This paper proposes a two-dimensional (2D) coupled model for wave and currentseabed-pipeline interactions to examine oscillatory non-cohesive soil liquefaction around a partially buried pipeline in a trench. Unlike previous studies, two new features are included in this model: (1) wave-current interactions around the pipeline; and (2) fully coupled processes for the wave and current-seabed-pipeline system. In this study, the Reynolds Averaged Navier-Stokes (RANS) equations are applied to simulate the flow field around the pipeline, and Biot's poro-elastic theory for porous media is imposed to govern the soil response due to the wave-current loading. After being validated using data available in the literature, the 2D model is used to investigate the effects of the current velocity, the soil properties, and the wave characteristics on oscillatory non-cohesive soil liquefaction. Using the model, a function for the critical backfill thickness and the wave steepness under various flow and soil conditions is proposed to facilitate engineering practice.
Tip vortex cavitation (TVC) is an important type of cavitation. There is an urgent need for the accurate prediction of its inception condition. The water quality, i.e., the distribution of nuclei, is one of the main contributors to the TVC inception. Since there is no available cavitation model involving the effect of water quality, a new model suitable for TVC prediction is investigated based on the bubble dynamics. The migration and growth of nuclei are simulated in a tip vortex flow. An analytic method is developed to calculate the capture time of nuclei so that we can determine the critical nucleus in a vortex flow according to a filtering principle. The comparisons of the effect of water quality obtained in simulations and analytics are performed. It validates that the embodiment of water quality is rational and the analytical method is applicable for engineering purpose. Finally, the prediction model is quantitatively improved by considering the effect of water quality, and it is a new model for the prediction of tip vortex cavitation inception.
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