Project Overview

Summary:

     Dr. Junhong Liang at Louisiana State University’s College of the Coast and Environment was awarded an RFP-VI grant at $457,588 to conduct the RFP-VI project titled, “Effects of Turbulence and Waves on the Dispersion, Transport and Fate of Oil Droplets in the Upper Ocean: A Large Eddy Simulation Study”. The project consisted of 2 other institutions (University of California Los Angeles and the University of Maryland Center for Environmental Science), 1 principal investigator (Liang), 3 co-PIs (Drs. Benfield, McWilliams, Rose), 2 PhD students (Yuan, Liu), and 1 research scientist (Shan).

     Spilled oil in the upper ocean can have damaging effects on the marine ecosystem, and adversely affect the associated coastal communities by posing a health threat and by interrupting economic activities. After entrance into the upper ocean, either rising from a deep ocean blowout or from a near-surface release, spilled oil moves, disperses, and undergoes a series of physical, chemical and biological transformations under the influence of oceanic flows at scales ranging from basin-scale circulation to three-dimensional turbulence scale. Current operational oil spill models are able to resolve oceanic flows from basin- to mesoscale due to recent developments in forecasting ocean models and observing networks, the effects of submesoscale and boundary layer turbulence in these models requires further study.

     The primary objective of this project is to better understand the dispersion and transport of oil, and the aggregation processes between oil droplets and large particulate matters, in the turbulent upper ocean. The objective is achieved by a state-of-the-art large eddy computer simulation framework that is capable of simulating ocean currents from fine-scale turbulence to submesoscale currents, and the impact of the currents on the evolution oil droplets and other particulate matters.

     The proposed study will advance knowledge in Theme-I “Physical distribution, dispersion, and dilution of petroleum (oil and gas), its constituents, and associated contaminants (e.g., dispersants) under the action of physical oceanographic processes, air–sea interactions, and tropical storms." The proposed research addresses fundamental oceanic dynamical problems on how turbulence influences the dispersion, transport and transformation of non-reactive and reactive tracers. It will complement some of GoMRI’s ongoing efforts to study particle dispersion in submesoscale flows (by the CARTHE consortium). The proposed project will improve our capability to predict the evolution and transformation of oil in the upper ocean, and will provide better and more accurate scientific basis for public-policy decision makers and industry on a range of issues related to short-term and long-term responses and mitigation of oil spills. Although the study focuses on oil droplets, the conclusions can also be generalized to the turbulence influence on gaseous and particulate materials in the ocean including gas bubbles, marine debris and particulate matters.

Research Highlights

     Dr. Liang’s research, which included 4 outreach products and activity, resulted in 2 peer-reviewed publications, 6 scientific conference presentations to date, and 2 datasets submitted to the GoMRI Information and Data Cooperative (GRIIDC), which are available to the public.  Significant outcomes of their research (all related to GoMRI Research Theme 1) are highlighted below.

Liang et al. (2018) develops a theoretical model and computer simulations to quantify oil dispersion under the exclusive influence of ocean surface boundary layer currents. Before our study, the dispersion effect due to boundary layer current is usually represented by an isotropic and uniform random walk. The study demonstrates that the dispersion of oil is anisotropic under the exclusive influence of turbulent ocean surface boundary layer turbulence. It is determined by surface meteorological conditions, geographic location, water column stratification, and water column stratification. The study also proposes a parameterization for horizontal dispersion (to replace the isotropic and uniform random walk model) was proposed in the same study. The parameterization has been implemented in an operational particle tracking model (this result will be reported in a manuscript soon to be submitted)

Liu et al. (2019) develops computer simulations to study the flocculation of cohesive (fine) sediment in coastal ocean turbulence. It is motivated by the need to better quantify settling (terminal) velocity of particles in coastal ocean models where settling velocity is currently tuned through matching observation. The formation and settling of oil-particle aggregate is a natural way to sequestrate oil from the water column. We found that the size, settling velocity, and mass concentration of sediment flocs in the water column are influenced by wave-driven Langmuir turbulence and breaking waves, as the two dynamical processes suspend flocs and alter the rate of floc aggregation and breakup. Furthermore, flocculation models derived from laboratory observations cannot be directly applied to the coastal ocean environment. 

 Proposal Abstract - RFP-VI PI Junhong Liang