Wave-Induced Loads Acting on Monopile Configurations Considering Wake Effects

Abstract

Abstract This comparative study investigated wave-induced impact loads acting on two aligned cylinders placed in a wave canal. Initially, loads acting on a single cylinder in a focused wave were experimentally measured to validate the associated numerical predictions. Subsequently, four scenarios were considered, of which the first scenario dealt with the direct calculation of loads on a single cylinder, albeit with cylinders of three different diameters. The second scenario considered two cylinders of the same diameter, which were implemented in tandem. The loads acting on the upstream and downstream cylinders were calculated directly considering the wake effects on the downstream cylinder. For the third scenario, both cylinders were removed, and the loads on the downstream cylinder were determined using the Morison equation. In the fourth scenario, only the downstream cylinder was removed to examine whether loads on the downstream cylinder can be approximated using the Morison equation. Employing an unsteady Reynolds-averaged Navier-Stokes (URANS) equations solver coupled with the volume of fluid (VoF) method, flow velocities were computed at different height positions corresponding to the location of the missing downstream cylinder in scenarios three and four, and these velocities were used in the Morison equation. Flow accelerations were derived from flow velocities using the central difference scheme. These load predictions enabled finding out how well the Morison equation is able to provide useful load predictions even in the presence of wake effects. Wake effects of the front cylinder on the loads acting on the rear cylinder were computed and analyzed. It turned out that maximum impact loads were favorably predicted using the Morison equation, even for the scenario that considered wake effects. However, the timely evolution of these loads after impact differed from comparable measurements.