NONLINEAR MODEL EVALUATION VIA SYSTEM IDENTIFICATION OF A MOORED STRUCTURAL SYSTEM

Complex nonlinear and chaotic responses have been observed and demonstrated in various compliant ocean systems characterized by nonlinear mooring restoring force and coupled fluid-structure interaction exciting force. The design of these systems, with inherent high degree of nonlinear dynamics, presents a challenge to the engineer. 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. Three alternative multiple-input/single-output models, nonlinear-structure linearly-damped (NSLD) model, nonlinear-structure coupled hydrodynamically-damped (NSCHD) model, and nonlinear-structure nonlinearly-damped (NSND) model distinguished by the different inputs and outputs used are derived and Reverse Multiple-Input/Single-Output technique are examined. 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 detailed study has been conducted on the different reverse dynamic models to identify the most suitable physical representative model for the ocean mooring system considered