Added mass and damping on a long horizontal cylinder of a square cross section (Model A) and a vertical surface-piercing square cylinder or column with a long horizontal cylinder of a square cross section (Model B) oscillating in water of finite and infinite depths, are measured using a planar motion mechanism. The width of both the vertical and horizontal cylinders is 22.86 cm. The horizontal cylinder comprises a test section of 91.44 cm in length at the center and two 91.44-cm dummy sections on each end of the test section. The model was forced to sway and heave sinusoidally with small amplitudes for several submergences below a free surface. The added-mass and wave-damping coefficients are shown to be influenced strongly by the free-surface effect and are presented as a function of water depth, frequency and direction of oscillation and of depth of submergence from the free surface. There clearly exists a critical non-dimensonal frequency near ω2 a/g = 0.3 for the heave oscillations near the free surface, as was measured previously but not predicted by a potential theory for a long, 2- D horizontal cylinder in intinite depth (Chung, 1977). Also, negative added mass is measured at ω2 a/g = 0.4∼0.8 for the shallow subergence, and it was cinfirmed by the present computation. The general trend of the added mass curve shows a behavior similar to the results of the previous 2-D horizontal cylinder except for the differences in their values. The added mass coefficients are larger for finite depth, while a limited number of submergences was tested. The experimental values are generally larger than theoretical predictions. As the model is placed closer to the bottom, the discrepancy becomes larger.


This paper experimentally investigates the hydrodynamic coefficients of the harmonic oscillations of a model in still water of finite and infinite depth having a free surface.

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