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Supporting Virtual Aircraft Certification via Provenance
No full textExhaustive physical testing ensures the airworthiness of an airplane and is time-consuming and costly. With the latest advancements in computational models and computing power, testing parts virtually becomes feasible. Ensuring the reliability and trustworthiness of such virtual verification processes is a critical point. We collect and assess the obligations and requirements stated by the certification authorities Federal Aviation Administration (FAA) and European Union Aviation Safety Agency (EASA) and from the contributors towards virtual certification. Then, we discuss the possible applications and benefits of using provenance data, which is the documentation of the origins and history of data. By recording detailed metadata, it can support traceability and thus reliability. We propose two provenance models, the first one captures only the workflow between the contributors and their tools. The second one shows the steps of each tool in detail so that the data flow is traceable. These models can be connected by the inputs and outputs of each tool. In the end, the certification authority can use the workflow provenance graph to request the simulation and tool provenance graphs of each contributor. The certifiers have detailed insights into the computational analyses, while the contributors do not reveal their business secrets to each other. Integration of provenance can support regulatory compliance by fulfilling many of the stated obligations and is therefore a promising approach
End-to-End Development and Validation of GNC Algorithms: Towards an Iterative and Automated Process
No full textThe development of Guidance, Navigation, and Control (GNC) algorithms traditionally follows a sequential process, where critical issues often emerge late and require costly rework. To address this, a workflow has been established that begins with rapid prototyping in MATLAB/Simulink, progresses through automated Model-in-the-Loop (MiL) testing, C++ code generation, Software- and Embedded-in-the-Target validation, and culminates in Hardware-in-the-Loop (HiL) testing on real-time platforms. This process is driven by reliability, agility, and automation, leveraging a GitLab-based CI/CD pipeline to ensure consistent, traceable, and repeatable testing across the toolchain. Although challenges remain due to system complexity, computational demands, and safety-critical requirements, advances in tools now enable integrated automation, supporting agile development, standardization, and reusability enablers for reducing risk, cost, and delays in increasingly fast-paced and reusable space missions
Influence of Ink Composition and Drying Technique on the Performance and Stability of Fe-N-C-Based High-Temperature Proton Exchange Membrane Fuel Cells
No full textFe–N–C catalysts have emerged as a potentially cost-effective alternative to Pt-based catalysts in high-temperature polymer electrolyte membrane fuel cell cathodes. However, the optimal design and deposition method of the Pt-free catalyst layer remain unclear. Herein, the effect of conventional oven drying compared with freeze-drying on the performance of commercial Fe–N–C catalyst layers is investigated. The gas diffusion electrodes are fabricated by doctor blade coating. Freezing the wet catalyst layer at –26 °C and subsequent sublimation of the solvents leads to a 45 % increase in mass-normalized peak power density compared to the conventional oven drying. This is attributed to a templating mechanism of the solvents, resulting in a thicker catalyst layer and improved acid retention, which enables optimal reactant transport. In contrast, freeze-drying with liquid nitrogen negatively impacts the catalyst morphology, leading to reduced porosity and performance. During 100 h of operation, the performance decreases by a similar magnitude, regardless of the fabrication method used. Operando electrochemical impedance spectroscopy with the distribution of relaxation times shows no catalyst deactivation through the fabrication methods. The results highlight the importance of optimizing catalyst layer fabrication methods for Fe–N–C catalysts to achieve improved performance in fuel cell applications
Water-Tunnel Investigation of Geometry-Induced Separation of a Turbulent Boundary Layer
No full textThe separation of a turbulent boundary layer developing over a flat plate at nearly-zero pressure gradient was experimentally studied in this work in the Large Water-Tunnel Braunschweig. The reported measurements were conducted via Temperature-Sensitive Paint and Lagrangian Particle Tracking by Shake-The-Box in the region downstream of a backward-facing ramp, which induced a turbulent separation bubble. The examined Reynolds numbers, based on the ramp location, were in the range 1.2 to 2.7 million
Effect of fabrication parameters on the vibro-acoustic behavior of 3-D printed membrane-type resonators
No full textThe rising interest in acoustic metamaterial applications stems from the ability to manipulate sound waves through locally resonant structures. Membrane-type resonators continue to arouse the curiosity of researchers, particularly because of their potential for low-frequency sound insulation purposes. When designing a membrane-type resonator, the magnitude of stress within the membrane is a critical factor in attenuating targeted frequencies. The fused deposition modeling (FDM) method offers versatile fabrication options for resonator design via multi-material printing capabilities. The residual stress resulting from the one-shot printing process of a thin, flexible membrane and a relatively rigid frame is expected to vary according to the fabrication parameters. To address this, the effect of these parameters within the FDM process on the pre-stress of membrane resonators is examined. This study involves modal analysis to determine pre-stress using a laser Doppler vibrometer, with results compared to numerical simulations. Finally, the sound transmission loss of selected samples is measured using an impedance tube
Stepping forward: Exploring biological control concepts to advance robotic locomotion
No full textIn biology, motions arise from the tight and complementary integration of morphology, control, and environment rather than hierarchical structures controlling individual joints. Understanding each aspect of this biological concept of embodied intelligence is a grand challenge that holds the promise of achieving equally elegant movements in robots. In this quest, sharing knowledge between these two fields can benefit both sides, as demonstrated in this dissertation for the control of dynamic compliant movements. Initial human experiments carried out as part of this dissertation revealed that the Central Nervous System (CNS) appears to apply topographically precise gain scaling of motoneurons, which functions analogously to a robotic autoencoder derived in previous research. This controller has been shown to be effective in exciting, simple intrinsic motions in compliant robots, suggesting that the CNS might do the same. This aligns with the idea that humans exploit their intrinsic body dynamics in motions, which was further supported by another human study presented in this work, showing that humans can intuitively estimate nonlinear dynamics and excite those in compliant interactions. To compare the suggested bio-plausible robotic controller with other bio-inspired controllers like Central Pattern Generators, both were implemented on a
biomimetic leg. By comparing quantifiable metrics for energy efficiency and stability, this work highlighted that not only is the correct entrainment of the control signal to the mechanical system important, but the signal shape also needs to match the actuator. This inspired two further experimental investigations into modeling and exploiting motor dynamics and improving sim-to-real transfer for realistic robotic simulations. The frameworks from these investigations were combined with the bio-plausible robotic controller and recent advances in nonlinear mode theory to explore locomotion based on embodied intelligence in the novel highly-compliant quadruped eBert. Its mechanics encode six different modal oscillations, which can be validated on hardware using the bio-inspired simple robotic controller. Each modal oscillation suggested a matching
foot pattern that was added with a black-box optimized step length. Through this, each mode naturally developed into a different gait, where the gait velocity related to the underlying mode frequency. Combined, this dissertation advanced biological understanding through robotic tools while applying new concepts for compliant robots inspired by biology, highlighting the potential of bi-directional knowledge transfer between the two fields
Measurement of real-world emission indices for typical aircraft engine types at Frankfurt Airport
No full textExperimental Performance Analysis of a 50 kW Brayton Turbomachine Heat Pump Demonstrator
No full textThe high-temperature heat pump CoBra is the first demonstrator of a closed-loop Brayton heat pump realizing sink temperatures above 150 °C. The experimental results can proof the feasibility of a turbomachine-driven Brayton heat pump delivering heat and cold simultaneously. The German Aerospace Center (DLR) developed the Cottbus Brayton cycle heat pump CoBra, a closed-loop Brayton heat pump utilizing dry air as the working medium. The CoBra is fully operational and has been used for experiments since spring 2024. This work evaluates the steady-state performance of the CoBra heat pump demonstrator experimentally for the first time. In the current setup, the heat pump achieves a heating capacity of up to 55 kW and can supply process heat up to 170°C with a coefficient of performance (COP) of 1.39 using air at TIII = 15 °C as sole heat source. The heat pump’s operational envelope and performance in terms of supplied thermal power, supply temperature and efficiency is analyzed for different operating conditions. Increasing compressor speed raises both heating power and supply temperatures. Using recuperation raises both supply temperature and COP. Fluid inventory control is experimentally confirmed to be a promising control strategy for closed-loop Brayton machines. It widens the operational envelope towards part load operation at constant supply temperatures while maintaining constant efficiency. Operating points in the compressor map remain on the same operating line, thus compressor stability is not impacted by this control method
Safety Assessment of Maritime Autonomous Surface Ships: A Scenario-Based Approach
No full textMaritime Autonomous Surface Ships (MASS) promise enhanced efficiency in shipping operations, but ensuring their safety presents significant challenges. Traditional distance-based testing, where safety is assumed after travelling a predetermined distance without incident, is impractical for MASS due to prohibitively large distance requirements. Drawing inspiration from the automotive domain, we apply scenario-based testing, where the space of operating conditions is divided into traffic scenarios. Scenario-based testing makes it possible to increase the efficiency of testing by specifically targeting high-risk scenarios. We employ maritime Traffic Sequence Charts (mTSCs) to formally specify test scenarios and corresponding requirements. Our approach encompasses three key elements. First, in a hazard analysis, risk-triggering scenario properties are systematically identified through expert-guided brainstorming and investigation of causal relationship. This results in abstract test cases and safety requirements, which are formally specified as mTSCs. In a second step, concrete test scenarios are generated for each abstract test case by converting mTSCs into mathematical SMT problems and solving these for vessel movements modelled as Bézier splines. Finally, runtime monitors derived from mTSCs are used to continuously evaluate requirement satisfaction during testing. We find that systematic hazard analysis, automated scenario generation, and runtime monitoring can successfully be applied to the verification of maritime systems. The formal specification enables automatic test execution and evaluation in both simulation and real-world environments
Zwischen Forschung und Praxis: Der Erlebensatlas als Impulsgeber für Mobilität 4.0
No full textDer Erlebensatlas untersucht, wie Reiseerfahrungen entlang intermodaler Mobilitätsketten psychometrisch valide erfasst und in einer interaktiven Karte in Echtzeit visualisiert werden können. Ziel ist es, kollektive wie individuelle Erlebnisverläufe sichtbar zu machen, um Schwachstellen in Reiseketten zu identifizieren und datenbasierte Grundlagen für Serviceinnovationen im öffentlichen Verkehr zu schaffen. Methodisch kombiniert das Projekt subjektive Selbstauskünfte, physiologische Messungen und kontextuelle Reisedaten, die über die Forschungs-App KeepMoving synchronisiert werden.
Die Präsentation wird zentrale Herausforderungen dieses Ansatzes beleuchten. Im Fokus stehen zum einen psychometrische Fragen, etwa die Modellierung von Erlebnisdimensionen und die Sicherstellung reliabler Messungen im Feld. Zum anderen werden die technischen Anforderungen an eine Echtzeit-Visualisierung diskutiert, die eine Integration heterogener Datenströme in dynamische Karten erfordert. Darüber hinaus sollen die Implikationen für die Einbettung in bestehende Mobilitätsökosysteme, für die Nutzung in datengetriebenen Innovationsprozessen und für strategische Beratungsansätze thematisiert werden.
Der Erlebensatlas adressiert damit nicht nur grundlegende Forschungsfragen an der Schnittstelle von Mobilität, Psychometrie und Datenvisualisierung, sondern eröffnet zugleich neue Perspektiven für die Gestaltung nutzerorientierter und resilienzfördernder Mobilitätsangebote im Kontext von Mobilität 4.0