Wave Forces on Cylinders near Plane Boundaries
01 Feb 1979-Journal of the Waterway, Port, Coastal and Ocean Division (American Society of Civil Engineers)-Vol. 105, Iss: 1, pp 1-13
TL;DR: In this paper, a horizontal circular cylinder was experimentally measured to determine the influence of a plane boundary (e/D), A/D, and water depth (h/D) on these forces.
Abstract: Wave forces on a horizontal circular cylinder were experimentally measured to determine the influence of a plane boundary (e/D), water particle displacement (A/D), and water depth (h/D) on these forces. The transition from potential flow conditions to real flow conditions is considered. The variation of force coefficients of inertia, lift, and drag with respect to e/D, A/D, and h/D is identified.
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TL;DR: In this paper, the authors deal with the flow around a circular cylinder placed near a plane wall and exposed to an oscillatory flow and show that the flow pattern and the pressure distribution change significantly because of the close proximity of the boundary where the symmetry in the formation of vortices breaks down, and also the characteristic transverse vortex street observed for wall-free cylinders for 7 < KC < 13 disappears.
Abstract: This study deals with the flow around a circular cylinder placed near a plane wall and exposed to an oscillatory flow. The study comprises instantaneous pressure distribution measurements around the cylinder at high Reynolds numbers (mostly at Re ∼ 105) and a flow visualization study of vortex motions at relatively smaller Reynolds numbers (Re ∼ 103–104). The range of the gap-to-diameter ratio is from 0 to 2 for the pressure measurements and from 0 to 25 for the flow visualization experiments. The range of the Keulegan–Carpenter number KC is from 4 to 65 for the pressure measurements and from 0 to 60 for the flow visualization tests. The details of vortex motions around the cylinder are identified for specific values of the gap-to-diameter ratio and for the KC regimes known from research on wall-free cylinders. The findings of the flow visualization study are used to interpret the variations in pressure with time around the pipe. The results indicate that the flow pattern and the pressure distribution change significantly because of the close proximity of the boundary where the symmetry in the formation of vortices breaks down, and also the characteristic transverse vortex street observed for wall-free cylinders for 7 < KC < 13 disappears. The results further indicate that the vortex shedding persists for smaller and smaller values of the gap-to-diameter ratio, as KC is decreased. The Strouhal frequency increases with decreasing gap-to-diameter ratio. The increase in the Strouhal frequency with respect to its wall-free-cylinder value can be as much as 50% when the cylinder is placed very close to the wall with a gap-to-diameter ratio of O(0.1).
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TL;DR: In this article, a modified description of the potential flow in front of the pipe is developed, from which the lift force is evaluated if the undisturbed flow has no velocity gradients (shear-free flow).
Abstract: This paper considers the lift forces acting on a pipe with or without a small gap between the pipe and the seabed. From simple physical considerations, it is explained why the potential theory that predicts a downward lift force fails. A modified description of the potential flow in front of the pipe is developed, from which the lift force is evaluated if the undisturbed flow has no velocity gradients (shear‐free flow). The paper also discusses the effect of shear on the lift coefficient. The theoretical findings are supported by experiments.
34 citations
19 Mar 2013
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TL;DR: In this paper, the authors investigate the sources of very low frequency (0.01 to 1.0 Hz) ambient seismic noise in the shallow continental margin sediments using Ocean Bottom Seismometers (OBS).
Abstract: Sources of very low frequency (0.01 to 1.0 Hz) ambient seismic noise in the shallow (<100 m) water continental margin sediments are investigated using Ocean Bottom Seismometers (OBS). The predominant seismic motions are found to be due to surface gravity (water) waves and water-sediment interface waves. Actual experimental measurements of seabed acceleration and hydrodynamic pressure are given, including side by side comparisons between buried and plate-mounted OBS units. OBS-sediment resonant effects are found to be negligible at the low frequencies under investigation. Wherever there exists relative motion between the seabed and the water, however, an exposed OBS is subject to ‘added mass’ forces that cause it to move with the water rather than the sediments. Calculations based on measured seabed motions show that a neutral density, buried seismometer has superior sediment coupling charactersitics to any exposed OBS design.
19 citations
TL;DR: In this article, the authors measured the forces on a cylinder, laid on, or partly buried in the bed with a parallel twin dummy cylinder nearby and without it, and were determined by measuring the pressure distribution on the cylinder in the case of a steady current.
19 citations