Effectiveness of using pipe-in-pipe (PIP) concept to reduce vortex-induced vibrations (VIV): Three-dimensional two-way FSI analysis

Pipe-in-pipe (PIP) systems have been increasingly used in offshore applications because of their favourable thermal insulation capacity. Very recently, the conventional PIP system was slightly revised by using carefully designed springs and dashpots to connect the inner and outer pipes. This revised PIP system can be considered as a structure-Tuned Mass Damper (TMD) system. It therefore has the potential to mitigate the offshore structural vibrations induced by various sources such as earthquake excitation and/or vortex shedding. This paper carries out three-dimensional (3D) numerical simulations to investigate the effectiveness of the proposed method. The cross-flow oscillation of the conventional and optimized PIP systems are numerically investigated by developing a two-way coupled Fluid-Structure Interaction (FSI) framework for computational fluid dynamics (CFD) analysis. The developed FSI model is validated with the available experimental and numerical benchmark data on a single cylinder. This validated model is then extended to the PIP system to study its efficiency for Vortex-Induced Vibration (VIV) suppression. Numerical results show that the optimized PIP system can noticeably reduce VIV.