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LIF-based quantification of the species transport during droplet impact onto thin liquid films : Species transport during droplet impact onto thin liquid films
Get PDFIn the present study, laser-induced fluorescence (LIF) is used to investigate the mixing process of a droplet impacting onto a thin liquid film. A robust multidimensional calibration procedure is developed enabling the extraction of local instantaneous dye concentrations as well as film heights. A series of validation measurements are conducted confirming a low reconstruction error of 4.53%. The impact-induced mixing process is thoroughly investigated across various liquid film thicknesses to examine the propagation of the mixing zone and the instantaneous radial concentration gradients within it. It is shown that the maximum extent of the mixing zone scales inversely proportional with the thickness of the liquid film. Within our experiments, we discover the formation of wall-induced vortex ring instabilities subsequent to impact. The disintegration of vortex rings during droplet impact significantly enhances convection-driven mixing, as quantified by the coefficient of variation
Ultra-high-speed time-resolved PIV of turbulent flows using a continuously pulsing fiber laser
Get PDFThe application of a compact pulsed fiber laser for high-speed time-resolved particle image velocimetry (TR-PIV) measurements in the potential core of a turbulent round jet is presented at repetition rates of up to 500 kHz. The master oscillator power amplifier laser architecture consists of a pulsable seed diode whose emission is amplified in a Yb-doped fiber. The pulsed laser is operated continuously at repetition rates ranging from 10 kHz to 1 MHz with adjustable pulse widths at an output power of 50 W. The maximum rated pulse energy of 486 μJ is reached at 100 kHz, making the laser suitable for measurements of turbulent flows and highly transient phenomena. To demonstrate the feasibility of the laser for flow velocimetry, TR-PIV is conducted in a turbulent round jet. Two different high-speed camera systems are employed: a high-speed CMOS camera running at 200 kHz and 400 kHz and an in situ storage CCD camera for burst-mode PIV measurements at 500 kHz. For the CMOS system, the capability of measuring several characteristic quantities of turbulent flows is discussed with regard to the effects of uncertainty and spatial resolution. The presented system extends the range of suitable laser systems for high-speed PIV measurements offering continuous pulsing at repetition rates of up to 1 MHz at a compact footprint. The amount of consecutive images is solely limited by the onboard storage of the camera, which enables unprecedented temporal dynamic ranges
Longitudinal bunch diagnostics in the Terahertz domain at TELBE using fast room temperature operable zero-bias Schottky diodes
Get PDFModern accelerator-based light sources rely on short bunches to generate intense photon pulses. To achieve this, the electron bunches from the accelerator need to be compressed longitudinally in a magnetic chicane. A valuable tool for the measurement of the signal in the bunch compressor is the use of broadband EM-detectors covering a spectral range from few 100 GHz up to THz frequencies. With this setup, bunch length variations caused by instabilities in the acceleration process can be measured that in turn also affects the secondary photon beam. In this paper, we demonstrate the pre-commissioning of broadband, room temperature Schottky THz detectors for the diagnosis of compressed short electron bunches at the TELBE facilities at the Helmholtz-Zentrum Dresden-Rossendorf, Germany. Qualitative bunch compression measurements have been carried out to diagnose the beam to optimize the machine setup and provide feedback to the beam-line scientists for optimum machine operation. These detectors are scheduled to be commissioned at free-electron facilities in near-future
Two steps forward, one step back? Party competition, cooperative federalism, and transport policy reforms in Germany
Get PDFBackground: Transport policy has regained political relevance in Germany. The successful realization of the Verkehrswende,—the extensive transition toward sustainable transport and mobility—is central to reaching climate neutrality. In 2020, the Federal Government proposed the reform of two key ordinances that have regulated road traffic so far. The amendment was aimed at implementing several provisions at the expense of car drivers and, at the same time, in favor of cyclists and pedestrians. Due to cooperative federalism, the governments of the 16 constituent units (Länder) had to adopt the amendment in the Bundesrat, Germany’s second chamber. In the legislative process, however, the reform ultimately failed in its original scope. Using it as a particularly instructive case study, we show how and why party competition and cooperative federalism hamper comprehensive transport policy reforms in Germany.
Results: In the German political system, political interests interact within a complex web of cooperative federalism. To understand partisan encroachment on the federal decision-making processes, this paper uses a process-tracing approach. To investigate decision-making in the Bundesrat and its outcomes, the empirical analysis combines qualitative analyses of several publicly available sources. We can empirically demonstrate that political parties influenced legislative procedures. The reform failed in its original scope because the three political parties with veto power in the Bundesrat insisted on their positions and were not willing to agree on a compromise.
Conclusions: For the implementation of the Verkehrswende, the German federal system proves to be both a blessing and a curse. On one hand, the institutional design of the Bundesrat constrains extreme positions and helps promote decisions most citizens may agree with. The Länder governments and administrations can also contribute their expertise and local experience to federal legislation via the Bundesrat. On the other hand, veto powers are ubiquitous in the German system of cooperative federalism. Therefore, it is prone to blockades. The actions of the political parties in the Bundesrat have hampered the comprehensive reform of road traffic regulations that was originally envisaged. Policymaking took two steps forward toward implementing the Verkehrswende, only to immediately take one step back again
The crustal stress field of Germany: a refined prediction
Get PDFInformation about the absolute stress state in the upper crust plays a crucial role in the planning and execution of, e.g., directional drilling, stimulation and exploitation of geothermal and hydrocarbon reservoirs. Since many of these applications are related to sediments, we present a refined geomechanical–numerical model for Germany with focus on sedimentary basins, able to predict the complete 3D stress tensor. The lateral resolution of the model is 2.5 km, the vertical resolution about 250 m. Our model contains 22 units with focus on the sedimentary layers parameterized with individual rock properties. The model results show an overall good fit with magnitude data of the minimum (Shmin) and maximum horizontal stress (SHmax) that are used for the model calibration. The mean of the absolute stress differences between these calibration data and the model results is 4.6 MPa for Shmin and 6.4 MPa for SHmax. In addition, our predicted stress field shows good agreement to several supplementary in-situ data from the North German Basin, the Upper Rhine Graben and the Molasse Basin
Three-dimensional Many-objective Path Planning and Traffic Network Optimization for Urban Air Mobility Applications Under Social Considerations
Get PDFThis dissertation proposes and investigates solution approaches to two problems in urban air mobility, considering the different perspectives of many stakeholders, including societal interests. The many-objective path planning problem seeks Pareto-optimal, three-dimensional, and smooth paths connecting two given locations in the city. The multi-objective traffic network optimization problem searches for Pareto-optimal and three-dimensional transportation networks that can be constructed from a given set of paths. Since this work also explicitly considers social objectives within these problems, it has both a societal and a practical relevance. This thesis analyzes both stated problems and proposes a new framework to solve the first problem efficiently. Then, it shows how the optimized paths can be combined into a three-dimensional traffic network. Afterward, this dissertation presents another new framework to optimize the obtained traffic network in terms of multiple objectives. It tests the influence of integrating social criteria on the economic costs of the networks obtained.
Using geospatial data from four different cities, paths and networks were optimized to evaluate the efficiency of the path planning framework against current methods and to compare the network solutions with conventional strategies. The developed path planning framework showed a significant advantage over comparable approaches. When traffic networks were optimized, including social criteria, their social acceptance increased much more than the monetary costs. An essential finding of this work is that the many-objective path planning problem can be solved efficiently in the three-dimensional operation space by an intelligent combination of existing algorithms and the inclusion of three new algorithmic features. Beyond that, it is beneficial to integrate social criteria into optimization problems when the solutions obtained are the basis for decisions in the area of conflict between the economy and human welfare
„Sprachenexpedition rund um die Ostsee“. Erfahrungen aus einem internationalen Projekt des Goethe-Instituts zum mehrsprachigen Potenzial der Deutschlernenden
Get PDFDer Praxisbericht präsentiert das im Schuljahr 2021/2022 durchgeführte Projekt „Sprachenexpedition rund um die Ostsee“. Die Schüler*innen lernten die Mehrsprachigkeit im eigenen Land sowie in den Nachbarländern kennen und setzten ihre sprachlichen Ressourcen beim Erschließen neuer Sprachen ein. Die länderübergreifende Kooperation hob das Potenzial der Sprachenkenntnisse und die Brückenfunktion des Deutschen hervor. Die beteiligten Lehrkräfte wurden im Projekt kleinschrittig begleitet und für den mehrsprachigen Unterricht fortgebildet. Der Beitrag präsentiert das didaktische Gesamtkonzept und dessen Umsetzung. Die Erfahrungen der beteiligten Schüler*innen und Lehrkräfte runden den Bericht ab. Das Lehrmaterial ist mittlerweile publiziert und kann grundsätzlich weltweit im Deutschunterricht eingesetzt werden
Learning Graphon Mean Field Games and Approximate Nash Equilibria
Get PDFRecent advances at the intersection of dense large graph limits and mean field games have begun to enable the scalable analysis of a broad class of dynamical sequential games with large numbers of agents. So far, results have been largely limited to graphon mean field systems with continuous-time diffusive or jump dynamics, typically without control and with little focus on computational methods. We propose a novel discrete-time formulation for graphon mean field games as the limit of non-linear dense graph Markov games with weak interaction. On the theoretical side, we give extensive and rigorous existence and approximation properties of the graphon mean field solution in sufficiently large systems. On the practical side we provide general learning schemes for graphon mean field equilibria by either introducing agent equivalence classes or reformulating the graphon mean field system as a classical mean field system. By repeatedly finding a regularized optimal control solution and its generated mean field, we successfully obtain plausible approximate Nash equilibria in otherwise infeasible large dense graph games with many agents. Empirically, we are able to demonstrate on a number of examples that the finite-agent behavior comes increasingly close to the mean field behavior for our computed equilibria as the graph or system size grows, verifying our theory. More generally, we successfully apply policy gradient reinforcement learning in conjunction with sequential Monte Carlo methods
Forward-Backward Latent State Inference for Hidden Continuous-Time semi-Markov Chains
Get PDFHidden semi-Markov Models (HSMM's) - while broadly in use - are restricted to a discrete and uniform time grid. They are thus not well suited to explain often irregularly spaced discrete event data from continuous-time phenomena. We show that non-sampling-based latent state inference used in HSMM's can be generalized to latent Continuous-Time semi-Markov Chains (CTSMC's). We formulate integro-differential forward and backward equations adjusted to the observation likelihood and introduce an exact integral equation for the Bayesian posterior marginals and a scalable Viterbi-type algorithm for posterior path estimates. The presented equations can be efficiently solved using well-known numerical methods. As a practical tool, variable-step HSMM's are introduced. We evaluate our approaches in latent state inference scenarios in comparison to classical HSMM's
Enhancing Radar Model Validation Methodology for Virtual Validation of Automated Driving Functions
Get PDFAutomated vehicles and mobility services are increasingly becoming part of everyday road traffic. The safety of these systems is of paramount importance. For this reason, safety validation of automated driving systems is playing an increasingly major role. However, it has been shown that safety can no longer be demonstrated through real test drives, as the complexity of the systems and the resulting scenarios do not allow for an economical implementation. For this reason, simulations are used, but they need to be validated.
In addition to other sensors, radars are used as an essential component for environmental detection in automated vehicles. Therefore, the effects and uncertainties of radar sensor validation measurements and their impact on the validation of radar sensor models are the focus of this thesis. For this purpose, requirements for acceptance criteria for radar sensor models are derived from radar measurements and quantified using the further developed double validation metric (DVM) in the thesis. It consists of an estimate of the mean error and the variance in the dispersion of uncertainties. The metric is applied to radar data structures in different abstraction levels. Effects can be represented by dedicated measurement setups, objects and environmental conditions. In the following, a measurement setup is derived to isolate the influence of previously identified effects and effect correlations on the radar cross section (RCS). It is shown that the vehicle models investigated have a large influence on this value and that other factors, such as the height of the mounting position, show little sensitivity on the RCS. In addition to the RCS, a detailed analysis of the reflection centers of the investigated objects is carried out.
Reference sensors are used in such dynamic scenarios to transfer the driven trajectories into a simulation environment with minimal additional uncertainties. The presented experiments to quantify the uncertainties of the reference sensors and the transfer to the simulation are qualified with the help of the super reference. The tests confirm the accuracy of the reference sensors used. Finally, a metrics-based validation is performed on an exemplary radar model by recording a validation test with a real sensor. Different levels of abstraction of the radar data are analyzed using the DVM. In particular, the combination of the metric results with a satellite image allows an objective root cause analysis.
The newly acquired methods and test designs form a further basis for the standardization of validation tests for radar sensors and their models