Search results for "Turbulence"
showing 10 items of 378 documents
Giant collective incoherent shock waves in strong turbulence
2016
Contrary to conventional coherent shocks, we show theoretically and experimentally that nonlocal turbulent flows lead to the emergence of large-scale incoherent shock waves, which constitute a collective phenomenon of the incoherent field as a whole.
Incoherent Dispersive Shocks and Spectral Collapse
2014
We predict the existence of incoherent dispersive shock waves and collapse-like singularities that occur in the spectral evolution of incoherent optical waves propagating in a noninstantaneous nonlinear medium.
Shock-induced complex phase-space dynamics of strongly turbulent flows
2017
Shock waves have been thoroughly investigated during the last century in many different branches of physics. In conservative (Hamiltonian) systems the shock singularity is regularized by weak wave dispersion, thus leading to the formation of a rapidly and regular oscillating structure, usually termed in the literature dispersive shock wave (DSW), see e.g. [1]. Here, we show that this fundamental singular process of DSW formation can break down in a system of incoherent nonlinear waves. We consider the strong turbulent regime of a system of nonlocal nonlinear optical waves. We report theoretically and experimentally a characteristic transition: Strengthening the nonlocal character of the non…
High order accurate shock capturing schemes for two-component Richtmyer-Meshkov instabilities in compressible magnetohydrodynamics
2011
We design a conservative and entropy satisfying numerical scheme to perform numerical simulations of two component Richtmyer-Meshkov (RM) instabilities in compressible magnetohydrodynamics (MHD). We first formulate a conservative model of a two-component compressible MHD fluid ruled under two ideal gases with different adiabatic exponents. The formulation includes a level set function that allows to evolve the two components of the plasma in a conservative and consistent way. We present a set of examples including two-component Riemann problems and high Mach shock wave interactions with entropy contact waves that validate the high order accurate numerical scheme. We observe that turbulent r…
A Shoreline model for breaking waves
2011
In order to simulate the wave motion and, in turn, the flow, within the nearshore region, in the last decades the derivation and the application of depth-integrated type of models have been widely investigated and developed. However, in such models, the problems of facing wave breaking and the moving shoreline are not trivial and therefore several approaches have been proposed. About wave breaking, approaches both based on the adoption of an artificial eddy viscosity Zelt (1991) and on the concept of roller Veeramony (2000), Karambas (2003), Musumeci (2005) have been implemented. As regards the shoreline boundary condition, a couple of numerical techniques have been mainly adopted, namely t…
Route diversity analyses for free-space optical wireless links within turbulent scenarios
2013
Free-Space Optical (FSO) communications link performance is highly affected when propagating through the time-spatially variable turbulent environment. In order to improve signal reception, several mitigation techniques have been proposed and analytically investigated. This paper presents experimental results for the route diversity technique evaluations for a specific case when several diversity links intersects a common turbulent area and concurrently each passing regions with different turbulence flows.
Applicability of LES turbulence modeling for CZ silicon crystal growth systems with traveling magnetic field
2010
Abstract To examine the applicability of LES turbulence modeling for CZ silicon crystal growth systems with traveling magnetic fields, LES calculations with Smagorinsky–Lilly turbulence model and van Driest damping at the solid walls are carried out. The program package for the calculations was developed on the basis of the open-source code library OpenFOAM ® . A previously published laboratory model with low temperature melt InGaSn, a 20” crucible, and process parameters corresponding to industrial Czochralski silicon systems is considered. Flow regimes with two crystal and crucible rotation rates and with different strengths of the traveling magnetic field “down” are analyzed. The calcula…
Piemaisījumu difūzijas caur šķidra silīcija dinamisku brīvu virsmu pētīšana
2018
Pēdējos gados arvien pieaug pieprasījums pēc augstas (99.9999%) tīrības jeb solāras kvalitātes silīcija, kuru var iegūt, īpaši attīrot šķidru silīciju no tajā esošajiem piemaisījumiem. Šajā nozarē notiek aktīva pētniecība, meklējot veidus, kā attīrīšanas procesu būtu iespējams optimizēt. Šajā darbā tiek pētīta potenciāla iespēja celt piemaisījumu aizvades efektivitāti, uz šķidrā silīcija radot virsmas viļņus. Tādēļ darbā veikti skaitliski aprēķini, kas ļauj konstatēt, kā attīrīšanas gaitā piemaisījumi pamet šķidro silīciju, kā arī ļauj saprast, kāda ietekme uz to ir dažādiem virsmas viļņu parametriem – amplitūdai, frekvencei, viļņa garumam. Izdarot aprēķinus, tiek noskaidrots, ka piemaisīju…
State Estimation of a Nonlinear Unmanned Aerial Vehicle Model using an Extended Kalman Filter
2008
An Extended Kalman Filter is designed in order to estimate both state variables and wind velocity vector at the same time for a non conventional unmanned aircraft. The proposed observer uses few measurements, obtained by means of either conventional simple air data sensors or a low cost GPS. To cope with the low rate of the GPS with respect to the other sensors, the EKF algorithm has been modified to allow for a dual rate measurement model. State propagation is obtained by means of an accurate six degrees of freedom nonlinear model of the aircraft dynamics. To obtain joint estimation of state and disturbance, wind velocity components are included in the set of the state variables. Both stoc…
Statistical mechanics and thermodynamics of turbulent quantum vortex tangles
2010
In this paper we present some phenomenological ideas about the thermodynamics of quantized vortex loops arising in superfluid turbulence. The system of vortex loops may be seen as a dissipative structure, not existing on its own but only under the influence of an external heat flux. Starting from a simple definition of the temperature of the vortex tangle and from the relation between energy and vortex length, we obtain the entropy of the system, as well as the caloric and thermal equations of state, relating internal energy and pressure to temperature and volume. We discuss the connection between our macroscopic results and microscopic results on vortex length distribution function having …