literature, as opposed to the desired TCS system design in this thesis project, concern the systems’ operating mode and the pressure and temperature-conditions. The first difference is that only one of the examined systems pumps the solid VIII powder salt around the system in contrast to the others that keep the salt static inside the reactors and pumped only the ammonia around the system, as chosen in the current system. The second difference concerns the operating conditions during absorption and desorption reactions, where these different systems operate at a widely different pressure and temperature conditions as compared to the current system expectations. Thus, there are four main lessons that were learnt via this literature analysis, to improve the TCS system at DTU to the desired new system in this work. The first lesson is related to the reactants’ transportation mechanism that should be used in this system. Regarding this, it was decided to maintain the solid salt (metal halide) stationary inside each reactor (but not pumping it instead of ammonia), similar to the majority of designs discussed from literature. According to the second and third lessons, the solid-gas reaction is the most suitable solution and only the reactions of absorption and desorption between SrCl2∙NH3 and SrCl2∙8NH3 are considered, following the experience from literature (for the reasons explained earlier). The last lesson regards the system’s suitable operating conditions and more specifically the TCS system’s temperatures that should match the district heating temperatures. Thus, the temperature point that was chosen as a priority was 80 °C, from the range 40- 80 °C set in the partner project NHS. To maintain this condition, therefore, the most suitable condition of pressure of both reactions (according to the equilibrium pressure vs temperature curve) was chosen to be at around 8 bar. This same pressure was chosen for both reactions, since the pressure difference between these reactors and the storage of ammonia (i.e. from 8 to 10 bar) should be as small as possible due to the high costs that can arise in the case of a higher pressure difference (i.e. requiring more compressors and heat exchangers). Inspired by these literature cases, firstly a conceptually suitable TCS system was proposed in this project and after that the final desired system was designed and was implemented and evaluated numerically. The numerical design and optimization of the chosen TCS system was performed herein by using the software Aspen Plus (version 9), which contains both fluids and solids in a simulation environment, using consistent physical properties. This TCS system is designed to store and release heat at around 80 °C and 8 bar through absorption and desorption by using two identical reactors respectively. Each reactor includes the amount of around 1 kg (more specifically 0.985 kg) strontium chloride salt reacting with 1.7 kg of ammonia. A verification system is also modelled in Aspen, using available experimental data from literature. Here, the modelled novel system design was adapted to this chosen other system layout from literature which uses the same reaction pair, yet at different operating conditions. This adapted system design in Aspen was then used to verify the chosen configuration and the reliability of the constructed system for the NHS project. Good agreements between the modelled results in Aspen against the available experimental data of this verification model are obtained. A sensitivity analysis is also conducted herein on the proposed novel TCS system to identify the optimum operating conditions and the behaviour of the chosen most important parameters of the system. The designed system provides an energy storage capacity of 0.5 kWh for the specific amounts (in volumetric flow rates) of ammonia and monoammine of strontium chloride, that comes from the analysis, of 1.08696 e-05 kmol/s and 1.5528 e-06 kmol/s respectively. For these specific values of the HTF, the analysis showed that the volumetric flow rates of the heat and cold external sources must be 1.56 l/min (which is decreasing with the increase of the inlet HTF temperature) and 0.42 l/min (which is increasing with the increase of the inlet HTF temperature) respectively. In conclusion, this study presents an ammonia-SrCl2 TCS benchscale system design that allows continuous heat storage and release, in an easy-to-scale up design, also suggesting optimum operating conditions.
En av de mest avgörande frågorna i dag är skyddet av miljön och utfasningen av fossila bränslen som används allmänt över hela världen för mer effektiva och förnybara resurser. Den största delen av den globala energibehovet idag avser uppvärmnings- och kylapplikationer. Ett sätt att minska fossilbaserad termiskenergianvändning är att lagra överskottsvärmeenergi genom termokemiska lagringsmaterial (TCM) och använda den för värme- och kylbehov vid olika tidpunkter och platser. I samband med detta är ett termokemiskt värmelagringssystem numeriskt utformat i detta mastersexamensprojekt, som en del av ett samarbetsprojekt Neutrons for Heat Storage (NHS) finansierat av Nordforsk. Det termokemiska lagringssystemet (TCS) som är konstruerat utnyttjar den reversibla kemiska reaktionen av ammoniak med en metallhalogenid (MeX) för en värmelagringskapacitet på 0.5 kWh, och frigör och lagrar värme respektive under absorption och desorption av ammoniak till och från MeX. Systemet är designat för lågtemperaturuppvärmningstillämpningar runt 40-80 °C. SrCl2 väljs som det mest lämpliga metallhalogeniden för systemet, baserat på studier som utförts av NHS-projektpartnerna. I ammoniak SrCl2-systemet beaktas endast absorption och desorption mellan SrCl2NH3 och SrCl28NH3. De huvudsakliga orsakerna till detta är att absorptionen/desorptionen mellan den sista aminen och SrCl2 kräver ett betydligt högre/lägre reaktionstryck (för en given temperatur), och resulterar i en betydande volymförändring jämfört med resten av aminerna, och är därför praktiskt taget mindre kostnadseffektivt. Detta mastersexamensprojekt inkluderar en detaljerad genomgång av fyra olika TCS-system från litteratur som använder reaktionen mellan ammoniak och metallhalogenider. Dessa väljs här eftersom dessa anses vara de mest relevanta (från litteratur) jämfört med det valda systemet i denna studie. Det första undersökta systemet är ett system byggt av NHS-projektpartnerna vid Danmarks Tekniska Universitet (DTU). Detta har valts på grund av likheterna med det önskade systemet i det aktuella mastersexamensprojektet, vad gäller systemdesign och parametrar. Detta system fungerar i batch-läge, vilket endast tillåter antingen absorption (dvs värmeavgivning) eller desorption (dvs värmelagring) under en specifik cykel. Således kan en uppgraderad design av detta TCS-system vid DTU möjligen vara en lämplig lösning på forskningsmålen för detta mastersexamensprojekt. Dessutom använder detta TCS-system från DTU ganska liknande driftsförhållanden (temperaturer och tryck) i nivå med det aktuella projektets önskade lågtemperaturintervall på 40-80 °C. Det andra systemet från den litteratur som diskuterats använder två reaktorer för kyla och värmeproduktion, vilket innebär att både laddningsoch urladdningsprocesser sker samtidigt. Denna samtidiga operation är främst anledningen till att systemet undersöktes, eftersom detta är en önskad funktion att uppnå i det aktuella projektet. Nästa system från den litteratur som diskuteras häri använder också två reaktorer för absorptions- och desorptionsprocesser, som fungerar reversibelt när varje process är klar, precis som önskat i detta projekt. Dessa två system (dvs det andra och det tredje diskuterade systemen) använder den reversibla fastgasreaktionen för absorption och desorption mellan SrCl2NH3 och SrCl28NH3, dock vid olika tryck- och temperaturförhållanden. Det andra systemet arbetar nämligen under kombinationer av absorption och desorption av 96 °C, 15 bar och 87 °C, 11 bar, medan det tredje systemet arbetar vid 103 °C, 16 bar respektive 59 °C, 3 bar. Det sista systemet som diskuterats från litteraturen arbetar vid samma temperatur som det önskade systemet gör (dvs. 80 ° C) och genom olika lågtrycksexperiment visar att den fasta salt-gasreaktionen är ett bättre val än reaktionen av det fasta saltet med flytande gasreaktion. De viktigaste skillnaderna mellan alla dessa diskuterade system från litteratur i motsats till det önskade TCS-system i detta mastersexamensprojekt, avser systemdriftläge samt deras tryck och X temperaturförhållanden. Den första skillnaden är att endast ett av alla undersökta system pumpar saltet i fast pulverform, till skillnad från de andra som håller saltet stillastående i reaktorerna och endast pumpar ammoniak. Den andra skillnaden gäller driftsförhållandena under absorptions- och desorptionsreaktioner där dessa system arbetar vid mycket olika tryck- och temperaturförhållanden jämfört med det nuvarande systemet. Således, från översynen av alla system, finns det fyra huvudsakliga lärdomar för att förbättra TCS-systemet vid DTU till det önskade nya systemet. Den första är relaterad till reaktanttransportmekanismen som bör användas i detta system. I detta avseende har det beslutats att hålla det fasta saltet (metallhalogenid) stillastående i varje reaktor (men inte pumpa det istället för ammoniak), till skillnad från de flesta system i litteraturen. Enligt dem andra och tredje lektionerna är den fasta gasreaktionen den mest lämpliga lösningen och endast reaktionerna på absorption och desorption mellan SrCl2∙NH3 och SrCl2∙8NH3 bör övervägas enligt erfarenheten från litteraturen (av de skäl som förklarats tidigare). Den sista lärdomen avser systemets lämpliga driftsförhållanden och mer specifikt TCS-systemets temperaturer för att matcha fjärrvärmetemperaturerna. Den temperaturpunkten valts som prioritet, från området 40-80 °C inställt av moderprojektet NHS, sattes till 80 °C. För att bibehålla detta tillstånd var det lämpligaste tryckvillkoret för båda reaktionerna (enligt jämviktstrycket kontra temperaturkurva) valdes att ligga på cirka 8 bar. Samma tryck valdes för båda reaktionerna, eftersom tryckskillnaden mellan dessa reaktorer och lagring av ammoniak (dvs. från 8 till 10 bar) borde vara så liten som möjligt på grund av de höga kostnaderna som kan uppstå vid högre tryckskillnad (dvs. fler kompressorer krävs och värmeväxlare). Inspirerad av denna litteratur föreslogs för det första ett konceptuellt lämpligt TCS-system i detta mastersexamensprojekt, varefter det slutliga systemet implementerades och utvärderades numeriskt för de önskade förhållandena. Den numeriska utformningen och optimeringen av det valda TCS-systemet utfördes här med hjälp av programvaran Aspen Plus (version 9), som innehåller både vätskor och fasta ämnen i en simuleringsmiljö, med konstant fysiska egenskaper. Detta TCS-system är utformat för att lagra och släppa värme vid cirka 80 °C och 8 bar genom absorption och desorption med användning av två identiska reaktorer respektive. Varje reaktor innefattar cirka 1 kg (närmare bestämt 0.985 kg) strontiumkloridsalt reagerande med 1.7 kg ammoniak. Ett verifieringssystem modelleras också i Aspen med hjälp av tillgängliga experimentella data från litteraturen. I detta anpassades den modellerade nya systemdesignen till denna valda andra verifieringssystemlayout från litteratur, som använder samma reaktionspar, men under olika driftsförhållanden. Denna anpassade systemdesign i Aspen användes sedan för att verifiera den valda konfigurationen och tillförlitligheten för det designade systemet för NHS-projektet. Här erhålls ett bra avtal för denna verifieringssystemdesign mellan Aspenmodellresultaten och experimentdata. Här utförs också en känslighetsanalys för det utformade TCSsystemet i det aktuella projektet för att identifiera de optimala driftsförhållandena och beteendet för de valda viktigaste parametrarna i systemet. Det konstruerade systemet ger en energilagringskapacitet på 0.5 kWh för de specifika mängderna (i volymflöde) av ammoniak och monoamin av strontiumklorid, som kommer från analysen, av 1.08696 e-05 kmol/s och 1.5528 e-06 kmol/s respektive. För dessa specifika värden på värmeöverföringsvätskan visade analysen att de volymetriska flödeshastigheterna för värme och kalla yttre källor måste vara 1.56 l/min (vilket minskar när temperaturen på värmeöverföringsvätskan ökar) och 0.42 l/min (som ökar när temperaturen på värmeöverföringsvätskan ökar). Sammanfattningsvis presenterar denna studie ett ammoniak-SrCl2 TCS-bänkskålsystem som möjliggör kontinuerlig värmelagring och frigöring, har en design som är lätt att anpassa och föreslår också optimala driftsförhållanden.

Content: Sustainable tannery effluent treatment system in achieving required discharge standards including Total Dissolved Solids (TDS) is one of the major challenges faced by the World Leather Industry. Conventional treatment system reduces Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Suspended Solids (SS), heavy metals etc. and not the TDS and salinity. To achieve the TDS level, the tanneries in South India were forced to adopt Zero Liquid Discharge (ZLD) system by incorporating Reverse Osmosis (RO) system and Multiple Effect Evaporator (MEE). Though recovery of water is beneficial to certain extend in adopting ZLD system, the major challenges are high energy consumption, huge operation & maintenance cost and no safe disposal method for large quantity of mixed/contaminated salt generated from MEE. In view of the challenges faced in adoption of ZLD system, sustainable major technological developments have been made to control more than 50% of TDS in the effluent by adopting cleaner tanning process, segregation of saline streams, treatment and recovery of chromium and salt for reuse by the member units. The balance composited waste stream with low TDS is further treated and taken for mixing/dilution with treated domestic sewage to achieve all discharge standards including TDS. This development is being implemented in many tannery clusters in India such as Pallavaram in South India and Jajmau, Unnao, Banthar, etc. in North India. The Common Effluent Treatment Plants (CETPs) are being upgraded with financial support from Govt. of India and respective State Governments. Take-Away: Improved Chrome Recovery System for Reuse, Recovery of Salt from Saline Stream and Reuse, Sustainable TDS Management

El protagonisme creixent de la tecnologia solar termoelèctrica entre el ventall de les energies renovables es centra en la seva capacitat d’adaptar la seva producció a la demanda energètica exigida. La gestionabilitat d’aquest tipus de centrals s’ha aconseguit amb la integració de sistemes d’emmagatzematge tèrmic en les mateixes. La major part dels sistemes d’emmagatzematge tèrmic, ja sigui els que s’utilitzen a nivell comercial com aquells que es troben en fase de desenvolupament proposen l’ús de sals inorgàniques foses com a medi d’emmagatzematge. Aquestes sals presenten l’inconvenient de la seva alta corrosivitat a altes temperatures. Per un costat, s’han analitzat els fenòmens de corrosió associats a les sals solars utilitzades a la planta pilot TES-PS10 mitjançant la instal·lació de racks de testimonis de corrosió als tancs de sals. A més, al finalitzar l’operació de la instal·lació pilot s’ha dut a terme un estudi post-mortem dels seus. Finalment, amb l’objectiu d’abaratir el cost de l’inventari de sals, s’ha analitzat a nivell de laboratori la corrosivitat de diferents mescles de nitrats de baixa puresa. El segon bloc de la tesi es centra en els sistemes d’emmagatzematge tèrmic en calor latent. Concretament, s’analitza la corrosió associada a la mescla peritèctica 46% LiOH-54% KOH proposta com a material de canvi de fase en un mòdul d’evaporació d’instal·lacions termoelèctriques de generació directa de vapor. D’aquesta forma, s’han dut a terme una sèrie d’assajos a nivell de laboratori amb l’objectiu d’avaluar el comportament envers la corrosió de diferents materials en contacte amb aquests hidròxids.
El creciente protagonismo de la tecnología solar se centra en su capacidad para adaptar su producción a la demanda energética exigida. La gestionabilidad de este tipo de centrales se ha conseguido mediante la integración de sistemas de almacenamiento térmico en sales fundidas. El uso de sales fundidas en sistemas de almacenamiento térmico presenta el hándicap de su corrosividad a alta temperatura. El primer bloque de la Tesis analiza los fenómenos de corrosión asociados a las sales solares en la planta piloto TES-PS10 mediante la instalación de racks de corrosión en los tanques de sales. Además, se ha llevado a cabo un estudio post-mortem de componentes de la instalación. Finalmente, se ha analizado a nivel de laboratorio la corrosividad de distintas mezclas de nitrato de baja pureza. El segundo bloque de la tesis se centra en los sistemas de almacenamiento en calor latente. En concreto, se analiza la corrosión asociada a la mezcla peritéctica 46% LiOH-54% KOH propuesta como material de cambio de fase en el módulo de evaporación en plantas de generación directa de vapor. De este modo, se han llevado a cabo ensayos de corrosión a nivel de laboratorio para evaluar el comportamiento a corrosión de distintos materiales en contacto con los hidróxidos.
The growing of concentrated solar power (CSP) within the different renewable energies is due to its ability to adapt the production to the required energy demand. The dispatchability of this type of plants has been achieved through the integration of molten salts thermal storage systems (TES). Molten salts have a handicap associated to their corrosiveness at high temperature. First block of this Thesis analyzes the corrosion phenomena associated with solar salts used in TES-PS10 pilot plant by installing corrosion racks in the salt tanks. Moreover, a postmortem study of different components was performed after facility shut down. Finally, in order to reduce the cost of the salt inventory in TES systems, the corrosivity of different low purity nitrates mixtures has been analyzed at laboratory scale. The second block of the Thesis focuses on latent heat storage systems. Specifically, it has been analyzed the corrosion associated with the proposed 46% LiOH-54% KOH peritectic mixture as a phase change material in the evaporation module of direct steam generation (DSG) CSP plants. Thus, corrosion tests have been performed at laboratory level to evaluate the corrosion performance of several materials in contact with such hydroxides.

En la actualidad, todas las personas tienen miedo de contagiarse del COVID-19, es por ello que buscan soluciones óptimas y eficientes, que no involucren tanto contacto con otras personas, por medio de las nuevas tecnologías. Además, se ha visto un incremento en el uso de metodologías y sistemas ágiles para acelerar determinados procesos, que involucran gran pérdida de tiempo y dinero. Un gran ejemplo; es el uso de los medios digitales como intermediario para contactar a un experto legal y administrativo con el objetivo de que realice determinados trámites sin necesidad de que el cliente salga de su casa, se exponga al covid y realice colas afuera de la institución para solicitar asesoría; evitando así, pérdida de tiempo y mal humor. Por estas razones, hemos visto una oportunidad de negocio para generar valor en dichas personas; la cual se basa en la resolución de trámites más solicitados en la actualidad con la ayuda de profesionales capacitados y las nuevas redes de contacto, que permiten que todo sea más rápido y eficiente. En este presente trabajo, se procederá a desarrollar una investigación con el fin de ver la viabilidad y rentabilidad de nuestro proyecto con el fin de poder proceder a comercializar dicho servicio. Asimismo, se aplicará y desarrollará los conocimientos aprendidos durante el transcurso de la carrera al tratar temas relacionados a distintas áreas como finanzas, marketing, negocios internacionales, logística, entre otros.
At present, all people are afraid of catching COVID-19, which is why they seek optimal and efficient solutions, which are not involved as much contact with other people, through new technologies. In addition, there has been an increase in the use of agile methodologies and systems for certain processes, which involve a great loss of time and money. A great example; is the use of digital media as an intermediary to contact a legal and administrative expert in order to carry out certain procedures without the need for the client to leave their home, expose themselves to covid and queue outside the institution to request advice ; thus avoiding waste of time and bad mood. For these reasons, we have seen a business opportunity to generate value in these people; which is based on the resolution of the most requested procedures nowadays with the help of trained professionals and the new contact networks, which allow everything to be faster and more efficient. In this present work, an investigation will be carried out in order to see the viability and profitability of our project in order to be able to proceed to commercialize said service. Likewise, the knowledge learned during the course of the degree will be applied and developed by dealing with issues related to different areas such as finance, marketing, international business, logistics, among others.
Trabajo de investigación

PV systems in practice experience excessive thermal energy dissipation that is inseparable from the photo-electric conversion process. The temperature of PV cells under continuous illumination can approach 40°C above ambient, causing a drop in the electrical performance of about 30%. The significance of elevated temperature on PV cells inspired various thermal management techniques to improve the operating temperature of the cells and hence their conversion efficiency. Hybrid PV/Thermal (PV/T) collectors that can supply both electrical and thermal energy are attractive twofold solution, being able to cool the PV cells and thus improving the electrical power output as well as collecting the thermal energy by-product for practical utilization. The challenges present on the performance of PV systems due to elevated operating temperature is considered the research problem within this work. In this research, an integrated hybrid heat pipe-based PV/Thermoelectric (PV/TEG) collector is proposed and investigated theoretically and experimentally. The hybrid collector considers modular integration of a PV absorber rated at 170W with surface area of 1.3 m2 serving as power generator as well as thermal absorber. Five heat pipes serving as the heat transport mediums were attached to the rear of the module to extract excessive heat accumulating on the PV cells. The extracted heat is transferred via boiling-condensation cycle within the heat pipe to a bank of TEG modules consisting of five 40 mm x 40 mm modules, each attached to the condenser section of each heat pipe. In principle, the incorporation of heat pipe-TEG thermal waste recovery assembly allow further power generation adopting the Seebeck phenomena of Thermoelectric modules. A theoretical numerical analysis of the collector proposed is conducted through derivation of differential equations for the energy exchange within the system components based on energy balance concepts while applying explicit finite difference numerical approach for solutions. The models developed are integrated into MATLAB/SIMULINK environment to assess the cooling capability of the integrated collector as well as the addition power generation through thermal waste heat recovery. The practical performance of the collector proposed is determined experimentally allowing for validation of the simulation model, hence, a testing rig is constructed based on the system requirements and operating principles. Reduction in the PV cell temperature of about 8°C, which account for about 16% reduction in the PV cell temperature response compared to a conventional PV module under identical conditions is attained. In terms of the power output available from the PV cells, enhanced power performance of additional 5.8W is observed, contributing to an increase of 4% when compared with a PV module. The overall energy conversion efficiency of the integrated collector was observed to be steady at about 11% compared to that of the conventional PV module (9.5%) even at high ambient temperature and low wind speeds. Parametric analysis to assess the performance enhancements associated to the number of heat pipes attached to the PV module is conducted. Increasing the number of heat pipes attached to 15 pipes permits improved thermal management of the PV cells realised by further 7.5% reduction in the PV module temperature in addition to electrical output power improvement of 5%.

Thule Sweden AB utvecklar, tillverkar och marknadsför kompletta och funktionella lasthållarsystem för bilar. De erbjuder en mycket stor bredd av olika lasthållare till över 1500 bilmodeller. De tillverkar lasthållare som cykelhållare, boxar, skidhållare, hållare för vattensport och andra tillbehör. För att en bil skall kunna bära en takbox måste det tillverkas en lasthållare som placeras mellan biltaket och takboxen. En del i denna lasthållare kallas för takbleck och dess form tas fram med en speciell takskanner vilken analyserar biltakets form vid kanterna.

Till detta har en mjukvara tagits fram som Thule kan använda för att söka/lägga till/redigera takbleck, istället för att manuellt söka i en pärm bland 700 olika ritningar. Programvaran var först utvecklad i Microsoft® Visual Studio 2003 (.NET Framework 1.1), men på senare tid omarbetad från grunden i den nyare utvecklingsmiljön Microsoft® Visual Studio 2005 (.NET Framework 2.0).

Innan programmeringen av mjukvaran sattes igång utformades en kravspecifikation från Thule om vad de ville ha för funktioner i programmet. Denna kravspecifikation har under utvecklingens tid ändrats, både under de möten som hållits och på en speciell webbplats som skapats för återkoppling av programmet (”TBS Felhanterings-center”), i form av buggar/ändringar/annat.

Förutom en avdelning i rapporten som behandlar hur denna programvara är uppbyggd, vilka problem som uppstod och hur de löstes, finns även teoretisk information om databaser, XML och andra teknologier.

Resultatet av projektet blev en applikation för hantering av takbleck som kan användas ute i fält (hos kund) utan uppkoppling mot en gemensam databas hos företaget (mot vilken all information synkroniseras). All information som läggs till/redigeras sparas på användarens lokala dator i form av XML som sedan kan synkroniseras mot den gemensamma server-databasen på företaget.

Thule Sweden AB develop, manufacture, and market complete and functional load carriers for cars. They provide a large amount of different load carriers for over 1500 car models. They also manufacture carriers such as bike carriers, roof boxes, ski carriers and water sport carriers. To be able to put a roof carrier on a car, a load carrier must be manufactured and be placed between the car roof and the roof carrier.

We have developed software that the group of workers at Thule can use to search/add/edit brackets, instead of manually search in a folder containing over 700 drawings. The program was first developed in Microsoft Visual Studio 2003 (.NET Framework 1.1), but has been rewritten in Microsoft’s new develop environment Visual Studio 2005 (.NET Framework 2.0).

Before we started to write the program, Thule gave us a specification of requirements that contained information of possible functions in the program. The specification of requirements has been changed a couple of times during our work. We have also put up a website where bugs and changes could be reported.

Except a part in this report, where we describe how the program is built, how we have solved problems, there is also theoretical information about how databases, XML and other techniques work.

The result of this project became an application, which the personnel at Thule can use while they visit their customers. The saved information can later be synchronised with the server.

Dans la conception basée sur des modèles on construit un modèle mathématique du système que l'on utilise pour concevoir le système de sorte qu'il présente les propriétés souhaitées. Pour les systèmes de sûreté critique, il peut être d'une importance capitale de vérifier ces propriétés de sûreté sur le modèle, par exemple, pour tenir compte des variations des paramètres. Le calcul d'un nombre fini de comportements du système par le biais de simulation ne suffit pas à garantir des propriétés de sécurité. Avec une analyse d'atteignabilité on peut calculer une couverture de tous les comportements possibles du système, possiblement infinis. Cette analyse peut prendre en compte de non-déterminisme dans le modèle et peut garantir des propriétés de sécurité. Les systèmes d'intérêt présentent souvent à la fois un comportement continu et discret et de tels systèmes sont appelés systèmes hybrides. Le calcul d'atteignabilité est considéré comme difficile pour les systèmes continus et hybrides. Ce n'est que récemment que des méthodes pour le calcul d'accessibilité ont été développées qui peuvent être mis à l'échèlle. Ils sont basés sur des représentations implicites d'ensembles continus à l'aide du concepte mathématique de la fonction de support. Dans cette thèse, nous développons un outil extensible appelé SpaceEx pour le calcul d'atteignabilité des systèmes hybrides. Deux algorithmes d'atteignabilité ont été mis en œuvre dans SpaceEx, l'un basé sur l'outil PHAVer pour les automates linéaires hybrides et l'autre basé sur les fonctions de support pour les dynamiques affines par morceaux. L'algorithme de fonction support a été mis au point et sa mise à l'échelle a été amélioré en basculant entre différentes représentations d'ensembles continus. Nous proposons un algorithme de calcul d'image des transition discrètes amélioré qui réduit l'erreur de sur-approximation et nous illustrons sa précision et son efficacité avec plusieurs études de cas.

L'identification des modes vibratoires est un sujet prioritaire dans le cadre de la surveillance des structures civiles. Certaines techniques d'identification, les méthodes sous espace, ont prouvé leur adéquation pour l'identification et la détection de changements dans les caractéristiques vibratoires, ceci sous des conditions opérationnelles. Le but de cette thèse est l'amélioration de l'efficacité et de la robustesse de ces approches pour l'identification vibratoire et pour la détection des pannes dans les structures de grande taille, équipées d'un grand nombre de capteurs et fonctionnant en conditions environnementales diverses et bruitées. Dans cette thèse, quatre verrous majeurs ont été levés. D'abord, à partir de mesures collectées à différents points de mesure et sous différentes conditions environnementales, un algorithme d'extraction des déformées est proposé, alliant simplicité, modularité et compacité. Ensuite, une reformulation d'un problème moindre carrés amène à une amélioration conséquente du temps de calcul, lors du calcul multi ordre utilisé pour séparer les vrais modes de structures des modes parasites. D'autre part, une approche statistique pour la détection de pannes est améliorée et modifiée par l'usage d'un résidu robuste aux variations dans l'excitation ambiante inconnue. Finalement est considéré le problème de localisation de fautes quand l'absence de modèle aux éléments finis doit être compensée par un calcul direct de sensibilités à partir des données mesurées. Les différentes méthodes sont validées sur simulations et sont appliquées avec succès pour l'identification et la détection de fautes sur plusieurs structures civiles de grande taille.

An increasing number of software systems must safeguard their confidential data and code, referred to as critical program information (CPI). Such safeguarding is commonly accomplished by isolating CPI in a trusted execution environment (TEE), with the isolated CPI becoming a trusted computing base (TCB). TEE protection incurs heavy performance costs, as TEE-based functionality is expensive to both invoke and execute. Despite these costs, projects that use TEEs tend to have unnecessarily large TCBs. As based on our analysis, developers often put code and data into TEE for convenience rather than protection reasons, thus not only compromising performance but also reducing the effectiveness of TEE protection. In order for TEEs to provide maximum benefits for protecting CPI, their usage must be systematically incorporated into the entire software engineering process, starting from Requirements Engineering. To address this problem, we present a novel approach that incorporates TEEs in the Requirements Engineering phase by using natural language processing (NLP) to classify those software requirements that are security critical and should be isolated in TEE. Our approach takes as input a requirements specification and outputs a list of annotated software requirements. The annotations recommend to the developer which corresponding features comprise CPI that should be protected in a TEE. Our evaluation results indicate that our approach identifies CPI with a high degree of accuracy to incorporate safeguarding CPI into Requirements Engineering.
Master of Science
An increasing number of software systems must safeguard their confidential data like passwords, payment information, personal details, etc. This confidential information is commonly protected using a Trusted Execution Environment (TEE), an isolated environment provided by either the existing processor or separate hardware that interacts with the operating system to secure sensitive data and code. Unfortunately, TEE protection incurs heavy performance costs, with TEEs being slower than modern processors and frequent communication between the system and the TEE incurring heavy performance overhead. We discovered that developers often put code and data into TEE for convenience rather than protection purposes, thus not only hurting performance but also reducing the effectiveness of TEE protection. By thoroughly examining a project's features in the Requirements Engineering phase, which defines the project's functionalities, developers would be able to understand which features handle confidential data. To that end, we present a novel approach that incorporates TEEs in the Requirements Engineering phase by means of Natural Language Processing (NLP) tools to categorize the project requirements that may warrant TEE protection. Our approach takes as input a project's requirements and outputs a list of categorized requirements defining which requirements are likely to make use of confidential information. Our evaluation results indicate that our approach performs this categorization with a high degree of accuracy to incorporate safeguarding the confidentiality related features in the Requirements Engineering phase.

The aim of this research work is to propose a method allowing innovation integration in early design stages and supporting architecture design of complex systems that have significant implications for the rest of overall system life-cycle. Focusing on system architectures generation support, this method proposes to use Bayesian networks combined with Constraint Satisfaction Problem (CSP) techniques in order to semi-automatically generate and evaluate complex systems architectures. Bayesian network model is used to represent the design problem in terms of decision variables, constraints and performances. Furthermore, an architecture generation algorithm is proposed to generate feasible solutions and to cluster them with regard to a given confidence level threshold. This confidence level is representing the estimation of the uncertainty on the overall system. Estimation of architecture performances are also calculated within the Bayesian network. Once the system architectures are generated, a CSP model optimises the component placement regarding placement constraints and optimisation objectives defined by designers. Software has been developed for the purpose of problem modelling and solutions visualisation. Two industrial implementations yielded in a generation of a high number of architecture solutions. In order to test the feasibility of architecture selection in an industrial environment, a study was conducted integrating four system designers. This study underlined the difficulties in defining architecture selection criteria and provides recommendations for the future system architecture selection support.

South Africa has natural resources in mineral feedstock containing gold, manganese, chromium, vanadium, copper, antimony, phosphate rock, uranium, fluorspar and titanium. A high percentage of these ores are exported in unbeneficiated form. There are beneficiation opportunities to transform the raw materials to value-added products, thus increasing employment and stimulating the South African economy. Fluorocarbon (CxFy) gases can be produced via high-temperature plasma processes, where fluorspar and carbon (CaF2 + C) react at -6000K. These gases are traditionally separated by means of costly and unsafe cryogenic distillation. The focus of this project is to propose a feasible separation process and to interlink it to a plasma system in order to develop a conceptual plant that can produce 2500 t/a C2F4 and 625 t/a C3F6 safely and cost-effectively, both with 96% purity. To execute the above a literature survey was done giving vital information on absorption and distillation systems as well as membranes that can be used to separate CF4 from CxFy gas streams at acceptable pressures and temperatures.
Thesis (M.Sc. Engineering Sciences (Chemical Engineering))--North-West University, Potchefstroom Campus,

Trusted execution environments (TEEs) are an emerging technology that provides a protected hardware environment for processing and storing sensitive information. By using TEEs, developers can bolster the security of software systems. However, incorporating TEE into existing software systems can be a costly and labor-intensive endeavor. Software maintenance—changing software after its initial release—is known to contribute the majority of the cost in the software development lifecycle. The first step of making use of a TEE requires that developers accurately identify which pieces of code would benefit from being protected in a TEE. For large code bases, this identification process can be quite tedious and time-consuming. To help reduce the software maintenance costs associated with introducing a TEE into existing software, this thesis introduces ML-TEE, a recommendation tool that uses a deep learning model to classify whether an input function handles sensitive information or sensitive code. By applying ML-TEE, developers can reduce the burden of manual code inspection and analysis. ML-TEE's model was trained and tested on functions from GitHub repositories that use Intel SGX and on an imbalanced dataset. The accuracy of the final model used in the recommendation system has an accuracy of 98.86% and an F1 score of 80.00%. In addition, we conducted a pilot study, in which participants were asked to identify functions that needed to be placed inside a TEE in a third-party project. The study found that on average, participants who had access to the recommendation system's output had a 4% higher accuracy and completed the task 21% faster.
Master of Science
Improving the security of software systems has become critically important. A trusted execution environment (TEE) is an emerging technology that can help secure software that uses or stores confidential information. To make use of this technology, developers need to identify which pieces of code handle confidential information and should thus be placed in a TEE. However, this process is costly and laborious because it requires the developers to understand the code well enough to make the appropriate changes in order to incorporate a TEE. This process can become challenging for large software that contains millions of lines of code. To help reduce the cost incurred in the process of identifying which pieces of code should be placed within a TEE, this thesis presents ML-TEE, a recommendation system that uses a deep learning model to help reduce the number of lines of code a developer needs to inspect. Our results show that the recommendation system achieves high accuracy as well as a good balance between precision and recall. In addition, we conducted a pilot study and found that participants from the intervention group who used the output from the recommendation system managed to achieve a higher average accuracy and perform the assigned task faster than the participants in the control group.

I proposed the study of two distinct aspects of Ten-Eleven Translocation 2 (TET2) protein for understanding specific functions in different body systems. In Part I, I characterized the molecular mechanisms of Tet2 in the hematological system. As the second member of Ten-Eleven Translocation protein family, TET2 is frequently mutated in leukemic patients. Previous studies have shown that the TET2 mutations frequently occur in 20% myelodysplastic syndrome/myeloproliferative neoplasm (MDS/MPN), 10% T-cell lymphoma leukemia and 2% B-cell lymphoma leukemia. Genetic mouse models also display distinct phenotypes of various types of hematological malignancies. I performed 5-hydroxymethylcytosine (5hmC) chromatin immunoprecipitation sequencing (ChIP-Seq) and RNA sequencing (RNA-Seq) of hematopoietic stem/progenitor cells to determine whether the deletion of Tet2 can affect the abundance of 5hmC at myeloid, T-cell and B-cell specific gene transcription start sites, which ultimately result in various hematological malignancies. Subsequent Exome sequencing (Exome-Seq) showed that disease-specific genes are mutated in different types of tumors, which suggests that TET2 may protect the genome from being mutated. The direct interaction between TET2 and Mutator S Homolog 6 (MSH6) protein suggests TET2 is involved in DNA mismatch repair. Finally, in vivo mismatch repair studies show that the loss of Tet2 causes a mutator phenotype. Taken together, my data indicate that TET2 binds to MSH6 to protect genome integrity. In Part II, I intended to better understand the role of Tet2 in the nervous system. 5-hydroxymethylcytosine regulates epigenetic modification during neurodevelopment and aging. Thus, Tet2 may play a critical role in regulating adult neurogenesis. To examine the physiological significance of Tet2 in the nervous system, I first showed that the deletion of Tet2 reduces the 5hmC levels in neural stem cells. Mice lacking Tet2 show abnormal hippocampal neurogenesis along with 5hmC alternations at different gene promoters and corresponding gene expression downregulation. Through the luciferase reporter assay, two neural factors Neurogenic differentiation 1 (NeuroD1) and Glial fibrillary acidic protein (Gfap) were down-regulated in Tet2 knockout cells. My results suggest that Tet2 regulates neural stem/progenitor cell proliferation and differentiation in adult brain.

Tea is an important crop in Tanzania, contributing over US$45 million to exports each year. It is grown by over 30,000 smallholder households, and a further 10,000 people are employed in the estates sector. In this context, this study explores the current and potential contribution of the smallholder tea sector towards economic sustainability of the Tanzanian tea industry and rural livelihoods. Following literature review and an exploratory study of key stakeholders, a methodology incorporating two main components, an Asset Based Model of Sustainability and a Value Chain Assessment Model, was developed and applied to assess the sustainability of the smallholder tea production systems. The tea based livelihood systems and the associated tea value chains for three case study areas were compared involving a survey of over 300 tea growing and over 100 non-tea growing households, and three processing factories. The study showed that there is an existing synergy between processing factories and smallholder producers which is important for the future development as factories are set to expand the volume of greenleaf sourced from smallholders. At farm level, greenleaf prices, yield, access to input credit, access to research and extension support, availability of farm labour, and access to a reliable greenleaf markets were identified as critical factors that influence the livelihood of the tea growing households. The quantitative analysis showed clear association between farmers involvement in tea production and accumulation of assets (natural, physical and financial), confirming the role of tea in supporting livelihoods. The study concludes that the smallholder tea production systems can contribute to sustainable livelihood systems. Finally the study gives recommendation for various groups of stakeholders regarding ways to improve the performance of the smallholder production systems.

Tea is an important crop in Tanzania, contributing over US$45 million to exports each year. It is grown by over 30,000 smallholder households, and a further 10,000 people are employed in the estates sector. In this context, this study explores the current and potential contribution of the smallholder tea sector towards economic sustainability of the Tanzanian tea industry and rural livelihoods. Following literature review and an exploratory study of key stakeholders, a methodology incorporating two main components, an Asset Based Model of Sustainability and a Value Chain Assessment Model, was developed and applied to assess the sustainability of the smallholder tea production systems. The tea based livelihood systems and the associated tea value chains for three case study areas were compared involving a survey of over 300 tea growing and over 100 non-tea growing households, and three processing factories. The study showed that there is an existing synergy between processing factories and smallholder producers which is important for the future development as factories are set to expand the volume of greenleaf sourced from smallholders. At farm level, greenleaf prices, yield, access to input credit, access to research and extension support, availability of farm labour, and access to a reliable greenleaf markets were identified as critical factors that influence the livelihood of the tea growing households. The quantitative analysis showed clear association between farmers involvement in tea production and accumulation of assets (natural, physical and financial), confirming the role of tea in supporting livelihoods. The study concludes that the smallholder tea production systems can contribute to sustainable livelihood systems. Finally the study gives recommendation for various groups of stakeholders regarding ways to improve the performance of the smallholder production systems.

The world is ever increasing in its energy usage, making energy that is sustainable and secure harder to achieve. To fulfil the Paris agreement to limit global warming, the world needs to transition from fossil fuels toward more renewable energy sources, like wind and solar, but these sources have fluctuation in supply which often create a mismatch with demand. To combat this issue, thermal energy storage can be utilized, and one such technology is latent heat thermal energy storage. This study aimed to investigate the potential of latent heat thermal energy storage by developing a simple model of such a system and studying its impact on Rocklunda’s sport facilities. The model was developed by using MATLAB, primarily using the photovoltaic overproduction of the facilities to store as energy for the latent heat thermal energy storage. The implemented storage, based on the model’s result, had overall positive impact on the facilities. The optimized storage capacity was about 510 kWh, which throughout the storage’s lifetime would save ~4 989 MWh worth of heat by using the best performing phase change material: aluminium-silicon. The storage would also be able to utilize ~82% of the annual photovoltaic overproduction that would otherwise be unused/sold as well as reducing the heat demand by ~12% by using the heat stored via the storage. The implementation also proved to have beneficial effects on the environment as the saved heat was the equivalent of mitigating ~304 ton of CO2 emissions. Furthermore, there is a profit of ~236 000 SEK.
Reduction and Reuse of energy with interconnected Distribution and Demand (R2D2)

Radio signals transmitted by GPS satellites orbiting the Earth are modulated as they propagate through the electrically charged plasmasphere and ionosphere in the near-Earth space environment. Through a linear combination of GPS range and phase measurements observed on two carrier frequencies by terrestrial-based GPS receivers, the ionospheric total electron content (TEC) along oblique GPS signal paths may be quantified. Simultaneous observations of signals transmitted by multiple GPS satellites and observed from a network of South African dual frequency GPS receivers, constitute a spatially dense ionospheric measurement source over the region. A new methodology, based on an adjusted spherical harmonic (ASHA) expansion, was developed to estimate diurnal vertical TEC over the region using GPS observations over the region. The performance of the ASHA methodology to estimate diurnal TEC and satellite and receiver differential clock biases (DCBs) for a single GPS receiver was first tested with simulation data and subsequently applied to observed GPS data. The resulting diurnal TEC profiles estimated from GPS observations compared favourably to measurements from three South African ionosondes and two other GPS-based methodologies for 2006 solstice and equinox dates. The ASHA methodology was applied to calculating diurnal two-dimensional TEC maps from multiple receivers in the South African GPS network. The space physics application of the newly developed methodology was demonstrated by investigating the ionosphere’s behaviour during a severe geomagnetic storm and investigating the long-term ionospheric stability in support of the proposed Square Kilometre Array (SKA) radio astronomy project. The feasibility of employing the newly developed technique in an operational near real-time system for estimating and dissimenating TEC values over Southern Africa using observations from a regional GPS receiver network, was investigated.

The district heating load is seasonally dependent, with a low load during periods of high ambient temperature. Thermal energy storage (TES) has the potential to shift heating loads from winter to summer, thus reducing cost and environmental impact of District Heat production. In this study, a concept of high temperature borehole thermal energy storage (HT-BTES) together with a pellet heating plant for temperature boost, is presented and evaluated by its technical limitations, its ability to supply heat, its function within the district heating system, as well as its environmental impact and economic viability in Gothenburg, Sweden, a city with access to high quantities of waste heat. The concept has proven potentially environmentally friendly and potentially profitable if its design is balanced to achieve a good enough supply temperature from the HT-BTES. The size of the heat storage, the distance between boreholes and low borehole thermal resistance are key parameters to achieve high temperature. Profitability increases if a location with lower temperature demand, as well as risk of future shortage of supply, can be met. Feasibility also increases if existing pellet heating plant and district heating connection can be used and if lower rate of return on investment can be accepted. Access to HT-BTES in the district heating network enables greater flexibility and availability of production of District Heating, thereby facilitating readjustments to different strategies and policies. However, concerns for the durability of feasible borehole heat exchangers (BHE) exist in high temperature application.
Värmebehovet är starkt säsongsberoende, med låg last under perioder av högre omgivningstemperatur och hög last under perioder av lägre omgivningstemperaturer. I Göteborg finns en stor mängd spillvärme tillgängligt för fjärrvärmeproduktion sommartid när behovet av värme är lågt. Tillgång till säsongsvärmelager möjliggör att fjärrvärmeproduktion flyttas från vinterhalvår till sommarhalvår, vilket kan ge såväl lönsamhet som miljönytta. Borrhålsvärmelager är ett förhållandevis billigt sätt att lagra värme, och innebär att berggrunden värms upp under sommaren genom att varmt vatten flödar i borrhål, för att under vinterhalvåret användas genom att låta kallt vatten flöda i borrhålen och värmas upp. I traditionella borrhålsvärmelager används ofta värmepump för att höja värmelagrets urladdade temperatur, men på grund av höga temperaturkrav för fjärrvärme kan kostnaden för värmepump bli hög. I denna rapport föreslås ett system för att klara av att nå höga temperaturer till en lägre kostnad. Systemet består av ett borrhålsvärmelager anpassat för högre temperaturer (HT-BTES) samt pelletspannor för att spetsa lagrets utgående fluid för att nå hög temperatur. Syftet med rapporten är att undersöka potentialen för detta HT-BTES-system med avseende på dess tekniska begränsningar, förmåga till fjärrvärmeleverans, konsekvenser för fjärrvärmesystemet, samt lönsamhet och miljöpåverkan. För att garantera att inlagringen av värme inte är så stor att priset för inlagrad värme ökar väsentligt, utgår inlagringen från hur mycket värme som kyls bort i fjärrvärmenätet sommartid. I verkligheten finns betydligt mer värme tillgänglig till låg kostnad. När HT-BTES-systemet producerar fjärrvärme, ersätts fjärrvärmeproduktion från andra produktionsenheter, förutsatt att HT-BTES-systemets rörliga kostnader är lägre. I Göteborg ersätts främst naturgas från kraftvärme, men också en del flis. Kostnadsbesparingen beror på differensen för total fjärrvärmeproduktionskostnad med och utan HT-BTES-systemet. Undersökningen visar att besparingen är större om HT-BTES-systemet placeras i ett område där det är möjligt att mata ut fjärrvärme med lägre temperatur. Om urladdning från HT-BTES kan ske med hög temperatur ökar också besparingen. Detta sker om lagrets volym ökar, om avståndet mellan borrhål minskar eller om värmeöverföringen mellan det flödande vattnet i borrhålen och berggrunden ökar. Dessa egenskaper för lagret leder också till minskade koldioxidutsläpp. Storleken på besparingen beror dock i hög grad på hur bränslepriser utvecklas i framtiden. Strategiska fördelar med HT-BTES-systemet inkluderar; minskad miljöpåverkan, robust system med lång teknisk livslängd (för delar av HT-BTES-systemet), samt att inlagring av värme kan ske från många olika produktionsenheter. Dessutom kan positiva bieffekter identifieras. Undersökningen visar att HT-BTES-systemet har god potential att ge lönsamhet och minskad miljöpåverkan, och att anläggning och drift av lagret kan ske utan omfattande lokal miljöpåverkan. Det har också visats att de geologiska förutsättningarna för HT-BTES är goda på många platser i Göteborg, även om lokala förhållanden kan skilja sig åt. För att nå lönsamhet för HT-BTES-systemet krävs en avvägning på utformning av lagret för att nå hög urladdad temperatur utan att investeringskostnaden blir för stor. Undersökningen visar att om anslutning av HT-BTES-systemet kan ske mot befintlig anslutningspunkt eller till befintlig värmepanna kan investeringskostnaden minska och därmed lönsamheten öka. Placering av HT-BTES-systemet i områden med risk för överföringsbegränsningar kan också minska behovet av att förstärka fjärrvärmenätet, och således bidra till att minska de kostnader som förstärkning av nätet innebär. Betydelsefulla parametrar för att nå lönsamhet för HT-BTES-system inkluderar dessutom kostnaden för inlagrad värme liksom vilket vinstkrav som kan accepteras. Tillgång till HT-BTES möjliggör ökad nyttjandegrad och flexibilitet för fjärrvärmeproduktionsenheter, och därmed ökad anpassningsmöjlighet till förändrade förutsättningar på värmemarknaden. Dock återstår att visa att komponenter som klarar de höga temperaturkraven kan tillverkas till acceptabel kostnad.

The present study aims to declare strategies that a higher education institute (namely TEI of Athens) could apply, in order to dynamically offer distance learning courses and certifications. The study introduces distance learning, focusing not only on technology but also on its significance for students and adult professionals who are looking to enhance their knowledge and skills as well as advantages and disadvantages this may have. In order to define the axles upon which the proposed strategy will be set, a distance learning planning template is presented, in order to clarify recommendations that should be made for a successful distance learning implementation. Moreover, it presents the associated research carried out; the methodology used and finally presents the summary of its outcomes. The outcomes are merged with the planning template, and a set of suggestions is finally made to the institution, that may assist to a successful implementation of a potential distance learning implementation.

The focus of this thesis work was the development of an approachto couple a previosly existing Thermal Energy Storage (TES) modelwritten in C++ with a Simulink/Simscape plant model to simulate anAdvanced Adiabatic Compressed Air Energy Storage (AA-CAES) plant.After the creation and validation of such tool, the complete modelwas used to run simulations, with the aim of assessing the AA-CAESplant's performance under multiple patterns of charge anddischarge.Most of the works found in the literature only provide values ofstorage efficiency obtained from analytical approaches, whilethose that use simulation tools provide average values ofefficiencies when the plant is performing a series of identicalcycles of charge and discharge. During this thesis project,instead, simulations were performed for consecutive irregularcycles determined as the plant response to the electric grid powerrequest. The average efficiency values obtained provide thereforea better representation of how the plant would perform in realapplications.The results show that, under the assumptions made, the AA-CAESplant's overall storage efficiency is influenced very weakly byalterations of the charge-discharge patterns, and that goodperformances can be expected not only for identical chargedischargeconsucutive cycles, but for any pattern that observesthe cavern pressure limits, as long as the thermal energy storageis sized wisely.In addition, a sensitivity analysis was performed in order toassess the influence of turbomachinery efficiency on overallstorage efficiency, for a specified plant layout. The results showthat the turbine efficiency is the most affecting parameter to theplant's performance, while the impact of the main compressors'sinefficiency is mitigated by the thermal recovery that takes placein the TES.The present work confirms that AA-CAES is a promising technologyand that storage efficiencies above 70% can be achieved even inrealistic production scenarios.Finally, future steps for more accurate simulations of plants'performances and more detailed energy production scenarios areproposed.MSc ET 18007Examinator: Joakim WidénÄmnesgranskare: Ane HåkanssonHandledare:

Thesis (MEd)--University of Stellenbosch, 2005.
ENGLISH ABSTRACT: Research shows that misconceptions about calculations develop in many classrooms without being noticed and these are not corrected by repeated routine exercises. The misconceptions formed are at times the result of inappropriate models used to solve problems. An even bigger concern is that these particular models sometimes provide the correct answers by accident. This may result in the learner's belief in the models being reinforced, as described by Swan (n.d.). The aim of this study is to identify the misconceptions related to the use of decimal fractions by Grade 8 and 9 learners and then, through the use of an intervention program, to address the learners' misconceptions and attempt to correct them. Two schools were involved in this study. The group of learners from school A served as a control group to determine the success of the intervention in learners from school B. The results of school A, the frequency and nature of errors were compared with the test results of school B as well as described by interviews with learners from school B. After the diagnostic tests and interview, the learners' answers were compared with those already described in literature. The learners from school B participated voluntarily in the intervention program. Learners from both schools wrote a post-test and the results were compared with those of a pre-test. The conclusion of this study is that there are misconceptions concerning calculations with decimal fractions at Grade 8 and 9 level. These misconceptions are formed during the intermediate phase and are not suitably corrected. The intervention program, for various reasons, had limited success. These reasons are discussed and recommendations are made for future intervention programs.
AFRIKAANSE OPSOMMING: Navorsing toon dat wanbegrippe ten opsigte van berekeninge in baie klaskamers onopgemerk verbygaan en dat dit nie reggestel word deur herhaalde roetine oefeninge nie. Wanbegrippe wat kinders vorm is onder andere die gevolg van onvanpaste modelle wat gebruik word vir die oplos van probleme. 'n Groter gevaar is dat hierdie onvanpaste modelle toevallig die regte antwoord lewer. Dit kan dan veroorsaak dat die leerder se vertroue op die modelle net versterk word, soos Swan (s.j.) dit beskryf. Die doel van hierdie studie is om wanbegrippe ten opsigte van bewerkings met desimale breuke by Graad 8 en 9 leerders te identifiseer en dan deur middel van 'n intervensieprogram die leerders se wanbegrippe aan te spreek en te probeer regstel. Twee skole is by hierdie studie betrek. Die groep leerders van skool A sou dien as 'n kontrolegroep om die intervensie-sukses van die leerders van skool B te bepaal. Die skool A resultate en frekwensie van foute asook die aard daarvan is vergelyk met die toetse van skool B en beskryf op grond van onderhoude met die leerders van skool B. Ná die diagnostiese toets en onderhoud is die leerders se antwoorde vergelyk met dié wat reeds in die literatuur beskryf is. Die leerders van skool B is op vrywillige basis by 'n intervensieprogram betrek. Beide skole se leerders het daarna 'n natoets geskryf en die resultate is vergelyk met dié van die voortoets. Die gevolgtrekking wat uit hierdie studie gemaak word, is dat daar wanbegrippe ten opsigte van bewerkings met desimale breuke op graad 8 en 9 vlak aanwesig is. Hierdie wanbegrippe is in die intermediêre fase gevorm en nie reggestel nie. Die intervensieprogram het om verskeie redes slegs beperkte sukses gehad. Hierdie redes word bespreek en aanbevelings word gemaak vir toekomstige intervensieprogramme.

This thesis contains the development of a software capable of evaluating the performance of ten unique photovoltaic (PV) systems located 10 kilometers outside of Västerås, Sweden. The ten systems have different configurations according to this list: Dual-axis tracking Single-axis tracking with 30°tilt Ground mounted, free-standing with 19° tilt Ground mounted, free-standing with 41° tilt Roof mounted with 19°tilt   Each of the above configurations exist with and without installed power optimizers adding up to a total of ten unique systems. The development goal for the evaluation software is to provide the user with a variety of tools to determine which of the systems that has the best yield and performance. Integrated in the development of the software is therefore a literature study where it is investigate how photovoltaic systems operate and especially how their performance can be evaluated. Some of the frequently used parameters are; system yield, reference yield and performance ratio. The software features are focused around presenting the data collected from the PV systems in a variety of graphs. The different types of graph are designed to let the user easy compare the data between the systems and thus find how and why a particular system is performing better than the others. The software is developed in a Matlab environment and has an intuitive user interface. The thesis time-frame is too short for any conclusive result to be presented, but to showcase the software features a short-termed evaluation of the systems have been performed. The period evaluated is a three week period in the middle of May 2014. The short-termed evaluation highlights several scenarios and issues that can arise. It has been detected throughout the project that it is difficult to separate which effects that causes one system to be better than the other. Irregularities seen in the data can be caused by many factors. Some of the more evident are; installed power optimizers, differences in system configurations and shadow patterns. By using the software effects like array shading and inaccurate measurements has been discovered.
Evaluation of first MW PV plant in Sweden

In order to avoid the accidents like Fukushima Disaster and monitor the operation status of nuclear power plant, a wireless sensor system which is powered by the Thermoelectric Generator (TEG) Energy Harvester is designed and built. Meanwhile, a power converter circuit has also been designed to converter the output voltage of TEG Energy Harvester to a DC voltage to charge the battery or power the application systems. Several prototypes based on this power converter circuit have been built for Thermoelectric Generator (TEG) energy harvester and tested in both working and laboratory conditions. The reliability of the TEG Energy Harvester system in the gamma radiation environment has been examined in the experiments. Based on the experiments results, the design was optimized. And an optimized Maximum Power Point Tracking algorithm has also been applied in the prototype to extract the maximum power from the TEG Energy Harvester in all conditions. The TEG Energy Harvester system would be greatly simplified as a new type of sensor will be applied. The design of the signal conditioning circuit for this sensor has also been presented.
Master of Science

L'objectif de cette thèse est de définir un outil d'aide à la conception des associations machine-convertisseur et de leurs commandes ; partir d'un cahier des charges d'une application donnée. Afin d'établir les performances de ces ensembles, le concepteur utilise dans un premier temps, un outil de simulation de ces associations avant de construire un prototype. Les premiers chapitres sont consacrés à la description d'un tel outil avec comme objectif principal de permettre une génération automatique d'équations globales et de programmes de simulation à partir d'une description modulaire de l'application. Les derniers chapitres abordent les principes d'un système expert d'aide à la conception de ces associations. Ils présentent le côté itératif et systématique de la conception et proposent un formalisme de description de la connaissance qui a permis de mettre en oeuvre un système expert où certaines étapes du processus de conception sont systématisées

High-field magnetic resonance imaging (MRI) is a very promising concept as it benefits from a significant improvement in the signal-to-noise ratio (SNR), a measure that directly affects image resolution. However, as the resonant wavelength approaches the dimensions of the object being imaged, the wave propagation effects of the radio frequency (RF) field significantly deteriorate the uniformity of the excitation pattern, thus leading to contrast aberrations and distortions in the resulting image. Recent proof-of-concept studies have shown the merits of parallel transmission techniques in accurately controlling the RF magnetic field whereas novel coil arrangements, such as the TEM resonator, have provided the necessary platform for conducting truly parallel excitations experiments. The purpose of this thesis is to provide a comprehensive study on the design of the TEM resonator by comparing two modelling techniques. The first technique uses multi-conductor transmission line theory to model the coil; the second technique uses the brute-force computational algorithm called finite-difference time-domain (FDTD). The two techniques are compared in terms of the S11 trends observed while varying TEM resonator design parameters such as the capacitor values and the line element geometry. A difference of 15% in the coil response was observed for an MRI system of 3-Tesla field strength. This modelling error increases with resonant frequency and reaches the 40% mark for a high-field MRI system of 7-Tesla field strength. Despite the diverging results for increasing frequency, this study shows that the variation of design parameters in each modelling technique exhibit comparable trends.
L'imagerie par résonance magnétique (IRM) à haut champ est un concept très promettant car elle bénéficie d'une amélioration importante du rapport signal-bruit, une mesure qui affecte directement la résolution de l'image. Cependant, quand la longueur d'onde de résonance se rapproche des dimensions le l'objet sous examination, les effets de propagation d'onde du champ radiofréquence (RF) déteriore de façon significative l'uniformité du motif de champ d'excitation, ainsi menant à des aberrations de contraste et des distortions dans l'image. Des études récentes ont validé le principe de transmission parallèle pour contrôler le champ magnétique RF tandis que de nouveaux arrangements d'antennes, tel que le résonateur TEM, ont permis des expériences avec des transmission réellement en parallèle. Le but de ce mémoir est d'étudier la conception du résonateur TEM en comparant deux techniques de modélisation. La première technique utilise la théorie de ligne de transmission à conducteurs multiples; la deuxième technique utilise un algorithme de calcul par force brute: la méthode des différences finies dans le domaine temporel (FDTD). Les deux techniques sont comparées par rapport aux tendances observées lorsque les paramètres du résonateur TEM, tel que la valeur des condensateurs et la géométrie des lignes microbandes, sont variés. Une différence de 15% dans la réponse de l'antenne a été observé pour un système d'IRM de 3 Tesla. L'erreur de modélisation augmente avec la fréquence de résonance pour atteindre 40% dans un système d'IRM de 7 Tesla. Malgré les résultats divergents, cette étude démontre que la variation des paramètres de l'antenne présente des tendances comparables dans les deux méthodes.

International Telemetering Conference Proceedings / October 21, 2002 / Town & Country Hotel and Conference Center, San Diego, California
Replacing and maintaining sensors in existing legacy systems is costly and time consuming since no information beyond voltage or current is supplied by these sensors. When a sensor is replaced or added, information for that sensor has to be incorporated by the software programmer into the main system software – a costly and time-consuming process. A method has been developed to give these old sensors the intelligence to meet the requirements of the proposed IEEE P1451.3 standard. This is accomplished with no changes to the legacy hardware and a minor, one time change to the legacy main system software.