Work

Slender-body approach for computing second-order wave loads in the frequency domain

Year: 2025

Type: article

Abstract: This work presents a slender-body approach to evaluate the second-order wave loads acting on a floating structure in the frequency domain. The approach is in the same spirit as the common use of Morison’s equation to approximate the wave loads without solving the radiation/diffraction problem. To do so, we employ Rainey’s equation, which can be seen as an extension of the inertial part of Morison’s equation to include nonlinear effects. We introduce modifications to Rainey’s formulation in order to evaluate wave kinematics at the mean body position instead of the original approach of considering instantaneous displacements. We also propose a simple approximation to partially account for wave scattering effects on the second-order loads based on the analytical solution of a surface-piercing bottom-mounted vertical circular cylinder. Though limited to structures composed of cylinders, this slender-body approach is orders of magnitude faster than computing second-order wave coefficients with a radiation/diffraction code. We implemented this approach for difference-frequency (slow drift) loads in an open-source frequency-domain floating wind turbine model. We present comparisons against results obtained with radiation/diffraction theory for three reference floating wind turbine designs: the OC3-Hywind spar, the OC4-DeepCwind semisubmersible, and the VolturnUS-S semisubmersible. In general, the results show that the proposed slender-body approach with the correction to approximate wave scattering effects provides useful estimations of the difference-frequency wave loads and the resulting motions of the floater. • Slender-body approach for second-order wave loads in the frequency domain. • Using a modified version of Rainey’s equation to account for body motions. • Used an approximation for wave scattering effects. • Implemented this approach in RAFT, an open-source frequency-domain tool. • Verified the QTFs and the motions computed with RAFT against WAMIT.

Source: Ocean Engineering

DOI: 10.1016/j.oceaneng.2025.120558

Authors: Lucas Carmo, Matthew Hall

Institution: National Laboratory of the Rockies

Language: English

Topic: Wave and Wind Energy Systems

Subfield: Ocean Engineering

Field: Engineering

Domain: Physical Sciences

Open Access status: hybrid

Estimated APC paid: $4,150

Funders: U.S. Department of Energy, Wind Energy Technologies Office