Computational Fluid Dynamics for Enhanced Environment Protection and Water Management

Abstract

The increasing demand for energy contributed significantly to recent developments in offshore production and transportation of oil and gas. Offshore oil spills are major threat to environmental safety and marine life. Damage control and preparedness planning require better understanding of oil spill process, trajectory, and how Metocean and atmospheric forces influence the spatial and temporal spread of oil in seawater dramatically. Computational fluid dynamics (CFD) has proved to be an invaluable tools to analyze in detail the dispersion of pollutants, including oil, in sea shore area. However, CFD models for large scale domains, extending several kilometers offshore and along the coast, need grids with several millions of points to accurately predict the dynamic distribution of spilled oil. For such large scale domains, over simplification of the physical model or Metocean data may result in significantly different results. A detailed Computational Fluid Dynamics (CFD) based study is established to predict the trajectory of oil film during various spill scenarios in shallow water wave profile and the influence of wavelength and amplitude as well as current velocity. A three phase (Oil, water and air) Volume of Fluid (VOF) multiphase model in ANSYS FLUENT is used to capture the free surface and the motion of oil film. It is found that in the absence of sea current effects, buoyancy of oil droplets is dominant, and the diffusion-advection on the surface continues to progress forming thick oil slick even in the opposite direction of the wave transmission. Higher wavelength (less frequent) are associated with less extent of oil dispersion since shorter waves (more frequent) will cause relatively more violent water flow near sea surface which can transport oil droplets further up in wave direction. Furthermore, waves of smaller amplitudes cause more spread of the oil slick, especially in the direction opposite to wave direction. This is because less amplitude waves are associated with less turbulence and breaking energy, and hence less dynamic vertical dispersion of oil film in seawater. IntroductionOffshore production of oil and gas is growing significantly due to the constant increase in demand for energy and recent advances in offshore technology. Oil spill into seawater is likely to occur due to major incidents such as a pipeline failure or offshore well blowout. The discharge and transport of oil from a spill source at the sea bed to the sea water and eventually to the sea surface is a very complicated phenomenon, in which many parameters influence the oil motion and distribution. This paper presents the influence of wavelength, amplitude, and sea current velocity on the transport of spilled oil through water column and the spatial spread and thickness of an oil slick on the sea surface. The following discussion illustrates how accurate presentation of surface waves and sea current can affect the modeling of offshore oil spill. Tkalich, P. et al. (2003) developed a Multiphase Oil Spill Model (MOSM) to simulate ...