726 research outputs found
Large-time behavior of the weak solution to 3D Navier-Stokes equations
No full textThe weak solution to the Navier–Stokes equations in a bounded domain D ⊂ R[superscript 3] with a smooth boundary is proved to be unique provided that it satisfies an additional requirement. This solution exists for all t ≥ 0. In a bounded domain D the solution decays exponentially
fast as t → ∞if the force term decays at a suitable rat
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Strong solutions for the Navier–Stokes–Voigt equations with non-negative density
No full textThe aim of this work is to study the Navier–Stokes–Voigt equations that govern flows with non-negative density of incompressible fluids with elastic properties. For the associated nonlinear initial-and boundary-value problem, we prove the global-in-time existence of strong solutions (velocity, density and pressure). We also establish some other regularity properties of these solutions and find the conditions that guarantee the uniqueness of velocity and density. The main novelty of this work is the hypothesis that, in some subdomain of space, there may be a vacuum at the initial moment, that is, the possibility of the initial density vanishing in some part of the space domain.All authors were supported by the Grant No. AP19676624 Ministry of Science and Higher Education of the Republic of Kazakhstan
(Kazakhstan). The first author was also partially supported by CIDMA under the Portuguese Foundation for Science and Technology MultiAnnual Financing Program for R & D Units (FCT, https://ror.org/00snfqn58).publishe
Measure Attractors For Stochastic Navier-Stokes Equations
No full text: We show existence of measure attractors for 2-D stochastic Navier-Stokes equations with general multiplicative noise. Keywords: Stochastic Navier--Stokes equations, measure attractors AMS subject classification: Primary: 35Q30, 60H15, 60G60; Secondary: 35R60, 76D05, 60J25 The research of the first author was supported by an EPSRC Visiting Fellowship at the University of Hull and also partially by the KBN grant 2PO3A 064 08. Submitted to EJP on 15 May, 1997. Final version accepted on May 20, 1998. MEASURE ATTRACTORS FOR STOCHASTIC NAVIER--STOKES EQUATIONS MAREK CAPI ' NSKI AND NIGEL J. CUTLAND Abstract. We show existence of measure attractors for 2-D stochastic Navier-Stokes equations with general multiplicative noise. 1. Introduction This paper is concerned with existence of attractors in connection with stochastic Navier-Stokes equations in dimension 2. For deterministic Navier-Stokes equations, the existence of a global attractor in dimension 2 goes back to the work of Ladyzh..
Desenvolvimento de modelos de gás em rede para escoamentos monofásicos e bifásicos
No full textTese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico.Este trabalho divide-se em duas partes, na primeira parte é apresentado um método para determinação de permeabilidade intrínseca baseado em modelos de gás em rede. Mostra-se que estes modelos possuem um comportamento que pode ser descrito pelas equações de Navier-Stokes para baixo número de Mach. O método foi utilizado para determinação de permeabilidade de rochas de reservatório petrolíferos e os resultados comparados com dados experimentais. Também na primeira parte é apresentado o modelo de rede BGK (Lattice Boltzmann). Baseado na equação de Boltzmann este método permite a integração numérica da equação de Navier-Stokes. São apresentados resultados para escoamentos em uma cavidade quadrada e também a formação das esteiras de vórtices de von-Karman. Na segunda parte, é proposto um novo modelo para a simulação de fluidos imiscíveis baseado na idéia de um campo de mediadores que simulam interações a longa distância utilizando regras locais. Este modelo permite, além disso, o controle da tensão interfacial e da espessura da interface. A dinâmica do modelo é descrita e são apresentados resultados de simulações de diversos casos, incluindo a verificação da lei de Laplace, o fenômeno de coalescência, interações de pares de fluidos molhante/não-molhante com superfícies sólidas e a formação de uma gota sob a ação da gravidade. Estes resultados são comparados com os dados disponíveis
STREAmS-2.0: Supersonic turbulent accelerated Navier-Stokes solver version 2.0
No full textWe present STREAmS-2.0, an updated version of the flow solver STREAmS, first introduced in Bernardini et al. (2021) [1]. STREAmS-2.0 has an object-oriented design which separates the physics equations from the specific back-end, making the code more suitable for future expansions, such as porting to novel computing architectures or implementation of additional flow physics. Similarly to the previous version, STREAmS-2.0 supports NVIDIA-GPU and CPU back-ends. Additionally, this version features improvements of the input/output data management, new energy and entropy preserving schemes for the discretization of the convective fluxes, recycling/rescaling inflow boundary condition, and a model for thermally perfect gases with variable specific heats. New version program summary: Program Title: STREAmS CPC Library link to program files: https://doi.org/10.17632/hdcgjpzr3y.2 Developer's repository link: https://github.com/STREAmS-CFD/STREAmS-2 Licensing provisions: GPLv3 Programming language: Fortran, CUDA Journal reference of previous version: M. Bernardini, D. Modesti, F. Salvadore, and S. Pirozzoli. STREAmS: a high-fidelity accelerated solver for direct numerical simulation of compressible turbulent flows. Comput. Phys. Commun. 263 (2021) 107906. Does the new version supersede the previous version?: Yes. Reasons for the new version: New code structure and release of new features. Summary of revisions: • The original solver [1] has been rewritten following an object-oriented design implemented through Fortran derived types that include variables and type bound procedures. The new software architecture has been designed to increase modularity and extensibility of the code, allowing users to add new back-ends and physics equations while maintaining the same code structure. This allows users to reuse portions of the code that are independent of the physics equations, the back-end, or both. The layer of computing procedures maintains a lean structure that can be highly optimized with respect to the implemented back-end. • Input handling is now based on the classic.ini format improving both user readability and input data management. • A family of new kinetic energy and entropy preserving schemes (KEEP) are now available and can be selected for stable, non-dissipative and accurate spatial discretization of the convective terms of the Navier–Stokes equations in smooth flow regions [2]. Concerning the shock-capturing flux, the improved low-dissipative WENO-Z scheme proposed by [3] is now available. • New inflow boundary conditions based on the recycling/rescale approach [4] have been implemented for the simulation of spatially evolving compressible turbulent boundary layers. Moreover, a new inflow condition based on the solution of the compressible Blasius equation is available to take into account the case of laminar boundary layers. • The constitutive relations have been generalized to take into account thermally perfect gases with variable specific heats, approximated with polynomial functions of the temperature that can be specified by the user [5]. • A new stretching function has been implemented to improve the distribution of grid nodes for the computation of wall-bounded turbulent flows. The formulation blends uniform near-wall spacing with uniform resolution in terms of Kolmogorov units in the outer wall layer, guaranteeing accuracy with higher computational efficiency [6]. Nature of problem: The code solves the compressible Navier–Stokes equations in Cartesian coordinates for a thermally perfect gas. The solver is designed for direct numerical simulation (DNS) of compressible supersonic turbulent boundary layers and various canonical configurations are supported, including turbulent channel flow, laminar and turbulent boundary layer and shock-wave/boundary layer interaction. Solution method: The equations are discretized using high-order finite difference approximations with hybrid low-dissipative/shock-capturing capabilities and the time advancement is performed using a Runge–Kutta scheme. References: [1] M. Bernardini, D. Modesti, F. Salvadore, S. Pirozzoli, STREAmS: A high-fidelity accelerated solver for direct numerical simulation of compressible turbulent flows, Comput. Phys. Commun. 263 (2021) 107906. [2] Y. Tamaki, Y. Kuya, S. Kawai, Comprehensive analysis of entropy conservation property of non-dissipative schemes for compressible flows: KEEP scheme redefined, J. Comput. Phys. 468 (2022) 111494. [3] R. Borges, M. Carmona, B. Costa, W. Don, An improved weighted essentially non-oscillatory scheme for hyperbolic conservation laws, J. Comput. Phys. 227 (6) (2008) 3191–3211, https://doi.org/10.1016/j.jcp.2007.11.038 [4] S. Pirozzoli, M. Bernardini, F. Grasso, Direct numerical simulation of transonic shock/boundary layer interaction under conditions of incipient separation, J. Fluid Mech. 657 (2010) 361–393. [5] B. J. McBride, M. J. Zehe, S. Gordon, NASA Glenn coefficients for calculating thermodynamic properties of individual species, NASA/TP 211556, NASA, 2002. [6] S. Pirozzoli, P. Orlandi, Natural grid stretching for DNS of wall-bounded flows, J. Comput. Phys. 439 (2021) 110408.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.Aerodynamic
Geostrophic convective turbulence: The effect of boundary layers
No full textWe conduct computations of rotating Rayleigh-Bénard convection in the so-called geostrophic regime, characterized by strong thermal forcing (high Rayleigh numbers) and strong rotation (small Ekman numbers). We employ the full Navier-Stokes equations in our computations and compare no-slip and stress-free boundaries for the plates. The Ekman boundary layers, that exist in the no-slip case but not for stress-free, enhance convective heat transfer and prevent the formation of large-scale flow structures
On the interior regularity criteria and the number of singular points to the Navier-Stokes equations
No full textWe establish some interior regularity criteria for suitable weak solutions of the 3-D Navier-Stokes equations which allow the vertical part of the velocity to be large under the local scaling invariant norm. As an application, we improve Ladyzhenskaya-Prodi-Serrin's criterion and Escauriza-Seregin-verak's criterion. We also show that if a weak solution u satisfies parallel to u(.,t)parallel to L-P <= C(-t)((3-P)/2p) for some 3 < p < a, then the number of singular points is finite.MathematicsSCI(E)[email protected]; [email protected]
Resolvent Estimates in (weighted) Lp spaces for the Stokes Operator in Lipschitz Domains
No full textRecently, by Z. Shen, resolvent estimates for the Stokes operator were established in Lp(Ω) when Ω is a Lipschitz domain in Rd, with d≥3 and |1/p-1/2|<1/(2d)+ε. This result implies that the Stokes operator generates a bounded analytic semigroup in Lp(Ω) in the case that Ω is a three-dimensional Lipschitz domain and 3/2-ε<p<3+ε. To fully understand the work of Z. Shen, a lot of background information is needed. In this thesis the resolvent estimates are studied in detail in the case d=3. In the end the results of Shen are extended to resolvent estimates in Lp(w,Ω), where Ω is a three-dimensional Lipschitz domain, |1/p-1/2|<1/6, and w∈A2p/3∩RH3/(3-p) is a weight function that belongs to an intersection of a Muckenhoupt weight class and satisfies a reverse Hölder inequality
Race as an Institutional Factor in the Arrest, and the use of Excessive and Deadly Force against African American Males
No full textThese authors assert that race is a determinant used by police officers to arrest and use deadly force against African American males. Race is an institutionalized factor that is embedded and widespread in societys social structure. Hence, the institutional discrimination perspective is utilized to explain the issue of race. Institutional discrimination consists of practices or organizations and institutions that have a harmful effect on members of subordinate groups, in this case, African American males. Because race is institutionalized in the social structure, it is not surprising that law enforcement agencies use race as a factor in the arrest and deadly force against African Americans
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