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Biography

My principal areas of active research are all are concerned with practical fluid mechanical problems in the traditional heartland of Applied Mathematics.  Within this framework, the two principal areas of research are wave-current interactions and the modelling of wave-power devices.  Other areas of interest include wave-structure interactions (which shares a common interest with core aspects of wave-power device modelling), wind-induced circulations in lakes, flows through floodplains and blood flow through large arteries.  In most cases the work involves collaborative studies with engineers or fellow scientists, particularly as the studies require the acquisition of good experimental data for comparison with the numerical models.It is perhaps useful to provide some career background information to illustrate my research philosophy.  Following a PhD in Applied Mathematics at the University of Bristol, with a speciality in wave-current interactions, I undertook a post-doctoral position in the Department of Civil Engineering at the same university.  This involved undertaking experiments (and further modelling) of flow fields similar to those I had studied theoretically; it taught me how real fluids behave and what modelling approximations really involve – courses in mathematics provide no adequate preparation!  I also experienced the difficulties and pitfalls of performing experiments with water waves.  A second post-doctoral position, this time in Mathematics, was in the embryonic field of modelling wave-power studies.  When appointed to UCC, my brief was to work with engineers and in two fields that have continued to expand.  The strategy is clear: models and experiments must accompany each other and if models do not exist, then experiments must provide illumination.Within the remit of wave-current interactions, my work has been concerned with the interaction between water waves in two and three dimensions, usually of regular frequency, with a spatially varying mean flow that defines the current.  The topics of interest are primarily the prediction of the wave kinematics from given wave and current data.  This includes both linear and nonlinear wave regimes and the importance of vorticity and viscosity.  The study of conservation equations to describe the slowly-varying properties of the wave field is also a topic of major interest, particularly when vorticity is present.  As already stated, a particular feature of this work is that experimental studies play a crucial role in the development of good numerical models.  It would not be an exaggeration to say that I have played an integral part in all the major studies, theoretical and experimental, on the kinematics of two- and three- dimensional wave-current interactions.  This may seem to be in the past, with little or no application to the future, but the resource modelling for machines intended to extract power from tidal streams and currents requires all of these skills; present efforts concentrate upon these future applications.My second primary topic, the modelling of wave-power devices, has been restricted to fluid/structure interactions that can be described by diffraction models within the inviscid linear wave regimes.  This has enabled standard hydrodynamic theories and concepts, originally developed by naval architects, to be employed to model wave power devices.  Although the existence of such theories is broadly beneficial, there are also drawbacks in the sense that shortcomings associated with implementation of the earlier theories (such as the difficulties in calculating the hydrodynamic coefficients for particular geometries) remain.  Within this field my principal contributions to the generic knowledge base are associated with the design of wave-power devices from a hydrodynamic perspective and the hydrodynamics of arrays of wave-power devices; in both cases my work has been associated with the core developments.  This is now being extended to include control.  It should be noted that there is one major difference between this field and the others with which I have been concerned, viz. the majority of the important papers appear initially as conference or workshop papers; journal papers may or may not follow.  This simply reflects a rapidly varying field in which a wide range of disciplines are present.

Research Interests

MacIver, R. D., Simons R.R. & Thomas G.P.  2006  Gravity waves interacting with a narrow jet-like current, J. Geophys. Res. 111 (C3), C03009.

Voronovich V.I., Shrira V.I. & Thomas G.P.  2008  Can bottom friction suppress ‘freak wave’ formation?  J. Mech., 604, 263-296.

Most studies on freak (or rogue) involve many partners and huge computational effort in attempts to determine when freak waves will occur.  The scale of the phenomenon means that it is exceedingly difficult to reproduce experimentally.  This paper, resulting from a project funded by SFI, adopts a rather different and more economical approach by asking the complimentary question: are there circumstances under which freak waves cannot occur?  By employing a multiple time-and-length scale analysis to separate the local fast wave motion from the longer slow scales associated with measures of stability and by including the influence of bed friction, it was found via linear and nonlinear stability analyses that bed friction can have a stabilizing influence and prevent the instabilities that are known to lead to freak wave formation.  Such an analysis has not been attempted previously but does place restrictions upon the wave regime.  One reviewer commented that the paper would lead to much discussion and controversy!

Thomas G.P. 2008  The theory behind the conversion of ocean wave energy: a review.  In ‘Ocean wave power – current status and perspectives’, ed. by J. Cruz, Springer Verlag, 41-91.

The remit of this invited review paper was to describe the hydrodynamic processes that are associated with wave-power devices to a non-specialist engineering audience.  Such papers are always immense challenges, since a balance must be sought to describe a totality of concepts, difficulties and existing work to a non-specialist target audience while simultaneously not displeasing the cognoscenti.  From a personal perspective it presented an ideal opportunity to present and assess a body of work that been completed in UCC over a substantial time period and positioned within a much broader framework, which in turn  provided a favourable judgement.  Much of science is associated with levels of understanding and this provided an opportunity to move up a couple of levels, even if such a move was compulsory if the task was to be completed successfully.  Another benefit that always accrues from such exercises is the focus that identifies knowledge gaps and the necessity for future work.

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