Nonlinear behaviour of offshore flexible risers

This thesis was submitted for the degree of Master of Philosophy and awarded by Brunel UniversityAs the search for exploration of oil and gas moves to deeper waters, flexible unbounded risers have become the main means of extracting hydro carbonates from deep waters. In this context, structural integrity of flexible risers has become a crucial issue for the offshore industry. In this study, experimental tests and detailed finite element analyses were carried out on a scaled down model of a flexible riser pipe. The model used consists of four layers which include two cylindrical polycarbonate tubes and two steel helical layers. One helical layer represents the carcass layer in an actual flexible riser whilst the other represents the riser tendon armour layers, wounded around the pipe assembly. The model was first subjected to a three point bending load in order to study its bending-curvature behaviour experimentally. Then, the specimen was tested under compressive load with different pressure values to investigate the effect of pressure on the pipe deformation. Additionally, the effects of pure axial load and pure pressure with no load on the model were examined. The effects of static load on the deformation of a single helical tendon layer and creep behaviour (Shetty, 2013) of the layer were also studied. The investigation of a single tendon under axial load using finite element based software shows residual strains results are in good agreement with the experiments. The numerical model also shows a non-linear behaviour in bending-moment curvature for flexible pipe which is in a good agreement with the experimental data

Theoretical and practical approaches for novel composite evolute springs

A combined experimental/analytical approach for an efficient evaluation of stiffness and characteristic curves of fiber reinforced plastic volute springs is presented in this work. Before performing the analysis mentioned in previous lines, in the early chapters, it can find the most common types of fibers, resins (matrices) and manufacturing processes used to produce composite laminates been briefly described. It also describes the analytical approaches that currently exist to determine the elastic constants of composites such as the longitudinal and transversal modulus, Poisson’s ratios and shear moduli; it also describes the improved and semi-empirical formulas to calculate the effective shear moduli and the transversal modulus. At the end of the chapter, some manufacturing methods of fiber reinforced plastic springs are described. Since fiber reinforced plastic volute springs are novel products, the fourth chapter presents and describes basic considerations that it must be taken into account when selecting material (fibers, resins, and additives) to manufacture these springs. At the end of the chapter, a method to produce volute springs is presented. The fifth chapter presents the elastic constant calculations for laminates used to manufacture volute springs. An experimental/analytical method has also been performed to determine in-plane and out-of-plane shear moduli since these material constants are of greater importance in the rate spring calculation hence any crosssection of these springs shows the major load being torsional. On the one hand the analytical method to calculate these shear moduli is based on Sumsion’s guidelines that use the theory developed by Lekhnitskii for anisotropic materials; on the other hand, it has been done torsion test of rectangular bars, which were manufactured using vacuum infusion method, to obtain shear moduli experimentally. Finally, calculated values of shear moduli are used to determine stiffness and characteristic curves of volute springs in an analytical and experimental method. It is proposed to use the in-plane shear modulus in the classical calculation method for steel volute springs and to compare results obtained with compression test results carried out on fiber reinforced plastic volute springs. Consistent results are achieved by performing this combined analytical and experimental method concluding that the best behavior of fiber reinforced plastic volute springs is when fibers have an orientation of +/ 45° concerning the main axis of the laminate.Tesi

WINDERFUL Wind and INfrastructures

WINDERFUL (an acronym for Wind and INfrastructures: Dominating Eolian Risk For Utilities and Lifelines) is the title of a research project carried out by eight Italian Universities from the end of 2001 to the end of 2003. The project was centred on how "to keep a city running and ensuring quality services during and after major windstorms", avoiding "major failures" of engineering facilities and main infrastructures. The book reports the main results obtained in the project, and for each typology the tool for assessing its reliability are discussed, together with the criteria for its improvement