Characterization of Self Exciting and Self Limiting VIV of Freely Oscillating Riser Pipes in Time Domain

摘要

The ability to predict Vortex Induced Vibration (VIV), at least withinrnengineering accuracy, is very important for deep water risers, flowlines,rnand wellheads. Uncertainty driven designs and operations cost thernindustry tremendously. Best practice synchronized perfect lock-inrnresponse calculations of VIV and VIM (Vortex Induced Motions) hasrnbrought new challenges to all subsea, umbilicals, risers, and flowlinesrn(SURF) designs. A new simplified "Wake-Oscillator" model has beenrndeveloped to characterize self-exciting and self-limiting nature ofrnvortex induced vibration of transversely oscillating cylinders, in timerndomain. The model is then extended to capture fluid structurerninteraction due to inline motions and predict associated vortex sheddingrninduced combined in-line and transverse vibration of a freelyrnoscillating cylinder. This is a novel simple engineering type fluidrnstructure coupling model which will provide time dependent forcerncoefficients along the length of risers and flowlines, based on therncharacterization of self-exciting and self-limiting nature of VIV. A fullrndirect time integration, using the time and space dependent lift forces,rnresults in a more realistic vibration response amplitudes andrnfrequencies including effects from all participating modes