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Wind tunnel experiments were conducted, in particular focusing on slow unsteady variations of aerodynamic forces as a potential
cause of the knuckle effect of a new soccer ball (Teamgeist) under non-spinning condition. The experiments included simultaneous
measurements of the drag, the side force and the surface pressure on a ball surface, and the tuft visualisation to investigate
the flow field behind a ball. Of particular interest was the erratic nature of the knuckle effect resulting from the unsteady
movement of vortical wake structure in the supercritical Reynolds number regime. A simple 2-D numerical simulation of the
ball flight trajectory was performed by taking into account the unsteady side force data measured in the present experiments. 相似文献
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Masahide Murakami Masato Iwase Kazuya Seo Yuji Ohgi Reno Koyanagi 《Sports Engineering》2014,17(4):217-225
Ski jumping flight posture was analyzed for achieving large flight distance on the basis of high-speed video images of the initial 40 m part of 120-m ski jumping flight. The time variations of the forward leaning angle and the ski angle of attack were measured from the video images, and the aerodynamic forces were calculated from the kinematic data derived from the images. Some correlations were investigated between the initial-speed corrected flight distance and such parameters as the angles of jumper, the initial transition time and the aerodynamic force coefficients. The result indicated that small body angle of attack was a key for large flight distance in the initial phase of flight because of small drag force, and that the most distinctive fault of beginners was too large body angle of attack and ski angle of attack leading to aerodynamic stall. Too small drag force does not give an optimal condition for large flight distance because the lift force is also too small. The ratio of the lift to the drag was larger than 0.95 for advanced jumpers. 相似文献
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Masahide Inuzuka 《文物保护研究》2016,61(1):23-30
From rainy season to summer in Japan, the climate is humid. Especially in these seasons, it is difficult to maintain suitable conditions of temperature and relative humidity in exhibition and storage rooms in museums. Such climate conditions and problems are common to many countries in East Asia. Analysis using computer simulation can be a powerful tool because it is cheap and allows the simulation of a range of conditions without having to make changes to buildings and environments surrounding cultural objects. In this study, a storage building in which there is no air-conditioning unit was chosen as a target. The modelling of temperature and relative humidity in storage spaces was conducted using the Thermal and Airflow Network Model Simulation Program for buildings (NETS). The effect of seismic retro-fitting on the variation of temperature was predicted using NETS and the results were evaluated by comparing with the measured values. As a result, the heat transfer was successfully calculated and the modelled temperature represents the measured values reasonably well. Computing relative humidity by taking into account the effect of porous hygroscopic materials is challenging. In order to overcome this problem, the κ-ν model was adopted. We have some improvements but the study is still ongoing. 相似文献
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ABSTRACTAmong more than 600 decorated tumuli in Japan, we focused on Hinooka tumulus in Fukuoka prefecture. In order to preserve the stone chamber and paintings, a reinforced concrete shelter was built in 1964 on the stone chamber. From the preservation point of view, one of the main problems in the shelter is condensation on the ceiling especially in winter. In order to understand the mechanism of the formation of condensation in the shelter for Hinooka tumulus and to consider countermeasures to prevent it, the thermal environment inside the shelter was investigated by in situ measurements and computer simulations. Since the relative humidity inside the shelter is almost 100% throughout the year, it turned out that dew condensation tends to occur especially in winter when the temperature on the surface of the ceiling becomes low. The results obtained by computer simulation suggests that the amounts of condensation on the surface of the ceiling can be reduced if the thermal insulation of the roof is increased by adding materials which do not attract pests. Synthetic heat insulation material is one of the candidate materials for reducing condensate on the ceiling of the shelter for the Hinooka tumulus. 相似文献
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A badminton shuttlecock flies in a high-drag, and thus, the sport has been a subject of research from the point of view of aerodynamics. A badminton shuttlecock generates significant aerodynamic drag and has a complex flight trajectory. It also has the smallest ballistic coefficient and exhibits the largest in-flight deceleration of any airborne sporting projectile. The ballistic coefficient of a projectile is a measure of its ability to overcome air resistance in flight and is inversely proportional to deceleration. The primary objectives of this study were to measure the aerodynamic properties of feather shuttlecocks under a range of the wind speed (10–60 m/s) and pitch angle (0°–25°). In particular, measurements of aerodynamic forces were performed at high Reynolds numbers (more than Re = 210,000), and the effect of shuttlecock deformation on aerodynamic properties was also investigated, because it is presumed that the flight dynamics is affected by the deformation of the shuttlecock skirt. A shuttlecock skirt is composed of an array of diverging stems, the ends of which are at the convergent end of the skirt, joined together in an end ring. The shuttlecock rotates about its major axis in actual flight, and thus, the experiments were performed on shuttlecocks with and without rotation (spin). Furthermore, the effect of the flow passing through the gaps between the slots (stiffeners) located at the leg portion of the shuttlecock skirt on aerodynamic characteristics is demonstrated by means of a shuttlecock model without gaps, which was completely covered with cellophane tape. The free rotation rate of a shuttlecock increased with an increase in the Reynolds number, and the drag coefficient gradually decreased above Re = 86,000 for a non-rotating shuttlecock. The reduction of drag can be explained by the deformation of the skirt observed in wind tunnel experiments at high speed. In this study, for a rotating shuttlecock, a reduction of drag was not observed over a whole range of Reynolds numbers, because deformation of the skirt for a rotating shuttlecock becomes smaller than that for a non-rotating shuttlecock. However, there was no significant difference in drag coefficient between rotating and non-rotating shuttlecocks, in contrast to the difference in drag coefficient between shuttlecocks with and without gaps. The drag coefficient for a shuttlecock without gaps was significantly smaller than that for a standard shuttlecock (with gaps). For a standard shuttlecock, the air flowed through the gaps into the shuttlecock skirt, and this flow was related to high aerodynamic drag. 相似文献
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