Aqwa extracts the eigenvalues of the linearized stiffness matrix at the equilibrium position by the standard Jacobi successive rotation method. The following equation is solved:

(11–12)

of which positive eigenvalues of imply stable equilibrium, and zero eigenvalues imply neutral stability. If any of the eigenvalues are negative the body will not return to its equilibrium position after a small disturbance in any of the corresponding modes. As a special case, these eigenvalues are analogous to the metacentric height, GM, in transverse stability analysis of a free-floating ship.

At present, Aqwa only provides valid stability information for small displacements about the equilibrium position. You should be aware of this limitation, and the corresponding risk associated with extrapolating such data to large displacements from the equilibrium position.

However, it is possible to generate a stability report, for a single structure acted on by gravity and hydrostatic forces only (see Large Angle Stability). Such a report gives a list of positions of the structure and the corresponding forces at each position.