Investigations of the velocity and vorticity fields in the wake of a flexible riser with a length to diameter ratio of 181 were conducted in a towing tank at moderate Reynolds numbers in the range of 9400-47,000. Wake velocity measurements were made with the riser freely vibrating in both in-line and cross-flow directions. The motion and wake field of the riser, undergoing free vibration, were simultaneously measured by accelerometers installed inside the riser and by using a DPIV (digital particle image velocimetry) system. The VIV (vortex-induced vibration) results show that the riser freely oscillated at multiple vibration frequencies and amplitudes at each Reynolds number. Mixed vortex modes, '2S', '2P' and 'P+S', were observed in the near wake of the riser at different instants of time. The occurrence of these vortex modes depended on the Reynolds number, dominant frequency and mean amplitude. At lower Reynolds number, the single stable mode '2S' dominated the wake. With the increase of Reynolds number, the percentage of the '2S' modes decreased while the percentage of '2P' modes increased steadily except at Reynolds numbers of 14,100 and 47,000. The 'P+S' modes occurred mostly at a Reynolds number of 14,100 accompanied by more '2P' modes and less '2S' modes. At this Reynolds number, the frequency of the VIV was very close to the natural frequency of 0.72 Hz, which was obtained from a riser decay test in steady water and the average amplitude to diameter ratio reached 0.95, the highest found in these tests.
Vortex modes and vortex-induced vibration of a long, flexible riser
Wirbelerscheinungsformen und wirbelinduzierte Schwingungen entlang eines langen, flexiblen Steigrohres
Ocean Engineering ; 36 , 6-7 ; 456-467
2009
12 Seiten, 33 Quellen
Aufsatz (Zeitschrift)
Englisch
Numerical investigation of vortex shedding and vortex-induced vibration for flexible riser models
Online Contents | 2010
|Numerical investigation of vortex shedding and vortex-induced vibration for flexible riser models
DOAJ | 2010
|VORTEX-INDUCED VIBRATION (VIV) SUPPRESSION OF RISER ARRAYS
Europäisches Patentamt | 2020
|VORTEX-INDUCED VIBRATION VIV SUPPRESSION OF RISER ARRAYS
Europäisches Patentamt | 2017
New model for vortex-induced vibration of catenary riser
Tema Archiv | 2008
|