PhD Position in Modelling and Analysis of Vortex-Induced Vibrations of Slender Marine Structures, University of Aberdeen, UK

July 5, 2010

Job Description:

Slender marine structures such as risers, mooring cables, umbilicals and tethers play crucial roles in global offshore exploration, installation and production activities. As exploitation of offshore oil and gas fields is moving into deeper waters, the nonlinearities in the system and the fluid-solid interaction phenomena become more and more important, and advanced modelling and analysis is required to describe and predict the behaviour of the system in general and vortex-induced vibrations (VIV) in particular. The VIV accelerates the fatigue damage of undersea structures and limits the service life of overall subsea systems. Based on the analytical/numerical tools existing in academia and industry, there are still considerable uncertainties and discrepancies in the theoretical-experimental comparison of VIV response predictions [1]. In addition, a number of insightful aspects of VIV are far from being fully understood and many experimental frameworks are unable to capture or explain all of the non-linear VIV characteristics of long flexible cylinders [2]. This certainly gives rise to the overestimated structural design and the overuse of VIV control devices which, in turn, produce substantial costs in offshore operations.

From a theoretical and practical perspective, there are some significant knowledge, concerns and limitations of previous/current investigations related to the VIV of marine structures. First of them is related to the structural model, as often the associated effects of geometric nonlinearities and overall displacement coupling are disregarded. The next important aspect is the flow. Both uniform and sheared current flows are mostly considered for straight structures resulting in the well-known classification of cross-flow and in-line VIV. However, in practice the current is spatially non-uniform and multi-directional. Depending on the flow characteristics, the most crucial task is to determine how to model and recreate the hydrodynamic forces associated with vortex shedding behind the structure. Indeed, due to computational concerns it is still impractical to directly make use of a computation fluid dynamics (CFD) for long slender structures and for high-velocity flows. To overcome this, one might develop a so-called wake oscillator to empirically approximate the space-time varying hydrodynamics, by accounting for also some fundamental VIV phenomena [3]. This reduced-order fluid model saves a large amount of computational efforts. Recently, there are several new wake oscillator models in literature but most of them have been developed particularly for cross-flow VIV. Therefore, the improved wake oscillator models – having the interactions with the structural equations of motion and valid for the coupled cross-flow/in-line VIV – are needed.

To cope with the fluid-structure interaction problems, the finite element method (FEM) in conjunction with the CFD might ideally provide the most accurate solution. However, this bundled FEM-CFD application is enormously time-consuming because of solving many degrees of freedom in the time domain. Therefore, it is not recommended in industry, and offshore engineers usually rely on .

Application Procedure

Formal applications can be completed online: http://www.abdn.ac.uk/sras/postgraduate/apply.shtml. You should apply for MSc with a view to transfer to PhD in Engineering, to ensure that your application is passed to the correct College for processing. Please note, you should apply at least 4 days before the deadline to allow us to contact you for further information, if required. All applications received up to, and including the closing date, will be processed.

Informal academic enquiries should be directed to Dr E Pavlovskaia (e.pavlovskaia@abdn.ac.uk)

Application Deadline :23 August 2010

Start Date: October 2010

For further details:

Scholarship Tags: Aberdeen, Analysis, Induced, Marine, Modelling, PhD, Position, Slender, Structures, UK, University, Vibrations, Vortex