EFFECT OF SPECIFIC GRAVITY OF SEDIMENT ON RIPPLE FORMATION

Abstract

The plane granular bed when subjected to shear under fluid flow, usually starts deforming in statistically regular bed for-mations called 'ripples'. However, there are certain flow condition, under which the plane bed remains stable. The mechanism of such ripple formation has been studied by a number of investogators usually varying grain properties and flow conditions. But the effect of variation of fluid properties has been only studied by Sahgal. He observed during the course of experimentation that visco-sity inhibits rippling for smaller grain size material where/s it promotes rippling for bigger grains. Rippling was found to depend upon the properties of bed material and liquid besides flow conditions, hence on a dimensionless aramter g1/2 d3/'2/, He fu rthe r (AY Y,&dh t suggested the use of y parameter in his plot instead of Y~7 i/2 3/2 1 t4.;. g d /y so as to take into account the density of fluid and bed AJLJ*t material. But in his data the variation in At is quite small • 2 rs hence the validity of (A Y A l v could not be checked. In the present series of experiments an attempt was made to vary A Ys by using Baira of two different sizes. The median diameter, d50, varied from 1.44 mm to 1.68 mm. The specific gravity of the grains was 1.23. Lubricating oil and Kerosene oil mixtures were used to get wide range of viscosity. The viscosity was varied from 2.5 to 6 times that of water. Each run was continued till uniform flow was attained and required data was collected. The whole d ata was plotted on Fr Vs y • . (AY f"p d3/2 but was found that the data of present series fell above the Sahgal's curve. So the plot was made between N Fr Vs (l 2 d•312 ) x.( Y is , Sahgal's data was also plotted s f on it. It was found to separate out the rippling and non-rippling zone's well. The author correlated Kenedy's 'J' and Y (-172Vd3 x (•-~-f ) by the following equation. g d Ys- Yf 3 3.1 log X + 6.26 Y whe se X is Cgl x t t