Experimental investigation of the flow-induced vibration of a hybrid riser conveying severe slugging

This paper reports the experimental results of the vibration response of a hybrid riser conveying severe slugging. The hybrid riser comprises a vertical rigid riser made of a transparent acrylic tube and a flexible jumper made of a transparent silica gel tube with a length to internal diameter ratio of 261. The horizontal span and vertical height of the flexible jumper are 83.5 and 45 cm, respectively. The flow-induced vibration tests were carried out in the liquid superficial velocity range of V_sl = 0.098-0.688 m/s and the gas superficial velocity range of V_sg = 0.177-0.649 m/s using non-intrusive optical measurement with high-speed cameras. Five flow regimes are observed, including the severe slugging I (SSI), severe slugging II (SSII), severe slugging III (SSIII), stable flow (ST), and oscillation flow regimes. The vibration response of the flexible jumper is related to the flow regime. As the flow regime changes from SSI to SSII, the absence of the slug production stage results in an augmented amplitude. In contrast, the response amplitude is significantly reduced when the flow regime shifts to ST. For the SSI regime, the response amplitude varies over the stage, and the occurrence of multiple frequencies is associated with the pressure fluctuation as well as the different duration of stages. The maximum amplitude is observed in the liquid fallback stage in spite of the limited duration, and the vibration frequency is close to the fundamental natural one. The liquid slugs of different lengths passing through the jumper at different velocities contribute to the presence of the traveling wave characteristic.