Cooperative dynamics in the penetration of a group of intruders in a granular medium

An object moving in a fluid experiences a drag force that depends on its velocity, shape and the properties of the medium. From this simplest case to the motion of a flock of birds or a school of fish, the drag forces and the hydrodynamic interactions determine the full dynamics of the system. Similar drag forces appear when a single projectile impacts and moves through a granular medium, and this case is well studied in the literature. On the other hand, the case in which a group of intruders impact a granular material has never been considered. Here, we study the simultaneous penetration of several intruders in a very low-density granular medium. We find that the intruders move through it in a collective way, following a cooperative dynamics, whose complexity resembles flocking phenomena in living systems or the movement of reptiles in sand, wherein changes in drag are exploited to efficiently move or propel

A survey of free software for the design, analysis, modelling, and simulation of an unmanned aerial vehicle

The objective of this paper is to analyze free software for the design, analysis, modelling, and simulation of an unmanned aerial vehicle (UAV). Free software is the best choice when the reduction of production costs is necessary; nevertheless, the quality of free software may vary. This paper probably does not include all of the free software, but tries to describe or mention at least the most interesting programs. The first part of this paper summarizes the essential knowledge about UAVs, including the fundamentals of flight mechanics and aerodynamics, and the structure of a UAV system. The second section generally explains the modelling and simulation of a UAV. In the main section, more than 50 free programs for the design, analysis, modelling, and simulation of a UAV are described. Although the selection of the free software has been focused on small subsonic UAVs, the software can also be used for other categories of aircraft in some cases; e.g. for MAVs and large gliders. The applications with an historical importance are also included. Finally, the results of the analysis are evaluated and discussed—a block diagram of the free software is presented, possible connections between the programs are outlined, and future improvements of the free software are suggested. © 2015, CIMNE, Barcelona, Spain.Internal Grant Agency of Tomas Bata University in Zlin [IGA/FAI/2015/001, IGA/FAI/2014/006

The walking behaviour of pedestrian social groups and its impact on crowd dynamics

Human crowd motion is mainly driven by self-organized processes based on local interactions among pedestrians. While most studies of crowd behavior consider only interactions among isolated individuals, it turns out that up to 70% of people in a crowd are actually moving in groups, such as friends, couples, or families walking together. These groups constitute medium-scale aggregated structures and their impact on crowd dynamics is still largely unknown. In this work, we analyze the motion of approximately 1500 pedestrian groups under natural condition, and show that social interactions among group members generate typical group walking patterns that influence crowd dynamics. At low density, group members tend to walk side by side, forming a line perpendicular to the walking direction. As the density increases, however, the linear walking formation is bent forward, turning it into a V-like pattern. These spatial patterns can be well described by a model based on social communication between group members. We show that the V-like walking pattern facilitates social interactions within the group, but reduces the flow because of its "non-aerodynamic" shape. Therefore, when crowd density increases, the group organization results from a trade-off between walking faster and facilitating social exchange. These insights demonstrate that crowd dynamics is not only determined by physical constraints induced by other pedestrians and the environment, but also significantly by communicative, social interactions among individuals.Comment: 18 pages; 6 figures; Accepted for publication in PLoS ON

Fly with a little flap from your friends

In-air measurements of northern bald ibises flying in a V formation show that the birds conform to predictions for saving energy by regulating their relative body position and synchronizing their flapping motion