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 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 A MATLAB toolbox for the Scintrex CG-5 gravimeter at GIS(2017) Gu, SiyunThis thesis is about a MATLAB toolbox for the Scintrex CG-5 gravimeter. The aim of this toolbox is to offer a basic data process for gravity measurement, which is compatible for most applications in geodesy. In particular, the toolbox covers: 1. data selection, 2. adjustment, 3. gravity gradient computation, 4. gravity visualization, 5. calibration factor estimation. A graphical user interface enables users without deeper programming knowledge to operate this toolbox and obtain the results like adjusted values or figures.Item Open Access Bemannte Missionen zum Mars mit kontinuierlichen Antrieben(2005) Schmidt, Tanja D.; Auweter-Kurtz, Monika (Prof. Dr.-Ing habil.)Im Rahmen dieser Arbeit werden bemannte Missionen zum Mars für unterschiedliche Antriebskonzepte im Hinblick auf Flexibilität, kurze Gesamtmissionsdauern, kurze Transferzeiten und moderate Startmassen untersucht und verglichen. Die untersuchten Antriebskonzepte sind kontinuierliche elektrische Antriebe sowie chemische und nuklear-thermische Antriebe, die zur Kategorie der impulsiven Antriebe gehören. Die im Rahmen dieser Arbeit hierzu erstellten Programme bzw. Routinen zur Bahnsimulation und -optimierung werden vorgestellt. Es werden die Ergebnisse einer detaillierten, systematischen Bahnanalyse für helio- und planetozentrische Bahnen und für Rundreise-Missionen aufgezeigt. Speziell für die kontinuierlichen elektrischen Antriebe werden Variationen der Antriebsparameter (Schub, spezifischer Impuls und Triebwerkswirkungsgrad) durchgeführt und deren Einfluß auf Flugzeit und Startmasse bzw. Treibstoffmasse untersucht. Es werden die hierfür notwendigen minimalen Antriebsparameter für bemannte Marsmissionen ausgearbeitet und verschiedene elektrische Antriebskonzepte hinsichtlich Anwendbarkeit untersucht. Die atmosphärischen Flugsegmente einer solchen Mission werden im Rahmen dieser Arbeit mittels Literaturstudien untersucht. Die in der Literatur diskutierten Konzepte für Schwerlaststartraketen an der Erde, Marsaufstiegsfahrzeuge sowie Aermanöver-Vehikel für Mars und Erde werden hinsichtlich Anwendbarkeit für bemannte Marsmissionen evaluiert und Konzeptvorschläge ausgearbeitet. Neben dem Antriebssystem werden im Rahmen dieser Arbeit die Lebenserhaltung, Habitate und die Energieversorgung untersucht. Es werden Modelle für diese Subsysteme erstellt und verschiedene Konzepte miteinander verglichen. Basierend auf den Ergebnissen dieser Arbeit wird ein Konzeptvorschlag einer bemannten Marsmission mit kurzer Gesamtmissionsdauer unter Verwendung kontinuierlicher elektrischer Antriebe vorgestellt.Item Open Access Dynamic water masks from optical satellite imagery(München : Verlag der Bayerischen Akademie der Wissenschaften, 2019) Elmi, Omid; Sneeuw, Nico (Prof. Dr.-Ing.)Investigation of the global freshwater system has a vital role in critical issues e.g. sustainable development of water resources, acceleration of the hydrological cycle, variability of global sea level. Measurement of river streamflow is vital for such investigations as it gives a reliable estimate of freshwater fluxes over the continents. Despite such importance, the number of river discharge gauging station has been decreasing. At the same time, information on the global freshwater system has been increasing because of various types of ground observations, water-use information and spaceborne geodetic observations. Nevertheless, we cannot answer properly crucial questions about the amount of freshwater available on a certain river basin, or the spatial and temporal dynamics of freshwater variations and discharge, or the distribution of world’s freshwater resources in the future. The lack of comprehensive measurements of surface water storage and river discharge is a major impediment for a realistic understanding of the hydrological water cycle, which is a must for answering the aforementioned questions. This thesis aims to improve the methods for monitoring the surface extent of inland water bodies using satellite images. Satellite imaging systems capture the Earth surface in a wide variety of spectral and spatial resolution repeatedly. Therefore satellite imagery provides the opportunity to monitor the spatial change in shorelines, which can serve as a way to determine the water extent. Each band of a multispectral image reveals a unique characteristic of the Earth surface features like surface water extent. However selecting the spectral bands which provide the relevant information is a challenging task. In this thesis, we analyse the potential of multispectral transformations like Principal Component Analysis (PCA) and Canonical Correlation Analysis (CCA) to tackle this issue by condensing the information available in all spectral bands in just a few uncorrelated variables. Moreover, we investigate how the change between multispectral images at different epochs can be highlighted by using the transformations. This study proposes an automatic algorithm for extracting the lake water extent from MODIS images and generating dynamics lake masks. For improving the accuracy of the lake masks and computational efficiency of the algorithm, two masks are defined for limiting the search area. The restricting masks are developed according to DEM of the surrounding area together with a map of the long-term variation of pixel values. Subsequently, an unsupervised pixel-based classification algorithm is applied for defining the lake coastline. The algorithm particularly deals with the challenges of generating long time series of lake masks. We apply the algorithm on five lakes in Africa and Asia, each of which demonstrates a challenge for lake area monitoring. However in the validation section, we demonstrate that the algorithm can generate accurate dynamic lake masks. Rivers show diverse behaviour along their path due to the contribution of different parameters like gradient of the elevation, river slope, tributaries and river bed morphology. Therefore for generating accurate river reach mask, we need to consider additional sources of information apart from pixel intensity. The region-based classification algorithm that we propose in this study takes advantages of all types of available information including pixel intensity and spatial and temporal interactions. Markov Random Fields provide a flexible frame for interaction between different sources of data and constraint. To find the most probable configuration of the field, the Maximum A Posteriori solution for the MRF must be found. To this end, the problem is reshaped as an energy minimization. The energy function is minimized applying graph cuts as a powerful optimization technique. The uncertainty in the graph cuts solution is also measured by calculating the minimum marginal energies. The proposed method is applied to four rivers reaches with different hydrological characteristics. We validate the obtained river area time series by comparing with in situ river discharge and satellite altimetric water level time series. Moreover, in this study, we present river discharge estimation models using the generated river reach masks. Our aim is to find an empirical relationship between the average river reach width and river discharge. The statistics in the validation periods support the idea of using river width-discharge prediction models as a complementary technique to the other spaceborne geodetic river discharge prediction approaches.Item Open Access The zero gravity curve and surface and radii for geostationary and geosynchronous satellite orbits(2017) Sjöberg, L. E.; Grafarend, Erik W.; Joud, M. S. S.A geosynchronous satellite orbits the Earth along a constant longitude. A special case is the geostationary satellite that is located at a constant position above the equator. The ideal position of a geostationary satellite is at the level of zero gravity, i.e. at the geocentric radius where the gravitational force of the Earth equals the centrifugal force. These forces must be compensated for several perturbing forces, in particular for the lunisolar tides. Considering that the gravity field of the Earth varies not only radially but also laterally, this study focuses on the variations of zero gravity not only on the equator (for geostationary satellites) but also for various latitudes. It is found that the radius of a geostationary satellite deviates from its mean value of 42164.2 km only within ±2 m, mainly due to the spherical harmonic coefficient J22, which is related with the equatorial flattening of the Earth. Away from the equator the zero gravity surface deviates from the ideal radius of a geosynchronous satellite, and more so for higher latitudes. While the radius of the former surface increases towards infinity towards the poles, the latter decreases about 520 m from the equator to the pole. Tidal effects vary these radii within ±2.3 km.Item Open Access Application of neural networks and transfer learning to turbomachinery heat transfer(2022) Baumann, Markus; Koch, Christian; Staudacher, StephanModel-based predictive maintenance using high-frequency in-flight data requires digital twins that can model the dynamics of their physical twin with high precision. The models of the twins need to be fast and dynamically updatable. Machine learning offers the possibility to address these challenges in modeling the transient performance of aero engines. During transient operation, heat transferred between the engine’s structure and the annulus flow plays an important role. Diabatic performance modeling is demonstrated using non-dimensional transient heat transfer maps and transfer learning to extend turbomachinery transient modeling. The general form of such a map for a simple system similar to a pipe is reproduced by a Multilayer Perceptron neural network. It is trained using data from a finite element simulation. In a next step, the network is transferred using measurements to model the thermal transients of an aero engine. Only a limited number of parameters measured during selected transient maneuvers is needed to generate suitable non-dimensional transient heat transfer maps. With these additional steps, the extended performance model matches the engine thermal transients well.Item Open Access Entwicklung und Untersuchung eines Partikelverfahrens zur Simulation elektromagnetischer Wechselwirkungen in verdünnten Plasmaströmungen(2015) Stindl, Torsten; Auweter-Kurtz, Monika (Prof. Dr.-Ing. habil.)In einer Vielzahl von technischen Prozessen und Geräten, insbesondere in der Raumfahrt, spielen verdünnte Plasmaströmungen eine signifikante Rolle. Zur Erforschung, Auslegung und Optimierung dieser Prozesse und Geräte können numerische Plasmasimulationen einen wertvollen Beitrag liefern. Aufgrund der dünnen Plasmen und der damit verbundenen Ungültigkeit der Kontinuumsannahme werden Partikelverfahren verwendet. Gekoppelte PIC-DSMC-Verfahren zur Approximation der Boltzmanngleichung können sowohl elektromagnetische Interaktionen als auch Kollisionen der Partikel behandeln. Ein solches Verfahren wird derzeit in einer Kooperation zwischen dem Institut für Raumfahrtsysteme (IRS) und dem Institut für Aerodynamik und Gasdynamik (IAG) der Universität Stuttgart entwickelt, mit früheren Beteiligungen des Karlsruher Institut für Technologie (KIT), des Höchstleistungsrechenzentrums Stuttgart (HLRS) und der German Research School der RWTH Aachen. Die vorliegende Arbeit befasst sich mit der Entwicklung und Untersuchung von Teilen der PIC-Komponente dieses gekoppelten PIC-DSMC-Verfahrens und stellt die implementierten Verfahren und Techniken sowie die durch die Verifizierung und Untersuchung gewonnenen Erkenntnisse vor. Die theoretischen Grundlagen und physikalischen Zusammenhänge sowie die grundlegenden Gleichungen werden vorgestellt. Die Modellierung und Implementierung des PIC-Verfahrens wird erläutert und die räumlichen und zeitlichen Diskretisierungsmethoden sowie Randbedingungen des Verfahrens werden präsentiert. Der Fokus der Arbeit liegt auf der Partikelbehandlung. Dazu gehören unter anderem die Partikellokalisierung und -verfolgung bezüglich des Rechengitters sowie die Randbehandlung der Partikel. Die entwickelten und vorgestellten Methoden ermöglichen eine zuverlässige und schnelle Verfolgung der Partikel auf unstrukturierten Gittern mit nicht planaren Flächen zwischen Gitterelementen. Dadurch wird allgemein die sichere Anwendung von Randbedingungen, für das PIC-Verfahren die korrekte Zuordnung der Partikel zu den Rechengitterelementen und für das DSMC-Verfahren die schnelle Erfassung der in einem Element befindlichen Partikel gewährleistet. Ein weiterer Aspekt der Partikelbehandlung ist die Deposition der Ladungen von den Partikeln auf das Rechengitter selbst, für die verschiedene Methoden präsentiert werden. Durch eine grundlegende Untersuchung dieser Methoden hinsichtlich Rechenaufwand, Ladungserhaltung und -verteilung wird deren Eignung für verschiedene Anwendungsbereiche und deren spezifischen Anforderungen identifiziert. Für die bisher verwendete Formfunktionsmethode wurde eine Alternative hoher Ordnung auf der Basis von B-Splines eingeführt, die durch die Verwendung eines kartesischen Hintergrundgitters zur Deposition zu einer signifikanten Reduzierung des Rechenaufwands führt. Da die Simulation der meisten Anwendungsfälle aufgrund der Notwendigkeit von hohen Partikelzahlen und hochaufgelösten Rechengittern sehr rechenintensiv ist und somit die Verwendung von parallelen Hochleistungsrechnern erfordert, ist das Verfahren voll parallelisiert. Die Methoden zurParallelisierung der einzelnen Teile des Verfahrens werden vorgestellt. Darüber hinaus wird die Skalierbarkeit und die Verteilung der Rechenlast gezeigt. Das PIC-Verfahren wird verifiziert und die Anwendbarkeit des Verfahrens am Beispiel der Simulation einer Strömung durch das Gitter eines Ionentriebwerks demonstriert. Die in dieser Arbeit vorgestellten Verfahren und Techniken ermöglichen die parallele Simulation von dreidimensionalen verdünnten Plasmaströmungen auf komplexen Geometrien unter Verwendung des Discontinuous Galerkin Verfahrens hoher Ordnung, wofür die hierfür entwickelten und untersuchten Partikelbehandlungsmethoden einen wesentlichen Beitrag leisten.Item Open Access Setting-up of GPS reference stations and investigating the effects of antenna radome(2003) Ogonda, Godfrey OnyangoWith the shutting down of Selective Availability (S/A) in year 2000 , accuracies as better as 5 to 9 metres in the horizontal and 8 to 9 metres in the vertical have been guaranteed in GPS positioning using code measurements in Single Point Positioning (SPP) mode. Although the accuracies attainable through unassisted SPP are sufficient for most applications such as navigation, GIS and recreation, a whole range of experience has shown that millimetre accuracies can be attained through performance of GPS surveys using enhanced satellite systems, improved equipment and streamlined field procedures. Such concepts include the tendency to use reference stations (i.e. relative Positioning) to generate DGPS corrections and maintenance of reference frames. The precisions and accuracies at which the reference stations are established and monitored are very high. All the possible sources of error to which the antennas and receivers at the site are susceptible to, must be identified and minimised or eliminated. This include Phase Centre Variation (PCV) and multipath. To protect the antennas from bad weather and vandalism, reference station antennas are usually covered. The PCV patterns are further complicated from the fact that addition of antenna covers (radomes) are known to have effects on the positions and the existence of several correction models. In this study, two reference stations were established and an investigation on the effect of conical radome on one of the reference stations was carried out. A baseline of about 5 metres was set-up on top of the building housing the Institute of Navigation on Breitscheid 2. At one end of the baseline was station 1, mounted with a choke ring antenna, and the other end station 2, mounted with a compact L1/L2 antenna. Twenty four hour GPS observations at a data rate of 2 seconds were carried out in six consecutive days. The antenna setting for every two days was the same. Part of the data files collected on day 1 was used to fix the positions of the two reference stations with respect to the SAPOS network. A further analysis was done with the six day data files to determine the effect of the radome and the radome mount plate on station 1. The solutions obtained show that the reference stations were successfully established and that the conical radome has a negligible effect of about 1.5 mm on the height component of station 1.Item Unknown Maintenance strategies for large offshore wind farms(2012) Scheu, MattiWhich equipment is needed and how shall tasks be scheduled in order to implement the economically most efficient operation and maintenance strategy for large offshore wind farms? This is the question motivating this research project. Considering production losses due to turbine downtime as well as local geographical and weather conditions, an efficient operation and maintenance (O&M) solution shall be achieved for two reference sites at the UK east coast. For this purpose, a Matlab-based tool has been developed, consisting of the following five main modules: Weather, Failures, Resources, Strategy and Cost. The "Weather" module is able to generate future sea states and wind speeds based on historical data. It uses a finite state Markov chain in discrete time to model significant wave heights. Wind speeds are then generated according to their conditional probability distribution at the corresponding wave height. In order to validate the weather module, several time series were generated and compared with existing data. For comparison, the mean values, standard errors, linear correlations and cumulative distribution functions for persistence of operational weather windows were chosen, both for synthetic and observed wind speed and wave height time series. Both reference sites in the UK North Sea were considered for validation. Failure rates are the basis for the "Failure" module. As an input, data gathered from onshore reliability investigations are used, which can be updated once more detailed data is available for offshore turbines. The outcomes of this module are turbine-failures occurring at a certain time. Within the “Resources” module, it is defined which equipment and personnel is available for O&M activities. The equipment is specified by its technical characteristics, e.g., the maximum transportable personnel and the operational wave height boundary. Another key parameter is the "Strategy". The main goal of this module is to take the decision whether to perform an operation or not. Within this thesis, one specific strategy has been used, but references are made to possible modifications in the according paragraphs. The measurement of economic performance is done in the "Cost" module. Here, production losses are quantified by combining the wind speed during a failure with the linearized power curve of the turbine and the local buyback price system. Therefore, the worth of additional or better maintenance equipment can be seen directly as an increase in availability and a decrease of production losses. Results show how sensitive availability and therefore production losses change with respect to changes in the maintenance fleet, reliability characteristics of components and distance to shore. Major improvements of availability were achieved by applying maintenance vessels with a higher operational wave height boundary. An increase of this constraint from one to 1.8 m significant wave height raised the availability by up to 30 percent, leading to a much better economic performance. The influence of the weather forecast accuracy on the number of maintenance vessel and crane deployments is also stated, showing a significant increase of deployments if the weather forecast is only accurate for short times. An improvement of component-reliability, modeled as a 50% decreased annual failure rate, could save up to 440 k€ of yearly production losses for each modeled wind turbine. Higher transit times, due to a greater distance to shore, strongly decrease the wind park availability.Item Open Access IEA Wind Task 32: Wind Lidar : identifying and mitigating barriers to the adoption of wind lidar(2018) Clifton, Andrew; Clive, Peter; Gottschall, Julia; Schlipf, David; Simley, Eric; Simmons, Luke; Stein, Detlef; Trabucchi, Davide; Vasiljevic, Nikola; Würth, InesIEA Wind Task 32 exists to identify and mitigate barriers to the adoption of lidar for wind energy applications. It leverages ongoing international research and development activities in academia and industry to investigate site assessment, power performance testing, controls and loads, and complex flows. Since its initiation in 2011, Task 32 has been responsible for several recommended practices and expert reports that have contributed to the adoption of ground-based, nacelle-based, and floating lidar by the wind industry. Future challenges include the development of lidar uncertainty models, best practices for data management, and developing community-based tools for data analysis, planning of lidar measurements and lidar configuration. This paper describes the barriers that Task 32 identified to the deployment of wind lidar in each of these application areas, and the steps that have been taken to confirm or mitigate the barriers. Task 32 will continue to be a meeting point for the international wind lidar community until at least 2020 and welcomes old and new participants.