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Response of a Double Pendulum Compliant Offshore Tower to Collinear Wave and Current Forces

Mohd Moonis Zaheer, Nazrul Islam, Moazzam Aslam

Compliant offshore platforms are designed to allow controlled movement of the platform as an alternative to near rigid resistance to environmental forces by fixed platform designs. The dynamic response of a double articulated offshore loading structure to collinear wave and a steady current is studied for large and moderate sea states. The governing equations of motion are derived by the Lagrange’s method where the wave and current forces are computed by a modified Morison’s equation which takes account for the relative velocity of the water particle with respect to the oscillating tower. The analysis is carried out in time domain assuming rigid body motion, and the solution is generated by Wilson-𝛉 method integration scheme. Numerical studies are conducted to compare the responses under large and moderate sea states with and without current forces. Results show that the presence of current in the wave field increases the responses in all the cases taken for the study