149544 research outputs found
Sort by
Gravity field recovery from simulated satellite data of the MAGIC (Mass-Change and Geosciences International Constellation) constellation
Full text linkThis thesis focuses on the analysis of Gravity Field Recovery (GFR) with artificial data sets created for the preliminary design of the Mass-Change and Geosciences International Constellation (MAGIC), a new bender type constellation designed to provide data continuity for he Gravity Recovery and Climate Experiment - Follow On (GRACE-FO) satellite mission.
Mock-data for the MAGIC constellation is prepared for a set of different scenarios in order to evaluate the impact of certain parameters, like inclination, altitude, and instrument accuracy on the GFR results. Additionally, comparison to a GRACE-FO-like mission is done, where spatial and temporal resolution is assessed, as well as the gravity field solutions themselves.
The GFR tool used for the creation of the mock-data and computation of GFR is introduced and the processes are laid out in detail. In order to provide greater understanding on the processes of GFR, the theoretical background for the classical variational approach is introduced. The different mathematical models, such as background models, noise models, and observation models are explained. The goal of this thesis is to provide a great overview on the topic of GFR while applying the concepts to the new MAGIC constellation in order to estimate optimal parameters, as well as evaluate the performance to its predecessor
Do they influence me? Impact of an additional pedestrian's presence and behavior on your own crossing decision as pedestrian in interaction with a highly automated vehicle communicating via external human-machine interface and vehicle kinematics
No full textThe introduction of highly automated vehicles (HAVs) into traffic offers significant benefits, but also presents challenges, especially in interactions with pedestrians, who are among the most vulnerable road users (VRUs). One critical situation is when pedestrians cross in front of HAVs, a topic studied extensively. However, the influence of other pedestrians on one pedestrian's crossing decision still remains underexplored, as research so far has mostly addressed one-to-one interactions in rather low-complex scenarios. Our current study examines how the presence and behavior of another pedestrian impacts an individual's decision to cross in front of a HAV, whether an external human-machine interface (eHMI) signaling the HAV's intentions alters crossing decisions, and whether entrainment effects occur when multiple pedestrians are present. To address these issues, an online-experiment (N = 136) used videos and questionnaires to analyze pedestrian decision-making. Results confirmed that eHMI signals and vehicle kinematics influenced perceived safety and willingness to cross. More importantly, results revealed that the other pedestrian's behavior significantly affected these decisions, highlighting the influence of other road users. This emphasizes the need to consider additional pedestrian interactions beyond mere one-to-one pedestrian-HAV interactions in designing effective eHMI systems to ensure safe and efficient future traffic systems
Towards a two-photon E1-M1 clock transition excitation in ^{174}Yb for quantum clock interferometry
No full textAtom interferometry experiments measuring gravitational redshift require access to long-lived internal states, such as the 1S0-3P0
optical transition in group II atoms. An E1-M1 two-photon excitation
directly access the clock state from the ground state by coupling to a
far detuned intermediate state through a pair of electric and magnetic
dipole allowed transitions [1]. This avoids state mixing, enhancing the
excited state’s lifetime. Moreover, using counter-propagating photons
with degenerate frequencies eliminates first-order Doppler effects.
We report the progress of our experimental setup to drive the clock
transition. We prepare an ultra-cold atomic ensemble of 174Yb through a dual-stage magneto-optical trap sequence, followed by evaporative cooling in a crossed optical dipole trap [2]. To excite the transition, we utilize a high power (10 W), narrow-linewidth l1156 nm laser system referenced to a high-finesse cavity and a frequency comb.
We discuss further applications of the two-photon Doppler-free excitation as a beam splliting method for quantum clock interferometry experiments.
[1]PRA 90, 012523 (2014). [2]J.Phys.B 54, 035302 (2021
Vortrag "Modelling the effects of anonymization in O/D matrices obtained from mobile phone data"
No full textMobile phone data promise a ubiquitous traffic surveillance without the need of additional hardware. Yet, within most European countries, the data have to be anonymized to disallow the recognition of individuals. To understand the effects of applying the anonymization methodology, we use the results of an agent-based demand model as the ground truth and apply a well-described anonymization method to the trips performed by the simulated population. Besides investigating the segmentation of the area and the time aggregations used by the data supplier T-Systems, we iterate over different cell sizes and aggregation times. The results show how the completeness of the reported data deteriorates with a decrease of cell size and time span used for aggregation. As well, the original segmentation of the area using a variable grid shows to be a good compromise between a fine-grained resolution and the reported number of trips
Runtime Monitoring of Complex Scenario-based Requirements for Autonomous Driving Functions
No full textAutonomous driving functions (ADFs) are becoming more relevant and complex. Still, their safe and correct operation must be guaranteed. Scenario-based testing, i.e. confronting the ADF under test with other traffic in specified scenarios is an established approach for the validation and verification of ADFs, but tests currently often only consider simple technical requirements. Safe and correct operation is not only the absence of collisions but involves complex spatio-temporal requirements on the externally observable, functional driving behaviour in traffic.
In this work, we consider Traffic Sequence Charts (TSCs) as a visual formalism for the specification of complex, functional ADF requirements. We define a monitoring problem for TSCs and finite, sampled observations of ADF behaviour and discuss how monitor verdicts contribute to requirements testing. We show that such monitors can effectively be constructed for realistic requirements and that they can contribute to efficient testing by assessing ADF behaviour at runtime
Novel Control-like Approach for the Robust Integration of Functional Mock-Up Units into Digital Twins
Full text linkA novel approach for the robust integration of Functional Mock-up Units (FMUs) into Modelica is proposed, which maintains the computational robustness of the Modelica base model and minimizes the simulation time. Using a control-like approach, the base model is retained and mimics the FMU outputs. On the one hand, the controller can be interpreted as a numerical tool designed to provide a correct steady-state solution and
minimize transient errors. On the other hand, the additional low-pass filter can also be used to represent the inertia of a system. The application of this easy-to-implement approach is demonstrated for a digital twin of the overall thermal management system (TMS) of a future hybrid electrical regional aircraft, which aims at identifying critical conditions and flight cases in advance of hardware tests and virtually demonstrating the behavior of the
TMS during complete flight missions. To this end, a base model of the TMS is first set up using the Thermofluid Stream Modelica Library, which focuses on computational robustness, in order to define the boundaries and interfaces of the different subsystems. Then, the subsystems are gradually replaced by validated FMUs to enable virtual demonstrations, where the novel control-like approach proves to be crucial
Simulating a Pneumatics Network using the DLR ThermoFluidStream Library
Full text linkModeling and simulation of pneumatics networks is still a challenging task, plagued by initialization problems even in sophisticated environments such as the Modelica Fluid Library. The recently proposed DLR ThermoFluid Stream Library uses a promising new approach to cope with such problems. Therefore, it should be a convenient basis for a more specialized pneumatics
library. The essential concepts and components of such a library are presented, with a special focus on the notorious tee branch components. Their dynamic behaviour is very complex, since it couples the effects of dynamic pressure changes and friction losses, and often leads to stability problems. Results of systematic tests as well as more realistic models are discussed. They show that even though some problems with stability remain in special examples, the new library generally allows for the simulation of pneumatics networks using realistic tee branch models, which are more accurate than previous implementations
Multistage Turbomachinery Optimization for HighTemperature Heat Pumps with the Reverse Rankine Cycle
No full textThe electrification of process heat generation will be a key to achieving carbon neutrality in the coming decades. One of the most promising approaches is to replace conventional heat supply systems with high-temperature heat pumps (HTHPs). A promising heat pump concept is based on the reverse Rankine cycle that uses water as its working fluid. By using turbomachinery for the compression process in this cycle, the performance of the HTHP can be increased compared to the volumetric displacement systems, like screw or
piston compressors. Although the design of the compressor geometry can be done sequentially in relation to the HTHP cycle design, better results can be obtained by an approach that integrates turbomachinery and the thermodynamic cycle design. Against this background, an automated optimization method for a reverse Rankine HTHP with two radial
turbo-compressors in series is presented. In contrast to the current state of the art, the presented novel optimization approach uses 3D computational fluid dynamics data to calculate the compressor’s performance. Furthermore, the integration of low-fidelity compressor specific reduced-order models are used to accelerate the gradient-free optimization process by a CO-Kriging surrogate model. The advantages of the novel approach are justified by comparing the numerical effort and the final values of the optimization objectives
Generation of Digital Terrain Models from Digital Surface Models using a Watershed Transformation Approach
No full textThe basis of Urban Digital Twins are 3D city models generated from airborne or spaceborne remote sensing imagery. These remote sensing data allows the extraction of digital surface models (DSMs) representing the absolute geographical height of each pixel together with orthorectified image mosaics. But for the derivation of a city model also the height of the urban objects and the height of the ground - the digital terrain model (DTM) - is needed. So in a first step there has to be a method to derive the digital terrain model (DTM) from the generated digital surface model (DSM). The extraction of DTMs from DSMs is already a basic task for many decades and there are many approaches but still there is no general fully satisfying solution for this demand. In this paper we present a novel method for deriving a DTM from a provided urban DSM based on the inverted watershed-transformation. The watershed-transformation normally fills up sinks in a DSM up to a ridge-line where two sinks meet. So the result is a segmentation of a DSM to distinct sinks. Using the inverted watershed-transformation delivers a segmentation to single elevated objects. The boundary points where each of these elevated segments meet are taken as possible candidates for ground areas. But such boundaries may also lie for example between adjacent roofs. Using a dynamically determined threshold in the height distribution of each watershed segment gives a possible ground candidate area of the segment. Merging all ground candidate areas and taking only larger areas with special properties into account gives all ground candidates. Keeping only the heights of these areas as real ground and filtering and filling them gives the final DTM. In the presented paper we describe the method in detail and apply the method to different DSMs of rather flat and hilly urban and non-urban environments, discuss the results and give finally an evaluation of the quality of the results