Power-law decaying oscillations of neutrally buoyant spheres in continuously stratified fluid

The free sinking motion of small spheres is experimentally investigated in a laboratory tank filled up with continuously stratified salt solutions. Special attention is paid to the late stage oscillations around the gravitational equilibrium level. Such motion is generated by slowly decaying weak internal waves originating from the interaction of the solid sphere with the surrounding fluid. The temporal decay of oscillation amplitudes and velocities can be best described by a power law of exponent value close to −3∕2. Up to our best knowledge, none of the existing theories can predict a similar algebraic decay.