Effects of Sea-Surface Fluctuations on Response of Offshore Structures

The magnitudes of the effects of the sea-surface fluctuations on the response of wave-excited offshore structures are assessed. Such fluctuations are accounted for by using the linear wave theory in combination with two distinct approaches: “stretching” and “vertical extrapolation.” Structural responses are calculated for water-particle kinematics obtained by applications of the unmodified linear-wave theory, linear-wave theory in combination with the stretching approach, and linear-wave theory in combination with the vertical extrapolation technique. These responses are examined by separating the associated static and dynamic effects for wide ranges of natural frequencies. It is shown that responses obtained for the stretching approach are almost the same as those calculated for the unmodified wave-theory model. It is further shown that applications of the vertical-extrapolation technique lead to the evaluation of peak responses that are generally larger than those obtained for the unmodified wave model,...