Morphological changes during giant ripples formation by long-period oscillatory flow in a circular flume

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  • 円筒水槽内の長周期振動流によるジャイアントリップルの形成過程における形態変化
  • エントウ スイソウナイ ノ チョウシュウキ シンドウリュウ ニヨル ジャイアント リップル ノ ケイセイ カテイ ニオケル ケイタイ ヘンカ

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Abstract

Wave ripples observed in nature commonly have wavelengths between a few and a few dozen centimeters, while those that have wavelengths over a meter are rarely found. These large wave ripples are called “giant ripples”, and are assumed to form under extreme wave conditions. Many studies have focused on the formation of ripples in the predominant size range, but there has been little research on giant ripples. This study examined the formation of giant ripples in a circular flume. The morphological changes related to giant ripple formation from a flatbed were observed during a long-period oscillatory flow, a 50-s period, and a 25-s period. The results revealed regular patterns in morphological changes. During giant ripple formation, increased ripple size is due to slightly changing crest positions. When a small ripple disappears, the larger ripples on both sides approach each other to form equal intervals among all ripples. The changes of ripple sizes and positions during giant ripple formation may be controlled by the vortex shape of the oscillatory flow near the bed. This phenomenon was also observed in the formation of average-sized ripples.

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