Beam buckling on random elastic foundations

Abstract

This thesis explores the impact of the seafloor on the buckling load of an undersea pipeline via beam on elastic foundation buckling theory. Undersea pipelines are used for the conveyance of hydrocarbons from wells located on the seafloor to facilities located on the ocean surface. As worldwide demand for hydrocarbon fuels increases and onshore reserves are depleted hydrocarbon production is forced offshore and increasingly into deep water. Increases in pipeline temperature and pressure result in axial loads sufficient to cause buckling. Pipelines do not require trenching in deep water as fisherman's trawling equipment is unlikely to come into contact with them. This lack of confinement results in lateral displacements from the as-laid position multiple pipe diameters in length. Pipeline design must predict and accommodate these lateral movements to avoid ruptures, which makes lateral buckling a subject of both industry and academic interest. A finite element model of a beam on an elastic foundation of randomly varying stiffness (BOREF) has been developed to explore the impact of the seafloor foundation on the critical buckling load of a pipeline. The Monte-Carlo method is used in conjunction with a random field generator to calculate a probability of failure due to buckling for a given axial load. A realistic example is presented in the thesis. This research demonstrates the importance of describing the mechanical properties of natural materials stochastically when modeling. In geotechnical analysis deterministic descriptions of natural materials can result in non-conservative predictions even in instances where the material has been characterized extensively.