Analytical Solution for Computation of Drift Forces Including Waves and Currents on Marine Structures

Abstract

In the design stage of marine structures, the calculations of drift force due to drag considering the viscous effect have not been well performed recently. It is very important to consider the drift force acting on vertical cylindrical marine structures such as offshore wind substructure, semisubmergible by considering both waves and currents. In this paper, we obtained an analytical solution for the drift force acting on a cylindrical structure considering waves and currents. The part of the cylinder that is above the free surface is called the splash zone, and the part that is submerged under the free surface is called the submerged zone. When waves are only present, they are considered only in the splash zone, and when waves and currents are included, equations were derived for both the splash zone and the submerged zone, and the drift forces acting on fixed and floating types of marine structures were compared. Except for the case where only waves are considered in the splash zone, the magnitude of the drift force acting on the floating cylinder is found to be larger than that acting on the relatively fixed cylinder in most frequency ranges, and it can be seen that the increase is greater especially when the current is considered to be relatively more important. Therefore, it is possible to calculate the drift force by given design variables using the formulas derived in this study so far, and determine whether the magnitude of the drift force corresponding to each case has a quantitative effect within a specific physical range. © 2025 Society of Naval Architects and Marine Engineers. All rights reserved.