A study on vibration-suppression mechanism for risers using flexible structural joints

Abstract

These new mechanisms for suppressing vibration in large diameter intake pipes and pumping systems has been developed for use in Floating Liquefied Natural Gas (FLNG) facilities. Like existing devices such as fairings and strakes, this mechanism is designed for practical use and has a flow path inside the pipe. The mechanism is designed to suppress vibration caused by both float motion and vortex-induced vibration (VIV) due to currents. Experiments were conducted using a scale model, and numerical calculations were used to evaluate the mechanism’s ability to reduce vibration. As a result, the natural frequencies of the pipes were analyzed, and it was found that the vibration damping mechanism, when installed at appropriate locations, can provide effective vibration suppression against the motion of the upper float and vibration caused by VIV due to currents over the entire length of the pipe, even at limited installation locations. On the other hand, it was found that the vibration suppression effect could not be achieved without appropriate positioning, and that the longer the pipe length, the more limited the vibration damping capability.