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Development of a Reachability Analysis Algorithm for Space Applications
Get PDFIn the last decades developments in space technology paved the way to more challenging missions like asteroid mining, space tourism and human expansion into the Solar System. These missions require difficult tasks such as real-time capable guidance schemes for re-entry, landing on celestial bodies and implementation of large angle maneuvers for spacecraft. There is a need for an analysis tool to increase the robustness and success of these missions. Reachability analysis contributes to this requirement by obtaining the set of all achievable states for a dynamical system starting from an initial condition with given admissible control inputs of the system. In this study, an optimal control based reachability analysis algorithm is developed for evaluating the performance of the guidance and control methods for space missions considering the desired performance index. The developed method considers a soft-landing problem for a Moon mission as the case study, and attainable area of the lander as the performance index. The method computes feasible trajectories for the lunar lander between the point where the terminal landing maneuver starts and points that constitutes the candidate landing region. The candidate landing region is discretized by equidistant points on a two dimensional plane, i.e. in downrange and crossrange coordinates, and for each grid point a distance function is defined. This distance function acts as an objective function for a related optimal control problem (OCP). Each infinite dimensional OCP is transcribed into a finite dimensional Nonlinear Programming Problem (NLP) by using Pseudo-Spectral Methods (PSM). The NLPs are solved using available tools to obtain feasible trajectories and approximated reachable sets with information about the states of the dynamical system at the grid points. The proposed method approximates reachable sets of the lander with propellant-to-reach and time-to-reach cost by solution of NLPs. A polynomial-based Apollo guidance scheme is used to compare the results for the developed method. The coefficients that define the position of the lander are obtained by solving a series of explicit equations for the given initial and final states. A model inversion based PD controller is designed to track the generated trajectory. Feasible solutions that satisfy safe landing conditions are filtered and the results are compared for the two different approaches. Finally, the uncertainties which are characterized by initial state error and system parameters are also considered. A multivariate trajectory interpolation tool is used to interpolate RS with different initial states. A Riccati equation-based controller is designed to track the previously obtained reference trajectories within presence of the uncertainties. Monte Carlo (MC) simulations are carried out to obtain safe attainable landing area of the lunar lander as probability maps. The same uncertainty set is used to verify these probability maps by propagating the uncertainties using unscented transform. The developed tool analyzes the different guidance and control methods, for the attainable landing area of the lander, under various landing scenarios, with different dynamical models and controller parameters. Numerous quality metrics are used to compare the change of characteristics of the attainable landing area and performance of the guidance and control methods, and selected design parameters
#NoG20. Ergebnisse der Befragung von Demonstrierenden und der Beobachtung des Polizeieinsatzes
Get PDFAm 7. und 8. Juli 2017 fand in Hamburg das zwölfte Treffen der Gruppe der zwanzig wichtigsten Industrie- und Schwellenländer (G20) statt. Gemeinsam mit dem Forschungszentrum Ungleichheit und Sozialpolitik (Socium) und dem Göttinger Institut für Demokratieforschung (GIfD) haben Wissenschaftler innen des Instituts für Protest- und Bewegungsforschung eine Befragung der Protestierenden für zwei zentrale Demonstrationszüge durchgeführt: die bereits für den 2. Juli, also am Wochenende vor dem offiziellen Gipfel, angesetzte Demonstration G20 Protestwelle , zu der vor allem Umweltorganisationen, Bündnis 90/Die Grünen und das Mobilisierungsnetzwerk Campact aufgerufen hatten, sowie die Abschlussdemonstration am 8. Juli mit dem Titel Grenzenlose Solidarität statt G20! , für die ein Bündnis linker, überwiegend antikapitalistischer Organisationen und Parteien warb. Es werden zentrale Ergebnisse der Fragebogenstudie und einer Demonstrationsbeobachtung dargestellt, wobei insbesondere der Frage nachgegangen wird, ob sich die Protestierenden nicht doch ähnlicher sind, als die unterschiedliche Charakterisierung der beiden Demonstrationen suggeriert. Erleben wir ein erneutes Aufleben der globalisierungskritischen Bewegung oder eher eine Parallelität einzelner Protestereignisse, die keinen gemeinsamen Nenner mehr besitzen? Diesen Fragen wird nachgegangen, indem die Motive, Überzeugungen und Einstellungen der Protestierenden in den Mittelpunkt der Untersuchung gestellt werden. Die Protestbeobachtung liefert darüber hinaus eine Analyse der eskalierenden Dynamik polizeilicher Maßnahmen, die letztlich vor allem darauf gerichtet waren, Protest zu erschweren. Zusammen liefert die Studie auch ein Gegengewicht zu der öffentlichen Fokussierung auf die den Gipfel begleitende Gewalt
Empirische Studie zur Anwendung der Logistik-AGB in der Speditionsbranche
Get PDFDie vorliegende Bachelorarbeit Empirische Studie zur Anwendung der Logistik-AGB in der Speditionsbranche hat insofern eine Bedeutung, da die Thematik der logistischen Zusatzleistungen aus Sicht der Logistiker weiter am Wachsen ist. Neben der Spezialisierung auf verschiedene Branchen, übernehmen Spediteure mehr und mehr Auslagerungstätigkeiten. Vereinbarungen wie die Logistik-AGB sind insbesondere bei erstmaligen Auslagerungen, sowie Mehrwertdienstleistungen im Alltagsgeschäft eine wichtige Grundlage. Zudem werden AGB immer wieder überarbeitet oder neue AGB werden auf dem Markt integriert, sodass Kenntnisse über den derzeitigen Anwendungsstand der Logistik-AGB von Relevanz sind. Eine IST-Erfassung der Marktdurchdringung ist daher zu untersuchen. Neben einer Internetrecherche wurden Interviews durchgeführt, um offen gebliebene Fragen aus dem Hauptanalyseteil der Internetrecherche zu beantworten. Die Untersuchung wurde zwischen Klein- und mittelständischen Unternehmen und Großunternehmen unterschieden. Zudem wurden die betrachteten Spediteure analysiert, ob diese in bestimmten Branchen aktiv sind, um weitere Unterscheidungsmerkmale der Logistik-AGB zu erhalten. Die Ergebnisse wurden dabei aus verschiedenen Blinkwinkel untersucht. Es hat sich gezeigt, dass die Logistik-AGB zu ca. einem Viertel in der Speditionsbranche veröffentlicht wurden. Der Logistik-AGB Anteil steigt bis zu einem Anteil von 42 Prozent, wenn nur die Unternehmen betrachtet werden, die auch Mehrwertdienstleistungen tätigen. Die Ergebnisse der Internetrecherche und Ansichten von Interviewpartnern in den richtigen Kontext zu setzten ist daher umso wichtiger, wenn verschiedene Betrachtungsweisen zur Anwendung kommen
Replacive formation of sulphides in the oceanic lithosphere and the effect on rock porosity evolution
Get PDFThis thesis describes the replacive formation of sulfides in the oceanic lithosphere through the interplay of discharging hydrothermal fluids and seawater. Chemical and 3D analyses on sulfate chimneys showed that anhydrite precipitation and corrosion likely control porosity and sulfide formation in the chimney conduit. Batch experiments using several oceanic lithologies and a synthetic, H2S-bearing vent fluid showed that sulfide root zones were more easily formed in less reducing rock types where sulfur activity was highest. The onset of anhydrite growth in fractured basalt in a flow-through experiment was found to be only possible at temperatures above 120 degrees C and was accompanied by many Fe-bearing phases in the basalt core. The results of this thesis stress the importance of porosity for sulfide formation in hydrothermal processes
Finding Lost & Found. Designer s Notes from the Process of Creating a Jewish Game for Learning
Get PDFThis article provides context for and examines aspects of the design process of a game for learning. Lost & Found (2017a, 2017b) is a tabletop-to-mobile game series designed to teach medieval religious legal systems, beginning with Moses Maimonides Mishneh Torah (1180), a cornerstone work of Jewish legal rabbinic literature. Through design narratives, the article demonstrates the complex design decisions faced by the team as they balance the needs of player engagement with learning goals. In the process the designers confront challenges in developing win-states and in working with complex resource management. The article provides insight into the pathways the team found through the challenges in the creation of the game
Highly Automated Formal Verification of Arithmetic Circuits
Get PDFThis dissertation investigates the problems of two distinctive formal verification techniques for verifying large scale multiplier circuits and proposes two approaches to overcome some of these problems. The first technique is equivalence checking based on recurrence relations, while the second one is the symbolic computation technique which is based on the theory of Gröbner bases. This investigation demonstrates that approaches based on symbolic computation have better scalability and more robustness than state-of-the-art equivalence checking techniques for verification of arithmetic circuits. According to this conclusion, the thesis leverages the symbolic computation technique to verify floating-point designs. It proposes a new algebraic equivalence checking, in contrast to classical combinational equivalence checking, the proposed technique is capable of checking the equivalence of two circuits which have different architectures of arithmetic units as well as control logic parts, e.g., floating-point multipliers
Using Lipid Biomarkers and their Isotopic Composition to reconstruct the Late Pleistocene Paleoclimate of the Amazon Basin
Get PDFThis thesis deals with the reconstruction of the late Pleistocene climate and vegetation history of the Amazon basin and is made up of three manuscripts: In the first manuscript biomarker based paleosalinity proxies are tested. It is shown that the stable hydrogen isotope composition of palmitic acid reflects the salinity conditions in the Amazon Outflow Plume, while the stable hydrogen isotope composition of alkenones is influenced by factors other than salinity. The second manuscript deals with the transport of long-chain n-alkanes in the Amazon River and its main tributaries. It is demonstrated that long-chain n-alkanes mainly originate from the lowland basin, contrasting the dominant inorganic sediment source in the Andes. The third manuscript deals with the application of plant wax proxies in a marine sediment core covering the late Pleistocene. It is shown that forest vegetation persisted through drier conditions during the last glacial maximum, while minor savanna expansion occurred during Heinrich Stadials
R/V METEOR Cruise Report M114, Natural hydrocarbon seepage in the southern Gulf of Mexico, Kingston - Kingston, 12 February - 28 March 2015.
Get PDFMaterial- und Prozessmodellierung zur effizienten FEM-Berechnung der Verzugsentstehung beim Laser-Sintern von teilkristallinen Thermoplasten
Get PDFThis thesis presents a method for fast numerical calculation of warpage in laser sintering of semicrystalline thermoplastics. The developed model is based on the simulation of the thermal interaction in the building chamber, caused by different thermal boundary conditions. For that purpose, a finite element mesh of the whole building space is generated. The interaction of the thermal boundary conditions causes a time dependent temperature eld, which influences the crystallization progress and in consequence the volume shrinkage. Subsequently to the thermal calculation, that shrinkage strain is used as time-space dependent mechanical load in a sequence of static mechanical FEM-computations of the part distortion. The developed approach allows the prediction of part warpage caused by macroscopic boundary conditions of real parts for the first time and has been used to analyse several test samples as well as real industrial parts
Laser Ranging Interferometry for Future Gravity Missions : Instrument Design, Link Acquisition and Data Calibration
Get PDFThe presented study aims to improve the design solution adopted for the Laser Ranging Instrument of the GRACE Follow-On mission in terms of instrument layout, algorithms for the laser link acquisition and techniques for mitigating the range measurement noise. The first part of this work describes viable layout solutions of a heterodyne interferometer employed for intra-satellite range metrology and the major noise contributions which degrade the overall accuracy of the instrument. Together with the optical layout of the instrument, novel design concepts of the instrumenta s subsystems are also analyzed and tested. Precisely, a phasemeter designed to autonomously acquire and track a heterodyne signal with low signal-to-noise ratio in a frequency band that spans from 1MHz to 25MHz is presented. Particular attention is also dedicated to the mathematical modeling of the steering mirror dynamics and to the enhancement of its pointing performance by means of feedforward control. In the second part of this work, solutions for autonomously acquiring a laser signal buried in noise are analyzed and put in relation with the boundary constraints of the acquisition problem. The acquisition algorithms presented and the robustness of their design is verified mainly using numerical simulations. Experimental tests have also been performed for validating the simulation hypothesis and verifying their compliancy to a realistic mission scenario. The last part of this work describes a calibration algorithm which has been developed for minimizing, during data post-processing, the noise due to the tilt-to-piston coupling which represents one of the highest contributors to the overall measurement noise