Environmental Load on an Ocean Semisubmersible Structure in the Presence of Rogue Waves With Currents

Abstract Renewable and low-carbon energy sources are critical to helping to reduce greenhouse gas emissions in the fight against global warming. One method for generating this renewable, low-carbon energy is offshore wind farms. A consistent wind source is always dependable for carbon-free energy production, equipment performance, and operational safety. In contrast to on land, offshore wind velocities are often steady. All structures in the offshore areas are subjected to a variety of environmental loadings due to the presence of very large waves and strong currents that can have significant impacts on the operation cycles of such structures. The presence of large waves and strong currents, as well as their interactions with the base structures and mooring lines, might produce hazardous operational circumstances. The operation and safety of such structures may be more vulnerable especially when a large wave travels against a strong current and produces abnormally high rogue waves. In this study, the tensions in the mooring lines of a tethered semisubmersible structure due to the presence of large waves, strong currents, various incident angles, and their consequent interactions are considered. The semisubmersible structure often serves as a fundamental framework capable of supporting energy-generating equipment such as wind turbines. Numerical simulations were conducted using an in-house developed 3D tool that incorporates mass, momentum, and energy-balanced equations. Additionally, two commercial codes, OrcaFlex™ and STAR-CCM+™, were employed for result comparisons. OrcaFlex™ is an implicit and explicit commercial code that uses lumped mass elements to streamline equations and the STAR-CCM+™ uses Navier Stokes equations. To explore numerous instances, settings for incident wave and current conditions were systematically changed in the simulations. The semisubmersible structure’s geometry and still water depth were maintained constant. The semisubmersible was anchored to the sea bottom with four mooring lines, one from each column’s bottom, in all simulations. The model is used for the computation of the hydrodynamic loads on a semisubmersible and its mooring lines in a wave and current co-existence field.