This thesis proposes a complete modeling and control design methodology for a multifunctional single-phase bidirectional PWM converter in renewable energy systems. There is a generic current loop for different modes of operation to ease the transition between different modes, including stand-alone inverter mode, grid-tied inverter mode, grid-tied rectifier mode and grid-tied charger/discharger mode. Under stand-alone mode operation, ac voltage regulation is of importance because of the sensitive loads. In this thesis, different multi-loop-based control schemes are investigated and compared, especially between the load current feedback control, PR control and capacitor current loop control. It shows that PR controller reduces the steady-state error, while load current feedback controller improves the transient response. However, the load current feedback controller and capacitor current loop controller presents unstable outputs under some filter load condition. Single-phase d-q frame control is also studied. In order to ease the implementation effort, an unbalanced d-q frame control is proposed to achieve zero steady-state error voltage regulation without generating β-axis component. Based on the same principle, a d-q frame-based single-phase PLL is also proposed to achieve the fast dynamic response with the zero steady-state error phase tracking. The entire control system is verified on a modified 7 kW single-phase PWM converter prototype with a simple DSP-based digital implementation. The load step response test is presented under different modes of operation. The controllers for stand-alone mode are also done under no load, 1 kW resistive load, 1kVar capacitive load, and non-linear load conditions verifying that the single-phase d-q achieves 70% steady-state error improvement if taking the normal PID controller as the baseline design. In the end, the proposed PLL is compared with the standard PLL by experiments showing that the steady-state error can be reduced by 80%. / Master of Science

The condition of water and wastewater pipelines has been deteriorating with time and since this infrastructure is out-of-sight, the assessment has been neglected over the years. The advancement of technology in various fields has provided pathway for development of several technologies for assessment of the condition of pipeline systems. However, there is no standard guidance or tool for the utilities to use these technologies appropriately. The utilities are unaware of the present state-of- the- art technologies. The predictability and condition assessability indices will help utilities predict a probable failure and take steps to prevent it. The predictability index will indicate the inherent, theoretical predictability of key types of pipe failures. The pipe failure predictability index would be a score calculated by identifying high priority pipe types, characterizing their failure modes, mechanism, conditions, and indicators, reliability of indicators, lead-time of the indicators, and other factors. The condition assessability index will indicate the technical and economical methods of preventing key types of pipe failures. The pipe failure condition assessability index is similar to the predictability index, but it takes into account the capability of existing inspection technologies for measuring the required failure indicator parameters. Prestressed Concrete Cylinder Pipes are used in large diameter water pipelines throughout the United States to convey large volumes of water. Prestressed Concrete Cylinder Pipes are complex composite pipes. Therefore, prediction and prevention of failure of these pipelines is complex and requires a better understanding of the system. This research concentrates around development of Predictability and Condition Assessability Indices for PCCP pipelines. / Master of Science

An innovative implementation of the Herschel-Quincke tubes concept for the reduction of noise from turbofan engines is proposed here. The approach consists of installing circumferential arrays of Herschel-Quincke (HQ) tubes or waveguides in the inlet of the turbofan engine. An analytical technique was developed to predict the effects of HQ tubes applied to circular inlets. The modeling technique involves modeling the tubes-inlet interfaces as finite piston sources that couple the acoustic field inside the inlet with the acoustic field within the HQ tubes. An optimization technique based on genetic algorithms was also developed to be able to design and optimize the system parameters. The accuracy of the model was validated with experimental data obtained from two types of turbofan engines. Analytical predictions are shown to correlate well with experimental data. The analytical model is then used to provide insight into the noise control mechanisms involved in the system. It is shown that the energy in an incident mode is in part reflected back to the fan and that some energy is also scattered into other higher-order modes. Thus, the suppression of a particular mode is due to the combination of the scattered contributions from the various incident modes. The effects of the system parameters were analyzed and parametric studies were conducted. Different configurations for the arrays of HQ tubes such as helical patterns or tubes at an angle with respect to the inlet axis were also investigated. The results show the great potential of the HQ tubes system to reduce noise from turbofan engines. / Master of Science

Pallet durability is a key characteristic with significant impact on a company's supply chain. Physical durability is defined as the number of trips that the pallet will accomplish before requiring repairs. Numerous studies have focused on understanding how durability is affected by different pallet components and warehouse environment characteristics. The VPI FasTrack is a testing sequence created to predict the performance of a pallet in a warehouse environment through different handling modes. However, this simulation has not been updated since its creation in 1993; therefore, a revision is needed to make it more closely reflect the behavior of a pallet in terms of durability. The objective of the current research was to investigate the ability of the FasTrack procedure to replicate the damages caused by material handling and storage systems in modern warehouses. This investigation was conducted through visual inspections of the damages seen on pallets used in the field, and pallets tested with FasTrack. The results of this study show the differences between the simulation-tested pallets and those from the field. The FasTrack simulation focuses heavily on top lead deckboard and stringer damage. The occurrence of damage modes such as splits and missing wood, were identified for these components. It was found that most of the damages from this simulation are created due to forklift handling. Because of substantial forklift handling damages, an experimental design was developed to investigate the effects of entry speed, payload, forklift type, and pallet design on the stresses exerted on a pallet, measured in terms of peak acceleration. The factors with the greatest effect on forklift peak acceleration and pallet peak acceleration were identified. The research shows that the acceleration in the pallet is approximately 4.4 times greater than the acceleration recorded in the forklift; however, the model of pallet acceleration based on forklift acceleration as a predictor shows poor performance. Different modifications to FasTrack are proposed according to the findings of this research. It is advised that they continue the FasTrack procedure past the point of repairable damage in a pallet, which is the usual practice when pallets are handled in the field. Further investigation of steps such as the flow rack and the stack storage are proposed, due to their low damage output during the simulation. The experimental design also showed that different damage severity levels from the FasTrack simulation are possible with variations in top load and entry speed. These changes could improve the ability of the VPI FasTrack to replicate the damages that pallets experience in the field. / Master of Science / Pallet durability refers to the number of uses that can be expected from a pallet before it needs to be repaired. Durability is an important performance characteristic, with a direct effect on the supply chain for any company. By further understanding how the warehouse environment and material handling systems affect pallet durability, companies can significantly reduce costs and improve their supply chain operations. The FasTrack procedure was created to satisfy the need for an effective durability simulation procedure. Created in 1993, FasTrack features different handling modes and interactions with handling equipment to reproduce the damages that a pallet could suffer in a real warehouse environment. However, warehouse environments have changed since the creation of FasTrack, which makes it important to assess the performance of this procedure in predicting pallet durability. The goal of this research was to investigate the ability of the FasTrack procedure to replicate the damages caused by material handling and storage systems in modern warehouses. This study was conducted through visual inspection of damaged locations, damage types, and damage severity levels for pallets used in the field and for pallets tested with FasTrack. The results obtained show differences between FasTrack and the field. The damage distribution in FasTrack for components of the pallet such as stringers and top lead deckboard is significantly higher than that measured in the field. The interaction of the pallet with the forklift could explain common damage modes, such as splits and missing wood, which were identified as the most damaged components in the pallets. An experimental design was developed to investigate the effects of entry speed, top load, forklift type, and pallet design on the stresses produced during interactions between forklifts and pallets. This interaction was measured in terms of horizontal shock impact acceleration. The most influential factors for forklift and pallet peak accelerations were identified with this study. An opportunity to predict pallet acceleration with forklift acceleration was identified, which could allow further investigation of the FasTrack simulation compared to the field. The results of the investigation show that FasTrack does not accurately reproduce the damages that pallets experience in the field. To improve the performance of the VPI FasTrack, the research proposes a revision of the steps during which damage output is low, such as the flow rack and the stack storage. The experimental design identified forklift entry speed and top load on the pallet as potential variables that could be customized in FasTrack, reflecting different severity levels based on a customer's unique environment characteristics. These changes could improve the correlation of the damages seen from the FasTrack simulation and the field, which would grant the industry a more reliable prediction of pallet durability.

No / The existing empirical literature on foreign direct investment (FDI) entry strategies tends to allow a binary choice between wholly owned enterprises (WOEs) and equity joint ventures (EJVs) or between greenfield investment and acquisition only. The current study specifies a multinomial logit model for the choice from all four FDI entry modes in China. Five hypotheses are developed based on transaction cost economics and tested on a data set covering 10,607 foreign investment projects in China. A foreign investor seems to prefer the WOE mode given its large investment commitment, a high level of the host country's experience in attracting FDI, a good specific industrial location, and a high asset intensity in the host industry. If the conditions of host country experience and good specific location are not met, the EJV and the joint stock company (JSC) modes seem to be of greater use. A good specific location also makes the contractual joint venture (CJV) a preferable entry mode. Compared with overseas Chinese investors from Hong Kong, Macao, and Taiwan, other foreign investors prefer EJVs over WOEs and CJVs. The results have important implications for managers.

A fundamental study of the Herschel-Quincke (HQ) tube concept for the reduction of noise in circular ducts is presented here. Recent testing of the Herschel-Quincke tube concept on the Pratt-Whitney JT15D and AlliedSignal TFE731-60 engines showed the potential for the practical application of this approach. A model of the HQ-system has been developed to aid in the design of the system tested. The model has revealed new noise control mechanisms associated to the implementation of multiple HQ-waveguides in a duct in the presence of higher order modes. However, the practical nature of these engine facilities results in limitations with regard to the fundamental research knowledge that could be gained from testing in a more controlled laboratory environment. A series of experiments was conducted at the NASA Langley Research Center 0.30 m ducted fan test facility where detailed modal measurements were performed. The main goals of this research endeavor were to evaluate the accuracy of the previously developed theoretical model and provide insight into the noise control mechanisms. Experiments were performed with different disturbance mode structures, number of HQ tubes and arrays, and axial positions. The modes in the duct were generated with an array of acoustic drivers (no flow case) and measured with logarithmically spaced circumferential and helical microphone arrays located on the duct wall. The modal amplitudes of the incident, transmitted, and reflected modes in the duct were determined from the microphone measurements. This allowed for the comparison of analytical and experimental modal amplitudes, modal powers, total power, and reductions. The results of this study provide insight into the three noise control mechanisms associated with this approach: reflection, circumferential scattering, and radial scattering. Comparison with the experimental results shows that the model accurately predicts the sound power attenuation except near the cut-off frequency of the modes where it tends to overestimate the attenuation. The effect of the number of tubes in the array and its axial position was also evaluated. Overall, the results of this study validate the general modeling approach for the HQ tube concept. / Master of Science

This dissertation investigates the role of digital media for contentious collective action. More precisely, it focuses on German anti-asylum-shelter (AAS) groups on Facebook and the way these organizations’ usage of platform affordances can be read from an adaptation of the framework of Modes of Coordination (MoC) of collective action. To do so, the thesis starts with an inquiry of the theoretical debate on the role of information and communication technology for social movements and collective action and highlights some misconceptions and discrepancies, especially on the role of formal organizations (chapter II). It argues to carefully explore the different interorganizational ties that form between AAS-groups and the networks that emerge from these in light of the two dimensions of resource exchange and boundary definition. After that, chapter III provides detailed accounts of case selection and data collection and of the research questions that structure the subsequent analyses. To answer these, chapter IV-i explores the temporal and spatial activity patterns of AAS-groups both on- and offline, finding a clear correspondence between the two. Chapter IV-ii uses topic modelling to explore the content of groups’ communication, identifying a narrative of the reasonable and peaceful in-group and a combination of criminal (asylum-seekers), treacherous (politicians) and lying (press) outgroups. This clearly debunks a narrative of centrist “concerned citizens” and shows the deeply racist and right-wing extremist nature of AAS activity. The third empirical part (chapter IV-iii) discusses five types of networks that emerge from groups’ activities and combines these into four different MoC. We can identify a prevalence of the organizational mode of coordination, that involves limited exchange in terms of both resource exchange and boundary definition. However, a small but dense network also emerges from those ties that are defined by the social movement mode. Exponential Random Graph Modelling shows that while spatial proximity is a key determinant for tie formation across all modes, the role of formal organizations (right-wing parties) must not be dismissed. In fact, it differs both by party and by MoC in question. Overall, as chapter V sums up, the dissertation proves the relevance of a relational perspective to the study of digitally mediated collective action in general, as well as of an adapted framework of MoC in particular.

Dans ce projet de mémoire, on tente de définir une commande nouvelle d’un système modélisé à paramètres variables. La commande par mode glissant définie dans le plan de phase constitue la base de la transformation afin de trouver la nouvelle commande recherchée. Celle-ci est effectivement optimale en minimisant le temps de la réponse temporelle en plus de s'assurer de la stabilité du système. Utilisant la transformation, il a été possible de prédire les trajectoires dans le plan d’état. De ce cas, une commande glissante en forme explicite est obtenue. Une plate-forme mobile de soudage (PFM) est choisie comme le système étudié pour appliquer ces commandes. Par ailleurs, une plate-forme informatique aux trois niveaux est construite pour faire la transformation et la visualisation d’application des commandes proposées ci-dessus. Mots clés : variables d’état, plan de phase, plan d’état, commande par mode glissante, commande glissante. / In this thesis a new control method have been defined to apply in the variable parameters model system. A sliding mode control defined in the phase plane is the basis of the transformation for finding this new desired control. The sliding mode control is an optimal method for both minimizing the response time and ensuring the stability of system. With this transformation, it is possible to predict the trajectories in the state plan. In this case, a sliding control with an explicit form can be obtained in the state plan. A mobile platform of welding (PFM) is chosen as example for applying the sliding mode controls and the sliding control. Furthermore, an IT platform with three levels is built up to do the transformation and visualize the application of those controls mentioned above. Key words : variables states, phase plane, state plan, sliding mode control, sliding control.

Ce travail de thèse propose des solutions pour la commande de systèmes non linéaires incertains en se basant sur la théorie des modes glissants. Ce mémoire présente la théorie des modes glissants et des modes glissants d'ordre supérieur, en distinguant des notions souvent confondues, comme les commandes équivalente et nominale, ou les modes glissants d'ordre supérieur idéal et réel. Une preuve originale de la convergence de l'algorithme du super twisting est également présentée. Une commande par modes glissants à amplitude adaptative a été proposée dans le but de pour réduire le chattering. Elle a été testée sur le banc d'essais d'actionneur électropneumatique de l'IRCCyN, dont les modèles de simulation et de synthèse sont exposés. L'autre théorie présentée dans ce mémoire est celle de la commande à temps minimal pour des systèmes parfaitement connu. Des algorithmes de calcul de la surface de commutation à temps minimal sont présentés. Un lien est fait avec la théorie de la commande par modes glissants d'ordre supérieur. Le résultat est une commande ayant la robustesse et la précision asymptotique des modes glissants d'ordre supérieur et la vitesse de convergence héritée de la commande à temps minimal. Une solution au problème du chattering, spécialement délicat pour cette commande, est également proposée.

<p>SAMMANFATTNING</p><p>Vi lever i en tid av ständiga och snabba förändringar. Detta sägs även gälla i arbetslivet. Framförallt kvinnornas roll i arbetet är i förändring, de tar allt större plats inom företagsmarknaden. Det blir allt vanligare att kvinnor startar och driver företag, många av dessa är små.</p><p>Vårt gemensamma intresse för den realistiska livsformsanalysen och kvinnligt företagande blev grunden för detta arbete. Det var av intresse för oss att söka finna svar på hur kvinnliga småföretagare upplever sin situation gällande balans mellan fritid och arbete. Vi ville ta reda på vilka livsformer dessa kvinnor lever för att öka vår förståelse för hur detta påverkar synen på vad som är viktigt i livet och vilka medel de tar till för att nå sina mål i enlighet med detta.</p><p>Livsformsanalysen söker öka vår förståelse för andra individer och hur de väljer att leva sina liv. Alla har vi olika mål och medel för att nå dessa och olika definitioner på vad som är det goda livet. Den livsform vi lever styr på många sätt hur vi ser på verkligheten. Vi utgick från att ett livsformsperspektiv skulle vara fruktbart för denna undersökning då det skulle ge oss förklaringar till det som skiljer olika företagare åt. Vår förförståelse var att kvinnor till större del tar ansvar för hem och familj, det var därför spännande att utröna hur de klarar av att balansera detta ansvar med företagande.</p><p>Då det är upplevelsen av de kvinnliga småföretagarnas situation vi velat undersöka valde vi att göra en kvalitativ undersökning. Vi genomförde fem intervjuer med småföretagande kvinnor som visade sig leva olika livsformer och därmed ha olika förutsättningar för sitt företagande. Gemensamt för dem är att de alla delvis lever självständighetens livsform. I enlighet med detta har de svårt att skilja arbetsliv från privatliv. Analyser av materialet visade att den eller de livsformer företagaren lever påverkar hur hon söker finna balans i tillvaron.</p><p>Nyckelord: Livsformer, kombinationslivsform, balans, småföretagare och kvinnor</p> / <p>ABSTRACT</p><p>We are living in a time of constant and rapid change. This also applies to work life. This applies in particular on the women’s role at work, women gain more ground in the business market. It is becoming more common for women to start and lead their own businesses, many of these are small.</p><p>Our mutual interest in the realistic life mode analysis and in women who run their own businesses became the base of this composition. It was in our interest to find answers about how self employed women experience their situation concerning balance between leisure time and the time of work. We aspired to find out what life modes these women live. This in order to increase our understanding of how this influences their view of what is most important in life and the means they use to acquire their goals.</p><p>The life mode analysis was created to increase our understanding of other individuals and the way they chose to live their lives. All of us have different goals and means to reach them, we have also got different views of what the good life is. The life mode one person lives in many ways predicts how he or she looks upon reality. We assumed that a life mode perspective analysis would be productive on this study since it would explain the differences amongst the self employed women. Our pre understanding was that women usually take on the main responsibility for the home and family .It was interesting to us to find out how they manage to balance this responsibility and their businesses.</p><p>Since we wanted to explore the women’s experiences in our study we chose to make a qualitative research. We made five interviews with self employed women. We found out that they live different life modes, this gives them different conditions under witch they run their businesses. What they all have in common is that they, in part, live the independent life mode. In accordance to this they find it difficult to separate their time of work from their leisure time. Our analysis shows that the life mode or life modes influences how the business woman chooses to find her balance in life.</p><p>Key words: Life modes, combinations of life modes, balance, self employed women</p>