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A new method for measuring the speed distribution of blown sand grains using He-Ne laser beam has been developed. This method enables us to measure the rate of sand movement as well as the number of b...lown sand at the some region in the wind tunnel and field. The apparatus is composed of a He-Ne laser (l mW)., a photodetection system with a slit (width: 0.3-3.0 mm), a five channel pulse width analyzer and a multi-purpose counter. When a sand grain passes across the laser beam, a shadow is thrown upon the light sensitive area of photodetector. The change in photocurrent after amplification and pulse shaping, is fed to the pulse width analyzer. The pulse width has information on both the speed and size of blown sand. Using nearly uniform size of sand grains, the speed distribution of blown sand can be measured. This method has many merits for studying the physical phenomena of blown sand in the field. First, the laser beam does not disturb the stream line of wind, but this condition is not satisfied in the case of using the sand trap. Second, in case of use of sand trap, the base of this must be buried in the sand surface and this handling affect the physical properties of sand surface. Third, this method is strong differential method in time and space, whereas the sand trap is .strong in integral method and easy handling.show more
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| Table of Contents |
§１ 緒言 §２ 装置の構成とその原理 §３ パルス巾分布分析器 §４ 装置の検定に関する考察 §５ 装置の検定結果 §６ 風洞実験とその結果 §７ 結論
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