Laminar natural convection heat transfer from the vertical surface of a cylinder is a classical subject, which has been studied extensively. Furthermore, this subject has generated some recent interest in the literature. In the present investigation, numerical experiments were performed to determine average Nusselt numbers for isothermal vertical cylinders (103 < RaL < 109, 0.5 < L/D <10, and Pr = 0.7) with and without an adiabatic top in a quiescent ambient environment which will allow for plume growth. Results were compared with commonly used correlations and new average Nusselt number correlations are presented. Furthermore, the limit for which the heat transfer results for a vertical flat plate may be used as an approximation for the heat transfer from a vertical cylinder was investigated.

ABSTRACT The purpose of the study is to design and test the devices(de-draggers) that can be incorporated to cylinders to reduce wave forces¡C Two force gauges have been designed to measure simultaneously the x- and z-direction wave forces, especially, for a horizontal cylinder, and the x- and y-direction wave forces, for a vertical cylinder¡C A device with water-drop shape has been fabricated to streamline the flow pattern around the cylinder that can effectively reduce the wake-induced wave force¡C The study will be performed in a wave tank by varying wave conditions and the positions of the cylinder¡CWave forces on the vertical and horizontal cylinders will be measured and compared for the cylinders with and without de-draggers,¡@respectively¡C

The present work investigates, numerically, the process of melting and solidification in hollow vertical cylinders, filled with air and phase change material (PCM). The PCM used is sodium nitrate, which expands upon melting. Therefore, a void must be present within the cylinder, which is filled with air. The influence of cylinder shape on melting time is determined. The numerical model takes both conductive and convective heat transfer into account during the melting process. The Volume-of-Fluid (VOF) model is used to track the interface between the PCM and air as the PCM melts. Three dimensionless numbers represent the characteristics of the problem, which are the Grashof, Stefan, and Prandtl numbers. The Stefan and Prandtl numbers are held constant, while the Grashof number varies. Inner Aspect Ratio (AR) is used to characterize the shape of the cylinder, which is defined as the ratio of the height to the diameter of the vertical cylinder. In this study, a range of AR values from 0.23 to 10 is investigated. Cylinders with small AR, corresponding to high Grashof numbers, lead to lower melting times compared with cylinders with high AR. The molten PCM velocity was also influenced greatly by this difference between solid PCM shape between high and low AR cases. Cylinders with small AR, corresponding to high Grashof numbers, lead to higher solidification times compared with cylinders with high AR. It was found that the velocity decreased during the solidification process, but the shape of the cylinder had an effect on the decrease. Natural convection velocity was found to decrease during the solidification process and, therefore, its effects diminish as solidification proceeds.

Les travaux portent sur l’étude de la formation de motifs sédimentaires à l’aval d’un cylindre vertical soumis à un courant. Le cylindre simule une fondation monopieu d’éolienne en mer, ou une pile de pont. Une modélisation théorique est développée. Les résultats obtenus sont en bon accord avec les résultats expérimentaux acquis au cours de la thèse. Une étude préliminaire expérimentale et théorique sur le tri sédimentaire au voisinage du cylindre est également effectuée. / This work concerns the study of sediment patterns formation downstream a vertical cylinder under a steady current. The cylinder simulates an offshore monopile foundation, or a bridge pile. A theoretical modeling is developed. The results are in good agreement with the experimental results obtained in the framework of this PhD. An experimental and theoretical preliminary study on sediment segregation in the vicinity of the cylinder is also performed.