University of Siegen
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Publication Access status: Open Access , Analyse gesamtsystemischer Zusammenhänge von hybriden Antriebsstrangkonzepten bezüglich kundenrelevanter Anforderungen(2020)System-level design of hybrid electric vehicles focuses on the analysis and optimization of hybrid powertrains within a high-dimensional solution space with regard to the variety of variants and requirements. Existing methodical approaches are based on the identification of optimal system designs with regard to predefined powertrain requirements. In this thesis, the possibility of substituting certain engine-power classes of the product portfolio with hybrid concepts whose system performance is largely defined by the electric drive system is investigated. A significant reduction of the combustion engine power within the overall system compared to conventional drives requires a verification of the original powertrain requirements in the context of customer relevance. In contrast to previous investigations, the method presented in this thesis identifies for the first time the demands in power and energy sizing of the electric drive system and the electric energy storage, which result from the fulfillment of original powertrain requirements. The additional influence on driving comfort spans a region of conflict between powertrain efficiency, performance and driving comfort, in which the relevant overall systemic relationships for decision-making are analysed. For this purpose, systemic influencing factors such as a reduction of the maximum velocity requirement are identified and their influence on a customer-relevant powertrain design is evaluated. In the course of this work, visualization techniques from the field of machine learning provide a comprehensible and transparent basis for substantiated decision-making. Furthermore, well-known optimization-based operating strategy approaches are extended by methods of fuzzy logic with regard to the solution of the problem. The latter is mainly enabled by considering a timeframe-based analysis for the complete characterization of the performance requirements of the electrical components.Source Type:Doctoral ThesisSeries:Schriftenreihe der Arbeitsgruppe Mess- und Regelungstechnik - Mechatronik, Department MaschinenbauVolume number:61 8 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Optimierung der mechanischen Eigenschaften von Beta-Titanlegierungen durch die Verwendung von Wasserstoff als temporäres Legierungselement(2019)The use of hydrogen as a temporary alloying element as a part of the thermomechanical process is considered being a promising approach for improving mechanical properties especially of titanium cast alloys. The present study shows, that this so-called thermohydrogen processing (THP) improves monotonic and cyclic strength even of complex metastable beta titanium alloys by taking advantage of the reversibility of the titanium-hydrogen interaction and by exerting an selective influence on phase equilibria, kinetics of phase transformation and the distribution of alloying elements. Thermohydrogen processing is applied on two beta titanium alloys differing considerably with respect to beta stability. Thermohydrogen processing of highly beta stabilized titanium alloy Ti-3Al-8V-6Cr-4Mo-4Zr (Ti-38644) increases yield strength by more than 4 % and fatigue limit by 8 % as compared to a duplex aged (reference) microstructure. The 5-step Hi-Read-process (Hydride-induced Rearrangement of Dislocations) optimizes the precipitation behavior of the secondary alpha phase in a completely recrystallized beta microstructure, coming from hydride-induced multiplication of dislocations within beta solid solution. Designating the THP contributes to the mechanism of dislocation formation as initially described by Frank Read. The 4-step HiRe-Beta process (Hydride-induced Recrystallization of beta Phase) applied on high-strength beta titanium alloy Ti-10V-2Fe-3Al (Ti-1023) provides the best way to improve strength by maximizing the driving force for precipitation of the secondary alpha phase. Despite complete destabilization of globular primary alpha phase, hydride-induced recrystallization of the beta phase simultaneously preserves a fine beta microstructure. As compared to the conventionally heat-treated material the THP increases yield strength by more than 8 %. Fracture of samples occurred within the elastic region of the stress-strain curve is attributed to the existence of process-related crack formation. Both THP designed for beta titanium alloys fundamentally differ with respect to hydrogen uptake. The Hi-Read process utilizes time-independent Sieverts-type hydrogenation behavior at high temperature. In contrast, hydride formation already occurs during hydrogenation at low temperature in the HiRe-Beta process. Therefore, the volume fraction of precipitated hydrides is immediately affected by hydrogenation time (time-dependent hydrogenation behavior). Determination of THP-strategies for both metastable beta titanium alloys relies on studies on the relationship between microstructure and mechanical properties, exhibiting the detrimental effect of precipitate-free zones and grain boundary alpha phase, both decreasing yield strength and fatigue limit and additionally promoting the propagation of long cracks. Studying the kinetics and thermodynamics of hydrogen uptake and the effect of hydrogen on phase stability enables to establish specified hydrogen concentrations in metastable beta titanium alloys Ti-38644 and Ti-1023. Evaluation of hydrogen concentration profiles emerged from diffusion annealing of electrochemically hydrogenated small titanium bars enables the determination of hydrogen diffusion coefficients. Assuming an exclusively diffusion-controlled (ideal) hydrogen uptake, the hydrogen diffusion coefficients are used to calculate necessary hydrogenation times by means of numerical methods. Volumetric measurements reveal that even at temperatures above the stability limit of the titanium oxide an exclusively diffusion-controlled hydrogen uptake cannot be facilitated. The impact of the surface on the kinetics of hydrogen uptake is therefore considered by means of correction factors, which are used to estimate the times being necessary for complete hydrogen uptake and release. Specified hydrogen concentrations and homogeneous hydrogen distributions are established within the cross-sections of the samples in this way. Coating samples of both beta titanium alloys electrochemically with the hydrogen absorber palladium considerably accelerates the kinetics of hydrogen uptake, thereby facilitating feasible process times even at lower temperatures. Both beta titanium alloys studied exhibit a distinct reduction of the transition temperature (beta transus) with increasing hydrogen concentration. In case of Ti-38644 the modified beta transus decreases until the eutectoid transformation of the beta phase into alpha phase and hydride begins. For Ti-1023 the modified beta transus decreases continuously and remains constant over a wide range of hydrogen concentration after reaching the eutectoid temperature. Since hydride formation (eutectoid transformation) is considered to play the key role for microstructure optimization via thermohydrogen processing the location of the solubility limit of beta solid solution for hydrogen is determined roughly within the phase diagrams of both beta titanium alloys. Knowing the modified beta transus and the hydrogen solubility limit of beta solid solution is essential since it enables specification of thermohydrogen process routes within the phase diagrams of beta titanium alloys Ti-38644 und Ti-1023. Thermohydrogen processing of metastable beta titanium alloys Ti-38644 und Ti-1023 led to microstructures which cannot be facilitated through conventional thermomechanical processes. Additionally, the Hi-Read and HiRe-Beta thermohydrogen process provide the opportunity for adjusting the microstructures of both beta titanium alloys gradually according to prevailing load situations. Therefore, both THP show all features of an innovative heat treatment.Source Type:Doctoral ThesisSeries:Siegener werkstoffkundliche BerichteVolume number:244 11 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Abschlussbericht zum BMBF-Forschungsprojekt MultiForm - Entwicklung eines Hochleistungsverfahrens zur simultanen Umformung von faserverstärkten Kunststoffen mit Metallblechen : Projektzeitraum: 01.08.2014-31.07.2018(2019); ; Die Herstellung von Hybridbauteilen aus Metall und Kunststoff für automobile Leichtbauanwendungen erfolgt in der Regel in getrennten Fertigungsschritten und Werkzeugen. Für die Blechumformung ist das Tiefziehen ein etabliertes Fertigungsverfahren und Kunststoffbauteile können in Spritzgieß- oder Fließpress-Verfahren hergestellt werden. In einer nachfolgenden Fügeoperation können Metall und Kunststoff zu einem hybriden Bauteil zusammengeklebt werden. Im öffentlich geförderten Forschungsprojekt „MultiForm“ wird eine wirtschaftliche Verfahrenskombination („Hybridpressen“) des Tiefziehens von Metallblechen und dem Fließpressen von langfaserverstärkten Thermoplasten (LFT) entwickelt. Dabei wirkt die thermoplastische Kunststoffschmelze wie ein Wirkmedium in hydromechanischen Prozessen (z.B. Innenhochdruckumformung) und formt zusammen mit dem Werkzeugstempel hochfeste Stahlbleche. Durch Einsatz eines Haftvermittlers als Vorbeschichtung auf dem Metallblech wird gleichzeitig eine stoffschlüssige Verbindung zum Thermoplast hergestellt. Somit werden beim Hybridpressen drei Fertigungsschritte (Metall Tiefziehen, LFT-Fließpressen, Kleben) in einem Schritt vereint, sodass Hybridbauteile deutlich wirtschaftlicher gefertigt werden können. Das neuartige Verfahren „Hybridpressen“ wird im vorliegenden Projektbericht anhand zweier Bauteile aus dem Fahrwerksbereich demonstriert.Source Type:BookSeries:Siegener Schriftenreihe AutomobiltechnikVolume number:33 6 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Energy management system for automated driving(2019)With increasing levels of driving automation, the responsibility for the vehicle control and passengers’ safety is shifted from the driver towards the automation system. This results in increased reliability and safety requirements for the subsystems involved in the automated vehicle motion. In case of a safety-critical failure, an automated transition to a vehicle standstill must be executed without any driver interaction and supervision for high and full driving automation. Therefore, in addition to the functionality of the safety-critical subsystems, also their reliable power supply for the duration of the transition to the standstill must be guaranteed by the vehicle powernet. According to the functional safety norm ISO 26262, all safety-critical subsystems must be designed with an appropriate automotive safety integrity level (ASIL). Since reliable power supply is one of the prerequisites for their correct functionality, it becomes safety-critical itself. The need for new fail-operational powernet topologies and appropriate control strategies fulfilling the increased reliability and availability requirements arises. The work presented in this dissertation proposes a new generic energy management system for the safety-based range extension, supporting the optimization of the powernet and powertrain control for arrival at the safest possible location for the passengers. The key element of the proposed energy management system is the online energy distribution optimization with an integrated degradation concept. Using the predicted values for the available energy resources and for the energy required to complete a driving mission, the control strategy automatically adapts the energy flows within the vehicle powernet. Furthermore, it estimates appropriate degradation step for the comfort loads, driving profile and driving destination with the goal to reach the safest destination with a maximum of comfort in a minimum of time under consideration of the available energy resources. With this approach, also the fault reactions of the functional safety concept, required by ISO 26262 for all safety-critical functions, are automated and optimized. In this way, the energy management system finds autonomously the best suited fault reactions for achieving the defined control goal. The energy demand required for the completion of a driving mission depends on the velocity profile, road slope and stops on the way to the destination. Using the electronic horizon, a driving trajectory from the current vehicle position to the destination is approximated online, which is then used for the route based estimation of the required propulsion energy. In powertrain topologies with multiple traction motors, the overall driving efficiency and hereby also the driving range can be increased significantly with an appropriate strategy for the torque distribution between individual motors. Therefore, a torque distribution profile is estimated online based on the theory of optimal control for the entire driving mission, enabling an accurate and realistic prediction of the propulsion energy required for the safety based range extension. In addition to the driving efficiency increase also symmetrical discharge of independent traction batteries, required for approximately the same driving range in case of a breakdown of one battery, is incorporated in the control strategy. Furthermore, also the balancing of the energy losses in powertrain components is considered for the torque distribution, which is required to avoid their overheating possibly leading to faster aging and wear. The application of the generic framework for the energy management system is exemplified on two different powernet and powertrain topologies with a single and multiple traction motors. The benefits are verified using simulation results for both, fault-free and failure case operation. With the proposed torque distribution strategy a decrease in the energy losses of up to 12 % for the given use case was achieved. Also the optimization of the fault reactions shows the ability of the energy management system to achieve the control goals despite multiple faults. In addition to the concepts presented in this dissertation, also runtime optimized algorithms are proposed, implemented and validated by means of simulation. By enhancing the reliability of the power supply and fail-operability of the powertrain, the work presented in this dissertation contributes to the establishment of the evolving automated driving technology and provides a generic framework for model predictive energy management for future implementation in automated vehicles.Source Type:Doctoral Thesis11 8 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Ermittlung von Materialkennwerten für additiv gefertigte Bauteile im Kreuzverbund nach dem FDM-Verfahren zur numerischen Berechnung der FestigkeitseigenschaftenAdditiv gefertigte Bauteile finden immer stärkeren Einzug in Produktionsprozesse. Es ist daher unerlässlich im Vorfeld eine Aussage zu deren Festigkeitseigenschaften treffen zu können. Üblicherweise werden Aussagen zum Festigkeitsverhalten von Bauteilen mit beliebiger Geometrie mit Hilfe von FEM-Analysen gewonnen. Hierfür werden Elastizitätsgrößen und Materialgesetze als Eingangsparameter für die durchzuführende Analyse benötigt. In den vorliegenden Untersuchungen wird gezeigt, welches Materialgesetz sich für die Beschreibung eines Bauteils eignet, dass mit Hilfe des FDM-Verfahrens im Kreuzverbund generiert wird. Weiterhin wird gezeigt, wie die benötigten Elastizitätsgrößen einfach messtechnisch mit einem alternativen Verfahren zum klassischen Zugversuch ermittelt werden können.Source Type:Article6 12 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , The influence of forcing schemes on the diffusion properties in pseudopotential-based Lattice Boltzmann models for multicomponent flowsThe talk presents the influence of the choice of forcing schemes in pseudopotential-based LBM methods for multi-phase flows (e.g. Shan & Doolen (1995) or He & Doolen (1998)) on the diffusion coefficient, obtained via Chapman-Enskog analysis. The critical value of G is obtained und known relations used in the literature are subsequently derived based on this theory (e.g. Huan et al. (2007)). The often observed shift at tau=1 for the critical value of G can be directly derived. Simulation show excellent agreement between the diffusion coefficient and Fick’s law for various values of G.Source Type:Other3 6 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Stand zur IT-Sicherheit deutscher Stromnetzbetreiber : technischer BerichtInnerhalb des Forschungsprojektes „Sichere Informationsnetze bei kleinen und mittleren Energieversorgern“ (SIDATE) wurde eine Umfrage zum Stand der IT-Sicherheit bei deutschen Stromnetzbetreibern durchgeführt. Das Projekt selbst beschäftigt sich mit der Informations- Sicherheit bei kleinen und mittleren Energieversorgern. Zur Durchführung der Umfrage wurden alle 881 im August 2016 bei der Bundesnetzagentur gelisteten Betreiber angeschrieben. In dem Umfragezeitraum vom 1. September 2016 bis zum 15. Oktober 2016 antworten 61 (6.9%) der Betreiber. Der Fragebogen fokussiert die Umsetzung der rechtlichen Anforderungen und die Implementierung eines Informationssicherheitsmanagementsystems (ISMS). Weiterhin wurden Fragen zu dem Leitsystem, Netzaufbau, Prozessen, organisatorischen Strukturen und der Büro-IT gestellt.Source Type:Book1 8 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , VHCF7 Seventh International Conference on Very High Cycle Fatigue : July 3-5, 2017, Dresden, Germany(2017)The proceedings contain the contributions wich are delivered as presentations during the Seventh International Conference on Very High Cycle Fatigue taking place from 3rd through 5th of July 2017 in Dresden, GermanySource Type:Conference ProceedingsSeries:Siegener werkstoffkundliche BerichteVolume number:142 9 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Parallel multi-scale simulations with octrees and coupled applications(2016)Physical simulations often require the consideration of many phenomena and scales. For example in aeroacoustic problems, both, the flow generating the noise and the sound wave propagation needs to be considered. This work investigates numerical approaches to such problems on large distributed and parallel computing systems. The coupling framework KOP is parallelized as far as possible and to overcome fundamental scalability limits a new framework APES is developed. Both implementations utilize high-order discretizations, as these allow for accurate simulations with less degrees of freedoms than lower order methods. This property of high-order methods is an important feature for modern supercomputing systems, as memory to represent degrees of freedom in a simulation is a scarce resource. The presented methods enable the transient simulation of multi-scale setups but detailed resolutions still require large amounts of computational resources. A focus is put on the efficient utilization of modern computing systems to address this need. Besides the scalability of the implementations, the importance of single core optimization and vectorization is illustrated. KOP uses discrete points to realize the coupling and allows for the interaction between domains with differing discretizations and solved equation systems. Arbitrary mesh configurations are supported and both, structured and unstructured mesh solvers are available in the framework. In both framworks explicit time integration methods are deployed to resolve the time dependent simulations. The coupling allows for a varying time step width over the participating domains by a sub-cycling method. Various conservation laws can be solved by the presented frameworks ranging from Maxwell’s equations and linearized Euler equations to full compressible Navier-Stokes equations. A fully distributed coupling approach is developed that allows for coupling of those in a large-scale simulation to solve, for example, aeroacoustic problems. APES enables high-order discretizations in the spectral regime. It involves a fully scalable toolchain for mesh-based simulations featuring a mesh generation and a post-processing tool to support the solvers. The common foundation of these tools is an Octree representation for the mesh, and this work specifically covers the generation of high-order geometry approximations in the developed mesh generator Seeder. This robust mechanism works for arbitrarily complex surfaces and offers a practical way to tackle engineering tasks with spectral element discretizations.Source Type:BookSeries:Simulation techniques in Siegen - STSVolume number:11 3 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Mörtel für die Erhaltung historischer Kalkputze : Haftmörtel, Hinterfüllmörtel und Kalkputze(1997)Im Rahmen der Dissertation wurde ein Mörtelsystem für die Restaurierung historischer Kalkputze entwickelt. Die Literaturübersicht dieser Dissertation befaßt sich mit Ursachen für Schäden an Putzen, dabei wird ausführlich auf herstellungsbedingte Fehler eingegangen und chemische, physikalische und mikrobiologische Gründe für die Entstehung von Putzschäden behandelt. Ausführlich werden mögliche Schäden durch ungeeignete Restaurierungsmörtel behandelt, die z. B. Alkalisalze eintragen, aber auch Ettringit- und Thaumasitbildung durch Reaktionen mit Sulfaten in historischen Mörtel verursachen können. Ein bedeutender Teil der Dissertation widmet sich der Untersuchung von historischen Putzen der Torhalle in Lorsch, der Einhardbasilika in Steinbach, des Magdeburger Domes und des ehemaligen Zisterzienserklosters Heydau in Morschen. Die Eigenschaften dieser Putze werden umfangreich nicht nur hinsichtlich ihrer Mörtelzusammensetzung und ihrer mechanischen Eigenschaften, sondern auch ihrer hygrischen Eigenschaften (Wasseraufnahme, Wasserabgabe, Wasserdampf-Diffusionswiderstand), ihrer Porenstruktur und Phasenausbildung geprüft. Die gewonnenen Daten dienten zur Definition von Anforderungsprofilen für Restaurierungsmörtel, die zum einen den historischen Bestand sichern (Haftmörtel, Hinterfüllmörtel), zum anderen als Ersatzmörtel bei Fehlstellen dienen (Kalkputze) sollen. Die verschiedenen Mörtel sollen die folgenden Aufgaben bei einer Restaurierung übernehmen: - Haftmörtel sollen vor der Verfüllung hohlliegender Putzbereiche zu deren Randsicherung und zum Wiederbefestigen lockerer Putzschollen dienen und mechanisch wieder leicht entfernbar sein, ohne die Altsubstanz zu schädigen. - Hinterfüllmörtel dienen zum Verfüllen hohlliegender Putzpartien, die im Anschluß an die Maßnahme wieder einen ausreichenden und dauerhaften Verbund mit dem Untergrund aufweisen sollen. Sie können drucklos mit Spritzen eingebracht werden und müssen ein gutes Penetrationsvermögen aufweisen, damit alle Hohlräume sicher gefüllt werden. - Kalkputze entweder auf Basis von Sandkalk (mit feuchtem Sand trocken gelöschter Branntstückkalk) oder auf Basis handelsüblichen Weißkalkhydrates (WKH) sollen, möglichst exakt den historischen Vorbildern nachgestellt, als Ersatz für abgängigen historischen Putz eingesetzt werden.Source Type:Book6 9
