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 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 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 Mesoscopic homogenization method of mechanical properties of fused filament fabrication structures considering void shapes and filament interfaces(2025) Springmann, Marlies; Middendorf, PeterThe Fused Filament Fabrication process (FFF) is an additive manufacturing process for thermoplastic polymers based on material extrusion. It offers a large range of material options and high potential for manufacturing parts with complex geometry. Mechanical properties of parts produced with this method are, however, highly anisotropic and depend on process parameters and resulting inner mesostructures. The relationships between process parameters, mesostructures and mechanical properties are complex. Characteristics of the FFF mesostructures, such as voids and the interfaces between filaments, cannot yet be sufficiently taken into account in macroscopic design methods. In this work, a method for homogenising mechanical properties is developed. This is based on the inner FFF mesostructure: shape and size of the voids are determined using micrographs and the size of the coalescence areas between the filaments is also estimated. Representative volume elements with periodic boundary conditions are then created in a finite element environment and homogenised mechanical properties are derived. These are compared with analytical and experimental values, and the results are discussed. The method presented here provides an approach on how different characteristics of FFF mesostructures can be transferred to macroscopic simulations. Results of the numerical approach are in good agreement with the experimental data.Item Open Access Simulation analysis and implementation of a permanent magnet configuration on an RF helicon-based plasma thruster(2026) Papavramidis, Konstantinos; Blank, Sebastian; Souhair, Nabil; Skalden, Jonathan; Gutierrez, Elizabeth; Herdrich, GeorgSatellites in very low Earth orbit (VLEO) decay over time due to drag. However, payloads can be benefited, potentially improving performance and costs. To enable VLEOs, the Institute of Space Systems (IRS) is developing an atmosphere-breathing electric propulsion (ABEP) system. The current design is based on an electrodeless RF helicon-based plasma thruster (IPT) laboratory prototype. It features a solenoid that provides the external magnetic field for plasma confinement and acceleration. Based on this, a vacuum capable model is developed, using as alternative a magnet configuration. Different ring magnet configurations are investigated, optimizing the magnetic field topology. Performance and plasma properties are extracted by a theoretical model. A simulation process approach is presented. A sensitivity analysis is conducted, identifying factors affecting the magnetic field topology. A simple way is proposed to change the field strength, keeping field topology and geometry the same by adjusting the internal diameter of the magnets. As a result, changes of the field strength and the resulting performance parameters, required by future developments of the IPT, can be accounted for.Item Open Access Validation of the safety requirements of the landing gear using fault tree analysis(2022) Iven, Leander; Zaidi, YaseenWe analyze the functionality of the landing system of a regional aircraft in the extension and cruise flight modes and validate safety requirements through the fault tree analysis. The main landing gear system is captured in the electromechanical-fluidic domain and system behavior is abstracted in an elementary hydraulic circuit. The functional representation is then constructed into a fault tree which allows analysis of the failure propagation originating at different branch terminals, for instance, at the main landing gear actuator which extends the gear and holds it retracted during the cruise, door actuator, door uplocks, and hydraulic power supply. Each component is assigned a failure probability. Each failure mode is abstracted as a top-level event having a probability of failure and through Boolean combinations of component failures in the lower branches. Two reliability aspects considered are the availability to fully lower the landing gear and the integrity of inadvertent gear or door extension while cruising. Architectural changes through undercarriage system reconfiguration and component redundancy have been exploited to improve system failure rates. The analysis determines the overall system failure rate against the flight cycles. The process is agile to accommodate design changes with the evolution of architecture during the systems engineering lifecycle.Item Open Access 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.Item Open Access Numerical simulation of wake interactions on a tandem wing configuration in high-speed stall conditions(2023) Kleinert, Johannes; Stober, Jonathan; Lutz, ThorstenIn this work, the interaction of the separated wake of the front wing with the rear wing of a tandem configuration is investigated for high-speed stall conditions by means of hybrid RANS/LES simulations, using the zonal AZDES method. After a characterization of the transonic buffet on the front wing, the development of the separated turbulent wake behind the wing is investigated. The interaction of the separated wake with the rear wing is then analyzed in detail. The results reveal that there is a strong variation in the wake characteristics over the buffet cycle, caused by the varying amount of separation on the front wing. During the upstream movement of the shock, the flow is largely separated, resulting in a thick wake with strong, high-frequent fluctuations that can be attributed to large turbulent vortices. On the contrary, when the shock travels downstream, there is only a small amount of separation present, resulting in a thin wake with comparatively low fluctuations that are caused by corresponding smaller turbulent vortices. The impact of the wake of the front wing causes a strong variation in the rear wing loading. An oscillation with a comparatively low frequency can be distinguished from high-frequent fluctuations. The low-frequent oscillation is caused by the variation in the downwash behind the front wing as its lift changes during the buffet cycle. The high-frequent fluctuations are due to the impingement of the turbulent structures onto the rear wing. Because both size and frequency of those vortices vary significantly within the buffet cycle, the amplitude and frequency of the lift and surface pressure fluctuations also change accordingly.Item Open Access Potentials and limitations of the a priori data-augmentation of turbulence closure models(2026) Mandler, Hannes; Weigand, Bernhard (Prof. Dr.-Ing. habil.)Turbulent flows occur in numerous technical applications. In some applications, turbulence is deliberately exploited to increase their efficiency. In others, the efficiency can be increased by suppressing turbulence to the greatest extent possible. The ability to accurately predict turbulent flows is, therefore, of immense importance. Nowadays, mainly numerical simulation methods are used for this purpose. As solving the Navier-Stokes equations would be far too costly for most applications of practical interest, the Reynolds-averaged Navier-Stokes equations are typically considered instead. However, their solution requires closure models to describe the influence of the turbulence on the mean flow. As a result of structural and parametric deficiencies of existing models, especially the popular eddy viscosity models, the accuracy of the predicted flow fields often no longer meets the current quality requirements. One way to address these deficiencies is to replace the empirical but often constant model coefficients by functions of the local mean flow field. Unlike the classical modeling approach, which seeks to derive such functional dependencies from theory and physical reasoning, leveraging machine learning instead allows for extracting the desired coefficient functions from publicly available DNS data. The models could, therefore, be calibrated for applications that are still simple but exceed the complexity of the traditional calibration cases, e.g., applications governed flow separation and reattachment. This thesis investigates the merits of this approach with respect to the accuracy of the flow field predictions and the possibility of developing more universal closure models. To this end, an a priori augmentation method for existing closure models was developed. A two-stage procedure was proposed to find appropriate functions for the closure coefficients. First, using the DNS data, the extended closure model is inverted to obtain the spatial distribution of the optimal coefficients for a particular training case. These allow the optimal structure of the constitutive equation to be determined in order to prevent any structural deficiencies. By subsequently solving a regression problem, functions represented by neural networks can be inferred that predict those optimal values of the coefficients as a function of the local mean flow state. Based on three examples, namely the flows through a plane channel, a plane channel with periodic hills, and a square duct, the data-augmented development of such model corrections was demonstrated. The errors in the prediction of the velocity field for the respective training cases could be reduced by up to 65%. The accuracy achieved with this method is typically unmatched even for significantly more complex existing closure models. In addition, it was proven that the extended models provide at least equivalent, but often more accurate predictions than the baseline model for a wide range of Reynolds numbers. The same applies to applications that differ geometrically, but not phenomenologically from the training case. However, if the test case was characterized by different flow phenomena than the training case, a sometimes considerable decrease in the predictive accuracy compared to the baseline model was observed. The obvious strategy of dealing with this loss of universality, i.e., deriving the coefficient functions from a more diverse training data set, proved to be ineffective. This is considered to be due to the complexity of the structure of the coefficient functions, which is limited for stability reasons and, hence, usually not sufficient to actually reflect the diversity of the training data. The method developed in this work for the data-driven augmentation of existing closure models is representative of a number of similar approaches that seek to improve flow field predictions via a more accurate description of the Reynolds stress tensor. In summary, such methods are suitable for developing highly specialized models that achieve the desired accuracy gains for a class of not too complex and phenomenologically similar flows. These two limitations could probably be remedied by CFD-integrated training and well-designed combinations of many such expert models.