Numerical Study of a Flexible Riser Lock-in Phenomenon by Using 2-Way FSI Method

Abstract The riser that is operated on the offshore oil and gas exploration in deep water, have complicated behaviour under the influence current load. Vortices are shed along the riser’s surface when it travels against the sea current, creating a transverse force that varies frequently on the riser vibration known as the VIV. In this paper, several problems related to frequency natural of the riser and frequency of vortex shedding at several current velocities were studied regarding the lock-in phenomenon of riser. The study was carried out numerically by using the 2-way Fluid Structure Interaction method. The simulation results show the potential for lock-in to occur at certain fluid velocity, namely V=0.2 m/s and 0.4 m/s, which produce vortex shedding frequencies that are close to the natural frequency of the structure, namely fn-2=2.455 Hz and fn-3=4.057 Hz.