Dynamic modeling of offshore towers with general damping subjected to earthquakes.

The modeling problem of offshore towers subjected to earthquake excitation is considered. A model is proposed which includes viscous and hydrodynamic drag damping and takes into account the stochastic nature of the problem. The model is decoupled into a set of modal equations by using the complex mode theory. A technique is developed to identify the modal parameters and the complex mode shapes. This technique is computationally efficient and accurate in the sense of minimizing a criterion function of the estimates variance. A simulation example is presented to demonstrate the results. (A)