59 research outputs found
Phase-space Lagrangian dynamics of incompressible thermofluids.
No full textPhase-space Lagrangian dynamics in ideal fluids (i.e, continua) is usually related to the so-called {\it ideal tracer particles}. The latter, which can in principle be permitted to have arbitrary initial velocities, are understood as particles of infinitesimal size which do not produce significant perturbations of the fluid and do not interact among themselves. An unsolved theoretical problem is the correct definition of their dynamics in ideal fluids. The issue is relevant in order to exhibit the connection between fluid dynamics and the classical dynamical system, underlying a prescribed fluid system, which uniquely generates its time-evolution. \
The goal of this paper is to show that the tracer-particle dynamics can be {\it exactly} established for an arbitrary incompressible fluid uniquely based on the construction of an inverse kinetic theory (IKT) (Tessarotto \textit{et al.}, 2000-2008). As an example, the case of an incompressible Newtonian thermofluid is here considered
Modelling of Anthropogenic Pollutant Diffusion in the Atmosphereand Applications to Civil ProtectionMonitoring
No full textA key aspect of fluid mechanics concerns the frictionless phase-space dynamics of particles in an incompressible fluid. The issue, besides its theoretical interest in turbulence theory, is important in many applications, such as the pollutant dynamics in the atmosphere, a problem relevant for civil protection monitoring of air quality. Actually, both the numerical simulation of the ABL (atmospheric boundary layer) portion of the atmosphere and that of pollutant dynamics may generally require the correct definition of the Lagrangian dynamics which characterizes arbitrary fluid elements of incompressible thermofluids. We claim that particularly important for applications would be to consider these trajectories as phase-space trajectories. This involves, however, the unfolding of a fundamental theoretical problem up to now substantially unsolved: namely the determination of the exact frictionless dynamics of tracer particles in an incompressible fluid, treated either as a deterministic or a turbulent (i.e., stochastic) continuum. In this paper we intend to formulate the necessary theoretical framework to construct such a type of description. This is based on a phase-space inverse kinetic theory (IKT) approach recently developed for incompressible fluids (Tessarotto et al., 2004-2008). Our claim is that the conditional frictionless dynamics of a tracer particles - which corresponds to a prescribed velocity probability density and an arbitrary choice of the relevant fluid fields - can be exactly specified
Lagrangian Dynamics of Incompressible Thermofluids
No full textA key aspect of fluid dynamics is the correct definition of the phase-space Lagrangian dynamics which characterizes arbitrary fluid elements of an incompressible fluid. Apart being an unsolved theoretical problem of fundamental importance, the issue is relevant to exhibit the connection between fluid dynamics and the classical dynamical systems underlying incompressible and non-isothermal fluid, typically founded either on: a) a configuration-space Lagrangian description of the dynamics of fluid elements; b) a kinetic description of the molecular dynamics, based on a discrete representation of the fluid. The goal of this paper is to show that the exact Lagrangian dynamics can be established based on the inverse kinetic theory (IKT) for incompressible fluids recently pointed out (Tessarotto et al., 2004-2006, Ellero2004). The result is reached by adopting an IKT approach based on a restricted phase-space representation of the fluid, in which the configuration space coincides with the physical fluid domain. The result appears of potential importance in applied fluid dynamics and CFD
Unique representation of an inverse-kinetic theory for incompressible Newtonian fluids
No full textFundamental aspects of inverse kinetic theories for the incompressible Navier-Stokes equations [Ellero and Tessarotto, 2004, 2005] include the possibility of defining uniquely the kinetic equation underlying such models and furthermore, the construction of a kinetic theory implying also the energy equation. The latter condition is consistent with the requirement that fluid fields result classical solutions of the fluid equations. These issues appear of potential relevance both from the mathematical viewpoint and for the physical interpretation of the theory. Purpose of this work is to prove that under suitable prescriptions the inverse kinetic theory can be determined to satisfy such requirements
The Computational Complexity of Traditional Lattice-BoltzmannMethods for Incompressible Fluids
No full textIt is well-known that customary direct solution methods (based on the discretization of the fluid fields) for the fluid equations of incompressible fluids may be affected by a high computational complexity. This is due primarily to the numerical solution of the Poisson equation for the fluid pressure and occurs when the scale-length of turbulent fluctuations becomes comparable to the discretization scale which characterizes the numerical solution method. An alternative, which can reduce significantly the complexity caused by the numerical solution of the fluid equations for incompressible fluids, may be achieved by so-called particle simulation methods. In such a case the dynamics of fluids is approximated in terms of a set of test particles which advance in time in terms of suitable evolution equations defined in such a way to satisfy identically the Poisson equation. Particle simulation methods rely typically on appropriate kinetic models for the fluid equations which permit the evaluation of the fluid fields in terms of suitable expectation values (or momenta) of the kinetic distribution function f(r,v,t), being respectively r and v the position an velocity of a test particle with probability density f(r,v,t). These kinetic models can be continuous or discrete in phase space, yielding respectively continuous or discrete kinetic models for the fluids. However, also particle simulation methods may be biased by an undesirable computational complexity. In particular, a fundamental issue is to estimate the algorithmic complexity of numerical simulations based on traditional LBM's (Lattice-Boltzmann methods; for review see Succi, 2001 Succi). These methods, based on a discrete kinetic approach, represent currently an interesting alternative to direct solution methods. Here we intend to prove that for incompressible fluids fluids LBM's may present a high complexity. The goal of the investigation is to present a detailed account of the origin of the various complexity sources appearing in customary LBM's. The result is relevant to establish possible strategies for improving the numerical efficiency of existing numerical methods
The Lagrangian dynamics of thermal tracer particles in Navier-Stokes fluids
No full textA basic issue for Navier-Stokes (NS) fluids is their characterization in terms of the so-called NS
phase-space classical dynamical system, which provides a mathematical model for the description of the
dynamics of infinitesimal (or ideal ) tracer particles in these fluids. The goal of this paper is to analyze
the properties of a particular subset of solutions of the NS dynamical system, denoted as thermal tracer
particles (TTPs), whose states are determined uniquely by the NS fluid fields. Applications concerning
both deterministic and stochastic NS fluids are pointed out. In particular, in both cases it is shown that
in terms of the ensemble of TTPs a statistical description of NS fluids can be formulated. In the case of
stochastic fluids this feature permits to uniquely establish the corresponding Langevin and Fokker-Planck
dynamics. Finally, the relationship with the customary statistical treatment of hydrodynamic turbulence
(HT) is analyzed and a solution to the closure problem for the statistical description of HT is proposed
An inverse kinetic theory for the incompressibleNavier-Stokes equations
No full textAn inverse kinetic theory applying specifically to incompressible Newtonian fluids which
permits us to avoid the N2 algorithmic complexity of the Poisson equation for the fluid
pressure is presented. The theory is based on the construction of a suitable kinetic equation in
phase space, which permits us to determine exactly the fluid equations by means of the velocity
moments of the kinetic distribution function. It is found that the fluid pressure can also be
determined as a moment of the distribution function without solving the Poisson equation, as
is usually required in direct solution methods for the incompressible fluid equations. Finally,
the dynamical system, underlying the incompressible Navier–Stokes equations and advancing
in time the fluid fields, has been also identified and proven to produce an unique set of fluid
equation
SABERES E TERRITORIALIDADES: O CASO DOS JOVENS QUILOMBOLAS DO MATÃO-PB
No full textO presente artigo tem por objetivo construir pontes e diálogos conceituais que buscam esclarecer relevante aspecto do complexo fenômeno comunicacional implementado em uma comunidade tradicional no interior da Paraíba. Nosso olhar se fixa na comunidade quilombola do Matão, que vivenciava as afetações introduzidas pelas mídias contemporâneas em seu território, a exemplo das mídias massivas via parabólicas. O impulsionamento e aceleração do tempo/espaço na comunidade quilombola fora acoplada em 2014 com o projeto de inclusão digital do Governo Eletrônico de Serviços ao Cidadão (GESAC). O GESAC (TCU, 2015) é uma iniciativa que provê com internet via satélite localidades isoladas geograficamente. Neste sentido, pretendemos trazer o estudo de caso que descreve a ocorrência deste fenômeno demarcado pela ida destes jovens às redes sociais (DJICK, 2013) e, ao mesmo tempo, a presença energética de uma territorialidade ancestral traduzida pelo “totem território quilombo” (TESSAROTTO, 2021). Este elemento simbólico evocado e apropriado por crianças daquela comunidade permite perceber a existência de uma força contra as fragmentações deste “tempo de turbilhão” da midiatização (FAUSTO NETO, 2014; BRAGA, 2015; ROSA, 2016)
- …
