Selection of appropriate numerical models for modelling the stresses in mooring chains

Mooring chains are key components for floating platforms. The failure of these components can be catastrophic in terms of the economic and environmental impacts, especially when dealing with the potential failure of FPSOs. However, mooring failures have been regularly occurring much earlier in their service lives than expected, with almost 50% of the reported failures happening in the first 3 years of 20-year design lives. Although the operating stresses play a major role in determining the failure mechanisms of mooring chains, the methods of predicting the operating stresses in mooring chains vary in the openly available literature, and the accuracy of these different numerical methods for predicting types of mooring failures is unknown. There is currently little evidence provided for when one model is appropriate for a particular scenario. Therefore, this paper benchmarks the different available methods for modelling mooring chains under tension, including FE models found in the literature. These models are calibrated and verified against previous studies and compared with experiments and a developed FE explicit model. There is a significant difference in the way that the numerical models behave, which are discussed in terms of their applicability and limitations in modelling mooring chains. The results of this study show that the explicit modelling approach should be utilised for accurate assessment of mooring lines, as it provides the most realistic response, with a substantial reduction in the computational cost and without any convergence problems.

Benchmarking, Contact stresses, Finite element method (FEM), Mooring line failures

10.1016/j.marstruc.2020.102864

0951-8339

Gemilang, Gilang Muhammad

8bf58690-0ac6-4dfb-9772-e90dbb33befb

Reed, Philippa

8b79d87f-3288-4167-bcfc-c1de4b93ce17

Sobey, Adam

e850606f-aa79-4c99-8682-2cfffda3cd28

January 2021

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) Selection of appropriate numerical models for modelling the stresses in mooring chains. Marine Structures, 75, [102864]. (doi:10.1016/j.marstruc.2020.102864).

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Abstract

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Manuscript of MASTR-D-20-00115R1 - Accepted Manuscript

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Accepted/In Press date: 8 September 2020

e-pub ahead of print date: 29 September 2020

Published date: January 2021

Additional Information: Funding Information: A number of parametric studies are performed to allow a comparison of the numerical models for different failure modes. Table 8 is compiled to show when a numerical model is appropriate, where a circle indicates the results are within 10% of the explicit model (CEx8R) in predicting important parameters for that particular failure analyses and a cross indicates they are not. Here the explicit model is deemed appropriate based on the match to the available experimental data. Zarandi and Skallerud [47] measure the residual stresses in a mooring chain experimentally, which shows good agreement with a prediction from an FE model employing the implicit reduced eight-order model (C8R), supporting the fact that the FE models with contact interaction (C20R, C8R, C8I, CEx8R) are good for the residual stress prediction.The authors gratefully acknowledge the funding by the Indonesia Endowment Fund for Education (LPDP) and the support of the Lloyd's Register Foundation (LRF). The authors also acknowledge the support of the University of Southampton for access to its IRIDIS5 High-Performance Computing Facility. Funding Information: The authors gratefully acknowledge the funding by the Indonesia Endowment Fund for Education ( LPDP ) and the support of the Lloyd's Register Foundation ( LRF ). The authors also acknowledge the support of the University of Southampton for access to its IRIDIS5 High-Performance Computing Facility. Publisher Copyright: © 2020 Elsevier Ltd

Keywords: Benchmarking, Contact stresses, Finite element method (FEM), Mooring line failures