Extreme response of floating structures in combined wind and waves

The paper highlights the problem of evaluating the extreme surge response of a floating, deep water structure subjected to stochastic loading from concurrent wind and waves. Additional load effects associated with ocean currents are also briefly discussed. Both long-crested and short-crested waves are considered, whereas the wind field is assumed to be unidirectional. The probability density function (PDF) of the combined wave frequency and low frequency response of the structure, due to waves, is calculated by an eigenvalue analysis and convoluted with the corresponding PDF from the wind loads, to obtain the PDF of the global response. The necessity of employing full, biquadratic transfer functions to evaluate the low frequency part of the wave loads is amply documented. The effect of short-crested versus unidirectional seas on the TLP motion response is discussed at some length, along with various numerical aspects related to the mathematical modelling and to the convergence and accuracy of the obtained solutions. Numerical solutions are presented for a wide range of harsh weather type, environmental parameters.