Tootfinder

Cross-Border Data Flows in Africa: Examining Policy Approaches and Pathways to Regulatory Interoperability
https://fpf.org/blog/cross-border-data-flows-in-africa-examining-policy-approaches-and-pathways…

🧲 MRI method maps blood flows in reverse for deeper insight into brain physiology
#medicine

MRI method maps blood flows in reverse for deeper insight into brain physiology
The venous system maintains the health of our brains by removing deoxygenated blood and other waste products, but its complexity and variability have made scientific study difficult. Now, a UC Berkeley-led team of researchers has developed an innovative MRI technique that may expand our understanding of this critical system.

#silentSunday #RockyMountainNationalPark
#sunrise in Moraine Park. October 2015

observing the (approximate) 55th anniversary of the disastrous/canceled powder ridge festival by sitting in traffic in #connecticut.

This https://arxiv.org/abs/2505.12195 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_mat…

Structural stability of supersonic spiral flows with large angular velocity for the Euler-Poisson system
This paper concerns the structural stability of smooth cylindrically symmetric supersonic spiral flows with large angular velocity for the steady Euler-Poisson system in a concentric cylinder. We establish the existence and uniqueness of some smooth supersonic Euler-Poisson flows with nonzero angular velocity and vorticity including both cylindrical spiral flows and axisymmetric spiral flows. The deformation-curl-Poisson decomposition for the steady Euler-Poisson system is utilized to deal with…

Weekend #Plankton Factoid 🦠🦐
While less discussed, there is a similar circulation to the AMOC in the #Antarctic called the Southern Meridional Overturning Circulation (SMOC). This is also vital to deep circulation, algal productivity, ecosystem function, and the global

This https://arxiv.org/abs/2505.24075 has been replaced.
initial toot: https://mastoxiv.page/@ar…

Extracting dominant dynamics about unsteady base flows
A wide range of techniques exist for extracting the dominant flow dynamics and features about steady, or periodic base flows. However, there have been limited efforts in extracting the dominant dynamics about unsteady, aperiodic base flow. These flows appear in many applications such as when there is a sudden change in the flow rate through a pipe, when an airfoil experiences stall, or when a vortex forms. For these unsteady flows, it is valuable to know not only the dynamics of the base flow b…

Very high-order accurate finite volume scheme for the streamfunction-vorticity formulation of incompressible fluid flows with polygonal meshes on arbitrary curved boundaries
Ricardo Costa (Institute for Polymers and Composites, University of Minho, Azur\'em Campus, 4804-058 Guimar\~aes, Portugal, Department of Polymer Engineering, University of Minho, Azur\'em Campus, 4804-058 Guimar\~aes, Portugal), St\'ephane Clain (Centre of Mathematics, University of Coimbra, 3000-143 C…

Very high-order accurate finite volume scheme for the streamfunction-vorticity formulation of incompressible fluid flows with polygonal meshes on arbitrary curved boundaries
Conventional mathematical models for simulating incompressible fluid flow problems are based on the Navier-Stokes equations expressed in terms of pressure and velocity. In this context, pressure-velocity coupling is a key issue, and countless numerical techniques and methods have been developed over the decades to solve these equations efficiently and accurately. In two dimensions, an alternative approach is to rewrite the Navier-Stokes equations regarding two scalar quantities: the streamfunct…

This https://arxiv.org/abs/2505.24762 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_mat…

Branched $α$-combinatorial Ricci flows on closed surfaces with Euler characteristic $χ\le 0$
This paper investigates branched $α$-flows on weighted triangulated closed surfaces with Euler characteristic \(χ\leq 0\), focusing on establishing their connections with topological (combinatorial) and geometric structures. In Euclidean (\(\mathbb{E}^2\)) and hyperbolic (\(\mathbb{H}^2\)) geometries, we define branched $α$-curvatures and corresponding branched $α$-flows. By introducing branched $α$-potentials, we prove the existence and uniqueness of constant branched $α$-metrics through…

Savage-Dickey density ratio estimation with normalizing flows for Bayesian model comparison
Kiyam Lin, Alicja Polanska, Davide Piras, Alessio Spurio Mancini, Jason D. McEwen
https://arxiv.org/abs/2506.04339

Savage-Dickey density ratio estimation with normalizing flows for Bayesian model comparison
A core motivation of science is to evaluate which scientific model best explains observed data. Bayesian model comparison provides a principled statistical approach to comparing scientific models and has found widespread application within cosmology and astrophysics. Calculating the Bayesian evidence is computationally challenging, especially as we continue to explore increasingly more complex models. The Savage-Dickey density ratio (SDDR) provides a method to calculate the Bayes factor (eviden…

OatFi, whose APIs handle underwriting, origination, and capital deployment for B2B payment providers, raised a $24M Series A led by White Star Capital (Ryan Lawler/Axios)
https://www.axios.com/pro/fintech-deals/2025/06/03/oatfi-24-milliom-b2b-credit

Exclusive: OatFi nabs $24M for embedded B2B credit
Slow payment terms choke company cash flows across the $35 trillion B2B economy.

This https://arxiv.org/abs/2405.05969 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_…

Learned harmonic mean estimation of the Bayesian evidence with normalizing flows
We present the learned harmonic mean estimator with normalizing flows - a robust, scalable and flexible estimator of the Bayesian evidence for model comparison. Since the estimator is agnostic to sampling strategy and simply requires posterior samples, it can be applied to compute the evidence using any Markov chain Monte Carlo (MCMC) sampling technique, including saved down MCMC chains, or any variational inference approach. The learned harmonic mean estimator was recently introduced, where ma…

Renormalization group flows in area-metric gravity
Johanna Borissova, Bianca Dittrich, Astrid Eichhorn, Marc Schiffer
https://arxiv.org/abs/2507.02034 http…

Renormalization group flows in area-metric gravity
We put forward the first analysis of renormalization group flows in an area-metric theory, motivated by spin-foam quantum gravity. Area-metric gravity contains the well-known length-metric degrees of freedom of standard gravity as well as additional shape-mismatching degrees of freedom. To be phenomenologically viable, the shape-mismatching degrees of freedom have to decouple under the renormalization group flow towards lower scales. We test this scenario by calculating the renormalization grou…

This https://arxiv.org/abs/2503.03913 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_qbi…

Proton Flows, Proton Gradients and Subcellular Architecture in Biological Energy Conversion
Hydrogen cations, or protons, provide the medium by which energy is stored and converted in biological systems. Such pre-eminence relies on the interplay between interfacial and bulk chemical transformations, according to mechanisms that are shared by organisms in all phyla of life. The present work provides an introduction to the fundamental aspects of biological energy management by focusing on the relationship between vectorial proton flows and the geometry of energy producing organelles in …

This https://arxiv.org/abs/2403.10282 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_mat…

Non-Conforming Structure Preserving Finite Element Method for Doubly Diffusive Flows on Bounded Lipschitz Domains
We study a stationary model of doubly diffusive flows with temperature-dependent viscosity on bounded Lipschitz domains in two and three dimensions. A new well-posedness and regularity analysis of weak solutions under minimal assumptions on domain geometry and data regularity are established. A fully non-conforming finite element method based on Crouzeix-Raviart elements, which ensures locally exactly divergence-free velocity fields is explored. Unlike previously proposed schemes, this discreti…

Insights into Chromospheric Large-Scale Flows using Nobeyama 17 GHz Radio Observations I. The Differential Rotation Profile
Srinjana Routh, Anshu Kumari, Vaibhav Pant, Jaydeep Kandekar, Dipankar Banerjee, Mohd. Saleem Khan, Dibya Kirti Mishra
https://arxiv.org/abs/2507.02630

Insights into Chromospheric Large-Scale Flows using Nobeyama 17 GHz Radio Observations I. The Differential Rotation Profile
Although the differential rotation rate on the solar surface has long been studied using optical and extreme ultraviolet (EUV) observations, associating these measurements to specific atmospheric heights remains challenging due to the temperature-dependent emission of tracers observed in EUV wavelengths. Radio observations, being primarily influenced by coherent plasma processes and/or thermal bremsstrahlung, offer a more height-stable diagnostic and thus provide an independent means to test an…

This https://arxiv.org/abs/2505.23527 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_csLG_…

Normalizing Flows are Capable Models for RL
Modern reinforcement learning (RL) algorithms have found success by using powerful probabilistic models, such as transformers, energy-based models, and diffusion/flow-based models. To this end, RL researchers often choose to pay the price of accommodating these models into their algorithms -- diffusion models are expressive, but are computationally intensive due to their reliance on solving differential equations, while autoregressive transformer models are scalable but typically require learni…

Transient dispersion in oscillatory flows: auxiliary-time extension method for concentration moments
Weiquan Jiang, Guoqian Chen
https://arxiv.org/abs/2507.01870

Transient dispersion in oscillatory flows: auxiliary-time extension method for concentration moments
The dispersion phenomenon of mass and heat transport in oscillatory flows has wide applications in environmental, physiological and microfluidic flows. The method of concentration moments is a powerful theoretical tool for analyzing transport characteristics and is well-developed for steady flows. However, the general solutions of moments derived by Barton (J. Fluid Mech., vol. 126, 1983, pp. 205-218) cannot be applied directly to unsteady flows. Prior studies needed to re-solve the governing e…

Scaling particle-size segregation in wide-ranging sheared granular flows
Tianxiong Zhao, Daisuke Noto, Xia Li, Tom\'as Trewhela, Hugo N. Ulloa
https://arxiv.org/abs/2507.01248

Scaling particle-size segregation in wide-ranging sheared granular flows
Scaling relationships have been proposed to describe shear-driven size segregation based on intruder experiments and simulations. While these models have shown agreement with experimental and numerical results under uniform shear rate, their validity across varying shear-rate conditions remains uncertain. Here, we employ Discrete Element Method (DEM) simulations to investigate particle size segregation in sheared granular flows under wide-ranging shear-rate conditions. We find that the scaling …

Stochastic Conformal Flows in Even Dimensions
Jack Piazza
https://arxiv.org/abs/2506.01217 https://arxiv.org/pdf/2506.01217

Stochastic Conformal Flows in Even Dimensions
We define two stochastic analogs of a geometric flow on even-dimensional manifolds called $Q$-curvature flow, and use the theory of Dirichlet forms to construct weak solutions to both. The first of these flows, which we call the normalized $Q$ flow (NQF), preserves the intrinsic volume normalization from the deterministic setting. The second, which we call the Liouville $Q$ flow (LQF), has a different normalization motivated by a similar flow studied in arXiv:1904.10909. The volume dynamics of …

Rumors on evolving graphs through stationary times
Vicenzo Bonasorte
https://arxiv.org/abs/2506.04386 https://arxiv.org/pdf/2506.0438…

Rumors on evolving graphs through stationary times
We study rumor spreading in dynamic random graphs. Starting with a single informed vertex, the information flows until it reaches all the vertices of the graph (completion), according to the following process. At each step $k$, the information is propagated to neighbors of the informed vertices, in the $k$-th generated random graph. The way this information propagates from vertex to vertex at each step will depend on the ``protocol". We provide a method based on strong stationary times to study…

Topology optimization of actively moving rigid bodies in unsteady flows
Yuta Tanabe, Kentaro Yaji, Kuniharu Ushijima
https://arxiv.org/abs/2506.23895 https…

Topology optimization of actively moving rigid bodies in unsteady flows
This study proposes a novel topology optimization method for unsteady fluid flows induced by actively moving rigid bodies. The key idea of the proposed method is to decouple the design and analysis domains by using separate grids. The design grid undergoes rigid body motion and is then overlapped onto the analysis grid. After the overlap, key quantities such as the Brinkman coefficient are transferred between the grids. This approach provides a direct and efficient means of representing object …

Novel methodology to obtain transonic solutions for dissipative flows around compact objects
Shilpa Sarkar
https://arxiv.org/abs/2505.24839 https://…

Novel methodology to obtain transonic solutions for dissipative flows around compact objects
A novel methodology to obtain global transonic solutions around compact objects is reported here. A unified methodology to obtain accretion as well as wind solutions around these objects has been presented. Flows around compact objects are dissipative, and the conservation equations are therefore stiff. In such conditions, obtaining of sonic point(s) and hence, the transonic solution is not trivial. The conserved equations of motion fail to integrate in the presence of realistic viscosity, ther…

Pseudo-Anosov flows on hyperbolic L-spaces
John A. Baldwin, Steven Sivek, Jonathan Zung
https://arxiv.org/abs/2505.21113 https://arxi…

Pseudo-Anosov flows on hyperbolic L-spaces
We prove that for each $n\in\mathbb{N}$ there is a hyperbolic L-space with $n$ pseudo-Anosov flows, no two of which are orbit equivalent. These flows have no perfect fits and are thus quasigeodesic. In addition, our flows admit positive Birkhoff sections, which we argue implies that they give rise to $n$ universally tight contact structures whose lifts to any finite cover are non-contactomorphic. This argument involves cylindrical contact homology together with the work of Barthelmé, Frankel, …

Curvature Rigidity Through Level Sets of Lyapunov Exponents in Geodesic Flows
Sergio Roma\~na
https://arxiv.org/abs/2507.02482 https://

Curvature Rigidity Through Level Sets of Lyapunov Exponents in Geodesic Flows
In this paper, we establish new geometric rigidity results through the study of Lyapunov exponent level sets via invariant measures. First, we prove that for a manifold $M$ without focal points, if the zero Lyapunov exponent level set has full measure with respect to a fully supported invariant measure, then $M$ must be flat. This result recovers and extends a result of Freire and Mañé (cf. [9]). Second, we prove that if the level set of the Lyapunov exponents has full measure with respect to…

🚨 New paper alert 🚨
Together with my co-authors, we compare two different diagnostic clinics of Moorfields Eye Hospital in London regarding their spatial designs and effective patient flows
We highlight the importance of line of sight relationships between diagnostic test stations to ease patient flow and coordination and suggest an ideal clinic configuration based on queuing models
Published

Lanes, clusters, sightlines: modelling patient flow in medical clinics | Buildings & Cities

This https://arxiv.org/abs/2404.09319 has been replaced.
initial toot: https://mastoxiv.page/@arXi…

Impact of curved elements for flows over orography with a Discontinuous Galerkin scheme
We present a quantitative assessment of the impact of high-order mappings on the simulation of flows over complex orography. Curved boundaries were not used in early numerical methods, whereas they are employed to an increasing extent in state of the art computational fluid dynamics codes, in combination with high-order methods, such as the Finite Element Method and the Spectral Element Method. Here we consider a specific Discontinuous Galerkin (DG) method implemented in the framework of the de…

We just went for a walk in Bad Tölz. Nothing special, just going for a walk along the river #isar.
Enjoy your Sunday!
#silentsunday #badtoelz

Accuracy and scalability of asynchronous compressible flow solver for transitional flows
Aswin Kumar Arumugam, Shubham Kumar Goswami, Nagabhushana Rao Vadlamani, Konduri Aditya
https://arxiv.org/abs/2506.03027

Accuracy and scalability of asynchronous compressible flow solver for transitional flows
To overcome the communication bottlenecks observed in state-of-the-art parallel time-dependent flow solvers at extreme scales, an asynchronous computing approach that relaxes communication and synchronization at a mathematical level was previously developed. This approach preserves high-order accuracy of computations near processing element boundaries using asynchrony-tolerant (AT) schemes while significantly improving the scalability. The numerical properties of the AT schemes were studied bas…

This https://arxiv.org/abs/2505.19165 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_csAI_…

OrgAccess: A Benchmark for Role Based Access Control in Organization Scale LLMs
Role-based access control (RBAC) and hierarchical structures are foundational to how information flows and decisions are made within virtually all organizations. As the potential of Large Language Models (LLMs) to serve as unified knowledge repositories and intelligent assistants in enterprise settings becomes increasingly apparent, a critical, yet under explored, challenge emerges: \textit{can these models reliably understand and operate within the complex, often nuanced, constraints imposed b…

Branched $\alpha$-combinatorial Ricci flows on closed surfaces with Euler characteristic $\chi\le 0$
Wenjun Li, Rongyuan Liu, Guohao Chen, Aijin Lin
https://arxiv.org/abs/2505.24762

Branched $α$-combinatorial Ricci flows on closed surfaces with Euler characteristic $χ\le 0$
This paper investigates branched $α$-flows on weighted triangulated closed surfaces with Euler characteristic \(χ\leq 0\), focusing on establishing their connections with topological (combinatorial) and geometric structures. In Euclidean (\(\mathbb{E}^2\)) and hyperbolic (\(\mathbb{H}^2\)) geometries, we define branched $α$-curvatures and corresponding branched $α$-flows. By introducing branched $α$-potentials, we prove the existence and uniqueness of constant branched $α$-metrics through…

Linear instability of plane Couette and Poiseuille flows
Sergey G. Chefranov, Alexander G. Chefranov
https://arxiv.org/abs/2506.04242 https://

Linear instability of plane Couette and Poiseuille flows
It is shown that linear instability of plane Couette flow can take place even at finite Reynolds numbers which meets with known experimental data. This new result of the linear theory of hydrodynamic stability is obtained only due by abandoning traditional assumption of the longitudinal periodicity of disturbances in the flow direction.

Conformal Operator Flows of the Deconfined Quantum Criticality from $\mathrm{SO}(5)$ to $\mathrm{O}(4)$
Shuai Yang, Liang-dong Hu, Chao Han, W. Zhu, Yan Chen
https://arxiv.org/abs/2507.01322

Conformal Operator Flows of the Deconfined Quantum Criticality from $\mathrm{SO}(5)$ to $\mathrm{O}(4)$
The deconfined quantum critical point (DQCP), which separates two distinct symmetry-broken phases, was conjectured to be an example of (2+1)D criticality beyond the standard Landau-Ginzburg-Wilson paradigm. However, this hypothesis has been met with challenges and remains elusive. Here, we perform a systematic study of a microscopic model realizing the DQCP with a global symmetry tunable from $\mathrm{SO}(5)$ to $\mathrm{O}(4)$. Through the lens of fuzzy sphere regularization, we uncover the ke…

This https://arxiv.org/abs/2411.03751 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_mat…

Migrating elastic flows II
We solve a variant of Huisken's problem for open curves: we construct migrating elastic flows under the natural boundary conditions, extending previous work from the nonlocal flow to the purely local flow.

Critical demand in a stochastic model of flows in supply networks
Yannick Feld, Marc Barthelemy
https://arxiv.org/abs/2505.24813 https://

Critical demand in a stochastic model of flows in supply networks
Supply networks are essential for modern production, yet their critical properties remain understudied. We present a stochastic model with random production capacities to analyze material flow to a root node, focusing on topology and buffer stocks. The critical demand, where unsatisfied demand diverges, is examined mostly through numerical simulations. Without stocks, minimal production dictates behavior, making topology irrelevant. With stocks, memory effects arise, making topology crucial. In…

Solar Cycle Variations in Meridional Flows and Rotational Shear within the Sun's Near-surface Shear Layer: #solar rotation: https://www.nature.com/articles/d44151-025-00101-6 - scientists uncover how deep plasma flows reshape the Sun’s rotation and hint at mysteries below its surface.

Automated Web Application Testing: End-to-End Test Case Generation with Large Language Models and Screen Transition Graphs
Nguyen-Khang Le, Quan Minh Bui, Minh Ngoc Nguyen, Hiep Nguyen, Trung Vo, Son T. Luu, Shoshin Nomura, Minh Le Nguyen
https://arxiv.org/abs/2506.02529

Automated Web Application Testing: End-to-End Test Case Generation with Large Language Models and Screen Transition Graphs
Web applications are critical to modern software ecosystems, yet ensuring their reliability remains challenging due to the complexity and dynamic nature of web interfaces. Recent advances in large language models (LLMs) have shown promise in automating complex tasks, but limitations persist in handling dynamic navigation flows and complex form interactions. This paper presents an automated system for generating test cases for two key aspects of web application testing: site navigation and form …

This https://arxiv.org/abs/2410.03590 has been replaced.
initial toot: https://mastoxiv.page/@a…

Enhancement to Fusion Reactivity in Sheared Flows
Sheared flow increases the reactivity of fusion plasma. In unmagnetized plasma with flow gradients comparable to the mean free path of reacting ions, fusion reactivity can be more than doubled. The effect is of particular relevance to inertial confinement fusion (ICF), where it allows implosion kinetic energy to contribute to the fusion burn even before thermalizing. In fast ignition, this allows remarkable energy savings because colder fuel stops alpha particles more quickly, enabling ignition…

On gradient descent-ascent flows in metric spaces
Noboru Isobe, Sho Shimoyama
https://arxiv.org/abs/2506.20258 https://arxiv.org/pdf/…

On gradient descent-ascent flows in metric spaces
Gradient descent-ascent (GDA) flows play a central role in finding saddle points of bivariate functionals, with applications in optimization, game theory, and robust control. While they are well-understood in Hilbert and Banach spaces via maximal monotone operator theory, their extension to general metric spaces, particularly Wasserstein spaces, has remained largely unexplored. In this paper, we develop a mathematical theory of GDA flows on the product of two complete metric spaces, formulating…

Generative flow-based warm start of the variational quantum eigensolver
Hang Zou, Martin Rahm, Anton Frisk Kockum, Simon Olsson
https://arxiv.org/abs/2507.01726

Generative flow-based warm start of the variational quantum eigensolver
Hybrid quantum-classical algorithms like the variational quantum eigensolver (VQE) show promise for quantum simulations on near-term quantum devices, but are often limited by complex objective functions and expensive optimization procedures. Here, we propose Flow-VQE, a generative framework leveraging conditional normalizing flows with parameterized quantum circuits to efficiently generate high-quality variational parameters. By embedding a generative model into the VQE optimization loop throug…

Cybersecurity Issues in Local Energy Markets
Al Hussein Dabashi, Sajjad Maleki, Biswarup Mukherjee, Gregory Epiphaniou, Carsten Maple, Charalambos Konstantinou, Subhash Lakshminarayana
https://arxiv.org/abs/2507.01536

Cybersecurity Issues in Local Energy Markets
Local Energy Markets (LEMs), though pivotal to the energy transition, face growing cybersecurity threats due to their reliance on smart grid communication standards and vulnerable Internet-of-Things (IoT)-enabled devices. This is a critical issue because such vulnerabilities can be exploited to manipulate market operations, compromise participants' privacy, and destabilize power distribution networks. This work maps LEM communication flows to existing standards, highlights potential impacts of …

Radiation GRMHD Models of Accretion onto Stellar-Mass Black Holes: I. Survey of Eddington Ratios
Lizhong Zhang, James M. Stone, Patrick D. Mullen, Shane W. Davis, Yan-Fei Jiang, Christopher J. White
https://arxiv.org/abs/2506.02289

Radiation GRMHD Models of Accretion onto Stellar-Mass Black Holes: I. Survey of Eddington Ratios
We summarize results from a survey of radiation-dominated black hole accretion flows across a wide range of mass accretion rates, as well as two values of black hole spin and initial magnetic field geometry. These models apply an algorithm targeting direct solutions to the radiation transport equation in full general relativity and have been enabled by access to modern exascale computing systems. Super-Eddington accretion flows form geometrically thick radiation pressure supported disks that dr…

Analysis of Drone-Assisted Building Inspection Training in VR vs 2D Monitor Display: an EEG Study
Pengkun Liu, Jackson Greene, Jiali Huang, Pingbo Tang, Yu Hou
https://arxiv.org/abs/2507.01471

Analysis of Drone-Assisted Building Inspection Training in VR vs 2D Monitor Display: an EEG Study
Researchers have been using simulation-based methods for drone-assisted inspection training. Multiple brain regions are associated with information processes and decision-making, and the connectivity of these regions may further influence inspectors' performance. However, researchers do not understand the pathways of the information flows when drone pilots process the maintenance and manipulation of information, which may affect the efficiency of tacit knowledge transfer. This study aims to rev…

This https://arxiv.org/abs/2504.18903 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_mat…

Numerical analysis of an H(div)-conforming divergence-free DG method with a second-order explicit Runge-Kutta scheme for incompressible flows
Recently, H(div)-conforming DG type methods coupled with Runge-Kutta (RK) time stepping have been widely employed for simulating high Reynolds number flows, with the convective terms treated explicitly. Although the analysis techniques of RKDG methods were well developed, the extension to incompressible flows is highly nontrivial due to the exactly divergence-free constraint, where the key lies in analyzing the convective terms. We neglect viscosity effects, and conduct an error analysis for an…

This https://arxiv.org/abs/2505.23527 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_csLG_…

Normalizing Flows are Capable Models for RL
Modern reinforcement learning (RL) algorithms have found success by using powerful probabilistic models, such as transformers, energy-based models, and diffusion/flow-based models. To this end, RL researchers often choose to pay the price of accommodating these models into their algorithms -- diffusion models are expressive, but are computationally intensive due to their reliance on solving differential equations, while autoregressive transformer models are scalable but typically require learni…

An Ergodic Spectral Decomposition Theorem for Singular Star Flows
Maria Jose Pacifico, Fan Yang, Jiagang Yang
https://arxiv.org/abs/2506.19989 https://

An Ergodic Spectral Decomposition Theorem for Singular Star Flows
For Axiom A diffeomorphisms and flows, the celebrated Spectral Decomposition Theorem of Smale states that the non-wandering set decomposes into a finite disjoint union of isolated compact invariant sets, each of which is the homoclinic class of a periodic orbit. For singular star flows which can be seen as ``Axiom A flows with singularities'', this result remains open and is known as the Spectral Decomposition Conjecture. In this paper, we will provide a positive answer to an ergodic version of…

Extracting dominant dynamics about unsteady base flows
Alec J. Linot, Barbara Lopez-Doriga, Yonghong Zhong, Kunihiko Taira
https://arxiv.org/abs/2505.24075

Extracting dominant dynamics about unsteady base flows
A wide range of techniques exist for extracting the dominant flow dynamics and features about steady, or periodic base flows. However, there have been limited efforts in extracting the dominant dynamics about unsteady, aperiodic base flow. These flows appear in many applications such as when there is a sudden change in the flow rate through a pipe, when an airfoil experiences stall, or when a vortex forms. For these unsteady flows, it is valuable to know not only the dynamics of the base flow b…

An efficient GPU-accelerated adaptive mesh refinement framework for high-fidelity compressible reactive flows modeling
Yuqi Wang, Yadong Zeng, Ralf Deiterding, Jianhan Liang
https://arxiv.org/abs/2506.02602

An efficient GPU-accelerated adaptive mesh refinement framework for high-fidelity compressible reactive flows modeling
This paper presents a heterogeneous adaptive mesh refinement (AMR) framework for efficient simulation of moderately stiff reactive problems. This framework features an elaborate subcycling-in-time algorithm along with a specialized refluxing algorithm, all unified in a highly parallel codebase. We have also developed a low-storage variant of explicit chemical integrators by optimizing the register usage of GPU, achieving respectively 6x and 3x times speedups as compared to the implicit and stan…

This https://arxiv.org/abs/2403.06708 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_mat…

Tikhonov Regularization for Stochastic Non-Smooth Convex Optimization in Hilbert Spaces
To solve convex optimization problems with a noisy gradient input, we analyze the global behavior of subgradient-like flows under stochastic errors. The objective function is composite, being equal to the sum of two convex functions, one being differentiable and the other potentially non-smooth. We then use stochastic differential inclusions where the drift term is minus the subgradient of the objective function, and the diffusion term is either bounded or square-integrable. In this context, un…

This https://arxiv.org/abs/2008.00887 has been replaced.
link: https://scholar.google.com/scholar?q=a

Stability of shear flows near a boundary
This book is devoted to the study of the linear and nonlinear stability of shear flows and boundary layers for Navier Stokes equations for incompressible fluids with Dirichlet boundary conditions in the case of small viscosity. The aim of this book is to provide a comprehensive presentation to recent advances on boundary layers stability. It targets graduate students and researchers in mathematical fluid dynamics and only assumes that the readers have a basic knowledge on ordinary differential …

A Chimera domain decomposition method with weak Dirichlet-Robin coupling for finite element simulation of particulate flows
Raphael M\"unster, Otto Mierka, Dmitri Kuzmin, Stefan Turek
https://arxiv.org/abs/2506.22831

A Chimera domain decomposition method with weak Dirichlet-Robin coupling for finite element simulation of particulate flows
We introduce a new multimesh finite element method for direct numerical simulation of incompressible particulate flows. The proposed approach falls into the category of overlapping domain decomposition / Chimera / overset grid meshes. In addition to calculating the velocity and pressure of the fictitious fluid on a fixed background mesh, we solve the incompressible Navier-Stokes equations on body-fitted submeshes that are attached to moving particles. The submesh velocity and pressure are used …

This https://arxiv.org/abs/2404.08524 has been replaced.
initial toot: https://mastoxiv.page/@arXi…

Active nematic liquid crystals under a quenched random field
Coupling between flow and orientation is a central issue in understanding the collective dynamics of active biofilaments and cells. Active stresses generated by motor activity destroy (quasi-)long-range orientational order and induce chaotic flows with many vortices. In cellular and subcellular environment, alignment is also hindered by heterogeneous filamentous structures in extracellular matrix and various intracellular organelles. Here we address the effects of a quenched random field on the…

Technical report on a quantum-inspired solver for simulating compressible flows
Raghavendra Dheeraj Peddinti, Stefano Pisoni, Egor Tiunov, Alessandro Marini, Leandro Aolita
https://arxiv.org/abs/2506.03833

Technical report on a quantum-inspired solver for simulating compressible flows
This document presents a quantum-inspired solver for 2D Euler equations, accepted at the final phase of the Airbus-BWM Group Quantum Computing Challenge (ABQCC) 2024. We tackle the case study of Quantum Solvers for Predictive Aeroacoustic and Aerodynamic modeling tasks. We propose a tensor network based solver that scales polylogarithmically with the mesh size, in both runtime and memory. This provides a promising avenue for tackling the curse of dimensionality that plagues the direct numerical…

Aggregation of vortex structures in 2D: the blob-wave system and its role in zonal flows
Franco Flandoli, Matteo Palmieri, Milo Viviani
https://arxiv.org/abs/2505.22700

Aggregation of vortex structures in 2D: the blob-wave system and its role in zonal flows
We give a rigorous mathematical result, supported by accurate numerical simulations, of the aggregation of a concentrated vortex blob with an underlying non constant vorticity field: the blob moves in the direction of the gradient of the field. It is a unique example of Lagrangian explanation of aggregation of vortex structures of the same sign in 2D inviscid fluids. A conceptual model of zonal flow maintenance and modulation based on this idea is then developed, which produces shapes in accord…

This https://arxiv.org/abs/2505.13626 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_…

Methods to Test the Source of the Extreme Gas Motions in WS 35
We present theoretical arguments toward the plausibility of a stellar wind}to explain the 16000\,km\,$s^{-1}$ line broadening in the optical spectra of WS 35, the central star in the Pa 30 nebula. The wind model is discussed in the context of super-Eddington flows. We argue that WS 35 potentially occupies a new regime of wind driving theory as the first metal-only wind. While this framework provides a promising avenue for explaining the high speed flow, questions remain about the source's true …

Global resistive MHD accretion flows around spinning AGNs: impact of resistivity on MAD state
Ramiz Aktar, Kuo-Chuan Pan, Toru Okuda
https://arxiv.org/abs/2505.23051

Global resistive MHD accretion flows around spinning AGNs: impact of resistivity on MAD state
In this study, we investigate the effect of resistivity on the dynamics of global magnetohydrodynamic accretion flows (Res-MHD) around a spinning supermassive black hole. We perform a comparative study of 2D and 3D resistive models around black holes. We examine accretion flow dynamics considering globally uniform resistivity values, ranging from $\sim 0$ to 0.1. During the simulation time of $t \lesssim 1000~t_g$, we find that the mass accretion rate is comparable for both the 2D and 3D models…

On the Invariance of Expansive Measures for Flows
Eduardo Pedrosa, Elias Rego, Alexandre Trilles
https://arxiv.org/abs/2506.21533 https://

On the Invariance of Expansive Measures for Flows
We study expansive measures for continuous flows without fixed points on compact metric spaces, as introduced in [6]. We provide a new characterization of expansive measures through dynamical balls that, in contrast to the dynamical balls considered in [6], are actually Borel sets. This makes the theory more amenable to measure-theoretic analysis. We then establish a version of the Brin-Katok local entropy formula for flows using these generalized dynamical balls. As an application, we prove th…

The $\mathcal{R}$-boundedness of solution operators for the $Q$-tensor model of nematic liquid crystals
Daniele Barbera, Miho Murata
https://arxiv.org/abs/2506.05152

The $\mathcal{R}$-boundedness of solution operators for the $Q$-tensor model of nematic liquid crystals
In this paper, we consider a resolvent problem arising from the $Q$-tensor model for liquid crystal flows in the half-space. Our purpose is to show the $\mathcal{R}$-boundedness for the solution operator families of the resolvent problem when the resolvent parameter lies near the origin. The definition of the $\mathcal{R}$-solvability implies the uniform boundedness of the operator and, consequently, the resolvent estimates for the linear system.

This https://arxiv.org/abs/2408.08129 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_mat…

Efficient and scalable atmospheric dynamics simulations using non-conforming meshes
We present the massively parallel performance of a $h$-adaptive solver for atmosphere dynamics that allows for non-conforming mesh refinement. The numerical method is based on a Discontinuous Galerkin (DG) spatial discretization, highly scalable thanks to its data locality properties, and on a second order Implicit-Explicit Runge-Kutta (IMEX-RK) method for time discretization, particularly well suited for low Mach number flows. Simulations with non-conforming meshes for flows over orography can…

This https://arxiv.org/abs/2505.21124 has been replaced.
initial toot: https://mastoxiv.page/@ar…

UniFoil: A Universal Dataset of Airfoils in Transitional and Turbulent Regimes for Subsonic and Transonic Flows
We present UniFoil, a large publicly available universal airfoil dataset based on Reynolds-averaged Navier-Stokes (RANS) simulations. It contains over 500,000 samples spanning a wide range of Reynolds and Mach numbers, capturing both transitional and fully turbulent flows across incompressible to compressible regimes. UniFoil is designed to support machine learning research in fluid dynamics, particularly for modeling complex aerodynamic phenomena. Most existing datasets are limited to incompre…

Large-Scale Simulations of Turbulent Flows using Lattice Boltzmann Methods on Heterogeneous High Performance Computers
Adrian Kummerl\"ander, Fedor Bukreev, Yuji Shimojima, Shota Ito, Mathias J. Krause
https://arxiv.org/abs/2506.21804

Large-Scale Simulations of Turbulent Flows using Lattice Boltzmann Methods on Heterogeneous High Performance Computers
Current GPU-accelerated supercomputers promise to enable large-scale simulations of turbulent flows. Lattice Boltzmann Methods (LBM) are particularly well-suited to fulfilling this promise due to their intrinsic compatibility with highly parallel execution on both SIMD CPUs and GPUs. A novel LBM scheme for wall-modeled LES in complex geometries is described with a special focus on the efficient implementation in the open source LBM framework OpenLB. Detailed scalability results are provided for…

Phase-based analysis and control of low Reynolds number aeroelastic flows
Chathura R. Sumanasiri, Tulsi Ram Sahu, Aditya G. Nair
https://arxiv.org/abs/2506.00306

Phase-based analysis and control of low Reynolds number aeroelastic flows
Flutter in lightweight airfoils under unsteady flows presents a critical challenge in aeroelastic stability and control. This study uncovers phase-localized mechanisms that drive the onset and suppression of flutter in a freely pitching airfoil at low Reynolds number. By introducing targeted impulsive stiffness perturbations, we identify critical phases that trigger instability. Using phase-sensitivity functions, energy-transfer metrics, and dynamic mode decomposition, we show that flutter aris…

This https://arxiv.org/abs/2406.11379 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_mat…

On existence of Sadovskii vortex patch: A touching pair of symmetric counter-rotating uniform vortex
The Sadovskii vortex patch is a traveling wave for the two-dimensional incompressible Euler equations consisting of an odd symmetric pair of vortex patches touching the symmetry axis. Its existence was first suggested by numerical computations of Sadovskii in [J. Appl. Math. Mech., 1971], and has gained significant interest due to its relevance in inviscid limit of planar flows via Prandtl--Batchelor theory and as the asymptotic state for vortex ring dynamics. In this work, we prove the existen…

This https://arxiv.org/abs/2411.07064 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_mat…

Rigorous enclosure of Lyapunov exponents of stochastic flows
We develop a powerful and general method to provide rigorous and accurate upper and lower bounds for Lyapunov exponents of stochastic flows. Our approach is based on computer-assisted tools, the adjoint method and established results on the ergodicity of diffusion processes. We do not require any structural assumptions on the stochastic system and work under mild hypoellipticity conditions and outside of perturbative regimes. Therefore, our method allows for the treatment of systems that were s…

On a mathematical definition of laminar and turbulent fluid flow
F. Javier Garcia Garcia, Pablo Fari\~nas Alvari\~no
https://arxiv.org/abs/2507.00974 https…

On a mathematical definition of laminar and turbulent fluid flow
As stated in the title, the present research proposes a mathematical definition of laminar and turbulent flows, i.e., a definition that may be used to conceive and prove mathematical theorems about such flows. The definition is based on an experimental truth long known to humans: Whenever one repeats a given flow, the results will not be the same if the flow is turbulent. Turbulent flows are not strictly repeatable. From this basic fact follows a more elaborate truth about turbulent flows: The …

This https://arxiv.org/abs/2410.16466 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_mat…

An Immersed Interface Method for Incompressible Flows and Geometries with Sharp Features
The immersed interface method (IIM) for models of fluid flow and fluid-structure interaction imposes jump conditions that capture stress discontinuities generated by forces that are concentrated along immersed boundaries. Most prior work using the IIM for fluid dynamic applications has focused on smooth interfaces, but boundaries with sharp features such as corners and edges can appear in practical analyses, particularly on engineered structures. The present study builds on our work to integrat…

A Thermodynamically Consistent Free Boundary Model for Two-Phase Flows in an Evolving Domain with Moving Contact Lines, Variable Contact Angles and Bulk-Surface Interaction
Patrik Knopf, Yadong Liu
https://arxiv.org/abs/2507.01618

A Thermodynamically Consistent Free Boundary Model for Two-Phase Flows in an Evolving Domain with Moving Contact Lines, Variable Contact Angles and Bulk-Surface Interaction
We derive a thermodynamically consistent model, which describes the time evolution of a two-phase flow in an evolving domain. The movement of the free boundary of the domain is driven by the velocity field of the mixture in the bulk, which is determined by a Navier--Stokes equation. In order to take interactions between bulk and boundary into account, we further consider two materials on the boundary, which may be the same or different materials as those in the bulk. The bulk and the surface ma…

Surface curvature and secondary vortices in steady dense shallow granular flows
C. Gadal, C. G. Johnson, J. M. N. T. Gray
https://arxiv.org/abs/2506.22665 …

Surface curvature and secondary vortices in steady dense shallow granular flows
Dense granular flows exhibit both surface deformation and secondary flows due to the presence of normal stress differences. Yet, a complete mathematical modelling of these two features is still lacking. This paper focuses on a steady shallow dense flow down an inclined channel of arbitrary cross-section, for which asymptotic solutions are derived by using an expansion based on the flow shallowness combined with a second-order granular rheology. The leading order flow is uniaxial, with a streamw…

Existence and uniqueness results of unsteady reactive flows in porous media
Pankaj Roy, Satyajit Pramanik
https://arxiv.org/abs/2506.22225 https://

Existence and uniqueness results of unsteady reactive flows in porous media
Miscible reactive flows in porous media play crucial roles in many engineering and industrial applications. In this work, we establish several results regarding the existence and uniqueness of solutions for a system of time-dependent, nonlinear partial differential equations that describe the flow and transport of miscible reactive fluids with variable viscosity in heterogeneous porous media with variable permeability. Fluid flow is modelled via the unsteady Darcy-Brinkman equation with Kortewe…

Jacobian-free Multigrid Preconditioner for Discontinuous Galerkin Methods applied to Numerical Weather Prediction
Philipp Birken, Andreas Dedner, Robert Kl\"ofkorn
https://arxiv.org/abs/2505.24504

Jacobian-free Multigrid Preconditioner for Discontinuous Galerkin Methods applied to Numerical Weather Prediction
Discontinuous Galerkin (DG) methods are promising high order discretizations for unsteady compressible flows. Here, we focus on Numerical Weather Prediction (NWP). These flows are characterized by a fine resolution in $z$-direction and low Mach numbers, making the system stiff. Thus, implicit time integration is required and for this a fast, highly parallel, low-memory iterative solver for the resulting algebraic systems. As a basic framework, we use inexact Jacobian-Free Newton-GMRES with a pr…

This https://arxiv.org/abs/2504.08648 has been replaced.
initial toot: https://mastoxiv.page/@ar…

Rational constitutive law for the viscous stress tensor in incompressible two-phase flows: Derivation and tests against a 3D benchmark experiment
We analyze the representation of viscous stresses in the one-fluid formulation of the two-phase Navier-Stokes equations, the model on which all computational approaches making use of a fixed mesh to discretize the flow field are grounded. Recognizing that the Navier-Stokes-like equations that are actually solved in these approaches imply a spatial filtering, we show by considering a specific two-dimensional flow configuration that the proper representation of the viscous stress tensor requires …

Should we care about the spatial heterogeneity in coral reefs under unidirectional turbulent flows?
Akshay Patil, Clara Garc\'ia-S\'anchez
https://arxiv.org/abs/2506.03021

Should we care about the spatial heterogeneity in coral reefs under unidirectional turbulent flows?
In this work, we systematically investigate the similarities and differences observed between a hydraulically rough wall comprised of an array of cylinders, massive corals, and branching corals arranged in a staggered manner, along with a stochastically generated coral bed using a scale-resolving computational framework. Our data suggests that for all the flow parameters of interest, there is a substantial difference observed between the stochastic coral bed and the regularly arranged coral bed…

Magnetic Stabilization of Compressible Flows: Global Existence in 3D Inviscid Non-Isentropic MHD Equations
Jiahong Wu, Fuyi Xu, Xiaoping Zhai
https://arxiv.org/abs/2507.00888

Magnetic Stabilization of Compressible Flows: Global Existence in 3D Inviscid Non-Isentropic MHD Equations
Solutions to the compressible Euler equations in all dimensions have been shown to develop finite-time singularities from smooth initial data such as shocks and cusps. There is an extraordinary list of results on this subject. When the inviscid compressible flow is coupled with the magnetic field in the 3D inviscid non-isentropic compressible magnetohydrodynamic (MHD) equations in $\mathbb{T}^3$, this paper rules out finite-time blowup and establishes the global existence of smooth and stable s…

This https://arxiv.org/abs/2407.11746 has been replaced.
initial toot: https://mastoxiv.page/@ar…

Sparse data assimilation for under-resolved large-eddy simulations
The need for accurate and fast scale-resolving simulations of fluid flows, where turbulent dispersion is a crucial physical feature, is evident. Large-eddy simulations (LES) are computationally more affordable than direct numerical simulations, but their accuracy depends on sub-grid scale models and the quality of the computational mesh. In order to compensate related errors, a data assimilation approach for LES is devised in this work. The presented method is based on variational assimilatio…

This https://arxiv.org/abs/2410.16466 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_mat…

An Immersed Interface Method for Incompressible Flows and Geometries with Sharp Features
The immersed interface method (IIM) for models of fluid flow and fluid-structure interaction imposes jump conditions that capture stress discontinuities generated by forces that are concentrated along immersed boundaries. Most prior work using the IIM for fluid dynamic applications has focused on smooth interfaces, but boundaries with sharp features such as corners and edges can appear in practical analyses, particularly on engineered structures. The present study builds on our work to integrat…

Transport of spherical microparticles in a 3D vortex flow
Marine Aulnette, Noa Burshtein, Arash Alizad Banaei, Luca Brandt, Simon J. Haward, Amy Q. Shen, Blaise Delmotte, Anke Lindner
https://arxiv.org/abs/2506.02820

Transport of spherical microparticles in a 3D vortex flow
Particles are common in biological and environmental flows and are widely used in industrial and pharmaceutical applications. Their motion and flow dynamics are strongly affected by interactions with the surrounding flow structure. While particle-flow interactions have been extensively studied in low Reynolds number (Re) flows as well as in fully developed turbulence, the transport mechanisms of these particles in intermediate flow regimes remain less explored. Here, we investigate the response…

This https://arxiv.org/abs/2502.12316 has been replaced.
initial toot: https://mastoxiv.page/@ar…

Large-scale clustering of inertial particles in a rotating, stratified and inhomogeneous turbulence
We develop a theory of various kinds of large-scale clustering of inertial particles in a rotating density stratified or inhomogeneous turbulent fluid flows. The large-scale particle clustering occurs in scales which are much larger than the integral scale of turbulence, and it is described in terms of the effective pumping velocity in a turbulent flux of particles. We show that for a fast rotating strongly anisotropic turbulence, the large-scale clustering occurs in the plane perpendicular to …

Monotone Multispecies Flows
Lauren Conger, Franca Hoffmann, Eric Mazumdar, Lillian J. Ratliff
https://arxiv.org/abs/2506.22947 https://

Monotone Multispecies Flows
We present a novel notion of $λ$-monotonicity for an $n$-species system of partial differential equations governed by mass-preserving flow dynamics, extending monotonicity in Banach spaces to the Wasserstein-2 metric space. We show that monotonicity implies the existence of and convergence to a unique steady state, convergence of the velocity fields and second moments, and contraction in the Wasserstein-2 metric, at rates dependent on $λ$. In the special setting of Wasserstein-2 gradient desc…

This https://arxiv.org/abs/2307.09778 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_mat…

Addressing the checkerboard problem in an Eulerian meshless method for incompressible flows
In this paper, we look at the pressure checkerboard problem that arises in an Eulerian meshless method that solves the incompressible Navier-Stokes equations using the generalized finite difference method (GFDM). Although, the checkerboard problem has been dealt with extensively in mesh-based methods, the literature in connection with meshless methods is comparatively scarce. In this paper, we explore the occurrence of the checkerboard problem in a meshless method. A few unsuccessful attempts t…

This https://arxiv.org/abs/2501.11744 has been replaced.
initial toot: https://mastoxiv.page/@ar…

Confinement-induced proliferation of vortices around marine invertebrate larvae
The ocean is teeming with a myriad of mm-sized invertebrate planktonic larvae, which thrive in a viscous fluid environment. Many of them rely on ciliary beating to generate fluid flows for locomotion and feeding. Their larval forms, local morphologies, and ciliation patterns exhibit remarkable diversity, producing intricate and dynamic 3D flows that are notoriously difficult to characterize in laboratory settings. Traditional microscopic imaging techniques typically involve gently squeeze-confi…

This https://arxiv.org/abs/2409.10875 has been replaced.
initial toot: https://mastoxiv.page/@arXiv_mat…

Adaptively Coupled Domain Decomposition Method for Multiphase and Multicomponent Porous Media Flows
Numerical simulation of large-scale multiphase and multicomponent flow in porous media is a significant field of interest in the petroleum industry. The fully implicit approach is favored in reservoir simulation due to its numerical stability and relaxed constraints on time-step sizes. However, this method requires solving a large nonlinear system at each time step, making the development of efficient and convergent numerical methods crucial for accelerating the nonlinear solvers. In this paper…

Helical flows spontaneously generated by salt fingers
Adrian E. Fraser, Adrian van Kan, Edgar Knobloch, Keith Julien, Chang Liu
https://arxiv.org/abs/2506.22581

Helical flows spontaneously generated by salt fingers
We study the dynamics of salt fingers in the regime of slow salinity diffusion (small inverse Lewis number) and strong stratification (large density ratio), focusing on regimes relevant to Earth's oceans. Using three-dimensional direct numerical simulations in periodic domains, we show that salt fingers exhibit rich, multiscale dynamics in this regime, with vertically elongated fingers that are twisted into helical shapes at large scales by mean flows and disrupted at small scales by isotropic …

Relaxation enhancement by controlling incompressible fluid flows
Kai Koike, Vahagn Nersesyan, Manuel Rissel, Marius Tucsnak
https://arxiv.org/abs/2506.22233

Relaxation enhancement by controlling incompressible fluid flows
We propose a PDE-controllability based approach to the enhancement of diffusive mixing for passive scalar fields. Unlike in the existing literature, our relaxation enhancing fields are not prescribed $\textit{ab initio}$ at every time and at every point of the spatial domain. Instead, we prove that time-dependent relaxation enhancing vector fields can be obtained as $\textit{state trajectories of control systems described by the incompressible Euler equations}$ either driven by finite-dimension…

Diff-SPORT: Diffusion-based Sensor Placement Optimization and Reconstruction of Turbulent flows in urban environments
Abhijeet Vishwasrao, Sai Bharath Chandra Gutha, Andres Cremades, Klas Wijk, Aakash Patil, Catherine Gorle, Beverley J McKeon, Hossein Azizpour, Ricardo Vinuesa
https://arxiv.org/abs/2506.00214

Diff-SPORT: Diffusion-based Sensor Placement Optimization and Reconstruction of Turbulent flows in urban environments
Rapid urbanization demands accurate and efficient monitoring of turbulent wind patterns to support air quality, climate resilience and infrastructure design. Traditional sparse reconstruction and sensor placement strategies face major accuracy degradations under practical constraints. Here, we introduce Diff-SPORT, a diffusion-based framework for high-fidelity flow reconstruction and optimal sensor placement in urban environments. Diff-SPORT combines a generative diffusion model with a maximum …

Nonlinear Stability and Dynamics of Supersonic Compressible Flows
Symphony Chakraborty (Institute of Astronomy,Astrophysics, Academia Sinica), Hsien Shang (Institute of Astronomy,Astrophysics, Academia Sinica)
https://arxiv.org/abs/2505.21650

Nonlinear Stability and Dynamics of Supersonic Compressible Flows
The study of shear layer instability in compressible flows is key to understanding phenomena from aerodynamics to astrophysical jets. Blumen's seminal paper [``Shear layer instability of an inviscid compressible fluid," J. Fluid Mech. {\bf 40}, 769--781 (1970)] established a linear stability framework for inviscid compressible shear flows, emphasizing velocity gradients and compressibility effects. However, the nonlinear regime remains insufficiently explored. This research extends Blumen's fra…

A features-embedded-learning immersed boundary model for large-eddy simulation of turbulent flows with complex boundaries
Zhideng Zhou, Fengshun Zhang, Xiaolei Yang
https://arxiv.org/abs/2506.21985

A features-embedded-learning immersed boundary model for large-eddy simulation of turbulent flows with complex boundaries
The hybrid wall-modeled large-eddy simulation (WMLES) and immersed boundary (IB) method offers significant flexibility for simulating high Reynolds number flows involving complex boundaries. However, the approximate boundary conditions (e.g., the wall shear stress boundary condition) developed for body-fitted grids in the literature are not directly applicable to IB methods. In this work, we propose a features-embedded-learning-IB (FEL-IB) wall model to approximate IB boundaries in the hybrid W…

Cone-jet Stokes solutions in strong viscous flows: the vanishing flow rate limit
Alfonso M. Ganan-Calvo, Miguel A. Herrada, Jens Eggers
https://arxiv.org/abs/2505.24741

Cone-jet Stokes solutions in strong viscous flows: the vanishing flow rate limit
Steady tip streaming in the vanishing flow rate limit has been evidenced both experimentally and numerically in the literature. However, local conical Stokes flow solutions supporting these results at vanishing small scales around the emitting tip have remained elusive. This work presents approximate local conical solutions in liquid-liquid flow focusing and tip streaming, in general, as the limit of a macroscopic vanishing issued flow rate. This provides mathematical foundations for the existe…

Theory and simulation of elastoinertial rectification of oscillatory flows in two-dimensional deformable rectangular channels
Uday M. Rade, Shrihari D. Pande, Ivan C. Christov
https://arxiv.org/abs/2505.22799

Theory and simulation of elastoinertial rectification of oscillatory flows in two-dimensional deformable rectangular channels
A slender two-dimensional (2D) channel bounded by a rigid bottom surface and a slender elastic layer above deforms when a fluid flows through it. Hydrodynamic forces cause deformation at the fluid-solid interface, which in turn changes the cross-sectional area of the fluidic channel. The nonlinear coupling between flow and deformation, along with the attendant asymmetry in geometry caused by flow-induced deformation, produces a streaming effect (a non-zero cycle-average despite time-periodic fo…

Effective flows across diffusio-phoretic membranes
Kevin Wittkowski, Pier Giuseppe Ledda, Edoardo Carlo Giordano, Fran\c{c}ois Gallaire, Giuseppe Antonio Zampogna
https://arxiv.org/abs/2505.22197

Effective flows across diffusio-phoretic membranes
Flows enabled by phoretic mechanisms are of significant interest in several biological and biomedical processes, such as bacterial motion and targeted drug delivery. Here, we develop a homogenization-based macroscopic boundary condition which describes the effective flow across a diffusiophoretic microstructured membrane, where the interaction between the membrane walls and the solute particles is modeled via a potential-approach. We consider two cases where potential variations occur (i) at th…

This https://arxiv.org/abs/2411.11553 has been replaced.
initial toot: https://mastoxiv.page/@ar…

Dynamical regimes of thermally convective emulsions
Emulsions are paramount in various interdisciplinary topical areas, yet a satisfactory understanding of their behavior in buoyancy-driven thermal flows has not been established. In the present work, we unravel the dynamical regimes of thermal convection in emulsions by leveraging a large set of mesoscale numerical simulations. Emulsions are prepared with a given volume fraction of the initially dispersed phase, $ϕ$, ranging from dilute (low values of $ϕ$) to jammed emulsions (high values of $…

Lattice Boltzmann wall boundary conditions for RANS-based simulations with wall functions
Jorge Ponsin, Carlos Lozano
https://arxiv.org/abs/2506.03905 http…

Lattice Boltzmann wall boundary conditions for RANS-based simulations with wall functions
In this study, we investigate wall boundary condition schemes for Lattice Boltzmann simulations of turbulent flows modeled using RANS equations with wall functions. Two alternative schemes are formulated and assessed: a hybrid regularized boundary condition and a slip-velocity bounce-back scheme. Their performance is evaluated using two canonical turbulent flow cases, a fully developed channel flow and a zero-pressure-gradient flat plate boundary layer (BL), selected specifically to isolate and…

Dynamics of thin film flows on a vertical fibre with vapor absorption
Souradip Chattopadhyay, Zihao Yu, Y. Sungtaek Ju, Hangjie Ji
https://arxiv.org/abs/2505.22379

Dynamics of thin film flows on a vertical fibre with vapor absorption
Water vapor capture through free surface flows plays a crucial role in various industrial applications, such as liquid desiccant air conditioning systems, water harvesting, and dewatering. This paper studies the dynamics of a silicone liquid sorbent (also known as water-absorbing silicone oil) flowing down a vertical cylindrical fibre while absorbing water vapor. We propose a one-sided thin-film-type model for these dynamics, where the governing equations form a coupled system of nonlinear four…

A simplified unified wave-particle method for diatomic gases with rotational and vibrational non-equilibrium
Sirui Yang, Chengwen Zhong, Ningchao Ding, Junzhe Cao, He Zhang, Congshan Zhuo, Sha Liu
https://arxiv.org/abs/2507.00720

A simplified unified wave-particle method for diatomic gases with rotational and vibrational non-equilibrium
The hypersonic flow around near-space vehicles constitutes a multi-scale flow problem. Due to insufficient molecular collisions to achieve equilibrium, rarefied gas effects are present in the flow field. Thus, numerical methods capable of accurately resolving multi-scale flows are required. Furthermore, high-temperature gas effects in hypersonic flows mean vibrational excitation of polyatomic molecules. Consequently, numerical methods accounting for non-equilibrium in rotational and vibrational…

Improving Spatio-Temporal Accuracy of the Stochastic Particle Fokker-Planck Model
Joonbeom Kim, Eunji Jun
https://arxiv.org/abs/2506.23142 https://

Improving Spatio-Temporal Accuracy of the Stochastic Particle Fokker-Planck Model
Accurate prediction of rarefied gas flows is important for space vehicle design, particularly in rarefied regimes where the Navier-Stokes equations are no more valid. While the direct simulation Monte Carlo (DSMC) method acts as a numerical solver for rarefied gas flows, it becomes inefficient when dealing with near-continuum regimes. The Fokker-Planck (FP) model improves computational efficiency by approximating particle collisions as a drift-diffusion process. The FP model has been extended t…

Topological Entropy of Stationary Turbulent Flows
Ankan Biswas, Amal Manoharan, Ashwin Joy
https://arxiv.org/abs/2506.20973 https://a…

Topological Entropy of Stationary Turbulent Flows
Topological entropy serves as a viable candidate for quantifying mixing and complexity of a highly chaotic system. Particularly in turbulence, this is determined as the exponential stretching rate of a fluid material line that typically necessitates a Lagrangian description. We extend the recent work [A. Manoharan, S. Subramanian, and A. Joy, arXiv:2412.08996] to three dimensions, and present an exact Eulerian framework for the topological entropy in stationary turbulent flows that is devoid of…

Simulating acoustically-actuated flows in complex microchannels using the volume penalization technique
Khemraj Gautam Kshetri, Amneet Pal Singh Bhalla, Nitesh Nama
https://arxiv.org/abs/2506.20034

Simulating acoustically-actuated flows in complex microchannels using the volume penalization technique
We present a volume penalization technique for simulating acoustically-actuated flows in geometrically complex microchannels. Using a perturbation approach, the nonlinear response of an acoustically-actuated compressible Newtonian fluid moving over obstacles or flowing in a geometrically complex domain is segregated into two sub-problems: a harmonic first-order problem and a time-averaged second-order problem, where the latter utilizes forcing terms and boundary conditions arising from the firs…

This https://arxiv.org/abs/2407.16059 has been replaced.
initial toot: https://mastoxiv.page/@ar…

Near-inertial echoes of ageostrophic instability in submesoscale filaments
Ocean submesoscales, flows with characteristic size around 10 m - 10 km, are transitional between the larger, rotationally-constrained mesoscale and three-dimensional turbulence. In this paper we present simulations of a submesoscale ocean filament. In our case, the filament is strongly sheared in both vertical and cross-filament directions and is unstable. Instability indeed dominates the early behaviour with a fast extraction of kinetic energy from the vertically sheared thermal wind. However…

Predicting any small-scale statistics of high-Reynolds-number turbulence using ensemble simulations
Lukas Bentkamp, Michael Wilczek
https://arxiv.org/abs/2506.23712

Predicting any small-scale statistics of high-Reynolds-number turbulence using ensemble simulations
The complex small-scale statistics of turbulence are a result of the combined cascading dynamics through all scales of the flow. Predicting these statistics using fully resolved simulations at the high Reynolds numbers that typically occur in engineering, geophysical, and astrophysical flows will exceed the capabilities of even the largest supercomputers for the foreseeable future. A common observation is that high-Reynolds-number flows are organized in clusters of intense turbulent activity se…

This https://arxiv.org/abs/2503.13007 has been replaced.
initial toot: https://mastoxiv.page/@ar…

On the characteristic structure of the adjoint Euler equations and the analytic adjoint solution of supersonic inviscid flows
The characteristic structure of the two-dimensional adjoint Euler equations is examined. The behavior is similar to that of the original Euler equations, but with the information travelling in the opposite direction. The compatibility conditions obeyed by the adjoint variables along characteristic lines are derived. It is also shown that adjoint variables can have discontinuities across characteristics and the corresponding jump conditions are obtained. It is shown how this information can be u…