Oil Layer Flow around Skimming Vessels

Abstract

The flow of an oil layer around an advancing skimming vessel has been investigated theoretically under the following assumptions : (1) the oil layer is so thin that the velocity distribution is uniform over the depth ; (2) there is no shear and tension at the oil-water interface ; and (3) the density difference between oil and water is so small that the elevation of the air-oil interface is negligible. The results of the investigation have showed that the oil layer flow is replaced by a supercritical flow in a shallow open-channel which is characterized by the densimetric Froude number in the ideal case of inviscid fluids with no interfacial tension. The other factors which have been neglected in the theoretical model, namely the nature of viscosity and interfacial tension, are investigated and the effect of them on the theoretical model is quantitatively evaluated. It is shown that the effect will only appear on small model ships.Tank tests have been carried out to verify the theoretical model and its law of similarity of an oil layer flow, using geosim models of a mono-hull vessel. The geosim models with different entrance angles have been tested, at varying ship speeds and oil layer thicknesses. Furthermore, models having different hull-form with the geosim models have been tested to investigate the effect of hull-form on the theoretical model. The test results show that the theoretical model and the law of similarity are valid at lower densimetric Froude numbers, and the effect of the Froude number appears at higher densimetric Froude numbers. And the flow is characterized only by the entrance angles independent of the form of section and draft of vessels.