1,720,969 research outputs found
Between low and strong stratification regimes for rotating heat-conducting fluids
No full textWe consider the Navier-Stokes-Fourier system for a heat conducting compressible fluid under the effects of rotation and stratification. We investigate the low Mach, Rossby and Froude number limit towards a quasi geostrophic balance in a stratification range between the so-called low and strong stratification regimes. The limit is studied in the context of weak solutions with ill-prepared initial data
Gevrey regularity for the Euler–Bernoulli beam equation with localized structural damping
No full textWe study a Euler-Bernoulli beam equation
with localized discontinuous structural damping.
As our main result, we prove that the associated
-semigroup is of Gevrey class \delta>24 for t>0,
hence immediately differentiable. Moreover, we show that
is exponentially stable
Hidden symmetry in turbulence and analytic study of shell models
No full textThis short communication concerns symmetries in developed turbulence and analytic study of shell models. However scale-invariance is broken due to the intermittency phenomenon, is possible to established a hidden self-similarity in turbulent flows. Using a shell model, the author in [18] (see also [19]) addressed the problem deriving a scaling symmetry for the inviscid equations. Here, first we discuss the analysis presented in [18], then, from the mathematical perspective, we propose an analytic study for the shell model with the presence of the viscous terms. This brief paper should be understood as an introductory note to this new scaling symmetry with implications for mathematical analysis [5]
Navier - Stokes equations and related problems
No full textDisertační práce je věnována studiu matematických problémů Navierových -
Stokesových rovnic v kontextu rigorózního matematického odvození modelů
a jejich matematické analýzy. Zejména je práce zaměřena na problematiku
singulárních limit v mechanice tekutin pro stlačitelné tekutiny (režim malého
Machova čísla, velkého Reynoldsova čísla, redukce dimenze) a problematice regularity pro nestlačitelné tekutiny.NeobhájenoThe present thesis is devoted to the study of mathematical problems related to
the Navier-Stokes equations in the context of mathematical rigorous derivation
of models and their analysis. In particular we deal with the problem of singular
limits in fl uid mechanics for compressible fl uids (low Mach number limit and
high Reynolds number limit, reduction of dimension) and the problem of global
regularity for incompressible fl uids
Analysis of the turbulence parameterisations for the atmospheric surface layer
No full textThe purpose of this short communication is to present a method that aims to express the turbulent variables in the atmospheric surface-layer in function of the stability of the atmosphere. The case of very stable conditions (strong strati cation), where theoretical approaches provide conflicting results (see Luhar et al. [11]), is analysed in detail to provide some insight into the limits of applicability for some of the most popular models of turbulence. The problem of the existence of the critical flux Richardson number is also taken into account
Aeroacoustic simulations in thermally non-homogeneous fluid flows
No full textThe cooling system, comprising heat exchangers and cooling fans, is essential for maintaining the power performance and acceptable operational conditions of a vehicle. However, running of the cooling fan produces unwanted noise, which often becomes dominant sound produced by the vehicle. To model the noise generated by turbulent flow and heat transfer around cooling fan blades, an appropriate flow model is essential. This study employs the compressible Navier-Stokes equations with an restricted relation between temperature and density for efficient handling of non-homogeneous temperature fields, combined with Delayed Detached Eddy Simulation (DDES) for advanced turbulence modeling. For the aeroacoustic analysis, a hybrid aeroacoustic approach is adopted, utilizing the Acoustic Perturbation Equation (APE) to model acoustic generation and propagation. The main aim of this study is to model the flow and the acoustic problem in the consistent way for the considered simple test case of heated cylinder walls in cross-flow. As most prior investigations focused only on isothermal conditions the model considered in this study presents an important generalization. A part of the problem is to select an efficient numerical software capable to treat temperature non-homogeneities in the flow and the aeroacoustic solver while being prepared for a possible future industrial application. The obtained results for varying thermal conditions show the significant sensitivity of produced sound pressure levels
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Note on the use of Camassa-Holm equations for simulation of incompressible fluid turbulence
No full textThe aim of this short communication is to briefly introduce the Camassa-Holm equations as a working model for simulation of incompressible fluid turbulence. In particular we discuss its application for turbulent boundary layer flows. This model (and related models) is studied for several years in mathematical community, starting from Leray [23]. It can be understood as a generalization of some classical fluid models (Navier-Stokes equations, Prandtl boundary layer equations), showing some interesting mathematical properties in the analysis of the behavior of it's solution (e.g. Layton and Lewandowski [22]). It has been found however, that the model predictions can lead to surprising extensions of the use of the model in technical applications, namely in simulating the turbulent fluid flows. This brief paper should be understood as an introductory note to this novel class of models for applied scientists
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