SURFIT: USING MOMENT RESPONSE SURFACES TO ESTIMATE EXTREME RESPONSE FROM WAVE, WIND, AND CURRENT

This document is written to be read in conjunction with RMS Technical Note TN-3 (Ude and Winterstein, 1996). As noted above, that reference documents a prototype software implementation of the IFORM methodology. SURFIT is a specialized version of this IFORM software, combining its general optimization code with a new driver and a new response (GRENZ) subroutine. This document first describes the random environmental variables X and the resulting extreme response Y(X) involved in the IFORM problem solved by SURFIT. Next it details the implementation of the GRENZ() routine that computes the extreme response Y at any given X, using fitted spline surfaces to the moments and average cycle rate of the underlying response process. Users may wish to proceed first to the following section, which directly describes input and output format, referring back to the implementation details as needed. They may also proceed directly to the examples, for which input and output are also demonstrated. These examples include (1) Extreme wave crest in a 3-hr seastate and (2) Extreme surge offset of a spar in a 3-hr storm. The input and output for Example (1) has been included with the SURFIT software.