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1 OILSPILLMODELINTHELITERATURE
1.1 Typesofoilspillmodels
Oil weathering models predict the changes in oil
characteristics–evaporate,emulsifyanddisperseinto
thewatercolumn.Thechangesmayoccurovertime
underthe influence of environmental conditionslike
water temperature, wind speed, wave heights, sea
state, salinit
y, sediment concentration. The
appropriateenvironmentalconditionsandoiltypeare
selectedfromthemodel’sdatabase.
Trajectoryordeterministicmodelsallowtopredict
not only weathering profiles but also potential
migration of an oil slick over time, slick volume, oil
properties like viscosity or flash point and other
detailssuchaspotentia
lbeachingsitesorthelengths
ofcoastlineimpacted.
Stochasticmodels(probabilitymodels)arebuilton
thebasisofhistoricalwindrecords.Thefrequencyof
wind speed and direction is allowed to estimate the
probability of where an oil spill might travel in
definedtimeperiods.Theresultsindicat
ewatersand
shorelines which are most at risk during various
seasons.
Hind‐cast models (backtrack models) are allowed
toestimatethespillorigin.Thesemodelsruncontrary
tothetrajectorymodels.
Three dimensional models (3D) estimate oil spill
trajectories, weathering profiles, oil component
concentrations and make simulations of dispersion
into the water column. These models required
complex current data and a sophi
sticated oil
characterization. These are the only models which
considertheoilmigrationatdepth.
Details of these models are described in the
TechnicalPaper(ITAC).
Oil Spill Models: A State of the Art of the Grid Map as
a Function of Wind, Current and Oil Parameters
J
.Mazurek&L.Smolarek
GdyniaMaritimeUniversity,Gdynia,Poland
ABSTRACT: An integrated model, which contains flow and tra nsport‐fate modules, will be presented for
simulatingtransportandfateofoilspillsatseas.Theflowmoduleusesdifferentkindsofmeshesthatprovide
great flexibility for modeling the flow in complex geometries of currents and barriers. The refined grid
resolutioninregionsofint
erestisimportant.Horizontaldiffusionissimulatedusingrandomwalktechniques
inaMonteCarloframework,whereastheverticaldiffusionprocesscanbesolvedonthebasisoftheLangeven
equation.Themodelcontainsthemostsignificantprocesseswhichaffectthemotionofoilpart
icles.Forabetter
fittothecurvatureof the coastlinethereareusedunstructurednonoverlappingrectangularortrianglegrid
cells. Special attention must be paid to choose the horizontal and vertical resolution in simulating the oil
trajectoryinthecoastalarea.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 7
Number 1
March 2013
DOI:10.12716/1001.07.01.02
20
1.2 Inputdataofoilspillmodel
Thequalityofthedatausedhasahugeinfluenceon
the effectiveness of the model results. The data
requirebymostoilspillmodelsrelatehydrodynamic
data,winddataandoiltype.
The most important parameter is hydrodynamic
data. Gathering a database
of currents is costly and
time consuming but currents have the greatest
influenceonoilmigration.Technological advance,the
development of models and simulation allow to
forecast currents but it is not useful in extreme
environments such as storms or high runoff.
Advective currents in oil spill simulations may be
derived from current atlases or other static
approximations. Wind data are much easier to
acquire.Weatherforecastingservicesprovidegeneral
informationonwinddirectionandmagnitude.Theoil
types are available from database of modeling
systems.Oildatabasecontainsessentialoilproperties.
1.3 Oilweatheringmodel
The Figure 1 presents the
general layout of
weathering model. Under the influence of hydro‐
meteorological condition and oil type there are
occured physical and chemical processes, which are
directorindirectlinked.Reedinthepaper(Reedetal.
1999) investigates an overview of different
approaches applied in numerical models of the
behaviorof
oilspillinthemarineenvironment.Early
oil spill models were typically two‐dimensional
models, present study use three‐dimensional
processes. The oil moves in the marine environment
notonlyhorizontallybutalsovertically,onandinthe
sea.Oilistransportedhorizontallyunderforceofthe
wind, current, wave and
vertically in the water
column as droplets of various sizes. In light winds
without brea king waves, 3.5% of the wind speed in
the direction of the wind gives a good simulation of
oil slick drift in offshore areas. As wind speed
increases,oilwillbedispersedintothewatercolumn,
andcurrentshearsbecomemoreimportant.
Figure1.Generallayoutofoilweathering(Reedetal.1999)
All physical and chemical processes related oil
spill have a huge impact on the oil composition and
propertieswithtime.Estimatesofslickareaandfilm
thicknessareusedinthecomputationofevaporation.
Estimates ofevaporativelosses are requiredinorder
to assess the lifetime of the spill. In addition,
these
estimatesarerequiredfor evaluation of thepotential
efficiency of different oil spill combat methods, and
forassessmentsofenvironmentalimpacts.
1.4 Oilspillsimulation
Numerical prediction models have been generally
used to solve the movement and diffusion of water‐
borne pollutants. To simulate oil transported on the
sea
surface there is used the advection‒diffusion
equation,(Choietal.2010).Itisthegeneral Eulerian
equation,commonmathematicalmodeldefinedas:
()
C
UC DC S
t
(1)
whereCisthedensityofoil,Uisthevelocityvector,
Disthediffusivitycoefficient,andSisexternalfluxes.
Equation1iscalculated from Lagrangian formula as
follows:
current wind random
L=(U + U ) t+L
(2)
whereListhemovingdistanceofeachparticleduring
Δt, α is the wind drift factor (usually taken as 0.03),
current
U
istheoceancurrentvelocityattheseasurface,
and
ind
U
w
is the wind velocity at 10 m above the
water surface, respectively. The advection due to
turbulent diffusion
random
L is computed by the
randomwalkmethodforGaussian“spillets”as
random
LR6D/t
(3)
whereRistherandomnumberbetween−1and1.The
empiricaldiffusivitycoefficientDistakenas10m
2
/s.
The oil spill model, Equation 2, calculates the oil
transportation.
Choiinthearticle(Choietal.2010)constructedof
the high resolution oil spill forecast simulation
system. This model was built for the whole routes
between Japan and Middle East, so to verify of the
performance and accuracy of
the simulation system
there was used the accident of the Russian tanker
“Nakhodka” in the East/Japan Sea, in January 1997.
Simulationexperimentofthisaccidentwasconducted
and the simulation results were compared with the
observationandthepreviousstudy.
Figure2.The Yang grid (on the left), the Yin grid (in the
middle), their composition – the Yin‐Yang grid (on the
right)(Choietal.2010)