During offshore installation, steel lined pipes are subjected to severe plastic bending, resulting in detachment of the thin-walled liner pipe from the outer pipe and eventually, the formation of local buckling in the form of shortwave wrinkles that menace the structural integrity of the pipeline. The paper focuses on the mechanical behaviour of mechanically lined pipes subjected to monotonic bending, considering for the presence of low and moderate levels of internal pressure, aimed at preventing or delaying wrinkle formation, and improving structural performance. The problem is solved numerically, accounting for geometric non-linearities, local buckling phenomena and elastic-plastic material behaviour for both the liner and the outer pipe. Two types of lined pipes are examined, with and without mechanical bonding between liner and outer pipe referred to as tight-fit and snug-fit lined pipe, respectively. The results demonstrate that the bending performance of lined pipes, under low or moderate internal pressure levels, is significantly improved. The influence of initial geometric imperfections on liner pipe buckling is also examined, showing the imperfection sensitivity of bi-material pipe bending behaviour.
The present work investigates structural response of tidal stream turbine blades subjected to impact loads from sea animals. A full-scale tidal turbine blade model was developed using a finite element modelling software ABAQUS, while a simplified geometry of an adult killer whale (Orcinus orca) was assumed in simulating impact on the blade. The foil profiles along the turbine blade were based on the NACA 63-8XX series, while the geometric and material properties of the sea animal were calibrated with experimental results. The numerical model simulated the dynamic response of the blade, accounting for radial velocities of the blade corresponding to real life scenarios. Different magnitudes and trajectories of the velocity vector of the sea animal were simulated, in order to investigate their influence on the turbine blade’s plastic deformation. Furthermore, multiple impacts were analysed, in order to monitor the accumulation of plastic strain in the material of the blade. Finally, the potential application of stainless steel material in tidal stream turbine blades for impact resistance was evaluated, through comparison of numerical results obtained from models using stainless steel and mild carbon steel materials.
The effects of manufacturing process on mechanically lined pipe structural performance are investigated. Alternative manufacturing processes are considered, associated with either purely hydraulic or thermo-hydraulic expansion. The problem is solved numerically, accounting for geometric nonlinearities, local buckling phenomena, inelastic material behavior and contact between the two pipes. A three-dimensional model is developed, which simulates the manufacturing process in the first stage of the analysis and, subsequently, proceeds in the bending analysis of the lined pipe. This integrated two-stage approach constitutes the major contribution of the present research. Thermo-hydraulically expanded lined pipes are examined, with special emphasis on the case of partially heated liners, and reverse plastic loading in the liner pipe wall has been detected during depressurization. Furthermore, the numerical results show that the thermo-mechanical process results in higher mechanical bonding between the two pipes compared with the purely mechanical process and that this bonding is significantly influenced by the level of temperature in the liner pipe. It is also concluded that the value of initial gap between the two pipes before fabrication has a rather small effect on the value of liner buckling curvature. Finally, numerical results on imperfection sensitivity are reported for different manufacturing processes, and the beneficial effect of internal pressure on liner bending response is verified.
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