Practical Airgap Prediction for Offshore Structures

Sweetman, Bert

doi:10.1115/1.1710870

Cited by 18 publications

(4 citation statements)

References 16 publications

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“…These preliminary results, therefore, reveal the importance of nonlinearities in the incident wave in predicting minimum air-gap clearance. The importance of nonlinearities in incident wave height for practical air-gap predictions has also been discussed in Sweetman (2004) where the incident waves used were Stokes 2nd order wave. As discussed by the author, there are several levels of approximate methods for practical air-gap predictions, and incident wave nonlinearity is an important contributor to the minimum air-gap.…”

Section: Resultsmentioning

confidence: 99%

“…The present method can yield minimum air-gap considering full nonlinear incident waves in the time domain which turned out to be lower than when prediction are made with linear waves. Following the methods proposed in Sweetman (2004), the results from regular nonlinear incident computations can be statistically analysed to derive important design information in irregular waves. Detailed studies on multi-body simulations as well as under-deck clearance including validation will be reported in subsequent work.…”

Section: Resultsmentioning

confidence: 99%

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Time-domain simulation of large-amplitude wave–structure interactions by a 3D numerical tank approach

Ganesan

Sen

2015

J. Ocean Eng. Mar. Energy

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A time-domain 3D Rankine panel method based on a simplified variant of the mixed Eulerian-Lagrangian scheme under certain approximations is developed for studying steep nonlinear waves interacting with practical ship and offshore configurations at zero speed. Appropriate techniques have been developed that enable the method to produce very long-duration simulation results. Two levels of time-domain computations are performed: (1) a fully linear formulation where all external forces are computed on the mean wetted surface, and (2) an approximate nonlinear computation where the hydrodynamics interaction forces (diffraction and radiation forces) are determined on the mean surface and the forces arising from the incident steep waves and hydrostatic restoring forces are determined based upon the exact wetted surface under the nonlinear incident wave. Numerical computations for three practical marine structures, the barge, the S175 hull, and the semisubmersible are presented. The linear computations for which very longduration simulations are achievable from the present method are validated against results from other available methods. As the method is developed for stationary floating bodies undergoing oscillation about their mean location, it cannot be applied for a fully unrestrained body which can freely drift. In absence of physical restraints, the approximate nonlinear calculation requires imposition of artificial constraints partially or fully restraining the horizontal motions. Very long-duration simulations under the influence of steep nonlinear large-amplitude waves for all the three structures considered could be achieved. Comparative studies between different force and motion components in large-amplitude waves from linear and the approximate nonlinear computations are made to bring out the influence of the incident wave nonlinearities on these structures. It is found that the nonlinearities of the forces and motions are strongly dependent on the above water hull geometry. Compared to a small water-plane area hull (the semisubmersible), or a wall-sided hull (the barge), a flared hull (S175) results in pronounced nonlinear features in the forces and motion time-histories.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Time-domain simulation of large-amplitude wave–structure interactions by a 3D numerical tank approach

Ganesan

Sen

2015

J. Ocean Eng. Mar. Energy

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“…The vessel vertical motions can be calculated by using the measured heave, roll and pitch motions [23]:…”

Section: Vertical Motions Effect On Relative Wavesmentioning

confidence: 99%

Shallow water effects on high order statistics and probability distributions of wave run-ups along FPSO broadside

et al. 2015

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“…Sweetman [5] combines extreme value theory with statistical regression to predict extreme air gap for the model test data. Various statistical analysis methods have been applied over the years.…”

Section: Introductionmentioning

confidence: 99%

Enhancing Air Gap Design and Assessment in Deepwater Floating System Performance

Zeng

2015

All Days

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This paper discusses how to enhance air gap design and assessment for the deepwater floating systems. The authors first establish an analytical method to predict air gap considering global upwelling due to wave diffraction, as well as random wave effects. Then the authors apply the analytical method to simulate the air gap of typical deepwater floating systems through uncoupled analysis combining frequency domain and time domain global motion analysis. For comparison, a coupled analysis with hull structure, mooring and riser system is also carried out. The authors then look into model test verification and correlation analysis of air gap prediction, especially how to deal with random motion effects on deriving the extreme values of air gap. Furthermore, the authors illustrate how to improve deepwater floating system performance and cost-effectiveness by utilizing a practical and reliable air gap design approach.The air gap simulation results derived from the proposed analytical procedure correlate well with the wave basin model test results. This analytical procedure has also been applied to deepwater floating system design for field development projects, which can be considered as a practical and reliable air gap design solution for optimizing global configuration to improve deepwater floating system performance and cost effectiveness.

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Practical Airgap Prediction for Offshore Structures

Cited by 18 publications

References 16 publications

Time-domain simulation of large-amplitude wave–structure interactions by a 3D numerical tank approach

Time-domain simulation of large-amplitude wave–structure interactions by a 3D numerical tank approach

Shallow water effects on high order statistics and probability distributions of wave run-ups along FPSO broadside

Enhancing Air Gap Design and Assessment in Deepwater Floating System Performance

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