Hydrodynamic Forces on Rectangular Cylinders of Various Aspect Ratios Immersed in Different Flows

Hamel-Derouich, Djamel (1993) Hydrodynamic Forces on Rectangular Cylinders of Various Aspect Ratios Immersed in Different Flows. PhD thesis, University of Glasgow.

Abstract

Previous studies of fluid loading on rectangular and circular cylinders are critically reviewed in this study. This review revealed that whilst comprehensive experimental data on circular cylindrical forms have been accumulated over the past 30 years or so, comparatively little experimental data on rectangular cylinders exist particularly in wavy flow and in combined wavy and steady flows. Experiments were therefore carried out at the Hydrodynamics Laboratory of the Department of Naval Architecture and Ocean Engineering at the University of Glasgow. Rectangular cylinders of various cross- sectional aspect ratios were constructed and tested vertically, as surface piercing, and horizontally, with their axes parallel to wave crests, in steady flow, wavy flow and a combination of the two flows to simulate the presence of currents along with waves. Force measuring systems were designed and incorporated into the test section of each cylinder, hi-line and transverse forces were measured for the surface piercing vertical cylinders and in-line and vertical forces were measured for the horizontally submerged cylinders. This thesis presents the results of experiments conducted on sharp-edged rectangular cylinders in terms of hydrodynamic coefficients of inertia CM, drag CD and lift CL coefficients as well as in terms of the maximum CFmax and the r.m.s. value CFrms measured forces. In steady flow, the drag coefficients measured were smaller than those measured earlier by other investigators who conducted experiments in two dimensional flow using cylinders with a very high length to width L/D ratio spanning the entire height of a wind tunnel or by testing cylinders mounted between end plates. In wavy flow, the inertia coefficients of the cylinders of aspect ratios 1 and 2 horizontally submerged in regular waves decreased rapidly with increasing KC number. The inertia coefficients of the horizontal cylinders were found to be smaller than those of the vertical cylinders. The drag coefficients for the different cylinders were found to have high values as the KC number approached zero and to decrease sharply with increasing KC number. The lift coefficients for the different vertical cylinders were found to have high values as the KC number approached zero and to decrease rapidly as the KC number increased. These coefficients were also found to be affected by xxu variations in the cylinder's aspect ratio. The variations of CM and CD coefficients with the KC number in wavy flow were generally found to be different from those in planar oscillatory flow. The various hydrodynamic force coefficients measured in combined wavy and steady flows were found to be smaller than those measured in wavy flow. At very low KC numbers, the presence of currents was found to be most important and caused significant reduction in the drag coefficient. In wavy flow, the Morison equation using measured CM and CD coefficients was found to predict the measured forces well. In combined wavy and steady flows, the modified Morison equation using measured CM and CD coefficients under these flow conditions was found to predict the measured forces well. However, when using measured CM and CD coefficients, obtained in wavy flow, in combined wavy and steady flow conditions, the modified Morison equation was found to overestimate the measured forces. The measured inertia coefficients for the square cylinder were found to be higher than those predicted by the potential flow theory. For the cylinders with aspect ratios of 0.5 and 2, however, the measured inertia coefficients were found to be only slightly higher than those predicted by the potential flow theory. In terms of forces, the theory was found to underestimate the total forces for the square cylinder. However, good agreement was found between the measured and predicted forces on the cylinders with aspect ratios of 0.5 and 2.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Adviser: A Incecik
• Keywords: Ocean engineering, Fluid mechanics
• Date of Award: 1993
• Depositing User: Enlighten Team
• Unique ID: glathesis:1993-74858
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 27 Sep 2019 15:48
• Last Modified: 27 Sep 2019 15:48
• URI: https://theses.gla.ac.uk/id/eprint/74858