06 Fakultät Luft- und Raumfahrttechnik und Geodäsie

Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/7

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Publication Type: search.filters.UBSTyp.Abschlussarbeit (Master)Subject: search.filters.subject.500

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    Computational simulation of fluid-structure interaction of soft kites
    (Stuttgart : University of Stuttgart, Institute of Mechanics, Structural Analysis and Dynamics, 2018) Adam, Niklas Johannes
    In order to aid the development and automation of airborne wind energy (AWE) systems, the foundation for fluid-structure interaction (FSI) simulations considering soft kites is developed. FSI simulations are used as a way to predict the deformation of highly flexible structures exposed to a fluid flow and the resulting interaction of solid and fluid. This is especially important for kites since the aeroelastic effects can not be neglected if a realistic approach is regarded. Therefore, the open-source structural multibody dynamics solver MBDyn is coupled to an extension of the open-source computational fluid dynamics (CFD) solver OpenFOAM, namely FOAM-FSI, via the coupling environment preCICE. Relevant modeling features of MBDyn for soft kites such as membrane elements and appropriate boundary conditions are evaluated by means of simple test cases. Furthermore, an adapter for the communication between preCICE and MBDyn is developed and assessed as well. Since an adapter for FOAM-FSI and preCICE already exists, no efforts considering this aspect had to be made. Using this approach, a simple FSI simulation on a ram-air kite section is performed. Due to convincing results regarding the test cases, MBDyn is considered to be a suitable solver for the simulation of soft kites. Moreover, the correct implementation of the adapter is verified by the coupled FSI simulation of a modified benchmark with respect to the aforementioned participating solvers. An approach to FSI simulations on soft kites is successfully developed and verified. However, no reliable final evaluation for the kite section can be made due to the lack of reference solutions.
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    Understanding the limitations of Sentinel-3 inland altimetry through validation over the Rhine River
    (2022) Schneider, Nicholas M.
    Satellite altimetry is developing into one of the most powerful measurement techniques for long-term water body monitoring thanks to its high spatial resolution and its increasing level of precision. Although the principle of satellite altimetry is very straightforward, the retrieval of correct water levels remains rather difficult due to various factors. Waveform retracking is an approach to optimize the initially determined range between the satellite and the water body on Earth by exploiting the information within the power-signal of the returned radar pulse to the altimeter. Several so-called retrackers have been designed to this end, yet remain one of the most open study areas in satellite altimetry due to their crucial role they play in water level retrieval. Moreover, geophysical properties of the stratified atmosphere and the target on Earth have an effect on the travel time of the transmitted radar pulse and can amount to severalmeters in range. In this study we provide an overall analysis of the performances of the retrackers dedicated to the Sentinel-3 mission and the applied geophysical corrections. For this matter, we focus on nine different locations within the Rhine River basin where locally gauged data is available to validate the Sentinel-3 level-2 products. Furthermore, we present a reverse retracking approach in the sense that we use the given in-situ data to determine the offset to each altimetry-derived measurement of every epoch. Under the assumption that these offsets are legitimate, they can be seen as an a-posteriori correction which we project onto the range and thus on a waveform level. Further analyses consist in the investigation of the relationship these a-posteriori corrections have to the waveform properties of the same epoch. Later, the question whether the a-posteriori corrections to the initial retracking gates are appropriate for the retrieval of correct water levels, drives us to assign a probability to each and every bin of the waveform. Following this idea, we design stochastic-based retrackers which determine the retracking gate for water level retrieval from the bin with the highest probability assigned to it. To distribute the probabilities across all bins of the waveform, we consider three empirical approaches that take both the waveform itself and its first derivative into account: Addition, multiplication and maximum of both signals. For all three of the new retrackers, we generate the water level timeseries over the aforementioned sites and validate them against in-situ data and the retrackers dedicated to the Sentinel-3 mission.