A Finite Element Tool for Investigation of Vortex-Induced Vibration of Marine Risers

Abstract

Vortex-induced vibration (VIV) is a major design issue for all deep-water riser systemsoperating in regions where severe sea currents can be expected. This highly complexphenomenon has resulted in a great deal of experimental work that today's empiricalmodels are based upon. These models are based on frequency domain dynamic solutionsand are therefore not directly applicable in a non-linear time domain model.The purpose of the present work is to develop an approach to combine frequency domainmodels with a time domain analysis software in order to predict VIV, and implementthis into a procedure named FEDEM-VIV. A force prediction algorithm is developedto compute VIV response amplitudes with the Newmark time integration algorithm inFEDEM Software.A validation study is carried out to compare the results from FEDEM-VIV with VIVANA- a frequency domain code. Damping due to large amplitude is pragmaticallyhandled. Response shapes are for this reason not well captured, but maximum responseamplitudes are in some cases close to VIVANA estimates. High number of iterationswill in general over-estimate the response, and high amplitude damping is not predictedwell. Dening a lower limit of the excitation coecient for damping, with a low iterationlimit showed feasible predictions of the excitation force distribution. Excitationzone predictions in VIVANA and FEDEM-VIV are in good agreement.However, with the simplications in mind, the current approach represents a good solutionfor a time domain VIV predictor when all the essential hydrodynamical eects areaccounted for in FEDEM-VIV.