Second Order Motion Responses of Semi-submersibles: Numerical and Experimental Study

In this study, numerical and experimental assessment of the 2nd order
responses of a twin hulled semi-submersible subjected to monochromatic,
bi-chromatic and random seas has been attempted. For
numerical analysis, the 2nd order wave forces resulting from the 2nd
order temporal acceleration and the structural 1st order motions have
been obtained. The latter has been estimated by an iterative frequency
domain analysis. Experimentally, the semi-submersible was modeled
to a scale of 1:100 using Froude's scaling law principles. The measured
drift force has been compared with available formulae in the literature
and reported. The numerical results have shown good agreement with
the experimental results.
KEYWORDS: Second order drift forces; Low frequency motion
responses; Nonlinear dynamic analysis; Frequency domain analysis;
Semi-submersible model; Time domain analysis; Wave basin testing.