Model Testing for Vortex Induced Motions of Spar Platforms

Irani, Mehernosh; Finn, Lyle

doi:10.1115/omae2004-51315

Cited by 25 publications

(13 citation statements)

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“…The locked-in VIM response is then sustained for a range of u r . As indicated in some literatures (for example, the study of Irani et al [9] ) which studies on classic spars and truss spars, finally, at u r approximately greater than 9-10, the lock-in will no longer be maintained, and the vortex shedding frequency returns to its normal value and the maximal y/D-values decrease. While in this study for the cell-truss spar, it seems that the lock-in sustains a little longer.…”

Section: Results and Analysismentioning

confidence: 92%

Computational fluid dynamics and experimental study of lock-in phenomenon in vortex-induced motions of a cell-truss spar

Wang

Yang

Lü

2009

J. Shanghai Jiaotong Univ. (Sci.)

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Spar platforms could be subject to vortex-induced-motions (VIM) in certain current conditions. Lockin is a phenomenon which occurs in a range of reduced velocities in VIM. In this paper, a new concept of spar platform called cell-truss spar is studied using both computational fluid dynamics (CFD) and model test to investigate the VIM of the spar under different reduced velocities. The unique configuration of the cell-truss spar is carefully considered, and the unsteady flow around the spar is calculated and visualized in CFD simulations. A physical model with a scale ratio of 1 : 100 of the cell-truss spar is fabricated, and model tests are carried out in the current-generating ocean engineering basin. Many important parameters in VIM of the cell-truss spar are obtained, the occurrence of lock-in phenomenon is successfully simulated, and the mechanism and rules of lock-in are analyzed.

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Section: Results and Analysismentioning

confidence: 92%

Computational fluid dynamics and experimental study of lock-in phenomenon in vortex-induced motions of a cell-truss spar

Wang

Yang

Lü

2009

J. Shanghai Jiaotong Univ. (Sci.)

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“…The relative direction of current with respect to the model can be seen in Figure 3. The effectiveness of helical strakes to mitigate VIM of Spar hulls is well demonstrated in the literature [4] [6]. However, the performance of the strakes is argued to be affected by the placement of appurtenances like mooring chains, fairleads etc., that run along the length of the hull (Figure 2).…”

Section: Model Testsmentioning

confidence: 98%

CFD Simulation of Truss Spar Vortex-Induced Motion

Atluri

Halkyard

Sirnivas

2006

Volume 4: Terry Jones Pipeline Technology; Ocean Space Utilization; CFD and VIV Symposium

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Helical strakes are used to suppress the Vortex-Induced Motion of Truss Spars. Model experiments have demonstrated the efficiency of strakes in the Truss Spar design but also indicate that the VIM response is sensitive to the details of strake design and placement of appurtenances around the Spar hull. It is desirable to study these hydrodynamic effects using CFD. The following paper is a continuation of some of the earlier CFD simulations on this subject (see, J. Halkyard, et al., "Benchmarking of Truss Spar Vortex-Induced Motions Derived from CFD with Experiments", Proceedings of OMAE'05). This paper in particular deals with the effect of holes in the strakes and appurtenances and their placement. All the simulations were done at model scale (1:40 scale model of an actual Truss Spar design) to compare the motions with experimental results. Mesh sensitivity and turbulence modeling issues are also discussed. Calculations were done using general purpose CFD code Acusolve TM .

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“…Additionally, experiments by Finn et al [2] established a direct relationship between hull geometry and VIM response, highlighting the correlation between towing tests and those performed at water channels. According to those results, a formal procedure for testing VIM on spar-type platforms was presented in Irani and Finn [3], including concerns about the right consideration of the restoring system in small-scale tests. By focusing on operational conditions and concurrently aware of the VIM susceptibility to other hydrodynamic mechanisms, Finnigan et al [4] started experiments considering VIM and free surface waves simultaneously.…”

Section: Introductionmentioning

confidence: 98%

Experimental Comparison of Two Degrees-of-Freedom Vortex-Induced Vibration on High and Low Aspect Ratio Cylinders with Small Mass Ratio

Gonçalves¹,

Rosetti²,

Fujarra

et al. 2012

Journal of Vibration and Acoustics

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Vortex-induced motion (VIM) is a specific way for naming the vortex-induced vibration (VIV) acting on floating units. The VIM phenomenon can occur in monocolumn production, storage and offloading system (MPSO) and spar platforms, structures presenting aspect ratio lower than 4 and unity mass ratio, i.e., structural mass equal to the displaced fluid mass. These platforms can experience motion amplitudes of approximately their characteristic diameters, and therefore, the fatigue life of mooring lines and risers can be greatly affected. Two degrees-of-freedom VIV model tests based on cylinders with low aspect ratio and small mass ratio have been carried out at the recirculating water channel facility available at NDF-EPUSP in order to better understand this hydro-elastic phenomenon. The tests have considered three circular cylinders of mass ratio equal to one and different aspect ratios, respectively L/D ¼ 1.0, 1.7, and 2.0, as well as a fourth cylinder of mass ratio equal to 2.62 and aspect ratio of 2.0. The Reynolds number covered the range from 10 000 to 50 000, corresponding to reduced velocities from 1 to approximately 12. The results of amplitude and frequency in the transverse and in-line directions were analyzed by means of the Hilbert-Huang transform method (HHT) and then compared to those obtained from works found in the literature. The comparisons have shown similar maxima amplitudes for all aspect ratios and small mass ratio, featuring a decrease as the aspect ratio decreases. Moreover, some changes in the Strouhal number have been indirectly observed as a consequence of the decrease in the aspect ratio. In conclusion, it is shown that comparing results of small-scale platforms with those from bare cylinders, all of them presenting low aspect ratio and small mass ratio, the laboratory experiments may well be used in practical investigation, including those concerning the VIM phenomenon acting on platforms.

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Model Testing for Vortex Induced Motions of Spar Platforms

Cited by 25 publications

References 0 publications

Computational fluid dynamics and experimental study of lock-in phenomenon in vortex-induced motions of a cell-truss spar

Computational fluid dynamics and experimental study of lock-in phenomenon in vortex-induced motions of a cell-truss spar

CFD Simulation of Truss Spar Vortex-Induced Motion

Experimental Comparison of Two Degrees-of-Freedom Vortex-Induced Vibration on High and Low Aspect Ratio Cylinders with Small Mass Ratio

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