06 Fakultät Luft- und Raumfahrttechnik und Geodäsie
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/7
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Item Open Access Measurement of soot precursor particles under atmospheric and low pressure conditions by means of time-of-flight mass spectrometry(2009) González Baquet, Tania; Aigner, Manfred (Prof. Dr.-Ing.)During the last decades a great progress has been achieved in the understanding of the combustion of hydrocarbons. The gas phase reactions governing the first steps in the combustion process are well understood. The existing models describing the growth of soot particles and the formation of soot aggregates are widely accepted, as well. However, the so-called inception, i.e. the mechanism leading to the formation of the first solid particles from gas phase molecules, is still a controversial issue. This is mainly due to the lack of adequate experimental techniques capable of detecting particles in the low nanometer range like those created in the nucleation process in flames. At present most of the combustion models stress the importance of PAH formation and growth in the soot formation process. Other models, however, propose a soot formation mechanism based on the formation of large three dimensional structures without crystallinity. In the present work, the detection and characterization of soot precursor particles, as transition species between gas phase molecules and solid soot particles in the combustion process, is attempted by means of mass spectrometry. To this end a ”custom-built” reflectron time-of-flight mass spectrometer of high sensitivity and with a large mass range is used. Measurements are carried out in different premixed ethylene laboratory flames at different pressures and in a wide range of stoichiometries. Additionally, the exhaust of a gasoline and a diesel engine is investigated. These measurements require the development of a sampling technique capable of transporting the sample from atmospheric conditions to the high vacuum of the mass spectrometer. The resulting fast pulsed sampling system minimizes undesirable sampling line effects while it enables the generation of an optimized molecular beam. Photo ionization of the sample is provided by an excimer laser. The main findings of this work can be summarized as follows: 1. Different types of soot precursor particles can coexist in the flame. For the first time two different types of soot precursor particles with diameters ranging from approximately 1 to 5 nm have been simultaneously detected. The different soot precursor particle modes, in the following referred to as mode A and mode B, show different features. Thus, the existence of at least two different types of soot precursor particles is postulated. Mode A particles are found in a wide range of flame stoichiometries. They are characterized by an ionization order close to two and show a fragmentation threshold of around 0.12 MW/cm2. These particles are considered amorphous, more characteristic of low temperature flames and associated to the soot precursor particles described by D’Alessio et al.. Mode B particles are only observed in a limited stoichiometric range associated with rather high flame temperatures. Mode B particles show an ionization order close to one and a relatively high fragmentation threshold close to 2.24 MW/cm2. These particles are considered to be similar to the ones described by Dobbins et al., i.e. stacks of planar PAHs. 2. Soot precursor particles, although considered to be very reactive, can survive the flame and be emitted. 3. Soot precursor particles are found in significant amounts only at flame stoichiometries above the soot threshold. The lower stoichiometric limit for particle generation is still an issue discussed in the combustion community. All results of this study indicate that the onset of particle formation takes place at flame stoichiometries close to the soot threshold. Consequently, the emission of soot precursor particles seems not to be an outstanding problem in the case of gasoline combustion engines, since the latter work under fairly stoichiometric burning conditions and are characterized by a homogeneous fuel-mixture. This is confirmed by the measurements carried out in the exhaust gas of a gasoline generator. Conventional diesel engines work under globally lean burning conditions but are characterized by a heterogeneous fuel-mixture. Consequently, high particle emissions are expected. The measurements carried out in the exhaust gas of a diesel generator, however, show negligible soot precursor particle emissions. In this case soot precursor particles are oxidized due to the excess of oxygen in the exhaust gas. Soot precursor particle losses due to coagulation with soot particles are also expected. This work demonstrates the utility of time-of-flight mass spectrometry for the detection and study of soot precursor particles. The experimental data presented in this thesis provide new information about the transition region between gas phase molecules and soot particles in the combustion process. This improves the understanding of the soot formation process and stimulates the revision of current combustion models.Item Open Access Faserverbundwerkstoffe im Automobilbau: methodischer Ansatz zur Analyse von Schäden(2012) Schmidt, Alexandra Priska; Drechsler, Klaus (Prof. Dr.-Ing.)Schadensanalyse beinhaltet die Beurteilung geschädigter Bauteile von der Schadenserkennung bis zur Entscheidung über Tolerierbarkeit, Reparatur oder Austausch. Es gibt derzeit keine allgemeine Bewertungsgrundlage, um die zulässige Schadensgröße für Bauteile aus kohlenstofffaserverstärkten Kunststoffen (CFK) an Fahrzeugen im praktischen Einsatz zu ermitteln. Die vorliegende Arbeit liefert einen methodischen Ansatz zur Entscheidungsfindung. Die Arbeit befasst sich mit Schäden, die nachträglich in die Fahrzeugstruktur eingebracht werden. Dies kann etwa durch Fehlgebrauch, Unfälle oder Steinschläge geschehen. Fertigungsfehler werden nicht berücksichtigt. In einem Versuchsprogramm wurde die Restfestigkeit von vorgeschädigten CFK Rohren mit unterschiedlichem Lagenaufbau unter Druckbelastung ermittelt. Realitätsgetreue Impacts werden zunächst durch einfache Bohrungen sowie Längs- und Quernuten auf akademische Weise angenähert und die Ergebnisse mit ungeschädigten Proben verglichen. Der Einfluss der Faserorientierung sowohl auf die Schadensausbreitung bei Impactschäden als auch auf die Restfestigkeit wird betrachtet. Deutliche Zusammenhänge zwischen Schadensgröße und Bruchlast konnten ermittelt und analytisch beschrieben werden. Dadurch ist eine Vorhersage der Restfestigkeit bei weiteren Schadensgrößen möglich. Zur potenziellen Reduktion der Versuchsumfänge wird die Möglichkeit der Computersimulation geprüft. Es wird deutlich, dass Simulationsmodelle die umfangreiche empirische Datenbasis derzeit nicht vollständig ersetzen können. Anhand des seitlichen Dachrahmens eines Automobils wird gezeigt, nach welchen Kriterien die Entscheidung über kritische oder unkritische Schäden erfolgt. Dazu wird der Standardlastfall des Dacheindrücktests verwendet. Die Ergebnisse der Versuche dienen als Bewertungsgrundlage. Ein 7-Punkte-Plan fasst die entwickelte Methodik zusammen und dient als Grundlage für die Analyse. Das exemplarisch durchgeführte Vorgehen kann auf beliebige Geometrien und weitere Lastfälle übertragen werden. Die Erkenntnisse dieser Arbeit können bereits in der Entwicklungsphase eines Automobils als Entscheidungsgrundlage dienen. Unter Berücksichtigung eines geeigneten zerstörungsfreien Prüfverfahrens zur Detektion der Schädigungen eignet sich die vorgestellte Methodik auch zum Einsatz im automobilen Kundenservice. Es wurden verschiedene Methoden miteinander verglichen. Neben Ultraschall und Computertomographie bietet sich die Optische Lock-In Thermographie für den praktischen Einsatz an.Item Open Access Analysis of water volume change of the lakes and reservoirs in the Mississippi River basin using Landsat imagery and satellite altimetry(2021) Wang, LingkeIn recent years, the demand for freshwater has been steadily increasing owing to population growth and economic expansion. Surface waters such as lakes and reservoirs function as a dominant factor in mankind's freshwater provision. Analysis of changes in their water storage is consequently vital for understanding of the global water cycle and water resources. However, the water volume changes in lakes or reservoirs cannot be measured directly from space, but can be inferred from lake areas and lake water levels. Lake area can be measured globally from space but lake water level is not easy to be obtained globally. Because the number of in situ stations is few, and in situ data are only accessible for some lakes with few measurement epochs, despite in situ stations can measure lake water level and provide high accuracy observations. Although the altimetry technique can generate the time series of the water level for the majority of lakes, they are not global coverage due to the distance between satellite tracks and the gap between different missions. Therefore, in situ data and satellite altimetry measurements of water levels of lakes and reservoirs are not always available. For example, there are only 22 lakes or reservoirs in this study covered by satellite altimetry or in situ stations out of 90 research cases in Mississippi River Basin. Then, in case of unavailable in situ data or altimetry measurements, this research proposes an alternative method to estimate the water level through Digital Elevation Model (DEM). Because satellite imagery offers global coverage and DEM is the global digital representation of the land surface elevation with respect to any reference datum, this study allows for the evaluation of global water volume changes by acquiring lake area data from space and lake height data from DEM. Therefore, the objective of this study is that changes in water volume in lakes or reservoirs can be successfully monitored even when in situ data and satellite altimetry measurements are not available for lakes or reservoirs. Hereby, we investigate 90 lakes and reservoirs in the Mississippi River Basin and develop an alternative remote sensing technique to monitor the water volume changes by combining the improved water mask with DEM. Meanwhile, we propose practical methods to detect the shoreline pixels of the water body from improved water mask. Given the assumption that all pixels in the shoreline should have the same height, four water level estimation models are developed, including water level estimation model based on statistical analysis, frequency maps, change pixels and pixel pair analysis. To this end, the study estimates the time series of lake height from water level estimation model and obtains the time series of lake surface area from HydroSat. Subsequently, this study builds the unique function between the lake water level and the lake surface area and then develops the function between the lake water volume change and the lake surface area. Finally, this study analyses the water volume changes of lakes and reservoirs in the Mississippi River Basin using this alternative remote sensing method. Four water level estimation models are proposed and evaluated. They are respectively based on statistical analysis, frequency maps, change pixels and pixel pair analysis. As a result of their actions, the first model based on statistical analysis, with an average correlation of 0.62 and an average RMSE of 0.91 meters, functions in the majority of situations and demonstrates excessive outlier removal in some cases. The second model based on frequency maps is more general than the first, with an average correlation of 0.66 and an average RMSE of 1.11 meters. The average correlation for the third model based on change pixels is 0.71, and the average RMSE is 0.99 meters. The resulting model based on pixel pair analysis obtains a mean correlation of 0.67 and a mean RMSE of 1.00 meters. Finally, these models behave differently in different seasons, so they exhibit distinct monthly behaviour. To conclude, the above validation results show that this alternative method can be used in different lakes and reservoirs in case of absence of water level observation data, and achieve to monitor the water volume changes during a long period.Item Open Access A method for evaluating population and infrastructure exposed to natural hazards : tests and results for two recent Tonga tsunamis(2023) Thomas, Bruce Enki Oscar; Roger, Jean; Gunnell, Yanni; Ashraf, SalmanBackground: Coastal communities are highly exposed to ocean- and -related hazards but often lack an accurate population and infrastructure database. On January 15, 2022 and for many days thereafter, the Kingdom of Tonga was cut off from the rest of the world by a destructive tsunami associated with the Hunga Tonga Hunga Ha’apai volcanic eruption. This situation was made worse by COVID-19-related lockdowns and no precise idea of the magnitude and pattern of destruction incurred, confirming Tonga’s position as second out of 172 countries ranked by the World Risk Index 2018. The occurrence of such events in remote island communities highlights the need for (1) precisely knowing the distribution of buildings, and (2) evaluating what proportion of those would be vulnerable to a tsunami.
Methods and Results: A GIS-based dasymetric mapping method, previously tested in New Caledonia for assessing and calibrating population distribution at high resolution, is improved and implemented in less than a day to jointly map population clusters and critical elevation contours based on runup scenarios, and is tested against destruction patterns independently recorded in Tonga after the two recent tsunamis of 2009 and 2022. Results show that ~ 62% of the population of Tonga lives in well-defined clusters between sea level and the 15 m elevation contour. The patterns of vulnerability thus obtained for each island of the archipelago allow exposure and potential for cumulative damage to be ranked as a function of tsunami magnitude and source area.
Conclusions: By relying on low-cost tools and incomplete datasets for rapid implementation in the context of natural disasters, this approach works for all types of natural hazards, is easily transferable to other insular settings, can assist in guiding emergency rescue targets, and can help to elaborate future land-use planning priorities for disaster risk reduction purposes.Item Open Access Aeroacoustic simulation of turbulent boundary layer induced automotive gap noise(2021) Erbig, Lars; Munz, Claus-Dieter (Prof. Dr. rer. nat.)Item Open Access New methods for 3D reconstructions using high resolution satellite data(2021) Gong, Ke; Fritsch, Dieter (Prof. Dr.-Ing. habil. Prof. h.c.)Item Open Access Automated pipe design in 3D using a multi-objective toolchain for efficient decision-making(2024) Neumaier, Moritz; Kranemann, Stefan; Kazmeier, Bernd; Rudolph, StephanItem Open Access Modeling, testing and application of tuned liquid multi-column dampers for floating offshore wind turbines(2024) Yu, Wei; Cheng, Po Wen (Prof. Dr.)Item Open Access On the heritage of Kurt Magnus in gyro technology(2024) Wagner, Jörg F.Kurt Magnus (1912-2003) is one of the personalities who shaped research and teaching in applied mechanics during the 20th century. Through his work with his doctoral supervisor Max Schuler at the University of Göttingen, gyrodynamics became his most important field of work, which also led to his research in oscillations, multi‐body systems, and mechatronics. Magnus made significant contributions in all these fields. He was regarded as a gifted lecturer, and the close connection between scientific research and practical application was important to him. Life and scientific work of Kurt Magnus were, however, also characterized by his 7‐year deportation to the USSR in 1946. Despite this fate, he was able to continue his research under certain restrictions during this time. After returning to Germany, he became Professor of Mechanics at the University of Stuttgart in 1958. His appointment coincided with the gradual resumption of industrial activities in Germany in the field of gyro technology-activities that had come to a standstill at the end of World War II. In the years that followed, Magnus' institute became the scientific center for gyrodynamics in Germany. The activities of that time are reflected in a preserved collection of gyro instruments for research and teaching as well as in the co‐founding of an annual international conference on inertial technology, which continues to this day. Magnus' subsequent move to the Technical University of Munich in 1966 did nothing to change this. At that time, he was regarded as a doyen of gyro technology. After a short biography of Kurt Magnus, the paper addresses the recent revision and digitization of the gyro instrument collection and presents an outline of the history of the conference series providing details on how gyro technology has developed since his work in Stuttgart.Item Open Access Modell-basierte Systemsimulation eines Kleinsatelliten mit einem FPGA-basierten On-board-Computer(2009) Falke, Albert; Röser, Hans-Peter (Prof. Dr.-Ing.)Die vorliegende Dissertation beschäftigt sich schwerpunktmäßig mit der Systemsimulation des Satelliten Flying Laptop unter Weltraumbedingungen, mit dem Ziel die Funktionalitäten des Satellitensystems als Ganzes zu verifizieren. Simulation bezeichnet allgemein das Nachahmen des Verhaltens eines Systems oder Prozesses zum Zwecke der Analyse von Systemen, die für die theoretische oder formelmäßige Behandlung zu kompliziert sind. Auch im Kontext einer Kleinsatellitenmission ist das Satellitensystem bereits so komplex, dass man ohne die systemweite Simulation keine detaillierte Analyse unter Berücksichtigung der vielen miteinander interagierenden Komponenten mehr durchführen kann. Bereits seit einigen Jahren verwenden renommierte Satellitenhersteller Simulationstechnologien, um bereits während der Satellitenentwicklung und Fertigung den größtmöglichen Missionserfolg zu gewährleisten. Eine dieser Technologien ist die Modell-basierte Entwicklungs- und Verifikationsumgebung der Firma EADS Astrium GmbH aus Friedrichshafen. Sie bietet ein systematisches und standardisiertes Entwicklungs- und Verifikationsrahmenwerk im Sinne eines systemweiten Satellitensimulators an, um die Entwicklung von Satelliten, die Verifikation der On-board Software und den Gesamtfunktionsnachweis des Satelliten zu unterstützen. In diesem Simulator können alle Satellitenkomponenten modelliert und die On-board Software somit auf funktionaler Ebene verifiziert werden. Auf diese Weise können aufwendige und kostenintensive Entwicklungsmodelle einzelner Subsysteme und Schlüsseltechnologien wegfallen. Insbesondere sei hier die Verifizierung der Genauigkeit des Lageregelungssystems angesprochen. Als technologische Voraussetzung bringt gerade diese Entwicklungstechnologie budgetschwache Kleinsatellitenprojekte der Realisierung einen deutlichen Schritt näher und erhöht gleichzeitig die Güte des Systemdesigns des Satelliten. Im Rahmen einer Kooperation wurde diese Simulationsumgebung dem Institut für Raumfahrtsysteme zur Adaption und Anwendung im Stuttgarter Kleinsatellitenprogramm zur Verfügung gestellt. Zur Anwendung der Systemsimulation im Kleinsatellitenprojekt Flying Laptop sind alle relevanten Satellitenkomponenten im Simulator durch entsprechende, detaillierte Softwaremodelle abgebildet worden. Der sukzessiven Entwicklung der Komponentenmodelle ist durch den schrittweisen Aufbau von immer komplexeren Testständen der Software-Verifikations-Einrichtung Rechnung getragen worden. Infolgedessen erweiterten sich die Simulationsfähigkeiten von ersten Orbitsimulationen mit wenigen Komponentenmodellen, aber mit geschlossenem Simulationskreislauf, über die Simulation von Energie- und Thermalbilanzen unter Betriebsbedingungen bis hin zu vollständigen Systemsimulationen unter Einbindung der realen On-board Kontrollalgorithmen auf einem FPGA-Entwicklungsboard. Gerade dieses charakteristische FPGA-basierte On-board Computer System mit den darauf betriebenen Kontrollalgorithmen führt zu einer großen Herausforderung bei der modellhaften Repräsentation derselbigen im Systemsimulator. In diesem Zusammenhang stellt die Einbindung der realen On-board Kontrollalgorithmen auf einem FPGA-Entwicklungsboard in den geschlossenen Simulationskreislauf eine erfolgreich realisierte technische Neuerung dar. Zum Zeitpunkt der Fertigstellung dieser Arbeit steht dem Projekt Flying Laptop durch die Einbindung der realen On-board Kontrollalgorithmen auf dem FPGA-Entwicklungsboard ein umfangreicher Teststand mit großem Potential zur Entwicklung und zum Funktionsnachweis der On-board Kontrollalgorithmen zur Verfügung. Dieser wurde, wie die vorgestellten Simulationsergebnisse zeigen, bereits intensiv zum Testen der ersten Lageregelungsalgorithmen genutzt und kann auch zukünftig sukzessive mit Funktionserweiterungen der On-board Kontrollalgorithmen angewandt werden. Typische Missionsszenarien wie die Transition zwischen zwei Betriebsmodi des Satelliten oder der automatische Übergang in den SAFE Mode bei einem Fehler können jetzt simuliert und getestet werden. Die Ergebnisse dieser Simulationen dienen nicht nur dem reinen Funktionsnachweis der On-board Kontrollalgorithmen, sondern fließen direkt in die Optimierung der Kontrollalgorithmen zurück und führen so zu einem iterativem Verbesserungsprozess. Der Systemsimulator ist mit seiner Datenbank als Teil seiner Infrastruktur ganz gezielt so implementiert worden, dass einzelne Testszenarien einfach und ohne wiederholten Konfigurationsaufwand reproduziert werden können. Somit unterstützt der Systemsimulator den sich in der Softwareentwicklung typischerweise iterativ wiederholenden Verifikationsprozess in einer optimalen Form.