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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