THE TEST ON RELATION BETWEEN PIPELINE UNDERCUTTING AND WAVE FORCE CHANGES

Due to the special meanings of submarine oil and gas pipelines in marine energy development,researchers have had a large number of safe experimental studies, and especially pay attention to the combined experiments made in different bottoms, different wave conditions and different burying depths. This present gutter test of wave aims at scouring and hanging-up which are dangerous to the pipeline security,in order to understand the relation between wave pressure on pipelines and the undercutting in silty seafloor represented by the Yellow River delta.The test result indicates that the pressure change is closely related with the undercutting course.Our continuous test shows that submarine pipeline is closely correlative with soil of sea bed and waves. The scouring and undercutting of pipeline under wave action experience three developing stages:silt stirring stage, current tunnel developing stage, swift undercutting and scouring equilibrium stage.Flow from the current tunnel plays an important role in scouring and undercutting.With scouring and undercutting, pipeline wave action transforms regularly from positive to negative force gradually, which can be divided into four developing stages:the initial scouring stage during which pipeline wave function is mainly positive,and pipeline shows vibrations under positive force; tunnel development stage during which pipeline vibrates up and down under the wave-crest lifting force and wave-trough downward-pulling force; pipeline hanging-up stage:pipeline vibrates forward and backward according to the negative wave crest and positive wave trough efforts; scouring equilibrium stage:pipeline vibrates mainly under negative force.