1,721,137 research outputs found
Long duration experiments in irregular waves, to determine 10,000-year wave loads on a 3.5m diameter vertical cylinder
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On the irrotational flow around a horizontal cylinder beneath waves
No full textMilne-Thomson's circle theorem is used to study the characteristics of the two-dimensional irrotational flow around a horizontal cylinder under long-crested waves. Even when the cylinder diameter is small compared with the wavelength, the circumferential velocity and pressure distributions are unsteady and differ markedly from those corresponding to uniform ambient flow with similar velocity and acceleration vectors
Hydrodynamic damping of a cylinder at B-10(6)
No full textThis paper describes delicate, but large-scale, experiments aimed at measuring the hydrodynamic damping of a circular cylinder oscillating in still water and transversely in a current. Attention is concentrated on the regime of very small Keulegan–Carpenter numbers, in which the drag coefficient is inversely proportional to the Keulegan–Carpenter number. Measurements in still water at ?=650 000 and 1250 000 point to drag coefficients about twice those appropriate to two-dimensional laminar flow, in common with earlier measurements at ??105. In the presence of a slowly varying transverse current (generated by placing the cylinder at the node of standing waves of long period), the damping increased with the reduced velocity of the ambient flow at a rate that increased with the Reynolds number.<br/
History forces and the unsteady wake of a cylinder
No full textHistory forces on a stationary cylinder in arbitrary unsteady rectilinear flow are calculated by means of a model based on the asymptotic properties of the steady-state wake. The results capture many features found in numerical solutions of the Navier–Stokes equation for the same flows, though quantitative agreement deteriorates as the Reynolds number increases over the range 2 to 40. The cases studied are the impulsive start, stop, and reverse, and oscillatory flow
Planar oscillatory flow forces at high Reynolds numbers
No full textMeasurements of pressures around a circular cylinder with fine surface roughness in planar oscillatory flow reveal considerable changes in drag and inertia coefficients over the Reynolds number range 2.5 × 105 to 7.5 × 105, and at Keulegan-Carpenter numbers between 5 and 25. In most respects, these results are shown to be compatible with previous measurements in planar oscillatory flow, and with previous measurements in which the same 0.5-m-dia cylinder was tested in waves
Steady flow past a vertical surface-piercing circular cylinder
No full textThis paper describes experiments in which a vertical surface-piercing circular cylinder with a large draught was towed at steady speeds through water initially at rest. The cylinder diameter d was 210 mm, and measurements were made of pressures around its circumference at elevations between 2.4d below still water level to 0.7d above, at Froude numbers (based on d) up to 1.67. The tests were carried out at a constant ratio of Reynolds number to Froude number of 2.79 x 10(5). The total resistance coefficient reached a maximum at a Froude number of about 1, when that part of the loading that can be attributed to the presence of the free surface was equivalent to the submerged form drag on a length of cylinder of about 0.9d. Measurements are also presented of the run-up on the front of the cylinder and of the depth of the depression at the back. Previous measurements by Hay (Flow about Semi-submerged Cylinders of Finite Length. Princeton University Report, Princeton, NJ, 1947) for the case of a cylinder with a submerged free end, and by Hsieh (Proc. Am. Soc. Civil Eng. 90 (1964) 161) of forces on cylinders standing on the floor of an open channel, are reanalysed. In most respects these results are found to be compatible with the present data for a cylinder of large draught
Discrete vortex model of jet-forced flow in circular reservoir
No full textA computer model of two-dimensional steady flow in a confined space is described in this paper. The simplest case of radial jet-forced flow within a circular cylinder with a single inlet and outlet is considered. The first stage in the numerical model consists of mapping the circular flow boundary onto a rectangle by means of a Schwarz-Christoffel transformation. As a result, two opposite sides of the rectangle represent the inlet and outlet. A potential uniform flow solution is then obtained for the flow in the rectangle and hence the cylinder. In the second stage of the flow simulation, discrete vortices are added at the inlet in order to model the inflow shear layers. Velocity components resulting from the discrete vortices and their images in the walls of the cylinder are superimposed on the potential uniform flow solution. The positions of the vortices are updated using a finite-difference time-stepping scheme. Thus, a qualitative simulation of the complete flow is built up. The results show reasonable agreement with experimental observations. <br/
The fluid structure interaction of wave energy devices: some old and some new theoretical and experimental challenges
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