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On the relationship between stochastic turnpike and dissipativity notions
No full textIn this article, we introduce and study different dissipativity notions and different turnpike properties for discrete-time stochastic nonlinear optimal control problems. The proposed stochastic dissipativity notions extend the classic notion of Jan C. Willems to LR random variables and to probability measures. Our stochastic turnpike properties range from a formulation for random variables via turnpike phenomena in probability and in probability measures to the turnpike property for the moments. Moreover, we investigate how different metrics (such as Wasserstein or Lévy-Prokhorov) can be leveraged in the analysis. Our results are built upon stationarity concepts in distribution and in random variables and on the formulation of the stochastic optimal control problem as a finite-horizon Markov decision process. We investigate how the proposed dissipativity notions connect to the various stochastic turnpike properties and we work out the link between different forms of dissipativity
Preheating options for novel design concepts for metal hydride storage tanks – Numerical modeling, simulation and evaluation
No full textA geospatial assessment toolbox for spatial allocation of large-scale nature-based solutions for hydrometeorological risk reduction
No full textThe compounding effects of hydrometeorological hazards are being driven by climate change. As urban areas expand, this leads to degradation of the surrounding environment and exposes more people to hazards. Growing losses show that conventional approaches to addressing these issues can compound these problems. Over the last few decades, nature-based solutions (NBSs) have become an increasingly popular alternative. These measures, inspired by natural processes, have shown potential for reducing hazards by complementing traditional approaches and providing co-benefits in the form of eco-system services. With the adoption of NBSs becoming a more mainstream approach, there is a need for tools that support the planning and implementation of interventions. Geospatial suitability assessment is a part of this planning process. Existing tools are limited in their application for large-scale measures. This paper intends to improve this by building upon a multi-criteria analysis (MCA)-based approach that incorporates biophysical and land use criteria and conditions for mapping the suitability of large-scale NBSs. The methodology was developed and tested on six sites to assess the suitability of floodplain restoration, retention or detention, afforestation, and forest buffer strips. The resulting suitability maps also show potential for combining two or more measures for greater risk reduction
Adaptive finite element phase-field simulation of dynamic brittle fracture
No full textIn finite element analysis, mesh refinement is typically employed to improve accuracy by increasing spatial resolution in regions with steep solution gradients. This study presents an adaptive mesh refinement technique for dynamic fracture simulation based on the phase-field method. A multi-level node distance function is introduced using the phase-field variable to control mesh density. As damage evolves, the nodal spacing is adaptively refined according to the prescribed maximum spacing; whenever the computed distance exceeds this threshold, a new field node is introduced at the element center, ensuring the mesh evolves consistently with crack propagation. In addition, material damping effects are incorporated into the phase-field formulation to capture realistic dynamic fracture responses. Time integration is investigated using the Newmark scheme, the generalized-α method, and the backward implicit approach. The results indicate that, while the first two schemes are commonly applied, the backward implicit method provides superior stability in dynamic simulations. Furthermore, a staggered solution strategy is proposed in which both displacement and phase-field variables are iteratively and consistently updated within each solution step. The effectiveness of the proposed methodology is demonstrated through three numerical examples. The responses of elastic energy, kinetic energy, and energy dissipated by crack propagation are evaluated, together with the effects of material damping. The results confirm that the presented approach significantly improves computational efficiency while preserving accuracy and exhibits robust convergence behavior in highly dynamic fracture simulations
TUHH-Twin – Ein digitaler Zwilling für einen nachhaltigen Smart Campus
No full textUniversitäten spielen im Rahmen der zunehmenden Digitalisierung eine wichtige Rolle, da sie nachhaltige Lösungen und Innovationen fördern können, die langfristig zu einer ökologischeren und sozialeren Entwicklung moderner Städte beitragen. Sogenannte smarte Universitäten – die innovative Technologien zur Digitalisierung in Lehre und Forschung anwenden – können hier bspw. als real existierende Versuchsstätten angesehen werden, da sie im kleinen Maßstab später auf größere Konzepte, wie bspw. Smart Cities übertragbar sind. Zudem bieten universitäre Umfelder die Möglichkeit, junge Menschen in allen interdisziplinären Themen auszubilden, die für die Entwicklung von smarten Bildungseinrichtungen erforderlich sind. Jedoch verfügen viele Hochschulen nicht über ausreichende Lösungen, um Forschungsdaten, die aus Entwicklungen neuer Konzepte erfasst werden, systematisch und langfristig zu verwalten, weshalb viele Projekte nicht weiterverfolgt werden. Ein vielversprechender Ansatz zur besseren Verwaltung von Daten sind digitale Zwillinge oder Digital Twins. Diese bieten eine einheitliche kollaborative Umgebung mit zentraler, standardisierter Verwaltung sowie einem Echtzeitzugriff auf Forschungsdaten. Sie bilden somit die Grundlage für eine ganzheitliche und dynamische Gestaltung von Campus-Umgebungen, in denen das Lern- und Arbeitsumfeld verbessert und gleichzeitig Energieverbräuche minimiert werden
Untersuchung von Entropie-Produktionsmechanismen an einer sorptionsgestützten Luft-Entfeuchtungsanlage
No full textBeim Betrieb von sorptionsgestützten Klimatisierungsanlagen ist der Betrieb und der Energieaufwand von vielen Parametern abhängig. Hierbei ist der Exergiebedarf von zwei faktoren Abhängig: der geforderte Zustand der behandelten Luft und die Entropieproduktion im Prozess. Da die Anforderungen meist fest sind, ist die Optimierung des Betriebs einer solchen Anlage nur mit der Reduzierung von Irreversibilitäten möglich. Hierzu ist eine Untersuchung der Entropiequellen im System erforderlich. Diese Arbeit zeigt die Ergebnisse einer solchen Untersuchung, wo die verschiedenen Mechanismen der Entropieproduktion (Wärme- und Stoffübertragung, Druckverlust und Mischung) direkt beschrieben und ausgewertet werden. Neben der Unterscheidung nach Entstehungsmechanismus wird auch lokale Entropieproduktion berechnet. Diese direkte Berechnung wird anhand einer indirekten Methode validiert. Anschließend werden verschiedene Betriebspunkte hinsichtlich Entropieproduktion analysiert. Es wird gezeigt, dass die größte Entropiequelle die irreversible Wärmeübertragung ist (ca. 53 % im Referenzfall), gefolgt von Stoffübertragung (20 %) und Mischung (18 %). Ebenfalls wird gezeigt, dass es für eine geforderte Wasserbeladung des behandelten Luftstromes ein Optimum existiert, in dem Entropieproduktion am geringsten ist. In diesem Punkt sind die Irreversibilitäten aufgrund von Wärmeübertragung und Mischung bei einem Minimum, wobei die Irreversibilitäten aufgrund von Stoffübertragung für konstante Austritts-Wasserbeladungen auch eher konstant bleiben. Weiterhin steigt im optimalen Betriebspunkt die Gesamt-Entropieproduktion exponentiell mit der extrahierten Wasserdampfmenge, wobei die Anteile von Wärme- und Stoffübertragung weitgehend konstant bleiben (Anstieg < 5 %pt.). Ebenfalls wird anhand eines idealisierten Stofftrennungsprozesses gezeigt, dass höhere Regenerationstemperaturen als im Idealfall auf Irreversibilitäten zurückzuführen sind. Hinsichtlich auf die Optimierung des Systems wird gezeigt, dass die Entropieproduktion quadratisch mit der Temperaturspreizung am Radaustritt korreliert, was als Optimierungskriterium zur Reduzierung von Entropieproduktion im Betrieb genutzt werden kann.Hamburgische Investitions- und Förderban
Harmonizing distribution system planning and the operation of integrated DC systems
No full textThe ongoing energy transition leads to a drastic increase in the number of power-generating and -consuming units as well as the accumulated installed power in the German power system. The exploitation of operational flexibility offers the potential to reduce the resulting need for power system reinforcement and expansion. The integration of DC systems into existing AC distribution systems provides operational flexibility with assets that by European legislation can be owned by distribution system operators (DSO). Consequently, the DSO can decide on their operational behavior, numbers, location, power rating, and availability. However, the corresponding planning task requires procedures that involve operational considerations. This paper employs a customized optimal power flow based operational strategy for DC links within a planning study, evaluates mutual implications between planning and operation, and derives necessary adjustments for their harmonization. The representative case study on medium-voltage grid planning demonstrates that the integration of controllable DC links in combination with a suitable operational strategy can significantly reduce the number of reinforcement measures required to resolve overloading of grid assets for increasing power demand compared to non-controllable alternatives
Reduction of fluid noise in modern aircraft hydraulics by integrated broadband attenuators
No full textNew axial piston pumps with fixed displacement volumes, such as the high efficient power package (HEPP) pumps operate at variable rotational speeds and thus variable flow rates in a wide range. Using intelligent pump control systems, small and light packages are possible. In contrast, the fluid pulsations vary due to the rotational speed and have to be controlled avoiding stress or wear in the hydraulic system components (e.g. seals of tubing) and potentially impacting cabin noise. Due to the excitation frequencies, a broadband silencer for high pressure applications is required. This is realised by a multi-Helmholtz-resonator (MHR) concept within one cylindrical volume. The design will be adapted for pump-specific frequency characteristics in aircraft hydraulic conditions and fine adjusted during test verification by means of an adjustable tube-inside a pressure shell. For cost, weight and complexity reason a common broadband attenuator is integrated in the hydraulic circuit connecting the two redundant HEPP motorpumps. The attenuator position is optimised to achieve maximal acoustic performance and minimize pulsation stress on the pump, especially at the main operating point. The proof of concept has been achieved experimentally comparing a HEPP piston pump with and without the MHR
Latency-aware placement of stream processing operators in modern-day stream processing frameworks
No full textThe rise of the Internet of Things has substantially increased the number of interconnected devices at the edge of the network. As a result, a large number of computations are now distributed in the compute continuum, spanning from the edge to the cloud, generating vast amounts of data. Stream processing is typically employed to process this data in near real-time due to its efficiency in handling continuous streams of information in a scalable manner. However, many stream processing approaches do not consider the underlying network devices of the compute continuum as candidate resources for processing data. Moreover, many existing works do not consider the incurred network latency of performing computations on multiple devices in a distributed way. To avoid this, we formulate an optimization problem for utilizing the complete compute continuum resources and design heuristics to solve this problem efficiently. Furthermore, we integrate our heuristics into Apache Storm and perform experiments that show latency- and throughput-related benefits compared to alternatives
On the dynamic JKR adhesion problem
No full textShui et al. (2020) have recently shown that applying high-frequency vibrations, we can increase the mean adhesion between viscoelastic solids. This is due to the fact that oscillating contact area leads to an effect of increased apparent surface energy during the retraction phase which can be described by the well known empirical Gent and Schultz law (GS). However, Shui et al solution surprisingly appears not to depend on GS constants, which would imply perhaps no amplification. Yi et al. (2024) have made similar experiments, and proposed a simpler fitting model, which seems to work however with widely different GS constant when changing the sphere radius. Here, we solve the JKR dynamic adhesion problem for a sphere oscillating on a substrate by imposing an harmonic oscillation of the contact area, which permits to obtain a very simple solution by simply averaging the resulting cycle of indentation. We find that the solution is close to a JKR form for the mean indentation vs mean force, which we find in a simple approximation. Although there is saturation in the amplification when the contact radius shrinks to zero and the problem becomes that of impacts at large amplitudes of vibrations, experiments show that other saturations occurs first, presently unclear. We discuss also the influence of resonances. We find reasonable agreement with experiments conducted on PDMS