Model Test Experience on Vortex Induced Vibrations of Truss Spars

Dijk, Radboud van; Magee, Allan; Perryman, Steve; Gebara, J.

doi:10.4043/15242-ms

Cited by 27 publications

(11 citation statements)

References 3 publications

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“…Some studies on VIM of spars with consideration of appurtenances have been carried out by others [2], [3], [4], [5]. While helical strakes alone are effective in suppressing VIM, albeit this behavior is heading dependent, the presence of other appurtenances namely anodes, pipes and chains together with the strakes may result in significantly higher VIM in spars [3].…”

Section: Introductionmentioning

confidence: 99%

The Effect of Appurtenances on the VIM Performance of a TLP for Southeast Asia

et al. 2014

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In Southeast Asia, the characteristic operating environment is strong and persistent currents with small to moderate waves, which encourages vortex induced motion (VIM) in floating platforms. Scaled model tests have always been used by the industry to check the performance of floating platforms including VIM. With improved hardware and software capacilities, numerical methods such as Computational Fluid Dynamics (CFD) analysis are now able to simulate floating platform motions in viscous fluid flow and thus have the potential to complement model tests in VIM studies. Hull appurtenances such as tendon porches, steel catenary riser (SCR) porches, caissons, pipes, chains, fairleads and anodes interact with the boundary layers and affect the points of flow separation along the hull columns which control the vortex shedding pattern of the hull. In this study, the effect of appurtenances on the VIM performance of a Tension Leg Platform (TLP) for Southeast Asian environment is investigated using a series of model tests and CFD analysis.The findings from this study may be used as a reference to properly account for the effect of VIM. The measured or calculated amplitudes of VIM may be used as input for additional load conditions to be considered in the design of the tendon mooring and riser systems of the TLP.Previous studies by others on the same subject were carried out for spars. Multi-column floating platforms do not have strakes on the columns unlike spars. Thus, significant difference in VIM behaviors between multi-column floating platforms and spars is expected. The wake is expected to remain turbulent in both full scale and model scale. For smooth cylinders, the separation point along the columns is scale dependent and this may affect the VIM responses. If the flow separates from a sharp appurtenance like a pipe, the VIM behaviors should be similar in full scale and in model scale. The results from CFD analysis generally agree with those from model test. The differences in the results from the two methods are discussed and areas for further investigation suggested.Significant VIM can adversely impact the platform mooring and riser systems in terms of both strength and fatigue life requirement and has to be properly accounted for in the platform design. Left unchecked, VIM can lead to loss of production due to unplanned repairs of the risers.

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Section: Introductionmentioning

confidence: 99%

The Effect of Appurtenances on the VIM Performance of a TLP for Southeast Asia

et al. 2014

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“…In fact, the small-scale experiments on a truss spar platform performed by van Dijk et al [1] already showed that, despite the strong susceptibility to geometric aspects of the hull, the VIM phenomenon clearly presents both the self-excitation and the selfcontrolled characteristics, in general terms, similar to the VIV on risers. Moreover, despite focused on mitigating the effects of VIM on such a type of platform by adding strakes, those authors also showed that, without suppressors, the maximum response amplitude occurs in a range of reduced velocities between 5 and 9, making explicit mention to eight-shaped trajectories, in a quite evident coupling between the in-line and transverse motions.…”

Section: Introductionmentioning

confidence: 92%

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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“…It is important for keeping the similarity between prototype and model. Thus, the Froude scaling approach recommended by van Dijk et al [23] was used. It is essential to note that the Reynolds number (Re = UD/ν, where U is the current velocity, D is the projected width of the column and ν is the kinematic viscosity of the fresh water) for the prototype DDS is in the order of 10 7 while the Reynolds number at model scale is significantly lower.…”

Section: Model Set-upmentioning

confidence: 99%

Experimental and numerical study on vortex-induced motions of a deep-draft semi-submersible

Liang

Tao

Xiao

et al. 2017

Applied Ocean Research

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An experimental study on vortex-induced motions (VIM) of a deep-draft semi-submersible (DDS) was carried out in a towing tank, with the aim to investigate the VIM effects on the overall hydrodynamics of the structure. In order to study the fluid physics associated with VIM of the DDS, a comprehensive numerical simulation was conducted to examine the characteristics of vortex shedding processes and their interactions due to multiple cylindrical columns. The experimental measurements were obtained for horizontal plane motions including transverse, in-line and yaw motions as well as drag and lift forces on the structure. Spectral analysis was further carried out based on the recorded force time history. These data were subsequently used to validate the numerical model. Detailed numerical results on the vortex flow characteristics revealed that during the “lock-in”, the vortex shedding processes of the upstream columns enhance the vortex shedding processes of the downstream columns leading to the rapid increase of the magnitude of VIM. In addition to the experimental measurements, for the two uniform flow incidences (0° and 45°) investigated, comprehensive numerical data of the parametric study on the VIM characteristics at a wide range of current strength will also serve as quality benchmarks for future study and provide guidance for practical design

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Model Test Experience on Vortex Induced Vibrations of Truss Spars

Cited by 27 publications

References 3 publications

The Effect of Appurtenances on the VIM Performance of a TLP for Southeast Asia

The Effect of Appurtenances on the VIM Performance of a TLP for Southeast Asia

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

Experimental and numerical study on vortex-induced motions of a deep-draft semi-submersible

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