Study On The Particle Tracking Based,Two-Layer Forecast Model For Oil Spills On The Sea

Maritime oil spill will seriously damage the marine ecological environment.The more accurately we predict the trajectory and scale of the spilled oil,the better we can develop contingency plans and conduct the removal work after fatal oil spilling.This paper summarizes the behavior and destination of existing marine oil spill numerical simulation theory,with the help of the wind field model,the tidal current hydrodynamic model and the particle tracing method,successfully establishes a double-layer oil spill prediction model for oil film and suspended oil droplets in the sea.Wind is one of the key driving factors for the migration and diffusion of oil spills on the sea.The accurate prediction of the wind field is the basis for the prediction of the oil film drift trajectory.This paper analyzes the historical wind data of the Bohai Sea(BS)and part of the north Yellow Sea(YS).According the correlation between the winds of different regions and the differences among the winds in different periods,this paper divides the wind section and time period in the studied sea area.The probability prediction model of the wind field has established according to the probability of transition between two specified directions,the average duration of the wind and the energy level.The model predicts a southwesterly wind with a high frequency of 4 m/s in the June wind time series,consistent with historical samples.The stochastic wind time series,generated by the prediction model,can provide a reliable wind dynamic environment for high precision oil spill prediction on the sea.Ocean current is the main hydrodynamic factor of oil spill on the sea.Considering the areas where oil spills always occur have complex coastal topography,this paper selects the physical marine model(FVCOM),which can fully utilizes the advantages of irregular grids to fit the complex boundary and the characteristics of mass momentum conservation in the calculation area and have successfully applied in the simulations of the ocean current in the interested field.Using the FVCOM,this paper simulates the oceanic currents in the BS and the parts of YS.By comparatively analyzing the draws of the ocean tidal current map and elliptical ocean current flow range from 1990 to 2010,we find that the terrain changes in the BS coastline have insignificant effect on the ocean currents.A large number of work shows that the oceanic tidal current simulation based on FVCOM model can provide a reasonable hydrodynamic basis for high-precision oil spill prediction on the sea.Based on the wind field prediction model and the tidal current hydrodynamic model,and using the Particle Tracking method,a Two-Layer Forecast Models for Oil Spills has established.In order to accurately simulate the exchange process of oil between the sea surface and the suspension layer in water,and finely computes the evaporation,dissolution,sedimentation,emulsification and suspension processes of the simulated oil.The model adopts oil and water separation double grid technology.Firstly,we calculate the flow field in the slightly rough grid,and then use the particle tracking method to simulate the migration and transformation for oil spills in another set of more sophisticated grid,which can help to facilitate the use of oil particles and oil spill concentration and oil film thickness real-time conversion technology.When the oil spill simulation is calculated,the water flow drift velocity of each oil particle can be obtained by inverse distance weighted interpolation of the velocity value at the grid point of the hydrodynamic module.This can smooth the oil particle velocity changes in different positions and keep velocity gradients continuous,which is more consistent with the actual situation of continuous film movement.In addition,the classical theoretical formula for simulating the oil film expansion process is mostly derived on the ideal hypothesis oil film shapes such as circular or elliptical,which does not match the irregularities in the real occasions.In order to overcome this limitation,we use the oil film dynamic block extension technique to simulate the oil film condition of the real sea oil spill,including the shape and the thickness of the oil film.By simulating the oil spill in the BS Strait,the movement trend of the oil film is reproduced,and the rationality of the oil spill model is confirmed to a certain extent.The cumulative evaporation of oil spill has reached 50% of the total oil spill,so it is concluded that oil film evaporation is one of the main components of oil spill destination.The model can be used to provide effective support for the implementation of pre-disaster protection in environmentally sensitive areas,the proper selection of clean oil treatment methods and the development of post-sea oil spill emergency measures to reduce the impact of oil spills.