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Low-cycle fatigue assessment of offshore mooring chains under service loading

Low-cycle fatigue assessment of offshore mooring chains under service loading
Low-cycle fatigue assessment of offshore mooring chains under service loading
The integrity of mooring chains is essential to the safety of a range of offshore platforms. However, mooring line failures are occurring earlier than their design lives, with a high number of these failures occurring due to fatigue. Early in the fatigue life of the component fatigue initiation processes occur, where the fatigue hotspot is sensitive to the mean load and there is plastic strain accumulation from the multiaxial stress-strain responses of the material, leading to cyclic plastic damage accumulation. The traditional SN approach suggested by mooring
standards does not consider these effects, and it is proposed that this lack of consideration under low-cycle fatigue conditions is the reason for the current non-conservative fatigue assessments of mooring chains. This paper aims to develop a fatigue approach based on a critical plane multiaxial fatigue criterion for mooring chains that can consider the damage-induced by the cyclic plasticity and the mean load effect, to investigate the importance of incorporating low-cycle fatigue into the mooring chain life prediction. To develop the critical
plane approach, the multiaxial stress-strain states are extracted for the critical plane at the fatigue hotspot from a finite element model of a mooring chain. This is then correlated with a fatigue life prediction provided by conventional fatigue design data. It uses a simulation of an FPSO as a case study to demonstrate the importance of low cycle fatigue, which shows that the mean load effect is significant in reducing the fatigue life for mooring chain applications, while the effect of fatigue damage-induced cyclic plasticity is limited. The fatigue damage
accumulation predicted by the critical plane approach is significantly higher than that of the traditional SN approach and should be accounted for in mooring line design.
0951-8339
Gemilang, Gilang Muhammad
8bf58690-0ac6-4dfb-9772-e90dbb33befb
Reed, Philippa
8b79d87f-3288-4167-bcfc-c1de4b93ce17
Sobey, Adam
e850606f-aa79-4c99-8682-2cfffda3cd28
Gemilang, Gilang Muhammad
8bf58690-0ac6-4dfb-9772-e90dbb33befb
Reed, Philippa
8b79d87f-3288-4167-bcfc-c1de4b93ce17
Sobey, Adam
e850606f-aa79-4c99-8682-2cfffda3cd28

Gemilang, Gilang Muhammad, Reed, Philippa and Sobey, Adam (2021) Low-cycle fatigue assessment of offshore mooring chains under service loading. Marine Structures, 76, [102892]. (doi:10.1016/j.marstruc.2020.102892).

Record type: Article

Abstract

The integrity of mooring chains is essential to the safety of a range of offshore platforms. However, mooring line failures are occurring earlier than their design lives, with a high number of these failures occurring due to fatigue. Early in the fatigue life of the component fatigue initiation processes occur, where the fatigue hotspot is sensitive to the mean load and there is plastic strain accumulation from the multiaxial stress-strain responses of the material, leading to cyclic plastic damage accumulation. The traditional SN approach suggested by mooring
standards does not consider these effects, and it is proposed that this lack of consideration under low-cycle fatigue conditions is the reason for the current non-conservative fatigue assessments of mooring chains. This paper aims to develop a fatigue approach based on a critical plane multiaxial fatigue criterion for mooring chains that can consider the damage-induced by the cyclic plasticity and the mean load effect, to investigate the importance of incorporating low-cycle fatigue into the mooring chain life prediction. To develop the critical
plane approach, the multiaxial stress-strain states are extracted for the critical plane at the fatigue hotspot from a finite element model of a mooring chain. This is then correlated with a fatigue life prediction provided by conventional fatigue design data. It uses a simulation of an FPSO as a case study to demonstrate the importance of low cycle fatigue, which shows that the mean load effect is significant in reducing the fatigue life for mooring chain applications, while the effect of fatigue damage-induced cyclic plasticity is limited. The fatigue damage
accumulation predicted by the critical plane approach is significantly higher than that of the traditional SN approach and should be accounted for in mooring line design.

Text
Low-cycle Fatigue Assessment of Offshore Mooring Chains Under Service Loading - Accepted Manuscript
Restricted to Repository staff only until 25 November 2021.
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More information

Accepted/In Press date: 4 November 2020
e-pub ahead of print date: 25 November 2020
Published date: March 2021

Identifiers

Local EPrints ID: 445977
URI: http://eprints.soton.ac.uk/id/eprint/445977
ISSN: 0951-8339
PURE UUID: 11fa961d-a723-4be5-8f88-7e4aec0c1b41
ORCID for Gilang Muhammad Gemilang: ORCID iD orcid.org/0000-0001-9641-9495
ORCID for Philippa Reed: ORCID iD orcid.org/0000-0002-2258-0347
ORCID for Adam Sobey: ORCID iD orcid.org/0000-0001-6880-8338

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Date deposited: 18 Jan 2021 17:30
Last modified: 18 Feb 2021 17:30

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