ABSTRACT: The risk of failing to achieve the acceptable performance (performance risk) of a free floating structure under the combined action of various wave frequencies is investigated in the frequency domain. Here, performance is quantified in terms of no exceedance of a threshold for the response level corresponding to each degree of freedom. Quantification of the performance risk is based on a Monte Carlo simulation technique. The numerical analysis of the free floating structure is carried out using a three dimensional hydrodynamic analysis. Several cases of different combinations of wave frequencies are investigated. The second-order hydrodynamic interactions of pertinent wave frequencies are considered in the analysis for each combination examined. Two issues are investigated, namely:performance and
performance risk for the free floating structure considered. The performance and risk levels of the second-order solution are compared with the results of the corresponding first-order solution in order to investigate the significance of second-order quantities in the assessment of both performance and performance risk levels. According to the results generated by the present study, secondorder wave effects can generally strongly affect performance and performance risk levels.
INTRODUCTION Considering the case of a free floating body subjected to the simultaneous action of two or more wave frequencies, non-linear hydrodynamic analysis needs to be carried since second-order wave effects can highly affect the response of the free floating body. This happens because several effects can hardly be predicted when using linear (first-order) theory, such as wave drifting and interaction between wave trains of different frequencies (Murao, 1960; Newman, 1990 and 2004 and McIver, 1992). For this reason, plenty of investigations, relevant to the analysis and computation of second-order wave effects have been carried out including among others Kosmeyer et al. (1988), Lee (1991) and Kim M.H. (1992 and 1993).