Added mass and buoyancy oscillations in stratified fluids
Résumé
Added mass, also called virtual mass, characterizes the additional inertia and damping force experienced by a body moving in a fluid, as a consequence of the flow that this motion generates within the fluid. An outline is presented of the way stratification affects added mass, by giving rise to buoyancy forces and internal gravity waves. The added mass coefficients for the small-amplitude oscillations of an elliptic cylinder in two dimensions, and a spheroid in three dimensions, are calculated; only translational motions are considered, with rotational motions left for future study. The results are applied to three types of oscillations, all governed by buoyancy: the free oscillations of a body displaced from its neutral buoyancy level then released; the pressure-controlled oscillations of the so-called ludion or Cartesian diver; and the impulse response setup used for the measurement of added mass in the laboratory. The first two of these have close ties to the Lagrangian midwater floats used for oceanographic measurements.