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On the Uncertainty of a Simple Estimator for Remote Source Monitoring over ALOHA Channels
No full textEfficient remote monitoring of distributed sources is essential for many Internet of Things (IoT) applications. This work studies the uncertainty at the receiver when tracking two-state Markov sources over a slotted random access channel without feedback, using the conditional entropy as a performance indicator, and considering the last received value as current state estimate. We provide an analytical characterization of the metric, and evaluate three access strategies: (i) maximizing throughput, (ii) transmitting only on state changes, and (iii) minimizing uncertainty through optimized access probabilities. Our results reveal that throughput optimization does not always reduce uncertainty. Moreover, while reactive policies are optimal for symmetric sources, asymmetric processes benefit from mixed strategies allowing transmissions during state persistence
OpSTAR: Lighting the Path to the Future of PNT
No full textIn recent years, society has undergone
a digital transformation. Today, the
invisible foundation of our modern
society actually extends beyond pure
digital data-it hinges on integrating
data with spatial and temporal information. Positioning, navigation and timing
(PNT) systems serve as the backbone
of countless critical functions from
synchronizing stock exchanges and
energy grids to guiding aircraft, shipping fleets, and emergency responders.
The ability to determine the "where"
and the "when" with high precision
is no longer optional-it has become a
crucial enabler for responding to key
societal challenges.
For decades, space-based PNT systems, such as Europe's Galileo, have
provided global, reliable PNT services. These systems bring significant
socio-economic, political and strategic
benefits by enhancing efficiency, safety
and productivity across various sectors.
Acknowledging the evolving geopolitical landscape, the growing ecological
challenges posed by climate change, and
the rapidly increasing reliance of the
economic and defence sectors on GNSS,
the demands on current and future PNT
systems are rising dramatically.
Considering these ever-increasing
demands and, on the downside, the
growing threats to critical PNT infrastructure, Europe faces a strategic
decision to either maintain the current
PNT capabilities and risk European PNT
becoming obsolete, or embracing novel
technologies to ensure its leadership in
an evolving world.
Among those novel technologies that
can offer improved performance, greater
autonomy, resilience and extended reach,
laser-based connectivity for optical
inter-satellite links (OISL) and optical
ground-to-space links (OGSL) stand out
as the most promising technology for
PNT systems in the near to mid-term
future. Already revolutionizing the field
of satellite communications, optical link
technologies are now poised to transform PNT systems and applications.
The key question is not whether this
transition to optical PNT will happen,
but when and under whose lead
Methodology for Exploring SOFC System Layouts in a Highly Integrated Hybrid Propulsion System
No full textThis paper presents a methodology to compare different layouts of a solid oxide fuel cell (SOFC) system, focusing on component integration and constraints for low-emission aircraft propulsion. The SOFC system is a subsystem of an Integrated Power and Propulsion System (IPPS) fueled by hydrogen and tightly coupled with a micro gas turbine (mGT). The methodology presented here is applied to the case study of a mGT-SOFC and will later help to define the SOFC system layout for the 1MW+ IPPS of the FlyECO project.
Due to the low power density of current SOFCs designed for stationary applications, technology projections are used to explore a scenario of entry into service in 2050. Parametric analyses have been performed to consider possible future developments and performance opportunities on the basis of anticipated increases in SOFC power density, which so far could only be implemented on a laboratory scale.
Different SOFC system layouts are defined by assuming different aircraft operating conditions (take-off and cruise) as design point, due to the important impact of ambient pressure and temperature in-flight variation on the SOFC system, the related components and the overall performance. To maximize the synergy between SOFC and mGT, all layouts are based on a pressurized SOFC and include a heat exchanger for heat recovery and flow pre-heating.
The system performance exploration is carried out with the W-TEMP software, varying the hybridization factor of the mGT-SOFC system between 5% and 20%, and comparing its performance to a baseline H2-fueled mGT. The results obtained for this performance exploration report details on the coupling aspects between the micro gas turbine and the SOFC system and show clearly the advantages of mGT-SOFC integration in terms of net efficiency and production of water, which can be used in the combustion chamber of the mGT to limit the formation of NOx. In conclusion, a procedure to preliminary estimate the mass of the main components in each layout is also presented, to assess how different choices in the design of the mGT-SOFC can affect its weight
Development of PFAS-free silver-based Gas Diffusion Electrodes for electrochemical CO2 reduction
No full textObjective:
Development of fluorine-free gas diffusion electrodes
Decoupling hydrophobicity and mechanical stability via new production method
Investigate optimal incorporation of the hydrophobic componen
OnboardEU: Urban light rail vehicle-track interaction for infrastructure condition monitoring (Version 1.0.0)
No full textThe dataset provides a data catalogue of axle-box accelerations with corresponding vehicle speed and travelled distance profiles measured on in-service light rail vehicles for rail infrastructure condition monitoring.
The data set was created and published within the mFUND project OnboardEU
Ludwig, Rudolf und Emil Rüb - Vergessene deutsche Flugzeug- und Hubschrauber Pioniere
Get PDFLudwig Rudolf Rüb, ein leidenschaftlicher Erfinder und enthusiastischer - aber meist unterfinanzierter - Visionär, lebte die meiste Zeit seines Lebens in Armut und ist in der Gemeinschaft der Drehflügler praktisch unbekannt. Seine ersten Erfindungen betrafen Verbrennungsmotoren und Motorräder. Um 1900 baute er im Auftrag des Grafen Zeppelin ein Schaufelradflugzeug, als nächstes entwarf und baute er in München eine erste Version eines Koaxialrotor-Hubschraubers und zog dann nach Ulm, um ein großes Starrflügelflugzeug zu bauen. Keines dieser Projekte wurde jemals fertiggestellt. Zu Beginn des Ersten Weltkriegs griff er mit Unterstützung der deutschen Armee eine verfeinerte Version seines Konzepts eines KoaxialrotorHubschraubers auf, der als äußerst wendiger und manövrierfähiger Ersatz für die damals verwendeten Beobachtungsballons gedacht war und auch aktiv an der Kriegsführung teilnehmen sollte, indem er die Installation eines Maschinengewehrs oder Granatenabwurf vorsah. Er enthielt einige erstaunlich fortschrittliche Funktionen und mit Hilfe seiner Söhne wurde die Konstruktion im Juni 1918 abgeschlossen und mit den Bodentests begonnen. Mit dem Ende des Krieges wurden alle Arbeiten sofort eingestellt. Der Vertrag von Versailles verlangte die Zerstörung des Vehikels und beendete damit Rübs aeronautische Arbeit. Ludwig Rüb, ein kluger Mann mit guten Ideen, jedoch ohne akademische Bildung, starb 1918, ohne seine Rotoren sich drehen gesehen zu haben
Next-Generation Molten Salt Thermal Energy Storage Based on Chlorides: Stirring Dynamic Corrosion Tests on Commercial Alloys
No full textMolten salts can be used in many ways as thermal energy storage media. The use
of chloride salts is very promising in this regard, as it reduces investment costs and increases efficiency. However, due to their extremely high corrosiveness, they are not yet used commercially, as this would require special and very expensive alloys.
Initial experiments show, however, that with suitable pre-treatment of the salt,
corrosion of commercial stainless steels can be significantly reduced. These experiments were all carried out statically. However, since the salt moves in the real
operation of a salt based thermal energy storage, this thesis attempts to take this
into account through a dynamic experiment.
It shows that the corrosion rates increase significantly and the value required by
the US government (below 15 µm) cannot be met. Chromium depletion and the
associated pitting corrosion are the main causes of this.
To minimize the impact of corrosion, Nickel based alloys have to be used which are
expensive for commercial scale deploymen
Coupled Finite element simulation of SMA-sheet for morphing applications
Get PDFIn recent years, Shape Memory Alloys (SMA) have become increasingly available as sheet stock, offering a promising solution for morphing applications of large-scale aircraft structures. However, the utilization of SMA sheets presents several challenges compared to traditional SMA wires, which are commonly used in morphing structures concepts. While SMA wires are easy to handle and calculate, they often lack the necessary force to achieve significant deformations in stiff structures. In contrast, sheet SMA offers a more powerful alternative, but its deformation behavior and activation methods require further understanding. One of the primary challenges with using sheet SMA is the complex deformation behavior as well as nonhomogeneous strains and stresses within the sheet during the shape-memory effect (SME). With regards to SMA wires, these effects are well understood and activation through electrical heating is commonly used but can’t be transferred to sheet SMA. Non-uniform heating through Joule heating influences the transformation behavior in an unknown way. To address these challenges, coupled finite element (FE) methods to simulate the deformation behavior of sheet SMA in stiff morphing structures were used. By combining static structural simulations with thermo-electric simulations, non-uniform heating through electric heating was taken into consideration and its effects could be studied. A 3D material model for the SME developed by Auricchio was used. The simulation involved placing two identical SMA sheets on each side of an arbitrary flat carbon fiber reinforced plastic (CFRP) plate. Both sheets were prestrained and then bonded to the plate in order to use the one-way-effect. One sheet was heated and thus contracted due to the SME, while the other remained at room temperature. Therefore, a bending of the structure is achieved. The simulation results showed that significant deformations can be achieved, even with stiff structures. In the evaluation of the results, emphasize is put on stresses and strains within the bonding of the SMA sheets to the CFRP plate in order to gain requirements for later bonding methods. Elastic and transformation strains within the SMA sheets are analyzed to gain an understanding of the SMA material behavior. In conclusion, this presentation provides a first look into the possibilities and limitations of using sheet SMA for large-scale morphing applications. The research highlights the possibilities of using sheet SMA as well as the need for further investigation to overcome current challenges and unlock the full potential of this SMA sheets. A further outlook is given for the necessary steps until the simulated structure can be realized
Influence of Injector and Chamber Design on LOX/CH4 Combustion Instabilities
Get PDFA shear-coaxial element is a prominent choice in terms of injection technology for bipropellants with a high density ratio. While this type of injector performed well for liquid-oxygen and hydrogen combustion in an optically accessible single-element combustor and a multi-injector thrust chamber, the same combustion devices featured instabilities using liquid oxygen/natural gas. Both experiments showed short-lived events of oscillatory combustion and high-amplitude and high-frequency limit-cycle combustion instabilities within the analyzed tests. The stochastic distributed occurrence of such intermittent events of heightened excitation is typically related to the operation of the combustion system close to its stability boundary. Analyzing the high-speed imaging of the optically accessible experiment during these phases showed injector-generated hydrodynamic phenomena preceding the short-lived combustion instabilities. Finally, depending on the chamber configuration and operating conditions -primarily the momentum flux ratio -these events triggered high-frequency combustion instabilities. Consolidation of the data obtained from different hardware configurations highlighted the significant role of recessed injector elements in developing combustion instabilities