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Model based assessment of maximal surface temperatures and heat flow in edge trimming of UD CFRP with tools of different type
No full textExcessive heating during edge trimming of CFRP components leads to matrix degradation impairing their quality. The thermal response of unidirectional CFRP when machining with different tool types is studied: PCD cutters, coated carbide routers, and diamond grinding pins. Temperature and torque were measured at various fibre orientation angles Φ and cutting conditions. Based on an analytical model, key thermal parameters were identified from experimental data. For all tools, temperatures exceeded the matrix glass transition temperature under most conditions. Maximum of temperature changes was observed at Φ = 135°, minimum at Φ = 90° was most pronounced for the cutter, less noticeable for the router, and almost absent for the grinding pin. At Φ = 90°, the thermal contact length and heat flow ratio typically reached maximum values, while the heat flux was at its lowest. Regarding cutting conditions for both the cutter and router, an increase in cutting speed led to higher equivalent heat flux, heat flow, and temperature change. In contrast, for grinding pins, temperature change increased at the lower cutting speed or feed rate. In grinding, heat flow, equivalent heat flux and thermal contact length were primarily influenced by the fibre orientation symmetry angle, whereas heat flow and equivalent heat flux were nearly independent of the cutting conditions. Thus, the tool types exhibit different thermal parameters and patterns of their dependencies on the machining conditions, which are differentiated by the model and can be explained by pulsed point, pulsed linear or continuous surface contact of individual cutting edges
Non-interactive threshold BBS+ from pseudorandom correlations
No full textThe BBS+ signature scheme is one of the most prominent solutions for realizing anonymous credentials. Its prominence is due to properties like selective disclosure and efficient protocols for creating and showing possession of credentials. Traditionally, a single credential issuer produces BBS+ signatures, which poses significant risks due to a single point of failure.I n this work, we address this threat via a novel t-out-of-n threshold BBS+ protocol. Our protocol supports an arbitrary security threshold t≤n and works in the so-called preprocessing setting. In this setting, we achieve non-interactive signing in the online phase and sublinear communication complexity in the number of signatures in the offline phase, which, as we show in this work, are important features from a practical point of view. As it stands today, none of the widely studied signature schemes, such as threshold ECDSA and threshold Schnorr, achieve both properties simultaneously. In this work, we make the observation that presignatures can be directly computed from pseudorandom correlations which allows servers to create signatures shares without additional cross-server communication. Both our offline and online protocols are actively secure in the Universal Composability model. Finally, we evaluate the concrete efficiency of our protocol, including an implementation of the online phase and the expansion algorithm of the pseudorandom correlation generator (PCG) used during the offline phase. The online protocol without network latency takes less than 14 ms for t≤30 and credentials sizes up to 10. Further, our results indicate that the influence of t on the online signing is insignificant, ≤6% for t≤30, and the overhead of the thresholdization occurs almost exclusively in the offline phase. Our implementation of the PCG expansion shows that even for a committee size of 10 servers, each server can expand a correlation of up to 217 presignatures in less than 100 ms per presignature
Competitive and cooperative: on the reorganisation of the relationship between private and public media in the digital age
No full textThe relationship between private and public service media in Germany has traditionally been perceived and regulated as one of competitive coexistence and reciprocal counterbalancing. However, digital transformation and the rise of platform dominance challenge this perspective. In response, this article argues for a coopetition approach, where competition and collaboration coexist to strengthen democratic public spheres. We propose a framework for cooperation between private and public service media, highlighting infrastructure sharing and other forms of public value contributions. Such a coopetition framework allows rethinking media relationships through unilateral and strategic collaborations, which can enhance media diversity and resilience in the digital era
Advancing humanoid robotics with Rust: An open framework for runtime efficiency
No full textThe development of software frameworks plays a pivotal role in the research on humanoid robotics. This paper introduces a novel robotics framework designed to address challenges in the RoboCup and robotics in general. We present an overview of existing frameworks within the RoboCup Standard Platform League (SPL), highlighting their benefits and limitations. We define a set of requirements that serve as a guiding principle for the development of robotic frameworks. Our novel framework emphasizes modularity and parallelization while optimizing for minimal runtime overhead and complexity. Implemented in Rust, we combine computational efficiency with safety, positioning it as a robust solution for robotic applications. We show that the framework’s runtime overhead on a NAO robot has little impact. We conclude with case studies of its application at Team HULKs and other teams, showing its real world use case and impact in the RoboCup SPL
A provably safe controller for the needle-steering problem using online strategy synthesis
No full textAutonomous systems often address complex planning problems, which require both prospective action planning and retrospective data evaluation. Timed games could aid since they automatically synthesize strategies that, provably correct, solve those planning problems; yet, they assume a static model of the environment, which is not realistic for autonomous systems. However, many autonomous systems are control applications, which employ sensors that capture system behavior at run time and can thus compensate for incomplete knowledge at modeling time. In this paper, we propose an online strategy synthesis, which, based on offline strategy synthesis on the one hand and on sensor information about the current state of the physical world on the other hand, derives formal safety guarantees while reacting and adapting to environment changes. We formalize the needle-steering problem from medical robotics, i.e., the problem of navigating a (flexible and beveled) needle through partially unknown tissue towards a target without damaging its surroundings, by interpreting it as a timed game. Further, we introduce a new representation of its environment through different region types that determine the acceptance of action plans and trigger local correcting actions. We present an algorithm for online strategy synthesis and, for the given region representation, formally prove that it returns safe online controllers. The algorithm is implemented on top of Uppaal Stratego. For two medical applications of needle steering, peridural anesthesia and predefined needle trajectory, we demonstrate the necessity of online adjustments in a series of simulations with various degrees of initial knowledge about the environment, and show that the overhead of online synthesis remains practical
Use case: layout and control optimization of a hybrid ship power system in the early design stage ; system Integration & hybridization
No full textWith the trend in shipping industry to switch primary fuels to renewable low flash-point alternatives, the abilities of internal combustion engines of handling transient loads are reduced. This has a major impact on maneuverability of ships and is therefore crucial for regulatory, contractual and safety aspects. Hybridization of the power systems including energy storage and shaft alternators can compensate for disadvantages by providing additional degrees of freedom, making stable control of the power system essential. The decision for an appropriate power system and its control system needs to be made in early design stage to avoid increased project costs for late changes. Thus, fast and accurate simulations based on limited project data are required. The simulation tool HyProS depicts a software solution to estimate the performance of shipboard power systems for such use cases. Part of it is a generic mean-value model of medium- and high-speed engines, which is parameterized with e.g., project guide data. The focus of this work is on optimizing control strategies
for a typical use case with respect to different objectives using HyProS. The power plant architecture envelopes hybrid power supply and hybrid propulsion. The influence of different control settings for major components on the system behavior is worked out and considered for designing the controllers for the objectives of high dynamic performance and overall efficiency. The results are highlighting two things: the capabilities of system hybridization for optimizing vessel operation for different objectives and the benefits of fast simulations in early project phases. The generic engine model allows for a fast simulation setup and provides an advanced understanding of engine limits and their influence on maneuverability compared with models with lower fidelity
Interconnected and data-driven aircraft cabin systems: consistent integration of ARINC 853 messaging standard into model-based aircraft systems development
No full text<div class="section abstract"><div class="htmlview paragraph">Increasing digitalization of the aircraft cabin, driven by the need for improved operational efficiency and an enhanced passenger experience, has led to the development of data-driven services. In order to implement these services, information from different systems is often required, which leads to a multi-system architecture. When designing a network that interconnects these systems, it is important to consider the heterogeneous device and supplier landscape as well as variations in the network architecture resulting from airline customization or cabin upgrades. The novel ARINC 853 Cabin Secure Media-Independent Messaging (CSMIM) standard addresses this challenge by specifying a communication protocol that relies on a data model to encode provided and consumed information. This paper presents an approach to integrate CSMIM-specific communication concepts into a Model-Based Systems Engineering (MBSE) framework using the Systems Modeling Language (SysML). This enables a streamlined model-based method to design and implement aircraft cabin systems interconnected through a CSMIM-based communication network as well as to create airline-customized configurations. Based on the Cabin Data and Communication Modeling Language (CDACML), a SysML mean to link system interfaces with the CSMIM data model across multiple development levels is proposed. Multiple development levels as part of the left side of the widely-accepted V-model are supported to enable a model-based handover into the system level, for example, reducing the risk for interface inconsistencies. The link to the CSMIM data model is designed such that it can be used to extract system interface definitions for implementation activities through Model-to-Text (M2T) transformations. To show the validity of the approach, a smart aircraft seat occupancy detection use case is designed using the proposed approach as part of the activities of the left side of the V-model including the development of a prototype CSMIM communication module. The communication module is then deployed on networked hardware that is configured through a M2T transformation and which is technically realizing this use case.</div></div></jats:p
GPU accelerated multi-patch reconstruction
No full textThe multi-patch approach in magnetic particle imaging is used to capture large field of views. System-matrix-based image reconstruction for this approach often considers a joint system of equations to minimize artifacts. Due to the prohibitive size of this inverse problem, reconstructions rely on iterative algorithms that do not need to keep the entire system matrix in memory. This work shows a graphical processing unit accelerated implementation of a generalized multi-patch operator. The achieved runtime improvements allow for multi-patch reconstructions using different optimization algorithms, which in turn allow for a flexible choice of regularization terms
A workflow for designing stiffness-optimized structures in the context of additive manufacturing of endless fiber-reinforced composites
No full textThis paper investigates the interface between structural optimization for anisotropic materials and modern additive manufacturing methods by presenting and evaluating a workflow for the design of structures for fused filament fabrication using endless fiber-reinforced filament. The process chain consists of optimizing the material orientations and topology of the anisotropic structure simultaneously, non-planar slicing and load-oriented path planning for additive manufacturing. The design workflow is demonstrated using an academic example and validated by a more practical example including mounting regions for bolts and multiple load cases. The results expose requirements for additive manufacturing of continuously fiber-reinforced structures that have to be considered by the optimization process for narrowing the gap between optimization results and simulated performance of the manufactured parts. At the same time, the potential of the presented workflow for designing parts while taking manufacturability into account is demonstrated successfully