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