Dynamics of low-viscosity oils retained by rigid and flexible barriers

Abstract

Oil spills are of major environmental concern in coastal regions. Experience shows that even the best efforts have not prevented the occasional occurrence of major accidents on the sea. As long as massive oil spills are probable, special techniques and equipment will remain essential for facilitating spill cleanup in coastal regions. Mechanical oil barriers, or “booms”, are used to contain or divert oil spills on water and are key tools in oil spill response. Recently, an anti-pollution boom, called the Cavalli system, was designed with the intention of preventing the spread of spilled oil by trapping it inside a flexible floating reservoir and improving the pumping operation by decreasing the reservoir surface, consequently increasing the oil layer thickness. The main aim of the present study is to investigate the response of barriers of different types (rigid/flexible) in oil slick containment and to evaluate the capability of a trapping reservoir, i.e., the Cavalli system, as a particular case. For this purpose, both experimental and numerical approaches were pursued. Two-dimensional experiments with rigid and flexible barriers containing a low-viscosity oil were conducted in a laboratory flume. To enhance the understanding of the mechanisms associated with oil containment, numerical simulations were also carried out. The slick shape evolution and dynamics, failure initiation, and rate of oil loss under different conditions were examined and analyzed. An empirical relationship was suggested in order to assess the maximum permissible oil–water relative velocity as a function of barrier draft and oil characteristics. Equations were also proposed to predict the slick length and headwave thickness as a function of contained oil volume.