Numerical Study Of Hydrodynamic Characteristics On Submarine Piggyback Pipeline Suspended Over Scoured Trenches

Regular wave past piggyback pipeline suspended over a scoured trench is numerically investigated to provide a valuable scientific theory and data for researchers and engineers.The two-dimensional Reynolds-averaged Navier-Stokes equations are solved by a three-step finite element method with the standard k-co turbulence closure. Based on the computational Lagrangian-Eulerian advection remap volume of fluid method the numerical wave flume is developed. The absorbing wave maker boundary on the left side of the flume is present to decrease the effect of reflected wave. For a comparative analysis with physical modeling experiment’s result, it is shown that the numerical wave flume is very effective. The wave flume can be employed to predict the piggyback pipelines’hydrodynamic characteristic.Following a relevant numerical model the effect of scoured trenches with different depths S/D and the KC number on the vortex shedding and the hydrodynamic forces on piggyback pipelines is investigated. It is found that the scour hole has significant effect on the piggyback pipeline’s hydrodynamic characteristics. The inline and uplift forces’amplitude of large pipeline and small pipeline have decreased and their phase position is different when the scour hole is existent. Under regular wave, the uplift forces oscillate two times in a wave period and there are two times vortex shedding around piggyback pipelines. Compared with single pipeline configuration, the inline force’s amplitude of the larger pipeline in piggyback pipeline configuration is reduced by54%than single pipeline and the uplift force’s amplitude and phase is different from single pipeline. With increasing S/D, the larger pipeline’s CMand CL is gradually reducing, but the CD is increasing when S/D<0.2and decreasing when S/D>0.2. The change of S/D has a weak influence on smaller pipeline. With increasing KC number, the larger and smaller pipelines’CD and CL, is gradually decreasing and reach a constant when.KC>35.5, but their CM constantly increase. Also, with increasing turbulence intensity, the energy spectrum curves of lift force appear multiple peaks at twice, triple, four times wave oscillation frequency.