Hydrodynamic Problems in Oil-Spill Control And Removal
Authors: Leibovich S. 
Published: December 2007

The theoretical performance of equipment for the control and removal of oil spills is considered. Mathematical models of oil-spill recovery devices are developed that may be used in evaluating equipment or in simulating the operation of an oil-spill response system.

Introduction

Oil spills involve a bewildering number of hydrodynamic problems. The oil-water system is so complex, particularly problems. The oil-water system is so complex, particularly when substantial wave motion is involved, that it has been difficult even to identify the essential problems in a useful way.

This paper considers some fluid-mechanics problems that have, or might be expected to have, important effects on oil-spill control and removal. The purpose is to develop background information that will assist in the evaluation of oil-spill-control equipment needs, and that should be of value when planning an oil-spill response system.

Mathematical models for oil volume collection rates in calm water of several types of skimmers are presented. "Calm" water refers to situations that have a frame of reference in which events are steady in time. Each class of skimmer is considered in a general way, and results are applicable (when suitably adapted) to individual designs in the class. Specifically treated are (1) weir skimmers, with and without pumps for maintaining an inflow water current, (2) rotating disk skimmers, and (3) endless oleophilic-belt skimmers. Attention is directed to the role of oil-layer instabilities as a cause of performance failure in some skimmers. Detailed theoretical performance curves may be calculated from the models presented (or from the more complete ones from which the present material is abstracted), but this is not the objective here. The intention throughout the paper is to educe effects and to seek parametric trends.

Oil-spill removal and control in open water is seldom conducted in calm conditions, so the effects of waves and turbulence on the performance of oil-spill equipment must be faced. These effects are readily apparent but are difficult to model theoretically. In cases where performance trends strongly depend on a critical water performance trends strongly depend on a critical water velocity, such as entrainment failure in booms, calm-water results may be generalized to include wave orbital speeds. Such quasi-steady adaptations of calm-water results are potentially of realistic value only if the acceleration potentially of realistic value only if the acceleration effects associated with the waves are relatively unimportant.

In addition to wave orbital speed and acceleration effects on skimming action, a number of other effects of waves and water turbulence play a role. Some of these effects are discussed in the second part of this paper. The specific questions dealt with follow.The combined action of wave breaking and turbulence can cause floating oil films to disintegrate and become mixed into the water column as droplets. The extent and importance of mixing depends on oil type and the vigor of turbulence and wave breaking. Once large amounts of oil are removed from the surface by natural means, containment and cleanup operations are pointless. This question was studied in Ref. 1 and is reviewed here.Reflections and focusing of short waves are striking occurrences in containment booms; these effects are analyzed in this paper. Enhanced turbulence in the containment region can occur due to wave breaking, which can lead to loss of oil into the water column.

JPT

P. 311