Further Work on the Effects of Nonlinear Wave Spreading and its Impact on Current Jack-up Assessment Practice

Hoyle, Mike; Smith, Susan M.; Ahilan, R.V.; Hunt, Rupert J.; Marcom, M.R.

doi:10.4043/otc-20297-ms

Cited by 2 publications

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“…This directional spreading formulation is as recommended in ISO (2005) and typical values of spreading factor φ include 0.867 for tropical cyclones at latitude of less than 40 degree, 0.88 for Monsoons in latitudes less than 15 degree and ~0.9 for the North Sea, as discussed in Smith et al (2006) and Hoyle et al (2009). A value of 0.88 is assumed for the numerical examples in this paper.…”

Section: Wave Modellingmentioning

confidence: 99%

Offshore foundation systems for resource recovery: Assessing the three-dimensional response of jack-up platforms

Cassidy

2011

KSCE J Civ Eng

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Self-installing mobile jack-ups platforms retain a dominate role in the exploration of offshore oil and gas in water depths up to around 120 m. However, significant challenges in assessing their stability and dynamic performance under large storm loading remain. For instance, their long slender truss-work legs and large inverted conical spudcan footings cause the natural period of the jack-up to approach the dominant frequency of ocean waves. The spudcan stiffness is also non-linear and requires a methodology to integrate it numerically within the environmental loading and structural analysis. Modern jack-ups are also increasing in size. Spacing of over 50 m between legs requires accurate evaluation of both the magnitude and timing of storm loads on each leg. To address these issues, this paper details a methodology for numerically integrating the fluid, structure and soil behaviour for large three-legged jackups. A six-degree-of-freedom strain-hardening plasticity model for integrating the load-displacement behaviour of spudcan footings into three-dimensional structural analysis is reviewed. It will be shown that non-linear behaviour of soils can be accommodated within an established theoretical framework, and as the response of the foundation is expressed in terminology consistent with structural mechanics, the models can be coupled directly to the numerical analysis of a structure. The influence of the spatial variability and directional wave spreading on jack-up response is also investigated. Example analyses of a jack-up installed in sand highlight the effect of wave direction, spreading function and foundation modeling assumption on the dynamic jack-up response.

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Section: Wave Modellingmentioning

confidence: 99%

Offshore foundation systems for resource recovery: Assessing the three-dimensional response of jack-up platforms

Cassidy

2011

KSCE J Civ Eng

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“…Smith et al [13] also quantified the level of load reduction in jack-ups using a second-order directional NewWave theory and consequently the effect of randomness again was not explicitly included. This study was extended by Smith et al [19] and Hoyle et al [20] by introducing a formula to calculate a kinematic reduction factor based on jack-up dimensions, wave characteristic and water depth and was intended to be applied in conjunction with a regular wave analysis. The formula was proposed by a parametric study conducted using a number of independent variables for five different rig classes.…”

Section: Introductionmentioning

confidence: 99%

Performance of an example jack-up platform under directional random ocean waves

Mirzadeh

Kimiaei

Cassidy

2016

Applied Ocean Research

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This article presents the results of nonlinear dynamic analyses that explore the effects of directionality and the random nature of ocean waves on the overall structural performance of a sample jack-up platform. A finiteelement model is developed which rigorously includes the effects of the material and geometrical nonlinearities in the structure and the nonlinear soil-structure interaction. Two wave theories, NewWave and Constrained NewWave, are adopted to simulate the water surface and water particle kinematics, which are implemented in the numerical model developed. Analyses are performed for both two and three-dimensional wave models, and the results are compared in terms of the deck and spudcan foundation displacements. The results obtained from the analyses indicate that the inclusion of wave spreading can result in reductions in the deck displacements of the sample jack-up platform. The level of reduction is greater when considerable plasticity occurs in the foundation. Furthermore, the probability of failure can be significantly decreased when the wave-spreading effects are included. In addition, it is shown that the effects of wave-spreading on the response and failure of the sample jack-up is increased when wave period is decreased.

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Further Work on the Effects of Nonlinear Wave Spreading and its Impact on Current Jack-up Assessment Practice

Cited by 2 publications

References 0 publications

Offshore foundation systems for resource recovery: Assessing the three-dimensional response of jack-up platforms

Offshore foundation systems for resource recovery: Assessing the three-dimensional response of jack-up platforms

Performance of an example jack-up platform under directional random ocean waves

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