Seabed stiffness model for steel catenary risers

Aubeny, Charles; White, Timothy; Langford, Thomas; Meyer, VM; Clukey, Edward C.

doi:10.1201/b18442-36

Cited by 15 publications

(3 citation statements)

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“…During the first 100 cycles the unloading stiffness falls, mirroring the secant penetration stiffness and reflecting the remoulding process. The trends shown by this data reflect the short-term model tests results presented by Aubeny et al (2015), as well as the calculation model they present. However, in later cycles the unloading stiffness rises, reflecting the reconsolidation process.…”

supporting

confidence: 83%

“…A limited range of experimental studies have been used to validate these models, through short term cyclic loading (Bridge et al, 2004;Aubeny et al, 2008). Recent work has focussed on calibrating the reduction in stiffness caused by remoulding in the first few tens of movement cycles (Aubeny et al, 2015). In addition, threedimensional simulations of a catenary riser touchdown zone have been performed at various scales, yielding bending moment profiles through the TDZ (Bridge and Willis, 2002;Hodder and Byrne, 2010;Elliot et al, 2014;Wang et al, 2014) Current prediction models for riser-seabed interaction do not explicitly incorporate the strength properties of the seabed soil to quantify the resistance to cyclic motion of the riser.…”

Section: Introductionmentioning

confidence: 99%

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The evolution of seabed stiffness during cyclic movement in a riser touchdown zone on soft clay

2017

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Steel catenary risers are pipelines that convey fluids from the seabed to floating structures. The stiffness of the pipe-seabed response, which is the ratio between soil resistance and pipe embedment, in the touchdown zone strongly affects the fatigue accumulation rate, so is an important design parameter. This paper reports a centrifuge modelling study into the longterm pipe-seabed interaction forces on soft clay seabeds, with tests representing many months of behaviour at prototype scale. The results show that the penetration and extraction resistance during large amplitude cycles degrades during the initial few tens of cycles, in the same way that cyclic penetrometer tests capture the fall in soil strength from the intact to the remoulded state. Calculations using bearing capacity factors for a cylinder provide good predictions of this response, although if the cycles of movement involve the pipe breaking away from the soil then the resistance reduces by more than the ratio of intact to remoulded strength, and this is attributed to entrainment of water in the soil around the pipe. However, with further cycles, as pore pressure dissipation occurs, the seabed stiffness recovers due to the gain in soil strength from consolidation. Eventually, the remoulding and water entrainment effects are wholly erased, and the stiffness exceeds the initial state. These observations suggest that current design practice-which factors down the soil stiffness to represent the influence of the cyclic degradation and remoulding process-may overlook a significant effect that raises the seabed stiffness, and potentially also reduces the fatigue life. The evolution of seabed stiffness during Yuan, White & O'Loughlin cyclic movement in a riser touchdown zone

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confidence: 83%

Section: Introductionmentioning

confidence: 99%

The evolution of seabed stiffness during cyclic movement in a riser touchdown zone on soft clay

2017

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“…The strength of the soft soil is degraded compared to a virgin seabed that has not been penetrated. Although some authors indicate that the loosed soil, if left for a long period, can reconsolidate and regain appreciable strength (Hodder et al 2009, Yuan et al 2017, other authors suggested that the strength regained is significantly less than that before the seabed was penetrated (Aubeny et al 2015, Clukey et al 2008). However, the degradation of the seabed strength in stiffness and suction is captured by the RQ model (Randolph and Quiggin 2009).…”

Section: Pre-trench Resistance and Scr Tdz Bending Momentsmentioning

confidence: 99%

Simulation stage-based seabed pre-trenching technique for steel catenary riser touchdown fatigue analysis

Ogbeifun

Oterkus

Race

et al. 2022

Ships and Offshore Structures

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The development of seabed trench by the steel catenary riser (SCR) touch down zone (TDZ) in its early life can be caused by installation loads, direct hydrodynamic loads and vessel first and second-order motion imposed on the SCR during and after its installation. Several studies have been conducted to investigate the SCR TDZ fatigue response as the excited SCR TDZ progressively trench itself into the seabed, while other studies have investigated the impact of existing trench or pre-trench on the SCR fatigue response. However, most of these investigations were conducted using a series of regular wave loads through quasi-static simulations. Also, though important information on the trench effect on SCR TDZ fatigue response is known in the research domain, little has been said about how to incorporate them in the actual riser design process. This paper (part 1) presents a numerical technique by which pre-trench can be initiated for fatigue response calculations during SCR detailed design analysis. Examples are presented to demonstrate the new approach and how the SCR fatigue response can be calculated in the presence of the created pre-trench. The SCR (after the pre-trenching process) is allowed to respond to the vessel first order six degrees of freedom motions about its nominal position in the presence of the created pre-trench. As demonstrated in this paper, the pre-trenching technique makes it possible to conduct a full time-domain, irregular wave simulations of the SCR in the presence of a pre-trench created using the hysteretic non-linear pipe soil interaction model.

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Pipeline Soil Interactions

Wang

Guo

2022

Encyclopedia of Ocean Engineering

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Seabed stiffness model for steel catenary risers

Cited by 15 publications

References 0 publications

The evolution of seabed stiffness during cyclic movement in a riser touchdown zone on soft clay

The evolution of seabed stiffness during cyclic movement in a riser touchdown zone on soft clay

Simulation stage-based seabed pre-trenching technique for steel catenary riser touchdown fatigue analysis

Pipeline Soil Interactions

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