Numerical Simulation Of Oil Spill Spread And Transport In The Tidal Waterways

As the high speed development of china economy and increasing demand for foreign oil and the shipping boom, oil spill accidents happened frequently nowadays. The oil pollution caused by oil spill accidents has become one of the main factors of the water environment pollution. The spill accidents not only cause loss of property, but also the serious destruction of ecological environment. So much attention has been paid by local government. The research on the movements of oil spill has been of important significance to take emergency measures to response and evaluate water environment pollution after spill accidents, and so has received more and more attention in recent decades. It is becoming a new rapid developing discipline.In china there are vast maritime territory, stretches of coastline and abundant shipping resources on inland waterways as well. In the economically developed coastal region, some famous tidal waterways such as the Yangtze River, the Pearl River and the Huangpu River are not only main arteries of vehicle transports between sea and inland waterway, but also key maritime hub for import and export trade. Except for inland river shipping, these rivers have diverse function,such as the living and industrial water source, biological habitat, aquaculture, landscape sight, etc, As soon as the oil spill accident happened, it will pose a threat to people's daily life and the local ecological environment. With the rapid development of the national economy in China today, our government has put developing circular economy and protecting the ecological environment on the agenda, so how to prevent oil spill pollution in inland rivers is particularly urgent.Since the 1960s, scientists have paid lots of attention on the research of oil spill pollution problems. A lot of researches have been done and many achievements have been obtained but the fate and the transport of the spilled oil is a very complex process and is difficult to be described with a single model, therefore there are many topics left still to be studied.In the previous research some semi-theory and semi-experimental formulae have been obtained and established under the condition of oil spill happened on static water or steady fluid flow mostly. In recent several decades, a lot of numerical models have been presented to simulate the fate and transport of spilled oil. But owing to most of oil spill accidents occurred in the marine, so attention has always been focused on the marine environment, less on the river, especially on tidal waterways.In this dissertation, based on the experiments of the flume, the movement of oil spill in tidal waterways is simulated by using mathematical and physical model and the behavior of oil spill in tidal waterways is discussed. The following two aspects of work have been done:Firstly, for the tidal waterway connected with sea in the estuary, the tidal flow in marine has a great effect on the flow in tidal waterway, so it belongs to unsteady flow. Hydrodynamics in the waterway governs the behavior of the spread and transport of oil spill, so accurate hydrodynamics simulation is a key step in numerical simulation of movement of spilled oil. In this paper, we present a new combined scheme to simulate tidal flow in tide waterways, i.e., MacCormack technique combined with finite analysis method for solving unsteady convection-diffusion equations. MacCormack method was widely used in aerodynamics early, and subjected to a time-step method substantially. Unlike other time-step methods used for all equations, in this approach only MacCormack technique is used for solving the continuity equation, while the momentum equations are calculated by FAM. The advantages of FAM's auto-upwind, high accuracy, numerical stability and the MacCormack technique's two-order precision for time and space derivative respectively are incorporated entirety to obtain a good stability and excellent convergence for the algorithm. Especially,the use of a single mesh diminish the complex compared with most schemes which the multigrid system has to be used. The algorithm itself is also very straightforward. In order to verify the present method, hydraulics simulation is carried out for a section down mainstream of the Huangpu River. The numerical results are in good agreement with the measured data. By the use of orthogonal curvilinear coordinate system, the methods can be easily extended to the numerical simulation of the tidal flow in a curved conduit.Secondly, the simulation of the oil trajectory for instant and continuous oil spills in tidal waterways, the Huangpu River, has been carried out based on particle approach, the experiments of oil spill and unsteady tidal flow model. The simulation for one dimension and two dimension spill procedure is carried out respectively under different tidal process and the existence of the wind field. Numerical results of one dimensional oil spill model are in good agreement with the experimental results during overall tidal period and reveal that this approach can reflect the movement of spilled oil. Furthermore, two-dimensional oil spill model combined with drawing software can predict well the variation of the spilled oil shape, scale of size, the movement and polluted scope of the oil slick intuitively. Both numerical and experimental results show that the behavior of tidal process in the waterway has enormous impacts on the movement of spilled oil. So various emergent responses to the oil spill accidents should be made in regard to different tides. it also shows that numerical simulation can predict well the movement of oil slick when proper mathematical and physical model are used, and can provide visualized and scientific references for the track of the oil slick in the tidal waterways.