Refine
Document Type
- Habilitation thesis (18) (remove)
Has Fulltext
- yes (18)
Is part of the Bibliography
- no (18)
Year of publication
Keywords
- Computersimulation (2)
- Oscillator (2)
- Oszillator (2)
- Phase noise (2)
- Phasenrauschen (2)
- Recycling (2)
- Abraumförderbrücke (1)
- Abraumkippe (1)
- Active inductor (1)
- Active medium forming (hydroforming) (1)
- Adsorption (1)
- Advanced welding manufacturing (1)
- Aeroelasticity (1)
- Aeroelastizität (1)
- Aktive Spule (1)
- Aufbereitung (1)
- Bemessung (1)
- Beneficiation (1)
- Bergbaunachfolgelandschaft (1)
- Biogas residues (1)
- Braunkohlenbergbau (1)
- Ceramics (1)
- Cereal straws (1)
- Cold pressure welding (1)
- Competition theory (1)
- Computational welding mechanics (1)
- Constraint qualifications (1)
- Contaminents (1)
- DMD (1)
- Demolition (1)
- Diagnose (1)
- Diagnosis (1)
- Dye effluents (1)
- Dynamic mode decomposition (1)
- Eigendehnung (1)
- Elektromagnetisches Feld (1)
- Energiemarkt (1)
- Energiewirtschaft (1)
- Energy economics (1)
- Erdgasantrieb (1)
- Eutrophication (1)
- Eutrophierung (1)
- FSI (1)
- Farbstoff (1)
- Farbstoffabbau (1)
- Fault Tolerance (1)
- Fehlertoleranz (1)
- Feinpartikelsysteme (1)
- Fertigbauteil (1)
- Filtration (1)
- Fine particulates (1)
- Flocculation (1)
- Flockung (1)
- Flugzeugbau (1)
- Fluid–structure interaction (1)
- Flächennutzung (1)
- Fügeverfahren (1)
- Gemeinschaft (1)
- Geologische Erkundung (1)
- Gerromorpha (1)
- Gestaltung (1)
- Getreide Stroh (1)
- Großtafelbau (1)
- Grundwasserwiederanstieg (1)
- Gärresten (1)
- Handelbare Flächennutzungsrechte (1)
- Heteroptera (1)
- High level architecture (HLA) (1)
- Hochfrequenztechnik (1)
- Hydrodynamics (1)
- Hydrologie (1)
- Implicit variables (1)
- Implizite Variablen (1)
- Induktionshärten (1)
- Induktive Erwärmung (1)
- Inherent strain (1)
- Innenkippe (1)
- Intelligente Fertigung (1)
- Joining technologies (1)
- Kaltpressschweißen (1)
- Keramik (1)
- Kleingewässer (1)
- Konstruktion (1)
- Konzeptionelle Modellierung (1)
- Kraftfahrzeug (1)
- Küste (1)
- Leichtbau (1)
- Lightweight construction (1)
- Lignin (1)
- Material nonlinearity (1)
- Material transformation (1)
- Materialnichtlinearität (1)
- Mathematical optimization (1)
- Mathematische Optimierung (1)
- Metallischer Werkstoff (1)
- Micro-gravity (1)
- Mikrogravitation (1)
- Möbius (1)
- Natürliche Ressourcen (1)
- Nepomorpha (1)
- Nichtlineares mathematisches Modell (1)
- Niederlausitz (1)
- Numerics (1)
- Numerik (1)
- Nutzungsrecht (1)
- Oberfläche (1)
- Optimality conditions (1)
- Optimalitätsbedingung (1)
- Optimalitätsbedingungen (1)
- Optimierung (1)
- Organic compounds (1)
- Organischer Abfall (1)
- Oszillator; Spule <Elektrotechnik> (1)
- Oszillatorschaltung (1)
- Plattenbauten (1)
- Prefabricated buildings (1)
- Processing (1)
- Prozessmodell (1)
- Punktschweißen (1)
- Radio frequnecy (1)
- Reaktionssystem (1)
- Refinement (1)
- Regularität (1)
- Regularitätsbedingungen (1)
- Regulation (1)
- Regulierung (1)
- Resonator (1)
- Reststoff (1)
- Reuse of building components (1)
- Richten <Fertigung> (1)
- Rückbau (1)
- Saale (1)
- Saale River (1)
- Sanierungsbergbau (1)
- Schadstoffe (1)
- Schnabelkerfe (1)
- Schweißeigenspannungen (1)
- Schweißen (1)
- Schweißsimulation (1)
- Schweißspannung (1)
- Schweißverzug (1)
- Selbstreparatur (1)
- Selbsttest (1)
- Self-Repair (1)
- Self-Test (1)
- Simulation (1)
- Spot welding (1)
- Stabilisierung (1)
- Stabilization (1)
- Stoffumwandlung (1)
- Strukturmechanik (1)
- Strömungsmechanik (1)
- Thermomechanik (1)
- Tradable permission rights (1)
- Tragfähigkeit (1)
- Umweltverträgliches Produkt (1)
- VCO (1)
- VLIW (1)
- Variable (1)
- Variational analysis (1)
- Variationsanalysis (1)
- Variationsrechnung (1)
- Verbrennungsmotor (1)
- Veredlung (1)
- Vortgeschrittene Schweißfertigung (1)
- Wanzen (1)
- Wasseraufbereitungsanlage (1)
- Wasserbehandlung (1)
- Wasserqualität (1)
- Wasserressourcen-Management (1)
- Water quality (1)
- Water resources management (1)
- Watertreatment (1)
- Welding distortions (1)
- Welding residual stresses (1)
- Wettbewerb (1)
- Wettbewerbsökonomie (1)
- Wiederverwendung von Bauteilen (1)
- Willingness-to-pay (1)
- Wirkmedienbasierte Umformverfahren (1)
- Zahlungsbereitschaft (1)
- Zahlungsbereitschaftsanalyse (1)
- organische Stoffe (1)
- Ökologie (1)
Institute
- FG Aufbereitungstechnik und Sekundärrohstofftechnologie (ehemals) (2)
- FG Aerodynamik und Strömungslehre (1)
- FG Füge- und Schweißtechnik (1)
- FG Hybride Fertigung (1)
- FG Hydrologie (1)
- FG Mikroelektronik (1)
- FG Optimale Steuerung (1)
- FG Technische Informatik (1)
- FG Technische Mechanik und Maschinendynamik (1)
- FG Theoretische Elektrotechnik (1)
The development of computer technologies allows using numerical simulations in the early stages of aircraft design more and more often. The role of both wind tunnels and initial test flights used to validate of solutions seems to be diminishing. Big systems for three-dimensional simulations of Fluid-Structure Interactions (FSI) constitute highly specialized and costly software. Most of the codes are based on many simplifications. One of them is the assumption of linearity of the structural model being in contradiction with real-life situations. The postdoctoral dissertation presents the results of simulations for complex, multi-scale objects and non-linear structure models and extended structure testing in relation to damage in macroscale analysis. What is crucial for carrying out the assumed analyses is to extend a numerical tool comprising a flow and a structural program and a space grid deformation model for a system allowing to take into consideration the non-linearity of the structure. The point of reference for testing the suggested approaches are the existing solutions of the aeroelastic linear problems. Results of the recent research might be applied for the construction of increasingly common unmanned aerial vehicle (UAV). Modern structure is a key element that affects the basic parameters as mass or range of these vehicles. Until now the research and development of the aeroelastic calculation algorithm for commonly used materials in the framework of linear geometry and linear-elastic material behavior was used. The current developments of materials for light-weight design common use of 3D printing technology causes the increasingly widespread use of new alternative materials in the aviation industry. This is particularly true for the design and construction of UAV, where the basic requirements are the lightness of the structure and the maximum range. Unfortunately, the fulfillment of the above criteria means that the materials used are often loaded not only in a elastic range but also more often above this limit. In case of analyzing aeroelastic phenomena for a loaded structure we should take a closer look at the behavior of the material outside the elastic range in which the damage occurs. The process of destroying in the face of such dangerous phenomena as flutter in aircraft constructions requires a deeper analysis of the mechanics of materials, in particular for new materials and their manufacturing techniques. As part of joint experiments and numerical simulations, detailed research was carried out to describe the behavior of printed materials, which will be increasingly used in the design of aircraft structures. Extending the postdoctoral dissertation with the research carried out at BTU will allow further development of the existing FSI algorithm, taking into account the structural behavior more accurately and the possibility of predicting damage processes.
Das Schweißen führt zu einer lokalen, ungleichmäßigen Erwärmung der Fügestelle. Die dadurch hervorgerufenen lokalen plastischen Verformungen und metallurgischen Werkstoffveränderungen bewirken nach der Abkühlung bleibenden Verzug und Eigenspannungen. Diese beeinflussen die reibungslose Durchführung des Fertigungsprozesses und die Qualität der geschweißten Konstruktion und schließlich stellen letztlich deren Einsatz in Frage. Somit steht für die meisten Industrieanwendungen die gesicherte Minimierung bzw. Beherrschung des Schweißverzuges und der Schweißeigenspannungen, insbesondere bei großen Konstruktionen im Vordergrund.
Mittels der Vorkenntnis über den zu erwartenden Verzug und die Entwicklung der Eigenspannungen während und nach dem Schweißen können zum einen geeignete Gegenmaßnahmen, wie beispielsweise Einspannszenarien, Vorverformungen oder Schweißreihenfolgen sowie eine gezielte Vor-, Zwischen- oder Nachwärmebehandlung zweckmäßig gewählt werden. Zum anderen ist es möglich, die darauffolgenden notwendigen Nachbehandlungen, wie z.B. das thermische Richten, schon in einem sehr frühen Stadium des Produktentwicklungsprozesses vorauszuplanen. Demzufolge besteht seitens der Forschung ein sehr großes Interesse an der Entwicklung verlässlicher Modelle und Methoden zur Schweißverzugs- und Eigenspannungsberechnung.
Die vorliegende Habilitationsschrift befasst sich mit den theoretischen Grundlagen und den simulationstechnischen Aspekten der Schweißverzug- und Eigenspannungsberechnung von großen komplexen Schweißkonstruktionen. Im Mittelpunkt stehen die analytisch-numerische Hybridmodelle. Diese bestehen aus einem analytischen Teil für die lokale thermomechanische Berechnung und einen numerischen Teil für die globale strukturmechanische Berechnung. Die beiden Teilaufgaben sind stark gekoppelt. Der Schwerpunkt liegt in der Weiteentwicklung und in den Umsatzmöglichkeiten des analytischen Ansatzes. Darüber hinaus wird die Anwendung der Hybriden Modellierung zur Berechnung von Verzug und Eigenspannungen in praxisrelevanten Schweißkonstruktionen an zahlreichen Beispielen demonstriert. Die Aspekte der Einbringung der Simulation in die Fertigungs- oder Produktkette werden ebenso thematisiert.
This thesis is concerned with the phenomenon of implicit variables in optimization theory. Roughly speaking, a variable is called implicit whenever it is used to model the feasible set but does not appear in the objective function. At the first glance, such variables seem to be less relevant for the purpose of optimization.
First, we provide a theoretical study on optimization problems with implicit variables. Therefore, we rely on a model program which covers several interesting problem classes from optimization theory such as bilevel optimization problems, evaluated multiobjective optimization problems, or optimization problems with cardinality constraints. We start our analysis by clarifying that the interpretation of implicit variables as explicit ones induces additional local minimizers. Afterwards, we study three reasonable stationarity systems of Mordukhovich-stationarity-type for the original problem as well as some comparatively weak associated constraint qualifications. The obtained results are applied to the three example classes mentioned above.
Second, we introduce switching- and or-constrained optimization problems. Exploiting the observation that each or-constrained optimization problem can be transferred into a switching-constrained optimization problem with the aid of slack variables, one can interpret or-constrained programs as optimization problems comprising implicit variables. Necessary optimality conditions and constraint qualifications for both problem classes are derived. Furthermore, some approaches for the numerical solution of both problem classes are discussed and results of computational experiments are presented. The shortcomings of implicit variables are highlighted in terms of or-constrained optimization.
Third, we study three different scenarios where optimality conditions and constraint qualifications for challenging optimization problems can be constructed while abstaining from the introduction of implicit variables. We start by deriving a generalized version of the linear independence constraint qualification as well as second-order necessary and sufficient optimality conditions for so-called disjunctive optimization problems, which cover several interesting but inherently irregular problem classes like mathematical programs with complementarity, switching, or-, and cardinality constraints. Afterwards, we exploit several different single-level reformulations of standard bilevel optimization problems in order to find first- and second-order sufficient optimality conditions. Finally, we study sequential stationarity and regularity conditions for nonsmooth mathematical problems with generalized equation constraints with the aid of the popular limiting variational analysis. The investigated model problem covers the one we use for the theoretical analysis of implicit variables.
The GeoFlow (Geophysical Flow) experiment on the International Space Station (ISS) and the AtmoFlow (Atmospherical Flow) experiment are designed to study convective processes under microgravity conditions in the spherical gap geometry. By applying a high voltage field between two concentric spherical shells and utilizing a dielectric working fluid it is possible to maintain an artificial radial force field that is comparable to a planetary gravitational field. This makes it possible to study convection such as known from the Earth's outer core, the Earth's mantle, or planetary atmospheres. The radial force field is based on the dielectrophoretic effect and is described by thermo-electro hydrodynamics (TEHD). This habilitation thesis presents a comprehensive view on modeling TEHD and the numerical simulation of the governing equations with a focus on GeoFlow and AtmoFlow. The GeoFlow experiment investigated thermal convection with and without dielectric (internal) heating under long-time micro-gravity conditions on the ISS. This unique experimental setup consisted of a bottom heated and top cooled spherical gap, filled with the silicon oil M5 or 1-Nonanol. Rotation, varying voltage, and temperature differences across the gap could be applied, to spread the experimental parameter space. The main focus of GeoFlow was the investigation of flow properties such as the convective onset, the transition from laminar to turbulent flows, and the influence of rotation on convection. Experimental outcomes were compared with theoretical and numerical results via advanced post-processing techniques. This includes pattern recognition algorithms and statistical evaluation of the numerical simulations. The TEHD model was validated on the onset of convection through linear stability analysis, on properties of columnar cells and global convective structures such as regular laminar flows. It is shown that TEHD based convection is comparable with Rayleigh-Benard convection and that is can be described by the quasi-normal approximation. For rotating cases and low super-criticalities the Proudman-Taylor theorem dominated the fluid flow which resulted in global columnar cells. In summary, the presented TEHD model is able to explain certain aspects of convective flows observed in GeoFlow. It is the first validation for such a model at all stages. The AtmoFlow experiment is based on GeoFlow but is designed to investigate global cells and planetary waves which are known from planetary atmospheres. Its unique feature are the atmospheric-like boundary conditions. Understanding the interaction between atmospheric circulation and a planet's climate, be it Earth, Mars, Jupiter, or a distant exoplanet, contributes to various fields of research such as astrophysics, geophysics, fluid physics, and climatology. AtmoFlow is currently under construction and is planned for operation on the ISS in 2024.
Die Habilitationsschrift zielt darauf ab, den Erkenntnisstand zur Bauteilwiederverwendung (Produktrecycling) und zum Materialrecycling (stoffliches Recycling) aufzuzeigen. Wissenschaftlich fundiert und Impuls gebend werden unter Nachhaltigkeitsprämissen potenzielle Wiederverwendungsmöglichkeiten für großformatige Betonbauteile und Verwertungsmöglichkeiten für Bauschuttfraktionen herausgearbeitet. Die Untersuchungen konzentrieren sich auf die Rohbaukonstruktion industriell errichteter Wohnbauten der DDR-Zeit, die zum Rückbau anstehen. Bewertet werden baustoff-, -technische,- rechtliche, -technologische, wirtschaftliche, ökologische sowie logistische Kriterien für das Produkt- und Materialrecycling. Anhand von untersuchten Szenarien wird auch verdeutlicht, dass Ressourcen- und Energieeffizienz miteinander vernetzt sind. Im Rahmen des Materialrecyclings wird aus Ressourceneffizienzgründen vordergründig die Verwertung von rezyklierten Gesteinskörnungen zur Herstellung von Beton diskutiert. Des Weiteren werden hauptsächlich die in Plattenbauten anzutreffenden schadstoffhaltigen Baustoffe aufgezeigt inklusive deren gesundheitliche und abfallwirtschaftliche Auswirkungen und Behandlungsoptionen. Im Ergebnis der Analysen wird empfohlen, wie Bauten zukunftsorientiert zu errichten sind und dass sich das Lehrangebot an die sich verändernden Bedingungen, unter dem Aspekt nachhaltig zu bauen/Schließung von Stoffkreisläufen, verändern muss.
This thesis focuses on computer modelling issues such as i) uncertainty, including uncertainty in parameters, data input and model structure, ii) model complexity and how it affects uncertainty, iii) scale, as it pertains to scaling calibrated and validated models up or down to different spatial and temporal resolutions, and iv) transferability of a model to a site of the same scale. The discussion of these issues is well established in the fields of hydrology and hydrogeology but has found less application in river water quality modelling. This thesis contributes to transferring these ideas to river modelling and to discuss their utilization when simulating river water quality.
In order to provide a theoretical framework for the discussion of these topics several hypotheses have been adapted and extended. The basic principle is that model error decreases and sensitivity increases as a model becomes more complex. This behaviour is modified depending if the model is being upscaled or downscaled or is being transferred to a different application site.
A modelling exercise of the middle and lower Saale River in Germany provides a case study to test these hypotheses. The Saale is ideal since it has gained much attention as a test case for river basin management. It is heavily modified and regulated, has been overly polluted in the past and contains many contaminated sites. High demands are also placed on its water resources. To provide discussion of some important water management issues pertaining to the Saale River, modelling scenarios using the Saale models have been included to investigate the impact of a reduction in non-point nutrient loading and the removal and implementation of lock-and-weir systems on the river.
Im Rahmen der vorliegenden Arbeit wird auf grundlegende Unterschiede im Brennverfahren von Benzin- und Erdgasmotoren eingegangen. Außerdem werden verschiedene Maßnahmen dargestellt, die bei einer konsequenten Auslegung des Brennverfahrens auf den Kraftstoff Erdgas zu deutlichen Wirkungsgradvorteilen führen und somit den Nachteil der geringen Speicherdichte von Erdgas (Reichweite von Erdgasfahrzeugen) verringert.
Die vorliegende Arbeit soll dem interessierten Ingenieur und Studenten des Maschinenbaus einen Überblick über die Nutzung gasförmiger Kraftstoffe für den Antrieb von Kraftfahrzeugen geben. Auf die Grundlagen der Thermodynamik und der motorischen Verbrennung wird dort näher eingegangen, wo es für das Verständnis der Zusammenhänge unabdingbar ist. Hier sei auch auf die einschlägige Literatur verwiesen. Ziel ist es zu zeigen, inwiefern sich die Brennverfahren für einen kleinvolumigen Pkw-Motor von den Großgasmotoren hinsichtlich des Nutzungsprofils unterscheiden und welche Wege zur Wirkungsgradsteigerung möglich sind.
In modern information technology, increasingly powerful electronic circuits are required for the targeted generation of complex signals with well-defined amplitudes and phases. In circuits of this type, oscillators frequently form the central element because of its phase noise and stability, which essentially determines the achievable precision in the signal generation. Further requirements are derived from the electronic definability of the signal properties and the operational behavior of the oscillators. Conventional oscillator circuit models autonomous circuits, mainly consist of a passive frequency-selective or phase-selective network and an active amplifier element, which together produce an oscillatory circuit via a suitable feedback. At first glance, the circuit topology seems to be quite simple, and can often be explained quite visibly. However, when it comes to describing in particular the very important phase noise dynamics and stability of oscillators, it very soon becomes apparent that highly complex structures are involved. A fundamental difficulty in the theoretical description arises due to the non-linear behavior of oscillators, the understanding of which is crucial for a reliable description of jitter and oscillator phase noise. The resonant condition of oscillators arises due to the fact that the noise in the oscillator circuit is always present in the system, which is amplified in a frequency-selective manner to the extent that a stable oscillation arises at most at a fixed frequency because of non-linear limitation of the amplification. The frequency selectivity arises due to the frequency selectivity or phase selectivity of the passive feedback path. The non-linear limitation of the amplification in the oscillator normally results in a very reliable control of the amplitude noise of the output oscillation. It is well understood that any particular oscillator’s phase noise could be improved by increasing the generated signal amplitude or increasing the quality factor of the resonant network. Increasing the signal level is limited by the utilized supply voltage or the break down limits of transistors and cannot be increased further to improve the phase noise. Accordingly, the remaining phase noise, which can normally be minimized via resonating circuits with pronounced phase selectivity and therefore a high quality factor resonator, is of great importance for oscillators. Traditional high Q-factor resonators (ceramic resonator, surface acoustic wave, bulk acoustic wave, dielectric resonator, YIG resonator, Whispering gallery mode resonator, Optoelectronic resonator, etc.) are usually 3-dimensional structures and bulky for both handheld and test-measurement equipments and does not offer integration using current foundry technology. The current and later generation wireless communication market is pushing the need for miniaturization to its limits. Printed coupled transmission line resonator is a promising alternative due to its ease of integration and compatibility with planar fabrication processes but limited by its large physical size and low quality factor, making it a challenging choice to design low phase-noise oscillators. This problem is more prominent in integrated circuits (ICs) where high degrees of thin conductor losses reduce the quality factor by orders of magnitude compared to hybrid circuit technologies.
This thesis describes the design and investigation of a variation of printed resonators using Möbius slow-wave and Metamaterial structures for the applications in oscillator circuits. A novel Möbius slow-wave mode-coupled structure offers additional degrees of freedom (higher Q-factor and multi-band characteristics for a given physical size) as compared to conventional transmission line printed resonators. A design study has been carried out to optimize the phase noise performance by using the novel resonant structures (mode-coupled, slow-wave, Möbius strips, evanescent mode, negative index material-Metamaterial) in conjunction with mode locking and injection locking for improving the overall performances, beyond the limits imposed by conventional limitations. The thesis also covers a broad spectrum of research on DRO and OEO ranging from practical aspects of circuit implementation and measurement, including the modeling of optical fiber delay line used as a thermally stable high Q-factor resonator structure. This thesis is research work carried out from 2004-2014, organized in 11 chapters, theoretical and experimental results documented by a range of specific measurement results and substantiated by over 200 scientific publications over dozen patents. The Metamaterial Möbius technology discussed in this thesis can open new era in the field of imaging, sensors, cloaking, energy harvesting and energy efficient microwave circuit and system Solutions.
This thesis introduces a comprehensive approach for making a particular class of embedded processors self-testing and self-repairing, such that a limited amount of permanent hardware faults that occur during the lifetime of these processors in the field will not prohibit the functional behavior of the user application running on the processor. The presented concepts all use redundant hardware, but the techniques used for administrating the hardware-redundancy range from hardware-based methods over hybrid methods to pure software-based methods, whereby the focus is on the latter ones. The proposed methods will be demonstrated by using a processor that is well designed for diagnostic self-test and self-repair purposes. This will also highlight some architectural properties of such a processor, which are beneficial for performing a software-based self-test and self-repair process.
Chapter 1 is an introduction to the field of dependable systems and fault tolerance. Fundamental terms and notations, which are used throughout this thesis for classification and evaluation, are provided. The used processor model – the VARP processor – is introduced in chapter 2 together with a hardware-based self-repair scheme for that processor. The results are used as reference values for evaluating the software-based methods. Chapter 3 introduces the fundamental concept of the software-based self-repair. In chapter 4 hybrid methods are derived by combining software-based and hardware-based methods, highlighting the synergy effects of the combination. Finally, in chapter 5, a diagnostic and adaptive software-based self-test scheme is introduced. This self-test scheme provides the diagnostic capability that is needed in the field for identifying defect components in the VARP processor and completes the comprehensive software-based self-test and self-repair approach.
The significance in the production of bio-based products is enhanced with the abundance and renewability of biogenous raw and residue materials in comparison to the depleting fossil fuels especially in producing environment friendly products and their applications in energy (CO2-neutral) as well as material applications. This work concentrates mainly on the production of bio-based products through innovative processing and refinement of biogenous residues originating from agricultural (cereal straws), industrial (lignin from black liquors) and biotechnological (biogas residues) processes. The innovative processing and refinement of the processes and their end-products solve the challenges which were not possible within the conventional processes. The innovative processes improve the cascading as well as sustainable utilization possibilities with a simultaneous value addition of the residues. Converting biogenous residues into a valuable end-product requires various preprocessing of the raw materials and are material specific (physical and chemical compositions). Agglomeration of theses residues is chosen as one of the main innovative processes making the handling of the products easier. Agglomeration in this work is carried out using press / densification processes in case of cereal straws, build-up processes in case of black liquors and encapsulation processes in case of biotechnological residues.