Analyze Of The Loading Capacity Of Slope Submarine Pipeline Under The Action Of Oblique Waves

Offshore pipeline is widely used in the Marine oil and gas resources development,due to the pipeline generally settled from the undulating seabed to shore,which result in the different angle between wave propagation direction and pipe axis is exists.Therefore,the pipeline's stress and local scour will be inevitably affected by the existence of the slope and the change of wave propagation direction,which is directly related to the safe operation of the pipeline.Hence,the study of stress characteristics of pipeline settled in slope and wave force act on the pipeline and its surface has important scientific value and practical significance by considering the combine of wave force and scour.The physical model tests are carried out in the harbor basin by changing the wave elements,buried depth,and incident angle,moreover,the 1:15 slope was paved prototype sand with the median particle size of 0.219 mm,the incident angle is 45 degrees between the slope toe line and wave propagation,the steel pipe was selected as the pipeline model with 0.048 m diameter.Experiment results show that: Under the action of wave oblique propagation,the wave point pressure and its change trendency are different in the different position of the pipeline surface.When the pipeline is tiled on the seabed,the absolute value of point pressure amplitude increases first and then decreases with the increase of relative height H/h or Kc number.The analysis of wave force on the cross section of pipeline is based on the drag coefficient CD,inertia force coefficient CM,and lift coefficient CL,those coefficient are adopted by Mo Linsen equation.The total wave force of X,Y and Z directions are measured by force balance,the experiment results indicate that the force in X direction is maximum,the force in Z direction comes second,and the force in Y direction is close to zero.The total force when pipeline is paved on ashore is greater than which is tiled by changing the wave elements and the buried depth.The stress amplitude on three directions all increased first and then decreased with the increases of incident angle,but the maximum value on three directions are different,meanwhile,as the buried depth increases,the force in X direction is reduced,the force in Y,Z direction is increased and then decreased.The three dimensional scour topography is not uniform because of the wave energy is lost on the process of propagation,the wave spread to the left side of the slope firstly and resulting in a reflection wave,the phenomenon can be testified by the va riation of wave height before and after the pipeline.The relationship between the equilibrium scour depth and the point pressure along the axis of the pipeline: the pressure decreases and the scour depth becomes larger.