Article
Mechanics
Frieder Kaiser, Malte von der Burg, Joel Sommeria, Samuel Viboud, Bettina Frohnapfel, Davide Gatti, David E. Rival, Jochen Kriegseis
Summary: The study investigated the interaction between unsteady vortex-wall of animal propulsion by examining a vorticity-annihilating boundary layer during the spin-down of a vortex from solid-body rotation. The experiment demonstrated that at high Reynolds numbers, the onset of transition occurs earlier, leading to similar rates of vorticity annihilation in the early stages of spin-down.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Niklas Fehn, Martin Kronbichler, Peter Munch, Wolfgang A. Wall
Summary: This study contributes to the investigation of the well-known energy dissipation anomaly in inviscid limit by conducting high-resolution numerical simulations of the three-dimensional Taylor-Green vortex problem. The interesting observation is made that the kinetic energy evolution does not tend towards exact energy conservation as the spatial resolution of numerical scheme increases. This raises the question of whether the results obtained can be seen as a numerical confirmation of the famous energy dissipation anomaly and elaborates on an indirect approach for the identification of finite-time singularities based on energy arguments.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
P. Baj, F. Alves Portela, D. W. Carter
Summary: In this study, we characterize the incompressible turbulence cascade by examining the inter-scale and inter-space exchanges of scale-by-scale energy, helicity, and enstrophy. We derive governing equations for scale-by-scale helicity and enstrophy similar to the second order structure function. Our analysis focuses on forced periodic turbulence and von Karman flow at different scales. We observe the random sweeping effect in all three individual budgets and between energy and enstrophy transfers. Additionally, we find a kinematic connection between the energy cascade and helicity. Overall, this work extends a classic framework and provides novel insights into turbulence dynamics.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Rishita Das, Sharath S. Girimaji
Summary: By examining the effects of large-scale forcing on small-scale velocity-gradient (VG) dynamics, we found that forcing has subtle but crucial implications on the local streamline geometry, VG magnitude, and dissipation intensity. The interplay between forcing and inertia, pressure, and viscous effects leads to different balance outcomes under different topology conditions. These findings contribute to a better understanding of small-scale processes in turbulence and offer guidance for the development of VG models.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
L. Djenidi, R. A. Antonia, S. L. Tang
Summary: This passage discusses the representation of the nth-order velocity structure function Sn in homogeneous isotropic turbulence, which is usually expressed as S-n similar to r(xi n). Different predictions for xi(n) have been proposed, with the first one by Kolmogorov using a dimensional argument. The use of the Hölder inequality allows for the assessment of differences between these predictions.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Chemistry, Physical
S. Arman Ghaffarizadeh, Gerald J. Wang
Summary: Through molecular dynamics simulations, we studied a model active-matter system and discovered a range of interesting transport phenomena. By adapting existing results, we established a new relationship in active systems that connects transport and structure, providing a promising step towards predictive and generalizable models.
JOURNAL OF PHYSICAL CHEMISTRY LETTERS
(2022)
Article
Mechanics
Wenwei Wu, Lipo Wang, Enrico Calzavarini, Francois G. Schmitt
Summary: We study the statistical properties of scalar fields undergoing reversible chemical reactions in a turbulent environment by means of numerical simulations. Our analysis reveals that the scalar correlation and energy spectra are jointly determined by both the chemical source and the flow configuration.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
S. L. Tang, R. A. Antonia
Summary: The paper introduces a new hypothesis that suggests near-wall small-scale statistics, when suitably normalized, are independent of flow type as well as Reynolds and Peelet numbers. While the available wall turbulence direct numerical simulations data in a channel flow and a boundary layer provide good support for independence with respect to the Reynolds number, more data are needed to fully validate this hypothesis, particularly for higher-order statistics and other types of wall flows with different surface conditions.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mathematics, Applied
Marcos A. G. dos Santos Filho, Francisco E. A. dos Santos
Summary: This article presents a method for obtaining statistical quantities of the velocity field in superfluids using the Weak Wave Turbulence (WWT) theory. By introducing an auxiliary wavefunction, a simpler description of the velocity field is achieved, allowing for the extraction of the incompressible energy spectrum.
PHYSICA D-NONLINEAR PHENOMENA
(2022)
Article
Mechanics
Ricardo P. Xavier, Miguel A. C. Teixeira, Carlos B. da Silva
Summary: This study investigates the characteristics of velocity fluctuations in turbulent flows using theoretical analysis and numerical simulations, revealing the asymptotic laws for variance of velocity fluctuations, Taylor micro-scale, and viscous dissipation rate at different distances from turbulent/non-turbulent interface. The results are confirmed to be independent of Reynolds number and applicable to other flow configurations with appropriate kinetic energy spectra.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Jin-Han Xie, Shi-Di Huang
Summary: Through simulations of an idealized isotropic convection system, we provide evidence for the existence of Bolgiano-Obukhov (BO) scaling in Rayleigh-Benard convection (RBC) and establish its association with the inverse kinetic energy cascade. We also observe strong intermittent effects in the buoyancy field, but not in the velocity.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Physics, Multidisciplinary
Attilio L. Stella, Aleksei Chechkin, Gianluca Teza
Summary: This passage discusses the occurrence of anomalous diffusion phenomena across different length scales, and introduces a specific form of decay related to the probability density function. It also explains the implications of this decay on the normalized cumulant generator, and provides examples related to second-order phase transition singularities in continuous time random walks. In the case of bias, scaling is limited to displacements in the drift direction, and there is no equilibrium analogue for the singularities.
PHYSICAL REVIEW LETTERS
(2023)
Article
Mechanics
Taye Melaku Taddesse, Joseph Mathew
Summary: This study investigates the velocity field characteristics of stationary, turbulent twin round jets. Large-eddy simulations were conducted to obtain the flow fields, revealing that the two jets develop independently and merge into a single jet with an elliptic cross-section downstream. The merged jet becomes circular after a certain distance. The fluctuation levels of the merged jet scale with the local maximum mean velocity, and the mean streamwise velocity reaches a peak at a certain distance from the inflow plane. The velocity and length scales of the merged jet are connected to the input parameters through simple relations, and the far field development can be scaled using intrinsic scales.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Physics, Fluids & Plasmas
G. Boffetta, S. Musacchio
Summary: In this study, a numerical investigation was conducted to examine the turbulent evolution of the mixing layer formed by the Rayleigh-Taylor instability in circular and spherical geometries. The results revealed that the convergent geometry caused the center of the mixing layer to drift towards the center of the domain, and a simple geometric relation based on mass conservation was derived to explain this inward drift. Furthermore, an inward-outward asymmetry in the radial profiles was observed in the late stage of the evolution.
Article
Mechanics
Ali Akhavan-Safaei, Mohsen Zayernouri
Summary: In this study, the spectral transfer model for turbulent intensity in passive scalar transport is reconsidered and a modification to the scaling of scalar variance cascade is proposed. A revised scalar transport model is obtained based on the modified spectral transfer model, using a fractional-order Laplacian operator to include the non-local effects from large-scale anisotropy in the turbulent cascade. The developed model is analyzed through numerical simulation, comparing it with the standard version in terms of scalar variance, scalar gradient statistics, and two-point statistical metrics of turbulent transport.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mathematics, Applied
Melanie Kobras, Valerio Lucarini, Maarten H. P. Ambaum
Summary: In this study, a minimal dynamical system derived from the classical Phillips two-level model is introduced to investigate the interaction between eddies and mean flow. The study finds that the horizontal shape of the eddies can lead to three distinct dynamical regimes, and these regimes undergo transitions depending on the intensity of external baroclinic forcing. Additionally, the study provides insights into the continuous or discontinuous transitions of atmospheric properties between different regimes.
PHYSICA D-NONLINEAR PHENOMENA
(2024)
Article
Mathematics, Applied
Shu-hong Xue, Yun-yun Yang, Biao Feng, Hai-long Yu, Li Wang
Summary: This research focuses on the robustness of multiplex networks and proposes a new index to measure their stability under malicious attacks. The effectiveness of this method is verified in real multiplex networks.
PHYSICA D-NONLINEAR PHENOMENA
(2024)
Article
Mathematics, Applied
Julien Nespoulous, Guillaume Perrin, Christine Funfschilling, Christian Soize
Summary: This paper focuses on optimizing driver commands to limit energy consumption of trains under punctuality and security constraints. A four-step approach is proposed, involving simplified modeling, parameter identification, reformulation of the optimization problem, and using evolutionary algorithms. The challenge lies in integrating uncertainties into the optimization problem.
PHYSICA D-NONLINEAR PHENOMENA
(2024)
Article
Mathematics, Applied
Alain Bourdier, Jean-Claude Diels, Hassen Ghalila, Olivier Delage
Summary: In this article, the influence of a turbulent atmosphere on the growth of modulational instability, which is the cause of multiple filamentation, is studied. It is found that considering the stochastic behavior of the refractive index leads to a decrease in the growth rate of this instability. Good qualitative agreement between analytical and numerical results is obtained.
PHYSICA D-NONLINEAR PHENOMENA
(2024)
Article
Mathematics, Applied
Ling An, Liming Ling, Xiaoen Zhang
Summary: In this paper, an integrable fractional derivative nonlinear Schrodinger equation is proposed and a reconstruction formula of the solution is obtained by constructing an appropriate Riemann-Hilbert problem. The explicit fractional N-soliton solution and the rigorous verification of the fractional one-soliton solution are presented.
PHYSICA D-NONLINEAR PHENOMENA
(2024)
Article
Mathematics, Applied
Marzia Bisi, Nadia Loy
Summary: This paper proposes and investigates general kinetic models with transition probabilities that can describe the simultaneous change of multiple microscopic states of the interacting agents. The mathematical properties of the kinetic model are proved, and the quasi-invariant asymptotic regime is studied and compared with other models. Numerical tests are performed to demonstrate the time evolution of distribution functions and macroscopic fields.
PHYSICA D-NONLINEAR PHENOMENA
(2024)
Article
Mathematics, Applied
Carlos A. Pires, David Docquier, Stephane Vannitsem
Summary: This study presents a general theory for computing information transfers in nonlinear stochastic systems driven by deterministic forcings and additive and/or multiplicative noises. It extends the Liang-Kleeman framework of causality inference to nonlinear cases based on information transfer across system variables. The study introduces an effective method called the 'Causal Sensitivity Method' (CSM) for computing the rates of Shannon entropy transfer between selected causal and consequential variables. The CSM method is robust, cheaper, and less data-demanding than traditional methods, and it opens new perspectives on real-world applications.
PHYSICA D-NONLINEAR PHENOMENA
(2024)
Article
Mathematics, Applied
Feiting Fan, Minzhi Wei
Summary: This paper focuses on the existence of periodic and solitary waves for a quintic Benjamin-Bona-Mahony (BBM) equation with distributed delay and diffused perturbation. By transforming the corresponding traveling wave equation into a three-dimensional dynamical system and applying geometric singular perturbation theory, the existence of periodic and solitary waves are established. The uniqueness of periodic waves and the monotonicity of wave speed are also analyzed.
PHYSICA D-NONLINEAR PHENOMENA
(2024)
Article
Mathematics, Applied
Wangbo Luo, Yanxiang Zhao
Summary: We propose a generalized Ohta-Kawasaki model to study the nonlocal effect on pattern formation in binary systems with long-range interactions. In the 1D case, the model displays similar bubble patterns as the standard model, but Fourier analysis reveals that the optimal number of bubbles for the generalized model may have an upper bound.
PHYSICA D-NONLINEAR PHENOMENA
(2024)
Article
Mathematics, Applied
Corentin Correia, Ana Cristina Moreira Freitas, Jorge Milhazes Freitas
Summary: The emergence of clustering of rare events is due to periodicity, where fast returns to target sets lead to a bulk of high observations. In this research, we explore the potential of a new mechanism to create clustering of rare events by linking observable functions to a finite number of points belonging to the same orbit. We show that with the right choice of system and observable, any given cluster size distribution can be obtained.
PHYSICA D-NONLINEAR PHENOMENA
(2024)
Article
Mathematics, Applied
Enyu Fan, Changpin Li
Summary: This paper numerically studies the Allen-Cahn equations with different kinds of time fractional derivatives and investigates the influences of time derivatives on the solutions of the considered models.
PHYSICA D-NONLINEAR PHENOMENA
(2024)
Article
Mathematics, Applied
Yuhang Zhu, Yinghao Zhao, Chaolin Song, Zeyu Wang
Summary: In this study, a novel approach called Time-Variant Reliability Updating (TVRU) is proposed, which integrates Kriging-based time-dependent reliability with parallel learning. This method enhances risk assessment in complex systems, showcasing exceptional efficiency and accuracy.
PHYSICA D-NONLINEAR PHENOMENA
(2024)
Article
Mathematics, Applied
Chiara Cecilia Maiocchi, Valerio Lucarini, Andrey Gritsun, Yuzuru Sato
Summary: The predictability of weather and climate is influenced by the state-dependent nature of atmospheric systems. The presence of special atmospheric states, such as blockings, is associated with anomalous instability. Chaotic systems, like the attractor of the Lorenz '96 model, exhibit heterogeneity in their dynamical properties, including the number of unstable dimensions. The variability of unstable dimensions is linked to the presence of finite-time Lyapunov exponents that fluctuate around zero. These findings have implications for understanding the structural stability and behavior modeling of high-dimensional chaotic systems.
PHYSICA D-NONLINEAR PHENOMENA
(2024)
Article
Mathematics, Applied
Christian Klein, Goksu Oruc
Summary: A numerical study on the fractional Camassa-Holm equations is conducted to construct smooth solitary waves and investigate their stability. The long-time behavior of solutions for general localized initial data from the Schwartz class of rapidly decreasing functions is also studied. Additionally, the appearance of dispersive shock waves is explored.
PHYSICA D-NONLINEAR PHENOMENA
(2024)
Article
Mathematics, Applied
Vasily E. Tarasov
Summary: This paper extends the standard action principle and the first Noether theorem to consider the general form of nonlocality in time and describes dissipative and non-Lagrangian nonlinear systems. The general fractional calculus is used to handle a wide class of nonlocalities in time compared to the usual fractional calculus. The nonlocality is described by a pair of operator kernels belonging to the Luchko set. The non-holonomic variation equations of the Sedov type are used to describe the motion equations of a wide class of dissipative and non-Lagrangian systems. Additionally, the equations of motion are considered not only with general fractional derivatives but also with general fractional integrals. An application example is presented.
PHYSICA D-NONLINEAR PHENOMENA
(2024)