In this paper application is made both numerically and experimentally of the Swept Sine Wave (SSW) technique in the study of the hydrodynamic excitation of compliant bottom-pivoted cylinders. These studies have supported the contention that the radiation and drag-dependent damping mechanisms that are present as a result of the dynamic response of such cylinders can be considered to be independent of each other and are applicable to both the diffraction and Morison loading regimes. Experimental studies using SSWs on cylinders responding principally in an inertia dominant forcing regime, have indicated that a "drag" dependent hydrodynamic damping mechanism appears to be significant despite the relatively minor role drag force would have in the actual hydrodynamic forcing process itself.


A great deal of interest in the modelling of the dynamic response of compliant offshore structural forms to hydrodynamic loading effects has been shown by research workers in recent times (Wilson, 1984; Sarpkaya and Isaacson, 1981; Chakrabarti, 1987). The hydrodynamic loading regime that would be applicable to such structures is dependent primarily on the diameter to wavelength ratio (DA) of the principal elements of the structure concerned and upon the Keulegan-Carpenter number, KC, for the wave conditions under consideration. Swept Sine Waves (SSWs) have been commonly used by mechanical engineers as an input to electro-mechanical exciters in the experimental study of the vibration characteristics of mechanical structural systems. Chirp signal generation (a form of SSW) is a featured option available on modem signal generators which may form part of a physical testing system used by such engineers in laboratory or field applications. Only recently however, (Haritos, 1988; Haritos et al., 1989; Haritos, 1989a) has this technique been systematically used for both laboratory and numerical modelling studies of the dynamic response characteristics of compliant offshore structural systems.

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