Jauch, C. ., Jost, R. ., & Kloft, P. . (2024). Hydraulic variable inertia flywheel. Applied Energy, 360, 16. http://doi.org/https://doi.org/10.1016/j.apenergy.2024.122830 (Original work published Februar 2024)
Abstract
A novel variable inertia flywheel that uses the mass of a rotating hydraulic fluid is proposed in this paper. In contrast to variable inertia flywheels that use solid masses, this flywheel stands out for its simplicity. In contrast to many other common energy storages, it does not require any environmentally harmful, rare or expensive materials. The basic working principle and the equations that cover the hydraulic behaviour, the pneumatic behaviour and the energy from angular momentum are introduced. These equations are applied to the geometry of the proposed flywheel concept, which allows quantifying the pressures that act on the different mechanical flywheel components. These pressures, together with the centrifugal acceleration from rotation, lead to the loads that have to be withstood by the mechanical components. A simple method for quantifying these loads, and for dimensioning the mechanical components, allows deriving the stationary masses and inertias. A parameter study is conducted, in which different parameters of the flywheel are varied in order to find the maxima in energy density and specific energy. The results of this parameter study reveal that the proposed hydraulic variable inertia flywheel is a very simple and safe energy storage that could provide AC power systems with inertia and control power to support their frequency.
Weidling, G. ., Krieter, J. ., Lübben, R. ., & Czycholl, I. . (2024). Dominance hierarchy does not influence distances travelled and area utilization in a large group of ponies. Applied Animal Behaviour Science, 271. http://doi.org/https://doi.org/10.1016/j.applanim.2024.106178 (Original work published Februar 2024)
Abstract
In order to improve existing horse husbandry practices by providing social contact and exercise opportunities, it is necessary to fully understand the behaviour of horses in relation to group housing. Therefore, this study investigated the influence of dominance hierarchy on the locomotor behaviour and area utilization in a large group of horses in a pasture-based housing system in Northern Germany. The movements of 40 ponies with established group affiliations were observed over approximately one month from late August to early October 2022 using GPS technology. Their dominance hierarchy was determined by testing each possible combination in separate pair-feeding tests. For the determination of area utilization, the available space was divided into a total of 8889 quadrants with 3x3 m each. Analysis of daily distances travelled by the horses revealed an average of 5.4 ± 1.2 km/day, with no significant effect of social rank. However, age had a significant effect, with older horses walking shorter distances. Quadrants used per hour, as measure of area utilization, averaged 37.9 ± 6.4, with no effect of social rank but a significant effect of age observed. Heat maps showed full pasture utilization, with lower ranked horses having less access to resources around the watering trough and a greater use of less attractive grazing areas. The study suggests that in this specific setting, social rank did not significantly affect locomotor behaviour or area use. Although the study did not find a correlation between dominance rank and locomotor behaviour or area use, it highlighted the need for further research in different group sizes and housing systems to optimise group housing practices for horses, especially in settings with limited space and resources.
Baganal-Krishna, N. ., Lübben, R. ., Liotou, E. ., Katsaros, K. V., & Rizk, A. . (2024). A federated learning approach to QoS forecasting in cellular vehicular communications: Approaches and empirical evidence. Computer Networks, 242, 110239. http://doi.org/https://doi.org/10.1016/j.comnet.2024.110239
Abstract
QoS forecasting for cellular vehicular communications allows cooperative, connected and automated mobility applications to tailor their behavior to the expected communication conditions on the road. In a nutshell, vehicles may, for example, execute cooperative maneuvers if the communication quality of service is only above a certain quantitative level whereas if not they revert to the individual autonomous mode. In this paper, we propose and show empirical methods for estimating packet-based QoS metrics obtained from 5G network measurements with a direct application to vehicular applications. As many distributed vehicular applications possess strict QoS requirements, we focus here on bounding packet-based statistical QoS quantiles, specifically for latency and loss. Our approach is based on training regression neural networks in a federated learning fashion and show that it can obtain predictions on par with centralized training without the vehicles needing to transmit raw measurement data. In contrast to QoS prediction using physical layer information, we briefly discuss the embedding of such much simpler application-level service within the 5G architecture. We also validate our approach through recovering classical closed-form delay quantiles that are obtained from analytical models of simple queueing systems. We show that our approach goes beyond these simple models in that it provides quantile estimates for the complex scenario of cellular vehicle communications and under different application traffic patterns including empirical data traffic traces as well as 5G testbed measurements.
Gürgan, S. ., Bertel, S. ., Gall, C. ., Henze, V. ., Mayer, L. ., Seller, A. ., … Hahn, M. . (2023). SonoGame. Ultraschall Med, 44(S 01). http://doi.org/https://doi.org/10.1055/s-0043-1772423
Voigt, A. . (2023). An algorithm to approximate the real trilogarithm for a real argument. ArXiv. http://doi.org/https://doi.org/10.48550/arXiv.2308.11619 (Original work published August 2023)
Abstract
We present an algorithm to approximate the real trilogarithm for a real argument with IEEE 754-1985 double precision accuracy. The approximation is structured such that it can make use of instruction-level parallelism when executed on appropriate CPUs.
Alhrshy, L. ., Lippke, A. ., & Jauch, C. . (2023). Variable Blade Inertia in State-of-the-Art Wind Turbine Structural-Dynamics Models. Energies, 16(16), 22. http://doi.org/https://doi.org/10.3390/en16166061 (Original work published August 2023)
Abstract
This paper presents a comparison of two methods to represent variable blade inertia in two codes for aero-servo-elastic simulations of wind turbines: the nonlinear aeroelastic multi-body model HAWC2 and the nonlinear geometrically exact beam model BeamDyn for OpenFAST. The main goal is to enable these tools to simulate the dynamic behavior of a wind turbine with variable blade inertia. However, current state-of-the-art load simulation tools for wind turbines cannot simulate variable blade inertia, so the source code of these tools must be modified. The validity of the modified codes is proven based on a simple beam model. The validation shows very good agreement between the modified codes of HAWC2, BeamDyn and an analytical calculation. The add-on of variable blade inertias is applied to reduce the mechanical loads of a 5-megawatt reference wind turbine with an integrated hydraulic-pneumatic flywheel in its rotor blades.
van der Sluis, H. ., & Tausch-Nebel, L. . (2023). “You can concentrate better on the topics and invest more time in it”: A case study evaluating the impact of immersive scheduling on students. Compass: Journal of Learning and Teaching, 16(2), 16. http://doi.org/https://doi.org/10.21100/compass.v16i2.1413 (Original work published August 2023)
Sietas, J. ., Petersen, K. ., & Gerken, J. M. (2023). Evaluierung und Optimierung von Business-Intelligence-Systemen in der öffentlichen Verwaltung - Ein Use-Case-basierter Ansatz. Anwendungen Und Konzepte Der Wirtschaftsinformatik (AKWI), 17. (Original work published Juli 2023)
Tausch-Nebel, L. ., & van der Sluis, H. . (2023). „Man ist mehr im Stoff drin“ – Befunde aus der Verblockung von Grundlagenkursen. Die Neue Hochschule (DNH), (3/2023), 4. (Original work published Juni 2023)
Salleh, N. ., Mendes, E. ., Mendes, F. ., Lekamlage, C. ., & Petersen, K. . (2023). Value-based Software Engineering: A Systematic Mapping Study. E-Informatica Software Engineering Journal, 17.