Analisis Kekuatan Struktur Drilling Riser Akibat Efek Squall Pada Semi-Submersible Kondisi Operasi

Zaini, Muhamad Iqbal (2023) Analisis Kekuatan Struktur Drilling Riser Akibat Efek Squall Pada Semi-Submersible Kondisi Operasi. Other thesis, Institut Teknologi Sepuluh Nopember.

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Abstract

Indonesia sebagai satu negara yang memiliki potensi minyak dan gas terbesar di dunia, kegiatan operasi selain di onshore tetapi juga offshore, semi-submersible yang terdiri dari deck, kolom, dan ponton, menjadi salah satu pilihan karena memiliki stabilitas dan mobilitas yang lebih baik dibandingkan dengan kapal. Selama proses pengeboran, dibutuhkan alat atau sistem untuk menghubungkan semi-submersible dengan seabed atau BOP. Alat yang digunakan tersebut yaitu riser. Kegiatan yang dilakukan di laut lepas pantai tidak lepas dari kondisi yang berubah-ubah, tidak menentu dan terkadang bersifat sementara. Salah satunya adalah peristiwa squall. Squall merupakan peristiwa di mana angin kencang datang secara tiba-tiba dengan durasi selama beberapa menit sampai puluhan menit, serta perubahan arah angin yang terjadi secara tiba-tiba. Pada penelitian ini, dilakukan analisis kekuatan drilling riser, tension pada riser, dan pergerakan pada semi-submersible dengan variasi squall time rise (TR) 2.5 menit, 5 menit, 7.5 menit, dan 10 menit. Dari hasil analisis, didapatkan bahwa karakter gerakan dari semi-submersible yang telah dimodelkan memiliki gerakan dengan nilai maksimal RAO tidak lebih dari 1 m amplitudo gelombang. Diketahui bila respons struktur lebih kecil dari amplitudo gelombang, maka struktur lebih stabil dalam menghadapi gelombang. Selanjutnya, analisis pengaruh variasi squall menggunakan model sintetik squall menyebabkan peningkatan pada nilai mula-mula tinggi gelombang signifikan (Hs) 2.5 m dan peak periode (Tp) 8.66s, di mana variasi squall time rise (TR) 2.5 menit menjadi nilai paling tinggi dibandingkan variasi lainnya yaitu sebesar 3m (20%) untuk Hs, 9s (8.31%) untuk Tp. Untuk mooring line tension terbesar ada pada arah 45° dan 90° sebab luasan area yang dihantam gelombang lebih besar. Selain itu, untuk pergerakan semi-submersible terbesar ada pada arah 0° dan 180°, serta nilai tension dan pergerakan terbesar didapat pada variasi squall time rise (TR) 10 menit sebab lamanya perubahan kecepatan squall membuat pergerakan dan nilai maksimum mooring line tension menjadi paling besar sesuai dengan artikel yang dibuat oleh Lu Y.(2015). Sementara itu, untuk nilai von misses stress terbesar terdapat pada arah datang gelombang 0° dan time rise (TR) 10 menit karena memiliki offset atau pergerakan yang paling jauh sehingga menghasilkan nilai stress yang lebih besar pula. ===============================================================================================================================
Indonesia, as a country with the largest potential for oil and gas in the world, conducts not only onshore but also offshore operations. Semi-submersibles, consisting of decks, columns, and pontoons, are one of the choices because they have better stability and mobility than ships. During the drilling process, equipment or systems are needed to connect the semi-submersible with the seabed or BOP. The equipment used is called a riser. Activities carried out offshore are subject to constantly changing, uncertain, and sometimes temporary conditions. One of them is the occurrence of squalls. Squalls are sudden and strong winds that last for several minutes to tens of minutes, as well as sudden changes in wind direction. In this study, an analysis of the strength of the drilling riser, riser tension, and movement of the semi-submersible was conducted with variations of squall time rise (TR) of 2.5 minutes, 5 minutes, 7.5 minutes, and 10 minutes. From the analysis, it was found that the motion characteristics of the modeled semi-submersible had a maximum RAO value of no more than 1 m wave amplitude. It is known that if the structural response is smaller than the wave amplitude, the structure is more stable in facing waves. Furthermore, the analysis of the effect of squall variations using a synthetic squall model resulted in an increase in the initial values of significant wave height (Hs) to 2.5 m and peak period (Tp) to 8.66 s, where the squall time rise (TR) variation of 2.5 minutes was the highest value compared to other variations at 3m (20%) for Hs and 9s (8.31%) for Tp. For the largest mooring line tension, it was in the direction of 45° and 90° because the area hit by waves was larger. In addition, for the largest semi-submersible movement, it was in the direction of 0° and 180°, and the largest tension and movement values were obtained with a squall time rise (TR) variation of 10 minutes because the length of the squall velocity change made the movement and maximum mooring line tension value the highest according to the article by Lu Y. (2015). Meanwhile, for the largest von Misses stress value, it was in the direction of 0° and with a time rise (TR) of 10 minutes because it had the farthest offset or movement, resulting in a larger stress value.

Item Type:	Thesis (Other)
Uncontrolled Keywords:	squall, riser, mooring line, stress
Subjects:	T Technology > TC Hydraulic engineering. Ocean engineering > TC1680 Offshore structures V Naval Science > VM Naval architecture. Shipbuilding. Marine engineering > VM161 Ships--Hydrodynamics
Divisions:	Faculty of Marine Technology (MARTECH) > Ocean Engineering > 38201-(S1) Undergraduate Thesis
Depositing User:	Muhamad Iqbal Zaini
Date Deposited:	31 Mar 2023 01:28
Last Modified:	31 Mar 2023 01:28
URI:	http://repository.its.ac.id/id/eprint/97821

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