Application and Verification of Deepwater Green Function for Water Waves

Abstract

An efficient method for the numerical evaluation of the free-surface Green function for deep-water application was presented by Telste & Noblesse (1986) and again by Ponizy et al (1994). A FORTRAN code was include in their 1986 paper. The numerical method makes use of known mathematical functions. Numerical values of some of these mathematical functions were depicted, but no verification on the accuracy of the Green function routine in an application was given. The purpose of this paper is to compare their numerical values in the near-field and far-field regions with other similar computation for the infinite-depth Green function. The results of the infinite-depth Green function are also compared with the results from the finite-depth Green function that is more time consuming. Based on the accuracy of the various methods, the regions of application of the efficient deepwater Green function formulation and the effect of the water depth on the Green function are discussed. Any regions of inaccurate results are noted. Forces on submerged offshore structures and motions of the floating structures are determined using the lower-order panel method and these different Green function routines. The results on the motions of a semisubmersible in various water depths are compared and the accuracy of these routines in various regions is shown. The presented results will help the hydrodynamicist and designer to evaluate the suitable formulation and its regions of application for the accurate analysis and design of offshore structures.