06 Fakultät Luft- und Raumfahrttechnik und Geodäsie
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Item Open Access Towards improved targetless registration and deformation analysis of TLS point clouds using patch-based segmentation(2023) Yang, Yihui; Schwieger, Volker (Prof. Dr.-Ing. habil. Dr. h.c.)The geometric changes in the real world can be captured by measuring and comparing the 3D coordinates of object surfaces. Traditional point-wise measurements with low spatial resolution may fail to detect inhomogeneous, anisotropic and unexpected deformations, and thus cannot reveal complex deformation processes. 3D point clouds generated from laser scanning or photogrammetric techniques have opened up opportunities for an area-wise acquisition of spatial information. In particular, terrestrial laser scanning (TLS) exhibits rapid development and wide application in areal geodetic monitoring owing to the high resolution and high quality of acquired point cloud data. However, several issues in the process chain of TLS-based deformation monitoring are still not solved satisfactorily. This thesis mainly focuses on the targetless registration and deformation analysis of TLS point clouds, aiming to develop novel data-driven methods to tackle the current challenges. For most deformation processes of natural scenes, in some local areas no shape deformations occur (i.e., these areas are rigid), and even the deformation directions show a certain level of consistency when these areas are small enough. Further point cloud processing, like stability and deformation analyses, could benefit from the assumptions of local rigidity and consistency of deformed point clouds. In this thesis, thereby, three typical types of locally rigid patches - small planar patches, geometric primitives, and quasi-rigid areas - can be generated from 3D point clouds by specific segmentation techniques. These patches, on the one hand, can preserve the boundaries between rigid and non-rigid areas and thus enable spatial separation with respect to surface stability. On the other hand, local geometric information and empirical stochastic models could be readily determined by the points in each patch. Based on these segmented rigid patches, targetless registration and deformation analysis of deformed TLS point clouds can be improved regarding accuracy and spatial resolution. Specifically, small planar patches like supervoxels are utilized to distinguish the stable and unstable areas in an iterative registration process, thus ensuring only relatively stable points are involved in estimating transformation parameters. The experimental results show that the proposed targetless registration method has significantly improved the registration accuracy. These small planar patches are also exploited to develop a novel variant of the multiscale model-to-model cloud comparison (M3C2) algorithm, which constructs prisms extending from planar patches instead of the cylinders in standard M3C2. This new method separates actual surface variations and measurement uncertainties, thus yielding lower-uncertainty and higher-resolution deformations. A coarse-to-fine segmentation framework is used to extract multiple geometric primitives from point clouds, and rigorous parameter estimations are performed individually to derive high-precision parametric deformations. Besides, a generalized local registration-based pipeline is proposed to derive dense displacement vectors based on segmented quasi-rigid areas that are corresponded by areal geometric feature descriptors. All proposed methods are successfully verified and evaluated by simulated and/or real point cloud data. The choice of proposed deformation analysis methods for specific scenarios or applications is also provided in this thesis.Item Open Access Ein Beitrag zur Stützung eines Software GNSS Empfängers mit MEMS-Inertialsensoren(2016) Gäb, Michael; Kleusberg, Alfred (Prof. Dr.-Ing.)Die genaue Bestimmung von Position und Geschwindigkeit mit einem globalen Navigationssatellitensystem (engl. Global Navigation Satellite System) (GNSS) in Echtzeit bildet eine essentielle Grundlage für viele Anwendungen in der Navigation. Bei mobilen Navigationsanwendungen finden häufig GNSS-Messungen unter ungünstigen Beobachtungsbedingungen statt, so dass Fehler in den Ergebnissen auftreten können. In diesem Fall ist der GNSS-Empfänger in Bewegung, so dass die Empfangsumgebung sich ständig ändert. So können Objekte, wie z.B. Gebäude, Bäume, Tunnel usw. zu Reflektionen, Dämpfung bzw. Abschattung der GNSS-Signale führen. Eine hohe zusätzliche Dynamik bzgl. der beobachteten Dopplerfrequenzverschiebung erfährt das empfangene GNSS-Signal durch die Bewegung des GNSS-Empfängers. Das beeinflusst die Signalnachführung (Tracking) und verursacht Fehler bei der Positions- und Geschwindigkeitsbestimmung oder eine Bestimmung ist sogar unmöglich. Eine Verbesserung der Positions- und Geschwindigkeitsbestimmung wird durch die gleichzeitige Messung mit einem GNSS-Empfänger und einem inertialen Navigationssystem (engl. Inertial Navigation System) (INS) ermöglicht. Kostengünstige INS beinhalten heute Mikro-Elektro-Mechanische Systeme (engl. Micro Electro Mechanical Systems) (MEMS), die als MEMS-Inertialsensoren bezeichnet werden. Die gemeinsame Nutzung der Messdaten von GNSS und INS wird als GNSS/INS-Integration bezeichnet. Diese Arbeit befasst sich mit der Tiefen GNSS/INS-Integration, so dass mit der Information eines INSs in die Tracking Loop des GNSS-Empfängers eingegriffen wird, um Verbesserungen beim Tracking des Signals und der daraus bestimmten GNSS-Beobachtungen zu erzielen. Dieser Eingriff wird auch als Stützung (engl. aiding) bezeichnet. Die Stützung erfolgt über die Regelgrößen (Dopplerfrequenz und Codephase) in der Tracking Loop für den jeweiligen Kanal des GNSS-Empfängers. Dazu werden die Regelgrößen zunächst prädiziert, bevor diese beim Tracking des empfangenen GNSS-Signals berücksichtigt werden können. Für die Prädiktion müssen die Position und Geschwindigkeit des Satelliten und des Empfängers vorliegen. Außerdem müssen die Uhrenfehlerrate des Satelliten und des Empfängers bekannt sein. Aus diesen Größen kann die Dopplerfrequenz und daraus die Rate der Codephase berechnet werden. Die zeitliche Integration der Codephasenrate ergibt die aktuelle Codephase. Aus den Ephemeriden des GNSS-Satelliten kann die Position, die Geschwindigkeit und die Uhrenfehlerrate für einen zeitnahen beliebigen Zeitpunkt berechnet werden. Die Uhrenfehlerrate des Empfängers wird hierbei mittels einer Extrapolation vorausbestimmt. Mit den MEMS-Inertialsensoren kann die Position und Geschwindigkeit des Empfängers fortgeführt werden. Diese Fortführung erfolgt über eine Lose GNSS/INS-Integration mittels einer Strapdown-Rechnung und einem Kalman-Filter für 15 Fehlerzustände. Als Stützwerte für den Kalman-Filter dienen hier die Position und Geschwindigkeit des SGEs. Die Stützung sollte bei einem Signalabriss oder für die Stabilisierung des Trackings eingeschaltet werden. Die Stützungsmethode wird mit einem Software GNSS-Empfänger (SGE) und einer Inertiale Messeinheit (engl. inertial measurement unit) (IMU) aus MEMS-Inertialsensoren (MEMS-IMU) in der Landfahrzeugnavigation getestet und analysiert. Der SGE ist für die Signale des globalen Positionierungssystem (engl. Global Positioning System) (GPS) mit dem C/A-Code auf der L1-Frequenz entwickelt und bestimmt die Position und Geschwindigkeit mit einer Messrate von 1 kHz. Die MEMS-IMU beeinhaltet 6 Freiheitsgrade mit jeweils einem 3-achsigen MEMS-Beschleunigungs- und MEMSDrehratensensor. Die Messrate des MEMS-Beschleunigungssensors beträgt 1 kHz und die Messrate des MEMS-Drehratensensors beträgt 800 Hz. Mit diesem Messsystem ist es möglich, die Prädiktion der Regelgrößen für jede Millisekunde durchzuführen, so dass diese bei jedem Tracking-Durchlauf mit dem C/A-Code vorliegen. Aufgrund der hohen Messraten können nur wenige Minuten Messdaten erfasst werden und die Auswertung erfolgt in der Nachbearbeitung (engl. post-processing). Die Stützungsmethode wird durch Fahrten mit einem Messfahrzeug getestet. Dazu werden Messfahrten mit verschiedenen Fahrmanöver ausgeführt, um im empfangenen GPS-Signal unterschiedliche Raten in der Dopplerfrequenz zu erzeugen. Eine Fahrt unter Bäumen ermöglicht den Einfluss des zeitlichen Verlaufs im Signal-Rauschverhältnis (engl. signal-to-noise ratio) (S/N) des empfangenen GPS-Signals auf die Stützungsmethode zu untersuchen. Bei dieser Messfahrt treten auch immer wieder kurzzeitige Signalabrisse auf. Die in der vorliegenden Arbeit dokumentierten Messfahrten und Ergebnisse zeigen, dass die Stützung für einen SGE erfolgreich in der Landfahrzeugnavigation durchgeführt werden kann. Die prädizierten Regelgrößen werden für die verschiedenen Messfahrten zuverlässig berechnet und das Tracking kann damit stabilisiert und sogar bei einem Signalabriss vorgesteuert werden. Außerdem können Ausreißer direkt in den Beobachtungen minimiert werden, so dass Verbesserungen in der Positions- und Geschwindigkeitsbestimmung des SGEs erzielt werden können.Item Open Access Lebensdauerabschätzung von metallischen Strukturen mittels der Diskrete-Elemente-Methode im gekoppelten thermo-mechanischen Feld(2012) Hahn, Manfred; Kröplin, Bernd (Prof. Dr.-Ing. habil.)Aufgrund der hohen Streubreite der physikalischen Eigenschaften von metallischen Werkstoffen kann man deren Verhalten nicht zuverlässig voraussagen. Dies stellt insbesondere bei der Lebensdauervorhersage von industriell gefertigten Konstruktionen ein Problem dar. Der atomare Aufbau eines metallischen Werkstoffs besteht in der Regel aus einem Hauptelement und einem oder mehreren Nebenkomponenten was dazu führt, dass beim Erstarren einer Metallschmelze auf der Atomskala die Anreihung der Atome nicht strukturiert erfolgt, sondern mit zufällig verteilten Fehlern. Betrachtet man den Werkstoff auf einer göberen Skala so fällt auf, dass metallische Schmelzen an vielen Stellen zu erstarren beginnen und dass die Erstarrungskeime und die Grenzen der Erstarrungsfronten stochastisch verteilt sind. Die metallischen Werkstoffe sind also bei genauerer Betrachtung kein Kontinuum sondern ein Diskontinuum in dem die physikalischen Eigenschaften global betrachtet zu den in den Laborexperimenten beobachteten Werten verschmieren. Ziel der vorliegenden Arbeit ist es, den Werkstoff als ein Diskontinuum darzustellen, um die stochastisch verteilten physikalischen Eigenschaften auf einer kleinen Skala zu erfassen. Im Weiteren sollen auf einer größeren Skala die physikalischen Eigenschaften zu den global beobachteten Werten verschmieren. Dabei soll die in dieser Arbeit vorgestellte numerische Methode der diskreten Elemente im mechanischen Feld ausgebaut und im Folgenden auf andere physikalische Felder übertragen werden. In metallischen Werkstoffen gehen bei zyklischen Belastungen im Inneren des Werkstoffs mikroplastische Verformungen vonstatten, welche mit zunehmender Zyklenzahl den Werkstoff an diskreten Stellen mit Mikroschäden sättigen. Dabei schreitet die diskrete Sättigung solange voran, bis der diskrete Ort übersättigt bzw.~geschwächt ist und im Folgenden versagt. Die mikroplastischen Verformungen sind, wie auch die anderen physikalischen Parameter, mit einer statistischen Größe behaftet. Die diskrete Akkumulation der statistisch verteilten mikroplastischen Schädigung soll in das numerische Modell der Diskreten-Elemente-Methode (DEM) mit aufgenommen werden, so dass sich auf numerischem Weg Lebensdauersimulationen durchführen lassen. Ein wesentlicher Teil dieser Arbeit beschäftigt sich mit den mathematischen Beweisen für die Gültigkeit der DEM als numerische Methode, sowohl für das mechanische als auch für das thermische Feld. Die Beweisführung erfolgt über eine vergleichende Betrachtung mit der Finite-Volumen-Methode (FVM), der Finite-Differenzen-Methode (FDM) und der Finite-Elemente-Methode (FEM). Dabei wird aus der FVM die Idee übernommen, dass physikalische Flüsse übertragen werden. Im Weiteren ergibt die Assemblierung von sechs Stäben, welche die physikalische Feldgröße übertragen, zusammen mit dem lokalen physikalischen Gleichgewicht den Finite-Differenzen-Stern der FDM. Zuletzt wird das globale Gleichgewicht mittels der FEM gewonnen. Im Nachlauf der Finite-Elemente-Rechnung lassen sich die Flussgrößen zurückbestimmen. In dieser Arbeit wird gezeigt, wie die Kopplung des mechanischen und thermischen Feldes mittels der DEM vorgenommen werden kann. Dazu wird ausgeführt, wie die beiden Felder zusammen wirken und wie stark deren Kopplung ist. Abschließend wird eine Lebensdauersimulation an einer thermo-mechanisch belasteten virtuellen Probe vorgeführt. Das Ergebnis dieser Arbeit zeigt, dass die DEM eine Methode ist, um partielle Differentialgleichungen zu lösen, sowohl für Einzelfelder, als auch für gekoppelte Felder. Außerdem kann der Werkstoff durch die Methode als ein Diskontinuum betrachtet werden, so dass sich Lebensdauersimulationen mittels eines erweiterten Werkstoffmodells vornehmen lassen.Item Open Access Thermodynamic analysis and numerical modeling of supercritical injection(2015) Banuti, Daniel; Weigand, Bernhard (Prof. Dr.-Ing. habil.)Although liquid propellant rocket engines are operational and have been studied for decades, cryogenic injection at supercritical pressures is still considered essentially not understood. This thesis intends to approach this problem in three steps: by developing a numerical model for real gas thermodynamics, by extending the present thermodynamic view of supercritical injection, and finally by applying these methods to the analysis of injection. A new numerical real gas thermodynamics model is developed as an extension of the DLR TAU code. Its main differences to state-of-the-art methods are the use of a precomputed library for fluid properties and an innovative multi-fluid-mixing approach. This results in a number of advantages: There is effectively no runtime penalty of using a real gas model compared to perfect gas formulations, even for high fidelity equations of state (EOS) with associated high computational cost. A dedicated EOS may be used for each species. The model covers all fluid states of the real gas component, including liquid, gaseous, and supercritical states, as well as liquid-vapor mixtures. Numerical behavior is not affected by local fluid properties, such as diverging heat capacities at the critical point. The new method implicitly contains a vaporization and condensation model. In this thesis, oxygen is modeled using a modified Benedict-Webb-Rubin equation of state, all other involved species are treated as perfect gases. A quantitative analysis of the supercritical pseudo-boiling phenomenon is given. The transition between supercritical liquid-like and gas-like states resembles subcritical vaporization and is thus called pseudo-boiling in the literature. In this work it is shown that pseudo-boiling differs from its subcritical counterpart in that heating occurs simultaneously to overcoming molecular attraction. In this process, the dividing line between liquid-like and gas-like, the so called Widom line, is crossed. This demarcation is characterized by the set of states with maximum specific heat capacity. An equation is introduced for this line which is more accurate than previous equations. By analyzing the Clausius-Clapeyron equation towards the critical limit, an expression is derived for its sole parameter. A new nondimensional parameter evaluates the ratio of overcoming molecular attraction to heating: It diverges towards the critical point but shows a significant pseudo-boiling effect for up to reduced pressures of 2.5 for various fluids. It appears reasonable to interpret the Widom-line, which divides liquid-like from gas-like supercritical states, as a definition of the boundary of a dense supercritical fluid. This may be used to uniquely determine the radius of a droplet or the dense core length of a jet. Then, a quantitative thermodynamic analysis is possible. Furthermore, as the pseudo-boiling process may occur during moderate heat addition, this allows for a previously undescribed thermal jet disintegration mechanism which may take place within the injector. This thermal jet break-up hypothesis is then applied to an analysis of Mayer’s and Branam’s nitrogen injection experiments. Instead of the constant density cores as predicted by theory, the majority of their cases show an immediate drop in density upon entering the chamber. Here, three different axial density modes are identified. The analysis showed that heat transfer did in fact take place in the injector. The two cases exhibiting a dense core are the cases which require the largest amount of power to reach the pseudo-boiling temperature. After this promising application of pseudo-boiling analysis, thermal break-up is tested numerically. By accounting for heat transfer inside the injector, a non dense-core injection can indeed be simulated for the first time with CFD. Finally, the CFD model is applied to the A60 Mascotte test case, a reactive GH2/LOX single injector operating at supercritical pressure. The results are compared with experimental and other researcher’s numerical data. The flame shape lies well within the margins of other CFD results. Maximum OH* concentration is found in the shear layer close to the oxygen core and not in the shoulder, in agreement with experimental data. The axial temperature distribution is matched very well, particularly concerning position and value of the maximum temperature.Item Open Access Volcanic evolution of Southern Tenerife (Canary Islands) during the Pleistocene and Holocene(2009) Kröchert, Jörg; Buchner, Elmar (PD Dr.)The Canary Islands are a group of volcanic ocean islands in the Central Atlantic near the continental margin of northwest Africa. Tenerife, with a volcanic history of more than 12 Ma of subaerial eruptions, is the largest island of the Canaries and is situated in the centre of the Archipelago. The Quaternary Bandas del Sur Formation in the South of Tenerife comprises a complex sequence of pyroclastic rocks and lavas and is part of the southern rift zone. In contrast to the northwest and northeast rift zones on Tenerife, the southern rift zone comprises a number of characteristics with respect to the morphological features, eruption cyclicity, and the geochemistry of the volcanic deposits. Various flank eruptions of the Las Cañadas volcano associated with basaltic lavas and the formation of cinder cones within the Bandas del Sur are important volcanic units for understanding the explosive volcanic cycles during the Pleistocene on Tenerife. Paleomagnetic studies, geochemical analysis of major and trace elements, and two radioisotopic dating (K-Ar) have been carried out on prominent cinder cones, to determine their stratigraphic position. By combining the results with previous K-Ar data in the Literature, the cones and lavas can be subdivided into three stratigraphic units. Cinder cones that belong to the first unit show reverse magnetization and Y/Nb ratios between 0.37-0.41; cinder cones of the second unit show normal magnetization and Y/Nb ratios of <0.35. The third unit comprises cinder cones with normal magnetization and Y/Nb ratios of about 0.47. The first two units were constructed between ~0.948-0.779 Ma and 0.323-0.300 Ma. These units define volcanic cycles that culminated in violent Plinian eruptions. The third and youngest unit possibly marks the beginning of a further volcanic cycle that started ~0.095 Ma ago. In order to reconstruct the uplift history of Tenerife, numerous uplifted fossil beaches and tuff cones were investigated. In the North and Northeast of Tenerife, the positions of fossil beaches indicate stable conditions since 130 ka. The uplift rates in southern Tenerife (within the Bandas del Sur) amount to a minimum of 15 m since 778 ka at Montaña Pelada and to a maximum of up to 45 m since 10 ka in the area of El Médano, suggesting an asymmetrical uplift of the island complex. The uplift in the South could be caused by seismic activity or mass loss due to flank collapse events. However, uplift due to ascending magma is more plausible. The fossil beach deposits of the El Médano area exhibit tubular-shaped concretions and concretionary dykes. These sediment structures have been interpreted as the result of a) the interaction between hot ignimbrites that overflowed wet beaches, b) fast accumulation of beach sands on hot and degassing ignimbrites, c) paleoliquefaction caused by an earthquake (seismites). Based on the interpretation as seismites, an intense paleoearthquake was proposed to be responsible for the generation of the paleoliquefaction structures. However, the sedimentary structures in question show the general criteria diagnostic for rhizocretions and root tubules with respect to their orientation, size, branching system, and style of cementation. Faults of a well-defined strike direction that precisely coincides with the southern rift fault system occur in the El Médano site. This fault system was generated contemporaneously with a chain of cinder cones ~948 ka ago. Open fractures in ignimbrites (~668 ka) and the fossil beach deposits (~10 ka) of the El Médano area suggest that the rift-associated fault system has been seismically active in the aftermath and probably is still active. A further fault system striking perpendicular to the rift-associated faults probably originates from a Holocene paleoearthquake of moderate intensity. Earthquake-induced ground effects in the fossil beach deposits of the study area are consistent with seismically induced ground effects of several recent and well-documented earthquakes and gravitational sliding triggered by an intense earthquake in Nicoya/Costa Rica in 1990. Both, the rift-associated and the earthquake-induced fault system, initially produced open cracks in the fossil beach deposits that were occupied by plants and subsequently stabilized by cementation. These results accentuate that the densely settled southern part of Tenerife is latently endangered by volcanic and seismic activity, though, currently, there are no indications of increasing volcanic activity in this region. Uplift due to recent magma loading is not observable and the intensity of a paleoearthquake in the El Médano area was probably considerably lower than mentioned in the literature.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 Application-specific UML profiles for multidisciplinary product data integration(2011) Reichwein, Axel; Rudolph, Stephan (Priv.Doz. Dr.-Ing.)This thesis examines the suitability of the UnifiedModeling Language (UML) to establish a central product model for multidisciplinary product data integration. Computer-aided product design involves the use of specialized discipline-specific software applications in order to model and simulate various product aspects. Dependencies between models are thereby frequent as the same product information often appears redundantly in various engineering models. In addition, dependencies exist due to relationships between distinct features of various models. As a result, model modifications frequently require the update of dependent models. Data consistency between models is achieved automatically through model-to-model data exchange software. The use of a central product model enables to reduce the required number of data exchange connections. Central product models store product information which is spread across several models and achieve data consistency through data exchange connections between themselves and specific models as in a hub-and-spoke network. Central product models are especially useful for automatic data consistency in design scenarios which include a high number of inter-model dependencies and model modifications. The integration of geometry and therefrom derived models such as structural analysis or computational fluid dynamics models has already been successfully addressed in numerous central product models. However, the multidisciplinary integration of more diverse models, such as geometric, software, controller and multibody system models, currently presents a challenge. Although several central product models have been developed for multidisciplinary design, none has yet gained, in contrast to geometry-focused central product models, wide acceptance nor reached the status of an international standard. The unmanageable high number of diverse discipline- and application-specific modeling concepts hinders the development of a standardized holistic central product representation. This thesis investigates the possibility of establishing an interdisciplinary central product model based on the common modular structure of models from various disciplines. Most models which are edited with current state-of-the-art software applications are composed of modular components in order to support the exchange and reuse of model information. Models from different disciplines therefore share common modeling concepts for the specification of modular model components. However, there is yet no overarching modeling standard to describe the common characteristics of modular model components from various disciplines. Object-oriented modeling concepts currently mainly describe software modules called objects. Object-oriented modeling concepts are generic and can be used to represent modular components in general. The Unified Modeling Language (UML) has been since its emergence in 1997 the de facto standard for object-oriented modeling. This thesis examines the use of the object-oriented modeling concepts of the UML to uniformly describe widely used application-specific geometric, dynamic and multibody system models in a central product model. Application-specific model information was represented in UML through generic UML modeling concepts in combination with lightweight UML extensions in the form of stereotypes. UML profiles regrouped stereotypes which corresponded to a specific modeling application. The automatic translation of UML model information into the specific models and vice versa was implemented in order to test and validate the application-specific UML profiles. The UML-based central product model was used in several test cases to automatically generate consistent models for the simulation and evaluation of various product configurations. The test cases included models for the simulation of slider-crank mechanisms, the evaluation of cabin pressure control systems, the design of conveyor system configurations, the evaluation of satellite configurations and the generation of customized aircraft geometry. The workflows within the test cases included the automatic creation and modification of UML models as well as the invocation of data exchange connections. The workflows were described in executable UML activity diagrams or Java programs. The thesis demonstrates that the UML can be used beyond conventional software modeling to establish a central holistic product representation. The modeling concepts of geometric, dynamic and multibody system models were translated mostly according to one-to-one mappings into corresponding UML modeling concepts with their respective stereotype. As a result, the specific model information is easily recognizable in the UML-based central product model. Furthermore, the use of a UML-based central product model is facilitated for the many modelers who are already familiar with the widespread and standardized UML modeling language.Item Open Access Entwicklung laserspektroskopischer Methoden zur Analyse der Verdunstungseigenschaften von Brennstofftropfen(Stuttgart : Deutsches Zentrum für Luft- und Raumfahrt, Institut für Verbrennungstechnik, 2021) Werner, Stefanie; Riedel, Uwe (Prof. Dr. rer. nat.)Die steigenden Emissionen des klimaschädlichen Treibhausgases CO2 durch die Verbrennung von fossilen, endlichen Energieträgern müssen möglichst schnell und nachhaltig reduziert werden. Ein vielversprechender Lösungsansatz zur Reduzierung der Schadstoffemissionen bei der Verbrennung liegt in dem Einsatz von alternativen und erneuerbaren Brennstoffen. Als Energieträger bieten sich auf Grund ihrer hohen Energiedichte vor allem flüssige Brennstoffe an. Diese werden typischerweise durch Druckzerstäubung in die Brennkammer eingebracht, verdunstet und dann mit dem Oxidationsmittel vermischt und verbrannt. Die Verdunstung der kleinen Brennstofftropfen des sogenannten Sprays ist von entscheidender Bedeutung für den Gesamtverbrennungsprozess in Verbrennungsmotoren und Gasturbinen. Im Allgemeinen bestimmt die Verdunstungsrate die Verbrennungsrate. Daher sind Modelle notwendig, die eine genaue Vorhersage der Brennstoffverdunstung ermöglichen. Zur Validierung dieser Modelle werden quantitative Messungen unter genau definierten Randbedingungen benötigt. Da die Prozesse in technischen Brennkammern sehr komplex sind, werden Experimente zur Tropfenverdunstung häufig mit linearen, monodispersen Tropfenketten durchgeführt, um die Kopplung zwischen den verschiedenen Effekten zu minimieren. Durch die geringe Größe der Tropfen (typischerweise wenige hundert Mikrometer oder weniger), erfordert die experimentelle Untersuchung eine hohe räumliche Auflösung. In dieser Arbeit wurden quantitative, laseroptische Messtechniken mit hoher räumlicher Auflösung zur experimentellen Untersuchung der Tropfenverdunstung an monodispersen Tropfenketten entwickelt. Mit den Messtechniken wurden Validierungsdaten für die Verdunstungseigenschaften von verschiedenen Brennstoffen bestimmt. Konzentrationsmessungen von verdunsteten Kohlenwasserstoffen wurden unter Verwendung von Infrarot-Laserabsorptionsspektroskopie und laserinduzierter Fluoreszenzspektroskopie (LIF) durchgeführt. Tropfenketten wurden mit einem Tropfenkettengenerator erzeugt, welcher vertikal in einem Strömungskanal installiert wurde. Die untersuchten Brennstoffe waren Cyclohexan, iso-Octan, n-Heptan, n-Pentan, 1-Butanol und Anisol. Der Strömungskanal wurde mit einer laminaren Luftströmung bei verschiedenen Temperaturen (313 K - 430 K) durchströmt. Da die untersuchten Tropfen einen Durchmesser in der Größenordnung von 120 bis 160 µm hatten und die Konzentrationsgradienten nahe der Tropfenoberfläche groß waren, war eine hohe räumliche Auflösung der Messtechniken erforderlich. Die Absorptionsmessungen wurden mit der Infrarotstrahlung eines HeNe-Lasers bei λ = 3,39 µm durchgeführt, um die CH-Streckschwingung der Kohlenwasserstoffe anzuregen. Die für die Quantifizierung der Brennstoffkonzentrationen benötigten Absorptionsquerschnitte wurden in einer beheizten Gaszelle für Temperaturen von 300 K - 773 K bestimmt. Die räumliche Auflösung im Strömungskanal betrug < 50 µm über eine Länge von 2 mm (Halbwertsbreite). Durch die Zylindersymmetrie und gute Stabilität der Tropfenketten konnten zeitliche Mittelungs- und Tomografieverfahren angewandt werden. Hierdurch konnten radiale Konzentrationsprofile an mehreren Positionen im Strömungskanal erhalten werden. Aus dem Anstieg der Dampfkonzentration an verschiedenen Messpositionen konnte die Verdunstungsrate bestimmt werden. Die Verdunstungsraten wurden in Abhängigkeit von der Mantelstromtemperatur (313 K - 430 K), der Tropfengeschwindigkeit (8 m/s - 23 m/s), der Tropfenerzeugungsfrequenz (12 kHz - 75 kHz) und dem Tropfenabstand (300 µm - 685 µm) gemessen. Im untersuchten Temperaturbereich steigt die Verdunstungsrate des Brennstoffs linear mit der Temperatur an. Die Reihenfolge der Brennstoffe in Bezug auf die Verdunstungsrate entspricht den Siedepunkten der einzelnen Brennstoffe. Da technische Brennstoffe häufig eine Mischung mehrerer Komponenten sind, ist die Untersuchung von Brennstoffgemischen von großem Interesse. Daher wurde ein Messverfahren entwickelt, um binäre Gemische zu untersuchen. Das Verfahren wurde verwendet, um eine Mischung aus Cyclohexan und Anisol zu untersuchen. Zwei Messtechniken - laserinduzierte Fluoreszenz (LIF) und Infrarot Absorptionsspektroskopie - wurden verwendet, um beide Spezies zu messen. Um λ = 3,39 µm ist der Absorptionsquerschnitt von Cyclohexan um etwa den Faktor 8 größer als von Anisol. Im untersuchten Fall war die Konzentration aufgrund des höheren Dampfdrucks ebenfalls deutlich größer. Daher konnte das Infrarot-Absorptionssignal praktisch ausschließlich Cyclohexan zugeordnet werden. Anisol hat bei Anregung bei λ = 266 nm eine sehr gute Fluoreszenzquantenausbeute, während Cyclohexan keine Fluoreszenz zeigt. LIF ermöglicht daher die Quantifizierung von Anisol (oder anderen Aromaten) ohne Interferenz durch Kohlenwasserstoffe. Es wurde ein Messverfahren entwickelt, welches Halationseffekte vermeidet, die typischerweise in planaren LIF-Experimenten an Tropfenketten auftreten. Kalibrationsmessungen, die im gleichen Strömungskanal durchgeführt wurden, ermöglichten die Quantifizierung der verdunsteten Anisolkonzentrationen. Die räumliche Auflösung betrug 80 µm. Ähnlich wie bei den Einzelkomponentenmessungen wurden Verdunstungsraten bestimmt. Wie aufgrund des niedrigeren Dampfdrucks zu erwarten, ist die Verdunstungsrate von Anisol niedriger als die von Cyclohexan. Die Verdunstungsrate von Cyclohexan in der binären Mischung stimmt gut mit den Einzelkomponentenmessungen überein. Das entwickelte Messverfahren ist sehr vielversprechend für weitere Untersuchungen an Mehrkomponentenmischungen. In dieser Arbeit konnte damit erstmals mit hoher räumlicher Auflösung die Verdunstung von Brennstoffkomponenten mittels Absorptionsspektroskopie in der Nähe von Brennstofftropfen untersucht werden. Zusätzlich wurden in Kombination mit laserinduzierter Fluoreszenzspektroskopie Messungen an binären Mischungen durchgeführt. Damit steht ein wertvoller Datensatz zur Validierung von numerischen Simulationen zur Verfügung.Item Open Access Integrated flight loads modelling and analysis for flexible transport aircraft(2006) Reschke, Christian; Well, K. H. (Prof. Ph.D.)This thesis is concerned with the derivation of nonlinear equations of motion for flexible aircraft in flight. These equations are intended for the accurate simulation of the flight dynamics of flexible aircraft in general and for the analysis of resulting dynamic structural loads in particular. The main focus is on the inertial coupling effects between the maneuvering flight and structural dynamics of the airframe. The field of flight loads computation is concerned with the provision of loads due to maneuvering flight or turbulence. Hereby, the underlying simulation model consists of a model for the flexible aircraft as well as peripheral models, like the Electronic Flight Control System, a pilot model, etc. The analysis is performed for a variety of flight points and load cases. Subsequently a loads envelope is determined. It consists of maximum structural loads over the airframe due to prescribed maneuvers, gust and turbulence at different flight points and loading conditions. Traditionally, specific models are used for either maneuver loads or gust loads computation. A six degree of freedom (6DOF) nonlinear aircraft model is employed for maneuver simulation. The dynamic response of the aircraft due to turbulence and gust is estimated with linear aeroelastic models, primarily employed in the frequency domain. Particularly for large flexible transport aircraft, these specific models have important limitations. Commercial transport aircraft are getting larger and the airframes are becoming more slender and flexible due to lightweight design. This causes an increasing interaction of flight mechanics and structural dynamics, including inertial coupling effects. Therefore, it is important to extend 6DOF quasi-flexible maneuver loads models with finite element based full flexible aircraft models. Secondly, it may become necessary to perform dynamic response analysis in the time domain in order to account for nonlinear flight control systems. For this reasons a consistent mathematical model that integrates methods and data from both disciplines has to be developed. This implies a derivation of equations of motion and the development of equations for the computation of loads. Furthermore the integration of the respective aerodynamic models has to be addressed. In a first step the equations of motion are derived from first principles. The formulation is developed in such a way that industrial model data and industrial constraints can be considered and efficiently incorporated. The inertial coupling terms are cast in generalized form providing differential equations suited for rapid time domain simulation. In a second step the generalized equations of motion are augmented with a consistent set of nonlinear equations for the computation of internal structural loads over the airframe. The new formulation accounts for nonlinear flight mechanical motion and inertial coupling effects with structural dynamics. In a third step external forces, particularly aerodynamic forces that are driving the equations of motion are modeled. The approach is tailored towards the integration of industrial aerodynamic models used in maneuver loads and dynamic response analysis. The presented integration method extents the distributed quasi-flexible aerodynamic model as used for maneuver loads analysis by unsteady dynamic force increments. The developed set of equations of motion and equations of loads are implemented in a state-of-the-art industrial simulation environment in order to validate the formulation and to perform simulations. A relevant test case is studied to analyze maneuvering flight, dynamic response and structural loads. The influence of inertial coupling effects is emphasized and structural components that are significantly affected are indicated. The key result of this thesis is the increased precision of simulation and loads computation at the cost of a minimum increase of computing effort. No additional model data other than currently used for industrial maneuver loads and dynamic response analysis is required.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.