Modified reliability reassessment of fixed offshore structures for Malaysian water

Fixed offshore platform structures are subjected to external loadings such as gravity loads, environmental loads, hydrodynamic loads and accidental loads. The structures continuously undergo modifications and upgrading in order to meet safety and production demands or due to structural damage on cri...

Full description

Saved in:

Bibliographic Details
Main Author:	Henry, Zulkipli
Format:	Thesis
Language:	English
Published:	2018
Subjects:	TJ Mechanical engineering and machinery
Online Access:	http://eprints.utm.my/id/eprint/87199/1/ZulkipliHenryPSKM2018.pdf
Tags:	Add Tag No Tags, Be the first to tag this record!

id	my-utm-ep.87199
record_format	uketd_dc
spelling	my-utm-ep.871992020-11-30T09:00:44Z Modified reliability reassessment of fixed offshore structures for Malaysian water 2018 Henry, Zulkipli TJ Mechanical engineering and machinery Fixed offshore platform structures are subjected to external loadings such as gravity loads, environmental loads, hydrodynamic loads and accidental loads. The structures continuously undergo modifications and upgrading in order to meet safety and production demands or due to structural damage on critical components. The aim of this research is to propose an improved Structural Reliability Assessment (SRA) methodology for fixed offshore platforms in Malaysian waters by including the effect of wave-in-deck and to quantify the impact of key design parameters on overall platform structural response. Case studies on the sensitivity of marine growth profile, current blockage factor, drag and inertia coefficients on overall structural loading are performed to quantify the overall impact of these key parameters. The platform reliability based on proposed improved method is compared against an existing method, the Simplified Structural Reliability Assessment (SSRA). For the case and sensitivity studies, the examples of existing fixed offshore jacket structures in Malaysian water region are used. In structural integrity assessment of existing platforms, structural utilization factor is used to measure the level of stress on structural members and foundation. The study on structural integrity assessment shows that the drag coefficient and current blockage factor have significant impact on the overall loading of jacket structures in Malaysian waters as compared to marine growth profile and inertia coefficient. The sensitivity study on drag coefficient quantifies the percentage increases on base shear for operating and storm conditions, ranging from 17% to 72% and 18% to 70% respectively. The current blockage factor sensitivity study for operating and storm conditions shows the base shear increase from 10% to 16% and 6% to 9% respectively. The existing platforms may not be able to meet today’s integrity requirement without performing costly strengthening. Therefore, a modified SRA method is proposed to demonstrate the fit-for-purpose of the platforms based on As Low As Reasonably Practical (ALARP) concept which has been proven to be a cost effective solution to non-compliant existing and ageing platforms. The advantage of the method is its ability to estimate the magnitude of wave height that causes platform failure and takes into consideration the wave-in-deck in the calculation of platform Reserve Strength Ratio (RSR). The study demonstrates that including additional loading contribution from wave-in-deck in the RSR calculation is more practical, realistic and accurate. The case study demonstrates the platform RSR decreases from 4.13 to 3.40 which is equivalent to 17% reduction. In the final phase, this study proposes a unique parameter Alpha, (??) which is used to calculate the wave height that causes platforms to collapse. The ?? depends on platform geometrical configuration. The sensitivity study concludes the values of a for fixed offshore structures at Malaysian water ranging from.1.5 to 2.5. 2018 Thesis http://eprints.utm.my/id/eprint/87199/ http://eprints.utm.my/id/eprint/87199/1/ZulkipliHenryPSKM2018.pdf application/pdf en public http://dms.library.utm.my:8080/vital/access/manager/Repository/vital:134248 phd doctoral Universiti Teknologi Malaysia, Faculty of Mechanical Engineering Faculty of Mechanical Engineering
institution	Universiti Teknologi Malaysia
collection	UTM Institutional Repository
language	English
topic	TJ Mechanical engineering and machinery
spellingShingle	TJ Mechanical engineering and machinery Henry, Zulkipli Modified reliability reassessment of fixed offshore structures for Malaysian water
description	Fixed offshore platform structures are subjected to external loadings such as gravity loads, environmental loads, hydrodynamic loads and accidental loads. The structures continuously undergo modifications and upgrading in order to meet safety and production demands or due to structural damage on critical components. The aim of this research is to propose an improved Structural Reliability Assessment (SRA) methodology for fixed offshore platforms in Malaysian waters by including the effect of wave-in-deck and to quantify the impact of key design parameters on overall platform structural response. Case studies on the sensitivity of marine growth profile, current blockage factor, drag and inertia coefficients on overall structural loading are performed to quantify the overall impact of these key parameters. The platform reliability based on proposed improved method is compared against an existing method, the Simplified Structural Reliability Assessment (SSRA). For the case and sensitivity studies, the examples of existing fixed offshore jacket structures in Malaysian water region are used. In structural integrity assessment of existing platforms, structural utilization factor is used to measure the level of stress on structural members and foundation. The study on structural integrity assessment shows that the drag coefficient and current blockage factor have significant impact on the overall loading of jacket structures in Malaysian waters as compared to marine growth profile and inertia coefficient. The sensitivity study on drag coefficient quantifies the percentage increases on base shear for operating and storm conditions, ranging from 17% to 72% and 18% to 70% respectively. The current blockage factor sensitivity study for operating and storm conditions shows the base shear increase from 10% to 16% and 6% to 9% respectively. The existing platforms may not be able to meet today’s integrity requirement without performing costly strengthening. Therefore, a modified SRA method is proposed to demonstrate the fit-for-purpose of the platforms based on As Low As Reasonably Practical (ALARP) concept which has been proven to be a cost effective solution to non-compliant existing and ageing platforms. The advantage of the method is its ability to estimate the magnitude of wave height that causes platform failure and takes into consideration the wave-in-deck in the calculation of platform Reserve Strength Ratio (RSR). The study demonstrates that including additional loading contribution from wave-in-deck in the RSR calculation is more practical, realistic and accurate. The case study demonstrates the platform RSR decreases from 4.13 to 3.40 which is equivalent to 17% reduction. In the final phase, this study proposes a unique parameter Alpha, (??) which is used to calculate the wave height that causes platforms to collapse. The ?? depends on platform geometrical configuration. The sensitivity study concludes the values of a for fixed offshore structures at Malaysian water ranging from.1.5 to 2.5.
format	Thesis
qualification_name	Doctor of Philosophy (PhD.)
qualification_level	Doctorate
author	Henry, Zulkipli
author_facet	Henry, Zulkipli
author_sort	Henry, Zulkipli
title	Modified reliability reassessment of fixed offshore structures for Malaysian water
title_short	Modified reliability reassessment of fixed offshore structures for Malaysian water
title_full	Modified reliability reassessment of fixed offshore structures for Malaysian water
title_fullStr	Modified reliability reassessment of fixed offshore structures for Malaysian water
title_full_unstemmed	Modified reliability reassessment of fixed offshore structures for Malaysian water
title_sort	modified reliability reassessment of fixed offshore structures for malaysian water
granting_institution	Universiti Teknologi Malaysia, Faculty of Mechanical Engineering
granting_department	Faculty of Mechanical Engineering
publishDate	2018
url	http://eprints.utm.my/id/eprint/87199/1/ZulkipliHenryPSKM2018.pdf
_version_	1747818536515928064

Modified reliability reassessment of fixed offshore structures for Malaysian water

Similar Items