ABSTRACT

Most of the existing researches either focus on vortex-induced vibrations (VIV) of a pipeline near a rigid boundary, or on seabed scour around a fixed pipeline. In the fields, pipeline vibration and seabed scour are actually always coupled. Based on the similarity analysis, a series of tests were conducted with a hydro-elastic facility to investigate the influence of pipe vibration on the local scour and the effects of scour process on the pipeline dynamic responses. Experimental results indicate that, there exist two phases in the process of sand scouring around the pipeline with small embedment, i.e.

  • scour beneath pipe without VIV, and

  • scour with VIV of pipe.

It is also found that the gap-to-diameter ratio (e/D) has much effect upon the scour depth for the fixed pipes. For a given value of e/D, the vibrating pipes with close proximity to seabed may induce a deeper scour hole than the fixed ones. Within the examined gap-to-diameter ratio range (-0.25 < e/D < 0.75), the influences of gap-to-diameter ratio on the maximum values of scour-depth for the case of vibrating pipes are not as much as those for the case of fixed pipes.

INTRODUCTION

When a pipeline is constructed on seabed and subjected to currents, there exits a complex interaction between current, pipeline and seabed. If the pipeline is not buried, unsupported spans may exist in some locations, especially at the uneven zones of seabed. Seabed erosion around pipeline may also result in the spanning of pipeline. When exposed to currents or other hydrodynamic loadings, such a suspended pipeline may experience vortex-induced vibrations (VIV), which have been widely recognized as one of the main causes for the fatigue damage to pipeline.

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