Saputra, Leonard Fernanda Dhimas (2025) Analisis Penentuan Panjang Bentang Bebas Kritis (Critical Span Length) Dengan Pendekatan Metode Analitik Dan Vortex Induced Vibration (VIV) Pada Pipa Bawah Laut. Other thesis, Institut Teknologi Sepuluh Nopember.
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Abstract
Pipa bawah laut adalah salah satu fasilitas yang berperan penting dalam proses distribusi minyak dan gas bumi di Indonesia. Pipa bawah laut merupakan infrastruktur transportasi minyak dan gas bumi jarak dekat. Salah satu tantangan dalam operasi pipa bawah laut adalah keberadaan free span, yaitu bagian pipa yang menggantung tanpa dukungan langsung di dasar laut. Ketika free span terlalu panjang, pipa bawah laut berisiko mengalami tegangan berlebih, deformasi, hingga kegagalan mekanik seperti fatigue dan vibrasi akibat interaksi dari arus laut (vortex induced vibration atau VIV). Untuk mengetahui ada tidaknya vortex induced vibration atau VIV pada pipa diperlukan satu parameter, yaitu panjang bentang kritis span (Critical Span Length). Penelitian ini bertujuan untuk menentukan panjang bentang bebas kritis dengan pendekatan metode analitik dan simulasi numerik vortex induced vibration (VIV). Metode analitik digunakan untuk mengidentifikasi parameter-parameter utama yang menentukan panjang bentang kritis pada pipa. Sementara itu, analisis VIV dilakukan untuk mengetahui apakah pipa mengalami kegagalan kelelahan akibat VIV. Studi ini memanfaatkan model teoritis menggunakan data desain untuk menghasilkan hubungan antara parameter-parameter desain, panjang bentang bebas kritis, dan pengaruh VIV tersebut terhadap kekuatan pipa. Tujuan dari tugas akhir ini adalah untuk menentukan panjang bentang bebas kritis maksimumnnya yang didapatkan sebesar 21.9 m. Hasil nilai frekuensi natural untuk parameter screening untuk arah inline dan crossflow didapatkan masing – masing sebesar 0.31 hz dan 0.36 hz. Hasil screening criteria berdasarkan DNV RP F105 menunjukkan bahwa pipa dengan panjang bentang kritis 21.9 m lolos terhadap screening criteria DNV RP F015. Hasil tegangan equivalent dari perhitungan manual didapatkan hasil sebesar 209.35 MPa dan hasil tegangan equivalent dari pemodelan software ANSYS didapatkan hasil sebesar 289.94 MPa. Hasil dari kedua tegangan equivalent tersebut memenuhi rasio tegangan terhadap kriteria allowable stress ASME B31.4.
Kata kunci : Panjang Bentang Bebas Kritis, Vortex Induced Vibration (VIV), Metode Analitik, Frekuensi Natural, Screening Criteria, Tegangan Equivalent.
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Subsea pipelines are one of the key facilities in the distribution of oil and natural gas in Indonesia. Subsea pipelines serve as the transportation infrastructure for short-distance oil and natural gas distribution. One of the challenges in subsea pipeline operations is the presence of free spans, which are sections of pipeline suspended without direct support on the seabed. When the free span is too long, the subsea pipeline risks experiencing excessive stress, deformation, and mechanical failures such as fatigue and vibration caused by interaction with ocean currents (vortex-induced vibration or VIV). To determine the presence of vortex-induced vibration or VIV in the pipeline, one parameter is required: the critical span length. This study aims to determine the critical free span length using an analytical approach and numerical simulation of vortex-induced vibration (VIV). The analytical method is used to identify the main parameters that determine the critical span length of the pipeline. Meanwhile, VIV analysis is conducted to determine whether the pipeline experiences fatigue failure due to VIV. This study utilizes a theoretical model using design data to generate relationships between design parameters, critical free span length, and the effect of VIV on pipe strength. The objective of this final project is to determine the maximum critical free span length, which was obtained to be 21.9 m. The natural frequency values for the screening parameters in the inline and crossflow directions were obtained as 0.31 Hz and 0.36 Hz, respectively. The screening criteria results based on DNV RP F105 indicate that the pipe with a critical span length of 21.9 m meets the DNV RP F015 screening criteria. The equivalent stress results from manual calculations were 209.35 MPa, and the equivalent stress results from ANSYS software modeling were 289.94 MPa. Both equivalent stress results meet the stress ratio criteria for allowable stress per ASME B31.4.
Keyword : Critical Span Length, Vortex Induced Vibration (VIV), Analytical Method, Natural Frequency, Screening Criteria, Equivalent Stress.
| Item Type: | Thesis (Other) |
|---|---|
| Uncontrolled Keywords: | Panjang Bentang Bebas Kritis, Vortex Induced Vibration (VIV), Metode Analitik, Frekuensi Natural, Screening Criteria, Tegangan Equivalent. Critical Span Length, Vortex Induced Vibration (VIV), Analytical Method, Natural Frequency, Screening Criteria, Equivalent Stress. |
| Subjects: | T Technology > TJ Mechanical engineering and machinery > TJ930 Pipelines (General). Underwater pipelines. |
| Divisions: | Faculty of Marine Technology (MARTECH) > Offshore Engineering > 54040-(S1) Undergraduate Thesis |
| Depositing User: | Leonard Fernanda Dhimas Saputra |
| Date Deposited: | 30 Jul 2025 09:59 |
| Last Modified: | 30 Jul 2025 09:59 |
| URI: | http://repository.its.ac.id/id/eprint/123880 |
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