Theory and Model Test Data for Tether Forces on Tensioned Buoyant Platforms

Abstract

This paper presents comparisons between the results of hydrodynamic analysis and two sets of large scale model test data for the wave induced motion response of tensioned buoyant platforms.The comparisons are presented with emphasis on the measured and predicted behaviour of the tether elements. 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 demonstrate the problem of possible vortex induced ringing for tethers with a large pretension.Although this feature is not modelled by the hydrodynamic analysis, the time history data are used to interpret the physical mechanism behind this observed vortex induced tether ringing. I .0" CI.JO