Variables Affecting the Simulation

Jessica Walker

Variables Affecting Oil SpillDispersion

1. Surface Tension2. Specific Gravity3. 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 onan 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  

1 0.8 0.5 0.9 0.6 1.0 0.7 1.1 0.8 2 1.5 1.0 1.7 1.2 1.8 1.2 2.0 1.4 3 2.0 1.4 2.3 1.5 2.6 1.8 2.9 2.0 4 2.4 1.6 2.7 1.8 3.1 2.1 3.5 2.4 5 2.8 1.9 3.2 2.2 3.7 2.5 4.2 2.8 6 3.1 2.1 3.5 2.4 4.2 2.9 4.8 3.2 7 3.4 2.3 3.8 2.6 4.7 3.2 5.3 3.6 8 3.7 2.5 4.2 2.8 5.1 3.5 5.8 3.9 9 4.0 2.7 4.5 3.1 5.5 3.7 6.2 4.2 10 4.3 2.9 4.9 3.3 5.9 4.0 6.7 4.5 11 4.7 3.2 5.3 3.6 6.3 4.3 7.1 4.8 12 5.1 3.5 5.8 3.9 6.7 4.6 7.6 5.2 13 5.4 3.7 6.1 4.2 7.1 4.8 8.0 5.5 14 5.8 4.0 6.6 4.5 7.5 5.1 8.5 5.8 15 6.2 4.2 7.0 4.8 8.1 5.5 9.2 6.2 16 6.7 4.6 7.6 5.2 8.7 5.9 9.8 6.7 17 7.3 5.0 8.2 5.6 9.5 6.5 10.7 7.3 18 7.8 5.3 8.8 6.0 10.3 7.0 11.6 7.9

River Velocity at NO, LA

Velocity of Mississippi 10 feet: Mean = 4.3 ft/sec. @ 60% depth 4.9 ft/sec @ surface

As can be seen, The depth affects the velocity.

Maximum=5.9 ft/sec @ 60% depth 6.7 ft/sec @ 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 yValue of y

% change= 1,000,000-998,0001,000,000

% change=.002%change/20=.0001Therefore, 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.

=.99821 g/cm3

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

)()(c)(

cDcut

1 waterofdensityThe

velocityu ntcoeffieciediffusionTheD

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. www.meteorologie.eu.org/mothy/iosc1995.pdf

The horizontal diffusion coefficient, D, is equal to 2000 m2 /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 kilometersWidth: (east to west) 1,800 kilometers

So, a direct scale of the two would be:1,800 kilometers/ 350 units

= 5.142857143 kilometers/unit

Scaling All Parameters Everything has to be scaled Velocity: .976 units/hour Diffusion: .273 units2/hour