PREDICTION OF EXTREME DYNAMIC RESPONSE OF A JACK-UP PLATFORM USING NONLINEAR TIME DOMAIN SIMULATIONS

Jack-up platforms designed to operate in deep waters are dynamically very sensitive. Furthermore, the wave and current induced loading on these platforms is of a highly nonlinear nature. Design of such offshore structures may then require a time domain stochastic structural analysis, at least for checking and calibration of simpler structural analysis methods. An important part of this type of analysis is the estimation of extreme response from the simulated samples and assessment of the uncertainties related to these estimated. In this paper, the estimation of short term storm extreme response of a jack-up platform by fitting analytical probability models to the simulated response samples is discussed. The effect of using shorter time series than the actual storm duration is addressed and the statistical uncertainty in the simulated extreme response is quantified. The study indicates that for this type of platform a three- parameter Weibull model fits the simulated response maxima well. Also it is found that a Weibull model combined with shorter time series and extrapolation gives adequately accurate estimated of extreme response.