TWO-PHASE FLOW INDUCED VIBRATIONS: METHODOLOGY VALIDATION - PART 2

Multiphase flow through pipelines can result in severe pipe vibrations and subsequent fatigue damage. Commonly, finite element analyses are used to define the dynamic pipe stresses and to calculate the lifetime of subsea piping. The fluid flow excitation forces can be estimated from measured data, estimated with empirical models or simulated in detail using computational fluid dynamics (CFD). Forces can be applied to the finite element model both in the time domain and in the frequency domain. The findings from Random Vibration Theory using a given forcing PSD, reconstructed force time histories from a single forcing PSD either as a 1-off or using a Monte Carlo approach with thirty 60 second realizations, and CFD predicted time varying forces are compared by applying them to structural calculations of a test rig and an 8'' subsea jumper. Random Vibration Theory is an efficient method to estimate the dynamic response in terms of RMS values. The Monte Carlo analysis showed the mean prediction of RMS vibration velocities asymptotes to the Random Vibration Theory predicted result, but there was significant variation in individual realizations of the force time histories. The RMS and peak values for a single transient analysis were found to asymptote at different rates. For the analysis of multiphase flow induced vibrations the Random Vibration Theory approach in the frequency domain is generally recommended as it gives good overall results and is computationally efficient, compared to transient structural analysis. Care should be taken when the piping system has phasing between the bends, in which case transient CFD analysis may need to be carried out.