CFD Simulation of Truss Spar Vortex-Induced Motion

Atluri, Sampath; Halkyard, John; Sirnivas, Senu

doi:10.1115/omae2006-92400

Cited by 17 publications

(12 citation statements)

References 7 publications

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“…That is, the predominant motion was always in the transverse (sway) and in-line (surge) directions to the incoming flow and negligible in all other directions. Moreover, the sway motion is more predominant compared to surge in VIM [6] . In this paper, we are primarily concerned with the sway motion.…”

Section: Spar Geometry and Environmental Conditionmentioning

confidence: 94%

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: Spar Geometry and Environmental Conditionmentioning

confidence: 94%

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 frequency of these eddies can be estimated empirically, but precise knowledge of the vortex shedding frequency cannot be determined using analytical means. The effect of these eddies has been previously studied for cylinders or spar platforms by Skop and Luo (2001), Ikeda et al (2003), Fischer et al (2004) and Atluri et al (2006). These forces are primarily perpendicular to the oncoming flow and, in the case of moored spars, can produce motions with displacements up to 80% of the spar's diameter when vortices are shed near the moored spar's natural frequency (Fischer et al 2004).…”

Section: Introductionmentioning

confidence: 94%

Mitigation of vortex-induced disturbances for the rapidly deployable stable platform

VanZwieten

Balas

et al. 2010

Ships and Offshore Structures

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The rapidly deployable stable platform (RDSP) is a concept vessel that is being developed for missions, such as at-sea cargo transfer, that will benefit from a stable spar-like platform that can transit under its own power at medium speeds (∼5-10 m/s). The stability and transit qualities of the RDSP extend from its two distinct modes of operation. These operating modes are the horizontal transit mode (HTM), where the RDSP is configured like a trimaran and the vertical operating mode (VOM), where the RDSP is configured like a spar buoy. In VOM, the RDSP will use the thrusters that are located on its spar section to manoeuvre at slow speeds, mitigate disturbances and dynamically position itself. When the RDSP is moving through the water in VOM, vortices will oscillate off of its spar section and produce forces that are primarily perpendicular to the direction of oncoming flow. Mitigating these disturbances is the focus of this work and is done using an adaptive control algorithm. This algorithm includes a disturbance rejection component that is capable of compensating for any unknown disturbance and phase information, as well as a phase locked loop (PLL) that improves the disturbance frequency estimate on-line. Using this technique, the vortex-induced motions are reduced to 18% of their open loop values using control inputs that are obtainable for the proposed RDSP thrusting system.

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“…The dimensions used in the semi-submersible model were taken from Atluri et al (2006). The width of the strakes was calculated to be 13% of the column width (0.13x17.80=2.3 m), as proposed by Atluri et al (2006). Figure 9 shows one of the four identical columns with a helical strake covering each curve.…”

Section: Geometrymentioning

confidence: 99%

“…These strakes have been shown to be very effective, reducing the transverse forces of the spar-platforms by up to 80%, as mentioned in Section 2.6. The dimensions used in the semi-submersible model were taken from Atluri et al (2006). The width of the strakes was calculated to be 13% of the column width (0.13x17.80=2.3 m), as proposed by Atluri et al (2006).…”

Section: Geometrymentioning

confidence: 99%

“…Numerical studies mimicking experiments are also conducted using CFD in order to allow for correlation between the experimental and numerical results. As reported in Atluri et al (2006), to assess the performance of helical strakes, CFD analyses were performed on spar-platforms with helical strakes appended. They carried out two series of tests for three different models.…”

Section: Helical Strakesmentioning

confidence: 99%

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Full-scale CFD investigations of helical strakes as a means of reducing the vortex induced forces on a semi-submersible

2017

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This version is available at https://strathprints.strath.ac.uk/60458/ Strathprints is designed to allow users to access the research output of the University of Strathclyde. Unless otherwise explicitly stated on the manuscript, Copyright © and Moral Rights for the papers on this site are retained by the individual authors and/or other copyright owners. Please check the manuscript for details of any other licences that may have been applied. You may not engage in further distribution of the material for any profitmaking activities or any commercial gain. You may freely distribute both the url (https://strathprints.strath.ac.uk/) and the content of this paper for research or private study, educational, or not-for-profit purposes without prior permission or charge.Any correspondence concerning this service should be sent to the Strathprints administrator: strathprints@strath.ac.ukThe Strathprints institutional repository (https://strathprints.strath.ac.uk) is a digital archive of University of Strathclyde research outputs. It has been developed to disseminate open access research outputs, expose data about those outputs, and enable the management and persistent access to Strathclyde's intellectual output.1 | P a g e ABSTRACTAs the search for oil in the Gulf of Mexico (GoM) moves into deeper waters, floating platforms such as semi-submersibles are in increasing demand. As semi-submersibles increase in size, the effect of vortex-induced motions (VIMs) becomes a significant problem in their design. VIMs stem from transverse forces caused by the current affecting the platform, with vortexes moving downstream on either side of the structure. The loop/eddy current phenomenon in the GoM leads to a constant current being present in the area, with speeds of up to 1.8 m/s. The accurate prediction of the vertical and transverse motions of semi-submersibles is crucial for the design of the riser systems. It is therefore beneficial to investigate the hydrodynamic forces acting on the geometry, and means of reducing these forces. A common method of reducing transverse forces is the addition of column appendages, such as helical strakes. In this paper, full-scale computational fluid dynamic analyses are carried out to examine the transverse forces caused by this vortex shedding using realistic current velocities in the GoM. Helical strakes are attached to the geometry to break up the coherence of the vortex shedding and the performance of these strakes is investigated numerically.

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CFD Simulation of Truss Spar Vortex-Induced Motion

Cited by 17 publications

References 7 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

Mitigation of vortex-induced disturbances for the rapidly deployable stable platform

Full-scale CFD investigations of helical strakes as a means of reducing the vortex induced forces on a semi-submersible

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