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<p>Successful navigation requires an accurate mental spatial representation of the environment that can be updated during movement. Experiments with animals and humans have demonstrated the existence of two forms of spatial representation: egocentric (observer-centered) and allocentric (environment-centered). Unfortunately, specifically how humans use these two systems is not well understood. The current dissertation was focused on providing evidence differentiating human use of egocentric and allocentric spatial reference frames, specifically examining the characteristics and contributions from body-based sources. Two empirical chapters are presented that include experiments involving two common spatial tasks. In Chapter 2, updating of feature relations within a room-sized environment was examined by having observers provide directional judgments to learned features with respect to an imagined orientation that was either congruent or incongruent with their physical orientation. The information available for updating the physical orientation was manipulated across experiments. Performance differences between congruent and incongruent conditions demonstrated the reliance on egocentric representations for updating, and differentiated body- and knowledge-based components of the egocentric updating process. The specificity of the body-based component was examined in Chapter 3 by having observers detect changes made to a tabletop spatial scene following a viewpoint shift resulting from their movement, scene rotation or both. The relation between the extent of observer movement and the magnitude of the experienced viewpoint shift was manipulated. Change detection performance was best when the extent of observer movement most closely matched the viewpoint shift, and declined as the match declined. Thus, body-based cues contributed specific information for updating self-to-feature relations that facilitated scene recognition. Throughout the course of the research program it has become clear that humans rely on egocentric representations to complete these tasks, and sensory and motor modalities involved in self-motion are integrated for updating spatial relations of novel environments.</p> / Doctor of Philosophy (PhD)

<p>Previous human behavioral research has provided support for the existence of different frames of reference utilized during spatial processing that can be dependent or independent of the observer. These are known respectively as egocentric and allocentric frames of reference. However, it has been difficult to dissociate these two different processes under realistic conditions. Importantly, how these frames of reference are influenced by the visual and non-visual information is not well understood. Therefore, the studies of this thesis evaluated spatial processing utilizing realistic and ecologically valid stimuli in environments of different scales, while systematically manipulating the visual and non-visual information available during learning. We demonstrated that non-visual information generated by actively walking through an environment leads to more egocentric processing, whereas the same visual motion information presented passively via a video leads to more allocentric processing (Chapter 2). Further, characteristics of the visual scene can also influence how it is processed, dependent on the strength of the verbal identity of the features in the environment (Chapter 3). Specifically, in a small room environment subject’s representations of corners-to-corners (corners do not have an obvious verbal component) were not as strongly encoded relative to each other in comparison to objects-to-objects (objects with an obvious verbal identity ). Finally, we demonstrated differential influences of non-visual information dependent on whether the features in the visual scene were more allocentrically processed or egocentrically processed (Chapter Four). Specifically, when different features of layouts are made distinguishable by their identity, this lead to more allocentric processing whereas when different features are made distinguishable by their relative position, this lead to more egocentric processing. Further, non-visual information made available during spatial updating when the observer is changing viewpoints benefitted tasks focused on differentiating changes to objects’ identity and less so for differentiating changes in relative object position.</p> / Doctor of Philosophy (PhD)

We study the benefits of resource flexibility, considering two different flexibility structures. First, we want to understand the impact of the firm's pricing strategy on its resource investment decision, considering a partially flexible resource. Secondly, we study the benefits of a flexible resource strategic approach, considering a resource flexibility structure that has not been studied in the previous literature. First, we study the capacity investment decision faced by a firm that offers two products/services and that is a price-setter for both products/services. The products offered by the firm are of varying levels (complexities), such that the resources that can be used to produce the higher level product can also be used to produce the lower level one. Although the firm needs to make its capacity investment decision under high demand uncertainty, it can utilize this limited (downward) resource flexibility, in addition to pricing, to more effectively match its supply with demand. Sample applications include a service company, whose technicians are of different capabilities, such that a higher level technician can perform all tasks performed by a lower level technician; a firm that owns a main plant, satisfying both end-product and intermediate-product demand, and a subsidiary, satisfying the intermediate-product demand only. We formulate this decision problem as a two-stage stochastic programming problem with recourse, and characterize the structural properties of the firm's optimal resource investment strategy when resource flexibility and pricing flexibility are considered in the investment decision. We show that the firm's optimal resource investment strategy follows a threshold policy. This structure allows us to understand the impact of coordinated decision-making, when the resource flexibility is taken into account in the investment decision, on the firm's optimal investment strategy, and establish the conditions under which the firm invests in the flexible resource. We also study the impact of demand correlation on the firm's optimal resource investment strategy, and show that it may be optimal for the firm to invest in both flexible and dedicated resources when product demand patterns are perfectly positively correlated. Our results offer managerial principles and insights on the firm's optimal resource investment strategy as well as extend the newsvendor problem with pricing, by allowing for multiple resources (suppliers), multiple products, and resource pooling. Secondly, we study the benefits of a delayed decision making strategy under demand uncertainty, considering a system that satisfies two demand streams with two capacitated and flexible resources. Resource flexibility allows the firm to delay its resource allocation decision to a time when partial information on demands is obtained and demand uncertainty is reduced. We characterize the structure of the firm's optimal delayed resource allocation strategy. This characterization allows us to study how the revenue benefits of the delayed resource allocation strategy depend on demand and capacity parameters, and the length of the selling season. Our study shows that the revenue benefits of this strategy can be significant, especially when demand rates of the different types are close, while resource capacities are much different. Based on our analysis, we provide guidelines on the utilization of such strategies. Finally, we incorporate the uncertainty in demand parameters into our models and study the effectiveness of several delayed capacity allocation mechanisms that utilize the resource flexibility. In particular, we consider that demand forecasts are uncertain at the start of the selling season and are updated using a Bayesian framework as early demand figures are observed. We propose several heuristic capacity allocation policies that are easy to implement as well as a heuristic procedure that relies on a stochastic dynamic programming formulation and perform a numerical study. Our study determines the conditions under which each policy is effective. / Ph. D.

To obtain predictive modeling of a spacecraft, the author investigates the effects of adding cables to a simple structure with the goal of developing an understanding of how cables interacting with a structure. In this research, the author presents predictive and accurate modeling of a cable-harnessed structure by means of the Spectral Element Method (SEM). A double beam model is used to emulate a cable-harnessed structure. SEM modeling can define the location and the number of connections between the two beams in a convenient fashion. The proposed modeling is applied and compared with the conventional FEM. The modeling approach was compared to and validated by measurement data. The validated modeling was implemented to investigate the effect of the number of connections, of the spring stiffness of interconnections, and of mass portion of an attached cable. Damping has an important role in structural design because it reduces the dynamic response, thereby avoiding excessive deflection or stress, fatigue loads, and settling times. Experimental results with some specimens indicate a clear change of damping on the main structure with the inclusion of cable dynamics. The author investigated the modification of the damping of the host structure induced by various attached cables. The identification of a damping matrix is performed using measured data. The effect of the flexibility of a cable harness on damping is observed through experiments with various types of cables. The effect of the number of connections on damping is also investigated by changing the number of connections. Moreover, to overcome the sensitivity to noise in measured data of damping matrix identification approach, various methods are compared with a simulated lumped model and real test results. An improved damping matrix identification approach is proposed and can generate the unique damping matrix over the full frequency range of interest. / Ph. D.

In science and engineering, many applications require the solution of a sequence of linear systems. There are many ways to solve linear systems and we always look for methods that are faster and/or require less storage. In this dissertation, we focus on solving these systems with Krylov subspace methods and how to obtain effective preconditioners inexpensively. We first present an application for electronic structure calculation. A sequence of slowly changing linear systems is produced in the simulation. The linear systems change by rank-one updates. Properties of the system matrix are analyzed. We use Krylov subspace methods to solve these linear systems. Krylov subspace methods need a preconditioner to be efficient and robust. This causes the problem of computing a sequence of preconditioners corresponding to the sequence of linear systems. We use recycling preconditioners, which is to update and reuse existing preconditioner. We investigate and analyze several preconditioners, such as ILU(0), ILUTP, domain decomposition preconditioners, and inexact matrix-vector products with inner-outer iterations. Recycling preconditioners produces cumulative updates to the preconditioner. To reduce the cost of applying the preconditioners, we propose approaches to truncate the cumulative preconditioner updates, which is a low-rank matrix. Two approaches are developed. The first one is to truncate the low-rank matrix using the best approximation given by the singular value decomposition (SVD). This is effective if many singular values are close to zero. If not, based on the ideas underlying GCROT and recycling, we use information from an Arnoldi recurrence to determine which directions to keep. We investigate and analyze their properties. We also prove that both truncation approaches work well under suitable conditions. We apply our truncation approaches on two applications. One is the Quantum Monte Carlo (QMC) method and the other is a nonlinear second order partial differential equation (PDE). For the QMC method, we test both truncation approaches and analyze their results. For the PDE problem, we discretize the equations with finite difference method, solve the nonlinear problem by Newton's method with a line-search, and utilize Krylov subspace methods to solve the linear system in every nonlinear iteration. The preconditioner is updated by Broyden-type rank-one updates, and we truncate the preconditioner updates by using the SVD finally. We demonstrate that the truncation is effective. In the last chapter, we develop a matrix reordering algorithm that improves the diagonal dominance of Slater matrices in the QMC method. If we reorder the entire Slater matrix, we call it global reordering and the cost is O(N^3), which is expensive. As the change is geometrically localized and impacts only one row and a modest number of columns, we propose a local reordering of a submatrix of the Slater matrix. The submatrix has small dimension, which is independent of the size of Slater matrix, and hence the local reordering has constant cost (with respect to the size of Slater matrix). / Ph. D.

Getriebeheulphänomenen wird in der industriellen Praxis zum Teil noch immer ausschließlich mit Hilfe einer optimierten Verzahnungsauslegung zur Minimierung des Drehfehlers begegnet. Bei auffälligen Resonanzerscheinungen werden zudem Strukturoptimierungen am Getriebegehäuse und den Karosserieanbindungspunkten des Antriebsstrangs vorgenommen, ohne auf die internen Systemkomponenten verstärkt einzugehen. Zudem kann bisher die verlässliche Erkenntnis, dass zur Einhaltung akustischer Grenzwerte die Konstruktion nochmals überarbeitet werden muss, erst spät im Entwicklungsprozess während der akustischen Versuchsdurchführung an Prüfständen oder im Fahrzeug getroffen werden. Durch sogenannte Sekundärmaßnahmen, die typischerweise nicht unmittelbar das Anregungsverhalten oder die Dynamik des Antriebsstrangs, sondern den karosserieseitigen Transferpfad betreffen, kann eine Reduktion des Schalldruckpegels im Fahrzeuginnenraum in gewissen Grenzen erzielt werden. Dies ist zumeist weder aus ingenieurstechnischer Sicht noch aus Sicht steigender Entwicklungskosten als optimal zu bezeichnen. Basierend auf einem detaillierten Abgleich zwischen Experiment und Simulation, angefangen auf Einzelteilebene über die Baugruppenebene bis hin zur Methodenentwicklung der Validierung von nichtrotierenden Gesamtsystemen mittels künstlicher Anregung, werden in dieser Arbeit möglichst akkurate Simulationsergebnisse angestrebt, um die Auswirkung von akustischen Optimierungen innerhalb der Simulationsumgebung realitätsnah vorherzusagen. Schließlich wird ein Prozess vorgeschlagen, der eine getriebeinterne Transferpfadanalyse zur Identifikation sensitiver Körperschallpfade vorstellt. Mit dieser Methode wird aufgezeigt, dass es möglich ist, akustische Schwachstellen auf der Antriebsstrangseite vorherzusagen. Dabei kann zum einen akustisches Optimierungspotenzial des Welle-Lager-Systems abgeleitet werden, zum anderen werden auch die aktuellen Möglichkeiten und Grenzen der Verfahren beleuchtet.:Inhaltsverzeichnis Abbildungsverzeichnis Formelzeichen und Abkürzungen 1 Einleitung 2 Stand der Technik 2.1 Getriebeakustik – Einflussgrößen und Begrifflichkeiten 2.1.1 Verzahnungsanregung von unter Last stehenden Zahnrädern 2.1.2 Verzahnungsinduzierte Körper- und Luftschallweiterleitung in Fahrzeugen 2.1.3 Maßnahmen zur Reduktion von Körperschallpfaden 2.2 Strukturdynamische Analysemethoden in der Getriebeakustik 2.2.1 Numerische Modalanalyse 2.2.2 Experimentelle Modalanalyse und Betriebsschwingformanalyse 2.2.3 Unkonventionelle Methoden zur Erregung von Bauteilstrukturen 2.2.4 Computerunterstützte Modellanpassung 2.2.5 Transferpfadanalyse 2.3 Getriebesimulation 2.3.1 Getriebetypische Kontaktmodellierung 2.3.2 Finite-Element-Modellierung und Reduktionsverfahren 2.4 Fazit 3 Zielsetzung und Vorgehensweise 4 Methoden zur Analyse von Getriebekomponenten 4.1 Verzahnungsanalyse 4.2 Strukturdynamische Untersuchungen an Einzelteilen 4.3 Strukturdynamische Untersuchungen an Baugruppen 4.4 Verhalten von Wälzlagern 4.5 Fazit 5 Methode zur Gesamtsystemvalidierung 5.1 Modellierung des Getriebesystems mit Prüfstandsanbindung 5.2 Getriebeinterne Anregung mittels Zahnaktor 5.2.1 Voruntersuchungen 5.2.2 Implementierung einer torsionalen Anregung in Frontgetrieben 5.2.3 Simulative und experimentelle Untersuchungen 5.3 Fazit 6 Getriebeinterne Transferpfadanalyse 6.1 Identifikation sensibler Körperschalltransferpfade 6.2 Optimierungsansätze 6.3 Fazit 7 Zusammenfassung und Ausblick 8 Literaturverzeichnis / Gear whine phenomena are typically mitigated by optimising gear design to minimise Transmission Error. Additionally, structural optimisations on the gearbox housing and on the gearbox-to-chassis mounts may be conducted most likely without a detailed consideration of internal components‘ dynamics. Moreover, it is not unusual that in the final stages of drivetrain developments when the gearbox is tested on test benches or in vehicles NVH targets are not met. The countermeasures applied often do not alter the source of excitation nor the dynamics of the drivetrain at this stage, but the vehicle transfer paths through the chassis. Thus, sound power level reduction may be exclusively limited to vehicle transfer path improvements. In most cases this is not regarded as an optimal solution neither from an engineering perspective nor from the commercial point of view due to increased development costs. Based on detailed correlation activities where simulation has been run against measurement the work strives to achieve accurate gearbox NVH predictions to forecast more realistically the effect of design optimisations. The correlation approach starts on single component level moving on to sub-assembly level and finally up to the development of a method which is able to artificially excite the entire but non-rotating drivetrain. After various successful correlation studies, a process has been elaborated which proposes a gearbox internal transfer path analysis to identify potentially critical structure-borne noise paths. The method illustrates the capability of successfully predicting weak spots at the active side of a drivetrain early in the development process. Additional room for improvement can be derived when implementing this method by considering the rotating components of a drivetrain such as gear blanks, shafts and bearings.:Inhaltsverzeichnis Abbildungsverzeichnis Formelzeichen und Abkürzungen 1 Einleitung 2 Stand der Technik 2.1 Getriebeakustik – Einflussgrößen und Begrifflichkeiten 2.1.1 Verzahnungsanregung von unter Last stehenden Zahnrädern 2.1.2 Verzahnungsinduzierte Körper- und Luftschallweiterleitung in Fahrzeugen 2.1.3 Maßnahmen zur Reduktion von Körperschallpfaden 2.2 Strukturdynamische Analysemethoden in der Getriebeakustik 2.2.1 Numerische Modalanalyse 2.2.2 Experimentelle Modalanalyse und Betriebsschwingformanalyse 2.2.3 Unkonventionelle Methoden zur Erregung von Bauteilstrukturen 2.2.4 Computerunterstützte Modellanpassung 2.2.5 Transferpfadanalyse 2.3 Getriebesimulation 2.3.1 Getriebetypische Kontaktmodellierung 2.3.2 Finite-Element-Modellierung und Reduktionsverfahren 2.4 Fazit 3 Zielsetzung und Vorgehensweise 4 Methoden zur Analyse von Getriebekomponenten 4.1 Verzahnungsanalyse 4.2 Strukturdynamische Untersuchungen an Einzelteilen 4.3 Strukturdynamische Untersuchungen an Baugruppen 4.4 Verhalten von Wälzlagern 4.5 Fazit 5 Methode zur Gesamtsystemvalidierung 5.1 Modellierung des Getriebesystems mit Prüfstandsanbindung 5.2 Getriebeinterne Anregung mittels Zahnaktor 5.2.1 Voruntersuchungen 5.2.2 Implementierung einer torsionalen Anregung in Frontgetrieben 5.2.3 Simulative und experimentelle Untersuchungen 5.3 Fazit 6 Getriebeinterne Transferpfadanalyse 6.1 Identifikation sensibler Körperschalltransferpfade 6.2 Optimierungsansätze 6.3 Fazit 7 Zusammenfassung und Ausblick 8 Literaturverzeichnis

Recent years have seen increasing research interest in structural health monitoring (SHM). Among the many advances in SHM research, “smart” wireless sensors capable of embedded computing and wireless communication have been highly attractive. Wireless communication in SHM systems was originally proposed to significantly reduce the monetary and time cost for installing lengthy cables in an SHM system. Besides wireless sensing, the next revolution in sensor networks has been predicted to be mobile sensor networks that implant mobility into traditional wireless sensor networks. This research explores decentralized structural model updating and damage detection using mobile and wireless sensors. In the first stage of this research, mobile sensing nodes (MSNs) are developed for SHM purposes. The MSNs can maneuver upon structures built with ferromagnetic/steel materials, conduct measurement, and communicate with pears or remote servers wirelessly. The performance of the MSNs is validated through laboratory and field experiments. To further investigate the mobile sensing strategy, a decentralized structural damage detection procedure is proposed herein for the MSNs using transmissibility functions. Laboratory experiments are conducted on a steel portal frame where various structure damage scenarios are emulated. Besides experiments with MSNs, this study also investigates the nature of transmissibility functions for damage detection in an analytical manner based on a general multi-DOF spring-mass-damper system. Finally, this research also explores substructure model updating through minimization of modal dynamic residuals, which can best benefit from dense mobile or wireless sensor data concentrated in one area. Craig-Bampton transform is adopted to condense the structural model, and minimization of the modal dynamic residuals is determined as the optimization objective. An iterative linearization procedure is adopted for efficiently solving the optimization problem. The presented substructure updating method is validated through a few numerical examples. For comparison, a conventional approach minimizing modal property differences is also applied, and shows worse updating accuracy than the proposed approach. The performance of the proposed substructure model updating approach is further investigated on the effects of substructure location and size.

La prévision des crues est un exercice hydrologique complexe : les incertitudes y sont nombreuses, aussi bien dans le processus de modélisation hydrologique, dans la détermination de l'état initial du bassin versant avant le lancement de la prévision, que dans l'évolution des conditions météorologiques futures. Dans le cas des bassins versants non jaugés, où les observations de débits sont lacunaires voire absentes, ces incertitudes sont encore plus importantes, et le besoin de les réduire devient incontournable. Cette thèse s'intéresse à des méthodes simples et robustes qui peuvent apporter de l'information pertinente pour quantifier les incertitudes de prévision dans les bassins versants non jaugés. Le but est d'étudier la meilleure stratégie pour chercher l'information dans les bassins jaugés "donneurs", et pour la transférer vers le site non jaugé. Nous étudions les besoins pour mettre en place un modèle de simulation pluie-débit et pour effectuer une mise à jour du modèle de prévision en temps réel. Ces deux composantes de la prévision sont ainsi découplées dans notre approche. Cette thèse s'appuie sur une large base de données constituée d'environ 1000 bassins versants français, dont un jeu clé de 211 bassins versants qui permet la validation des approches développées. Elle s'appuie également sur une archive d'environ 4,5 années de prévisions d'ensemble de pluies, utilisées en forçage à la modélisation hydrologique journalière. La démarche adoptée consiste à intégrer les scenarios de transfert de l'information régionale disponible et les scenarios de la prévision météorologique d'ensemble dans un système de prévision orienté vers les bassins versants non jaugés. L'approche de prévision d'ensemble est ainsi généralisée à ce cas particulier de la prévision hydrologique. A travers plusieurs scénarios de débits futurs, nous cherchons à quantifier les incertitudes de prévisions dans les sites cibles non jaugés. Pour évaluer les différents scénarios des prévisions hydrologiques émis, un cadre de diagnostic d'évaluation des principales qualités d'un système de prévision d'ensemble, comprenant plusieurs critères numériques et graphiques, a été mis en place. Dans cette thèse, une attention particulière est prêtée aux attributs "fiabilité" et "précision" des prévisions. Nous proposons ainsi un nouveau critère graphique, nommé diagramme de précision d'ensemble. Ce critère permet notamment de mettre en valeur la qualité des prévisions qui ne sont pas forcément fiables, mais qui sont précises. Les résultats obtenus ont mis en évidence que la fiabilité des prévisions peut être améliorée sur un bassin versant non jaugé par l'utilisation de plusieurs jeux de paramètres issus des bassins versants voisins. Si la variabilité apportée par le voisinage géographique influe sur la dispersion des membres, et augmente ainsi la fiabilité des prévisions, la prise en compte des caractéristiques physiques, principalement de la surface des bassins versants, est apparue comme une alternative intéressante, influençant positivement aussi l'attribut précision des prévisions sur le site cible. De plus, il a été montré que la précision des prévisions d'ensemble sur le site non jaugé est améliorée par l'intermédiaire du transfert des bassins versants jaugés vers le site cible des corrections faites lors de la mise à jour sur les bassins voisins (mise à jour caractérisée ici par l'assimilation de la dernière observation de débit dans le modèle hydrologique, avant l'instant de prévision). Les différentes mesures de performance ont montré que la meilleure option pour améliorer la précision des prévisions serait de considérer les corrections effectuées sur le bassin le plus proche à chaque pas de temps de prévision. Le krigeage a également donné des résultats satisfaisants, marqués en plus par l'influence positive sur l'attribut fiabilité des prévisions. / Flood forecasting is a complex hydrological task: there are numerous uncertainties in the hydrological modelling process, in the determination of the initial catchment conditions before launching the forecast, and in the evolution of future weather conditions. In ungauged catchments, where streamflow observations are incomplete or absent, these uncertainties are even greater, and the need to reduce them becomes essential.This thesis focuses on simple and robust methods that can provide relevant information to quantify the uncertainty in ungauged catchments. The aim is to study the best strategy to search for information in gauged "donors" basins and to transfer it to the ungauged site. We investigate what information is needed to set up a rainfall-runoff model and to perform forecast updating in real time. These two components of a flood forecasting system are thus decoupled in our approach.This thesis is based on a large database of about 1000 French catchments, which includes a key set of 211 catchments that are used to validate the developed approaches. It also relies on an archive of about 4.5 years of ensemble forecasts of rainfall, which are used for hydrological modelling on a daily time step. The methodology adopted here integrates the scenarios of regional transfer of information and the scenarios of weather forecasting together in a forecasting system for ungauged basins. The approach of ensemble forecasting is thus generalised to this particular case of hydrological forecasting. Using several scenarios of future flows, we seek to quantify the predictive uncertainty in ungauged sites.To evaluate the flow forecast scenarios of the hydrological ensemble prediction system, a diagnostic framework with several numerical and graphical criteria is developed. Special attention is paid to the attributes of "reliability" and "accuracy" of the forecasts. We propose a new graphic criterion, named "diagram of ensemble accuracy". This criterion allows to highlight the quality of forecasts that are not necessarily reliable, but are accurate.The results show that forecast reliability in ungauged sites can be improved by using several sets of parameters from neighbour catchments. If on the one hand the variability brought by the information from the geographical proximity influences the spread of the ensemble forecasts, and thus improves forecast reliability, on the other hand taking into account the physical characteristics of the catchments, especially the surface, emerged as an interesting alternative, as it positively influences also the accuracy of the forecasts at the ungauged site.It is also shown that the accuracy of ensemble forecasts at ungauged sites can be improved with the transfer of updating information from gauged neighbour catchments (forecasting updating is here characterized by the assimilation of the last discharge observation in the hydrological model before the time of forecast). The updating information transferred to the ungauged site is the correction applied to the routing reservoir of the hydrological model. Different measures of forecast performance showed that the best option to improve forecast accuracy is to consider the corrections made at the closest gauged site. Kriging also gave satisfactory results, with additionally a positive impact also on the reliability of the ensemble flow forecasts.