82 research outputs found
Perturbation theory for large Stokes number particles in random velocity fields
We derive a perturbative approach to study, in the large inertia limit, the
dynamics of solid particles in a smooth, incompressible and finite-time
correlated random velocity field. We carry on an expansion in powers of the
inverse square root of the Stokes number, defined as the ratio of the
relaxation time for the particle velocities and the correlation time of the
velocity field. We describe in this limit the residual concentration
fluctuations of the particle suspension, and determine the contribution to the
collision statistics produced by clustering. For both concentration
fluctuations and collision velocities, we analyze the differences with the
compressible one-dimensional case.Comment: Latex, 12 pages, 2 eps figures include
Relating the microscopic rules in coalescence-fragmentation models to the macroscopic cluster size distributions which emerge
Coalescence-fragmentation problems are of great interest across the physical,
biological, and recently social sciences. They are typically studied from the
perspective of the rate equations, at the heart of such models are the rules
used for coalescence and fragmentation. Here we discuss how changes in these
microscopic rules affect the macroscopic cluster-size distribution which
emerges from the solution to the rate equation. More generally, our work
elucidates the crucial role that the fragmentation rule can play in such
dynamical grouping models. We focus on two well-known models whose
fragmentation rules lie at opposite extremes setting the models within the
broader context of binary coalescence-fragmentation models. Further, we provide
a range of generalizations and new analytic results for a well-known model of
social group formation [V. M. Eguiluz and M. G. Zimmermann, Phys. Rev. Lett.
85, 5659 (2000)]. We develop analytic perturbation treatment of the original
model, and extend the mathematical to the treatment of growing and declining
populations
Motion Simulation of Transport Aircraft in Extended Envelopes: Test Pilot Assessment
The European research project SUPRA (“Simulation of Upset Recovery in Aviation”) produced an extended aerodynamic model for simulation of a generic transport aircraft, capturing the key aircraft behavior beyond aerodynamic stall. As described in the current paper, a group of 11 test pilots with in-flight experience in stall conditions assessed the validity of this aerodynamic model, in combination with new motion cueing solutions in a conventional hexapod platform as well as a centrifuge-based device. Results showed that the SUPRA model was considered representative outside the normal flight envelope, and on both simulators the enhanced cueing solutions received higher subjective ratings than the comparison condition. The pilots unanimously rejected exercising these conditions without motion. It is concluded that the SUPRA model successfully demonstrates upset conditions, including stall, and that conventional hexapod motion cueing can be improved for the purpose of upset simulation. If available, a ground-based g-device is recommended to provide g-awareness training
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