Universität Stuttgart
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Item Open Access Tensorgesteuerte Entwicklung biokompatibler Strukturen(2021) Däges, Johannes-MaximilianDie vorliegende Arbeit verfolgt den Ansatz einer Topologieoptimierung um würfelförmige Strukturen zu erstellen die ein vorgegebenes elastisches Verhalten haben. Hierzu wird die Methode der Homogenisierung nach G. P. Steven angewendet um aus einem gegeben Steifigkeitstenor Beschränkungen für eine Topologieoptimierung zu entwickeln. Zudem wurde die Mandel-Notation in die Homogenisierung eingebaut. Das langfristige Ziel ist es, Femurnägel aus vielen Einzelstrukturen zusammen zu setzen und so auftretendes Stress shielding im Femurknochen zu verringern. Die Ergebnisse verschiedener Konfigurationen sind durchaus vielversprechend und unterstützen eine weitere Untersuchung des Ansatzes.Item Open Access Water level monitoring at SAPOS stations through GNSS-IR : a case study at the station Iffezheim(2023) Wagner, Sven B.The German SAPOS-Network comprises approximately 270 permanent GNSS receivers, capturing signals from Global Navigation Satellite Systems such as GPS, GLONASS, Galileo, and BeiDou. Primarily employed for generating kinematic, mathematical, and physical models within their respective regions, these receivers hold untapped potential for alternative applications. GNSS receivers capture multipath errors, typically considered unwanted interferences resulting from signal reflections off surfaces beneath the antenna. Despite their potential to adversely affect data precision, these interferences contain valuable information about the reflecting surface. As satellites pass through the receivers’ field of view at specific elevation angles, the interference between the direct and reflected signals leads to constructive and destructive patterns. This phenomenon occurs due to variations in signal phase between the direct and reflected signal, enhancing or dampening the signal strength. These variations in signal strength are captured in the satellites Signal-to-Noise Ratio (SNR) data. Spectral analysis of the SNR data can be used to determine the frequency of the interference pattern. Combining this frequency with the corresponding signal wavelength and satellite elevation angles allows the calculation of the vertical distance between the antenna phase centre and the reflecting surface on Earth. This method, known as GNSS Interferometric Reflectometry (GNSS-IR), provides a valuable means of monitoring surface information, including soil moisture, snow depth, and water levels. At SAPOS stations near rivers and water bodies, GNSS-IR offers a cost-effective, accessible, and innovative opportunity to gather water level information using the already existing infrastructure. This research explores the potential of GNSSIR for water level monitoring at SAPOS stations focusing on the Iffezheim station along the Rhine River near the City of Karlsruhe in southern Germany.Item Open Access Analysis of coordinate transformation with different polynomial models(2017) Gao, YueqingThe main task of geodesy is providing geodetic networks with fixed points in order to create a uniform geographical spatial reference frame as a fundament for the data collection by the official geodesy survey institutes. A german geodesy survey institute called AdV (Arbeitsgemeinschaft der Vermessungsverwaltungen der Länder der Bundesrepublik Deutschland) declared in 1991 that the ETRS89 datum should be introduced in Germany as a reference system. In order to transform the already exciting coordinate informations in the Gauß-Krüger coordinate system into the later introduced UTM coordinate system, different transformation models have been developed and discussed. Besides the most commonly used 7-parameter Helmert transformation and 6-parameter affine transformation models, polynomial transformation models can also be applied. A method for improving the transformation results of a polynomial model will be discussed, with which a significance test (T-test) for each parameter will be done and the polynomial terms with lower significance to the model will be eliminated in order to get the optimal polynomial model. Here different transformation models are reviewed and the transformation results based on these models with the Least Squares estimation method are compared and analysed.Item Open Access Analyzing the spatio-temporal behavior of Poyang Lake using Google Earth Engine(2020) Schneider, Nicholas M.Poyang Lake, China’s largest freshwater lake, undergoes a yearly repeating cycle of drastic inundation and subsequent considerable shrinkage. Essentially, as a result of local precipitation and feedings from its tributaries, as well as a natural water exchange with the Yangtze River, Poyang Lake experiences such dimensional fluctuations on a annual and interannual scale. The ongoing change plays a significant role for the surrounding anthropogenic activity and wildlife. Despite being considered as a hydrological phenomenon, the dynamics of this Chinese water body set up a hurdle for any accurate documentation of its regime and therefore remains insufficiently studied upon to this day. Further impeding the comprehension of Poyang Lake’s behavior is the near inaccessibility and nonexistence of in situ data, such as water level measurements and bathymetric maps. Consequently, this study, driven by its aim to analyze the spatio-temporal behavior of Poyang Lake, focuses solely on satellite observations. Making use of the cloud computing platform, Google Earth Engine, image time series are used from Landsat-8 and Sentinel-1 datasets in order to map Poyang Lake’s spatio-temporal behavior on an annual and interannual scale. Produced from the Landsat-8 dataset, results show that only under circumstances, do techniques, such as the combination of visible and infrared bandsand the calculation of the Normalized Difference Water Index, provide a reasonable approach for the delineation of continental water bodies. For the study on Poyang Lake, a water body subject to humid climate and thus frequent cloud coverage, these techniques do not apply very well. With synthetic aperture radar observations from the Sentinel-1 dataset, dynamic water masks, involving the removal of certain elevated areas and the classification of water from thresholding, could be generated. The resulting binary water masks are then merged with a digital terrain model to create monthly maps of the study area. The results show an evident correlation between this study’s visual and numeric findings. Although the results are nearly impossible to compare with any in situ data, they show a trend that annually occurs in Poyang Lake’s hydrological regime. In particular, they reveal the cycle of drastic inundation in rainy summer months and considerable shrinkage in dry winter months, especially when examining the years prior to 2019. Using SAR imagery for continental water body delineation, particularly in humid climates, proved to be a suitable technique and should be considered for future documentations of the lake.Item Open Access Sea surface altimetry using GNSS-R(2018) Li, FanxiangThe Global Navigation Satellite Systems Reflectometry (GNSS-R) aims to retrieve information about the Earth surface by analyzing the signals emitted by GNSS transmitters (such as GPS, GLONASS, GALILEO and COMPASS...), and captured by an elevated platform after the signal has rebounded off of the oceans, lakes, land or ice and snow. The sea surface altimetry is an essential oceanic application of the GNSS-R. In this thesis, a method is introduced to solve this altimetric problem. Besides, a set of experimental data based on the campaign "Gold Test" carried out over the Mediterranean Sea in 2005 provided by the Institut de Ciències de l’Espai (ICE) is tested.Item Open Access Analysis of helicopter-borne gravity gradiometry(2017) Xia, ZhugeNowadays the FALCON partial tensor gravity gradiometer is the only applied AGG instrument to be used in a helicopter to collect high-resolution data for commercial demand. In order to know its principles and make full use of its advantages, in this study thesis, a helicopterborne gravity gradiometry data set offered by USGS is processed and analysed. It is interesting to figure out that whether the gradient tensor invariants are truly "invariant". Also through Fourier transformation, all gradient tensor components can be determined mathematically. Besides, the effects of terrain corrections and different flight line spacings and drape heights are also concerned to obtain high-resolution data in the easiest way.Item Open Access Validierung der 3D-Prozesskarte und Entwicklung von Prozessstrategien für das äquiaxiale Kornwachstum im Laserstrahlschweißen von Aluminium(2021) Nasr, YassinUm das äquiaxial dendritische Kornwachstum abhängig von den Prozessparametern im Laserstrahlschweißprozess von Aluminiumlegierungen einstellen zu können wurde die 3D-Prozesskarte entwickelt. Diese gibt eine erforderliche tiefenspezifische Laserleistung, welche für das äquiaxiale Kornwachstum absorbiert werden muss, für eine beliebige Aluminiumlegierung in Abhängigkeit der Schweißgeschwindigkeit an. In vorangegangenen Experimenten wurde der prozessseitige Einfluss auf die Kornstruktur für die Legierung EN AW-6016 untersucht und validiert. Um den werkstoffseitigen Einfluss auf die Kornstruktur zu validieren, wurden im Rahmen dieser Arbeit Laserstrahlschweißungen mit fünf verschiedenen Legierungen durchgeführt. Dabei wurden die Prozessparameter Fokusdurchmesser, Laserleistung, Schweißgeschwindigkeit und Blechstärke variiert. Die Kornstruktur der Schweißnähte wurde anschließend mithilfe metallografischer Schliffe untersucht.Item Open Access Efficient sampling of transition constraints for motion planning under sliding contacts(2020) Khoury, Marie ThereseIn contact-based motion planning we consider for humanoid and multiped robots problems like going up a staircase, walking over an uneven surface or climbing a steep hill. Solving such tasks requires finding sequences of fixed and sliding contacts and planning the transition from one contact in the environment to another. However, most existing algorithms do not take sliding contacts into account for navigation problems or consider them only for manipulation scenarios. We propose an approach to contact-based planning that uses sliding contacts and exploits contact transitions. Such transitions are elementary operations required for whole contact sequences. To model sliding contacts, we develop a sliding contact constraint that permits the robot to slide on an object’s surface. To exploit contact transitions, we utilize three constraint modes to enable passage: contact with a start surface, no contact and contact with a goal surface. We develop a sampler that samples these transition modes uniformly. In this thesis we focus on the motion of one robot link’s end from an initial contact point toward a designated goal surface while the other end of the robot remains in sliding contact with the initial surface. Our method is evaluated by testing it on manipulator arms of two, three and seven degrees of freedom with different objects and various sampling-based planning algorithms. From the considered manipulator arm, it would be possible to transfer our concept to more complex robots and scenarios and extend it to a whole sequence of contacts.Item Open Access Analysis of river surface slope using ICESat-2 satellite altimetry(2022) Bao, JingyiItem Open Access Detektion von Fehlern am Gleis mittels Frequenzanalyse am Beispiel eines Fahrweg-Fahrzeug-Modells(2018) Aboul Seoud, IbrahimDurch die kontinuierlich steigende Verkehrsleistung im Eisenbahnverkehr erhöht sich auch die Anzahl der gefährlichen Ereignisse. Einige dieser Eisenbahnunfälle könnten durch eine frühzeitige Identifizierung von Fehlern am Fahrweg vermieden werden. Dabei könnte die kontinuierliche Überwachung und Bewertung des Fahrwegzustands in Echtzeit durch an Regel-zügen angebrachten Sensoren erfolgen, wodurch auch eine erhebliche Kostenersparnis und Erhöhung des Fahrkomforts sowie der Sicherheit ermöglicht würde. Zur Erkennung von Feh-lern können typische Frequenzbereiche genutzt werden. Um diese zu generieren wurde am Institut für Eisenbahn- und Verkehrswesen der Universität Stuttgart ein Modell gebaut. Im Modell können Gleisfehler mit unterschiedlichen Geometrien und Steifigkeiten am Fahrweg installiert werden. Zur Fehlerdetektion wurde die vertikale Beschleunigung mit einem Beschleunigungssensor am Fahrzeug erzeugt. Für das Beschleunigungssignal im Bereich von Fehlern wurden dann die Frequenzen analysiert. Der Vorteil des Modells ist, dass die Positionen der Fehler im Modell bekannt sind, wodurch leicht zwischen den einzelnen Fehlern im Mess-schrieb unterschieden werden kann. Um Einzelfehler im Messschrieb bewerten zu können, ist eine Klassifikation der detektierten Fehler notwendig. Im Rahmen der Bachelorarbeit erfolgt deshalb eine Frequenzanalyse zu einzelnen im Modell existierenden Fehlern. Die Messschriebe im Bereich von Fehlern wurden mittels Fast Fourier Transformation, der spektralen Beschleunigungsdichte und der Wavelet-Analyse untersucht. Darauf aufbauend wurde einer Logik zu Detektion der Gleisfehler im Modell entwickelt und mittels der Software Enterprise Architect diese dargestellt. Anschließend wurde diese Logik mit der Software MATLAB umgesetzt und getestet.