Method for Predicting Geometry and Load Distribution in an Anchor Chain from a Single Point Mooring Buoy to a Buried Anchorage

Gault, John A.; Cox, William R.

doi:10.4043/2062-ms

Cited by 21 publications

(7 citation statements)

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“…The foundation load at the padeye becomes smaller than the corresponding line load at the mudline, and the loading angle at the padeye will be greater than the loading angle at the mudline. Gault and Cox (1974) observed that the soil resistance normal to the chain has little influence on the total load transferred to the padeye but has a greater influence on the direction of a line. The soil resistance results in an inverse-catenary mooring line shape of the embedded chain.…”

Section: "Seplamentioning

confidence: 97%

Design Procedures for Marine Renewable Energy Foundations

Stevens

Soosainathan

Rahim³

et al. 2015

All Days

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The Geotechnics Sub-Committee of the American Society of Civil Engineers (ASCE) Coasts, Oceans, Ports, and Rivers Institute (COPRI) Marine Renewable Energy (MRE) Committee is preparing a guide document for marine renewable energy foundations. That guide would use standard design codes for fixed foundations and mooring anchors in API RP 2GEO and DNV.The static method of computing axial pile capacity described in API RP 2GEO (2011) is generally used to compute ultimate compressive and tensile capacities of pipe piles driven to a given penetration. Lateral soil resistance -pile deflection (p-y) data for clays and sands are usually developed using procedures proposed by Matlock (1970) andMurchison (1983), respectively, and outlined in API RP 2GEO (2011). Marine energy foundations are unique in several ways. Axial pile capacity computations are usually based on a reasonable lower bound, in contrast to the soil resistance to driving, which is based on a reasonable upper bound. For structures supporting wind turbines, however, underestimating (or overestimating) the soil stiffness could require a change in turbine operation and a loss of power production. Although the classical API method is recognized as an appropriately conservative design method for offshore pile foundations, a prediction method is more well suited for structures supporting wind turbines, such as the CPT-based methods for predicting pile capacity in granular soils presented in API RP 2GEO (2011). If a prediction method is used to compute the soil resistance to driving, the evaluation of pile drivability may be overly conservative. Ageing in both clay and sand should also be taken into account. Wind turbines are often supported on large diameter monopiles. The applicability of the p-y data for such large diameter piles needs to be verified. Finally, marine renewable energy generated by in-stream hydrokinetics, ocean thermal energy conversion, and wave energy converters may be floating devices usually anchored to the seafloor. There are uncertainties in the design and installation of these anchors, which become critical for large sustained tensile loads that may degrade due to creep and cyclic loading.

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Section: "Seplamentioning

confidence: 97%

Design Procedures for Marine Renewable Energy Foundations

Stevens

Soosainathan

Rahim³

et al. 2015

All Days

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“…Behaviour of the embedded chain may be obtained by integrating the governing equilibrium from one end of the chain to the other [13,[16][17][18][19]. Here T is the tension in the chain acting over the incremental chain length ds, θ the chain angle to the horizontal, wc the submerged weight of chain per unit length, and Q and F respectively the normal and frictional soil resistances per unit length in the directions perpendicular and parallel to the chain axis.…”

Section: Appendix -Existing Design Relationshipsmentioning

confidence: 99%

Numerical investigations of the effect of strain softening on the behaviour of embedded mooring chains

Sun

Feng

Bransby

et al. 2019

Applied Ocean Research

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Mooring systems typically consist of an anchor and a mooring line and chain that connect the anchor to the floating infrastructure. When the anchor connection point (the 'padeye') is below the seabed surface, the interaction between the chain and the seabed will affect the amount of load transferred to the anchor and the load angle at the padeye. Reliable methods are needed therefore to assess these aspects in order to determine appropriate anchor design. Available solutions for the interaction between soil and chain generally ignore any reduction in the undrained shear strength of the soil as it is remoulded under the large strains associated with tensioning of the anchor chain. This is an unconservative assumption for anchor design, hence providing motivation for the study presented here. The system behaviour and the interaction of short chain segments with the seabed have been studied using a coupled Eulerian-Lagrangian (CEL) approach. The findings have led to two new design approaches that encapsulate how remoulding of the soil (which affects sliding resistance more than bearing resistance) affects the chain system response. Calculations using these methods captured the modelled chain system response well. Both the global chain analyses and the proposed design approaches suggest that approximately the entire chain load at the seabed surface (the 'mudline') is likely to be transferred to the anchor padeye, challenging conventional design practice.

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“…Previously, the only available method for predicting the resulting anchor chain profile and load development involved numerical integration of the governing differential equations, together with iteration of one of the unknown boundary conditions in order to match the known boundary conditions, This method was initially performed using small circular elements of chain, as presented by Reese (1973) and Gault & Cox (1974). Vivatrat et al (1982) simplified the method by assuming small curvi-linear chain segments.…”

Section: Introductionmentioning

confidence: 99%

Performance of Embedded Anchor Chains and Consequences for Anchor Design

Neubecker

Randolph

1995

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Mth the growth in popularity of floating systems for offshore oil production, there has been an increased focus on the design of permanent mooting systems. It is widely acknowledged that the anchor chain plays an important part in the total mooting system by developing t?ictional load and introducing an inclination of the load at the subseabed anchorage.By making a simple and valid assumption, the force equilibrium equations of the chain are simplified to produce c/osed form expressions for both the force distribution and the geometric profile of the anchor chain. This paper then shows how these equations can be applied to simpli~the design of anchor piles and drag anchors.

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Method for Predicting Geometry and Load Distribution in an Anchor Chain from a Single Point Mooring Buoy to a Buried Anchorage

Cited by 21 publications

References 0 publications

Design Procedures for Marine Renewable Energy Foundations

Design Procedures for Marine Renewable Energy Foundations

Numerical investigations of the effect of strain softening on the behaviour of embedded mooring chains

Performance of Embedded Anchor Chains and Consequences for Anchor Design

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