The Lagrangian picture of heat transfer in convective turbulence

We present a fluid dynamics video which illustrates the Lagrangian aspects of local heat transfer in turbulent Rayleigh-Benard convection. The data are obtained from a direct numerical simulation.Comment: Abstract of video submission to the Gallery of Fluid Motion (APS-DFD Meeting in Minneapolis

Automatische Erfassung präziser Trajektorien in Personenströmen hoher Dichte

Simulations can help make facilities for pedestrians safer and more comfortable. A proper understanding of crowd dynamics is essential to developing reliable models for such simulations. Detailed and reproducible datasets of real crowd movements are needed for analysis and modelling. Such datasets are also required for later calibration and validation of said models. This thesis describes the collection of such data from overhead video recordings. Individual trajectories are extracted and make it possible to obtain the most relevant quantities of the dynamic e.g. pedestrian density, velocity and flow. Traffic jams and other high density situations are of special interest since this is where critical situations are to be expected. Therefor the developed methods have to also reliable extract an individual’s movement in such situations. The movement of pedestrians is affected by many factors such as geometry, crowd density, motivation and culture. To investigate these numerous influences a large number of experiments with a huge number of participants have been carried out. The automatic extraction of the trajectories provides a significant advantage compared to manual methods in terms of the time required, accuracy and reproducibility. The extraction process consists of the image calibration followed by the detection, tracking and determination of the real world position of all individuals. For the detection of a person various markers and corresponding extraction techniques have been developed for the different applications and local conditions. A markerless method was also developed, which is especially useful for field studies. Through the use of stereo cameras high detection rates were achieved without markers, even in high density situations. All developments regarding the extraction process have been integrated into the software PeTrack. To enable a deeper understanding of the results the technical aspects of the trajectory collection are described in addition to the recognition techniques

New insights into pedestrian flow through bottlenecks

Capacity estimation is an important tool for the design and dimensioning of pedestrian facilities. The literature contains different procedures and specifications which show considerable differences with respect to the estimated flow values. Moreover do new experimental data indicate a stepwise growing of the capacity with the width and thus challenge the validity of the specific flow concept. To resolve these differences we have studied experimentally the unidirectional pedestrian flow through bottlenecks under laboratory conditions. The time development of quantities like individual velocities, density and individual time gaps in bottlenecks of different width is presented. The data show a linear growth of the flow with the width. The comparison of the results with experimental data of other authors indicates that the basic assumption of the capacity estimation for bottlenecks has to be revised. In contradiction with most planning guidelines our main result is, that a jam occurs even if the incoming flow does not overstep the capacity defined by the maximum of the flow according to the fundamental diagram.Comment: Traffic flow, pedestrian traffic, crowd dynamics, capacity of bottlenecks (16 pages, 8 figures); (+ 3 new figures and minor revisions

Microscopic insights into pedestrian motion through a bottleneck, resolving spatial and temporal variations

The motion of pedestrians is subject to a wide range of influences and exhibits a rich phenomenology. To enable precise measurement of the density and velocity we use an alternative definition using Voronoi diagrams which exhibits smaller fluctuations than the standard definitions. This method permits examination on scales smaller than the pedestrians. We use this method to investigate the spatial and temporal variation of the observables at bottlenecks. Experiments were performed with 180 test subjects and a wide range of bottleneck parameters. The anomalous flow through short bottlenecks and non-stationary states present with narrow bottlenecks are analysed

Universal flow-density relation of single-file bicycle, pedestrian and car motion

The relation between flow and density is an essential quantitative characteristic to describe the efficiency of traffic systems. We have performed experiments with single-file motion of bicycles and compare the results with previous studies for car and pedestrian motion in similar setups. In the space-time diagrams we observe three different states of motion (free flow state, jammed state and stop-and-go waves) in all these systems. Despite of their obvious differences they are described by a universal fundamental diagram after proper rescaling of space and time which takes into account the size and free velocity of the three kinds of agents. This indicates that the similarities between the systems go deeper than expected.Comment: 5 pages, 5 figure

Data archive for exploring pedestrian dynamics and its application in dimensioning of facilities for multidirectional streams

In this paper an overview of an open data archive with data from experiments investigating pedestrian dynamics is presented. As an example of the use of this data the analysis of recently published data about the capacity of crossings is shown

Inflow process of pedestrians to a confined space

To better design safe and comfortable urban spaces, understanding the nature of human crowd movement is important. However, precise interactions among pedestrians are difficult to measure in the presence of their complex decision-making processes and many related factors. While extensive studies on pedestrian flow through bottlenecks and corridors have been conducted, the dominant mode of interaction in these scenarios may not be relevant in different scenarios. Here, we attempt to decipher the factors that affect human reactions to other individuals from a different perspective. We conducted experiments employing the inflow process in which pedestrians successively enter a confined area (like an elevator) and look for a temporary position. In this process, pedestrians have a wider range of options regarding their motion than in the classical scenarios; therefore, other factors might become relevant. The preference of location is visualized by pedestrian density profiles obtained from recorded pedestrian trajectories. Non-trivial patterns of space acquisition, e.g., an apparent preference for positions near corners, were observed. This indicates the relevance of psychological and anticipative factors beyond the private sphere, which have not been deeply discussed so far in the literature on pedestrian dynamics. From the results, four major factors, which we call flow avoidance, distance cost, angle cost, and boundary preference, were suggested. We confirmed that a description of decision-making based on these factors can give a rise to realistic preference patterns, using a simple mathematical model. Our findings provide new perspectives and a baseline for considering the optimization of design and safety in crowded public areas and public transport carriers.Comment: 23 pages, 6 figure