The force on cylinders oscillating sinusoidally in water

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1970

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Abstract

This investigation deals with the modeling of wave forces on offshore structures. The model chosen is a sinusoidally oscillating cylinder in a body of water otherwise at rest. This model represents a sinusoidal progressive wave moving past a single fixed leg of a platform. The dynamic force generated by the water-cylinder interaction was measured by means of strain gages. Oscillations of amplitudes ranging from 0.67 to 9.6 cylinder diameters and frequencies from 10 to 60 cycles per minute were covered in the investigation. Results are presented in the form of diagrams of force versus velocity with acceleration as a parameter and of maximum force versus the amplitude parameter, A/d. The recorded force data had been corrected by the harmonic dynamic force component due to the mass of the cylinder. The represented force values could not be correlated with the amplitude parameter which is equivalent to the frequency parameter [equation] sinusoidal motion. However, within the range of this investigation, the force acting on a cylinder is composed of a component due to velocity only (obtained at low accelerations) and a component due to acceleration only, which is a function of the actual velocity value and decreases with increasing velocity. The force due to velocity follows, for certain ranges of velocities, very closely the curves for the drag in uniform flow. The ranges of these actual velocity values depend on the diameter of the cylinder.

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