149544 research outputs found
Sort by
Brief communication: Daily, gap-free snow cover information based on a combination of NPP VIIRS and MODIS data
Get PDFCombining Moderate Resolution Imaging Spectroradiometer (MODIS) and Visible Infrared Imaging Radiometer Suite (VIIRS) snow cover data and applying cloud- and data gap interpolation steps can be utilized to generate daily, gap-free snow cover information. Provided by the German Aerospace Center (DLR) under the name “Global SnowPack”, this product has undergone several improvements, comprising the inclusion of VIIRS, a new threshold for the Normalized Difference Snow index (NDSI), and considerable validation. The Global SnowPack offers unique opportunities for analyzing time series of snow cover data since September 2000 and is freely available for visualization and download from DLRs GeoServic
Model-based Systems Engineering in Preparation of Space Operations: The COMPASSO Mission On-Board the ISS as Use Case
No full textThe COMPASSO mission of the German Aerospace Center plans the in-space demonstration of optical clocks and
optical space to ground links. These technologies can increase the performance of Global Navigation Satellite Systems
(GNSS) due to a more precise timing and a higher orbit determination accuracy. A Model-based Systems Engineering
(MBSE) approach is used to manage the development process of the COMPASSO system.
MBSE is based on formalized data models that describe the requirements, functions, architecture, and behavior of a
system. The COMPASSO system design has been developed and modeled starting from the initial project idea and the
high-level mission goals to a coarse system design followed by a logical and functional architecture and finally the
physical system architecture.
In this paper a workflow is proposed using the MBSE model to enable the mission operations team to gain insights
how to operate COMPASSO during the design phase of the project and involve them in the design process. The focus
is placed on the functional level of the COMPASSO model, as at this architecture layer all functionalities of the
subsystems are modelled and interconnected. This functional architecture allows further analysis of the behaviour of
the complete system.
The mission objectives are the highest level of requirements and have been defined at the beginning of the project.
They have been imported into the COMPASSO Capella model, where so-called functional chains have been derived
from the mission objectives. Functional chains are defined in the logical model and describe a functional flow through
the system to carry out specific functionalities. For every experiment that needs to be executed to achieve a mission
objective, a functional chain has been defined in the COMPASSO model. Since at least one functional chain is
available for each mission objective, a comprehensive analysis is possible to determine which subsystems and
functions are involved at which point for each of the experiments to be executed and, ultimately, to achieve the defined
mission objectives. Furthermore, state machines for the whole system are modelled, which enable, in combination with
a self-developed state machine simulator a first analysis on how COMPASSO needs to be operated to carry out the
planned experiments. This information serves as input for the mission operations team to start developing operational
procedures and helps to save time by allowing early identification and resolve of inconsistencies, as they are involved
in the design process at an early stage of the missio
Road Crack Detection and Orientation Estimation Using Airborne Synthetic Aperture Radar
Get PDFCracks on road surfaces are a significant safety hazard that can progress into larger potholes, posing risks to vehicles and passengers. Synthetic aperture radar (SAR) data acquired by high-resolution airborne SAR systems are sensitive to changes on the road surface and can be utilized for periodic road condition monitoring. This study proposes a novel method that combines an adaptive thresholding algorithm with the Radon transform for detecting road cracks and estimating both their severity and orientation. In this approach, the adaptive thresholding algorithm detects the cracks, while the Radon transform qualitatively quantifies their severity using the maximum Radon magnitude from the sinogram and estimates their orientation as bearing angles relative to true north. While the proposed method is applicable to various airborne SAR platforms, it is demonstrated in this study with X-band airborne SAR data acquired by DLR’s F-SAR system with a spatial resolution of 25 cm. The detected cracks and orientations were validated against Google Earth images, showing close agreement with the locations and orientations of the actual cracks. This research underscores the potential of airborne SAR data in supporting predictive road maintenance efforts through early identification of surface defects
Complexity analysis and scalability of a matrix-free extrapolated geometric multigrid solver for curvilinear coordinates representations from fusion plasma applications
Get PDFTokamak fusion reactors are promising alternatives for future energy production. Gyrokinetic simulations are important tools to understand physical processes inside tokamaks and to improve the design of future plants. In gyrokinetic codes such as Gysela, these simulations involve at each time step the solution of a gyrokinetic Poisson equation defined on disk-like cross sections. The authors of [KKR21,KKR22] proposed to discretize a simplified differential equation using symmetric finite differences derived from the resulting energy functional and to use an implicitly extrapolated geometric multigrid scheme tailored to problems in curvilinear coordinates.
In this article, we extend the discretization to a more realistic partial differential equation and demonstrate the optimal linear complexity of the proposed solver, in terms of computation and memory. We provide a general framework to analyze flops and memory usage of matrix-free approaches for stencil-based operators. Finally, we give an efficient matrix-free implementation fo the considered solver exploiting a task-based multithreaded parallelism which takes advantage of the disk-shaped geometry of the problem.
We demonstrate the parallel efficiency for the solution of problems of size up to 50 million unknowns
Aerosol Transmission and Air Quality in a Generic Conference Room - Comparison of Aerosol- and Tracer-Gas-Based Methods
No full textAssessing air quality indicators, including the age of air, by means of tracer-gas measurements is a prevalent technique used to evaluate the effectiveness of indoor ventilation systems. The COVID-19 pandemic has recently drawn attention to the transmission of pathogens via indoor air flows. Measurement techniques for the investigation and characterization of ventilation effects have moved from global to local measurements, using local aerosol sources and particle sensors to determine the aerosol dispersion of specific source-receptor combinations. The study at hand introduces a new test environment that can be used to carry out such investigations. It is a n modular conference room equipped with 20 thermal manikins that simulate the obstruction and heat release of a human body. The study further aims to determine the capacity to estimate air age using investigations that involve distributed or local tracer injections
Modeling and Simulation of Lithium-Ion Batteries with Silicon Anode and Ionic Liquid Electrolyte
No full textWe owe the ubiquity of lithium-ion batteries (LIBs), and therefore much of our modern lifestyle, to the continuous development and improvement of this electrochemical energy storage technology. The latest approaches are pursuing the integration of novel materials with higher storage capacity, above all silicon. Here, especially nanostructured silicon anodes are promising due to their higher intrinsic stability. With their large electrochemical window, ionic liquids are an excellent counterpart to such low-potential anodes. Furthermore, the safety of LIBs is a prominent issue which can be addressed by applying non-flammable ionic liquids. Modeling and simulation support the development of such next-generation batteries. Modeling strategies based on physical and chemical concepts provide intrinsic understanding of the components.
This thesis focuses on thermodynamically consistent transport theories for the description of different materials relevant for LIBs. This includes the application of a transport theory for highly concentrated electrolytes like ionic liquids and a chemo-mechanically coupled model for deforming anode materials like silicon. The theories include important aspects of the respective materials to accurately capture their transport behavior under operating conditions. Special attention is given to the relevance of reference frames. A variation of the electrolyte transport theory in the center-of-volume frame of reference is presented - in contrast to the widespread center-of-mass reference frame.
This volume-based theory is applied to experimental measurements of ion mobilities obtained via electrophoretic nuclear magnetic resonance (eNMR). This method is powerful since it directly detects ion mobilities in highly concentrated electrolytes. The volume-based reference frame describes the experimental findings from ionic liquids and ionic liquid mixtures best. It was found that the relevant boundary condition in the eNMR setup is a vanishing volume flux in contrast to a vanishing momentum flux. On that basis, the focus is brought to transference numbers, which are frame-dependent transport parameters. They are not only an important performance indicator for electrolytes but also a necessary input for physics-based simulations. Transference numbers in different reference frames are presented together with the respective transformation rules.
Finally, ionic liquids and silicon anodes are combined into a full cell modeling framework using the respective transport theories. Here, eNMR measurements provide some of the important input parameters for the ionic liquid electrolyte mixture. A volume-averaged 1d+1d modeling framework is used to study in particular different aspects of a silicon nanowire anode. Physics-based simulations enable the visualization of usually inaccessible quantities like for example the stress distribution in the anode. Nanostructured materials are beneficial due to the slow lithium-ion diffusion in silicon. Nevertheless, it is important to consider the volumetric expansion of silicon when simulating such anodes. Parameter studies on certain anode geometry parameters highlight the importance of supplying sufficient pore space for the volumetric expansion of silicon even with nanostructured anodes
A Systematic Literature Review on the Intersection of Self-X System Classes
Get PDFAlongside the vision of autonomous systems, similar system concepts are being discussed in the research fields of highly automated, intelligent, adaptive, autonomic, and organic systems. Although these types of system are studied in scattered research fields that consider them as distinct system classes, they share similar characteristics and are interrelated to some extent. Experts in various fields present a very heterogeneous view on the intersection of autonomous and comparable system concepts, for example, as interchangeable, distinct, or complementary research approaches. Therefore, this study performs a systematic literature review based on more than 300 articles to investigate the intersection of the system classes, emphasizing their similarities, differences, and relationships from the current state of the art
Hybrid Laser Spectroscopy for Real-Time Standoff Detection of Explosive Residues on Individuals
No full textOur technical demonstrator for the rapid standoff detection of explosive residues on individuals aims
towards a significant advancement in security screening technology, particularly for airport security
checks. This innovative system integrates Mid-Infrared (MIR) and Raman spectroscopy with advanced
tracking, auto-focusing, and real-time analysis capabilities, focusing on enhancing sensitivity to achieve
low detection limits for explosive residues on peoples’ shoes.
Achieving the desired sensitivity and low detection limits presents challenges. When scanning peoples’
shoes for explosives, the shoe materials themselves are bound to influence the quality and clarity of
the spectral results making analysis difficult. Additionally, the useable laser power is limited due to
regulations regarding eye and skin safety. To tackle these challenges, the development of sophisticated
analytical algorithms for both Raman and MIR spectroscopy is essential
Controller Tests for Molten Salt Parabolic Trough Systems with Loop-Wise Control Valves
Get PDFConcentrated Solar Power systems are used to generate thermal and electrical energy from solar radiation. Molten salt as a heat transfer medium offers the possibility of a higher temperature in the solar field and at the same time the use of direct energy storage. The Évora Molten Salt Platform (EMSP) is a research platform to study molten salt in the solar field on a precommercial scale. The use of molten salt requires to adapt control concepts used in thermal oil fields since the temperature rise over the loop and the loop length are different from those of thermal oil. One approach is to use automatic valves in each loop to individually control the loop outlet temperatures. This poster presents controller tests performed at molten salt loop of the EMSP in normal operation and start-up mode. Results are the basis for an individual loop flow control strategy