Numerical Analyses of Scaling Effects and the Flow Field Inside an Innovative Sea State Independent Oil Skimming System: SOS

Due to improved regulations and high safety standards, the quantity of oil spilled in tanker accidents is notably decreasing over the last years. Despite this progress, the factor of human failure and hence the eventuality of an oil spill with catastrophic ecological and economical consequences can never be excluded. Current oil recovery systems are able to operate in wave heights up to 1.5 m. In severe weather they have to wait until conditions are improving. To prevent emulsification and weathering processes, it is necessary to skim the oil film off the sea surface shortly after the accident. This can only be achieved by an oil recovery system with high transit velocities on the one side, and the capability of operating in rough seas on the other side. A Sea state-independent Oil Skimming System (SOS) that satisfies these requirements has been developed and gradually optimized in various numerical and experimental analyses. The skimming process was already successfully validated in compliance with Froude’s law, but scaling effects were observed. In order to understand the complex flow phenomena around and through the SOS, numerical analyses based on a RANSE/VOF (Reynold-Averaged Navier-Stokes Equations / Volume Of Fluid) approach are conducted. Here, in addition to Froude’s and Morton’s law, viscous effects and the physical characteristics of oil and water are also scaled correctly according to Reynolds’ law. The results of these investigations present essential information for the transfer of the entire oil skimming process to full scale. This paper presents a further step of development towards a marketable system (see Fig. 1). The latest innovations — which are already applied for a patent — comprise a hermetically closed moon pool with pressure regulation and a hatch system with separate inlet and outlet flaps. In addition to the improved hull strength, this new design enables better individual control of the oil skimming process — hence the efficiency in dependency of environmental conditions — by pressure control of the water fluid level inside the moon pool.