الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 119 |  |  |
| | | from | 119 | | |
Abstract
Pipelines are the main means of transport of oil and gas products in the industry. Products are being transported from well or reservoir to subsea manifolds, shore, or production facility platforms for end-users. Arrival to optimum design for subsea pipeline system, many complicated engineering studies are required. This starts with pipeline sizing, material selection, pipeline routing, on-bottom stability design, etc.
On-bottom stability analysis is one of the most important and fundamental tasks during the design process of subsea pipelines. On-bottom stability is necessary to ensure vertical and lateral stability for the as-laid pipeline on the seabed against hydrodynamic loads from waves and currents. The external concrete coating layer is mostly used to add weight to the pipe as a cost-effective solution for pipeline stabilization.
In this thesis, the factors that affect the pipeline stability are discussed, the conventional and advanced methods for the on-bottom stability design are expounded, and a case study is conducted using three design approaches: static analysis approach, calibrated methods approach, and dynamic analysis approach.
For on-bottom stability design using static analysis and calibrated methods approach, on-bottom stability analysis software is developed using MATLAB programming language in compliance with the recommended practice DNVGL-RP-F109. AGA/PRCI Level 2 program is also used as another calibrated method. AGA/PRCI Level 2 was developed by the Pipeline Research Council International (PRCI) that was a part of the American Gas Association (AGA). Comparison between both calibrated methods from DNVGL and AGA/PRCI is carried out as well as a sensitivity analysis for various water depths.The dynamic on-bottom stability analysis is performed using a finite element-based advanced offshore engineering simulation software called Flexcom to predict the pipeline response in a time-domain simulation based on a given environmental condition. The resultant maximum lateral displacements and the associated stresses are examined via different thicknesses of the concrete weight coating. Pipeline response from the numerical simulation is investigated and reasons behind the dynamic response are defined, and seven simulation runs using random seed numbers are performed to confirm the on-bottom stability against different random sea states. It is observed from the results the importance of several factors on pipeline stability such as pipeline submerged weight using the simple friction model, hydrodynamic loads induced by random sea states on the stresses and lateral displacements, and soil friction model being used incorporating the passive soil resistance term.Comparison between the three stability approaches is conducted to study the effect of ignoring passive soil resistance and the importance of dynamic stability analysis to optimize the on-bottom stability design. The comparison has emphasized the reduction in concrete weight coating using dynamic stability analysis if the actual case is modeled accurately.