Numerical Simulation Of Vortex-induced Vibration For An Actual Drilling Riser System With Auxiliary Lines

Human demand for petroleum resources is increasing day by day,and the ocean has gradually replaced land as the main exploration and development zone for petroleum resources.The riser,as a key equipment for marine oil and gas developments,may be damaged due to the vortex-induced vibration under the action of ocean currents,which affects the normal drilling work and even causes the loss of life and property.Therefore,this study takes an actual drilling riser system serving in the engineering of South China Sea oil and gas development as the research object,carries out numerical simulation on a multi-cylinder system containing multi-size and irregularly arranged auxiliary lines,and the influence of the auxiliary lines on the characteristics of the flow and vortex-induced vibration under different incoming angles of attack,reduced velocities and center-to-center spacings is discussed.The research work is as follows:1.The open source software Open FOAM is utilized embedding the multi-cylinder synchronous motion solution module,and a solver suitable for the multi-cylinder vortex-induced vibration is obtained.Comparing the numerical and experimental results of the flow and vortex-induced vibration of single cylinder and double cylinders of previous scholars,the reliability of the numerical model and calculation method in this work is verified.2.The flow past the actual drilling riser system is numerically simulated,and the influence of the auxiliary lines on the lift and drag coefficient,vortex shedding frequency and flow field structure of the main line under different incoming angles of attack and typical reduced velocities is discussed.It is found that the auxiliary lines can reduce the average drag coefficient and lift coefficient amplitude on the main line except for individual conditions,but the effect is closely related to the angle of attack and the reduced velocity.3.The vortex-induced vibration of the actual drilling riser system is numerically simulated,and the influence of the auxiliary lines on the amplitude,vibration frequency,motion trajectory and flow field structure of the riser system under different incoming angles of attack and typical reduced velocities is discussed.It is found that the auxiliary lines can reduce the vibration amplitude of the riser system except for individual conditions,and it has a certain suppression effect on the vortex-induced vibration,but the effect is closely related to the angle of attack and the reduced velocity,and it is most obvious when the angle of attack is 210° and 330°.When the vibration amplitude is large,the power spectrum has a unique dominant frequency with a large peak value and the vibration frequency is close to the natural frequency of the riser system.The irregular arrangement of multiple auxiliary lines makes the motion trajectory of the riser system more complicated.Many new forms have appeared,such as raindrop shape,inclined inverted raindrop shape,inclined "8" shape and flat ovals shape.4.The C&K lines and Booster line in the original actual drilling riser system are evenly arranged around the main line every 120°,and the relative position with the Hydraulic lines and Chemical line is unchanged.The rearranged riser system is numerically simulated,and the influence of the auxiliary lines on the characteristics of the flow and vortex-induced vibration at different angles of attack and center-to-center spacings are discussed.It is found that the rearranged auxiliary lines can reduce the average drag coefficient and lift coefficient amplitude on the main line except for a few individual conditions,but the effect is closely related to the angle of attack and the center-to-center spacing.When the center-to-center spacing ratio is 0.98 and 1.18,the effect is better than the original riser system.After rearrangement,the auxiliary lines can significantly reduce the vibration amplitude of the riser system,and have a good suppression effect on the vortex-induced vibration,but the effect is closely related to the angle of attack and the center-to-center spacing.When the center-to-center spacing ratio is 1.18,the overall effect is similar to the original riser system.5.The reason why the lift coefficient amplitude and vortex-induced vibration amplitude of the riser system are significantly reduced is mainly due to the auxiliary lines on both sides limit the shear layer separated by the main line to a small area,making it unable to be freely discharged,and the vortex that has fallen off interacts with the vortex of the auxiliary lines to quickly dissipate,and no obvious discrete vortex can be formed near the wake region,thereby effectively inhibiting the vortex discharge of the riser system.