149544 research outputs found
Sort by
Beschleunigung instationärer transsonischer Lastensimulation mittels einer hybriden viskosen/nicht-viskosen Wandvernetzungsstrategie
No full textModerne Transportflugzeuge zeigen beim Durchflug von Böen in Teilen der Flugenvelope nichtlineare aerodynamische Effekte durch Strömungsablösung und Stoßwanderung. Diese Effekte haben einen signifikanten Einfluss auf die Lasten im Flügel. Um diese bei der Auslegung der Struktur zu berücksichtigen, müssen RANS-basierte CFD-Verfahren angewandt werden. In diesem Vortrag wird eine Vernetzungsstrategie vorgestellt, welche es zulässt, die Simulationen massiv zu beschleunigen. Neben Vergleichen verschiedener Netze, wird auch ein geeignetes Turbulenzmodell ausgewählt, welches die Nichtlinearität hinreichend genau widergibt
The effect of grassland management and landscape structure on arthropod communities
No full textInsect diversity is declining globally, driven largely by habitat loss and agricultural intensification. Landscapes with low biodiversity offer fewer ecosystem functions and are less resilient to climate extremes. Grasslands can serve as biodiversity hotspots within agricultural areas, but not all are species-rich or multifunctional. Management practices strongly influence
grassland species composition, including insect biodiversity, as well as ecosystem functioning. However, it remains poorly understood how specific management practices and use intensity levels affect diverse insect taxa on broad scales. Here, we analyze the effects of grassland management and landscape structure on arthropod diversity in Bavaria, Germany.
Most German grasslands are regularly mown, with mowing times varying across parcels. To capture this, we used a high-resolution mowing dataset derived from satellite time series. We also included a hedgerow map for Bavaria, generated from orthophotos using deep learning. This data was linked to a large arthropod dataset (~12,000 BIN species across 450 families), sampled throughout Bavaria. The spatial data were intersected with the point data by calculating spatial statistics (e.g. mean, variance) for hexagons (200 m edge length) surrounding the points. Using Generalized Linear Mixed Effects Models (GLMMs), we analyze the influence of variables related to grassland mowing dynamics as well as landscape features on insect diversity. First results show that the mean mowing frequency has a significant negative influence on the arthropod diversity over all orders. Further analyses focus on the contribution of e.g. early mowing, variance in mowing dynamics or hedges for overall arthropod diversity and various subgroups such as flying or red list insects. With this analysis, we aim to expand our understanding of how grassland management and landscape structure influence insect diversity across a broad range of grasslands
A decoding algorithm for terminated convolutional codes over the blockwise noncoherent channel
No full textA decoding algorithm for convolutional codes (CCs) is proposed to eliminate the need for pilot symbols in short-packet communication systems operating over a blockwise noncoherent channel, i.e., a channel that introduces a random phase rotation of the transmitted codeword block. The algorithm is tailored to M-PSK modulations and applied to zero-tail terminated CCs. It works by implementing a three-step Viterbi-based noncoherent decoder, where the performance of a first blind decoding stage is enhanced through a code-aided phase estimation (CPE) that allows for correction of previous errors. In this framework, it provides a gain of approximately 0.5 dB compared to a pilot-aided decoder, with a manageable increase in complexity. Furthermore, numerical results show a performance within a few tenths of a dB from finite-length achievability bounds with both BPSK and QPSK modulations
A Summary of Hypersonic Flight Missions and recent Developments by Mobile Rocket Base
Get PDFFounded as a launch service provider for sounding rocket flight missions in the sixties, Mobile Rocket Base (MORABA) has conducted more than 500 sounding rocket missions. For the longest time, focus of the research supported was on astronomy, atmospheric physics and microgravity research. Two decades ago, hypersonics research and testing became a relevant field of engagement, spurring developmental efforts to adapt our traditional sounding rocket portfolio and flight systems to the special needs of hypersonic testing. This encompassed advances in thermal hardening of exposed flight structures and suppressed trajectory designs providing flight Mach numbers up to eight for more than two minutes. Four flight missions also involved vehicle configurations that deviated from the traditional, rotational symmetry of sounding rockets, posing additional challenges to flight stability. The keynote speech provides a summary of our flights in service of hypersonic research from the angle of flight performance and developmental advances on the launch vehicle side. It also strives to give an outlook onto currently planned missions and ongoing launch vehicle developments
GMGPolar v2.1.0
No full textGMGPolar offers a taylored Geometric Multigrid solver for geometries described by curvilinear coordinates (in its simplest case, by polar coordinates). GMGPolar uses an implicit extrapolation scheme to raise the convergence order. For nonstandard finite elements, this result has been shown theoretically and for nine-point finite difference stars, we observed up to convergence order four in all numerical simulations. This extrapolation scheme can be used likewise for other domains described by tensor- or product-format meshes in 2D. For curvilinear domains, suited smoothing schemes have been developed and implemented. GMGPolar offers a matrix and matrix-free version for most of its operators. Its original application is on cross-sectional views of realistic Tokamak geometries for fusion plasma simulations
Multi-Process Stochastic Error Models for DFMC GBAS Carrier Smoothed Code Processing and Preliminary Airborne Results
No full textCarrier phase (CP) smoothing of code pseudorange (PR) measurements is an important means to mitigate PR noise and multipath,
especially for high-accuracy Global Navigation Satellite Systems (GNSS) precision approach and landing applications like
Ground-Based Augmentation Systems (GBAS) and Space-Based Augmentation Systems (SBAS). Traditionally, statistical error
bounding of smoothed PR errors has been done assuming that carrier smoothed code (CSC) filters are in steady-state conditions.
With emerging dual frequency multi-constellation (DFMC) applications, such as the proposed GBAS approach service type E
(GAST-E), it is desirable to be able to statistically bound the smoothed error throughout CSC filter convergence. Building on
recent developments in error bounding of correlated error sources in integrated navigation applications, this paper proposes the
use of Gauss-Markov processes for modeling multipath and other correlated errors in CSC processing along with white noise and
random bias terms. The paper provides a general theoretical development of this approach and then looks at specific examples
for root-mean-square (RMS) over-bounding of airborne DFMC GBAS measurements obtained from flight test campaigns on
different air transport class aircraft. Results for two model sets are shown: a “three-term model” consisting of a single first-order
Gauss-Markov (FOGM) process along with bias and noise components and a “four-term model” with two FOGM processes
plus bias and noise components. The four-term error model is able to provide a significantly less conservative RMS over-bound
to the observed CSC errors during both filter convergence and steady-state conditions. These results demonstrate the feasibility
of using linear stochastic models for statistical error bounding of airborne GNSS errors although the final form of the model
and associated parameters to incorporate into future standards will require further validation efforts
The Discontinuation of TradeLens and What Can Be Learned: Cryptographic Requirements For a New Global Maritime Logistics Infrastructure
Get PDFIn this paper, we examine the recent discontinuation of the blockchain-based platform TradeLens developed by IBM and Maersk, where many obstacles of maritime logistics have been addressed.
With the discontinuation there are lessons to be learned and there is room for new approaches.
We elaborate important cryptographic properties and discuss some issues of a global maritime logistics infrastructure.
In particular, we address three points:
(1)~Centralization, federation and power struggles within the network;
(2)~zero-knowledge properties and applications for maritime logistics;
(3)~the use of post-quantum secure cryptographic primitives
Konstruktive Entwicklung eines modularen Reaktors zur thermochemischen Energiespeicherung auf Basis der CaO/Ca(OH)2 - Reaktion unter Berücksichtigung experimenteller Erkenntnisse
No full textDie Arbeit befasst sich mit der konstruktiven Ausarbeitung eines Reaktors zur Umsetzung der thermochemischen Energiespeicherung, basierend auf der reversiblen CaO/Ca(OH)2 - Reaktion. Als Grundlage für die Konstruktion dienen experimentelle Untersuchungen, die im Rahmen der Arbeit an einem bestehenden mechanischen Wirbelschichtreaktor vorgenommen wurden
Uncertainty Quantification for Multi-hole Pneumatic Probe Measurements in Transonic Turbomachinery Flows
No full textThe continuous pursuit of turbomachinery performance improvements leads o constantly increasing demands on measurement data from turbomachinery flows. Accurate measurements with intrusive multi-hole probes are articularly challenging in transonic flow due the Mach number insensitivity of onventional multi-hole probes near Mach number unity. This has led to the evelopment of probes featuring an additional pressure hole which is not affected by the insensitivity. The paper aims to quantify the effect resulting from random errors on a probe measurement in transonic flow. Two operating modes, the Front Pressure Mode (FPM), a conventional five-hole probe method, and the Base Pressure Mode (BPM), using the base pressure, are compared.
This constitutes the first published comprehensive uncertainty
quantification for a multi-hole probe with a base pressure hole.
Uncertainties from the probe calibration and the turbomachinery measurement are considered. Uncertainties resulting from
the interpolation in the lookup table containing the calibration
data are determined experimentally. The overall uncertainty of
the probe yaw angle and the total pressure in the transonic turbomachinery flow remains relatively unaffected by the mode of
operation. In contrast, uncertainties of the pitch angle and the
static pressure are reduced by about 40 % and 75 % respectively
in BPM