Optimasi Desain Struktur Jacket Berbasis Keandalan

Hastuti, Hastuti (2023) Optimasi Desain Struktur Jacket Berbasis Keandalan. Masters thesis, Institut Teknologi Sepuluh Nopember.

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Abstract

Eksplorasi dan eksploitasi minyak dan gas di lepas pantai memerlukan infrastruktur andal, seperti anjungan lepas pantai. Tantangan utama dalam membangun anjungan ini adalah menjaga biaya rendah agar harga produksi stabil, sambil memastikan keandalan struktur dalam jangka waktu yang panjang, termasuk dalam kondisi ekstrem, untuk mencapai tujuan produksi. Oleh karena itu, keandalan dipertimbangkan selama proses optimasi sebagai bagian dari evaluasi struktural. Tesis ini bertujuan melakukan optimasi pada desain struktur jacket minimalis kaki tiga, yang merupakan jenis struktur yang masih sering digunakan dalam industri migas karena efisiensinya. Reliability-based Design Optimization (RBDO) diterapkan untuk mencapai desain yang lebih realistis. Penelitian yang telah dilakukan ini fungsi objektif optimasi adalah meminimumkan biaya struktur dengan membentuk surrogate model sebagai constrains. Variabel desain yang diperhitungkan dalam penelitian ini adalah ketebalan dan diameter luar bracing member jacket. Proses optimasi yang digunakan adalah NonLinear Optimization with Constraints dengan metode kriging surrogate model dengan menggunakan perangkat lunak MATLAB. Hasil penelitian menunjukkan bahwa hasil RBDO mengalami penurunan berat sebesar 21,69%. Variabel desain yang paling berkontribusi terhadap optimasi adalah member diagonal atas, khususnya tebal brace dengan persentase penurunan rata-rata 40%. Desain struktur jacket RBDO ini juga menunjukkan kinerja lebih baik dengan Probability of Failure (PoF) yang rendah sebesar 0,001 sehingga menunjukan indeks keandalan sebesar 3,24 yang memenuhi standar batas indeks keandalan sebesar 3,09. Hal ini menunjukan metode RBDO lebih baik dalam memberikan hasil optimsi yang mampu menurunkan atau meminimumkan berat struktur dengan tetap mempertimbangkan keandalannya.
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Exploration and exploitation of oil and gas offshore requires reliable infrastructure, such as offshore platforms. The main challenge in building these platforms is to keep costs low so that production prices are stable while ensuring the reliability of the structure over the long term, including under extreme conditions, to achieve production goals. Therefore, reliability is considered during the optimization process as part of the structural evaluation. This thesis aims to optimize the design of a minimalist three-legged jacket structure, which is still often used in the oil and gas industry because of its efficiency. Reliability-based Design Optimization (RBDO) is applied to achieve a more realistic design. In this research, the objective function of optimization is to minimize structural costs by forming a surrogate model as a constraint. The design variables considered in this research are the thickness and outer diameter of the bracing member jacket. The optimization process used is NonLinear Optimizatio Kriging Constraints with the kriging surrogate model method using MATLAB software. The research results showed that the RBDO results experienced a weight reduction of 21,69%. The design variable that most contributes to optimization is the upper diagonal member, especially the brace thickness with an average reduction percentage of 40%. This RBDO jacket structure design also shows better performance with a low Probability of Failure (PoF) of 0.001, thus showing a reliability index of 3,24 which meets the standard reliability index limit of 3,09. This shows that the RBDO method is better in providing optimization results that are able to reduce or minimize the weight of the structure while still taking into account its reliability.

Item Type:	Thesis (Masters)
Uncontrolled Keywords:	Probability of Failure, Keandalan, Optimasi desain, Nonlinear, RBDO, Struktur jacket, Probability of Failure, Reliability, Design optimization, Nonlinear, RBDO, Jacket structure
Subjects:	T Technology > TC Hydraulic engineering. Ocean engineering > TC1680 Offshore structures
Divisions:	Faculty of Marine Technology (MARTECH) > Ocean Engineering > 38101-(S2) Master Thesis
Depositing User:	Hastuti Hastuti
Date Deposited:	15 Dec 2023 08:41
Last Modified:	15 Dec 2023 08:41
URI:	http://repository.its.ac.id/id/eprint/105288

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