Radiation force

The radiation force is the hydrodynamic reaction on a body oscillating in calm water, produced by the waves the body itself radiates, and it splits into an added-mass part in phase with acceleration and a damping part in phase with velocity. In the potential-flow radiation problem each mode of motion generates a radiated wave field; integrating its pressure over the hull gives the frequency-dependent coefficients a_ij (added mass) and b_ij (radiation damping). Radiation damping is the only ideal-fluid damping in heave and pitch, while in roll it is small, leaving viscous and bilge-keel damping to dominate. With the diffraction (exciting) force it completes the linear seakeeping force model.