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 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 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.Item Open Access Experiments meet simulations : understanding skeletal muscle mechanics to address clinical problems(2024) Ateş, Filiz; Röhrle, OliverThis article aims to present some novel experimental approaches and computational methods providing detailed insights into the mechanical behavior of skeletal muscles relevant to clinical problems associated with managing and treating musculoskeletal diseases. The mechanical characterization of skeletal muscles in vivo is crucial for better understanding of, prevention of, or intervention in movement alterations due to exercise, aging, or pathologies related to neuromuscular diseases. To achieve this, we suggest an intraoperative experimental method including direct measurements of human muscle forces supported by computational methodologies. A set of intraoperative experiments indicated the major role of extracellular matrix (ECM) in spastic cerebral palsy. The force data linked to joint function are invaluable and irreplaceable for evaluating individual muscles however, they are not feasible in many situations. Three‐dimensional, continuum‐mechanical models provide a way to predict the exerted muscle forces. To obtain, however, realistic predictions, it is important to investigate the muscle not by itself, but embedded within the respective musculoskeletal system, for example, a 6‐muscle upper arm model, and the ability to obtain non‐invasively, or at least, minimally invasively material parameters for continuum‐mechanical skeletal muscle models, for example, by presently proposed homogenization methodologies. Botulinum toxin administration as a treatment option for spasticity is exemplified by combining experiments with modeling to find out the mechanical outcomes of altered ECM and the controversial effects of the toxin. The potentials and limitations of both experimental and modeling approaches and how they need each other are discussed.Item Open Access Nicht-intrusive Messung der Wärmestromdichte auf transpirationsgekühlte Oberflächen(2024) Hufgard, Fabian; Fasoulas, Stefanos (Prof. Dr.-Ing.)In dieser Arbeit ist die Entwicklung von drei nicht-intrusiven Methoden zur Bestimmung der transienten Wärmestromdichte in eine transpirationsgekühlte Oberfläche beschrieben. Transpirationskühlung ist ein aktives Kühlverfahren, das aufgrund seiner hohen Effektivität für den Einsatz in Luft- und Raumfahrtanwendungen untersucht wird. Bei Transpirationskühlung besteht das Hitzeschild aus einem porösen Material, durch das ein Kühlgas nach außen gedrückt wird. Das bewirkt sowohl die aktive Kühlung der Wand durch Advektion als auch die Reduktion des konvektiven Wärmeeintrags in die Oberfläche durch das Kühlen der Strömungsgrenzschicht. Für die Auslegung solcher Hitzeschilde ist die Oberflächenwärmestromdichte eine wichtige Variable, weil sie die Wandtemperatur diktiert. Die in dieser Arbeit entwickelten Methoden zur Wärmestromdichtebestimmung basieren auf der transienten und nicht-intrusiven Messung des Drucks im Plenum, d.h. dem bedruckten Bereich zwischen dem Durchflussregler und der porösen Wand. Dazu wird das Systemverhalten infolge der Oberflächenwärmestromdichte durch eine Modellgleichung mathematisch abgebildet. Die Modellparameter werden durch einen zerstörungsfreien Kalibrieransatz identifiziert. Die Eingangsgrößen der Modellgleichung sowie deren Nutzung zur Bestimmung der Oberflächenwärmestromdichte unterscheidet sich zwischen den Methoden. Bei der Pressure-based Non-Integer System Identification (NISIp) Methode korreliert die Wärmestromdichte direkt mit dem Plenumsdruck. Die kalibrierte Modellgleichung ermöglicht die Berechnung der Druckimpulsantwort. Mit dieser wird die Wärmestromdichte unter Anwendung inverser Methoden aus der transienten Druckmessung bestimmt. Dazu ist der Emissionsgrad der einzige erforderliche Materialparameter. Durch experimentelle und numerische Analysen der NISIp-Methode wird gezeigt, dass für die Beschreibung des zugrundeliegenden thermodynamischen Prozesses das Plenum als endliches Volumen mitberücksichtigt werden muss. Dadurch kann sich der Massenstrom durch die poröse Wand signifikant ändern, auch wenn der Massenstrom am Durchflussregler konstant ist. Es wird gezeigt, dass die Reduktion der Parameter Plenumsvolumen, Länge sowie spezifische Wärmekapazität der porösen Wand zu einem schnelleren Ansprechen des Plenumsdrucks auf die Oberflächenwärmestromdichte und damit zu einem kleineren Messfehler führt. Für die Parameter Massenstrom, Umgebungsdruck, Querschnittsfläche und Permeabilität der porösen Wand gilt das Gegenteil. Die Anwendung eines NISIp-Sensors im Plasmawindkanal PWK4 ergab für Wärmestromdichten bis ca. 400 kW/m2 eine Messunsicherheit von nur 17%. Der Non-Integer System Identification with Fluid Temperature (NISITf) Ansatz erweitert den Einsatzbereich zu Szenarien mit stark veränderlichem Umgebungsdruck. Dafür wird der Plenumsdruck mit der Darcy-Forchheimer-Gleichung in die mittlere Fluidtemperatur in der porösen Wand umgerechnet. Diese dient als Eingangsgröße in die NISITf-Modellgleichung zur Korrelation mit der Oberflächenwärmestromdichte. Die Bestimmung der Wärmestromdichte aus der kalibrierten Modellgleichung erfolgt analog zur NISIp-Methode. Mit einem NISITf-Sensor wurden im Plasmawindkanal PWK1 Wärmestromdichten von bis 13,9MW/m2 gemessen. Mit der Cooling Adjustment for Transpiration Systems (CATS) Technologie wird die Oberflächenwärmestromdichte in Echtzeit bestimmt und entsprechend die Kühlintensität der Transpirationskühlung angepasst. Dazu werden ausschließlich nicht-intrusive Messgrößen erfordert. Die Wärmestromdichte wird direkt aus einer kalibrierten Modellgleichung bestimmt. Mit der Anwendung eines CATS-Regelsystems im PWK4 wurde erstmals die Funktionalität eines Reglers zur automatischen Anpassung der Kühlintensität der Transpirationskühlung auf die aktuell wirkende Oberflächenwärmestromdichte nachgewiesen. Darüber hinaus wurde ein CATS-System erfolgreich auf der HIFLIER1-Höhenforschungsrakete getestet. Das HIFLIER1-CATS-System bestimmte dieWärmestromdichte während des Hyperschallflugs und passte entsprechend den Kühlgasmassenstrom wie vorgesehen an.