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In-situ microscopic and macroscopic mechanics of flexible aerogels
No full textAerogels are lightweight, open-porous materials, that exhibit high specific surface area and low thermal conductivity [1]. Among the different types of aerogels, the super flexible silica aerogels exhibit advantageous material characteristics with regards to their mechanical behaviour for practical applications [2]. Moreover, a modification of the density of flexible silica aerogels allows for increased lightweight characteristics without a considerable reduction in heat insulation efficacy [3]. However, there is a lack of knowledge regarding the mechanical behaviour and damping properties of flexible silica aerogels, particularly with regard to their suitability for low-temperature insulation necessary for aerospace and hydrogen applications.
In order to address these challenges, this study aims to provide insights into the micro- and macroscopic behaviour of flexible silica aerogels using computer tomography (CT) and dynamic mechanical analysis (DMA). Flexible silica aerogels of different densities were developed using moulds and shaping of geometries needed for testing was facilitated by the use of razor blades. Resulting geometries were scanned and measured using 3D-scanning technology. In-situ CT is employed while the aerogels undergo compressive loading to track the variation in pore size distribution across the aerogels specimen as a function of compressive strain. Additionally, compression tests were conducted using DMA, which has been employed for non-flexible silica composites previously [4, 5], to examine the mechanical and damping characteristics as a function of temperature and frequency. These combined findings have the potential to accelerate the advancement of flexible aerogel development and facilitate their practical implementation in low-temperature aerospace and insulation applications.
References:
[1] Hüsing N, Schubert U. Aerogels-Airy Materials: Chemistry, Structure, and Properties. Angewandte Chemie International Edition. 1998;37:22-45.
[2] Hayase G, Kanamori K, Nakanishi K. New flexible aerogels and xerogels derived from methyltrimethoxysilane/dimethyldimethoxysilane co-precursors. Journal of Materials Chemistry. 2011;21:17077-9.
[3] Steffens K, Bialuschewski D, Milow B. Tuning density and morphology of organic-inorganic hybrid-silica aerogels through precursor dilution for lightweight applications. Journal of Sol-Gel Science and Technology. 2024;112:768-75.
[4] Churu G, Zupancic B, Mohite D, Wisner C, Luo H, Emri I, et al. Synthesis and mechanical characterization of mechanically strong, polyurea-crosslinked, ordered mesoporous silica aerogels. Journal of Sol-Gel Science and Technology. 2015;75:98-123.
[5] Li Y, Du A, Shen J, Zhang Z, Wu G, Zhou B. Temperature dependence of dynamic mechanical behaviors in low density MTMS-derived silica aerogel. Journal of Porous Materials. 2018;25:1229-35
Residual GNSS Ionospheric Error Analysis in Future Low Earth Orbit Applications
Get PDFFuture low Earth orbit (LEO) applications such as LEO positioning, navigation, and timing (PNT) and LEO-based monitoring of global navigation satellite systems (GNSS) are expected to experience a residual ionospheric delay depending on the altitude a constellation would be deployed. The ionosphere reaches its peak concentration in the F-region at and altitude of 300 km to 400 km. The concentrations of charged particles beyond this altitude constitute the topside ionosphere and may contain a non-negligible density as high up as 1000 km. The literature on dealing with the residual ionospheric error is scarce, and the impact of the residual error has not been yet studied thoroughly in the context of future LEO applications. In this paper we aim to quantify and analyze this residual error. We aid our analysis with 3D-ionospheric model estimates and compare them to collected in-situ total electron content (TEC) measurements from LEO. Thus, we aim to characterize the expected uncorrected error magnitude and its distribution for a single-frequency GNSS receiver depending on the LEO altitude, and on the solar and geomagnetic activit
DEEP LEARNING-BASED ACTIVE TRIM PANELS FOR ENHANCED AIRCRAFT INTERIOR NOISE CONTROL
Get PDFActive noise control (ANC) trim panels offer an effective solution to suppress multi-tonal noise in aircraft. The selective fixed-filter ANC (SFANC) method, characterized by low computational complexity, high robustness and rapid response, is suitable to handle multi-tonal engine noise that varies in frequency due to changes in the rotational speed of the engine shaft. However, real-world conditions introduce variations in lining temperature, altering acoustic and structural paths and degrading noise reduction performance. To address this challenge, a temperature-perceptive SFANC (TP-SFANC) approach is proposed that employs a lightweight one-dimensional convolutional neural network (1D CNN) trained using a multi-task learning strategy. By processing both reference and error signals, the
1D CNN learns frequency and temperature characteristics to dynamically select the optimal control filter. Numerical simulations demonstrate the effectiveness of the proposed method in attenuating multi-tonal noise across varying frequencies and lining temperatures
Complex plasma with Janus particles as a model active-matter system
No full textActive matter is a collection of active particles, each of which can extract energy from their environment and convert it into directed motion, thereby driving the whole system far from equilibrium. Janus particles have two halves of different properties. A two-dimensional complex plasma containing active Janus particles was studied experimentally. A single layer of micrometer-sized plastic microspheres coated on one side with a 10-nm layer of platinum was suspended in the plasma sheath above the lower electrode in a capacitively coupled radio-frequency low-pressure discharge in argon. When suspended in plasma, the Janus particles acquired self-propulsion and moved in characteristic looped trajectories suggesting a combination of spinning and circling motion; their suspension was in a highly disordered liquid state. We study various spatio-temporal correlations in this homogeneous isotropic active liquid state and discuss whether it has characteristics of active turbulence
Mountain Wave Momentum Flux Estimates From Airborne Lidar Measurements in the Middle Atmosphere Above the Southern Andes
Get PDFCross-mountain flow over the Southern Andes and strong zonal winds extending higher up in the atmosphere allowed for mountain waves to penetrate into the mesosphere on 11/12 September 2019 during the Southern Hemisphere Transport, Dynamics, and Chemistry–Gravity Waves (SOUTHTRAC-GW) campaign. The middle atmosphere responses above and in the lee of the mountain ridge were observed by the Airborne Lidar for Middle Atmosphere Research (ALIMA) onboard the German High-Altitude and Long-Range research aircraft (HALO), which provided temperature measurements with both high horizontal (approx.
10 km) and high vertical (1.5 km) resolution. The observations reveal a complex wave field with multiple superimposed wave packets with horizontal scales ranging from about 33 to 395 km. This paper employs spectral analysis of observational data and results of Fourier ray modeling to decompose the wave field and analyze the scales and properties of gravity wave packets. Profiles of the vertical flux of horizontal mountain wave momentum reveal contributions of each wave packet to the total momentum flux and gravity wave drag. The derived momentum flux spectrum suggests a spectral response of the form with the exponent in the range -1.0 to -1.2
and peak momentum flux occurring at approximately \lamba_h = 45 km. Results show that > 80% of the total mountain wave momentum flux is carried by waves with horizontal wavelengths shorter than 100 km
Design of Low-Noise Fan Engines for Urban Air Mobility and Sound Quality Analysis Using Virtual Flyovers
Get PDFUm eine neue Form des urbanen Luftverkehrs zu ermöglichen, werden neue Flugzeugkonzepte mit verteilten Antriebssystemen erforscht, die mit einer größeren Anzahl von Triebwerken ausgestattet sind, beispielsweise mit verteilten, ummantelten Fans. Aufgrund von akustischen und psychoakustischen Effekten werden sich die Geräusche solcher Antriebssysteme von denen bestehender Antriebe unterscheiden, wodurch die Lärmwahrnehmung zu einem entscheidenden Faktor für die gesellschaftliche Akzeptanz wird.
In dieser Arbeit werden tonale Schallminderungseffekte für langsam drehende, ummantelte Fanstufen mit weniger Stator- als Rotorschaufeln untersucht. Es wird analysiert, wie solche Fanstufen für die urbane Luftmobilität ausgelegt werden können, sodass sie nicht nur leiser sind als konventionelle Designs, sondern auch als weniger unangenehm empfunden werden. Dazu wird das Schaufelzahlverhältnis variiert, wodurch drei akustisch vorteilhafte Designräume identifiziert werden. Zwei tonale Schallminderungseffekte werden analytisch, numerisch und experimentell analysiert, und darauf aufbauend zwei Entwurfsregeln abgeleitet.
Die tonalen Schallminderungseffekte werden an zwei Fanstufen mit reduzierter Stator-schaufelzahl demonstriert. Diese werden anschließend virtuell in ein verteiltes Antriebssystem eines Flugtaxis integriert. Trotz vergleichbarer aerodynamischer Leistung zeigen sie deutliche Unterschiede in der Schallabstrahlung. Die Geräuschqualität wird über virtuelle Überflugsimulationen bewertet. Die Ergebnisse zeigen eine Reduktion des EPNL um mehr als 6 dB sowie eine deutliche Verringerung von Lautstärke, Tonalität und Rauheit gegenüber einem Referenzdesign
A Generic SpaceWire Transport Layer
No full textThe transport layer is the essential part in the
open system interconnection (OSI) reference model, since it
is the interface between the software-oriented layers 5-7 and
hardware-oriented layers 1-3. On the one hand, it provides a
general approach for data exchange with the software-oriented
layers, independent of the underlying hardware. On the other
hand, it is responsible for an efficient and reliable use of the
underlying hardware. These characteristics make the transport
layer crucial for the effective usage of a communication system, as
it significantly reduces the implementation effort for the software-oriented layers.
The lack of a transport layer is a huge disadvantage. Combining the functionality of different communication layers into
single application specific protocols can lead to the coexistence
of multiple, non compatible approaches, resulting in a higher
implementation effort for integrating new applications. Therefore, the existence of a transport layer is fundamental for both
communication software and hardware, to provide established
communication concepts, which are a precondition for the use
of standardized software libraries, and to integrate modern
computing trends (e.g. Big Data, Data-Mining, machine learning,
cyber security).
SpaceWire does not yet define a general transport layer. This
paper presents the approach of a minimalist SpaceWire transport
layer, as common base for the implementation of higher level
protocols. It comprises both the hardware related SpaceWire
transport node and the associated software counterpart as well
as the associated protocol. The transport layer implementation
is one result of our longstanding SpaceWire development and is
already in use in several robotic systems
Surface science on Phobos with the navigation cameras of the MMX IDEFIX rover
Get PDFPhobos, the largest and closest moon to Mars, is the principal target of the Martian Moon eXploration (MMX) JAXA mission, which is scheduled for launch in 2026. The mission will orbit Phobos and perform multiple fly-bys of Deimos, send a rover to the surface of Phobos (Michel et al., 2022) and retrieve and return ≥10g of Phobos regolith back to Earth in 2031 (Kawakatsu et al., 2023; Kuramoto et al., 2022). The primary objective of the mission is to provide a definitive answer regarding the origin of the martian moons. The mission comprises an orbiter and a small rover, designated IDEFIX. The latter is a contribution from the Centre National d’Etudes Spatiales (CNES) and the German Aerospace Center (DLR). The instrument suite on board the rover will comprise the navigation cameras (a stereo pair), two wheel cameras, a Raman spectrometer and a mini radiometer. The cameras (NavCams & Wheelcams) are a contribution from CNES, whereas the remaining two instruments are provided by DLR
