Fluid-Sediment-Object Interaction Under Oscillatory Flow

A series of laboratory experiments on fluid-sediment-object interaction were conducted to thoroughly study the combined effect of sediment angularity, fluid stresses, bed roughness, and relative specific gravity on the object’s mobility and burial. The experiments consisted of oscillating a sediment tray in an otherwise still fluid, with the object placed on the sediment bed and moving with the frame of reference. Comparisons between flat-bed cases showed that burial increases with the object’s mobility number (ratio of fluid stresses to the object’s weight) and its relative specific gravity (ratio of the object’s specific gravity to that of the sediment), with no clear dependency on sediment angularity. Mobility over flat beds also increases with the object’s mobility number and its relative specific gravity, yet decreases 12-40% in angular sediments. Over bed roughnesses with length scales similar to those of the object, objects placed at the top of the roughness elements showed more mobility due to the unstable nature of their location. Objects whose axes were oriented perpendicular to the flow also showed more mobility than those parallel to the flow. When located at the flank of the roughness elements, objects showed consistently less mobility in angular sediments.