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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Meteorologische Einflüsse auf die Konzentrationen feiner und grober atmosphärischer Aerosolpartikel in Deutschland

Engler, Christa 19 March 2014 (has links) (PDF)
Atmosphärische Aerosolpartikel können durch ein breites Spektrum an natürlichen oder anthropogenen Emissionen mit unterschiedlich hohen Konzentrationen in die Atmosphäre freigesetzt werden. Sie beeinflussen den Strahlungshaushalt und damit auch das Klima der Erde und können außerdem durch ihre Präsenz in der Atmosphäre Wechselwirkungen mit Mensch und Natur, also dem gesamten Ökosystem haben. Seit dem Jahr 2010 gelten in der EU Grenzwerte für die PM10 Tagesmittelkonzentration, die jedoch bereits wenige Monate nach Beginn der Gültigkeit an vielen Messstationen überschritten wurden. Das Ziel der vorliegenden Arbeit war eine objektive Bewertung der Herkunft und des Zustandes der an einem Messort ankommenden Luftmasse und der damit verbundenen Schadstoffniveaus. Im ersten Teil der Arbeit wurden PM10 Messdaten aus fünf Jahren in und um Leipzig sowie analog in fünf verschiedenen Regionen deutschlandweit in Bezug auf PM10 Grenzwertüberschreitungen untersucht. Es wurden Rückwärtstrajektorien für eine Clusteranalyse verwendet, mit der spezifische Wetterlagen unterschieden wurden und diesen dann die einzelnen Messtage mit den zugehörigen Schadstoffkonzentrationen zugeordnet wurden. Hierbei wurde deutlich, dass durch entsprechende meteorologische Bedingungen sowohl lokal als auch regional emittierte Schadstoffe in Bodennähe akkumulieren oder aber auch räumlich verteilt werden können. Außerdem wurde in dieser Arbeit eine Modellvalidierung vorgestellt. Es wurde das Modellsystem COSMO-MUSCAT/ext-M7 verwendet, dessen Ergebnisse mit Beobachtungsdaten verglichen wurden. Als erstes wurde die Beschreibung der meteorologischen Bedingungen, dann die räumliche Verteilung von PM10, die chemische Partikelzusammensetzung sowie physikalische Aerosolparameter wie Partikelanzahl, -volumen und -durchmesser verglichen. Die Ergebnisse deuten darauf hin, dass nach wie vor Probleme bei der Beschreibung der mikrophysikalischen Aerosoleigenschaften bestehen. Die Größenordnungen der verglichenen Parameter können vom Modell abgebildet werden, dennoch müssen Modellergebnisse nach wie vor mit Vorsicht interpretiert werden, insbesondere hinsichtlich von Prozessen, bei denen die Partikelanzahl eine Rolle spielen.
32

Improving Emergency Department performance using Discrete-event and Agent-based Simulation

Kaushal, Arjun 14 February 2014 (has links)
This thesis investigates the causes of the long wait-time for patients in Emergency department (ED) of Victoria General Hospital, and suggests changes for improvements. Two prominent simulation techniques have been used to replicate the ED in a simulation model. These are Discrete-event simulation (DES) and Agent-based modeling (ABM). While DES provides the basic modeling framework ABM has been used to incorporate human behaviour in the ED. The patient flow in the ED has been divided into 3 phases: input, throughput, and output. Model results show that there could be multiple interventions to reduce time taken to be seen by the doctor for the first time (also called WTBS) either in the output phase or in the input phase. The model is able to predict that a reduction in the output phase would cause reduction in the WTBS but it is not equipped to suggest how this reduction can be achieved. To reduce WTBS by making interventions in the input phase this research proposes a strategy called fast-track treatment (FTT). This strategy helps the model to dynamically re-allocate resources if needed to alleviate high WTBS. Results show that FTT can reduce WTBS times by up-to 40%.
33

Improving Emergency Department performance using Discrete-event and Agent-based Simulation

Kaushal, Arjun 14 February 2014 (has links)
This thesis investigates the causes of the long wait-time for patients in Emergency department (ED) of Victoria General Hospital, and suggests changes for improvements. Two prominent simulation techniques have been used to replicate the ED in a simulation model. These are Discrete-event simulation (DES) and Agent-based modeling (ABM). While DES provides the basic modeling framework ABM has been used to incorporate human behaviour in the ED. The patient flow in the ED has been divided into 3 phases: input, throughput, and output. Model results show that there could be multiple interventions to reduce time taken to be seen by the doctor for the first time (also called WTBS) either in the output phase or in the input phase. The model is able to predict that a reduction in the output phase would cause reduction in the WTBS but it is not equipped to suggest how this reduction can be achieved. To reduce WTBS by making interventions in the input phase this research proposes a strategy called fast-track treatment (FTT). This strategy helps the model to dynamically re-allocate resources if needed to alleviate high WTBS. Results show that FTT can reduce WTBS times by up-to 40%.
34

Wide-Area Measurement Application and Power System Dynamics

Chen, Lang 01 December 2011 (has links)
Frequency monitoring network (FNET) is a GPS-synchronized distribution-level phasor measurement system. It is a powerful synchronized monitoring network for large-area power systems that provides significant information and data for power system situational awareness, real time and post-event analysis, and other important aspects of bulk systems. This work explored FNET measurements and utilized them for different applications and power system analysis. An island system was built and validated with FNET measurements to study the stability of the OTEC integration. FNET measurements were also used to validate a large system model like the U.S. Eastern Interconnection. It tries to match the simulation result and frequency measurement of a real event by adjusting the simulation model. The system model is tuned with the combination of different impact factors for different confirmed actual events, and some general rules and specific tuning quantities were concluded from the model validation process. This work also investigated the behavior of the power system frequency during large-scale, synchronous societal events, like the World Cup, Super Bowl and Royal Wedding. It is apparent that large groups of people engaging in the same event at roughly the same time can have significant impacts on the power grid frequency. The systematic analysis of the accumulating and statistical FNET frequency data presents an incisive point of view on the power grid frequency behavior during such events. To better understanding of system events recorded by FNET, a visualization tool was developed to visualize major events that occurred in the North American power grid. The measurement plot combined with the geographical contour map provides intuitive visualization of the event. Finally, the EI system was simplified and clustered into four groups based on FNET measurements and simulation results of generator trip cases. The generation and load capacity of each cluster was calculated based on the clustering result and simulation model, and a flow diagram of this simplified EI system was demonstrated with clusters and power flow between them.
35

Robust state estimation and model validation techniques in computer vision

Al-Takrouri, Saleh Othman Saleh, Electrical Engineering & Telecommunications, Faculty of Engineering, UNSW January 2008 (has links)
The main objective of this thesis is to apply ideas and techniques from modern control theory, especially from robust state estimation and model validation, to various important problems in computer vision. Robust model validation is used in texture recognition where new approaches for classifying texture samples and segmenting textured images are developed. Also, a new model validation approach to motion primitive recognition is demonstrated by considering the motion segmentation problem for a mobile wheeled robot. A new approach to image inpainting based on robust state estimation is proposed where the implementation presented here concerns with recovering corrupted frames in video sequences. Another application addressed in this thesis based on robust state estimation is video-based tracking. A new tracking system is proposed to follow connected regions in video frames representing the objects in consideration. The system accommodates tracking multiple objects and is designed to be robust towards occlusions. To demonstrate the performance of the proposed solutions, examples are provided where the developed methods are applied to various gray-scale images, colored images, gray-scale videos and colored videos. In addition, a new algorithm is introduced for motion estimation via inverse polynomial interpolation. Motion estimation plays a primary role within the video-based tracking system proposed in this thesis. The proposed motion estimation algorithm is also applied to medical image sequences. Motion estimation results presented in this thesis include pairs of images from a echocardiography video and a robot-assisted surgery video.
36

Computer Model Verification and Testing of an Apricus AP-30 Evacuated Tube Collector Array

January 2011 (has links)
abstract: Evacuated tube solar thermal collector arrays have a wide range of applications. While most of these applications are limited in performance due to relatively low maximum operating temperatures, these collectors can still be useful in low grade thermal systems. An array of fifteen Apricus AP-30 evacuated tube collectors was designed, assembled, and tested on the Arizona State University campus in Tempe, AZ. An existing system model was reprogrammed and updated for increased flexibility and ease of use. The model predicts the outlet temperature of the collector array based on the specified environmental conditions. The model was verified through a comparative analysis to the data collected during a three-month test period. The accuracy of this model was then compared against data calculated from the Solar Rating and Certification Corporation (SRCC) efficiency curve to determine the relative performance. It was found that both the original and updated models were able to generate reasonable predictions of the performance of the collector array with overall average percentage errors of 1.0% and 1.8%, respectively. / Dissertation/Thesis / M.S. Mechanical Engineering 2011
37

Study of power plant with carbon dioxide capture ability through modelling and simulation

Biliyok, Chechet January 2013 (has links)
With an increased urgency for global action towards climate change mitigation, this research was undertaken with the aim of evaluating post-combustion CO2 capture as an emission abatement strategy for gas-fired power plants. A dynamic rate-based model of a capture plant with MEA solvent was built, with imposed chemical equilibrium, and validated at pilot scale under transient conditions. The model predicted plant behaviour under multiple process inputs and disturbances. The validated model was next used to analyse the process and it was found that CO2 absorption is mass transfer limited. The model was then improved by explicitly adding reactions rate in the model continuity, the first such dynamic model to be reported for the capture process. The model is again validated and is observed to provide better predictions than the previous model. Next, high fidelity models of a gas-fired power plant, a scaled-up capture plant and a compression train were built and integrated for 90% CO2 capture. Steam for solvent regeneration is extracted from the power plant IP/LP crossover pipe. Net efficiency drops from 59% to 49%, with increased cooling water demand. A 40% exhaust gas recirculation resulted in a recovery of 1% efficiency, proving that enhanced mass transfer in the capture plant reduces solvent regeneration energy demands. Economic analysis reveals that overnight cost increases by 58% with CO2 capture, and cost of electricity by 30%. While this discourages deployment of capture technology, natural gas prices remain the largest driver for cost of electricity. Other integration approaches – using a dedicated boiler and steam extraction from the LP steam drum – were explored for operational flexibility, and their net efficiencies were found to be 40 and 45% respectively. Supplementary firing of exhaust gas may be a viable option for retrofit, as it is shown to minimise integrated plant output losses at a net efficiency of 43.5%. Areas identified for further study are solvent substitution, integrated plant part load operation, flexible control and use of rotating packed beds for CO2 capture.
38

Vytvoření a validace výpočtového FEM modelu kliky dveří pro crashové výpočty / Car Door Handle FEM Model Creation and Validation for Crash Simulations

Raffai, Peter January 2012 (has links)
The aim of this master’s thesis was to create a component model of a door handle stiffener used by the Volkswagen concern, which can be used for crash computations. Also to tune its parameters the way, its behavior corresponds the most to the real part’s. In the theoretical part the current regulations of the Euro NCAP are presented, concerning the testing and evaluation of the passive safety of new vehicles. Attention is focused on the evaluation of the side impact barrier tests, where the effect of the door handle stiffener’s damage is reflected the most. Shown are the reasons for the effort to simulate the real behavior of the stiffener, the factors, which initialized the born of the studied problem. The practical part starts with the creation of the FEM mesh of the part based on its 3D CAD model, also describes the requirements for the mesh quality, as well as the used tools and methods. Further on investigated are the characters of real damages of the door handle area during side impacts, based on which the component tests are proposed for the validation of the simulation model. Experimental research consists of the stiffener’s testing for simple bend and twist loads, three specimens each. After the execution of the tests the results get compared with the corresponding simulations. Modifications are made on the model according to the acquired results: refinement of the FEM mesh, new material model usage with failure for shell elements and definition of real material characteristics for the used thermoplastics. The latest obtained simulation dependencies are compared with the measured values again, the results are evaluated at last.
39

Validation of Bus Specific Powertrain Components in STARS

Karlsson, Karl January 2007 (has links)
The possibilities to simulate fuel consumption and optimize a vehicle's powertrain to fit to the customer's needs are great strengths in the competitive bus industry where fuel consumption is one of the main sales arguments. In this master's thesis, bus specific powertrain component models, used to simulate and predict fuel consumption, are validated using measured data collected from buses. Additionally, a sensitivity analysis is made where it is investigated how errors in the powertrain parameters affect fuel consumption. After model improvements it is concluded that the library components can be used to predict fuel consumption well. During the work, possible model uncertainties which affect fuel consumption are identified. Hence, this study may serve as foundation for further investigation of these uncertainties.
40

A time series analysis of price formation in power markets

Khan, Ibrahim 14 March 2018 (has links)
This study examines price formation in one of the largest wholesale electricity markets in the world: the Pennsylvania Jersey Maryland Interconnection, which serves 13 states and the District of Columbia with over 60 million consumers. The contribution of this thesis is to apply a variety of time series models offered in the literature to a large data set describing a single market, allowing for a comparison of their performance as well as demonstrating their validity. A central question that drives market deregulation is if it has created efficiency gains. To formalize this notion of efficiency, we implement tests for stationarity to measure the degree of randomness over time, finding that short run volatility can result in the outcomes for these tests that are inconclusive. We explore this volatility structure using Asymmetrical Power Autoregressive Conditional Heteroskedastic (APARCH) framework which captures the asymmetric nature of price shocks, finding that this behavior is unique to electricity returns, and that APARCH offers a better modelling alternative than simpler representations. Additionally, we account for long memory given the seasonal drivers of electricity prices which are persistent using Autoregressive Fractionally Integrated Moving Averages (ARFIMA). Temperature related market drivers are further modelled using Fourier based seasonality functions which enable us to capture cycles over multiple frequencies. Lastly, we provide an application of Markov Regime Switching models to account for the possibility of multiple states. Although appealing from a theoretical perspective, we find that the increased complexity of the model does not necessarily translate to better performance over simpler non-switching alternatives. These findings highlight the importance of establishing the features of the time series before selecting an appropriate model, and motivating it with economic rationale. / Graduate

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