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Osawa, Kazuhito*; Goto, Junya*; Yamakami, Masahiro*; Yamaguchi, Masatake; Yagi, Masatoshi*
Physical Review B, 82(18), p.184117_1 - 184117_6, 2010/11
Times Cited Count:118 Percentile:95.22(Materials Science, Multidisciplinary)The configuration of multiple hydrogen atoms trapped in a tungsten monovacancy is investigated using first-principles calculations. Unlike previous computational studies, which have reported that hydrogen in BCC metal monovacancies occupies octahedral interstitial sites, it is found that the stable sites shift towards tetrahedral interstitial sites as the number of hydrogen atoms increases. As a result, a maximum of twelve hydrogen atoms can become trapped in a tungsten monovacancy.
Inoue, Masahiro*; Hidaka, Yuki*; Yamakami, Mitsunori; Hatakeyama, Nobuya; Okuzono, Akihiko*; Sakai, Tetsuo*
no journal, ,
A series of experimental study using a scaled model concerning the behavior of ventilation air during a mine fire was carried out. The model consists of two vertical shafts, three horizontal ducts and a exhaust fan. The cross section of the shaft and duct is 0.2m square. The height of the shafts is 3.4m. The length of the ducts is 1.5m. The airflow rate can be adjusted by regulators installed in each duct. The behavior of the fire gas was measured by anemometer, thermometer, and visualized image using laser light. Some amount of fire gas of high temperature rose upward gradually along the shaft wall regardless of the downward ventilation. Then the direction of main ventilation air suddenly reversed upward in the shaft. The direction of ventilation reversed in many places in the model and the fire gas reached even the part not anticipated. It was also found that the direction of ventilation in the shaft reversed upward entirely when the initial velocity of the airflow was small.
Inoue, Masahiro*; Hidaka, Yuki*; Nakaba, Nozomi*; Yamakami, Mitsunori; Hatakeyama, Nobuya; Okuzono, Akihiko*; Sakai, Tetsuo*
no journal, ,
A fire in a deep underground structure has a potential threat that it may result in a big disaster because the ventilation system is fully disturbed and the fire gas spread to unanticipated places by the effect of buoyancy of the fire gas. The result of the study using scaled model experiment and computer simulation on the fire gas movement is described in the report.
Inoue, Masahiro*; Nakaba, Nozomi*; Yamanishi, Takeshi; Yamakami, Masanori*; Hatakeyama, Nobuya; Yamazaki, Masanao; Sakai, Tetsuo*; Okuzono, Akihiko*
no journal, ,
The fire gas generated by a mine fire changes ventilation system by the buoyancy and the throttling effect, the adverse airflow along the roadway ceiling. As the result, the fire gas can reach upwind areas where was thought that the fire gas will never reach. These phenomena are remarkable around shafts which have large altitude differences. In order to prevent the accidents, it is important to make an accurate prediction of the behavior of ventilation air during a mine fire and the effective control of the ventilation air. However, this behavior has not been studied well so far. For this reason, the authors studied this behavior using a scaled model experiments and ascertained the major change of ventilation air. Then the effect of ventilation air control was studied. Following the results, a computer program to simulate the behavior of the fire gas by CFD method. It was confirmed that the program shows sufficient accuracy within the practical calculation time.