Variables Affecting the Simulation Jessica Walker

Variables Affecting Oil Spill Dispersion 1. Surface Tension 2. Specific Gravity 3. Viscosity

Surface Tension Measure of attraction between surface molecules of a liquid The higher the oil tension, the more likely it will stay in place The lower the oil tension, the more likely it will spread without wind or water current. Factors affecting this value: Increased temperature yields lower surface tension

Specific Gravity Density of the substance compared to the density of water Because most oils are lighter than water, oils tend to lay flat, float on the water’s surface. Factors affecting this value: Specific gravity of an oil spill varies. It can increase if lighter substances within the oil evaporate.

Viscosity Measure of a liquid’s resistance to flow The higher the viscosity of oil, the better chance the oil will stay in place.

Natural Forces Acting on an Oil Spill 1. Weathering 2. Evaporation 3. Oxidation 4. Biodegradation 5. Emulsification

Weathering Series of Chemical and Physical changes that causes spilled oil to break down and become heavier than water. Includes: Winds, Waves, and Currents Breaking a slick into droplets, distributed over water. Can result in a thin film on top of water.

Evaporation The lighter substances within the oil mixture become vapors and leave the surface of the water. Leaves behind the heavier components of the oil, which may undergo further weathering, or may sink to the ocean floor. Factors affecting evaporation: Wind, waves, and currents increase evaporation.

Oxidation Oil contacts the water and oxygen combines with the oil to produce water- soluble compounds. This process affects oil slicks around the edges primarily. Partial oxidation of a thick slick will produce a tar ball.

Biodegradation Micro-organisms such as bacteria feed on oil. A wide range of micro-organisms is required for a significant reduction of the oil. Nitrogen and Phosphorus additions increase this. Factors affecting this: Biodegration works best in warm water environments.

Emulsification Process that forms emulsions consisting of a mixture of small droplets of oil and water. Two types 1. Water-in-oil: water becomes trapped in viscous oil. 2. Oil-in-water: these sink due to higher specific gravity.

Velocity of the Mississippi Yet another variant Values differ due to depth, season, month, rainfall, etc..

To make this simpler, we regarded the gauge height to be 10 feet, near the mid point. River Velocities at New Orleans, LA. Gage Height(ft) ____________ MEAN__________ __________MAXIMUM__________ NGVD At 60% Depth Surface At 60% Depth Surface (86 Adj) t/sec mi/hr ft/sec mi/hr ft/sec mi/hr ft/sec mi/hr River Velocity at NO, LA

Velocity of Mississippi 10 feet: Mean = % depth 4.9 surface As can be seen, The depth affects the velocity. Maximum=5.9 60% depth 6.7 surface Average velocity is 4.6 ft/sec.

Density Equation: = m/v Density=, Mass=m, Volume=v The density is regarded as a scalar. It is not!!! Factor affecting density:

Water Temperature Density As noted, the temperature affects the density of water

Density of Water Density varies, Why can we regard it as a constant? %Change/20 degrees? % change= Highest value of y – lowest value of y Value of y % change= 1,000, ,000 1,000,000 % change=.002 %change/20=.0001 Therefore, the density does not change much with respect to temperature.

Density Since density does not change much with respect to temperature, density can be regarded as a constant. Usually density is measured at 20 degrees Celcius. = g/cm 3 We shall set the density value at 1, which is adimensional. (Without dimension) We had to do this so that the units in the final equation would be physically accurate.

As seen before

Horizontal Diffusion In our simulation, we shall only take into account the horizontal diffusion. Therefore the concentration of the pollutant is measured in percent/ area. On this website, I found the horizontal diffusion coefficient. The horizontal diffusion coefficient, D, is equal to 2000 m 2 /s.

Scaling Variables We wish to rescale units to uniformity. Note that colleagues used the dimensions 350 height, 400 width. the gulf of Mexico’s dimensions on this scale is approximately 350 units wide, 250 units high.

Grid Plot

Length Scale However, the real dimensions of the Gulf of Mexico are as follows: Height: (north to south) 1,300 kilometers Width: (east to west) 1,800 kilometers So, a direct scale of the two would be: 1,800 kilometers/ 350 units = kilometers/unit

Scaling All Parameters Everything has to be scaled Velocity:.976 units/hour Diffusion:.273 units 2 /hour