Directional pedestrian counting with a hybrid map-based model

Detection-based pedestrian counting methods produce results of considerable accuracy in non-crowded scenes. However, the detection-based approach is dependent on the camera viewpoint. On the other hand, map-based pedestrian counting methods are performed by measuring features that do not require separate detection of each pedestrian in the scene. Thus, these methods are more effective especially in high crowd density. In this paper, we propose a hybrid map-based model that is a new directional pedestrian counting model. Our proposed model is composed of direction estimation module with classified foreground motion vectors, and pedestrian counting module with principal component analysis. Our contributions in this paper have two aspects. First, we present a directional moving pedestrian counting system that does not depend on object detection or tracking. Second, the number and major directions of pedestrian movements can be detected, by classifying foreground motion vectors. This representation is more powerful than simple features in terms of handling noise, and can count the moving pedestrians in images more accurately.

     

Shelter effect of a fir tree with different porosities

Windbreak has been used for centuries as a natural wind-fence. The functional effects of windbreaks are directly related to the flow structure. In the present study, the flow around a real fir tree placed in a wind tunnel was quantitatively visualized using PIV (particle image velocimetry) technique. The effects of tree porosity and leaves on the shelter effect were investigated as well. Tree leaves not only reduce the porosity, but also increase the wind-speed reduction and turbulence kinetic energy in the leeward region behind the tree canopy. The leaves of tree canopy induce updraft toward the top region and downdraft toward the ground in the upstream region of the tree. The momentum difference of these two flows generates peculiar upwelling flow characteristics. The large reduction in mean velocities and turbulence intensities of flow around a tree is attributed to tree leaves providing a good shelter zone in the leeward region.     

Jet flow characteristics of sinusoidal wavy nozzles

The flow characteristics of jets issued from a sinusoidal nozzle with in-phase and 180° out-of-phase exit configurations were investigated using PIV (particle image velocimetry) and flow visualization techniques. The experiments were carried out at a Reynolds number of about 6300 based on the mean width of the jet nozzle. Compared to a normal rectangular jet, the sinusoidal nozzle jets have smaller velocity deficits as the flow goes downstream. In addition, the turbulence intensity is suppressed in the horizontal center plane. For the case of in-phase wavy nozzle jet, the length of the potential core exhibits small variations along the lateral direction, while the 180° out-of-phase wavy nozzle jet shows large lateral variation in the length of potential core. The turbulent kinetic energy of the 180° out-ofphase nozzle jet also shows sinusoidal variation in the horizontal planes. Large-scale vortices shed from the sinusoidal edge of the nozzle interact strongly and migrate toward the center plane as the flow develops downstream.