MECHANICS OF A RESTRAINED LAYER OF FLOATING OIL ABOVE A WATER CURRENT

This paper determines the relative importance of interfacial shear stress and dynamic pressure in determining the thickness distribution of a layer of floating oil contained by a barrier above a water current. This is done by use of an equation relating vertical location of the oil-water interface, dynamic pressure, and shear stress. The interfacial shape is measured experimentally. The dynamic pressure is determined by numerical solution of potential flow problem for flow beneath the measured shape. The aforementioned equation then yields the shear stress distribution. The rear portion of restrained oil layers are found to be governed by shear stress as are the forward portions for low current speeds. At higher current speeds, both dynamic pressure and shear stress are important in determining the shape of the forward portions. Large friction coefficients are shown to be due to flow over a rough interface resulting from the generation of Kelvin-Helmholtz waves on the interface. The entrainment of oil droplets into the water flow is shown to be the result of breaking of the Kelvin-Helmholtz waves.