Project Overview

Summary:

In January 2016, Dr. Drennan at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science was awarded an RFP-V grant of $992,274 to lead the GoMRI project entitled Investigation of Oil Spill Transport in a Coupled Wind-Wave Current Environment Using Simulation and Laboratory Studies. The effort included one collaborative institution (University of Minnesota, co-PI Dr. Shen) and approximately ten research team members, including both graduate and undergraduate students.

This proposal aims at studying the transport of oil droplets in the upper ocean subject to active breaking waves, and the transport of oiled sprays in wind over waves, as part of theme 1 of the GoMRI Request for Proposals. The focus of study is on the effects of wind-wave-current interactions when the wave influences are significant, including hurricane conditions. The feedback mechanisms among wind, waves, and upper ocean currents and turbulence play an essential role in the transport of oil slicks. Despite their importance, due to the complexity of the problem, previous simulation and measurement studies were unable to adequately capture the interaction dynamics. Existing models often reply on simplified approximations, such as flat sea surface treatment, vortex force approximation of Langmuir cells using uniform and constant Stokes drift, ad hoc prescribed sea surface roughness for marine atmospheric boundary layer, etc. In this study, novel models will be developed with the above limitations removed. Innovative measurements in the state-of-the-art Surge-Structure-Atmosphere INteraction (SUSTAIN) laboratory at University of Miami were performed. The ultimate goal of this joint experiment and simulation study is to obtain substantially deepened physical understanding of and much improved modeling and prediction capability for the wind-wave-ocean interaction dynamics and the effects on oil transport.

The specific objective of this study are: (i) establish a high-fidelity computational framework for the interactions among wind, waves, and currents in upper oceans; (ii) use the unique capabilities of wind-wave tanks in the SUSTAIN laboratory to obtain accurate measurement data in air and water with wave phases resolved; (iii) use the laboratory study to provide input for the LES; (iv) establish an advanced simulation tool for the modeling and prediction of oil transport in both water and air under a variety of wind and wave conditions; and (v) assess the effects of wind and waves with various intensities, including hurricane conditions, on the transport of oil.

Research Highlights

As of December 31, 2019, this project’s research resulted in 0 publicatitons 8 scientific presentations and 16 datasets being submitted to the GoMRI Information and Data Cooperative (GRIIDC), which are/wand ill be made available to the public.

The project also engaged 4 PhD students over its award period, with the GoMRI data forming the basis for three dissertations. In all cases, the first three years of Ph.D. support were from GoMRI, with the two institutions covering the remaining support (nominally two years) through to the completion of the dissertations. The two years of funding from the Universities of Miami and Minnesota commenced this year and will continue through 2021. The doctoral students are progressing well with their research, and are expected to finish late 2020, late 2021 or early 2022. As such, many of the project goals are yet to be realized. This was anticipated in the original proposal, and progress is ongoing. There are no refereed publications at this point.  

Significant outcomes to date of this project’s research according to GoMRI Research Theme 1 are highlighted below.

            Theme One:  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.

i) Impact of oil film on small scale waves. At low to moderate winds (5-15m/s, 10m equivalent), the primary impact of the oil on mean square slope is the suppression of small waves (gravity and gravity-capillary waves) through modified surface tension. At higher winds, the air water interface with oil film was broken down by the dominant wind-induced breaking waves. Oil was transported below the surface, and higher wavenumber gravity-capillary and capillary waves developed by parasitizing on the breaking front.  While the initial wind-induced small-scale gravity waves are not resolved in the model, the small-scale waves produced at the breaking front are resolved by the model.  

ii) Time scales: In the aftermath of breaking waves, the volumes of bubbles and oil droplets can be approximated as exponential functions during the decay stage. However, the decay stage for the water droplets can be divided into two parts: exponential decay part and constant part. Exponential decay rates of oil droplets (), bubble (), and water droplets () were calculated. It was found that , which indicates that water droplets decay the fastest while oil droplets decay the slowest.  Of particular interest the water droplet concentrations reached a constant (non-zero) value, possibly due to additional production from the bursting of rising bubbles as they reach the surface (creating film droplets). This remains under investigation.

iii)  The model has provided a precise description of the process by which surface oil slick is initially stretched then broken up by a breaking (plunging) wave. The numerical solution follows the evolution of the breaking event through the creation of an air cavity, the entrainment of oil below the surface due to the circulation of the cavity, and the creation of a splash (secondary) jet. This will allow for the calculation of residence times of oil in energetic conditions.

iv)  Profiles of sea spray in the air were collected in both presence/absence of oil in a range of wind conditions. Distributions in the presence of oil are comparable to earlier laboratory results. We are in the process of quantifying the changes in the presence of oil.   

 Click to view Theme 1 - Project Highlights

 Proposal Abstract - RFP-V PI William Drennan