Mooring system reliability in tropical cyclone and North Sea winter storm environments
Mooring system reliability in tropical cyclone and North Sea winter storm environments
The characteristics of waves, winds and currents in a tropical cyclone environment differ significantly from those in a winter storm environment, like the North Sea. This can have a significant effect on the reliability of a mooring system that is designed to satisfy 100 yr conditions with specified Factors of Safety in accordance with ISO19901-7 or API RP 2SK. This paper presents reliability analysis of the mooring system of a permanently connected Floating LNG vessel, placed at two locations: (a)a tropical cyclone environment of the North West Shelf of Australia and (b)a winter storm environment of the North Sea. It is demonstrated that as a result of differences in the long term distribution of environmental parameters (waves, winds)between a North Sea environment and a tropical cyclone environment, the long term distribution of the mooring line response differs significantly in these two locations. This paper shows that a mooring system which is designed in accordance with ISO (or API), in these two environments, will achieve very different reliability levels because of the significant differences in environmental characteristics. In order to achieve the same reliability for the mooring system at these two geographical locations, Factors of Safety for use with 100 yr environmental conditions (Ultimate Limit State)were derived to achieve the same target probability of failure of 10
−4
/annum. It was found that for the North Sea environment, a factor of 1.5 is required for both the mooring chain and the pile, while for the tropical cyclone environment the required Factor of Safety has to be increased to 2.1. These differences are very significant and design standards need to be revised to reflect these findings.
Cyclonic environment, Factors of safety, Mooring lines, Piles, Reliability, Winter storm
306-316
Stanisic, Dunja
cd348460-7097-49e3-9f5d-765354e4eb53
Efthymiou, Mike
acaa9a55-c6d9-41b5-a01d-0b7cb4ed40c6
White, David J.
a986033d-d26d-4419-a3f3-20dc54efce93
Kimiaei, Mehrdad
8324495a-122a-43d8-a8d0-d38182a39104
July 2019
Stanisic, Dunja
cd348460-7097-49e3-9f5d-765354e4eb53
Efthymiou, Mike
acaa9a55-c6d9-41b5-a01d-0b7cb4ed40c6
White, David J.
a986033d-d26d-4419-a3f3-20dc54efce93
Kimiaei, Mehrdad
8324495a-122a-43d8-a8d0-d38182a39104
Stanisic, Dunja, Efthymiou, Mike, White, David J. and Kimiaei, Mehrdad
(2019)
Mooring system reliability in tropical cyclone and North Sea winter storm environments.
Applied Ocean Research, 88, .
(doi:10.1016/j.apor.2019.05.004).
Abstract
The characteristics of waves, winds and currents in a tropical cyclone environment differ significantly from those in a winter storm environment, like the North Sea. This can have a significant effect on the reliability of a mooring system that is designed to satisfy 100 yr conditions with specified Factors of Safety in accordance with ISO19901-7 or API RP 2SK. This paper presents reliability analysis of the mooring system of a permanently connected Floating LNG vessel, placed at two locations: (a)a tropical cyclone environment of the North West Shelf of Australia and (b)a winter storm environment of the North Sea. It is demonstrated that as a result of differences in the long term distribution of environmental parameters (waves, winds)between a North Sea environment and a tropical cyclone environment, the long term distribution of the mooring line response differs significantly in these two locations. This paper shows that a mooring system which is designed in accordance with ISO (or API), in these two environments, will achieve very different reliability levels because of the significant differences in environmental characteristics. In order to achieve the same reliability for the mooring system at these two geographical locations, Factors of Safety for use with 100 yr environmental conditions (Ultimate Limit State)were derived to achieve the same target probability of failure of 10
−4
/annum. It was found that for the North Sea environment, a factor of 1.5 is required for both the mooring chain and the pile, while for the tropical cyclone environment the required Factor of Safety has to be increased to 2.1. These differences are very significant and design standards need to be revised to reflect these findings.
Text
Stanisic et al. 2019 AM
- Accepted Manuscript
More information
Accepted/In Press date: 6 May 2019
e-pub ahead of print date: 15 May 2019
Published date: July 2019
Keywords:
Cyclonic environment, Factors of safety, Mooring lines, Piles, Reliability, Winter storm
Identifiers
Local EPrints ID: 431930
URI: http://eprints.soton.ac.uk/id/eprint/431930
ISSN: 0141-1187
PURE UUID: c51077fd-9778-421a-b3f7-74737d922f73
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Date deposited: 21 Jun 2019 16:30
Last modified: 18 Mar 2024 05:23
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Contributors
Author:
Dunja Stanisic
Author:
Mike Efthymiou
Author:
Mehrdad Kimiaei
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