Experiments and numerical simulations on lasing in random media

2004 ◽  
Author(s):  
Sushil Mujumdar ◽  
Renato Torre ◽  
Stefano Cavalieri ◽  
Diederik S. Wiersma
Keyword(s):  
Numerical Simulations ◽  
Random Media

Long distance time reversal and imaging in random media: Numerical simulations

2001 ◽  
Vol 110 (5) ◽  
pp. 2633-2633 ◽  
Author(s):  
Peter Blomgren ◽  
George Papanicolaou ◽  
Hongkai Zhao
Keyword(s):  
Numerical Simulations ◽  
Time Reversal ◽  
Random Media ◽  
Long Distance

The effective diffusivity of ordered and freely evolving bubbly suspensions

2018 ◽  
Vol 840 ◽  
pp. 215-237 ◽  
Author(s):  
Aurore Loisy ◽  
Aurore Naso ◽  
Peter D. M. Spelt
Keyword(s):  
Numerical Simulations ◽  
Peclet Number ◽  
Random Media ◽  
Chemical Species ◽  
Effective Diffusivity ◽  
Passive Scalar ◽  
Solid Particles ◽  
Péclet Number ◽  
Mechanical Dispersion ◽  
Fixed Beds

We investigate the dispersion of a passive scalar such as the concentration of a chemical species, or temperature, in homogeneous bubbly suspensions, by determining an effective diffusivity tensor. Defining the longitudinal and transverse components of this tensor with respect to the direction of averaged bubble rise velocity in a zero mixture velocity frame of reference, we focus on the convective contribution thereof, this being expected to be dominant in commonly encountered bubbly flows. We first extend the theory of Kochet al.(J. Fluid Mech., vol. 200, 1989, pp. 173–188) (which is for dispersion in fixed beds of solid particles under Stokes flow) to account for weak inertial effects in the case of ordered suspensions. In the limits of low and of high Péclet number, including the inertial effect of the flow does not affect the scaling of the effective diffusivity with respect to the Péclet number. These results are confirmed by direct numerical simulations performed in different flow regimes, for spherical or very deformed bubbles and from vanishingly small to moderate values of the Reynolds number. Scalar transport in arrays of freely rising bubbles is considered by us subsequently, using numerical simulations. In this case, the dispersion is found to be convectively enhanced at low Péclet number, like in ordered arrays. At high Péclet number, the Taylor dispersion scaling obtained for ordered configurations is replaced by one characterizing a purely mechanical dispersion, as in random media, even if the level of disorder is very low.

Analysis of conductivity of random media using dc, MT, and TEM

Geophysics ◽  
2003 ◽  
Vol 68 (2) ◽  
pp. 506-515 ◽  
Author(s):  
Jürgen Bigalke
Keyword(s):  
Electrical Properties ◽  
Finite Difference ◽  
Numerical Simulations ◽  
Random Media ◽  
Normalization Procedure ◽  
Transient Electromagnetic ◽  
Random Lattices ◽  
Two Component ◽  
Isotropic Random

In geophysics, the geoelectric (dc), magnetotelluric (MT), and transient electromagnetic (TEM) measuring procedures are commonly used to investigate electrical properties of the ground. Finite difference codes are available for all these methods and, in this paper, the data obtained from numerical simulations are compared with regard to two‐component cubic random lattices. Provided the usage of a convenient normalization procedure, it was expected that in case of statistically homogeneous and isotropic random lattices dc, MT, and TEM would yield the same results. Surprisingly, this is not true for the MT data; the lowest MT conductivities are only one‐fifth of the corresponding TEM values.

scholarly journals FRONT PROPAGATION IN RANDOM MEDIA: FROM EXTREMAL TO ACTIVATED DYNAMICS

2002 ◽  
Vol 13 (06) ◽  
pp. 751-757 ◽  
Author(s):  
RUNE SKOE ◽  
DAMIEN VANDEMBROUCQ ◽  
STÉPHANE ROUX
Keyword(s):  
Low Temperature ◽  
Numerical Simulations ◽  
Power Law ◽  
Random Environment ◽  
Random Media ◽  
Front Propagation ◽  
Force Distribution ◽  
Zero Temperature ◽  
Arrhenius Behavior ◽  
Very Low Temperature

Front propagation in a random environment is studied close to the depinning threshold. At zero temperature we show that the depinning force distribution exhibits a universal behavior. This property is used to estimate the velocity of the front at very low temperature. We obtain a Arrhenius behavior with a prefactor depending on the temperature as a power law. These results are supported by numerical simulations.

Saturation mechanism and generated viscosity in gravito-turbulent accretion disks

2020 ◽  
Vol 640 ◽  
pp. A53
Author(s):  
L. Löhnert ◽  
S. Krätschmer ◽  
A. G. Peeters
Keyword(s):  
Growth Rate ◽  
Numerical Simulations ◽  
Accretion Disks ◽  
Gravitational Instability ◽  
Turbulent Viscosity ◽  
Radial Distance ◽  
Maximum Growth ◽  
Wave Number ◽  
Radiative Cooling ◽  
Mixing Length

Here, we address the turbulent dynamics of the gravitational instability in accretion disks, retaining both radiative cooling and irradiation. Due to radiative cooling, the disk is unstable for all values of the Toomre parameter, and an accurate estimate of the maximum growth rate is derived analytically. A detailed study of the turbulent spectra shows a rapid decay with an azimuthal wave number stronger than ky−3, whereas the spectrum is more broad in the radial direction and shows a scaling in the range kx−3 to kx−2. The radial component of the radial velocity profile consists of a superposition of shocks of different heights, and is similar to that found in Burgers’ turbulence. Assuming saturation occurs through nonlinear wave steepening leading to shock formation, we developed a mixing-length model in which the typical length scale is related to the average radial distance between shocks. Furthermore, since the numerical simulations show that linear drive is necessary in order to sustain turbulence, we used the growth rate of the most unstable mode to estimate the typical timescale. The mixing-length model that was obtained agrees well with numerical simulations. The model gives an analytic expression for the turbulent viscosity as a function of the Toomre parameter and cooling time. It predicts that relevant values of α = 10−3 can be obtained in disks that have a Toomre parameter as high as Q ≈ 10.

Random media with temperature controlled connectivity

1992 ◽  
Vol 2 (5) ◽  
pp. 503-510 ◽  
Author(s):  
F. Carmona ◽  
E. Valot ◽  
L. Servant ◽  
M. Ricci
Keyword(s):  
Random Media ◽  
Temperature Controlled
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