For marine structures subjected to environmental loads (i.e. waves, current, wind), the fatigue damage and long-term response characteristics can frequenlty expressed in terms of the environmental parameters by polynomial response surfaces. For both types of “response”, an integration across the range of variation for all the environmental parameters is required. The location of the intervals which give rise to the dominant contribution to these integrals is studied. Convergence studies are performed by applying response surfaces of increasing order, from linear to cubic expressions. In addition, response surfaces with lower cut-off limits at specific values for the environmental parameters are also investigated. Having obtained general expressions on non-dimensional form, various examples which correspond to specific response quantities for marine structures are considered. Typical values for the polynomial coefficients, and for the statistical distributions representing the environmental parameters, are applied. Convergence studies are subsequently performed for the particular example response quantities which are considered in order to make comparison with the general formulation. For the extreme response, the application of “extreme contours” obtained from the statistical distributions of the environmental parameters in combination with the response surface is explored.
Short-term extreme response and fatigue damage of an integrated offshore renewable energy system