Parametric Identification and Sensitive Study of a Nonlinear Moored Structure

The highly nonlinear responses of compliant ocean structures characterized by a large-geometry restoring force and a coupled fluid-structure interaction excitation are of great interest to ocean engineers. Practical modeling, parameter identification, and incorporation of the inherent nonlinear dynamics in the design of these systems are essential and challenging. An experimental mooring system exhibiting nonlinear behavior due to geometric nonlinearity of mooring line angles and the complexity of hydrodynamic excitations is chosen for the study. An IndependentFlow-Field (IFF) model based on Morison equation and its associated nonlinear system identification algorithm is used to evaluate the system parameters of an experimental submerged mooring system. With the input wave and output system response data known, based on multiple input/single-output linear analysis of reverse dynamic system, the methodology identifies the linear and nonlinear system properties. A sensitive analysis is conducted to investigate the coupled hydrodynamic forces modeled by the Morison equation, nonlinear stiffness from mooring lines and nonlinear response.