38 research outputs found
Persistence analysis of velocity and temperature fluctuations in convective surface layer turbulence
Persistence is defined as the probability that the local value of a
fluctuating field remains at a particular state for a certain amount of time,
before being switched to another state. The concept of persistence has been
found to have many diverse practical applications, ranging from non-equilibrium
statistical mechanics to financial dynamics to distribution of time scales in
turbulent flows and many more. In this study, we carry out a detailed analysis
of the statistical characteristics of the persistence probability density
functions (PDFs) of velocity and temperature fluctuations in the surface layer
of a convective boundary layer, using a field-experimental dataset. Our results
demonstrate that for the time scales smaller than the integral scales, the
persistence PDFs of turbulent velocity and temperature fluctuations display a
clear power-law behaviour, associated with self-similar eddy cascading
mechanism. Moreover, we also show that the effects of non-Gaussian temperature
fluctuations act only at those scales which are larger than the integral
scales, where the persistence PDFs deviate from the power-law and drop
exponentially. Furthermore, the mean time scales of the negative temperature
fluctuation events persisting longer than the integral scales are found to be
approximately equal to twice the integral scale in highly convective
conditions. However, with stability this mean time scale gradually decreases to
almost being equal to the integral scale in the near neutral conditions.
Contrarily, for the long positive temperature fluctuation events, the mean time
scales remain roughly equal to the integral scales, irrespective of stability
Hysteretic behavior of spatially coupled phase-oscillators
Motivated by phenomena related to biological systems such as the
synchronously flashing swarms of fireflies, we investigate a network of phase
oscillators evolving under the generalized Kuramoto model with inertia. A
distance-dependent, spatial coupling between the oscillators is considered.
Zeroth and first order kernel functions with finite kernel radii were chosen to
investigate the effect of local interactions. The hysteretic dynamics of the
synchronization depending on the coupling parameter was analyzed for different
kernel radii. Numerical investigations demonstrate that (1) locally locked
clusters develop for small coupling strength values, (2) the hysteretic
behavior vanishes for small kernel radii, (3) the ratio of the kernel radius
and the maximal distance between the oscillators characterizes the behavior of
the network
RANDOM WALK APPROACH FOR SIMULATION OF PARTICLE DEPOSITION FROM TURBULENT FLOWS
This study deals with a random walk simulation of particle transport and deposition
from a stationary, isotropic turbulent flow: This is an inplernentation of the well-known Lagrangian approach. which treats the disperse phase as many particles. The trajectory
of each particle is calculated according to the equations of the mottion assuming a discrete
eddy-field.
The ensemble-ayeraged quantities describe the behavior of the particle-fluid system,
and these have been used to validate numerical solutions of a kinetic (probability density
function transport) equation which models the same system. In this work we have only
considered relatively large particles: particle-particle interactions and the influence of the
particle phase on fluid phase have been neglected
LARGE-EDDY SIMULATION OF TURBULENT PLANE COUETTE FLOW
The purpose of this study was to explore the central core region of a plane turbulent Cou-
ette flow by means of large-eddy simulations. First it was demonstrated how accurately a
low Reynolds number flow could be simulated. After having verified the reliability of the
LES approach. simulations were performed at a substantially higher Re. It was observed
that the mean velocity exhibited a practically linear variation in the core region. The
extent of the core increased with Re, whereas the slope of the mean velocity profile was
significantly reduced
Genetic Algorithm for Combinatorial Path Planning: The Subtour Problem
The purpose of this paper is to present a combinatorial planner for autonomous systems. The approach is demonstrated
on the so-called subtour problem, a variant of the classical traveling salesman problem (TSP): given a set of possible goals/targets, the optimal strategy is sought that connects ≤ goals. The proposed solution method is a Genetic Algorithm coupled with a heuristic local search. To validate the approach, the method has been benchmarked against TSPs and subtour problems with known optimal solutions. Numerical experiments demonstrate the success
of the approach