28 research outputs found
PERKIRAAN UMUR KELELAHAN KONSTRUKSI LAMBUNG FSO DENGAN METODE SPECTRAL-BASED FATIGUE ANALYSIS
Get PDFMakalah ini menyampaikan studi mengenai perkiraan umur kelelahan dari konstruksi lambung FSO Arco Ardjuna yang beroperasi di perairan Laut Jawa Barat. Metode full spectral dan pendekatan tegangan hotspot diterapkan dalam studi ini. Sebagai tahapan awal, studi dilakukan melalui analisa beban gelombang dengan bantuan piranti lunak hidrodinamika, untuk memperoleh besaran respon struktur global (gaya geser vertikal dan momen lengkung vertikal). Respon struktur global ini merupakan input utama dalam analisa struktur global elemen hingga untuk memperoleh RAO tegangan setiap lokasi kritis. Analisa spektra kemudian dilakukan dan menghasilkan parameter-parameter stokastik yang digunakan untuk mengidentifikasi tegangan yang terjadi pada kondisi gelombang laut riil yang bersifat acak. Prosedur analisa kurun waktu pendek (distribusi Rayleigh) dan kurun waktu panjang (distribusi Weibull) dilakukan untuk mengetahui distribusi tegangan serta memperoleh rentang tegangan ekstrem terbesar selama masa operasional FSO. Teori komulatif Palmgren-Miner digunakan untuk menghitung indeks kelelahan yang berkorelasi langsung dengan umur kelelahannya. Persamaan kelelahan terangkai, dengan parameter bentuk dari distribusi Weibull, digunakan untuk memperkirakan umur kelelahan pada lokasi struktur kritis lainnya pada FSO. Dari hasil studi, diperoleh nilai tegangan ekstrem terbesar sebesar 62.29 MPa pada sambungan antara struktur memanjang LS-30 dan struktur melintang Frame No.20. Pada lokasi yang sama umur kelelahan minimal terjadi, yaitu sebesar 71.02 tahun
Analysis of the Effect of Welding Sequence Variations on Residual Stresses and Distortions for Welding Pressure Vessels Structures at PT. Petrokimia Gresik using the Finite Element Method
Get PDFThe development of oil and gas industry technology has been very advanced, one of the implementation is to connect material materials to support oil and gas industry facilities. Residual stress may occur due to high temperature differences due to welding and also uneven heat distribution. This causes the material to become hard but brittle so that it may cause structural failure in the connection area. In this final project will be simulated welding pressure vessels to determine the structure of residual stresses that occur as well as the influence of Post Weld Heat Treatment on residual stress itself. The material used is aluminum and WPS data coming from the fabrication company. The simulation is divided into 2 steps: thermal and structural analysis. The value of the residual voltage of 1 to pathline pathline 3 is 189 MPa, 124.8 MPa, 100.76 MPa with distortion value of 40.43 mm. Then analyzed Post Weld Heat Treatment referring to AWS D1.1: 2000 to reduce residual stresses that occur. From the results of the Post Weld Heat Treatment value of the residual stress can be reduced significantly. After being treated Post Weld Heat Treatment with variations of temperatures of 200 C, 300 C The maximum residual voltage reduction occurs in pathline 1 to pathline 3 at 125 MPa, 93 MPa, 100 MPa
Analisis Kekuatan Konstruksi Crane Pedestal Pada Mooring Storage Tanker Niria
Get PDFPada penelitian ini akan membahas kekuatan konstruksi crane pedestal akibat konversi Motor Tanker menjadi Mooring Storage Tanker (MST). MST ini tentunya memiliki karakteristik operasional yang berbeda dengan Motor Tanker. MST bersifat tetap, tentunya kapal harus memenuhi beberapa karakteristik tertentu dan cukup kuat untuk menahan beban operasional tambahan saat menjadi Mooring Storage Tanker di perairan Natuna. Dalam penelitian ini akan ditinjau kekuatan dari konstruksi crane pedestal sebagai penambahan fasilitas yang didesain sedemikian rupa sehingga memenuhi aturan yang ditetapkan Lloyd’s Register. Karakteristik kapal dapat kita lihat dengan RAO dimana motion yang paling dominan adalah gerakan heaving dan pitching.Trend RAO mengalami kondisi puncak pada kondisi heaving pada arah datang gelombang head sea (180º) dengan encountering frekuensi sebesar 0.088 rad/sec dan besar simpangan RAO 0.9913. Sedang pada kondisi pitching diperoleh trend RAO dengan kondisi puncak pada arah datang gelombang head sea (180º) pada encountering frekuensi sebesar 0.442 rad/sec dan besar simpangan RAO 0.896. Hasil perhitungan longitudinal bending momen terbesar pada arah pembebanan 180° sebesar 113.095.780,8 ton.m dan shear force sebesar 515.841,91 ton .Hasil analisis dengan FEM untuk crane pedestal menunjukkan besar tegangan maksimum ( von misses stress ) sebesar 192 N/mm2 dari arah pembebanan head sea (180°). Tegangan ijin mengacu pada Lloyd’s Register (Section 8) sebesar 216 N/mm2 sehingga konstruksi crane pedestal masih dalam batas aman
Analisa Pemasangan Loop Ekspansi Akibat Terjadinya Upheaval Buckling pada Onshore Pipeline
Get PDFPada pipa yang dipendam didalam tanah sering terjadi kegagalan deformasi. Kegagalan deformasi global yang menyebabkan pipa menekuk vertikal ke atas yang disebut sebagai upheaval buckling. Lengkungan awal pada pipa penyalur yang terpasang bisa terjadi akibat kombinasi dari kenaikan temperatur saat operasional dan gaya friksi tanah akan menghasilkan gaya tekan aksial efektif pada pipa. Salah satu cara yang akan dibahas pada penelitian ini jika terjadi upheaval buckling adalah pemasangan loop ekspansi pada daerah yang mengalami upheaval buckling. Loop ekspansi akan divariasikan dengan 2 tipe yaitu tipe loop horizontal dan tipe loop vertical. Pada penelitian ini terlebih dahulu pipa dimodelkan dengan panjang pipa tertentu kemudian ujung-ujungnya diberi tumpuan sehingga didapatkan besar tegangan longitudinal sebesar 41366,563 Psi. Tegangan tersebut melebihi tegangan ijin sehingga pipa mengalami ekspansi termal atau elongasi yang membentuk lengkungan keatas dengan tinggi 0.259 meter. Maka dilakukan pemodelan loop ekspansi untuk meredam elongasi tersebut dengan panjang loop 5.3 meter. Kedua loop tersebut mampu meredam tegangan aksial menjadi 3662 Psi untuk tipe loop horizontal dan 3670 Psi untuk tipe loop vertikal. Dari kedua tipe loop tersebut kemudian juga dilakukan perbandingan besar tegangan yang terjadi pada bagian elbow. Maka didapatkan bahwa tipe loop horizontal mengalami tegangan relatif lebih kecil dari pada tipe loop vertikal sehingga sebagai bahan rekomendasi maka pemasangan loop horizontal lebih diutamakan.</p
Failure mechanisms of suction caisson foundations in clay under vertical and inclined pullout loads
No full textA suction caisson typically consists of a hollow cylinder or a cluster of cylinders made of steel or concrete with a closed top. This novel foundation consists of massive cells, typically 10 to 30 meters in diameter and up to 40 to 50 meters deep. The caissons will form a tight seal with the soft submarine sediments, and provide the necessary uplift resistance, when pressure reduction is created below the closed top. In this study, finite element method was used to investigate the development of suction force, based on D'Arcy's law, by implementing some user subroutines provided in ABAQUS. Contact between suction caisson and soil surface was simulated using a contact surface model. Soil material was modelled as a porous medium and its plastic behaviour was characterized using a modified camclay model. -- The study to validate the results of the above numerical analysis used four laboratory tests carried out in different locations, for different purposes and with different set-ups. The test data used are the Massachusetts Institute of Technology (MIT) suction caisson tests [Cauble, 1997], University of Texas at Austin suction caisson tests [El-Gharbawy, 1998], Indian Institute of Technology (ITT) Madras (India) friction single pile tests [Prasad, 1992], and suction caisson tests [Rao et al., 1997]. All these tests gave a total of twenty-nine experimental results to validate results from finite element analyses. In addition, scale model analyses for 1g, ng, and prototype models were also carried out. Failure patterns observed in soil were modelled by relevant soil failure models available in literature. Moreover, comparison of 3D and axisymmetric-asymmetric analyses for inclined pullout loads with different inclination angle and anchor point attachments, were also carried out. -- Suction pressure generation in suction caisson model finite element analyses consistently gave close matches with results obtained from laboratory vertical pullout tests carried out at MIT, University of Texas at Austin, and IIT Madras. Suction pressure development, carried out in this study, simulated the suction force or pressure (built up below the caisson top) properly, and the difference between good numerical and experimental results ranging between 0.3% to 7% (based on suction force) for the MIT tests, 10% to 20% (based on suction pressure) for the Texas tests, and 22.7% to 26% for the IIT Madras tests by Rao et al. However, less accurate results ranged from 27% to 70%. -- The finite element models gave a stiffer displacement response and as such did not match very well with some (especially University of Texas) of the experimental measurements. -- Based on the combined contours of shear stress to shear strength ratios (based on direct shear tests and triaxial extension tests) under vertical and inclined pullout loads, failure surfaces similar to the failure surfaces obtained for the Snorre suction caisson model pullout tests (carried out by the Norwegian Geotechnical Institute [Andersen et al., 1993]) were obtained in this study.Bibliography: leaves 266-281
Analisis Perilaku Conductor Leg Dari Monopod Platform Akibat Pembebanan Lateral Dan Aksial Dengan Metode Elemen Hingga
Get PDFA minimalist platform is a platform with a smaller and simpler deck and has less equipment. Minimalist platforms are generally designed for fields with lower reservoir reserves and are expected to have low costs in terms of fabrication and installation. One of the studies in developing a minimalist platform is about a conductor pipe that functions as a well and as the leg of the platform. This platform is susceptible to deflection under lateral and axial loads. In this research, an analysis will be carried out on the conductor pipe as a single pile which is subjected to a combination of lateral and axial loads to determine the stress and deflection that occurs in the conductor leg. This study was conducted using the finite element method with ABAQUS software. Inclination variations were carried out to determine the strength of the conductor leg when an inclination occurs. The result of this study was found that the conductor leg with an inclination of up to 1.5 degrees still had a stress below 0.6 yield. The result of this analysis shows that the conductor leg’s stress increases with increasing inclination. The maximum stress occurs at 1.5o of inclination which is 82.45 MPa under operating conditions and 125.45 MPa under extreme conditions. This stress is still below the allowable stress of 213 MPa (0.6 yields).Platform minimalis merupakan platform dengan dek yang lebih kecil dan sederhana serta memiliki equipment pendukung yang lebih sedikit. Platform minimalis pada umumnya didesain untuk field dengan cadangan reservoir yang lebih kecil dan diharapkan memiliki nilai cost yang rendah dalam hal fabrikasi serta instalasi. Salah satu upaya dalam pengembangan platform minimalis yaitu dilakukan studi mengenai pipa conductor yang berfungsi sebagai sumur sekaligus menjadi kaki platformnya. Platform jenis ini sangat rentan terhadap defleksi akibat beban lateral maupun aksial yang mengenai struktur. Dalam penelitian ini telah dilakukan analisis terhadap pipa conductor sebagai single pile yang dikenai kombinasi beban lateral dan aksial untuk mengetahui tegangan serta defleksi yang terjadi pada conductor leg. Penelitian dilakukan dengan metode elemen hingga menggunakan software ABAQUS. Variasi kemiringan dilakukan untuk mengetahui kekuatan pada conductor leg ketika terjadi kemiringan struktur. Hasil analisis menunjukkan bahwa tegangan conductor leg meningkat seiring bertambahnya kemiringan. Tegangan maksimum terjadi pada saat kemiringan 1.5o yaitu 82.45 MPa untuk kondisi pembebanan lingkungan operasi dan 125.45 MPa untuk kondisi pembebanan lingkungan ekstrim. Tegangan tersebut masih dibawah tegangan yang diijinkan yaitu 213 MPa (0.6 yields
Offshore structure response due to ship collision on jacket legs
Get PDFThis paper discusses graded and collision velocity supply vessel influence to local and global structure damage subject to collision. This case study for CONOCO BELANAK wellhead platform that approaching with of 2500 tonnes of supply vessel with tidal variation for each collision scenario. Deformation of the jacket leg occurs causes by material inability to proof against pressure. This paper uses 2 software are ANSYS LS-DYNA 9.0 to acquire local deformation and GT-STRUDL 27.0 version to acquire global deformation included dynamic transient analysis. Outside diameter of Jacket Leg is 1.651 m with wall thickness is 0.0381 m. Normal velocity in each sideway, stern; manoeuvring collision and extreme velocity is 0.28 m/s, 0.39 m/s and 0.74. Extreme velocity in each sideway and stern collision is and 10% exceedance velocity is 0.54 m/s, 0.73 m/s and 1.29 m/s. The result of this paper is dent of the landing platform for each normal and extreme is 0.2725 m, 0.2352 m, and 0. 3241 m/s it must be repaired or changed because of it is 30% larger than spacing frame. Maximum displacement x, y, z direction is 0.2423 m on 0.38 s, 0. 0559 m on 0.39 s, 0.7492 m on 0.41 s. The deformation in landing platform, jacket leg and jacket structure is smaller than research result indeed
Ultimate Strength of the Buoy Structure due to the Loads Arise from the Tanker and Mooring Lines
No full textDevelopment of Structural Dynamic Analysis Software of Truss Structure Using Monte Carlo Finite Element Method
No full textStructural reliability analysis is increasingly used in conjunction with the design of offshore structures which have high uncertainty. Two problems i.e. reliability and complexity of the structures resulted in Monte Carlo Finite Element Method (MCFEM) method of analysis. In the first part of this research, we will show results comparison between deterministic analysis software made in Proposed Software and analysis using commercial established software. In this case, object will assume as a simple Plane Truss structure with multi degrees of freedom applied dynamic load in the support of structure. The second part after obtaining a deterministic result compared by commercial software, further we will apply MCFEM algorithm to the deterministic analysis algorithm which has been made. The results of this research, contains a new procedure in the form of reliability simulation algorithm by combining Monte Carlo Simulation and Finite Element Method in Dynamic Model
Development of Structural Dynamic Analysis Software of Truss Structure Using Monte Carlo Finite Element Method
No full textStructural reliability analysis is increasingly used in conjunction with the design of offshore structures which have high uncertainty. Two problems i.e. reliability and complexity of the structures resulted in Monte Carlo Finite Element Method (MCFEM) method of analysis. In the first part of this research, we will show results comparison between deterministic analysis software made in Proposed Software and analysis using commercial established software. In this case, object will assume as a simple Plane Truss structure with multi degrees of freedom applied dynamic load in the support of structure. The second part after obtaining a deterministic result compared by commercial software, further we will apply MCFEM algorithm to the deterministic analysis algorithm which has been made. The results of this research, contains a new procedure in the form of reliability simulation algorithm by combining Monte Carlo Simulation and Finite Element Method in Dynamic Model
