Studi Prediksi Umur Kelelahan Floating Storage and Offloading Akibat Initial Crack

Murdiyantono, Muhammad Falivan Ganefiansyah (2026) Studi Prediksi Umur Kelelahan Floating Storage and Offloading Akibat Initial Crack. Masters thesis, Institut Teknologi Sepuluh Nopember.

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Abstract

Struktur Floating Storage and Offloading (FSO) mengalami pembebanan siklik akibat gelombang laut yang dapat menyebabkan kelelahan struktural dan perambatan crack pada detail sambungan kritis. Analisis kelelahan konvensional berbasis kurva S–N menunjukkan bahwa sambungan side longitudinal dengan side transverse memiliki umur kelelahan global yang sangat panjang, yaitu lebih dari 100 tahun, sehingga secara global memenuhi kriteria desain. Namun, pendekatan tersebut belum merepresentasikan pengaruh initial crack dan mekanisme perambatan crack terhadap integritas struktural jangka panjang. Penelitian ini mengombinasikan analisis kelelahan berbasis spektral dan mekanika crack elastis linier untuk mengevaluasi perambatan crack dan umur kelelahan struktur FSO. Analisis hidrodinamika dilakukan dalam domain frekuensi untuk memperoleh Response Amplitude Operator (RAO) momen lentur vertikal dan gaya geser vertikal pada berbagai arah datang gelombang. Hasil analisis global di-transfer ke model lokal menggunakan pendekatan sub-modelling. Model lokal dibangun dengan elemen solid tiga dimensi dan pemodelan initial crack berbasis pre-meshed crack, sedangkan perambatan retak dianalisis menggunakan metode elemen hingga dengan SMART Crack Growth dan hukum Paris. Hasil analisis menunjukkan nilai rata-rata Stress Intensity Factor (SIF) berada pada kisaran 170.7–263.7 MPa√mm, dengan panjang crack rata-rata berkisar antara 97.4–105.3 mm untuk berbagai variasi lokasi dan kondisi multi-crack. Akibat mekanisme perambatan crack, umur kelelahan struktur menurun secara signifikan menjadi 2.99–10.82 tahun. Temuan ini menegaskan bahwa perambatan crack merupakan faktor pengendali utama kegagalan struktur dan perlu dipertimbangkan dalam evaluasi integritas dan strategi inspeksi FSO.
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Floating Storage and Offloading (FSO) structures are subjected to cyclic wave-induced loading that can lead to structural fatigue and crack propagation at critical welded joints. Conventional S–N curve–based fatigue analysis indicates that the side longitudinal–side transverse joint has a global fatigue life exceeding 100 years, satisfying design requirements. However, this approach does not adequately account for the influence of initial cracks and crack propagation mechanisms on long-term structural integrity. This study combines spectral-based fatigue analysis and linear elastic fracture mechanics to evaluate crack propagation behavior and fatigue life of an FSO structure. Hydrodynamic analysis is performed in the frequency domain to obtain Response Amplitude Operators (RAOs) of vertical bending moment and vertical shear force for various wave headings. The global response is transferred to a detailed local model using a sub-modelling approach. The local model is developed using three-dimensional solid elements with pre-meshed initial cracks, while crack propagation is simulated using the finite element method with SMART Crack Growth and Paris’ law. The results show that the average Stress Intensity Factor (SIF) ranges from 170.7 to 263.7 MPa√mm, with average crack lengths between 97.4 and 105.3 mm for different crack locations and multi-crack conditions. Due to crack propagation effects, the fatigue life is significantly reduced to 2.99–10.82 years. These findings demonstrate that crack propagation governs fatigue failure and must be considered in integrity assessment and inspection planning of FSO structures.

Item Type:	Thesis (Masters)
Uncontrolled Keywords:	FSO, Beban Gelombang, Spektral, Perambatan Crack, Umur Lelah
Subjects:	V Naval Science > VM Naval architecture. Shipbuilding. Marine engineering V Naval Science > VM Naval architecture. Shipbuilding. Marine engineering > VM156 Naval architecture
Divisions:	Faculty of Marine Technology (MARTECH) > Naval Architecture and Shipbuilding Engineering > 36101-(S2) Master Thesis
Depositing User:	Muhammad Falivan Ganefiansyah Murdiyantono
Date Deposited:	03 Feb 2026 09:49
Last Modified:	03 Feb 2026 09:49
URI:	http://repository.its.ac.id/id/eprint/131877

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