Analytical predictions of the air gap response of floating structures

Two separate studies are presented here that deal with analytical predictio ns of the air gap for floating structures. 1) To obtain an understanding ol the importance of first and second-order incident and diffracted wave effe cts as well as to determine the influence of the structure's motions on the instantaneous air gap, statistics of the air gap response are studied unde r various modeling assumptions. For these detailed studies. a single field point is studied here-one at the geometric center (in plan) of the Troll se mi-submersible. 2) A comparison of the air gap at different locations is st udied by examining response statistics at different field points for the se mi-submersible. These include locations close to columns of the four-column ed semi-submersible. Analytical predictions, including first and second-ord er diffracted wave effects, are compared with wave tank measurements at sev eral locations. In particular, the gross root-mean-square response and the 3-h extreme response are compared.