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 Experimental investigation of low-frequency sound and infrasound induced by onshore wind turbines(2024) Blumendeller, Esther; Cheng, Po Wen (Prof. Dr.)Climate change has a global impact and is increasingly affecting our environment. This is driving the continuous expansion of renewable energies, with wind energy playing a major role. As wind energy becomes more widespread, an increasing number of people will live near wind turbines in complex terrain. In such scenarios, wind turbines are often positioned at elevated locations, while residents live in valleys. In complex terrain, such as a steep escarpment, local turbulence, wind speed, and direction are strongly influenced by topography, contributing to the complexity of sound propagation or impacts the background noise situation in valleys, for example, due to shielding effects. The operation of wind turbines is associated with both visual and sound-related impact, with sound being generated at various frequencies. There is a growing interest in low-frequency sound and infrasound, characterized by long wavelengths that propagate over considerable distances without significant attenuation. This is in contrast to higher-frequency sound, and might increase the impact of wind turbine sound at residential areas located several hundred meters or a few kilometers away from the wind farm. In the context of complex terrain, this work investigates wind turbines in complex terrain as sources of low-frequency sound and infrasound. The investigations on characterization of sound generation and propagation are based on measurements in the vicinity of two wind farms. Measurements were conducted within four measurement campaigns at two wind farms located close to an escarpment at the Swabian Alb in Southern Germany over a period of about nine month. Acoustic data was obtained in the proximity of the wind turbines and at residential buildings in 1–1.7km distance to the wind farms in municipalities located within a valley. Besides acoustic measurements including the infrasonic frequency range, a comprehensive data set with ground motion data, wind turbine operating data, meteorological data and data from a noise reporting app supports the investigation. Two aspects require analysis: Firstly, the aspect of generation and propagation of wind turbine low-frequency sound and infrasound in complex terrain, and secondly, the relation with annoyance. Results show that sounds within the infrasonic range assigned to the blade passage at the tower are transmitted through the air over distances of 1 km. Low-frequency sounds were found to be amplitude-modulated and were investigated as amplitude modulation. Infrasound and amplitude modulation occurrences were more likely during morning, evening and night hours and during atmospheric conditions with positive lapse rate, vertical wind shear and low turbulence intensity. The occurrence of both infrasound and amplitude modulation was typically observed during rated rotational speed but below-rated power. To allow predictions, a standard prediction method was extended to include the lowfrequency sound and infrasound range and adapted to the measurement data in order to apply it to complex terrain. The sound level difference of the measured data aligns well with the predictions within the frequency range of 8 Hz and 250 Hz. Investigations regarding outdoor-to-indoor sound reductions showed influences from structural resonances and room modes, which depend on the characteristics of the building and the specific room under investigation. Combining acoustic measurements with annoyance reports showed that rated wind turbine operation appears to be a contributing factor in annoyance ratings obtained through a noise reporting app, ranging from “somewhat” to “very” levels. Furthermore, the analysis indicates that varying levels of annoyance at a distance of 1km from the wind farm, both outside and inside buildings, do not correspond to significant differences in the averaged and A-weighted sound pressure levels. Overall, this work contributes to a better understanding of the low-frequency sound and infrasound generated from wind turbines and provides insight into the sound characteristics of measured wind turbine sound at residential locations in complex terrains.Item Open Access Smart ground support equipment : the design and demonstration of robotic ground support equipment for small spacecraft integration and verification(2024) Kottmeier, Sebastian; Wittje, Philipp; Klinkner, Sabine; Essmann, Olaf; Suhr, Birgit; Kirchler, Jan-Luca; Ho, Tra-MiIn order to reduce the costs of integration and verification processes and to optimize the assembly, integration and verification (AIV) flow in the prototype development of small- and medium-sized spacecrafts, an industrial six-axis robot was used as a universal mechanical ground support equipment instead of a tailored prototype specific ground support equipment (GSE). In particular, a robotic platform offers the possibility of embedding verification steps such as mass property determination into the integration process while offering a wider range of ergonomic adaption due to the enhanced number of degrees of freedom compared to a classical static Mechanical GSE (MGSE). This reduces development costs for projects and enhances the flexibility and ergonomics of primarily mechanical AIV operations. In this paper, the robotic MGSE system is described, the operational prospects for in-line verification are elaborated and an example is given showing the possibilities and challenges of its operational use as well as its in-line mass determination capabilities. For this purpose, a method has been developed that allows for the precise measurement of the spacecraft mass using the robot’s existing technology without the need for additional hardware. Subsequent work will extend this to determine the center of gravity and the moments of inertia of the payload on the robotic MGSE.Item Open Access Analyzing and characterizing spaceborne observation of water storage variation : past, present, future(2024) Saemian, Peyman; Sneeuw, Nico (Prof. Dr.-Ing.)Water storage is an indispensable constituent of the intricate water cycle, as it governs the availability and distribution of this precious resource. Any alteration in the water storage can trigger a cascade of consequences, affecting not only our agricultural practices but also the well-being of various ecosystems and the occurrence of natural hazards. Therefore, it is essential to monitor and manage the water storage levels prudently to ensure a sustainable future for our planet. Despite significant advancements in ground-based measurements and modeling techniques, accurately measuring water storage variation remained a major challenge for a long time. Since 2002, the Gravity Recovery and Climate Experiment (GRACE) and its successor GRACE Follow-On (GRACE-FO) satellites have revolutionized our understanding of the Earth's water cycle. By detecting variations in the Earth's gravity field caused by changes in water distribution, these satellites can precisely measure changes in total water storage (TWS) across the entire globe, providing a truly comprehensive view of the world's water resources. This information has proved invaluable for understanding how water resources are changing over time, and for developing strategies to manage these resources sustainably. However, GRACE and GRACE-FO are subject to various challenges that must be addressed in order to enhance the efficacy of our exploitation of GRACE observations for scientific and practical purposes. This thesis aims to address some of the challenges faced by GRACE and GRACE-FO. Since the inception of the GRACE mission, scholars have commonly extracted mass changes from observations by approximating the Earth's gravity field utilizing mathematical functions termed spherical harmonics. Various institutions have already processed GRACE(-FO) data, known as level-2 data in the GRACE community, considering the constraints, approaches, and models that have been utilized. However, this processed data necessitates post-processing to be used for several applications, such as hydrology and climate research. In this thesis, we evaluate various methods of processing GRACE(-FO) level-2 data and assess the spatio-temporal effect of the post-processing steps. Furthermore, we aim to compare the consistency between GRACE and its successor mission, GRACE-FO, in terms of data quality and measurement accuracy. By analyzing and comparing the data from these two missions, we can identify any potential discrepancies or differences and establish the level of confidence in the accuracy and reliability of the GRACE-FO measurements. Finally, we will compare the processed level-3 products with the level-3 products that are presently accessible online. The relatively short record of the GRACE measurements, compared to other satellite missions and observational records, can limit some studies that require long-term data. This short record makes it challenging to separate long-term signals from short-term variability and validate the data with ground-based measurements or other satellite missions. To address this limitation, this thesis expands the temporal coverage of GRACE(-FO) observations using global hydrological, atmospheric, and reanalysis models. First, we assess these models in estimating the TWS variation at a global scale. We compare the performance of various methods including data-driven and machine learning approaches in incorporating models and reconstruct GRACE TWS change. The results are also validated against Satellite Laser Ranging (SLR) observations over the pre-GRACE period. This thesis develops a hindcasted GRACE, which provides a better understanding of the changes in the Earth's water storage on a longer time scale. The GRACE satellite mission detects changes in the overall water storage in a specific region but cannot distinguish between the different compartments of TWS, such as surface water, groundwater, and soil moisture. Understanding these individual components is crucial for managing water resources and addressing the effects of droughts and floods. This study aims to integrate various data sources to improve our understanding of water storage variations at the continental to basin scale, including water fluxes, lake water level, and lake storage change data. Additionally, the study demonstrates the importance of combining GRACE(-FO) observations with other measurements, such as piezometric wells and rain-gauges, to understand the water scarcity predicament in Iran and other regions facing similar challenges. The GRACE satellite mission provides valuable insights into the Earth's system. However, the GRACE product has a level of uncertainty due to several error sources. While the mission has taken measures to minimize these uncertainties, researchers need to account for them when analyzing the data and communicate them when reporting findings. This thesis proposes a probabilistic approach to incorporate the Total Water Storage Anomaly (TWSA) data from GRACE(-FO). By accounting for the uncertainty in the TWSA data, this approach can provide a more comprehensive understanding of drought conditions, which is essential for decision makers managing water resources and responding to drought events.Item Open Access Science planning for the DESTINY+ Dust Analyzer : leveraging the potential of a space exploration instrument(2024) Sommer, Maximilian; Srama, Ralf (Apl. Prof. Dr.-Ing.)The DESTINY+ Dust Analyzer (DDA) is a highly sophisticated planetary science instrument to provide cutting-edge in-situ characterization of individual cosmic dust grains, with respect to their composition, as well as their physical and dynamical properties. As such, it constitutes a critical component of the upcoming JAXA mission DESTINY+, which is scheduled to launch in 2025. After a three-year cruise phase, the spacecraft will perform a flyby of the target asteroid 3200 Phaethon, with the goal of observing the enigmatic Geminids parent body with two camera instruments, and sampling particles released from its surface with the DDA. Until that flyby, DESTINY+ will execute a highly diverse, ion-engine-driven flight plan that allows DDA to extensively study the dust environments of the Earth, Moon, and interplanetary space - a breadth of science opportunities that is unique to this mission and instrument. This dissertation provides a comprehensive study of the dust types and phenomena possibly encountered by DDA during its journey to Phaethon and applies the principles and methods of science planning to prepare for the operational phase of the mission. The work synthesizes technical considerations and scientific analyses of relevant cosmic dust populations, aiming to optimize DDA’s scientific potential. Detailed examinations of spacecraft and instrument factors, such as the dynamic spacecraft attitude during the near-Earth phase or the instrument’s two-axis pointing mechanism, lay the groundwork for the scientific planning. The thorough analysis of known (and lesser known) dust populations in the inner solar system and of previous relevant measurements by other dust instruments form the core of the study. Finally, the findings are consolidated into a draft science activity plan for the entire mission, as well as exemplary pointing timelines to be executed by the instrument for optimal scientific return. The latter is accomplished with the DOPE tool, which aids in intuitive and efficient planning of DDA observations, having been developed in the scope of this project. The presented work builds the foundation for the scientific operations of DDA, setting it up for a successful and scientifically impactful mission. The findings of this study also provide a valuable perspective for other ventures of in-situ dust astronomy to the inner solar system and contribute to the field of cosmic dust as a whole.Item Open Access Coupled simulation of turbomachinery flutter and forced response blade vibrations using nonlinear frequency domain methods(2024) Berthold, Christian; Krack, Malte (Prof. Dr.)The central topic of this work is the simulation of nonlinear blade vibrations in turbomachinery. Two main causes of blade vibrations are flutter, denoting self-excited vibrations of the blades, and forced response due to e.g. aerodynamic rotor-stator interactions. During operation, the vibration levels of the blades must not exceed critical values in order to prevent high cycle fatigue or immediate failure of the engine. This motivates the development of numerical methods for the prediction of blade vibrations in order to evaluate the robustness of mechanical designs against flutter and forced response. In this work, the focus is laid on bladed turbine disks with interlocked shrouds, which represent a challenging task for numerical simulation. While interlocked shrouds introduce friction (and thus damping) into the structural system, possibly reducing the level of vibrations, they can alter the vibration shape and vibration frequency with increasing amplitude. This in turn makes the aerodynamic damping of the blade motion a nonlinear function of the vibration amplitude. Thus, the mechanical system is bidirectionally coupled, since the two physical domains (fluid and solid) interact with each other. Current numerical analysis tools like the energy method or the use of influence coefficients have deficits in resolving these nonlinear fluid-structure interactions. This motivates the development of improved numerical methods for the simulation of nonlinear blade vibrations. In this work, a refined energy method and a bidirectionally coupled fluid-structure solver are suggested for this purpose. For both approaches, the Harmonic Balance method is employed, which approximates a periodic motion of the blades very efficiently in the frequency domain. The novel methods are applied to numerical test cases of low pressure turbines to demonstrate the methods' capabilities and to investigate the potential influence of nonlinear contact forces on the blade vibrations. Here, the refined energy method allows to gain valuable insight on the impact of shroud contact interfaces on the aerodynamic damping. It is found, that the nonlinear structural contact forces can give rise to stable limit cycle oscillations as well as stability limits, which mark the amplitude level where blade vibrations become unstable if it is exceeded. Furthermore, the coupled solver reveals the complex interaction between a vibrating blade with shroud contact interfaces and a shock motion. For the analysis of forced response, the coupled solver is embedded into a path continuation procedure with a sequential and a parallel variant. The coupled method not only demonstrates the influence of nonlinear friction on the forced response but also reveals, that the superposition assumption regarding the aerodynamic wake excitation and the blade vibration induced aerodynamic forces can lead to inaccurate results.Item Open Access Untersuchungen zum geometrischen Verhalten von Holz mittels optischer Sensoren(2024) Schmitt, Annette; Schwieger, Volker (Prof. Dr.-Ing. habil. Dr. h.c.)In Deutschland geht rund ein Drittel des jährlichen CO2-Ausstoßes auf dem Bausektor zurück. Davon ist zwar nur ein Viertel dem Bau von Hochbauten zu zuschreiben. Gerade deshalb müssen im Hochbau Innovationen und alternative Materialien und Bauweisen entwickelt werden, damit Deutschland seine Klimaziele erreicht. Neben dem hohen CO2-Ausstoß hat die Betonbauweise den Nachteil, dass die Rohstoffe von Beton wie zum Beispiel Kies, Sand oder Kalkstein, endliche Ressourcen sind. Eine Alternative zur Betonbauweise ist der jahrtausendealte Holzbau, der in letzten Jahren eine Renaissance erlebt hat. Durch einen nachhaltigen Holzanbau und eine nachhaltige, ressourcenschonende Bauweise kann Holzbau zu einer echten Alternative werden. Jedoch ist Holz ein anisotroper, inhomogener und poröser Werkstoff, dessen Eigenschaften stark richtungsabhängig und abhängig von Umwelteinflüssen sind. Dies macht die Bemessung von Holzbauwerken kompliziert und unattraktiv. Speziell bei Flächentragwerken wie Schalen, die in der Regel sehr filigran sind, haben Umwelteinflüsse wie Feuchte und Temperatur einen Einfluss auf die Standfestigkeit. Daher ist eine regelmäßige Überwachung der Struktur notwendig. Im Bauingenieurwesen werden für solche Aufgaben häufig Dehnmessstreifen eingesetzt. Diese liefern lediglich sehr lokal geltende Messwerte, von denen nur mittels mechanischer Modelle auf das gesamte Objekt geschlossen werden kann. Daher bietet es sich an, für Flächentragwerke optische Sensoren wie zum Beispiel Laserscanner einzusetzen. Im Rahmen dieser Arbeit werden verschiedene Holzobjekte, wie zum Beispiel Platten, Vierkanthölzer und Schalen, unter verschiedenen Umwelteinflüssen, wie Feuchte und Temperatur, untersucht. Ziel ist es dabei, die auftretenden Formänderungen durch Umwelteinflüsse mittels Laserscanner und Lasertracker zu detektieren. Unter anderem werden mehrere Holzplatten in Klimakammern unter definierten Bedingungen untersucht. So wird in einem ersten Versuch der Einfluss von Temperaturänderungen auf eine Holzplatte untersucht. Es zeigt sich, dass dieser zwar sehr gering ist, aber mittels Lasertracker zumindest in radialer Faserrichtung signifikant aufdeckbar ist. In einem weiteren Versuch werden Holzplatten zunächst in einer Klimakammer mit Feuchteregelung bei 95 % Luftfeuchte gelagert und anschließend bei 12 % Luftfeuchte getrocknet. Zwischenzeitlich werden die Platten mittels Lasertracker und Laserscanner vermessen. Hier lassen sich die Verformungen mit dem Lasertracker in allen drei Faserrichtungen signifikant detektieren. Die Messungen mit dem Laserscanner ermöglichen aufgrund des aus der Aufnahmekonfiguration folgenden Registrierungsfehlers keine Aufdeckung der Verformungen, da der Schwellwert für signifikante Verformungen zu hoch ist. In einem weiteren Laborversuch werden die Verformungen durch die Umwelteinflüsse auf belastete Vierkanthölzer untersucht. Auch hierfür kann gezeigt werden, dass der Lasertracker genutzt werden kann. Verifiziert wurden die Ergebnisse hierbei durch eine Finite-Elemente-Simulation, der Materialparameter aus der Literatur zugrunde liegen. Neben den Laborversuchen werden auch Untersuchungen an einem adaptiven Schalentragwerk aus Holz mit dem Laserscanner durchgeführt. Für die Auswertung der Laserscannerdaten wird eine Methode zur Detektion von signifikanten Formänderungen auf Basis von synthetischen Punktfehlern und der Deformationsanalyse implementiert. Alle Ergebnisse der Messungen sind plausibel und mit Literaturangaben vergleichbar, dennoch ist Holz als natürlich wachsender Rohstoff sehr anspruchsvoll und individuell.Item Open Access Electrical conductivity of monolithic and powdered carbon aerogels and their composites(2024) Kröner, Jessica; Platzer, Dominik; Milow, Barbara; Schwan, MarinaThe electrical conductivity of powdered carbon aerogels is one of the key factors required for electro-chemical applications. This study investigates the correlation between the structural, physical, mechanical and electrical properties of pure and activated carbon aerogels, as well as aerogel-composites. The thermal activation with carbon dioxide led to higher electrical conductivity and a decrease in density and particle size. Furthermore, the influence of applied force, compressibility of aerogels and aerogel composites on electrical conductivity was studied. A number of different carbonaceous powdered additives with various morphologies, from almost spherical to fiber- and flake-like shaped, were investigated. For two composites, theoretical values for conductivity were calculated showing the great contribution of particle shape to the conductivity. The results show that the conductive behavior of composites during compression is based on both the mechanical particle arrangement mechanism and increasing particle contact area.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 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 Modeling freezing and BioGeoChemical processes in Antarctic sea ice(2024) Pathak, Raghav; Seyedpour, Seyed Morteza; Kutschan, Bernd; Thom, Andrea; Thoms, Silke; Ricken, TimThe Antarctic sea ice, which undergoes annual freezing and melting, plays a significant role in the global climate cycle. Since satellite observations in the Antarctic region began, 2023 saw a historically unprecedented decrease in the extent of sea ice. Further ocean warming and future environmental conditions in the Southern Ocean will influence the extent and amount of ice in the Marginal Ice Zones (MIZ), the BioGeoChemical (BGC) cycles, and their interconnected relationships. The so‐called pancake floes are a composition of a porous sea ice matrix with interstitial brine, nutrients, and biological communities inside the pores. The ice formation and salinity are both dependent on the ambient temperature. To realistically model these multiphasic and multicomponent coupled processes, the extended Theory of Porous Media (eTPM) is used to develop Partial Differential Equations (PDEs) based high‐fidelity models capable of simulating the different seasonal variations in the region. All critical variables like salinity, ice volume fraction, and temperature, among others, are considered and have their equations of state. The phase transition phenomenon is approached through a micro‐macro linking scheme. In this paper, a phase‐field solidification model [4] coupled with salinity is used to model the microscale freezing processes and up‐scaled to the macroscale eTPM model. The evolution equations for the phase field model are derived following Landau‐Ginzburg order parameter gradient dynamics and mass conservation of salt allowing to model the salt trapped inside the pores. A BGC flux model for sea ice is set up to simulate the algal species present in the sea ice matrix. Ordinary differential equations (ODE) are employed to represent the diverse environmental factors involved in the growth and loss of distinct BGC components. Processes like photosynthesis are dependent on temperature and salinity, which are derived through an ODE‐PDE coupling with the eTPM model. Academic simulations and results are presented as validation for the mathematical model. These high‐fidelity models eventually lead to their incorporation into large‐scale global climate models.