A number of tender assisted drilling platforms (TAD) are built to offer comfortable accommodation for crew, onsite construction and maintenance for production platforms. The two platforms are usually connected by a telescopic gangway. The safety and feasibility of gangway are essential during personnel transfer operation. In this paper, a TLP-TAD coupled system was investigated numerically and experimentally to study the gangway motion responses. The numerical model was established in frequency domain using 3D multi-body diffraction/radiation wave theory. Then time domain simulation was performed to consider the second-order drift loads and nonlinearity of mooring lines and hawsers. A systematic model test was also conducted for the coupled system. The connection point between gangway and platform was regarded as a joint, so gangway motion could be derived by global motions of TLP and TAD. Both single-body and multi-body cases were studied for comparison. The differences of global responses between two cases were relatively small, indicating that multi-body hydrodynamic interaction was not quite significant. The interaction aroused sway-surge and sway-heave coupling, and shielding effect also existed. Based on the above, gangway extension was investigated to analyze which degree of freedom (DOF) of global motion governed it.

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