Comparisons of Theory With Model Test Data for Tensioned Buoyant Platforms

This paper presents comparisons between the results of hydrodynamic analysis and two sets of model test data for the wave-induced motion response of tensioned buoyant platforms. The comparisons are presented with emphasis on the measured and predicted behavior of the tether elements. The two sets of data used are from (i) tests performed jointly by Heriot-Watt University and University College London at the National Maritime Institute (NMI) Ltd., and (ii) published data from tests at the Norwegian Hydrodynamics Laboratory. The hydrodynamic analysis used in the comparisons is described, together with the assumptions underlying its formulation and the manner in which the lateral dynamics of the tethers are accounted for. The analysis and test data show good agreement for surge motions although discrepancies are observed for the tether tension amplitude response at certain wave frequencies. The paper also presents detailed tether tension time histories from tests in regular long-crested waves at NMI. These data demostrate the problem of high-frequency tension oscillations (often called ringing) in tethers. Although this feature is not modeled by the hydrodynamic analysis, time history data are presented to enable interpretation of the underlying physical mechanism of this phenomenon.