Ripple Formation and Grain Sorting with Multiple-sized Sand: a Report of the Preliminary Wave-flume Experimentation

Abstract

造波水槽の性能と，混合粒径砂がリップル形成に与える影響を調べるために，3組の実験を行った。最初の一連の実験では，固定床を用いて造波水槽の性能評価を行った。その結果，波高/造波板ストロークの比が予想値よりやや小さいことがわかった。その他の2組の実験では，混合粒径砂の砂床を設置して実験を行い，次の二つのことが明らかになった。(1)混合粒径砂では，均一粒径砂の時よりもリップルが形成するmobility numberが大きい。(2)流速の岸沖方向での非対称性に応じて，リップルの岸側斜面と沖側斜面の粒径が異なる。

Three series of wave-flume experiments were performed for the purposes of assessing capability of a wave-flume and investigating an effect of multiple-sized sand on ripple formation. The first series of experiments were performed under fixed-bed condition, indicating that the measured performance of wave height-to-stroke ratio was only slightly smaller than theoretically expected. The other two series with multiple-sized sand beds facilitated the following: (1) the critical value of the mobility number for ripple formation with multi-sized sands may be larger than the critical value with uniform sands; and (2) as more asymmetrical oscillatory flow, the difference of grain size between onshore-slope and offshore-slope appeared more prominently.