The spill is considered to be initially circular, formed under the action of gravity, inertia, viscous and surface-tension forces. Any other initial shape could equally well be considered. At subsequent times, the spill, while advected by the hydrodynamic field and subjected to various weathering processes, takes arbitrary shapes which are predicted by the present model. The effects of spreading, the impact of breaking waves, evaporation, natural dispersion, dissolution, emulsification, photo-oxidation and biodegradation are also considered in this work.

The model utilizes an Eulerian two-phase flow approach [1,2]. The "Renormalization group (k-epsilon) model" was concluded to be a "best" choice and as such it was adopted for the present study.

The finite-volume method [3] was used for the numerical solution of the system of equations.The algorithm used for the solution of the equations is the interphase slip algorithm (IPSA) [1,2]. The linkage between pressure and velocity is handled via a more efficient version of the well-known semi-implicit method for pressure-linked equations (SIMPLE) algorithm [3] which is called SIMPLE-shortened (SIMPLEST) [4].

The results appear grid independent for grids of 120x95x16. A time step of 750s proved to be adequate for time-step independent solutions while using 100 iterations per time step. The runs were performed on a Silicon Graphics Origin 200 machine (4 CPU R 10000). A typical run using a 120x95x16 grid for 20 time steps (15000 secs real time) requires 12 hrs CPU time on the above machine, using UNIX and 5 hrs using LINUX, on a Pentium IV, 2.4 GHz, 512 MB.

In the case of simulating the behaviour and the fate in the marine environment of the various petrol fractions that form an oil spill, use was made of a simpler model, the so-called algebraic slip model, that was appropriately extended for the present problem. The model capabilities are demonstrated by applying it to two regions of different topography and bathymetry, in the framework of impact assessment studies. These two regions are near Carava, on the island of Lesvos, and near Eretria, in the Evvoikos bay, both being in the Aegean Sea.

The model is general and can simulate realistically the fate of an oil spill under given conditions. Therefore, it can respond to the demand for actions following an accident; and, if the ecosystems of the area are known, it is feasible to estimate the ecological and environmental risk.

1

Spalding D.B., "A general purpose computer program for multi-dimensional one-and two-phase flow", Maths and Computers in Simulation, North Holland Press, Vol. 13, pp. 267-276, 1981. doi:10.1016/0378-4754(81)90083-5

2

Markatos N.C., "Modelling of two-phase transient flow and Combustion of granular propellants", Int. J. Multiphase Flow, Vol. 12, 6, pp. 913-933, 1986. doi:10.1016/0301-9322(86)90035-2

3

Patankar A.S.V., Spalding D.B.,"A calculation procedure for heat, mass and momentum transfer in three-dimensional parabolic flows", Int. J. Heat Mass Transfer, 15, 1787, 1972. doi:10.1016/0017-9310(72)90054-3

4

Patel M.K., Markatos N.C., "An evaluation of eight discretisation schemes for two-dimensional convection-diffusion equations", Int. J. Numer. Meths. Fluids, Vol 6, pp. 129-154, 1986. doi:10.1002/fld.1650060304

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