Open-Access-Journals @ Otto-von-Guericke-Universität Magdeburg
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Robotik trifft Kunst: Der Lightpainting-Roboter 2.0
No full textIm Rahmen des LEGO-Mindstorms- Praktikums 2023 wurde der letztjährige Lightpainting-Roboter ,,Sally can Draw‘‘ weiterentwickelt. Dieser ist in der Lage, mittels einer Lichtquelle zweidimensionale Formen und Zeichnungen darzustellen. Die dazu verwendeten Konzeptideen sowie deren technische Umsetzungen, Verbesserungen und Probleme werden im Folgenden chronologisch dargestellt
Yet another elasto-plasticity formulation
No full textAn elasto-plasticity formulation is presented that requires no intermediate (stress-free) configuration, since all describingtensors are solely of proper-Eulerian or proper-Lagrangean type. This formulation - based on commutative-symmetrical elasticplastic stretch tensor products with symmetrizing-rotation tensors in the middle - is discussed and compared with the Bilby-Kröner-Lee formulation, which defines an intermediate (stress-free) configuration that is not well-determined - as noted, e.g., by Casey & Naghdi (1980). For an Eulerian continuum description, it turns out that the symmetric elastic part of the presented formulation (with only proper-Eulerian tensors) has similarities with the elastic tensor factor eF of the Bilby-Kröner-Lee multiplicative elasto-plastic decomposition F = eF . pF of the deformation gradient F. From a Lagrangean point of view, however, the symmetric elasticity tensors of the two models differ considerably: the elastic right stretch and Cauchy-Green deformation tensor of the new formulation are proper-Lagrangean tensors, while the corresponding tensors of the Bilby-Kröner-Lee formulation are not well-determined, since they refer to an intermediate (stress-free) configuration. As finite orthotropy modeling requires a material reference configuration in which (imaginary) fibers are perpendicular to each other, finite elastic orthotropy and finite plastic orthotropy can only be modeled simultaneously based on proper-Lagrangean elastic and plastic tensors provided by commutative-symmetrical deformation tensor products and not by Bilby-Kröner-Lee formulations
Wer behaust hier wen? Sozial-ökologische Wohnungsfragen in und für die Postwachstumsstadt
No full textDie Wohnungskrise wird in diesem Artikel im Spannungsfeld sozial-ökologischer Mehrfachkrisen verortet, die insbesondere durch gesellschaftliche Wachstumsorientierung und -zwänge verursacht werden. Aus Sicht von Postwachstumspolitiken lohnt sich der Verweis auf die Perspektive der starken Nachhaltigkeit: Wohnungsmärkte sind letztlich in gesellschaftliche (Re-)Produktionsprozesse eingebettet, die wiederum nur durch das fragile „Haus der Erde“ ermöglicht werden. Nach einer Herausarbeitung der sozialen und ökologischen Dimension gegenwärtiger Wohnungsfragen formuliert der Beitrag drei konkrete, bislang wenig beachtete Hebelpunkte: Ein Neubau-Moratorium zur Reduzierung der Flächenneuinanspruchnahme, die Begrenzung des individuellen Wohnflächenkonsums sowie die verdrängungsneutrale Steigerung der energetischen Sanierungsquote. Zuletzt werden wohnungspolitische Akteurslogiken und multiple Strategien beleuchtet.In this article, the housing crisis is located in the context of socio-ecological multiple crises, which are caused in particular by societal growth orientation and imperatives. From the perspective of post-growth policies, it is worth referring to the perspective of strong sustainability: housing markets are ultimately embedded in social (re)production processes, which in turn are only made possible by the fragile "house of the earth". After elaborating the social and ecological dimensions of current housing issues, the article formulates three concrete points of leverage that have received little attention so far: A moratorium on new constructions of buildings to reduce the use of new land, the limitation of individual consumption of living space as well as a displacement-neutral increase in the rate of energy-efficient renovations. Finally, it examines the logic of housing policy actors and multiple strategies
Stability analysis of hygro-magneto-flexo electric functionally graded nanobeams embedded on visco-Pasternak foundation
No full textIn this paper, the stability analysis of hygro-magneto-flexo electricity (HMFE) on functionally graded (FG) viscoelastic nanobeams accommodate in viscoelastic foundation based on nonlocal elasticity theory is addressed. Higher order refined beam theory is used for the expositions of the displacement components and the viscoelastic foundation is included with Winkler-Pasternak layer. The governing equations of nonlocal gradient viscoelastic FG nanobeam are obtained by Hamilton\u27s principle and solved by administrating an analytical solution for different boundary conditions. A power-law index model is adopted to describe continuous variation of temperature-dependent material properties of FG nanobeam. A parametric study is presented to inquire the effect of the nonlocal parameter on various physical variables
SURFACE LAYER’S SOUND SPEED PROFILES: CLIMATOLOGICAL ANALYSIS AND APPLICATION FOR THE CNOSSOS-EU NOISE MODEL
No full textNoise pollution and exposure are important environmental issues that need to be investigated and regulated. To do this,we need to know about micrometeorology to figure out how noise travels from the source to the receiver. Accordingly, the sound propagation part of the common noise assessment methods (CNOSSOS-EU) developed by the European Commission for different sources of noise needs detailed meteorological databases. Using data from the SYNOP stations maintained by the Hungarian Meteorological Service (HMS) and the ERA5 meteorological reanalysis database, the standard noise propagation conditions are determined. The primary objective of this study is to ascertain the probability distribution of stability classes for a variety of source-receiver orientations, utilizing either 25 or 2 stability classes, and several different aggregation levels. Relative frequencies and year-to-year variability have been calculated for favourable noise propagation conditions where the sound speed profile grows with height (downward refraction condition) and unfavourable noise propagation conditions where the sound speed profile constant or decreases with height (so-called homogeneous conditions). Favourable noise propagation occurs in approximately one-third of cases during the daytime while in approximately two-third of cases during the evening and night-time where the noise exposure is increasing. Furthermore, using the SoundPLANnoise software, sound propagation model calculations were performed on a study area near Budapest, using different values of parameter pf describing the probability of occurrence of favourable conditions on sound propagation during different periods of the day. This area is crossed by Highway 4, which is a major road according to the 49/2002 EU Directive, as it has more than three million vehicles passing on the examined section every year. The results show considerable deviations in annual average A-weighted sound levels calculated using different versions of parameter pf. The largest difference between the A-weighted sound levels calculated with the highest and lowest generated annual pf values was 1.65 dB(A); 1.42 dB(A) and 0.75 dB(A) for day, evening and night periods, respectively. 
Turbulent mixing simulation using the Hierarchical Parcel-Swapping (HiPS) model
No full textTurbulent mixing is an omnipresent phenomenon that permanently affects our everyday life. Mixing processes alsoplays an important role in many industrial applications. The full resolution of all relevant flow scales often poses a major challenge to the numerical simulation and requires a modeling of the small-scale effects. In transported Probability Density Function (PDF) methods, the simplified modeling of the molecular mixing is a known weak point. At this place, the Hierarchical Parcel-Swapping (HiPS) model developed by A.R. Kerstein [J. Stat. Phys. 153, 142-161 (2013)] represents a computationally efficient and novel turbulent mixing model. HiPS simulates the effects of turbulence on time-evolving, diffusive scalar fields. The interpretation of the diffusive scalar fields or a state space as a binary tree structure is an alternative approach compared to existing mixing models. The characteristic feature of HiPS is that every level of the tree corresponds to a specific length and time scale, which is based on turbulence inertial range scaling. The state variables only reside at the base of the tree and are understood as fluid parcels. The effects of turbulent advection are represented by stochastic swaps of sub-trees at rates determined by turbulent time scales associated with the sub-trees. The mixing of adjacent fluid parcels is done at rates consistent with the prevailing diffusion time scales. In this work, a standalone HiPS model formulation for the simulation of passive scalar mixing is detailed first. The generated scalar power spectra with forced turbulence shows the known scaling law of Kolmogorov turbulence. Furthermore, results for the PDF of the passive scalar, mean square displacement and scalar dissipation rate are shown and reveal a reasonable agreement with experimental findings. The described possibility to account for variable Schmidt number effects is an important next development step for the HiPS formulation. This enables the incorporation of differential diffusion, which represents an immense advantage compared to the established mixing models. Using a binary structure allows HiPS to satisfy a large number of criteria for a good mixing model. Considering the reduced order and associated computational efficiency, HiPS is an attractive mixing model, which can contribute to an improved representation of the molecular mixing in transported PDF methods
Consistent Routing for Local Same-Day Delivery via Micro-Hubs
No full textAn increasing number of local shops offer local same-day delivery to compete with the online giants. However, the distribution of parcels from individual shops to customers reduces the rare consolidation opportunities in the last mile even further. Thus, shops start collaborating on urban same-day delivery by using shared vehicles for consolidated transportation of parcels. The shared vehicles conduct consistent daily routes between micro-hubs in the city, serving as transshipment and consolidation centres. This allows stores to bring orders to the next micro-hub, where the parcel is picked up by a vehicle and delivered to the microhub closest to its destination – if it is feasible with respect to the vehicle’s consistent daily schedule. Creating effective schedules is therefore very important. The difficulty of finding an effective consistent route is amplified by the daily uncertainty in order placements. We model the problem as a two-stage stochastic program. The first stage determines the vehicle schedules. The second stage optimises the flow of realized orders. The goal is to satisfy as many orders per day as possible with the shared vehicles. We propose a multiple scenario approach and suggest problem-specific consensus functions for this framework. We assess the method’s performance against an upper bound, a practically-inspired heuristic, and the original consensus function. Our approach clearly outperforms the practically-inspired heuristic and the original consensus function. We observe that collaborative delivery via micro-hubs is worthwhile for delivery time promises of two hours or more. Noticeably, for these service promises, the cost of consistency are surprisingly low
Modeling and simulation of power system dynamics for studying the impacts of increasing wind power in a weak grid system
No full textDie Sorge um die Umwelt und die Bemühungen, die Abhängigkeit von fossilen Brennstoffen zu verringern, führen dazu, dass erneuerbare Energieressourcen bei der Stromerzeugung in den Vordergrund rücken. Die Windenergie hat in den letzten Jahrzehnten weltweit einen rasanten Ausbau erfahren, was zu Herausforderungen im Systembetrieb in Bezug auf Frequenz- und Spannungsstabilität führt. Die Untersuchung und Bewertung der Auswirkungen großer Windkraftanlagen auf die Dynamik des Stromnetzes ist ein wesentlicher Schritt zur Verbesserung des frequenz- und spannungsstabilen Betriebs. Ziel dieser Arbeit ist es, die Auswirkungen der Windenergie zu untersuchen und Maßnahmen zur Verbesserung des dynamischen Verhaltens von elektrischen Netzen mit verschiedenen Netztopologien vorzuschlagen. Der doppelt gespeiste Asynchrongenerator (DFIG) ist der am weitesten verbreitete Windturbinentyp, da er mit variabler Windgeschwindigkeit betrieben werden kann, über einen Teillastumrichter verfügt und in der Lage ist, den Generator bei anormalen Bedingungen synchron mit dem Netz zu halten. Daher wird in dieser Arbeit ein detailliertes Modell von DFIG-basierten Windturbinengeneratoren verwendet, um den Einfluss eines steigenden Windenergieanteils in einem großen Netzsystem zu veranschaulichen. Die netzdynamischen Modelle umfassen Synchrongeneratoren, automatische Spannungsregler, Turbinenregelungssysteme, DFIG-basierte Windturbinengeneratoren, verschiedene Steuerelemente, Übertragungssysteme und Transformatoren. Die mathematischen, dynamischen Modelle werden mit Hilfe numerischer Integrationstechniken gelöst. Zu diesem Zweck wird ein Tool zur dynamischen Simulation von Stromsystemen in MATLAB/Simulink entwickelt. In dieser Arbeit werden vier Testnetze, einschließlich einer Fallstudie für das äthiopische Stromnetz, verwendet, um die dynamischen Reaktionen in verschiedenen Netztopologien zu simulieren. Die verschiedenen Simulationsszenarien und Netztopologien bestätigen, dass eine Erhöhung des Windenergieanteils die transiente Stabilität des Systems verschlechtert. Die Ergebnisse zeigen, dass die Erhöhung des Windkraftanteils zu einer Verringerung der dynamischen Spannungsstabilitätsreserven, einer Erhöhung der Frequenzänderungsrate und einer Verringerung der Wirkleistungsübertragungsfähigkeit führen. Darüber hinaus wird beobachtet, dass sich die DFIGs als Reaktion auf Netzspannungseinbrüche bei schweren Fehlerereignissen selbst vom Netz trennen, um die rotorseitigen Back-to-Back-Umrichter vor Rotorüberströmen zu schützen. Die dynamischen Auswirkungen von DFIG-basierten Windgeneratoren werden bewertet und es werden Regelungsstrategien vorgeschlagen, die die Windgeneratoren nicht nur unterstützen, am Netz zu bleiben, sondern auch die Systemstabilität bei Netzstörungen zu verbessern. Es wird eine neue Regelungsstrategie vorgeschlagen, um die Fähigkeit von DFIG-Windgeneratoren zum Niederspannungs-Ride-Through zu verbessern. Die vorgeschlagene Regelungsstrategie umfasst die gemeinsame Anwendung eines STATCOM und einer Rotor-Überdrehzahl-Strategie. Der STATCOM wird hauptsächlich eingesetzt, um den Stator-Spannungseinbruch zu reduzieren und die Rotor-Überdrehzahl-Strategie wird verwendet, um die Rotorüberströme bei Stator-Spannungseinbrüchen zu reduzieren, was zu einer geringeren Ausgangsleistung führt. Die Überdrehzahlregelung wird eingesetzt, um den Wirkleistungssollwert so anzupassen, dass er proportional zum Spannungseinbruch an der Klemme ist. Auf diese Weise wird die Turbine veranlasst, die Rotordrehzahl bis zur maximal zulässigen Grenze zu erhöhen, sodass die Ausgangsleistung so lange reduziert bleibt, bis der Spannungseinbruch am Stator durch den schnell reagierenden STATCOM wieder ausgeglichen wird. Der zweite Beitrag dieser Doktorarbeit befasst sich mit Lösungen für die Verbesserung der Netzfrequenzstabilität bei höherem Durchdringungsgrad von Windenergie. Es wird ein neuer Ansatz vorgestellt, mit dem die Betreiber von Windkraftanlagen ihre Windenergieerzeugung so planen können, dass sie den Prozess der Wiederherstellung der Netzfrequenz unterstützen. Das vorgeschlagene Frequenzregelungsmodul auf Anlagenebene überwacht den Beitrag der verschiedenen Betriebseinheiten in einem großen Windpark auf der Grundlage ihrer jeweiligen Windgeschwindigkeit und der Netzfrequenzabweichung. Die dynamischen Simulationsergebnisse zeigen, dass die vorgeschlagenen Spannungsund Frequenzregelungsstrategien effizient sind, um den Spannungsabfall in Echtzeit zu regulieren und die Steuerbarkeit von Spannung und Frequenz bei einem höheren Durchdringungsgrad der Windenergie zu verbessern.The issue of environmental concerns and efforts to decrease dependency on fossil fuel are bringing renewable energy resources to the mainstream of electric power generation. Wind energy has undergone fast expansions worldwide in recent decades, but it also results in challenges in system operation related to frequency and voltage stabilities. Investigating and evaluating the impact of large-scale wind power on power system dynamics is an essential step to enhance the stable operation of frequency and voltage. This thesis work is intended to investigate the impacts of wind power and propose mitigation measures to enhance the dynamic behaviors of power systems with various network topologies. Doubly-fed induction generator (DFIG) is the most common wind turbine type due to its ability to operate at variable wind speed, partial-load converter and its capability to sustain the generator in synchronism with the system during abnormal conditions. Therefore, in this thesis work, a detailed model of DFIG-based wind turbine generators is employed to illustrate the influence of increasing wind power share in a large network system. The network dynamic models include synchronous generators, automatic voltage regulators, turbine-governor systems, DFIG-based wind turbine generators, various control elements, transmission systems and transformers. The mathematical dynamic models are solved using numerical integration techniques. For this purpose, a power system dynamic simulation tool is developed in the MATLAB/Simulink environment. In this thesis work, four test networks, including a case study for the Ethiopian power system, are employed to simulate the dynamic responses in different network topologies. The various simulation scenarios and network topologies confirm that an increase in wind power share deteriorates the transient stability of a system. The results effectively show that the increase in wind power penetration level has contributed to reducing the dynamic voltage stability margins, increasing the rate of change of frequency and reducing active power transfer capability. Moreover, the DFIGs are observed to disconnect themselves from the grid in response to grid voltage dips under severe fault events so as to protect the back-to-back rotor-side converters from rotor over-currents. The dynamic impacts of DFIG-based wind generators are assessed and control strategies are proposed to help them not only to remain connected but also to support the system stability during grid fault events. A new control strategy is contributed to enhance the low voltage ride-through capability of DFIG-based wind generators. The proposed control strategy comprises a joint application of a STATCOM and rotor over-speeding schemes. The STATCOM is mainly employed to improve the stator voltage dip and the rotor overspeeding strategy is employed to reduce the rotor over-currents during stator voltage dips that results in reduced output power. The over-speeding scheme is initiated to adjust the active power reference to be proportional to the voltage dip at the terminal. Thus, the turbine is made to increase the rotor speed till the maximum allowable limit so that the output power remains reduced until the stator voltage dip is recovered by the fast-acting STATCOM. The second contribution is related to solutions to the grid frequency challenges with higher penetration level of wind power. A new approach is introduced by which wind power plant operators can schedule their wind power generations so as to give support in the frequency restoration process. The proposed frequency control module at plant level monitors the contribution of various operating units in a large wind farm, based on their respective wind speed and the grid frequency deviation. The time-domain simulation results indicate that the proposed voltage and frequency control strategies are efficient to regulate the real-time voltage dip and enhance the voltage and frequency controllability with higher penetration level of wind power
Artemis: Der Bogenschießroboter
No full textIm Rahmen des diesj¨ahrigen LEGOMindstorms-Praktikums wurde mit Hilfe des LEGO-Baukastens ein Roboter konstruiert, der Mithilfe von NXT-Steuerung und MATLAB-Programmierung in der Lage ist, einen Pfeil abzuschießen und mit Hilfe eines Abstandssensors ein Obejkt in einem vorgegebenen Bereich zu erkennen. In den folgenden Abschnitten werden die einzelnen Schritte der Entwicklung des Roboters Artemis beschrieben
Smart Car
No full textDas Projektseminar Elektrotechnik und Informationstechnik findet jährlich an der Otto-von-Guericke-Universität Magdeburg statt. Im Rahmen des diesjährigen Projektseminars wurde ein Auto entwickelt. Dieses trägt dazu bei, die Zahl der Verkehrsunfälle zu reduzieren. Die Entwicklung und Konstruktion des Autos erfolgte auf Basis von LEGO Mindstorms-Sets und dem LEGO NXT-Steuerungscomputer. Die softwaretechnische Umsetzung wurde mit MATLAB realisiert. In diesem Papier werden der Aufbau und die Funktionsweise des Autos vorgestellt. Des Weiteren werden einige Herausforderungen während des Konstruktionsprozesses sowie deren Lösungsansätze diskutiert