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The dynamics of contained oil spills is investigated based on multiphase CFD (Computational Fluid Mechanics) model. The oil slick shape behind the oil boom under water current is studied. The velocity field in the oil slick is compared with the velocity field in pure water flow. The thickness of the oil slick is studied quantitatively. It is found that there is a fixed linear relationship between the oil slick relative thickness and the Froude number for different oil, different current velocity, different boom draft and different volume of oil.

Marine oil spills can cause serious damage to natural resources and to those whose livelihoods depend on these resources. Therefore, it is important to improve techniques and equipment that facilitate spill cleanup [

Besides wind and wave effects, there are three failure mechanisms for the oil boom in the current [

Although oil boom is widely used, it is far from being fully investigated. For understanding the boom failure mechanism, it is important to investigate the oil slick behavior behind the boom and the details of the flow field near the boom. For the limit of the measurement approach, it is hard to know the details of the flow field in the oil slick. CFD has its advantages to obtain the process of the oil slick propagation and the details of the flow field in the oil slick. Tkalich et al. [

For the purpose of investigating the oil slick behavior behind the boom under a water current, a CFD software, OpenFOAM, is employed to carry out the numerical simulation. In this software, the Reynolds averaged Navier- Stokes equations (RANS equations) are solved numerically and

where

where

The turbulent eddy viscosity

where

where

The numerical simulation scenarios are chosen as the similar geometry with the real situation of the Singapore sea area. The computational domain is 30 m long and 5 m deep (see

There are four type of oil (listed in ^{3} or 3.6 m^{3} per unit boom length.

A summary of cases are listed in

For the numerical simulation of all the case, the same meshes are adopted with just slight difference between different boom drafts. The total number of cells is about 53,000. The minimum cell size is 0.025 m. The finest cells are placed near the boom and the water surface.

First at all, a case without oil has been carried out to compare with the case with oil.

Density of oil ^{3}) | Viscosity of oil ^{−6} m^{2}/s) | |
---|---|---|

Oil 1 | 888 | 70 |

Oil 2 | 949 | 3500 |

Oil 3 | 943 | 300 |

Oil 4 | 978 | 2300 |

D (m) | Oil type Q (m^{3}/m) | 1 | 2 | 3 | 4 |
---|---|---|---|---|---|

1 | 1.2 | a | e | i | m |

3.6 | b | f | j | n | |

0.5 | 1.2 | c | g | k | o |

3.6 | d | h | l | p |

field near the boom of these two cases. It shows that the current velocity distribution is almost same at the section far from the boom in the case without oil (left). But for the case with oil (right), the velocity distribution is changed in the oil slick. This phenomenon means that it is not enough to estimate the boom efficiency only based on the velocity field of the case without oil. It is necessary to carry out the numerical simulation of the case with oil based on multiphase model.

And the relative thickness is defined as the ratio of the oil slick thickness h and the oil characteristic length

This formula shows that the oil slick thickness is an function of initial oil volume Q, the current velocity U, the density of oil

A series of numerical simulation cases are carried out based on OpenFOAM multiphase solver in order to study the oil slick behavior behind the oil boom. The flow field near the boom is studied. The relationship of the relative thickness of oil slick with the Froude number is analyzed. It is found that there is a linear relationship between the relative oil slick thickness and the Froude number. This means that we can estimate the relative oil slick thickness using Froude number by the fixed linear relationship regardless of boom draft, initial oil volume and oil type.