PROBABILISTIC SPECIFICATION OF METOCEAN CRITERIA: GENERATING AND SEARCHING N-YEAR CONTOURS FOR EXTREME RESPONSE ESTIMATION

The purpose of this report is -to present updated routines to both generate N-year environmental contours, and search them to find critical values (i.e., N-year response levels). Specifically, the three routines are as follows: HTCNTR: An interactive routine to generate contours, and create Hs,Tp-pairs for plotting of contours at a specified return period. IFORM: A general "inverse-FORM" implementation, which both constructs the N-year contour and searches it for a user-defined response function g. As in standard (forward) applications of FORM (First Order Reliability Methods), the user is required to code their g-function in a Fortran subroutine. SURFIT: A specificalized version of IFORM. Specifically, this routine also constructs the N-year contour and searches it to find a corresponding N-year response. In contrast to IFORM, the response function g is automatically constructed by response-surface fitting, using grids of wave and wind-response moments (mean, standard deviation, skewness, and kurtosis) as functions of environmental variables such as the significant wave height H8 and peak spectral period Tp, mean wind speed and turbulence intensity. Earlier versions of these routines have been handed out separately and individually documented; e.g., in RMS Technical Note TN3 (HTCNTR and IFORM) and in RMS Report 28 (SURFIT). This document supercedes these previous documents.