Field Measurements of Vortex Induced Motions of a Deep Draft Semisubmersible

Rijken, Oriol; Leverette, Steve

doi:10.1115/omae2009-79803

Cited by 27 publications

(15 citation statements)

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“…The geometry of semi-submersibles, i.e., multi-column and multi-pontoon, implies a more complex VIM phenomenon than that of single cylindrical structures, such as spar and monocolumn platforms. The confirmed presence of VIM on deep-draft semi-submersibles was found in field measurements by Rijken and Leverette (2009) and Ma et al (2013). Waals et al (2007) performed VIM tests on both semi-submersibles and tension-leg platforms (TLPs) to examine the influences of the mass ratio, draft conditions, and pontoons.…”

Section: Introductionsupporting

confidence: 70%

Experimental and numerical studies of the pontoon effect on vortex-induced motions of deep-draft semi-submersibles

Liu

Xiao

Liang

et al. 2017

Journal of Fluids and Structures

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The vortex-induced motion (VIM) is a critical issue in mooring and riser system design for column-type deepwater platforms. As regards to deep-draft semi-submersibles (DDS), even though VIM is mainly excited by vortex shedding around columns, the large-volume pontoons beneath the columns are also responsible for the wake interference, implying a non-negligible influence on VIM behavior. An experimental study and three-dimensional numerical simulations were performed to analyze the pontoon effect on the VIM of two semi-submersibles and a four-column structure without pontoons. The numerical results using Detached Eddy Simulation (DES) are in good agreement with the experimental measurements obtained from the towing model tests. The present investigations indicate that the resonant phenomenon is observed for all configurations. However, the four-column structure without pontoons shows the most significant transverse responses and yaw motions at both 0°- and 45°-incidences owing to the largest fluctuating lift forces induced by the well-established wake. Additionally, the negative values of work done by the pontoons at all reduced velocities confirm their damping effect on the VIM response

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Section: Introductionsupporting

confidence: 70%

Experimental and numerical studies of the pontoon effect on vortex-induced motions of deep-draft semi-submersibles

Liu

Xiao

Liang

et al. 2017

Journal of Fluids and Structures

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“…However, there had been field measurements of deep draft semisubmersibles that reported prototype motion amplitudes to be significantly lower than those measured during model tests [11]. There remains further work to be carried out, i.e.…”

Section: Resultsmentioning

confidence: 96%

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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“…Based on the time history data collected for 68 h, they divided the responses into lock-in period responses and post lock-in period responses. The comparison of present experimental results with field measurements of Rijken and Leverette 4 is shown in Figure 22(a) and (b) for the VIM-induced surge and sway responses. Even though the current measurements were not mentioned in their data, they reported that the maximum surge/sway responses ( A XS * / A YS * ) occur at U rs of 6 in the lock-in period and U rs of 12 in the post lock-in period.…”

Section: Resultsmentioning

confidence: 80%

“…Since present experimental set-up and procedures closely replicate the real-world scene, the field prototype measurements of Rijken and Leverette 4 are used for verification and comparison. The VIM-induced surge and sway responses are compared, and it is noted that the authors measured the VIM responses of prototype semi-submersible in the open ocean field for a time of approximately 68 h. However, as per the details available and reported, the sea state and current velocities were not mentioned for the data collected.…”

Section: Resultsmentioning

confidence: 99%

An experimental study on vortex-induced motion responses of a moored semi-submersible with and without riser

Domala

Sharma

2020

Proceedings of the Institution of Mechanical Engineers, Part M:

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This article presents an experimental study on the “vortex-induced motion” responses of a moored “semi-submersible without catenary riser” and “semi-submersible with catenary riser.” An eight-point catenary mooring system is adopted for the study in which eight rollers are installed on the pontoons for guiding the mooring lines and the semi-submersible design is of two rectangular pontoon and two circular columns on each of the pontoons. To replicate the real-world scene, the experiments are conducted in wave-cum-current flume with five directions of current (i.e. 0°, 30°, 45°, 60°, and 90°) to study the vortex-induced motion under the surge and sway degrees of freedom at high dimensionless reduced velocities (i.e. 6< Urs<50.86). Along with the surge and sway degrees of motion, the roll and pitch degrees of motion are investigated too with their paths for semi-submersible (i.e. amplitude traces). A “stainless steel flexible braided hose” with an aspect ratio of 157 till the touchdown point is used as a catenary riser. Results are presented with the definitions of degrees of freedom with respect to the axes defined at the center of gravity of semi-submersible and show that above the reduced velocity of 25 for the sway and surge degrees of freedom, the vortex-induced motion responses show a complex variation without any monotonicity. Furthermore, it is observed that (1) in traces there are no eight-shaped trajectories; (2) for both the semi-submersible without catenary riser and semi-submersible with catenary riser, the higher responses occur along the diagonals; (3) there are couplings of the pitch with surge, and roll with sway dofs; (4) the catenary riser reduces the vortex-induced motion responses for most of the current directions; and (5) galloping instabilities may be occurring and higher amplitudes may be related to them. Finally, it is shown that the vortex-induced motion response of semi-submersible reduces the vortex-induced vibration response of riser and that the motions in pitch and roll are likely to become critical and they demand a detailed analysis to be addressed in future to improve the operational range of semi-submersible and catenary riser in deep water depths under harsh marine environment of high current velocities.

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Field Measurements of Vortex Induced Motions of a Deep Draft Semisubmersible

Cited by 27 publications

References 0 publications

Experimental and numerical studies of the pontoon effect on vortex-induced motions of deep-draft semi-submersibles

Experimental and numerical studies of the pontoon effect on vortex-induced motions of deep-draft semi-submersibles

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

An experimental study on vortex-induced motion responses of a moored semi-submersible with and without riser

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