Vortex induced vibration and structural integrity of deep-water flexible risers

The long flexible slender multi-layered pipes, called unbonded flexible risers, are considered as the new-generation risers for deep water applications. However their complex design and highly non-linear behviour coupled with the fact that they undergo types of extreme loadings which are different to those experienced by conventional rigid risers, currently pose many challenges to the offshore industry. The focus this work is on developing fluid, structural, and coupling models and the numerical procedures for the prediction of dynamic response of flexible risers due to vortex induced vibration, in cases where accurate simulation of their complex non-linear behaviour is a critical step in the analysis. In the structural simulation, it is intended to adopt a multi-scale non-linear finite element procedure which consistently links simulations conducted at a detailed small scale and a large structural scale. The fluid simulation work involves the development of a quasi-three-dimensional fluid code to model the cross flow around the flexible risers. The structural and fluid codes will be coupled together by developing an efficient fluid-solid interaction algorithm. The results from the numerical simulation will be validated against the results of experiments which will also be carried out as part of the project.

This project contains both fundamental research and a targeted application. As a result, the outcome of this project will have a considerable positive impact not only on the academic and research community but also on the offshore industry, as well the wider community and the environment. Within the off-shore industry, the manufacturers of flexible risers will be provided with a numerical simulation tool of unprecedented accuracy, capable of capturing the effects of small geometric or material design changes in the layers used in the make up of flexible risers, and the effect of alterations in the riser loading condition. By replacing expensive and time-consuming experiments with virtual testing capabilities delivered by this project, the manufacturers will be able to explore a much wider range of new designs, conduct design optimisation and significantly reduce their time to market. The code will also provide structural consultants for oil and gas operators in the off-shore industry with a very powerful tool for integrity management, and life extension of flexible risers. The positive impacts on the oil and gas industry will be cascaded to the general community in terms of increased availability of hydrocarbons for a longer period, giving more time for the development of viable renewable energy technologies, resulting in a smoother transition to a low-carbon economy. The environment will hugely benefit from this research as the considerable increase in the accuracy of the simulation tool developed will result in safer designs, with significantly reduced risks of riser structural failure which can have catastrophic environmental implications. The advanced and innovative numerical models that will be developed in this project will be at the forefront of international research in this field and will therefore have a particularly strong positive impact on the academic and research community working on other multi-scale fluid-solid interaction problems.