Experimental Study on Behavior of a Riser by Using Geometrical Similarity Model

It is well known that VIV (Vortex-Induced Vibration) occurs in a riser. Effects of the top tension and the surface roughness of a riser have not been clear for a behavior of a riser. In this study, the model test in which geometrical similarity models are used is carried out in order to understand the behavior of a riser including VIV phenomenon. The model risers correspond to the production riser of 120m in a real scale, and the corresponding model tests are carried out in scales of 1/50. The behaviors in uniform flows, waves and under the forced oscillation are measured three dimensionally by the real time graphic data processing system. This model test focuses on the effect of top tension and the surface roughness.The present paper shows the vertical distributions of a maximum horizontal displacement and the time histories at arbitral point of the corresponding riser model. The results show that the behavior characteristics of the risers differ against the top tension. Then VIV is remarkably influenced by the top tension. In addition, the maximum horizontal displacement is different about 20% due to the surface roughness.