The dynamic heave responses of the semi-submerged axisymmetric buoy of two different geometries to the excitations equivalent to impulse excitation technique were represented by mechanical single-degree-of-freedom models. Founded on linear and 2-dimensional potential flow theory, the fluid-structure interactions were modeled and simulated with finite element approach. The numerical results obtained in transient harmonic oscillations were implemented with the frequency analysis tools and scaled by the input force spectrum. The records of the frequency response receptance were used in the assessment of hydrodynamic added mass and damping coefficients at the apparent linear resonance frequency. The buoyancy stiffness was calculated with relation to the hydrostatic pressure. Comparison with the experimental and analytical results lent validity to the numerical models.