Atmospheric Controls on the Development of Shallow Convective Clouds in Large Eddy Simulations

This thesis makes use of a new atmospheric community model MONC (the Met Office and NERC Cloud Model) to explore atmospheric controls on the development of shallow, non-precipitating convective clouds. Simulations presented here are initialised using profiles based on those observed during the COPE (COnvective Precipitation Experiment) field campaign in 2013. Isolated convective clouds are generated using heterogeneous surface fluxes, which act upon a turbulent convective boundary layer (CBL). The CBL is capped by an inversion, above which the environment is statically stable. A cloud tracking algorithm is used to track and study individual clouds, including those which split and merge over time. The role of sub-cloud variability (produced during turbulent model spinup) on convective cloud development is explored, and is concluded to play a significant role in modulating cloud vertical transport, both through determination of properties at cloud base and through different rates of turbulent entrainment along the edge of the cloud. Gravity waves develop during these simulations, propagating in all directions, and are shown to produce large-scale environmental subsidence with comparable magnitude to that generated by localised subsiding cloud shells enveloping the core, as well as influencing the regeneration of individual clouds

A study of the age related changes on the endocranial surface of the skull

SIGLEAvailable from British Library Document Supply Centre-DSC:DXN012472 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Impact of flow pulsatility on arterial drug distribution in stent-based therapy

Drug-eluting stents reside in a dynamic fluid environment where the extent to which drugs are distributed within the arterial wall is critically modulated by the blood flowing through the arterial lumen. Yet several factors associated with the pulsatile nature of blood flow and their impact on arterial drug deposition have not been fully investigated. We employed an integrated framework comprising bench-top and computational models to explore the factors governing the time-varying fluid dynamic environment within the vasculature and their effects on arterial drug distribution patterns. A custom-designed bench-top framework comprising a model of a single drug-eluting stent strut and a poly-vinyl alcohol-based hydrogel as a model tissue bed simulated fluid flow and drug transport under fully apposed strut settings. Bench-top experiments revealed a relative independence between drug distribution and the factors governing pulsatile flow and these findings were validated with the in silico model. Interestingly, computational models simulating suboptimal deployment settings revealed a complex interplay between arterial drug distribution, Womersley number and the extent of malapposition. In particular, for a stent strut offset from the wall, total drug deposition was sensitive to changes in the pulsatile flow environment, with this dependence increasing with greater wall displacement. Our results indicate that factors governing pulsatile luminal flow on arterial drug deposition should be carefully considered in conjunction with device deployment settings for better utilization of drug-eluting stent therapy.National Institutes of Health (U.S.) (grant NIH R01 GM-49039

Evaluation of Different Meshing Techniques for the Case of a Stented Artery

The formation and progression of in-stent restenosis (ISR) in bifurcated vessels may vary depending on the technique used for stenting. This study evaluates the effect of a variety of mesh styles on the accuracy and reliability of computational fluid dynamics (CFD) models in predicting these regions, using an idealized stented nonbifurcated model. The wall shear stress (WSS) and the near-stent recirculating vortices are used as determinants. The meshes comprise unstructured tetrahedral and polyhedral elements. The effects of local refinement, as well as higher-order elements such as prismatic inflation layers and internal hexahedral core, have also been examined. The uncertainty associated with individual mesh style was assessed through verification of calculations using the grid convergence index (GCI) method. The results obtained show that the only condition which allows the reliable comparison of uncertainty estimation between different meshing styles is that the monotonic convergence of grid solutions is in the asymptotic range. Comparisons show the superiority of a flow-adaptive polyhedral mesh over the commonly used adaptive and nonadaptive tetrahedral meshes in terms of resolving the near-stent flow features, GCI value, and prediction of WSS. More accurate estimation of hemodynamic factors was obtained using higher-order elements, such as hexahedral or prismatic grids. Incorporating these higher-order elements, however, was shown to introduce some degrees of numerical diffusion at the transitional area between the two meshes, not necessarily translating into high GCI value. Our data also confirmed the key role of local refinement in improving the performance and accuracy of nonadaptive mesh in predicting flow parameters in models of stented artery. The results of this study can provide a guideline for modeling biofluid domain in complex bifurcated arteries stented in regards to various stenting techniques