Analysis of Offshore Guyed Tower Platforms to Wind and Wave Forces

The fundamental frequency of guyed tower platforms is designed to be low, and, therefore, it is susceptible to low-frequency excitation caused by fluctuating components of the wind velocity. The dynamic response of a simplified model of the Lena guyed tower is obtained for the fluctuating component of the wind force and the wave force. Both wind velocity and water particle kinematics due to wave motion are modeled as stationary random processes and are simulated from their respective power spectral density functions. The response analysis is performed by an iterative frequency domain procedure which duly considers the nonlinearities produced due to the drag effect and the nonlinear guyline resistance. The responses are also obtained in the presence of current. A parametric study is conducted to evaluate the relative contribution to the responses made by the wind force. The parametric study also illustrates how the current modifies the overall dynamic response. It is shown that the wind force significantly influences the first mode displacement response of the tower; the bending moment and shear force are not much affected by it. The current velocity tends to modify the peaks of the power spectral density function of the displacement response.