Contractile floating barriers for confinement and recuperation of oil slicks

Marine oil spills can cause serious environmental damages to natural resources and to those whose sustenance depends upon these resources. Unfortunately experience shows that even the best efforts have not prevented occasional occurrences of major accidents on the sea. As long as massive oil spills are probable, special techniques and equipments will remain essential to facilitate spill cleanup in coastal regions. Oil spill containment booms are the most commonly adopted techniques to collect and contain oil on the sea surface, or to protect specific areas against slick spreading. Recently, an anti-pollution boom called the Cavalli system, has been 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, and consequently increasing the oil layer thickness. Although flexible barriers have become increasingly common as a cleanup facility, there is no more than inadequate elaborate knowledge about their behavior. According to an extensive literature review, most of existing researches, either physical or numerical, have been done for rigid barriers. The main motivation for introducing the present research project is to study the efficiency and operational limits of the Cavalli system. However, the objectives are not constrained to this particular case. The present investigation focuses on the behavior of flexible barriers containing spilled oil. Previous researches of containment booms, even for the case of rigid barriers, have been mainly carried out in calm water. Accordingly, the main concentration is devoted to the response of a flexible barrier in presence of sea waves. Both experimental and numerical approaches were pursued to evaluate the efficiency limits and behavior of flexible barriers. Two-dimensional experiments have been carried out in a laboratory flume 6.5 m long, 1.2 m deep, and 12 cm wide. Flexible and rigid barriers containing rapeseed oil were examined, with and without waves. As the first step, the behavior of a flexible barrier in currents without waves was studied and compared to that of a rigid barrier. The key challenge was to contain the oil behind a flexible barrier that can freely deform in the water flow. This could be achieved using a slitted side skirt on the boom where it faces the lateral wall of the flume. The failure mode observed for rapeseed oil was entrainment failure. The initial failure velocity of different experimental conditions was studied and 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. The geometrical characteristics of the contained slick were examined and empirical equations were proposed to predict the slick length and headwave thickness as a function of contained oil volume. The second and more significant step was to conduct experiments with a fl