Response surface parameterization for estimation of fatigue damage and extreme response of marine structures

摘要

The present paper is concerned with marine structures subjected to environmental loads (i.e. waves, current, wind) which are characterized by a number of parameters. The fatigue damage and long-term response characteristics are expressed in terms of the environmental parameters by polynomial response surfaces. In both cases, the result of interest is obtained by an integration across the range of variation for all the environmental parameters. The location of the intervals which give rise to the dominant contribution to these integrals depend on the relative magnitude of the coefficients defining the polynomials. These issues are studied on a non-dimensional form. The loss of accuracy which results when applying response surfaces of too low order is also investigated. Convergence studies are performed by applying response surfaces of increasing order, starting from linear to quadratic to higher order expressions. As a particular case, 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 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.