We are concerned with the high-fidelity subsurface imaging of the soil, which commonly arises in geotechnical site characterization and geophysical explorations. Specifically, we attempt to image the spatial distribution of the Lame parameters in semi-infinite, three-dimensional, arbitrarily heterogeneous formations, using surficial measurements of the soil's response to probing elastic waves. We use the complete waveforms of the medium's response to drive the inverse problem. Specifically, we use a partial-differential-equation (PDE)-constrained optimization approach, directly in the time-domain, to minimize the misfit between the observed response of the medium at select measurement locations, and a computed response corresponding to a trial distribution of the Lame parameters. We discuss strategies that lend algorithmic robustness to the proposed inversion schemes. To limit the computational domain to the size of interest, we employ perfectly-matched-layers (PMLs). The PML is a buffer zone that surrounds the domain of interest, and enforces the decay of outgoing waves. In order to resolve the forward problem, we present a hybrid finite element approach, where a displacement-stress formulation for the PML is coupled to a standard displacement-only formulation for the interior domain, thus leading to a computationally cost-efficient scheme. We discuss several time-integration schemes, including an explicit Runge-Kutta scheme, which is well-suited for large-scale problems on parallel computers. We report numerical results demonstrating stability and efficacy of the forward wave solver, and also provide examples attesting to the successful reconstruction of the two Lame parameters for both smooth and sharp profiles, using synthetic records. We also report the details of two field experiments, whose records we subsequently used to drive the developed inversion algorithms in order to characterize the sites where the field experiments took place. We contrast the full-waveform-based inverted site profile against a profile obtained using the Spectral-Analysis-of-Surface-Waves (SASW) method, in an attempt to compare our methodology against a widely used concurrent inversion approach. We also compare the inverted profiles, at select locations, with the results of independently performed, invasive, Cone Penetrometer Tests (CPTs). Overall, whether exercised by synthetic or by physical data, the full-waveform inversion method we discuss herein appears quite promising for the robust subsurface imaging of near-surface deposits in support of geotechnical site characterization investigations.

Cette thèse s’inscrit dans la thématique d’évaluation des ouvrages par des méthodes nondestructives. Le double objectif est de développer un code permettant d’effectuer au choixl’identification de paramètres par analyse inverse en utilisant un algorithme méta heuristique, ou dedéfinir une métrologie optimale (nombre de capteurs, positions, qualité) sur une structure, en vued’une identification de paramètres. Nous avons développé un code permettant de répondre à cesdeux objectifs. Il intègre des mesures in situ, un modèle mécanique aux éléments finis de lastructure étudiée et un algorithme d’optimisation méta heuristique appelé algorithme d’optimisationpar essaim particulaire. Ce code a d’abord été utilisé afin de caractériser l’influence de la métrologiesur l’identification de paramètres par analyse inverse, puis, en phase expérimentale, nous avonstravaillé sur des problèmes d’interactions sol structure. Un travail a également été réalisé surl’identification et la caractérisation de défauts par sollicitations au marteau d’impact. Enfin unexemple d’optimisation de métrologie (nombre de capteurs, positions et qualité) a été réalisé enutilisant le code original adapté pour cette étude. / This thesis deals with non-destructive evaluation in civil engineering. The objective is of two-fold:developing a code that will identify mechanical parameters by inverse analysis using a metaheuristicalgorithm, and developing another code to optimize the sensors placement (with respect tothe number and quality of the sensors) in order to identify mechanical parameters with the bestaccuracy. Our code integrates field data, a finite element model of the studying structure and aparticle swarm optimization algorithm to answer those two objectives. This code was firstly used tofocus on how the sensors placement, the number of used sensors, and their quality impact theaccuracy of parameters’ identification. Then, an application on a soil structure interaction wasconducted. Several tests to identify and characterize defaults using an impact hammer were alsocarried on. The last application focused on the optimization of the metrology in order to identifymechanical parameters with the best accuracy. This last work highlights the possibilities of theseresearches for structural health monitoring applications in civil engineering project.

With the increasing importance of CO2 as natural refrigerant with low Global Warming Potential(GWP) ejectors have been used in a number of recent installations to recover expansion work atthe high operating pressures of these systems. In colder climates, this is particularly seen in combinationwith heat recovery due to the high compressor discharge pressures.This work analyses the field measurement data of two ice rink refrigeration systems with integratedvapor ejectors and two supermarket refrigeration systems with integrated liquid ejectors, alllocated in northern Europe. The aim is to evaluate the interaction of the ejector with the refrigerationsystem in practical applications. A theoretical model of the ejector systems is developed andevaluated in parallel as a reference for the analysed system installations.The model of the analysed vapor ejector system shows an increasing eciency improvement potentialby the ejector for higher gas cooler outlet temperatures, while the liquid ejector systemmodel indicates higher eciency improvement potential at relatively lower gas cooler outlet temperaturesand pressures.From the vapor ejector field data evaluation, this is confirmed with additional findings of lowejector work recovery eciencies at low gas cooler outlet temperatures. Furthermore, problemsin the ejector operation are found for too low evaporation temperatures in one of the systems. Inaddition, an unstable ejector control at certain operating conditions is linked to a decreasing ejectorperformance. While the ejector is found not to provide any significant savings in one of the systemsmainly due to low evaporation temperatures, the other ice rink system is found to achievetotal energy savings of 7% from the ejector.For the liquid ejector field data evaluation, the ejectors are found to work as expected for the purposeof removing liquid from the low-pressure receiver. However, overfed evaporation conditionsare only found temporarily for most cabinets in the analysed systems, with remaining high averagesuperheat values. Low required air supply temperatures in the cabinets and the dimensioning of theexpansion valves at the evaporator inlet are identified as possible limitations for a further decreaseof the superheat and increase of the evaporation temperature. / Med den ökande betydelsen av CO2 som naturligt köldmedium med låg global uppvärmningspotential(GWP) har ejektorer använts i ett antal nya installationer för att återvinna expansionsarbetevid de höga drifttrycken i dessa system. I kallare klimat är detta särskilt vanligt i kombination medvärmeåtervinning på grund av de höga utloppstrycken i kompressorerna.I detta arbete analyseras fältmätdata från två kylsystem för isbanor med integrerade ångejektoreroch två kylsystem för livsmedelsbutiker med integrerade vätskeejektorer. Samtliga system finns inorra Europa. Syftet med studien är att utvärdera ejektorns samverkan med kylsystemet i praktiskatillämpningar. En teoretisk modell av ejektorsystemen utvecklas och utvärderas parallellt som referensför de analyserade systeminstallationerna.Modellen för det analyserade ångejektorsystemet visar att potentialen för e ektivitetsförbättringgenom ejektorn ökar vid högre utloppstemperaturer för gaskylare, medan modellen försystemet med vätskeutkastare visar att potentialen för e ektivitetsförbättring ökar vid relativt lägreutloppstemperaturer och tryck för gaskylare.Detta bekräftas i utvärderingen av fältdata från ångejektorsystemen som vid låga utloppstemperatureri gaskylaren samtidigt ger låg e ektivitet för ejektorn. Dessutom noteras problemmed ejektorns funktion vid för låga förångningstemperaturer i ett av systemen. En instabilstyrning av ejektorn vid vissa driftsförhållanden leder vidare till en minskad ejektore ektivitet.Medan ejektorn inte ger några betydande besparingar i det ena systemet, främst på grund av lågaavdunstningstemperaturer, har en total energibesparing på 7% från ejektorn hittats i den andra isbanan.När det gäller utvärderingen av fältdata för vätskeejektorer konstateras att ejektorerna fungerar somförväntat för att avlägsna vätska från vätskeavskiljaren. För de flesta kyldiskar i de analyseradesystemen syns dock bara kortvarigt flödad tillstånd i förångrarna, och i övrigt en kvarvarande höggenomsnittlig överhettning. Låg erforderlig tilluftstemperatur i kyldiskarna och dimensioneringenav expansionsventilerna vid förångarens inlopp identifieras som möjliga begränsningar för enytterligare minskning av överhettningen och en ökning av förångningstemperaturen.

Scalar fields are used to represent physical quantities measured over a domain of interest. Study of symmetric or repeating patterns in scalar fields is important in scientific data analysis because it gives deep insights into the properties of the underlying phenomenon. This thesis proposes three methods to detect symmetry in scalar fields. The first method models symmetry detection as a subtree matching problem in the contour tree, which is a topological graph abstraction of the scalar field. The contour tree induces a hierarchical segmentation of features at different scales and hence this method can detect symmetry at different scales. The second method identifies symmetry by comparing distances between extrema from each symmetric region. The distance is computed robustly using a topological abstraction called the extremum graph. Hence, this method can detect symmetry even in the presence of significant noise. The above methods compare pairs of regions to identify symmetry instead of grouping the entire set of symmetric regions as a cluster. This motivates the third method which uses a clustering analysis for symmetry detection. In this method, the contours of a scalar field are mapped to points in a high-dimensional descriptor space such that points corresponding to similar contours lie in close proximity to each other. Symmetry is identified by clustering the points in the descriptor space. We show through experiments on real world data sets that these methods are robust in the presence of noise and can detect symmetry under different types of transformations. Extraction of symmetry information helps users in visualization and data analysis. We design novel applications that use symmetry information to enhance visualization of scalar field data and to facilitate their exploration.

Anthropogenic climate change is approaching predicted tipping points and there is an urgent need to de-carbonize energy systems on a global scale. Generation technologies that do not emit greenhouse gas need to be rapidly deployed, and energy grids need to be updated to accommodate an intermittent fluctuating supply. Rapidly advancing battery technology, cost reduction of solar and wind power and other emerging generation technologies are making the needed changes technically and economically feasible. Extracting energy from fast-flowing tidal currents using turbines akin to those used in wind farms, offers a reliable and predictable source of GHG free energy. The tidal power industry has established the technical feasibility of tidal turbines, and is presently up-scaling deployments from single isolated units to large tidal farms containing many turbines. However there remains significant economic uncertainty in financing such projects, partially due to uncertainty in predicting the long-term energy yield. Since energy yield is used in calculating the project revenue, it is of critical importance. Predicting yield for a prospective farm has not received sufficient attention in the tidal power literature. this task has been the primary motivation for this thesis work, which focuses on establishing and validating simulation-based procedures to predict flows through large tidal farms with many turbines, including the back effects of the turbines. This is a challenging problem because large tidal farms may alter tidal flows on large scales, and the slow-moving wake downstream of each rotor influences the inflow to other rotors, influencing their performance and loading. Additionally, tidal flow variation on diurnal and monthly timescales requires long-duration analysis to obtain meaningful statistics that can be used for forecasting. This thesis presents a hybrid simulation method that uses 2D coastal flow simulations to predict tidal flows over long durations, including the influence of turbines, combined with higher-resolution 3D simulations to predict how wakes and local bathymetry influence the power of each turbine in a tidal farm. The two simulation types are coupled using a method of bins to reduce the computational cost within reasonable limits. The method can be used to compute detailed 3D flow fields, power and loading on each turbine in the farm, energy yield and the impact of the farm on tidal amplitude and phase. The method is demonstrated to be computationally tractable with modest high-performance computing resources and therefore are of immediate value for informing turbine placement, comparing turbine farm-layout cases and forecasting yield, and may be implemented in future automated layout optimization algorithms. / Graduate

At present there are different reliability standards that are being used for carrying out reliability prediction. They take into consideration different factors, environments and data sources to give reliability data for a wide range of electronic components. However, the users are not aware of the differences between the different reliability standards due to the absence of benchmarks of the reliability standards that would help classify and compare between them. This lack of benchmark denies the users the opportunity to have a top-down view of these different standards and choose the appropriate standard based on qualitative judgement in performing reliability prediction for a specific system. To addres this issue, the benchmark of a set of reliability standards are developed in this dissertation. The benchmark helps the users of the selected reliability standards understand the similarities and differences between them and based on the evaluation criterion defined can easily choose the appropriate standard for reliability prediction in different scenarios. Theoretical reliability prediction of two electronic products in Bombardier is performed using the standards that have been benchmarked. One of the products is matured with available incident report from the field while the other is a new product that is under development and yet to enter in service. The field failure data analysis of the matured product is then compared and correlated to the theoretical prediction. Adjustment factors are then derived to help bridge the gap between the theoretical reliability prediction and the reliability of the product in field conditions. Since the theoretical prediction of the product under development could not be used to compare and correlate any data due to unavailability, instead, the accelerated life test is used to find out the product reliability during its lifetime and find out any failure modes intrinsic to the board. A crucial objective is realized as an appropriate algorithm/model is found in order to correlate accelerated test temperature-cycles to real product temperature-cycles. The PUT has lead-free solder joints, hence, to see if any failures occurring due to solder joint fatigue has also been of interest. Additionally, reliability testing simulation is a performed in order to verify and validate the performance of the product under development during ALT. Finally, the goal of the thesis is achieved as separate models are proposed to predict product reliability for both matured products and products under development. This will assist the organization in realizing the goal of predicting their product reliability with better accuracy and confidence. / För närvarande finns det olika tillförlitlighetsstandarder som används för att utföra tillförlitlighet förutsägelse. De tar hänsyn till olika faktorer, miljöer och datakällor för att ge tillförlitlighetsdata för ett brett spektrum av elektronikkomponenter. Men användarna inte är medvetna om skillnaderna mellan de olika tillförlitlighetsstandarder på grund av avsaknaden av riktmärken för tillförlitlighetsstandarder som skulle hjälpa klassificera och jämföra mellan dem. Denna brist på jämförelse förnekar användarna möjlighet att få en top-down bakgrund av dessa olika standarder och välja lämplig standard baserad på kvalitativ bedömning att utföra tillförlitlighet prognos för ett specifikt system. För att lösa detta problem, är riktmärket en uppsättning av tillförlitlighetsstandarder som utvecklats i denna avhandling. Riktmärket hjälper användarna av de utvalda tillförlitlighetsstandarder förstå likheter och skillnader mellan dem och på grundval av bedömningskriteriet definieras kan enkelt välja lämplig standard för pålitlighet förutsägelse i olika scenarier. Teoretisk tillförlitlighet förutsäga två elektroniska produkter i Bombardier utförs med hjälp av standarder som har benchmarking. En av produkterna är mognat med tillgängliga incidentrapport från fältet, medan den andra är en ny produkt som är under utveckling och ännu inte gå in i tjänsten. Analysen av den mognade produkten fält feldata jämförs sedan och korreleras till den teoretiska förutsägelsen. Justeringsfaktorer sedan härledas för att överbrygga klyftan mellan den teoretiska tillförlitlighet förutsägelse och tillförlitligheten av produkten i fältmässiga förhållanden. Eftersom den teoretiska förutsägelsen av produkt under utveckling inte kan användas för att jämföra och korrelera alla data på grund av otillgängligheten, i stället är det accelererade livslängdstest som används för att ta reda på produktens tillförlitlighet under dess livstid och reda ut eventuella felmoder inneboende till styrelsen . Ett viktigt mål realiseras som en lämplig algoritm /modell finns i syfte att korrelera accelererade provningen temperaturcykler på verkliga produkttemperatur cykler. PUT har blyfria lödfogar därmed att se om några fel inträffar på grund av löda gemensam trötthet har också varit av intresse. Dessutom är tillförlitlighet testning simulering en utförs för att verifiera och validera produktens prestanda under utveckling under ALT. Slutligen är målet med avhandlingen uppnås som separata modeller föreslås att förutsäga produktens tillförlitlighet för både förfallna och produkter under utveckling. Detta kommer att hjälpa organisationen att förverkliga målet att förutsäga deras tillförlitlighet med bättre noggrannhet och förtroende.