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DEFORMATION ANALYSIS OF OFFSHORE PLATFORM USING GPS TECHNIQUE AND ITS APPLICATION IN STRUCTURAL INTEGRITY ASSESSMENT

WIDJAJANTI, NURROHMAT WIDJAJANTI (2010) DEFORMATION ANALYSIS OF OFFSHORE PLATFORM USING GPS TECHNIQUE AND ITS APPLICATION IN STRUCTURAL INTEGRITY ASSESSMENT. PhD thesis, UNIVERSITI TEKNOLOGI PETRONAS.

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Abstract

One of a major problem with offshore platform is the occurrence of deformation which can have serious and potentially fatal consequences. The implementing of a deformation monitoring system to maintain regular surveillance of the stability is a means to address both human safety and company profitability. The approach developed in this study uses a precise relative Global Positioning System (GPS) which is advantageous for deformation monitoring in terms of long-baseline data as offshore platforms are located hundreds of kilometres from shore. This research focused on customizing GPS data processing of offshore platform deformation and its implementation for structural integrity assessments. A preliminary investigation was performed on simulated GPS network to ensure tool reliability, processing method feasibility and enhanced precision of the processed data. Additionally, preventative steps were taken on the network simulation to ensure that the technique was capable of detecting any deformation. Commercial software was found to be inadequate for long-baseline processing and was substituted with GAMIT/GLOBK scientific software, capable of processing GPS data for offshore platforms. This case study refers a Jacket-type offshore platform using secondary three epochs GPS data to analyze deformation. The results of data processing revealed deformation magnitude in the form of three dimensional displacement, dx, dy and dz which was then used to assess platform’s structural integrity, focusing on four points of the main pile located on the upper deck. The structural integrity assessment identified that translation and rotation of all structural joints was influenced by any displacements of restrained joints. These translations and rotations increase almost nearly proportional to the increased displacement value. In the simulation epoch of 10 years, the greatest value displacement of North is approximately 18-26 cm, East is around 6-18 cm and Up is about 15-50 cm. These values are assumed as linear function of the displacement of two month epochs. The great effect occurs on the upper deck with the value of U1 = ±6 cm (point 67), U2 = ±30 cm (point 68), U3 = ±60 cm (point 78), R1 = ±3 radian ix (point 80), R2 = ±0.5 radian (point 67) and R3 = ±1 radian (point 84). The greatest effect arises at the translation in the direction of Z. In the seabed, the achievement value of R1 = ±5 radian (point 13), R2 = ±0.3 radian (point 14), R3 = ±0.1 radian (point 14) with no translation effect of in the directions of X, Y and Z. The occurring translations and rotations in the structural joints contribute to the stability of the platform, confirming deformation monitoring to be a viable technique in structural integrity assessment. The deformation analysis indicated coordinate differences among the three epoch observations, however, a significant test did not categorise these as a significant displacement. To conclude, a precise GPS relative positioning technique was found to be a reliable approach for offshore platform monitoring deformation, enabling precise detection to a few millimeters. This level of precision could be increased with implementation of processing and observational strategies.

Item Type: Thesis (PhD)
Subject: UNSPECIFIED
Divisions: Engineering > Civil
Depositing User: Users 5 not found.
Date Deposited: 05 Jun 2012 08:32
Last Modified: 25 Jan 2017 09:43
URI: http://utpedia.utp.edu.my/id/eprint/2840

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