The problem of seakeeping consists, among other aspects, of studying how a ship reacts to the environmental conditions during navigation, to establish operational limits and verify the seaworthiness of the vessel. A classic approach is to model the ship as a filter, with a set of Response Amplitude Operators (RAO) transforming the wave elevation time series into the motions in the six degrees of freedom.
Thanks to the convolutional properties of the Fast Fourier Transform, a wave elevation time series can then be converted to the prediction of ship motions in real time. For different ship speeds, wave directions and wave frequencies, the RAOs can be determined from the added masses, damping and hydrostatic coefficients, and wave-induced forces and moments. These entities can be obtained from the solutions of suitable complex-valued potential flow problems, in an offline phase.
This work, developed as part of the Winning a Sea State project in collaboration with Cetena, illustrates the extension of the potential flow solver -BEM to support these formulations, in order to provide an efficient, scalable, open source basis for a pipeline of this type. Results for the added mass and damping coefficients of a semi-submerged sphere in the zero-speed case compare favorably with the theory.
