Stability of pipeline under oblique waves

A marine pipeline laid on the ocean floor, without burial, is exposed to current and wave induced hydrodynamic forces. If the pipeline does not have enough submerged weight to resist the hydrodynamic forces, the pipeline will be unstable, moving up and down (due to lifting force) and back and forth (due to drag and inertia force). The excessive pipe movement and oscillatory motions may cause high stress and fatigue damage to the pipe. In the past, the on-bottom stability of a pipeline under oblique waves was calculated by reducing the hydrodynamic forces due to the oblique wave angle. However, this approach gives a conservative result. In reality, a pipeline at an oblique wave angle is exposed to positive (at wave crest) and negative (at wave trough) forces, simultaneously. The counter forces will act like an anchor and keep the pipeline from moving. This paper describes how the oblique wave angle affects the marine pipeline laid on the ocean floor. The anchoring effect due to the oblique wave angle is presented.