| Summary: | The hydrodynamic forces exerted on a pipeline partially buried in a permeable seabed subjected to combined random oscillatory flow are investigated experimentally. The tests were carried out in a re-circulating flume that can generate steady currents, oscillatory flow and combined flow, known as the O-tube. The performance of the testing facility was validated against published experimental data under regular oscillatory flow conditions. Four tests with different embedment depths, under random oscillatory flow conditions were then carried out. The flow velocity, hydrodynamic pressure around the model pipe and pore pressure in the soil were monitored. The hydrodynamic forces were calculated through pressure integration around the model pipe. The hydrodynamic force reduction due to embedment was compared with the model given in the most widely-used pipeline stability design guideline, DNV-RPF109. A horizontal load reduction of 55% was found for the fully buried pipe, which was lower than the 70% reduction suggested by DNV-RP-F109. The variation of the vertical hydrodynamic load with embedment ratio (embedment depth to pipe diameter) was also found to be different from the model suggested by DNV-RP-F109. It was found the fully buried pipe experienced a large vertical force, even higher than that of the fully exposed pipe, under low KC number conditions.
|
|---|