Yunxiang You

Modeling underwater transport of oil spilled from deepwater area in the South China Sea

Based on a Lagrangian integral technique and Lagrangian particle-tracking technique, a numerical model was developed to simulate the underwater transport of oil from a deepwater spill. This model comprises two submodels: a plume dynamics model and an advection-diffusion model. The former is used to simulate the stages dominated by the initial jet momentum and plume buoyancy of the spilled oil, while the latter is used to simulate the stage dominated by the ambient current and turbulence. The model validity was verified through comparisons of the model predictions with experimental data from several laboratory flume experiments and a field experiment. To demonstrate the capability of the model further, it was applied to the simulation of a hypothetical oil spill occurring at the seabed of a deepwater oil/gas field in the South China Sea. The results of the simulation would be useful for contingency planning with regard to the emergency response to an underwater oil spill.

An investigation on internal waves generated by towed models under a strong halocline

Experiments are performed for the characteristics of internal waves generated by four horizontally towed models, including a sphere and three slender models with different aspect ratios in a density stratified fluid with a strong halocline. The Reynolds number ranges within 3500 < Re = UD/ν < 126 000, and the Froude number ranges within 0.4 < Fr = U/NmaxD < 18. Based on the time histories of the density perturbation and analysis of the correlation velocity of internal waves generated by the towed models, it is shown that the body-generated waves are stationary multiple-mode Lee waves, while the wake-generated waves are non-stationary wake waves mainly produced by the large-scale coherent structure in turbulent wakes acting as a moving excitation source. The transition between body-generated and wake-generated internal waves occurs at a critical Froude number Frc which is linearly dependent on the model aspect ratio. Before the transition, when the wave height H changes with the variation of Fr, a peak val...

Numerical Studies on Vortex-Induced Motions of a Semi-Submersible With Four Columns Based on IDDES Model

The vortex-induced motions (VIM) of deep draft semi-submersible platforms have been challenging engineering issues because of its impact to the fatigue life of mooring and riser systems. This paper presents numerical studies on the vortex-induced motions (VIM) of a deep draft semi-submersible. Numerical simulations are performed by using an improved delayed detached eddy simulation (IDDES). VIM amplitudes for in-line (surge), transverse (sway) and yaw motions and hydrodynamic force coefficients are obtained for different current incidence angles. The sensitivity analyses on grids and time step sizes are carried out to ensure convergences of the computational results. Comparisons with experimental data demonstrate the capability of the present numerical model. It is observed that the transverse motions for 22.5° current incidence are larger than those for 0° and 45° current incidences. The mean drag force coefficients for these simulated current incidence angles tend to grow as the transverse motion amplitudes increase. In addition, parametric studies have also been performed to examine the effects of the column corner radius on VIM.Copyright