Q: Why is the hydrostatic bending moment different from the structural one computed from RAOs?
REV 7.05

A: The two results deserve to be different:

For the hydrostatic bending moment, MOSES assumes that the wave changes the shape of the water surface into a sine wave, finds equilibrium with this "lumpy" sea and then computes the moment.

For the hydrodynamic results, linear hydrodynamics is assumed; i.e. the sea remains flat but there is a pressure field and the sum of the forces is no longer zero, but is Ma.

Thus, on the one hand you have a nonlinear sea (but ignoring radiation and diffraction) that is equilibrated with buoyancy and the other you have a linear sea that includes all of the effects and that is equilibrated with inertia. The differences get greater the more that the mass distribution differs from the buoyancy distribution