Study On The Vertical Mixing Of Oil Droplets By Breaking Waves

Oil spills at sea can be dispersed by a variety of natural processes, of which the influence of breaking wave is dominant. Breaking waves are able to split the slick into small droplets; facilitating oil mixing in the water column. Due to the buoyancy, the droplets may rise back to the water surface with the terminal velocity. When droplet Reynolds numbers are large, dynamic pressure force of turbulence flows is the cause of droplet breakup, When droplet Reynolds numbers are small, however, viscous shear associated with small turbulent eddies is the cause of breakup. Therefore, droplet formation, size distribution and dynamics of the quantitative expression are the central issue of this paper.Based on the theoretical statistical model of Yuan Yeli (2009) for wave breaking, using dimensional analysis and similarity theory, I deduce the expression of oil droplets entraining rate. I further deduce the relation between number of oil droplets entrained by breaking wave and droplet radius, turbulence energy dissipation rate, surface tension coefficient. So I get the theoretical expression of droplet number distribution varying with radius, N , which is the main result of this paper. The results are in a good agreement with observations. This article also improved Tkalich and Chan (2002) dynamic model of oil droplets, in which wave breaking parameters (the rate of the wave energy dissipation and the intrusion depth) are more consistent with the real sea waves. Finally, Bohai Sea"Caofeidian"oil spill accident in 2006 is simulated by Spherical MASNUM-WAM wave model, wave breaking statistical model and improved the T&C (2002) droplet dynamic model. Discusses the main factors residual mass of sea surface oil and the mass of oil droplets involved in the water column. The simulation result agrees well with Envisat ASAR data, anyway, the results are satisfying.This study, combining theoretical study and practical work together, will play a guiding role in oil spills emergency response and assessment.