Nonlinear response of an articulated offshore towe

A single-degree-of-freedom model of an articulated tower with regular harmonic wave excitation is studied in this thesis. Of particular interest are the various nonlinearities which may influence the response. Specifically, the nonlinearity in the drag force and the nonlinearity in the expression for the fluid particle acceleration are given special consideration.;Three different forms of fluid particle acceleration are used in the appropriate expression for the wave kinematics. One of these is simply the local fluid particle acceleration which does not introduce a nonlinearity to the equation of motion. The use of this form of fluid particle acceleration allows the effect of the drag force nonlinearity to be considered independently. The other two forms of fluid particle acceleration include the local as well as the convective acceleration terms and it is the convective terms which contain the nonlinearity. It was found that this nonlinearity significantly influences the response of an articulated tower.;An Adams-Bashforth-Moulton numerical method is used to integrate the equations of motion of the articulated tower for a wide variety of system parameters. Numerical integration is necessary in this case due to the complicated form of non- linearities present which means that analytical solutions are not available. Results indicate that the response of an articulated tower subjected to the excitation of regular harmonic waves depends significantly on the system parameters and shows a wide range of nonlinear behaviour. In particular, subharmonic response is a common phenomenon. As well a period doubling route to chaotic response was also observed for the case of large wave height and small drag coefficient. Coexistence of multiple competing solutions and jump phenomena were also identified for certain ranges of system parameters.