STATISTICAL ANALYSIS OF THE AIRGAP OF OFFSHORE STRUCTURES

Abstract

The statistical analysis of the airgap response of column-based offshore structures is performed in this thesis. The wave statistics due to second-order diffraction is investigated using the crossing rate approach. The application is a bottom-supported cylindrical structure. A new efficient statistical method is developed to get the exact distribution of the general stochastic process comprising linear, sum-frequency and difference-frequency components. Moreover, refinements are proposed to improve the efficiency for computing the free surface integral. Subsequently, the airgap analysis of semi-submersible floating structures is carried out in time domain as a benchmark, considering various nonlinearities. The frequency domain approach is developed based on the linearization of nonlinearities. The linear and quadratic transfer functions of airgap response are derived, preserving all the phase relationships. The proposed statistical method is implemented for the prediction of extreme airgap statistics of semi-submersibles. The influence of various nonlinearities on the airgap statistics are systematically investigated.