Investigation On Interference Response Of Different Diameter Flexible Risers Arranged In Tandem

The marine riser system is composed of a variety of risers,which are deployed under the offshore platforms.Due to the platform movement and the background ocean current,complex interactions and even collisions will occur among the risers.However,the current research and understanding of this interaction is insufficient.In order to ensure the safety during the riser operation,conservative space between risers is usually selected in the design,which results in a waste of floating platform space.Therefore,Therefore,the thoroughly experimental investigation of the mutual interference between the risers and its mechanism characteristics is of significance in ocean engineering.It can provide theoretical and data support for the design of the offshore platform deep-water riser system,safely,economically and efficiently.Based on the above requirements,the interference response characteristics of different outer diameters flexible risers with tandem arrangements are studied experimentally,and the theory of riser interference wake field is analyzed.Firstly,the investigation of riser interference is summarized,and the related basic theories are introduced,including the vortex induced vibration(VIV),shadowing effect,wake induced vibration(WIV)and wake field theory.In addition,the wake field of the tandem risers are stated in detail.Then,the experiment about the interference of the risers with big ratios is explained,including the design concept of the experiment,the experimental setups,the riser model,the mothed of dealing with the experimental data and its reliability.The VIV dynamics of two tandem risers with different spaces are mainly focused.Based on the experimental data,typical characteristics of VIV of two tandem risers under different tensions are analyzed and discussed,such as the RMS value of cross-flow(CF)amplitudes,the CF vibration frequency,the motion of both risers and the vibration displacement in the in-line(IL)direction.Finally,the wake field model is deduced in detail.Based on the experimental results,the model is modified.Then the VIV of tandem risers subjected to uniform current is numerically studied by using Matlab.And the corresponding wake flow field model is used to calculate the static response of the riser under different working conditions,and the test results are compared to verify the reliability of the corrected wake flow field model.