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Ecological and economical considerations motivate the search for ways to reduce the skin friction drag in turbulent flows. Several numerical studies have shown that wall shear stress can be lowered at low Reynolds numbers by applying a small amount of wall transpiration. In this study it is investigated how another type of actuation, active wall deformation, could be used to yield a similar effect. . Ã??Ã?? First. discrete time-dependent wall deformation is studied in laminar flow. Lacking background turbulence, the baseflow allows clear identification of the flow perturbation. The analysis reveals that a downward moving actuator is surrounded by a region of negative wall-normal velocity and vice versa. Comparably less intuitive are the vorticity fields which often display complicated structures. A similar, subsequent study in turbulent flow shows that, indeed, active wall deformation can restruckJre wall turbulence. Seised on thesA findings, a series of experiments were conducted on opposition control. This scheme . aims at opposing the velocity sensed away from the wall by imposing velocity of opposite direction at the wall. By locally deforming the wall accordingly, skin friction reductions of up to 15% are observed. Parameters critical to the performance of the control scheme, such as actuation scales and deformation limiters, are identified and analysed. As Reynolds number and actuation scales are much smaller than in practical applications, the results are of limited applicability but encouraging for prospective drag reduction at higher Reynolds numbers. In a separate study a novel control method based on non-linear global stabilisation of the perturbed Navier-Stokes equations was tested. Using body forcing over the entire domain as actuation. the flow

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Using a purpose built molecular dynamics (MD) code. we simulate a range of infinite and finite length H-terminated carbon nanotubes in vacuo. We find that the radial breathing mode (RBM) of the finite nanotubes approaches that of the infinite nanotubes for nanotubes greater than 5 nm in length. We investigate the effect on the RBM frequency' of immersion in water and find that external wetting is responsible for an upshift in the RBM of around 4-10 wave numbers. and internal wetting approximately 2-6 wave numbers. The upshift is comprised of two components: increased hydrostatic pressure on the nanotube due to curvature effects. and the dynamic coupling of the RBM with a shell of adsorbed fluid: In contrast to much of the current literature, we find that the latter of the two effects . is dominant. The upshift can be modelled analytically by considering the adsorbed fluid as an infinitesimally thin shell which interacts with the nanotube via-a continuum Lennard-Jones potential. Using MD, the RBM of carbon nanotubes in fluids can be accurately reproduced by replacing the fluid molecules with a mean field harmonic shell potential. greatly reducing simulation times. The pressure dependence of shifts in the vibrational modes of individual carbon nanotubes is strongly affected by the nature of the pressure transmitting medium as a result of adsorption at the nanotube sUrfade. Using analytical methods, as well as MD, we observe an as yet unreported low frequency breathing mode for the adsorbed fluid at around 50 cm-1 , as well as diameterdependent upshifts in the RBM frequency with pressure, suggesting metallic nanotubes may wet more than semiconducting ones. Finally. we describe a methodology for the continuous pumping of fluid through carbon nanotubes. Fluid is imbibed from a reservoir at 300 K. heated. and subsequently ejected from the hot end. Very high pressures are developed in the smaller nanotubes due to strong capillary forces, suggesting thAir use as nanoscale reaction vessels. A theoretical framework is developed allowing us to predict pumping fluxes over a range of nanotube diameters and temperatures.

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The aim of the work presented here is to develop a pipe inspection tool that is capable of detecting, locating and then sizing any defects that may be present in the pipe section under test. The work is primarily directed towards quantifying any improvements that can be made to the current screening system by using synthetically focused imaging algorithms. The algorithms are first tested for plate imaging using a linear array and then modified for use on cylindrical structures. The minimal modifications make use of similarities between the guided wave structure in plates and pipes. The pipe imaging system is then rigorously tested using data from 3D finite element model predictions and laboratory experiments. The performance of the system is established at various inspection frequencies in terms of detection sensitivity to circumferential cracks, resolution and robustness towards set up errors. It is found that the defect sensitivity is increased by around 15 dB over the simple screening tool and cracks of circumferential extent larger than ~1.5? can be directly sized from the pipe image.

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No description available.

No description available.