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Gel stability in waves : breakage, behaviour, and implications for oil spill remediation Cunnningham, Richard Joseph

Abstract

While oil spills are becoming less common, they are an ever-present threat associated with use of petroleum. New developments in chemistry have brought gellants back into the spotlight as a promising spill remediation technique. These chemicals change the material properties of spilled oil, making it more solid. This could help prevent the spreading or weathering of spilled oil, extending the window-of-opportunity available for remediation. While oil-gelling technology shows great promise, the behaviour of surface gels subject to linear ocean waves has not yet been investigated. Determining what wave conditions result in the breakup of a gel layer could help predict the utility of these technologies in the field. This study adopts an experimental perspective to provide insight into the behaviour of gels subjected to wave action, specifically addressing the stretching induced by spatially-variable velocity gradients. Bottom-of-tank experiments were designed to allow the isolation of wave-induced stretching effects from wave-induced bending. In these experiments, a dense gel (gelatin) was placed on the bottom of a wave tank and constrained vertically. As particle orbits in a shallow-water wave decay vertically with depth, this is an effective means of applying the same spatial velocity gradients that would be observed on the water surface. Analytical models were developed to describe the response of a viscoelastic gel to periodic, spatially-variable velocity gradients for Maxwell and Kelvin-Voigt materials. The analytical models matched experimental data in terms of trend, but under-predicted strain by a constant factor. Ultimately, gel breakage was determined to be related to peak stress across the gel’s cross-section. By connecting breaking criteria in monochromatic, linear waves from tank tests to real-world conditions, this project provides an initial perspective on when wave-induced stretching alone could cause the fracture of a marine surface gel.

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