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dc.contributor.authorThorsen, Mats Jørgen
dc.contributor.authorSævik, Svein
dc.date.accessioned2017-11-28T10:28:40Z
dc.date.available2017-11-28T10:28:40Z
dc.date.created2017-10-27T13:38:26Z
dc.date.issued2017
dc.identifier.isbn978-0-7918-5764-9
dc.identifier.urihttp://hdl.handle.net/11250/2468232
dc.description.abstractThe theoretical background of an empirical model for time domain simulation of VIV is reviewed. This model allows the surrounding flow to be time varying, which is in contrast to the traditional frequency domain tools. The hydrodynamic load model consists of Morison’s equation plus an additional term representing the oscillating effect of vortex shedding. The magnitude of the vortex shedding force is given by a dimensionless coefficient, and this force is assumed to act perpendicular to the relative velocity between the cylinder and the fluid. The time variability of the vortex shedding force is described by a synchronization model, which captures how the instantaneous frequency reacts to cylinder motion. The parameters in the time domain load model are calibrated against a commonly used frequency domain VIV analysis tool, VIVANA. To do this, a finite element model of a vertical tensioned riser is established, and the structure is exposed to a linearly sheared flow. Key results such as cross-flow displacements along the riser, frequency content, r.m.s. of bending stresses and mean in-line displacements are compared, and it is shown that the frequency and time domain methods are close to equivalent in this simple case with stationary flow. Finally, the time domain model is utilized to study VIV of a riser subjected to regular waves. The characteristics of wave induced VIV are discussed in light of the simulation results. It is seen that VIV is excited in the zone close to the surface, and the energy is transported downwards as traveling waves. The vibrations typically build up as the horizontal water particle velocity is high, and die out as the velocity decreases. The effect of varying the wave amplitude and period is investigated, and it is found that the dominating frequency, mode and r.m.s. stresses increase together with the wave height. The effect of the wave period is however more complicated. For example, reducing the wave period increases the dominating mode but decreases the displacements. Hence the stress may increase or decrease, depending on which of these effects are strongest.nb_NO
dc.language.isoengnb_NO
dc.publisherAmerican Society of Mechanical Engineers (ASME)nb_NO
dc.relation.ispartofproceedings OMAE
dc.titleSimulating riser VIV in current and waves using an empirical time domain modelnb_NO
dc.typeChapternb_NO
dc.typePeer reviewednb_NO
dc.description.versionacceptedVersionnb_NO
dc.identifier.doi10.1115/OMAE2017-61217
dc.identifier.cristin1508351
dc.relation.projectNorges forskningsråd: 237929nb_NO
dc.description.localcodeThis chapter will not be available due to copyright restrictions (c) 2017 by ASMEnb_NO
cristin.unitcode194,64,20,0
cristin.unitnameInstitutt for marin teknikk
cristin.ispublishedtrue
cristin.fulltextoriginal
cristin.qualitycode1


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