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Flow over traveling and rotating cylinders using a hybrid Eulerian–Lagrangian solver
No full textHybrid Eulerian–Lagrangian solvers have gained increasing attention in the field of external aerodynamics, particularly when dealing with strong body–vortex interactions. This approach effectively combines the strengths of the Eulerian component, which accurately resolves boundary layer phenomena, and the Lagrangian component, which efficiently evolves the wake downstream. This study builds on our team's previous work by enhancing the capabilities of a two-dimensional hybrid Eulerian–Lagrangian solver. We aim to upgrade our solver which was initially designed for static cases, to now also simulate cases involving moving objects. To ensure the reliability and applicability of a new solver, it is essential to validate its performance in complex cases. Here, the solver is validated across the case of a traveling cylinder and the case of a rotating cylinder in two different rotational speeds at low Reynolds numbers. In the realm of Eulerian solvers, such as OpenFOAM (utilized for the Eulerian component of this hybrid approach), traditional techniques include the use of morphing meshes, overset meshes, and Arbitrary Mesh Interfaces (AMI) to model body motion. The proposed methodology involves extending the Eulerian mesh up to a short distance from the solid boundary and moving it entirely as a solid entity. Then the Lagrangian solver is responsible for calculating the updated boundary conditions, thereby completing the hybrid solver's functionality. This approach is very similar to the overset mesh technique. However, unlike the traditional method where an Eulerian mesh moves on top of a static one, our method involves the motion of an Eulerian mesh over a Lagrangian grid. We compared the results from our hybrid solver with those from a purely Eulerian solver, specifically OpenFOAM. The comparison demonstrates that our solver can replicate OpenFOAM's results with high accuracy. Another interesting point highlighted in this study is the presence of high-frequency oscillations in the body forces in hybrid solvers that incorporate the redistribution of Lagrangian particles and do not utilize surface elements such as vortex panels, specifically when dealing with dynamic mesh simulations. When the Eulerian mesh travels on top of the Lagrangian grid of particles, the positions of the particles with respect to the Eulerian mesh continuously change. This results in a constant shift of particles near the solid body, where the highest vorticity is observed. Particles that are close to the solid boundary at one time step may find themselves inside the boundary at the next time step, leading to their removal. This pattern continuously changes during the simulation, causing fluctuations in the boundary conditions of the Eulerian solver and manifesting as oscillations in the forces acting on the body. It is shown that this issue can be alleviated either by increasing the spatial resolution of the Lagrangian solver or by synchronizing the movement of the Lagrangian grid with the motion of the Eulerian mesh. The results of the study make the solver trustworthy and pave the way for more demanding external aerodynamic simulations.Wind EnergyAerodynamic
Efficient Neural Ranking Using Forward Indexes and Lightweight Encoders
No full textDual-encoder-based dense retrieval models have become the standard in IR. They employ large Transformer-based language models, which are notoriously inefficient in terms of resources and latency.We propose Fast-Forward indexes - vector forward indexes which exploit the semantic matching capabilities of dual-encoder models for efficient and effective re-ranking. Our framework enables re-ranking at very high retrieval depths and combines the merits of both lexical and semantic matching via score interpolation. Furthermore, in order to mitigate the limitations of dual-encoders, we tackle two main challenges: Firstly, we improve computational efficiency by either pre-computing representations, avoiding unnecessary computations altogether, or reducing the complexity of encoders. This allows us to considerably improve ranking efficiency and latency. Secondly, we optimize the memory footprint and maintenance cost of indexes; we propose two complementary techniques to reduce the index size and show that, by dynamically dropping irrelevant document tokens, the index maintenance efficiency can be improved substantially.We perform an evaluation to show the effectiveness and efficiency of Fast-Forward indexes - our method has low latency and achieves competitive results without the need for hardware acceleration, such as GPUs.Web Information SystemsMultimedia Computin
Guest editorial: Advances in conductive and wireless powering and charging technologies for transportation applications
No full textSupport Electrical Sustainable EnergyDC systems, Energy conversion & StorageLarge Scale Energy Storag
The Re-Risking State: The Limits of Property Insurance in Florida
No full textFlorida’s property insurance market is in crisis. Many of the Sunshine State’s insurers are raising rates or pulling out of communities, zip code by zip code. The average Florida homeowners insurance premium rose to nearly $11,000 in 2023, with notably higher rates in coastal South Florida cities—the costliest in the nation. This brewing insurance affordability crisis is particularly acute for Florida’s half-million housing cost-burdened households with mortgages, who must continue to purchase insurance or face default on their mortgage. That’s because mortgage lenders require borrowers to maintain insurance—a measure designed to protect the banking system, but which also places many frontline households in a serious affordability bind.Urban Development Managemen
The Clebsch-Gordan coefficients for a family of natural modules of the Modular Double of the quantum group Uq(sl(2,R))
No full textWe will study the Clebsch-Gordan coefficients of the modular double of the quantum group Uq(sl(2, R)). This will be done by studying and taking a good look at how B. Ponsot and J. Teschner showed how to compute the Clebsch-Gordan coefficients [1]. Moreover, we will also take an introductory look at the concept of quantum groups by looking at some general theory on Hopf ∗-algebras and their representations. The Clebsch-Gordan coefficients can roughly be described as a relation between a basis of a tensor product U ⊗V of two simple Uq(sl(2, R))-modules and a basis of the decomposition of U ⊗V into simple modules. We will show that this relation can be explicitly described by an integral transformation. Since this describes a relation between modules of a quantum group, the first part of this thesis will give the necessary information to introduce the reader to the concept of quantum groups and their modules. This will be done by introducing Hopf algebras and their modules and then look at their quantum deformations. This first part will also introduce several examples of algebras, Hopf algebras and quantum groups to make the reader get used to the concept of Hopf algebras and quantum groups.Applied Mathematic
The effect of mangroves on coastline stability
No full textMangrove ecosystems are dynamic environments that provide numerous ecological, economic, and societal benefits, such as shoreline protection, carbon sequestration, and flood protection. These ecosystems are exclusively found in tropical and subtropical regions and thrive at the interface of land and sea. Despite their many benefits, mangroves face significant threats, leading to substantial losses over the past century. The degradation of mangroves compromises flood protection and shoreline stability, increasing the risk of severe coastline erosion and flooding. Current research highlights the role of mangroves in flood protection but presents conflicting theorieson their impact on coastline stability. Two competing theories exist regarding the effect of mangroves on coastline stability, namely the ”land-builders” and the ”land-consolidators” theory. According to the ”land-builders” theory, mangroves actively accumulate sediment and contribute to the expansion of coastlines. In contrast, the ”land-consolidators” theory suggests that mangroves play a more passive role in stabilizing existing landforms and serve as buffers against erosion. The debate on the primary function of mangroves remains unresolved. Furthermore, existing studies often date back over 50 years and are limited by specific hydrodynamic and geomorphic settings, leaving a gap in understanding broad trends. This research aims to bridge this gap through a global assessment of the influence of mangroves on coastline development, complemented by a local assessment to explore detailed interactions in specific case study areas. The study’s objective is to explore the dynamic impact of mangroves on coastline stability through an extensive analysis of historical datasets to identify trends and patternsin coastline changes associated with mangrove ecosystems. The focus lies on observing trends between coastline stability and the presence of mangroves, the relationship between coastline stability and mangrove forest width, and the influence of the state of mangrove forests (contracting, expanding, stable) on coastline stability.Civil Engineering | Hydraulic Engineerin
Wind pattern clustering of high frequent field measurements for dynamic wind farm flow control
No full textIn this work, we investigate a method to derive characteristic dynamic flow field behavior from field measurements. We further explore how these changes impact the performance of a wind farm flow control strategy. For a long time, hourly to 10-min averaged data has been the predominant form to store meteorological quantities such as wind speeds and wind directions. With the decreasing cost of digital storage and improvements in measurement technology, the assimilation of higher frequent data has become more feasible. We use one of these open-source datasets provided by the KNMI to explore what characteristic flow behavior is described in the high-frequency recordings of a Wind-LiDAR located in the North-Sea. To this end we employ a K-Means algorithm to cluster 10-min time series of wind direction changes sampled at 20 s. Our study finds that the majority of wind direction changes within this time window can be described by five main clusters with clock- and counterclockwise changes of the wind direction in the range of ±4 deg. Subsequently we investigate the implications for quasi-steady wind farm flow control. We employ look-up table yaw-steering control next to baseline control in selected cases in a turbulent Large Eddy Simulation to verify the predictions made by a dynamic parametric engineering wake model. We find good agreement between both simulation environments and use the engineering model to investigate all wind directions in 2 deg resolution. The results show that the identified wind direction changes can have a significant negative impact on the power generated by a 10 turbine wind farm. The study also shows that the fixed yaw-steering set-points are still favorable over baseline operation for wind direction changes in the range of ±1.6 deg, but can act detrimental for larger changes.Team Jan-Willem van WingerdenWind Energ
Photoactivity of amorphous and crystalline TiO<sub>2</sub> nanotube arrays (TNA) films in gas phase CO<sub>2</sub> reduction to methane with simultaneous H<sub>2</sub> production
No full textThis study assessed the photoactivity of amorphous and crystalline TiO2 nanotube arrays (TNA) films in gas phase CO2 reduction. The TNA photocatalysts were fabricated by titanium anodization and submitted to an annealing treatment for crystallization and/or cathodic reduction to introduce Ti3+ and oxygen vacancies into the TiO2 structure. The cathodic reduction demonstrated a significant effect on the generated photocurrent. The photoactivity of the four TNA catalysts in CO2 reduction with water vapor was evaluated under UV irradiation for 3 h, where CH4 and H2 were detected as products. The annealed sample exhibited the best performance towards methane with a production rate of 78 μmol gcat−1 h−1, followed by the amorphous film, which also exhibited an impressive formation rate of 64 μmol gcat−1 h−1. The amorphous and reduced-amorphous films exhibited outstanding photoactivity regarding H2 production (142 and 144 μmol gcat−1 h−1, respectively). The annealed catalyst also revealed a good performance for H2 production (132 μmol gcat−1 h−1) and high stability up to five reaction cycles. Molecular dynamic simulations demonstrated the changes in the band structure by introducing oxygen vacancies. The topics covered in this study contribute to the Sustainable Development Goals (SDG), involving affordable and clean energy (SDG#7) and industry, innovation, and infrastructure (SDG#9).Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Micro and Nano Engineerin
Protein Structure and Sequence Co-Design through Graph Based Generative Diffusion Modeling
No full textProteins are fundamental biological macromolecules essential for cellular structure, enzymatic catalysis, and immune defense, making the generation of novel proteins crucial for advancements in medicine, biotechnology, and material sciences. This study explores protein design using deep generative models, specifically Denoising Diffusion Probabilistic Models (DDPMs). While traditional methods often focus on either protein structure or sequence design independently, recent trends emphasize a co-design approach addressing both aspects simultaneously. We propose a novel methodology utilizing Equivariant Graph Neural Networks (EGNNs) within the diffusion framework to co-design protein structures and sequences. We modify the EGNN architecture to improve its effectiveness in learning intricate data patterns. Experimental results show that our approach effectively generates high-quality protein sequences, although challenges remain in producing plausible protein backbones and ensuring strong sequence-structure correlation.Computer Science | Artificial Intelligenc
How cytoskeletal crosstalk makes cells move: Bridging cell-free and cell studies
No full textCell migration is a fundamental process for life and is highly dependent on the dynamical and mechanical properties of the cytoskeleton. Intensive physical and biochemical crosstalk among actin, microtubules, and intermediate filaments ensures their coordination to facilitate and enable migration. In this review, we discuss the different mechanical aspects that govern cell migration and provide, for each mechanical aspect, a novel perspective by juxtaposing two complementary approaches to the biophysical study of cytoskeletal crosstalk: live-cell studies (often referred to as top-down studies) and cell-free studies (often referred to as bottom-up studies). We summarize the main findings from both experimental approaches, and we provide our perspective on bridging the two perspectives to address the open questions of how cytoskeletal crosstalk governs cell migration and makes cells move.BN/Gijsje Koenderink La