This paper describes results from a combined theoretical and experimental study that has been carried out in the Michell Laboratory at the University of Melbourne to investigate the effect of structural damping on "drag" dependent hydrodynamic damping mechanisms for vertical bottom-pivoted cylinders under excitation by irregular Pierson-Moskowitz waves in both inertia dominant and drag significant Morison forcing regimes_ The main aim of this investigation is to validate (or otherwise) the theoretical models for damping levels established in previous work by Haritos (Haritos & Yang, 1991). Experimental verification of the co-existence of drag dependent hydrodynamic damping with radiation damping and the influence made by structural damping is provided from the results of the experimental programme over a wide range of cylinder test conditions.


With offshore structures operating in increasingly deeper waters, structural designs are becoming more flexible, and consequently their response to the effect of wave loading is largely dynamic in character. Damping can significantly influence the level and character of the resultant dynamic response of a structure, since damping controls the level of this response in the so-called "resonance bandwidth" of the structure concerned. Current theory suggest, that structural damping can have an effect on the level of one or the sources of hydrodynamic damping considered in the model being adopted in this paper. Consequently, detailed studies of the interaction between structural and hydrodynamic damping would be of significant interest to engineers responsible for compliant/dynamic offshore structure designs and in the verification of theoretical models for their description. In general, for many offshore structure designs (such as for jacket platfonns) the value of the ratio of the characteristic dimensions of the structure to the dominant wavelength of the wave climate (D/A) is less than 0.2 so that the Morison regime would be applicable to this loading.

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